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
    Mund-, Kiefer- und Gesichtschirurgie 3 (1999), S. 92-97 
    ISSN: 1434-3940
    Keywords: Schlüsselwörter Ca-P-Keramiken ; Knochenersatzmaterialien ; Röntgendiffraktometrie ; Kristallisation ; Key words Calciumphospate ceramics ; Bone regeneration materials ; X-ray diffractometry ; Cristallisation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Introduction: The crystalline structure of hydroxyapatite (HA) and tricalciumphosphate (TCP) used as bone regeneration materials affects their physical and probably also their biological properties. Varying velocities of the HA solution process seem to be correlated to different results in powder diffraction analysis (RDX) [1], a validated, routine procedure in mineralogy [2, 6] to analyse crystallized materials. As far we know there are no comparative RDX analyses for the TCP materials in clinical use. Goals: The dimension and quality of the crystallization of several bone regeneration materials are analysed by RDX. Material and methods: The materials analysed were divided in different groups: hydroxyapatite, tricalciumphosphate and bioglass. The materials are characterized by the specific intensity curve measurements. Results: The HA products, with the exception of Algipore, seem to be monophasic. Ceros80 and Endobone were the only ones which seem to be totally crystallized. The TCP products Biobase and Cerasorb are nearly monophasic, whereas Ceros82 seems to contain a mixture of 30% HA and 70% β-TCP. All TCPs show a high crystallization. The bioglasses did – as suspected – not show crystalline structures. Discussion: There are many possible causes for inhomogeneous crystallization of the investigated materials, as they are composites of different foreign ions, extremely small crystals or abnormal (deficient) apatites. How this affects the biological behaviour is not known. Summary: We found differences between the examined materials; how this affects the biological behaviour is unknown. Further investigations are neccesary to correlate the characteristics of the materials to the clinical outcome.
    Notes: Einleitung: Die kristalline Struktur von Knochenersatzmaterialien wie Hydroxylapatitkeramiken (HA) oder Trikalziumphosphatkeramiken (TCP) beeinflußt deren physikalische und sicher auch biologische Eigenschaften. Unterschiedliches Löslichkeitsverhalten von synthetischem und biologischem HA scheinen mit unterschiedlichen Ergebnissen in der Röntgenpulverdiffraktometrie (RDX), einem Routineverfahren der Materialwissenschaften [2, 6] zur Analyse kristalliner Strukturen, korreliert zu sein [1]. Vergleichende RDX-Analysen von TCP liegen in der einschlägigen Literatur nicht vor. Best et al. [4] unterstrichen in jüngster Zeit die Bedeutung der Charakterisierung der Knochenersatzmaterialien zum Verständnis der Resorptionsmechanismen [4]. Fragestellung: Ausmaß und Qualität der Kristallisation verschiedener z. Z. verfügbarer Knochenersatzmaterialien wurden mittels RDX-Analyse bestimmt. Material und Methoden: Die verwendeten Materialien wurden in 3 Gruppen eingeteilt: Hydroxylapatitkeramiken, Trikalziumphosphatkeramiken und Biogläser. Anhand der mittels Pulverdiffraktometer gewonnenen Intensitätsspektren können die Materialien hinsichtlich ihrer Zusammensetzung und Kristallisation charakterisiert werden. Ergebnisse: Die HA-Materialien (bis auf Algipore) scheinen monophasige Produkte zu sein, wobei nur Ceros80 und Endobone eine hohe Kristallisation aufweisen. Auch die TCP-Produkte Biobase und Cerasorb sind nahezu monophasig, während Ceros82 aus einer Mischung von 30% HA und 70% β-TCP zu bestehen scheint. Alle TCP weisen einen hohen Kristallisationsgrad auf. Die Biogläser zeigten erwartungsgemäß keine kristallinen Strukturen. Diskussion: Die möglichen Ursachen der inhomogenen Kristallisation der untersuchten Materialien reichen von der Zusammensetzung aus kleinen Einzelkristalliten über Fremdioneneinschlüsse zu defizitären Apatiten durch Kalziumkarbonatbeimengungen. Deren Bedeutung für das biologische Verhalten ist nicht geklärt. Resümee: Es fanden sich Unterschiede zwischen den untersuchten Materialien, deren Bedeutung für das biologische Verhalten nicht geklärt ist. Weiterführende Untersuchungen sind erforderlich, um diese Eigenschaften mit dem klinischen Verhalten zu korrelieren.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1434-3940
