Interfacial reactions of nitrogen-based refractories with lanthanum oxide and lanthanum aluminate

Ma Fei-xiang, Li Hongxia, Liu Guoqi, Gu Qiang

2025, (5): 369-374. doi：10.3969/j.issn.1001-1935.2025.05.001

To develop specific lining materials for rare earth steel nozzles,LaAlO₃ powder was first synthesized by high-temperature solid-phase synthesis at 1 400 ℃ for 3 h using La₂O₃ and Al₂O₃ powders as raw materials.Then BN,AlN,Si₃N₄ and TiN powders were pressed into Φ30 mm×7 mm substrate samples with PVA as the binder under 120 MPa.Equal amounts of La₂O₃ and LaAlO₃ powders were placed on their surfaces,reacting at 1 550 ℃ for 3 h in different atmospheres (reducing and argon conditions).The interfacial reactions of the four nitride (BN,Si₃N₄,AlN,and TiN) substrate samples with La₂O₃ and LaAlO₃ in different atmospheres were studied,respectively.The results show that in reducing and argon atmospheres,the intensity order of the reactions between the four nitrides and La₂O₃ is Si₃N₄>BN>AlN>TiN.In the reducing atmosphere,the reaction intensity order of the four nitrides with LaAlO₃ is Si₃N₄>AlN≈TiN>BN.However,in the argon atmosphere,the order is Si₃N₄>BN>AlN≈TiN.TiN has good structural stability in both reducing and argon atmospheres,and reacts slightly with La₂O₃ and LaAlO₃.It is a relatively good anti-clogging lining material for rare earth steel nozzles.

Interfacial decarburization reaction between ZrO₂-C material and molten steel under applied electric field

Wang Dongxue, Chen Kaiwang, Sun Shiyu, Yuan Lei, Li Hongxia

2025, (5): 375-380. doi：10.3969/j.issn.1001-1935.2025.05.002

Abstract ( ) PDF (1913KB)( )

In view of the deterioration of slab quality and the decrease of the continuous casting efficiency caused by the serious corrosion at the slag line of submerged entry nozzles,taking the ZrO₂-C refractory material in the slag line of the submerged entry nozzle as the research object,the dissolution behavior and oxidation characteristics of the ZrO₂-C material in molten steel under the action of applied electric field were systematically studied.The effect of different polarities (positive and negative) and different voltages (0,1.5,3,and 4.5 V) under direct current electric field on the decarburization reaction of the ZrO₂-C material was compared and analyzed.The results show that (1)the application of the electric field affects the activity of graphite,and then changes the corrosion resistance of the slag line;(2)when the positive electric field is applied to the ZrO₂-C material,graphite is more likely to lose electrons and undergoes dissolution and oxidation reactions under the electric field force,promoting the decarburization of the material;the thickness of the decarburized layer gradually increases with the increasing voltage;when the negative electric field is applied,the alloy elements in molten steel gradually deposit on the slag line surface under the electric field force and electrostatic force,forming a dense Al₂O₃ enrichment layer on the surface,which effectively inhibits the decarburization of ZrO₂-C material,and the thickness of the decarburized layer reduces with the increasing voltage;(3)when a voltage of 3 V is applied,the decarburization thickness of the samples under both the positive and negative electric fields is the optimal overall.

Influence of TiN on characteristics of reaction-bonded SiC ceramics shaped by slip casting

Liu Xingyu, Chen Ding, Gu Huazhi, Huang Ao, Fu Lyuping

2025, (5): 381-385. doi：10.3969/j.issn.1001-1935.2025.05.003

Abstract ( ) PDF (1825KB)( )

When preparing reaction-bonded SiC ceramics by slip casting,due to the introduction of a large amount of solvent,problems of high porosity and low strength exist for the products after subsequent drying,vacuum Si infiltration,and sintering.To enhance the mechanical properties of reaction-bonded SiC ceramics prepared by slip casting,fine SiC powder,carbon black,and graphite were used as main starting materials,sodium carboxymethyl cellulose as the binder,polyvinylpyrrolidone as the dispersant,and TiN powder as the additive to prepare SiC ceramic slurries with TiN extra-addition of 0,2.5%,5%,and 7.5%,by mass.SiC ceramics were obtained after slip casting and heat treatment at 1 740 ℃ for 2 h in the Si embedded condition.The effect of the TiN addition on the physical properties,phase composition,and microstructure of the reaction-bonded SiC ceramics was investigated.The results show that when the TiN addition increases from 0 to to 7.5%,the apparent porosity shows a slight downward trend,while the bulk density increases accordingly;TiN can react with free Si to generate TiSi₂ with high fracture toughness,and to some extent consume the free Si in the sample,improving the mechanical properties of the reaction-sintered SiC ceramics.Therefore,when the TiN addition increases from 0 to 7.5%,the modulus of rupture increases from 204.8 MPa to 304.3 MPa,an increase of 48.6%,and the fracture toughness also increases from 3.76 MPa·m^1/2 to 4.42 MPa·m^1/2,with a growth rate of 17.6%.When the TiN powder addition is 7.5%,the reaction-sintered SiC sample exhibits the optimal comprehensive performance.

