| Research Abstract |
We have investigated the reaction kinetics of evaporation/condensation of interstellar dust and also the chemical erosion rates of planetary surface as functions of temperature, pressure, and chemical compositions, by means of laboratory experiments using nebular and/or planetary atmosphere analogue. We have devised a new system that allowed a mixing in desired ratios of the three most fundamental elements, H, O, and C.In order to generate the analogue nebular gas, H_2, CO_2, and CO were controlled for their flow rates with precision automatic flowmeters, and introduced into the mixing vessel inside a high vacuum chamber. A quadrupole mass spectrometer has been attached to this system to allow gas analyses.
To achieve a thermodynamic equilibrium inside the vessel at a prescribed temperature, granular Pt catalyses were doped inside the PtRh reaction cell. An alumina protection tube was devised to prevent PtRh from excessive evaporation at high T in vacuo. The gas controlling system was c
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onnected to the mixing vessel inside the vacuum furnace, and is being tested for its utility at high temperatures up to 1600℃. We have developed a computer program that calculates partial pressures of various radicals including oxygen under various T, P, and composition conditions. With this program we are able to predict the relationships between the concentration of various radicals and the reaction rate that occurs in actual experiments.
As a first-order approximation to the real situation in the nebula, we have carried out investigation on the reaction rate of interstellar dust materials during evaporation/condensation processes. We have found that the reaction rate was proportional to the concentration of atomic hydrogen, we also found that the temperature dependence of the reaction rate was reflecting the activation energy required for breaking a chemical bond between metallic element and oxygen. The fact that the recondensation rate was inversely proportional to the atomic hydrogen pressure have indicated an involvement of OH radical in the reaction. We have also found a temperature effect on recondensation, that enhanced with temperature, its cause is under investigation. Less
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