Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Patent
1993-06-16
1995-02-07
Bell, Mark L.
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
501120, 501127, C09C 168, C04B 3510
Patent
active
053872681
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a sintered alumina abrasive grain comprised of alpha-alumina crystals and having a microcrystalline structure, and to a grinding wheel and other abrasive products made of the sintered alumina abrasive grain.
The abrasive grain of the invention has high hardness and toughness, and therefore, a grinding wheel, a coated abrasive, and other abrasive products made of the abrasive grain have excellent grinding performances.
BACKGROUND ART
Grinding performances of a sintered alumina abrasive grain are generally enhanced with a decrease of crystal size and an increase of hardness thereof. It is known that, to make microcrystals, magnesium oxide as a sintering aid is added into alumina whereby a magnesium spinel is formed at the crystalline grain boundaries. Further, in Japanese Unexamined Patent Publication No. 56-32369, it has been proposed that, in a process for making an abrasive grain by a sol-gel method, cobalt, hafnium, magnesium, nickel, zinc, zirconium or other metal is added to alumina prior to the step of a gel formation to yield a sintered alumina abrasive grain having a microcrystalline structure.
In Japanese Unexamined Patent Publication No. 60-231462, it has been proposed to dispersing finely divided alpha-alumina seeds in an alumina sol whereby a microcrystalline structure having a crystal size of a submicron order is obtained. In this publication, it is taught that an oxide of silicon, chromium, magnesium or zirconium may be added to an alumina gel.
In Japanese Unexamined Patent Publication No. 61-254,685, it has been proposed that, in a process for making an alumina abrasive grain by a sol-gel method, a nucleating agent such as alpha-alumina or alpha-ferric oxide is added to alumina prior to the drying step. It is taught in this publication that a precursor of an oxide of magnesium, zinc, cobalt, nickel, zirconium, hafnium, chromium or titanium may be added into an alumina gel dispersion.
In Japanese Unexamined Patent Publication No. 64-11184, it has been proposed that, in a process for making an alumina abrasive grain by a sol-gel method, an oxide of zirconium, hafnium, cobalt, nickel, zinc, magnesium and/or a rare earth metal element, or a precursor of the oxide is impregnated in a calcined alumina grain whereby an abrasive grain characterized in that the added metal element is distributed at a higher concentration on the surface and in the vicinity of the surface than that in the inner portion is obtained.
Sintered alumina abrasive grains having a microcrystalline structure can be produced by the above-proposed processes, but the uniformity of the microcrystalline structure and the hardness are not completely satisfactory. Therefore, there is an eager desire of abrasive grains having a uniform microcrystalline structure and a high hardness, and exhibiting excellent grinding performances.
DISCLOSURE OF INVENTION
In view of the foregoing, the object of the invention is to provide a sintered alumina abrasive grain which have characteristics desired for abrasives, especially excellent hardness and toughness and which provide abrasive products having excellent grinding performances.
In accordance with the present invention, there is provided a sintered alumina abrasive grain characterized as being comprised of alpha-alumina crystals and a spinel crystalline phase which does not form a continuous phase but is in the form of finely divided discrete crystals which are deposited on triple points in crystal boundaries and are substantially uniformly distributed over the sintered alumina abrasive grain.
Preferably, the alpha-alumina crystals have an average particle diameter of not larger than 1 micron, and the spinel crystalline phase is composed of alumina and an oxide of at least one metal element selected from nickel, magnesium and zinc.
In accordance with the present invention, there are further provided a grinding wheel, a coated abrasive, and other abrasive products, which are made of the above-mentioned sintered alumina abrasive grain.
BRIEF DESCR
REFERENCES:
patent: 4314827 (1982-02-01), Leitheiser et al.
patent: 4906255 (1990-03-01), Nikitina et al.
Hiraiwa Tadashi
Ono Fumiyoshi
Bell Mark L.
Jones Deborah
Showa Denko Kabushiki Kaisha
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