Synthesis of highly porous Al2O3-YAG composite ceramics

Al2O3-YAG composite was obtained by sintering of porous Al2O3 preforms infiltrated with water solution of aluminium nitrate nonahydrate, Al(NO3)(3)center dot 9H(2)O and yttrium nitrate hexahydrate, Y(NO3)(3)center dot 6H(2)O. Al2O3 preforms with porosity varying from 26 to 50% were obtained after sintering at temperature ranging from 1100 to 1500 degrees C. Sintering of the infiltrated Al2O3 preforms led to formation of YAG particles due to reaction between Y2O3 and Al2O3 at high temperature. It was found that variation of porosity of alumina preforms and sintering temperature is an effective way to fabricate Al2O3-YAG composite with an unusual combination of properties. Open porosity was in the range 15-35%, specific surface was 0.6-6.1 m(2)/g, pore size was 150-900 nm whereas compressive strength was from 50 to 250 MPa. The effect of sintering temperature on YAG formation and phase composition were investigated using X-ray diffractometry whereas microstructure of the composite was analysed by scanning electron microscopy

Biomimetic synthesis and properties of cellular SiC

Biomorphous beta-SiC ceramics were produced from several species of wood such as ash, wild cherry, black alder, Persian walnut, sessile oak and European hornbeam. The wood was pyrolysed, impregnated with tetraethyl orthosilicate (TEOS) sol in repeated cycles and thermally treated at 1800 degrees C in vacuum. Four specimen groups included charcoal and three groups with 1, 3 and 5 cycles of impregnation were analyzed. Flexural and compressional strength of charcoal and woodlike SiC ceramics were measured using three-point and compression testing in different directions. Experimental results showed that mechanical properties of woodceramics were improved by repeating of impregnation cycles. Porosity measurement, dilatometric analysis, XRD and SEM analysis were used to study the macroscopical and microscopical properties of the resulting biomorphic SiC ceramics

Transformation of Cs-exchanged clinoptilolite to CsAlSi5O12 by hot-pressing

Dense CsAlSi5O12 was successfully obtained by hot pressing of Cs-exchanged clinoptilolite at 900 degrees C. Simultaneous application of high temperature and mechanical pressure allowed formation of CsAlSi5O12 at temperature considerably lower than 1150 degrees C which was the lowest reported temperature of CsAlSi5O12 formation in pressureless sintered Cs-exchanged clinoptilolite. CsAlSi5O12 formation was preceded by complete amorphisation of Cs-exchanged clinoptilolite in temperature range between 700 and 900 degrees C. Bearing in mind that clinoptilolite possesses high affinity for Cs cation it is believed that hot pressing of Cs-exchanged clinoptilolite might be an efficient way to immobilize radioactive Cs by its incorporation into crystal lattice of stable CsAlSi5O12. The samples sintered at 950 degrees C had relative density about 84% of theoretical density and open porosity of only 6% which is expected to result in low Cs leaching rate