Study On Influence Of Chemical Composition And Microstructure On Properties Of MgO-ZrO₂ Series Refractories

The refractory products with different composition of magnesia and zirconia are made by adopting fused magnesite, MgO partially stabilized zirconia(PSZ) and CaO fully stabilized zirconia(FSZ) as raw materials and appropriate technological process. The microstructure and properties of the samples are investigated comprehensively. Conclusions are as follows:(1) In the magnesia riched zone of the range of composition of the refractories in MgO-ZrO₂ system, the addition of zirconia can promote the sintering of magnesia refractory. With the addition of zirconia, microcracks are produced between aggregates and matrix and among different parts of matrix, moreover, it became more and bigger. The addition of zirconia increases considerably direct bond between grains in magnesia refractory, and the direct bond between grains increases gradually with the addition of zirconia. Zirconia can absorb the component of CaO from the silicate and consequently modify the composition and the quantity as well as the distribution of silicate in the samples. (With the increase of zirconia content in magnesia refractory, silicate mainly composed of low melting point mineral phases of C₃MS₂ and CMS gradually became into that mainly composed of high melting point minerals of M₂S. And the continuous distribution of the filmy silicate penetrating into magnesia grains turns into the separate distribution of the insular silicate among magnesia grains).The effect of zirconia aggregate on the microstructure of magnesia refractory is similar to that of zirconia powder. FSZ and PSZ have fundamentally identical effect on the microstructure of magnesia refractory. In the zirconia riched zone, the addition of magnesia can promote remarkably the sintering of zirconia refractory and increase the direct bond between zirconia grains which results in densification of the matrix. And also it leads to the formation of various microcracksin zirconia refractory. In addition, it can increase considerably the direct bond between grains in zircoina refractory. Further more, the direct bond between grains increases gradually with the addition of magnesia.(2) In the magnesia riched zone of the range of composition of the refractories in MgO-ZrO₂ system, the modulus of elasticity and the cold modulus of rupture and the cold crushing strength of the magnesia refractory decrease gradually with the addition of PSZ powder and are approximately linear with the quantity of PSZ powder. The addition of PSZ aggregate, compared with equal quantity of PSZ powder, decreases more seriously the modulus of elasticity and the cold modulus of rupture and the cold crushing strength of the magnesia refractory. The effect of FSZ on the modulus of elasticity and the cold modulus of rupture and the cold crushing strength is similar to that of PSZ, however, compared to equal quantity of PSZ, it is relatively slight. In the zirconia riched zone of the range of composition of the refractories, the addition of 5% magnesia decreases noticeably the modulus of elasticity and the cold modulus of rupture and the cold crushing strength of zirconia refractory, the addition of more magnesia has scarce effect on the modulus of elasticity and the cold modulus of rupture and the cold crushing strength of zirconia refractory.(3) In the magnesia riched zone of the range of composition of the refractories in MgO-ZrO₂ system, the MOR^T curves of magnesia refractory only composed of electrocast magnesite takes on the characteristics of the type â…¡ .The MOR^T curves of magnesia refractories based on electrocast magnesite and PSZ takes on the characteristics of the type â…  .The modulus of rupture at low or medium temperature of magnesia refractory decreases gradually with the addition of PSZ powder, and the hot MOR(1400°C) of magnesia refractory increases gradually with addition of PSZ and is linear with the quantity of PSZ powder. The hot MOR of magnesia refractory containing zirconia aggregates is lower than that of magnesia refractory containing equal quantity of zirconia powder. The effect of FSZ on th...