An analysis of the erosional properties of carbonized lignin with a Si content of 0 to 40% under the simulated atomic oxygen (AO) conditions found in low earth orbit was carried out. The AO environment was produced using a laser detonation atomic oxygen beam source. X-ray photoelectron spectroscopy revealed an increase in the atomic concentration of oxygen-related groups on the surface of the carbonized lignin with and without Si. The erosion rate was found to be low for the case of carbonized lignin with>20% Si. The Si-free sample exhibited a resistance to oxidation due to the formation of an oxide area that protected it from further AO effects on chemical bonds such as C=C bonds. The surface chemistry of the Si-free samples was similar to that of diamond-like carbon (DLC). These experimental results suggest that carbonized lignin derived from Sugi wood has the potential to be used in materials for space applications.
Magnesium alloy is expected as one of the environmentally benign materials for significant weight reduction of the components due to its high specific strength. It is, however, necessary to improve its Young's modulus when Mg alloys are applied to structural components. Ceramics hard particles are generally used as reinforcements to improve the stiffness of Mg matrix composite. However, they also cause the decrease of ductility of the composite materials. In the present study, pure Ti particles were used as reinforcement because they had enough ductility and high Young's modulus compared to Mg alloys. For the materials design of Mg matrix composites reinforced with Ti particles, the wetting behavior of Ti by the molten Mg alloy should be investigated to fabricate a good coherence at the interface between the matrix and dispersoids. The sessile drop test results showed an extremely good wettability between pure Mg and pure Ti due to a thermite reaction at the interface between Mg and TiO2 surface films of the Ti substrate. The wettability between Mg-Al alloy (AZ80) and Ti was investigated in high-purity argon gas atmosphere at 1073K. In particular, the effect of Al element contained in AZ80 on the wetting behavior was examined. When AZ80 was dropped on the pure Ti plate (t=0s), the contact angle between the droplet and the Ti plate was 10°. The contact angle and the droplet height were gradually reduced with increasing time. Ti plate was completely covered with molten AZ80 in 60s. The result indicated the wettability of pure Ti by molten Mg-Al alloy was extremely good compared to the combination of pure Mg and pure Ti. When the specimen was kept at 1073K for 180s, Al was enriched on interface between AZ80 and Ti, but Al-Ti intermetallic compounds were not formed. It was concluded the wetting phenomenon of Ti by Mg alloy droplet reached termination before formation of Al-Ti intermetallics and Al element of AZ80 had no harmful effect on the wetting behavior between Mg alloy and Ti.
A hydroxyapatite/titania composite (HAp/TiO2) film was developed for application in air purification and as an antibacterial, antifouling film. This HAp/TiO2 film has the ability for adsorbing and decomposing organic matter. To obtain the HAp/TiO2 film, we used two kinds of aerosol beams. They were composed of TiO2 and HAp particles accelerated by flow of helium gas, respectively. First layer, TiO2 film, was formed on a glass plate with a TiO2 aerosol beam. Second layer, HAp film, was created on the first layer, TiO2 film. Neither the substrate nor HAp and TiO2 particles were heated during deposition. Acetaldehyde concentration reduced by the HAp/TiO2 film was measured to evaluate the film's ability for adsorbing and decomposing organic matter.