발간논문

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An effective technique for evaluating the effects of rapid solidificaton on the undercooling and crystallization behavior of high temperature materials is through containerless drop tube processing. Also solidification of metal can be performed under the microgravity environment, if the metal droplet is solidified during free fall. A laboratory scale (3m) drop tube has been developed and studied both of the effects on solidification behavior of metals. The free fall of a liquid metal drop and heat transfer from the drop to its inert gaseous environment are described. To analyze the undercooling history and quantitative microgravitational condition during drop tube processing, heat flow modelling has been developed and the model has been tested experimentally.

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A new way of producing alumina from the alkoxide is reported. Aluminum oxalate is first synthesized by reactions which allow controlled precipitation. Alumina powder is obtained by subsequent thermal decomposition. 1) The addition of H₂C₂O₄, in the Boehmite Sol. was able to reduce the Geling time. 2) The first generated particles in the size of 10㎛ were agglomerated in chain type. 3) The recovery of A1₂O₃ was increased with increasing PH of solution and decreasing both the mole ratio of H₂C₂O₄/ Alkoxide and reaction temperature. 4) The grain size of the calcined products was increased with increasing PH of solution, mole ratio of H₂C₂O₄/ Alkoxide and reaction temperature, however, decreased significantly in the range of PH 1.

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