Acheson Process Research Articles

Gas transport mechanisms and the behaviour of impurities in the Acheson furnace for the production of silicon carbide

The Acheson process still remains the method of choice for the industrial production of silicon carbide. The furnace operates in an unsteady thermal regime thus making it difficult to determine the kinetics of the process. In the present study, FactSage Software was used to get an insight and verify the dominant reactions occurring during operation. Moreover, the effect of impurities on the overall process efficiency and product quality is also discussed. The study is intended to clarify the effect of varying the SiO2/C ratio on the composition of the reactants taking part in the SiC formation reaction. Further, a deeper understanding of the formation process is developed and verified.

An Analysis of Heat Distribution in the Production of SiC Process

Abstract SiC has been produced by the Acheson process in bulk. The efficiency of the process is quite low. Only about 15 to 18% of the total charge gets converted into SiC as against the theoretical value of about 42%. A heat transfer analysis of the process shows that it can be improved further to increase its efficiency. It has been done based on laboratory scale hot model unit and industrial furnace in terms of energy balance. This has been presented in this article. Based on the analysis, it is found that most of the losses in an industrial furnace occur due to the heating of charge by supplying excess electric energy than required and radiation. The latter has been improved at the laboratory scale furnace by enclosing the most part of the furnace.

Micron-sized silicon carbide particle production via rapid unloading of high-pressure liquid CO2

We describe a novel methodology for micron-sized silicon carbide particle production via rapid unloading of high-pressure liquid CO2. The method is based on the physical characteristics of liquid CO2 such as low viscosity, high permeability, and a high dilation coefficient. A series of silicon carbide powdering experiments were performed. The overall process includes water saturation, water and silicon carbide filling, pressure initialization, CO2 filling, high pressure initialization, and CO2 gasification, which is a completely physical process. After high-pressure penetration and CO2 gasification expansion, the silicon carbide will immediately be converted into micron-sized particles. Most importantly, this method is much more effective than the most popular method of SiC synthesis (Acheson method). Laser grain size analysis indicates that the grain size of the silicon carbide particles ranges between 30 and 50 μm, and the percent grain size less than 176.9 μm accounts for 90%. The rapid unloading of high-pressure liquid CO2 method is much more environmentally friendly, efficient, energy saving, and effective.

Fabrication of Silicon Carbide from Recycled Silicon Wafer Cutting Sludge and Its Purification

Around the world, silicon carbide (SiC) is used as a raw material in several engineering applications because of its various beneficial properties. Currently, though the Acheson method is one of the most emblematic to manufacture SiC, the direct carbonization of metallic silicon is simple and beneficial. In this reaction, silicon wafer cutting sludge can be used as an alternative silicon source material. The silicon wafer sludge contains silicon, ethylene glycol, cooling water, and a small amount of impurities. In this study, SiC was synthesized using silicon wafer sludge by a carbothermal process. In a typical experiment, the silicon sludge was mixed with carbon at different molar ratios. Then, the mixture was turned into pellets, which were placed in alumina crucibles and heat-treated at a temperature from 1400 °C to 1600 °C to fabricate SiC. To deduce the optimum condition for the synthesis of SiC, an investigation was carried out on the effects of different mixing ratios, temperatures, and heating times. To ensure sufficient carbonization, excess carbon was mixed, and the synthesized SiC was characterized by X-ray diffraction (XRD). Subsequently, purification of the synthesized SiC products by oxidation of excess carbon was performed. The removal of extra carbon could be confirmed by XRD and attenuated total reflectance (ATR) spectroscopy. This process can give basic information for the development of a technology to produce SiC using recycling Si wafer cutting sludge waste.

Real-Time Measurements and Characterization of Airborne Particulate Matter from a Primary Silicon Carbide Production Plant.

