Many ceramic powders are prepared by emulsion method. Among the various emulsion systems determined by selecting solvents which is used in emulsion method, the system using octanol and acetonitrile was studied. The dispersant for emulsion method was hydroxyprophyl cellulose(HPC). The starting materials of powders were various metal-alkoxides, but especially aluminum-sec-butoxide(ASB) and Ti-isopropoxide.
The main topics of study are the following four items.
First, by postulating single-burst nucleation proposed by Lamer et al, and rapid coagulation equation proposed by Smoluchowski, the average size and distribution of metal-alkoxide droplets during coagulation were obtained. The consequence was reasonable, when it was compared with experimental results.
Second, by constructing the model of hydrolysis and condensation reaction of metal-alkoxide droplets during coagulation, the differential equation describing the model were induced. The solution equation with empirical order was obtained and the empirical order was determined from some values of experimental data. The solution equation with empirical order determined above describes all values of experimental data well.
Third, the different powder size when metal alkoxide concentration was varied was explained in the view of the different ratio of reacted part of metal alkoxide to initial total metal alkoxide when the coagulation ended. The ratio of reacted part was calculated postulating the equation of the second item. And it was regarded that increasing or decreasing of the powder size when alkoxide concentration increased depended on which became dorminant between (hydrolysis and condensation) reaction rate and coagulation rate when alkoxide concentration was increased.
Fourth, temperature dependence of powder size was induced. It was studied by the method below. First of all, temperature dependences of physical and chemical constants(hydrolysis and condensation reaction rate constant, coagulation constant etc.) were induced. And the physical and chemical constants which is used in the solution equation of second item were trasformed through the temperature dependency induced above. The result from the transformed equation shows good agreement with experimental with experimental data.
