Influence of TiO₂ addition on phase composition and properties of porous SiC ceramics

Deng Chengji, He Feng, Liang Yiming, Li Ji, Gao Chao, Mu Meng

2024, (2): 93-98. doi：10.3969/j.issn.1001-1935.2024.02.001

To achieve high porosity and strength,porous SiC ceramics were fabricated by utilizing α-SiC powder,Si powder and TiO₂ powder as starting materials and firing at 1 400 ℃ for 3 h in an argon atmosphere.The influence of the TiO₂ addition (0,2%,4% and 8%,by mass) on the phase composition,micromorphology,pore size distribution and main physical properties of the materials was studied.The results show that as the TiO₂ addition increases,the diffraction peak of Si gradually diminishes,while Ti₃O₅ and TiSi₂ are detected in the materials.With the formation of these new phases,SiC particles are bonded more tightly,resulting in reduced apparent porosity and average pore size along with significantly improved mechanical properties.When the TiO₂ addition is 8%,exceptional comprehensive properties of the material are achieved in terms of the apparent porosity of 33.6%,cold modulus of rupture of 29.6 MPa and average pore size of 0.27 μm.

Effects of zirconia and lanthana co-doping on properties of porous cordierite ceramics

Zhang Hui, Chai Qian, Zhang Hong, Wang Yixing, Hao Chenxi, Wang Xingyu

2024, (2): 99-103. doi：10.3969/j.issn.1001-1935.2024.02.002

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To achieve the low temperature synthesis of cordierite,according to its theoretical ratio,porous cordierite ceramics were prepared using calcined kaolin (≤0.044 mm),sintered magnesia (≤0.074 mm) and silica micropowder (d₅₀=2.6 μm) as main raw materials,analytically pure zirconia and lanthana as sintering aids,and polyvinyl alcohol (PVA) solution as the binder,pressing to samples of 30 mm×30 mm at 60 MPa,drying and calcining.The effects of the extra additions of zirconia (0 and 8%,by mass) and lanthana (0,0.2%,0.4%,0.6% and 0.8%,by mass) and calcination temperatures (1 200,1 250 and 1 300 ℃) on the cold physical properties,phase composition and microstructure of the porous cordierite ceramics were studied.The results show that:(1)the sample fired at 1 300 ℃ and introduced with 8% zirconia and 0.6% lanthana shows good physical properties;(2)the co-doping of zirconia and lanthana can improve the mechanical properties of the sample while maintaining the apparent porosity,and promote the formation of cordierite;(3)the co-doping of zirconia and lanthana can reduce the synthesis temperature of cordierite and improve the comprehensive performance of the sample.

Preparation of soil polymers and their effects on properties of corundum castables

Yang Dekai, Wang Zhou-fu, Liu Hao, Ma Yan, Wang Xitang, Zhou Jing

2024, (2): 104-109. doi：10.3969/j.issn.1001-1935.2024.02.003

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In order to find safe and low-cost salt-activated materials to prepare soil polymers,light burned metakaolin was obtained after firing Guangxi kaolin at 850 ℃ for 4 h and added with different amounts of condensed aluminum phosphate,lithium phosphate and lithium silicate (3%,4% and 5% of the metakaolin mass,respectively) as the additives to prepare soil polymers.Subsequently,the mixtures of metakaolin with lithium silicate,lithium phosphate or condensed aluminum phosphate were added to the corundum castable system,respectively,and the performance of the castables was compared with that of calcium aluminate bonded corundum castables.The effects of the additives on the solidification time,phase composition and microstructure of the obtained soil polymers as well as the soil polymers on the properties of the castables were explored.The results show that:(1)the solidification time of the soil polymers increases from 2 h to 5 h with the increasing additive addition,and the preferred addition is 4%;(2)at 20 ℃,condensed aluminum phosphate reacts with metakaolin to form gelling SiP₂O₇,while lithium silicate and lithium phosphate react with metakaolin to form LiAlSiO₄,forming a layered structure or a gelling film attached to the surface of metakaolin,thus resulting in a gelation effect of soil polymers;(3)at 1 100 ℃,soil polymers gradually form mullite,and layered metakaolin becomes thinner and cross connected;at 1 600 ℃,the mullitization of soil polymers is complete,forming needle and rod structures that cross connect with each other,and a small amount of liquid is generated,densifying the sample;(4)replacing calcium aluminate cement with soil polymers in the same proportion as the binder,the castable has a certain gap in performance compared to the calcium aluminate cement bonded castable.

