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  • 11
    Electronic Resource
    Electronic Resource
    In vitro and in vivo mechanical evaluations of plasma-sprayed hydroxyapatite coatings on titanium implants: The effect of coating characteristics (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 37 (1997), S. 335-345 
    Details
    ISSN: 0021-9304
    Keywords: bonding-strength ; shear-strength ; simulated body fluid ; push-out measurement ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: This study was undertaken to evaluate the effect of coating characteristics on the mechanical strengths of the plasma-sprayed HA-coated Ti-6Al-4V implant system both in vitro and in vivo. Two types of HA coatings (HACs) with quite different microstructures, concentrations of impurity-phases, and indices-of-crystallinity were used. In vitro testings were done by measuring the bonding-strength at the Ti-6Al-4V-HAC interface, with HACs that had and had not been immersed in a pH-buffered, serum-added simulated body fluid (SBF). The shear-strength at the HAC-bone interface was investigated in a canine transcortical femoral model after 12 and 24 weeks of implantation. The results showed a bonding degradation of approximately 32% or higher of the original strength after 4 weeks of immersion in SBF, and this predominantly depended on the constructed microstructure of the HACs. After the push-out measurements, it was demonstrated that the HACs with higher bonding-strength in vitro would correspondingly result in significantly higher shear-strength at each implant period in vivo. Nevertheless, there were no substantial histological variations between the two types of HACs evaluated. The most important point elucidated in this study was that, among coating characteristics, the microstructure was the key factor in influencing the mechanical stability of the HACs both in vitro and in vivo. As a consequence, a denser HAC was needed to ensure mechanical stability at both interfaces. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 37, 335-345, 1997.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Changes in phases and crystallinity of plasma-sprayed hydroxyapatite coatings under heat treatment: A quantitative study (1995)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 1483-1492 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: With three kinds of plasma-sprayed hydroxyapatite coatings (HACs) prepared, the objectives of this study were (1) to establish the calibration methods for quantitatively measuring the concentration of impurity phases and the degree of crystallinity of the HACs, and (2) to explore the effects of postheat treatments at various temperatures in vacuo on the changes of phases and crystallinity of the HACs. By the internal standard method used, the concentrations of impurity phases, such as α-TCP, β-TCP, and TP, of the assprayed HACs were significantly higher than those measured by the direct intensity-ratio method, and the CaO phase was lower than the direct intensity-ratio method. When the HACs were heat treated in the temperature interval 630-850°C, the concentrations of impurity phases obviously decreased, and the coating crystallinity apparently increased. After annealing at 850°C, an HAC consisting of at least 95% crystallinity with few impurity phases was obtained. As the annealing temperatures in the interval 850-1000°C were applied, however, the HA phase seriously decomposed, resulting in the appearance of a large number (higher than 20 wt%) of impurity phases in the HACs. This work suggests that the optimum heat treatment conditions in vacuo for maximizing crystallinity and minimizing impurity phases of the HACs do not occur at the same temperature. © 1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820291204
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  • 13
    Electronic Resource
    Electronic Resource
    Intramedullary implant of plasma-sprayed hydroxyapatite coating: An interface study (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 36 (1997), S. 39-48 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: An intramedullary implant model in the canine femora was developed to evaluate the mechanical and histological responses between cancellous bone and plasma-sprayed hydroxyapatite coatings (HACs) on Ti-6A1-4V implants, with 12- and 24-week follow-ups. HACs of different thicknesses were investigated. Results of the mechanical testings revealed that after 24 weeks of implantation, the mean shear strength (2.49 ± 0.12 MPa) of the 50 μm HACs was significantly higher (p 〈 0.05) than that of the 200 μm HACs (1.44 ± 0.19 MPa). However, using backscattered electron images (BEIs) throughout all the implant periods, no substantial histological variations in the extent of new bone apposition between the two HACs were observed. Occasionally, solution-mediated disintegration of the 50 μm HAC was found 24 weeks postimplantation. Histomorphometric studies from the BEIs demonstrated that for both HACs the percentage of the direct HAC-cancellous bone contact was approximately 50% at 12 weeks and 75% at 24 weeks. After the mechanical tests, the 200 μm HACs had fracture sites either inside the coating layers or at the HAC-titanium interfaces, which might explain why the mechanical performance of the 200 μm HACs was inferior to that of the 50 μm HACs even though both HACs had the same histological behaviors. © 1997 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Dielectric relaxation of collagen and gelatin (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 11 (1973), S. 737-758 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dielectric dispersions of reconstituted collagens and gelatin were measured from 0.1 to 10 kHz and -160 to +160°C. At 0.1 kHz there is a γ transition at -80°C which is attributed to the H2O-coupled local modes. The process has an activation energy of 7.5 kcal. A devitrification process is observed at 10-20°C. Both of these processes have their counterparts in the dynamic mechanical measurements. The tan δ values are up to 3 times as great for the dynamic mechanical dispersions. There is an additional hightemperature dielectric loss transition which does not correspond to any seen with the mechanical experiments. A probable mechanism for this absorption is the Maxwell-Wagner-Sillars effect.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.180110408
