- Solid Reaction in the MgO Excess Region of the System MgO-TiO_2-Al_2O_3
In a permeable MgO ceramic containing TiO_2 and Al_2O_3 as matrix MgO ・ Al_2O_3-2MgO・TiO_2 solid solutions were detected and no Al_2O_3・TiO_2 was observed. Therefore, the solid state reaction among MgO, TiO_2 and Al_2O_3 with excess MgO was studied at various firing temperatures. The formation mechanism of MgO・Al_2O_3-2MgO・TiO_2 solid solutions was studied from the results of interface reactions between MgO-TiO_2 and MgO-Al_2O_3. MgO・Al_2O_3-2MgO・TiO_2 solid solutions were detected at 1573-1673 K and increased with the firing temperature. 2MgO・TiO_2 was formed in the system MgO-TiO_2, but was not produced in the system MgO-TiO_2-Al_2O_3, because the amount of Mg diffusion at the interface of aggregate and matrix additives was not enough due to the large aggregate size of MgO. MgO・Al_2O_3 and 2MgO・TiO_2 formed at the interface between MgO-TiO_2 and MgO-Al_2O_3 decreased with the firing time at 1873 K. On the other hand, MgO・Al_2O_3-2MgO・TiO_2 solid solutions increased. Mg was recognized in the matrix without addition of MgO as a matrix. Al diffused in the layer of MgO-TiO_2, in opposition Ti diffused in the layer of MgO-Al_2O_3 by EPMA analysis. From the above results, the formation mechanism of a MgO・Al_2O_3-2MgO・TiO_2 solid solution was proposed; (1) Mg diffusion at the interface of MgO aggregate and matrix additives, (2) formation of MgO・TiO_2 and MgO・Al_2O_3, (3) formation of 2MgO・TiO_2 due to the reaction with MgO・TiO_2 and MgO, (4) reaction of the solid solution with MgO・Al_2O_3 and 2MgO・TiO_2. In the reactions between MgO・TiO2 and MgO-Al_2O_3 the product layer of MgO・Al_2O_3-2MgO・TiO_2 solid solution increased as the firing time increased. The diffusion coefficient of Mg was about 4.8×10^<-7>(cm^2/s), in a good agreement with that of Mg which was reported.
- Journal of the Ceramic Society of Japan
Journal of the Ceramic Society of Japan 100 (1163), 918-923, 1992-07-01
The Ceramic Society of Japan