Carbothermal Reduction Temperature Research Articles

Regulating the phase composition and microstructure of Fe3Si/SiC nanofiber composites to enhance electromagnetic wave absorption

The rational introduction of multi-components to fabricate electromagnetic wave absorbing (EMA) materials with synergistic conductive/dielectric/magnetic losses promises lightweighting and excellent EMA performance, but it remains a challenge. In this work, multicomponent Fe3Si/SiC nanofibre composites with network structure were constructed by electrostatic spinning method and in-situ carbothermal reduction strategy. Design of microstructures and multicomponent modulation by controlling the carbothermal reduction temperature. As a result, the presence of a large number of non-homogeneous interfaces, three-dimensional (3D) conductive network structures and defect structures in Fe3Si/SiC nanofibre composites induces a combination of multiple loss mechanisms that significantly improve the EMA performance. When the filling amount of Fe3Si/SiC in the paraffin transmission matrix is 20 wt%, the maximum effective absorption bandwidth (EABmax) of the fabricated material reaches 5.84 GHz with a thin thickness of 2.02 mm. Moreover, the minimum reflection loss (RLmin) value at 10.96 GHz is as low as −67.57 dB. Meanwhile, the radar cross-section (RCS) simulation verifies that the F-4 peak RCS is reduced to −30.37 dB in the range of −60°<θ < 60°. It indicates that the Fe3Si/SiC nanofiber composites have a good radar-wave dissipation capability in practical applications. In summary, the comprehensive performance of lightweight multicomponent Fe3Si/SiC nanofiber composites can meet the new application requirements and is expected to become an emerging multifunctional wave-absorbing material suitable for harsh environments.

Synthesis, microstructure, properties of nonstoichiometry high entropy carbide (MoNbTaTiW)C4.5

AbstractA dense, fine‐grained, and toughened nonstoichiometry high entropy carbide (HEC) (MoNbTaTiW)C4.5 was synthesized via a two‐step way of carbothermal reduction‐solid solution using metal oxides and carbon. The effects of carbothermal reduction temperature, sintering temperature, and carbon content on the phase, microstructure, mechanical and thermal properties of (MoNbTaTiW)C4.5 were studied. The results showed dense and single phase (MoNbTaTiW)C4.5 were synthesized through reduction of metal oxides at 1600°C and sintered at and above 1950°C by spark plasma sintering. Reduced carbon content and higher solid solution temperature were beneficial to obtain dense HECs with better mechanical properties. With a carbon content of 90%, a reduction temperature of 1600°C, a holding time of 20 min, and a sintering temperature of 1950°C, the as‐synthesized (MoNbTaTiW)C4.5 showed a higher fracture toughness (5.2 MPa·m1/2). Besides, the (MoNbTaTiW)C4.5 showed a low thermal conductivity (5.9 W/m·K, at room temperature).

Rice husk-based biogenic silica-anchored Sn-Co bimetallic catalysts for cellulose hydrogenolysis: Structural regulation and mechanism study

The production of high value-added chemicals and materials from renewable biomass is significant for the sustainable development of chemical industry. Herein, rice husk-based biogenic silica-anchored Sn-Co catalysts with adjustable activity are successfully prepared for biomass valorization. By regulating the pretreatment method and carbothermal reduction temperature of catalysts, the interaction between Co, Sn and biogenic silica can be regulated, thereby regulating the catalytic activity of the catalyst for cellulose hydrogenolysis. 50.7 % yield of acetol and 63.4 % yield of C3 products can be obtained. A series of characterizations show that the hydrothermal pretreatment in CoCl2 solution promotes the combination of Co2+ and biogenic silica, which inhibits the excessive doping of Sn4+ and promotes the formation of Co3Sn2 alloy. The Sn-O-Si and Co3Sn2 species in 3Sn-5Co@RHC are the key active sites catalyzing glucose isomerization and fructose retro-aldol condensation. The intermediates experiments show that controlling the hydrolysis rate of cellulose to avoid excessive concentration of monosaccharide intermediates in the reaction system is crucial for inhibiting side reactions and improving the yield of acetol. The use of agroforestry waste-based catalytic materials for biomass conversion in this work can provide inspiration for exploiting the intrinsic characteristics of biomass to develop high value-added materials and chemicals.

