Carbothermal Method Research Articles

Overcoming the ultra-high C-rate limitation of LiFeBO3 with careful optimization of carbothermal synthesis conditions

Carbon coating with sucrose as the precursor under a moderate synthesis temperature of 500 °C results in a high-purity monoclinic LiFeBO3 phase. This material has a high specific discharge capacity of 200 mAh/g at 0.02 C, which is close to its theoretical capacity. However, its poor performance at high C-rates limits its utility in electric vehicles. Achieving ultra-high C-rate capability of more than 5 C for LiFeBO3 cathode for lithium-ion batteries is uncommon. To overcome this challenge, this study carefully optimizes the synthesis conditions, such as temperature and reducing atmosphere. In this work we utilize carbothermal synthesis method for modulating the reducing conditions. Usually, the carbothermal reaction is carried out using carbon at high temperatures which leads to the formation of CO and CO2 gases. In our work, we have utilized a mixture of sucrose and oxalic acid as the carbon source, that is intimately mixed with the other precursors to create moderate reducing conditions. Oxalic acid decomposes to generate CO which helps to attain the limited reducing atmosphere condition necessary to retain the low valence state of iron. This is important because the low valence state of iron is essential for a good rate-performance. However, if the amount of carbon source is too low, it can lead to poor rate-performance. On the other hand, if the amount of carbon source is too high, it can generate impurity phases, which can be detrimental to the material’s properties. The optimized sample can deliver electrochemical activity at ultra-high C-rates, even up to 30 C, which is achieved for the first time in this material. Comprehensive spectroscopic analyses reveal that multitude of factors, including improved particle crystallinity and better graphitization, favor the retention of the monoclinic phase during electrochemical cycling. A stable specific discharge capacity of 104 mAh/g at 10 C sets it as a benchmark for this material.

Study on the preparation mechanism of novel WC-Cr2(C, N)-Co nanocomposites

In this work, the WC-Cr2(C, N)-Co nanocomposites were synthesized by using the one-pot carbothermal reduction nitridation hydrothermal precursor method. The preparation mechanisms, including phase and morphology evolutions, were investigated by differential thermal analysis (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and thermodynamic analysis. The results showed that phase evolution, with temperature increasing, follows the sequences of (amorphous phase, WO2.72) → (CoWO4, WO2.72, WO2, CrWO3) → (WO2, CoWO4, Co6W6C, CrWO3) → (W2C, Co3W3C, WC) → (WC, W2C, Co3W3C) → (WC, Co, Co3W3C trace amount). Through comparing different heat treatment conditions, the powder particle size was more easily affected by temperature than holding time. The higher temperatures or longer time holding resulted in the aggregation of powder particles. Finally, WC-Cr2(C, N)-Co nanopowders with about 60 nm were obtained at 1050 °C for 1 h under the N2 flow of 1 L/min with the oxygen content of 0.22 wt% and the free carbon content of 0.19 wt%. The TEM elements mapping revealed that Cr distributes uniformly with WC grains, Co and WC grains are combined well. The surface of WC-Cr2(C, N)-Co determined by XPS is mainly composed of W, Co, Cr, C, N, and O. The spark plasma sintering (SPS) sintered WC-Cr2(C, N)-Co composite shows a nanocrystalline microstructure with the average grain size ∼170 nm, and the excellent comprehensive mechanical properties with the Vickers hardness 1730 Kg·mm−2 and fracture toughness 11.5 MPa·m1/2, respectively.

Влияние морфологических и структурных параметров тетраподов ZnO на их активность в реакции фотокаталитической деградации ципрофлоксацина

The influence of morphological and structural parameters of microdimensional tetrapods ZnO on their activity in the reaction of photocatalytic degradation of ciprofloxacin under the influence of UV light has been studied. The greatest activity (velocity constant 25.5 · 10-3 min-1) was demonstrated by unalloyed ZnO tetrapods obtained in the presence of Au in the initial charge, which had the smallest geometric parameters. The photocatalytic activity of tetrapods is explained by the highly defective structure of their near-surface layers. Photoactive microsize tetrapods ZnO, synthesized by the carbothermal method, can be used in the mineralization of toxic organic compounds.