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  • 15
    Electronic Resource
    Electronic Resource
    Rheo-optical studies of the nature of the α mechanical loss mechanism of polyethylene (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 11 (1973), S. 1891-1939 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dynamic x-ray diffraction and dynamic birefringence techniques are employed to determine the nature of the molecular motions associated with the α mechanical loss processes for low-density polyethylene. The results indicate that the low-temperature part of this loss (designated α1) is associated with an interlammellar “grain boundary” slip process while the higher temperature process (α2) involves intracrystalline motion and plasticity of the crystal itself. The activation energy for α1 determined by x-ray response is 25-30 kcal/mole, while that for α2 is 30-60 kcal/mole. The findings are consistent with dynamic infrared and dynamic light-scattering results which indicate that the motion of amorphous chains is closely correlated with that of the crystals. The relative contributions of amorphous and crystalline regions to the birefringence are dependent on the thermal treatment of the sample. The effect of static strain on the dynamic response indicates that crystal orientability is first increased with strain, probably because of splaying apart of lamellae, is subsequently decreased because of the restrictions of interlamellae tie chains, but then increases again as the spherulites are destroyed at high strain. The static strain reduces the orientability of amorphous regions.
    Additional Material: 29 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.180111004
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  • 16
    Electronic Resource
    Electronic Resource
    A shock tube study of methyl-methyl reactions between 1200 and 2400 K (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 27 (1995), S. 1179-1196 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The methyl-methyl reaction was studied in a shock tube using uv narrowline laser absorption to measure time-varying concentration profiles of CH3. Methyl radicals were rapidly formed initially by pyrolysis of various precursors, azomethane, ethane, or methyl iodide, dilute in argon. The contributions of the various product channels, C2H6, C2H5 + H, C2H4 + H2, and CH2 + CH4, were examined by varying reactant mixtures and temperature.The measured rate coefficients for recombination to C2H6 between 1200 and 1800 K are accurately fit using the unimolecular rate coefficients reported by Wagner and Wardlaw (1988). The rate coefficient for the C2H5 + H channel was found to be 2.4 (±0.5) × 1013 exp(-6480/T) [cm3/mol-s] between 1570 and 1780 K, and is in agreement with the value reported by Frank and Braun-Unkhoff (1988). No evidence of a contribution by the C2H4 + H2 channel was found in ethane/methane/argon mixtures, although methyl profiles in these mixtures should be particularly sensitive to this channel. An upper limit of approximately 1011 [cm3/mol-s] over the range 1700 to 2200 K was inferred for the rate coefficient of the C2H4 + H2 channel. Between 1800 and 2200 K, methyl radicals are also rapidly removed by CH3 + H ⇒ 1CH2 + H2. In this temperature range, the reverse reaction was found to have a rate coefficient of 1.3 (±0.3) × 1014 [cm3/mol-s], which is 1.8 times the room-temperature value. © 1995 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550271205
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  • 17
    Electronic Resource
    Electronic Resource
    A new model for the prediction of the relaxation behavior of vinyl polymers in the primary transition region (1985)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 23 (1985), S. 825-829 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1985.180230415
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  • 18
    Electronic Resource
    Electronic Resource
    Pyrolysis of poly(vinyl chloride) (1974)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 12 (1974), S. 2927-2941 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A pyrolysis-gas chromatography-mass spectrometric technique has been developed to study the thermal degradation of poly(vinyl chlorides) polymerized at different temperatures. Hydrogen chloride and benzene evolution during successive stages of pyrolysis have been quantitatively determined and correlated to the tacticity and molecular weight of the polymer. It was found that lowering the temperature of polymerization and molecular weight depresses benzene evolution and increases char weight but does not affect the HCl yield. It is suggested that the syndiotactic trans microstructure favored at low temperature of polymerization yields polyenes which cannot cyclize to form benzene. As the molecular weight decreases, the increase in number of vinyl chain ends facilitates pyrolytic crosslinking and char formation.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1974.170121219
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