Effect of modified mullite-SiC recycled brick aggregates addition on properties of Al₂O₃-SiC-C castables

Lei Changkun, Qiao Jiaqi, Ding Donghai, Xiao Guoqing, Sang Chao, Wang Cangshuo

2026, (4): 277-281. doi：10.3969/j.issn.1001-1935.2026.04.001

Mullite-SiC brick recycled aggregates (MSRA) have high water absorption and apparent porosity,which limits their extensive application in refractory castables.In this work,Al₂O₃-SiC-C castables were fabricated using brown alumina,alumina sol modified MSRA,silicon carbide,white fused alumina,and reactive alumina as the primary raw materials.The influences of the alumina sol modified MSRA addition (0,14%,18%,22%,26%,and 30%,by mass) on the properties of the castables were investigated.The results indicate that alumina sol can generate an Al₂O₃ coating on the surface of MSRA,which fills the internal pores of recycled aggregates and reduces the water absorption.After heat treating at 1 450 ℃,the castable achieves the optimal comprehensive performance at an alumina sol modified MSRA addition of 18%:the corresponding bulk density,apparent porosity,cold modulus of rupture,cold compressive strength,and MOR retention ratio after thermal shock are 2.98 g·cm^-3,16.7%,17.4 MPa,73.3 MPa,and 36%,respectively.The alumina sol modified MSRA facilitates the in-situ formation of mullite at the aggregates-matrix interface,which can effectively deflect cracks,prolong crack propagation paths,and consequently improve the thermal shock resistance of the castables.

Influence of Ti(C,N) composite powder and silicon powder on properties of alumina carbon refractories for submerged entry nozzles

Pan Lei, Gao Zhi, Fu Weidong, Meng Hongtao, Wang Zuochuang, Ma Beiyue

2026, (4): 282-288. doi：10.3969/j.issn.1001-1935.2026.04.002

Abstract ( ) PDF (2004KB)( )

To develop Si-free antioxidants for the body of submerged entry nozzles (SENs),alumina-carbon (Al₂O₃-C) refractories were prepared using tabular corundum,flake graphite,α-Al₂O₃ powder,Ti(C,N) composite powder and silicon powder as raw materials,phenolic resin as the binder,and industrial alcohol as the solvent.The prepared samples were cured at 200 ℃ for 24 h,followed by heat treatment at 1 000 ℃ for 3 h under an argon atmosphere.The effects of the Ti(C,N) composite powder or Si powder addition (mass fractions of 0,0.5%,0.75%,1.0%,1.25% and 1.5%) on the mechanical properties,thermal shock resistance and oxidation resistance of the materials were investigated.The results show that with the increasing addition of Ti(C,N) composite powder or Si powder,the apparent porosity,bulk density and cold modulus of rupture of the heat-treated samples have no obvious change.Nevertheless,Ti(C,N) composite powder can significantly improve the cold crushing strength,with the maximum achieved at a Ti(C,N) addition of 0.75%.The hot modulus of rupture of the samples first increases and then decreases with the rising addition of either Si powder or Ti(C,N) composite powder.The MOR retention ratio of the samples increases gradually with the increasing Si addition,while a decreasing trend is observed with the increasing Ti(C,N) addition.The sample with 0.75% Ti(C,N) composite powder exhibits the optimal oxidation resistance.This is mainly because TiN and TiC possess lower Gibbs free energy of oxidation reaction,and their oxidation products TiO₂ and Al₂TiO₅ have superior volume expansion effects,which can pre-ferentially form a dense protective layer to block internal pores.In summary,the sample with 0.75% Ti(C,N) composite powder delivers excellent comprehensive performance,showing promising application potential to replace silicon-containing antioxidants.

