Carbothermal Reduction Nitridation Reaction Research Articles

Synthesis of Nano-aluminum Nitride powder at low temperature by Sol-gel method

In this paper, molecular-level mixed aluminum nitride has been prepared from aluminum sec-butyl alcohol, glucose, and urea by sol-gel processing. Then, the nano-aluminum nitride powder with uniform particle size distribution was obtained by carbothermal reduction nitridation reaction. The effects of different feed ratios, reaction temperatures, and holding times on the phase of AlN powder were systematically studied. The prepared nano-aluminum nitride powder has a uniform particle size and a near-spherical shape, and its grain size is approximately 20~30 nm. The preparation temperature in this method was significantly reduced from the same preparation method of aluminum nitride powder.

Synthesis of high‐quality vanadium nitride particles by one‐step vacuum carbothermal reduction–nitridation method: Theoretical and experimental study

AbstractOwing to its high hardness, favorable stability, and good electrical performance, vanadium nitride (VN) has been extensively used as an alloy additive, an electrode material, a ceramic material, and a catalyst. However, traditional VN synthesis methods require high temperatures and long soaking times. In this study, high‐quality VN particles were prepared from V2O3 powder at a lower temperature and shorter soaking time by a one‐step vacuum carbothermal reduction–nitridation (VCRN) method. Thermodynamic and kinetic analyses elucidated the mechanism of this process. Thermodynamic analysis showed that vacuum was conducive to the carbothermal reduction of V2O3, reducing the initial reaction temperature, and the main reaction path was V2O3→VO→VxCy(VC/ V2C/ V8C7/ V6C5)→VN. Kinetic results indicated that the one‐step VCRN method was a gas–solid reaction. Within the temperature range of 1373–1473 K, the rate‐determining step was controlled by the carbothermal reduction–nitridation reaction, combination control of the reduction–nitridation reaction and the interlayer diffusion, and interlayer diffusion control of N2 during the different reaction processes. High‐quality VN particles obtained at a temperature of 1473 K, pressure of 300 Pa, and soaking time of 3 h were characterized by X‐ray diffraction, transmission electron microscopy, energy dispersive X‐ray spectroscopy, and particle size distributions. The O and N contents, measured by an O/N analyzer, were 0.85% and 19%, respectively, and the C content, measured by a C/S analyzer, was 0.92%. These analyses indicate that high‐quality VN can be obtained by a one‐step VCRN method.

Effect of Residual Oxygen Concentration on the Lattice Parameters of Aluminum Nitride Powder Prepared via Carbothermal Reduction Nitridation Reaction.

Residual oxygen in wurtzite-type aluminum nitride (AlN) crystal, which significantly affects phonon transport and crystal growth, is crucial to thermal conductivity and the crystal quality of AlN ceramics. In this study, the effect of residual oxygen on the lattice of AlN was examined for as-synthesized and sintered samples. By controlling reaction time in the carbothermal reduction nitridation (CRN) procedure, AlN powder was successfully synthesized, and the amount of residual oxygen was systematically controlled. The evolution of lattice parameters of AlN with respect to oxygen conc. was carefully investigated via X-ray diffraction analysis. With increasing amounts of residual oxygen in the as-synthesized AlN, lattice expansion in the ab plane was induced without a significant change in the c-axis lattice parameter. The lattice expansion in the ab plane owing to the residual oxygen was also confirmed with high-resolution transmission electron microscopy, in contrast to the invariant lattice parameter of the sintered AlN phase. Micro-strain values from XRD peak broadening confirm that stress, induced by residual oxygen, expands the AlN lattice. In this work, the lattice expansion of AlN with increasing residual oxygen was elucidated via X-ray diffraction and HR-TEM, which is useful to estimate and control the lattice oxygen in AlN ceramics.

