Wollastonite is an industrial mineral containing chemicals like calcium, silicon and oxygen. Molecular formula of Wollastonite is CaSiO3 and its approximate theoretical composition consists of 48.28% of CaO and 51.72% of SiO2. Natural Wollastonite may contain traces or minor amounts of various metal ions such as aluminum, iron, magnesium, potassium and sodium. Wollastonite is infrequently found in pure form and generally contains other minerals namely calcite, garnet and dropsied as gangue minerals or impurities those removed during extraction process. Optimum performance can be obtained by properly toning suitable pairing agent at the suitable concentration level to the polymer formulations. It possesses properties like lower moisture content and oil absorption with low volatile content. Surface modification of Wollastonite enhances its physical properties.
Wollastonite was named in honor William Hyde Wollaston (1766-1828), a British chemist and physicist noted for his inventions in optics.
Wollastonite is a mineral blessed with many unique characteristics. Till 1970, the primary use of Wollastonite was as a decorative stone. Since the past 4 decades, one of the uses has been as a replacement for asbestos in products like insulating board and panels, paint, plastics, roofing tiles, and in friction devices such as brakes and clutches. Wollastonite is one of the most versatile functional filler and reinforcement agents. Wollastonite increases the performance of products like polymers, plastics, paints and coatings, construction materials, friction devices, ceramic, etc. It also been employed for metallurgical applications.
In the construction field, Wollastonite has been recognized as a substitute for asbestos in fire-resistant building products. As a functional additive, Wollastonite increases flexural and impact strengths. Wollastonite’s low thermal conductivity and high aspect ratio structure extends its possibility to utilize for fire resistant. Wollastonite is useful in interior and exterior construction boards, roof tiles, shaped insulation products, sheets, panels and sidings.
Wollastonite can be used as partial substitute of cementitious material and sand in cement concrete. Studies show that replacement with wollastonite by 10% in concrete mixes enhances its compressive strength by 28 - 35% and flexural strength (36-42%) at 28 and 56 days respectively. By incorporation of Wollastonite, reduction in water absorption, drying-shrinkage and abrasion loss of concrete, and enhancement in durability against alternate freezing-thawing and sulphate attack were observed. Because of high concrete strength and abrasion resistance, a better utilization of concrete cross section is possible. Alternatively, thickness of pavement slab can be reduced by incorporation of Wollastonite micro-fibres in concrete mixes.
Paints and Coatings: In coatings, fine acicular particles act as a good flattening agent and allow paint to settle out after application to produce a dry film of uniform thickness, and the interlocking particles improve toughness and durability of the coating with excellent tint retention, scrub, and weather resistance. High brightness and whiteness reduce pigment load and typically very low oil absorption, reduces the volume of binder required and contributes to reduced pigment costs. As noted earlier, wollastonite can also act as a pH buffer for improved in-can paint stability over long periods of time. The acicular structure and alkaline nature of wollastonite also make it an ideal auxiliary pigment in industrial coatings and primers for improved corrosion resistance.
Ceramics: Wollastonite can be used in a variety of ceramic applications including ceramic glazes and bodies, enamels, frits, fluxes and in sanitary-ware. This industrial mineral is a source of CaO to alkaline glaze formulations to improve the strength of the glaze. Wollastonite also has a low LOI (< 1%) which gives minimal gas evolution during firing resulting in a smooth surface with diminished pinholing. Due to its acicular structure, wollastonite improves green strength and reduces crazing and checking especially during rapid heating and cooling. It has a low sintering temperature (approximately 991-1196°C) which is comparable to that of most natural frits.
The implementation of Wollastonite can be further extended in Concrete technology and Geotechnical engineering. In addition to individual utilisation of Wollastonite, it may be added together with some pozzolanic materials like Fly ash, etc in a view of getting good results. It is concluded based on the effects of Wollastonite and Fly ash in concrete.
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