The UK customer order 30 tons magnesia chrome bricks.
Direct combination of magnesia-chrome brick technology and performance application
Directly bonded magnesia-chrome bricks are refractory materials manufactured by special processes such as high-grade magnesia, chrome concentrate, and increased firing temperature. Due to the small number of silicate phases and the large number of secondary spinels, the silicate phases become islands, and there are “direct bonds” between periclase-perclase and periclase-chromite. Thus, direct bonding endows it with good high temperature resistance, erosion resistance and thermal shock resistance.
White is a substance with a higher atomic number
During firing, chromium diffuses from chromite into the magnesia matrix to form periclase solid solution. When the temperature decreases, MgO·R2O3 is precipitated from the supersaturated solid solution of periclase to form secondary spinel. Since chromium changes the properties of periclase, the silicate phase is not easy to wet the periclase phase, resulting in the formation of direct bonds between periclase and periclase and between periclase and magnesia-chrome spinel. The research of Goto et al. showed that in the direct bonded magnesia-chrome refractories, at a resolution of 0.3nm, it was found that there were “direct bonds” between periclase-periclase particles and between periclase-chromite particles . However, direct bonding is not found in periclase-magnesia-alumina-spinel refractories.
The price of directly combined magnesia-chrome bricks is relatively high, but it has good performance in high temperature resistance, corrosion resistance, heat shock resistance and kiln skin hanging, so it is suitable for the firing zone of various cement rotary kilns.
Before the 1980s, foreign countries advocated three high-tech technologies – the technology of using high-purity raw materials, high-pressure molding, and high-temperature firing to make refractory materials; after the 1990s, more and more foreign companies used cheap Chinese refractory raw materials, and fell in love with ” Flexibility”. For example, the Austrian company Veitsch-Radex has developed alkaline bricks with “flexibility”. At 1200 °C, the previous magnesia-chrome bricks can only produce 0.5% strain before being damaged by cyclic stress, and the flexible material can produce 3% to 5% strain.
It should be pointed out that the so-called “flexibility” or “toughening” is only the reduction of brittleness, not that refractory materials really have the toughness similar to metal materials, or the flexibility similar to organic polymer materials. As mentioned earlier, refractories are brittle materials, which are determined by covalent bonds and ionic bonds, and are unchangeable in nature. The “pseudo-plasticity” and “pseudo-flexibility” shown by some refractory materials before failure are just the result of a large number of microcracks. For example, when inorganic fiber-reinforced silicate materials are damaged, the material as a whole will be greatly deformed. However, microscopically, it is nothing more than a combination of a series of dissociation and fiber pullout processes at the fiber interface. Each local failure is a typical brittle failure with little plastic deformation.
As for some foreign refractory companies, it is completely wrong to say that “elasticity” and “thermoelasticity” mean good thermal shock resistance or large pseudoplastic deformation.
In fact, elasticity is a property of a material, which refers to the property that a material is deformed by an external force, the amount of deformation is proportional to the magnitude of the external force, and the property that the material can return to its original shape after the external force is removed. Plasticity is the property of a material to permanently deform under a given load. The strength of plasticity can be expressed by elongation and reduction of area. Toughness is the ability of a material to absorb energy and undergo plastic deformation before fracture.
When damaged, although some new inorganic non-metallic materials have a large elongation macroscopically, the shrinkage rate of the section is not large. From a microscopic point of view, only a series of small microscopic brittle failures replace a large macroscopic brittle failure. Although the material has been improved, the performance and service life have also been significantly improved, but the resistance to crack propagation is still far from that of metal materials.