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A kind of laminated composite named Al2O3/Nylon/Al with high work of fracture was prepared by a simple process using epoxy resin adhesives as binder in a leaky mold at a pressure of 5 MPa. Light microscopy and scanning electron microscopy were employed to observe the microstructures and crack propagation of the laminated composites. The flexural strength and fracture toughness were measured through three-point bending test, and the work of fracture of the laminated composite was calculated from load-displacement curves of three-point bending test. The experimental results show the composite have low Young's modulus and flexural strength, however, the work of fracture of the laminated composite appears to be high of 2850 J/m2, and the fracture toughness reaches about 11 MPa•m1/2. Analysis of microstructure and crack propagation reveals that the failure of the laminated composite exhibit distinctive characteristic.

A new method called cation extraction process has been applied to improve the oxidation resistance of silicon nitride ceramics with sintering additives. It is found that the high temperature oxidation rate of the Si3N4 ceramic treated by the process decreased remarkably in contrast to the oxidation rate of the Si3N4 without the process. The oxidation rate of Si3N4 ceramics with the cation extraction process is reduced more than 50% comparing with that of the Si3N4 ceramics without the process. The morphological characteristic and phase composition of the oxides were analyzed by means of SEM and XRD. The oxidation rate of silicon nitride after cation extraction treatment is determined by the quality of the “purified layer” formed below the pre-oxide scale. Thicker oxide layer formed in pre-oxidation, higher extraction temperature and longer extraction time are helpful to form a good “purified layer”.

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The influence of leucite on dental porcelain properties is investigated in this paper. The nanosized leucite powder prepared by sol-gel method was added into a low-fusing temperature frit to fabricate dental porcelain fused to metal. The porcelains with different leucite contents were sintered at the temperatures ranging from 780° to 900°C. The flexural strength and the thermal expansion coefficient (TEC) of the dental porcelain containing leucite particles are evaluated. The micro- structure and phases of the porcelain are characterized and the mechanism that nanosized leucite particles strengthening the porcelain is discussed.