Synthesis technology and properties of cordierite from solid waste resources

Tan Qitong, Zhao Huizhong, Yu Jun, Zhang Han, Tan Liqiang

2024, (3): 185-189. doi：10.3969/j.issn.1001-1935.2024.03.001

To effectively utilize solid waste resources and relieve resource constraints,cordierite refractory raw materials were prepared according to the chemical composition of cordierite,using 12 mass% fused magnesia dust powder,40 mass% fused corundum dust powder and 48 mass% quartz tailings as starting materials,calcining at 1 320,1 350,1 380,1 390,1 400 and 1 410 ℃ for 3 h,respectively.The effects of the calcination temperature on the phase composition,microstructure and physical properties of the cordierite specimens were studied.The results show that below 1 390 ℃,magnesium aluminate spinel and cristobalite gradually react to form cordierite until cristobalite is completely exhausted;when the calcination temperature reaches 1 390 ℃,the cristobalite content in the sample reaches 94 mass%,and the secondary crystal phase is magnesium aluminate spinel;at this time,the sample has the optimal comprehensive performance:the lowest thermal expansion coefficient of 3.2×10^-6℃^-1,a low bulk density of 1.85 g·cm^-3,a low thermal conductivity of 1.279 W·(m·K)^-1 and dense microstructure.

Synthesis of porous MgAl₂O₄ fibers by solid-state reaction

Wang Xinyue, Xu Qing, Zhu Xinxin, Zhou Ruiqi, Duan Hongjuan, Zhang Haijun, Li Shaoping

2024, (3): 190-194. doi：10.3969/j.issn.1001-1935.2024.03.002

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The gas phase method is the main preparation method of MgAl₂O₄ fibers,but it has problems such as high reaction temperatures,high cost,and low yield.Porous MgAl₂O₄ fibers were prepared using basic magnesium sulfate whiskers as templates,mixing with alumina sol or α-Al₂O₃ micropowder through the solid-state reaction.The effects of the heat treatment temperature (1 000,1 100 and 1 300 ℃),holding time (3 and 10 h),and alumina source (alumina sol and α-Al₂O₃) on the synthesis of the porous MgAl₂O₄ fibers were studied.The results show that:(1)compared with the fiber using α-Al₂O₃ as the alumina source,the one using alumina sol generates more MgAl₂O₄;(2)as the heat treatment temperature increases,Al₂O₃ tends to react completely with MgO,thus continuously increasing the forming amount of MgAl₂O₄,and the synthesized porous MgAl₂O₄ fibers have small and uniform nanopores;(3)the optimal synthesis process is using alumina sol as the alumina source and firing at 1 300 ℃ for 3 h.

Effect of Y₂O₃ on properties of oxide-bonded Ti(C,N) composites

Cheng Xu, Deng Chengji, Dong Bo, Zou Qiliang, Ding Jun, Wang Zhoufu, Zhu Wanzheng, Xiao Yuyan, Zhu Hongxi, Yu Chao

2024, (3): 195-198. doi：10.3969/j.issn.1001-1935.2024.03.003

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To investigate the effect of rare earth oxides on the properties of Ti(C,N) composites,oxide-bonded Ti(C,N) materials were prepared by carbothermal reduction nitridation at 1 600 ℃ using TiO₂ powder,graphite powder and Si powder as raw materials,and Y₂O₃ powder as sintering aids.The effect of the Y₂O₃ addition (1%,2%,and 4%,by mass) on the phase composition,microstructure,and physical properties of the Ti(C,N) composites was investigated.The results show that the primary phases in the samples after high-temperature firing are Ti(C,N),Ti₃O₅,α-quartz,and Y₂Si₂O₇.As the Y₂O₃ addition increases,there is a corresponding rise in the production of the liquid phase within the specimens,resulting in coarsening of Ti(C,N) grains and non-uniform distribution of Y₂Si₂O₇,ultimately leading to a degradation in the mechanical properties of the specimens.When the Y₂O₃ addition is 1%,the average size of Ti(C,N) grains is approximately 0.76 μm,the composite exhibits high density and excellent mechanical properties,with the apparent porosity of 0.8%,cold modulus of rupture of 242.2 MPa,and elastic modulus of 230.3 GPa.

