Ores And Minerals #1768584

A white nonmetallic, natural mineral identified chemically as calcium metasilicate, CaSiO3. It is the only commercially available pure white mineral that is wholly acicular (needle-like crystals). Wollastonite is available in fine particle size powders as well as fibrous 'high aspect ratio' products (20:1). This material has a very unusual texture; it does not flow at all (a hand full can be picked up with fingers downward). They vary in purity; some require almost no beneficiation; others may require removal of up to 80% impurities such as garnet, diopside, limestone, and dolomite (e.g. by magnetic separation, froth flotation, optical sorting). Synthetic wollastonite is also made by combining quicklime with quartz, calcium carbonate and calcium hydrate. The fibrous form of wollastonite can be very beneficial in bodies. In low fired ceramics wollastonite reduces drying and firing shrinkage and drying and firing warpage. It also promotes lower moisture and thermal expansion in the fired product and increases firing strength. It fires with no LOI and its fibers help vent out gassing. These factors have made it a valuable component in tile bodies, especially for fast fire. It is common to see 10% wollastonite in low fire earthenware recipes. Vitreous and semi vitreous bodies can also show reduced shrinkage with small additions (2-5%), however wollastonite becomes a stronger flux as temperatures go above 1100C. Wollastonite exhibits a slight solubility in water, but slips containing it can become more alkaline (potentially affecting rheological properties). This affects its tendency to form agglomerates during storage (which create lumps in glazes necessitating sieving). Manufacturers warn that stock should be rotated to prevent it getting too old, that it should be stored in dry conditions and that pallets should not be stacked more than two high. At higher temperatures the powdered form is valuable as a source of CaO flux in glazes (and bodies). The other main raw source of CaO is whiting but it releases a high volume of gases of decomposition which produce suspended micro-bubbles that demand slow firing to clear. Also, since wollastonite sources silica as well, glaze recipes employing it do not need as much raw silica powder. Further the SiO2 and CaO react more readily to form silicates. Thus wollastonite is used as a major flux in high temperature sanitaryware and electrical insulators. In glass and fiberglass making wollastonite melts more readily (lower energy costs) and microbubble generation is lower than limestone-sand mixes. Wollastonite is also used in stain and frit formulations to supply CaO in a more easily melted form. Even though powdered samples may appear quite similar to feel and the naked eye, pay attention to the amount of +325 material if you need to switch brands or suppliers.

Silica Sand Pyrophyllite PowderThe chemical compound silica, also known as silicon dioxide, is the oxide of silicon, chemical formula SiO2. Silica is found in nature in several forms, including quartz and opal. The most common constituent of sand in inland continental settings and non-tropical coastal settings is silica, usually in the form of quartz because the considerable hardness of this mineral resists erosion. However, the composition of sand varies according to local rock sources and conditions. Our Silica Sand which is widely applicable and uniform in size is used for water filtration, foundry, painting, water treatment and plastering. The product is fine in texture with uniformed quality. Features:Correct compositionOptimum qualityMoisture proofSafe usageEffectiveAdvantages:No chemicals to purchase for maintenanceDurable material with long life and temperature rangeSub-Angular shape enhances filtration propertiesIdeal for non-silica sensitive sub-fill requirements

Calcined KaolinCalcined Kaolin is also called Anhydrous Aluminum Silicates. Calcined clay is made by the thermal treatment of water-washed and bleached kaolin to achieve purity, improved residues, brightness, and achieve a desired particle size distribution, and then subject to calcinations (heat treatment) to effect the anhydrous state through the removal of 14% water of hydration. Calcined grades differ by method of exposure to heat. Conventional calcined grades are processed in vertical kilns with a substantial period of exposure. The unique calcination method is to flash calcine the material by exposing the feed clay to higher temperatures for only a few seconds duration. Both methods fully remove the water of hydration, but effect different particle shapes, specific gravity, and optical characteristics. Low-temperature calcination, at about 650-700C, removes structural hydroxyls and forms amorphous metakaolin. Specific gravity is reduced from 2.58 to about 2.50 in the process, while hardness and porosity, and thus brightness, opacity and oil absorption, are increased. Fully calcined clays, with maximum brightness and opacity, are produced in the 1000-1150C range. This is hot enough to totally collapse the amorphous structure, with a consequent increase in specific gravity to 2.6-2.7, without causing the mineralogical transformation to mullite (specific gravity 3.2, hardness 6-7). The balance of opacity and sheen derived from calcined clays can be manipulated by the temperature, rate of heating and fluxes used in the calcination process. The primary use of kaolin in coatings is as a TiO2 extender in waterborne architectural paints. Calcined clays generally provide the best brightness, TiO2 extension and dry hide. Water-washed and delaminated grades also contribute to extension and dry hide, as well as covering power and gloss control (finer particle size = higher gloss). [LESS]