Airborne particulate matter in the silicon carbide (SiC) industry is a known health hazard. The aims of this study were to elucidate whether the particulate matter generated inside the Acheson furnace during active operation is representative of the overall particulate matter in the furnace hall, and whether the Acheson furnaces are the main sources of ultrafine particles (UFP) in primary SiC production. The number concentration of ultrafine particles was evaluated using an Electrical Low Pressure Impactor (ELPITM, Dekati Ltd., Tampere, Finland), a Fast Mobility Particle Sizer (FMPSTM, TSI, Shoreview, MN, USA) and a Condensation Particle Counter (CPC, TSI, Shoreview, MN, USA). The results are discussed in terms of particle number concentration, particle size distribution and are also characterized by means of electron microscopy (TEM/SEM). Two locations were investigated; the industrial Acheson process furnace hall and a pilot furnace hall; both of which represent an active operating furnace. The geometric mean of the particle number concentration in the Acheson process furnace hall was 7.7 × 104 particles/cm3 for the UFP fraction and 1.0 × 105 particles/cm3 for the submicrometre fraction. Particulate matter collected at the two sites was analysed by electron microscopy. The PM from the Acheson process furnace hall is dominated by carbonaceous particles while the samples collected near the pilot furnace are primarily rich in silicon.

Cellular responses of human astrocytoma cells to dust from the Acheson process: An in vitro study

Silicon carbide (SiC) is largely used in various products such as diesel particulate filters and solar panels. It is produced through the Acheson process where aerosolized fractions of SiC and other by-products are generated in the work environment and may potentially affect the workers’ health. In this study, dust was collected directly on a filter in a furnace hall over a time period of 24h. The collected dust was characterized by scanning electron microscopy and found to contain a high content of graphite particles, and carbon and silicon containing particles. Only 6% was classified as SiC, whereof only 10% had a fibrous structure. To study effects of exposure beyond the respiratory system, neurotoxic effects on human astrocytic cells, were investigated. Both low, occupationally relevant, and high doses from 9E-6μg/cm2 up to 4.5μg/cm2 were used, respectively. Cytotoxicity assay indicated no effects of low doses but an effect of the higher doses after 24h. Furthermore, investigation of intracellular reactive oxygen species (ROS) indicated no effects with low doses, whereas a higher dose of 0.9μg/cm2 induced a significant increase in ROS and DNA damage. In summary, low doses of dust from the Acheson process may exert no or little toxic effects, at least experimentally in the laboratory on human astrocytes. However, higher doses have implications and are likely a result of the complex composition of the dust.

Les facteurs de risque professionnels des cancers bronchopulmonaires Quelle surveillance médicale après exposition à des cancérogènes pulmonaires professionnels ?

Lung cancers are the most frequent of occupational cancers, with to date numerous etiologies or situations of exposure for which the link is retained as certain in man by the International Agency for Research on Cancer: asbestos, crystalline silica, diesel exhaust, X and Y radiations, radon-222 and its decay products, plutonium, arsenic, nickel compounds, hexavalent chromium compounds, beryllium, cadmium, bischloromethylether and chloromethyl methyl ether, Acheson process, several sources of exposure to polycyclic aromatic hydrocarbons (aluminum production, coal gasification, coke production, soots, iron and steel foundry), underground hematite mining, painting, rubber production, secondhand tobacco smoke, welding fumes. The identification of exposures and the implementation of preventive actions to eliminate or minimize them are an essential step for occupational health actors. A recommendation of good practice was drawn up in France in 2015 under the auspices of the French Society of Occupational Medicine, the French Society of Pneumology and the French Society of Radiology, which advocates to assess in some departments the feasibility and relevance of screening for lung cancer by low-dose chest CT-scan in populations at high risk for lung cancer. The chest physician must also be vigilant in identifying prior occupational exposures to occupational carcinogens for any incident case of lung cancer, due to the important medico-social issues at the individual and collective level.