Preparation of nano-TiN powders by Ni-catalysed carbothermal reduction nitridation

TiN nanoparticles were prepared at 900–1100 °C by Ni-catalysed carbothermal reduction nitridation from sol-gel using tetrabutyl titanate, citric acid monohydrate and nickel chloride hexahydrate as starting materials. The catalytic effects of nickel on the carbothermal reduction nitridation of xerogels were investigated. Ni has a crucial promoting effect on the carbothermal reduction reaction of the xerogels and visibly enhanced carbothermal reduction and nitridation reactions. The dry gel with 5% NiCl2 was added to obtain nano-TiN at 900 °C. The transmission electron microscopy analysis and Materials Studio simulation results showed that the facilitating effect of Ni on carbothermal reduction nitridation reaction was ascribed to the provision of heterogeneous nucleation sites for amorphous titania, promoting crystallisation and adsorption of N2, resulting in its smooth dissociation into highly active N atoms and consequently enhancing the carbothermal reduction nitridation.

Synthesis of titanium nitride via hybrid nanocomposites based on mesoporous TiO2/acrylonitrile

In the present study, the synthesis of titanium nitride (TiN) by carbothermal reduction nitridation (CRN) reaction using nanocomposites made of mesoporous TiO2/acrylonitrile with different content of inorganic phase were explored. The choice of hybrid nanocomposite as precursor for the synthesis of TiN was made due to the possibility of having an intimate interface between the organic and inorganic phases in the mixture that can favours CRN reaction. Subsequently, the hybrid composites have been subjected to four-step thermal treatments at 290 °C, 550 °C, 1000 °C and 1400 °C under nitrogen atmosphere. The XRD results after thermal treatment at 1000 °C under nitrogen flow show the coexistence of two crystalline phases of TiO2, i.e. anatase and rutile, as well as TiN phase, together with the detection of amorphous carbon that proved the initiation of CRN reaction. Furthermore, the observations based on XRD patterns of samples thermally treated at 1400 °C in nitrogen atmosphere were in agreement with SEM analysis, that shows the formation of TiN by CRN reaction via hybrid nanocomposites mesoporous TiO2/acrylonitrile.

Preparation of AlN under vacuum by the alumina carbothermal reduction nitridation method

With good electrical, thermal and mechanical properties, aluminium nitride is widely used in microelectronics and other fields. However, high temperatures are still needed for the method of alumina carbothermal reduction nitridation (CRN) for AlN preparation. Herein, thermodynamics calculation and experimental research were adopted to investigate the preparation of AlN under vacuum by the alumina CRN reaction in order to lower reaction temperature. The results demonstrate that lower pressure benefits the alumina CRN reaction. A single phase of AlN was successfully obtained at 1823 K for 2.5 h with a N2 gas pressure of 300 Pa. Moreover, an underlying growth mechanism of AlN during the alumina CRN process under vacuum was proposed, which is different from that under atmosphere or elevated pressure. The rate limiting step of alumina CRN process was determined. The results also indicate that Al4C3 and Al2OC play important roles in the process of alumina CRN under vacuum.

Effects of reducing environment and fusible components on carbothermal reduction–nitridation reaction of coal gangue at high temperature under N2 atmosphere

The synthesis of SiAlON materials by the carbothermal reduction–nitridation (CRN) method paves the way for utilization of coal gangue with significant economic benefits. Excessive carbon (C), which provides a high residual C content in the product, is added to the raw materials to ensure a high yield of SiAlON. The industrial solid waste of coal-coke powder is used as a reductant. In this study, the effects of the reducing environment and C content on the CRN reaction of coal gangue using corundum and graphite crucibles are investigated and a method to reduce the amount of C added to the raw materials is proposed. The process is carried out under a N2 flow in the range of 1300–1500 °C with a holding time of 3 h. The effects of fusible components including CaO, Fe2O3, and MgO on the CRN reaction and micromorphology are discussed. The graphite crucible considerably promotes the conversion of mullite to β-SiAlON and is effective for the reduction in residual C content in the product. When the graphite crucible is used, the mullite wholly transforms to β-SiAlON and corundum, and β-SiAlON and AlN at 1400 °C when the C contents in the raw materials are 11% and 18%, respectively. The content of residual C in the product is approximately 1% (or lower). The β-SiAlON content decreases with the additions of CaO and MgO in the raw materials owing to sintering and melting. The addition of Fe2O3 promotes the formation of β-SiAlON whiskers according to the vapor–liquid–solid mechanism. These results would be useful in parameter optimization for a cleaner production of β-SiAlON powder using the CRN method.

