Production Of Carbide Research Articles

Heat Treatment of Nanostructured Powders Obtained by Spark Erosion of WC-8Co Cemented Carbide in Oil

Spark erosion of WC-8Co carbide pieces in oil resulted in a powder consisting of nanostructured spherical microparticles formed by rapid crystallization of the melt. These particles consist of rounded WC grains with an average diameter of about 0.18 μm, surrounded by cobalt. The process productivity, specific energy consumption, microstructure, particle size distribution, chemical and phase compositions of the obtained powder are determined. It was found that as a result of oil pyrolysis, free carbon is formed (3.4 %), which makes this powder unsuitable for the production of carbide products from it. A technique has been developed and the process of controlled removal of excess carbon by annealing the obtained powder in a CO2 atmosphere at a temperature of 1000 °C has been studied. As a result of annealing for 120 minutes, the carbon content decreases to the required value (5.6 %). Studies of the phase composition and microstructure showed that the obtained particles consist of elongated WC grains, the average diameter of which increased to 0.43 μm.

Influence of feed architecture on heat and mass transfer in calcium carbide electric furnace

It is of particular important to optimize the feed of calcium carbide (CaC2) production by improving the productivity and reducing the energy consumption. In this present paper, a transient mathematical model was established to analyze the effects of feed on heat and mass transfer characteristics of CaC2 electric furnace. The model was adopted to study the effects of powder and compressed feed on heat and mass transfer characteristics. In addition, the influence of the size of compressed feed particles on physical field distribution in the equipment was also investigated. The results displayed that the application of compressed feed is better than traditional powder feed in reducing serious local overheating and increasing the CaC2 production. When the three-phase alternating current (I) level increases from 10,000 A to 14,000 A, the average maximum temperature of the compressed feed furnace is about 8.8% lower than that of the traditional powder feed furnace. However, when furnace feed switches from powder feed to compressed feed, the average CaC2 production increases by about 18.6%. Small sizes of compressed feed is qualified with significant advantages in increasing the output. When I = 12,000 A and the size of compressed feed particle decreases from 5.0 mm to 0.4 mm, CaC2 production increases by about 26.5%, while when compressed feed particle size≤ 1.0 mm, with further size reduction, the differences in CaC2 output is not obvious. The study on the feed of CaC2 electric furnace on heat and mass transfer characteristics contributes to the optimization of performance in CaC2 electric furnace smelting.

Development of calcium coke for CaC2 production using calcium carbide slag and coking coal

A type of calcium coke was developed for use in the oxy-thermal process of calcium carbide production. The calcium coke was prepared by the co-pyrolysis of coking coal and calcium carbide slag, which is a solid waste generated from the chlor-alkali industry. The characteristics of the calcium cokes under different conditions were analyzed experimentally and theoretically. The results show that the thermal strength of calcium coke increased with the increase in the coking coal proportion, and the waterproof property of calcium coke also increased with increased carbonation time. The calcium coke can increase the contact area of calcium and carbon in the calcium carbide production process. Furthermore, the pore structure of the calcium coke can enhance the diffusion of gas inside the furnace, thus improving the efficiency of the oxy-thermal technology.

Analysis and optimization about electromagnetics-temperature-component distribution in calcium carbide electric furnace

It is of particular value to optimize the electromagnetics-temperature-component multi-physical field in electric furnace in improving productivity and reducing energy consumption. In this paper, the effects of three-phase alternating current and electrode immersion ratio on multi-physical field in calcium carbide electric furnace were studied. Meanwhile, a new criterion called benefit evaluation factor was proposed. Benefit evaluation factor is used to comprehensively evaluate the consumption of electric energy and calcium carbide production in electric furnace. Additionally, to improve the physical field distribution in the equipment, an innovative multi-layer electrode furnace was proposed. The results show that the energy consumption and calcium carbide production decrease with the increase of electrode immersion ratio or the decrease of current. Considering benefit evaluation factor and operate temperature, the recommended electrode immersion ratio range is 0.25–0.48. More importantly, the application of multi-layer electrode has a beneficial effect on smelting performance of electric furnace. The average benefit evaluation factor of two-layer-electrode furnace is 7.5% higher than that of traditional calcium carbide electric furnace when electrode immersion ratio equals to 0.25. In this paper, the newly proposed index contributes to the calcium carbide electric furnace smelting performance evaluation, and the multi-layer electrode furnace proposal opens up novel ideas in new furnace design.