Low-temperature synthesis of silicon carbide powder using shungite

The paper presents the results of investigation the novel and simple method of synthesis of silicon carbide. As raw material for synthesis was used shungite, natural mineral rich in carbon and silica. The synthesis of SiC is possible in relatively low temperature in range 1500–1600°C. It is worth emphasising that compared to the most popular method of SiC synthesis (Acheson method where the temperature of synthesis is about 2500°C) the proposed method is much more effective. The basic properties of products obtained from different form of shungite and in wide range of synthesis temperature were investigated. The process of silicon carbide formation was proposed and discussed. In the case of synthesis SiC from powder of raw materials the product is also in powder form and not requires any additional process (crushing, milling, etc.). Obtained products are pure and after grain classification may be used as abrasive and polishing powders.

Method for determining the bulk temperature of the acheson graphitization furnace core

In order to reduce energy consumption in graphitization of electrode products in Acheson furnaces, a method for rapid assessment of the bulk temperature of the furnace core, which is based on the furnace energy balance equation and takes into account active energy loss at the furnace entrance; heat loss from the core surface; heat loss and moisture evaporation; heat loss in the core booster gasification process was developed. The unknown coefficients of the method - the temperature dependences of the effective heat transfer coefficient from the core surface and the proportionality factor, which takes into account active energy loss in the direct core insulation heating, were determined by calculation using the verified numerical model of heat-electro-mechanical state of the Acheson furnace. Analysis of the results showed that the nature of temperature dependence of the proportionality coefficient, which takes into account active energy loss in the direct core insulation heating is similar to the temperature dependence of the specific electrical resistivity of the furnace core (core booster). Verification of the developed method showed good agreement with the numerical simulation results. The developed method was tested in conditions of the electrode manufacturer PJSC Ukrgrafit, Ukraine and has allowed to reduce specific energy consumption while maintaining the necessary quality level of graphitized products.

Carborundum-bearing carbon reducing agents in silicon and silicon-ferroalloy production

As theoretically predicted, the manufacture of silicon and its ferroalloys is improved if carborundum abrasive produced in Acheson furnaces is introduced in the batch. Approaches to the production of carborundum-bearing carbon reducing agents in ferroalloy electrofurnaces are considered. Two-stage technology is shown to be more effective than the existing technology.

Toxicological investigations on the respirable fraction of silicon carbide grain products by the in vitro vector model

Increased lung cancer incidence with workers at the production site of crude silicon carbide (SiC) using the Acheson process has been reported. Several agents derived from the process were discussed as causative factors. Recently concern had been expressed about the presence of cleavage fragments (CFs) in commercial products fulfilling the WHO criteria for fibers. This study has focused on the toxicological significance of such CFs. The test samples were respirable fractions of five different commercial samples of SiC grains. The CF content (scanning electron microscopy) was in the range 17–493 fibers/µg. Crystalline silica and whiskers could not be detected. Quartz DQ12, cristobalite, SiC whisker, UICC crocidolite and electrocorundum were used as control reference samples. Biological activity was assessed with the in vitro vector model (VM) on ex vivo rat and guinea pig alveolar macrophages (AMs). The dose range of the VM is derived from calculated AM loads from intratracheal instillation experiments and confirmed by measured AM loads from inhalation studies on alumina monohydrate particles with low biological activity: ≤120 pg/AM. The response of the references was clearly different from that of the SiC grains which yielded low toxicity overall. However, the parameter reactive oxygen species secreted by AMs was elevated at the higher SiC doses, but not related to the CF content of these samples. Our data showed that CFs seem to have no biological relevance. This is in agreement with results from recent studies in which no carcinogenic activity had been demonstrated for CFs.

