Effect Of Residual Carbon Research Articles

Experimental study on the effects of residual carbon on ash fusion characteristics of high-alkali Zhundong coal under deep oxygen-staged condition

Experimental study on the effects of residual carbon on ash fusion characteristics of high-alkali Zhundong coal under deep oxygen-staged condition

Effect of residual carbon on silicon carbide ceramics in photopolymerization-based additive manufacturing

Silicon carbide (SiC) is widely used in various industrial fields for its excellent properties. Vat photopolymerization (VP) technology stands out in the fabrication of SiC ceramics due to its enhanced design flexibility and capability to produce intricate geometries. However, the excessive residual carbon content in VP technology directly affects the sintering performance of SiC ceramics, leading to cracking and deformation defects. To address this issue, we systematically studied the residual carbon content of SiC under different debinding atmospheres in forming by VP technology. We found that the debinding atmosphere can effectively control the residual carbon content in SiC ceramics. Residual carbon exists in samples with a lower degree of defect, promotes grain growth, reduces neck size, and results in flexural strength of 253.13 MPa after pressureless sintering. This research promotes the application of VP technology in SiC ceramics and opens up a new avenue for the development of high-performance SiC ceramics.

Effect of residual carbon on coal ash melting characteristics in reducing atmosphere

The melting behavior of coal ash at high temperatures directly affects slag discharge in gasifiers. Residual carbon is a key factor that influences the melting and transformation process of coal ash, affecting its melting characteristics, mineral composition, phase transformation, and melt structure. This study examines how residual carbon affects the melting process through mineral transformation, melt structure, phase transformation, atmosphere reaction, dissolution, and collapse of the physical structure of slag. The type and amount of residual carbon have different effects on the melting process. Changes in minerals result in complex changes in the phase transformation process. Residual carbon deprives some Fe and Si elements of the liquid phase, forming new aggregated minerals that compete with others. Residual carbon disrupts the equilibrium and eutectic structure of the system, dissociates the Si-O structure, and reduces the Fe-O structure, forming Fe0 or Fe2+. Free iron atoms form melt structures, such as Fe3C and FeSi.

Effect of Residual Carbon on Spin‐Polarized Coupling at a Graphene/Ferromagnet Interface

AbstractVertical stacks of graphene and ferromagnetic layers are predicted to be efficient spin filters, while the experimentally observed figures of merit systematically remain below the theoretical predictions. According to general consensus, a vaguely defined interface contamination is found responsible for this discrepancy. Here, it is demonstrated how the spin‐polarized electronic structure of single‐layer graphene supported on a ferromagnetic cobalt substrate is affected by the presence of an interfacial carbidic buffer layer, formed by residual carbon present in the Co substrate. It is found that the Co‐C hybridized single‐spin state near the Fermi level disappears upon thermal segregation of bulk carbon at the graphene–Co interface, which determines the electronic decoupling of graphene from the ferromagnetic support and consequently, the suppression of net spin polarization. These observations are shown to be independent of the graphene azimuthal orientation with respect to the high symmetry directions of the substrate. The findings provide clear evidence that the realization of highly polarized spin currents in graphene/ferromagnet heterostacks depends on careful control of the graphene growth process in order to eliminate interfacial carbon.

Effect of residual carbon on the phase transformation and microstructure evolution of alumina-mullite fibers prepared by sol-gel method

Sol-gel method, as one of the most effective methods, has been widely used in producing high-property ceramics. In this method, the pyrolysis of precursor significantly influences the following microstructure evolution and properties of ceramic materials. In this work, the effect of residual carbon, influenced by the pyrolysis atmosphere, on the phase transition and microstructure evolution of the alumina-mullite fibers was investigated. It was revealed that the phase transition path of the preheated fibers with 0.53 wt% residual carbon was amorphous phase → aluminosilicate → tetragonal mullite → orthorhombic mullite + θ-Al2O3. The phase transition path of the preheated fibers with 10.51 wt% residual carbon became amorphous phase → γ-Al2O3 → orthorhombic mullite + α-Al2O3 + θ-Al2O3. In addition, the residual carbon contributes to improve the densification of alumina-mullite fibers and refine the fiber grain size. The effect of residual carbon on the formation of mullite coarse grains was further discussed.