Corrosion mechanisms of CaO to MgAl₂O₄ materials and ZrO₂-MgAl₂O₄ materials

Liu Zhongfei, Wu Feng, Li Xinwei, Liang Xiaocheng, Luo Xudong, Qian Guohua

2024, (3): 199-203. doi：10.3969/j.issn.1001-1935.2024.03.004

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This work aims to study the corrosion mechanisms of CaO to MgAl₂O₄ materials and ZrO₂·MgAl₂O₄ materials.MgAl₂O₄ micropowder,desilicated zirconia micropowder,and analytically pure calcium carbonate were used as raw materials.CaO micropowder was obtained by calcining the calcium carbonate and crushing,and then the MgAl₂O₄ material was prepared with the mass ratio of MgAl₂O₄ micropowder to CaO micropowder of 4∶1 and the ZrO₂-MgAl₂O₄ material was prepared with the mass ratio of desilicated zirconium powder,MgAl₂O₄ micropowder and CaO micropowder of 3∶4∶1.Both the materials were heat treated at 1 500,1 600 and 1 700 ℃ for 3 h,respectively.The possible reactions in the system were analyzed using phase diagrams and thermodynamic calculations.The phase composition and microstructure of the fired samples were analyzed by XRD and SEM.The results show that:for the MgAl₂O₄ material,CaO reacts with MgAl₂O₄ to form low-melting-point CaO·Al₂O₃ and 12CaO·7Al₂O₃; for the ZrO₂-MgAl₂O₄ material,a large amount of CaO reacts with ZrO₂ to generate high-melting-point c-ZrO₂ and CaZrO₃,while the remaining small amount of CaO reacts with MgAl₂O₄ to form CaO·Al₂O₃,which reduces the formation of low-melting-point phases.

Preparation of calcium zirconate materials by two-step sintering

Wang Meng, Wen Shuhua, Yu Jingkun, Yuan Lei, Wen Tianpeng

2024, (3): 204-207. doi：10.3969/j.issn.1001-1935.2024.03.005

Abstract ( ) PDF (1492KB)( )

In order to improve their density,calcium zirconate (CaZrO₃) materials were prepared with calcium carbonate and zirconia as raw materials by the two-step sintering method:pre-firing—crushing—pressing—high temperature sintering.The effects of the pre-firing temperature (1 200,1 300,1 400,and 1 500 ℃) on the microstructure and cold properties of the CaZrO₃ materials were studied.The results show that:(1)the two-step sintering method can make the distribution of raw materials uniform and the reaction thorough,and avoid the expansion cracking of the sample caused by zirconia phase transformation;(2)when the pre-firing temperature is 1 400 ℃,the sample has the optimal comprehensive properties:the main crystalline phase CaZrO₃ reaches 99 mass%,the average grain size is 4-5 μm,the apparent porosity is 1.6%,the bulk density is 4.40 g·cm^-3,and the cold compressive strength is 590 MPa.

Effects of polypropylene fibers on thermal shock resistance of corundum-calcium hexaaluminate castables

Tian Pengdan, Wang Gang, Du Penghui, Feng Haixia, Wang Laiwen, Pan Yuanshuai

2024, (3): 208-212. doi：10.3969/j.issn.1001-1935.2024.03.006

Abstract ( ) PDF (1850KB)( )

To enhance the properties of corundum-calcium hexaaluminate (CA₆) castables,hydrous alumina bonded corundum-CA₆ castables were prepared using corundum,CA₆ and activated α-Al₂O₃ micropowder as main raw materials.The effects of different polypropylene fiber extra-additions (mass fractions of 0,0.04%,0.08%,0.12% and 0.16%) on the properties of the castables were studied,especially on the thermal shock resistance.The results show that:(1)the polypropylene fiber addition can reduce the average linear thermal expansion coefficient while decrease the strength and bulk density of the specimens,which leads to a decrease in the elastic modulus;(2)an appropriate addition of polypropylene fibers can improve the thermal shock resistance of the specimens,but excessive polypropylene fibers loosen the internal structure of the material and decrease the density,thereby worsening the thermal shock resistance of the specimens;(3)when the polypropylene fiber addition is 0.08%,the specimen has the highest retention ratio of modulus of rupture of 53.5%,showing the best thermal shock resistance.

