There are numerous types of sands that exist which have various applications. The principal mineral phase in them all is quartz. They are classified on the level of other oxides present and their respective particle size distributions. Depending on the nature of the application sand is subjected to various treatments to produce the desired grade.
Ceramic grade sand is less than 75μm and has a silica content above 97.5%, impurities include <0.55% Al2O3 and <0.2 Fe2O3. It is used in the production of glazes and ceramic materials.
Foundry sand is produced at particle size of less than 75μm. It has a silica content of 98% with limits placed upon on the amounts of magnesia (MgO) and lime (CaO) present. In additional to this a refractory grade is produced for the manufacture of refractory materials which can be slightly lower in purity (>95%SiO2).
Flux sand for iron and steel making >90%SiO2.
Consolidated sandstone is fairly resilient which favours its use in the construction industry. Sandstone is both crushed and graded for use as an aggregate or alternatively if it is aesthetically attractive it may be cut into slabs for building (dimension stone.) The use of silica aggregate is by far it biggest use in the construction industry.
Silica is used as a raw material feedstock for the production of glass where it is mixed with lime and soda to produce domestic glass for windows, bottles, jars, light bulbs and plate glass. Alternatively it may be mixed with boron oxide and soda to produce thermal shock resistant glass for cooking such as Pyrex. High-grade fused silica may be used on its own for the production of glass where a high thermal stability and shock resistance is required such as in the windows of the NASA Shuttle.
The majority of domestic glass tends to be made via the float glass method whereby a ribbon of molten glass is fed across a bath of liquid tin in a controlled atmosphere. The Pilkington Brothers in the UK first developed this process for glass production.
Fused silica is used in the refractory casting slurry, where it coats a wax replica of the component to be cast. The refractory stucco is fired and molten metal is poured into the mould. Finally, the fused silica shell is knocked out. Fused silica makes this knock out stage easier than other refractories such as zirconia and aluminosilicates.
The grindability of silica to specific particle size distributions facilitates its use as a filler material to bulk out products. Silica is commonly used as a filler in paints, plastics, rubber, adhesives, putty and sealants.
Silica fume or microsilica is a by-product of producing silicon metal or ferrosilicon alloys. One of the most beneficial uses for silica fume is in concrete. Due to its chemical and physical properties, it is a very reactive pozzolan. Concrete that contains silica fume can have very high strength and be very durable. Silica fume consists of amorphous silicon dioxide. Each individual particle of silica fume is very small in the order of 1/100th the size of a cement particle.
Silica fume is also used as a filler material in refractory concretes, where its function is to improve the particle packing of the product increasing strength and reducing porosity.