Carbothermal Reduction Nitridation Research Articles

Microstructure and mechanical properties of (Ti, W, Mo, Nb, Ta) (C0.78, N0.22) high entropy cermets with 5–25 wt% Co–Ni binders

In this study, high entropy (Ti0.6,W0.1,Mo0.1,Nb0.1,Ta0.1)(C0.78,N0.22) ceramics (HECN) powders were synthesized by carbothermal reduction nitridation. (100-x) HECN-(x/2) Co-(x/2) Ni (x = 5–25 wt%) cermet was prepared by vacuum sintering. The relationship between microstructure and mechanical properties of HECN-based cermet sintered at 1450 °C and 1500 °C was studied. The results show that the second phase (W,Mo,Ti)3+x(Co, Ni)3−xC appears at both sintering temperatures, and its content decreases with the increase of binder Co, Ni content and sintering temperature; At the same time, the grain size of the hard phase of the cermet grows with the increase of Co and Ni content. In terms of mechanical properties, at both sintering temperatures, the cermet showed a decrease in hardness and an increase in fracture toughness with the increase of Co and Ni content, while the bending strength increased and then decreased. Among them, when the content of Co and Ni is 20 wt%, the bending strength of HECN-based cermet sintered at 1450 °C is the best, and the bending strength reaches 1640 MPa. This is attributed to the combined influence of many elements in high entropy cermet, which on the one hand leads to serious lattice distortion; On the other hand, improving the wettability and density of the cermet has a strengthening effect on the cermet. In addition, with the increase in Co and Ni content, the plastic deformation of the bond phase will inhibit crack propagation. The main paths are crack deflection and crack bridging, which increase the energy required for crack propagation and lead to a gradual increase in fracture toughness.

Synthesis of hollow AlN microsphere by hydrothermal and carbothermal reduction–nitridation hybrid technique

The synthesis of hollow AlN microsphere was studied because of its potential applications in various areas associated with high surface area and lightweight. A combined technique of hydrothermal and carbothermal reduction–nitridation (CRN) was adopted to synthesize spherical precursor and to transform to AlN, respectively, using Al-nitrate, sucrose, and urea. The precursor having different morphology were obtained after hydrothermal treatments at 180 °C for 12 h, depending on starting material combinations, where urea/Al molar ratio = 1 resulted in amorphous hollow microsphere. By CRN at 1500 °C for 4 h in a flowing N2 atmosphere, approximately 5 μm-sized hollow microsphere composed of AlN, α-Al2O3, or γ-AlON could be synthesized. CRN at higher temperature (1600 °C for 4 h) or for longer holding time (1500 °C for 10 h) is required to obtain pure AlN microsphere. Further tests at nine different hydrothermal conditions were performed to find an optimal synthesis condition, while the possible formation mechanism for hollow AlN microspheres was also proposed based on observations.

Formation of HfCxNy by carbothermal reduction nitridation and their laser ablation behavior

Hafnium carbonitride (HfCxNy) powders have been successfully prepared by heating a mixture of fine-grained HfO2 and nano-carbon powders during 1873 K-2273 K in nitrogen. The carbothermal reduction nitrdation (CTRN) process is composed of two steps: (1) the formation of microporous HfC and (2) catalytic nitridation of microporous HfC. The results demonstrate that the as-prepared HfCxNy powder consists of a single phase and various nitrogen content through different sintering parameters. The mechanism consists of three stages: (1) Formation of cubic mixed crystal HfCxOy, (2) Transformation into microporous hafnium carbide, and (3) Crucially, microporous hafnium carbide catalyzes the activation and dissociation of nitrogen molecules, leading to the formation of HfCxNy. Additionally, we introduce a laser etching method to confirm the ultra-high-temperature melting behavior of HfCxNy. This study enhances our understanding of HfCxNy powders synthesis and their laser ablation performance, offering valuable insights for future material applications.

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.

