Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-02-04
2003-06-03
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S469000, C428S472000, C428S697000, C428S698000, C428S701000, C428S702000, C427S585000, C427S255190, C427S255395, C051S309000, C407S119000
Reexamination Certificate
active
06572991
ABSTRACT:
BACKGROUND OF THE INVENTION
Aluminum oxide (alumina, Al
2
O
3
) exists in many metastable polymorphs such as &ggr;, &eegr;, &thgr;, &dgr;, &kgr;, and &khgr; in addition to the thermodynamically stable &agr;-Al
2
O
3
phase (corundum). When produced by chemical vapor deposition (CVD), Al
2
O
3
crystallizes into &kgr;-Al
2
O
3
and &thgr;-Al
2
O
3
modifications in addition to the stable &agr;-Al
2
O
3
. Earlier CVD coatings were usually mixtures of several polymorphs, the most commonly occurring metastable Al
2
O
3
modification being &kgr;-Al
2
O
3
. Today, both &agr;-Al
2
O
3
and &kgr;-Al
2
O
3
polymorphs are used as hard coatings, and they can be deposited in a controlled way by modern CVD technology shown, for example in U.S. Pat. Nos. 5,137,774 and 5,700,569.
Dopants of hydrogen sulfide (H
2
S), phorphorus chloride (PCl
3
) carbonoxysulfide (COS) or phosphine (PH
3
) can be applied in order to increase the growth rate and thickness uniformity of the alumina layers. The most commonly applied dopant is H
2
S as also disclosed in U.S. Pat. No. 4,619,886. While amounts of H
2
S in the total CVD gaseous mixture of from 0.003 to 1% by volume and temperatures of 700 to 1200° C. are broadly disclosed in that patent, all exemplifications of the process therein are below 0.5 vol % and generally around 0.1 to 0.3 vol % H
2
S used at temperatures of 1000-1030° C. H
2
S has been called the “magical dopant” in view of its effect on improving the growth rate and uniformity of Al
2
O
3
coatings applied by conventional CVD techniques at temperatures around 980° C. See, Oshika et al., “Unveiling the Magic of H
2
S on the CVD-Al
2
O
3
Coating”, J. Phys IV France 9 (1999), Pr 8-877-Pr 8-883.
CVD &kgr;-Al
2
O
3
is considered to exhibit morphological advantages (smaller grain size and lower porosity), lower thermal conductivity and even a higher hardness when compared with the CVD &agr;-Al
2
O
3
phase. These are important properties when metal cutting is concerned. However, at the relatively high temperatures (>1000° C.) reached during metal cutting, metastable &kgr;-Al
2
O
3
may transform to the stable &agr;-Al
2
O
3
polymorph. &ggr;-Al
2
O
3
, when deposited using physical vapor deposition (PVD) or plasma assisted CVD has been found to exhibit high hardness and good wear properties. See, for example, WO 9924634 and U.S. Pat. No. 5,879,823. However, &ggr;-Al
2
O
3
has not been available using conventional CVD techniques.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of this invention to avoid or alleviate the problems of the prior art.
It is further an object of this invention to provide &ggr;-Al
2
O
3
using conventional CVD.
In one aspect of the invention there is provided a coated body having as the outer layer, a layer of &ggr;-Al
2
O
3
deposited by chemical vapor deposition.
In another aspect of the invention there is provided a method of forming a coated body having a layer of &ggr;-Al
2
O
3
comprising coating the body with a gaseous mixture of AlCl
3
, CO
2
, H
2
and H
2
S at a temperature of from about 600 to 800° C., the H
2
S being present in amounts of at least 0.7% of the total mixture.
REFERENCES:
patent: 5137774 (1992-08-01), Ruppi
patent: 5587233 (1996-12-01), König et al.
patent: 5674564 (1997-10-01), Ljungberg et al.
patent: 5700569 (1997-12-01), Ruppi
patent: 5879823 (1999-03-01), Prizzi et al.
patent: 6139921 (2000-10-01), Täschner et al.
patent: 6210726 (2001-04-01), Schiller et al.
patent: 6254984 (2001-07-01), Iyori
patent: 686707 (1995-12-01), None
patent: 9924634 (1999-05-01), None
Hirohisa Iisuka et al., “Growth of Single Crystalline -Al2O3Layers on Silicon by Metalorganic Molecular Beam Epitaxy”,Applied Physics Letters, US, American Institute of Physics, New York, vol. 61, No. 25, Dec. 21, 1992, pp. 2978-2980.
Yom, S.S. et al., Growth of &ggr;-Al2O3Thin Films on Silicon by Low Pressure MEtal-Organic Chemical Vapour Deposition,Thin Solid Films, CH, Elsevier-Sequoia S.A. Lausanne, vol. 213, No. 1, May 29, 1992, pp. 72-75.
Ueki Mitsui et al., “CVD Coating of Alumina Film on WC-betat-Co Cemented Carbide by Using Hydrogen Sulphide Contained Atmosphere”,Journal of The Japan Society of Powder and Powder Metallurgy, Jun. 1994, published by Funtai Funmatsu Yakin Kyokai, Kyoto, Japan, vol. 41, No. 6, Jun. 1994, pp. 727-731.
Patent Abstracts of Japan, vol. 1998, No. 8, Oct. 3, 1998, & JP 10 068076 A (Mitsubishis Materials Corp), Mar. 10, 1998.
Oshika et al., “Unveiling the Magic of H2S on the CVD-Al2O3Coating”, J. Phys IV France 9 (1999), Pr 8-877-Pr-8-883. No Month.
Jones Deborah
McNeil Jennifer
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