Characteristics of phosphate bonded high alumina bricks
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Time：
2024-02-19
1. Structural characteristics
Phosphate combined high alumina bauxite clinker contains a large amount of α~ Al2O3, when mixed with phosphoric acid, begins to combine at 0 ℃~120 ℃, generating aluminum phosphate and pyrophosphate within the range of 124 ℃~427 ℃. At 510 ℃, most of it forms aluminum phosphate, becoming the connecting aggregate for high alumina bricks. AlPO4 has a spatial skeleton structure of SiO2, and [PO4] [AlO4] are tetrahedral structures. According to Thomson's Law of 1947, aluminum in phosphates formed at high temperatures tends to combine to the fourth power. Aluminum in silicates formed at low or high temperatures tends to exhibit a hexagonal combination. Therefore, before the decomposition of aluminum phosphate at<1500 ℃, it has a stable structure, which has chemical stability, wear resistance, thermal stability, and high temperature strength below 1500 ℃.
2. Thermodynamic properties
The Al2O3 content in phosphate bonded high alumina bricks is generally above 80%. Therefore, Al2O3 plays a dominant role in the chemical thermodynamic properties. CaO has a higher affinity for oxygen than Al, while Si is lower than Al. However, based on the phase diagram analysis of CaO~Al2O3~P2O5, it is necessary to form a eutectic at 1440 ℃. This provides a theoretical basis for the use of phosphate bonded high alumina bricks in the pre heating zone, decomposition zone, and cooling zone.
3. Chemical stability characteristics
The main mineral composition of phosphate bonded high alumina bricks is AlPO4 in the form of square quartz, which is stable before decomposition into AI2O3. However, at higher temperatures, its mechanical strength slightly decreases due to the gradual decomposition of AlPO4 above 1500%.
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