Carbothermal Reduction Nitridation Process Research Articles

Preparation and blast furnace slag corrosion behavior of SiC–Sialon–ZrN free-fired refractories

Sialon–ZrN powders were synthesized from low-grade bauxite using a zirconite additive by carbothermal reduction nitridation (CRN). The as-synthesized Sialon–ZrN powders were subsequently used as SiC-based free-fired refractories. Their phase compositions and microstructures of the powders were determined using X-ray diffraction and scanning electron microscopy. The physical properties and blast furnace (BF) slag resistance of the SiC–Sialon–ZrN free-fired refractories were also studied. The results show that the low-grade bauxite and zirconite powders were transformed to β-Sialon and ZrN by the CRN process at 1600°C. The phenolic resin provided a strongly bonded interface between the Sialon–ZrN matrix and SiC particles and thus enhanced their combined strength after drying at 150°C. The strength increased as the temperature was elevated from 1000°C to 1500°C. As the ZrN content increased, the slag erosion rate of the SiC–Sialon–ZrN free-fired refractories initially decreased and then increased after being heated at 1500°C. The presence of ZrO2 in the slag (oxidized from ZrN) revealed that the ZrO2 did not react with other oxides in the BF slag to form low melting point phases. This may play a crucial role in its BF slag erosion resistance. The corrosion mechanism of the BF slag towards the as-prepared SiC–Sialon–ZrN free-fired refractories was determined to be oxidation-erosion-dissolution-penetration.

Fabrication of β-Sialon/ZrN/ZrON composites using fly ash and zircon

β-Sialon/ZrN/ZrON composites were successfully fabricated by an in-situ carbothermal reduction-nitridation process with fly ash, zircon and active carbon as raw materials. The effects of raw materials composition and holding time on synthesis process were investigated, and the formation process of the composites was also discussed. The phase composition and microstructure of the composites were characterized by means of XRD and SEM. It was found that increasing carbon content in a sample and holding time could promote the formation of β-Sialon, ZrN and ZrON. The proper processing parameters to synthesize β-Sialon/ZrN/ZrON composites were mass ratio of zircon to fly ash to active carbon of 49:100:100, synthesis temperature of 1550 °C and holding time of 15 h. The average grain size of β-Sialon and ZrN(ZrON) synthesized at 1550 °C for 15 h reached about 2 and 1 μm, respectively. The fabrication process of β-Sialon/ZrN/ZrON composites included the formation of β-Sialon and ZrO2 as well as the conversion of ZrO2 to ZrN and ZrON.

Influence of yttrium dopant on the synthesis of ultrafine AlN powders by CRN route from a sol–gel low temperature combustion precursor

Y-doped ultrafine AlN powders were synthesized by a carbothermal reduction nitridation (CRN) route from precursors of Al2O3, C and Y2O3 prepared by a sol–gel low temperature combustion technology. The Y dopant reacted with alumina and thus forming yttrium aluminate of AlYO3, Al3Y5O12 and Al2Y4O9, which formed a liquid at about 1400°C and promoted the transformation of Al2O3 to AlN and the growth of AlN particles. Compared with the conventional solid CRN process, Y dopant reduced the synthesis temperature by 150°C, and Al2O3 transformed to AlN completely at 1450°C. The content of Y dopant had little effect on the synthesis temperature of AlN whereas it influenced the phase of Y compounds in the products. As the Y/Al molar ratio was in the range of 0.007648–0.022944, the particle sizes of Y-doped AlN powders synthesized at 1450°C were 150–300nm.

Synthesis of β-Si3N4 powder from quartz via carbothermal reduction nitridation

Abstract β-Si 3 N 4 powder was synthesized via carbothermal reduction nitridation (CRN) method using quartz as starting material. The influence of synthesis temperature, C/SiO 2 molar ratio and amount of Fe 2 O 3 additive on the phase transformation and micro-morphology of β-Si 3 N 4 powder was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The results showed that the optimal experimental conditions for the CRN synthesis of β-Si 3 N 4 powder were 3 h sintering at 1600 °C in flowing nitrogen atmosphere with C/SiO 2 molar ratio of 2.0 and amount of Fe 2 O 3 additive of 5.0 wt.%. The prepared β-Si 3 N 4 grains present a short hexagonal, rod-like morphology. Changes in experimental parameters affect the phase compositions and the morphology of the product. Excessive carbon promoted the formation reaction of β-SiC. Fe 2 O 3 additive exerted a significant promotion on the formation of β-Si 3 N 4 in CRN process by forming the low melting point eutectics.

