Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 2 (1994), S. 427-430 
    ISSN: 1573-4846
    Keywords: Y-Ba-Cu-O ; oxycarbonate ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract High T c -superconducting powders of the Y-Ba-Cu-O system are prepared by a solution-polyacrylamide gel using citric acid as a complexing agent. This method provides an easy way to prepare reactive YBaCuO powders by sol-gel synthesis. However this synthesis involves intermediate phases formation which impedes the obtention of the pure phase at low temperature. An intermediate oxycarbonate phase forms between 800° and 850°C in flowing oxygen. From powder X-ray diffraction, thermal analysis and IR spectroscopy, it is concluded that the intermediate oxycarbonate has an average tetragonal structure—SG P4/mmm—similar to that of the parent oxide with a stoichiometry close to YBa2Cu2.95(CO3)0.35O6.6. The carbonate group is located in the center of the basal CuO square. This compound has superconducting properties. A pure 123 phase is obtained when the xerogel precursor is annealed at 925°C in O2 or at 800°C in Ar, then in O2. The grain growth and microstructure development of YBaCuO have also been investigated and compared using two different powders, i.e. sol-gel route and commercial powder from Hoechst.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Physics and chemistry of minerals 27 (2000), S. 495-503 
    ISSN: 1432-2021
    Keywords: Key words Thermal decomposition ; Kinetics ; Siderite ; CRTA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The mechanism of the thermal decomposition of two siderites (a pure synthetic and a natural Mg-containing sample) has been determined from comparison of the results obtained from linear heating rate (TG) and constant rate thermal analysis (CRTA) experiments in high vacuum. The thermal decomposition of the synthetic siderite takes place approximately 200 K below the decomposition temperature of the natural sample. The mechanism and the product of the thermal decomposition are different for the siderite samples. In fact, an A2 kinetic model describes the thermal decomposition of the synthetic siderite, whereas the thermal decomposition of the natural sample obeys an F1 kinetic law. Decomposition products of the synthetic siderite are iron and magnetite, those of the natural siderite are wüstite and minor magnetite.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1572-8943
    Keywords: Constant Rate Thermal Analysis (CRTA) ; solid state kinetics ; Stepwise Isothermal Analysis (SIA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The results obtained in this work point out that both SIA and CRTA traces, simulated assuming the same values of the reaction rate, are identical provided that either 'n order’ or diffusion controlled kinetics are concerned. The α-T CRTA plots of solid state reactions fitting an Avrami-Erofeev kinetic model show that the temperature decreases with increasing α until reaching a minimum at a value of the reacted fraction α = αmin characteristic of the Avrami-Erofeev exponent. The shapes of the corresponding SIA diagrams are quite different and a very long isothermal step is obtained. Moreover, the reaction rate is not maintained constant during the isothermal period but it shows a maximum at a value of α depending on the Avrami-Erofeev coefficient. It is important to point out that this αmax value agrees with the corresponding αmin calculated from a CRTA curve by assuming the same Avrami-Erofeev exponent.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1572-8943
    Keywords: CRTA ; material synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Some examples of the use of the CRTA method for the synthesis of materials with controlled texture and structure are given. BaTiO3 has been obtained from the thermal decomposition of Barium Titanyl Oxalate (BTO) and Barium Titanyl Citrate (BTC) by controlling the reaction temperature in such a way that the partial pressure of the gases generated in the reaction was maintained constant at a value close to 10-2 mbar. It has been shown that this method allows getting BaTiO3 with crystal sizes considerably lower than those obtained by decomposing the same precursors by conventional methods. This small crystal sizes lead to the stabilisation of the metastable cubic phase with regards to the tetragonal phase. It has been also shown that the control of the CO generated in the carbothermal reduction of silica allows tailoring the phase composition of the silicon nitride obtained as final product.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of the thermal decomposition of smithsonite has been determined from a comparison of the results obtained from isothermal, linear heating rate (TG), and Constant Rate Thermal Analysis (CRTA) experiments. Two important precautions have been taken in this work. Firstly, the chemical composition of the sample has been checked in order to be sure that pure anhydrous zinc carbonate has been used. Secondly, the experimental conditions have been selected in such a way to avoid the influence of heat and mass transfer phenomena on the forward reaction. It has been shown that the mechanism for the thermal decomposition of smithsonite depends upon temperature. Thus, at temperatures lower than 650 K, approximately, an A0.5 kinetic model describes the reaction, whereas, at temperatures roughly higher than 690 K the above reaction obeys a F1 kinetic law. An interpretation of this behavior is given. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 647-655, 1998
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...