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Si3N4 ceramics with 10 mol% (MgSiN2+Y2O3) additives were prepared by sintering at 1900 °C for 8 h in 1 MPa N2 atmosphere. Both the bending strength and thermal conductivity of the ceramics increase with increasing content of MgSiN2, and reached 689 MPa and 97 Wm−1K−1 with the addition of (7 mol% MgSiN2 + 3 mol% Y2O3). The bending strength and thermal conductivity were enhanced to 698 MPa and 105 Wm−1K−1 by post annealing at 1400 °C for 20 h. By annealing at 1600 °C, the thermal conductivity could be further improved to 117 Wm−1K−1, but the strength decreased to be 517 MPa. From the experimental results, adding more MgSiN2 and increasing the annealing temperature are helpful to improve the thermal conductivity, by reducing the grain boundary phase and increasing the grain size.

The preparation of solar grade silicon (Si) is popularly carried out in silica (SiO2) crucible containing porous α-Si3N4 coating, in which poorly wetting SiO2 film around α-Si3N4 particles act as barrier for Si infiltration. The present investigation studies the influence of oxygen (O) content in coating on wettability and infiltration for Si/α-Si3N4/SiO2 ternary system. The amorphous SiO2 film surrounding Si3N4 particles is firstly synthesized by pre-oxidizing coating in air, and the O content is controlled by adjusting pre-oxidizing temperature and holding time. In this work, dynamic wetting behavior of Si drop on coating containing various content of O is investigated using the sessile drop method. Meanwhile, via microstructural analysis, infiltration under the drop and infiltration beyond the drop (including infiltration on coating surface and under coating surface) are distinguished on coatings with different O content. Finally, wettability transformation (from wetting to non-wetting) is analyzed; mechanism of infiltration resistance for O in coating is interpreted by analytical model.

ZnSe powders have been prepared by vapor reaction during combustion synthesis. The powders contain both cubic and hexagonal ZnSe, where the fraction of the hexagonal phase increases with increasing distance from the evaporation source. The powders consist of spherical particles and rod-like crystals with sizes from submicron to a few microns. In UV–Vis region, the ZnSe powders have two absorption edges at 450–500 nm and 650–700 nm, likely connected with intrinsic band-gap transition and defect energy levels. From the optical absorption data, the band-gap of the ZnSe powders is estimated to be 2.4–2.5 eV. Under an UV or blue excitation, the ZnSe powders show very weak near-band-edge emission but strong defect-induced red emission. It appears that the ZnSe powders synthesized by vapor reaction clearly differ from the bulk ZnSe sample by melt solidification in both phase composition and optical properties.

Heat dissipation is important in high-power LEDs and depends on the thermal conductivity of the substrate. This work investigates the heat dissipation performance of AlN ceramic substrate in high-power LEDs. AlN substrate with a thermal conductivity of 193 W m −1 K −1 and flexural strength of 380 MPa has been prepared by pressureless sintering, and then bonded with a Cu film by direct plating copper (DPC). By using the AlN substrate for heat dissipation, the junction temperature (78 °C) is lowered by 42 °C compared with the case using Al 2 O 3 substrate and well below the upper limit of the operation temperature of the LEDs. From the experimental results, AlN ceramic substrate with a high thermal conductivity is a promising candidate for heat dissipation in high-power LEDs.

This paper investigates the reaction mechanism in mechanochemical synthesis of Cu 2-x Se by vibrational milling of (Cu+Se) powder mixture. The effects of milling time, milling mode, ball-to-powder weight ratio (BPWR), and Cu/Se molar ratio in the starting composition on the phase assemblage of the products are investigated. It is found that, the synthesis of Cu 2-x Se is improved by increasing milling time, BPWR, and Cu/Se ratio. For a fixed total milling time, continuous milling is better than intermittent milling to facilitate the formation of Cu 2-x Se. By continuous milling for 20 min with BPWR = 6 and Cu/Se = 2, almost single-phase β-Cu 2-x Se is produced except for minor un-reacted Cu. A diffusion-controlled reaction mechanism is proposed for the mechanochemical synthesis of Cu 2-x Se, where intermediate phases such as CuSe and Cu 3 Se 2 with lower Cu/Se ratios are produced at first and then gradually converted into Cu 2-x Se with the diffusion of Cu atoms.

