Effect of Ti-Si-Fe alloy addition on structure and properties of Si₃N₄ bonded SiC refractories

Yao Luyan, Han Bingqiang, Zhang Jinhua, Ke Changming

2024, (4): 277-283. doi：10.3969/j.issn.1001-1935.2024.04.001

In order to improve the densification of Si₃N₄ bonded SiC refractories and reduce the nitriding temperature of Si powder,Si₃N₄-bonded SiC refractories were produced by reaction sintering at 1 350 ℃ for 5 h under an carbon embedded atmosphere,using SiC particles and fine powder,and Si power as the main raw materials,and introducing Ti-Si-Fe alloy extracted from high-titanium blast furnace slag to partially replace the Si powder.The effects of the Ti-Si-Fe alloy addition (0,1.8%,3.6%,5.4% and 7.2%,by mass) on the nitriding behavior of Si powder,as well as the mechanical properties and microstructure of the material were investigated,and the nitriding reaction sintering mechanism was also explored.The results show that:(1)with the increase of the Ti-Si-Fe alloy addition,the cold mechanical properties and the hot modulus of rupture of the refractories are obviously improved,and the refractoriness under load exceeds 1 700 ℃;the property enhancement is slowed down with Ti-Si-Fe alloys addition above 3.6%;(2)Ti-Si-Fe alloy promotes the complete nitridation of Si powder and the reaction sintering of the material at a lower temperature;the volume growth during the nitridation process of the Ti-Si-Fe alloys and Si powder can effectively fill pores,nitriding products improve the bonding state between aggregates and matrix,and that inside matrix,thereby increasing the densification and improving the mechanical properties of the material;(3)after the introduction of Ti-Si-Fe alloys,the liquid phase rich in Ti,Si,N,and Fe components is formed in the reaction system;besides the traditional VS and VLS mechanisms,the dissolution-precipitation mechanism plays a leading role in the formation of short columnar β-Si₃N₄ and granular TiN;the cross-linked α-Si₃N₄ whiskers,short columnar β-Si₃N₄ and granular TiN enhance the mechanical properties of the material.

Process and bonding performance of ZrO₂ thermal barrier coatings with vertical cracks by high energy plasma spraying

Liu Baoxia, Zhang Meng, Zhou Xuqiang, Niu Yunsong, Huang Di, Yang Qinqian, Bao Zebin, Zhu Shenglong

2024, (4): 284-289. doi：10.3969/j.issn.1001-1935.2024.04.002

Abstract ( ) PDF (2324KB)( )

In order to prolong the service life of ZrO₂ thermal barrier coatings,HS188 alloy was used as the substrate,and NiCrAlY powder (base layer,d₅₀=106 μm) and yttria stabilized zirconia (YSZ,d₅₀=50 μm) were employed as sprayed feeder to prepare NiCrAlY+YSZ thermal barrier coatings using high-energy plasma spraying equipment with a progressive exploration method.The microstructure of the coatings was controlled by adjusting the stand-off distance (85,95,105 and 115 mm) and air-cooling manner (rear air cooling,rear air cooling+gun cooling,front air cooling,and front air cooling+gun cooling).The bonding strength of the coatings was evaluated by the drawing method.The results indicate that under the conditions of long stand-off distance and low cooling rate,it is difficult for the coatings to form a vertical crack structure due to the low instantaneous heating temperature and insufficient quenching on the sample surface.However,when the instantaneous heating temperature reaches the critical value and the air cooling rate is excessive,un-melted spray particles exist.When the stand-off distance is 85 mm and the cooling method is front air cooling,a thermal barrier ceramic coating with vertical crack morphology was obtained on HS188 alloy.Simultaneously,it has a moderate density of vertical cracks,the highest bonding strength and the best toughness.