Effect of Al(H₂PO₄)₃ and SiO₂ sol on microstructure and properties of zirconia-based coatings

Zhong Xing-yu, Zhao Shixian, Wang Gang, Li Hongyu, Li Lingfeng, Liang Pengpeng, Tian Pengdan, Li Hongxia, Liu Xue-zhi

2025, (5): 386-390. doi：10.3969/j.issn.1001-1935.2025.05.004

Abstract ( ) PDF (1640KB)( )

In order to prepare zirconia-based coatings with excellent mechanical properties and salt fog corrosion resistance on the surface of yttria-stabilized zirconia (YSZ) thermal barrier coatings,zirconia-based coatings were obtained using fused yttria-stabilized zirconia as the main raw material,Al(H₂PO₄)₃ and SiO₂ sol as binders,followed by brush coating and thermal curing.The effects of different binder additions (silica sol addition accounts for 0,10%,20%,30%,and 100% of the Al(H₂PO₄)₃ addition,by mass) on the microstructure,mechanical properties,and salt fog corrosion resistance of the coatings were investigated.The results show that:(1)the synergistic effect of an appropriate amount of silica sol and Al(H₂PO₄)₃ promotes the formation of a network structure in the coating paste,effectively eliminating shrinkage and bubbling during curing,improving the coating quality,and enhancing the corrosion resistance;(2)silica sol reacts with zirconia at high temperatures to form ZrSiO₄,leading to structural damage in the coating;during thermal shock,the internal thermal stress causes cracking,significantly reducing the service life under thermal attack at 1 400 ℃;the coating without silica sol exhibits the best thermal shock resistance but low strength and hardness;(3)when the silica sol addition accounts for 20% of the Al(H₂PO₄)₃ addition,the optimal overall performance can be obtained,with a tensile strength of 16.08 MPa,Vickers hardness of 597 HV,and service life of 166 h under salt fog corrosion.

Preparation and properties of SiO₂-Al₂O₃ composite aerogels

Wang Zhizheng, Guo Yuxiang, Wang Xin, Yang Bo, Sun Peisong, Zhang Fengchuang

2025, (5): 391-397. doi：10.3969/j.issn.1001-1935.2025.05.005

Abstract ( ) PDF (3873KB)( )

To improve the performance of SiO₂-Al₂O₃ aerogels and expand their application field at high temperatures,SiO₂-Al₂O₃ composite aerogels were prepared by the sol-gel method followed by ambient pressure drying,adopting ethyl orthosilicate as the silicon source,aluminum chloride hexahydrate as the aluminum source,water and ethanol as the solvent,and trimethylchlorosilane/n-hexane as the modifier.The effects of n(Si)∶n(Al) (2∶1,1∶1,1∶2,1∶3 and 1∶4) on the gelling time,microstructure,specific surface area and thermal conductivity of the composite aerogels were studied.On this basis,the SiO₂-Al₂O₃ composite aerogels were heat treated at different temperatures (600,800,1 000,1 100 and 1 200 ℃) for 2 h,and then characterized and analyzed by SEM,XRD,BET,TG-DSC,and FT-IR.The results show that:(1)when n(Si)∶n(Al)=1∶3,the SiO₂-Al₂O₃ composite aerogel has the best performance,the gelling time is 7.64 min,and the specific surface area is 397 m²·g^-1;(2)SiO₂ in the composite aerogel inhibits the crystal transformation of Al₂O₃,and the gel network formed by Al—O—Si bond improves the strength,thermal stability and high temperature thermal insulation performance of the aerogel;(3)when n(Si)∶n(Al)=1∶3,after the heat treatment at 1 200 ℃,α-Al₂O₃ is not detected in the SiO₂-Al₂O₃ composite aerogel,and the porous structure still maintains intact,and its thermal conductivity at room temperature is 0.053 W·m^-1·K^-1。