Effects of pre-synthesized magnesia-zirconia sand and calcination temperature on properties of magnesia-zirconia materials

Liu Zhongfei, Feng Yu, Liang Xiaocheng, Luo Xudong, Li Guangwei, Wu Feng

2024, (2): 110-115. doi：10.3969/j.issn.1001-1935.2024.02.004

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To improve the hot properties of magnesia-zirconia materials,magnesia-zirconia sand was pre-synthesized with Xiuyan second grade magnesite and desilicated zirconia,and then magnesia-zirconia materials were prepared using the pre-synthesized magnesia-zirconia sand and fused magnesia,mixing,molding,drying and calcining.The effects of the pre-synthesized magnesia-zirconia sand addition (10%,20% and 30%,by mass) and calcination temperature (1 500,1 600 and 1 700 ℃) on the bulk density,apparent porosity,linear shrinkage rate on heating,cold modulus of rupture,thermal shock resistance and slag resistance of the materials were investigated.The phase composition and microstructure were also analyzed.The results show as follows:(1)as the pre-synthesized magnesia-zirconia sand addition and calcination temperature increase,the bulk density and cold modulus of rupture increase,while the apparent porosity decreases;(2)the linear shrinkage rate decreases with the increasing pre-synthesized magnesia-zirconia sand addition and increases with the increasing calcination temperature;(3)when the pre-synthesized magnesia-zirconia sand addition is 20% and the calcination temperature is 1 600 ℃,the sample performs the best thermal shock resistance,which is improved due to microcrack toughening induced by the pre-synthesized magnesia-zirconia sand;(4)when the pre-synthesized magnesia-zirconia sand addition is 20% and the calcination temperature is 1 700 ℃,the sample shows the optimal slag resistance,which is mainly due to the fact that ZrO₂ reacts with the slag to generate CaZrO₃ and spinel,preventing the further corrosion and penetration of the steel slag.

Research on properties and thermal stability mechanism of aluminum-niobium slag

Gong Shuai, Zhao Hui-zhong, Yu Jun, Zhang Han, Tan Liqiang

2024, (2): 116-121. doi：10.3969/j.issn.1001-1935.2024.02.005

Abstract ( ) PDF (2524KB)( )

To develop and utilize aluminum-niobium slag,a kind of non-ferrous metallurgical waste residue produced in the preparation of metal niobium by the aluminothermic reduction method,the chemical composition,phase composition,microstructure and properties of aluminum-niobium slag were studied by ICP,XRD,SEM,TG-DTA and other characterization techniques.The results show that the oxidation of Nb and NbO leads to the poor volume thermal stability of aluminum-niobium slag.After heat treating the aluminum-niobium slag at different temperatures (400-1 500 ℃),it is found that high temperature pre-firing treatment can effectively solve the problem of poor volume thermal stability of the aluminum-niobium slag.After pre-firing at 1 400 ℃ or above,the aluminum-niobium slag has stable phase composition and volume change rate as well as the refractoriness >1 790 ℃,which meets the basic requirements of refractories for raw materials and lays a good foundation for its resource utilization.

Effect of sodium carboxymethyl cellulose addition on properties of MgAl₂O₄ porous insulation materials

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

2024, (2): 122-126. doi：10.3969/j.issn.1001-1935.2024.02.006

Abstract ( ) PDF (2779KB)( )

This work aims at improving the energy utilization efficiency of kilns.Magnesium aluminate spinel porous insulation materials were prepared as follows.Medium-grade magnesia fine powder and calcined alumina powder were mixed in a mass ratio of 35∶65,dried,and crushed into powders of d₅₀=2.3 μm.Then different amounts of sodium carboxymethyl cellulose (CMC) as a foam stabilizer and 0.6 mass% potassium oleate as a foaming agent were added to obtain the foaming slurry.Finally the slurry was injected into molds of 40 mm×40 mm×40 mm,demolded,dried at 110 ℃ for 24 h,and fired at 1 500 ℃ for 3 h.The effects of the CMC addition (0,0.1%,0.2%,0.3%,0.4%,and 0.5%,by mass,extra adding) on the properties of the slurry and the fired samples were studied.The results show that:(1)when the CMC addition is higher than 0.1%,the slurry has decreased expansion ratio,increased viscosity,and less and smaller bubbles;(2)when the CMC addition is 0.2%,the slurry has the maximum Zeta potential absolute value of 18.3 mV,which is the most stable;the sample has the most pores,which are spherical and closed;the apparent porosity,bulk density,and cold compressive strength of the sample are 73.5%,0.95 g·cm^-3,and 13.1 MPa.

