Effect of SiC nanowires on performance of atmosphere plasma sprayed Si coatings

Wang Bo, Zhuang Xinpeng, Li Gui, Wang Yulong, Li Yuanqi, Shi Wei, Li Jiayan

2024, (5): 369-375. doi：10.3969/j.issn.1001-1935.2024.05.001

This work aims at improving the toughness of Si coatings in C/SiC composite surface and the bonding strength between them.C/SiC composites with the sizes of 10 mm×10 mm×10 mm were used as the matrix and a 20 μm SiC nanowire (SiCnws) porous layer was in-situ generated on the matrix surface;then,Si coatings with different thicknesses (30,60,and 90 μm) were sprayed on the matrix with or without the SiC nanowire porous layer by the atmosphere plasma sprayed method.The effect of the SiCnws on the bonding strength and oxidation resistance of the coated samples were investigated.The phase and morphology of the SiCnws and SiCnws/Si coatings were characterized by XRD,SEM,TEM and EDS.The results show that (1) the obtained SiCnws have flat shapes,smooth surface,random orientation,with diameters of 100-200 nm,which are β-SiC with a preferential growing direction along [111];(2)the bonding strength of the SiCnws/Si with the matrix is higher than that of the Si coating with the matrix,so the introduction of SiCnws increases the bonding strength;(3)the mass loss of the SiCnws/Si coatings is 20.7%-37.2% lower than that of the Si coatings after suffering 12 cycles of thermal shocks between the room temperature and 1 400 ℃,indicating that SiCnws release the thermal stress,prevent the formation and growth of cracks,and enhance the oxidation resistance.

Effect of ρ-Al₂O₃-CAC composite sintering aid on properties of porous SiC ceramics

Pan Jinwen, Jiang Hongyi

2024, (5): 376-380. doi：10.3969/j.issn.1001-1935.2024.05.002

Abstract ( ) PDF (1671KB)( )

In order to improve the performance of porous SiC ceramics,green silicon carbide was used as the main raw material,graphite as the pore forming agent,and ρ-Al₂O₃-CAC as a composite sintering aid which is prepared from calcium aluminate cement (CAC) and hydrated alumina (ρ-Al₂O₃),firing at 1 450 ℃ for 3 h.The effect of the ρ-Al₂O₃-CAC addition (2.5%-20%,by mass) on the phase composition,microstructure,and properties of porous SiC ceramics was studied.The results reveal several key findings:ρ-Al₂O₃-CAC facilitates the oxidation of silicon carbide and reacts in situ with SiO₂ produced by the oxidation of silicon carbide,forming a glass-mullite composite;bubbles are introduced into the composite phase,with their size increasing with the rising ρ-Al₂O₃-CAC addition;at an ρ-Al₂O₃-CAC addition of 12.5%,the prepared porous SiC ceramics exhibit the optimal comprehensive properties:the apparent porosity is 39.1%;the flexural strength is 39.3 MPa;the air permeability reaches 26.74 m³·h^-1·kPa^-1·m^-2,and the thermal shock resistance is the best.

In-situ preparation and properties of ZrB₂ ceramics by boron/carbothermal reduction combined with hot pressing sintering

Liu Miaowei, Jia Quanli, Peng Xigao, Zhang Xiaohui, Zhang Ziying, Wang Haimei, Wang Jia

2024, (5): 381-386. doi：10.3969/j.issn.1001-1935.2024.05.003

Abstract ( ) PDF (2009KB)( )