Synthesis of Ti(C,N) Powder via CRN Method from Rutile/Carbon Mixtures

Ti(C,N) powder was prepared via carbothermal reduction nitridation (CRN) using rutile and carbon black as the raw material. The phase evolution and the reaction mechanism during the CRN synthesis of Ti(C,N) were investigated, and the effect of reaction temperature and C/TiO2molar ratio on the phase composition and x value in TiC1–xNxwas analyzed. The XRD and SEM results show that: Ti(C,N) powder was synthesized at 1500°C for 4h with the C/TiO2molar ratio of 2.2, under the nitrogen pressure of 0.2MPa. Irregular granular structure and the growth stripes were observed in the final products. The growth of Ti(C,N) grains in CRN process was followed by the gas-solid mechanism.The phase compositions of the products were quite dependent on the reaction temperature and the C/TiO2molar ratio. The TiN content in Ti(C,N) decreased with the increase of reaction temperature. TiC1–xNxpowder with different x values can be synthesized by optimizing the experiment conditions including the synthesis temperature and the C/TiO2molar ratio.

Synthesis of Sialon-Based Eco-Materials from Gold Mineral Tailings

Sialon-based eco-materials were synthesized by using the gold mineral tailings that containing abundant Si and Al elements as the major raw material with minor additives through the carbothermal reduction nitridation route. This study realized the conversion of eco-materials from solid waste, gold mineral tailings. The effects of sintering temperature, holding time and x value during carbothermal reduction nitridation process on the phase composition and microstructure of as-fabricated Sialon-based materials were explored. The XRD results indicated that when sintering temperature is 1550°C, holding time is 6h, and x value is 1.0, Ca-α-Sialon/SiC/Fe3Si composites was successfully synthesized. The relative contentSubscript textof each phase in the products is I(α-Sialon): I(SiC): I(Fe3Si)=82:10:8. The SEM images showed the densificated microstructure and uniform grains with the long column shape.

Phase behavior of serpentine mineral by carbothermal reduction nitridation

In this paper, the effects of reductant addition and reaction temperature on phase behavior of serpentine by in situ carbothermal reduction nitridation (CRN) treatment were studied. A brief discussion on the synthesis mechanism of CRN process was also included. The results show that temperature and carbon content were two essential factors that determined the nitridation of serpentine and the formation of β-Si3N4 grains. Serpentine could be transformed into high-temperature composites containing Mg2SiO4, β-Si3N4, Si2N2O and β-SiC at temperatures higher than 1400°C. At 1550°C, more Si2N2O was nitrided to β-Si3N4 as the increase of carbon content, in the final products of samples with carbon addition excess 100wt.% of theoretical quantity, Mg2SiO4 coexisted with β-Si3N4 as the main crystal phases. This transformation provided a feasible way of dealing with serpentine waste for high-temperature utilization.

Effects of synthesis temperature and raw materials composition on preparation of β-Sialon based composites from fly ash

β-Sialon based composites were successfully prepared from fly ash and carbon black under nitrogen atmosphere by carbothermal reduction-nitridation process. Effects of heating temperature and raw materials composition on synthesis process were investigated, and the formation process of the composites was also discussed. The phase composition and microstructure of the composites were characterized by X-ray diffraction and scanning electronic microscopy. The results show that increasing heating temperature or mass ratio of carbon black to fly ash can promote the formation of O′-Sialon. The β-Sialon based composites can be synthesized at 1723 K for 6 h while heating the sample with mass ratio of carbon black to fly ash of 0.56. The as-received β-Sialon in the composites exists as granular with an average particle size of 2–3 μm. The preparation process of β-Sialon based composites includes the formation of O'-Sialon, X-Sialon and β-Sialon as well as the conversion processes of O′-Sialon and X-Sialon to β-Sialon.

Synthesis of TiN-Si3N4 composites from rutile and quartz by carbothermal reduction nitridation

TiN-Si3N4 composite powders were prepared by carbothermal reduction nitridation using rutile and quartz as raw materials. The influence of temperature and carbon addition on the phase evolution and microstructure of the products were investigated. The equilibrium phase diagram of Si-C-N-O and Ti-C-N-O system at different temperatures under 0.2 MPa nitrogen pressure was drew. The results show that the optimum parameters for synthesizing TiN-Si3N4 by carbothermal reduction nitridation process are carbon addition of stoichiometric content, temperature of 1873 K for 4 h and nitrogen pressure of 0.2 MPa. The produced TiN-Si3N4 in this experiment exist in granular and hexagonal columnar shape, and the average particle size of the synthesized powders is 2 ~ 10 ?m.