Mechanism and kinetics of combustion-carbothermal synthesis of AlN nanopowders

Abstract In this work, the carbothermal reduction-nitridation process of low-temperature combustion synthesis (LCS) (Al 2 O 3 +C) precursor was investigated in detail. Compared with conventional precursor, the LCS precursor possesses many advantages such as amorphous structure, nanosized particles, homogeneous mixing at molecular level. The experimental results indicate that the methods for preparing precursor exert great influence on phase transformation of Al 2 O 3 , onset temperature of nitridation and reaction activity. During the calcination, the phase transformation of Al 2 O 3 is hindered by a large amount of surrounding C particles rendering Al 2 O 3 maintains high reactivity. Accordingly, the nitridation reaction initiates at 1300 °C and completes at 1500 °C for 2 h. Furthermore, the reaction mechanism was also discussed on the basis of experiments. More significantly, it is established that the activation energy of carbothermal reduction-nitridation reaction using LCS precursor is Eα=336 KJ/mol.

Preparation of Sialon/Si<sub>3</sub>N<sub>4</sub>-SiC Composite Refractories Using Kyanite Tailings

Sialon-SiC composite powders were synthesized from kyanite tailings through the carbothermal reduction nitridation (CRN) technique. Using Sialon-SiC composites to substitute Si3N4 composites via the CRN technique synthesize Sialon/Si3N4-SiC composite refractories. The phase composition, cross section morphology, and the substituent amount of Sialon-SiC composites impact on refractories mechanical properties were investigated, respectively. The optimized synthesis temperature for the CRN reaction was found to be 1550 °C for 4 h with the excess carbon 20%. The substituent amount of Sialon-SiC was 25%, the mechanical properties of Sialon/Si3N4-SiC composite refractories reached optimal performance, which bending strength value was 41.8 MPa and compression strength value was 61.6 MPa.

A smart processing of silicon oxynitride ceramic powders with variable morphology controlled by hard template assistance

Spherical and rod-like Si2N2O ceramic powders were successfully prepared using a hard template strategy to meet different application background. The mesoporous silica spheres and rod-like silica (SBA-15) particles were selected as hard templates and also served as reactants. Highly active mesoporous silica is reacted through a combination of sucrose-nano-casting and carbothermal reduction nitridation (CRN) to successfully synthesize spherical and rod-like powders. Temperature and holding time of calcination are found to be significant factors for the formation of pure and well-crystallized powders. Insufficient temperature and holding time cause an incomplete reaction between silica, carbon and nitrogen, and also lead to the formation of amorphous phase. In the processing, sucrose was used as carbon source to incorporate evenly into mesopores of templates to assist CRN reaction. Big surface areas and high porosity of mesopores in SiO2 provide an additional driving force to decrease the formation temperature of Si2N2O phase to 1280°C. As-synthesized powders inherit same morphology as their parental mesoporous templates, which indicate that two mesoporous templates play an important role in guiding the growth of ceramic particles. In the research, we develop a smart processing for synthesis of oxynitride powders with variable morphology controlled by template.

Synthesis of Sialon-SiC Composites from Kyanite Tailings by Carbothermal Reduction Nitridation

Sialon-SiC composites were synthesized from kyanite tailings via the carbothermal reduction nitridation (CRN) technique. The phase composition, morphology, and microstructure of the CRN samples were investigated by x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and elected-area electron diffraction. A brief discussion on the synthesis mechanism of CRN process was investigated based on the thermodynamic analysis of the SiO2-Al2O3-C-N2 system. The results show the phase compositions depended on the synthesis temperature. With the increasing heating temperature, SiO2 was first changed into Si2N2O and then transformed into Si3Al3O3N5 through reacting with N2, Al2O3, and C. At the same time, the excess SiO2 changed into SiC by a carbothermal reduction reaction. The optimized synthesis temperature for the CRN reaction was found to be at 1550°C for 4 h. The Si3Al3O3N5 and SiC phases were proved coexisting in the same CRN particle. This transformation provided a feasible utilization route of kyanite tailings for high-temperature application.