This paper reports combustion synthesis of α-Si 3 N 4 with the addition of NH 4 Cl. The effect of NH 4 Cl on the phase composition of the products is investigated, and the reaction mechanism in the nitridation of Si with the participation of NH 4 Cl is discussed. The content of α-Si 3 N 4 in the products increases with increasing content of NH 4 Cl in the starting compositions, and reaches 93% when 10 wt% NH 4 Cl is added. It is proposed that the addition of NH 4 Cl promotes the nitridation of Si by gaseous reaction and improves the formation of α-Si 3 N 4 . In the reaction, NH 4 Cl decomposes into HCl and NH 3 , and HCl reacts with Si to form SiCl 4 , which is later nitridized into Si 3 N 4 . In the nitridation of Si, HCl acts as a catalyst and a carrier to transfer Si atoms from solid and liquid Si particles into gas phase. The contribution of NH 3 to the nitridation of Si is limited, and most N atoms required for the synthesis of Si 3 N 4 are provided by N 2 .

AlN ceramic substrates are prepared by tape casting and presureless sintering at 1850 °C for 10 h, with 8 wt% Y2O3 and yttrium aluminates of Y3Al5O12 (YAG), YAlO3 (YAP), and Y4Al2O9 (YAM) as sintering additives. The effects of the sintering additives on the phase assemblage, microstructure, thermal conductivity, and bending strength of the sintered AlN ceramics are discussed. With Y2O3, YAG, YAP, and YAM as sintering additives, the secondary phases in the sintered AlN ceramics are YAM, YAG, YAP + YAG, and YAM + YAP, and the average sizes of AlN grains are 5.5, 3.6, 4.4, and 4.9 µm, respectively. In the order of sintering additives with decreasing Y2O3/Al2O3 ratio, viz. Y2O3 > YAM > YAP > YAG, both the thermal conductivity and bending strength of the sintered AlN ceramics decrease. With Y2O3 as the sintering additive, the sintered AlN sample shows the maximum thermal conductivity of 205 W/(m K) and bending strength of 295 MPa.

ZrN and AlN nitride ceramic powders have been synthesized by combustion synthesis using Si 3 N 4 and BN as solid nitrogen sources. The experimental results show that the metallic particles of Zr and Al are fully nitridized by the solid nitrogen sources and are converted into ZrN and AlN. Zr reacts with both Si 3 N 4 and BN in a self-sustained way, while Al reacts only with Si 3 N 4 and does not react with BN. By using Si 3 N 4 and BN as solid nitridizing agents, this work provides an alternative way to synthesize the nitrides of ZrN and AlN, which differs from the conventional nitridation method using N 2 gas as a nitridizing agent.

Ti1−xWxC solid solution powders have been prepared by combustion synthesis in two reaction modes of self-propagating high-temperature synthesis (SHS) and thermal explosion (TE). The reaction mechanism in combustion synthesis is investigated and the effects of processing parameters are discussed. Two reaction paths are proposed for the formation of the Ti1−xWxC solid solution. In path 1, Ti1−xWxC crystals are directly precipitated from Ti-W-C melt, and in path 2 the Ti1−xWxC phase is formed by solid-state reaction between TiC and WC. The availability of the two reaction paths depends on the x value and reaction temperature. For smaller x values and higher temperatures, the reaction path 1 dominates and almost full conversion is achieved. For larger x values and lower temperatures, however, path 2 becomes dominant. In path 2, the rate-limiting step is the formation of WC by slow diffusion-controlled solid-state reaction between W and C, which is unable to be completed during the short reaction period and results in the presence of W2C and unreacted W in the products. The reaction between W and C cannot be improved by the addition of excessive C, but can be promoted by using carbon black instead of graphite powder as C source or carrying out the synthesis in a high-pressure N2 atmosphere instead of vacuum. In the fast combustion reaction with high heating/cooling rates, a non-equilibrium state is likely to be created because the mass transfer and energy exchange are limited. The non-equilibrium condition has a strong influence on the reaction kinetics, where the decomposition of W2C is avoided, a localized compositional heterogeneity is caused, and ultrafine grains on a submicron scale are obtained in the products.

Graphene with tuned surface area has been prepared by combustion synthesis (CS) from the reaction between Mg powders and CO2 gas. The content of the MgO diluent has an important influence on the morphology, crystallinity, surface properties, and thus adsorption performance of the prepared graphene. Graphene exhibits a macroporous microstructure with a broad pore size distribution and is abundant in wrinkles and ripples. From adsorption experiments, methyl orange (MO) molecules can be effectively removed by the graphene. The adsorption data fit the Langmuir isotherm well and the adsorption kinetics follows the pseudo-second-order rate reaction.

