Bibliothek

Notizen: Nitride-based optoelectronic devices prepared in the c orientation have been successfullyintroduced to the global marketplace and are changing the way we think about lighting. A part ofthe research interest has shifted toward nonpolar and semipolar orientations, which has the potentialto broaden the scope and impact of this technology. This is because quantum-well structuresprepared in nonpolar and semipolar orientations are able to suppress the quantum-confinementStark effect, which has a negative impact on optoelectronic device performance. The lower crystalsymmetry of such orientations provides spontaneously polarized light emission. Despite theseattractive properties of nonpolar and semipolar orientations, the corresponding materials growth isnot trivial. The present chapter discusses our efforts on growth of III-nitride materials in nonpolarand semipolar orientations and the related material properties

Notizen: Nanoscopic optical characterization using scanning near-field optical microscopy wasperformed on both InxGa1-xN/GaN single quantum wells (SQWs) grown on polar (0001) orientationand a semipolar (1122) microfacet SQW fabricated by a re-growth technique. Thephotoluminescence intensity of a conventional (0001) SQW emitting in the blue was completelyindependent of the threading dislocations (TDs) due to the small diffusion length less than 100 nm. Incontrast, the photoluminescence intensity was well correlated with the TDs in the sample emitting inthe green due to the association of In-rich clusters with dislocations, and the effect was enhanced bythe larger diffusion length contribution from the longer radiative recombination lifetime. It was foundthat in a (1122) SQW, the suppression of the piezoelectric field leads to orders-of-magnitude fasterradiative lifetime and consequently, a shorter diffusion length. In addition, the highest internalquantum efficiency was approximately 50% at 520 nm, which is about 50 nm longer than in (0001)QWs, suggesting that (1122) QWs are suitable for green emitters

Notizen: The effect of high energy milling on powders of a FeNi (50/50) alloy and a 316L stainless steelhas been evaluated by means of X-Ray Diffraction (XRD). The average microstrain as function of themilling time (1/2h, 1h and 8h) was determined from XRD data. The displacement and broadening of the(XRD) peaks were used for estimate the stacking fault energy (SFE), using the method of Reed andSchramm. It was estimated SFE=79 mJ/m2 for the FeNi (50/50) alloy and SFE=14 mJ/m2 for the 316Lstainless steel. The better experimental conditions for determining the SFE by XRD are discussed

Notizen: Threading dislocations (TDs) in (Al,In,Ga)N semiconductors are known to affect theluminescence efficiency of near-band-edge (NBE) emissions in bulk films and quantum structures.However, the principal role of point defects such as vacancies on the luminescent properties has notbeen fully understood. In this article, impacts of point defects on the luminescence quantumefficiency of NBE emissions and on the intensity of deep emission bands will be described, based onthe results of steady-state and time-resolved photoluminescence (TRPL) and positron annihilationmeasurements. The room temperature nonradiative lifetime (τNR) of the NBE excitonicphotoluminescence (PL) peak in polar (0001) and (000-1) , nonpolar (11-20) and (10-10), andzincblende (001) GaN layers prepared by various growth techniques was shown to increase with thedecrease in concentration or size of Ga vacancies (VGa) and with the decrease in gross concentrationof point defects including complexes, leading to an increase in the NBE PL intensity. As the edge TDdensity decreased, the concentration or size of VGa tended to decrease and τNR tended to increase.However, there existed remarkable exceptions. The results indicate that the nonradiativerecombination process is governed not by single point defects, but by certain defects introduced withthe incorporation of VGa, such as VGa-defect complexes. Similar relations were found in AlxGa1-xNalloy films grown by metalorganic vapor phase epitaxy: i. e. τNR at room temperature increased withthe decrease in the concentration of cation vacancies (VIII) and with the decrease in grossconcentration of point defects. In addition to nonradiative processes, the VIII concentration was foundto correlate with the intensity ratio of characteristic deep emission band to the NBE emission(Ideep/INBE). For example, Ideep/INBE at low temperature for the deep emission bands at 4.6, 3.8, and 3.1eV of AlN epilayers grown by NH3-source molecular beam epitaxy had a linear correlation with theconcentration or size of Al vacancies (VAl). Since the relative intensities of 3.1 eV and 3.8 eV bandsincreased remarkably with lowering the supply ratio of NH3 to Al (V/III ratio) and growthtemperature (Tg), they were assigned to originate from VAl-O as well as VAl-shallow donor complexes.The VAl concentration could be decreased by adjusting the V/III ratio and Tg. In the case of AlxGa1-xNalloys, the concentration or size of VIII and Ideep/INBE at 300 K increased simultaneously with theincrease in x up to approximately 0.7. Similar to the case for GaN and AlN, the deep emission bandwas assigned as being due to the emission involving VIII-O complexes

Notizen: It is discussed the difference between the magnetic reversal mechanisms: i) coherentrotation, ii) nucleation, iii) unpinning of domain walls. The main argument to suggest pinning asthe coercivity mechanism of Sm(CoFeCuZr)z magnets is the low initial susceptibility ofmagnetization curves of thermally demagnetized magnets. However, coherent rotation also impliesin low initial susceptibility, since the grain size of the magnets is near the single domain particlesize. It is unlikely that pinning could be the coercivity mechanism in this case, since the anisotropyfield of Sm2Co17 phase is 65 kOe, whereas the coercivity of magnets can be higher than 40 kOe.Such coercive field of 60% of the anisotropy field indicates coherent rotation as mechanism. Amodel for describing the abnormal coercivity behavior in Sm(CoFeCuZr)z magnets is proposed

Notizen: ZnO has received great attention in many applications due to its electronic andoptical properties. We report on the preparation of ZnO and gallium-containing ZnO(ZnO:Ga) nanoparticles by the precipitation method. The nanoparticles have the wurtzitestructure and a high crystallinity. Gallium ions are present as Ga3+, as evidenced by thebinding energies through XPS. Porosity and surface area of the powder increased underincreasing gallium level, explained by the smaller particle size of ZnO:Ga samples comparedwith ZnO. The estimated optical band gap of ZnO was 3.2 eV, comparable to ZnO:Ga

Notizen: The use of titanium and its alloy as biomaterial is increasing due to their lowmodulus, superior biocompatibility and enhanced corrosion resistance when compared tomore conventional stainless steel and cobalt-based alloys. Ti-13Nb-13Zr is a titanium alloyspecifically developed for surgical implants. In this work, highly porous titanium foams, withporosities above from 50%, are reached using an efficient powder metallurgical process,which includes the introduction of a selected spacer into the starting powders. Samples wereproduced by mixing of initial metallic powders followed by uniaxial and cold isostaticpressing with subsequent densification by sintering. The samples presented a Widmanstättenlikemicrostructure in an open cellular morphology with pore size between 200-500 μm

Notizen: Thermomechanical and electrical properties of zirconia-based ceramics have led toa wide range of advanced and engineering ceramic applications like solid electrolyte inoxygen sensors, fuel cells and furnace elements and its low thermal conductivity has allowedits use for thermal barrier coatings for aerospace engine components. A comparisonbetween CoNiCrAlY bond coat and zirconia plasma sprayed coatings on creep tests of theTi-6Al-4V alloy was studied. The material used was commercial Ti-6Al-4V alloy. Yttria (8wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasmasprayed on Ti-6Al-4V substrates by Sulzer Metco Type 9 MB. Constant load creep tests wereconducted on a standard creep machine in air on coated samples, at stress levels of 520MPa at 500ºC to evaluate the oxidation protection on creep of the Ti-6Al-4V alloy. Resultsindicate that the creep resistance of the ceramic coating was greater than metallic coating

Notizen: The corrosion resistance of 17-4PH stainless steel obtained by powder injectionmolding (PIM) was investigated in a phosphate buffer solution (PBS) that simulatesphysiological solution and compared with that of 17-4PH steel obtained by conventionalmetallurgy. The corrosion resistance was investigated by electrochemical techniques fordifferent immersion times. The cytotoxicity of both types of 17-4PH steel was alsoinvestigated using a minimum Eagle’s medium (MEM). The MEM solution is a type of cellculture medium, which simulates physiological fluids. The cytotoxicity assay was carried outby neutral red uptake methodology utilizing NCTC L929 cell line from ATCC bank and noneof the steels showed cytotoxic effects. The resulting extracts obtained by immersion of thesteel samples in MEM were analyzed by neutron activation analysis and the results indicatedliberation of chromium and cobalt as corrosion products but in very low amounts. Theelectrochemical evaluation of both steels indicated that they are passive in PBS but presentedsusceptibility to pitting. The 17-4PH PIM steel was slightly more susceptible to pitting thanthat fabricated by conventional metallurgy due to its inherent porosity

Notizen: Porosity and pore size are critical features for biomaterial scaffolds as they play anessential role in bone formation and bone ingrowth in vivo. Therefore, techniques forscaffolds evaluation are of great importance for their design and processing. Porous titaniumhas been used for grafts and implant coatings as it allows the mechanical interlocking of thepores and bone. In this study, porous titanium samples were manufactured by powdermetallurgy. The porosity quantification was assessed by optical quantitative metallographicanalysis, and non-destructive gamma-ray transmission and X-ray microtomographytechniques, in order to compare their efficacy for porosity evaluation. Pore morphology andsurface topography were characterized via scanning electron microscopy. These techniqueshave demonstrated to be suitable for titanium scaffolds evaluation, and micro-CT was the onethat allowed the three-dimensional porosity assessment

Notizen: Fine magnetic powder has been produced using the hydrogenationdisproportionation desorption and recombination (HDDR) process. The first goal of this workinvolved an investigation of a range of disproportionation/desorption temperatures between800 and 900°C with the purpose of optimizing the HDDR treatment for a Pr14Fe80B6 alloy.The cast alloy was annealed at 1100°C for 20 hours for homogenization. The optimumdisproportionation temperature for achieving high anisotropy was 820°C. The influence of thereaction temperature on the microstructure and magnetic properties of Pr14Fe80B6 HDDRpowders and magnets has been shown. A second stage of this study involved thecharacterization, for each temperature, of the HDDR processed powder using X-raydiffraction analysis. Samples of the HDDR material have been studied by synchrotronradiation powder diffraction using the Rietveld method for cell refinement, phasequantification and crystallite sizes determination. Scanning electron microscopy (SEM) hasalso been employed to reveal the morphology of the HDDR powder