One-Step Carbothermal Reduction Synthesis of Metal-Loaded Biochar Catalyst for In Situ Catalytic Upgrading of Plastic Pyrolysis Products

A novel biochar-supported metal catalyst was prepared in this study using a one-step carbothermal reduction synthesis method for the catalytic pyrolysis of plastics. Several catalysts with different metals (Cu, Fe, Ni, and Ru) loaded on three biochar supports from lignin, soybean straw, and Chlorella vulgaris were evaluated using XRD, FTIR, NH3-TPR, and TEM. Zerovalent metal nanoparticles, including Ni, Cu, and Ru, and various functional groups were observed on the biochar surface. The chemical selectivities of gasoline hydrocarbons (C4–C12 hydrocarbons) reached 76.2% with a remarkable catalytic cracking effect of Ni/lignin biochar on low density polyethylene (LDPE). Catalytic performance was comparable to that of the Ru-based catalyst, which contributed to 85.6% of gasoline hydrocarbons. The Ni/lignin catalytic cracking of plastic waste simulated by LDPE, polypropylene (PP), and polystyrene (PS) showed a maximum selectivity of 87.9% for C4–C12 hydrocarbons and yields of 78.1 mg/g for benzene, toluene, and xylene (BTX). The mechanism related to the cleavage of long chain radicals of polyethylene, polypropylene, and polystyrene as well as the aromatization of aliphatics were proposed.

Study of possibility of manufacture of the complex titanium-containing ferroalloy via single-stage carbothermal method

The object of research is the melting technology of a complex titanium-containing ferroalloy by single-stage slagfree carbothermal method using high-ash coals as a reducing agent. The ilmenite concentrate (Shokash deposit, Aktobe region, Kazakhstan), rich titanium slag, which was obtained by the scientists of the Chemical and Metallurgical Institute named after Zh. Abishev (Karaganda, Kazakhstan), as well as high-ash coal as a reducing agent were used as charge materials. Several physical-chemical characteristics of used charge materials were previously studied to carry out large-scale labour tests on the complex titanium-containing ferroalloy melting via single-stage slag-free carbothermal method. The chemical and phase composition of materials was established and two optimal compositions of the charge mixture for alloy melting were selected on their basis. The first composition contains: coal – 67.35 %; rich titanium slag – 26.12 %; quartzite – 6.5 %. The second composition includes coal – 66.95 %; rich titanium slag – 23.1 %; ilmenite – 3.3 %; quartzite – 6.61 %. Tests for melting of a new complex titanium-containing ferroalloy were conducted in the ore-smelting furnace with 0.2 MVA transformer power. As a result of the tests, a batch of new complex titanium-containing ferroalloy was obtained, with the following average chemical composition: Ti – 18-21 %; Si – 35-45 %; Al – 10-20 %; P is no more than 0.08 %, the rest is Fe. Also metallographic studies of the alloy sample were carried out in the work. The obtained alloy according corresponds in its titanium content to the brand FeTi25 (GOST 4761-91). The test results showed the principal possibility of obtaining a new complex titanium-containing ferroalloy from rich titanium slag and ilmenite concentrate using high-ash coal as a reducing agent. The research was conducted within the framework of the study which was financially supported by the Scientific Committee of the Ministry of Education and Science of Kazakhstan Republic (grant No. AP09058310).

Carbothermal Synthesis of Sludge Biochar Supported Nanoscale Zero-Valent Iron for the Removal of Cd2+ and Cu2+: Preparation, Performance, and Safety Risks

The practical application of nanoscale zero-valent iron (NZVI) is restricted by its easy oxidation and aggregation. Here, sludge biochar (SB) was used as a carrier to stabilize NZVI for Cd2+ and Cu2+ removal. SB supported NZVI (SB-NZVI) was synthesized using the carbothermic method. The superior preparation conditions, structural characteristics, and performance and mechanisms of the SB-NZVI composites for the removal of Cd2+ and Cu2+ were investigated via batch experiments and characterization analysis. The optimal removal capacities of 55.94 mg/g for Cd2+ and 97.68 mg/g for Cu2+ were achieved at a Fe/sludge mass ratio of 1:4 and pyrolysis temperature of 900 °C. Batch experiments showed that the SB-NZVI (1:4-900) composite had an excellent elimination capacity over a broad pH range, and that weakly acidic to neutral solutions were optimal for removal. The XPS results indicated that the Cd2+ removal was mainly dependent on the adsorption and precipitation/coprecipitation, while reduction and adsorption were the mechanisms that play a decisive role in Cu2+ removal. The presence of Cd2+ had an opposite effect on the Cu2+ removal. Moreover, the SB-NZVI composites made of municipal sludge greatly reduces the leaching toxicity and bio-availability of heavy metals in the municipal sludge, which can be identified as an environmentally-friendly material.