This paper reports the combustion synthesis of α-Si3N4 using green additives of water and alcohol. The addition of water and alcohol is demonstrated to be effective in controlling the reaction kinetics and improving the formation of α-Si3N4 by vapor reactions. With increasing proportion of additives in the starting composition, the content of α-Si3N4 in the product is clearly enhanced. In contrast to the ammonium halides usually employed as additives in the combustion synthesis of α-Si3N4, the green additives used here are nontoxic, noncorrosive, and thus more attractive for industrial applications.

TiB 2 -TiC-WB composite ceramic powders have been prepared by fast combustion synthesis from Ti, W and B 4 C, by coupling the weak exothermic reaction of W + B = WB with strong ones of Ti + 2B = TiB 2 and Ti + C = TiC. With increasing W/(Ti + W) ratio, the reaction temperature and heating rate decrease while the content of WB increases, and unreacted W appears for W/(Ti + W) = 0.24. The addition of excessive B 4 C leads to lower reaction temperature, smaller grain size, and formation of WB 2 . The products show a homogeneous microstructure without element segregation on the scale of agglomerates, and in most products the average grain size is smaller than 1 µm.

Cu 2 SnSe 3 samples with different secondary phases are prepared from compositions of Cu x SnSe 3 (x=1.8–2.2) and Cu 2 Sn y Se 3 (y=0.8–1.2), and their thermoelectric properties are investigated. For Cu x SnSe 3 samples, the secondary phase is SnSe 2 for x=1.8 and 1.9 and SnSe for x=2.2, and nearly single-phase Cu 2 SnSe 3 is obtained for x=2.0 and 2.1. For Cu 2 Sn y Se 3 samples, the secondary phase is CuSe for y=0.8 and SnSe for x=1.1 and 1.2, and single-phase Cu 2 SnSe 3 is produced for y=0.9 and 1.0. The lattice structure of synthesized Cu 2 SnSe 3 depends on the x and y values, which is cubic for x≤2.0 or y≤1.0 and monoclinic for x>2.0 or y>1.0. Compared with the single-phase Cu 2 SnSe 3 sample (ZT=0.4 2 at 77 3 K), the samples with SnSe 2 secondary phase show a greatly-enhanced ZT of 0.84 at 773 K, which is likely the best result for un-doped Cu 2 SnSe 3 up to now. The samples with SnSe secondary phase exhibit poor thermoelectric properties.

ZTA-TiC-FeCrNi cermets are prepared by a fast and furnace-free way called high-gravity combustion synthesis. The synthesized cermet samples show the maximum relative density of 97.6% and a hierarchical microstructure with grain sizes from submicron to >50 µm. The content of TiC has a strong influence on the microstructure and mechanical properties of the cermet samples. A higher TiC content results in refined microstructure, improved hardness, and reduced coefficient of friction. With increasing TiC content, the strength and toughness of the samples first increase and then drops, and reach the maximum of 469±26 MPa and 11.3±0.2 MPa m 1/2 at 20% TiC. Compared with commercial polycrystalline Al 2 O 3 ceramics, the ZTA-TiC-FeCrNi cermets exhibit better wear resistance, and the volume loss is lower by one magnitude than Al 2 O 3 under the same condition.

Si3N4 coating is widely used in the production of photovoltaic silicon ingots. This work investigates the influence of pre-oxidation of Si3N4 powders on the interaction between Si3N4 coating and molten Si based on sessile drop experiments. It is found that the surface tension and surface roughness affect the contact angle and accordingly wetting behavior. A new mechanism for the permeation of molten Si in Si3N4 coating is proposed, where the driving force for the permeation is provided by chemical reaction between SiO2 and Si instead of usual capillary force.

Porous magnesium aluminate spinel (MgAl 2 O 4 ) ceramic supports were fabricated by reactive sintering from low-cost bauxite and magnesite at different temperatures ranging from 1100 to 1400 °C and their sintering behavior and phase evolution were evaluated. The effects of sintering temperature on the pore structure, size and distribution as well as on the main properties of spinel ceramic supports such as flexural strength, nitrogen permeation flux and chemical resistance were investigated. The supports prepared at 1300 °C showed a homogeneous pore structure with the average pore size of 4.42 μm, and exhibited high flexural strength (35.6 MPa), high gas permeability (with nitrogen gas flux of 3057 m 3 m −2 h −1 under a trans-membrane pressure of 0.1 MPa) and excellent chemical resistance.