Effects of particle gradation on microstructure and mechanical properties of recrystallized SiC honeycomb ceramics

Min Changsheng, Dong Bo, Yu Chao, Deng Chengji, Xing Guangchao, Ding Jun, Liu Hao, Zhu Hong-xi

2024, (2): 127-131. doi：10.3969/j.issn.1001-1935.2024.02.007

Abstract ( ) PDF (1955KB)( )

SiC honeycomb ceramics were prepared by recrystallization sintering using α-SiC powders of different particle sizes (0.5,25,38,and 45 μm) as raw materials.The effects of the particle gradation on the micro-morphology,pore size distribution,and leading physical properties of the recrystallized silicon carbide (R-SiC) were investigated.The results show that:(1)after sintering at 2 200 ℃ for 1 h,compared with the honeycomb ceramics with only 25 and 0.5 μm SiC,those with the gradual introduction of 38 and 45 μm SiC have similar sintered density,larger average sintered neck area between R-SiC coarse particles,higher median aperture size,more concentrated pore size distribution,and fist increased and then declined cold compressive strength;(2)the mechanical properties of R-SiC honeycomb ceramics are the optimal when the particle gradation is 25,0.5,and 38 μm,with the cold compressive strength,bulk density,and apparent porosity of 18.0 MPa,1.81 g·cm^-3,and 40.8%,respectively.

Preparation of silicon carbide based porous ceramics with network cell wall and their particulate matter capture

Liu Jingjing, Yue Weidong, Xiong Fei, Shan Yanfang

2024, (2): 132-136. doi：10.3969/j.issn.1001-1935.2024.02.008

Abstract ( ) PDF (1418KB)( )

In order to improve the filtration performance,silicon carbide porous ceramics with network cell wall were fabricated via the polyurethane foaming method using silicon carbide powder,alumina powder,polyether polyol,polymethylene polyphenyl polyisocyanate,dibutyltin dilaurate,triethylenediamine and silicone oil (foam stabilizer) as raw materials.The effects of the solid loadings of the slurry (45%,50%,55% and 60%,by mass) on the microstructure,physical properties and their filtration properties towards particulate matters were studied.The result shows that:(1)with the increasing solid loading,the bulk density and cold compressive strength gradually increase,and the apparent porosity decreases;(2)the micropores generated during the polyurethane foaming process are distributed on the ceramic pore wall to form a network cell wall structure,which increases the collision probability between particles and the wall pores and improves the filtration efficiency;meanwhile,the network cell wall structure also improves the pore interconnectivity and reduces the press drop;(3)when the solid loading is 55%,the silicon carbide based porous ceramics have the bulk density of 0.57 g·cm^-3,apparent porosity of 79.2%,cold compressive strength of 3.7 MPa,and the filtering efficiency of the particulate matter of 91.2%,achieving good regeneration performance.

Effects of SiC polymer precursor and Zn composite powders on properties of Al₂O₃-C unfired slide plate materials

Liang Baoqing, Zhang Zhifeng, Wang Quanxi, Shang Junli, Li Hongyu, Zhao Chenrui, Zhao Yue

2024, (2): 137-142. doi：10.3969/j.issn.1001-1935.2024.02.009

Abstract ( ) PDF (2517KB)( )

This work aims at improving the medium- and low-temperature strength of Al₂O₃-C unfired slide plate materials.Sucrose,nickel nitrate hexahydrate,ethyl orthosilicate and oxalic acid aqueous solution with the mass ratio of 1∶0.15∶2.7∶0.03 were added to ethanol aqueous solution in turn,and dried at 110 ℃ for 18 h,obtaining SiC polymer precursor.Then,tabular corundum,α-Al₂O₃ micropowder and flake graphite were used as the main raw materials,added with the SiC polymer precursor and Zn powder,pressed at 150 MPa into green bodies of 150 mm×25 mm×25 mm,cured at 180 ℃ for 24 h,and then heat treated at 600,800,1 000,1 200 and 1 400 ℃ for 3 h under carbon embedded conditions.The effects of the SiC polymer precursor and Zn powder on the properties of Al₂O₃-C materials were studied.The results show that the Al₂O₃-C material has the optimal comprehensive performance when adding 4.5% SiC polymer precursor and 1.5% Zn powder;at low temperatures,Zn powder melts and forms metal bonding phases in the material system;at medium temperatures,the pyrolysis reaction of the SiC polymer precursor and the catalysis of Zn powder after evaporation make the system form SiC fiber bonding phases.They work together to give Al₂O₃-C unfired slide plate material high medium- and low-temperature strength,which overcomes the failure problem caused by the low strength in application.

