The physical and chemical indicators of phosphate-bonded high-alumina bricks are: refractoriness ≥ 1970°C, 2kgf/cm2 load softening point temperature greater than 1350°C, volume capacity ≥ 2.75g/cm2, room temperature compressive strength ≥ 61.8MPa. It has high high-temperature compressive strength, good thermal shock stability, and low wear resistance. Its main characteristics are as follows
Structural properties
Phosphate combined high alumina bauxite clinker contains a large amount of a~Al203. When it is mixed with phosphoric acid, it starts to combine at 0°C~120°C. In the range of 124°C~427°C, aluminum phosphate and pyrophosphate are formed. At 510°C, most of them generate aluminum phosphate, which becomes the connecting aggregate of high alumina bricks. AlPO4 has a space skeleton structure of SiO2, and [PO4][AlO4] are all tetrahedral structures. According to the “Thomson’s Law” in 1947, the aluminum in the phosphate formed at high temperature tends to combine to the fourth power. Aluminum tends to combine to the sixth power in silicates formed at low temperature or high pressure. Therefore, aluminum phosphate has a stable structure before it decomposes at <1500°C. This stable structure has chemical stability, wear resistance, thermal stability and high temperature strength below 1500°C.
Thermodynamic properties
The Al2O3 content in phosphate bonded high alumina bricks is generally above 80%. Therefore, Al2O3 plays a leading role in chemical thermodynamic properties. The affinity of Ca0 to oxygen is greater than that of Al, and Si is smaller than that of Al. However, according to the phase diagram analysis of CaO~Al203~P205, eutectics can only be formed at 1440°C, which provides a theoretical basis for the use of phosphate-bonded high-alumina bricks in the preheating zone, decomposition zone, and cooling zone.
chemical stability
The structure of the main mineral composition of phosphate-bonded high-alumina bricks is cristobalite-type AlPO4, which is stable before decomposing into AI203, but at higher temperatures, its mechanical strength is slightly reduced, which is due to the gradual decomposition of AlPO4 above 1500%.