Effect of high-silica dolomite on properties of MgO-CaO based dry mixes for tundishes

Zhang Heng, Chen Ding, Ju Maoqi, Gu Huazhi, Huang Ao, Fu Lyuping , Li Shenghao, Zhang Shaojun

2026, (4): 289-294. doi：10.3969/j.issn.1001-1935.2026.04.003

Abstract ( ) PDF (1987KB)( )

CaO-containing refractories have the functions of desulfurization and dephosphorization.The introduction of CaO into MgO-based tundish dry mixes is conducive to improving the cleanliness of molten steel.As a common calcium source,high-silica dolomite is difficult to apply in refractories due to its high SiO₂ contents.First,high-silica dolomite raw materials were lightly calcined at different temperatures (700,800,900,1000 and 1 100 ℃) for 3 h,respectively,followed by heavy calcination at 1 600 ℃ for 3 h to prepare high-silica dolomite clinker.Subsequently,MgO-CaO based dry ramming mixes for tundishes were fabricated using the high-silica dolomite clinker heavy calcined after light calcining at the optinal light calcining temperature (0,15%,30%,45% and 60%,by mass) and fused magnesia as raw materials.The effects of the light calcination temperature on the properties of high-silica dolomite clinker,as well as its influences on the phase composition and performances of MgO-CaO tundish dry ramming mixes were investigated.The results show that during the heavy calcination at 1 600 ℃ for 3 h after the light calcination of high-silica dolomite at 1 000 ℃ for 3 h,dicalcium silicate in the light-calcined products transforms into tricalcium silicate.The obtained high-silica dolomite clinker exhibits the optimal comprehensive properties with a bulk density of 3.22 g·cm^-3 and an apparent porosity of 7.4%.The results indicate that with the increasing clinker addition,the apparent porosity of the dry mixes increases,the mechanical properties decrease slightly,and the slag resistance first declines and then improves.When the addition of high-silica dolomite clinker is 30%,the MgO-CaO dry mixes retain favorable mechanical strength and slag resistance,which enables the engineering application of low-grade high-silica dolomite in tundishes.

Effect of La(OH)₃ on properties of MgO-bonded corundum castables

Tang Yaping, Bi Wenjian, Zhang Hong-rui, Yang Zhisen, Zeng Zhihao, Li Fen, Chen Liugang

2026, (4): 295-299. doi：10.3969/j.issn.1001-1935.2026.04.004

Abstract ( ) PDF (2055KB)( )

To address the poor thermal shock resistance of MgO-bonded corundum castables,MgO-bonded corundum castable samples were fabricated using tabular corundum and reactive alumina micropowder as raw materials,reactive MgO powder as the binder,and La(OH)₃ as the precursor.The prepared samples were cured at room temperature for 24 h,dried at 110 ℃ for 24 h,and finally heat-treated at 1 600 ℃ for 3 h.The effects of La(OH)₃ additions (mass fractions of 0,1.12%,2.24%,4.48%,and 8.96%) on the properties of the corundum castables were investigated.The results show that:(1)after drying at 110 ℃,the cold compressive strength of the castables first increases and then decreases with the rising La(OH)₃ addition,while the apparent porosity shows a continuous increasing trend;(2)after the heat treatment at 1 600 ℃,the cold compressive strength of the castables decreases gradually with the increasing La(OH)₃ addition,the permanent linear change on heating increases steadily,and the thermal shock resistance of the castables is enhanced first and then weakened;(3)the castables achieve the optimal comprehensive performance at the La(OH)₃ addition of 2.24%.Specifically,the MOR retention ratio reaches the maximum of 98.8% after the heat treatment at 1 600 ℃ for 3 h.This is attributed to the in-situ reaction between the introduced La(OH)₃ and Al₂O₃/MgO in the castables,which generates lamellar LaMgAl₁₁O₁₉.An appropriate amount of such lamellar phases can effectively deflect cracks induced by thermal shock and thereby improve the thermal shock resistance of the castables.

