Physical properties
ALPHA alumina has stable crystal phase, high hardness and good dimensional stability, especially it can improve the compactness of ceramics. In addition, it has high resistivity and good insulation performance.
Uses
Alpha-alumina powder is widely used as a raw material of an abrasive.
Application
Fine polishing materials, metal products, semiconductor materials, plastics, vacuum coatings, special glass raw materials, fluorescent materials, special glass, composite materials and resin materials.
General Description
In the past few years the electronics industry has increased the use and manufactured quantity, as well as demand for higher quality, of high purity alumina substrate chips for circuitry substrates used in component parts of computers and other devices such as switches and calculators. These chips need to be produced from a very pure alpha alumina, utilized as a substrate for the deposition of the various electronic pathways. Impurities in this alumina would cause leakage of the electric current through the substrate and cause dielectric losses which make such chips unreliable.
Synthesis
To a large (12L) round bottom flask was added 4,000 grams (g) of water (H2 O), 1500 g of aluminum metal pellets (99.97% pure), and 800 milliliters (ml) of concentrated huydrochloric acid. After about 4 cubic feet (ft3) of hydrogen gas was evolved, as measured by a wet test meter, 1250 ml of concentrated hydrochloric acid and 1000 ml of water were added over a span of 25 hours at an interval time of 20 minutes for portions measuring 200 ml hydrochloric acid and 200 ml water. During this interval adding time period, 4500 g of additional aluminum pellets were introduced to the reaction mixture. Digestion at 96°-980° C. was carried out for 17 hours until 60 ft3 of hydrogen gas was evolved, at which time the sol was collected and the undissolved solids were filtered out by passing the sol through a fine linen cloth. This sol was then used in Example II below and produced a solids content ranging from about 0.1 to about 15.5% by weight solids based on aluminum with a preferred solids content of about 14 to about 15.5%.
