Nitrogen gas pressure sintering was successfully employed to achieve the in-situ formation of Si_(3)N_(4)-bonded MgO-C refractories.The primary objective was to investigate the influence of different gas pressures on ...Nitrogen gas pressure sintering was successfully employed to achieve the in-situ formation of Si_(3)N_(4)-bonded MgO-C refractories.The primary objective was to investigate the influence of different gas pressures on the mechanical properties and microstructure of MgO-C refractories.The results indicate that higher nitrogen pressure promotes the transformation of silicon nitride from theαphase to theβphase.This phase transition positively impacts the mechanical properties of Si_(3)N_(4)-bonded MgO-C refractories,leading to an enhancement in their overall strength.Notably,when the nitrogen pressure was set at 3 MPa,exceptional compressive strength of 109.7 MPa and an elastic modulus of 142.4 GPa were achieved by these prepared refractories.These findings highlight the great potential for utilizing gas pressure sintered Si_(3)N_(4)-MgO-C refractories.展开更多
Al_(4)SiC_(4) was synthesized from Al powder, silicon carbide, and graphite by microwave sintering, and characterized by XRD and SEM. Then the synthesized material was added to the magnesia carbon refractory brick to ...Al_(4)SiC_(4) was synthesized from Al powder, silicon carbide, and graphite by microwave sintering, and characterized by XRD and SEM. Then the synthesized material was added to the magnesia carbon refractory brick to study its effect on the oxidation resistance, apparent porosity, bulk density, elastic modulus, and modulus of rupture. It is found that Al_(4)SiC_(4) can be synthesized by microwave sintering at 1 300 ℃ and the addition of Al_(4)SiC_(4)-containing material as an antioxidant can enhance the oxidation resistance of the magnesia carbon refractory brick.展开更多
Wetting phenomena between MgO C and CaO SiO2 slags were investigated by varying carbon content.A sessile drop technique was adopted to study the wetting phenomena in conjunction with a high speed camera for the observ...Wetting phenomena between MgO C and CaO SiO2 slags were investigated by varying carbon content.A sessile drop technique was adopted to study the wetting phenomena in conjunction with a high speed camera for the observation of intrinsic wetting phenomena.The results show that the high content of SiO2 and the presence of Al2O3 in slags enhance the diffusion of Mg2+,leading to the promotion of reactive wetting.The carbon in MgO C refractory impedes the penetration of slags by repelling the slag and slowing the diffusion of Mg2+.This accounts for the non-wetting behavior of the slag on MgO C refractory with 17% (mass fraction) carbon similar to that of graphite.展开更多
Al2O3-SiC composite was synthesized with pyrophyllite and natural graphite as raw materials by carbothermal reduction reaction under argon atmosphere. The effect of synthesis temperature on phase composition and micro...Al2O3-SiC composite was synthesized with pyrophyllite and natural graphite as raw materials by carbothermal reduction reaction under argon atmosphere. The effect of synthesis temperature on phase composition and microstructure was investigated. Low-carbon MgO-C refractories were prepared by using the synthesized Al2O3-SiC composite as additive. The effect of its addition on the slag penetration and corrosion resistance as well as oxidation resistance of the refractories was investigated, and the slag resistance and oxidation resistance mechanisms of the Al2O3-SiC composite were also discussed. The results show that the synthesis temperature has a great influence on preparation of Al2O3-SiC composite. The Al2O3-SiC composite can be synthesized at 1873-1973 K under argon atmosphere, with pyrophyllite and natural graphite as raw materials, and particle sizes of the composite synthesized at 1973 K are mainly distributed as 1-2 μm. The slag penetration and corrosion resistance of low-carbon M80-C refractories can be remarkably improved by adding the synthesized Al2O3-SiC composite, and the oxidation resistance has an improvement to some extent. The increase of slag viscosity and the formation of MgAl2O4 can effectively inhibit the slag penetration and corrosion for the refractories.展开更多
An investigation on the oxidation mechanism of the graphite in the MgO-C refractory materials is helpful to improving both the quality of these materials and to preventing and/or lowering of the adverse effects of the...An investigation on the oxidation mechanism of the graphite in the MgO-C refractory materials is helpful to improving both the quality of these materials and to preventing and/or lowering of the adverse effects of the high-temperature oxidation. In this research, the oxidation behavior of the MgO-C refractories containing 5～20 wt% graphite was studied via weight-loss method. Atmospheric air was used for oxidation at temperatures ranging from 900℃ to 1300°C and the experimental data were compared with those obtained from the dimensionless kinetic equations of the shrinking core model, in order to determine the oxidation mechanisms of the refractories. The best fit was achieved with the porous layer diffusion control regime. Oxidation mechanism tends, however, to slightly deviate from pure pore diffusion control to pore diffusion-external gas transfer regime in the samples having more graphite contents (e.g. 20%).展开更多
The demand for low-carbon MgO–C refractories is ever growing to meet the development of advanced steelmaking technologies and efficient energy conservation.Meanwhile,to improve the oxidation resistance and inhibit th...The demand for low-carbon MgO–C refractories is ever growing to meet the development of advanced steelmaking technologies and efficient energy conservation.Meanwhile,to improve the oxidation resistance and inhibit the weakness of low-carbon MgO–C refractories,antioxidants are necessary.The application of ternary carbides that focused on improving the oxidation performance of MgO–C refractories has been explored,and the ternary carbides including Al_(4)O_(4)C,Al8B_(4)C_(7),Al_(4)SiC_(4),Ti_(2)AlC,Ti_(3)AlC_(2),and Ti_(3)SiC_(2)have been proved effective.The crystal structure,physical properties,oxidation behavior,and synthesis of these ternary carbides were summarized,and their oxidation mechanism in assisting antioxidation of MgO–C refractories was discussed.In addition,the potential aspects related to the usage and development of ternary carbides in low-carbon MgO–C refractories were proposed.展开更多