Effect of alumina ultra-fines with different particle sizes on medium- and low-temperature strength of alumina castables

Ye Qing, Shao Changbo, Li Dongmei, Li Guimei, Yan Lin, Li Hongchao, Li Lu, Chen Zhiqiang

2026, (4): 300-303. doi：10.3969/j.issn.1001-1935.2026.04.005

Abstract ( ) PDF (1496KB)( )

During baking and service,alumina castables generally suffer strength degradation after medium- and low-temperature heat treatment compared with their cohesive bonding strength at room temperature and sintering strength at high temperatures.To overcome this medium- and low-temperature strength defect,alumina castables were prepared using tabular corundum aggregates and fine powder,and alumina ultra-fines as main raw materials,and calcium aluminate cement as the binder.All specimens were dried at 110 ℃ for 24 h and subsequently heat-treated at different temperatures for 3 h:400,600,800,900,1 000,1 100 and 1 200 ℃.The cold modulus of rupture,cold compressive strength,phase composition and microstructure of castables containing Al₂O₃ micropowders with different average particle sizes (about 4,2,1 and 0.8 μm) were investigated.The results show that the strength of the specimens increases with the decreasing particle size of Al₂O₃ micropowder.In the temperature range of 110-1 200 ℃,the specimens with 0.8 μm Al₂O₃ micropowder exhibit the most stable cold modulus of rupture,which effectively avoids the medium- and low-temperature strength degradation of the castables.

Research progress on raw material optimization of low-carbon MgO-C refractories

Chen Xiaoyu, Xu Han, Yang Shoulei, Wang Shijie, Liu Xinhong

2026, (4): 304-310. doi：10.3969/j.issn.1001-1935.2026.04.006

Abstract ( ) PDF (911KB)( )

High carbon contents (12 mass%-20 mass%) in traditional magnesia-carbon (MgO-C) refractories lead to their easy oxidation,failing to meet the requirements of modern clean steel smelting and low-carbon environmental protection.Therefore,developing high-performance low-carbon and ultra-low-carbon MgO-C refractories has become a research hotspot in the industry.The current research achievements in raw material optimization of low-carbon MgO-C refractories were summarized,focusing on the optimization of magnesia aggregates,the introduction of nano-carbon sources,the composite and modification of binders,and the efficient utilization of antioxidants.The future research directions were prospected,aiming to provide references for promoting the further development of low-carbon MgO-C refractories.

Preparation and performance of mullite/yttrium silicate composite coatings

Min Zhiyu, Yuan Hongyue, Chen Mao, Chen Yongqiang, Fan Bingbing

2026, (4): 311-319. doi：10.3969/j.issn.1001-1935.2026.04.007

Abstract ( ) PDF (5774KB)( )

To enhance the high-temperature stability of silicon carbide ceramics,a spraying-sintering process was employed.Three slurries were prepared with mullite powder,yttrium silicate powder,and mullite/yttrium silicate mixed powder with a mass ratio of 4∶1,respectively.The slurries were then sprayed onto 10 cm × 10 cm × 5 cm silicon carbide substrates to form coatings of 100 μm in thickness and heat-treated at 1 400,1 500,and 1 600 ℃ for 3 h to obtain coated samples.The effects of the heat treatment temperatures on the microstructure and performance of the mullite coating,yttrium silicate coating,and mullite/yttrium silicate composite coating were investigated.The results indicate that:(1)the single-component mullite or yttrium silicate coating exhibits defects such as coarse grains,high porosity,and susceptibility to cracking;(2)in the mullite/yttrium silicate composite coating,mullite transforms from granular morphology into columnar crystals,forming a stable network structure that significantly enhances the coating density and strength;as the heat treatment temperature increases,a eutectic phase gradually forms between mullite and yttrium silicate,promoting the growth of mullite grains;the grain size increases significantly with the rising temperature,while intergranular porosity first decreases and then increases;(3)the mullite/yttrium silicate composite coating heat-treated at 1 500 ℃ demonstrates the optimal overall performance,which exhibits excellent thermal stability and adhesion in a high-temperature vacuum environment,effectively inhibits the reactions between silicon carbide and heat-resistant steel and shows outstanding thermal shock resistance.

