A Radioisotope Study of the Sintering Process of Magnesia Studies on Dead-burned Sea Water Magnesia, III

A radioisotope technique was used for the determination of the rate of movement of Ca2+ and Fe3+ ions in MgO added with or without a small amount of SiO2, Al2O3, etc. As the tracers RI45Ca and RI59Fe were used. The relationship between the rate of movement of these ions and the sintering behaviors of the mixtures were also studied.The results obtained were summarized as follows:(1) The movement of these ions is caused by thermal diffusion and draining. In MgO added with CaO and SiO2, the rate of movement of Ca2+ ion increased with increasing the molar ratio CaO/SiO2, reached to a maximum when CaO/SiO2≅1, and then decreared; no movement was observed when CaO/SiO2_??_2. Additions of Al2O3 and Fe2O3 to MgO together with CaO and SiO2, however, produced different results, i.e., the rate of movement of Ca2+ in this mixture increased with increasing the ratio (CaO/SiO2) without having a maximum.(2) Additions of oxides such as TiO2, Cr2O3, MnO2, B2O3, etc., which were found, by the author's previous works, to be effective in promoting sintering of MgO and the growth of periclase crystals, always increased the rate of movement of Ca2+.(3) Comparing with Ca2+ ions, Fe3+ ions in MgO had a low rate of diffusion. Draining occured only when Ca2+ coexisted in MgO.(4) X-ray analysis showed that the compounds, CaO⋅MgO⋅SiO2, 2CaO⋅Fe2O3, 4CaO⋅Al2O3⋅Fe2O3, etc., were produced in MgO by the movement of Ca2+ and Fe3+ ions.(5) It was suggested that when the above compounds melt at high temperatures producing the liquid phase, the loard-bearing capacity of MgO is lowered.