Volatilization of MgO from Ludwigite in Carbothermal Reduction-Nitridation Process

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.

<i>In Situ</i> Synthesis of β-Sialon Powder from Fly Ash

β-Sialon powder was synthesized by in-situ carbothermal reduction-nitridation process, with fly ash and carbon black as raw materials. The influence of raw materials composition on synthesis process was investigated, and the phase composition and microstructure of the synthesized products were characterized by X-ray diffraction and scanning electronic microscope. The carbothermal reduction-nitridation reaction process was also discussed. It was found that increasing carbon content in a sample could promote the decomposition of mullite in fly ash and the formation of β-Sialon. The β-Sialon could be synthesized at 1550°C for 6h by heating the sample with the mass ratio of fly ash to carbon black of 100:56. The β-Sialon as-received in this study existed as granular with an average particle size of about 2μm. The carbothermal reduction-nitridation reaction process consisted of the nitridation processes of mullite, SiO2 and Al2O3 in fly ash as well as the conversion process of X-Sialon to β-Sialon.

A novel carbothermal reduction nitridation route to MoN nanoparticles on CNTs support

MoN nanoparticles in a size range around 50 nm were obtained on CNTs support via a novel carbothermal reduction nitridation (CRN). For the first time, a common (NH4)6Mo7O24·4H2O can be used as a Mo source to prepare MoN nanoparticles. A Mo-containing precursor was in a first step carburized and was reduced to a MoOxCy/Mo mixture. During further carbothermal nitridation this mixture-phase was shifted to the MoN phase through either a Mo2C or MoOxNy intermediate. Compared with the conventional NH3-temperature-programmed treatment (TPT) route that produced Mo nitride from MoO2 with rigorous heating method, the CRN route favored the formation of Mo nitride from easily nitridable MoOxCy/Mo, MoOxNy and Mo2C intermediates. The phase structure of the Mo nitride product was greatly dependent on nitridation reaction pathway. The NH3-TPT route yielded cubic Mo2N, while the CRN process produced hexagonal MoN.

In Situ Synthesis of ZrN(ZrO2)/Si2N2O Composite Materials from Zircon by Carbothermal Reduction-Nitridation Process

ZrN(ZrO2)/Si2N2O composite materials were synthesized by in-situ carbothermal reduction-nitridation process, with zircon and carbon black as raw materials. The influences of heating temperature and carbon content on synthesis process were investigated, the phase composition and microstructure of the synthesized materials were characterized by X-ray diffraction and scanning electronic microscope. It was found that the decomposition of ZrSiO4 as well as the formation of ZrN and Si2N2O could be promoted by increasing heating temperature and carbon content. ZrN(ZrO2)/Si2N2O composite materials could be synthesized at 1480°C for 6h by heating the sample with ZrSiO4/C mass ratio of 100/40. The ZrN and Si2N2O in the synthesized materials existed in particle shape with an average grain size of about 1–2μm. Introduction Recently, an important research trend of refractories is to develop non-oxides materials such as nitrides, carbides, borides and silicides as well as their composites [1,2]. Among them, zirconium nitride (ZrN) and Silicon oxynitride (Si2N2O) display many outstanding properties, such as high melting points, hardness and strength, excellent corrosion and oxidation resistance [3-5]. zirconium oxide (ZrO2) also exhibits high toughness and strength, excellent corrosion and thermal shock resistance[6]. It is believed that combining ZrN, ZrO2 and Si2N2O into composite materials might yield excellent high temperature combination properties. In the present work, ZrN(ZrO2)/Si2N2O composite materials were synthesized by in-situ carbothermal reduction-nitridation process, with zircon and carbon black as raw materials. The influences of heating temperature and carbon content on synthesis process of the materials were investigated. The carbothermal reduction-nitridation reaction process was also discussed.

Synthesis of Ca-α-SiAlON:Eu x phosphor powder by carbothermal-reduction–nitridation process

Yellow-emitting Ca-α-SiAlON:Eu x phosphor powders have been synthesized by the carbothermal-reduction–nitridation of a homogeneous Ca–Si–Al–Eu–C–O mixture at 1550 °C in flowing nitrogen. The resulting phosphor powder emits yellow luminescence with a peak wavelength at 575–590 nm under ultraviolet excitation at 370 nm. Compared with commercial Ce 3+-doped yttrium aluminum garnet (YAG:Ce 3+) phosphor powder, the synthesized Ca-α-SiAlON:Eu x phosphor powder exhibits better thermal stability.