Mechanism and experimental study on preparation of high-quality vanadium nitride by one-step vacuum carbothermal reduction nitridation method

With high hardness, high electrical conductivity, and good catalytic activity, VN is widely used in alloy materials, catalysis and electrode materials, and other fields. However, the conventional carbothermal reduction nitridation (CRN) methods are often limited by high temperatures and long reaction times. In this paper, the reaction process of vanadium trioxide one-step vacuum carbothermal reduction nitridation (VCRN) synthesis of vanadium nitride was studied by combining theoretical calculation and experimental research. The experimental results show that reducing the pressure is favorable for the V2O3-CRN reaction and high-quality VN was successfully synthesized under the conditions of 1473 K (300 Pa, 3 h) and the carbon mass ratio (mC/mV2O3) is 0.25. In addition, the reaction mechanism of V2O3-VCRN was elucidated by ab initio molecular dynamics (AIMD) simulations. The results show that carbon plays important role in the VCRN reaction process of vanadium trioxide. First, Carbon catalyzes the dissociation of nitrogen molecules on the surface of V2O3–C, which promotes the formation of the V–N bond, second is to react with O in the V2O3 lattice and reduces V2O3.

Effect of temperature, holding time and gas atmospheres in the synthesis and evolution of polymer-derived nanoceramics: A pyrometallurgical approach to precision nanorecycling of multiphase microplastics

Microplastics (MPs) are a critical type of persistent anthropogenic micro debris reported globally as ubiquitous to urban and non-urban settings. These complex micropollutants are of great concern given their contribution to severe environmental impact across ecosystems, confirmed as hazardous to the soil, biota, as well as to human health. From the materials perspective MPs are a heterogeneous mixture constituted predominantly by multiphase synthetic and natural polymers in the form of fibres, fragments and particles, from which microfibers (MFs) account for ∼90% of the global MPs pollution. The recovery and batch recycling of MFs is still in early stages remaining operationally, technologically and economically challenging. Therefore, the objective of the present study is the valorization of MFs examining its feasibility as alternative precursor for the green synthesis of engineered polymer-derived nanoceramics. The strategic approach targets the precision nanorecycling via selective high-temperature fast carbothermal method, which to the best of our knowledge is first reported for MFs. The effect of temperature, retention time, and gas atmospheres on the output products was investigated in the temperature range of 1300 −1600 °C, under controlled argon and nitrogen flow. The compositional, structural evolutions, morphological and textural properties of the output products are discussed. The experimental results indicated the precursor contained an inherent compositional advantage, in which silica-containing polymers along with embedded trace metals favoured the evolution of the organic carbon into mesoporous graphitic carbon, as well as the development of self-assembled self-catalytic one-dimensional SiC crystalline nanostructures, in both atmosphere systems. Specifically, the N-doped nanoneedles demonstrated higher thermal and chemical stability providing a suitable candidate for harsh environment applications. The relevance and significance of this proposal lays in the advancement of MFs recovery via precision nanorecycling of carbon and silica at a molecular level for the synthesis of high-end engineered outputs.

Need a balance? relationship between removal reactivity of cationic dye and bacterial cytotoxicity by iron carbide-stabilized nano zero-valent iron

Nano zero-valent iron (nZVI) as an active species for environmental applications usually suffers from its poor stability by corrosion and strong toxicity to microbes. To relieve the fast surface passivation and cytotoxicity (for Escherichia coli, E. coli), in-situ modification of nZVI with iron species may be a feasible strategy for strengthening the stability/reactivity and biocompatibility of nZVI-based materials. Here, nZVI/iron carbide heterojunctions are in situ embedded in partly-graphitized carbon (nZVI/Fe3C/PGC) using a one-step carbothermal synthesis method. nZVI/Fe3C/PGC-700 (700 °C) with a specific surface area of 126.04 m2/g exhibits a promising Rhodamine B (15 mg/L) removal efficiency of 89.2 % within 10 min at pH = 3. After 15 d storage in air or the 4th use, the crystalline structure and morphology of nZVI/Fe3C/PGC-700 remain basically unchanged. Due to the in-situ binding of nZVI and Fe3C with mixed valence, the surface oxidation is quite difficult to occur, thereby stabilizing the reducing capacity of nZVI. The encapsulation of nZVI/Fe3C heterojunctions in PGC structure also contributes to the structural stability. Although nZVI/Fe3C/PGC-700 can influence the metabolic functions of E. coli cells and the integrity of cell structure, this Fe3C-bonded nZVI exhibits a lower bacterial cytotoxicity than bare nZVI and nZVI@SiO2 as indicated by lactate dehydrogenase and reduced superoxide dismutase assays. This novel strategy provides an interesting option for design of carbides-stabilized nZVI with balanced reactivity and cytotoxicity.

