Vacuum Carbon Research Articles

Removal of silicon carbide from kerf loss slurry by Al–Si alloying process

A novel method to separate silicon and silicon carbide from kerf loss slurry by Al–Si alloying process has been reported in this paper. The kerf loss slurry was washed and dried, and then aluminum was added on the top of these dry powders with silicon and silicon carbide. The Al–Si alloying process was performed in argon atmosphere using a vacuum carbon tube furnace at 1773K. In this way, an Al–Si ingot was obtained, on the surface of which a lot of hexagonal crystals were observed. The Al–Si ingot was characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence and electron probe micro-analyzer. The X-ray results indicated that the Al4C3 phase was obtained on the top of the cast. The scanning electron microscopy, X-ray diffraction and electron probe micro-analyzer results revealed that the Al–Si alloy without silicon carbide phase formed in the cast, which indicated that silicon and silicon carbide can be separated from slurry by this alloying process.

Activity and stability of immobilized carbonic anhydrase for promoting CO2 absorption into a carbonate solution for post-combustion CO2 capture

An Integrated Vacuum Carbonate Absorption Process (IVCAP) currently under development could significantly reduce the energy consumed when capturing CO2 from the flue gases of coal-fired power plants. The biocatalyst carbonic anhydrase (CA) has been found to effectively promote the absorption of CO2 into the potassium carbonate solution that would be used in the IVCAP. Two CA enzymes were immobilized onto three selected support materials having different pore structures. The thermal stability of the immobilized CA enzymes was significantly greater than their free counterparts. For example, the immobilized enzymes retained at least 60% of their initial activities after 90days at 50°C compared to about 30% for their free counterparts under the same conditions. The immobilized CA also had significantly improved resistance to concentrations of sulfate (0.4M), nitrate (0.05M) and chloride (0.3M) typically found in flue gas scrubbing liquids than their free counterparts.

Nano-lead particle synthesis from waste cathode ray-tube funnel glass

Waste cathode ray-tube (CRT) funnel glass is classified as hazardous waste since it contains high amount of lead. In the present study, a novel process for lead nanopowder synthesis from this type of glass was developed by combining vacuum carbon–thermal reduction and inert-gas consolidation procedures. The key trait of the process was to evaporate lead out of the glass to obtain harmless glass powder and synchronously produce lead nanoparticles. In the synthesis process, lead oxide in the funnel glass was firstly reduced to elemental lead, and evaporated rapidly in vacuum circumstance, then quenched and formed nano-size particles on the surface of the cooling device. Experimental results showed that temperature, pressure and argon gas flow rate were the major parameters controlling lead evaporation ratio and the morphology of lead nanoparticles. The maximum lead evaporation ratio was 96.8% and particles of 4–34 nm were successfully obtained by controlling the temperature, holding time, process pressure, argon gas flow rate at 1000 °C, 2–4 h, 500–2000 Pa, 50–200 ml/min, respectively. Toxicity characteristic leaching procedure (TCLP) results showed that lead leaching from the residue glass met the USEPA threshold. Accordingly, this study developed a practical and environmental-friendly process for detoxification and reclamation of waste lead-containing glass.

Investigation on Ti-Deoxidized Products Inducing Formation of Intragranular Ferrite

Steel samples were prepared using a vacuum carbon deoxidization process combined with a final Ti-deoxidation process. Ti-deoxidized products inducing formation of intragranular ferrite (IGF) was investigated by using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) through various specimens by different methods, as follows: metallographic specimens, electrolyzation, ion thinning technology, RTO method and so on. Mn is found to be more extensively distributed than S in the core of inclusion, which shows that Ti2O3 has character of absorbing Mn. The Mn-depleted zone (MDZ) exists in the peripheral steel of inclusion, the more near the inclusion, the more obvious depletion of Mn. It is also found that outer layer of inclusion exists S-rich and Mn depletion area in specimens prepared using RTO method under TEM. Mn- depleted zone in steel and Mn-depleted but S-rich layer in the periphery of the inclusion indicate that Mn diffuses and diverts is step by step in steel and inclusion, and the extent of S-rich and Mn depletion area should be related with degree of Mn absorbed by Ti2O3 and original precipitation amount of MnS.

Development of high purity large forgings for nuclear power plants

The recent increase in the size of energy plants has been supported by the development of manufacturing technology for high purity large forgings for the key components of the plant. To assure the reliability and performance of the large forgings, refining technology to make high purity steels, casting technology for gigantic ingots, forging technology to homogenize the material and consolidate porosity are essential, together with the required heat treatment and machining technologies. To meet these needs, the double degassing method to reduce impurities, multi-pouring methods to cast the gigantic ingots, vacuum carbon deoxidization, the warm forging process and related technologies have been developed and further improved. Furthermore, melting facilities including vacuum induction melting and electro slag re-melting furnaces have been installed. By using these technologies and equipment, large forgings have been manufactured and shipped to customers. These technologies have also been applied to the manufacture of austenitic steel vessel components of the fast breeder reactors and components for fusion experiments.

