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%.