Low-temperature synthesis of AlN powder with multicomponent additive systems by carbothermal reduction–nitridation method

AlN powders were synthesized at low temperatures (1300 and 1400 °C) by the carbothermal reduction–nitridation (CRN) method using multicomponent additive systems. The synthesis treatments were conducted in a graphite furnace with flowing nitrogen gas between 1200 and 1500 °C using powder mixtures with Al 2O 3:C molar ratio of 1:3 and 0.5–3 wt% of CaF 2, Y 2O 3, Li 2CO 3 and/or SrCO 3 as additives. In relation to the conventional CRN process, the use of multicomponent additive systems reduced the synthesis temperature in 200 °C (CaF 2–SrCO 3), 100 °C (CaF 2–Li 2CO 3 and CaF 2–Y 2O 3–Li 2CO 3) or <100 °C (CaF 2–Y 2O 3 and CaF 2–Y 2O 3–Li 2CO 3–SrCO 3). X-ray diffraction patterns showed that the additives reacted with the alumina powder forming aluminate phases, which vaporized with the increase of synthesis temperature. The enhanced AlN conversion rate was discussed in terms of the vaporization of aluminates in the reducing atmosphere.

Preparation of ZrN-Si 3N 4 composite powder with zircon and carbon black as raw materials

ZrN-Si 3N 4 composite powder with low cost from zircon was prepared by carbothermal reduction-nitridation process. The influence of mass ratio of C to ZrSiO 4 ( m(C)/ m(ZrSiO 4)) and soaking time on phase composition and microstructure of the products was studied by means of XRD and SEM-EDS. The formation process of ZrN-Si 3N 4 composite powder was also analyzed in detail. The results show that with the increase of m(C)/ m(ZrSiO 4) and soaking time, the formation of Si 3N 4 and ZrN can be promoted obviously. The ZrN-Si 3N 4 composite powder with size of 1–2 μm can be obtained at 1 773 K for 12 h when m(C)/ m(ZrSiO 4) is 0.4.

Influence of processing parameters on the phase composition of ZrN-Si3N4 synthesized from zircon

The optimum parameters were determined for synthesizing ZrN-Si3N4 composite powder from zircon by carbothermal reduction-nitridation (CTRN) process. The samples were prepared by mixing the carbon black of an average particle size less than 30 μm and the zircon of 40 μm with C/ZrSiO4 mass ratios of 0.2, 0.3, 0.4, and 0.5. The prepared samples were subjected to the CTRN process at temperatures of 1673, 1723, 1753, and 1773 K for 6, 9, and 12 h. The CTRN process was conducted in an atmosphere-controlled tubular furnace in a nitrogen gas flow of 1.0 L/min. All the products were examined by X-ray powder diffraction to determine the transformation. The results showed that the proper transformation of ZrN-Si3N4 occurred at 1773 K for 12 h with a C/ZrSiO4 mass ratio of 0.4.

Synthesis of O'-SiAlON/SiC Ecomaterials by Using Non-Traditional Resources: Yangtze River Sand

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.

Preparation of Ca-Substituted α-Sialon Eco-Materials by Utilizing Tungsten Molybdenum Bismuth Polymetallic Tailings

This presented a route to utilize the Tungsten Molybdenum Bismuth Polymetallic Tailings in Shizhuyuan of Hunan province to fabricate Ca-substitued α-Sialon eco-materials. The reaction mechanism in carbothermal reduction nitridation process was widely studied by separately considering the effect of sintering temperature and soaking time. Based on the optimized conditions, a composite containing 78% Ca-based α-Sialon has been fabricated at 1600°C for 8h.

Formation Process of Calcium-α SiAlON Hollow Balls Composed of Nanosized Particles by Carbothermal Reduction–Nitridation

Carbothermal reduction–nitridation (CRN) of SiO2–Al2O3–CaO powders was performed under various firing conditions to investigate the formation process of Ca-α sialon hollow balls composed of nanosized particles. Scanning electron microscopy and transmission electron microscopy observations of the samples obtained at different firing temperatures confirmed that solid spherical particles were formed at the early stage of the reaction, and nanosized particles were subsequently produced on the surface of these solid balls. From X-ray diffraction and energy-dispersive spectrometry analyses, it was found that the solid balls initially formed at 1450°C were mainly amorphous and contained Si, Al, Ca, O, and a small amount of N. Further nitridation at 1450°C gradually converted the solid balls into Ca-α sialon hollow balls over time. The results revealed that the formation of Ca-α sialon hollow balls depends on the formation of solid balls from the Si–Al–Ca–O liquid phase at the initial stage of the CRN process.