Minerals containing Alumina represent some 15% of the earth's crust. It is therefore an abundant material and virtually inexhaustible, unlike raw materials for many alloys developed for special applications. The combination of high thermal conductivity, low thermal expansion and high compressive strength leads to good thermal shock resistance, so alumina is suited to furnace use such as crucibles, tubes and thermocouple sheaths. High purity alumina can be used up to 1700℃ and is gas tight up to 1300℃. Few chemicals attack alumina. Alumina also shows good electrical insulation at high temperatures, good wear resistance and high hardness, making it suitable for components such as ball valves, piston pumps and deep drawing tools. Properties of alumina is as following:
Compound Formula |
Al2O3 |
Molecular Weight |
101.96 |
Appearance |
White rods |
Melting Point |
2040 °C (3700 °F) |
Boiling Point |
2,977° C (5,391°F) |
Density |
3.5 to 4.1 g/cm3 |
Solubility in H2O |
N/A |
Electrical Resistivity |
7 to 14*1010 Ω*m |
Poisson's Ratio |
0.22 to 0.24 |
Specific Heat |
870 to 940 J/kg*K) |
Tensile Strength |
210 to 290 MPa (Ultimate) |
Thermal Conductivity |
14 to 30 W/m*K |
Thermal Expansion |
6.8 to 8.2 µm/m*K |
Young's Modulus |
220 to 370 GPa |
Exact Mass |
101.948 g/mol |
Monoisotopic Mass |
101.94782 Da |
Alumina can be fabricated to tube, sheet, plate, rod and other shapes, for various application purpose. Alumina rod is generally immediately available in most volumes, including bulk quantities. Production process of alumina rod is: Raw material batching → grinding processing → pulping/mud making → molding → drying → powder making → hot-pressed sintering → sintering → inspection (cold processing)→ packaging and storage → delivery, for different shape and size product, different molding methods are applied including grouting, injection, drying, extrusion, cold isostatic pressing, hot pressing and hot isostatic pressing. Among them, injection molding is the earliest method and stilled wide used recently, and gypsum paper is mainly used for this method. Since molding is implemented via mud injection, it is widely used to produce low-cost alumina ceramics, and can also be used to produce large sized products with complex shape.