Two types of low carbon MgO - C refractories with 6% graphite were prepared using microporous magnesiarich spinel （5 - 3 and 3 - 1 mm ） and fused magnesia （5 - 3 and 3 - 1 mm ） as coarse aggregates, respectively, ...Two types of low carbon MgO - C refractories with 6% graphite were prepared using microporous magnesiarich spinel （5 - 3 and 3 - 1 mm ） and fused magnesia （5 - 3 and 3 - 1 mm ） as coarse aggregates, respectively, fused magnesia （ ≤1 mm） as fine aggregate, magnesia powder （≤ 0. 088 mm ） , flake graphite powder （ ≤0. 088 mm）, metal Al powder （ 〈0. 074 mm） as matrix, and phenol resin as binder. After curing at 220 ℃ and coke-embedded firing at 1 500 ℃ , the apparent porosity, cold crushing strength, cold modulus of rupture, permanent linear change on heating, thermal shock resistance and slag resistance of the specimens were studied comparatively. The results indicate that： （ 1 ） after curing at 220 ℃ and coke-embedded firing at 1 500 ℃, the specimen with microporous magnesia-rich spinel replacing fused magnesia has lower bulk density and higher apparent porosity than the common low car- bon MgO - C specimen. After curing at 220 ℃, the specimen with microporous aggregate has lower strength than common low carbon MgO - C specimen, but after coke-embedded firing at 1 500℃, it has higher strength and lower permanent linear change on heating; （2） low carbon MgO - C specimen using microporous magnesia-rich spinel to replace fused magnesia aggregate has better thermal shock resistance but worse slag resistance.展开更多
MgO-C refractories with stainless steel fibers were prepared to investigate the effects of stainless steel fibers addition on the thermal shock resistance,oxidation resistance,and microstructure of MgO-C refractories,...MgO-C refractories with stainless steel fibers were prepared to investigate the effects of stainless steel fibers addition on the thermal shock resistance,oxidation resistance,and microstructure of MgO-C refractories,and the optimum amount of stainless steel fibers was determined.The results showed that adding stainless steel fiber in MgO-C refractories can increase flexural strength and thermal shock resistance,with an optimal addition of 2 wt.%,owing to the bridging effect and crack deflection toughening of stainless steel fibers inside the material.The formation of MgAl1.9Fe0.1O4 composite spinel,which was responsible for higher oxidation resistance,produced volume expansion and prevented the diffusion of oxygen.The strengthening mechanism is physical embedding at room temperature,while it is reaction bonding at high temperature.展开更多
To solve the problem of poor high-temperature service performance caused by low carbonization of MgO-C refractories,low-carbon MgO–C refractories with excellent thermal shock,oxidation and corrosion resistances were ...To solve the problem of poor high-temperature service performance caused by low carbonization of MgO-C refractories,low-carbon MgO–C refractories with excellent thermal shock,oxidation and corrosion resistances were successfully designed by using SiC whiskers as reinforcing phases and introducing micro-Al_(2)O_(3) powders as additives.The results indicated that the addition of micro-Al_(2)O_(3) powders optimized the internal structure of the material,like the columnar β-Si_(3)N_(4) with a stepped distribution and the mosaic structure formed between granular and flaky Mg_(2)SiO_(4),which synergistically strengthened and toughened the material and gave the material excellent mechanical properties and thermal shock resistance.Specifically,the cold modulus of rupture and cold crushing strength after thermal shock were increased by 4.1 and 20.3 MPa,respectively.Moreover,the addition of micro-Al_(2)O_(3) powders promoted the formation of fine particles of Mg_(2)SiO_(4),MgAl_(2)O_(4) and MgO,as well as a dense protective layer of Mg_(2)SiO_(4) in the material under high-temperature environment.Furthermore,spinel and high-temperature solid solution were formed in the corrosion environment.The oxidation and corrosion resistances were greatly improved by 41%and 15%,respectively.展开更多
To improve the properties of low-carbonization of MgO–C refractories,the introduction of composite additives is an effective strategy.Al_(2)O_(3)–SiC composite powder was prepared from clay using electromagnetic ind...To improve the properties of low-carbonization of MgO–C refractories,the introduction of composite additives is an effective strategy.Al_(2)O_(3)–SiC composite powder was prepared from clay using electromagnetic induction heating and carbon embedded methods.Further,the Al_(2)O_(3)–SiC composite powder synthesized by electromagnetic induction heating at 600 A was added into low-carbon MgO–C refractories(4 wt.%)to improve their properties.The results showed that when the addition amount of Al_(2)O_(3)–SiC composite powder is within the range of 2.5–5.0 wt.%,the properties of low-carbon MgO–C samples were significantly improved,e.g.,the apparent porosity of 7.58%–8.04%,the bulk density of 2.98–2.99 g cm-3,the cold compressive strength of 55.72–57.93 MPa,the residual strength after three air quenching at 1100°C of 74.86%–78.04%,and the decarburized layer depth after oxidized at 1400°C for 2 h of 14.03–14.87 mm.Consequently,the idea for the rapid synthesis of Al_(2)O_(3)–SiC composite powder provides an alternative low-carbon MgO–C refractories performance optimization strategy.展开更多
