The rapid advancement of superalloy melting technology has increased the demands on crucible materials.Y_(2)O_(3) is a promising candidate for nickel-based superalloy melting due to its outstanding high-temperature st...The rapid advancement of superalloy melting technology has increased the demands on crucible materials.Y_(2)O_(3) is a promising candidate for nickel-based superalloy melting due to its outstanding high-temperature stability and non-wetting behavior with various alloys.However,its poor sintering performance limits its development.High-density Y_(2)O_(3) ceramics were successfully prepared via pressureless sintering at 1600℃ in a carbon-embedded atmosphere with talc powder as an additive.The resulting ceramics achieved optimal properties,including a bulk density of 4.27 g cm^(−3),apparent porosity of 1.1%,and cold compressive strength of 311.27 MPa.The talc powder introduced a liquid phase during sintering,which accelerated mass transfer and promoted grain growth and densification.During cooling,this liquid phase remained at the grain boundaries and acted as an intergranular bonding agent,strengthening grain cohesion.Nevertheless,excessive liquid phase hindered grain growth,negatively affecting sintering.Additionally,the extremely low porosity and the formation of the Mg_(2)SiO_(4) phase reduced the residual strength retention ratio of the Y_(2)O_(3) ceramic after thermal shock.展开更多
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
Magnesia-calcia refractories are widely used in the production process of clean steel due to their excellent high-tem-perature stability,slag resistance and ability to purify molten steel.However,there are still probl...Magnesia-calcia refractories are widely used in the production process of clean steel due to their excellent high-tem-perature stability,slag resistance and ability to purify molten steel.However,there are still problems such as difficult sintering and easy hydration.Magnesia-calcia materials with various calcium oxide contents were prepared by using induction sintering,and the sintering property combined with the hydration resistance of the materials was investigated.The experimental results showed that the magnesia-calcia materials prepared under induction field had higher density,microhardness and hydration resistance.In particular,the relative density of induction sintered magnesia-calcia materials with 50 mo1%CaO was greater than 98%,and the average grain size of CaO was 4.56μm,which was much larger than that of traditional sintered materials.In order to clarify the densification and microstructure evolution mechanism of the magnesia-calcia materials,the changes in temperature and magnetic field throughout the sintering process were analyzed by using finite element simulation.The results showed that the larger heating rate and higher sintering temperature under the induction sintering mode were beneficial to the rapid densification.In addition,the hot spots generated within the material due to the difference in high-temperature electric conductivity between MgO and CaO were the critical factor to realize selective sintering in MgO-CaO system,which provides a novel pathway to solve the problem of difficult sintering and control the microstructure of high-temperature composite material used in the field of high-purity steel smelting.展开更多
ZrB_(2)-based ceramic composites were prepared by spark plasma sintering using ZrB_(2) powder prepared by molten salt method as raw material and SiC and nano-graphite as additives.The effects of nano-graphite addition...ZrB_(2)-based ceramic composites were prepared by spark plasma sintering using ZrB_(2) powder prepared by molten salt method as raw material and SiC and nano-graphite as additives.The effects of nano-graphite addition on the physical properties and oxidation resistance of ZrB_(2)-based ceramic samples were investigated.The results show that the addition of an appropriate amount of nano-graphite can effectively improve the density of ZrB_(2)-based ceramic composites and improve the physical properties of the materials.The flexural strength of the ceramic sample with 8 vol.%nano-graphite reached 418.54 MPa,which was 53.14% higher than that of ZrB_(2)-SiC ceramic material(273.31 MPa),and its oxidation resistance was also significantly improved.It demonstrats that the addition of an appropriate amount of nano-graphite can effectively improve the physical properties and oxidation resistance of ZrB_(2)-SiC ceramic composites.Via prolonging its service life in application and promoting the development of ZrB_(2)-based ceramic composites,it is of great significance for clean steel smelting.展开更多
The rapid development of iron and steel metallurgy technology has promoted the continuous innovation and iteration of carbon-containing refractories for clean steel smelting.To meet the high-quality requirements for c...The rapid development of iron and steel metallurgy technology has promoted the continuous innovation and iteration of carbon-containing refractories for clean steel smelting.To meet the high-quality requirements for clean steel production and full exploit the performance advantages of carbon-containing refractories in dynamic smelting environment,it is necessary to explore the role of graphite and modified graphite in carbon-containing refractories.Based on this,graphite surface modification methods,including surfactants,surface oxidation,and surface coating,and their applications in carbon-containing refractories are reviewed.The advantages and disadvantages of each method are analyzed for practical use.Furthermore,combined with the existing problems,the application prospect of improved graphite in carbon-containing refractories is discussed.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
