A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

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The K2ZrF6 wetting process: Effect of surface chemistry on the ability of a SiC-Fiber preform to be impregnated by aluminum

International audienceSiC-ceramic materials, either as flat substrates or porous fiber preforms, are spontaneously wetted by aluminum at 700 °C to 800 °C when they have been pretreated with an aqueous solution of K2ZrF6. The wetting enhancement effect results from exothermic chemical reactions occurring at the SiC/Al interface. The first phenomenon thought to occur is a disruption of the alumina film covering liquid aluminum due to a reaction of A12O3 with K2ZrF6. Then alumina is totally dissolved at low temperatures by potassium/aluminum mixed fluorides, giving rise to a very fluid cryolitic liquid spreading out on the surface of liquid aluminum and to the true SiC/Al interface. Simultaneously, a large evolution of heat occurs, mainly due to the reduction of K2ZrF6 by aluminum and the formation of Al3Zr. The impregnation of 2D-SiC/SiC preforms by aluminum is modeled, and the effect of both the contact angle decrease and local temperature rise on the impregnation of the preforms, e.g., by gravity casting, is established

Estudo da viabilidade de obtenção de cerâmicas de SiC por infiltração espontânea de misturas eutéticas de Y2O3-AlN, Y2O3-Al2O3, R2O3-AlN Study of the viability to produce SiC ceramics by Y2O3-AlN, Y2O3-Al2O3, R2O3-AlN spontaneous infiltration

As cerâmicas de carbeto de silício, SiC, apresentam excelentes propriedades quando obtidas por infiltração de determinados líquidos. Na infiltração o tempo de contato entre o líquido e o SiC a temperaturas elevadas é muito curto, diminuindo a probabilidade de formação dos produtos gasosos que interferem negativamente na resistência da peça final, como ocorre na sinterização via fase líquida. O objetivo deste trabalho é mostrar uma correlação entre molhabilidade e capacidade de infiltração de alguns aditivos em compactos de SiC. Foram preparados compactos de SiC por prensagem isostática a frio e posterior pré-sinterização via fase sólida. Nesses compactos foram infiltradas misturas de Y2O3-AlN, Y2O3-Al2O3, R2O3-AlN, nas composições eutéticas, 10 ºC acima da temperatura de fusão das respectivas misturas por 4, 8 e 12 min. Após infiltração, as amostras foram analisadas quanto à densidade aparente e real, fases cristalinas, microestrutura e grau de infiltração, sendo que as amostras infiltradas com Y2O3-AlN apresentaram melhores resultados.<br>Silicon carbide ceramics, SiC, obtained by liquid infiltration have shown excellent properties. In infiltration process the contact time of the liquid with SiC at elevated temperature is short, decreasing the probability to form gaseous products that contribute negatively in the final product properties. This phenomenon occurs during SiC liquid phase sintering. The purpose of the present study was to investigate the correlation between wettability and infiltration tendency of some additives in SiC compacts. SiC compacts were prepared by cold isostatic pressing followed by solid phase pre-sintering. Into the compacts were introduced Y2O3-AlN, Y2O3-Al2O3, R2O3-AlN liquids with eutectic compositions at a temperature 10 ºC higher than the melting point of each mixture for 4, 8 and 12 min. Before infiltration, the samples were analyzed by determining densities, crystalline phases, and degree of infiltration. The better results were presented by sample with infiltration with the Y2O3-AlN mixture