Preparation of Si3N4 powder by carbothermal reduction and nitridation of glucose and water glass

Herein, Si3N4 powders were successfully synthesized via carbothermal reduction nitridation of glucose and water glass as starting materials. The effects of synthesis temperature, glucose-to-water glass molar ratio, and Si3N4 seeding on the production were investigated. The results show that the reduction rate of silica increases with increasing temperature. The highest Si3N4 yield of 98.5 % was observed at 1450 °C after 400 min. The conversion of amorphous silica to Si3N4 was increased when the molar ratio of glucose/water glass was from 3.6 to 9.0 and is slightly affected when this ratio is greater than 9.0. Moreover, the maximum nitrogen content (N wt%) was 39.1 % when Si3N4/water glass molar ratio was 0.05. In the early stage of the reduction process, SiO2 is mainly reduced to SiC which is then converted to Si3N4.

Effect of starting materials’ dispersion on the properties of AlN powder synthesized by carbothermal reduction and nitridation

This study examined the effects of starting material dispersion on the formation of AlN powder synthesized by carbothermal reduction-nitridation (CRN) route. After preparing aqueous and non-aqueous slurries containing 6.5 vol % of Al2O3 and carbon black powder with/without a dispersant, the particle dispersion was evaluated by sedimentation and viscosity measurements. The zeta potential was also measured to determine the optimal dispersion conditions for electrostatic repulsion because carbon black is challenging to disperse in water, owing to its low surface charge and poor wettability. The aqueous slurry prepared with 5 wt % Gen0451 dispersant at pH = 10 showed the highest degree of dispersion. Complete AlN conversion was achieved by nitridation at 1600 °C for 6 h under 10 L/min N2 flow. This result clearly showed the importance of starting material dispersion on the synthesis of AlN by CRN, demonstrating the feasibility of aqueous processing instead of conventional solvent-based processing.

Investigation on the synthesis mechanism and size control of (Ti,W,Mo,Cr)(C,N) solid solution powder

Complex interfaces in cermets limit its application as cutting or heat-work die materials. Interface modification of hard particles by composition optimization is proved to be an effective strategy for high-performance Ti(C,N)-based cermets. Herein, we prepared (Ti,W,Mo,Cr)(C,N) solid solution powder through carbothermal reduction nitridation method. The phase and microstructure were characterized to discover the synthesis mechanism. Oxides of Mo, W, Ti, and Cr participated in the reaction successively, MoO2 transformed to M2X (X is C and/or N, M is W, Mo and/or Cr) directly, both W2C and W formed simultaneously as the reduction products of WO3, TiO2 followed TiO2 → TinO2n-1 → (Ti, M)(C,N) (M is W, Mo and/or Cr), and Cr diffused into (Ti, M)(C,N) and M2X phases directly from its oxide. Finally, the solid solution powder with composition (Ti0.83W0.07Mo0.09Cr0.01)(C0.62N0.38) in the particle size of 0.73 μm with ∼0.14 wt% oxygen and ∼ 0.43 wt% free carbon was obtained at 1750 °C for 2 h. Our findings provide insight into developing advanced cermets with better comprehensive properties.

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.

Impact of Various Input Parameters on the Preparation of Different AlN Nanostructures by Hybrid Route of Hydrothermal and Carbothermal Reduction Nitridation Technique

Impact of Various Input Parameters on the Preparation of Different AlN Nanostructures by Hybrid Route of Hydrothermal and Carbothermal Reduction Nitridation Technique

Characterization of amorphous silicon nitride prepared from sand and coffee husk wastes by carbothermal reduction-nitridation

The continued coffee demand in Kenya has amplified the generation of its husk wastes causing disposal problems. This has led to serious pollution to the environment. Therefore, developing a greener and cost-effective ways to handle these wastes is necessary. The current study entailed the use of extracted silica and coffee husk biochar as novel precursor materials for the synthesis of silicon nitride .....

Performance of Si3N4 hollow microspheres prepared by spray drying and carbothermal reduction nitridation

A simple and scalable approach to fabricate monodispersed Si3N4 hollow microspheres (Si3N4 HMs) with uniform spherical structures is proposed in this study. This approach involves spray drying of Si3N4 precursor, followed by carbothermal reduction nitridation. The homogeneous Si3N4 precursor was first obtained by mixing phenolic resins and silicon resins, which are carbon and silicon sources, respectively. The spray drying process was then tuned by regulating the viscosity of the precursor by adding polyvinyl butyral in an appropriate ratio. Next, the hollow precursor microspheres were pyrolyzed at 1500 °C for 6 h, while ensuring that the shells of the obtained Si3N4 HMs remained intact. Porous Si3N4 ceramics with different contents of Si3N4 HMs were then prepared using the gel-casting method. It was observed that the densities and dielectric constants of the porous Si3N4 ceramics decreased with an increasing Si3N4 HMs content. Thus, the proposed approach can be used for the synthesis of Si3N4 HMs, that can be further processed into ceramic materials with both low densities and dielectric constants.

