在耐火原料应用中，胶结硅石的不同性能和用途

1.石英砂岩

  石英砂岩又称硅质砂岩，属胶结硅石，是机械沉积类型中的一种，岩石由碎屑和胶结物两部分组成。碎屑部分主要由石英颗粒组成，占90%以上，此外还有少量的铝硅酸盐矿物，如长石、云母，总量为1%~2%，最多不超过4%~5%，也有微量的燧石和碳酸盐矿物混入。胶结物绝大部分为硅质，有时为碳酸盐、铁质等。按胶结物类型不同可分为：硅质石英砂岩、钙质（白云石质）石英砂岩和铁质石英砂岩。

  石英砂岩的化学成分主要为SiO₂，一般含量在95%以上，其次含有Al₂O₃<1% ~ 3%，Fe₂O₃<1%，MgO<0.1%，CaO<0.6%，NaO +K₂0 <1%~2%。纯的石英砂岩为白色、灰白色；一般因混入一定杂质，故呈淡黄色、淡红色；当胶结物类型为铁质胶结时，呈褐色。岩石中石英颗粒常为很好的浑圆体，大小均一，有粗粒（0.5~1mm）的，也有细粒（0.1~0.25mm）的。

  岩石的断面粗糙，肉眼能看到石英颗粒。但有时石英砂岩的硅质（玉髓、蛋白石等）胶结物可在碎屑颗粒上结晶次生增长，此时肉眼难以区别其中的颗粒和胶结物。其耐火度高，可达1700℃。

  由于石英砂岩杂质成分多，致密性差、强度低，并且石英颗粒小，在烧成时氧化硅晶型转变较快，烧后易于松散。但它可用来制造一般硅砖，以及作为玻璃的原料。

  河北秦皇岛、四川铜梁、湖南湘潭、湖北葛店等地有质量较好且规模较大的石英砂岩矿床。

2.燧石岩

  燧石岩是硅质岩的一种，主要是由玉髓、石英或蛋白石组成的，主要成分为 SiO₂，还含有Al₂O₃、Fe₂O₃、CaO、MgO、K₂O、Na₂O等杂质，颗粒细小，多星次棱角状，硬度较大。

  我国山西五台山的复合硅石（也称赤白硅石）既属于该类型，又属于胶结硅石，这种复合硅石含有均匀的细分散含铁矿物和石英细粒，在加热时，SiO₂易于转化。

3.石英砂

石英砂别名硅砂，是由石英岩、石英砂、脉石英及含硅高的岩石风化后的碎屑，经过流水的搬运，在滨海、湖泊及河流中沉积而成的。石英砂的主要矿物为石英矿物，占95%以上，另含少量的长石颗粒（5%）和极少量的重砂物及有机质。石英颗粒大小均匀，表面光滑，圆度及分选性较好，粒度在0.15~0.5mm之间。质地纯净的石英砂为白色，因含有铁质，故多呈淡黄色、浅灰色或褐红色。其化学成分波动大，主要是SiO₂（90%以上）、Al₂O₃( <5% )、Fe₂0₃（<1%），其次还有TiO₂、Cr₂O₃、K₂O、Na₂O等。

  石英砂可作为一般硅砖的原料，大多用作捣打料。石英砂是制造玻璃的主要原料。

  我国江苏（东海）、山东、吉林（甘旗卡）、广东（新会、珠海）、湖南等地都有质量较好的石英砂。其中江苏东海石英砂采用东海石英加工而成，SiO₂含量高且杂质低，是生产熔融石英、玻璃制品、陶瓷、耐火材料等产品的首选原料，其化学成分为：SiO₂≥99.8%、Fe₂O₃≤0.015%、Al₂O₃≤0.025%、Na₂O≤0.003%、CaO≤0.005%。

Different properties and uses of cemented silica in refractory raw material applications

1.Quartz sandstone

  Quartz sandstone, also known as siliceous sandstone, belongs to cemented silica, which is one of the mechanical sedimentary types. The rock is composed of two parts: debris and cement. The debris part is mainly composed of quartz particles, accounting for more than 90%, in addition to a small amount of aluminosilicate minerals, such as feldspar, mica, the total amount is 1% to 2%, at most not more than 4% to 5%, there are also trace amounts of flint and carbonate minerals mixed. Most of the cement is siliceous, sometimes carbonate, iron and so on. According to different types of cement, it can be divided into siliceous quartz sandstone, calcareous (dolomitic) quartz sandstone and ferric quartz sandstone.

  The chemical composition of quartz sandstone is mainly SiO2, generally more than 95%, followed by Al2O3<1% ~ 3%, Fe₂O₃<1%, MgO<0.1%, CaO<0.6%, NaO +K₂0 <1%~2%. Pure quartz sandstone is white, gray white; Generally due to mixed with certain impurities, it is light yellow, light red; When the cement type is iron, it is brown. The quartz particles in the rock are often well rounded, uniform in size, with coarse grains (0.5~1mm) and fine grains (0.1~0.25mm).

  The cross-section of the rock is rough and quartz grains are visible to the naked eye. However, sometimes the siliceous (chalcedony, opal, etc.) cements of quartz sandstones can crystallize secondary growth on the clastic particles, and it is difficult to distinguish the particles and cements by naked eye. Its refractoriness is high, up to 1700℃.

  Due to the impurity composition of quartz sandstone, poor density, low strength, and small quartz particles, silicon oxide crystal transformation is fast during firing, and easy to loose after burning. But it can be used to make ordinary silicon bricks, and as a raw material for glass.

  There are large quartz sandstone deposits with good quality in Qinhuangdao, Tongliang in Sichuan, Xiangtan in Hunan and Gedian in Hubei.

2.Flint rock

  Flint rock is a kind of silicic rock, mainly composed of chalchalith, quartz or opal, the main component is SiO2, also contains Al2O3, Fe2O3, CaO, MgO, K₂O, Na2O and other impurities, fine particles, multi-star angular, hardness is larger.

  China’s Shanxi Wutai Mountain composite silica (also known as red and white silica) belongs to this type, but also belongs to cemented silica, this composite silica contains uniform fine dispersed iron minerals and quartz fine particles, in heating, SiO2 is easy to transform.

3.Quartz sand

  Quartz sand, also known as silica sand, is formed by the weathered debris of quartzite, quartz sand, gangue quartz and silicon-containing rocks, which are transported by flowing water and deposited in coastal, lakes and rivers. The main mineral of quartz sand is quartz mineral, accounting for more than 95%, and contains a small amount of feldspar particles (5%) and a very small amount of heavy sand and organic matter. The quartz particle size is uniform, the surface is smooth, the roundness and sorting are good, and the particle size is between 0.15 and 0.5mm. Pure quartz sand is white, because it contains iron, it is mostly light yellow, light gray or maroon. The chemical composition fluctuates greatly, mainly SiO2 (more than 90%), Al2O₃(<5%), Fe₂03 (<1%), followed by TiO2, Cr₂O3, K₂O, Na2O and so on.

  Quartz sand can be used as a general silica brick raw material, mostly used as ramming material. Quartz sand is the main raw material for making glass.

  China’s Jiangsu (East China Sea), Shandong, Jilin (Ganqi card), Guangdong (Xinhui, Zhuhai), Hunan and other places have good quality quartz sand. Among them, Jiangsu Donghai quartz sand is processed by East China Sea quartz, with high SiO2 content and low impurities, which is the preferred raw material for the production of fused quartz, glass products, ceramics, refractories and other products. Its chemical composition is: SiO2≥99.8%, Fe2O3≤0.015%, Al2O3≤0.025%, Na2O≤0.003%, CaO≤0.005%.