使用硅质原料，不能忽视的细节

一、原料的处理

  （一）水洗涤原料除去杂质

  硅石原料中，Al₂O₃是最有害的杂质，Al₂O₃多来源于黏土附着物，为此，硅石原料在使用前要经拣选、水洗涤。研究指出，冲洗可以将天然硅石中Al₂O₃的含量减少约0.2%。用这种方法可除去1/3的Al₂O₃和黏结在石英裂纹中的残留物。

  表7-10为山西五台山胶结硅石洗涤后化学成分和耐火度的变化情况。可以看出，洗涤后杂质含量明显降了下来，因此，工业生产中用水冲洗硅石是不可缺少的辅助手段。

  在玻璃窑用优质硅砖的化学成分中，要求（Al₂O₃+2R₂O）%（即熔蚀指数）≤0.5%。另有资料报道，20世纪90年代初，对瓶罐池窑选用的优质硅砖、普通硅砖的熔蚀指数（Al₂O₃+2R₂O）%要求分别为（ Al₂O₃+ 2R₂O）% ≤0.5% 和（Al₂O₃+2R₂O）%≤0.7%，可见硅石原料中，用水洗涤的方法除去杂质的重要性。

  （二）硅石块度应有一定要求

  GB 2416-81把硅石块度划分为5种规格，即：

  （1）20~40mm。最小不小于10mm，小于20mm的不大于10%；最大不大于50mm，大于40mm的不大于8%。

  （2）40~60mm。最小不小于30mm，小于40mm的不大于10%；最大不大于70mm，大于60mm的不大于8%。

  （3）60~120mm。最小不小于50mm，小于60mm的不大于10%；最大不大于130mm，大于120mm的不大于8%。

  （4）120~160mm。最小不小于110mm，小于120mm的不大于10%；最大不大于170mm，大于160mm的不大于8%。

  （5）160~250mm。最小不小于150mm，小于160mm的不大于10%；最大不大于260mm，大于250mm的不大于8%。

  很明显，块度小会引进过多的杂质，尤其是Al₂O₃。

二、原料的煅烧

  由于SiO₂在加热过程中发生晶型转变，并伴有体积变化，为此，在原料的煅烧过程中，应注意以下几点：

  （1）由于SiO₂各晶型转变温度会引起体积效应，所以升温要均匀、缓慢。

  （2）冷却时，在低于600℃时，应缓慢冷却，以防止冷裂。

  （3）在高温阶段，升温缓慢。终止温度要有足够的保温时间，以便生成多量的鳞石英。

三、提高硅砖的抗热震性

  硅砖的抗热震稳定性较差，为此，可添加金属以及它们的氧化物，如MnO、 TiO₂、Fe₂O₃、ZrO₂等其中加入ZrO₂，主要是利用ZrO₂相变和微裂纹增韧来提高硅砖的热震性能。关于ZrO₂相变和微裂纹增韧详见以后文章。

Using siliceous raw materials, the details cannot be ignored

1. 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.