In order to tackle the shortcomings of high brittleness,hard graphitization,and poor oxidation resistance resulted from carbonization of phenolic resin of Mg O- C refractories, effects of 2 mass% spherical Ni, and2 ma...In order to tackle the shortcomings of high brittleness,hard graphitization,and poor oxidation resistance resulted from carbonization of phenolic resin of Mg O- C refractories, effects of 2 mass% spherical Ni, and2 mass% spherical Ni plus 7. 5 mass% Al composite powder on microstructure of the secondary carbon in Mg O- C refractories matrix were investigated. The results show that a large number of carbon whiskers form after the carbonization of phenolic resin with Ni powder;in the Mg O- C refractories matrix with only Ni powder,the carbon microspheres form at all treatment temperatures and change slightly with the temperature rising;the carbon whiskers begin to generate in the specimens with composite powder at 1 000 ℃,the diameter of the carbon whiskers is about 0. 4- 0. 5 μm,and the length is about 3- 4 μm,and the formed carbon whiskers increase gradually with the temperature rising.展开更多
In this study,biomass cokes from sunflower seed hull(SFSH)and wood pellets(WP)were added to a MgO-C batch(3 mass%C)to replace 1.1 mass%of graphite.After hardening and carbonizing the samples,the influence of the bioma...In this study,biomass cokes from sunflower seed hull(SFSH)and wood pellets(WP)were added to a MgO-C batch(3 mass%C)to replace 1.1 mass%of graphite.After hardening and carbonizing the samples,the influence of the biomass cokes on the microstructure and thermal shock resistance was investigated.The replacement of flaky graphite by carbonized WP and SFSH reduced the bulk density and increased the apparent porosity after pressing and carbonization,but the degree was only marginal.This was confirmed by SEM investigations,where the biomass-coke containing samples exhibited a microstructure with a higher amount of pores between the fine MgO grains.The thermal shock resistance of the porous wood pellet coke containing MgO-C is at the same level as the reference sample but not superior to it.展开更多
In order to investigate the effect of the catalyst loading mode on the mechanical properties of Si_(3)N_(4) composite MgO-C refractories prepared by nitridation,fused magnesia,flake graphite,silicon powder,and phenoli...In order to investigate the effect of the catalyst loading mode on the mechanical properties of Si_(3)N_(4) composite MgO-C refractories prepared by nitridation,fused magnesia,flake graphite,silicon powder,and phenolic resin were used as the main raw materials,and ferric nitrate as the catalyst to prepare refractories by nitriding at 1350℃.The effects of different catalyst supports(silicon powder,silicon powder+phenolic resin)on the formation of Si_(3)N_(4) in MgO-C refractories and the properties of refractories were studied.The results show that the silicon powder+resin catalyst support promotes the participation ofα-Si_(3)N_(4) in the reaction to generateβ-Si_(3)N_(4) and MgSiN_(2),and generates more SiC.However,this loading mode causes more gas to escape from the refractories and loosens the material structure,which reduces the mechanical properties.On the contrary,MgO-C refractories prepared by nitridation with silicon powder-supported catalysts under the same conditions show higher density and better mechanical properties.展开更多
Magnesiu-Calcia materials containing 22 -53 wt% CaO hare been investigated Jot refinery slag corrosion and penetration resistance by Scanning Electron Microscopy （ SEM） .nd XRD. The corrosion and penetration resista...Magnesiu-Calcia materials containing 22 -53 wt% CaO hare been investigated Jot refinery slag corrosion and penetration resistance by Scanning Electron Microscopy （ SEM） .nd XRD. The corrosion and penetration resistance of MgO-CaO materials is enhanced with the increase of CaO content in specimens. It can be explained that, with increase of CaO content, the specimens reacted will＋ slag form higher melting point minerals of C3S ant C2S, creating a dense surface layer, which stopped others from penetrating further. Thus , the corrosion and penetration resistame was improved. No matter what kinds of slag were chosen, the depth of penetration decreased will＋ increase of CaO con,tent.展开更多
Carbon nanotubes （CNTs） have been extensively studied over the last two decades since they possess excellent properties.CNTs have been considered as new promising reinforcements for carbon containing refractories （...Carbon nanotubes （CNTs） have been extensively studied over the last two decades since they possess excellent properties.CNTs have been considered as new promising reinforcements for carbon containing refractories （CCRs）.Current research progress of the CNT-reinforced MgO-C and Al2O3-C refractories was summarized in this mini-review,and the CNT-reinforced CCRs possess remarkable mechanical properties and superior thermal shock resistance compared to CCRs without CNTs.展开更多
Corrosion resistance and penetration resistance of MgO-CaO materials with different CaO contents （22%, 42%, 49%, 53%, in mass）to refining AOD slag or VOD slag were investigated using static crucible technique by vis...Corrosion resistance and penetration resistance of MgO-CaO materials with different CaO contents （22%, 42%, 49%, 53%, in mass）to refining AOD slag or VOD slag were investigated using static crucible technique by visual observation, SEM and XRD. The corrosion resistance and penetration resistance of speci-mens decrease with the increase of CaO content. This may be caused by the formation of C3S and C2S during the reactions between specimens and the slag. The formed C3S and C2S can restrain the further penetration to the matrix. The higher the CaO content, the more the C2S or C3S formed, the lower the porosity of the speci-mens, and the lower the penetration depth and corrosion rate. The corrosion resistance to AOD slag is better than that to VOD slag, because the reaction between AOD slag and the matrix is slighter than that between VOD slag and the matrix.展开更多