To reduce the cost and improve the performance,ZrB₂ ceramics were prepared using ZrO₂,B₄C,and carbon black as the raw materials,with n(ZrO₂)∶n(B₄C)∶n(C) ratios of 2∶1∶3,2∶1.1∶3,2∶1.2∶3,2∶1.3∶3,by the boron/carbothermal reduction combined with hot pressing sintering.The probabilities and initial reaction temperatures of various reactions in the ZrO₂-B₄C-C system in different CO partial pressures (10⁵,10²,1,10^-2 Pa) were calculated using reaction thermodynamics.The effects of the n(ZrO₂)∶n(B₄C)∶n(C) ratios and the heat treatment temperatures (1 800,1 850,1 900,and 1 950 ℃) on the properties,phase composition,and microstructure of the specimens were investigated.The results indicate that:(1)low CO partial pressure significantly reduces the initial temperature of each reaction in the ZrO₂-B₄C-C system;(2)as the B₄C addition increases,the content of ZrB₂ increases;when n(ZrO₂)∶n(B₄C)∶n(C)=2∶1.2∶3,the oxygen content in the synthesized ZrB₂ powder (in the form of B₂O₃ and ZrO₂) is only 0.333 mass%;(3)with increasing heat treatment temperature,the specimen density and hardness gradually increase,while flexural strength and fracture toughness initially increase and then decrease;when the heat treatment temperature is 1 900 ℃,the specimen exhibits the best comprehensive performance,with the relative density,fracture toughness,flexural strength,and cold hardness of 91.75%,4.87 MPa·m^1/2,525 MPa,and 18.6 GPa,respectively

Effect of magnesite tailings powder on properties of MgO-SiO₂ castables

Zhang Xiaocun, Nie Jianhua, Liang Yonghe, Gao Dongsheng, Yan Wen, Yin Yucheng

2024, (5): 387-392. doi：10.3969/j.issn.1001-1935.2024.05.004

Abstract ( ) PDF (2791KB)( )

In order to improve the sintering performance of MgO-SiO₂ castables,shorten the sintering time and reduce the production cost,MgO-SiO₂ castables were prepared using fused magnesia,silica micropowder,tabular corundum powder,silicon carbide powder,and magnesite tailings powder as the main raw materials.The effects of the magnesite tailings powder addition (0,2%,4%,6% and 8%,by mass,respectively) on the fluidity,microstructure and mechanical properties of the castables were studied.The results show that:1)the in-situ reaction between highly active MgO generated by the decomposition of magnesite tailings powder and silica micropowder promotes the formation of forsterite neck connection,and the in-situ reaction between magnesia and corundum powder in raw materials promotes the formation of spinel neck connection;2)impurities such as CaO and SiO₂ in magnesite tailings react with MgO at high temperatures to form a low melting point calcium magnesium olivine phase,which exists as a liquid phase at 1 500 ℃,promoting the sintering of the sample;3)when 4% magnesite tailings powder is added,the comprehensive performance of the castable is the best.

Effect of hydroxylated TiO₂ on properties of lightweight magnesia aggregates for cement kilns

Sun Gege, Li Guohua, Jiao Changfa, Tian Lin, Deng Shudan

2024, (5): 393-399. doi：10.3969/j.issn.1001-1935.2024.05.005

Abstract ( ) PDF (4576KB)( )

In order to address the challenges of high load and high thermal conductivity of refractory materials in the firing zone of cement rotary kilns,suitable lightweight aggregates for cement kilns were developed.Foaming slurries were first prepared employing light-burned magnesia powder as the raw material,sodium dodecyl benzene sulfonate (SDBS) as the foaming agent,triethanolamine (TEA) as the dispersant,and TiO₂ as the sintering aid.Then MgO foam slurries were prepared,and lightweight magnesia aggregates were successfully synthesized after firing the MgO foam slurries at 1 600 ℃ for 2 h.The effects of the TiO₂ addition (0,0.5%,1.0%,1.5%,2.0%,and 2.5%,by mass)on the properties and microstructure of magnesia foam slurries and lightweight magnesia aggregates were investigated.The results show that (1)TiO₂ surface hydroxylates;as the TiO₂ addition increases,the viscosity of the foam slurries increases,while the surface tension and contact angle decrease;the average size of the bubbles in the slurries ranges from 114.30 to 53.76 μm;(2)TiO₂ reacts with CaO in the light-burned magnesia powder,forming CaTiO₃;as the TiO₂ addition increases,the average grain size of magnesia increases,the amount of intergranular pores decreases,the bulk density of the lightweight aggregates increases,and the apparent porosity decreases;(3)the optimum physical properties were achieved when the TiO₂ addition was 1.0%.

