Calcined Alumina
Calcined (or alpha) alumina is made by calcining a source alumina powder at 1200-1300C to convert it to pure Al2O3. This is the densest and most stable crystalline form of alumina. It is insoluble in water but is soluble in hydrofluoric acid and potassium bisulfate. When nearly 100% of the material converts to the large hexagonal, elongated tablet shaped crystals associated with the alpha phase, the product is referred to as "Tabular Alumina". Calcined aluminas are available in numerous grades based on the heat treatment applied, crystal size, soda content, and degree of thermal conversion to alpha phase.
Calcined alumina is made by firing a source alumina at various temperatures, depending upon desired level of calcination (burn), into alpha alumina varying from 5 – 100% moving it to its densest and most stable form. The calcined alumina particles appear as crystalline agglomerates which are larger when the degree of calcination is higher. Calcined alumina is generally used in the manufacture of refractories, glass and enamel, tile and porcelains and ceramics, including electronic ceramics, etc.
Calcined alumina is produced through the calcination (“heating”) of alumina to various temperatures. By controlling the calcination temperatures and time, the properties of the alumina can be controlled. Calcined alumina is therefore utilized in a variety of industrial applications including Structural ceramics, Technical ceramics, Polishing compounds for plastic, metal, and glass, Fillers for Rubber and Plastics, Friction - anti slip, Refractories, Paint & Coatings and Thermal Spray Powders.
Calcined alumina powder is produced by calcination of alumina. The manufacturing process is carried out at various temperatures, which control hardness and abrasive properties of calcined alumina powder, such as polishing and grinding. At temperature of 1200-1300ºC, calcined alumina is easily converted into pure Aluminum Oxide (Al2O3).
Demand for calcined alumina is driven by a number of factors. The major applications of calcined alumina include refractory & ceramics. The rising market penetration of high-quality steel accounts for the largest share in terms of application for refractories, in emerging economies, which drives the demand for high-end refractories, which are made from calcined alumina. The growing building & construction industry further substantiates the growth.
Activated Alumina
Activated alumina is manufactured from aluminium hydroxide by dehydroxylating it in a way that produces a highly porous material; this material can have a surface area significantly over 200 m²/g. The compound is used as a desiccant (to keep things dry by absorbing water from the air) and as a filter of fluoride, arsenic and selenium in drinking water. It is made of aluminium oxide (alumina; Al2O3). It has a very high surface-area-to-weight ratio, due to the many "tunnel like" pores that it has. Activated alumina in its phase composition can be represented only by metastable forms (gamma-Al2O3 etc.).
Activated alumina is an excellent desiccant for drying a wide variety of liquids and gases. Activated alumina is a porous, solid form of aluminum oxide, otherwise known as Al2O3 or alumina. This is the same mineral that makes up the precious gems ruby and sapphire, with impurities being the source of the stones’ bright colors. After activated alumina has been evacuated of existing moisture by heating it, the high surface area and many pores of the material allow for the uptake of water and other molecules through adsorption.
The U.S. activated alumina market was estimated at USD 217.0 million in 2016 and is anticipated to grow at a CAGR of 4.8% from 2017 to 2025. The increasing research being conducted in the field of activated alumina has helped in increasing the application scope of activated alumina over the years.
Activated alumina is a dry, granular chemical substance produced by de-hydroxylation i.e., the removal of hydroxyl group ion from aluminum hydroxide. This compound is treated as a desiccant, catalyst and used for filtering fluoride, arsenic and selenium in drinking water. Activated alumina has a high surface area to weight ratio due to its extensive pore structure, which is resistant to thermal shock and abrasion, and will not shrink, swell or soften when placed in water.
Activated alumina is prominently used as a reaction catalyst, in the oil and gas sector, and for the treatment of water. Growing investments in water treatment infrastructure and the ever-rising demand for oil and gas have been fueling the demand for activated alumina over the past few years. These trends are expected to continue during the forecast period, driving the market to expand at a CAGR of 4.2% between 2016 and 2024. The sales of activated alumina amounted to US$770.6 mn in 2015 and are projected to be worth US$1,108.9 mn by 2024.