The interaction of MgO-MgAl_(2)O_(4)-based and MgO-Cr_(2)O_(3)-based refractories with X70 molten steel was studied by immersion experiments at 1560℃.The effects of immersion time(30 and 60 min)on the contents of tot...The interaction of MgO-MgAl_(2)O_(4)-based and MgO-Cr_(2)O_(3)-based refractories with X70 molten steel was studied by immersion experiments at 1560℃.The effects of immersion time(30 and 60 min)on the contents of total oxygen(TO),Al,Nb,Si,Mn,and Cr as well as the composition,number density,and size distribution of inclusions in the molten steel were investigated.The influence of the penetration and erosion degree of the molten steel to the refractory on the steel-refractory interface layer was analyzed.The results show that,at 1560℃,the MgO-MgAl_(2)O_(4)-based refractory can better control the contents of TO and the composition of molten steel compared with the MgO-Cr_(2)O_(3)-based refractory.The TO content is only 16×10^(-4) wt.%in the molten steel after reacted with the Mg0-MgAl_(2)O_(4)-based refractory at the end point of refining,4 accounting for 11.5%of that reacted with the MgO-Cr_(2)O_(3)-based refractory(139×10^(-4) wt.%).The number density of inclusions is only 14 mm^(-2),and the average size ofinclusions is only 1.31μm,with thelargest proportion of inclusions in 1-2μm(70%).The Al_(2)O_(3)-MnS-CaO complex inclusions in the original steel changed to complex inclusions dominated by Cr-Nb-Mn-S-O and MgO.Al_(2)O_(3),corresponding to the MgO-Cr_(2)O_(3)-based and MgO-MgAl_(2)O_(4)-based refractories,respectively.The MgO.Al_(2)O_(3) layer was formed at the reaction interface between MgO-MgAl_(2)O_(4)-based refractory and molten steel,which is helpful to restrict the erosion of refractories and the pollution of molten steel.The damage mechanism of the MgO-Cr_(2)O_(3)-based refractory is mainly permeation and chemical reaction,while the damage of the MgO-MgAl_(2)O_(4)-based refractory is mainlyscouring erosion.展开更多
Henan refractories industry is a major refractory production base in China,which is also an advantage industry in Henan province.Recently,Henan provincial government has formulated relevant industrial and environmenta...Henan refractories industry is a major refractory production base in China,which is also an advantage industry in Henan province.Recently,Henan provincial government has formulated relevant industrial and environmental protection policies,and approved the construction of“Henan Province New Refractory Industry Cluster”.Henan’s main refractory enterprises have developed a series of green technologies,processes and products,and carried out automation and intelligent transformation,equipment upgrading,and the deep integration of information technology and refractory manufacturing through interconnection and digital empowerment.To promote the high-quality development of refractory industry,The Association of Henan Refractory Industry has established a series of standards and evaluation systems of refractories including air pollutant emission,energy consumption limits,carbon emission limits,green products,etc.The Association of Henan Refractory Industry also organized exchanges and mutual cooperation between enterprises inside and outside the region,and guided the development of specialization,refinement and innovation.This paper summarized the relevant works of refractories in Henan,and put forward some suggestions for solving the existing problems of refractories in Henan.展开更多
The development of efficient bonding agents is one aspect of the advancement of refractories. Based on a newly developed binder system, a new generation of tarresin bonded magnesia carbon products with high performanc...The development of efficient bonding agents is one aspect of the advancement of refractories. Based on a newly developed binder system, a new generation of tarresin bonded magnesia carbon products with high performance has been developed. Furthermore, the binder system characterized by high carbon yield after carbonization results in forming an extremely strong carbon bonding. It can improve refractories properties to get new product with more advantages than old refractories： more economic, lower cost and low toxicity. Tar-resin is not only used in shaped refractories, but also in more refractories types, such as monolithic refractories. Immersion experiments of MgO- C monolithic refractories samples in liquid steel at 1600℃ have been carried out for steel making industry. These experiments showed the formation of a dense and continuous MgO rich layer, on the interface between refractory and steel, and the possible formation of inclusions as large clusters protruding from the refractory surface. For the mechanical properties, the powder was heated up to 1400℃ in air to remove carbon, and was subsequently formed into brick shape. Standard ASTM was used to determine the MOR, porosity and density. It is found that antioxidantmaterials play an important role in improving the mechanical properties.展开更多
Mullite has a high melting point,high hardness,good thermal shock resistance,corrosion resistance,and high-temperature mechanical properties.Mullite raw materials are mostly synthesized by the sintering method and ele...Mullite has a high melting point,high hardness,good thermal shock resistance,corrosion resistance,and high-temperature mechanical properties.Mullite raw materials are mostly synthesized by the sintering method and electric fused method.The research and application progress of pure mullite and its composite refractories in fields such as ceramics,metallurgy,aerospace,military industry,cement and glass were reviewed.The future development trend of mullite in the application of refractories was prospected.展开更多
基金the financial support from the National Natural Science Foundation of China(U21A2057 and 52402034)the Key Research and Development Program of Hubei Province(2023BAB106).
