Detailed Microstructure and MineralogicalInvestigation of Basic Refractories

Vein and hydrothermal . sedimeOI~ry types of magnesite from eastern Iran probably originated from ascending hydrothermal solutions. The cryptocryistalline magnesite is very pure although it has a variable CaO/Si02 ratio. It is compact with a very fine and uniform texture. The mineralogy of samples of dead burned magnesites calcined at different temperatures and times arc variable and can be predicted from phase equilibria studies. The textural relationships studied using scanning electron microscopy show that matrix is concentrated at peric1ase crystal boundaries particularly at the triple points. The periclase crr-itals are larger at increased calcination temperatures and times. The amount of periclase - Periclase grain contact reduces by increasing the amount of impurities. Electron microprobe results confirm that CaO and FeO in periclase increase steadily with the increase in the CaOlSi02 ratio and FeO content of bulk chemistry respectively. The mineral chemistry of forsterite. monticellite. merwinite, dicalcium silicate and tricalcium silicate in dead burned magnesite indicate some solid solution between some phases, although sometimes it is difficult to analyse single phases. This study indicates that high quality dead burned magnesia bricks can be produced from the Iranian natural magnesite with low CaO , Si02 and FeO impurities and by maintaining the CaOlSi02 ratio of around 2:1.