Study on reaction mechanism for the synthesis of vanadium nitride by carbothermic reduction nitridation method

Vanadium nitride (VN), as a typical transition metal nitride, has widespread applications in various fields due to its high melting point, high hardness, and excellent thermal and chemical stability. In this study, VN was synthesized through the carbon thermal reduction nitridation method using V2O3 as the main material, and the reaction mechanism was thoroughly examined. Thermodynamic analysis, coupled with thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), revealed that the reaction mechanism was not simply a direct nitridation process nor a two-step coupling of reduction and carburization. Instead, it was the result of multiple reaction mechanisms working in conjunction. Direct nitridation of V2O3 occurred throughout the entire reaction process, while indirect nitridation of VO and VC also occurred with the variation of temperature. A kinetic model was constructed based on the material thermal weight loss curve and revealed that in the carbothermal reduction nitridation system of V2O3, the solid phase reaction followed a three-dimensional diffusion model, with an activation energy of 160.244 kJ/mol, while the gas phase reaction with the solid phase followed a one-dimensional interface model, with an activation energy of 169.015 kJ/mol.

Synthesis, microstructure, and properties of novel series of (Ti, W, Mo, Nb, Ta) (C0.78, N0.22) high entropy ceramic-based cermets

Five high-entropy carbonitride ceramic (HECN) powders consisting of pentavalent cations (Ti,W,Mo,Nb,Ta) (C0.78,N0.22) are synthesized by the carbothermal reduction-nitridation (CRN) method. Subsequently, a series of 85HECN-7.5Co-7.5Ni(wt.%) cermet is fabricated employing the powder metallurgy method. The phase constitution, microstructure, and composition distribution of the HECN powders are analyzed. The synthesis temperature of the HECN powders is reduced by 100 °C compared to the non-high-entropy (Ti,Me) (C,N) ceramic powder when ΔSmix >1.5R, which demonstrates that the high entropy effect promotes the synthesis of solid solution powder. A uniform element distribution, 600 nm single-phase (Ti0.6,W0.1,Mo0.1,Nb0.1,Ta0.1) (C0.78,N0.22) high-entropy ceramic solid solution powder, could be synthesized through the CRN at 1400 °C for 2 h under a 2 kPa N2 atmosphere. Subsequently, five types of (Ti,W,Mo,Nb,Ta) (C0.78,N0.22)-Co-Ni high-entropy cermets are prepared via vacuum sintering at 1500 °C for 1 h. Among them, the (Ti0·6W0·1Nb0·1Ta0·1Mo0.1) (C0.78,N0.22)-Co-Ni cermet exhibited the most outstanding performance with a Vickers hardness of 2053.4 HV, fracture toughness of 12.3 MPa m1/2, and TRS of 1220 MPa, which present an increase of 17.0 %, 16.2 %, and 60.0 %, respectively, compared with the non-high-entropy TiCN–Co–Ni cermet. It was attributed to the addition of high-entropy ceramic powders, which resulted in fine grain strengthening, severe lattice distortion, and long crack deflection paths. This study presents a novel approach for the preparation of high-entropy Ti(C,N)-based cermets.

Preparation of high-entropy (Ti,Nb,Ta,Mo,W)(C,N) ceramics via carbothermal reduction nitridation using different carbon source

The (W,Mo,Ta,Nb,Ti)(C,N) high-entropy carbonitride powders were synthesized by the carbothermal reduction nitridation method, utilizing equimolar proportions of either graphite or carbon black. The subsequent utilization of these pre-synthesized powders yielded carbonitride ceramics after spark plasma sintering. The choice of carbon source played an important role in the microstructure, phase compositions and mechanical properties. By employing carbon black with its fine particle size and high reactivity, the synthesized powder maintained finer size, narrow powder size distribution (350 ± 12 nm) and have less free-carbon (∼0.032 wt%), which contributed to the high hardness (26.8 ± 1.4 GPa) of the sintered ceramic. Conversely, utilizing graphite with its larger particle size and lower reactivity would increase the fraction of free-carbon, leading to the deterioration of the ceramic's performance.