Effects of Y₂O₃-MgO extra addition on properties of silicon nitride by Isobam gel tape-casting

Fu Jie, Liu Yuan, Zhao Zhenwei, Kong Yuan, Yang Lujun, Wang Anxiu, Ma Chengliang

2024, (5): 400-404. doi：10.3969/j.issn.1001-1935.2024.05.006

Abstract ( ) PDF (1575KB)( )

To address the problem of dense sintering difficulty of covalent bonded silicon nitride materials,Si tape-casting slices were prepared by gel tape-casting using the Isobam (Isobutylene-anhydride maleic) gel system and Si powder as raw materials,extra adding different amounts of sintering aid Y₂O₃-MgO (Y₂O₃ to MgO mole ratio of 4∶3,4%,6%,8% and 10%,by mass).Then they were treated by the two-step firing method,firing at 1 400 ℃ for 2 h and 1 750 ℃ for 2 h in the nitrogen atmosphere to prepare Si₃N₄ ceramic substrate specimens.The effect of the Y₂O₃-MgO addition on the properties of the Si₃N₄ ceramic substrates was investigated.The results show that adding Y₂O₃-MgO can promote the phase transition from α-Si₃N₄ to β-Si₃N₄ in the sintered specimens.With the increasing Y₂O₃-MgO addition from 4% to 8%,more liquid phases are generated during sintering,which promotes the liquid phase mass transfer and leads to the increased number and growth of long columnar β-Si₃N₄ grains,and the densification,hardness,fracture toughness,flexural strength,and thermal conductivity of the specimens increase.However,when the Y₂O₃-MgO addition is 10%,due to the abnormal growth of β-Si₃N₄ grains,all the properties of the specimens decrease.The silicon nitride specimen with 8% Y₂O₃-MgO performs the best comprehensive performance.

Preparation of submicron TiB₂ powder using sucrose as carbon source

Wang Xingguo, Chen Bin, Li Xin, Chang Shilun, Xu Chen, Yang Jianhong

2024, (5): 405-409. doi：10.3969/j.issn.1001-1935.2024.05.007

Abstract ( ) PDF (1546KB)( )

To explore the influence of the organic carbon source on the refining of TiB₂ powder,TiB₂ powder was prepared by borothermal/carbothermal reduction using TiO₂,B₄C and sucrose as raw materials,insulating at 1 150,1 250,1 350 and 1 450 ℃ for 30 min,respectively.The reaction mechanism of the TiO₂-B₄C-sucrose system,as well as the refining mechanism of TiB₂ grains was initially explored.The results show that Ti₂O₃ and TiC are two important intermediate products during the borothermal/carbothermal reduction process,which are both generated by the direct reaction of TiO₂ and C.Subsequently,TiB₂ may be generated with Ti₂O₃ or TiC as the titanium source reacting with B₂O₃ and C.In addition,the highly activated nanocarbon from sucrose pyrolysis has a pore structure,which can improve the reaction efficiency and successfully enable the preparation of submicron TiB₂ powder with an average particle size of 0.35 μm under the condition of insulating at 1 450 ℃ for 30 min.

Effects of rare earth oxides on low temperature solid phase synthesis of MgAl₂O₄ fibers

Guo Jiangpeng, Deng Changyu, Wang Xinyue, Chen Xinyu, Duan Hongjuan, Zhang Haijun

2024, (5): 410-413. doi：10.3969/j.issn.1001-1935.2024.05.008

Abstract ( ) PDF (3048KB)( )

To investigate the effects of rare earth oxides and heat treatment temperatures on their synthesis,MgAl₂O₄ fibers were prepared using basic magnesium sulfate whiskers and alumina sol as raw materials,and Y₂O₃,La₂O₃ and Nd₂O₃ as additives,heat treating at different temperatures.The effects of additive types (Y₂O₃,La₂O₃ and Nd₂O₃),additive additions (0,1%,2% and 3%,by mass) and heat treatment temperatures (800,1 000 and 1 200 ℃ for 3 h) on the low temperature solid phase synthesis of MgAl₂O₄ fibers were studied.The results show that:(1)with basic magnesium sulfate whiskers and alumina sol as raw materials and heat treatment temperature of 800 ℃,adding 3% Nd₂O₃ or Y₂O₃ can significantly promote the synthesis of MgAl₂O₄ fibers;(2)when the heat treatment temperature is 1 000 ℃,adding 3% Nd₂O₃ has the best effect on the synthesis of MgAl₂O₄ fibers.

