Plasma White Alumina
Quick Spec Summary
| Spec | Standard Grade | Premium Grade |
| Composition | Al₂O₃ 98.5%, SiO₂ 1%, other oxides balance | Al₂O₃ 99.5%, other oxides 0.5% |
| Size range | -270 mesh +15 microns, or -53 +15 microns | -20 +5 microns (finer cut) |
| Melting point | 2000°C (3630°F) | 2038°C (3700°F) |
| Macrohardness | Rc60 | Rc65 |
| Cross-sectional hardness | 690 DPH300 | 850–1000 DPH300 |
| Bond strength | Good | 5000 psi |
| Service temperature | ≤540°C (1000°F) | ≤540°C (1000°F) |
| Thickness limit | 0.020″ (0.5mm) | 0.020″ |
| Porosity | Low | Negligible |
| Surface finish achievable | 45–50 µin aa ground | 15–20 µin aa ground; down to 20 µin aa (0.5 micron) brushed |
| Wear resistance | Baseline | ~100% higher than standard grade |
| Emissivity | 0.2–0.3 | |
| Thermal shock resistance | Very good |
Need a quote? Call 888-725-0150 or send us a request. Our team replies the same business day.
Two Grades, One Family
A&A Coatings runs white alumina in two grades, and the difference isn’t cosmetic. Both start from aluminum oxide and produce hard, dense ceramic coatings that resist wear from fibers and threads, resist erosion at high temperature, work as thermal barriers, and — when sealed — hold up as electrical insulation at elevated temperatures.
The premium grade earns its name through purity and particle control. At 99.5% Al₂O₃ with a narrow, finer particle size distribution and controlled particle shape, the powder feeds smoother and more consistently through the gun. That translates directly into the coating: a smoother as-sprayed texture, a finer achievable finish, higher hardness, and — in A&A’s own slurry testing — roughly double the abrasive wear resistance of the standard grade.
Standard grade remains the right call for general wear and thermal-barrier work where that extra purity and finish aren’t load-bearing requirements. Premium grade is the one to spec when the job also needs a low coefficient of friction, a very fine surface, high dielectric strength, or the extra wear margin.
Composition
Standard Grade
| Typical composition | Aluminum oxide (98.5%), silicon dioxide (1%), other oxides (balance) |
| Typical size range | -270 mesh +15 microns, or -53 +15 microns |
| Melting point | 2000°C (3630°F) approximate |
Premium Grade
| Typical composition | Aluminum oxide (99.5%), other oxides (0.5%) |
| Typical size range | -20 +5 microns |
| Melting point | 2038°C (3700°F) approximate |
The premium grade’s narrower, finer cut is what gives it the smooth, consistent powder feed — and the smoother as-sprayed coating that follows from it.
Physical Properties of the Coating
Standard Grade
| Texture, as sprayed | 325–400 microinches RMS |
| Finish, ground | 45–50 microinches aa |
| Macrohardness | Rc60 |
| Cross-sectional hardness | 690 DPH300 |
| Density | 3.3 g/cc |
| Coating weight | 0.017 lb/ft² per 0.001″ |
| Porosity | Low |
| Bonding | Good |
| Emissivity | 0.2–0.3 |
| Thermal shock resistance | Very good |
Premium Grade
| Texture, as sprayed | 110–150 microinches RMS |
| Finish, ground | 15–20 microinches aa |
| Macrohardness | Rc65 |
| Cross-sectional hardness | 850–1000 DPH300 |
| Density | 3.43 g/cc |
| Coating weight | 0.018 lb/ft² per 0.001″ |
| Porosity | Negligible |
| Bonding | 5000 psi |
| Dielectric strength | 450–500 volts/mil |
| Thickness limitation | 0.020″ |
Side by side, the gap is clearest in as-sprayed texture — 325–400 RMS for standard against 110–150 for premium — and in cross-sectional hardness, where premium runs 850–1000 DPH300 against standard’s 690.
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.
Coatings of this material — both grades — are recommended for resistance to wear by abrasive grains, hard surfaces, particle erosion and cavitation at all temperatures below 540°C (1000°F).
Thickness Limitation
Both grades are designed for thin coatings, not more than 0.020″ (0.5mm) thick. If sprayed thicker, the probability of cracking and delamination increases rapidly, as is the case with thick coatings of all fine powders.
Surface Preparation
Plasma Sprayed White Alumina can be applied to most substrates which have been cleaned to remove surface oxides. This cleaning is accomplished with a light grit blast. Additionally, a bond coat is required in most cases. Contact us for substrate specific requirements.
Finishing
Standard grade can be ground to required finish size and polished to a 20 surface finish.
Because the as-sprayed texture of premium grade coating is so smooth, finishes down to 20 microinches aa (0.5 microns) are readily obtainable by brushing. Good finishes have been obtained 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. Premium grade coatings can also be wet ground with 150 grit and 400 grit diamond wheels, using standard speeds and feeds for grinding ceramics.
Applications
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.
QA / Spec
AS9100 and ISO 9001 certified. NADCAP requirements met. Our lab checks thickness, bond strength, hardness, and microstructure before parts ship. Customer specs welcome, with certification paperwork supplied on request.
Start a Quote
Call 888-725-0150 or send your part details through our quote form. Same business day reply. Tell us which grade you’re speccing — or send your application details and we’ll recommend one.
