Research On Preparation And Performance Of The MgO-CaO-ZrO₂ Materials

Since 1980's, from the cancellation of chrome harmful effects with the request of the environmental protection, the magnesia-chrome brick is eliminated gradually.The dolomite brick, the magnesia-spinel brick and magnesia-calcia-zirconia brick gradually become the main alkaline refractory for rotary cement kilns in the developed countries.The dolomite brick has the superior coating adherence and corrosion resistance to cement raw meal, but because of its hydration and bad thermal-shock resistance,the service life of the dolomite brick decreased when the stability of coatings is weaken in some rotary cement kilns which seldom run or turn on and off frequently. The magnesia-spinel brick has the good thermal-shock resistance however it has the disadvantages of the bad coating adherence and high heat-conducting rate which will shorten the life of the shell of kilns.While the magnesia-calcia-zirconia brick has the extensive and applied foreground because of its excellent thermal-shock resistance, higher refractoriness under load at high temperature, good corrosion resistance and good coating adherence, and become the hotspot of research on alkaline refractory for cement rotary kilns from 1990's.In the earlier period, the research of the magnesia-calcia-zirconia brick abroad is on the basis of the high pure raw materials and the high cost. This thesis is established in the refractory situation of our country. The natural low-cost raw materials such as 95 sintered magnesia clinker, 97 fused magnesia clinker, lightweight limestone, zirconite are used as the main composition. Through necessary craft measures and special designment,the MgO-CaO-ZrO2 materials are prepared. During the research, the properties and the improvement of the structure of the MgO-CaO-ZrO2 materials, the influence of chemical compositions, and the influence of the sintered temperature are investigated,which set up the good foundation for further investigation of the MgO-CaO-ZrO2 materials and for the industrialization of such materials.The experimental results show that by the reasonable blending of raw materials together with the certain craft measures, good performance MgO-CaO-ZrO2 materials for the rotary cement kilns can be prepared, whose phase constitutions should be MgO-CaO ZrO2-2CaO SiO2-3CaO-SiO2 or MgO-CaO-ZrO2-3CaO-SiO2-CaO. Here in this system the amount of affiliation of ZrO2 SiO2 should control at 4-7 wt% at the best.When CaO/SiO2 1.87+0.455ZrO2/SiO2(quality ratio), the phase with high melting point appears and the properties of the materials at high temperature are better;When CaO/ SiO2<1.87+0.455 ZrO2/SiO2(quality ratio), the ternary phase with low melting point are included and the performance of the materials is worse, at the same time because the temperature is a critical factor during sintering, the sintered temperature is not lower than 1700 C best.The results also indicate that the MgO-CaO-ZrO2 materials have better coating adherence and corrosion resistance to cement raw meal and the thermal-shock resistance should be further improved when the materials are used at higher temperature in the rotary cement kilns.