 Optical recording media on which information is stored and method of making same |
| In this invention, as a main chain structure of polydiacetylene, A-type bonding and B-type bonding ... |
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| Disc recording medium and method of fabricating the same |
| Accordingly, it is an object of the present invention to provide a disc recording medium that is ... |
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| Foam sign |
| We claim: 1. A foam sign comprised of a laminated substrate and a multiplicity of laminated cut ... |
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| Plastics optical fibers |
| We claim: 1. Plastic optical fibers comprising as a core component a polymer predominantly ... |
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| Optical fibres based on polycarbonate fibres, and a process for the production thereof |
| What is claimed is: 1. In the process for the production of optical fibres based on aromatic ... |
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| High temperature polyether imide compositions and method for making |
| What is claimed is: 1. A blend of 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane/bis(4-aminophenyl) ... |
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| Digital video disk substrate |
| What is claimed is: 1. A digital video disk substrate of a polycarbonate having a viscosity-average ... |
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| Optical information recording medium |
| It is an object of the present invention to provide an optical information recording medium ... |
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| Resist hardening process having improved thermal stability |
| OF THE PREFERRED EMBODIMENTS With reference to FIGS. 7a-b, a method for hardening photoresists ... |
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Dense SiC ceramic products
| Details |
Inventors: Trigg, Mark B.; Drennan, John; Hay, David G.; Oh, Chull H.; Dietrich, Rainer;
Assignee: Western Mining Corporation Ltd. (Melbourne, AU); Foseco Pty. Ltd. (Padstow, AU)
Primary Examiner: Bell; Mark L.
Assistant Examiner: Gallo; Chris
Attorney, Agent or Firm: Larson and Taylor
A process for the liquid phase sintering of silicon carbide, comprising forming a shaped, consolidated powder body which, not allowing for binder, comprises a powder mixture containing at least 75 wt % silicon carbide and from 1 to 25 wt % (calculated as Al.sub.2 O.sub.3) of a powder comprising a source of aluminum selected from alumina, precursors for alumina and mixtures thereof. The body is heated in a non-oxidising atmosphere to a sintering temperature of from 1500.degree. C. to 2300.degree. C. to form a liquid phase and a resultant liquid phase sintered body. In said heating step, the body is heated in the presence of a source of magnesium which is distinct from the source of aluminum and comprises at least one of magnesia, precursors for magnesia, magnesium vapour and combinations thereof, whereby said liquid phase produces secondary oxide constituent. |
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DETAILED DESCRIPTION The present invention seeks to provide an improved form of dense articles produced from SiC powder, and to an improved method of producing such articles.
In particular, the present invention is directed to providing such articles utilising Al.
sub.
2 O.
sub.
3.
However, in the present invention, the use of Al.
sub.
2 O.
sub.
3 is under conditions which overcome problems, exemplified by the prior art and confirmed by our findings, encountered with the use of Al.
sub.
2 O.
sub.
3 alone.
As detailed above, use of Al.
sub.
2 O.
sub.
3 alone as an additive in densification of SiC powder necessitates use of relatively high sintering temperatures and relatively long sintering times.
However, even with recourse to such conditions, we have found that it can be difficult to achieve a satisfactory product.
Indeed, unless other conditions are satisfied such as use of a powder bed or coating as taught by Suzuki et al in U.
S.
Pat.
No.
4,354,911, the resultant product can exhibit minimal, if any, densification and low strength, such that the product can readily crumble.
Also, even where a useful level of densification is achieved, this can be limited to an external surface layer, with the interior of the product being less satisfactorily densified and the sectioned product exhibiting a macroscopically visible cored structure.
The interior of a product exhibiting such structure can have a relatively high degree of densification, even comparable to that of the surface layer.
However, we have found that densification and composition al differences, or both, between the surface layer and core can result in the product exhibiting cracks which reduce the mechanical properties of the product.
These differences can be such that the product as formed has failed, for example by propagation of cracks or spalling of the surface layer from the core, due to stress generated in the product on cooling from the densification temperature.
Moreover, streaks of Al.
sub.
2 O.
sub.
3, such as reported in the above mentioned article by Lange, can be present in the microstructure of the product, and it is believed that such streaks can facilitate crack formation or propagation
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Manufacturing Materials 
