Alumina-based ceramics materials, abrasive materials and method

Details Alumina-based ceramics materials, abrasive materials and method Alumina-based ceramics materials, abrasive materials and method

1990-10-01

1993-06-01

Bell, Mark L.

Abrasive tool making process, material, or composition

Miscellaneous

51309, 501153, B24D 300, C04B 3510

Patent

active

052155510

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to improved alumina-based sintered ceramics materials which are made of ultrafine crystals produced by a sol-gel method and has a high hardness and a high density, and to abrasive materials such as abrasive grains, grinding wheels, coated abrasives as well as to their manufacture.


BACKGROUND ART

Manufacture of high-density, alumina (Al.sub.2 O.sub.3)-based polycrystalline sintered ceramics abrasive grains by a sol-gel method is known. Japanese Patent Publication JP-A-56-32369 discloses gelation of alumina monohydrate together with a precursor or precursors of at least one reforming component followed by dehydration and drying as well as sintering. The reforming component used in this case includes oxides of Co, Hf, Mg, Ni, Zn, and Zr. Japanese Patent Publication JP-A-60-231462 describes a method for the manufacture of alumina sol/gel in which increase of density of alumina is promoted by the addition of .alpha.-alumina seed crystals, and also that a crystal growth control agent comprising oxides of Si, Cr, Mg, and Zr.may be added to the gel. In particular, Japanese Patent Publication JP-A-61-254685 describes a method of adding .alpha.-alumina, .alpha.-ferric oxide or their precursors as a nucleating agent into a sol, and that the gel may contain precursors of oxides of Mg, Zn, Co, Ni, Zr, Hf, Cr and Ti.
The alumina-based sintered abrasive grains produced by the sol-gel method disclosed in the above-described Japanese Patent Publication JP-A-60-231462 make use of .alpha.-aluminization of alumina-based dry gel, and further of reduction in transformation energy of .alpha.-aluminization caused by the addition of fine grains of .alpha.-alumina to an alumina sol. Sintering the dry gel at a temperature no higher than 1,400.degree. C gives rise to a ceramics material composed of crystals of a fine structure having a particle diameter of from 0.2 to 0.4 .mu.m and a density of no lower than 90% of the theoretical density. When the material is used as an abrasive grain, it shows grindability superior to that of a monocrystalline abrasive grain obtained by a conventional fusion method. This is considered to be ascribable to the fine crystalline structure of a particle diameter of from 0.2 to 0.4 .mu.m.
However, ceramics materials having a fine crystalline structure of a particle diameter of no greater than 0.2 .mu.m, a density of no lower than 90% of the theoretical density and a hardness of no lower than 16 GPa cannot be obtained by the method disclosed in Japanese Patent Publication JP-A-60-231462.


DISCLOSURE OF INVENTION

An object of the present invention is to provide a ceramics material having a density equal to or higher than that of conventional .alpha.-alumina-based ceramics material and having a fine crystalline structure of an average particle diameter of no greater than 0.2 .mu.m and a method for the production of the same.
Keeping an eye on the fact that abrasive grains composed of a fine crystalline structure exhibit excellent grindability, the present inventors have made intensive investigation with an expectation that the finer the crystalline structure is, the more grindability increases, and as a result they have completed the present invention.
The present inventors studied on influences which the size of crystals of a sintered material might have on the strength of alumina-based sintered ceramics material and performance of abrasive grains made of it. As a result they have found that in the case where the material has characteristics, i.e., a density of no lower than 95% of the theoretical density and a Vickers hardness of no lower than 2,000 kg/mm.sup.2, the strength of the ceramics material and the performances of abrasive grains made of it are increased to extremely high levels when the crystal size of the sintered material reaches a value of no higher than 0.2 .mu.m which has never been produced earlier.
That is, the present invention provides an .alpha.-alumina-based ceramics material which is made of crystals of an average particle diameter

REFERENCES:
patent: 4314827 (1982-02-01), Leitheiser et al.
patent: 4574003 (1986-03-01), Gerk
patent: 4623364 (1986-11-01), Cottringer
patent: 4786292 (1988-11-01), Janz et al.
patent: 4799938 (1989-01-01), Janz et al.
patent: 5009676 (1991-04-01), Rue et al.

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