    Keywords: Schlüsselwörter ; Kalziumphosphatkeramiken ; Spezifische Oberfläche ; Knochenersatzmaterialien ; Poren ; Hydroxylapatit ; Key words ; Calciumphosphate ceramics ; Specific surface area ; Bone regeneration materials ; Pores ; Hydroxyapatite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: The surface area and the microporosity of bone regeneration materials influence their chemical and ¶biological properties. Therefore, the size of the specific surface area and the distribution of the pore diameters (pores 〈 1 μm) of bone regeneration materials were analyzed within this study. The analyzed hydroxyapatites were of synthetic, bovine, and phytotroph origin. The tricalcium phosphates and the bioglasses included only synthetic materials. The gas adsorption of each specimen was analyzed using a volumetric N2/Kr system (ASAP 2010, Micromeritics). Additionally, for materials with a specific surface area (〉 2 m2/g) the pore size distribution was evaluated by the BJH-method. Two of the ¶materials evaluated astonishingly large dimensions of the specific surface area (BioOss 79.7 m2/g, Algipore new 14.6 m2/g). A medium ¶surface area was found for Algipore old (4.9 m2/g) and Interpore200 ¶(2.64 m2/g). All other included materials showed only small sizes of the specific surface area (Ceros80 ¶1.8 m2/g, Ceros82 1.31 m2/g, Cerasorb 1.2 m2/g, Biobase 0.7 m2/g, Endobone 0.7 m2/g, Perioglas 0.6 m2/g, Allotropat50 0.23 m2/g, Biogran ¶0.2 m2/g). The materials with large and medium sizes of the specific surface area evaluated the following pore diameters: BioOss 2–50 nm, Algipore new 2–100 nm, Algipore old 5–50 nm, Interpore200 2–100 nm. Pore sizes less than 2 nm were not found in relevant numbers. The materials BioOss, old and new Algipore, and Interpore200 contain a large interconnecting mesopore system (diameter 〈 1 μm). For the materials Biobase, Endobone, Perioglas, Allotropat 50, and Biogran this cannot be assumed. The materials Ceros80, Ceros82, and Cerasorb evaluated a specific surface area between those and might include only a small part of these interconnecting pores. An influence of the interconnecting porosity and the different sizes of the specific surface areas on the biological behavior of the bone regeneration materials can be suggested.
    Notes: Fragestellung: Die Oberfläche sowie die Mikro- und Mesoporosität von Knochenersatzmaterialien beeinflussen deren chemische und biologische Eigenschaften. Daher wurden in dieser Untersuchung die Größe der spezifischen Oberfläche sowie die Verteilung der Porendurchmesser (Poren 〈 1 μm) in Knochenersatzmaterialien bestimmt. Material und Methode: Die untersuchten Hydroxylapatite waren synthetischen, bovinen und phytotrophen Ursprungs. Die Trikalziumphosphate und die Biogläser umfassten nur rein synthetische Materialien. ¶Die Gasadsorptionsuntersuchung je einer Probe erfolgte mit Hilfe eines volumetrischen N 2 -Kr-Systems (ASAP 2010, Micromeritics). Zusätzlich wurde für Materialien mit spezifischen Oberflächen ¶〉 2 m 2 /g die Porengrößenverteilung nach der BJH-Methode ermittelt. Ergebnisse: 1. Spezifische Oberfläche: 2 der Materialien zeigten eine auffallend große spezifische Oberfläche (BioOss 79,7 m 2 /g, Algipore neu 14,6 m 2 /g). Eine mittlere Oberfläche zeigten Algipore alt (4,9 m 2 /g) und Interpore 200 (2,64 m 2 /g). Die übrigen Materialien zeigten nur kleine Oberflächen (Ceros 80 1,8 m 2 /g, Ceros 82 ¶1,31 m 2 /g, Cerasorb 1,2 m 2 /g, Biobase 0,7 m 2 /g, Endobone 0,7 m 2 /g, Perioglas 0,6 m 2 /g, Allotropat 50 0,2 m 2 /g, Biogran 0,2 m 2 /g). 2. Häufigkeitsverteilung des Porendurchmessers: Die Materialien mit großen und mittleren spezifischen Oberflächen zeigten folgende Porendurchmesser: BioOss 2–50 nm, Algipore neu 2–¶100 nm, Algipore alt 5–50 nm, Interpore 200 2–100 nm. Porengrößen 〈 2 nm fanden sich kaum. Schlussfolgerungen: Die Materialien BioOss, Algipore alt und neu und Interpore 200 haben ein großes interkonnektierendes Mesoporensystem (Durchmesser 〈 1 μm). Für die Materialien Biobase, Endobone, Perioglas, Allotropat 50 und Biogran ist dies nicht anzunehmen. Die Materialien Ceros 80, Ceros 82 und Cerasorb zeigen eine dazwischen liegende spezifische Oberflächengröße und weisen einen mäßigen Anteil von solchen interkonnektierenden Poren auf. Ein Einfluss der interkonnektierenden Porosität und der deutlich unterschiedlichen spezifischen Oberflächen auf das Verhalten der Knochenersatzmaterialien in vivo ist nahe liegend.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 14 (1993), S. 699-725 
    ISSN: 1572-9567
    Keywords: argon ; caloric properties ; density ; equation of state ; Helmholtz function ; methane ; nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In order to describe the thermodynamic behavior of methane, argon, and nitrogen in the so-called “natural-gas region,” namely, from 270 to 350 K at pressures up to 30 MPa as accurate as possible with equations of a very simple form, new equations of state for these three substances have been developed. These equations are in the form of a fundamental equation in the dimensionless Helmholtz energy; for calculating the pressure or the density, the corresponding equations explicit in pressure are also given. The residual parts of the Helmholtz function representing the behavior of the real gas contain 12 fitted coefficients for methane, 8 for argon, and 7 for nitrogen. The thermodynamic relations between the Helmholtz energy and the most important thermodynamic properties and the needed derivatives of the equations are explicitly given; to assist the user there is also a table with values for computer-program verification. The uncertainties when calculating the density ρ, the speed of sound w, the isobaric specific heat capacity c p, and the isochoric specific heat capacity c v are estimated as follows. For all three substances it is Δρ/ρ≤±0.02 % for p≤ 12 MPa and Δρ/ρ ≤ ±0.05% for higher pressures. For methane it is Δw/w≤±0.02% for p≤10 MPa and Δw/w≤+-0.1% for higher pressures; for argon it is Δw/w≲-0.1 % for p≤ 7 MPa, Δw/w≤±0.3 % for 7 〈p≤30 MPa; and for nitrogen it is Δw/w≤±0.1% for p≤1.5 MPa and Δw/w±0.5% for higher pressures. For all three substances it is Δc p/c p≤±1 % and ΔC v/C v≤±1 % in the entire range.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 17 (1996), S. 391-404 
