Calcined alumina, also known as aluminium oxide or alumina, is a fine white powder derived from naturally occurring bauxite ore through calcination. The powder is composed of small crystalline alumina grains that are approximately 1 micrometer in diameter. Calcination involves heating bauxite to high temperatures above 1000°C to remove water and carbon dioxide from aluminium hydroxide, transforming it into an odorless white powder. Calcined alumina powder has a very high melting point of over 2000°C, making it one of the most refractory materials known. Properties and Characteristics Calcined Alumina Powder possesses some unique properties that contribute to its widespread usage. It has high purity levels above 99% and is mostly inert and non-reactive in nature. The powder has excellent electrical insulating properties and can withstand high temperatures without sustaining structural damage. Calcined alumina is also extremely hard with a Mohs hardness of 9, second only to diamond. It has low thermal conductivity combined with high thermal shock resistance. Other key properties include high compressive strength, low porosity, and high brightness that offers applications in abrasive and refractory materials. Uses in Abrasives One of the largest end uses of calcined alumina lies in abrasive applications due to its unparalleled hardness. It is predominantly used as a raw material in manufacturing grinding wheels, sharpening stones, honing sticks, coated abrasives and abrasive paper. The small, hard crystalline structure of the powder makes it ideal for cutting, grinding, sharpening and polishing a wide variety of materials even at high speeds. Calcined alumina increases the cutting life of abrasive products while providing consistent, contamination-free performance. Uses in Refractories Due to its exceptional heat resistance and thermal shock behavior, calcined alumina finds extensive application as a refractory material. It is used as a thermal insulation material in applications involving high temperature processes like steelmaking, glass production, cement manufacturing and petrochemical cracking. As a major component in refractory bricks and monolithics, calcined alumina helps retain the physical structure and integrity of furnaces and kilns withstanding high heat loads. Some other specialized uses in this area are acidic resistant gunning mixes, ramming mixes, insulations and backup materials for thermocouple protection. Ceramic and Advanced Applications Calcined alumina is widely used as a fundamental raw material in ceramic applications due to its compatibility, durability and corrosion resistance qualities. It is often used in ceramic glazes, tiles, sanitaryware, electrical insulators, and as filler material in porcelain enamels and whiteware production. In advanced applications, calcined alumina acts as an important material in technical ceramics, aluminum production cells and seals for fluid cracking catalysts. It also finds increased usage as a filler in plastics, paints, paper, and catalyst support due to its non-reactive nature and ability to enhance characteristics like strength, electrical resistance and brightness. Emerging applications include its use as a substrate for LEDs and as a polishing media in chemical mechanical polishing. Pharmaceutical and Medical Uses High-purity calcined alumina micropowders have generated considerable interest for use in pharmaceutical and biomedical applications. It is being evaluated as an alternative to silica in tablet excipients and as a binder/disintegrant due to benefits like acid resistance and non-toxicity. Research is also being conducted on utilizing nano alumina’s adsorptive properties for drug delivery and as bone graft substitutes. It has potential to serve as a substrate for drug coatings that provide controlled release. Some dental and orthopedic uses of alumina involve artificial tooth fillings and prosthetic components like hip joints and bone plates. Its outstanding hardness, biocompatibility and structural integrity make it appropriate for these advanced medical applications. Manufacturing Process Major steps involved in the production of calcined alumina powder: - Bauxite mining and beneficiation: Raw bauxite ore undergoes processes like washing, screening, crushing to remove impurities. - Alumina refining: Bauxite is mixed with caustic soda (NaOH) at high pressure-temperature to produce sodium aluminate. - Precipitation: Aluminum hydroxide is precipitated from sodium aluminate by seeding and settled in thickener. - Calcination: Aluminum hydroxide is fed into rotary kilns and heated to 1000-1200°C to remove water and produce alpha alumina. - Milling: Calcinid alumina is dry milled using ball or vertical mills to obtain desired particle size. - Classification: Fine alumina powder is separated using air classifiers to achieve specific surface area. - Packing: Final powder is packed in bags, drums or bulk containers for industrial applications. Strict quality controls are maintained during production to ensure calcined alumina powder meets consistent standards of purity, particle size and distribution for various commercial grade specifications. In summary, calcined alumina powder has emerged as one of the most versatile industrial minerals due to a unique set of superior properties like hardness, refractoriness, chemical inertness and electrical insulation. It acts as an essential raw material across major sectors including abrasives, refractories, ceramics as well as newer areas such as pharmaceuticals, electronics and advanced materials. With growing industrialization and tightening environmental norms, calcined alumina is projected to witness steady gains in global demand in the coming years.
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