Novel accordion-like structure of SiC/C composites for enhanced electromagnetic wave absorption

Two-dimensional (2D) composites have been identified as a rising star in the exploration of efficient electromagnetic wave (EMW) absorbers due to their structural designability and tunable dielectric constants. However, how to address the high filling rate of absorbers with 2D microstructures and the easy stacking problem between layers remain difficult and painful points. Inspired by the adjustable spacing of expanded graphite layers, it is rationally proposed to prepare unique and novel 2D accordion like SiC/C composites by microwave-assisted method and carbothermal reduction strategy. The microstructural modification and multicomponent modulation are achieved by regulating the carbothermal reduction temperature. The results confirm that the presence of plentiful inhomogeneous interfaces in 2D accordion like SiC/C composites, the enhanced dipole polarization, the improved conductive loss due to the unique 2D accordion like structure endow carriers with more paths, and the optimized impedance matching due to the porous structure synergistically result in superior EMW absorption properties. 2D accordion like SiC/C-2 exhibits a minimum reflection loss of −54.52 dB at 8.72 GHz with an ultra-low fill rate of 3%, and the effective absorption range covers 11.40 GHz (7.60–18 GHz) at a total thickness of 1.20 mm (1.23–2.43 mm), which is 71.25% of the whole range of frequencies. Additionally, radar cross section (RCS) simulations verify that 2D accordion like SiC/C-2 can dissipate more EMW in a real environment. This work provides a reference for the rational construction of novel high-performance 2D structural absorbers.

Synergistic magnetic/dielectric loss of Fe3Si/SiC composites for efficient electromagnetic wave absorption

It is confirmed that the multi-component strategy of combining magnetic and dielectric components with different dielectric properties is still challenging to achieve efficient electromagnetic wave (EMW) absorbing (strong absorption and a broad effective absorption bandwidth at a low filling level). Herein, a magnetic/dielectric multi-component of Fe3Si/SiC composites is constructed via an in-situ carbothermal reduction strategy. The heterogeneous magnetic/dielectric multi-component benefit to superior EMW absorption performance through forming multiple polarizations, magnetic loss, and dielectric loss effects. Especially, when the carbothermal reduction temperature is 1400 °C, the prepared Fe3Si/SiC composites exhibit the best EMW absorption performance at a very low filler loading of 10 wt%, with a minimum reflection loss (RLmin) of −61.67 dB and an effective bandwidth (EAB) for RLmin < −10 dB reaches 6.96 GHz. Additionally, the radar cross section (RCS) can be reduced to 17.08 dB m2 and the RCS value is completely lower than −5.98 dB m2 in the range of −60° to 60°, which signified the high attenuation performance of radar wave. This work guides to design an efficient EMW absorber with lightweight and strong absorption.

Microwave absorption performance of porous heterogeneous SiC/SiO2 microspheres

It is confirmed that the composites with multiple components and plentiful heterogeneous interfaces have been considered as preferred efficient electromagnetic (EM) wave absorbers. The special structure for hollow, porous, and core-shell has good adjustable dielectric properties. Herein, porous heterogeneous SiC/SiO2 microspheres are prepared based on the self-assembly technology and carbothermal reduction strategy. The structural evolution and composition control of porous heterogeneous SiC/SiO2 microspheres can be achieved by adjusting the carbothermal reduction temperature. The results indicate that structure and composition have a significant effect on the absorption performance. Especially, when the temperature is 1400 °C, the porous heterogeneous SiC/SiO2 microspheres exhibit the most excellent EM wave absorption properties; the minimal reflection loss (RLmin) value is −54.68 dB at 8.99 GHz. The maximum effective bandwidth (EABmax) for RLmin < −10 dB reaches 8.49 GHz, exhibiting absorption capacity in almost all bands (S, C, X, and Ku bands). It can well satisfy the comprehensive requirements of efficient EM wave absorption absorbers for lightweight and broad EAB characteristics. The excellent performance is due to the strong interfacial polarization caused by plentiful heterogeneous interfaces between different phases. Meanwhile, a highly porous structure and SiO2 phase can regulate complex dielectric constant, leading to better impedance matching. This work provides useful thinking for the design of efficient EM wave absorption absorbers.