Numerical simulation of heat transfer and chemical reaction of CaO-C porous pellets in the reaction layer of calcium carbide furnace

In this paper, a three-dimensional multi-physical model is established to analyze the heat transfer and chemical reaction processes during the production of calcium carbide from CaO-C porous pellets. The model considers simultaneously radiant heat transfer, convective heat transfer, heat conduction and chemical reaction process in the pellet bed. The multi-physical fields are solved by finite element method, and the numerical modeling method is verified based on literature data. The results show that the temperature field and the reaction region are strongly coupled and inhomogeneous in the reaction layer. The reaction diffuses from the surface of the pellet to the inside, and the center of the reaction region gradually shifts to the low temperature side. In the case of three-layer pellets, when heat is transferred from one layer to the upper layer, the time required is about 80% of the total reaction time of the current layer. In addition, the orthogonal test was carried out in the present study, and the result shows that the radius of the particles, velocity of the gas and the surface emissivity of the pellets have influence on the reaction process, and the degree of influence gradually decreases. When these three parameters changed from 1 mm to 0.71 mm, 0.01 m/s to 0.1 m/s and 0.7 to 0.9, the output of calcium carbide increased by 8.74%, 3.52% and 1.3% respectively in the same reaction time.

Modeling the Temperature Field in a High-Pressure Apparatus during the Sintering of Large-Sized Products Based on Boron Carbide

A computer model is developed on the basis of the finite-element method for the temperature field formed during the sintering of large-size boron carbide products in the working cell of a high-pressure apparatus at a pressure of 0.5–1.0 GPa and temperatures of 1700–1750°C. The dependence of the thermophysical properties of a sample on the porosity and temperature in the process of sintering is taken into account. It is shown that the selection of geometric parameters for the constructional elements of the working cell of a high-pressure apparatus makes it possible to find such a cell structure, whose application may provide a nearly uniform temperature field in a large-size sample under sintering and uniformity of the density and physicomechanical properties of the sintered sample.

Mechano-thermal reduction of molybdenite (MoS2) in the presence of Sulfur scavenger: New method for production of molybdenum carbide

In this research, carbothermic reduction of molybdenite in the presence of sodium carbonate as sulfur scavenger by mechanical activation and heat treatment was studied. Mechanical activation of the mixed powders of molybdenite, graphite and sodium carbonate with 1:4:2 mol ratios were carried out by ball milling process under argon atmosphere for 10,20,40,50 and 70 h. The X-ray diffraction (XRD) patterns of samples revealed that no reaction occurred in the mill even after 70 h of milling. In order to study the mechanism of carbothermic reduction of molybdenite in the presence of sodium carbonate, simultaneous thermal analysis (STA) under heating rate of 10, 15 and 20 °C/min was carried out on the activated samples. XRD patterns and thermodynamic analysis of reaction products indicated that carbothermic reduction of molybdenite in the presence of sodium carbonate was advanced through the formation of intermediate phases Na2MoO4, MoO2 in which the final products were Mo2C, Na2S. For separation of these two products, leaching by HCl and hot water was used. The XRD patterns of leached products were shown that molybdenum carbide with high purity was produced. The kinetics of reduction reaction was investigated and it was found that mechanical activation lowered the reaction temperature and activation energy.

Technological basis of the plasma-metallurgical production of zirconium carbide

Based on the interpretation of the results of theoretical and experimental studies, a continuous technological process for zirconium carbide production in the plasma-metallurgical reactor, including plasma generation, plasma processing of zirconium-carbon-containing raw materials, the formation of ZrC, forced cooling and its separation from the process gases flow leaving the reactor, was developed.