Effect of zirconia sol on properties of zirconia porous ceramics

Wu Chu, Liang Xiong, Xue Yanpeng, Li Yawei

2026, (4): 320-327. doi：10.3969/j.issn.1001-1935.2026.04.008

Abstract ( ) PDF (3181KB)( )

The traditional organic foam impregnation process has been hindered by insufficient control over the rheological properties of zirconia slurry and difficulties in zirconia sintering,resulting in insufficient strength and poor thermal shock resistance of zirconia porous ceramics.The zirconia slurry was prepared with yttria-stabilized zirconia powder as the primary raw material,sodium carboxymethyl cellulose as the thickener,zirconia sol as the binder and deionized water as the dispersion medium.Zirconia porous ceramics were fabricated via the organic foam impregnation method by loading the slurry onto polyurethane sponge templates with dimensions of 50 mm×50 mm×25 mm,and heat treating at 1 300,1 400 and 1 500 ℃ for 2 h.The effects of zirconia sol extra-additions (0,5%,10%,and 20%,by mass) on the rheological properties of the zirconia slurry,as well as the zirconia sol extra-additions and the heat treatment temperatures on the microstructure,mechanical properties and thermal shock resistance of the zirconia porous ceramics were investigated.The results indicate that:(1)zirconia sol significantly improves the rheological properties of the zirconia slurry;the slurry with 20% zirconia sol exhibits the optimal rheological performance;(2)zirconia sol coats ZrO₂ particles,fills interparticle gaps,and promotes neck formation; while it also transforms into nano-ZrO₂ during sintering,thus enhancing the sintering of the ceramics;(3)after heat treating at 1 500 ℃,the ZrO₂ porous ceramic with 20% zirconia sol exhibits the optimal overall performance,achieving a strut density of 3.70 g·cm^-3,a room temperature compressive strength of 2.16 MPa,and a residual room temperature compressive strength of 1.87 MPa after thermal cycling.

Effect of heat treatment temperature on formation of SiAlON phases in SiC-MgAl₂O₄ composites

Zou Yu-ying, Sun Honggang, Si Yaochen, Wang Ziming, Li Hongxia

2026, (4): 328-332. doi：10.3969/j.issn.1001-1935.2026.04.009

Abstract ( ) PDF (1767KB)( )

To enhance their performance,SiC-MgAl₂O₄ composites were prepared using SiC particles as aggregates,MgAl₂O₄ fine powder,α-Al₂O₃ micropowder,Al powder and Si powder as the matrix,and phenolic resin as the binder,heat treating at 1 400,1 450,1 500,1 550 and 1 600 ℃ for 5 h in a nitrogen atmosphere.The growth process and crystal morphology of in-situ formed SiAlON reinforcing phases at different heat treatment temperatures,as well as their effects on the properties of the composites,were investigated.The results show that:(1)β-SiAlON is formed at 1 400-1 550 ℃; with the rising temperature,its content increases and its morphology becomes well-developed gradually,evolving into intact hexagonal columnar grains at 1 550 ℃;while β-SiAlON transforms into Mg-SiAlON gradually at 1 600 ℃;(2)the transformation from β-SiAlON to Mg-SiAlON is a phase transition process facilitated by Mg vapor originating from spinel decomposition and the high-temperature environment;(3)hexagonal columnar β-SiAlON effectively enhances the strength of the composites,whereas plate-like Mg-SiAlON contributes little to strength improvement,therefore,as the β-SiAlON content increases,the mechanical properties of the material gradually improve;however,after β-SiAlON transforms into Mg-SiAlON,the mechanical properties decrease;accordingly,the optimal heat treatment temperature is 1 550 ℃.

Synergistic preparation of foamed ceramics using lepidolite tailings and waste glass

Chang Yue, He Guichun, Jiang Yinmei, Fu Hang, Zhang Yujie, Jiang Zhangsong

2026, (4): 333-337. doi：10.3969/j.issn.1001-1935.2026.04.010

Abstract ( ) PDF (1661KB)( )

The environmental issues caused by the stockpiling of lepidolite tailings urgently need to be addressed.Foamed ceramics were prepared via high-temperature sintering using lepidolite tailings as the main raw material,waste glass as the auxiliary raw material,and silicon carbide as the foaming agent.The effects of the SiC additions (0.1%,0.3%,0.5%,0.7%,and 0.9%,by mass),waste glass additions (5%,10%,15%,20%,and 25%,by mass) and heat treatment temperatures (1 120,1 140,1 160,1 180,and 1 200 ℃) on the properties of the foamed ceramics were investigated.The results show that: when the SiC addition is 0.5%,the waste glass addition is 15%,and the heat treatment temperature is 1 160 ℃,the foamed ceramics exhibit the optimal overall performance,with a bulk density of 0.71 g·cm^-3,a water absorption of 0.50%,and a room temperature compressive strength of 9.26 MPa.