Effects of residual carbon on the synthesis of 1.1 nm tobermorite from coal gasification ash

Coal gasification ash (CGA) is a solid waste produced by coal gasification. It can be used to produce autoclaved building materials because tobermorite, the main hydration product in such materials, can be formed from CGA and calcium oxide (CaO). In this study, tobermorite was prepared through the hydrothermal treatment of CGA. Given that residual carbon is usually present to some degree in CGA, its effects on the formation of tobermorite were specifically studied using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption–desorption tests. The results showed that tobermorite can be prepared from a CGA/calcium oxide mixture at 160°C without additional alkaline material. However, residual carbon can retard the transformation of calcium silicate hydrate into tobermorite and thus increase the required formation temperature while prolonging the formation time. With an increase in the residual carbon content, the morphology of the resulting tobermorite changes from needle-like and plate-like to irregular, which may also have a detrimental effect on the mechanical properties of the material.

Suppression effect and mechanism of fly ash on gas explosions

The research is aimed at promoting the suppression of gas explosion accidents. Gas explosion suppression experiments were performed in a 20 L spherical test apparatus with fly ash (FA) and modified fly ash (MFA) as explosion suppressants, and the effect of residual carbon in FA on the gas explosion was explored. The experimental results show that both FA and MFA have a good suppression effect on gas explosions. Under the same conditions, the explosion suppression effect of FA is superior to those of MFA and CaCO3. In addition, the thermal characteristics of FA and MFA were investigated by means of simultaneous thermal analysis. Based on the difference in the composition of FA before and after the explosion, it is found that residual carbon will participate in the explosion reaction, and residual carbon can enhance the explosion suppression effect. The explosion suppression efficiency of FA is at most 4.05 % higher than that of MFA under the same conditions. Finally, the explosion suppression mechanism of FA was expounded.

Effect of Residual Carbon on Primary and Secondary Recrystallization of Grain-oriented Silicon Steel

Effect of Residual Carbon on Primary and Secondary Recrystallization of Grain-oriented Silicon Steel

Effect of residual excess carbon on the densification of ultra-fine HfC powder

The residual carbon content of ultra-fine hafnium carbide (HfC) powder was controlled by the optimization of the synthesis process, and the effect of residual carbon on the densification of HfC powder was analyzed. The amount of residual carbon in the HfC powder could be reduced by the de-agglomeration of HfO2 powder before the carbo-thermal reduction (CTR) process. The average particle size of HfO2 powder decreased from 230 to 130 nm after the de-agglomeration treatment. Ultra-fine (d50: 110 nm) and highly pure (metal basis purity: >99.9 % except for Zr) HfC powder was obtained after the CTR at 1600 °C for 1 h using the C/Hf mixing ratio of 3.3. In contrast, the C/Hf ratio increased to 3.6 without the de-agglomeration treatment, indicating that a large amount of excess carbon was required for the complete reduction of the agglomerated HfO2 particles. HfC ceramics with high relative density (>98 %) were obtained after spark plasma sintering at 2000 °C under 80 MPa pressure when using the HfC powder with low excess carbon content. In contrast, the densification did not complete at a higher temperature (2300 °C) and pressure (100 MPa) when the HfC powder contained a large amount of residual carbon. The results clearly indicated that residual carbon suppressed the densification of HfC powder in case the carbide powder had low oxygen content, and the residual carbon content could be controlled by the optimization of the synthesis process. The average grain size and Vickers hardness of the sintered specimen were 6.7(±0.7) μm and 19.6 GPa, respectively.

