Quasielastic neutron scattering study of hydrogen motion in NbC0.71H0.28
In order to study the mechanism and parameters of H jump motion in the nonstoichiometric Nb carbides, we have performed quasielastic neutron scattering (QENS) measurements for NbC0.71H0.28 over the temperature range 11– 475 K. Our results indicate that about 30% of H atoms in this system participate in a fast diffusive motion. The temperature dependence of the corresponding H jump rate in the range 298–475 K follows the Arrhenius law with an activation energy of 328 ± 9 meV. The Q dependence of the QENS data suggests that the observed jump motion corresponds to long-range diffusion of H atoms along chains of the off-centre sites in carbon vacancies.
Zur Kristallstruktur der Carbohydride von Übergangsmetallen
Mit Hilfe von Neutronenbeugungs-Aufnahmen an hydrierten und deuterierten Ubergangsmetall-Carbiden wurden die Positionen der Kohlenstoff- und Wasserstoffatome ermittelt. In den ternaren Phasen Zr2C1-xHy y und Zr2C1-xD y besetzen H bzw. D die tetraedischen Lucken des Anti-CdJ2-Typs. In der kubischen Carbohydrid-Phase liegt der Kohlenstoff geordnet vor; der Wasserstoff fullt vorzugsweise die freien Oktaederlucken.
Brushite-collagen composites for bone regeneration.
Brushite-based biomaterials are of special interest in bone regeneration due to their biocompatibility and biodegradability; on the other hand, collagen is a well-known osteoconductive biomaterial. In the present study a new brushite-collagen composite biomaterial is reported. This new biomaterial was prepared by combining citric acid/collagen type I solutions with a brushite cement powder. The obtained biomaterial was a cement paste, with improved handling properties. The effect of collagen on the setting reaction of brushite cement was studied, and was found to speed up the cement setting reaction. The cement paste set into a hard ceramic material within 18.5+/-2.1min and had compressive strength similar to that of spongeous bone (48.9+/-5.9MPa in dry conditions and 12.7+/-1.5MPa in humid conditions). The combination of collagen with citric acid revealed an interesting synergistic effect on the compressive strength of the composite material. Moreover, this new biomaterial had excellent cohesion properties (ninefold better than brushite cement), and high cellular adhesion capacity (threefold higher than brushite cement). The composite biomaterial described in this study combines good handling properties, compressive strength, cohesion and cell adhesion capacity, along with the osteoconductive and biodegradable properties inherent in brushite and in collagen-based biomaterials.