Preparation of zero-valent iron-based composite catalyst with red mud and scrap tire as starting materials for Fenton-like degradation of methyl blue

Red mud (RM) is an attractive catalyst precursor due to its valuable components. In this study, we successfully synthesized a zero-valent iron-based composite catalyst by carbothermal reduction of RM with carbon black obtained by pyrolysis of the scrap tire as the reductant for the first time and evaluated the catalytic performance of the as-prepared catalyst for activating H2O2 to degrade methylene blue (MB) in an aqueous solution. The characterization results signified that a gradual transformation of iron-related species, i.e. Fe2O3 → Fe3O4 → FeO → Fe0, might occur by varying the carbothermal reduction temperature. The Fe@RM catalyst reduced at 900 °C exhibited much higher MB degradation efficiency than those reduced at 850 °C and below, proving that the stabilized zero-valent iron nanoparticles are more effective than iron oxides in the heterogeneous Fenton-like processes. The response surface methodology (RSM) based on Central composite design (CCD) was employed to design and optimize individual and interactive effects of the independent parameters. Chemical quenching tests ascertained the contributions of free radicals (•OH and O2−•) and singlet oxygen (1O2) reactive oxygen species to MB decomposition in the Fenton-like process. The present results demonstrate the promising reutilization of RM and scrap tires as low-cost raw materials for preparing zero-valent iron heterogeneous catalysts being active for the Fenton-like oxidation of organic pollutants in wastewater.

Thermodynamic Basis of Isothermal Carbothermic Reduction of Oxide in Liquid Steel for Simultaneous Analysis of Soluble/Insoluble Oxygen Contents in the Steel Specimens

Oxygen in liquid steel exists as soluble O (chemically dissolved in the steel matrix) and insoluble O (physically dispersed as the oxide inclusion). To measure the soluble O content ([S.O]) and the insoluble O content ([I.O]), both in the context of gas fusion analysis technique such as inert gas fusion infrared absorption method, it is necessary to melt the specimen under a C saturation condition in a “two-stage” isothermal heating mode. The first stage is carried out at a low temperature (TL), where only soluble O is extracted as CO(g). The second stage is subsequently carried out at a high temperature (TH), where the oxide inclusion is reduced by a carbothermic reaction. Therefore, it is necessary to identify the carbothermic reduction temperature of the oxide inclusion in the liquid steel at the C saturation (\( T_{{{\text{M}}_{x} {\text{O}}_{y} }}^{{{\text{Fe}}}} \)). A series of CALPHAD-type thermodynamic calculations were carried out to estimate the temperature of each oxide inclusion (Al2O3, FetO, SiO2, CaO, and MgO). It was found that the temperature depends on the metal content ([pct M]) and total pressure (P) inside the gas fusion chamber: increasing [pct M] or P increases \( T_{{{\text{M}}_{x} {\text{O}}_{y} }}^{{{\text{Fe}}}} \). The proposed method may be applied for the steel systems containing those inclusions except for FetO. In the case of Al2O3 inclusion containing steel ([pct Al] = 0.04), for example, \( T_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{{{\text{Fe}}}} \), lies in the range of 1791 K (1518 °C) to 1838 K (1565 °C) depending on P inside the gas fusion chamber. Possible range of the \( T_{{{\text{M}}_{x} {\text{O}}_{y}}}^{{{\text{Fe}}}}\) is reported.

