In order to utilize coal gangue and steel slag with high added value,foamed ceramics were prepared using coal gangue as the main starting material,and steel slag as the auxiliary starting material,adding appropriate amounts of flux (talc and potassium feldspar) and foaming agent silicon carbide.The effects of the steel slag addition (equivalent replacement of coal gangue,5%,10%,15%,20%,25%,30%,and 35%,by mass) and flux addition (fixing the total addition of talc and potassium feldspar at 20 mass%,replacing potassium feldspar with talc in the equal amount of 0,5%,10%,15%,and 20%,by mass) on the physical properties,microstructure and phase composition of the foamed ceramics were studied.The results show that:(1)with the increasing steel slag addition,the SiO₂ content in the skeleton structure decreases,the content of CaO,MgO and other oxides increases,and the viscosity decreases;excessive steel slag is not conducive to the formation of moderate-size and uniformly distributed pores due to the low SiO₂ content;the steel slag addition shall not exceed 30%;(2)the influence of talc and potassium feldspar flux on the foamed ceramics is mainly to change the contents of alkali metal oxides,as well as Al₂O₃ and SiO₂ which constitute the ceramic skeleton;(3)the optimal foamed ceramic formulation is:m(coal gangue)∶m(steel slag)∶m(potassium feldspar)∶m(talc)=50∶30∶10∶10,extra-adding 0.1 mass% SiC.

To optimize the preparation of Al₂O₃ aerogels,the sol-gel method was combined with supercritical drying,using aluminum isopropoxide (AIP) as precursor,ethanol (EtOH) as solvent,and acetic acid (HAc) as catalyst. The effects of the ethanol addition [n(AIP)∶n(EtOH)∶n(H₂O)∶n(HAc)=1∶8∶0.8∶2,1∶12∶0.8∶2,1∶16∶0.8∶2,and 1∶20∶0.8∶2] and acetic acid addition [n(AIP)∶n(EtOH)∶n(H₂O)∶n(HAc)=1∶16∶0.8∶1,1∶16∶0.8∶2,1∶16∶0.8∶3,and 1∶16∶0.8∶4] on the pore structure and specific surface area of Al₂O₃ aerogels were studied. The results show that ethanol affects the pore structure of Al₂O₃ aerogels by affecting the condensation probability of Al—OH groups,and acetic acid affects the pore structure of Al₂O₃ aerogels by affecting the reaction rate; when n(AIP)∶n(EtOH)∶n(H₂O)∶n(HAc)=1∶16∶0.8∶2,the Al₂O₃ aerogel has a porous microstructure,and its internal pore diameter is generally smaller than the average free path of air molecules,showing excellent thermal insulation characteristics,low density of 0.20 g·cm^-3,and the specific surface area of 458,102,and 51 m²·g^-1 at 25,1 000,and 1 200 ℃,respectively.

Bauxite-based homogenized grogs with 85 mass% Al₂O₃ were prepared through wet co-grinding homogenization and high-temperature heat treatment,and utilizing D-K type bauxite as the raw material.The evolution of the phase composition,microstructure,and properties of the bauxite-based homogenized grogs during the heating process (800-1 630 ℃) was systematically studied using thermodynamic software FactSage,XRD and SEM.The results show that the main crystal phases of the sample are corundum and mullite;as the heat treatment temperature increases,the corundum content decreases gradually while the mullite content increases gradually;(2)within 800-1 550 ℃,as the heat treatment temperature increases,the apparent porosity and water absorption of the sample rapidly decrease,while the linear shrinkage,bulk density,and the cold compressive strength significantly increase;within 1 550-1 630 ℃,the properties of the sample tend to stabilize,with the apparent porosity less than 3.4%,the water absorption rate less than 1.00%,the linear shrinkage rate of about 16%,the bulk density higher than 3.27 g·cm^-3,and the cold compressive strength higher than 460 MPa;the sample is basically densified;(3)after heat treatment at temperatures of 1 400 ℃ or below,the corundum crystals in the sample are small and porous,while the mullite crystals are microcrystalline and not fully developed;the pores are mainly open or through;after the heat treatment at 1 600 ℃ or above,the sample exhibits a typical network structure of alternating corundum and mullite phases;the glass phases are few and isolatedly distributed in the network structure of the corundum grains or mullite grains;the pores are mainly closed;(4)thermodynamic calculations show that the liquid phase is generated in the samples at 1 150 ℃,and the amount of the liquid phase gradually increases with the increasing temperature;while the viscosity of the hot liquid phase significantly decreases.