Influence of pore-forming agents on permeability coefficient of porous Si₃N₄ ceramics

Zhang Dian, Liang Qing-quan, Liu Xuan, Li Yanjun, Liu Yijun

2024, (4): 290-296. doi：10.3969/j.issn.1001-1935.2024.04.003

Abstract ( ) PDF (2665KB)( )

To improve their permeability,porous Si₃N₄ ceramics were prepared using Si powder as the raw material,Y₂O₃ and CaF₂ as sintering aids,and polymethyl methacrylate microspheres (5 and 20 μm) as pore-forming agents,gel-casting,binder-removing,and finally reaction sintering at 1 650 ℃ for 3 h in a nitrogen atmosphere.The effects of the particle sizes and additions (volume fractions of 0,15%,30%,45%,and 60%) of the pore-forming agents on the apparent porosity,pore size distribution,pore structure and permeability coefficient of the porous Si₃N₄ ceramics were studied.The results show that:(1)the samples with pore agents exhibit dual pore structures,which are composed of stacking-derived pores and spherical evolution pores,with bimodal pore size distribution;(2)with the same particle size,as the pore-forming agent addition increases,the apparent porosity and permeability coefficient of the samples increase,while the bulk density,bending strength,and fracture toughness decrease;(3)at the same addition,the samples with the smaller-sized agents (5 μm) have higher apparent porosity,permeability coefficient,and bending strength;using smaller-sized pore-forming agents can reduce the thickness of the pore walls and enlarge the pore sizes of the stacking-derived pores within the pore walls,thus enhancing the permeability of the pore walls;(4) the sample with 60% pore-forming agents of 5 μm has the best comprehensive performance,with the apparent porosity of 55.1%,permeability coefficient of 11.62×10^-14 m² and bending strength of 35.3 MPa.

Temperature resistance of alumina aerogels

Ren He, Tong Tianbai, Liu Mei, Wang Lina, Fan Zhaodong

2024, (4): 297-301. doi：10.3969/j.issn.1001-1935.2024.04.004

Abstract ( ) PDF (1981KB)( )

This work aims to investigate the high-temperature resistance and the thermal insulation of alumina aerogels at high temperatures.Alumina aerogels were prepared by the sol-gel method plus supercritical drying using aluminum isopropoxide as the precursor,ethanol as the solvent,and glacial acetic acid as the catalyst.The obtained alumina aerogels were then heat-treated at different temperatures (25,150,250,300,500,600,850,1 000 and 1 200 ℃) for 6 h.The effects of the heat treatment temperature on the phase composition,microstructure,pore structure and specific surface area of the alumina aerogels were studied by FT-IR,XRD,TGA,DSC,SEM,TEM and BET.The results show that:(1)with the increasing heat treatment temperature,the prepared alumina aerogels undergo phase transition;when the temperature is ≥600 ℃,the sample mass hardly changes;(2)when the temperature is 850 ℃,the prepared alumina aerogel still maintains a three-dimensional porous network skeleton structure,the average pore size is still less than 69 nm (the free path of air molecules),and there is no obvious macropore;(3)the specific surface area of the prepared alumina aerogel is 458 m²·g^-1 at room temperature,321 m²·g^-1 after heat treatment at 850 ℃,and 102 m²·g^-1 after heat treatment at 1 000 ℃.

Preparation of porous mullite ceramic-based aggregates from low-voltage electroceramic wastes and secondary aluminum dross

Zan Wenyu, Ma Beiyue, Chen Guangxin, Cao Changkun, Li Mengqiang

2024, (4): 302-306. doi：10.3969/j.issn.1001-1935.2024.04.005

Abstract ( ) PDF (1733KB)( )

This work aims at finding an effective and low-cost new process for the preparation of porous aggregates,while alleviating the pressure of industrial solid wastes.Porous mullite ceramic-based aggregates were developed through low-temperature sintering using low-voltage electroceramic wastes and secondary aluminum dross as the main raw materials,and activated carbon powder as the pore-forming agent.The influence of the secondary aluminum dross addition (5 mass% to 40 mass%) on the properties of the samples was studied.The results show that:(1)with the increasing addition of secondary aluminum dross,the bulk density of the samples gradually decreases,while the apparent porosity gradually increases,and finally both tend to be stable;the linear shrinkage ratio first slightly increases and then decreases,and the cold compressive strength gradually decreases;(2)the addition of secondary aluminum dross promotes the formation of mullite crystalline nuclei,reduces the viscosity of the alumina-silica liquid phase,making it easier for internal gases to diffuse through the liquid phase to the material surface,forming large pores;moreover,the increase in the linear growth rate of mullite crystals accompanied by volume expansion further inhibits the sintering shrinkage of the liquid phase;the decrease in the cold compressive strength of the samples is related to the decrease in the liquid phase viscosity;after cooling to room temperature,a coating of alumina-silica glass phases forms on the surface of the aggregates,reducing the number of micropores and increasing the number of macropores,leading to increased stress concentration around the pores;(3)when the secondary aluminum dross addition is 25 mass%,the comprehensive performance of the sample is optimal.