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
MgO–CaO refractories have attracted much attention in the field of clean steel due to the ability of their internal CaO to adsorb elements such as S and P in molten steel.However,there are still some problems such as...MgO–CaO refractories have attracted much attention in the field of clean steel due to the ability of their internal CaO to adsorb elements such as S and P in molten steel.However,there are still some problems such as difficult sintering and insufficient corrosion resistance existing in this system.Different contents of Y_(2)O_(3)were introduced into MgO–CaO system to prepare MgO–CaO–Y_(2)O_(3)ternary refractories via traditional and induction sintering methods.The influence of microstructural regulation on the slag-resistant properties of the refractories was investigated.The results show that the introduction of Y_(2)O_(3)in the MgO–CaO refractories prepared via the two sintering methods leads to the grain boundary reconstruction effect.Under the condition of traditional sintering,when a smaller amount of Y_(2)O_(3)is introduced into the MgO–CaO refractories,Y_(2)O_(3)is able to activate the lattice,promote sintering,and improve the densification of the refractories.However,when more Y_(2)O_(3)is introduced,the excess Y_(2)O_(3)hinders the sintering densification process.Combined with lamellar intergranular phase generated in the refractories,Y_(2)O_(3)-based solid solution can react with the slag,increase the slag viscosity and inhibit the penetration of the slag into the refractories.Under the condition of induction sintering,the solid solution of yttrium ions in CaO is increased by using the coupling of electromagnetic and thermal fields.Compared with the MgO–CaO refractories with high Y_(2)O_(3)content prepared by traditional sintering,the induction sintered refractories have higher densification,which further increases the corrosion resistance.The results provide a new path for developing long-life MgO–CaO based refractories.展开更多
基金financially supported by the National Natural Science Foundation of China(No.U21A2057).
文摘The rapid advancement of superalloy melting technology has increased the demands on crucible materials.Y_(2)O_(3) is a promising candidate for nickel-based superalloy melting due to its outstanding high-temperature stability and non-wetting behavior with various alloys.However,its poor sintering performance limits its development.High-density Y_(2)O_(3) ceramics were successfully prepared via pressureless sintering at 1600℃ in a carbon-embedded atmosphere with talc powder as an additive.The resulting ceramics achieved optimal properties,including a bulk density of 4.27 g cm^(−3),apparent porosity of 1.1%,and cold compressive strength of 311.27 MPa.The talc powder introduced a liquid phase during sintering,which accelerated mass transfer and promoted grain growth and densification.During cooling,this liquid phase remained at the grain boundaries and acted as an intergranular bonding agent,strengthening grain cohesion.Nevertheless,excessive liquid phase hindered grain growth,negatively affecting sintering.Additionally,the extremely low porosity and the formation of the Mg_(2)SiO_(4) phase reduced the residual strength retention ratio of the Y_(2)O_(3) ceramic after thermal shock.
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The authors would like to express the gratitude for the financial support from the National Natural Science Foundation of China(U20A20239).
文摘Magnesia-calcia refractories are widely used in the production process of clean steel due to their excellent high-tem-perature stability,slag resistance and ability to purify molten steel.However,there are still problems such as difficult sintering and easy hydration.Magnesia-calcia materials with various calcium oxide contents were prepared by using induction sintering,and the sintering property combined with the hydration resistance of the materials was investigated.The experimental results showed that the magnesia-calcia materials prepared under induction field had higher density,microhardness and hydration resistance.In particular,the relative density of induction sintered magnesia-calcia materials with 50 mo1%CaO was greater than 98%,and the average grain size of CaO was 4.56μm,which was much larger than that of traditional sintered materials.In order to clarify the densification and microstructure evolution mechanism of the magnesia-calcia materials,the changes in temperature and magnetic field throughout the sintering process were analyzed by using finite element simulation.The results showed that the larger heating rate and higher sintering temperature under the induction sintering mode were beneficial to the rapid densification.In addition,the hot spots generated within the material due to the difference in high-temperature electric conductivity between MgO and CaO were the critical factor to realize selective sintering in MgO-CaO system,which provides a novel pathway to solve the problem of difficult sintering and control the microstructure of high-temperature composite material used in the field of high-purity steel smelting.
