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The development of phosphate refractory bricks is summarized in the development of amorphous refractories and non-fired products. It is necessary to find some binders with excellent properties, and it is hoped that the binders not only have ideal room temperature properties, but also The high temperature performance is also required, and the influence on the host material is also minimized, so that the water glass and the silica sol are not ideal, and the phosphate is sufficient. Therefore, phosphate refractory bricks have been successfully applied to the main materials of some high-temperature kiln such as cement rotary kiln, shaft kiln and lime kiln.
1: ratio of phosphate refractory brick
In the particle grading, the coarse particles act as a skeleton to ensure the high temperature strength of the product. The phosphate refractory brick, the maximum particle size and the particle gradation are reasonable, which is the key to the compactness of the product. The fine powder acts as a filling void to wrap and adhere the coarse particles. Compared with the coarse particles, the fine powder has a large specific surface area, irregular crystal structure, large activity, easy binding agent, and proper dosage, which directly affects the strength and wear resistance. Therefore, in order to achieve the special requirements of such products, according to the principle of the closest packing, the use of "two large, medium small" particle grading, strict control of critical particle size, appropriate increase of fine powder, in order to shape and improve the wear resistance of the product and room temperature Pressure resistance.
Preparation of 2 phosphate refractory brick binder
Phosphate itself has no cohesiveness. When it comes into contact with refractory materials, it forms aluminophosphate and increases with temperature. The ions in the phosphate group are refined into chains, nets and space skeletons in various ways. The macromolecules of the structure undergo polymerization and adhesion to give the product strength.
The binder used in the phosphate refractory brick is an aluminum phosphate solution prepared by diluting the industrial phosphoric acid to the required concentration and processing aluminum hydroxide. The molar ratio is AL2O3:P2O=1:32, that is, the phosphoric acid and aluminum hydroxide 7:1 solution. It must be stirred and dissolved for 24 hours, and the specific gravity can reach 1.6~1.65, and the dosage is 8~10%.
3 phosphate refractory bricks
The purpose of the trapping material is to make the acid react with the iron in the mud to discharge the gas. If the trapping material is incomplete, the acid reacts with the impurity iron in the mud material, and the generated gas is liable to cause spallation during the pressing process. In order to prevent the occurrence of such phenomena, under the premise of strictly implementing the operating procedures, strict control of the trapping system. The mud material must be covered with a plastic sheet for 24 hours at a temperature of 25 ° C or above. If the temperature is low, the mud will freeze, and it will be easy to mold during the molding process, causing a lot of pockmarks and affecting product quality. .
4 phosphate refractory brick forming
The normal temperature strength of the product mainly comes from molding. Therefore, it must be formed by a press of more than 300t. The mold does not have a ruler, and the bulk density must be greater than 2.89g/cm3 to ensure that the finished product reaches 2.70g/cm3. Strictly control the layer crack and the film, the semi-finished product must be dried before it can be heat treated in the kiln.
5 Phosphate refractory brick heat treatment
Phosphate refractory brick, because the binder aluminum phosphate solution is a reaction of aluminum dihydrogen phosphate, it has normal gelation at normal temperature. During the hardening process, when heated to a certain temperature, the acid aluminum phosphate can be turned into coke. The aluminum phosphate and the aluminum metaphosphate undergo dehydration polymerization, and the strength of the combination is obtained due to the formation of the new compound and the formation of a strong adhesion at the same time. In addition, with the increase of temperature, in addition to polymerization, aluminum metaphosphate can also be decomposed to form AiPO4 and P2O5. This P2O5 can also react with AL2O3 present in refractory to form AiPO4, due to AiPO4. Formation also increases the density of the combined body.
The performance characteristics of phosphate refractory bricks are mainly high strength, strong corrosion resistance, low porosity and good thermal stability. The finished product has no shrinkage and slightly expands after heat treatment. It has high strength from room temperature to medium temperature and is excellent in the range of 1200~1300°C. The fired brick has good wear resistance and is gray or grayish white after heat treatment.
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