In vitro cellular responses to silicon carbide particles manufactured through the Acheson process: Impact of physico-chemical features on pro-inflammatory and pro-oxidative effects

Silicon carbide (SiC) an industrial-scale product manufactured through the Acheson process, is largely employed in various applications. Its toxicity has been poorly investigated. Our study aims at characterizing the physico-chemical features and the in vitro impact on biological activity of five manufactured SiC powders: two coarse powders (SiC C1/C2), two fine powders (SiC F1/F2) and a powder rich in iron impurities (SiC I). RAW 264.7 macrophages were exposed to the different SiC particles and the cellular responses were evaluated. Contrary to what happens with silica, no SiC cytotoxicity was observed but pro-oxidative and pro-inflammatory responses of variable intensity were evidenced. Oxidative stress (H2O2 production) appeared related to SiC particle size, while iron level regulated pro-inflammatory response (TNFα production). To investigate the impact of surface reactivity on the biological responses, coarse SiC C1 and fine SiC F1 powders were submitted to different thermal treatments (650–1400°C) in order to alter the oxidation state of the particle surface. At 1400°C a decrease in TNFα production and an increase in HO, COO− radicals production were observed in correlation with the formation of a surface layer of crystalline silica. Finally, a strong correlation was observed between surface oxidation state and in vitro toxicity.

INFLUENCE OF THE ELECTRODES BLANKS LOCATION ON THE ELECTRIC HEATING POWER DISTRIBUTION IN THE ACHESON FURNACES CORE

The modeling of electromagnetic and thermoelectric processes on the basis of numerical realization by finite element method of the generalized three-dimensional models of DC and AC graphitization is proposed. The features of furnace structure and side busbar packages, spatial arrangement of the electrodes blanks in the conductive backfill of core, temperature dependence of the electromagnetic and thermal properties of materials, technological regimes of graphitization are taken into account. The high accuracy and efficiency of numerical implementation are provided. The character and regularities of the spatial distribution of specific thermal power in the core at the vertical and horizontal location of the electrode blanks in the core are defined. It is revealed that the specific electric resistance of the core is determined by the ratio of specific electric resistance of electrode blanks, backfill materials, shunt layers and don’t practically depend on the orientation of the electrodes blanks in the Acheson furnace. It is found that in vertical stacking of blanks in the Acheson furnace core at diametric section blanks more heating capacity is allocated compared with the horizontal transverse stacking. Intensification of the heating, reduction in the duration the campaign and energy are provided

Preparation and Characterization of High Purity β-SiC Powder

SiC powder can be produced generally through the Acheson process and it is required long carbothermic reaction time of SiO2 with carbon powder around 2200 °C ~ 2400 °C. Due to the high reaction temperature and long reaction time of the process, the powders produced have a large particle size and consist of mostly alpha phase SiC. Synthetic temperature of beta phase SiC powder is known to produce at 1700 °C ~ 1900 °C which is lower temperature than that of alpha phase SiC powder. We prepared β-SiC powder by heating precursor derived from the mixture of phenolic resin and tetraethyl orthosilicate. The precursor was heated at 1800 °C for 4 h in an Ar atmosphere. In order to examine the pyrolysis residue after the heat treatment, the SiC powder was analyzed with XRD and SEM. The X-ray diffraction result of the SiC powder shows the diffraction peaks around 35°, 60°, and 73° corresponded to the beta SiC phase. β-SiC powder prepared in this study contains lower metallic impurities compare than that of α-SiC powder prepared from Acheson method and is able to use as a good starting material for SiC single crystal growing.

Utilização de matéria-prima aglomerada na produção de carbureto de silício em escala-piloto

O carbureto de silício (SiC), um material cerâmico amplamente utilizado na indústria de refratários, de fundição e de abrasivos, é produzido, industrialmente, no forno Acheson, através do aquecimento de grãos de carbono (normalmente o coque verde de petróleo) e areia silicosa. O aquecimento ocorre através da passagem da corrente elétrica através de uma resistência de grafite posicionada no centro da mistura, que atinge temperaturas acima de 3000ºC. Esse estudo teve por objetivo avaliar o impacto, em escala-piloto, da alteração na configuração (estrutura macrocóspica) da matéria-prima para produção de SiC. As matérias-primas (o coque e a areia) tiveram o tamanho reduzido e foram aglomeradas utilizando prensa de rolos. Esses aglomerados foram testados no forno em escala-piloto substituindo a matéria-prima original. Como resultado, percebeu-se que a utilização de matéria-prima aglomerada manteve a homogeneidade química durante o processo da produção do SiC e diminuiu a quantidade de energia necessária para produção de SiC (kWh/kg) em 5%.