The role of residual carbon on fusibility and flow properties of rice straw ash

Residual carbon is a non-negligible component in biomass gasification slag and is seen as a factor related to the flowability of slag. One purpose of this study was to explore the relationship between residual carbon and rice straw ash fusibility via an ash fusibility temperatures (AFT) test in an argon (Ar) atmosphere. A visual measurement method for slag flow velocity was also established to further reveal slag flow properties. Furthermore, to illustrate the reaction mechanism of residual carbon with mineral components in ash, the surface morphology and chemical components of ash prepared at high temperatures were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the effects of residual carbon on rice straw ash fusibility characteristics were quantitatively calculated by thermodynamic equilibrium calculations. The experimental results showed that the increase in residual carbon mass fraction in ash increased ash fusibility temperatures and reduced slag flow velocity. The characterization and thermodynamic calculations indicated that in the ash fusion process, the rod-like structure containing carbon in ash disappeared, and the surface became compact due to the carbothermic reaction with SiO2 with continuously rising temperatures. Then, the unreacted residual carbon and SiC could be completely covered by molten slag due to the further increase in the liquid phase caused by the melting CaMgSiO4 and CaMgSi2O6. The residual carbon in ash inhibited the formation of K2Si4O9, which further resulted in reduction of SiO2 migration to low melting silicate.

O66] Thermodynamic Modeling of Crystal Structures for High-Temperature Anti-Corrosion Coatings

As an important and inevitable component of gasification slag, residual carbon is an internal factor that influences the flow properties of slag. In this study, the effect of residual carbon on slag viscosity was investigated. Viscosity of slag containing graphite was measured at 1350–1680 °C under an argon (Ar) atmosphere. The fusibility of ash was examined with thermomechanical analyzer (TMA). X-ray diffraction (XRD) was used to investigate the mineral composition of ash processed at high temperatures and that of the slag after viscosity measurement. FactSage was employed to calculate the free energy (ΔG) of the reactions within ash and slag at high temperatures. The slag viscosity increased with increasing the mass fraction of residual carbon, and a sharp increase of viscosity with decreasing temperature was observed for slags containing residual carbon. The presence of residual carbon led to the formation of crystalline phases, and it had a significant effect on slag viscosity when the mass fraction exceeded 5%. Quartz and mullite was the two main crystalline phases for slags with less than 5% residual carbon. However, when the mass fraction of residual carbon was more than 5%, moissanite as well as quartz and mullite were formed in slags. Ash fusibility increased with increasing the mass fraction of residual carbon for the same reason. Thus, less than 5% of residual carbon within slag is desirable in order to prevent the above problems. FactSage calculation revealed that SiO2 preferred to react with CaO and Al2O3 to form anorthite and mullite at high temperatures. Moissanite was produced by carbothermic reaction among anorthite, mullite, free SiO2 and residual carbon. Furthermore, SiO2 became difficult to react with graphite as it was chemically combined with CaO and Al2O3. Due to the low ΔG of carbothermic reaction between SiO2 and residual carbon, coals with high S/A ratios are favorable to the carbothermic reaction due to the abundant free SiO2 in the ash and slag.

The internal and external factor on coal ash slag viscosity at high temperatures, Part 2: Effect of residual carbon on slag viscosity

Abstract As an important and inevitable component of gasification slag, residual carbon is an internal factor that influences the flow properties of slag. In this study, the effect of residual carbon on slag viscosity was investigated. Viscosity of slag containing graphite was measured at 1350–1680 °C under an argon (Ar) atmosphere. The fusibility of ash was examined with thermomechanical analyzer (TMA). X-ray diffraction (XRD) was used to investigate the mineral composition of ash processed at high temperatures and that of the slag after viscosity measurement. FactSage was employed to calculate the free energy (ΔG) of the reactions within ash and slag at high temperatures. The slag viscosity increased with increasing the mass fraction of residual carbon, and a sharp increase of viscosity with decreasing temperature was observed for slags containing residual carbon. The presence of residual carbon led to the formation of crystalline phases, and it had a significant effect on slag viscosity when the mass fraction exceeded 5%. Quartz and mullite was the two main crystalline phases for slags with less than 5% residual carbon. However, when the mass fraction of residual carbon was more than 5%, moissanite as well as quartz and mullite were formed in slags. Ash fusibility increased with increasing the mass fraction of residual carbon for the same reason. Thus, less than 5% of residual carbon within slag is desirable in order to prevent the above problems. FactSage calculation revealed that SiO2 preferred to react with CaO and Al2O3 to form anorthite and mullite at high temperatures. Moissanite was produced by carbothermic reaction among anorthite, mullite, free SiO2 and residual carbon. Furthermore, SiO2 became difficult to react with graphite as it was chemically combined with CaO and Al2O3. Due to the low ΔG of carbothermic reaction between SiO2 and residual carbon, coals with high S/A ratios are favorable to the carbothermic reaction due to the abundant free SiO2 in the ash and slag.

