After preparing samples (3mm long×4mm wide×36mm high) of Al2O3-MgAlON composites and sintered at 1500°C for 2 h in N2 atmosphere, samples’ cracks were carved by a Vickers hardometer’s pressing head on the center of the sample surface (4 mm×36 mm). Subsequently, the cracks were healed at 1000°C-1550°C for 6 h respectively. Effects of healing temperature on sample’s strength, crack healing dynamics and its molecular dynamics simulation were investigated. The results suggested that: the optimum range of cracks healing temperature was 1300°C-1550°C, and the healing process accelerated at 1300°C, meanwhile, the strength of samples increased significantly. Cracks completely healing finished at 1550°C. The dynamics equation of crack healing was lnν = -Q/kT+lnC. Through characterizing the crack healing rate with the recovering rate of sample’s strength, the diffusion activation energy Q = 4.264 × 10-30 J•K-1 and diffusion constant C=7.359 were claimed. The result of the molecular dynamics simulation suggested that cracks healing process was caused by diffusion could be divided into five stages: passivation of crack tips, formation of salient island, crack shrinkage, generation of secondary crack, and complete healing.

In this paper, the influence of synthetic conditions (the molar ratio of Mg2+ and Al3+; the concentration of cationic; the aging temperature and time) on the grain size and crystallinity of Mg-Al layered double hydroxide (LDH) has been investigated systematically based on the orthogonal experiment. Mg-Al LDH was prepared using magnesite through chemical precipitation and hydrothermal methods. The samples were characterized by X-ray diffraction (XRD). The grain size which along a and c axis were calculated through Scherrer formula. The experimental results showed that the grain size along a axis increased with the rise of synthesis temperature, while the grain size along c axis reduced. It was also found that the aging temperature and time had a great influence on the crystallinity of Mg-Al LDH.

Alumina ceramics can be widely used in electro vacuum area and microwave communication industry due to its excellent dielectric properties. However, the effects of the Y2O3addition on dielectric properties of alumina ceramics were rarely investigated. In this paper, alumina ceramics was prepared using Y2O3as additive, via both heterogeneous precipitation method (HP) and mechanical milling method (MM). The effect of Y2O3on phase transformation during sintering and dielectric properties of alumina ceramics were investigated, and the influencing mechanism was discussed. The results showed that different adding way influenced phase transformation during sintering, and polarization relaxation existed in alumina ceramics during 103~107Hz. Besides, the universal polarization relaxation relation could be applied to alumina ceramics.

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Alumina ceramics are the most widely used structural ceramics, especially in aviation, spaceflight and war industry area. However, alumina is of covalent bond, with low fracture toughness and poor thermal shock resistance, which baffle the application of the alumina ceramics in engineering. In this paper, mullite fiber was used to improve its toughness and thermal shock resistance. Alumina-mullite composite ceramics were prepared by hot press sintering. The effect of mullite fiber on thermal shock resistance of ceramics was investigated through indention quenching method. Meanwhile, the mechanism of its reinforcing and toughening and the relationship between mechanical properties and addition of mullite fiber were also discussed.