基金the project supported by the Natural Science Foundation of Hubei Province(Grant No.2023BAB106)the National Natural Science Foundation of China(Grant No.U20A20239)the Scientific Research Project of Education Department of Hubei Province(D20211104).
文摘ZrB_(2)-based ceramic composites were prepared by spark plasma sintering using ZrB_(2) powder prepared by molten salt method as raw material and SiC and nano-graphite as additives.The effects of nano-graphite addition on the physical properties and oxidation resistance of ZrB_(2)-based ceramic samples were investigated.The results show that the addition of an appropriate amount of nano-graphite can effectively improve the density of ZrB_(2)-based ceramic composites and improve the physical properties of the materials.The flexural strength of the ceramic sample with 8 vol.%nano-graphite reached 418.54 MPa,which was 53.14% higher than that of ZrB_(2)-SiC ceramic material(273.31 MPa),and its oxidation resistance was also significantly improved.It demonstrats that the addition of an appropriate amount of nano-graphite can effectively improve the physical properties and oxidation resistance of ZrB_(2)-SiC ceramic composites.Via prolonging its service life in application and promoting the development of ZrB_(2)-based ceramic composites,it is of great significance for clean steel smelting.
基金the project supported by the Natural Science Foundation of Hubei Province(Grant No.2023BAB106)the National Natural Science Foundation of China(Grant No.U20A20239).
文摘The rapid development of iron and steel metallurgy technology has promoted the continuous innovation and iteration of carbon-containing refractories for clean steel smelting.To meet the high-quality requirements for clean steel production and full exploit the performance advantages of carbon-containing refractories in dynamic smelting environment,it is necessary to explore the role of graphite and modified graphite in carbon-containing refractories.Based on this,graphite surface modification methods,including surfactants,surface oxidation,and surface coating,and their applications in carbon-containing refractories are reviewed.The advantages and disadvantages of each method are analyzed for practical use.Furthermore,combined with the existing problems,the application prospect of improved graphite in carbon-containing refractories is discussed.
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.
基金financially supported by the National Natural Science Foundation of China(Nos.U20A20239 and U21A2057)the Key Research and Development Project of Hubei Province,China(No.2023BEB017)2023 Longzhong Talent Support Plan(23).
文摘MgO–CaO refractories have attracted much attention in the field of clean steel due to the ability of their internal CaO to adsorb elements such as S and P in molten steel.However,there are still some problems such as difficult sintering and insufficient corrosion resistance existing in this system.Different contents of Y_(2)O_(3)were introduced into MgO–CaO system to prepare MgO–CaO–Y_(2)O_(3)ternary refractories via traditional and induction sintering methods.The influence of microstructural regulation on the slag-resistant properties of the refractories was investigated.The results show that the introduction of Y_(2)O_(3)in the MgO–CaO refractories prepared via the two sintering methods leads to the grain boundary reconstruction effect.Under the condition of traditional sintering,when a smaller amount of Y_(2)O_(3)is introduced into the MgO–CaO refractories,Y_(2)O_(3)is able to activate the lattice,promote sintering,and improve the densification of the refractories.However,when more Y_(2)O_(3)is introduced,the excess Y_(2)O_(3)hinders the sintering densification process.Combined with lamellar intergranular phase generated in the refractories,Y_(2)O_(3)-based solid solution can react with the slag,increase the slag viscosity and inhibit the penetration of the slag into the refractories.Under the condition of induction sintering,the solid solution of yttrium ions in CaO is increased by using the coupling of electromagnetic and thermal fields.Compared with the MgO–CaO refractories with high Y_(2)O_(3)content prepared by traditional sintering,the induction sintered refractories have higher densification,which further increases the corrosion resistance.The results provide a new path for developing long-life MgO–CaO based refractories.