Purifying Mechanism in the Acheson Process - A Thermodynamic Study

To improve the purity of SiC and the yield of high purity SiC in the conventional Acheson Process, the behaviour of metal oxide impurities (Al2O3, CaO, Fe2O3 and MgO) with/without addition of sodium chloride (NaCl) is studied with the help of FactSageTM from a thermodynamic point of view. Equilibrium phases and compositions during evaporation and gas deposition are examined in the system of SiO2 + 3C. The calculation results are compared with industrial observations and published data. Purifying mechanism is clarified for the first time since the invention of the Acheson Process in 1891.

Synthesis of titanium carbide powder by carbothermic reduction method

Carbothermic reduction method is an economical method for producing titanium carbide powder. In the present work, this method was used to produce titanium carbide powder using commercial raw materials. The starting materials were TiO2 and petroleum coke, which were mixed and milled, sieved and then placed in an electrical resistance furnace (Acheson furnace). The reduction was carried out between 25 and 30 V and the current of 1800–2000 A. When the raw materials molar composition ratio was TiO2/C=1 : 0·54, the best result was obtained. The samples were characterised by XRD, AAS and PSA techniques.

Ultrathin graphitic structures and carbon nanotubes in a purified synthetic graphite

A new class of carbon structure is reported, which consists of microscale graphitic shellsbounded by curved and faceted planes containing two to five layers. These structures wereoriginally found in a commercial graphite produced by the Acheson process, followedby a purification treatment. The particles, which could be several hundreds ofnanometres in size, were frequently decorated with nanoscale carbon particles, or shortnanotubes. In some cases, nanotubes were found to be seamlessly connected to the thinshells, indicating that the formation of the shells and that of the nanotubes areintimately connected. The structures are believed to form during a purificationprocess which involves passing an electric current through the graphite in thepresence of a reactive gas. In support of this, it is shown that similar particlescan be produced in a standard carbon arc apparatus. With their extremely thingraphene walls and high surface areas, the new structures may have a range of usefulproperties.

Title of simulation of the physicochemical processes of high-temperature treatment of carbon products in Acheson furnaces

A mathematical simulation technique for physicochemical processes occurring in the manufacture of electrode products in the Acheson graphitization furnaces was considered. The effects of the physicochemical properties of the carbon heat insulation of the furnace on the structure of its thermal field and the processes of mass transfer and gas evolution initiated by this field were studied. It was shown that, with the use of the carbon heat insulation based on anthracites from the Eastern Donbass, the homogeneity of the thermal field in the products treated can be substantially increased, whereas the thermal load on the refractory lining of the furnace can be decreased. The experimental data of commercial tests of different heat insulation compositions were given. The processes of silicon carbide formation in heat insulation were analyzed, and the areas of possible use of solid carbonaceous wastes from graphitization processes were determined.

An Object-Oriented Modeling Approach in Materials Processing: Case Study of the Acheson and Carburizing Processes

Numerical results can be conveyed effectively to any one using an object-oriented framework. Therefore, it becomes essential to couple the object-oriented approach with numerical analysis. A simple object-oriented methodology for creating a graphical user interface (GUI) as a framework is presented. This work tries to fill a gap between scientific computer code written in a noninteractive way and interactive programming in materials processing. The GUI interface framework has been created in such a way that at any point of time one need not create a new GUI framework. The user only needs to create the process object and attach it to the framework. Two examples have been presented involving interactive finite volume-based gas carburizing and interactive finite difference-based Acheson process (used for the production of silicon carbide).