Effect of Co-Reduction Conditions of Nickel Laterite Ore and Red Mud on Ferronickel Particle Size Characteristics and Grindability of Carbothermic Reduction Products

The carbothermic co-reduction of nickel laterite ore and red mud realized the simultaneous reduction of nickel, iron in laterite ore, and iron in red mud at high efficiency. Nickel and iron in nickel laterite ore and iron in red mud were recovered in the form of ferronickel. The size characteristics of ferronickel particles and grindability of carbothermic reduction products are essential for obtaining good technical indicators. The influence of co-reduction conditions on ferronickel particle size and relative grindability was investigated by a carbothermic reduction test, particle size analysis, and relative grindability determination. The mean size of ferronickel particles increased and the proportion of coarse particles grew with improving carbothermic reduction temperature, increasing appropriately anthracite dosage, and prolonging carbothermic reduction time. However, the relative grindability of carbothermic reduction products deteriorated when reduction temperature was improved and the reduction time was extended. The relative grindability was negatively correlated to the ferronickel particle size. The carbothermic reduction temperature had the most dominant effect on the ferronickel particle size and relative grindability, followed by the anthracite dosage and reduction time. More nickel-bearing and iron-bearing minerals were reduced to metallic state with raising reduction temperature and increasing appropriate anthracite dosage. The fine ferronickel particles agglomerated and merged into bulk ferronickel grains with a prolonged reduction time. The results will provide theoretical guidance for the recovery of nickel and iron by co-reduction of nickel laterite ore and red mud.

Tetrahydrofuran aided self-assembly synthesis of nZVI@gBC composite as persulfate activator for degradation of 2,4-dichlorophenol

• nZVI@gBC were synthesized by one-step carbothermal reduction method aided by Tetrahydrofuran. • The formation of graphene nano-shells greatly enhanced the stability of nZVI in the air environment. • The nZVI@gBC exhibited superior degradation performance to 2,4-DCP by activating PS. • Four active free radicals (SO 4 •− , •OH, O 2 •− and 1 O 2 ) were produced and participated in the degradation of 2,4-DCP. The defects of easy agglomeration and oxidation of nano zero valent iron (nZVI) limit its large-scale application in industry, especially in the field of environmental remediation. In this study, the iron nanoparticles encapsulated by graphene nano-shells which anchored on the surface of carbon substrate (nZVI@gBC) were synthesized by a one-step carbothermal reduction method aided by Tetrahydrofuran. When the mass ratio of carbon source to iron source is 2:3 and the carbothermic reduction temperature is 700 °C, stabilized nZVI @gBC can be successfully synthesized with a high iron loading rate of 32.5%. The multilayer graphene shell can effectively prevent the rapid passivation and agglomeration of the nZVI core, and the electronic interaction between the iron nanoparticles core and the graphene carbon shell further enhances the catalytic activity and stability of nZVI@gBC. Therefore, due to the unique structure of graphene nano-shells, nZVI@gBC can be stably stored in the air for more than 80 days. In addition, nZVI@gBC exhibited superior catalytic activity in the experiment of removing 2,4-dichlorophenol (2,4-DCP) in groundwater as a persulfate activator. Notably, both the electron paramagnetic resonance (EPR) and quenching tests showed that SO 4 •− , •OH, O 2 •− and 1 O 2 were both involved in the degradation process of 2,4-DCP, and SO 4 •− were the major active species. Simultaneously, three possible degradation pathways of 2,4-DCP were deduced by GC/MS, which were caused by dechlorination, dehydrogenation or carbon–carbon bond cleavage under the attack of SO 4 •− , •OH, O 2 •− and 1 O 2 . Besides, nZVI@gBC can use the dissolved oxygen in the liquid to generate hydroxyl radicals to effectively remove 2,4-DCP without persulfate. This kind of multifunctional nZVI@gBC may become a promising iron-carbon catalyst for large-scale applications in the field of environmental remediation.

