Research On The Synthesis Of Forsterite And Its Application

Forsterite have been widely used in metallurgy, heat engineering and cast, because of its excellent properties such as high melting point, good chemical stability, low thermal conductivity and strength corrosion resistance to molten metal. Forsterite is abundant in natural resources in our country, so it is very significant to synthesizing the forsterite raw materials and then to manufacturing the forsterite products with excellent properties in low cost for utilizing efficiently the mineral resources in China and expanding the utilization in related fields.To resolve the present problems existed in the research and application of forsterite, the researches on the related basic and applied have been carried out in this paper. The reaction systems related to the forsterite synthesis were analyzed by using thermodynamic, the synthesis process, reaction mechanism and reaction kinetics of forsterite were studied by experiments, and the effect of additives on the generating and sintering of forsterite and the properties of tundish dry materials added with forsterite were investigated. The obtained results are as follows.(1) The sequence for Gibbs standard free energy of compound formation in MgO-SiO2-TiO2system from high to low is as bellows, MgTiO3>MgSiO3> MgTi2O5>Mg2SiO4>Mg2TiO4. In MgO-SiO2-Y2O3system is MgSiO3>Mg2SiO4> Y2SiO5>Y2Si2O7. In MgO-SiO2-Ce2O3system, Ce2O3reacts with SiO2to form Ce2Si207, Ce2SiO5and Ce0.36Si0.23O. In MgO-SiO2-ZrO2system, MgO and ZrO2reacts to form solid solution, and ZrC>2reacts with2MgOSiO2to form ZrO2-2MgOSiO2system. In MgO-SiO2-Al2O3system, the sequence is Al6Si2O13> MgSiO3>MgAl2O4>Mg2SiO4.(2) In the synthesis process of forsterite, MgO was diffusion phase and it diffused to SiO2and then reacted to form forsterite and enstatite in the early synthesis. In the middle period, MgO diffused through crystal lattice of enstatite and low melting point phase to the particle surface of enstatite and then reacted with it to form forsterite, and which separated out in the particle surface of the early formed forsterite and made the join of forsterite particles and densification of forsterite materials. In the late, all MgO diffused from the in-situ particle and left pores, the pores would be decreased by sintering process.(3) The synthesis process be controlled by Mg2+diffusion, the reaction kinetic between MgO and SiO2could be described by Yang Deer equation and the apparent activation energy was220±20kJ·mol-1.(4) The preparation condition of densification forsterite was as that heating temperature was high than1550℃, holding time was long more than3hours and forming pressure was big more than150MPa.(5) The synthesis and sintering process of forsterite could be efficiently improved by TiO2, Y2O3and CeO2additive, however the effect of ZrO2and Al2O3additive was not remarkable. It is propitious to diffuse that solid solution of Ti4+into MgO lattice, formation of Ti containing compound with low melting point and separation of TiO2from Ti containing compounds. The formation of Y containing compound with low melting point and the existence of MgSiO3phase caused by Y2O3additive improved the diffusion of reactant. The added CeO2changed to Ce2O3at high temperature, and which reacted with SiO2to form Ce containing compound with low melting point. The compound with low melting point and MgSiO3phase increased the diffusion of reactant. ZrO2existed in MgO containing solid solution in grain boundaries and in composite compounds in matrix, and the composite compounds existing in matrix changed as MgSiO3+ZrSiO4â†'Mg2SiO5+MgSiO3+ZrSiO4->-Mg2SiO5+ZrSiO4+Zr02and then to separated out ZrO2in grain boundaries.(6) The bulk density and strength of tundish dry materials decreased with the increase of forsterite addition, however no change in the slag resistance, the properties of tundish dry materials added with sintered forsterite and raw forsterite showed a little change. The sintering and slag resistance of tundish dry materials could be improved by borax, ferric oxide, sodium tripolyphosphate and sodium silicate additive, however, it will cause the performance reduction of tundish dry materials if the additive amount is high much than an appropriate amount.