Papers by Author: Yun Long Ai

Abstract: The influences of Nb₂O₅ on the phase, microstructure and hydrochloric acid corrosion behaviors of Nb₂O₅-Al₂O₃ ceramics sintered with 2.45 GHz microwave energy were investigated. The results showed that Nb2O5 reacted completely with Al₂O₃ to form AlNbO₄ and densified the pure Al₂O₃ at a lower sintering temperature and in a short sintering time. Nb₂O₅-Al₂O₃ ceramic samples were corroded in diverse concentration hydrochloric acid for different time. Weight loss rate of Nb₂O₅-Al₂O₃ ceramic rose dramatically when the corrosion time was not longer than 4 h, and it increased slowly beyond 24 h. After Nb₂O₅-Al₂O₃ ceramic samples were corroded for 1 h, pitting corrosion was observed by scanning electric microscope, which was consistent with the analysis results of the scanning Kelvin Probe.

Abstract: The influence of Nb2O5 on the phase and microstructure evaluation and mechanical properties of Nb2O5-Al2O3 ceramics sintered with 2.45 GHz microwave energy was investigated. The results showed that Nb2O5 could densify the pure alumina with a lower sintering temperature and a short sintering time. Nb2O5 reacted with Al2O3 to form AlNbO4 completely and the amount of AlNbO4 increased with the increasing content of Nb2O5, distributing at the Al2O3 grain boundaries. The specimen doped with 10 vol.% Nb2O5 sintered at 1500 °C exhibited plenty of columnar grains with draw ratio about 1:3. The existence of columnar grains enhanced the microhardness and fracture toughness of Nb2O5-Al2O3 ceramics.

Abstract: Al2O3-ZrO2(n) composite ceramics were prepared by microwave sintering. The properties and microstructure were investigated, including vickers hardness, fracture toughness, bending strength, wear resistance and heat-shocking resistance. The results show that the properties and microstructure of alumina matrix ceramics are affected by the addition of nano-ZrO2 particles. When the content of ZrO2 is 15vol%, the hardness, fracture toughness and bending strength of the Al2O3-ZrO2 composites reach maximum values 13350MPa, 6.41MPa•m1/2 and 502MPa, respectively. The wear resistance of alumina matrix ceramics are improved only on the condition of adding an appropriate amount of nano-ZrO2. The wear mechanism of the composites are abrasive particle wear and adhesion wear co-existing. The crack propagation rate of Al2O3 matrix ceramics decreases remarkably with the addition of nano-ZrO2 particles. The mechanisms of ZrO2 improving the heat-shocking resistance of alumina matrix ceramics are mainly phase transfer toughening. Nano-ZrO2 particles exist in the intragranular and grain boundary of alumina matrix ceramics, and exist intragranular structures.

Abstract: The green bodies of LaNbO4/MoSi2 composite materials were compacted by warm pressing and cold pressing processes, and then the composites were prepared by microwave sintering. Effects of the two different compaction processes on sintering process and sintered samples were analyzed. The results show that the density of the microwave sintered sample by cold pressing (5.599g/cm3) is similar to that of warm pressing (5.593 g/cm3). But cold pressing has some disadvantages, such as longer sintering time, incomplete sintered samples, peeling easily on the surface and delaminating, existing internal stress, having microcrack and impurities, and occurring distortion easily in sintered samples. The samples compacted by warm pressing have higher heating rate in the microwave sintering process, which have more homogeneous structures, no clear microcrack and big cavities, and higher fracture toughness after sintering. Compared with cold pressing, the comprehensive properties of warm pressing are better.