To optimize the properties of self-bonded SiC refractories,the specimens were fabricated using silicon carbide (3-1,≤1,and ≤0.074 mm),silicon powder (≤45 μm) and graphite (≤10 μm) as raw materials,and Cr₂AlC powder (≤74 μm) as an additive,pressing under 150 MPa into 25 mm×25 mm×40 mm shapes,drying at 110 ℃ and heat treating at 1 300 ℃.The effects of the Cr₂AlC addition (0,1%,3%,and 5%,by mass) on the cold physical properties,sodium sulfate corrosion resistance,and steam oxidation resistance of the materials were investigated.The results reveal that with the increasing Cr₂AlC addition,the cold physical properties of the specimens after drying at 110 ℃ differ slightly;however,the cold physical properties of the specimens fired at 1 300 ℃ show a gradually increasing trend;while the sodium sulfate corrosion resistance initially increases and then decreases.When the Cr₂AlC powder addition is 3%,the specimen exhibits a low mass change rate in the steam,demonstrating good overall performance.

To improve the performance,reaction sintered Si₃N₄-SiC refractories were prepared by reaction sintering at 1 400 ℃ for 2 h using SiC (particles and fines) and Si powder as the raw materials,TiB₂ fine powder as the additive.The effects of the TiB₂ fine powder addition (0,0.2%,0.4%,0.6%,and 0.8%,by mass) on the bulk density,modulus of rupture,phase composition,and microstructure of the reaction sintered Si₃N₄-SiC refractories were studied using MIP,XRD,and SEM,and the densification mechanism was analyzed.The results show that:(1)adding an appropriate amount of TiB₂ helps to improve the bulk density and hot modulus of rupture at 1 200 ℃,increasing the proportion of small pores (≤1 μm);(2)with the increasing TiB₂ addition,the content of Si₂N₂O impurity phase decreases,the nitridation rate of silicon powder improves;Si₃N₄ exists as a whisker structure at the beginning,then evolves into well-developed long rods,and finally grows abnormally;(3)the densification mechanism is as follows:a small amount of TiB₂ can increase the partial pressure of SiO gasous phase and promote the growth of Si₃N₄ whiskers,which follow the gas-solid growth mechanism;when increasing the TiB₂ addition to 0.6%,Si₃N₄ develops into long-rod shapes under moderate high-temperature liquid phase,forming a three-dimensional network structure;when continuing to increase the TiB₂ addition to 0.8%,the liquid phase in the samples increases again,and the rod-shaped Si₃N₄ grows abnormally;(4)when the TiB₂ addition is 0.6%,the comprehensive performance of samples is the best,with the bulk density of 2.75 g·cm^-3,apparent porosity of 11.6%,cold modulus of rupture of 40.2 MPa,and hot modulus of rupture at 1 200 ℃ of 47.4 MPa.

To expand the utilization of iron tailings as secondary resources,lightweight closed-cell ceramsites were prepared using the SiC foaming method with iron tailings,quartz,and potassium feldspar as raw materials.The effects of the firing temperature (1 120,1 130 and 1 140 ℃ for 3 h),the ceramsite particle size (≤2.5,5-2.5 and 10-5 mm),and the addition of foaming agent SiC (1.0%,1.5%,2.0%,2.5% and 3.0%,by mass) on the structure and properties of the ceramsites were studied by XRD,SEM,FactSage software,etc.The results show that:(1)as the firing temperature and SiC addition increase,the bulk density and bearing capacity of the ceramsites decrease,and the ceramsites exhibit three pore structures: fine pore,honeycomb,and hollow;(2)with the firing temperature of 1 130 ℃,additions of 80.5 mass% iron tailings,10 mass% potassium feldspar,7 mass% quartz and 2.5 mass% SiC,as well as the ceramsite particle size of 10-5 mm,lightweight ceramsites can be obtained with a bulk density of 0.69 g·cm^-3 and bearing capacity of 311.2 N.