Effects of alumina particle size and zirconia powder extra-addition on sintering property of alumina granulated powder

Deng Jiang, Liu Xuexin, Li Wen, Zhang Ziyi, Yuan Wenjie

2024, (4): 307-313. doi：10.3969/j.issn.1001-1935.2024.04.006

Abstract ( ) PDF (1983KB)( )

This work aims at improving the sintering property of zirconia toughened alumina (ZTA) granulated powder.ZTA slurries were prepared through ball milling using alumina powder with different particle sizes (d₅₀:1.72 μm,3.48 μm and 13 nm) and yttria stabilized zirconia (YSZ) as the main starting materials,adding binders and dispersants.The effect of the YSZ extra-addition (0,5%,10%,15% and 20%,by mass) on the rheological property of the slurries was investigated.ZTA granulated powders were prepared using the spray drying method,and then the powders were pressed into shapes and fired at different temperatures (1 520,1 600,and 1 680 ℃).The linear shrinkage and relative density of the fired samples were determined.The results show that:(1)the ZTA slurries exhibit shear thinning behavior and possess a yield stress;the rheological properties of the slurries are well-described by the Herschel-Bulkley model,with a high correlation coefficient (>0.98);(2)the particle size of the prepared ZTA granulated powders is mainly within the range of 125 to 45 μm,demonstrating a wide distribution;(3)the optimal formulation is 99 mass% activated alumina powder (d₅₀=1.72 μm),1 mass% nano-alumina (d₅₀=13 nm),and 15 mass% YSZ (extra-adding);this formulation results in a Carr coefficient of 8.62%,a water content of 0.22%,and an angle of repose of 25.2°;after firing at 1 600 ℃ for 2 h,the sample exhibits a relative density of 94.8% and a linear shrinkage rate of 18.2%.

Influence of polyhydroxy saccharide binders on properties of Al₂O₃-SiC-C waterless taphole clay

Li Wenfeng, Shen Tianzi, Guo Huishi, Cao Jinjin, Kang Xiaoxu, Shi Kai, Kang Xiaoyang

2024, (4): 314-318. doi：10.3969/j.issn.1001-1935.2024.04.007

Abstract ( ) PDF (2302KB)( )

To reduce the pollution of taphole clay and develop environment-friendly taphole clay,Al₂O₃-SiC-C waterless taphole clay was prepared using brown corundum,SiC,coke,sericite,kyanite,clay,and Si₃N₄-Fe powder as the main raw materials,NS-FH as the composite sintering aid,and environmentally friendly polyhydroxy saccharides glucose and sucrose as the binders.The effect of the extra addition of glucose or sucrose solution (0,8%,9%,10%,11%,12% and 13%,by mass) on the properties of Al₂O₃-SiC-C waterless taphole clay was studied.The results show that the Al₂O₃-SiC-C waterless taphole clay with good comprehensive properties can be prepared using polyhydroxy saccharides glucose or sucrose as the binder;when the addition of sucrose solution is 12%,the performance of the waterless taphole clay is the best,the Marshall value is 1.14 MPa,and the sample fired at 1 350 ℃ in an atmosphere with carbon embedded has the linear shrinkage rate of 0.72%,bulk density of 2.41 g·cm^-3,apparent porosity of 24.4%,cold compressive strength of 40.1 MPa and hot modulus of rupture (embedded in carbon at 1 400 ℃ for 30 min) of 12.1 MPa.