Thermodynamic calculation and slag resistance analysis of Al₂O₃-SiC-C taphole clay during corrosion

Ju Maoqi, Xiao Yangwu, Xia Changyong, Liang Yonghe, Cong Peiyuan, Wei Jianxiu, Cai Wei, Chen Jinfeng

2024, (2): 143-147. doi：10.3969/j.issn.1001-1935.2024.02.010

Abstract ( ) PDF (2153KB)( )

Insufficient corrosion resistance of taphole clay leads to problems such as short tapping time or splashing during service,but the invisible service environment of taphole clay makes it difficult to analyze the corrosion process.Therefore,in response to this issue,the corrosion process of slag on Al₂O₃-SiC-C taphole clay at 1 450 ℃ was calculated using FactSage thermodynamic software,and the dynamic slag resistance test was used to analyze the corrosion of slag after different durations (0,8,16,24,and 32 min).The results show that in the process of slag corrosion,anorthite first forms,and then Al₂O₃ precipitates from the Al₂O₃ saturated liquid phase to generate an Al₂O₃ isolation layer;gehlenite forms at the interface between the taphole clay and the slag during the further corrosion,and the final corrosion products completely melt into the liquid phase.The results of the corrosion test are consistent with the thermodynamic calculation.The liquid phase and low-melting point-phases generated during corrosion reduce the critical strength of the taphole clay,leading to accelerated corrosion.When the corrosion time is 32 min,the sample is completely corroded.

Damage mechanism of magnesia-chrome refractories for side-blown copper smelting furnace

Fu Qiqi, Zhong Lihua, Bai Wenxian, Gan Yongtong, Deng Junjie

2024, (2): 148-154. doi：10.3969/j.issn.1001-1935.2024.02.011

Abstract ( ) PDF (4238KB)( )

In order to ensure the safe and stable operation of the side-blown furnace adopting new process,the corrosion damage mechanism of the magnesia-chrome brick of the side wall at the slag line in a side-blown copper smelting furnace was researched using a scanning electron microscope and an energy dispersive spectrometer.The results show that:(1)the magnesia-chrome bricks located at the slag line undergo alternating corrosion and infiltration of copper matte and slag,which is hardly to form a stable slag layer,resulting in a continuous cycle of infiltration-corrosion-spalling of magnesia-chrome bricks and the severest corrosion;the corrosion of the magnesia-chrome bricks above the slag line is slight,because the infiltration of copper matte in the bricks is obviously weaken,and a stable spinel and olivine dense layer is formed on the hot surface of the bricks,serving as a barrier against further penetration and corrosion of slag and copper matte to a certain extent;(2)although copper matte only penetrates along the pores and grain boundaries in magnesia-chrome bricks without participating in the corrosion reaction,it penetrates and wraps the matrix particles or grains,disrupting the direct bonding of magnesia-chrome bricks,destroying the stable structure of the original magnesia-chrome bricks and consequently reducing their resistance to slag and copper matte;(3)the copper matte primarily penetrates along the chromite particles,and gaps between periclase crystals after the precipitation of iron-rich spinel,which is disadvantageous for the resistance of magnesia-chrome bricks to the penetration and corrosion of SiO₂-FeO slag.

