Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Patent
1994-10-26
1996-12-17
Jones, Deborah
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
51307, 51308, 106 3, 106 8, 451 28, 451 36, 451 41, 451 56, 451 63, B24B 100, B24D 300
Patent
active
055848982
DESCRIPTION:
BRIEF SUMMARY
Beryllium has many properties that make it desirable for use in severe environments. Such properties include low density, good thermal conductivity, good infrared reflectivity, high stiffness, low coefficient of thermal expansion at cryogenic temperatures, and small nuclear cross section. However, the high toxicity of beryllium powders has minimized its use. In addition, superpolished beryllium surfaces tend to lose their low scatter quality due to oxidation. Beryllium also has a relatively high porosity, which can result in deleterious voids and etches forming on the finished product.
One such environment is computer hard disk drives and read-write heads. Hard disk drives require a thin disk, but one hard enough to avoid breakage at high speed, and hard enough to withstand thermal changes and also provide a smoother surface finish, thereby resulting in increased memory capacity.
As a result of the foregoing drawbacks of beryllium, when high strength silicon carbide (SIC) has been used in lieu of beryllium, it has demonstrated considerable advantages and much success in severe environment applications. It exhibits excellent oxidation and creep resistance, and is believed to outerform beryllium in many if not all applications.
For many applications including hard disk drive, super conductor wafer applications and high-reflective optics, superpolished surfaces are required. Conventional polishing techniques are capable of producing a polished surface having a surface roughness on the order of about 100.ANG. RMS (root mean squared). However, decreased surface roughness has obvious advantages depending on the application. For example, in computer hard disk drive applications, surface roughness less than 10.ANG. RMS would allow substantially more information per disk area. Similarly, in laser application, a 10.ANG. RMS mirror surface would allow for more efficient operation by creating higher laser reflectivity (therefore lower laser absorption), thus lessening the possibilility of mirror burns.
Accordingly, there exists a need for producing hard materials having superpolished surfaces with a surface roughness below about 20.ANG. RMS, and indeed, as low as about 0.5.ANG. RMS even with substrate diameters of 10-12 inches or larger.
SUMMARY OF THE INVENTION
The problems of the prior art have been solved by the present invention, which provides a process for superpolishing hard materials, and the resulting superpolished hard materials having surface roughnesses below about 20.ANG. RMS. The present invention is especially applicable to the polishing of silicon carbide, CVD-coated (chemical vapor deposit) silicon carbide, pure CVD silicon carbide, Alsimag.TM. (AIO.sub.2 TiC), alumina, sapphire, and other hard ceramic materials. The low angstrom finish can be achieved even with wafers having diameters as large as about 10 to 12 inches or larger. Flats, aspherics, cylinders, toroids, etc. can all be polished in accordance with the instant invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial view of the apparatus used in accordance with one embodiment of the present invention; and
FIG. 2 is an exploded partial view of the apparatus used in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, there is provided a polishing compound capable of providing hard ceramic materials with fine surface finishes when used in accordance with the present process. The polishing compound includes a polishing agent, which in turn includes a dispersion of oxides of alumina in water, the alumina having particle diameters of 0.05 microns and the dispersion having a pH of about 4. The polishing agent is available commercially from Nyacol Products, Inc. of Massachusetts. Alternatively, the polishing agent that can be used is a colloidal alumina polishing compound available commercially from Solutions Technology as "200A Ultra Sol Colloidal Alumina Compound". The polishing agent is then combined with deionized or distilled water and a
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Jones Deborah
Planar Technologies Inc.
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