Alumina comes from the word alum. Alum is a compound of aluminium and potassium disulphate. The manufacturing of alumina was started by using the sainte-claire deville process that consisted of attacking bauxite by sodiun carbonate followed by the preciption of alumina hydrate. Alumina (Al2O3) or aluminium oxide formed by the metal aluminium and occurs in nature as minerals corrundum, gibbsite and most commonly as bauxite. Silicon oxide also known as silica. Silica is a chemical compound that is an oxide of silicon with the chemical formula SiO2. Silica is most found in nature as sand or quartz. Silica is manufactured in several forms including fused quartz, crystal, fumed silica, colloidal silica and silica gel. After combining these two materials the mechanical tests are performed on various samples of different compositions. The various tests which are perform on samples are hardness, heat flow and compression. In the hardness test, the hardness increases with increase in the percentage of alumina and decreases with decrease in the percentage of alumina. In heat flow, the heat from one end of the plate and observed at other end it takes more time when increasing the percentage of alumina and it takes less time while decreasing the percentage of alumina. In compression test, the compression strength increases with increase in the percentage of alumina and decreases with decrease in the percentage of alumina.
From the above literature review it is concluded as alumina is an important material and the information about the properties with various compositions is scares. So, in this research work properties of alumina with various compositions are studied and the following objectives are made to fullfil this research work.
1. To press the specimen pieces with required composition.
2. To find out and compare hardness on the specimen pieces.
3. To study the heat flow of specimen pieces.
4. To find out and compare compression test on specimen pieces.
1. Specimen of alumina were prepared with composition of (30-32%, 50-52%, 70-72%, 90-92%).
2. Silicon oxide (in powder form) prepared with composition of ( 60-64%, 40-44%, 20-24%, 3-4%).
3. After preperation the composition of alumina and silicon oxide ,then proper mixing could be done of these two.
4. Then pressing should be done through steel pressing die.
5. After pressing firing will be done by oil fired furnance at various temperatures.
Aquisition of Alumina:-
Alumina is a common name for the compound aluminium oxide, Al2O3. It is most known for its use in the Hall-Heroult process, where it is a raw material used in the production of aluminium metal. However, alumina has a number of important applications itself, though the majority of alumina is put into aluminium production.
Bauxite is typically found close to the surface, within 4-6 metres under the topsoil layer . Open cast mining is common - some 80% of bauxite worldwide is produced in surface mines, leaving just a fifth to be mined underground . Most bauxite produced is of an acceptable grade, and does not need a largeamount of further processing, unlike other base metal ores.
Production by country
As in 2010, Australia is the world’s largest producer of raw bauxite, mining just under 63 megatonnes in that year. China followed this with 30 megatonnes, and Brazil with 25. World reserves of bauxite are estimated at between 55 and 75 billion tonnes, most of which is located in Africa.
Purification and processing
Alumina is extracted from bauxite by the Bayer process, which remains the most economic method of producing alumina . The Bayer process is outlined below:
1.Bauxite ore is finely ground and dissolved in sodium hydroxide at 157 degrees Celsius. This produces a solution of sodium aluminate, NaAl(OH)4.
2. Impurities, containing high proportions of ferrous oxides, are filtered out and are known as ‘red mud’.
3. The aluminate solution is cooled and allowed to precipitate aluminium trihydroxide, Al(OH)3. Silicate impurities remain in solution and are removed.
4. The precipitate is calcinated (in effect, dried out) in a carefully-controlled kiln to yield aluminium oxide as a fine white powder.