Effect of calcium source particle size on properties of low thermal conductivity anorthite ceramics

Yuan Hang, Zhan Huasheng, Luo Huaming, Wang Hanyu, Liu Jingyi, Qian Kun, Deng Tong, Hu Siming, Huang Zhaohui

2024, (5): 414-418. doi：10.3969/j.issn.1001-1935.2024.05.009

Abstract ( ) PDF (1886KB)( )

To prepare high-performance low thermal conductivity porous anorthite refractory materials,anorthite ceramics were prepared by the high temperature solid-phase reaction at 1 100,1 200,1 300,and 1 400 ℃ holding for 3 h,respectively,using quartz sand fine powder as the silicon source,Al(OH)₃ as the aluminum source,and limestone fine powder (1 110.3 nm of average particle size) and nano calcium carbonate of four particle sizes (653.1,564.4,362.2,and 313.5 nm of average particle size) as the calcium sources.The effects of the heat treatment temperature and calcium source on the properties of the anorthite ceramics were studied.The results indicate that different types of calcium sources (limestone and nano calcium carbonate) have little effect on the phase composition of the synthesized samples,but nano calcium carbonate can significantly reduce the formation temperature of anorthite.As the nano calcium carbonate average particle size decreases from 653.1 nm to 313.5 nm,the anorthite ceramics transform from granular to lamellar and plate columnar;the apparent porosity of the samples is around 18% and the bulk density is around 1.40 g·cm^-3,both of which are not significantly affected;the cold compressive strength of the samples increases from 15.3 MPa to 19.3 MPa,and the thermal conductivity decreases from 1.893 W·m^-1·K^-1 to 1.633 W·m^-1·K^-1.Nano calcium carbonate can reduce the thermal conductivity of anorthite ceramics,providing a technical approach for preparing low thermal conductivity ceramics.

Effect of reactive alumina addition on properties of activated magnesia bonded corundum-spinel castables

Gao Guangze, Zhang Hongrui, Li Jianwei, Chen Liugang

2024, (5): 419-423. doi：10.3969/j.issn.1001-1935.2024.05.010

Abstract ( ) PDF (2130KB)( )

To enhance their performance,reactive MgO-bonded corundum-spinel castables were prepared using tabular corundum,reactive alumina,reactive MgO and aluminum lactate as raw materials.The influence of the reactive alumina addition (0,8%,13% and 18%,by mass) on the microstructure,phase composition,physical properties,as well as the resistance to slag corrosion and penetration of the castables was investigated.The results reveal that:(1)the reactive alumina promotes the sintering of the reactive MgO-bonded corundum-spinel castables,enhancing the bonding between aggregates and matrix,thus densifying the microstructure;(2)with the increase of the reactive alumina addition,the volume stability of the samples increases,the apparent porosity decreases,the bulk density increases,and the cold modulus of rupture and cold crushing strength as well as the slag resistance are improved;(3)the reactive MgO-bonded corundum-spinel castable with 18% reactive alumina shows optimal comprehensive performance,with the bulk density of 3.05 g·cm^-3,apparent porosity of 18.5%,permanent linear change rate after heating of 0.31%,cold modulus of rupture of 13.5 MPa and cold compressive strength of 73.8 MPa,as well as the best slag resistance.However,considering particle size distribution and raw material costs,there is no need to further increase the reactive alumina addition.

Preparation of polysiloxazanes and their pyrolytic properties

Xu Hui, Du Yiang, Wang Fuwen, Li Wei, Xu Nana, Ou Yucheng, Wang Bing

2024, (5): 424-430. doi：10.3969/j.issn.1001-1935.2024.05.011

Abstract ( ) PDF (3079KB)( )

