Fused rebonded zirconium corundum bricks are made of AZS frit or fused AZS waste bricks as raw materials, with a small amount of kaolin or titania added as a binder. When heated to a certain temperature, the fused AZS aggregate seeps out the glass phase and forms mullite with the binder to sinter the brick body. The firing temperature needs to be 1600∽1700℃℃. The chemical-phase composition of the frit is very uniform, with a small amount of glass phase. The chemical-phase composition of the waste brick is uneven, with a large amount of glass phase (15%~25%); the chemical composition fluctuation range of the rebonded product (%6): A1203 50~60, Zr02 20-30, Si02 14~20.
When the fused-cast AZS product is heated, the glass phase melts and seeps out while also reacting with the main crystal phase to achieve mullite. At this time, the coexistence relationship between mullite and Zr02 is in the form of encapsulation and being encapsulated. According to this phenomenon, the cast brick debris broken into different particle sizes can be sintered into a solid brick body. In layman's terms, it is the basic principle of the so-called "self-sintering property" of the fused AZS brick debris to produce recombined zirconium corundum bricks.
The finer the fused AZS debris, the larger the specific surface area of the glass phase it contains. Without waiting for the above-mentioned peritectic reaction to occur, relying only on the dispersion of the glass phase, and processing at a relatively low temperature, a solid brick body can be formed by single-wave phase sintering. The key technical measure for the production of recombined AZS bricks is to consume the contained glass phase as much as possible, to cause peritectic reaction and to undergo mullite with the added AI203 component.
The microstructure of the rebonded zirconium corundum brick fired at high temperature still has significant changes, mainly manifested in
(1) The glass phase in the fine powder cast AZS material of the brick matrix reacts with the added active A1203 to achieve mullite;
(2) The glass phase of the coarse particles seeps out to the surface of the particles and reacts with the active A1203 to form a mullite shell, which closes the liquid phase seepage channel, thereby controlling the peritectic reaction inside the particles:
(3) The glass phase in the coarse particles seeps out and bridges, leaving cavities and gaps.
Relative to the volume of the brick blank, the volume effect of the above reaction includes both positive and negative aspects, so the linear expansion of its finished product is mostly 0-1.0%. Mullite matrix and inter-particle bonding are important conditions for the rebonded brick to have good high-temperature mechanical properties (strength, toughness and thermal shock), so it should be fully promoted. The microstructure of the rebonded product is basically a combination of various structural details of the original cast AZS.
Compared with the electric fusion products, the glass phase seepage phenomenon is greatly reduced and the seepage temperature is increased. It has good thermal shock resistance, high high temperature mechanical properties, especially creep resistance, and good glass erosion resistance.
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