Papers by Keyword: Combustion Synthesis (CS)

Abstract: The product formation of Mo-66.7at.%Si powders mixture during mechanical alloying using a high-energy vibratory type ball-milling machine was investigated by X-ray diffractometer (XRD). The temperature of the vial was measured at intervals during ball milling. The results showed that some MoSi2 was formed by the mechanically induced self-propagating reaction during a milling time of 105~110min; at the same time the surface temperature of the vial is increased. In early stages of milling, as a result of extensive fracturing and cold welding of powder particles, the interfacial energy between Mo and Si powders and cold deformation energy led to the formation of supersaturated solid solution of Mo(Si). And then mechanically induced self-propagating reaction of MoSi2 occurred immediately. After this, MoSi2 was gradually synthesized by diffusion. MoSi2 andMo(Si) were the end products, and the end products underwent the amorphous trend.

Abstract: N-doped SiC whiskers with diameters of about 0.2 μm and length of 3-7 μm were synthesized via combustion reaction of Si/C system in Ar atmosphere, using NH₄Cl as the dopant and polytetrafluoroethylene (PTFE) as the chemical activator. These whiskers are straight and curved morphologies. X-Ray powder diffraction pattern and energy-dispersive spectroscopy (EDS) confirm that the lattice constant of prepared whiskers is smaller than standard value of β-SiC due to the N doping arising.

Abstract: This paper presents the results of synthesizing porous Si₃N₄-glass composite with Y₂O₃ as additives by combustion synthesis. The effect of glass content on the final morphology was investigated in detail. The results reveal that the final morphology of products is depended on the glass content. With the increasing glass content, the porosity of the composite is decreasing and the highest strength is obtained when the glass content is 2wt%.

Abstract: Tungsten carbide cermets coating on carbon steel were fabricated by laser clad cooperation combustion synthesis method. The microstructure, phase, element distribution and microhardness have been analyzed with the aid of SEM, XRD, EDS, EPMA and microhardness-tester. It is shown that the coating consisted of WC, CW₃, W₂C, WCx, and FeNi₃. The results of hardness measurement showed that the hardness was superior to substrate. Analyze the effect of different laser power and different laser scanning speed on the quality of the laser cladding surface, the surface quality gets better with the increasing of the laser power, and gets better with the reducing of the scanning speed.

Abstract: This paper presents the results of synthesizing β-Si3N4 crystals with Y2O3 as additives by combustion synthesis. The effect of compact density on the final morphology was investigated. The results reveal that with the increasing of the compact density, the amount of rod-like crystals decreased. The growth mechanism of the β-Si3N4 crystals under the high temperature and high pressure is discussed.

Abstract: This paper presents the results of synthesizing rod-like -Si3N4 crystals with Y2O3 as additives by combustion synthesis under different nitrogen pressure. The effect of nitrogen pressure on the final morphology of rod-like -Si3N4 was investigated and the crystal growth mechanism was discussed in detail. The results reveal that the final morphology of products is depended on the nitrogen pressure. With the increasing nitrogen pressure, the ratio of rod-like crystals is increasing.

Abstract: Large bulk solidified TiC-TiB2 eutectic composite ceramics were prepared by combustion synthesis under high gravity, and the WO3 was introduced into the combustion synthesis as one of oxidants in thermit to obtain the Ti-W-Cr-C-B liquid, so near-full-density TiB2-(Ti,W)C eutectic composite ceramics without the macrocracks were achieved. The ceramic matrix was mainly composed of TiB2-(Ti,W)C eutectic microstructures, and a few of Al2O3 and Al2O3-ZrO2 eutectic structures were also detected in between Ti-W carbides. Due to the introduction of the high gravity field, Stocks immigration of the immiscible liquids took place due to their density differences, resulting in float-up of oxide liquid and settle-down of Ti-W-Cr-C-B liquid, and the layered melt consisting of oxide liquid and Ti-W-Cr-C-B liquid was formed, finally, TiB2-(Ti,W)C eutectic composite grown from the melt. Due to the mutual solubility of W-Ti, the W atom diffused into the TiC, leading to the formation of (Ti,W)C solid solution as same as crystal lattice structure of TiC. The relative density, Vickers hardness and fracture toughness of the composite ceramics measured 98.4%, 26.4 GPa and 7.6±0.5 MPa•m1/2, respectively.

Abstract: (Ti, W)C matrix metal ceramics were prepared through combustion synthesis under high gravity, structure formation mechanism of the ceramics was discussed and the properties of the ceramics were also measured. XRD and FESEM images show the matrix of metal ceramics was mainly composed of TiC and (Ti, W)C1-x. The formation mechanism mainly involves two stages: firstly, combustion reaction is advanced rapidly under high gravity, and the layered melt consisting of Ti-W-Fe-C-B liquid at the bottom and oxide liquid at the top is formed due to rapid liquid-liquid separation under high gravity, subsequently, TiC solids as the primary phase precipitates from Ti-W-Fe-C-B liquid due to the higher concentration and faster diffusion of C relative to B in the alloy liquid, whereas (Ti, W)C1-x solid nucleates and grows on the surface of TiC solids. The Vickers hardness, flexural strength and fracture toughness of the (Ti, W)C matrix Metal ceramics measured 25.6 GPa, 1060 MPa and 8.5 MPa•m1/2, respectively.

Abstract: Based on preparing the large-bulk solidified Al2O3-ZrO2 (Y2O3) ceramic composites by combustion synthesis under high gravity, the solidification behavior and microstructure transformation of the ceramics as well as their effects on the ceramic properties were investigated. XRD, SEM and EDS analyses showed the ceramic microstructures were composed of the irregular eutectics at the surface and the tetragonal ZrO2 micrometer spherical crystals in the center of the ceramics respectively. By combining with irreversible nucleation theory, it is considered that the formation of irregular eutectics with micro-nanocrystalline microstructures is a result of the leading nucleation of Al2O3 high-fusion-entropy phases followed by the coupled growth of Al2O3-ZrO2 phases, whereas the presence of the tetragonal ZrO2 spherical microstructures in the center of the ceramics results from the leading nucleation of ZrO2 cubic phases followed by the independent growth of Al2O3-ZrO2 phases. As a result, it is just the unique microstructure transformation during the solidification process that the highest hardness at the surface and the highest fracture toughness in the center of the ceramics are achieved respectively.

Abstract: TiSi2 (Titanium disilicide) has attracted great research interest due to its large silicon content, remarkably low electrical resistivity (about13–16μΩcm), good photocatalytic property, high temperature stability, and good corrosion resistance. It is an excellent electronic material and potential photocatalyst and high temperature structure material. In this work, TiSi2 was prepared by using the “chemical oven” enhanced self-propagating combustion method from the elemental powder compact. The mixture of Si and Ti (atomic ratio 3:5) were ignited as chemical oven. The composition of product was detected by XRD. Result shows the product is a single phase titanium disilicide with trace impurities. The maximum combustion temperature of Ti+2Si compact was up to 1472°C, which exceeds the lowest eutectic point (1330°C) of the Ti-Si binary mixture. Thus it can be predicted the formation of TiSi2 is primarily dominated by the solid-liquid mechanism, which includes dissolving solid reactants and precipitating silicide product. It could also be convinced by SEM photos of the combustion product and reacting zone of the compact.