Effect of pre-synthesized CaZrO₃ on properties of magnesia-zirconia refractories

Liang Xiaocheng, Feng Yu, Liu Zhongfei, Luo Xudong, Huang Min, Wu Feng

2024, (3): 213-217. doi：10.3969/j.issn.1001-1935.2024.03.007

Abstract ( ) PDF (2101KB)( )

In order to improve the properties of magnesia-zirconia refractories,the pre-synthesized CaZrO₃ (≤ 0.074 mm) with different CeO₂ extra-additions (0,1% and 2%,by mass) was firstly prepared using calcium carbonate,desilicated zirconia and CeO₂ as raw materials.Then,the pre-synthesized CaZrO₃ was mixed with fused magnesia (3-1,1-0.074 and ≤0.074 mm),and pressed into cylindrical and strip specimens under 250 MPa.The magnesia-zirconia refractories were prepared by heat treatment at 1 600 ℃ for 3 h.The effects of the pre-synthesized CaZrO₃ powder addition (10%,15% and 20%,by mass) on the properties of the materials were studied.The results show that:(1)a certain amount of CeO₂ forms a solid solution with ZrO₂,which makes ZrO₂ exist in the form of t-ZrO₂ at room temperature,stabilizes the crystal form of ZrO₂,and promotes the formation of CaZrO₃;(2)CeO₂ promotes sintering and is conducive to densification;the microcrack toughening caused by the difference on the thermal expansion coefficient between CaZrO₃,ZrO₂ and periclase improves the thermal shock resistance;the composite spinel and CaZrO₃ formed by the specimens and RH slag block pores and improve the slag resistance;(3)when adding 20% of the pre-synthesized CaZrO₃ with 1% CeO₂,the specimen has the optimal performance.

Properties of silica sol-phenolic resin co-bonded Al₂O₃-SiC-C bricks

Lyu Baodong, Gao Dongsheng, Ju Maoqi, Yang Fan

2024, (3): 218-223. doi：10.3969/j.issn.1001-1935.2024.03.008

Abstract ( ) PDF (1755KB)( )

To mitigate the structural deterioration of Al₂O₃-SiC-C bricks induced by phenolic resin carbonization and enhance their mechanical properties and slag resistance,silica sol-phenolic resin co-bonded Al₂O₃-SiC-C bricks were prepared using bauxite (5-3,3-1 and ≤1 mm) as aggregates,white fused corundum (≤0.045 mm),SiC (≤0.075 mm),α-Al₂O₃ micropowder and flake graphite (≤0.15 mm) as the matrix,and thermosetting phenolic resin and silica sol as the binders.Based on the extra addition of 4.5 mass% phenolic resin,the effects of the silica sol extra addition (mass fractions of 0,0.45%,0.90% and 1.35%,respectively) on the cold and hot mechanical properties and slag resistance of the bricks were investigated.The results show that an appropriate addition of silica sol can effectively improve the mechanical properties and slag resistance of the Al₂O₃-SiC-C bricks,and the specimen with 0.45% silica sol performs excellent cold and hot mechanical properties and slag resistance.