    ISSN: 1572-9567
    Keywords: coexistence curve ; equation of state ; Lennard Jones fluid ; thermodynamic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new equation of state (EOS) is proposed for the Helmholtz energyF of the Lennard Jones fluid which represents the thermodynamic properties over a wide range of temperatures and densities. The EOS is written in the form of a generalized van der Waals equation.F =F u +F v. WhereF u is a hard body contribution andF A an anttractive dispersion force contribution. The expression forF H is closely related to the hybrid Barker Henderson pertubation theory. The construction ofF A is accomplished with the Setzmann Wagner optimization procedure on the basis of virial coefficients and critically assessed computer simulation data. A comparison with the EOS of Johnson et al. shows improvement in the description of the vapor liquid coexistence properties, thepvT data. and in peculiar, of the calorie properties. A comparison with the EOS of Kolafa and Nezbeda which appeared after the bulk of this work was finished shows still by about 30%.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 10 (1989), S. 1103-1126 
    ISSN: 1572-9567
    Keywords: correlation equation ; equation of state ; least-squares principle ; optimization method ; search method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An optimization strategy is presented for optimizing the structure of empirical thermodynamic correlation equations. Based on a comprehensive functional expression for the physical dependence considered, which is called a “bank of terms,” the new procedure optimizes the structure and the length of the equation as well. The application of this method results in an equation which meets the quality wanted for representing the experimental data with the lowest number of fitted coefficients. The procedure can be used for the determination of the structure of any equation where the method of the linear least squares is applicable. A detailed description of the algorithm is given which includes values for the control parameters for different applications in the field of thermodynamics (vapor pressure equations, equations of state, etc.) and also for applications in other fields. The optimization steps are described using an equation which represents a relationship between variables in a general form. It is demonstrated how even the complex problem of the optimization of a fundamental equation for the Heimholtz energy can be written in terms of this general equation.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 19 (1998), S. 1121-1132 
    ISSN: 1572-9567
    Keywords: caloric properties ; density ; equation of state ; nitrogen ; thermodynamic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new formulation describing the thermodynamic properties of nitrogen has been developed. New data sets which have been used to improve the representation of the p–ρ–T surface of gaseous, liquid and supercritical nitrogen, including the saturated states are now available. New measurements on the speed of sound from spherical resonators have been used to improve the accuracy of caloric properties in gaseous and supercritical nitrogen. State-of-the-art algorithms for the optimization of the mathematical structure of the equation and special functional forms for an improved description of the critical region were used to represent even the most accurate data within their experimental uncertainty. The uncertainty in density of the new reference equation of state ranges from ±0.01% between 270 and 350 K at pressures less than 12MPa, within ±0.02% over all other temperatures less than 550 K and pressures less than 12 MPa, and up to a maximum of ±0.6% at the highest pressures. The equation is valid from the triple point to temperatures of 1000 K and pressures up to 2200 MPa. The new formulation yields a reasonable extrapolation up to the limits of chemical stability of nitrogen as indicated by comparison to experimental shock tube data. Constraints regarding the structure of the equation ensure reasonable extrapolated properties up to temperatures and pressures of 5000 K and 25 GPa. For typical calibration applications, the new reference equation is supplemented by a simple but also highly accurate formulation, valid only for supercritical nitrogen between 270 and 350 K at pressures up to 30 MPa.
    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...