Preparation and performance of anti-oxidation MoSi₂-CrB₂-SiC-Si composite coating for graphite materials

Yang Jiani, Guo Xiaoyang, Jiang Yan

2025, (5): 398-405. doi：10.3969/j.issn.1001-1935.2025.05.006

Abstract ( ) PDF (3314KB)( )

To enhance the oxidation resistance of graphite materials,a graphite substrate was used,with MoSi₂,CrB₂,and SiC powders as raw materials,anhydrous ethanol as the solvent,and phenolic resin as both the carbon source and binder to prepare the inner and outer coating slurry.The graphite substrate was first reacted,impregnated,and cured,followed by vacuum-assisted gas-phase silicon diffusion at 1 625 ℃ for 40 min,resulting in a MoSi₂-CrB₂-SiC-Si anti-oxidation composite coating on the graphite surface.The phase composition,microstructure,and oxidation resistance at 1 400 and 1 700 ℃ of the coating were investigated.The results indicate that:(1)the coating consists of MoSi₂,CrB₂,SiC,and Si,of dense structure without through cracks,exhibiting good adhesion to the substrate;(2)after 250 h of oxidation at 1 400 ℃,the coating retains intact with a mass gain of 0.36%,due to the formation of a dense Cr-Si-Mo-O multi-phase glass anti-oxidation layer on the coating surface,providing effective protection;(3)after the oxidation at 1 700 ℃ for 40 min,the mass of the coating increases by 1.51%,also due to the formation of a Cr-Si-Mo-O multi-phase glass anti-oxidation layer on the coating surface.However,after 60 min of oxidation,the mass decreases by 0.23% due to the volatilisation of gaseous by-products and the spalling of part of the oxide layer.

Preparation of high-purity ultrafine Ti₃(Al_1.2-xSn_x)C₂ powder and its mechanical properties based on solid solution route

Wu Peichen, Wang Lu, Li Dongting, Liu Ying

2025, (5): 406-412. doi：10.3969/j.issn.1001-1935.2025.05.007

Abstract ( ) PDF (3245KB)( )

As service conditions become harsh and performance requirements for components increase,single-phase Ti₃AlC₂ ceramics are difficult to meet the increasingly stringent requirements of modern industrial equipment because of their short comings of low toughness and poor wear resistance.It is urgent to develop effective methods for the controllable preparation of high-purity and small-particle size Ti₃AlC₂ solid solution powder and to fabricate Ti₃AlC₂ solid solution materials with good comprehensive mechanical properties.High-purity ultrafine Ti₃(Al_1.2-xSn_x)C₂(x=0,0.1,0.3 and 0.5) powders were prepared by mixing Ti,Al,Sn and TiC powders through the solid solution route in a planetary ball mill,two-step pressureless sintering and mechanical ball milling.Ti₃(Al_1.2-xSn_x)C₂ bulk samples were then prepared by spark plasma sintering.The results show that all the Ti₃(Al_1.2-xSn_x)C₂(x=0,0.1,0.3 and 0.5) powders have a purity of ＞99 mass% as well as a nano-layered structure.The mechanical properties of the Ti₃(Al_1.2-xSn_x)C₂ samples prepared by spark plasma sintering are greatly improved with the increase of the Sn solid solution,among which the Vickers hardness,bending strength,fracture toughness and compressive strength all increase first and then decrease.Sample Ti₃(Al_0.9Sn_0.3)C₂ has the best mechanical properties,with the Vickers hardness of 8.38 GPa,bending strength of 820.91 MPa,fracture toughness of 7.87 MPa·m^1/2 and compressive strength of 1 510 MPa.The improvement of the strength and hardness of Ti₃(Al_1.2-xSn_x)C₂ materials lies in solid solution strengthening and second phase strengthening,and the micro-characteristics of the materials,such as the layered structure,deflection of crack propagation and grain pull-out of the fracture surface,enhance the deformation and fracture resistance of the materials cooperatively.