Notizen: In this work, porous titanium samples processed by powder metallurgy and coated withbiomimetic coatings, obtained during different periods of immersion in a simulated body fluid(SBF), were tested for corrosion resistance in a phosphate buffer solution (PBS). Uncoated sampleswere also tested for comparison. The corrosion resistance of both types of titanium samples wasevaluated by electrochemical impedance spectroscopy and potentiodynamic polarisation curves. Theelectrochemical results indicated the formation of a surface film on the porous Ti samples withimmersion in the SBF solution and this biomimetic film increased their corrosion resistance. Thisfilm helps osteointegration besides increasing corrosion resistance

Notizen: The machinery used in coal thermoelectrical plants usually is submitted to erosive wear.The erosive wear occurs mainly in the metallic pipe set of heat exchangers due the flow of hot gasescarrying erosive particles. Jorge Lacerda’s thermoelectrical complex at Capivari de Baixo city holdsseven power units, where two units use approximately 20 000 ASTM A178 heat pipes. The set issubmitted to a semester maintenance schedule (preventive and corrective) where the damaged pipesare changed. So, in this work a set of erosive wear accelerated tests according ASTM G76 wereperformed in order to develop and specify materials and methods to diminish the erosive actioncaused by the combustion gases over the heat pipes. Specimens were coated with WC12Co andCr3C2-25NiCr alloys using the HVOF technique and the coated specimens were tested at 450°C, theheat pipes working temperature. Silica was used as abrasive material at 30° and 45° impact angles,simulating a harder erosive condition than the real condition. The best performance coating atlaboratory scale was later used in field condition. The results showed the coated specimenperformance is better than the ASTM A178 alloy. The erosion resistance of the Cr3C2-25NiCr andWC12Co coatings is eight times higher than the uncoated alloy, and the coatings also presented abetter corrosion resistance. This feature is important, because despite the erosive action thecirculating gases also present a large amount of sulfur in their composition. Sulfur at lowertemperatures forms H2SO4, causing intense corrosion of the pipes located at the heat exchangerscolder parts. Based on the results and considering the coating costs the Cr3C2-25NiCr alloy wasselected to coat a set of pipes mounted at the region of the heat exchanger with the most intenseerosive wear. At the moment these coated tubes are in field operation and under observationregarding their performance in comparison with the uncoated pipes located at the same heatexchanger. The real operation conditions of the coated pipes will be estimated from the field lifecycle analysis, and after all the cost-benefit of the studied coating

Notizen: The purpose of this paper is the evaluation of the use of a low power CO2 laser beam(50W) to promote the thermal treatment of AISI M2 high-speed steels and evaluate the tribologicalproperties of the graphite coating that takes place on the steel surface after laser irradiation. In orderto minimize the steel surface reflection at approximately 90% of the incident radiation wavelength(10.5 μm), an incident radiation absorber layer was applied to the steel surface sample. This coatingaims to absorber the incident heat and transfer part of heat to the steel surface. As results the surfacepresented high hardness and a thin coating of graphite on the surface. The micro-structural changes,occurred on the steels surface, resulting from heat transfer from the absorbing layer, were evaluatedthrough optical microscopy (MO), scanning electron microscopy (MEV), micro-hardness essays(MH), X-ray analysis (XRD), Raman spectroscopy and tribological testers on the graphite coating.MO analysis showed on the transversal section of the heated affected zone a brighter layer than thesample’s core, 30 micrometers thickness, in the surface sample a black coat 10 micrometersthickness. By MH analysis this brighter layer presented hardness approximately 30% superior thanthe regions without treatment, and by Raman spectroscopy it was evaluated the graphite coating.The XRD analysis on the surface sample reveals an increasing of the martensite and iron-carbidephase. The experimental results of pin-on-disk tests on the graphite coatings reveal a reducedcoefficient friction as compared to the original surface

Notizen: The purpose of this study is to evaluate the effect of the stages and temperingtemperatures in the microstructure, tenacity and hardness of the vacuum sintered high speed steelAISI T15. The material was uniaxial pressing at 700 MPa and sintered in a vacuum furnace at1275ºC. After that, different samples of the materials were submitted to the annealing treatment at870ºC, quenching at 1235ºC and tempering (single, double and triple) at 540, 550 and 560ºC.Concluded the treatments, Rockwell C measurements of hardness were accomplished and, toevaluate the toughness of the material, TRS (Transverse Rupture Strength) tests were done. Lateron, the materials were submitted to the metallographic preparation for microstructure analysis inoptical microscopy, SEM, EDX and X-ray diffraction. Finally, each property analyzed wasevaluated and correlated with the different tempering stages and temperatures accomplished

Notizen: SmCo5 sintered magnets are produced according the following main processing: millinguntil single crystal particle size, compaction and sintering. It is necessary high density to maximizeremanence, but small grain size to maximize coercivity. A sintering model able to incorporate both,the densification rate and the grain growth rate, is described. This makes easier to find the bettersintering conditions for optimization of the magnetic properties (coercivity and remanence). Thepresented model represents a refinement of previous sintering models, because it takes into accountthe coupled effects of grain size evolution and shrinkage

Notizen: The sintering of Sm2Fe17 compound prior to the nitrogenation process is studied as analternative process to produce dense Sm2Fe17N3 hard magnets with higher maximum energyproducts (BH)max than conventional polymer bonded magnets. In order to optimize sintering andnitrogenation processes, powders made from alloys, with different compositions, in the as-cast aswell in the as-homogenized state were used. It could be shown that the amount of α-Fe, formed inthe casting process, was reduced during sintering and that Sm selective loss is restricted to thesurface up to a depth of 100 +m. Moreover the density of the sintered samples was not muchaffected by the initial composition or by the prior homogenization of the alloys. Although thenitrogenation process was successful in producing the Sm2Fe17N3 as proved by the mass gain,magnetic properties measurements and X-Ray diffraction, the hard magnetic properties were muchlower than expected, indicating that other variables, which are discussed in the text, must beconsidered

Notizen: The known process as Metal Injection Molding is derived from the conventional powdermetallurgy (M/P) being an alternative for production of parts with complex geometry, greatdimensional precision and freedom of chemical composition. The present work has the objective toevaluate the processing of the Fe3Si alloy sintering in the vacuum furnace using as raw materialsiron powder carbonyl and prealloyed powder Fe45Si with D90〈10-m. Properties of microhardness,density, coercivity, magnetic permeability, and chemical composition was evaluated. The obtainedresults were compared with what is presented in the literature for parts processed by conventionalways and with parts processed by M/P. A density of 7,620 kg/m3, a coercive field (Hc) of 101.14A/m, a relative maximum permeability of 5,484 and a residual induction of 1.1 T was achieved byMIM. Comparing with conventional processes (where 100% of densification is reached), the MIMprocess results were worse, however they were better than P/M

Notizen: Ni-Fe based soft-magnetic alloys, processed via Metal Injection Molding (MIM), wereinvestigated regarding the influence of processing route on final magnetic properties and comparedto fully dense cast materials. The process variations included high and low temperature debinding,different sintering routes and the application of hot isostatic pressing (HIP). The different densitiesresulting from the process variations were related to maximum magnetic permeability. Results haveshown that density, in the range between 7,5g/cm³ and 8,0g/cm³, does not have significant influenceon the maximum permeability, allowing cost-effective process routes. It was also verified that fullydensecast alloys still exhibits superior properties, with lower coercive fields and higherpermeability, but results achieved after HIP process overcame even the values of these commercialgrade alloys

Notizen: The hydrogenation decrepitation process was employed to produce sintered magnetsusing a mixture of two alloys. The effect of niobium and boron content on the magnetic propertiesof Pr14FebalCo16BxNby-type sintered magnets was studied. Niobium and boron have a significanteffect on the magnetic behavior of these permanent magnets. The optimum amount of boron was 6at% and niobium should be kept below to 0.50 at%. The squareness factor (0.90) has been improvedconsiderably and good overall magnetic properties (Br=1320 mT, iHc=700 kAm-1 and (BH)max=315kJm-3) have been achieved for the sintered magnets prepared from the Pr14Fe63.85Co16B6Nb0.15 alloy

Notizen: This study reports the results of investigations carried out to determine the Curietemperature (Tc) of various homogenized praseodymium-based alloys represented by the formula:Pr14Fe79.9-xCo16B6Nbx (where x = 0, 0.01, 0.05, 0.1, 0.15, 0.50). The influence of niobium contenton the microstructure of these alloys has investigated. The Curie temperature decreased about 3 °Cfor x = 0.5 at. %. It has been observed a remarkable grain refinement on the microstructure of thePr14Fe79.8Co16B6Nb0.1 alloy when compared to the niobium-free alloy (x = 0 at. %)

Notizen: Pr14FebalCoxB6Nb0.1 magnets have been produced using the hidrogenationdisproportionation desorption recombination (HDDR) process. The effect of the Co content (x= 0,4, 8, 10, 12, 16) and the reaction temperature (800-900 ºC) on the microstructure and magneticproperties of the HDDR material have been investigated. The processing temperature(desorption/recombination) affected the microstructure and magnetic properties of the bondedmagnets. The alloy with low cobalt content (4 at.%) required the highest reaction temperature(880°C) to yield anisotropic bonded magnets. The optimum temperature for alloys with 8 at.% Coand 10 at.% Co were 840°C and 820°C, respectively. Alloys with high cobalt content (12 at.% and16 at.%) were processed at 840°C. Each alloy required an optimum reaction temperature andexhibited a particular microstructure according to the composition. Pr14Fe80B6Nb0.1 magnets havebeen processed for comparison

Notizen: Roller-ball milling (RBM) or planetary ball milling (PBM) have been used together withthe hydrogen decrepitation (HD) process to produce sintered permanent magnets based on a mixtureof Pr16Fe76B8 and Pr14.00Fe63.90Co16.00B6.00Nb0.10 magnetic alloys. Five distinct compositions havebeen studied comparing low- and high-energy milling. Magnets with a particular composition andprepared using these two routes exhibited similar magnetic properties. Modifications have beencarried out in the procedure of the HD stage for PBM in order to guarantee a high degree ofcrystallographic alignment. Pr15.00Fe69.95Co8.00B7.00Nb0.05 magnets showed the best maximum energyproduct for both processing routes (~ 247 kJm-3). A significant reduction in the milling time (93%)has been achieved with high-energy processing, the greatest advantage over the low-energy route