Effects of Residual Carbon and Hydrogen Atoms on Electrical Property of GaAsN Films Grown by Chemical Beam Epitaxy

The electrical behavior of nitrogen–hydrogen (N–H) complexes and carbon (C) atoms in GaAsN films grown by the chemical beam epitaxy (CBE) method have been studied by comparing H concentrations and hole concentrations. The contributions of H and C concentrations ([H] and [C]) to ionized impurity scattering have been also investigated. In the GaAsN films, there were three acceptor levels (A0, A1, and A2). The energy levels of A1 and A2 were 130 and 55 meV, respectively. The concentration of the deepest acceptor (A0) was more than 1019 cm-3, which was higher than [H] and [C]. A2 was observed only in films with a high [C]. The amount of A1 was proportional to [H]. Most of the residual H formed N–H complexes; thus, it is concluded that the N–H complex behaved as an acceptor in GaAsN films. At low temperatures, ionized impurity scattering limited the total hole mobility. The inverse numbers of the coefficients for the ionized scattering were consistent with [C] instead of [H]. This suggests that all the residual C atoms were ionized owing to compensation by the donors. A disagreement between N composition and alloy scattering has been also detected. This might indicate a fluctuation in the N composition in the GaAsN films.

Effects of Residual Carbon on Superconducting Properties of Y123 Melt-Solidified Bulks

Effects of residual carbon on the carrier-doping level and resulting superconducting properties were systematically investigated for Y123 melt-solidified bulks containing different amounts of carbon. The dependence of Tc on annealing temperature in flowing oxygen was almost identical among each sample from underdoped to optimally doped state and all the samples exhibited highest Tc when they were annealed at ~500degC. On the other hand, the carbon-free samples showed apparently lower Tc than those of the carbon containing samples in the overdoped state. Especially, a sample fabricated in air showed the quite small decrease in Tc by overdoping, suggesting that residual carbon suppresses effective carrier doping to be heavily overdoped state for Y123 melt-solidified bulks. Therefore, Y123 melt solidified bulk with less residual carbon exhibited higher Hirr and Jc properties at the overdoped state.

Effect of Residual Carbon on the Microstructure Evolution during the Sintering of M2 HSS Parts Shaping by Metal Injection Moulding Process

In this present investigation, Metal Injection Moulding (MIM) of M2 High Speed Steel (HSS) parts using a wax-High Density Polyethylene (HDPE) binder is shown. This work is focused on the examination of the sintering densification and microstructure evolution of the parts. The injection molding process of the feedstock has been optimized to obtain high quality green parts. The elimination of organic binder was carried out by thermal debinding under inert atmosphere. In order to keep carbon in the sample that could improve the sintering process, incomplete debinding was performed between 450 and 600 °C. The specimens were sintered at temperatures between 1210 and 1280oC in high vacuum atmosphere, obtaining the 98% of the theoretical density. A homogeneous distribution of fine M6C carbides was obtained as well as V-rich carbides (MX) during sintering which reinforced the HSS and hence increasing the mechanical properties of the parts. In the samples with higher residual carbon content, the sintering window was extended up to 20 degrees and the optimum temperature was lower.

Effect of carbon and post-annealing treatment on magnetic properties of high-quality iron thin films

High-quality (1 1 0) Fe films with thickness of 200 nm were grown on Al 2O 3 (0 0 0 6) substrates by low-pressure metal organic chemical vapor deposition (LP-MOCVD). The effects of residual carbon and post-annealing treatment on magnetic properties of Fe films were studied. X-ray photoelectron spectroscopy (XPS) measurements revealed that almost all the interstitial carbon atoms in Fe films can be removed by annealing at temperature of 600 °C. Vibrating sample magnetometer (VSM) showed that the in-plane (out-of-plane) coercivity of the film annealed at 600 °C is clearly larger (smaller) than that of as-grown one, which can be assigned to the tensile stress relaxation due to the removal of carbon. As the annealing temperature increased from 600 to 750 °C, the in-plane coercivity decreased while the out-of-plane coercivity increased. Meanwhile, the in-plane remanence ratios increased rapidly with the increase of annealing temperature, but the out-of-plane remanence ratios changed slightly. The origin of the changes of magnetic properties with annealing temperatures was discussed.