Development of a carbonate absorption-based process for post-combustion CO2 capture: The role of biocatalyst to promote CO2 absorption rate

An Integrated Vacuum Carbonate Absorption Process (IVCAP) for post-combustion carbon dioxide (CO2) capture is described. IVCAP employs potassium carbonate (PC) as a solvent, uses waste or low quality steam from the power plant for CO2 stripping, and employs a biocatalyst, carbonic anhydrase (CA) enzyme, for promoting the CO2 absorption into PC solution. A series of experiments were performed to evaluate the activity of CA enzyme mixed in PC solutions in a stirred tank reactor system under various temperatures, CA dosages, CO2 loadings, CO2 partial pressures, and the presence of major flue gas contaminants. It was demonstrated that CA enzyme is an effective biocatalyst for CO2 absorption under IVCAP conditions.

Study on the Oriented Recrystallization of Carbon-Coated Polyethylene Oriented Ultrathin Films

It is confirmed that a layer of vacuum-evaporated carbon on the surface of a preoriented ultrathin polymer film can lead to an oriented recrystallization of the polymer film. This has been attributed to a strong fixing effect of vacuum-evaporated carbon layer on the film surface of the polymer. To study the origin of the strong fixing effect of vacuum-evaporated carbon layer on the polymer films, the melting and recrystallization behaviors of the preoriented ultrathin PE film with a vacuum-evaporated carbon layer were studied by using atomic force microscopy, electron diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. We found that there exists some extent of chain orientation of carbon-coated polyethylene (PE) preoriented ultrathin film above its melting temperature. These oriented PE chain sequences act as nucleation sites and induce the oriented recrystallization of preoriented PE film from melt. Raman spectroscopy results suggest that new carbon-carbon bonds between the carbon layer and the oriented PE film are created during the process of vacuum carbon evaporation. As a result, some of the PE chain stems are fixed to the coated carbon substrate via covalent bond. Such a bonding has retarded the relaxation of the PE chains at the spot and, therefore, preserves the original orientation of the PE stems at high temperature, which in turn derives the recrystallization of the PE chains in an oriented structure.

Ti-Deoxidized Products and Formation Mechanism of Intragranular Ferrite in High Grade Pipeline Steels

High grade pipeline steels were prepared using vacuum carbon deoxidization process combined with a final Ti-deoxidation process. The microstructure of the as-cast steels was investigated by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM observation shows that the formation of intragranular ferrite (IGF) structure is induced by fine inclusions. TEM selected area diffraction (SAD) patterns and elemental distribution analysis indicate that these inclusions are mainly Ti 2O 3 and MnS. It is also found that Ti 2O 3 may act as nucleus in the formation of MnS during solidification process. Raman spectroscopic analysis demonstrates the presence of another phase, MnTiO 3, which could be formed through entrapment of Mn by Ti 2O 3. It is believed that the formation of Mn-depleted region in the inclusions and thus the formation of MnTiO 3 phase will increase the Mn pickup from matrix and promote the formation of IGF during solidification of molten steel.

Effect of vacuum carbonization treatment on the irreversible capacity of hard carbon prepared from biomass material

The large irreversible capacity of hard carbon limits its widespread commercialization for Li-ion batteries. To reduce the initial irreversible capacity of hard carbon, we investigated the effect of carbonization treatment of the precursor under vacuum on the irreversible capacity of resultant hard carbon. Compared with the sample carbonized under Ar atmosphere, the sample carbonized under vacuum obtained a lower irreversible capacity of 58 mA h g − 1 , due to the formation of pyrolytic carbon film on the surface, and the reduction of BET surface area, amount of heteroatoms and hydroxyl groups.

Kinetic Model of Decarburization and Denitrogenation in Vacuum Oxygen Decarburization Process for Ferritic Stainless Steel

The characteristics and classification of decarburization and denitrogenation in the vacuum vessel for stainless steel production are analyzed. Based on the analysis of movements of the liquid steel and bubbles, the kinetics of decarburization and denitrogenation in the vacuum oxygen decarburization (VOD) process has been studied. A kinetic model of decarburization and denitrogenation has been developed to simulate the VOD process, considering each reaction zone as oxygen blowing crater, bottom blowing plume, steel/slag interface, and plume eye. As a result, it is possible to quantify the contribution of each reaction zone in decarburization and denitrogenation rate at a different stage in the VOD process. Specific trials at a vacuum induction furnace were performed to refine stainless steel in vacuum carbon deoxidation (VCD) and VOD style, respectively. The trial results are in good agreement with the model calculation. Combining the trials and the model calculation and the influence of temperature control, critical carbon content selection on the terminal total [C] + [N] content can be discussed further to provide a reasonable proposal for high-quality ferritic stainless steel production.