Preparation of porous ceramics by impregnating mullite precursor with activated carbon and their perfor-mance

Xi Jianfei, Zhang Ling, Niu Shunan, Luo Shitong, Duan Mingjun

2025, (5): 413-421. doi：10.3969/j.issn.1001-1935.2025.05.008

Abstract ( ) PDF (3904KB)( )

The recycling of waste activated carbon is of great significance in environmental protection.Porous mullite ceramics were prepared by impregnating the mullite precursor with activated carbon,and adopting aluminum sulfate octahydrate,ammonia and silica micropowder as raw materials,waste activated carbon after heat treatment as the pore forming agent,and sodium polyacrylate (PASS) as the dispersant.The effects of the activated carbon addition (1.5%,3.0%,5.2% and 7.8%,by mass) and PASS addition (1%,2% and 3%,extra adding,by mass) on the physical properties,phase composition and microstructure of the porous ceramics were studied.The results show that:(1)as a pore forming agent,activated carbon promotes the formation of pores inside the sample,while the apparent porosity of the samples increases significantly with the increasing activated carbon addition;when the activated carbon addition is 7.8%,the apparent porosity of the sample is 65.7%,the cold crushing strength is 4.62 MPa,the peak pore size is around 3.5 μm,and the pore size distribution is uniform;(2) appropriate PAAS helps to improve the dispersion of activated carbon in the samples and the comprehensive performance of the porous mullite ceramics;when the PAAS addition is 2%,the apparent porosity of the sample is 71.8%,the cold compressive strength is 5.53 MPa,the peak pore size is around 3 μm,and the pore size distribution is optimized;however,excessive PAAS increases the liquid phase in the system,resulting in over sintering of mullite and a decrease in the porosity.

Aluminum ash corrosion resistance of alumina-silica refractory castables

Dong Yuchen, Zhang Sanhua, Qin Hongbin, Li Pengxin, Cao Yingnan

2025, (5): 422-426. doi：10.3969/j.issn.1001-1935.2025.05.009

Abstract ( ) PDF (2455KB)( )

To investigate their aluminum ash corrosion resistance,Al₂O₃-SiO₂ refractory castables were prepared using sintered mullite (grades SM45 and SM70) and white fused corundum as raw materials,and calcium aluminate cement as the binder.The aluminum ash corrosion resistance at 1 350 ℃ of the castables with different Al₂O₃ contents (44.26%,57.51%,69.61%,82.81% and 94.33%,by mass) was studied.The results show that:after corrosion,the strength of all samples declines,with the most striking decrease for the sample containing 69.61% Al₂O₃.During corrosion,cristobalite in the samples is corroded first,followed by mullite,and acicular corundum is formed.The sample with 69.61% Al₂O₃ exhibits the severest corrosion.The main effect of Na and Cl elements in aluminum ash on the samples during corrosion is infiltration.The higher the Al₂O₃ content in the samples,the better the infiltration resistance of the samples against Na,Cl and other elements from aluminum ash.The sample with 94.33% Al₂O₃ demonstrates the strongest resistance to aluminum ash corrosion,while the one with 69.61% Al₂O₃ shows the poorest corrosion resistance.

Preparation process of water based tape casting of plate-like silicon nitride ceramics

Zhao Chenxiao, Li Shipeng, Wang Gang, Yuan Bo

2025, (5): 427-431. doi：10.3969/j.issn.1001-1935.2025.05.010

Abstract ( ) PDF (1598KB)( )

To prepare plate-like silicon nitride ceramics with minimal deformation,low cost,and excellent performance,a water based silicon nitride slurry with a solid loading of 45 vol% was prepared using α-Si₃N₄ powder as the raw material,LiAlO₂ powder and Y₂O₃ powder as the sintering aids,deionized water as the solvent,tetramethyl ammonium hydroxide as the dispersant,acrylic resin emulsion as the binder,and water-soluble oligomer as the plasticizer.The influence of factors such as the dispersant addition (0.1%-0.9%,at an interval of 0.1%,by mass),ball milling time (1,3,5 and 7 h),binder addition (2.5%,5.0% and 7.5%,by mass),and mass ratio of plasticizer to binder (0,0.3,0.6 and 0.9) on the properties and tape casting effect of the slurry was studied.The results show that with the dispersant addition of 0.6%,the binder addition of 7.5%,the mass ratio of plasticizer to binder of 0.6 and the low speed ball milling time of 5 h,the water based silicon nitride slurry with a solid loading of 45% performs the best flowability and tape casting effect.Using this slurry for tape casting,drying,and laminating,plate-like silicon nitride ceramic green bodies were obtained.Then,they were pressureless sintered at 1 650 ℃ for 3 h in a nitrogen atmosphere to obtain plate-like silicon nitride ceramics.The ceramics have the relative density of 97.12%,hardness of 15.64 GPa,bending strength of 583.58 MPa and fracture toughness of 6.72 MPa·m^1/2.