Low temperature synthesis and densification of (Ti,V,Nb,Ta,Mo)(C,N) high-entropy carbonitride ceramics

The single-phase (Ti0.2V0.2Nb0.2Ta0.2Mo0.2)(C0.9N0.1) high-entropy carbonitride powder with an average particle size of 203 nm and a low oxygen content of 0.2915 wt% was synthesized by the carbothermal reduction-nitridation method at 1600 °C for 4 h. Subsequently, (Ti,V,Nb,Ta,Mo)(C,N) high-entropy carbonitride ceramics were prepared by hot pressing at temperatures of 1600 °C to 1900 °C. Increasing the sintering temperature is conducive to the uniform distribution of metallic elements, however, the hardness of high-entropy carbonitride ceramics is also reduced. (Ti,V,Nb,Ta,Mo)(C,N) ceramic hot-pressed at 1600 °C for 1 h has a relative density of 99.8%, an average grain size of 0.37 ± 0.08 µm, nanoindentation hardness of 32.4 ± 0.9 GPa, Vickers’ hardness of 24.0 ± 0.7 GPa at 9.8 N and fracture toughness of 4.87 ± 0.25 MPa·m1/2, which is comparable to those of high-entropy carbides and nitrides. In this study, a novel and convenient method for the preparation of (Ti,V,Nb,Ta,Mo)(C,N) high-entropy carbonitride ceramics was established.

Lithium Sulfide: Magnesothermal Synthesis and Battery Applications.

As a critical material for emerging lithium-sulfur batteries and sulfide-electrolyte-based all-solid-state batteries, lithium sulfide (Li2S) has great application prospects in the field of energy storage and conversion. However, commercial Li2S is expensive and is produced via a carbon-emissive and time-consuming method of reducing lithium sulfate with carbon materials at high temperatures. Herein we report a novel method of synthesizing Li2S by thermally reducing lithium sulfate with the first non-carbon-based reductant Mg. Compared with the commercial carbothermal method, our magnesothermal technique has multiple advantages, such as completion in minutes, operation at lower temperatures, emission of zero amount of greenhouse-gases, and a valuable byproduct MgO. Moreover, the prepared Li2S product demonstrates excellent cathode performance in lithium-sulfur batteries, in terms of cycling stability, activation voltage, and rate capability. Thus, this innovative method opens a new direction for the research of Li2S and has great potential for practical applications.

Atomic-Scale Homogeneous RuCu Alloy Nanoparticles for Highly Efficient Electrocatalytic Nitrogen Reduction.

Ruthenium (Ru) is the most widely used metal as an electrocatalyst for nitrogen (N2 ) reduction reaction (NRR) because of the relatively high N2 adsorption strength for successive reaction. Recently, it has been well reported that the homogeneous Ru-based metal alloys such as RuRh, RuPt, and RuCo significantly enhance the selectivity and formation rate of ammonia (NH3 ). However, the metal combinations for NRR have been limited to several miscible combinations of metals with Ru, although various immiscible combinations have immense potential to show high NRR performance. In this study, an immiscible combination of Ru and copper (Cu) is first utilized, and homogeneous alloy nanoparticles (RuCu NPs) are fabricated by the carbothermal shock method. The RuCu homogeneous NP alloys on cellulose/carbon nanotube sponge exhibit the highest selectivity and NH3 formation rate of ≈31% and -73μmol h-1 cm-2 , respectively. These are the highest values of the selectivity and NH3 formation rates among existing Ru-based alloy metal combinations.

Heteroepitaxial β-Ga2O3 thick films on sapphire substrate by carbothermal reduction rapid growth method

The heteroepitaxial β-Ga2O3 thick films were rapidly grown on various oriented sapphire substrates using carbothermal reduction method. The β-Ga2O3 films were prepared in our home-made vertical dual temperature zone furnace. The growth direction as well as surface morphology showed the strong dependence on the orientation of the sapphire substrate. The fastest growth rate was obtained reaching approximate 15 μm h−1 on c-plane sapphire substrate according to the average 30 μm thickness of β-Ga2O3 films grown for 2 h measured by cross-section scanning electron microscope. The Raman spectra indicated the pure-phase β-Ga2O3 films without obvious strain. The bandgap for grown films were in range of 4.6–4.7 eV confirmed by x-ray photoelectron spectra and Tauc plot from absorption spectra. Secondary ion mass spectrometry was used to check the impurities indicating a limited amount of residual carbon inside the films even though graphite as the reducing agent. The results in this work give promising alternative method of rapid epitaxial β-Ga2O3 thick films for the application on high-power electronic devices.