Effects of Sm₂O₃ addition and heat treatment temperature on properties of CA₆-MA materials

An Jiarui, Zhang Rui, Fan Bingbing, Wang Gang, Du Penghui

2024, (4): 319-322. doi：10.3969/j.issn.1001-1935.2024.04.008

Abstract ( ) PDF (1927KB)( )

To improve their properties,calcium hexaluminate-magnesium aluminate spinel (CA₆-MA) composites were prepared using CaO,MgO,Al₂O₃,and Sm₂O₃ as raw materials through a high-temperature solid-phase sintering method.The effects of the Sm₂O₃ addition (0,2%,4%,and 6%,by mass,extra-adding) and heat treatment temperature (1 400,1 500,and 1 600 ℃) on the phase composition,apparent porosity,bulk density,cold modulus of rupture,and microstructure of the CA₆-MA composites were investigated.The results indicate that:(1)the synthesis reaction of CA₆ can be promoted by increasing the heat treatment temperature appropriately;when the heat treatment temperature is 1 600 ℃,only CA₆ and MA exist in the sample;(2)the introduction of Sm₂O₃ promotes the crystal development of MA,and CA₆ tends to become equiaxed,significantly improving the density of the sample;(3)the sample with 6% Sm₂O₃ exhibits the optimal comprehensive properties after firing at 1 600 ℃,with the bulk density of 3.26 g·cm^-3,the apparent porosity of 13.4%,and the cold modulus of rupture of 135 MPa.

Effect of graphite type on properties of Al₂O₃-MgO castables

Li Ying, Wang Di, Zhao Li, Yin Yicheng, Jia Quanli

2024, (4): 323-328. doi：10.3969/j.issn.1001-1935.2024.04.009

Abstract ( ) PDF (2073KB)( )

To develop high-performance carbon-containing castables,SiC-coated graphite was prepared using Si powder and flake graphite as raw materials by a molten salt isolation method firing at 1 350 ℃ for 3 h.Then,flake graphite and SiC-coated graphite were introduced into tabular corundum particles,white corundum powder,fused magnesia powder,alumina micropowder,Secar 71 cement,and silica micropowder to prepare Al₂O₃-MgO castable blank samples and Al₂O₃-MgO-C castable samples by carbon embedded heat treatment at 1 100 and 1 600 ℃.The effect of different graphite types on the properties of the castables was studied.The results show that:(1)compared with the Al₂O₃-MgO castable sample without graphite,the castable sample with flake graphite has significantly increased water demand for molding,significantly reduced cold modulus of rupture,significantly increased apparent porosity but improved thermal shock resistance and slag resistance;the castable sample with SiC-coated graphite has slightly increased water demand,decreased cold modulus of rupture,slightly increased apparent porosity,and improved hot strength,thermal shock resistance,and slag resistance;(2)with the increase of the heat treatment temperature,the cold strength and permanent linear change rate on heating of the samples increase significantly;(3)when 5 mass% SiC-coated graphite is added and the heat treatment temperature is 1 600 ℃,the comprehensive properties of the sample are the best: the cold modulus of rupture is 16.9 MPa,the apparent porosity is 16.0%;the hot modulus of rupture is 2.0 MPa;and the thermal shock resistance and corrosion resistance are good.

Fabrication of reaction-bonded silicon carbide via phenolic/epoxy resin gelcasting

Ling Xiaxia, Xiang Yubo, Zheng Han, Wu Jiguang

2024, (4): 329-333. doi：10.3969/j.issn.1001-1935.2024.04.010

Abstract ( ) PDF (1660KB)( )

This work aims to explore a low-cost and environmentally friendly shaping method to prepare reaction-bonded silicon carbide (RBSC) materials,SiC fine powder and micropowder,phenolic resin,and epoxy resin were used as the main raw materials,tetramethylammonium hydroxide as the dispersant to prepare SiC ceramic slurries with a solid loading of 55 mass% and phenolic resin mass fractions of 13.5%,18%,22.5%,and 27%,respectively.The green bodies prepared by gelcasting and cured were heat treated at 800 ℃ for 2 h,followed by heat treatment at 1 760 ℃ for 3 h in vacuum to form the RBSC materials.The curing mechanism of the green bodies and the effect of the phenolic resin addition on the microstructure,phase composition,and physical properties of the samples were studied.The results show that:(1)the curing mechanism of the green body is that the hydroxymethyl groups in the phenolic/epoxy resin undergo cross-linking via condensation reactions with ortho-para hydrogen atoms in the aromatic ring,forming a high-strength bonding network;(2)with the increasing phenolic resin addition,the residual carbon in the resin system reacts with molten silicon,the cold modulus of rupture of the fired sample first increases and then decreases;when the addition of phenolic resin is 18%,the cold modulus of rupture of the sample is the highest,reaching 79.9 MPa;the apparent porosity and bulk density of the sample are 1.1% and 2.88 g·cm^-3,respectively.