Effect of Ruthenium on Microstructure and Properties of WC- (W, Ti, Ta) C-Co Cemented Carbide

Two different ruthenium content (0.5%, 1.0%) of WC - (W, Ti, Ta) C - Co cemented carbide were prepared by conventional cemented carbide production process. The results showed that adding ruthenium powder can improve the microstructure of alloy compared with excluding ruthenium carbide. The microstructure of alloy with ruthenium addition had uniform structure with less coarse grain.The addition of ruthenium could obviously promote the transverse rupture strength of WC - (W, Ti, Ta) C-Co cemented carbide, and when the adding amount was 1.0%, transverse rupture strength increased by 30%. The addition of ruthenium slightly increased the hardness of the alloy. The results of Scanning electron microscopy and spectrum analysis showed that ruthenium mainly existed in the bonding phase Co. The cutting test showed that the alloy with Ru had better wear resistance.

Dissolution behavior of TiN in liquid cobalt

A confocal scanning laser microscope (CSLM) with a hot stage was used to study the dissolution of TiN in liquid cobalt under different gas atmospheres. The dissolution of cubic carbonitrides in cobalt is a key step in the formation of the cobalt enriched zone (CEZ) during cemented carbide production. A model system of cobalt + TiN was used in this work and in-situ observations were made at 1500 °C and 1550 °C in 5%H2-Ar and 5%H2-N2. Dissolution was observed in 5%H2-Ar but not 5%H2-N2. At 1550 °C in 5%H2-Ar, gas bubbles were observed in the liquid cobalt and rapid dissolution was observed. The dissolution rate of TiN was quantified at 1500 °C in 5%H2-Ar. The rate-controlling step of TiN dissolution was hypothesized to be mass transfer of nitrogen in the liquid cobalt to the liquid/gas interface. This was tested by using the shrinking core model to calculate the diffusivity of nitrogen based on the measured dissolution rates. The diffusivity was between 6.4 × 10−5 cm2/s and 5.3 × 10−4 cm2/s, which was consistent with a previous study (approximately 1 × 10−4 cm2/s). The findings of this work can be utilized in detailed models of CEZ formation during cemented carbide production.

Highly thermally conductive nanocomposites synthesized by PVD for thermal management applications

Uniform Ag and Si layers were successfully prepared on the surface of graphite films (GF) to improve thermal conductivity (TC) by physical vapor deposition method (PVD). The results demonstrate that the unique cubic crystal structure of Ag layer with different deposition time show good interface bonding and no carbide product of Ag/GF composites. Meanwhile, the dense Si coating contribute to the enhancement of the thermal diffusion ability. The Ag/GF composites with the deposition time of 2 h possess the best comprehensive property with the TC of 9.93 (W/m·K), which is approximately 73.30% higher than untreated GF. The TC of Si/GF composites reach the maximum TC of 11.12 W/(m·K) and increase about 101.81% due to the nano-Si layer comparing with untreated GF. Those composites with high performance make them promising thermal management laminated materials.

Heat-Resistant Composite Materials Based on Secondary Material Resources

Heat-resistant properties of the cement stone are provided by both high-temperature filler and the modified matrix on the basis of the Portland cement. For production of heat-resistant compositions as high-temperature filler, it is offered to use the secondary and accompanying products of production of carbide of silicon (SiC) and production wastes of the abrasive tools on a ceramic base. Increase in heat-resistant properties of the Portland cement knitting substance is offered to be solved by introduction to the structure of a cement composition of single substituted orthophosphate of calcium. The choice as an additive to the Portland cement a single substituted orthophosphate of calcium (double superphosphate) is proved by questions of safety measures and ecology, when using ortho-phosphoric acid and its salts for giving to cement compositions heat-resistant properties. The multicomponent composition of fine-grained concrete makes it possible to operate effectively the processes of forming the structure of cement stone at all stages of the technology, and to obtain materials with the most diverse set of properties. An introduction to the structure of a composite of 5% of filler of cyclonic dust of carbide of silicon, and a replacement of quartz filler by waste of abrasive production gave the increase of the compressive strength at 12%, bending strength for 36%. The thermal firmness increased by 3 times. An introduction to the structure of heat-resistant composition of single substituted orthophosphate of calcium (double superphosphate) in a number of 0.2% of the mass of cement allowed to increase the thermal firmness of structures to 20 heat exchanges (water, 800 oС).