文摘Nitrogen gas pressure sintering was successfully employed to achieve the in-situ formation of Si_(3)N_(4)-bonded MgO-C refractories.The primary objective was to investigate the influence of different gas pressures on the mechanical properties and microstructure of MgO-C refractories.The results indicate that higher nitrogen pressure promotes the transformation of silicon nitride from theαphase to theβphase.This phase transition positively impacts the mechanical properties of Si_(3)N_(4)-bonded MgO-C refractories,leading to an enhancement in their overall strength.Notably,when the nitrogen pressure was set at 3 MPa,exceptional compressive strength of 109.7 MPa and an elastic modulus of 142.4 GPa were achieved by these prepared refractories.These findings highlight the great potential for utilizing gas pressure sintered Si_(3)N_(4)-MgO-C refractories.
基金This work was funded by Luoyang Major Science and Technology Innovation Project(2301009A)Henan Province Key Research and Development Project(231111230200)。
文摘Al_(4)SiC_(4) was synthesized from Al powder, silicon carbide, and graphite by microwave sintering, and characterized by XRD and SEM. Then the synthesized material was added to the magnesia carbon refractory brick to study its effect on the oxidation resistance, apparent porosity, bulk density, elastic modulus, and modulus of rupture. It is found that Al_(4)SiC_(4) can be synthesized by microwave sintering at 1 300 ℃ and the addition of Al_(4)SiC_(4)-containing material as an antioxidant can enhance the oxidation resistance of the magnesia carbon refractory brick.
基金supported by the R&D Center for Valuable Recycling(Global-Top Environmental Technology Development Program)funded by the Ministry of Environment(Project No.:11-C22-ID)
文摘Wetting phenomena between MgO C and CaO SiO2 slags were investigated by varying carbon content.A sessile drop technique was adopted to study the wetting phenomena in conjunction with a high speed camera for the observation of intrinsic wetting phenomena.The results show that the high content of SiO2 and the presence of Al2O3 in slags enhance the diffusion of Mg2+,leading to the promotion of reactive wetting.The carbon in MgO C refractory impedes the penetration of slags by repelling the slag and slowing the diffusion of Mg2+.This accounts for the non-wetting behavior of the slag on MgO C refractory with 17% (mass fraction) carbon similar to that of graphite.
基金supported by the National Science and Technology Major Special Project (No.2009ZX04006-032)the National Natural Science Foundation of China (No.50274021) and Baoshan Iron and SteelCo.,Ltd.,China
文摘Al2O3-SiC composite was synthesized with pyrophyllite and natural graphite as raw materials by carbothermal reduction reaction under argon atmosphere. The effect of synthesis temperature on phase composition and microstructure was investigated. Low-carbon MgO-C refractories were prepared by using the synthesized Al2O3-SiC composite as additive. The effect of its addition on the slag penetration and corrosion resistance as well as oxidation resistance of the refractories was investigated, and the slag resistance and oxidation resistance mechanisms of the Al2O3-SiC composite were also discussed. The results show that the synthesis temperature has a great influence on preparation of Al2O3-SiC composite. The Al2O3-SiC composite can be synthesized at 1873-1973 K under argon atmosphere, with pyrophyllite and natural graphite as raw materials, and particle sizes of the composite synthesized at 1973 K are mainly distributed as 1-2 μm. The slag penetration and corrosion resistance of low-carbon M80-C refractories can be remarkably improved by adding the synthesized Al2O3-SiC composite, and the oxidation resistance has an improvement to some extent. The increase of slag viscosity and the formation of MgAl2O4 can effectively inhibit the slag penetration and corrosion for the refractories.
文摘An investigation on the oxidation mechanism of the graphite in the MgO-C refractory materials is helpful to improving both the quality of these materials and to preventing and/or lowering of the adverse effects of the high-temperature oxidation. In this research, the oxidation behavior of the MgO-C refractories containing 5～20 wt% graphite was studied via weight-loss method. Atmospheric air was used for oxidation at temperatures ranging from 900℃ to 1300°C and the experimental data were compared with those obtained from the dimensionless kinetic equations of the shrinking core model, in order to determine the oxidation mechanisms of the refractories. The best fit was achieved with the porous layer diffusion control regime. Oxidation mechanism tends, however, to slightly deviate from pure pore diffusion control to pore diffusion-external gas transfer regime in the samples having more graphite contents (e.g. 20%).
基金The authors acknowledge the financial support from the National Natural Science Foundation of China(U20A20239)Natural Science Foundation of Hubei Province(2020CFB692).