Notizen: This work involved a morphological, microstructural and magnetic characterization ofnanosized powders and sintered samples of Ni-Zn ferrite doped with chromium. The effect ofsubstituting Fe3+ for Cr3+ on the final characteristics of the powders and sintered samples wasinvestigated. The Ni-Zn ferrite powders were prepared by combustion reaction using nitrates andurea as fuel, based on the concepts of propellant chemistry. The samples were uniaxially compactedby dry pressing (385 MPa) and sintered at 1200oC/2h, using a heating rate of 5ºC/min. The Ni-Znpowders and compacted samples were characterized by X-ray diffraction (XRD), scanning electronmicroscopy (SEM), and the measures of their magnetic properties. The results revealed theformation of the cubic crystalline phase of the inverse spinel of Ni-Zn-Cr ferrite. The averagecrystallite size was 21 nm and 57 nm while the saturation magnetization was 47.0 and 73.1 emu/gfor the powder and the sintered sample, respectively

Notizen: Ni-Zn ferrites are magnetic ceramics that are widely used in electric and electroniccomponents. Among Ni1-xZnxFe2O4 ferrites, Ni0.3Zn0.7Fe2O4 is known to be the one of highestmagnetic permeability in lower frequencies. This work is divided into two parts: the first part dealswith the influence of sintering temperature and forming conditions on the microstructure ofNi0.3Zn0.7Fe2O4 ferrite. The second part deals with the influence of sintering temperature andenvironmental variations of temperature on the complex magnetic permeability of such ferrite. Theferrite studied in this work was fabricated by means of the conventional ceramic method. Complexmagnetic permeability between 100 kHz – 100 MHz is discussed in relation to sinteringtemperature. The influence of environmental variations in temperature (-40 oC to +50 oC) on thecomplex magnetic permeability of the ferrite sintered at 1300 oC is discussed

Notizen: High-energy milling has been used for production of nano-structured WC-Co powders.During the High-Energy Milling, the powders suffer severe high-energy impacts in the process ofball-to-ball and ball-to-vial wall collisions of the grinding media. Hard metal produced from nanostructuredpowders have better mechanical properties after appropriate sintering process. During themilling the particles size of WC and Co can be reduced and plastic deformed. In the present work, amixture of WC-10%Co was produced by high energy milling. The starting powders of the WC (0.87μm - Wolfran Bergau) and Co (0.93 μm - H.C.Starck) were used to produce the hard metal. Theinfluence of the milling time on the particle size distributions and in the lattice strain wasinvestigated. Milling time of the 2, 10, 20, 50, 70, 100 and 150 hours were used. The powders aftermilling were characterized by X-ray diffraction (XRD) and Scanning Electronic Microscopy (SEM).The results show that 10 h milling were enough to reduce the crystallite size of WC and the increaseof the milling time reduces the crystallite size

Notizen: This work discusses on the effect of milling parameters on the TiB and TiB2 formation inTi-50at%B and Ti-66at%B powders, respectively. Both powder mixtures were processed in aplanetary ball Fritsch P-5 ball mill under Ar atmosphere, varying the milling parameters: rotaryspeed (150 and 200 rpm), size of balls (10 and 19mm diameter) and ball-to-powder weight ratio(2:1 and 10:1). In order to obtain the equilibrium structures the milled powders were heated at1200oC for 1h. Samples were characterized by X-ray diffraction (XRD), scanning electronmicroscopy (SEM), and thermal analysis (DSC). XRD results indicated that extended Ti(B) solidsolutions were formed during ball milling of Ti-50at%B and Ti-66at%B powders. After milling for170h it was noted the TiB and TiB2 formation in Ti-50B and Ti-66B powders processed underhigher-energy condition. DSC analysis revealed that the TiB2 formation was completed duringheating of mechanically alloyed Ti-66at%B powders only. After heating at 1200oC for 1h, a largeamount of TiB and TiB2 was found in Ti-B powders milled under higher energy condition

Notizen: This work discusses on the structural evaluation of mechanically alloyed Ti-Nb powders.The Nb amount was varied between 20 and 50 wt-%. The milling process was carried out in aplanetary Fritsch P-5 ball mill under Ar atmosphere. The structural evaluation was conducted byscanning electron microscopy, X-ray diffraction, and energy dispersive spectrometry. During ballmilling it was noted an excessive agglomeration of ductile Ti-Nb powders on the balls and vialsurfaces, and the final amount of remaining powders was then drastically reduced into the vials.This fact was more pronounced with the increased Nb amount in starting powders. Typical lamellastructures were formed during ball milling, which were refined for the longest milling times, andfine and homogeneous structures were formed in Ti-Nb (Nb=20-50wt-%) powders. XRD resultsindicated that the full width at half maximum values of Ti peaks were continuously increased whilethat the crystallite sizes were reduced for longer milling times due to the severe plastic deformationprovided during ball milling of Ti-Nb powders. However, the EDS analysis revealed the presence ofNb-rich regions in Ti-Nb powders after ball milling. The critical ball milling behavior of ductile Ti-Nb powders contributed for reducing the yield powder and increasing the structural heterogeneity

Notizen: A large amount of the Ti6Si2B compound can be formed by mechanical alloying andsubsequent heat treatment from the elemental Ti-22.2at%Si-11.1at%B powder mixture, but theyield powder after ball milling is reduced due to an excessive agglomeration of ductile particles onthe balls and vial surfaces. This work reports on the structural evaluation of Ti-22.2at%Si-11.1at%Bpowders milled with PCA addition, varying its amount between 1 and 2 wt-%. The milling processwas carried out in a planetary ball mill under argon atmosphere, and the milled powders were thenheated at 1200oC for 1h under Ar atmosphere in order to obtain equilibrium structures. Sampleswere characterized by X-ray diffraction, scanning electron microscopy, and thermal analysis.Results revealed that the PCA addition reduced the excessive agglomeration during the ball millingof Ti-22.2at-%Si-11.1at-%B powders. After heating at 1200oC for 1h, the Ti5Si3, Ti3O and/or Ti2Cphases were preferentially formed in Ti-22.2at%Si-11.1at%B powders milled with PCA addition,and the Ti6Si2B formation was inhibited

Notizen: W-Cu composite powders were prepared by high energy milling under two millingenvironments: cyclohexane and air. Composite particles are formed in both cases. The W particlesare fragmented and embedded into the Cu particles. Both, W and Cu, are heavily strained, mainly inthe first hours of milling. The composite powder has high homogeneity and is much finer than theoriginal Cu powder. The mean particle size of the powders milled in both conditions is very close,but the wet milling was near 25% longer than dry milling and the size distribution is wider. This isconsequence of the higher milling intensity of dry milling

Notizen: The behavior of different process control agents (PCAs) during mechanical activation ofNb75Al powder mixtures was investigated. Mechanical activation by high-energy ball milling wascarried out on a shaker mill (SPEX®8000) for 1 hour. Each PCA (Stearic acid, ethanol andmethanol) was added to the powder charge in two proportions (1 and 2 wt%). Shape andmicrostructure of activated powders (aggregates) were analyzed by scanning electron microscopy.Milled powder mixtures were uniaxially pressed in cylindrical compacts that were further vacuumreacted at a constant heating rate (30ºC/min) in order to produce NbAl3 intermetallic compound.The temperature of the samples was monitored by an S-type thermocouple. The results show thatthe shape and the microstructure of the milled powders were strongly affected by the type andquantity of PCAs, therefore changing the reaction behavior and the densification of the producedpellets. Although ethanol was more effective to control aggregate size, best densification resultswere attained with 2 wt% of stearic acid

Notizen: Research on determined alloys produced by metal injection molding has been done for costreduction purposes through the use of powders with bigger particle size. However, regarding feedstockhomogeneity, certain limitations are presented when coarse particles are used. For instance, homogeneitystrongly influences rheological behavior of the feedstock and dimensional control of the sintered part.Therefore, the purpose of this work was to evaluate effectiveness of a modified binder system with theaddition of a surfactant polymer which makes the feedstock more homogeneous. This study was carriedout on a FeNiP alloy currently processed by MIM, where 50%wt of the iron powder was replaced withcourse powder having a particle size distribution of D90 less than 47 ,m. Effectiveness of bindersystems using a Melt Flow Index (MFI) and the behavior of dimensional accuracy at sintered part wereanalyzed. Results showed more feedstock homogeneity and less dimensional deviation when a surfactantagent was used

Notizen: There are various methods for testing the viscosity of MIM feedstocks and described inthe literature, e.g. melt-indexer, capillary viscosimeter, etc. Typical factors taken into considerationfor choosing a proper method for feedstock characterization are the costs and the time needed formeasuring. The paper presents three methods which have been developed to check the feedstockconsistency directly on the injection molding machine. The first method is based on a slit-dierheometer. The second method considers the energy which is needed for conveying the melt insideof the plastification unit. And the third method is similar to a melt indexer but also in this case themeasurement is done directly on the injection molding machine. These novel methods are suitableto detect inconsistencies in feedstock preparation

Notizen: The production of titanium parts from powder metallurgy is one of the tendencies ofmodern metallurgy, since it allows obtaining structures with complex geometries and controlledporosity. The purpose of this study was to produce two types of dental implant prototype, andcompare them biologically. Smooth surface prototypes were obtained, by the conventional turningprocess and porous surface prototypes using Metal Injection Molding (MIM). The prototypes wereimplanted in rats that were euthanized after 3 weeks, and the bone/implant interface was analyzed.The results showed that all prototypes were clinically stable at the end of the healing period, butthose produced by the MIM process presented a significantly higher percentage of osseointegration(bone/implant contact) than the milled prototypes in the same healing period. It is concluded thatthe bone tissue grew independent of type of implant, enabling quick, rigid fixation already in thethird week of the healing process

Notizen: The work presents the research results of modern composite materials. The matrixmaterial was EN AC AlSi12 alloy while the reinforcement ceramic preforms, obtained throughsintering process of Al2O3 Alcoa CL 2500 powder with addition of carbon fibers as pore formingagent burned out during sintering. The composites were produced with use of porous materialpressure infiltration method. The main limitation of base technology is a difficulty in obtainingcomposite materials with volumetric participation of ceramic phase in amount not less than 20%.Obtained on the base of ceramic preforms composite materials were tested with scanning electronmicroscopy. Additionally, hardness and tensile test was performed for acquired materials. Achievedresults indicate the possibility of producing, with use of pressure infiltration method, porouspreforms composed of Al2O3 particles, new composite material with desired microstructure andproperties, being a cheaper alternative for materials with base of ceramic fibers