Preparation of porous magnesium-aluminate spinel materials by foaming-spontaneous solidification casting method

Jiao Changfa, Li Guohua, Sun Gege, Tian Lin, Kang Chi

2024, (3): 224-229. doi：10.3969/j.issn.1001-1935.2024.03.009

Abstract ( ) PDF (2775KB)( )

To improve the thermal efficiency of thermal kilns and reduce the thermal energy loss,porous magnesium-aluminate spinel materials were prepared by the foaming-spontaneous solidification casting method,using industrial-grade medium-grade magnesia fine powder (d₅₀=34.2 μm) and calcined alumina powder (d₅₀=3.4 μm) as raw materials,potassium oleate as a foaming agent,sodium carboxymethyl cellulose as a foam stabilizer,and an alternating copolymer of isobutylene and maleic anhydride (ISOBAM-104,referred to as “IB”) as a curing agent.The effects of the IB extra-addition (0,0.1%,0.2%,0.3%,and 0.4%,by mass) on the properties of the slurry and the specimens after firing at 1 500 ℃ for 3 h were studied.The results show that:(1)with the increase of the IB addition,the expansion ratio of the slurry decreases,and the absolute value of the Zeta potential firstly increases and then decreases;after firing,the apparent porosity of the specimen decreases,the bulk density increases,the cold compressive strength first increases and then decreases,the distribution of pores changes from closely packed to independently dispersed,the pore wall thickens,and the thermal conductivity firstly increases and then decreases;(2)when the IB addition is 0.3%,the Zeta potential is -52.6 mV and the slurry is the most stable;the fired specimen has the maximum cold compressive strength of 32.7 MPa,the apparent porosity of 54.4%,the bulk density of 1.63 g·cm^-3,the thermal conductivity of 0.205 W·m^-1·K^-1 at 350 ℃,and the minimum average pore size of 46.8 μm,the comprehensive properties are the best.

Effect of boron oxide on mechanical properties of Al₂O₃-SiC-C castables

Shao Rongdan, Ju Maoqi, Cheng Shui-ming, Xia Changyong, Li Xuzhi, Zhang Han, Shan Jiangbo

2024, (3): 230-233. doi：10.3969/j.issn.1001-1935.2024.03.010

Abstract ( ) PDF (2056KB)( )

To further improve their mechanical properties by utilizing the indirect sintering characteristics of boron oxide,Al₂O₃-SiC-C castables were prepared with mullite particles FM60,dense corundum,silicon carbide and α-Al₂O₃ micropowder as main raw materials and boron oxide (≤0.075 mm) as the sintering aid.The effect of the boron oxide fine powder addition (mass fractions of 0,0.2%,0.4% and 0.6%,respectively) on the structure and properties of the castables was investigated.The results show that adding boron oxide fine powder significantly increases the water demand of the castables,but it is beneficial for the formation of mullite whiskers,thereby strengthening the bonding between the aggregates and the matrix and significantly improving the mechanical properties of the samples.However,when the addition of boron oxide fine powder increases to 0.6%,the sample presents decreased length to diameter ratio of mullite whiskers and lower strength.Generally,the optimal boron oxide addition is 0.4%.

R&D and application of MgO-C bricks for slag line of steel ladles with high refining ratios

He Weixiang, Luo Ming, He Liang, Ke Jifeng

2024, (3): 234-237. doi：10.3969/j.issn.1001-1935.2024.03.011

Abstract ( ) PDF (1580KB)( )

To improve the service life of MgO-C bricks,based on analyzing the damage mechanism of MgO-C bricks in the slag line of a 210 t refining ladle with a high refining ratio in a steel plant in China,MgO-C bricks were prepared using fused magnesia grade 97,flake graphite,MgO-rich spinel micropowder,antioxidant (Al powder and Si powder),and phenolic resin as raw materials.The effects of the equivalent substitution of MgO-rich spinel micropowder (0,3% and 6%,by mass) for fused magnesia fines on the physical properties,oxidation resistance,and slag resistance of the samples were studied.The results show that compared with the sample without MgO-rich spinel micropowder,the sample with 3% MgO-rich spinel micropowder has significantly improved physical properties,oxidation resistance,and hot modulus of rupture,as well as decreased linear expansion rate;however,as the MgO-rich spinel micropowder addition increases to 6%,the overall performance of the sample shows a downward trend. After applying the MgO-C bricks with 3% MgO-rich spinel micropowder in the ladle slag line under the smelting condition of high refining ratios,the problems such as “steamed bread” melting loss and vertical cracks of MgO-C bricks were significantly relieved.