Study on the rapid synthesis of high-entropy carbonitride powder and its remarkable hardening effects on cemented carbide tool materials

As a novel high-entropy ceramic material with a multi-cation and multi-anion sublattice structure, high-entropy carbonitride ceramics (HECNs) have exhibited outstanding comprehensive properties and attracted increasing attention. In this study, a new WC-based cemented carbide material reinforced by high-entropy carbonitride (Ti0.2W0.2Mo0.2V0.2Nb0.2)(C0.7N0.3) (marked as HECN) was successfully fabricated by vacuum hot-pressed sintering. The mutual constraints between hardness and fracture toughness in extant WC-Co cemented carbide tool materials and their deficient high-temperature mechanical properties were effectively addressed. Moreover, for the low efficiency of the traditional carbothermal reduction nitridation, a novel method for rapidly preparing HECN powder was firstly proposed, namely the microwave-assisted carbothermal reduction nitridation, which could accelerate the heating rate and shorten the holding time. Single-phase HECN powder was successfully synthesized by this method, and the impacts of varying HECN content on the room and high-temperature mechanical properties of WC-based cemented carbide were investigated combined with the microstructure analysis by XRD\\SEM. The results revealed that HECN effectively inhibited the grain growth of WC in cemented carbide, and the refined WC grains provided a high-volume fraction of grain boundaries, which prevented dislocation movement and increased the hardness. With the optimized HECN content of 10 wt%, the Vickers hardness and fracture toughness of WC-HECN-Co composite reached 21.58 ± 0.36 GPa and 12.27 ± 1.17 MPa∙m1/2 respectively. Furthermore, WC-10HECN-10Co composites possessed outstanding high-temperature hardness and maintained a high hardness value of 13.16 ± 0.30 GPa at 800 °C, 37% higher than that of WC-10Co. The findings of this research hold significant practical implications for applying cemented carbide cutting tools in high-speed dry cutting.

Synthesis, mechanical properties and thermal conductivity of high-entropy (TiTaNbZrMox)(CN) ceramics

Novel high-entropy (TiTaNbZrMoX)(CN) (x = 0, 5, 10, 15, and 20 at%) carbonitride ceramics were synthesised using the carbothermal reduction-nitridation and spark plasma sintering methods. The effects of Mo doping on the microstructure, mechanical properties, and thermal characteristics of these high-entropy ceramics were investigated. The increase in Mo contents caused increased grain size, uniform distribution of elements, improved Vickers hardness and fracture toughness, and reduced thermal conductivity at the same temperature. High-entropy (TiTaNbZrMo0.2)(CN) ceramic displayed superior Vickers hardness of 21.41 GPa and fracture toughness of 4.34 MPa·m1/2, compared with 20.51 GPa and 3.94 MPa·m1/2 for (TiTaNbZr)(CN) ceramic, respectively. Density functional theory calculations indicated that adding Mo atoms promoted the hybridisation of metal and carbon elements, thereby preferentially enhancing electron filling in the bonding orbital due to high valence electrons. This, in turn, improved the mechanical properties of (TiTaNbZrMox)(CN) ceramics. Additionally, the increased Mo contents strengthened covalent bonding and induced lattice distortion, reducing the thermal conductivity of high-entropy ceramics.

