Atomic oxygen effects on boron nitride and silicon nitride: A comparison of ground based and space flight data
The effects of atomic oxygen on boron nitride (BN) and silicon nitride (Si3N4) were evaluated in a low Earth orbit (LEO) flight experiment and in a ground based simulation facility. In both the inflight and ground based experiments, these materials were coated on thin (approx. 250A) silver films, and the electrical resistance of the silver was measured in situ to detect any penetration of atomic oxygen through the BN and Si3N4 materials. In the presence of atomic oxygen, silver oxidizes to form silver oxide, which has a much higher electrical resistance than pure silver. Permeation of atomic oxygen through BN, as indicated by an increase in the electrical resistance of the silver underneath, was observed in both the inflight and ground based experiments. In contrast, no permeation of atomic oxygen through Si3N4 was observed in either the inflight or ground based experiments. The ground based results show good qualitative correlation with the LEO flight results, indicating that ground based facilities such as the one at Los Alamos National Lab can reproduce space flight data from LEO.
Evaluation of atomic oxygen interaction with thin-film aluminum oxide
Effects of atomic oxygen on thin-film (750/angstrom/) sputtered aluminum oxide (Al/sub 2/O/sub 3/) have been characterized. Experiments were conducted using the Los Alamos National Laboratory (LANL) O-atom facility. Diffusion of O-atoms through the Al/sub 2/O/sub 3/ thin films was observed, having an activation energy of 5.2 kcal/mole at an O-atom kinetic energy of 2 eV. Silver oxidation was used as the technique to detect penetration of O-atoms through thin-films. The Al/sub 2/O/sub 3/ films were deposited on silver (250/angstrom/), and the electrical resistance of the silver was measured in-situ during exposure. The thin films provided better protection of the substrate when deposited on smooth sapphire surfaces than when deposited on rougher alumina surfaces. The Al/sub 2/O/sub 3/ was amorphous before and after exposure, with less than 2% variation in oxygen atomic concentration and total Al/sub 2/O/sub 3/ thickness before and after exposure. 14 refs., 10 figs., 1 tab.
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.