Effects of spent iron trough castable addition on properties of Al₂O₃-SiC-C castables

Ju Maoqi, Ma Xiaoyi, Cheng Shuiming, Xia Changyong, Wei Jianxiu, Zhang Xiaocun, Shan Jiangbo, Gao Dongsheng

2024, (3): 238-241. doi：10.3969/j.issn.1001-1935.2024.03.012

Abstract ( ) PDF (1545KB)( )

To improve the resource recycling rate of spent refractories,Al₂O₃-SiC-C castables were prepared using brown corundum,spent iron trough castables,white corundum,silicon carbide,α-Al₂O₃ micropowder and silica micropowder as the main raw materials.The effects of the spent iron trough castable addition (0,14%,28%,42% and 56%,by mass) on the performance of the castables were explored.The results show that with the increase of the spent iron trough castable addition,the water demand of the castables significantly increases;the samples change from expansion to shrinkage after heat-treatment at 1 450 ℃ for 3 h;the bulk density,cold modulus of rupture and corrosion resistance of the samples after heat-treatment at 110 ℃ for 24 h and 1 450 ℃ for 3 h all show downward trends;however,when the spent iron trough castable addition is lower than 28%,the performance degradation is relatively smaller.The castables with 28% spent iron trough castables were served for the iron runner and slag runner of the iron trough of 1 080 and 1 350 m³ blast furnaces,achieving a good service effect with the service life of the main structure more than 70 days.

Effect of pre-oxidation on oxidation resistance of nitrides bonded silicon carbide materials for coke ovens

Meng Hongtao, Ma Longbin, Liu Xin

2024, (3): 242-245. doi：10.3969/j.issn.1001-1935.2024.03.013

Abstract ( ) PDF (1543KB)( )

To improve the oxidation resistance of silicon carbide materials for coke ovens,SiAlON-SiC,Si₂N₂O-SiC and Si₃N₄-SiC refractory samples were prepared by nitridation at 1 420 ℃ for 10 h with silicon carbide particles (2.5-1.43,1.43-0.5 and 0.5-0.088 mm) and fine powder (≤0.088 mm),silicon powder (≤0.088 mm),alumina micropowder (≤0.044 mm) and SiO₂ micropowder (≤1 μm) as raw materials and lignin as the binder.Then the samples were pre-oxidized at 650,850,1 050 and 1 250 ℃ for 5 h,respectively.The effect of pre-oxidation on the oxidation resistance of the nitrided samples was investigated.The results show that:(1)at low temperatures (≤850 ℃),the oxidation resistance of the Si₃N₄-SiC materials is better than that of the SiAlON-SiC and Si₂N₂O-SiC materials,while at 850-1 250 ℃,the oxidation resistance of the SiAlON-SiC materials is the best;(2)after pre-oxidation treatment at 1 250 ℃,the SiAlON-SiC materials show the lowest apparent porosity of 2.4% and the best oxidation resistance,because an oxide layer is formed on the surface of the samples,which can reduce the apparent porosity and improve the oxidation resistance;(3)for the heat exchanger of coke ovens,silicon nitride bonded silicon carbide materials are suitable below 850 ℃ and SiAlON bonded silicon carbide materials are suitable above 850 ℃;for the denitration tube of coke ovens,SiAlON bonded silicon carbide materials are suitable.

Preparation and properties of porous silicon carbide ceramic materials from iron tailings

Guan Yunhe, Zheng Lijun, Luo Xudong, Niu Shunan

2024, (3): 246-250. doi：10.3969/j.issn.1001-1935.2024.03.014

Abstract ( ) PDF (1661KB)( )