Fe–Sialon–Ti(C,N) composites from carbothermal reduction–nitridation of low-priced minerals and their application in taphole clay refractories

Fe–Sialon–Ti(C,N) composite materials were first synthesized via carbothermal reduction–nitridation reaction with low-priced mineral materials, such as ilmenite, quartz, aluminum dross and coke powders, as starting materials. Effects of temperatures on the phase compositions and microstructures of products were investigated. The investigation results indicated that the optimal synthesis temperature was 1550°C. Rise in synthesis temperature was beneficial for the synthesis of Sialon and Ti(C,N). The as-fabricated Fe–Sialon–Ti(C,N) composites were used as additives to produce taphole clay refractories, and the bending strength and erosion resistance against blast furnace slag of taphole clay refractories were studied. Taphole clay refractories with 20wt% Fe–Sialon–Ti(C,N) composite materials still owned good slag resistance. Bending strength of taphole clay refractories increased with the addition of Fe–Sialon–Ti(C,N) composite materials; when 15wt% Fe–Sialon–Ti(C,N) composite materials were added, bending strength reached its highest value of 13.36MPa.

Effects of processing parameters on in situ synthesis of β-Sialon/ZrN/ZrO2 from fly ash and zircon

β-Sialon(Si4Al2O2N6)/ZrN/ZrO2 ceramic powder was synthesised by an in situ carbothermal reduction–nitridation (CRN) process using fly ash, zircon and active carbon as raw materials. The effects of processing parameters on the phase composition and microstructure of the products were investigated by X-ray diffraction and scanning electronic microscope. The formation process of β-Sialon/ZrN/ZrO2 ceramic powder was also discussed. Increasing carbon content in a sample, reaction temperature and soaking time all could promote the CRN reaction and benefit the formation of β-Sialon and ZrN. The β-Sialon/ZrN/ZrO2 ceramic powder could be fabricated successfully at 1450°C for 2 h, then continually at 1550°C for 4 h while heating the sample with the zircon/fly ash/active carbon mass ratio of 49∶100∶100. The as received β-Sialon particles existed as flaky and their average grain sizes were about 2–3 μm, and the average grain size of ZrN and ZrO2 reached 1–2 μm. The formation process of β-Sialon/ZrN/ZrO2 ceramic powder included the decomposition of zircon and mullite, the formation processes of O’-Sialon (Si1·83Al0·17O1·17N1·83), X-Sialon (Si3Al6O12N2), β-Sialon and ZrN as well as the conversion processes of X-Sialon and O’-Sialon to β-Sialon.

Phase Behavior Analysis of Low-Grade Bauxite and Rutile by Carbothermal Reduction-Nitridation

In this study, β-Sialon/Al2O3/TiN diphase powder was synthesized using low-grade bauxite and rutile via carbothermal reduction-nitridation. The phase transitions of low-grade bauxite and rutile in the carbothermal reduction and nitridation process were analyzed by XRD, SEM and EDS. The effects of different reaction parameters such as reaction temperature, rutile addition on the phase composition and microstructure of products were analyzed. The results showed that β-Sialon/Al2O3/TiN powder was prepared using low-grade bauxite and rutile as raw materials and coke as reducing agent by carbothermal reduction-nitridation reaction in flowing nitrogen atmosphere of 0.03 MPa at 1350-1375 °C, for 4 h.

