Papers by Keyword: SHS

Abstract: A particle reinforced hardface coating was prepared by vacuum cladding process. Firstly, titanium carbide composite powders were prepared by self-propagating high-temperature synthesis (SHS). The hardface coating was then formed on plain carbon steel substrate with the TiC composite powders and high chromium iron-based alloy powders by vacuum sintering. The microstructure of the coating was observed and then the wear resistance was studied. The results show that TiC composite particles uniformly distribute in the coating. The coating and the steel substrate are chemical bonded with each other. When the size of TiC particles is unchanged, with the increase of quality fraction of the TiC particles, the hardness increased gradually and the wear resistance of composite coating under different conditions changed. The unit area weigh loss increased following by the load increasing, and the unit area weigh loss is the most under Alkaline condition. And the unit area weight loss increased following by the increase of the abrasive and the reaction time.

Abstract: Al₂O₃-TiC particles reinforced iron matrix functionally gradient material is successfully fabricated by combining the methods of self-propagating high-temperature synthesis (SHS) with casting. The SHS products are analyzed by SEM and XRD and EDS. The results show that the grain size of the particle is round 1μm~3μm, the composition of the Al₂O₃-TiC/ Fe surface composite takes on a gradient distribution from outside to inside, and transforms gradually to the matrix metal. The hardness below 0.5mm from exterior surface of the functionally gradient materials increases dramatically and gradually changes to the hardness of the matrix. Key words: In situ generation; SHS; Casting; Surface composite material; FGM

Abstract: Upgrade silicon powder have been prepared by a two-stage technique consisting of a self-propagating high-temperature synthesis (SHS) process in a SiO₂+Mg system in an inert atmosphere and the hydrometallurgical treatment of the combustion product. It was found from DTA curve that the initial starting temperature(T_in) of the reaction was 615°C. The adiabatic temperature (T_ad) of system was calculated under the different molar ratios of Mg/SiO₂ and the results showed the reaction would happen and be kept by the self-propagating way only when the excess coefficient(x) of Mg was more than 0.9. The value of Tad would increase with the increasing of x. XRD Pattern indicated MgO₂ and element Si were main phases in combustion products except a little matter MgSi₂O₄. The purity of the combustion-synthesized Si samples was greater than 99.98% after the acid leaching treatment, and the experimental yield of the powder was approximately 78%.

Abstract: High-yield and high-purity bamboo-like boron nitride nanotubes were synthesized via an effective chemical vapor deposition method by annealing porous precursor under ammonia atmosphere at 1150 °C. The porous precursor, prepared by self-propagation high temperature synthesis method, was the key to bulk synthesis process. The as-synthesized boron nitride nanotubes were characterized by SEM, TEM, HRTEM, XRD, Raman and FTIR spectroscopy. These nanotubes had a bamboo-like structure with uniform diameters about 90 nm and length of more than 10 μm. The associated growth model is proposed in this paper.

Abstract: Large cross-section composite rectangular steel tubes with ceramics inner liner, which can be used directly, and also cut into the ceramics clad plate, were made by a new effective way. The material type, shape and size parameters of cores were determined and thickness and hardness of the ceramic coating were measured. The bond stress between steel substrate and alumina ceramics were analyzed and the bond modes also were checked. The dimension parameters of hemming plate used in the experiment were determined and the bond strength between the coating and tube substrate in normal and tangential direction was examined. The results show that the ceramics coating surface is glossy, which thickness is among 1.5-3.5 mm, the hardness of alumina ceramics inner liner is above HV1100. Metallurgical bonding between steel substrate and ceramics coating could not come into being and the mechanical bonding with lower bonding force is the mainly joint mode.

Abstract: Self-propagating High-temperature Synthesis (SHS) was used to prepare complex oxide La_0.7Sr_0.3MnO₃, which is used as the cathode in solid oxide fuel cells (SOFCs). Experiments show that La_0.7Sr_0.3MnO₃ can be prepared via SHS under moderate conditions from a mixture of La₂O₃-SrO₂-Mn-NaClO₄-KMnO₄，using NaClO₄-KMnO₄ as dual oxidants. The proper addition of the second phase oxidant KMnO₄ makes the combustion wave movement stable. The product powders have an average particle size of 1-2μm and the particles are small aggregate. Pellets were sintered at 900 °C, 30 MPa for 10 min by spark plasma sinter (SPS). The electrical conductivity of sintered sample was 170 S•cm^-1 at 1000 °C in air.

Abstract: TiC particulates were prepared by self-propagating high temperature synthesis (SHS). The effect of elemental aluminum on the formation of TiC particulates was particularly studied by differential thermal analysis (DTA) and sintering experiments of Ti-C-Al system. The sintered products were examined by XRD and TEM. The results showed that Ti did not react with C directly in the absence of elemental Al. The sintering process of Ti-C-Al system presented typical high-temperature self-propagating synthesis (SHS) features. TiC particulates could be maximally obtained through the appropriate control of the Al content in the system. The size of the resultant TiC particulates was about 0.15μm.

Abstract: The processes of SHS synthesis ceramic materials with the using of titanium oxide and silicon were investigated. The ceramic materials with the high operating characteristics were obtained.

Abstract: The preparation, mechanism and electromagnetic absorbing properties of Hollow Ceramic Micro-spheres (HCMs) were studied in the present investigation. HCMs were produced by traditional flame spraying technology as well as equipments. Al-TiO₂ was chosen as a main reactive system. The self-reactive agglomerate powders were produced by spraying process by adopting a temperature-controlled media to get the high cooling rate to solidify and crystallize rapidly. HCMs with characteristic of hollow structure and in-situ synthesis were obtained. Electromagnetic parameter of HCMs has been tested and the reflectivity was analyzed. The results showed that HCMs possess the microwave absorbing properties. The relationship between intrinsic parameters of HCMs and microwave absorbing properties has been also investigated.

Abstract: Inter-metallic compound of Ti₃SiC₂ was produced via modified-SHS (self-propagating high temperature synthesis). Elemental powders of titanium, silicon and graphite were weighed according to their stoichiometric ratios (3:1:2) respectively. These powders were ball milled for 1 hour, then compacted into cylindrical shape. Synthesis of Ti₃SiC₂ was carried out by using arc melting method. The effect of different arc melting time of 10, 30 and 60 seconds was studied. Phase formation and microstructure were analyzed by using XRD and SEM. The formation of Ti₃SiC₂ was confirmed by XRD, and the SEM micrograph shows that the grain is in needle shape. XRD result also shows that the impurities are present in all the samples. TiC appeared to be the common and dominant impurity in all samples, with relatively low intensities in Ti₅Si₃ and TiSi₂ phases. Some raw materials phase was still existed in sample arc melted for 10 and 30 seconds. Hence, it can be deduced that the raw materials had not yet fully taking part in the formation of Ti₃SiC₂.