Plasma Premium Grade White Alumina
A&A Coatings material is a superfine premium grade of white, high purity, fused aluminum oxide designed to produce hard, dense ceramic coatings with excellent wear resistance.
This white alumina is designated as a premium grade material because it has excellent flow properties, as a result of its narrow particle size distribution, controlled particle shape and minimal percentage of ultrafine particles. Powder feed is smooth and consistent, producing coatings which are uniform and smoother as-sprayed.
In addition, coatings of premium grade white alumina exhibit higher wear resistance than coatings of standard grade Aluminum Oxide powders.
Coatings of this material are recommended for resistance to wear by abrasive grains, hard surfaces, particle erosion and cavitation at all temperatures below 540°C (1000°F). They can be used for many applications in any industry, particularly in mechanical seal areas such as pump seals.
Premium grade white alumina should also find use on applications where the requirement for wear resistance is accompanied with a need for a low coefficient of friction, such as computer recording heads or any machine element in contact with fibers and threads in the textile industry. These coatings can be finished to any one of a number of surface textures, over which the fiber or thread passes, to provide a particular friction characteristic.
Premium grade white alumina coatings also provide high dielectric strengths, which make them particularly suitable for use in the electronic industry. Plasma coatings typically show 450-500 volts/mil dielectric strength.
Material Powder Characteristics
| Typical Composition: | Aluminum Oxide (99.5%) Other Oxides (0.5%) |
| Typical Size Range: | -20 +5 microns |
| Melting Point: | 2038°C (3700°F) approximate |
Physical Properties of Coating
| Texture, as sprayed, (microinches RMS): | 110-150 |
| Finish, ground (microinches aa): | 15-20 |
| Macrohardness: | Rc65 |
| Cross-Sectional Hardness (DPH300): | 850-1000 |
| Density (g/cc): | 3.43 |
| Coating Weight (lb/ft2/.001″): | .018 |
| Porosity | Negligible |
| Bonding: | 5000psi |
| Dielectric Strength (Volts/Mil): | 450-500 |
| Thickness Limitation: | 0.020” |
Wear Resistance
Abrasive wear tests, using a water slurry of aluminum oxide, have been conducted to determine the relative abrasive grain wear resistance of premium grade white alumina coatings. Coatings of premium grade white alumina exhibit wear resistance approximately 100% higher than coatings of standard grade white alumina.
Finishing
Because the as-sprayed texture of the coating is so smooth, finishes down to 20 microinches aa (.5 microns) are readily obtainable by brushing. Good finishes have been obtained by using a urethane backed flexible brush (#167, manufactured by Minnesota Mining and Manufacturing) with Clover brand Grade A lapping compound (-280 grit) and with a slurry of 240-280 grit silicon carbide in water. The coating changes color from white to gray when brushed with lapping compound, because of the oil in the lapping compound. The discoloration is easily removed by vapor degreasing. The coatings can be wet ground with 150 grit and 400 grit diamond wheels, using standard speeds and feeds for grinding ceramics.