Ki-Chang Song

PREPARATION OF ALUMINUM HYDROXIDE GELS BY THE SOL-GEL METHOD

Aluminum hydroxide gels were prepared by ihe sol-gel method. The role of acid in sols was investigated through the analysis of telling lime and hydrolysis rale. The phase transformation of gels with calcination temperatures was also monitored with X-Ray diffraction.The gelling times of the aluminum hydroxide sols decreased with the increase of acid content. Exceptionally, the solution peplized with 0.07 HCI/alkoxide molar ratio look longer time than other solutions until the gellation. The hydrolysis rate of aluminum hydroxide was much faster as the acid concentration increased during peptization. In the case of NH4OH as a peptizing agent, there was Ihe lower rate of hydrolysis and thus the more alkoxyl groups were remained in the gel.

Measurement of thermal diffusion parameters of polystyrene using a thermal field flow fractionation method

Thermal diffustor parameters such as the thermal diffusion factor and the thermal diffusion coefficient for polystyrene in toluene are measured by using a thermal field flow fractionation (TFFF) method The dependence of these parameters upon temperature concentration and polymer molecular weight is ex-amined.The thermal diffusion coefficien is found to be independent of the molecular weight for sufficiently large polymer molecules but on the other hand the ordinary diffusion coefficient is known to be pronouncedly dependent on the molecular weight.This result indicates that the fractionation effect is primarily governed by the differences in ordinary dif-fusion coefficients.