Notizen: Recycle aluminum cans, an alternative route is presented in this work. The aluminumcans are cut in little flakes with a shears, and then the materials were milled, obtained fine powders.The weight ratio of the balls to powder was 10 to 1. Equipment of a horizontal high energy ball millwas utilized. The powder mixture was processed during 0.5, 1 and 2 hours at 950 rpm and aftermilling, the powders were directly hot extrusion. The extruder bars were submitted at a tensile testsand samples microstructures were analyzed by optical microscope. Experimental results obtainedshows that the technique utilized in this work is very important for economized routes andconsequently, less expensive, as compared with conventional methods

Notizen: Gamma uranium-molybdenum alloys has been considered as the fuel phase in plate typefuel elements for MTR reactors due to its performance under irradiation and metallurgicalprocessing. To its usage as dispersion phase in aluminum matrix, a necessary step is the conversionof the as cast structure into powder, and the technique considered at IPEN / CNEN - Brazil wasHDH (hydration-dehydration). This work has the aim to study the hydrogen incorporation bygamma-UMo alloys with 8% weight molybdenum. The samples were thermally treated underconstant flow of hydrogen, for temperatures varying from 500oC up to 600oC and times of 1 to 4hours. Some of the curves relating mass incorporation and time for the above temperatures wereobtained, and the results related to its microstructures and ease of fragmentation

Notizen: Powdered uranium silicide (U3Si2) 20% U235 enriched is an intermetallic compound usedas nuclear fuel material dispersed in aluminum to be the meat of fuel elements. U3Si2 powder is thestate-of-the-art as nuclear fuel material mostly used in modern research reactors. Its recentestablished fabrication in IPEN replaced the previous ceramic powder U3O8 used in the fuel of IEAR1(IPEN/CNEN, São Paulo, Brazil). The U3Si2 is a compound with 92.3%wtU and 7.7%wtSi. Itsproduction is made by induction furnace melting using metallic uranium, produced bymagnesiothermic reaction, and pure silicon. The induction furnace melts under argon controlledenvironment using zirconia crucible. Homogenization of liquid bath at 1800ºC is a compromisebetween crucible resistance and homogenized melting, avoiding hazardous happenings. IPENproduced its first lot of enriched U3Si2 in September 2004, with a continuous fabrication ever since.This research work represents the ability of having fully Brazilian supply of this strategic and highcost nuclear material. The fuel quality meets the world quality standards required by InternationalAtomic Energy Agency (IAEA) and RERTR standards. Brazilian production of U3Si2 powder notonly closed the fuel cycle, from uranium mineral to fuel element, but also allowed higherproductivity of nuclear medicine radioisotopes by IEA-R1

Notizen: Scrap tire is considered an environmental concern with inadequate final disposal. A goodalternative can be to use the tire as an energy source. Pyrolysis is a thermal process that cantransform the rubber portion of used tires into oil, gas and pyrolytic carbon. This type of carbon canbe converted into carbon black (CB). The lime industry that demands great amount of energy couldbe one of the ways to take advantage the scrap tires adequately as energy source. This work aimed tostudy the operational conditions of the pyrolysis process as well as investigating the possibility touse the pyrolysis products from used tires as industrial fuel. A batch pilot-scale pyrolysis unit wasbuilt. Temperatures from 400 to 600oC and relative pressures from 0 to -500 mmHg wereinvestigated in order to evaluate product distribution and quality. Experimental results showed thatas the reactor temperature was increased the pyrolytic carbon yield remained constant with a meanof 39.8 wt % and the pyrolytic oil yield reached a maximum value of 45.1 wt % at 500 °C. It is alsopossible to show that the pyrolytic oil can be used as liquid fuels because of its high heating value(40-42 MJ/kg), excellent viscosity (1.6-3.7 cS), and reasonable sulfur content (0.97-1.54wt %). Inaddition, chemical and physical characterization was made in order to compare the pyrolytic carbonand oil with currently fuels used in Brazilian lime industries (wood charcoal and coke ofpetroleum)

Notizen: Powder consolidation constitutes an important step in the manufacture of products ofhigh quality and precision. To obtain these components, with desired forms and final mechanicalproperties, it is of extreme importance to have knowledge about the processes to obtain powders,compacting and sintering. The objective of this work is to verify which model, obtained from theliterature, better describes the compaction densification behavior of iron powder in closed-die.Doraivelu’s criterion was carried through the method of the finite elements with the implementationof an elastoplastic model with hardening. The influence of the yield function coefficient against therelative density was evaluated, as well as, the yield function in the hydrostatic space

Notizen: Binders based on mixtures of polymers and waxes are suitable both for solventcombined with thermal extraction, as well as for pure thermal debinding. The recently developedplasma-assisted debinding and sintering (PADS) process has been targeted, for historical reasons,on a wax-polymer system, appropriated for solvent combined with thermal extraction processes.This paper shows experimental results related to the debinding rate of parts produced by metalpowder injection molding using the recently developed Plasma Assisted Debinding process.Influence of temperature and the ratio of cathodic area on the mass loss were studied

Notizen: Ti-35Nb-7Zr-5Ta alloy is a promising new material for a bone graft substitute with goodstrength properties and an elastic modulus closer to that of bone than any other metallic material.TNZT samples until 50 vol % porosity were manufactured using ‘‘space holder’’ technique andsintering methods. Irregular ammonium carbonate powders were used as a space holder material.Complete removal carbonate from the green compact was achieved by heating at 200 °C for 5 hoursand subsequent sintering at 1600 °C, with heating rate of 10 °C/min. For the alloy microstructuralcharacterization, scanning electron microscopy was used. Density was measured by Archimedesmethod. The results show that the blended elemental P/M process and the space holder techniqueare efficient for the obtainment of highly porous samples. Foams with porosities in the rangebetween 10% and 50% could be reached

Notizen: Protetive atmospheres are used in powder metallurgy to prevent oxidation and to reduceoxides, to control carbon contents of iron and iron alloys, and to flush volatilized lubrificants fromthe furnace. Another important function of the atmosphere during sintering is to burn and removethe hydrocarbon lubrificants used to compact the powdered metal. However, one of the mostimportant services that the Air Products "industrial gas company" can provide to its heat treatcustomers is assistance in troubleshooting their furnace(s) when there are problems.To be able to troubleshoot a furnace, it is important to know what the typical problems are thatarise, what causes them and how to fix or minimize to problem.This work should aid in finding the source of the problem with analysis equipment, and, by usingyour knowledge of the furnace and the process, solve the problem.Summarizing, (1) ensure system integrity, (2) Know the required safety interlocks, and (3) Verifytheir operation

Notizen: This work deals with the use of Fe-Cu alloys for use as matrix for diamonds in cuttingtools. In this case it was processed diamond beads for diamond wires - used in theslabbing of dimension stones. Normally, diamond beads are PM processed. The beads of thepresent work were manufactured using Fe-Cu alloy with addition of 1wt% of SiC as thematrix metallic bond. It was carried out shrinkage/swelling and microstructural analyses,Brinell hardness measurements, as well as the abrasion resistance of beads produced herein confront with commercial ones. The results indicate that it was processed beads withsimilar abrasion resistance and performance than those of the commercial diamond beads

Notizen: In this work, a study to process and characterize Fe-Cu alloys with reduced Co content isshown. The Fe-Cu-Co alloys were processed by elemental blending of powders of the system Fe-15%wtCu with various amounts of Co, pressing at 350MPa, and sintering at 1150°C/25min./10-2mbar. The sintered microstructure was observed. It was conducted hardness and wear tests, aimingto define the ideal Cu addition for future use in impregnated diamond tools. It was observed thathigher Co contents results in improved hardness and wear resistance in the studied Fe-Cu alloys

Notizen: This paper discusses the preparation of partially amorphous Al90Fe5Cr5 and Al90Fe7Cr3powder alloys by mechanical milling and their subsequent consolidation by hot milling. Samplesmilled for 60 hours showed a microstructure composed of amorphous phase and nanocrystalline Al.The heat treatment of these powders resulted in the equilibrium phases: fcc-Al + (Al3Fe and Al5Crintermetallic phases). Hot rolling these powders at 430°C resulted in consolidated samples with afine microstructure composed of Al, Al3Fe and Al5Cr intermetallic phases and high porosity. Thehigh hardness values of about 417HV of the intermetallic compounds formed during the rollingprocess presented the main obstacle to obtaining totally homogenous and consolidated samples

Notizen: A PADS (Plasma Assisted Debinding and Sintering) reactor developed by Lupatech S.A.has been employed to MIM process two Ni-based superalloys under Argon, at temperatures in the1280 -1310 ºC range, and for 2 to 3 hours. Both materials have chemical compositions similar to thatof standard Nimonic® 90 but differ considerably in their powder characteristics. One type of powderwas gas-atomized whereas the other was water-atomized. Samples of both materials in as-sinteredstates as well as subject to different HIP and heat treating conditions have been characterizedmechanically in tensile tests and by HV measurements. The best overall results are attained by thewater-atomized material sintered at lower temperatures. The PADS processing of these superalloysshows marked advantages over more conventional PM processing technologies. These results areparticularly relevant to the development of turbine components for the automotive and aerospaceindustries

Notizen: Borides, especially transition metal borides, like Mo2FeB2 ternary boride, are promisingcandidates for wear resistance applications. However, poor sinterability and extreme brittlenessraise difficulties to manufacture a structural material. In this work, the viability to obtain Fe-Mo-Balloys with high wear resistance materials obtained by PM techniques is studied.Other researchers use Cr and Ni alloyed steels and the B amount addition is very low. The mainobjectives are to increase the amount of B, not to use Cr alloyed steels and to decrease the sinteringtemperature. This can be obtained using mechanically alloyed Fe/B (50% by wt.) powders, whichare highly reactive after milling for 36 h.The mixture has a composition of 40%Mo-40%Fe-20%Fe/B, being characterized by flow rate andapparent density. These materials were uniaxially compacted and vacuum sintered. Specimens wereanalysed by SEM and physical and mechanical properties were evaluated (density, dimensionalchange, bending strength, hardness and wear)