Fabrication and Properties of Al<sub>2</sub>O<sub>3</sub>-SiC/Sialon Composite Refractories

Sialon powder was synthesized using low grade bauxite as raw materials by carbothermal reduction-nitridation reaction. The influence of synthesizing temperatures (1300°C, 1350°C, 1400°C, 1450°C, 1500°C and 1550°C) on the phases of the final products was studied by XRD technique. β-Sialon (Z=3) formed at 1350°C and decreased when the temperature was higher than 1450°C. The optimizing reaction temperature for preparing Sialon was 1450°C. The Al2O3-SiC/Sialon composite refractories were prepared at 200°C, 400°C and 600°C for 24h with white corundum, brown corundum, SiC, Sialon powders prepared at 1450°C and calcium aluminate cement. The bulk density, apparent porosity, water absorption and bending strength of the Al2O3-SiC/Sialon composite refractories at room temperature were studied. The results show that the bulk density decreased and then increased with the enhancing of the temperature and reached the highest value of 2.43g/cm3 at 200°C. The apparent porosity and water absorption reached the lowest values of 26.68% and 10.99% at 200°C respectively. The bending strength decreased as the temperature increased, reached the highest value of 0.73MPa at 200°C.

Luminescence Properties of Eu2+ Doped β-SiAlON Phosphor

Eu2+ doped b-SiAlON (z = 1, 3, 4) phosphor were synthesized by carbothermal reduction- nitridation (CRN) using precursors powder as materials. The precursors powder prepared by sol-gel method using the SiO2, AlCl3×6H2O, Eu(NO3)3, ammonia water, carbon powders as starting materials. The CRN reaction proceeded at 1380°C for 6 h in an N2 atmosphere. Eu2+ doped b-SiAlON (z = 1, 3, 4) had high adsorption in the UV-visible spectral region. While z = 1, one bands were observed in the emission spectrum centered at about 425 nm monitored at 282 nm. The excitation bands centered at about 282 nm. While z = 3, one bands were observed in the emission spectrum centered at about 425 nm monitored at 282 nm. The excitation bands centered at about 282 nm. While z = 3, the emission spectra exhibit one bands with maxima at about 419 nm under 280 nm excitation. The excitation bands centered at about 280 nm. While z = 4, the emission spectrum centered at about 419 nm monitored at 280 nm. The excitation bands centered at about 280 nm. In this work, luminescence properties of Eu2+ doped b-SiAlON (z = 1, 3, 4) are independent of z value. It is possible related to the low synthesis temperature.

<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.

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.

Preparation of titanium carbonitride nanoparticles from a novel refluxing-derived precursor

Titanium carbonitride (TiC x N 1 − x ) nanoparticles were prepared from a novel refluxing-derived precursor. The organic/inorganic hybrid precursor was prepared by two-stage refluxing method using hydrous TiO 2 as titania source and n-Dodecane as carbon source. The precursor was heat-treated to 1350 °C in flowing nitrogen to get TiC x N 1 − x nanoparticles. Electron microscopy photographs showed the particle size ranged from 20 to 60 nm. X-ray powder diffraction pattern indicated that the product was face-centered cubic TiC x N 1 − x with a lattice constant a = 4.2872 Å and average crystallite sizes of 33.4 nm. Long time refluxing results in Alkane dehydrogenation and the formation of coke occur and promotes the coke to large scale impinge on TiO 2 nanoparticles as carbon source in the carbothermal reduction–nitridation reaction.

Synthesis of nano Ti(C,N) powder by mechanical activation and subsequent carbothermal reduction–nitridation reaction

Abstract Nano Ti(C,N) powder with average particle size of below 100 nm was synthesized from nano anatase/carbon black mixtures employing mechanical milling activation and subsequent carbothermal reduction–nitridation (CRN) reaction. The activated and heat-treated powders have been characterized by X-ray diffraction (XRD), reaction dynamics of activated powders has been studied by thermogravimetry-differential scanning calorimetry (TGA-DSC), and Ti(C,N) products were evaluated by transmission electron microscope (TEM). The results show that CRN reaction of anatase was enhanced by pre-milling the starting powders. Thus, onset formation temperature and holding time of Ti(C,N) decreased from 1300 °C to 1150 °C and from 4 h to 2 h, respectively. However, mechanical activation did not alter phase evolution sequences of TiO2 CRN reaction.