INFLUENCE OF ENERGY ON THE PHASE COMPOSITION OF THE ULTRA-DISPERSED PRODUCT OF THE MOLYBDENUM-CARBON SYSTEM OBTAINED BY THE VACUUMLESS ARC DISCHARGE METHOD

Molybdenum carbides can be used in one of the most perspective sectors−hydrogen energy. Materials based on molybdenum carbide have high catalytic activity, which allows them to be used as effective inexpensive catalysts in hydrogen generation reactions, associated with the generation and oxidation of hydrogen. One of the main approaches to the obtaining of molybdenum carbides is the electric arc method based on the synthesis of material in DC arc plasma initiated in the gap between graphite electrodes. This article presents the results of a series of experiments on the production of molybdenum carbides, using a vacuumless arc discharge method, and on the influence of energy on the phase composition of the synthesis product.

Methodological approaches to optimization of grain composition of heat-resistant concrete

Heat-resistant concrete of fine-grained structure attracts special attention of refractory applications manufacturers. The task of optimizing the grain size composition of heat-resistant concrete fillers on the basis of by-products and related products of silicon carbide (SiC) production and waste products of abrasive tools production on a ceramic bond of fine-grained structure is of research and practical interest. It is proposed to use grain size compositions of gapped grading for a fine-grained cement system of heat-resistant concrete. The analysis of methodological approaches in the calculation of the grain size composition of concrete fillers allowed us to determine the Fuller formula as an optimal one from a practical perspective. Due to the use of gapped grading of the grain component of the concrete composition, an optimal ratio between the size of the grains of quartz sand and the waste of abrasive production was achieved. Balanced distribution of the filler in concrete mix made it possible to obtain intimate contact between their grains, which resulted in dense, “well-packed” concrete structure, and will further enable 5-10% saving of the cement binder. The compressive strength of samples with gapped grading filler was 38.7 MPa, the thermal resistance (water, 800°C) amounted to 16 thermal cycles.

Oil Purification Devices Used in Internal Combustion Engines

The article presents, developed operating modes and substantiates the parameters of a device that cleans motor oils from oxidation products and the resulting analytical relationships representing the movement of a mixture of acetone and used motor oil in viscosity states and the process of evaporation of the solvent from the oil during processing. It also substantiates the speed of movement of motor oil on a coneshaped surface based on its effect on refining and substantiates the dependence of the quality of refined oil on the temperature indicator of the mixture and the availability of the evaporation process and it was also found that motor oils are intensively contaminated with oxidation products during processing, thereby accelerating the friction process. During agricultural work, tractor engines due to congestion and oxidation of carbon, the content of carbine, carbide and asphalt products increases by 1.2%. Oxidizing products accelerate the deterioration of the quality of oils, which leads to an increase in the power consumption of the engine KShM and CPG by 15%. In addition, analytical relationships were obtained representing the movement of a mixture of acetone and used motor oil in viscosity states and the process of evaporation of the solvent from the oil during processing. The speed of motor oil on a cone-shaped surface is substantiated based on its effect on refining, and the dependence of the quality of refined oil on the temperature of the mixture and the availability of the evaporation process is justified

