Directional solidification and microstructural evolution between diopside and anorthite in the system CaO-MgO-Al2O3-SiO2

Silicate mixtures close to the diopside-anorthite tie line have been unidir ectionally solidified by float-zone melting in an are image furnace and the microstructures examined by optical microscopy scanning electron microscop y, electron microprobe analysis and from electron backscatter patterns. The structures which evolved have been interpreted by reference to available p hase diagram data for the anorthite-diopside eutectic surface within the fo ur-component oxide system, CaO-MgO-Al2O3-SiO2. It is demonstrated how the m icrostructures and segregation paths can be described in a visually explici t way within the quaternary system. The morphologies of primary diopside, a northite and the eutectic mixture are described and discussed. In this silicate system the low liquid diffusion rates lead to glass format ion at rapid cooling rates and at, temperatures close to the freezing point , so that. local equilibrium is only partially realized. The consequences a re interpreted with reference to the quaternary phase diagram.