Hideki Monma

Preparation of octacalcium phosphate by the hydrolysis of α-tricalcium phosphate

A new simple method of preparation for the thermodynamically unstable octacalcium phosphate [Ca8H2(PO4)6·5H2O; OCP] has been developed using the hydrolysis of α-Ca3(PO4)2 instead of the conventional hydrolysis of CaHPO4·2H2O. The hydrolysis experiments were carried out by treating an α-Ca3(PO4)2(1 g)-H2O(50 m) suspension for 3 h at temperatures in the range 40 to 80° C and at pHs in the range 3 to 7.5. The formation of OCR was limited to within a narrow region between formation regions of other phosphates. Favourable conditions for OCP preparation were, for example, 70° C, pH4.5 to 5.0 and 60° C, pH5.0. Particles of OCP were composed of tight aggregates of strip-like microcrystals growing probably along the [0 0 1] and (1 0 0) plane of the OCP structure. Nearly stoichiometric OCP was obtained under the most suitable conditions with good reproducibility. Pyrolytic processes of OCP were approximately consistent with the data published so far. However, the temperatures of the appearance and disappearance of pyrolytic crystalline phases and ionic species deviated slightly from the published data. Thermal dehydration up to 150° C without destruction of OCP and decomposition reactions above 300° C resulted in changes in surface area and average pore radius of OCP.

EFFECTS OF ADDITIVES ON SINTERING AND SOME PROPERTIES OF CALCIUM PHOSPHATES WITH VARIOUS CA/P RATIOS

The effects were studied of additives on the sintering and properties such as the compressive strength and chemical durability of ceramics of calcium pyrophosphate, tricalcium phosphate and hydroxyapatite. In improving the compressive strength of these calcium phosphates, the effect of additives was found to be in the order Na2O≫CaF2>MgOg≫Al2O3, SiO2 for the case of single-doping, and was most marked in the combination of Na2O-MgO-Al2O3 for the complex addition. It was also found that the chemical durability of the calcium phosphates was improved greatly by using a single or complex additives.

MATERIALS DESIGN OF GLASS AND DEVELOPMENT OF IMPROVED EXPERT SYSTEM

In order to support to develop new glasses we studied an expert system for materials design of glass which uses AI softwares ESHELL or KBMS. By using the expert system we can obtain various kinds of properties of glass by a dialogue method with a personal computer. Glass composition which has desired properties can be selected from table of 60 oxides.Knowledge base on glass formation ranges tells us the possibility of vitrification of the designed glass composition.

EXPERT SYSTEM FOR THE DEVELOPMENT OF SILICON NITRIDE CERAMICS

Expert system has been constructed to assist the development of silicon nitride ceramics. Thermodynamic functions of compounds and crystal chemical data of elements are collected as data base. Experimental data on sintering, microstructures and strength values are evaluated for knowledge base. An artificial intelligent soft is employed to reason sintering aids from various oxides and compute strength of ceramics at low and high temperatures. The reasoning has been done through dialogues with a computer.