Sol–gel synthesis of YAG/Al2O3 long fibres from water solvent systems

Y3Al5O12(YAG)/Al2O3 long fibres were prepared by a sol–gel method using water as the solvent. They were synthesized from aluminium nitrate and chloride solutions, aluminium salt, aluminium metal and Y2O3. The starting materials were dissolved by refluxing at 100°C for 2–18 h and were then condensed. The fibre spinnability was examined by a hand drawing method using a glass rod. In the nitrate solution system, the composition range available for fibre preparation was very limited because nitrate ions decomposed during the refluxing, raising the solution pH and precipitating the Y component. On the other hand, the composition range of the fibres prepared from the chloride system was 0/10⩽YAG/Al2O3⩽6/4 (volume ratio) and was wider than that from the nitrate system. The YAG/Al2O3 fibres prepared by firing at 1300°C became denser with faster heating rates. The grain size in the fired fibres was small, below the firing temperature at 1400°C, but increased greatly above that temperature.