REVIEW OF ENGINEERING MATERIALS

WOLLASTONITE

It is a fibrous and brittle silicate mineral. Wollastonite forms upon a contact metamorphism of carbonate rocks (primarily limestone), i.e. a phenomenon occurring when magma intrudes into shielding rocks. The mineral is named after the English mineralogist William Hyde Wollaston, who described it for a first time. Wollastonite is a rare mineral present only in some areas of the globe. Its deposits were surveyed in Poland, but in small quantities. Wollastonite has some specific properties which decide on its widespread usage. The mineral features low moisture and volatile substances content, and fibrous character of its particles. Wollastonite is also a perfect electrical insulator. It is used in ceramic, chemical and metallurgical industries – being prevalently incorporated into the manufacturing of slabs, paints, and as a casting flux. Incorporation of wollastonite into the manufacturing allows to obtain advantageous effects. In ceramics, wollastonite decreases shrinkage and gas evolution, and maintains brightness of a product during firing. When added to paints, it improves the durability of the paint film, improves paint resistance to weathering and reduces gloss. In plastics, wollastonite improves tensile and flexural strength, as well as thermal stability of these materials in elevated temperatures.

Wollastonite is also an attractive collectible mineral, sometimes used in jewellery.

VERMICULITE

Vermiculite is composed of hydrous aluminosilicates and exhibits a specific, lamellar crystal habit. It occurs mostly in South Africa, China and Brazil. The mineral has a specific property of significant, up to 15–20-fold, expansion when heated. In this process, an exfoliated vermiculite, which is resistant to temperatures up to 1,200°C, is formed. Thanks to its properties, vermiculite has numerous industrial uses. Prevalently, it is used in manufacturing of high temperature resistant and fireproof insulations, fireplaces, brake linings, acoustic panels and incombustible pipes and steel structures. Vermiculite is also utilized in manufacturing of insulating concrete, as well as in agriculture and horticulture.

CALCIUM SILICATE

Calcium silicate is a chemical compound of anti-caking properties being widely used for high temperature insulations. It is a base material for manufacturing calcium silicate boards, which have high mechanical strength and thermal stability. Boards, immune to compression and reducing gases, are used in manufacturing of fireplaces, furnaces, as well as in construction and petrochemical industry. Products made of calcium silicate (mostly boards as high temperature insulations) feature thermal resistance up to 1,000°C. The said boards are lightweight, durable, easy to process and health- and environment-friendly.

CERAMIC FIBRE

It is a ceramic material of high industrial importance. Ceramic fibres are present in a polycrystalline and monocrystalline forms. Monocrystalline form is especially important in thermal insulation industry. Monocrystalline fibres, so-called ‘whiskers,’ have a form of fibrous crystals. The said fibres have utmost mechanical strength and thermal resistance. The unique propertied of ceramic fibres are the reason of the widespread industrial uses. The fibre is resistant to rapid temperature changes, impermeable to infrared radiation, and does not accumulate significant amounts of heat upon heating. Ceramic fibres are mostly used as a heat insulating material for devices using fire. They are resistant to temperatures up to 1,425°C, and maintain their original structure to this temperature.