Hydrophobic modification of fiber reinforced SiO₂ aerogels for high thermal stability

Long Haiyi, Tian Xiang-yu, Zhang Bo

2025, (5): 432-437. doi：10.3969/j.issn.1001-1935.2025.05.011

Abstract ( ) PDF (2628KB)( )

To maintain their excellent hydrophobic properties after high temperature service,fiber reinforced SiO₂ aerogel composites were prepared with tetraethyl silicate and mullite fiber needled felt as the main raw materials.Then,trimethoxy (1H,1H,2H,2H-heptafluorodecyl) silane (HDFTES) was used as the hydrophobic modifier to modify their hydrophobic properties by vapor deposition (reaction time of 5-22 h).The microstructure,pore diameter and hydrophobic property of the composites were studied.The results show that the vapor deposition enables aerogels to attain highly stable hydrophobic properties while preserving their original structure.With the increase of the hydrophobic reaction time,the water contact angle of the sample first increases gradually and then remains basically.When the reaction time is 18 h,the water contact angle reaches the maximum of 147°;after hydrophobic modification,the sample can maintain a good hydrophobic state in acid and alkali corrosive solutions;after the heat treatment at 600 ℃ for 3 h,the water contact angle of the sample is maintained at 132°,after the heat treatment at 750 ℃ for 36 min,the water contact angle is maintained at 123°,and its microstructure shows no significant changes,demonstrating excellent thermal stability.

Research progress on hydration resistance of CaO-based refractories and their application

Lei Huicong, Li Yage, Li Hang, Gao Yabo, Wang Yongxin, Huang Zhong, Zhang Haijun

2025, (5): 438-443. doi：10.3969/j.issn.1001-1935.2025.05.012

Abstract ( ) PDF (928KB)( )

CaO-based refractories are widely used in the production of clean steel and special alloy steel owing to their excellent resistance to basic slag corrosion and the ability to purify molten steel.However,the easy hydration of CaO is the main factor for their damage.In this work,the anti-hydration methods and mechanisms of CaO-based refractories were reviewed,their application status in scenarios such as steel ladles,tundishes and crucibles as well as the existing problems was summarized,and their future development directions were prospected.

Advancements in evaluation and optimization of sintering performance of hot repair materials for converters

Dai Chenchen, Qian Fan, Zhao Jinxuan, Yang Jian, Nie Bohua

2025, (5): 444-449. doi：10.3969/j.issn.1001-1935.2025.05.013

Abstract ( ) PDF (911KB)( )

As an indispensable raw and auxiliary material in the daily converter front operations,the sintering performance of the hot repair materials determines the quality of hot repair and even the overall service life of the converter,which is of great significance to the development of steelmaking technology.Focusing on the sintering time and sintered strength,the evaluation methods,research progress and existing problems regarding the sintering performance of hot repair materials for converters in recent years were summarized,and the optimization and enhancement techniques for sintering performance were also summarized.As for the current development of steelmaking technology,several key research points that need to be focused on for hot repair materials for converters were put forward in order to provide references for refractory materials and steelmaking technicians.

Research progress on properties and applications of alumina-toughened zirconia composites

Ding Hewei

2025, (5): 450-454. doi：10.3969/j.issn.1001-1935.2025.05.014

Abstract ( ) PDF (913KB)( )

Alumina-toughened zirconia (ATZ) composites combine the excellent properties of both alumina and zirconia ceramics,and have broad application prospects in the industries field.The influencing factors of tetragonal zirconia stability in ATZ composites were discussed.The methods for improving the physical properties of ATZ composites and their application fields were summarized.Finally,the development prospect of ATZ composites was also expected.

Research progress of purging plugs for ladles

Cui Qingyang, Zhao Baoqun, Liu Lei

2025, (5): 455-460. doi：10.3969/j.issn.1001-1935.2025.05.015

Abstract ( ) PDF (910KB)( )

Inert gas is blown into the molten steel through purging plugs for stirring,so as to achieve the purposes such as uniform composition,temperature adjustment and inclusions removal.The performance of purging plugs directly affects the refining effect and the steel quality.Therefore,the service requirements of purging plugs for ladles were put forward,the research status of purging plugs in recent years was expounded,and the future development direction and research focus of purging plugs were prospected.

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