文摘The demand for low-carbon MgO–C refractories is ever growing to meet the development of advanced steelmaking technologies and efficient energy conservation.Meanwhile,to improve the oxidation resistance and inhibit the weakness of low-carbon MgO–C refractories,antioxidants are necessary.The application of ternary carbides that focused on improving the oxidation performance of MgO–C refractories has been explored,and the ternary carbides including Al_(4)O_(4)C,Al8B_(4)C_(7),Al_(4)SiC_(4),Ti_(2)AlC,Ti_(3)AlC_(2),and Ti_(3)SiC_(2)have been proved effective.The crystal structure,physical properties,oxidation behavior,and synthesis of these ternary carbides were summarized,and their oxidation mechanism in assisting antioxidation of MgO–C refractories was discussed.In addition,the potential aspects related to the usage and development of ternary carbides in low-carbon MgO–C refractories were proposed.
文摘Two types of low carbon MgO - C refractories with 6% graphite were prepared using microporous magnesiarich spinel （5 - 3 and 3 - 1 mm ） and fused magnesia （5 - 3 and 3 - 1 mm ） as coarse aggregates, respectively, fused magnesia （ ≤1 mm） as fine aggregate, magnesia powder （≤ 0. 088 mm ） , flake graphite powder （ ≤0. 088 mm）, metal Al powder （ 〈0. 074 mm） as matrix, and phenol resin as binder. After curing at 220 ℃ and coke-embedded firing at 1 500 ℃ , the apparent porosity, cold crushing strength, cold modulus of rupture, permanent linear change on heating, thermal shock resistance and slag resistance of the specimens were studied comparatively. The results indicate that： （ 1 ） after curing at 220 ℃ and coke-embedded firing at 1 500 ℃, the specimen with microporous magnesia-rich spinel replacing fused magnesia has lower bulk density and higher apparent porosity than the common low car- bon MgO - C specimen. After curing at 220 ℃, the specimen with microporous aggregate has lower strength than common low carbon MgO - C specimen, but after coke-embedded firing at 1 500℃, it has higher strength and lower permanent linear change on heating; （2） low carbon MgO - C specimen using microporous magnesia-rich spinel to replace fused magnesia aggregate has better thermal shock resistance but worse slag resistance.
基金supported by the Scientific and Technological Research Project of the Henan Provincial Department of Science and Technology of China(No.212102210579).
文摘MgO-C refractories with stainless steel fibers were prepared to investigate the effects of stainless steel fibers addition on the thermal shock resistance,oxidation resistance,and microstructure of MgO-C refractories,and the optimum amount of stainless steel fibers was determined.The results showed that adding stainless steel fiber in MgO-C refractories can increase flexural strength and thermal shock resistance,with an optimal addition of 2 wt.%,owing to the bridging effect and crack deflection toughening of stainless steel fibers inside the material.The formation of MgAl1.9Fe0.1O4 composite spinel,which was responsible for higher oxidation resistance,produced volume expansion and prevented the diffusion of oxygen.The strengthening mechanism is physical embedding at room temperature,while it is reaction bonding at high temperature.
基金the Scientific Research Fund of Hunan Provincial Education Department(22B0856)the Hengyang"Xiaohe"Science and Technology Talent Special Project([2023]45)+3 种基金the Guidance Plan Project of Hengyang City([2023]40)the National Natural Science Foundation of China(U20A20239)the College Students'Innovation and Entrepreneurship Training Project(S202311528055)the Characteristic Application Discipline of Material Science Engineering in Hunan Province([2022]351).
文摘To solve the problem of poor high-temperature service performance caused by low carbonization of MgO-C refractories,low-carbon MgO–C refractories with excellent thermal shock,oxidation and corrosion resistances were successfully designed by using SiC whiskers as reinforcing phases and introducing micro-Al_(2)O_(3) powders as additives.The results indicated that the addition of micro-Al_(2)O_(3) powders optimized the internal structure of the material,like the columnar β-Si_(3)N_(4) with a stepped distribution and the mosaic structure formed between granular and flaky Mg_(2)SiO_(4),which synergistically strengthened and toughened the material and gave the material excellent mechanical properties and thermal shock resistance.Specifically,the cold modulus of rupture and cold crushing strength after thermal shock were increased by 4.1 and 20.3 MPa,respectively.Moreover,the addition of micro-Al_(2)O_(3) powders promoted the formation of fine particles of Mg_(2)SiO_(4),MgAl_(2)O_(4) and MgO,as well as a dense protective layer of Mg_(2)SiO_(4) in the material under high-temperature environment.Furthermore,spinel and high-temperature solid solution were formed in the corrosion environment.The oxidation and corrosion resistances were greatly improved by 41%and 15%,respectively.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.U20A20239 and U1908227)the Fundamental Research Funds for the Central Universities(Grant No.N2125002)the open research fund for State Key Laboratory of Advance Refractories(Grant No.SKLAR202001).