Sol–Gel Synthesis of Highly Dispersed Tantalum Hafnium Carbide Ta4HfC5

Powders of nanocrystalline carbide Ta4HfC5 were produced by the sol–gel synthesis of a finely divided Ta2O5–HfO2–C composite powder (with tantalum pentaamyloxide and hafnium acetylacetonate as precursors and a phenolformaldehyde resin as a carbon source) with subsequent low-temperature carbothermal synthesis (1200–1300°C, 2–4 h, dynamic vacuum). The composition of the initial Ta2O5–HfO2–C composite powder was optimized by decreasing excess carbon content. The elemental and phase compositions of the obtained carbide product were found. It was shown that, at low temperature of the carbothermal synthesis, single-phase carbide Ta4HfC5 can decompose into a mixture of phases of tantalum hafnium carbide and hafnium tantalum carbide; however, an unambiguous conclusion was impossible to draw because the produced powders were finely divided (the crystallite size was ~23–40 nm, and the particle size (as determined by scanning electron microscopy) was ~37–45 nm). The thermal behavior of the obtained finely divided Ta4HfC5 powders in an air flow at 20–1000°C was studied, and the effect of the crystallite and particle sizes in the samples on the positions of exothermic peaks related to oxidation was established, It was noted that a product of the oxidation of the produced Ta4HfC5 powders is not only the Ta2O5 phase, but also the complex oxide Hf6Ta2O17.

Thermal response properties and surface insulation failure mechanism of epoxy resin under arc ablation

Arc ablation during the operation of HVDC circuit breakers can cause irreversible damage to the epoxy resin (EP) insulation pull rod. This is one of the critical factors that affect the reliability and lifetime of a HVDC circuit breaker. In this work, we built an arc ablation experimental platform and studied the thermal response properties of EP insulation under arc ablation. The surface charge evolution characteristics and the dielectric properties were analyzed to reveal the underlying surface insulation failure mechanism of EP after arc ablation. The results indicate that arc ablation can cause severe carbonization to EP insulation. With increasing arc duration, the EP gradually transforms into carbide and pore products. Arc ablation can decrease the molecular moment orientation polarizability and the relative dielectric constant of EP insulation, and thereby increasing the current density formed by Schottky injection. Therefore, when the external electric field is applied, the charge on EP insulation surface migrates from high voltage electrode to the ablating area, causing the regional accumulation of surface charge and the formation of local failure area. This can decrease the surface electrical performance of EP insulation and lead to insulation failure finally.

Deposition of Coatings Based on Boron Carbide by the Gas-Phase Method

We present the results of investigation of the production of boron carbide by the method of hydrogen reduction of boron trichloride BCl3 in a vapor of toluene C7H8. The thermodynamics and kinetic features of the deposition of boron carbides in the BCl3–C7H8–H2 system are investigated.

Controlled synthesis of β-SiC with a novel microwave sintering method

Abstract β-SiC was synthesized with coal and sodium silicate as the raw materials via a novel microwave sintering method. The uniform heating and short production cycle makes the microwave sintering process more energy efficient. The structure and property of the prepared samples were characterized using XRD, FT-IR, XPS, TEM and HRTEM techniques. The size of nano-scaled β-SiC range from 70 to 300 nm in diameter and can be achieved 75.7% in the silicon carbide products under the condition of 1600 °C × 60 min with microwave controlling.

Investigation of contact dermatitis caused by hard metal dust

Objective: To investigate the incidence of contact dermatitis among workers in cemented carbide production enterprises. Methods: From October 1997 to October 2017, an occupational epidemiological survey was conducted on a large-scale cemented carbide production enterprise, and occupational health examinations were conducted for employees. 152 people were exposed to hard metal dust (hard metal raw material dust and alloy dust) . The employees in the work group were contact groups, and 142 employees in the non-dusting operation of the company were in the control group. A detailed retrospective survey of hard metal production workers with contact dermatitis history in the two groups was conducted to analyze the risk factors of contact dermatitis exposure to hard metal dust. Results: The incidence of allergic diseases in the exposed group was significantly higher than that in the control group. The difference was statistically significant (χ(2)=23.793, P<0.05) . The incidence of contact dermatitis in the exposed group was significantly higher than that in the control group. The difference was statistically significant (χ(2)=24.659, P<0.05) ; the changes of contact dermatitis in the contact group were mainly allergic contact dermatitis, and some showed irritative contact dermatitis; the operator had respiratory symptoms (including work-related nasal congestion, cough, wheezing) , difficulty breathing may be the influencing factors of contact dermatitis (RR=2.60, 95%CI: 1.10-6.20, P<0.05) . Conclusion: Hard metal alloy enterprises are exposed to hard metal dust. The incidence of contact dermatitis is high in workers, and the occurrence of contact dermatitis may be associated with those with respiratory symptoms.