Preparation and performance of SiO₂ aerogel composite materials using composite silicon source

Wang Mengmeng, Liu Honghua, Li Zhanfeng, Wang Yanyan, Liu Ruixiang, Sun Chuanqin

2026, (4): 338-342. doi：10.3969/j.issn.1001-1935.2026.04.011

Abstract ( ) PDF (1981KB)( )

Traditional SiO₂ aerogel composite materials experience obvious structural collapse at relatively high temperatures,leading to a sharp decline in thermal insulation property.On the basis of sol hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) as silicon source,large-particle silica sol was introduced as the second silicon source to form composite silicon source.SiO₂ aerogel composite materials were fabricated by compositing with mullite fibers,and their microstructure,thermal resistance were analyzed.The results show that the aerogel composite prepared with TEOS as single silicon source suffers remarkable structural collapse after heat treatment at 1 000 ℃,while the composite silicon source derived aerogel composite can retain its original three-dimensional network structure.The thermal conductivity of the aerogel composite with composite silicon source is 0.030 W·(m·K)^-1 at room temperature and 0.055 W·(m·K)^-1 at 1 000 ℃.After quartz lamp test at 1 000 ℃ for 1 000 s,the maximum temperature of the cold surface is only 82.8 ℃,which possesses favorable thermal insulation performance.

Preparation of Al₂O₃ porous ceramics via direct foaming method and their performance

Yin Bo, Yang Biao, Fan Changlong

2026, (4): 343-346. doi：10.3969/j.issn.1001-1935.2026.04.012

Abstract ( ) PDF (1507KB)( )

Al₂O₃ particles possess strong hydrophilicity,which leads to problems including insufficient wet foam stability and poor mechanical properties when preparing pure Al₂O₃ porous ceramics by direct foaming method.Al₂O₃ porous ceramics were prepared through high-speed stirring and foaming using Al₂O₃ as the raw material,heptanoic acid as the foaming agent,and sepiolite fibers (SEPF) as the stabilizing agent,and heat treated at 1 450 ℃ for 2 h.The influence of varying SEPF additions (mass fractions of 0,0.2%,0.4%,0.6%,and 0.8%) on the properties of Al₂O₃ porous ceramics was investigated.The results indicate that as the SEPF addition increases,the cold modulus of rupture and cold compressive strength of the samples initially rise and then fall,while the corrosion depth first decreases and then increase.The sample shows the optimal comprehensive performance when the addition is 0.6%.An appropriate SEPF addition can enhance the stability of the foam slurry and create a multi-level pore structure; the orderly pore structure and dense pore walls can improve the mechanical properties and form a dense isolation layer at the corrosion interface,effectively delaying melt penetration and enhancing the corrosion resistance of the material.

Preparation of high-density sintered magnesia by two-step sintering method

Qin Jiachen, Zhou Chi, Wang Chunyan, Luan Jian, Wang Shushan

2026, (4): 347-350. doi：10.3969/j.issn.1001-1935.2026.04.013

Abstract ( ) PDF (1801KB)( )

In order to prepare high-density sintered magnesia,the concentrate powder of flotation magnesite was used as the raw material.The optimal light calcination condition of magnesia was determined via phase analysis,microstructure observation and citric acid activity test of flotation magnesite concentrate powder,and the two-step sintering procedure was confirmed by testing bulk density,apparent porosity and characterizing microstructure.The results show that the optimal light-burning system for flotation magnesite powder is holding at 800 ℃ for 3 h.From the perspectives of energy conservation and high density,the optimal two-step sintering condition is holding at 1 800 ℃ for 3 h,by which high-density sintered magnesia with a bulk density of 3.41 g·cm^-3 can be obtained.