文摘To improve the properties of low-carbonization of MgO–C refractories,the introduction of composite additives is an effective strategy.Al_(2)O_(3)–SiC composite powder was prepared from clay using electromagnetic induction heating and carbon embedded methods.Further,the Al_(2)O_(3)–SiC composite powder synthesized by electromagnetic induction heating at 600 A was added into low-carbon MgO–C refractories(4 wt.%)to improve their properties.The results showed that when the addition amount of Al_(2)O_(3)–SiC composite powder is within the range of 2.5–5.0 wt.%,the properties of low-carbon MgO–C samples were significantly improved,e.g.,the apparent porosity of 7.58%–8.04%,the bulk density of 2.98–2.99 g cm-3,the cold compressive strength of 55.72–57.93 MPa,the residual strength after three air quenching at 1100°C of 74.86%–78.04%,and the decarburized layer depth after oxidized at 1400°C for 2 h of 14.03–14.87 mm.Consequently,the idea for the rapid synthesis of Al_(2)O_(3)–SiC composite powder provides an alternative low-carbon MgO–C refractories performance optimization strategy.
文摘In order to tackle the shortcomings of high brittleness,hard graphitization,and poor oxidation resistance resulted from carbonization of phenolic resin of Mg O- C refractories, effects of 2 mass% spherical Ni, and2 mass% spherical Ni plus 7. 5 mass% Al composite powder on microstructure of the secondary carbon in Mg O- C refractories matrix were investigated. The results show that a large number of carbon whiskers form after the carbonization of phenolic resin with Ni powder;in the Mg O- C refractories matrix with only Ni powder,the carbon microspheres form at all treatment temperatures and change slightly with the temperature rising;the carbon whiskers begin to generate in the specimens with composite powder at 1 000 ℃,the diameter of the carbon whiskers is about 0. 4- 0. 5 μm,and the length is about 3- 4 μm,and the formed carbon whiskers increase gradually with the temperature rising.
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation),project number 461482547within the Research Training Group“GRK 2802:Refractory Recycling:A contribution for raw material-,energy-and climateefficiency in high temperature processes”The authors thankfully acknowledge the support of Dr.Gert Schmidt for the SEM/EDX investigations and Dr.Vânia Regina Salvini(Universidade Federal de São Carlos)for her inspiring input to conduct the thermal shock resistance investigation.
文摘In this study,biomass cokes from sunflower seed hull(SFSH)and wood pellets(WP)were added to a MgO-C batch(3 mass%C)to replace 1.1 mass%of graphite.After hardening and carbonizing the samples,the influence of the biomass cokes on the microstructure and thermal shock resistance was investigated.The replacement of flaky graphite by carbonized WP and SFSH reduced the bulk density and increased the apparent porosity after pressing and carbonization,but the degree was only marginal.This was confirmed by SEM investigations,where the biomass-coke containing samples exhibited a microstructure with a higher amount of pores between the fine MgO grains.The thermal shock resistance of the porous wood pellet coke containing MgO-C is at the same level as the reference sample but not superior to it.
基金supported by the National Natural Science Foundation of China(U20A20239)the Natural Science Foundation of Hubei Province(2020CFB692)the Scientific Research Fund of Hunan Provincial Education Department(18A428).
文摘In order to investigate the effect of the catalyst loading mode on the mechanical properties of Si_(3)N_(4) composite MgO-C refractories prepared by nitridation,fused magnesia,flake graphite,silicon powder,and phenolic resin were used as the main raw materials,and ferric nitrate as the catalyst to prepare refractories by nitriding at 1350℃.The effects of different catalyst supports(silicon powder,silicon powder+phenolic resin)on the formation of Si_(3)N_(4) in MgO-C refractories and the properties of refractories were studied.The results show that the silicon powder+resin catalyst support promotes the participation ofα-Si_(3)N_(4) in the reaction to generateβ-Si_(3)N_(4) and MgSiN_(2),and generates more SiC.However,this loading mode causes more gas to escape from the refractories and loosens the material structure,which reduces the mechanical properties.On the contrary,MgO-C refractories prepared by nitridation with silicon powder-supported catalysts under the same conditions show higher density and better mechanical properties.
文摘Magnesiu-Calcia materials containing 22 -53 wt% CaO hare been investigated Jot refinery slag corrosion and penetration resistance by Scanning Electron Microscopy （ SEM） .nd XRD. The corrosion and penetration resistance of MgO-CaO materials is enhanced with the increase of CaO content in specimens. It can be explained that, with increase of CaO content, the specimens reacted will＋ slag form higher melting point minerals of C3S ant C2S, creating a dense surface layer, which stopped others from penetrating further. Thus , the corrosion and penetration resistame was improved. No matter what kinds of slag were chosen, the depth of penetration decreased will＋ increase of CaO con,tent.
基金financially supported by the National Natural Science Foundation of China ( General program,51272188, 51472184 and 51472185 )the Natural Science Foundation of Hubei Province,China ( Contract No. 2013CFA086 )Foreign Cooperation Projects in Science and Technology of Hubei Province,China ( Contract No. 2013BHE002)
文摘Carbon nanotubes （CNTs） have been extensively studied over the last two decades since they possess excellent properties.CNTs have been considered as new promising reinforcements for carbon containing refractories （CCRs）.Current research progress of the CNT-reinforced MgO-C and Al2O3-C refractories was summarized in this mini-review,and the CNT-reinforced CCRs possess remarkable mechanical properties and superior thermal shock resistance compared to CCRs without CNTs.