Preparation and alkali corrosion resistance of mullite-corundum-magnesium aluminate spinel multiphase materials

Gao Yunqin, Guo Kaige, Ma Aiqiong, Niu Xingrong, Yang Guang, Zhang Xudong

2024, (4): 334-340. doi：10.3969/j.issn.1001-1935.2024.04.011

Abstract ( ) PDF (3942KB)( )

To improve the alkali corrosion resistance of mullite-corundum saggars,mullite-corundum-magnesium aluminate spinel multiphase materials were prepared using coal gangue,industrial alumina,and industrial magnesia as raw materials via a two-step calcination method.Effects of the industrial magnesia addition (1%,2%,3%,4%,and 5%,by mass) on the phase composition,microstructure,and physical properties of the samples were studied.The corrosion resistance mechanism of the samples to sodium ion battery cathode materials was explored.The results show that:(1)MgO can promote the growth of mullite crystals and the sintering densification of the samples;due to the direct bonding of mullite crystals and the toughening of microcrystalline magnesium aluminate spinel particles,all samples have high cold compressive strength,≥248 MPa;(2)the MgAl₂O₄ spinel distributed in different forms in the samples can form physical barriers to prevent Na⁺ penetration,block its reaction with mullite and corundum,and improve the alkali corrosion resistance of the samples;(3)considering the physical properties and the alkali corrosion resistance of the samples,the optimum addition of the industrial magnesia is 4%.

Effects of furnace lining materials and heating rates on agglomeration property of foundry coke

Yan Pengfei, Sun Zhanlong, Zhao Baolong, Lyu Jinshun, Yang Wengang, Wang Gang, Ma Weikui

2024, (4): 341-343. doi：10.3969/j.issn.1001-1935.2024.04.012

Abstract ( ) PDF (1461KB)( )

Coal cakes with dimensions of 500 mm×350 mm×400 mm were prepared using pulverized coal,coke powder,and coal pitch as raw materials,adding 10 mass% of water,and stamp charging.When the furnace temperature was 650 ℃,the coal cakes were placed in single-side heating furnaces,and heated at different heating rates till forming coke,with final coking temperature of 1 050 ℃.The effects of lining materials (clay bricks and silica bricks) and heating rates (0.5,0.6,and 0.7 ℃·h^-1) on the heating rate of the coal cakes and the properties of the formed coke were studied.The results show that due to the better thermal conductivity of silica bricks compared to clay bricks,the coal cakes in the furnace using the silica brick lining have a shorter water vaporization time,and a higher heating rate in the first shrinkage peak stage between 200-600 ℃,which leads to higher internal stress in the coal cakes and a lower coke agglomeration rate.Therefore,when using silica bricks as the wall of coke oven carbonization chambers,the heating rate should be 0.5 ℃·h^-1,while for clay bricks as the wall,the heating rate should be 0.6 ℃·h^-1.

Corrosion mechanism of working lining of refining ladle wall with different molding methods

Li Fei, Zhou Hui, Yang Zhichao, Tang Zhongdui, Wang Zhengfang, Liu Wei

2024, (4): 344-348. doi：10.3969/j.issn.1001-1935.2024.04.013

Abstract ( ) PDF (1803KB)( )

In order to explore the difference of the service condition and corrosion mechanism between corundum-spinel preforms and mechanically pressed corundum-spinel bricks as the working lining of the ladle wall,the appearance,chemical composition,phase composition,physical properties and microstructure of the corundum-spinel preforms and mechanically pressed bricks after 200 heats were studied.The results show that the corrosion rate of the corundum-spinel preforms is slightly lower than that of mechanically pressed bricks,and the thickness of the corrosion layer is much smaller than that of mechanically pressed bricks.Because the bonding strength between the particles of the unburned mechanically pressed bricks is much lower than that of the cement-bonded preforms,the bonding between the particles inside the machine-pressed bricks is more likely to be destroyed by the molten slag.Therefore,the preforms have better resistance to slag penetration.