Viscosity of niobium oxide systems for production of complex ferroalloys

The relevance of the development of modern technological solutions for the processing of niobium ore materials used for the production of complex ferroalloys of domestic deposits is shown. The need to develop new technological processes of processing is caused by the fact that when switching to new types of niobium concentrates, the chemical and phase compositions of the starting materials change, and, consequently, this leads to a change in the composition and properties of the melting products (both metallic and oxide). Using an electrovibration viscometer, the temperature dependences of viscosity were studied and the crystallization temperatures of oxide melts of the Nb2O5 – SiO2 – CaO – TiO2 – Al2O3 system were calculated. The compositions of the studied samples correspond to phosphorless niobium slags, which can be obtained by carbothermic method from rough concentrates. The samples were obtained by fusing oxide materials in a high-temperature laboratory electric furnace. On the basis of the obtained data, graphical dependences of viscosity – temperature are constructed. It was experimentally established that oxide melts containing 15 – 26 % Nb2O5 are more “long” (having a wide crystallization range) and unfavorable according to the characteristic viscosity – temperature dependence. An increase in the concentration of niobium pentoxide to 40 % translates slags into the category of “short” (with a high crystallization rate). It is shown that an increase in the concentration of niobium oxide Nb2O5 from 15 to 40 % leads to a decrease in the crystallization temperature of melts by 200 °C and a decrease in the viscosity of melts from 1.32 to 0.24 Pa·s at 1350 °C. The improvement of the physico-chemical characteristics of oxide melts with an increase in the concentration of niobium pentoxide can favorably affect the technical and economic indicators of ferroalloy production.

Influence of the gas atmosphere on the obtention of cobalt and iron based nanocomposites and core/shell nanoparticles by calcination in the presence of chitosan

In this work, CoFe2O4/CoFe2 nanoparticles with core/shell structure were synthesized by carbothermic reduction using chitosan beads impregnated with Fe3+ and Co2+ ions. The samples were synthesized at 400, 550, 650 and 750 ​°C, during intervals of 30, 90 and 120 ​min and under air, N2 and H2 gases. To apply the carbothermic method, chitosan was thermally decomposed in presence of N2 gas. The structural and magnetic properties were studied using X-ray powder diffraction, transmission electron microscopy, vibrating sample magnetometry and Mössbauer spectroscopy. The results showed that the Co–Fe impregnated chitosan beads thermally treated, firstly, in air at a given temperature and afterwards treated at 400 and 550 ​°C in H2 for 30 and 90 ​min led to the formation of CoFe2O4/CoFe2 nanoparticles, the samples treated at higher temperatures were single phase of CoFe2. However, the Co–Fe chitosan beads treated in N2 for 120 ​min at 550, 650 and 750 ​°C favored the formation of a core/shell (CoFe2O4/CoFe2) nanoparticles with CoFe2 concentration ranging from 75.5 to 35.0 ​Wt %, the amount of CoFe2 increased with the increase of temperature. The highest saturation magnetization of 227.7 emu/g was achieved for the sample treated at 550 ​°C under N2 atmosphere.

Ultrafast Carbothermal Shock Constructing Ni3Fe1-xCrx Intermetallic Integrated Electrodes for Efficient and Durable Overall Water Splitting.

The development of the electrocatalyst-integrated electrodes with HER/OER bifunctional activity is desirable to reduce the cost and simplify the system of the practical water electrolyzers. Herein, we construct a new type of Ni3Fe1-xCrx (0 ≤ x < 0.3) intermetallic integrated electrodes for overall water splitting via an ultrafast carbothermal shock method. The obtained Ni3Fe0.9Cr0.1/CACC electrode exhibits the optimum performance among all developed electrocatalyst electrodes in this work, and the overpotential is merely 239 mV for OER and 128 mV for HER at 10 mA cm-2. In addition, the Ni3Fe0.9Cr0.1/CACC electrode shows excellent durability during both OER and HER stability tests at a high current density of 100 mA cm-2. An electrolyzer, which was assembled with Ni3Fe0.9Cr0.1/CACC electrodes as both the anode and cathode, operates with a low cell voltage of 1.59 V at 10 mA cm-2. It has been found that the impressive OER activity of Ni3Fe0.9Cr0.1 nanoparticles (NPs) can be ascribed to the stimulative formation of the OER-active Ni3+/Fe3+ species by the substituted Cr, while the enhanced HER activity is caused by the Cr substitution, which decreases the water dissociation energy barrier. This work provides an ultrafast and facile strategy to develop electrocatalyst-integrated electrodes with low cost and impressive HER/OER bifunctional performance for overall water splitting.