文摘Corrosion resistance and penetration resistance of MgO-CaO materials with different CaO contents （22%, 42%, 49%, 53%, in mass）to refining AOD slag or VOD slag were investigated using static crucible technique by visual observation, SEM and XRD. The corrosion resistance and penetration resistance of speci-mens decrease with the increase of CaO content. This may be caused by the formation of C3S and C2S during the reactions between specimens and the slag. The formed C3S and C2S can restrain the further penetration to the matrix. The higher the CaO content, the more the C2S or C3S formed, the lower the porosity of the speci-mens, and the lower the penetration depth and corrosion rate. The corrosion resistance to AOD slag is better than that to VOD slag, because the reaction between AOD slag and the matrix is slighter than that between VOD slag and the matrix.
基金support from the National Natural Science Foundation of China(Grant Nos.U1860205 and 52204352)Youth Project of Hubei Natural Science Foundation(Grant No.2022CFB593)+1 种基金Key R&D Project of Hubei Province(Grant No.2022BAA021)Guiding Project of Scientific Research Plan of Hubei Provincial Department of Education(Grant No.B2022019).
文摘The interaction of MgO-MgAl_(2)O_(4)-based and MgO-Cr_(2)O_(3)-based refractories with X70 molten steel was studied by immersion experiments at 1560℃.The effects of immersion time(30 and 60 min)on the contents of total oxygen(TO),Al,Nb,Si,Mn,and Cr as well as the composition,number density,and size distribution of inclusions in the molten steel were investigated.The influence of the penetration and erosion degree of the molten steel to the refractory on the steel-refractory interface layer was analyzed.The results show that,at 1560℃,the MgO-MgAl_(2)O_(4)-based refractory can better control the contents of TO and the composition of molten steel compared with the MgO-Cr_(2)O_(3)-based refractory.The TO content is only 16×10^(-4) wt.%in the molten steel after reacted with the Mg0-MgAl_(2)O_(4)-based refractory at the end point of refining,4 accounting for 11.5%of that reacted with the MgO-Cr_(2)O_(3)-based refractory(139×10^(-4) wt.%).The number density of inclusions is only 14 mm^(-2),and the average size ofinclusions is only 1.31μm,with thelargest proportion of inclusions in 1-2μm(70%).The Al_(2)O_(3)-MnS-CaO complex inclusions in the original steel changed to complex inclusions dominated by Cr-Nb-Mn-S-O and MgO.Al_(2)O_(3),corresponding to the MgO-Cr_(2)O_(3)-based and MgO-MgAl_(2)O_(4)-based refractories,respectively.The MgO.Al_(2)O_(3) layer was formed at the reaction interface between MgO-MgAl_(2)O_(4)-based refractory and molten steel,which is helpful to restrict the erosion of refractories and the pollution of molten steel.The damage mechanism of the MgO-Cr_(2)O_(3)-based refractory is mainly permeation and chemical reaction,while the damage of the MgO-MgAl_(2)O_(4)-based refractory is mainlyscouring erosion.
文摘Henan refractories industry is a major refractory production base in China,which is also an advantage industry in Henan province.Recently,Henan provincial government has formulated relevant industrial and environmental protection policies,and approved the construction of“Henan Province New Refractory Industry Cluster”.Henan’s main refractory enterprises have developed a series of green technologies,processes and products,and carried out automation and intelligent transformation,equipment upgrading,and the deep integration of information technology and refractory manufacturing through interconnection and digital empowerment.To promote the high-quality development of refractory industry,The Association of Henan Refractory Industry has established a series of standards and evaluation systems of refractories including air pollutant emission,energy consumption limits,carbon emission limits,green products,etc.The Association of Henan Refractory Industry also organized exchanges and mutual cooperation between enterprises inside and outside the region,and guided the development of specialization,refinement and innovation.This paper summarized the relevant works of refractories in Henan,and put forward some suggestions for solving the existing problems of refractories in Henan.
文摘The development of efficient bonding agents is one aspect of the advancement of refractories. Based on a newly developed binder system, a new generation of tarresin bonded magnesia carbon products with high performance has been developed. Furthermore, the binder system characterized by high carbon yield after carbonization results in forming an extremely strong carbon bonding. It can improve refractories properties to get new product with more advantages than old refractories： more economic, lower cost and low toxicity. Tar-resin is not only used in shaped refractories, but also in more refractories types, such as monolithic refractories. Immersion experiments of MgO- C monolithic refractories samples in liquid steel at 1600℃ have been carried out for steel making industry. These experiments showed the formation of a dense and continuous MgO rich layer, on the interface between refractory and steel, and the possible formation of inclusions as large clusters protruding from the refractory surface. For the mechanical properties, the powder was heated up to 1400℃ in air to remove carbon, and was subsequently formed into brick shape. Standard ASTM was used to determine the MOR, porosity and density. It is found that antioxidantmaterials play an important role in improving the mechanical properties.
基金supported by the Starting Grants of Institute of Metal Research,Chinese Academy of Science(E255L401).
文摘Mullite has a high melting point,high hardness,good thermal shock resistance,corrosion resistance,and high-temperature mechanical properties.Mullite raw materials are mostly synthesized by the sintering method and electric fused method.The research and application progress of pure mullite and its composite refractories in fields such as ceramics,metallurgy,aerospace,military industry,cement and glass were reviewed.The future development trend of mullite in the application of refractories was prospected.