To explore the reuse of iron tailings,the porous silicon carbide ceramic materials were prepared by carbothermal reduction with iron tailings and anthracite as raw materials.The effects of the molar ratio of C to SiO₂ (3∶1,4∶1,5∶1 and 6∶1) and the heat treatment temperature (1 200,1 300,1 400 and 1 500 ℃) on the microstructure,mechanical properties,and thermal conductivity of the porous silicon carbide ceramic materials were studied.The results show that the main crystalline phase of the porous silicon carbide ceramic materials is β-SiC,and the secondary crystalline phases are Fe₅Si₃ and Fe₃Si;with the increasing heat treatment temperature and the molar ratio of C to SiO₂,the carbothermal reduction reaction tends to be complete,the β-SiC content increases gradually,the bulk density and cold compressive strength decrease,the apparent porosity increases and the thermal conductivity decreases.When the heat treatment temperature is 1 500 ℃ and the molar ratio of C to SiO₂ is 6∶1,the optimal properties can be achieved:the bulk density of 1.25 g·cm^-3,the apparent porosity of 62.3%,the cold compressive strength of 35.0 MPa,and the thermal conductivity of 0.150 W·m^-1·K^-1 at 800 ℃.

Research progress on refractories for smelting reduction ironmaking process

Liu Ran, Liu Yanting, Gao Yanjia, Deng Yong

2024, (3): 251-256. doi：10.3969/j.issn.1001-1935.2024.03.015

Abstract ( ) PDF (1436KB)( )

Compared with the blast furnace ironmaking process,HIsmelt and Corex smelting reduction ironmaking processes hardly use coke and have high resource utilization efficiency and outstanding environmental advantages.However,the FeO content of the slag in these two processes is generally high,and the technical maturity and in-depth understanding of the reaction mechanism in the furnace are still insufficient,resulting in a lower lifespan of the smelting reduction furnace than that of the blast furnace.The process characteristics of HIsmelt and Corex processes were analyzed.The research status of material selection,maintenance and performance optimization of the refractories for HIsmelt and Corex processes was summarized.The existing problems and improving directions of the refractories for smelting reduction ironmaking were pointed out.

Research progress on impurity removal and quality improvement of magnesite

Qi Xiao, Fu Liangliang, Bai Dingrong, Xu Guangwen

2024, (3): 257-262. doi：10.3969/j.issn.1001-1935.2024.03.016

Abstract ( ) PDF (1175KB)( )

The existance of impurities significantly affects the quality and application of magnesia products,so the impurity removal and quality improvement of magnesite is of vital significance.The recent research progress on the technology of the impurity removal and quality improvement of magnesite was reviewed,and the future development direction of the technology was prospected,expecting to provide assistance for increasing the resource utilization rate of magnesite.

Research progress on hydrogen metallurgy process and refractories for hydrogen-based shaft furnaces

Chen Tianren, Wang Zhanmin, Qin Hongbin, Liang Chengkai, Li Xuzhi

2024, (3): 263-269. doi：10.3969/j.issn.1001-1935.2024.03.017

Abstract ( ) PDF (998KB)( )

Under the background of advocating the dual-carbon goal of energy conservation and emission reduction,the hydrogen metallurgy related technology in the steel industry is constantly improving.With the development and promotion of smelting process for hydrogen reduction shaft furnaces,new requirements have been put forward for the performance of refractory materials and the related research has received widespread attention.Therefore,the research and development status of hydrogen metallurgy related principles and process technologies were summarized.The research progress on the service behavior of refractories under H₂ atmosphere and refractories for hydrogen-based shaft furnaces was introduced.The research trend and future development direction of refractories for hydrogen-based shaft furnaces were prospected.

Research progress on preparation of high thermal conductivity silicon nitride ceramics

Zhou Yudong, Li Shipeng, Wang Wenwu, Zhang Yifan, Zhao Chenxiao

2024, (3): 270-276. doi：10.3969/j.issn.1001-1935.2024.03.018

Abstract ( ) PDF (939KB)( )

Silicon nitride ceramics have attracted much attention due to their excellent thermal conductivities and are widely used in many fields such as electronics,energy,aerospace and chemical industries.The research progress on the preparation of high thermal conductivity silicon nitride ceramics was reviewed,focusing on the research achievement of raw powder materials,sintering aids,as well as shaping and sintering processes,in order to deeply understand the frontier progress in this field and reveal the future development trend.

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