Research on dielectric and microwave absorbing properties of TiO2/TiB2/Thermoplastic polyurethanes (TPU) composite materials

TiO2/TiB2 materials are prepared by the carbothermal method and high-temperature calcination. Further, the phase composition, microstructure, dielectric and electromagnetic (EM) wave absorption characteristics are investigated. The results display that the product is composed of TiO2, TiB2 and impurity phases. The complex permittivity increases at elevated TiO2/TiB2 loading and slowly decreases with rising frequency in 2-18 GHz. When the TiO2/TiB2 content is 45 wt%, the minimum reflection loss (RLmin ) reaches -43.12 dB at 11.68 GHz with a thickness of 1.9 mm. The effective absorption band (EAB, RL<-10 dB) can reach 3.68 GHz at 2.3 mm as the TiO2/TiB2 content is 30 wt%. The enhanced EM wave absorption owes to the strong polarization loss and high conductivity loss. It goes without saying that TiO2/TiB2 materials can acquire important breakthroughs in the development of novel EM wave absorbers with outstanding absorption loss, wider EAB and smaller thicknesses.

High-entropy metal carbide nanowires

The development of high-entropy ceramic nanomaterials has significant scientific and technological potential, yet studies on these materials are rare. Here, we successfully synthesize (Hf0.25Ta0.25Nb0.25Ti0.25)C high-entropy metal carbide (HEC-1) nanowires—a class of high-entropy ceramic nanomaterials—via a facile bamboo-based carbothermal method with an Fe-Ni catalyst. The growth of HEC-1 nanowires occurs through a classical vapor-liquid-solid mechanism based on the solubility of metal, carbon, and HEC-1 in the Fe-Ni alloy. After high-temperature treatment, HEC-1 nanowires show good thermal stability without morphological evolution below 1,600°C, while they evolve into “pearl-necklace”’-like nanostructures or particles above 1,600°C due to the Rayleigh instability mechanism. After high-pressure treatments, HEC-1 nanowires are broken into nanorods above 1 GPa, in which brittle fracture without any dislocations, slip bands, or amorphous shear bands is directly observed at nano and atomic scales.

Thermodynamic and kinetic analyses of vacuum synthesis of AlN by the alumina carbothermal reduction nitridation method

AbstractUltrafine single‐phase aluminium nitride (AlN) particles were successfully synthesized by the vacuum carbothermal reduction nitridation (VCRN) method at shorter times and lower temperatures. The mechanism of the process was investigated. By analyzing the X‐ray diffraction (XRD) patterns and thermodynamic calculations, the main reaction path was determined to be Al2O3→Al2CO→Al4C3→Al5C3N→AlN. By investigating the kinetics mechanism, the process was a gas–solid reaction model, which was controlled by the crystalline chemical reaction from 0.5 to 1.5 h, combination control from 1.5 to 2 h, and gas diffusion control from 2 to 2.5 h. Moreover, the apparent activation energy (Ea) was calculated from the nitridation ratio, the value obtained, 237.71 kJ mol–1, is 31% of the energy reported for the conventional synthesis method. These results show that ultrafine AlN could be effectively synthesized at 1823–1873 K and 300 Pa N2 pressure for 2.5 h.

A novel approach to prepare reticulated porous TiN ceramics with high strength and high porosity by in-situ synthesis

Titanium nitride (TiN) with high porosity (90%) was successfully in-situ prepared by a novel approach with the combination of carbothermic reduction nitriding method and replication template method. The microstructure of porous TiN prepared with different temperature and phenolic resin (PF) content were revealed by XRD, Raman spectrum, SEM, TEM, respectively. The results show that when the mass ratio of PF and TiO2 is 1:2 and the sintering temperature is 1850 ℃, porous TiN with high purity and ideal strength could be synthesized. In addition, the synthesis path and thermodynamic mechanism of porous TiN were analyzed by TG-DSC and Gibbs free energy calculation. The mechanical properties and corrosion resistance were preliminarily explored.