Using siliceous raw materials, the details cannot be ignored

Treatment of raw materials

(A) water washing raw materials to remove impurities

Among silica raw materials, Al₂O3 is the most harmful impurity, Al₂O3 mostly comes from clay attachments, therefore, silica raw materials should be selected and washed with water before use. Studies have shown that flushing can reduce the Al₂O3 content in natural silica by about 0.2%. In this way, 1/3 of Al₂O3 and the residue bonded in the quartz crack can be removed.

Table 7-10 shows the chemical composition and fire resistance changes of Shanxi Wutaishan cemented silica after washing. It can be seen that the impurity content is obviously reduced after washing, therefore, washing silica with water in industrial production is an indispensable auxiliary means.

In the chemical composition of high-quality silicon brick for glass kiln, the requirement is (Al₂O3+2R₂O) % (that is, the melting corrosion index) ≤0.5%. It is also reported that in the early 1990s, the corrosion index (Al2O3+2R2O) % of the high-quality silicon brick and ordinary silicon brick selected for the tank kiln is (Al2O3+2R2O) %≤ 0.5% and (Al2O3+2R2O) %≤0.7%, which can be seen in the silica raw materials. The importance of washing with water to remove impurities.

2 The degree of silica block should have certain requirements

GB 2416-81 divides the silica lumpiness into five specifications, namely:

(1) 20~40mm. Minimum is not less than 10mm, less than 20mm is not more than 10%; The maximum is not greater than 50mm, and the size greater than 40mm is not greater than 8%.

(2) 40~60mm. The minimum is not less than 30mm, and less than 40mm is not more than 10%; The maximum is not greater than 70mm, and the size greater than 60mm is not greater than 8%.

(3) 60~120mm. The minimum is not less than 50mm, and less than 60mm is not more than 10%; The maximum is not more than 130mm, and the maximum is not more than 8%.

(4) 120~160mm. The minimum is not less than 110mm, and less than 120mm is not more than 10%; The maximum is not more than 170mm, and the size greater than 160mm is not more than 8%.

(5) 160~250mm. Minimum is not less than 150mm, less than 160mm is not more than 10%; The maximum is not greater than 260mm, and the size greater than 250mm is not greater than 8%.

Obviously, small clumpiness introduces excessive impurities, especially Al2O3.

2.Calcination of raw materials

Due to the crystal transformation of SiO2 in the heating process, accompanied by volume changes, for this reason, in the calcination process of raw materials, the following points should be paid attention to:

(1) Because the SiO₂ crystal transition temperature will cause volume effect, the temperature should be uniform and slow.

(2) When cooling, it should be cooled slowly when it is below 600 ° C to prevent cold cracking.

(3) In the high temperature stage, the temperature rises slowly. The termination temperature should have sufficient holding time in order to generate a large amount of squamite.

3Improve the thermal shock resistance of silicon brick

The thermal shock resistance of silicon bricks is poor, for this reason, metals and their oxides can be added, such as MnO, TiO2, Fe2O3, ZrO2, etc. ZrO2 is added, mainly by using ZrO2 phase transition and micro-crack toughening to improve the thermal shock performance of silicon bricks. For details on ZrO2 phase transition and micro-crack toughening, see a later article.