Papers by Keyword: Carbothermal Reduction-Nitridation

Abstract: This paper focuses on the influence of temperature and holding time on synthesizing MgAlON-SiAlON powders applying CRN method. The results were analyzed by chemical and XRD analysis technology. The experimental results revealed that β-SiAlON, as an intermediate phase, appeared in the synthesized products at 1200°C. With the increase of synthesis temperature, β-SiAlON was translated into Mg-SiAlON polytypoid (Mg_1.25Si_1.25Al_2.5O₃N₃) and reached the maximum at 1450°C. Increasing synthesis temperature was beneficial to generate MgAlON, and the optimal condition of temperature for powders synthesis was 1500°C. β-SiAlON disappeared with the increase of holding time. MgAlON and Mg-SiAlON polytypoid became the main crystalline phases with a holding time of 4h. Whats more, the phase compositions had no evident change with longer holding time. Flaky MgAlON grains and elongated Mg-SiAlON grains were observed in synthesized powders.

Abstract: Phase behaviors of zircon at different temperatures via carbothermal reduction-nitridation were investigated in this study. By using zircon as raw material, with carbon coke as reducing agent, the influence of reaction temperatures (1450, 1500, 1550 and 1600 °C, respectively) on phase behaviors and microstructure of the products was characterized by X-ray diffraction analysis (XRD), scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). The results shows that by carbothermal reduction-nitridation, the main phases in the final products of zircon are m-ZrO₂, c-ZrO₂, β-SiC, ZrN and β-Si₃N₄ at different temperatures for 4 hours.

Abstract: Based on thermodynamic analysis, the reduction and volatilization of magnesium in ludwigite were studied using carbothermal reduction-nitridation method. The experimental result show that the total mass loss rate of samples increase with temperature rising, which the maximum is 52.88 wt% in the range from 1440°C to 1470°C. Magnesia in ludwigite was reduced and volatilized as gaseous magnesium vapour in the process of carbothermal reduction, and its mass loss rate go up to 98.138%. Part of the volatilized matter formed white powder deposited at the opening of furnace tube and adhered to tube wall together with boride/silicon volatilized. It was proved that there is volatilization of MgO from ludwigite in the process of carbothermal reduction-nitridation.

Abstract: The output quantity of iron tailings increases rapidly with the development of metallurgical industry and the growth of the requirement for minerals in the world, which could cause severe hazard to our environment. Therefore, it is very important to recover and reuse these tailings to protect the environment and use natural resources effectively. In this paper, the Fe-Si-Ti multiphase composite ceramic has been synthesized from the Iron ore tailings of Panzhihua region with the carbothermal reduction nitridation (CRN) method. The phases and microstructures of sintered body were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FSEM) and energy dispersive spectroscopy (EDS). The XRD pattern indicates that the main phases of the samples are Fe3Si and Ti(C0.3, N0.7). Meanwhile, FSEM and EDS show that Fe3Si is surrounded by Ti(C0.3, N0.7). Besides, the physical properties of the sample are tested, especially the wear resistance. The test results show that the synthesized Fe3Si-Ti(C0.3, N0.7) composite ceramic has good wear resistant property, high hardness and larger thermal expansion coefficient, which indicates it can be used as the abrasion-proof material or transition layer between the metal and inorganic coating. At last, based on FSEM and EDS, the microstructure and elements of the abraded surface of sample is analyzed.

Abstract: In this paper, the research mainly focused on utilization of iron ore tailing of Panzhihua region. Based on the analysis of its components, Carbothermal Reduction Nitridation (CRN) method was selected to synthesize eco-friendly composite material. Different additives were tried to improve the property of the samples. The influence of different sintering temperature, holding time and contents of additives were taken into account, and orthogonal design was employed to obtain the optimal parameters. It indicated that only when the temperature was 1450°C and the holding time was 5 hours, the samples with the bulk density of 3.42g/cm3 was obtained. The phase and surface morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Experimental results showed that the phases of the product were Fe3Si and TiC0.3N0.7. The research provided a novel recycling process for ore tailings.

Abstract: O'-SiAlON/SiC ecomaterials were synthesized by using the Yangtze River sand that containing abundant Si and Al elements as the major raw material with minor additives through the carbothermal reduction nitridation route combined with colloidal process. This study realized the conversion of ecomaterials from non-traditional resources, Yangtze River sand. Orthogonal design was adopted to optimize the colloidal process parameters. The green compact with the largest bulk density was obtained when the solid volume loading is 50%, the addition mass fraction of SL is 0.8%, the addition mass fraction of CMC is 0.05%, the ball milling time is 10 h, the pH value is 9 and particle size distribution is multi-peak in the colloidal process. The effects of reduction agent, flowing rate of N2, sintering temperature during carbothermal reduction nitridation process on the microstructure of as-fabricated SiAlON materials were explored. The XRD results indicated that when sintering temperature is 1450°C, maintaining time is 6 h, flowing rate of N2 is 1.0 L/min and carbon black is selected as reduction agent, O-SiAlON/SiC composites was successfully synthesized. The SEM images showed the densificated microstructure and uniform grains with the short column shape.

Abstract: Single phase Sialon was synthesized successfully from fly ash by carbothermal reductionnitridation reaction in this paper. The effects of synthesizing temperature (1200°C, 1300°C, 1400°C and 1450°C) and carbon content (stoichiometric content, exceeding 10%, 50% and 100%) on the final production were studied by XRD and SEM. Synthesis mechanism of β-Sialon was also analysized. The results indicated that single phase β-Sialon with z=3 was obtained using fly ash as raw materials and carbon black of stoichiometric content as reducer by carbothermal reduction- nitridation reaction in flow nitrogen at 1450°C for 3h. Temperature and content of carbon had significant effect on the synthesis of β-Sialon.

Abstract: In this work, β-sialon ceramics were prepared from high-aluminium fly ash via carbothermal reduction-nitridation (CRN) and the physicochemical properties of the materials such as bulk density, apparent porosity, water absorption and flexural strength were also discussed. The results showed that the percentage of β-sialon phase in the product decreases as the temperature increases from 1400°C and the weight of the sintered specimen experienced an increase during 1350°C~1450°C due to the nitridation reactions, and followed by a gradual decrease till 1550°C for the decomposition of β-sialon. It is indicated that the optimum sintering temperature to obtain the highest yield of β-sialon ~93% lies in 1400°C~1450°C. The SEM images revealed that the prepared β-sialon sintered at 1400°C were mainly in shape of elongated prisms, typically ~5μm in length and 0.5~1μm in width. As the temperature increased to 1500°C and above, β-sialon decomposed and the new phases of SiC and AlN were formed at 1550°C as confirmed by XRD.

Abstract: Ultrafine β-sialon powder is synthesized by citrate sol-gel and carbothermal reduction and nitridation (CRN) process. The presence of small amounts of β-sialon as crystal seed can obviously accelerate the formation of final β-sialon product and lower its formation temperature. The effects of nitriding temperature on the formation of the final β-sialon are investigated. The mean particle size of the prepared β-sialon powder is 100 ~ 150 nm. The β-sialon precursor gel and the ultrafine β-sialon powder are characterized by XRD, TG-DTA and SEM. The isoelectric point of ultrafine β-sialon is pH 2.46.