Light-weight mullite insulation materials prepared using low-grade kyanite for lithium battery kilns

Sun Huayun

2024, (2): 155-160. doi：10.3969/j.issn.1001-1935.2024.02.012

Abstract ( ) PDF (2670KB)( )

In order to realize the comprehensive utilization of low-grade kyanite,light-weight mullite insulation materials were prepared by burnout method with low-grade kyanite,α-Al₂O₃ micropowder and clay as main raw materials,machine-pressing under 10 MPa,and hot treating at 1 450 or 1 500 ℃ for 3 h.Effects of the clay addition (5%,10%,15% and 20%,by mass) and hot treatment temperature on the bulk density,apparent porosity,cold crushing strength,thermal conductivity of samples,as well as the corrosion resistance to lithium battery cathode materials and microstructure were studied.The results show that the introduction of clay promotes the densification and mullitization reaction of the samples,and enhances the bulk density,thermal conductivity,and strength of the samples;the samples with 20% clay hot treated at 1 450 ℃ perform the best physical properties:bulk density 0.88 g·cm^-3,cold crushing strength 21.0 MPa,thermal conductivity 0.25 W·(m·K)^-1.The samples with 10% clay hot treated at 1 450 ℃ have good corrosion resistance to lithium battery cathode materials.

Effect of surfactant on microstructure of magnesia foam slurry and porous aggregates

Sun Gege, Li Guohua, Jiao Changfa, Tian Lin

2024, (2): 161-166. doi：10.3969/j.issn.1001-1935.2024.02.013

Abstract ( ) PDF (3095KB)( )

Magnesia foam slurry and porous magnesia aggregate were prepared by direct foaming with light-burned magnesia powder as the raw material and sodium dodecyl benzene sulfonate (SDBS) as the surfactant.Effects of surfactant SDBS on the microstructure of aqueous foam,magnesia foam slurry,and porous magnesia aggregate were studied.The results show that:(1)in aqueous foam,with the increase of the SDBS addition,the liquid films of aqueous foam thicken,the shape of foam changes from polygon to circle,and the foam stability increases;(2)the bubbles in the magnesia foam slurry are spherical,and magnesia coats around the bubbles to hinder the liquid film drainage and gas diffusion;(3)from magnesia foam slurry to porous aggregates,the number of aggregate pores decreases and the size increases,forming closed circular pores;when the SDBS addition exceeds 3 mass%,the pore shapes are incomplete;(4)the porous magnesia aggregate with the SDBS addition of 1%-4% (by mass) sintered at 1 600 ℃ has an average pore size of 40.83-92.90 μm and a porosity of 51.6%-73.9%.

Research progress of SiO₂,Al₂O₃,and MgO micropowder binders for refractory castables

Wang Yongxin, Gao Yabo, Fang Yaohua, Li Yage, Huang Zhong, Zhang Haijun

2024, (2): 167-173. doi：10.3969/j.issn.1001-1935.2024.02.014

Abstract ( ) PDF (939KB)( )

Binders are an important part of refractory castables,which not only provide early working performance and mechanical strength for refractory castables,but also affect their high-temperature performance.Hence,the research progress and problems of SiO₂,Al₂O₃ and MgO micropowder binders for refractory castables in recent years were summarized in order to promote the future research and application.

Research progress on preparation of mullite materials from industrial solid wastes

Sun Jiaqu, Liu Xin, Wu Feng, He Huiling, Luo Xudong

2024, (2): 174-178. doi：10.3969/j.issn.1001-1935.2024.02.015

Abstract ( ) PDF (908KB)( )

To solve the environmental pollution problem caused by the accumulation of bulk industrial solid wastes,the current research state on the preparation of mullite materials from industrial solid wastes was summarized.The preparation of mullite materials from alumina-rich and silica-rich industrial solid wastes was analyzed and summarized.The main problems encountered were pointed out,and the future development direction was looked forward.

Research progress of ambient pressure drying preparation technology of SiO₂-Al₂O₃ composite aerogel

Wang Zhizheng, Guo Yuxiang, Yang Xiaodong, Sun Peisong

2024, (2): 179-184. doi：10.3969/j.issn.1001-1935.2024.02.016

Abstract ( ) PDF (988KB)( )

SiO₂-Al₂O₃ composite aerogel (SAA) has shown a wide range of application in aerospace,chemical metallurgy,furnace insulation and other fields due to the characteristics of low bulk density,high specific surface area,low thermal conductivity and high temperature resistance.Ambient pressure drying has the advantages of low preparation cost,easy industrial mass production and so on,so it has a good practical application prospect.In this work,the preparation methods of SAA were introduced,with emphasis on the research status of precursors,surface modifiers and fiber reinforcements in the preparation of SAA by ambient pressure drying.Finally,the development direction of SAA prepared by ambient pressure drying was prospected.

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