Jasper, Carl Adrian (1990) Novel β' and α'/β' sialon ceramics. PhD thesis, University of Warwick.

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Abstract

ẞ +glass sialon materials are prepared with an Nd203 sintering additive. These materials exhibit similar property characteristics to equivalent ¥203-based compositions. With the absence of an Nd phase equivalent to YAG, phase relationships in the Nd-Si-Al-O-N system are examined to identify alternative grain boundary devitrification products. Materials in which the residual glass after sintering is recrystallised to give a mixture of Nd-N-O wollastonite and NdA103 are shown to exhibit high temperature property characteristics comparable to the conventional ẞ'+YAG sialon materials. The glass forming region in the Nd-sialon system is more extensive than for yttrium and new phases have been identified within the expanded volume. These also offer potential as fully crystalline matrix devitrification products. The most significant of these has the composition Nd3Si3Al30i2N2• B'«Nd3Si3Al30i2N2 materials are prepared and found to exhibit excellent properties up to * 1300°C.
The preparation of pure a' and α +ϐ’sialon materials by transient liquid phase sintering is particularly sensitive to starting composition. The fabrication of α +’ϐ +glass materials allows greater flexibility but high temperature properties are still sensitive to the chemistry and concentration of the liquid sintering additives and to post sintering heat treatments. α +’ϐ +glass materials are developed with a very minor amount of residual glass of a composition which allows full devitrification to form mainly YAG. Upon annealing, the a' species is particularly receptive to the non-stoichiometric elements which results in removal of the intergranular residual glass and subsequently increased solid/solid contact. To alleviate the interfacial energy anisotropy the YAG crystals are diffusively rearranged to an isolated equiaxed morphology. The limitations on high temperature use are mitigated by the discontinuous nature of this YAG phase. Component field trials and the potential of this new range of generic sialon materials are discussed.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > TP Chemical technology
Library of Congress Subject Headings (LCSH):	Ceramics, Composite materials, Metallurgy, Materials at high temperatures
Official Date:	May 1990
Dates:	Date Event May 1990 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Lewis, M. H. (Mike H.)
Sponsors:	Lucas Cookson Syalon Limited ; British Gas PLC
Extent:	[6], 89, [5] leaves : illustrations
Language:	eng

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