Reaction Processes and Characterization of ZrB2 Powder Prepared by Boro/Carbothermal Reduction of ZrO2 in Vacuum

The present work was concentrated mainly on the reaction processes of boro/carbothermal reduction (BCTR) of ZrO2 with B4C and carbon in vacuum, and characterization of morphology and sinterability of the obtained ZrB2 powder. Combining the thermodynamic calculations, X‐ray diffraction results, and the trend of furnace pressure with temperature during synthesis, a detailed explanation of the reaction processes of BCTR was developed. Most of the ZrB2 particles obtained at 1650°C presented a nearly spherical morphology, whereas those synthesized at 1750°C showed a nearly columnar morphology with an increased size. Compared with the powder synthesized at 1750°C as well as the commercially additive‐free powder used in the reported work, the ZrB2 powder synthesized at 1650°C showed a better sinterability due to its smaller particle size and lower oxygen content.

Improvement of the technology of the out-of-furnace treatment of wheel steel

Various versions of the deoxidation and out-of-furnace treatment of wheel steel under the OAO VMZ conditions are analyzed. The effective partial pressure of carbon monoxide over a melt in a 130-t ladle degasser is found to be 54 ± 9 kPa. Thermodynamic analysis of the deoxidation demonstrates that low oxygen concentrations in the melt of wheel steel can be achieved when it is deoxidized by aluminum, silicocalcium, aluminocalcium, or carbon in vacuum. Experiments and a thermodynamic calculation show that the vacuum-carbon deoxidation of a high-strength wheel steel provides oxygen concentrations in the metal that are comparable with the concentrations obtained by silicocalcium deoxidation (0.0023 ± 0.0005 wt %) and ensures the optimum morphology and concentration of oxide inclusions. The causes of the formation of the defects revealed by ultrasonic inspection in railway wheel templates are studied. The level of rejection controlled by these defects depends on the deoxidation method and is related to the number and morphology of the oxide inclusions that form during secondary oxidation.

Synthesis of vanadium carbonitride nanopowders from solution derived precursor via carbothermal reduction

A study on the carbothermal synthesis of nanopowders vanadium carbonitride was conducted by using a solution derived precusor mixture of ammonium vanadate (NH4VO3) and nanometre sized carbon black in a vacuum carbon tube furnace with gaseous nitrogen. The effect of isothermal treatment time ranging from 0˙5 to 2 h at a sintering temperature 1373 K was studied. The particles obtained in this work were characterised by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that VC1-xNx particles prepared at 1373 K for 1 h isothermal time are composed of a single phase and distributed homogeneously, exhibiting a spherical shape with an average particle size of ∼90 nm. The x value as a function of [N]/([C]+[N]) of different samples is given by Vegard's law, depending on the precise lattice parameter. The possible mechanism for the process is also discussed.

Effect of Brazing Temperature on the Microstructure and Property of Vacuum Brazed WC-Co and Carbon Steel Joint

The effect of brazing temperature on the properties of brazed joints between WC-Co hard alloy and SAE1045 carbon steel using Cu and ASTM C52100 bronze metal as insert fillers were investigated. A vacuum brazing furnace was employed to conduct the experiment with different sets of operational parameters (brazing temperature, bonding time and filler) were used. The experimental result shows that Fe-Co-Cu alloy layer was formed at the WC-Co/Cu filler interface. With increased brazing temperature and bonding time, the thickness of the Fe-Co-Cu layer increases. From the shear test, the maximum shear strength is 320±10 MPa for the joint brazed at 1140°C for 15 min using Cu filler. The shear strength of WC-Co/C52100/SAE1045 brazed joints was better than WC-Co/Cu/SAE1045 brazed joints. The increase of bonding time of WC-Co/C52100/SAE1045 joints improved the shear strength slightly.