Notizen: In this work, ultrahigh carbon steels (UHCS) obtained by powder metallurgy with CIPand argon sintered at 1150ºC. Then, they were rolled at 850 ºC with a reduction of 40 %. Finally,steels were quenched at 850 and 1000 ºC in oil. In each step, hardness, bending strength and wearperformance were evaluated. Obtained results are justified with a metallographic study by SEM.Both mechanical properties and wear resistance are highly favoured with the thermomechanicaltreatment that removes the porosity of the material. Moreover, final quenching highly hardens thematerial. The obtained material could be used as matrix for tool steels

Notizen: The deposition of pure tin onto pure aluminum powder in its self-convectivemotion by magnetron DC sputtering was examined in order to prepare Al-Sn compositepowder and thereby to improve the sintering of the aluminum particles, aiming at thedevelopment of highly structure-controlled porous aluminum materials. The fabrication ofporous aluminum materials was carried out by space-holder method using the prepared Al-Sncomposite powder in ordinary powder metallurgy processing. The effects of the sputterdepositionof tin on porous structure and mechanical properties of the sintered compact wereinvestigated. It was found that the porous structure of the sintered porous materials with theporosity 80% was better regulated by the sputter-deposition, compared to that without thedeposition. Regarding their compressive properties, it was found that the plateau stress of thesintered porous materials reached by the sputter-deposition twice as high as that without thedeposition. Therefore it was concluded that coating of aluminum powder with tin depositsenables the porous-structure to be controlled more effectively in fabricating sintered highlyporous aluminum materials, as well as improves their mechanical property

Notizen: Cr3C2-NiCr coatings have been used for corrosion and wear resistant applications. In thelast decade, thermal sprayed coatings using nanostructured feed stock of other materials hasexhibited higher hardness, strength and corrosion resistance. Hence, it is anticipated thatnanostructured Cr3C2-NiCr coatings will also exhibit these properties and therefore possesimproved performance characteristics. Preparation of nanostructured feed stock powders is the firststep in the synthesis of nanostructured coatings and mechanical milling is an effective process toobtain the powders. Preliminary studies in which commercial Cr3C2-NiCr powders were milled inhexane and gaseous nitrogen revealed that particle and crystallite size were significantly smaller inpowders milled in nitrogen. This paper presents the effect of hexane content and milling parameterson Cr3C2-Ni20Cr powder characteristics. Use of just sufficient hexane as the milling media reducedsignificantly the particle and crystallite sizes

Notizen: Titanium is an attractive material for structural and biomedical applications becauseof its excellent corrosion resistance, biocompatibility and high strength-to-weight ratio.Power metallurgy was used in this work to prepare 3D porous titanium. The powders becamefragile from hydrogenation process and were able to be used to obtain compacts withdifferent porosities by uniaxial pressing and sintering without applied pressure. Sincehydrogen dissolves easily in titanium to form titanium hydrides which have a stronginfluence on the microstructure coarsening and mechanical properties, the study of theporous compacts hydrogenation was carried out by hydrogenation at different temperatures(870 K up to 1070 K) in a hot filament reactor. Titanium surface morphology changes wereinvestigated by scanning electron microscopy. High resolution x-ray was used to characterizethe present phases. Evaluation of the porous titanium hydrides mechanical behavior wasrealized by flexion assay performed at three points

Notizen: Sintered stainless steel has a wide range of applications mainly in the automotiveindustry. Properties such as wear resistance, density and hardness can be improved by addition ofnanosized particles of refractory carbides. The present study compares the behavior of the sinteringand hardness of stainless steel samples reinforced with NbC or TaC (particles size less than 20 nm)synthesized at UFRN. The main aim of this work was to identify the effect of the particle size anddispersion of different refractory carbides in the hardness and sintered microstructure. The sampleswere sintered in a vacuum furnace. The heating rate, sintering temperature and times were20°C/min, 1290ºC and 30, 60 min respectively. We have been able to produce compacts with arelative density among 95.0%. The hardness values obtained were 140 HV for the reinforcedsample and 76 HV for the sample without reinforcement

Notizen: Atmosphere control in a continuous sintering furnace is one of the most importantvariables in a successful sintering process. This statement becomes even more weight whensintering of high chromium containing powders at elevated temperatures is applied. Depending onthe sintering atmosphere, de-carburization at the surface of a product is almost impossible to avoid.The production of more highly loaded PM parts by sintering requires higher sintering temperatures,which in turn increases the need for controlling the carbon level, and limiting surface decarburization.One way to control the carbon level is to add CO to the sintering atmosphere and increase thecarbon activity of the atmosphere. This idea has been used in conventional carburizing for decades.But is it applicable for sintering processes at temperatures up to 1250°C? The presented papershows results of tests on Astaloy CrM bodies with additions of up to 0.6% carbon that were sinteredat 1250°C in carbon monoxide containing atmospheres with and without hydrogen additions.Finally, an outlook of how this technology could be implemented in industrial scale sinteringfurnaces will be given

Notizen: Hardmetal alloys are processed by liquid phase sintering, which consist of one refractorycarbide, embebided in to a tough matrix of Co. These alloys extensively are used in applicationsthat demand abrasion resistance and high hardness. The present work has as objective to analyze thesintering of ultrafine powders of tungsten carbide (WC) with the addition of 10%wtCo. The alloyshad been prepared by using high pressure and high temperature technique. The sintering of theWC/10%pCo alloy was processed at the 3, 4 and 5 GPa, in temperatures of 1300,1400 and 1500ºC,during 2 and 4 minutes. The analysis was made by microstructure, densification, structure, Vickershardness and fracture toughness. The best results was density = 98.9%, hardness HV30 =10,77GPaand fracture toughness KIC = 15,57 MPa.m1/2

Notizen: Silicon-iron alloys with silicon content about 6.5wt.%Si offer a great potential forapplications aiming reduction of core loss in electric parts. Deposits of the Fe-6.5wt%Si alloyproduced by spray forming were annealed at temperatures between 400 and 1300oC, during 1h invacuum. The grain size has a great importance to the magnetic properties. In the present work, itwas analyzed the influence of the metallography parameters in order to get the best accuracy todetermine the grain size according to ASTM 112-96. Chemical composition, time andtemperature of specific etchings were modified and tested in different conditions of observationin light microscopy. Bright field, polarized light and dark field were used in the samples aimingto measure the grain size. The best etchings were Nital 10% and Marshall, both at roomtemperature. The results of grain measurement are presented in their relationship with themagnetic properties

Notizen: The particle circulation rate and gas–solid contacting efficiency are important parametersfor the project of spouted beds, applied in many industrial processes. Due to the restrictions foundin the identification of flow regimes through visual observation, new techniques have beendeveloped to obtain a better gas and particle dynamics description, necessary for the evaluation ofthese parameters. One of these techniques has been the CFD simulation. In this work the pattern ofsolids and gas flows in a spouted bed was numerically simulated using a 3D Eulerian multiphasemodel. Soybean particles had been used in the attainment of data of pressure drop fluctuation andpower spectrum as a function of gas velocity in an experimental apparatus. The 3D simulated solidsvolume fraction profiles allow the identification of the flow regimes showing a good agreementwith the experimental data

Notizen: The filtering hydrocyclone is a solid-liquid separation device patented by the ChemicalEngineering School of the Federal University of Uberlândia, which consists of a hydrocyclonewhose conical section was replaced by a conical filtering wall. During the operation of theseseparators, besides underflow and overflow streams, the existence of a filtrate stream generated bythe filtering process is found in the permeable conical region of the hydrocyclones. Vieira et al.(2006) got a filtering hydrocyclone that simultaneously presented low Euler Number and cut sizediameter because its geometric relationships has been optimized. The objective of this work was toanalyze the behavior of this optimized filtering hydrocyclone through computational fluid dynamicsand experimental studies. In the same operational conditions of the conventional hydrocyclone, theperformance of this optimized filtering hydrocyclone was significantly influenced by the filtration.The filtration caused decreases in the Euler number and increment in the total efficiency

Notizen: The minimum fluidization velocity is an important parameter in the design and operationof an industrial unit of fluidization. In the present work the minimum fluidization velocities of fineparticles were obtained through two experimental methodologies. The first one is the classicprocedure to determine that parameter analyzing the diagram of medium pressure drop in the bed infunction of the superficial gas velocity, during the defluidization of the bed. And the second is thetechnique of identifying the minimum fluidization velocity interpreting the behavior of thenormalized standard deviation of the pressure drop in the bed. A cylindrical bed of transparentacrylic was used in the process and the used particles were glass spheres, FCC and zinc powder. Tocompare the precision of the two methodologies some equations that predict the minimumfluidization velocity were used

Notizen: The suspended particles in the air are a factor that causes chronic illnesses to therespiratory system, which go from allergy to severe pulmonary damage. Particulary, breathableparticles (from 0,5 μm to 5,0 μm sizes) cause damages to the respiratory system. The penetrationand the deposition are the reason for the damages to the pulmonary alveolus.The industrial activity is the main responsible for the most part of the breathable particles emission.Because of that, Venturi scrubbers have been incorporated to the industrial process due to their highefficiency for particle collection.Venturi scrubbers are gas-atomizing devices. They are mechanical devices which rely on shearingand impaction forces to break water into fine droplets. Those droplets in contact with the particles,will collected them.This work consists of a Venturi scrubber of circular section operating horizontally, with liquidinjection through a single orifice located in the scrubber throat. The experiments will analyse theinfluence of the length throat, gas velocity, liquid flow and particles sizes on the Venturi´scollection efficiency

Notizen: The centrifugal technique was used to investigate the influence of particle size, appliedcompression and substrate materials (stainless steel, glass, Teflon® and PVC) on particle-surfaceadhesion force. Phosphate rock and manioc starch particles were used in a microcentrifuge thatcontained specially designed centrifuge tubes and reached a maximum rotation speed of 14,000rpm. The profile of adhesion force followed a log-normal distribution and adhesion force increasedlinearly with particle size and the increment of the compression force. The manioc starch particlespresented adhesion forces greater than those for the phosphate rock particles for all particle sizesstudied. The glass substrate showed a higher adherence than other materials, most probably due toits hardness and polishing

