TED-AJ03-215 MOLECULAR SCALE MECHANISM ON EVAPORATION AND REMOVAL PROCESSES OF ADHERENT MOLECULES ON SURFACE BY BURNT GAS

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From an ecological point of view, a dry-type "degreasing" method by flames is proposed and developed recently. Such a dry-type degreasing method by using flames can be considered as a thermal treatment in molecular scale because after such surface treatments, the adsorption of paints on base materials has been improved remarkably. Mechanisms of such improvement by flame treatments are not known clearly though some suppositions are proposed based on experimental observations. In order to understand evaporation and removal processes of adherent molecules on metallic surface by using high temperature gas flow, the interaction between adherent molecules and gas molecules is modeled in molecular scale and simulated by the molecular dynamics method. There are many important factors such as, gas temperature, surface temperature, the potential energy between adherent molecules and surface molecules and molecular structures in the processes. Methanol molecules are chosen as adherent molecules to investigate effects of adhesion quantity and gas molecular collisions because the industrial oil have too complex structures of fatty acid. Effects of adherent quantity, gas temperature and surface temperature on evaporation rate of adherent molecules and molecular removal mechanism are investigated and discussed in the present study. The calculation system is composed of a high temperature gas region, an adherent molecular region and a surface molecular region. When adhesion quantity on the surface corresponds to one layer of methanol molecules, methanol molecules sticking to the surface are hydrogen-bonded in the first layer from the surface. When adhesion quantity on the surface corresponds to two layers of methanol molecules, methanol molecules form molecular clusters on the first adherent layer. The state of adhesion in molecular scale changes largely depending on the quantity of adherent molecules. In the evaporation and removal processes of adherent molecules on surface, the evaporation and removal rate consists of that with gas molecular interactions and that without gas molecular interactions. These two different evaporation rates show different dependence on surface temperature and gas boundary temperature. With the increase of gas boundary temperature and the decrease of adhesion quantity, the ratio of evaporation with gas molecular interactions to that without gas molecular interactions has been enhanced. With the decrease of surface temperature, the ratio of evaporation with gas molecular interactions has increased relatively. Evaporation and removal rates of adherent molecules from metallic surface calculated by the molecular dynamics method showed similar dependence on surface temperature with experimental results.
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TED-AJ03-215 MOLECULAR SCALE MECHANISM ON EVAPORATION AND REMOVAL PROCESSES OF ADHERENT MOLECULES ON SURFACE BY BURNT GAS

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