Carbon membranes from cellulose and metal loaded cellulose

The focus of this work was to find a low-cost precursor for carbon molecular sieve (CMS) membranes, and a simple way of producing them. In addition, several ways of modifying a carbon material are described. The modification method used in this study was metal doping of carbon. CMS membranes were formed by vacuum carbonization of cellulose and metal loaded cellulose. Metal additives include oxides of Ca, Mg, Fe(III) and Si, and nitrates of Ag, Cu and Fe(III). The carbon membrane containing Fe-nitrate has promising separation performance for the gas pairs O 2/N 2 and CO 2/CH 4. Carbon containing nitrates of Cu or Ag show high selectivity, but reduced O 2 and CO 2 permeability compared to carbon with Fe-nitrate. Element analysis indicates that Cu migrates to the carbon surface, creating an extra layer resistance to gas transport. A silver mirror is also seen on the surface of Ag-nitrate-containing carbon. However, the Ag- and Cu-containing membranes show a high H 2 permeability. Adding metal oxides makes the carbon membranes retard the transport of easily condensable gases (e.g. CO 2). This can be exploited for enhanced H 2/CO 2 separation efficiency.

Electron emission from nanostructures

Stable electron emission sources have been produced in plasma-etched single crystal silicon, coated with ultra-thin amorphous diamond, using a vacuum carbon arc source, at room temperature. Diamond films have been characterised using spectroscopy, EDX and high-resolution transmission electron microscopy. Fabricated devices require significantly lower threshold fields (3 V/μm) for operation, compared to uncoated emitters and show much reduced emission current fluctuations of 3% compared to 9% for untreated arrays.

Carbon diffusion in uranium during thermal reprocessing in vacuum

It is shown that during annealing of uranium samples at 550–950°C in a 10–3 Pa vacuum carbon impurity diffuses from the interior volume to the surface of the samples. The diffusion flux of carbon directed toward the surface arises as a result of the formation of uranium oxymonocarbide, which contains carbon impurity, on the surface in the presence of low oxygen partial pressure. The carbon diffusion rate in α-uranium grains depends on the crystallographic orientation of the grains, i.e., carbon diffusion in α-uranium is anisotropic.

Origin of Oriented Recrystallization of Carbon-Coated Preoriented Ultrathin Polymer Films

The origin of oriented recrystallization behavior of vacuum carbon evaporated preoriented polymer thin films was studied by means of transmission electron microscopy and electron diffraction with elaborately designed experimental setups. Through the recrystallization of HDPE in the iPP/HDPE-C sandwich layers with its original chain orientation being preserved by the coated carbon other than epitaxially crystallized on the highly oriented iPP substrate as usually happened without carbon coating, the graphoepitaxial crystallization of the polymer melts on their surface carbon replicas is ruled out of the origin of the oriented recrystallization. Through the different melt recrystallization behavior of melt-drawn 1-iPB thin films on and with vacuum evaporated carbon layers, the strong fixing effect of vacuum evaporated carbon layers on the polymer films has been recognized. This is further confirmed by the dissolution test of the vacuum carbon deposited HDPE thin films. The exact mechanism of the fixing effect of vacuum evaporated carbon layers on the thin polymer films is not quite clear yet. The recognition of the fixing effect is, however, sufficient to explain the oriented recrystallization phenomenon of the carbon coated preoriented thin polymer films. Namely, the vacuum evaporated carbon layer on the polymer thin film has prevented the surface extended macromolecular stems of the crystals from melting or at least from a complete relaxing during high-temperature annealing, and the surface fixing confined crystallization has induced the oriented recrystallization of the thin polymer molten layer.

A Study on the Characteristics of the Boundaries in Bainitic Low Alloy Steels Using Electron Back-Scatter Diffraction (EBSD) Technique

Bainitic low alloy steel has a complex microstructure exhibiting several types of boundaries. The boundaries in bainitic steel, although certain boundaries are absent with respect to the alloy composition and the manufacturing process, could be typically divided into 4 types; dislocation cell boundary, lath boundary, packet boundary, and prior austenite grain boundary, in increasing order of size. The size and distribution of the respective boundaries are an important factor which controls the mechanical properties of the steels, including brittle fracture. In the present research, the characteristics of the boundaries in the bainitic low alloy steels were investigated in view of misorientation between grains enclosed by the respective boundaries.The alloys investigated were Mn-Mo-Ni low alloy forging steels having chemical compositions shown in TABLE 1. Steel-A was manufactured by the Vacuum Carbon Deoxidation(VCD) process. For the finer prior austenite grain size, Steel-B was produced by the aluminium addition and the silicon killing process. Before EBSD analysis, the microstructures of the alloys were observed using SEM and TEM. EBSD measurements were obtained using a Link OPAL system(Oxford) linked to a JEOL JSM 6300 SEM operating at 15KeV with the sample tilted at 70°.

IRCH system for HT-7 superconducting Tokamak

The main technical features of the IRCH system with a maximum output of 1 MW (60 s) that was built up for the superconducting Tokamak HT-7 at ASIPP are described. The system consists of a generator, transmission line, impedance matching network, antenna and feedthrough, RF-assisted vacuum carbonization system, RF-leakage detection system. The recent activities on expanding the RF designing capabilities and further improving the system performance are outlined.