Research progress of thermal barrier coatings with double bonding layer structure

Ni Wei, Zhao Shixian, Wang Wenwu, Li Hongyu, Li Lingfeng, Li Hongxia

2026, (4): 351-356. doi：10.3969/j.issn.1001-1935.2026.04.014

Abstract ( ) PDF (1073KB)( )

As one of the core technologies for raising the inlet temperature of gas turbine engines,thermal barrier coatings play an important role in improving equipment operational efficiency and extending service life.The bonding layer,which serves to relieve thermal stress and improve the oxidation and corrosion resistance of materials,directly affects the service performance of thermal barrier coatings.Conventional thermal barrier coatings with a single bonding layer have certain limitations in high-temperature service,thus many researchers have proposed the double bonding layer structure.In this work,the application fields and typical structures of thermal barrier coatings as well as the research progress of single and double bonding layers from the aspects of material system and preparation process were firstly introduced.Then,the effects of the optimized design of the double bonding layer structure on the performance of thermal barrier coatings were discussed from three perspectives:multi-layer gradient structure,thickness parameters and interface roughness.Finally,the existing problems in current researches and future research directions were proposed.

Research progress on preparation of silicon nitride-bonded silicon carbide materials by casting

Li Jiaxing, Li Yanjun, Yang Mingfang, Liu Donghua, Chen Jin, Ding Donghai, Xiao Guoqing

2026, (4): 357-362. doi：10.3969/j.issn.1001-1935.2026.04.015

Abstract ( ) PDF (954KB)( )

Silicon nitride-bonded silicon carbide composites have become a research hotspot for new-generation advanced materials due to their excellent comprehensive properties.Among various forming processes,casting has become one of the key manufacturing technologies,which enables the fabrication of workpieces with complex shapes and large-sized products.However,this process is prone to defects including voids formed by particle packing,bubbles entrapped during mechanical mixing,and gas evolution from hydration of silicon powder.These defects raise the apparent porosity and lower the bulk density and mechanical strength.Moreover,excessive gas yielded from hydration reactions may even lead to cracking of green bodies in the drying process.In this work, the research progress of casting technology applied to silicon nitride-bonded silicon carbide materials was reviewed,and the improvement strategies aimed at solving the aforementioned problems were focused on.

Research and application status of nondestructive testing technology for high-voltage electrical porcelain

Lei Taotao, Ding Donghai, Chong Xiaochuan, Xiao Guoqing, Yue Yonggang, Tian Xiaoyun, Dang Dawei, Li Zhihui

2026, (4): 363-368. doi：10.3969/j.issn.1001-1935.2026.04.016

Abstract ( ) PDF (892KB)( )

High-voltage electrical porcelain is a key component of power system equipment and plays an important role in electrical insulation.Its service reliability guarantees the safe and stable operation of the power grid.Internal cracks and other defects of electrical porcelain are the main cause of its unheralded damage.Accurate detection of such defects is crucial for ensuring safe power grid operation.Traditional detection methods are not only low in efficiency,but also may cause secondary damage to equipment,failing to meet the operating state detection requirements of modern power system equipment.With the advantages of non-destructiveness and high precision,nondestructive testing technology has become a research hotspot in the defect detection of high-voltage electrical porcelain.The basic principles of ultrasonic scanning,X-ray imaging,acoustic emission and other nondestructive testing technologies were systematically expounded,and their application status in high-voltage electrical porcelain defect detection was analyzed.In view of the problems of insufficient detection sensitivity and limited adaptability to complex working conditions existing in current technologies,in this work,the development directions such as multi-technology collaborative detection and terahertz radiation were further summarized and analyzed,so as to improve the intelligent level and engineering applicability of high-voltage electrical porcelain nondestructive testing,and provide technical support for extending the service life of high-voltage electrical porcelain.

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