沈殿剤前駆体添加法による被覆粒子の合成

Abstract

SiC whiskers were coated with alumina hydrate using a newly developed precipitant precursor injection method. This method has the following merits compared with the most popular aqueous coating, homogeous precipitation method using urea; (1) it is possible to coat at room temperature, and (2) only a stoichiometric amount of precipitant is required for coating. In the present method, the precursor of the precipitant was injected into the aqueous solution which inclued raw material for the coating layers in which core particles were dispersed. When ammonium hydrogen-carbonate solution was used as precipitant, alumina hydrate could be coated on SiC whiskers, whereas the coating layer on SiC whisker was not obtained with the injection of NH4OH solution. The difference in the morphology of the above coating layers is considered to be caused by the relatively low hydrolysis rate of hydrogen-carbonate ion. A more homogeneous coating layers was obtained with a higher stirring rate, and a low concentration of precipitant was also effective in obtaining more homogeneous coating layers. Furthermore, when formic acid which has pKa around the precipitation pH was added to the reaction solition, the smooth coating layers which have comparable surface morphology to the coated particle prepared by homogeneous precipitation method was obtained.