Papers by Author: Qiang Zou

Abstract: The production of silicon nitride whiskers in solid mixtures under nitrogen-containing atmospheres was investigated. Green bodies made of micron and nano silicon nitride powders with 2MgO×2Al2O3×5SiO2 as sintering additive were sintered at 1500~1560oC in flowing nitrogen-containing atmospheres. Resultantly whisker-like products were formed on the cold side of the graphite boat. X-ray diffraction analysis indicated that the formed whisker were α–Si3N4. The products were analyzed by transmission electron microscope. The morphologies of the resulting whisker were varied with sintering temperatures and atmospheres. Dislocation structures were observed on the edge of some whiskers. This suggested that the whisker growth proceeded through a vapor-solid (VS) mechanism. The mechanism of whiskers growth at different temperatures and atmospheres was discussed with a thermodynamic calculation based on a database software.

Abstract: Strontium bismuth titanate (SBTi) matrix composites containing Ag particles were synthesized by the conventional solid-state reaction method. The SBTi/Ag composites have been characterized by various techniques: x-ray diffraction, optical metallurgical microscope, scanning electron microscope and dielectric measurement. It is found that Ag doping significantly affect the physical properties of composites. By adding Ag particles to the SBTi matrix, the single-phase layered perovskite structure of the matrix is preserved and the sintering temperature of the system decrease from 1120°C of the single-phase SBTi to 950°C of the SBTi/Ag composites. With the increase of sintering temperature, the size of silver particles increase, but the SBTi grains have no significant growth. The SBTi/Ag composites show a significant change of the dielectric constant. By increasing Ag content, a gradual increase of the dielectric constant is observed and the dielectric loss of the SBTi/Ag composites remain unchanged when the temperature rangers from room temperature to 200°C, however, the Curie peak of dielectric constant is repressed, which has been interpreted based on the effective dielectric fields developed around conducting phases and the inhibition effect of nonferroelectric secondary phase to electro-strain.