WETTING BETWEEN PROSPECTIVE CRUCIBLE MATERIALS AND THE BA-CU-O MELT

The reaction between the Ba-Cu-O melt (with a Ba to Cu ratio of 3-5 or 3-7) used for crystal pulling of Y-123 and several prospective crucible materials (MgO, Y2O3, Al2O3, and YSZ) has been investigated by dipping these materials i-to the melt at 985-degrees-C and 1050-degrees-C in air. For comparison, MgO, YSZ, LaAlO3, and SrTiO3 single crystals were also investigated. In the case of MgO single crystals, no wetting or reactive layer has been observed, although with increasing time an increasing amount of MgO has been dissolved into the melt. The contact angle between melt and MgO single crystal can be estimated to be about 40-degrees, assuming a surface tension of 0.3 N/m. For all other materials, increasing time was accompanied by increasing wetting and/or an increasing reaction layer. For MgO polycrystals increased wetting with increasing time has been observed. For example, it takes about 30 min to wet the first 10 mm. The melt completely permeates samples with an apparent density of up to 85%. However, the permeated depth becomes very thin in samples with an apparent 95% density. It was found that Y2O3 is a better barrier to the melt at lower densities because even at 85% density the permeated layer is very thin, but the surface wetting occurs at a slightly faster rate for Y2O3 than for MgO.