Papers by Keyword: Carbothermal

Abstract: The synthesis of Si-based refractory compounds from coconut shells (CS) by carbothermal treatment was investigated. Coconut shells, an agro-waste was utilised in the processing of the Si-based refractory compounds in a single stage carbothermal processing route. The treatment scheduled was carried out in a conventional heat treatment furnace at a temperature window of (900-1900 °C) at 10 °C/min heating rate in a controlled atmosphere. X-ray Diffractometer (XRD) was used to analyzed and quantify the crystalline and amorphous phases in the reaction products. The results from Fourier transform infrared spectroscopy (FTIR) revealed that, the dominant functional groups present after the carbothermal treatment were mainly Si-O-Si and Si-C groups. Also, the XRD results showed that the polytypes are mainly of α-SiC type precipitating as hexagonal symmetry of 6H-SiC and 4H-SiC type. The silica polytypes amount to about 8-14 wt.% of the silica polytypes as observed for different processing temperatures adopted. However, the total yield of SiC-made up between 11 to 40 wt.% of the crystalline phases as identified by XRD from the process. It is evident that the adoption of this processing route is a viable option for the synthesis of coconut shells as potential reinforcement for composites design.

Abstract: SiC powder can be produced generally through the Acheson process and it is required long carbothermic reaction time of SiO2 with carbon powder around 2200 °C ~ 2400 °C. Due to the high reaction temperature and long reaction time of the process, the powders produced have a large particle size and consist of mostly alpha phase SiC. Synthetic temperature of beta phase SiC powder is known to produce at 1700 °C ~ 1900 °C which is lower temperature than that of alpha phase SiC powder. We prepared β-SiC powder by heating precursor derived from the mixture of phenolic resin and tetraethyl orthosilicate. The precursor was heated at 1800 °C for 4 h in an Ar atmosphere. In order to examine the pyrolysis residue after the heat treatment, the SiC powder was analyzed with XRD and SEM. The X-ray diffraction result of the SiC powder shows the diffraction peaks around 35°, 60°, and 73° corresponded to the beta SiC phase. β-SiC powder prepared in this study contains lower metallic impurities compare than that of α-SiC powder prepared from Acheson method and is able to use as a good starting material for SiC single crystal growing.

Abstract: In this paper, AlN powder and ceramic are prepared by microwave sintering under various sintering environments. The microstructures of the powder and the ceramic are characterized by scanning electron microscopy and X-ray diffraction technology. The mechanical and thermal properties of the ceramic are studied. It was found that the sintering environment has great influence on the material fabrication. The heat-assisted environment is beneficial to the synthesis of AlN powder. On the other hand, the carbothermal sintering environment has the two-sided influence to the sintering of AlN ceramic.

Abstract: Aluminum oxynitride powders were synthesized by carbothermal reduction, using nano-sized alpha-alumina, gamma-alumina and carbon as raw materials. Effects of the weight percentages of alpha-alumina in alumina (R) and synthesizing temperatures (T) on the preparation of single-phase AlON powders have been studied. The results showed that proper R can reduce the shrinkage and increase the formation rate of AlON phase, but a high R will reduce the formation rate of AlON phase, because the activity of alpha-alumina was lower than that of gamma-alumina. Single-phase AlON powder with excellent properties can be obtained under the condition of R=0.15, T=1700°C. Moreover, this single-phase AlON powder was well-dispersed with an average size of about 2 μm.

Abstract: The photoluminescence of the diverse nanostructures of nonstoichiometric ZnO grown via carbothermal reduction at 900°C was investigated. Various formations of different structures like wires, rods, tubes and tetrapods resulted from the inhomogeneity of the boundary diffusion layer associated with vapor current induced in the set-up. The band gap emission of these structures was observed at around 390 nm, which corresponds to energy of 3.20 eV. The study was extended to measure changes of crystal habit of ZnO nanostructures in terms of its fractal dimension.

Abstract: SiAlON ceramics were successfully produced in the form of powders from high purity kaolin, a hydrated aluminium silicate, Al2Si2O5(OH)4 type of clay mineral (comprises 83.85% kaolinite, 13.59% quartz, 0.88% feldspar, 1.37% others) of Canakkale-Can origin. Factors affecting SiAlON powder production were temperature, holding time, gas-flow rate and preparation methods. System optimisation was achieved following the results succeeded from numerous testing and characterisation (with XRD, SEM, EDS, BET, etc.) of each test. Changing in gas flow rate, temperature and holding time at plateau temperature had influences on the final powder yield, their morphologies and phase formation. The best conversion of kaolin clay mineral to SiAlON ceramic powder was the test run at 1475oC for 4 hour under 1 lt/min N2-flow. Product after the process was mainly of β'- Si3Al3O3N5 (z=3) powder along with small amounts of Al2O3, mullite and AlN phases. Some powder product exhibits furry type of wiskers morphology, which may be useful for using as a reinforcing material in particulate composite bodies.

Abstract: In this study, α-Si3N4 powder was produced by carbothermal reduction and nitridation (CRN) of quartz from Can-Canakkale. Carbon with a specific surface area of 110 m2g−1 and quartz powders were mixed then the powder mix was placed in an alumina tube furnace and reacted in between 1300-1500°C for 4 hours under nitrogen flow. The quartz powder was carbothermally reduced and nitrided to form silicon nitride powders. XRD results showed that the reaction product was mainly α-Si3N4 and contained some β-Si3N4 and residual quartz. In order to reduce amount of unreacted quartz, the raw materials mixture was grinded either with carbon black or with no carbon. After CRN reactions of separate grinded quartz powders with carbon, residual quartz was disappeared, reaction temperature was decreased and α-Si3N4 rate was increased. Hence, a better mixing of carbon and fine silica enhanced the α phase formation. SEM images and XRD pattern showed that sub micron particles (0.6–0.87m), high α-phase content Si3N4 powders can be produced at 1450°C for 4 h in flowing nitrogen gas during the CRN process.