In this work the densification of YBa2Cu3O7-x (or 123) ceramic starting from compacts with two compositions having lower Y-contents relative to the superconducting cationic Y:Ba:Cu ratios equal to 1.0:2.0:3.0 were analyzed. Thermal evolution of the powders was monitored by DTA-TG, under O2-flow, up to the peritectic decomposition temperature, Tp»1050ºC. The sintering/densification behavior of these compacts was followed by dilatometric runs under the same DTA-TG conditions. The main sintering mechanisms were analyzed using theoretical models fitted to the densification curves allowing the calculation of the apparent sintering enthalpies. According to dilatometric and DTA-TG runs, the liquid phase sintering (LPS) mechanism controls 85% of the total shrinkage in compact of composition Y0,7Ba2,0Cu3,3Ox (C2) presenting an early grain growth (GG) contribution to densification from 860ºC. It should be noted no GG was detected in compact of composition Y0,7Ba2,3Cu3,1Ox (C1) at temperatures lower than 900ºC. From 900ºC the LPS is thought to be present by the rearrangement stage and then, in the range 930-975ºC, the solution-precipitation process in LPS would be the main densification mechanism.

En este trabajo se analiza la densificación del cerámico superconductor YBa2Cu3O7-x (123) a partir de compactos conformados con dos composiciones deficientes en itrio con respecto a la relación catiónica superconductora Y:Ba:Cu = 1,0:2,0:3,0. La evolución térmica de los polvos se estudió por ATD-TG, en atmósfera de O2, hasta la zona de descomposición peritéctica del sistema YBa2Cu3O7-x (» 1050ºC). La densificación de estos compactos se analizó por medio de dilatometrías realizadas bajo similares condiciones a las establecidas para los ATD-TG. Los mecanismos dominantes del sinterizado fueron analizados por medio de modelos aplicados a las curvas dilatométricas. De acuerdo a los datos combinados de dilatometrías y ATD-TG, se verifica que el mecanismo de sinterización por fase líquida (SFL) controla el 85% de la contracción total del compacto de composición Y0,7Ba2,0Cu3,3Ox (C2), el cual presenta un temprano crecimiento de granos (CG) desde los 860ºC. El proceso de CG no se detecta en el compacto de composición Y0,7Ba2,3Cu3,1Ox (C1) a temperaturas menores a los 900ºC. Para ambas composiciones se postula que, a partir de 900ºC, el mecanismo de SFL está presente por medio del proceso de reacomodamiento y luego, en el rango 930-975ºC, el mecanismo de solución-precipitación es el proceso dominante en el SFL.

<i>O método sol-gel foi usado para obter pós com 3 composições estequiométricas correspondente a mulita (3 Al2O3.2SiO2): (i) alumina comercial e sílica por sol-gel, (ii) alumina e sílica por hidrólise parcial de alcóxido, (iii) alumina e sílica por hidrólise simultânea de alcóxido. Tetroetiloctosiliceto (teos) e tri-sec-butóxido de alumínio foram usados como precursores alcóxidos. Além disso, 5% em peso de bário, adicionado nas soluções precursoras como acetilacetonato de bário foi usado como aditivo para estudar sua influência na densificação e formação da fase mulita. Os pós precursores foram prensados uniaxialmente para formar compactos a verde, e posterior aquecimento a 1350</i>°<i>C por 2 h para obter corpos densificados. A difração raios X dos pós, preparados por moagem dos compactos sinterizados, mostrou diferenças importantes. Foram observadas maior densificação e formação de fase vítrea nas amostras dopadas com bário.</I>

The sol-gel route was employed to obtain three different powders with the stoichiometric composition corresponding to mullite (3 Al2O3.2SiO2): (i) commercial alumina and silica from sol-gel, (ii) alumina and silica by alkoxide partial hydrolysis, (iii) alumina and silica by alkoxide simultaneous hydrolysis. Tetraethylorthosilicate (TEOS) and aluminium tri-sec-butoxide were used as alkoxide precursor. Moreover, 5 wt% of barium, incorporated to precursor solutions as Ba-acetilacetonate, was used as additive to study its influence on densification and mullite phase formation. The precursor powders were pressed uniaxially to form green compacts, after that all samples were heated to 1350 °C for 2 hours to obtain densified pellets. X-ray diffration patterns of powders, obtained by milling of sintering compacts, showed important differences. In barium doped samples a higher grade of densification and a greater glassy phase formation were observed.