Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing
Patent
1989-10-31
1991-06-11
Group, Karl
Compositions: ceramic
Ceramic compositions
Carbide or oxycarbide containing
501 96, 501 98, 51309, C04B 3510
Patent
active
050232126
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The invention concerns a novel multiphase material based on alumina and aluminium oxycarbide and oxynitride; it also concerns the process for the preparation of that type of material and the uses thereof in the field of refractory materials and abrasives.
STATE OF THE ART
Refractory materials and abrasives based on electrically melted alumina (corundum) are well known. However those substances do not meet all the requirements made by the users thereof and efforts have been made over many years to improve them. It is known (French Pat. No. 1 308 862=U.S. Pat. No. 3,181,939) that the addition of 10 to 60% of zirconium oxide gives corundum substantially enhanced abrasive properties but the cost of zirconia means that the use thereof is reserved for particular applications.
In our French Pat. No. 2 460 315 (=U.S. Pat. No. 4,341,533) we described a new class of abrasives based on alumina and aluminium oxycarbides (Al.sub.4 O.sub.4 C and Al.sub.2 OC), produced by the treatment of melted alumina with a carbonaceous reducing agent, and cooling at a controlled speed. Those materials can also be used as refractory materials in iron and steel metallurgy.
At the present time there is a demand for new types of refractory materials and abrasives which combine qualities that are sometimes contradictory: moderate price, abrasive properties which are equal to or better than those of corundum-zirconia, stability in respect of the phases, resistance to thermal shock, wear and corrosion, capability of being wetted by metallurgical slags and metals, and resistance to alkali metals.
SUBJECT-MATTER OF THE INVENTION
A first subject of the invention is a novel class of electrically melted multiphase alumina-based materials characterised in that they have a combined carbon content of between 0.05 and 5% and a combined nitrogen content of between 0.05 and 5%, said contents preferably being between 1 and 4%. Those materials are also characterised by a fine crystalline structure (obtained by rapid cooling) and by the presence of the following phases: alumina (Al.sub.2 O.sub.3), aluminium oxynitride (AlON), aluminium oxycarbides (Al.sub.4 O.sub.4 C, Al.sub.2 OC) and aluminium oxycarbonitride (Al.sub.x C.sub.y N.sub.z O.sub.t) which are dispersed homogeneously in a corundum matrix.
A second subject of the invention is a process for the preparation of those novel materials characterised by effecting electrical melting of pure alumina or reducing electrical melting of an alumina-based compound such as bauxite, the melting operation being effected most generally in a polyphase electric arc furnace, and effecting an addition of carbonaceous reducing agent or nitrogen in predetermined amounts and very rapidly cooling the molten reaction product. The cooled product is then crushed and graded in dependence on the uses envisaged therefor.
A third subject of the invention is the application of those materials as high-performance abrasives.
A fourth subject of the invention is the application of those materials as refractory materials, in particular in the metallurgical industries.
DESCRIPTION OF THE INVENTION
We shall first describe the process for the preparation of the materials according to the invention. Operation is in a three-phase electric arc furnace with a maximum power of 170 kVA, and with a capacity of about 100 kg of electrically melted product. The molten alumina bath can be produced by melting pure alumina in the arc furnace itself or by reducing melting of bauxite, the reducing agent being a carbonaceous product such as coke in an amount which is so calculated as to reduce the oxides other than alumina and in particular the oxides of iron, silicon and titanium, to the state of metal which settles at the bottom of the furnace in the form of an Fe-Si-Ti alloy.
The carbonaceous electrodes are hollow so as to permit nitrogen to be injected into the arc. The carbonaceous reducing agent used is only slightly reactive coke (it would also be possible to use pieces of graphite) so that it is not o
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Dubots Dominique
Toulouse Pierre
Group Karl
Pechiney Electrometallurgie
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