Effect of MgCl2 addition on the preparation of ZrC–SiC composite particles by sol-gel

In the present study, an efficient sol-gel process combined with carbothermal reduction was designed to directly synthesize high purity hybrid ZrC–SiC powders by adding MgCl 2 at a lowered temperature. The composition and morphology evolution of the final products were studied in detail. The fabrication conditions of the ZrC–SiC powders, such as the amount of MgCl 2 , heat-treating temperature and soaking time, were optimized. Experimental results revealed that the addition of MgCl 2 could dramatically accelerate the formation of low carbon-residual ZrC–SiC powders even at 1400 °C, which is lower than the typical synthesis temperature of about 1600 °C. Thereinto, the ZrSiO 4 transition phase, which appeared after MgCl 2 addition, plays a vital role in reducing the carbothermal reduction temperature. Moreover, a stoichiometric carbon in the hybrid ZrC–SiC powders was realized by controlling MgCl 2 addition.

Improvement in the properties of low carbon MgO-C refractories through the addition of graphite-SiC micro-composite

Graphite–SiC micro-composites have been prepared in–house by carbothermal reduction process. Controlling the process parameters including the weight ratio of SiO2 to graphite as well as carbothermal reduction temperature during the micro-composite preparation favors the homogeneous formation of SiC with preferred morphologies like ribbons and whiskers/fibers. The micro-composite modified low carbon MgO-C refractories have exhibited significantly improved bulk properties over the standard composition. To understand the beneficial role of SiC reinforcement on hot strength performance under air oxidizing conditions, we propose a scaling parameter known as strength factor (fs) based on the ratio of hot strength (HMOR) to cold strength (CCS). Correlating the strength factor data (fs) with oxidative damage provides new insights into the reinforcing effects of distinct SiC morphologies in this new class of micro-composite fortified refractory systems over the standard compositions.

Valorization of electric arc furnace slag via carbothermic reduction followed by acid baking – water leaching

The current study is focused on developing a two-step pyro-hydrometallurgical process for the recovery of valuable components of electric arc furnace (EAF) slag produced by the steelmaking industry. The first step (hot step) involves carbothermic reduction of the EAF slag to recover iron along with niobium, chromium, and manganese in a metallic phase and titanium, magnesium, and aluminum in an iron-depleted slag phase. The second step (cold step) involves acid baking – water leaching of the iron-depleted smelting slag to recover these metals in an iron-depleted slag phase. Fractional factorial design of experiment and response surface methodology were utilized to find the optimum operating parameters of the two steps, respectively. The optimum operating conditions were determined to be smelting temperature of 1600 ºC, carbon to slag mass ratio of 0.12 g/gEAFS, and no flux addition for carbothermic reduction and baking temperature of 185 ºC, acid to smelting slag mass ratio of 2.03, baking time of 69.8 min, and water to acid-baked slag ratio of 5.83 for acid baking – water leaching. The metallic phase obtained in the smelting process contains 70.2 wt% iron, 17.3 wt% manganese, 7.0 wt% chromium, and 0.2 wt% niobium. The developed extraction process results in 86.4% titanium and 100% aluminum and magnesium extraction. We expect the findings of this study to help enable the EAF slag valorization using the two-step (hot and cold) pyro-hydrometallurgical process, contributing to sustainable recycling and circular economy.

Study on influencing factors and mechanism of high-quality tungsten carbide nanopowders synthesized via carbothermal reduction

In this study, high-quality WC powders with 100 nm were synthesized using a simple and efficient carbothermal reduction method. The effects of carbon source and temperature on the synthesis process, nucleation and growth mechanism of WC nanopowders were investigated in detailed. The results show that acetylene black with small particle size and good dispersion is the optimal carbon source to prepare WC nanopowders. The uniform precursor synthesized by acetylene black can significantly increase the contact probability of WO3 and C particles, greatly reduce the activation energy, and effectively improve the reaction efficiency during subsequent carbothermal reduction process. Moreover, the formation temperatures of WC are reduced to 1000 °C compared with other three carbon source. Further increasing carbothermal reduction temperature can provide the driving force of diffusing atoms, which promotes the carbothermal reduction reaction, but also significantly increases the diffusion rate of grain boundary resulting in rapid grain growth.