To possess the [SiN₃O] structure and low ceramization temperatures,polysiloxazane (PSOZ) precursors were prepared using triisocyanomethylsilicon [MeSi(NCO)₃] as the raw material by partial hydrolysis and ammonolysis reactions.The yield of disiloxane intermediate was increased by controlling the pH (4.7,5.4 and 5.9),material mole ratio (n(H₂O)∶n(MeSi(NCO)₃)=1∶3,1∶2 and 2∶3) and hydrolysis temperature (-10,-20,-30,-40 and -50 ℃) of MeSi(NCO)₃ hydrolysis reaction,thus increasing the ceramic yield of PSOZ precursors.The pyrolysis characteristics of PSOZ precursors were further studied.The results show that:(1)PSOZ precursors complete the inorganicization at 800 ℃; the silicomethyl [Si—CH₃] and isocyano [—NCO] in the sample are completely decomposed;after heat treatment at 1 400 ℃,ceramization begins,and Si₂N₂O microcrystals appear locally in the sample;after heat treatment at 1 600 ℃,highly crystalline Si₂N₂O ceramics are obtained;(2)under the conditions of pH of 4.7,n(H₂O)∶n(MeSi(NCO)₃) of 1∶2 and hydrolysis temperature of -40 ℃,the ceramic yield of the PSOZ precursor is the highest,57.1 mass%.

Corrosion mechanism of MgO-C bricks for AOD deferrization and nickel extraction process

Li Zhen, Qi Jiangtao, Tan Jianxing, Zheng Junguo, Li Yuangao

2024, (5): 431-435. doi：10.3969/j.issn.1001-1935.2024.05.012

Abstract ( ) PDF (1886KB)( )

To investigate the corrosion mechanism of MgO-C bricks for the argon-oxygen decarburization (AOD) deferrization and nickel extraction process,the used MgO-C bricks were sampled from the slag line of the AOD furnace,and their chemical composition,phase compositions and microstructure were researched.Additionally,the corrosion of deferrization slag to MgO-C bricks was simulated using FactSage thermodynamics software,and the effect on the purity of molten steel was compared with MgO-CaO bricks.The results show that,under the combined effects of smelting mechanical stress and the capillary force of refractories,the deferrization slag with high FeO content penetrates into the interface of the periclase phase.Due to the unlimited solid solubility between FeO and MgO,the bonding phase and part of the periclase phase at the phase interface dissolve into the deferrization slag,leading to the spalling of periclase in the refractories,the viscosity decrease of high-temperature liquid phases,and a reduction in the stress buffering capacity.Under the mechanical stress,the deferrization slag disturbs the refractories forming a mechanical spalling,the working surface of the used refractories is relatively flat and smooth,with a fractal dimension ranging from 1.1 to 1.2.During the dissolution of the high-temperature liquid phase into the deferrization slag,a significant amount of graphite phase in the MgO-C bricks is preserved in the strongly oxidizing environment,simultaneously reducing the impact of the MgO-C bricks on the molten nickel-iron.Compared to MgO-CaO bricks,the service life of the MgO-C brick lining is significantly improved,and the purity of the molten nickel-iron achieves the same effect.

Influence of mixing process on properties of green bodies for Al₂O₃-ZrO₂-C refractories

Cheng Hourui, Deng Chengji, Yin Xin, Wang Xuan, Ding Jun, Zhu Hongxi, Yu Chao

2024, (5): 436-439. doi：10.3969/j.issn.1001-1935.2024.05.013

Abstract ( ) PDF (2474KB)( )

Aiming at the regulation and optimization of microstructure and mechanical properties of Al₂O₃-ZrO₂-C refractories green bodies,Al₂O₃-ZrO₂-C refractory samples and their matrix samples were prepared by mechanical compression molding with the tabular corundum,zircon mullite and zircon corundum as aggregates,the α-Al₂O₃ micropowder,flake graphite and additives as fine powders,and the lignosulfonate as the binder.Influences of different fine powder mixing processes (0.5 h manual mixing,no mixing,2 h ball milling,and 5 h ball milling) on the bulk density,apparent porosity,cold compressive strength,and microstructure were investigated.The results indicate that the fine powder mixing process has minimal impact on the apparent porosity and bulk density,but it significantly affects the microstructure and cold compression strength.Ball milling ensures an even distribution of raw materials while reducing defects such as pores and cracks;it also enhances particle size uniformity and the specific surface area of matrix raw materials,which facilitates the adsorption and bonding with lignosulfonate solution,thereby obviously improving the strength.However,excessive ball milling may result in excessively fine particles or increased agglomeration,reducing the strength.When the fine powder is mixed by ball milling for 2 h,an optimal combination between the matrix components and the aggregates is achieved,resulting in the highest cold compressive strength.

