Jul 12 2002
Thixotropic casting involves vibratory casting of highly thixotropic slips of very high solids loadings that are fluid only under vibration, using porous or nonporous molds. It is quite different from other conventional and new methods for solid casting ceramics, including vibroforming, vibraforming, in situ flocculation, direct coagulation casting, and gel casting. This is demonstrated in Table 1.
Table 1. Thixotropic casting in comparison with the alternatives.
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Vibroforming – Requires a cement for setting
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Cement is not required for setting
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Vibraforming – Requires excess counterions and centrifugation for settling
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Addition of organic deflocculant/binder and vibration are the only necessary steps
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In situ flocculation – requires the addition of urea and heating to control the pH to the isoelectric point
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No urea additions, heating, control of pH, or attainment of the isoelectric point are required
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Injection moulding – required large quantities (15-30wt%) of entraining polymer and pressurized mould feeding
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Only traces (<1%) of binder are needed and no pressure needed for filling of moulds
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Direct coagulation casting – requires control of the pH through an enzyme catalysed decomposition reaction
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No enzyme additions or control of pH are required
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Gel casting – requires use of a neurotoxin to cause polymeric gelling
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No polymer additive or polymerization are required
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Thixotropic casting is a little-known derivative of solid slip casting, having reportedly been used in the refractories industry in the early 1970's. Since then, the refractories industry has since largely embraced low-cement and ultra-low-cement castables.
It is also a suitable process for forming ceramic matrix composites and metal-ceramic functionally gradient materials.
References are available for this article by referring to the original text (see below).
Primary author: N. Ehsani, A.J. Ruys and C.C. Sorrell
Source: Abstracted from International Ceramic Monographs, vol 2, “Thixotropic Casting of Monolithic Nonclay Ceramics”, 1996.