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The equilibrium compositions of a thermite reaction system (Fe2O3+Cr2O3+CrO3+NiO+O2+N2+TiO2+C+S+CaO+Al), which was used to prepare Ni-based alloys, were predicted by means of the free energy minimization method. The effects of the reactant contents on the equilibrium compositions and the adiabatic temperature of the thermite reaction system were analyzed. The microstructure of the Ni-based alloys was investigated. The thermodynamic analysis indicated that the products of the thermite reaction system contained primarily Al2O3, Fe, Ni, Cr, Ni3Al and NiAl, due to impurities C, N2 and S in the raw materials, there could also exist TiC, Cr7C3, CrN, CaS and TiN in the equilibrium products. The amount of Ni3Al and NiAl in the products increased with increase of the aluminum content in the starting materials. The microstructure investigation showed that the Ni-based alloys consisted of austenite, ferrite, Ni3Al and NiAl. The existence of Ni3Al and NiAl in the Ni-based alloys reconciled with the predictions of thermodynamic analysis, suggesting the free energy minimization method is useful in designing advanced materials with multiple components by thermite reaction technique.

Yttrium-stabilized α-SiAlON powders with rod-like crystals were fabricated by combustion synthesis. Effects of starting compositions including relative content of diluents on final phase assemblage and grain morphology of combustion products were discussed. With appropriate proportions of α-SiAlON seeds and NH4F additive, α-SiAlON powders with rod-like crystals could be fabricated. It was found that the addition of α-SiAlON and NH4F could improve the anisotropic growth of rod-like crystals. However, if too much NH4F was added, the phase purity of combustion products would be decreased obviously and more β-SiAlON was produced. Additionally, the as-synthesized α-SiAlON powders were heat treated at 1800 °C for 1 h to examine their stability at the elevated temperature. The experimental results showed that after the heat treatment, single-phase α-SiAlON was obtained, revealing the high stability of combustion synthesized α-SiAlON powders.

Single-phase Yb α-SiAlON ceramics in-situ toughened by elongated grains were prepared by pressureless sintering, with the crystalline powder prepared by combustion synthesis used as seed crystals. The effects of seed addition on the densification, phase transformation, microstructure development, and mechanical properties of the samples were investigated in detail. From the experimental results, it was found that the added seed crystals could promote the phase transformation and facilitate the growth of elongated grains. By adding seed crystals the fracture toughness of the sintered α-SiAlON ceramics was considerably improved, with no obvious degradation in the bulk density and hardness at the same time.

Aluminium nitride (AlN) with various morphologies was fabricated through a sublimation-recrystallization method. The influences of type of reactor and temperature gradient were explored, as well as the orientations and growth mechanism of the obtained AlN whiskers. In the early stage of preparation, a vapour-liquid-solid (VLS) mechanism dominated, producing AlN pillars, whiskers and noncrystalline fibres. In the later stage, as the catalyst liquid was removed by volatilization, the pillars and noncrystalline fibres stopped growing, but the growth of AlN whiskers continued through a vapour-solid (VS) mechanism. By Laue method and rotating-crystal method of x-ray diffraction, together with electron diffraction, most of the AlN whiskers were discovered to grow on planes \(\left\{ {2\bar 1\bar 10} \right\},\left\{ {0001} \right\} \), or \(\left\{ {10\bar 1|} \right\} \), where l = 0, 1, 2, 3, along crystal axes \(\left\{ {2\bar 1\bar 10} \right\},\left\{ {0001} \right\}\), or \(\left[ {10\bar 1w} \right] \), where w = 0, 1, 2, 3. Oblique grown whiskers also appeared, with a growth direction at an angle of about 54° to the growth plane, \(\left\langle {10\bar 12} \right\rangle \).

Aluminum nitride (AIN) ceramics, with binary additives B2O3-Y2O3, were sintered at temperatures from 1700 to 1850 °C. The microstructure and sintering characteristics were studied by XRD, HREM, SEM and TEM/EDS, which showed that Y2O3 gave different yttrium aluminates through the reaction with Al2O3 under different conditions. With the increase of sintering temperature, the yttrium-to-aluminum atomic ratio Y/Al decreased in the secondary phases of the sintered bodies. It was discovered that B2O3 could dissolve in the yttrium aluminates, forming some ordered structure with a superlattice. After sintering at 1850 °C for 4 h, a specimen with a fine microstructure and a thermal conductivity of 190 W m−1 K−1 was obtained.

Aluminum nitride (AlN) fibres were synthesized by carbothermal reduction of aluminum silicate fibres and carbon black in a flowing nitrogen atmosphere. XRD and SEM were employed to study the phase structure, chemical composition and morphologies of the products. It is suggested that aluminum silicate fibres can be converted into AlN fibres by carbothermal reduction. SEM confirmed that the fibres maintained the morphologies of aluminum silicate fibres during reduction, but their details of surface have been altered. A carbothermal nitriding model of the aluminum silicate fibres has been developed.

With Al2O3 and graphite as raw materials, CaF2 and B2O3 as additives, AlN whiskers were fabricated by a carbo-thermal reduction method. The fabrication mechanism and growth characteristics of AlN whiskers were investigated. At the beginning of the high-temperature fabrication, AlN whiskers grew by the vapour/liquid/solid (VLS) mechanism, and defects existed on the surfaces of the whiskers. In later stages, the VLS mechanism possibly changed to a vapour/solid (VS) mechanism, and the defects disappeared. The orientation of most AlN whiskers was normal to $$\{ 10\bar 1n\} $$ (n=0, 1, 2, 3), and normal to $$\{ \bar 12\bar 1n\} $$ (n=0, 1, 2). The growth processes of both two-dimensional nucleation and screw dislocations existed at the same time. © 1998 Kluwer Academic Publishers

Morphologies of AlN whiskers grown by the vapour–liquid–solid mechanism (VLS) were investigated. Several types of whisker structures, such as growth hill, wavy, crossed and stack structures, were found due to the variation of growth conditions. Growth mechanisms and orientations of AlN whiskers were also studied. Besides preferential crystallographic planes, several other planes were found to be growth layers due to the perturbation of the AlN lattice change caused by dissolution of oxygen. A screw dislocation growth mechanism was clearly confirmed. An oblique growth mechanism was found in this work, which may be the result of two processes: the vapour–liquid–solid process and dissolution of oxygen.