Synthesis of high purity nano-sized transition-metal carbides

Nano-sized transition-metal carbides with high purities were synthesized by vacuum carbothermal reduction coupled with a novel method for the removal of free carbon by molten calcium treatment. Transition-metals oxides were firstly reduced by excessive carbon black under vacuum condition, and then the obtained product was treated in molten calcium to remove the free carbon. After acidic leaching the product, pure carbides were obtained. The excess carbon in the carbothermic reduction stage could not only increase the contact between reactants and make the reduction more thorough, but also act as barrier to restrict the grain growth of the products. The effects of carbothermic reduction temperature, calcium treatment temperature and particle sizes of oxides on the reaction products were discussed in detail. It was concluded that after carbothermic reduction of corresponding oxides at 1823K in vacuum and the following calcium treatment at 1173K, TiC, ZrC, HfC, V8C7, NbC and TaC with the particle sizes of 100nm, 70nm, 130nm, 200nm, 150nm and 120nm, could be prepared, respectively.

The preparation and performances of lithium sulfide (Li2S)-oriented cathode composite via carbothermic reduction

Abstract The high theoretical energy density, high environmental adaptability and safety of lithium sulfide (Li2S)-oriented cathodes attract enough attention among lithium-sulfur batteries (LSBs). In this work, the lithium sulfide (Li2S)-oriented composite is fabricated via an in-situ carbothermic reduction method, in which lithium sulfate is reduced by CMK3 at an optimized temperature and subsequently the as-prepared Li2S is protected via the conformal carbon layer by carbonization of phenol-formaldehyde resin (PF). With the aid of the porous carbon structure of CMK3 and protection of PF-derived conformal carbon layer, the dispersity of Li2S and conductivity of cathode are availably enhanced. It has been found that the Li2S@CMK3-C prepared at optimum carbothermic reduction temperature of 835 °C has excellent electrochemical performance. The lithium-sulfur battery using Li2S@CMK3-C as cathode and metal Li as anode can deliver a high initial discharge capacity of 979 mAh g−1 at 0.1 C, the capacity retention after running at various current density is 94%, and the discharge specific capacity is still 530 mAh g−1 at 2 C after 450 cycles. Therefore, the preparation of CMK3-supported Li2S-based cathode material provides a new approach for the development and industrialization of new high-performance Li–S battery.

A novel stabilized carbon-coated nZVI as heterogeneous persulfate catalyst for enhanced degradation of 4-chlorophenol

Nano zero-valent iron (nZVI) and its composite materials have been extensively studied in the field of environmental remediation. However, the oxidation and agglomeration of nZVI limits the large-scale application of nZVI in environmental remediation. This study developed a two-step method to prepare stable carbon-coated nZVI (Fe0@C) which combined hydrothermal carbonization and carbothermal reduction methods and used glucose and iron oxide (Fe3O4) as precursors. When the carbothermal reduction temperature was 700 °C and the elemental molar ratio of carbon to iron was 22:1, stable Fe0@C can be generated. The nZVI particles are encapsulated by mesoporous carbon and embedded in the carbon spheres. The unique structure of carbon coating not only inhibits the agglomeration of nZVI, but also makes nZVI stable in air for more than 120 days. Not only that, the as-synthesized Fe0@C exhibited high catalytic activity toward the degradation of 4-chlorophenol (4-CP) by activating persulfate. Different from conventional nZVI catalysts in generation of sulfate radicals, Fe0@C selectively induced hydroxyl radicals for 4-CP degradation. Moreover, Fe0@C has been shown to efficiently degrade 4-CP by using the dissolved oxygen in water to form hydroxyl radicals. This study not only provides a simple, green method for the preparation of stabilized nZVI, but also provides the possibility of large-scale application of nZVI in the field of environmental remediation.