Notizen: This work is concerning to production of quicklime (CaO) from thermal decompositionof the calcite limestone (CaCO3) using analytical and instrumental techniques (TGA and MS) toevaluate kinetic and thermodynamic effects as well as heat/mass transfer associates with the processoperation. On the other hand, experiments of morphologic, structural and textural characterization(XRD, SEM and BET surface area) were carried out in order to evaluate the quality of thequicklime produced. Under experimental studied conditions it was observed that carbon dioxide(CO2) inhibits the thermal decomposition reaction rate. In addition, it was observed that steam(H2O) can catalyze this reaction but it can also cause sintering of the oxide formed. It was alsoobserved that the calcination reaction is greatly limited by mass transfer effects and that thecontrolled thermal decomposition generates an increase in the solid porosity. The formed CO2 havealso increased the sintering phenomena in the oxide structure, resulting in less reactive quicklime

Notizen: The settling vessels are equipment destined to solid-liquid separation; usually havecontinuous operation, with a circular section, presenting one conic and one cylindrical part. They arevery used in chemical industries: wastewater treatment, minerals industries; to concentrate or toremove the solids. The solid particle splitting with small granular becomes difficult through theoperation of conventional sedimentation. An expedient very used in the industry is the flocculantsubstance addition, whose objective is to promote the precipitation of particles, with decantationspeed is upper than the single one. The present work aim the study of the burst operationalconditions that influence the formation and the stability of these aggregates, the flake, the effect ofpH and the concentration of flocculant using kaolin suspension and genfloc, that contains aluminumsulfate, as a flocculant; and the capacity of conventional settling vessel, which area of thetransversal remains constant, considering this operational conditions

Notizen: These work present studies about influence of the high temperature at the antimicrobialproperties of the Bactericide Wood Polymer Composites (BWPC) after exposition during differenttimes at 110 oC. The composite was formulated containing Polypropylene (PP) as matrix polymeric,wood powder of the species Pinus and Triclosan additive as bactericide agent. The BWPC wasexposited during different times in the ambient and submitted to microbiological tests. The AgarDiffusion tests were applied with two kind bacteria, the Echerichia coli (EC - Gram Positive) andStaphylococcus aureos (SA - Gram Negative). The FT-IR and TGA techniques were utilized toavailable of the temperature effect in the chemical structure of the composites BWPC. The studiesshowed a strong dependence of the bactericide action of the composites with exposition time at 110oC and a constant bactericide action after 100 hours of exposition

Notizen: Rotary dryers are commonly used to dry particulate in a range of food and mineralprocessing industries. The purpose of this work was to study the design and performance of a rotarydryer. It was evaluated the number of flights and operational conditions that corresponding to theoptimal performance for the equipment. A set of equations to predict the solids holdup in flightswith three and two segments was also evaluated. Their predictions were compared to measurementsperformed with a pilot plant rotary dryer. The equation generated very accurate estimations

Notizen: Stainless steel parts have been manufactured by two different layer by layer additiveprocesses. The first one is a standard three dimensional process, in which metal powders are boundby selective deposition of binder with a printer head. The second one is a novel process, which isbased on the selective deposition of a solvent on metal-polymer granule beds. The microstructuresof green and sintered parts are characterized by optical and scanning electron microscopy, and themechanical properties evaluated by hardness and tensile tests. Solvent on granule printing allows toreach mechanical properties similar to those of metal injection moulding parts

Notizen: This paper presents a systematic study about ceramics made of zirconium oxide andtitanium oxide (ZrO2-TiO2) doped with tin oxide (SnO2), strontium oxide (SrO2) and niobium oxide(Nb2O5). These ceramics can be applied as dielectric resonators in microwave systems fortelecommunications. For a good microwave performance, these ceramics must reach someparameter values as high dielectric constant and high quality factor due to the dielectric losses. Theceramics were manufactured using suitable powder mixtures of ZrO2-TiO2 with additions of 1 % ofSnO2, SrO2 and Nb2O5, resulting in four different kinds of samples for analysis. The samples werecompacted by an uniaxial (190 MPa) and an isostatic (300 MPa) pressing, sintered at 1200 °C for 3hours, characterized in the chemical compound formation using X-ray Diffraction (XRD) andscanned for microstructure densification degree and grain distribution analysis in Scanning ElectronMicroscopy (SEM). The dielectric parameters were measured using a microwave system. The maingoal of present procedure is manufacture ceramic materials for promising application as dielectricresonators

Notizen: Diluted magnetic semiconductors (DMS), which have both semiconducting and magneticproperties, are those in which transitions metal ions substitute cations of host semiconductormaterials [1]. There is a great interest for DMS for use as the material of spintronics. In this study isreported the structural and morphologic characterization of Zn1.95Co0.05O nanoparticles obtained byPechini method and combustion reaction. The powders resulting were characterized by X-raydiffraction (XRD) for determination of the phases, crystalline phase and lattice parameter; nitrogenadsorption by BET for determination of the specific superficial area and calculation the particle sizefrom the superficial area and scanning electron microscopy (SEM) for morphologic analysis. TheXRD results demonstrated the viability of obtaining crystalline and nanosize powders by the bothsynthesis routes. For all samples the average crystallite sizes was nanosized, but the powdersobtained by reaction combustion is smaller. The SEM micrographs shows that the powders obtainedfor both syntheses are constituted of soft agglomerates

Notizen: Samples of the superconducting ceramics Hg0.82Re0.18Ba2Ca2Cu3O8+ were prepared bysolid-vapor reaction technique. The preparation of the ceramic precursor started with a mixture ofBa2Ca2Cu3Ox and ReO2 powders with molar ratio 1:0.18. The precursor material was submitted toannealing under three different partial pressures of oxygen using a mixture of oxygen/argon atratios: 5/95 (sample A), 10/90 (sample B) and 15/85 (sample C). X-ray powder diffraction analysisof the precursors identified the phases BaCuO2+x, Ba2Cu3O5+x, Ba4CaCu3O8+x, Ca2CuO3 andCa5Re2O12 at different ratios in the samples, indicating an increment in the oxygen content fromsample A to sample C. Finally, the precursors with different oxygen contents were blended withHgO at molar ratio 1:0.82 and treated in a sealed high pressure furnace to produce the high Tcsuperconducting ceramics. Rietveld refinement of XRD data showed differences in the crystalstructures of the samples. The measurement of thermopower at room temperature resulted in distinctvalues, confirming the different oxygen sample doping

Notizen: Yttria-stabilized zirconia is the most developed solid electrolyte for use in hightemperaturesolid oxide fuel cell (SOFC). Commercial yttria-stabilized zirconia powders reach highdensification at temperatures around 1400 ºC. The use of additives may increase the densificationrate by means of a liquid phase formation during sintering. However, these additives should notcause any degradation on the ionic conductivity of the electrolyte. The main purpose of this workwas to study the effect of Co addition on the densification and electrical conductivity of yttriastabilizedzirconia. Green compacts were prepared by pressureless sintering a mixture ofcommercial 8 mol% yttria-stabilized zirconia with cobalt carbonate. Linear shrinkage results showthat the temperature at which the shrinkage starts decreases with increasing Co content. Impedancespectroscopy measurements reveal that Co additions to stabilized zirconia decrease the totalelectrolyte conductivity even for Co contents as low as 0.05 mol%

Notizen: The soil humidity sensor plays fundamental role in the monitoring of hazard areas withlandflows and landslides, about which in Brazil stories exist since 1671. Nowadays, it is just knownthat the majority of the mass movements in the hillsides occur in rainy periods, what makes thewater the most important deflagrator agent of these movements, decreasing the soil resistance,increasing its specific weight and increasing the internal pressures as well. In this direction, thesensing elements developed by Group SUCERA/LAS/INPE uses the advantages presented forceramics, in particular metal oxides, in terms of their mechanical strength, their resistance tochemical attack and their thermal and physical stability. In this work the results of thecharacterization analyses of sensor elements of ZrO2-TiO2 doped with 1, 5, 10, 15 e 20 % Nb2O5porous ceramic, sintered at 1200 ºC are shown and discussed

Notizen: By using the active filler controlled polymer pyrolysis, new and cost-effective compositematerials can be obtained. In this work, ceramic matrix composites were prepared by using thisprecursor route, using a polysiloxane network filled with metallic niobium and aluminum powdersas active fillers. The mixtures were blended, uniaxially warm pressed, and pyrolyzed in flowingargon at 1400 ºC. Porous ceramic preforms were infiltrated with a LZSA glass material, in order toimprove the density of a porous composite material. The properties of the pyrolyzed compositematerial and the effect of the LZSA infiltration on the Al2O3-NbC-SiOC ceramic compositematerial were investigated. The results have showed that the infiltration processes has improved thephysical and mechanical properties of the composite material

Notizen: Y-TZP presents excellent properties at room temperature but these properties decrease asthe temperature increases. This paper studies the behavior 20vol%Si3N4-SiC when added in YTZPmatrix and heated under no pressure system. Al2O3 and Y2O3 were used to maintain the stability ofthe matrix and as sintering aids. The addition of Si3N4 and SiC in a Y-TZP matrix leads toformation of silicon oxynitride and it increases the mechanical properties like toughness andhardness. The mixture was milled and molded by CIP. Samples were heated at 1500ºC, 1600ºC and1700ºC for 2h without pressure under atmospheric conditions in bed-powders of Si3N4. Sampleswere characterized by XRD. Density, hardness, toughness, bending strength were measured. Thestructure of the material was observed in SEM/EPMA to verify the distribution of the materials inthe composite. The formation of Si2N2O was observed in the sintered material and it showed anincrement of both hardness and toughness as temperature increases. The samples presentedconsiderable resistance of oxidation at 1000ºC

Notizen: The presence of fissures in the cement material of an oil well due to thermo-mechanicconditions caused by steam injection and acidizing operations, tends to commit the mechanicalintegrity of the annular space, resulting in the environmental contamination of the phreatic sheetsand oil producing zones. However, the development of new materials for oil wells cementing haslead to several researches to achieve the optimization of this process. This work proposes theformulation of portland/polyurethane nonionic composites as a new material for oil wellscementing. The results prove the ability of the formulated composite to improve the mechanicalproperties when compared with portland/water cement slurry. Also, were obtained significantimprovements in mass losses when acids were present