Using a pure AlON powder synthesized by carbothermal reduction and nitridation, a bimodal particle size distribution (PSD) powder was prepared by planetary ball mill, and pressurelessly sintered at 1880 °C to fabricate transparent AlON ceramics. Relative density of ≥99.72% was achieved for all the obtained AlON ceramics samples held for 90–150 min. The maximum infrared transmittance for 3 mm thickness sample was up to 81.8% (93.8% of theoretical in-line transmittance). Therefore, the holding time to fabricate transparent AlON ceramics can be shortened to 90 min or 150 min, compared to 480 min holding reported in the literature. The fast sintering of transparent AlON ceramics is a combination of fast heating (40 °C/min) and shorter holding time, and should be mainly attributed to fast surface diffusion during heating due to the bimodal PSD of fine powder and fast grain boundary diffusion during both heating and holding due to the transient bimodal grain size distribution.

YAG glass-ceramic with a designed composition of 24Y2O3∙40Al2O3∙36SiO2 was prepared by a method which combines combustion synthesis with centrifugation. High temperature glass melt was produced from a highly-exothermic combustion reaction in Al/CuO system. Centrifugation induced high gravity field facilitates the crystallization of YAG from the glass melt. The effects of high gravity field on phase formation, composition distribution and morphology evolution of prepared YAG glass-ceramic were investigated. Morphology of YAG crystals changed gradually from dendritic to polygonal, and finally to columnar shape along high gravity direction. The density increased from 3.49 to 4.12 g cm−3, and the hardness increased from 7.8 to 9.7 GPa along high gravity direction.

Ultrafine mixed powders ( D 50 =0.21 μm) of Si 3 N 4 , AlN, Al 2 O 3 and Y 2 O 3 were firstly prepared by planetary ball mill, and then were hot-pressed to fabricate translucent Y-α-SiAlON ceramics at 1650–1920 °C for 0.5 h. All the sintered samples were measured by XRD and only α-SiAlON crystalline was detected, which implies α-Si 3 N 4 was completely transformed to α-SiAlON. It was found that a shrinkage process of the ultrafine mixed powders could be rapidly accomplished, the entire fast densification process lasted for only 5.83 min (from 1675–1850 °C at a heating rate 30 °C/min), which is much shorter than the shrinkage time needed for conventional powders (>30 min). Meanwhile, for the same infrared transmittance, the present α-SiAlON ceramics was sintered at 100–150 °C lower temperature than the reported translucent Y-α-SiAlON ceramics using conventional mixed powders. Correspondingly, holding time for the present α-SiAlON ceramics was shortened to 0.5 h, which is only half of the reported ones. The fast shrinkage, lower sintering temperature and shorter holding time may be attributed to the ultrafine mixed power employed in this paper. At the same time, all samples showed light transmission and a high, stabilized infrared transmittance (~60% for 1.2 mm thick sample) was measured for the samples sintered at 1800–1920 °C.

A simple and energy-efficient method combining a thermite reaction and centrifugal infiltration was applied to produce Ni/WC composites. Driven by a centrifugal force, the molten Ni in-situ produced by a thermite reaction infiltrated into a porous preform of WC powder compact. After solidification, a Ni/WC composite was obtained with two metallurgically bonded layers. Both of the two layers were composed of Ni and WC but with different contents. In different regions of the sample, WC particles with different morphologies and sizes were observed, which were caused by the competition of growth and relaxation of WC particles. The WC-rich layer showed an average hardness of 81.5 HRA, and the hardness of the Ni-rich layer gradually decreased from 61.4 HRA to 53.9 HRA.

Ca α-SiAlON powders with rod-like crystals were prepared by combustion synthesis from different starting compositions. The growth mechanism of the rod-like Ca α-SiAlON crystals was investigated and two growth modes were observed. One is liquid phase precipitation, and the other is nucleation and growth on smooth surfaces of the as-developed large crystals. During the development of the rod-like Ca α-SiAlON crystals, anisotropic growth occurred with the [0 0 1] direction being the fast growth direction.