Alkali vapor corrosion resistance of refractories for oxy-fuel combustion glass furnace

Deng Lina, Yi Shuai, Xue Fei, Pan Chuancai, Xu Qian, Jiang Chen, Bai Yaning

2024, (5): 440-444. doi：10.3969/j.issn.1001-1935.2024.05.014

Abstract ( ) PDF (3295KB)( )

Crucible method was used to compare the alkali vapor corrosion resistance of high-quality silicon brick,zero expansion silicon brick,fused cast zirconia corundum brick (AZS33) and α-β corundum brick for oxy-fuel combustion glass furnace insulated at 1 600 ℃ for 2 h.The microstructures of the samples after corrosion were analyzed.The results show that:(1)high-quality silica bricks and zero-expansion silica bricks have higher apparent porosity,under high temperature and vapor conditions,calcium silicate oxides and glass phases continuously precipitate and drip,continuously melting SiO₂ particles,resulting in poor resistance to vapor attack;(2)under the action of alkali vapor,fused cast zirconia corundum bricks produce more glass phases,which drip and form pores,however,the fused cast zirconia corundum bricks have low apparent porosity,the alkali vapor corrosion and penetration is slow,and the corrosion resistance to alkali vapor is excellent;(3)α-β corundum bricks have low glass phase content and low apparent porosity,after alkali vapor corrosion,the skeleton structure remains perfectly,which have stronger corrosion resistance to alkali vapor;(4)the alkali vapor resistance order of the four types of bricks is:α-β corundum brick>fused cast zirconia corundum brick>zero expansion silica brick>high-quality silica brick.

Resolving contamination issue in zirconia ceramic firing process based on TRIZ theory

Wang Jiangtao, Liu Guanghua, Zhao Shixian, Qiu Haifeng

2024, (5): 445-447. doi：10.3969/j.issn.1001-1935.2024.05.015

Abstract ( ) PDF (897KB)( )

The TRIZ theory was applied to analyze the causal chain of zirconia ceramic products contaminated by the atmosphere in the furnace,and the key problems were determined,and the optimal innovation scheme was generated under the guidance of TRIZ tools:when the furnace temperature is below 1 155 ℃,an oxygen enrichment pump is used to introduce oxygen-rich air into the furnace chamber;when the furnace temperature is above 1 155 ℃,the oxygen enrichment pump is turned off to reduce the oxygen content in the furnace chamber;a composite material is used to fabricate a sealed sagger,and the zirconia ceramic products are placed into the sagger in order to separate the MoO₃ contaminated atmosphere in the furnace chamber from the zirconia ceramic products.

Research progress on LCA and LCCA evaluation of refractories

Li Feng, Zhang Lifang, Wei Hengyong, Bu Jinglong, Zhang Guofan

2024, (5): 448-453. doi：10.3969/j.issn.1001-1935.2024.05.016

Abstract ( ) PDF (1038KB)( )

Life cycle assessment (LCA) and life cycle cost assessment (LCCA) are effective tools for refractory material enterprises to achieve “greening” development.This article summarizes the research progress of LCA and LCCA for refractory materials in China and overseas,analyzes the quantitative assessment results of environmental impact and environmental cost throughout the entire lifecycle of refractory products,identifies the main types and sources of environmental pollutants,and confirms the environmental characteristics and key links of refractory material production.The aim is to demonstrate the current research status in this field and reveal future research directions.

Clogging mechanism and optimization measures of submerged entry nozzle

Du Jinji, Chen Yu’e, Zuo Xiaotan, Zhao Li, Ren Bo, Wang Enhui, Hou Xinmei

2024, (5): 454-460. doi：10.3969/j.issn.1001-1935.2024.05.017

Abstract ( ) PDF (1878KB)( )

In the actual process of steel production,the submerged entry nozzle clogging seriously affects the stability of the flow field of the mould.This phenomenon not only affects the proceeding of the continuous casting process,but also may cause the nodules to flake off,thus reducing the quality of the casting billets.The research status of the clogging mechanism of the submerged entry nozzle is described.The measures to prevent the clogging of the submerged entry nozzle are summarized from four aspects:optimizing the structure and material of the nozzle,improving the cleanliness of the molten steel and applying the external electric field.The future direction of the anti-clogging of the submerged entry nozzle is prospected.

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