| Co-Investigator(Kenkyū-buntansha) |
NISHIMURA Fumio Tokyo Medical and Dental University, School of Dentistry, Associate Professor, 歯学部, 助教授 (10013856)
NOMOTO Sunao Tokyo Medical and Dental University, School of Dentistry, Professor, 歯学部, 教授 (10013799)
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| Research Abstract |
Titanium, one of the most ideal materials for dental use from the aspects of corrosion resistance, bio-compatibility, light specific gravity, economical cost, was difficult to apply for casting with the conventional silica investments because of the high reactivity at high temperature. This study for the first part investigated the reactivity of the metal of molten titanium with ceramics and that with gas to obtain the principle of reactivity and the basis to select materials in developing the new refractory investments. Based on these fundamental studies, the newly developed zirconia investments could produce the bright castings of titanium. The method of the heat treatment to strengthen titanium was also studied. The principal accomplishments were as follows : (1) From the experiments of the reaction between the single crystal ceramics and molten titanium, it was shown that the alkaline (basic) tendency of oxides as well as formation energy are important factors in the reactivity cha
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racteristics. (2) In this viewpoint, the oxide matrix refractory to the highly reactive metal was selected and super refractory zirconia investments were newly developed. (3) The decomposition behavior of gypsum used as a binder for conventional investments was also found to depend on the alkaline tendency of the matrix oxide. (4) As a new material for implants and bio-materials used in the human organization, titanium/apatite composite sintered materials and functionally gradient materials (FGM) are now under development, in which process the reactivity tendency was applied for the solution of the problems such as green setting, sintering, suppression of oxidation and enhancement of reduction. (5) In silica investments, the reaction with both ceramics and gas occurs simultaneously, whereas in non-reactive zirconia investments the reaction with gas is an independent process. Therefore, it is possible to strengthen titanium by heat treatment after casting. The methods of double step heat treatment and homogenizing anneal were developed to utilize solution hardening by interstitial alloying elements (oxygen, nitrogen, carbon). It can be applied for the surface hardening treatment and the control of elasticity of full denture. Less
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