The role of Si impurities in the transient dopant segregation and precipitation in yttrium-doped alumina

Y-doped alumina was sintered at 1500 degrees C for 10 h under ultra-clean experimental conditions without experiencing any abnormal grain growth. The yttrium was fairly homogeneously distributed at the grain boundaries, with a mean value of (Gamma) over bar (Y) = 5.5 at nm(-2). The Y-Al-O precipitates in the clean, Y2O3-doped alumina specimen were the YAP (YAlO3) phase, whereas only the YAG (Y3Al5O12) phase was present in the Y2O3-doped alumina samples contaminated with SiO2. The excess concentrations of Y and Si atoms at the grain boundaries that, at the same time, provoke the formation of structurally complex YAG precipitates and abnormal grain growth were both estimated to be at 4-5 at nm(-2). The compositions of the triple point pocket phases found in the region of the exaggeratedly grown alumina grains indicate the presence of alumino-silicate bulk liquids at the sintering temperature

Wetting of metals and glasses on Mo

The wetting of low melting point metals and Si-Ca-Al-Ti-O glasses on molybdenum has been investigated. The selected metals (Au, Cu, Ag) form a simple eutectic with Mo. Metal spreading occurs under nonreactive conditions without interdiffusion or ridge formation. The metals exhibit low (non-zero) contact angles on Mo but this requires temperatures higher than 1100 C in reducing atmospheres in order to eliminate a layer of adsorbed impurities on the molybdenum surface. By controlling the oxygen activity in the furnace, glass spreading can take place under reactive or nonreactive conditions. We have found that in the glass/Mo system the contact angle does not decrease under reactive conditions. In all cases, adsorption from the liquid seems to accelerate the diffusivity on the free molybdenum surface

Modelling of crystal plasticity effects in the fracture of metal/ceramic interfaces : bridging the length scales

This thesis discusses Modelling of crystal plasticity effects in the fracture of metal/ceramic interfaces

Niobium/alumina bicrystal interface fracture: a theoretical interlink between local adhesion capacit and macroscopic fracture energies

Explores the niobium/alumina bicrystal interface fracture and a theoretical interlink between local adhesion capacit and macroscopic fracture energies

Microsoft Word - Tomsia wetting of metals and glasses on Mo-saiz.doc

Wetting of metals and glasses on Mo The wetting of low melting point metals and Si─Ca─Al─Ti─O glasses on molybdenum has been investigated. The selected metals (Au, Cu, Ag) form a simple eutectic with Mo. Metal spreading occurs under nonreactive conditions without interdiffusion or ridge formation. The metals exhibit low (non-zero) contact angles on Mo but this requires temperatures higher than 1100 °C in reducing atmospheres in order to eliminate a layer of adsorbed impurities on the molybdenum surface. By controlling the oxygen activity in the furnace, glass spreading can take place under reactive or nonreactive conditions. We have found that in the glass/Mo system the contact angle does not decrease under reactive conditions. In all cases, adsorption from the liquid seems to accelerate the diffusivity on the free molybdenum surface