Takao Umegaki

Electrophoretic coating of multilayered apatite composite on alumina ceramics

By means of an electrophoretic deposition technique followed by sintering, alumina and zirconia ceramics were coated with apatitic composites composed of porous surface and intermediate layers of hydroxyapatite and an adhesive calcium phosphate layer. The electrophoretic deposition of these layers was attained by the use of a mixed solvent of acetylacetone and alcohol as well as the mixed powders of the calcium phosphates and alumina. The adhesive layer was formed by the codeposition of calcium phosphate glass powders (Ca/P = 1/2) with hydroxyapatite, while the open porosity of the surface layer was increased with the addition of alumina to the hydroxyapatite layers. The resultant phases of sintered composite layers were tricalcium phosphate and alumina with a small amount of hydroxyapatite.

Fabrication of green films of single- and multi-component ceramic composites by electrophoretic deposition technique

An electrophoretic technique for the formation of ceramic composites is demonstrated in the systems of biomedical hydroxyapatite–yttria-stabilized zirconia and ferroelectric barium titanate–strontium titanate. Ceramic powders show different behaviour depending on the nature of the solvent media chosen. For such purposes, a solvent mixture of acetylacetone and alcohols proved effective for adjusting the composition of deposited films.

High temperature pH sensitivities of stabilized zirconia films and ceria ceramics

Abstract Yttria-stabilized zirconia (YSZ) thick films and bulk ceria (CeO 2 ) ceramics used as membrane electrodes are shown to work as high temperature pH sensors. The YSZ film electrode shows a nearly ideal Nernstian response of the potential as a function of pH with mV pH = − 56.8 even at 353 K. The YSZ film electrode responded to pH changes within 30 s, while the response time of the samaria-doped ceria ceramic membrane electrode was 3 min. Complex impedance analysis revealed that the bulk conductivity of the ceria ceramics is higher than that of YSZ film, whereas the grain-boundary conductivity of the former was 10 2 times lower than that of the latter. Based on these results, it appears that at temperatures below 600 K, the pH sensory characteristics of these materials are dominated by the grain-boundary conductivity.