Corrosion of corundum mullite bricks by slag from rotary kilns

Li Kunpeng, Yan Shuangzhi, Zhang Tao, Shi Pengkun, Feng Zhiyuan, Fan Muxu, Wang Han, Liu Pengcheng

2024, (4): 349-353. doi：10.3969/j.issn.1001-1935.2024.04.014

Abstract ( ) PDF (3450KB)( )

The corundum-mullite bricks used in the combustion zone of a hazardous waste incineration rotary kiln were sampled,and the microstructure and composition of the sampled residual bricks were analyzed by XRD,SEM,and EDS.The corrosion mechanism of corundum mullite bricks under the corrosion of halogen-containing and high sodium salt content slag in hazardous waste incineration rotary kilns was investigated.The results demonstrate that the sodium salt,potassium salt,Br,Cl,and other elements in the slag possess strong corrosion and penetration abilities,generating low melting point and low density substances such as NaCl,KBr,and sodalite in the matrix,which decreases the hot performance of the brick in the combustion zone and accelerates the corrosion and wear of the brick.On the other hand,they cause irreversible volume expansion of the brick body,leading to spalling during the operation of the rotary kiln.

Application of energy dispersive X-ray fluorescence spectrometer in determination of magnesia composition

Xu Xiaoying, Cao Haijie, Wei Lichao, Ma Xufeng

2024, (4): 354-356. doi：10.3969/j.issn.1001-1935.2024.04.015

Abstract ( ) PDF (902KB)( )

Owning to the advantages of small size,low price,and fast analysis speed,energy dispersive X-ray fluorescence (EDXRF) spectrometers are widely used in the composition and morphology analyses of materials such as polymers,ceramics,concrete,and biomaterials.However,there are no relevant standards in the refractory material industry.To realize the rapid analysis of SiO₂,Al₂O₃,Fe₂O₃,TiO₂,CaO and MgO contents in magnesia by the EDXRF spectrometer,the instrument parameters and the sample preparation methods were optimized,and the precision and accuracy tests,as well as the comparison tests by EDXRF and wave length dispersive X-ray fluorescence (WDXRF) spectrometry were conducted.The results show that the contents of SiO₂,Al₂O₃,Fe₂O₃,TiO₂,CaO and MgO can be quickly tested by the EDXRF spectrometer through sampling with the fused cast-bead method,with a relative standard deviation of 0.09%-1.85%,showing satisfactory precision and accuracy.The detection difference by EDXRF and WDXRF meets the requirements of the allowable deviation in the current standard GB/T 21114—2019,so the data are reliable.

Development status of fused magnesia in southern Liaoning

You Jiegang, Zhao Xin, Qian Guohua, Zhang Xiao-fang, Zhang Guodong, Ma Beiyue

2024, (4): 357-361. doi：10.3969/j.issn.1001-1935.2024.04.016

Abstract ( ) PDF (1111KB)( )

Fused magnesia is a main irreplaceable raw material of magnesia-carbon bricks for the linings of steelmaking converters,steelmaking electric furnaces and refining ladle slag lines,which has a production capacity of 4 million tons in southern Liaoning.However,due to its downstream market,production raw materials,as well as production technology and equipment,problems for the fused magnesia production exist such as the imbalance of supply and demand,high energy consumption and large fluctuation of product quality.Therefore,the status and changes of fused magnesia in southern Liaoning in recent years were expounded.The future development trend of fused magnesia was pointed out.

Research progress of Ti₃SiC₂ matrix composites

Jia Huan, Feng Xu, Yuan Hudie

2024, (4): 362-368. doi：10.3969/j.issn.1001-1935.2024.04.017

Abstract ( ) PDF (1101KB)( )

As a new cermet material,Ti₃SiC₂ combines the properties of metals and ceramics,such as high thermal conductivity,high melting points,high yield strength,good thermal stability,high elastic modulus,and excellent thermal shock resistance.However,the pure Ti₃SiC₂ material has poor oxidation resistance at above 1 100 ℃,and its strength at high temperatures is reduced due to plastic deformation,which limits its application.At present,Ti₃SiC₂ matrix composites with excellent comprehensive properties are generally prepared by introducing reinforcements.The research status of Ti₃SiC₂ matrix composites in recent years was reviewed.The preparation methods,reinforcements and properties of several common Ti₃SiC₂ matrix composites were analyzed.The further development direction was put forward.

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