Influence of carbothermic reduction temperature on electromagnetic and microwave absorption properties of double loss Ti3SiC2/Co3Fe7 powders

In this study, we prepared double loss Ti3SiC2/Co3Fe7 powders by carbothermic reduction process at different temperatures. The powders were characterized and the electromagnetic wave absorption properties were investigated. As the carbothermic reduction temperature increased from 800 °C to 1000 °C, the intensities of diffraction peaks for Co3Fe7 increased and the particles grew up. For the Ti3SiC2/Co3Fe7 powders, the complex permittivity also increased but the complex permeability decreased with the rising temperature. The Ti3SiC2/Co3Fe7 powders synthesized at 900 °C owned the most favorable microwave absorption performance. For the sample in 2.4 mm thickness, an effective absorption bandwidth could be obtained in the frequency range from 8.79 to 11.92GHzwith a minimum reflection loss value of −31.2 dB at 10 GHz. Considering the excellent chemical stability and microwave absorption performance, the Ti3SiC2/Co3Fe7 powders could be used as a promising absorbent for high temperature application.

Synthesis of the ZrB&lt;sub&gt;2&lt;/sub&gt;-SiC Ceramic from Polymeric Precursor Pyrolysis

A ZrB2-SiC multiphase ceramic was fabricated with a precursor pyrolysis method by using zirconium boride organic precursor and polycarbosilane. In order to study the pyrolysis process of complex phase ceramics, the pyrolysis process of the two precursors was studied respectively at the beginning. The precursor and the mixture with different weight ratios both pyrolyzed at 800°C. ~1500°C. under argon atmosphere. The specimens were characterized by thermo-gravimetric analysis, infra-red, X-ray diffraction. It was found that the pyrolysis products of PCS remained amorphous below 1000°C. and converted into crystallization with temperature increasing. ZrO2as the intermediate pyrolysis product of ZrB2precursor initiate convert to t-ZrO2from m-ZrO2at 1200°C.. Finally, all kinds of ZrB2-SiC multiphase ceramic are successful obtained via pyrolysis of precursor after 1500°C. And the 40wt%ZrB2precursor initial carbothermal reduction temperature below the ZrB2precursor reactive temperature and the crystal degree of SiC is higher than pyrolysis product of PCS.

Polymer Technology of Porous SiC Ceramics Using Milled SiO2 Fibers

The paper describes a developed polymer composition and a process for manufacturing highporous chemically pure silicon carbide ceramics from this composition, using milled industrial wastes of quartz fiber non-woven fabrics as the source of silicon dioxide, which is important as a rational utilization of these wastes. The necessity of pre-milling of the SiO2 fibers was experimentally substantiated. Without this stage, the duration of treatment at 1400°C under dynamic vacuum considerably (≥12 h) increased, because of the non-uniform distribution of the components in the polymer composite. In the case of stoichiometric ratio of SiO2 and carbon formed upon pyrolysis of the polymeric phenol binder, the obtained SiC ceramic contained a large amount of unreacted carbon. This indicaties that side reactions take place to give volatile silicon monoxide, which is distilled off from the reactor. The effects of the milling time of SiO2 fibers and the carbothermal reduction temperature on the elemental and phase composition, density, and porosity of the obtained samples and the ultimate compressive strength were studied. Analysis of the experimental results served for optimization of the composition of the initial polymer composites. As a result, highly porous (83%) and relatively strong (ultimate compressive strength of 8.2MPa) SiC-ceramic samples free from unreacted carbon and silicon dioxide and other stubborn impurities were fabricated at 1400°C (dynamic vacuum, heat treatment for 4 h).