A promising one-step carbothermal reduction nitridation strategy for enhancing photoelectrochemical performance of TiO2 nanowire array-based catalysts with stable nitrogen doping and desired core-double shell structure

Non-metallic nitrogen doping and carbon coating may be considered as the most promising strategies to improve the performance of the TiO2 photoelectrocatalyst by reducing the carrier recombinant rate, enhancing stability, and broadening light corresponding spectrum. In this study, a one-stage carbothermal reduction nitridation (CRN) strategy is proposed to improve the photoelectrocatalytic performance (PEC) of the TiO2 nanowires for hydrogen production. TiO2 nanowires derived nitrogen-doped TiO2/Ti(C0.7N0.3) co-catalyst/nitrogen-doped carbon (N-TiO2/Ti(CN)/N-C) core-double shell nanowire arrays (NWAs) on the Ti substrate have been successfully developed with 2D g-C3N4 addition as nitrogen and carbon source. The unique N-TiO2/Ti(CN)/N-C composite structure offers superior PEC performance over the original TiO2 NWAs when exposed to both simulated sunlight and visible light conditions. The photocurrent density of N-TiO2/Ti(CN)/N-C can increase by approximately 20.5-fold and 18.4-fold when subjected to simulated sunlight and simulated visible light, respectively, compared to the pure TiO2 NWAs. The remarkable activity of the catalysis under visible light can be ascribed to the widened absorption spectrum that emanates from nitrogen doping, along with the reinforced conductivity that results from the dual-shell structure that promotes the separation and transfer of carriers that are generated by light.

Crystallographic Study of Product Phases of Carbothermic Reduction and Nitridation of Hafnium Dioxide.

Details of the carbothermic reduction/nitridation to synthesize hafnium nitride (HfN) and hafnium carbide (HfC) are scarce in the literature. Therefore, this current study was carried out to evaluate two pathways for synthesizing these two refractory materials: direct nitridation and carbothermic reduction/nitridation. Two mixtures of hafnium dioxide and carbon with C/HfO2 molar ratios of 2.15 and 3.1 were nitridized directly using flowing nitrogen gas at elevated temperatures (1300-1700 °C). The 3.1 C/HfO2 molar ratio mixture was also carbothermically reduced under flowing argon gas to synthesize HfC, which was converted into HfN by introducing a nitridation step under both N2(g) and N2(g)-10% H2(g). X-ray diffraction results showed the formation of HfN at 1300 and 1400 °C and HfC1-yNy at ≥1400 °C under direct nitridation of samples using a C/HfO2 molar ratio of 2.15. These phase analysis data together with lower lattice strain and greater crystallite sizes of HfC1-yNy that formed at higher temperatures suggested that the HfC1-yNy phase is preferred over HfN at those temperatures. Carbothermic reduction of 3.1 C/HfO2 molar ratio samples under an inert atmosphere produced single-phased HfC with no significant levels of dissolved oxygen. Carbothermic reduction nitridation made two phases of different carbon levels (HfC1-yNy and HfC1-y'Ny', where y' < y), while direct nitridation produced a single HfC1-yNy phase under both N2 and N2-10% H2 cover gas environments.

Utilization of industrial wastes in Al2O3‐SiC‐SiO2‐C refractories: Characterization of erosion and corrosion resistance

AbstractIndustrial waste has a high potential for reuse in the production of refractories, which can significantly lower costs. The purpose of the research is to access the role of three types of recycled industrial wastes (ferro‐titanium slag [FTS], ferhro‐chromium slag [FCS], and ferro‐vanadium slag [FVS]) utilized as aggregate in the traditional Al2O3‐SiC‐SiO2‐C refractories (ASSC). Erosion and corrosion resistance characterization was performed to determine whether these industrial waste‐containing ASSC still perform better than traditional ASSC during service. Based on the results, incorporating FVS into the ASSC was not recommended, its corrosion resistance was significantly reduced due to the presence of excessive liquid phase. Nonetheless, FTS and FCS could be added as aggregate to the ASSC without affecting their performance. This necessity of the proper amount of liquid phase in ASSC was highlighted in this research since the parameters could alter its properties. Furthermore, the Ti(C,N) transformed from TiO2 in FTS via carbothermal reduction nitridation could effectively prevent further corrosion, and Cr2O3 derived from the decomposition of (Al,Cr)2O3 solid solution in FCS could play the same role during the corrosion process, both of which may be potential raw materials to be used in refractories.

Seeded silicon nitride powders obtained by carbothermal reduction—nitridation of diatomite and various sources of carbon

Seeded silicon nitride powders obtained by carbothermal reduction—nitridation of diatomite and various sources of carbon