Epitaxial growth of aluminum borate whiskers and simultaneous joining of alumina ceramics via a sol-gel method

Aluminum borate whiskers were epitaxially grown on alumina by a sol-gel method. The morphology of the whiskers was investigated via scanning electron microscopy, X-ray diffraction and transmission electron microscopy. As the holding time and growth temperature increased, the length of the whiskers first increased and then decreased. The whiskers (Al4B2O9 and Al18B4O33) were 5-20 mm in length and hundreds of nanometres in diameter under all growth parameters. In addition, the whiskers synthesized by the sol-gel method were successfully used to join alumina in air. SEM images showed that the whiskers grew across the seam, and the width of the joint was consistently less than 10 mm. The shear test results showed that the highest strength of the joints reached 84.5 MPa at a bonding temperature of 950 degrees C maintained for 8 h. Fracturing consistently occurred within the network structure in the seam.