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Title: The fabrication and microstructural evolution, at elevated temperatures, of Syalon Ceramics
Author: Winder, Stephen Morley
ISNI:       0000 0001 3570 7231
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1985
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A number of experimental grade Syalon Ceramics, pressureless sintered materials prepared from the system Y-Si-Al-O-N, were prepared at Lucas-Cookson Syalon Ltd. (Birmingham). Different series of ceramics were composed with of α-Si3N4 powder provided by different manufacturers, and each series contained alloys of varying (effective) AIN content. Microstructural characterisation of selected alloys was completed using the techniques of optical microscopy, x-ray diffractometry, electron microscopy with x-ray microanalysis, and energy loss spectroscopy. For 'as-sintered' ceramics, the results Indicate a trend in microstructural parameters with (effective) AIN content, such that the mean Al2O3 substitution level in the βSi6-zAlzOzN8-z (major) phase, and the N/O ratio of the inter-β (minor) glassy phase, both increase with Increased AIN addition. A linear relationship between increasing (Y + 0) content in the 'as mixed' alloy composition and increasing glass volume fraction in the microstructure, formed under given sintering conditions, was demonstrated. Passive oxidation occurred during heat-treatment in air, in the temperature range 1100-1500°C, and formation of β-Y2Si2O7, crystals on the scale surface was noted. Two crystalline phases, Y3Al5O12 (YAG) and α, (yttrium disilicate), were produced during devitrification of the intergranular phase, in the temperature interval 1100-1500°C. The volume ratio Y3Al5012 : Y2Si2O7, in the heat-treated microstructures, was found to increase as heat-treatment temperature and glass nitrogen content Increased. Creep tests were performed in the temperature range 1100-1300°C and enhanced creep resistance was demonstrated for materials of lower intergranular phase content, in which nitrogen levels are higher. Morphological changes occurring in the sub-surface and bulk of the ceramics, due to oxidation and crystallisation reactions, were found to cause a time dependent transient in creep behaviour.
Supervisor: Not available Sponsor: Lucas Cookson Syalon Limited
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; TA Engineering (General). Civil engineering (General)