Notizen: The ceramic matrix composites (CMCs) can be fabricated by the pressure infiltrationtechnique. In this work it was studied porous preforms of quartzite that were infiltrated withaluminum liquid. For to produce the more resistant preforms of quartzite, it was additioned differentquantities of bentonite (5 and 10%) and the preforms were firing at 1100ºC and 1200ºC. For thecomposites production, the melted aluminum was introduced into preforms under a pressure of 7MPa. The characterizations of the composites were made by X-ray diffraction, scanning electronmicroscopy, and flexure strength. All the preforms studied presented sufficient strength for supportthe pressing during the process of squeeze casting. The results of X-ray diffraction of compositesshowed the presence of alumina, silicon and aluminum and fully interpenetration aluminum-siliconaluminacomposites were obtained by infiltration

Notizen: A comparative study between alumina added niobia ceramics and two alumina zirconiacomposites from nanostructured TZP (7% and 14% weight) was made. On this composites thezirconia were yttria stabilized and the alumina were submicron structured. As sintering aid amixture of magnesia, niobia and talc were used on all samples. The sintering was performed at1450 oC during 60 minutes. The characteristic grain size and shape of an alumina and zirconiapowders, aggregates and agglomerates were characterized. The sintering ceramics were evaluatedthrough hardness, fracture toughness and 4 point bending test. Weibull statistic was applied on theflexural results. Although the fracture toughness result from ZTA were lower, and seems to beaffected by the liquid fase, the hardness and Weibull modulus were higher than alumina niobia. Thegrains size and the homogeneity of its distributions on the microstructure of this ceramics wascorrelated to these higher values. The results from these alumina zirconia composites showed apotential to apply as a ballistic armor material

Notizen: Several researches have been developed in order to verify the porosity effect over the ceramicmaterial properties. The starch consolidation casting (SCC) allows to obtain porous ceramics by usingstarch as a binder and pore forming element. This work is intended to describe the porous mathematicalbehavior and the mechanical resistance at different commercial starch concentration. Ceramic sampleswere made with alumina and potato and corn starches. The slips were prepared with 10 to 50 wt% ofstarch. The specimens were characterized by apparent density measurements and three-point flexural testassociated to Weibull statistics. Results indicated that the porosity showed a first-order exponentialequation e-x/c increasing in both kinds of starches, so it was confirmed that the alumina ceramic porosityis related to the kind of starch used

Notizen: The ornamental rock industry generates huge amounts of waste in form of fine powder,demanding adequate alternatives for its final disposal. The possibility of using ornamental rockwaste as a flux in porcelain tile has been assessed. The porcelain tile formulations are constitutedmainly by kaolin, feldspar and quartz. The waste was added to a typical porcelain tile body,replacing the sodic feldspar by up to 15 wt. %. The prepared pastes were fired of 1240°C using afast-firing cycle. The specifications of porcelain floor tile in terms of physical properties wereachieved

Notizen: Zirconia stabilized with 8 mol% yttria (YSZ) is the most effective material for use aselectrolytes in solid oxide fuel cell. Ceramic powders of YSZ were synthesized in IPEN bycoprecipitation route and are composed by fine particles (less than 01μm) with large surface area(~60m2.g-1). These powders have a strong tendency to agglomerate. and it make difficult thecompaction process and to achieve a good density. To exert control over the compaction process.the powders were spray dried to obtain spherical granules. Thus the stability of slurries of thesepowders was studied by adding ammonium polyacrylate (Duramax D3005) as dispersant and thesuspension stability was measured by electrophoretic mobilities. Slurries prepared with the betterconditions were dried in a laboratory scale spray dryer. The prepared granules were characterizedby morphology observation (SEM). surface area (BET). Vickers hardness and sintered ceramicsbodies density were measured

Notizen: Aiming identification of the components most affected by corrosion under salineenvironment conditions, we have carried out X-ray diffraction measurements in ceramic and bondmaterials, all in the powder form. The ceramic is analyzed before and after thermal annealing at1000ºC, showing the same DRX peaks, although better defined after annealing. Identificationsuggests the presence of Al6Si2O13 (Mullite) and SiO2 (Quartz). Analysis of the junction (bond)material shows similar peaks, but a metallic preponderance is observed. Thermal annealing of thejunction is done at much lower temperature, because it melts in the range 135ºC-170ºC, when awhitish smoke begins to show up along with strong sulfur odor

Notizen: Due to their high hardness and wear resistance, Si3N4 based ceramics are one of the mostsuitable cutting tool materials for machining cast iron, nickel alloys and hardened steels. However,their high degree of brittleness usually leads to inconsistent results and sudden catastrophic failures.This necessitates a process optimization when machining superalloys with Si3N4 based ceramiccutting tools. The tools are expected to withstand the heat and pressure developed when machiningat higher cutting conditions because of their high hardness and melting point. This paper evaluatesthe performance of α-SiAlON tool in turning Ti–6Al–4V alloy at high cutting conditions, up to250 m min−1, without coolant. Tool wear, failure modes and temperature were monitored to accessthe performance of the cutting tool. Test results showed that the performance of α-SiAlON tool, interms of tool life, at the cutting conditions investigated is relatively poor due probably to rapidnotching and excessive chipping of the cutting edge. These facts are associated with adhesion anddiffusion wear rate that tends to weaken the bond strength of the cutting tool

Notizen: The α-SiAlON ceramic cutting tool insert is developed. Silicon nitride and additivespowders are pressed and sintered in the form of cutting tool inserts at temperature of 1900 oC. Thephysics and mechanical properties of the inserts like green density, weight loss, relative density,hardness and fracture toughness are evaluated. Machining studies are conducted on grey cast ironworkpiece to evaluate the performance of α-SiAlON ceramic cutting tool. In the paper the cuttingtool used in higher speed showed an improvement in the tribological interaction between the cuttingtools and the grey cast iron workpiece resulted in a significant reduction of flank wear androughness, because of better accommodation and the presence of the graphite in gray cast iron. Theabove results are discussed in terms of their affect at machining parameters on gray cast iron

Notizen: Silicon nitride samples were formed by pressureless sintering process, using neodymium oxide assintering aid. The short term compressive creep behavior was evaluated over a stress range of 50-300 MPaand temperature range 1200-1350 0C. Post sintering heat treatments in nitrogen with a stepwise decrementalvariation of temperature were performed in some samples and microstructural analysis by X-raydiffractometry and Transmission Electron Microscopy showed that the secondary crystalline phases whichform from the remnant glass is dependent upon heat treatment. For the non heat treated samples, glassyregions were revealed, by centered dark field images, using diffuse scattered electrons, to be located at threeand four point grain junctions. No direct evidence of microstructural changes involving dislocationgeneration or motion was detected in the stress and temperature range studied. Stress exponents near unity,related to grain boundary accommodation processes were obtained for low temperatures and for heat treatedsamples. The behaviors for the heat treated samples were correlated in terms of depletion of metallic rareearthions and impurities from grain boundaries and triple junctions, with subsequent crystallization of theprimary glass. The non heat treated samples showed higher creep rates at higher stresses and temperatures.The deformation processes in these cases were correlated to stress concentrations at grain boundary andtriple point junctions, caused by grains rotation and sliding, accommodated by cavitation

Notizen: There has been a great interest for improving the machining of cast iron materials in theautomotive and other industries. Comparative studies for tool used to machine grey cast iron (CI)and compacted graphite iron (CGI) on dry machining were also performed in order to find out whyin this case the tool lifetime is not significantly higher. However the machining these materialswhile considering turning with the traditional high-speed steel and carbide cutting tools present anydisadvantages. One of these disadvantages is that all the traditional machining processes involve thecooling fluid to remove the heat generated on workpiece due to friction during cutting. This paperpresent a new generation of ceramic cutting tool exhibiting improved properties and importantadvances in machining CI and CGI. The tool performance was analyzed in function of flank wear,temperature and roughness, while can be observed that main effects were found for tool wear, wereabrasion to CI and inter-diffusion of constituting elements between tool and CGI, causing crater.However the difference in tool lifetime can be explained by the formation of a MnS layer on thetool surface in the case of grey CI. This layer is missing in the case of CGI

Notizen: In this work the cyclic fatigue life of 3mol.%Y2O3-stabilized zirconia polycrystallineceramics, doped with 5%wt 3CaO.P2O5,-SiO2-MgO, has been investigated. Samples with 5 and10%wt were cold uniaxial pressed (80MPa) and sintered in air at 1200 and 1300oC for 120 minutes.Sintered samples were characterized by X-Ray diffraction and Scanning Electronic Microscopy.Hardness and fracture toughness were determined using Vicker’s indentation method, and Modulusof Rupture was determined by four-point bending testing. Furthermore, the cyclic fatigue tests werealso realized by four-point bending tests, under frequency of 25 Hz and stress ratio, R, of 0.1, for thebest condition. In this condition, highly dense samples were obtained and presented values ofhardness, fracture toughness and bending strength of 11.3 ±0.1GPa, 6.1±0.4MPa.m1/2 and320±55MPa, respectively. The increasing of stress level leads to decreasing of the number of cyclesand the number of run-out specimens. The stress induced tetragonal-monoclinic (t-m)-ZrO2transformation, observed by X-Ray diffraction, contributes to the increasing of the fatigue life.Samples 3Y-TZP presents clearly a range of loading conditions where cyclic fatigue can bedetected

Notizen: Many researchers became interested in the discovery of Bi2Sr2CaCu2O8+δ oxides withcritical temperature of around 80 K. It is known that the critical temperature is related to the CuO2planes of the material. For this reason, the study of the interstitial oxygen in these oxides is of greatrelevance. The samples were prepared by means of conventional solid state reactions, through thestoichiometric mixture of precursory powders. After the sinterization, the samples were submittedto measurements of density, electrical resistivity, x-ray diffraction, scanning electron microscopyand energy dispersion spectroscopy, with the objective of performing their characterization. Themeasurements of mechanical spectroscopy were performed by a torsion pendulum. The resultsshow three relaxation processes in the temperature range of 200 and 700 K, with activation energyof approximately 0.9 eV, which has been attributed to the dynamics of the interstitial oxygenpresent in the material

