A B S T R A C T Alumina/silicon carbide (Al 2 O 3 /SiC) composite ceramics with large self-crack-healing ability, high strength and high heat-resistance limit temperature for strength were developed and subjected to three-point bending. A semicircular surface crack 100 µm in diameter was made on each sample. Crack-healing behaviour was systematically studied, as functions of crack-healing temperature and healing time, and the fatigue strengths of the crack-healed sample at room temperature and 1373 K were investigated. Four main conclusions were drawn from the present study.(1) Al 2 O 3 /SiC composite ceramics have the ability to heal after cracking from 1273to 1673 K in air.(2) The heat-resistance limit temperature for strength of the crack-healed sample is ∼ =1573 K, and ∼ =68% of the samples fractured from outside the crack-healed zone in the testing-temperature range 873-1573 K. (3) The crack-healed sample exhibited very high fatigue limit at room temperature and also 1373 K. (4) The large self-crack-healing ability is a desirable technique for the high structural integrity of ceramic component.

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Fifteen kinds of mullite/SiC samples with different microstructures were prepared in order to examine the effect of Sic volume% and Sic grain size on mullite morphology and mechanical properties. Special attention was paid to the effect of heat-treatment on fracture stress. It is shown that these materials have damage self-healing characteristics. The best mullite/SiC system, within the given test conditions, is 20% by volume of Sic, having a grain sue of 0.56 pn, and the best condition for damage healing is a 1 h heat treatment at 1300°C in an air atmosphere.

Si3 N4 /SiC composite ceramics were sintered and subjected to three‐point bending on specimens made according to the appropriate JIS standard. A semi‐circular surface crack of 110 μm in diameter was made on each specimen. By using three kinds of specimen (smooth, cracked and crack healed), crack‐healing behaviour, cyclic and static fatigue strengths were determined systematically at room temperature and 1000 °C. The main conclusions are as follows: (i) Si3 N4 /SiC composite ceramics have the ability to heal after cracking; (ii) crack‐healed specimens showed similar cyclic and static fatigue strengths as smooth specimens, this being caused by crack healing; (iii) crack‐healed zones had a sufficient fatigue strength and most fractures occurred outside the pre‐cracked zone in those crack‐healed specimens.

Hydroxyapatite (HA) nano powders (20-60 nm) were synthesized using a sol-gel route with calcium nitrate and phosphoric acid as calcium and phosphorus precursors, respectively. Double distilled water was used as a diluting media for HA sol preparation and ammonia was used to adjust the pH. After aging, the HA gel was dried at 65°C and calcined to different temperatures ranging from 200-800°C. The dried and calcined powders were characterized for phase composition using X-ray diffractometry, elemental dispersive X-ray and Fourier transform infra-red spectroscopy. The particle size and morphology were studied using transmission electron microscopy. Calcination revealed HA nano powders of increased particle size and crystallinity with increase in temperature. For all calcinations temperatures, the particle size distribution analysis of HA powders showed skewed distribution plot. At temperature of 700°C and above, formation of CaO was noticed which was attributed to phosphorous volatilization. This study showed that high purity HA with varying degrees of crystallinity could be obtained using this simple technique.