Effect of residual carbon on sintering of high-speed steel made by modified injection moulding : J.M. Torralba et al. (University Carlos III, Madrid, Spain.) Metal. Mater. Trans. A, Vol 33A, No 6, 2002, 1843–1851

The objective of the investigation was to produce functionally graded, carbide alloyed multilayer coatings on M2 high-speed steel by laser alloying with direct injection of WC powder into the melt pool. Single layer coatings with a wide alloying range corresponding to 12–58 wt.% W and 1.3–4.3 wt.% C, respectively, were produced by varying laser beam power and beam traverse velocity. Depending on the alloying degree, four different types of structures were observed in laser alloyed coatings; they were characterized by scanning electron microscopy and X-ray microanalysis. Multiple laser alloying with beam power decreasing at each successive stage was used for producing a triple-layer coating with tungsten content increasing from layer to layer and reaching 75 wt.% in the upper layer. The observed hardness was in the 1100–1200 HV range for single layer coatings with 40–50% W and as high as 1600 HV in the upper layer of a triple coating with 75% W. The coating with 58 wt.% W showed wear resistance five times as high as compared with the unalloyed laser-melted M2 steel.

Effect of residual carbon on the sintering process of M2 high speed steel parts obtained by a modified metal injection molding process

In this article, we present the evolution of the microstructure during sintering of M2 high speed steel (HSS) parts obtained by a modified powder injection molding (PIM) process, which uses a new binder system based on a thermosetting resin. The most important characteristics of this process is that molding is carried out at room temperature by pouring the slurry (resin and tool steel previously mixed) directly into the mold. The mold is then heated to the curing temperature of the resin. The best mixture of polymer and steel powders was 60 pct volume of metal powder. The resin was removed by thermal debinding. The sintering process was carried out under vacuum atmosphere. We tested different debinding temperatures in order to retain residual carbon in the samples coming from the thermal degradation of the polymer. The best results were obtained at low debinding temperature (300 °C). In this case, residual carbon had a beneficial effect, extending the sintering temperature range by 100 deg, making it possible to reach very high density at temperatures as low as 1100 °C. The mechanism of this densification seems to be via supersolidus liquid phase (SPLS). The microstructural study of sintered parts revealed a homogeneous distribution of carbides that change their morphology with increasing temperature. Besides spherical M6C carbides, which appear in all the temperature ranges studied, a new rodlike M2C carbide appears.

Effects of residual carbon on phase formation of TlBa 2Ca n−1 Cu nO y ( n=3 and 4) superconductors

The effects of residual carbon in precursors on phase formation of single Tl–O layer superconductors of TlBa 2Ca n−1 Cu n O y ( n=3 and 4) have been investigated. The samples were prepared from Tl 2O 3 and precursors of Ba 2Ca n−1 Cu n O 2 n+1+ δ (C x ) ( n=3 and 4) with various residual carbon contents ( x=0.02–0.19). Even a small amount of carbon promotes the formation of double Tl–O layer phases of Tl 2Ba 2Ca n−1 Cu n O y ( n=3 and 4). Using the carbon reduced precursor ( x=0.02), a TlBa 2Ca 2Cu 3O y phase is synthesized directly in a silver-sheathed tape without such elements as Pb, Bi and Sr.

The effect of residual carbon on the phase stability of LaPO4 at high temperatures

Abstract Samples containing LaPO4 and polymeric binders were heated or hot-pressed in oxygen-poor environments to temperatures as high as 1585°C. Carbon analysis, powder X-ray diffraction and thermogravimetric analysis revealed that the residual carbon from the binders caused the LaPO4 to decompose into a lanthanum-rich phosphate compound, La3PO7, or a lanthanum oxide, La2O3, at temperatures above 750°C. These results agree with thermodynamic data, indicating that the driving force responsible for this carbothermic reduction reaction is the free energy of formation of P2O5, which is higher than the free energy of formation of CO above 750°C. It was also observed that this phenomenon would be detrimental to composites of LaPO4 and Al2O3, because LaAl11O18 and LaAlO3 were found to form at the interface, unless the samples were annealed in air after binder burnout.