Notizen: A new class of hybrid ruteno-cuprates – such as Ru-1212 and Ru-1222 – was discoveredin 1995 by Bauerfeind and collaborators. These materials present superconducting and magneticstates at low temperatures, an atypical duality in other superconductors. The superconductivity ismore easily observed in Ru-1222, while Ru-1212 is a more problematic case, due to the strongeffects of the preparation details in its superconducting properties, becoming the materialsuperconductor or not. Ru-1212 presents a critical temperature that can vary between 0 and 46 K,depending on the preparation conditions, and a temperature of magnetic transition of around 132 K.The samples were prepared through solid state reactions, by using a mixture of high purity powders,followed by calcination and sinterization in the nitrogen and oxygen atmospheres. This paper showsthe preparation process of Ru-1212 samples, followed by their structural and magneticcharacterization

Notizen: Polycrystalline SiC-diamond composites have been fabricated by high pressure and hightemperature, HPHT, sintering using a Si infiltration method. However, infiltration of liquid siliconaround the diamond particles results not only in SiC but also in free silicon, which causesdeterioration of the composite properties. In this work, a novel sintering procedure was developedto avoid the formation of free silicon in the composite structure. A disc composed of a mixture ofgraphite and silicon was first press-molded at room temperature. The disc was then placed abovethe diamond powder inside a high pressure chamber used for the HPHT sintering process. Thisarrangement permitted to preferentially form liquid Si in a C solution, which infiltrates in betweenthe diamond particles. Using this procedure, free silicon formation is inhibited and the SiC-diamondcomposite forms a rigid structure with improved properties

Notizen: The chemical methods allow obtaining powders with high reactivity and chemicalhomogeneity. This work studied the sintering of Y2O3-stabilized ZrO2 powders produced bypolymerization routes. In the three methods used were obtained powders via formation of gels,which were characterized by spectroscopy in the infrared. After the gel calcinations, the powdersobtained were characterized by X-ray diffraction and scanning electronic microscopy (SEM).Among the different chemical methods, there were differences in the coordination of the metallicions, which caused differences in the thermal behavior, reactivity, size and form of the particles ofthe powders. The powders were pressed and sintered at 1400 and 1600°C for 2 hours. The bodiessintered were characterized by SEM, apparent density and dilatometry. The average size of theparticles varied with the method, and the smallest particles were obtained by Pechini method. PCSmethod showed a strong reactivity of the powder and it was already partially sintered even in thestep of elimination of organic substances. Similarly, the sintered compacts presented differentproperties with each other, and the compacts obtained by PEG/FA method had the bestmicrostructure

Notizen: Ceramic components are frequently used as substrates for the production of temperaturesensing devices in petroleum industries, in view of their high thermal and electrical resistance andinertness in hostile ambient conditions. Complex cubic perovskite oxide ceramics have a greatadvantage in terms of their varied physico-chemical characteristics with the substitution ofstructural elements in the respective formula units. In this context, we have produced Ba2AlSnO5.5ceramics by solid state reaction process. Structural characteristics, studied by powder x-diffraction,reveal that Ba2AlSnO5.5 ceramic has an ordered complex cubic perovskite structure. Ba2AlSnO5;5ceramics were sintered in the form of circular discs of 10 and 15 mm diameters and 2 mmthickness, in the temperature 1200 to 14000C by normal sintering process. The microstruturalcharacteristics were studied by scanning electron microscopy on both polished and fracturesurfaces. The SEM micrographs show homogenous surface morphology and particle sizedistribution. Mechanical hardness of the sintered Ba2AlSnO5.5 ceramics were studied by Vicker´shardness tests. The results of these studies have been presented and discussed in this work

Notizen: The presence of pores in ceramics is directly related to the chosen forming process. So, inthe starch consolidation method, the ceramics show, after burning, pores with morphology similarto that presented by this organic material. On the other hand, the increase in solid load leads up toalterations in dispersion viscosity, increasing the thermal stresses during drying and sinteringprocesses. In order to verify the solid percentage influence in ceramic final properties, samples wereprepared with silicon carbide in different compositions using or not starch as binder agent and poreforming element. The characterization of the ceramic pieces was performed by superficialroughness measurements, porosity besides by optical and scanning electron microscopy. The resultsshowed ceramics with SiC and starch presented physical and microscopic properties slightly higherin relation to those with only ceramic powder in their composition. The presence of organicmaterial, agglomerated and foam during the forming were essential for the final properties of thestudied samples

Notizen: The aim of this work was to study the effect of temperature and heating rate on thedensification of two leucite-based dental porcelains: one low-fusion and one high-fusioncommercial leucite porcelains (Dentsply-Ceramco). Porcelain powders were characterized bydifferential thermal analysis (DTA), X-ray diffraction (XRD), particle size distribution, and heliumpicnometry. Bar samples were sintered from 650 to 1050oC, using heating rate of 55oC and10oC/min. Sintered samples were characterized in terms of bulk density, measured by theArchimedes method in water, and fractured surface microstructure by scanning electron microscopy(SEM). The results show that densification increases with increasing temperature and the increase inheating rate has no effect on the densification of the porcelains studied

Notizen: Despite of the wide use of hydroxyapatite (HA) for bone repair and regeneration, itsbrittleness has limited clinical application to less stressed body parts. Thus, evaluation of HAmechanical properties has been an important research matter. The aim of this study is to assess thecompressive strength of a stoichiometric HA with 1.66 Ca/P molar ratio, synthesized byhydrothermal method. Cylindrical samples were processed by uniaxial compacting, followed bysintering. Compressive strength of cylindrical samples with 2.0 medium diameter/height ratio wasmeasured according to ASTM C 1424. Load to failure divided by the cross-sectional area of thesamples were reported and microstructural characterization was made by MEV-EDS. Thecompression strength results were compared to values reported in the literature

Notizen: The aim of this work is to prepare and characterize Al2O3-ZrO2 powders by Pechinemethod and to evaluate them as supports for palladium catalysts in the selective reduction of NOwith CH4. The effect of aluminum ion on the final characteristics of the zirconia powder is alsoinvestigated. The catalytic supports were characterized by X-ray diffraction (XDR), scanningelectron microscopy (SEM) and catalytic activity. The XRD data showed the formation of tetragonalzirconia phase, with crystallite size of 6.3 and 6.1 nm for the supports prepared with 0.1 and 0.5moles of Al3+, respectively. Both supports showed porous and homogeneous agglomerates.Pd/Al2O3-ZrO2 catalysts were active NO reduction by CH4

Notizen: Reinforcement with yttria stabilized zirconia (YSZ) is an alternative to improvemechanical strength of hydroxyapatite (HAp) ceramic. However, calcium may react with zirconiumto form calcium zirconate. In addition, decomposition of HAp to tricalcium phosphate (TCP) occurswith water loss inhibiting ceramic densification. In order to minimize the formation of thesecompounds, two synthesis routes were compared in this work: coprecipitation of hydrous yttriastabilized zirconia in a calcium phosphate gel medium and powder mixture of individual calcinedpowders. Composite nominal compositions were fixed at 90 and 95 HAp wt%. Calcium, zirconiumand yttrium chlorides and ammonium hydrogen phosphate were the employed precursors.Ammonium hydroxide was the selected precipitation agent. Calcination was performed at 800oC for1 hour and pellets were sintered in the range of 1150 and 1350oC for 1, 3 and 5 hours. Ceramicsamples were characterized by scanning electron microscopy and apparent density measurements.Crystalline phases were quantified by Rietveld analysis of X-ray diffraction patterns. Resultsindicate that powders prepared by coprecipitation can cause porosity formation due to the higherchemical reactivity during synthesis process

Notizen: Today, the phosphate rock processed in the world represents around some 20 billiondollars per year. Some exploitable deposits are characterizing by low grade phosphate rocks,composed of the apatite group in association with a wide assortment of accessory minerals. Usuallya combination of beneficiation techniques is used to process a phosphate rock since run of mine,and then a flotation is applied to recovery apatite. This work proposes an evaluation of particle sizefor apatite recovery by column flotation in bench-scale. The variables collector dosage anddepressant dosage were investigated experimentally applying a factorial design. According to theexperimental results, the particle size range between 37&m and 105&m is an optimum size used toobtain simultaneously a product with the industry demand grade (at least 33%) and phosphorusrecovery, upper than 60%

Notizen: Mullite is a versatile material used in traditional and advanced ceramic, due to lowthermal expansion, high thermal shock and creep resistance. The production of waste from oreindustry is a problem that is increasing nowadays. The kaolin processing industry produces residuerich in Al2O3 and SiO2. These oxides are good precursors to produce mullite. The aim of this workis to use the residue from kaolin industry to produce mullite ceramic bodies. It was studied alumina,clay and residue from kaolin processing as raw materials. The material was dried and pressing inuniaxial press (30MPa). The samples were sintered at temperatures of 1450oC, 1500oC, 1550oC and1600oC. The ceramic bodies were characterized by X-ray diffraction. The density was measured byArchimedes method and the flexural strength by the three point bending technique. The resultsshowed that is possible to produce mullite with high amount of waste from kaolin processing

Notizen: Chromium rich, nickel based alloys Haynes 230 and Inconel 617 are candidate materialsfor the primary circuit and intermediate heat exchangers (IHX) of (Very)-High TemperatureReactors. The corrosion resistance of these alloys is strongly related to the reactivity of chromiumin the reactor specific environment (high temperature, impure helium).At intermediate temperature – 900°C for Haynes 230 and 850°C for Inconel 617 – the alloys underinvestigation are likely to develop a chromium-rich surface oxide scale. This layer protects from theexchanges with the surrounding medium and thus prevents against intensive corrosion processes.However at higher temperatures, it was shown that the surface chromia can be reduced by reactionwith the carbon from the alloy [1] and the bare material can quickly corrode. Chromium appears tobe a key element in this surface scale reactivity. Then, quantitative assessment of the surfacerequires an accurate knowledge of the chromium activity in the temperature range close to theoperating conditions (T ≈ 1273 K).High temperature mass spectrometry (HTMS) coupled to multiple effusion Knudsen cells wassuccessfully used to measure the chromium activity in Inconel 617 and Haynes 230 in the 1423-1548 K temperature range. Appropriate adjustments of the experimental parameters and in-situcalibration toward pure chromium allow to reach accuracy better than ± 5%.For both alloys, the chromium activities are determined. Our experimental results on Inconel 617are in disagreement with the data published by Hilpert [2]. Possible explanations for the significantdiscrepancy are discussed