Preparation of Leucite Powder with Controlled c-Phase fraction for a Variety of Dental Applications

摘要

Leucite (KAlSi_2O_6) is the main crystalline phase in feldspathic dental materials used for ceramic-fused-to-metal restorations. It occurs in two modifications, low temperature - tetragonal and at temperatures above 600°C high temperature - cubic modification. Tetragonal leucite dispersed in a glassy matrix increases the thermal expansion coefficient a of the ceramics to a value that of metals (13-15.10~(-6) K~(-1)) and so enables its fusion to a metal substrate. However the difference in a of the matrix (6-8.10~(-6) K~(-1)) and t- leucite (20-25.10~(-6) K~(-1)) induces stress leading to the development of flaws in the dental porcelain. Submicron leucite crystals stabilized in cubic modification can reduce the number of crack deflections in porcelain and increase the flexural strange. The aim of this work was to develop a low-temperature preparation technology of submicron leucite powders with varying ratio of tetragonal and cubic modification. The results show that analcime synthesized in hydrothermal conditions is the suitable precursor for the preparation of leucite with controlled fraction of the c-modification. Homogenous t-leucite having particle size from 2-5 μm was prepared by 4h ion-exchange in 4M KCl. Partially stabilized c-leucite was obtained by dual ion-exchange; 4h in 4M CsCl led to 48 % of c-modification in the final product.