To improve the comprehensive utilization rate of magnesite tailings and solve the problem of accumulation pollution,Mg₂SiO₄-MgO composite sand was prepared by the solid phase method with flotation magnesite tailings as the raw material and analytically pure Pr₆O₁₁ as the additive,firing at 1 600 ℃ for 3 h.The effects of the Pr₆O₁₁ addition (0,1%,2%,3% and 4%,by mass) on the phase composition,microstructure and physical properties of the composite sand were studied.The results show that:(1)the main crystal phase of the fired samples is Mg₂SiO₄,and the secondary crystal phases are MgO and MgAl₂O₄;when the Pr₆O₁₁ addition is ≥2%,Ca₂Pr₈(SiO₄)₆O₂ is formed;(2)Pr₆O₁₁ can promote the growth of Mg₂SiO₄ crystals and replace low melting point CaMgSiO₄ with high melting point Ca₂Pr₈(SiO₄)₆O₂,which gradually improves the thermal shock resistance of the composite sand with the increase of the Pr₆O₁₁ addition;(3)the proper Pr₆O₁₁ addition promotes the sintering and improves the cold modulus of rupture of the specimen;and the specimen with 2% Pr₆O₁₁ shows the best performance with the bulk density of 3.03 g·cm^-3,apparent porosity of 5.4%,cold modulus of rupture (CMOR) of 65.2 MPa,residual MOR retention ratio of 34.5%,and good thermal shock resistance.

To promote the chromium-free smelting of ultra-low carbon steel and high value-added utilization of spent refractories,MgAlON composites were in-situ synthesized by the carbothermal reduction nitriding method with spent slide bricks,spent MgO-C bricks and Al₂O₃ micropowder as raw materials through pressureless sintering at 1 600 ℃ for 3 h.The effects of the spent slide brick additions (0,22.22%,44.44% and 66.66%,by mass) on the phase composition,morphology and properties of the specimens were investigated.The molten steel corrosion resistance of some specimens was investigated as well.The results show that: the principal crystalline phase of all the specimens is MgAlON.With the spent slide brick addition increasing,Al₂O₃ in the specimens disappears,the amount of β-SiAlON and ZrN gradually increases,the internal porosity of the material decreases first and then increases,and the bulk density and bending strength increase first and then decrease;meanwhile,the fracture mode of the specimens changes from transgranular fracture to transgranular fracture with a small amount of intergranular fracture,and finally to cleavage fracture.When the spent slide brick addition is 44.44%,the specimen has the best comprehensive performance with the bending strength of 140.1 MPa,corrosion depth of 76 μm after corrosion in molten ultra-low carbon steel at 1 600 ℃ for 2 h and the utilization rate of the spent bricks of 55.56 mass%.

To analyze whether sintered chrome-corundum materials meet the requirements of the corrosion resistance of ceramic electric melting furnaces against borosilicate glass,the corrosion behaviours of simulated high level radioactive liquid waste vitrified glass to two sintered chrome-corundum refractories with different Cr₂O₃ contents (47.3% and 60.9%,by mass) at 1 200 ℃ through the rotary impregnation method were compared and investigated.The microstructure and phase composition of the two chrome-corundum refractories after the corrosion tests were analyzed.The results indicate that:(1)the sintered chrome-corundum refractories exhibit excellent corrosion resistance against the simulated molten glass,while showing a discontinuous corrosion process of matrix corrosion-grain spalling;(2) molten glass mainly infiltrates through the pores and phosphate phases between (Cr,Al)₂O₃ solid solution in the sintered chrome-corundum refractories;whereas Al₂O₃ of (Cr,Al)₂O₃ solid solution diffuses into the molten glass,and MgO,FeO,Fe₂O₃,etc. diffuse from the molten glass into (Cr,Al)₂O₃ solid solution,forming Al₂O₃-poor composite spinel;(3)the sample with 60.9% Cr₂O₃ has slightly worse corrosion resistance than the one with 47.3% Cr₂O₃,because the poor solid solubility of (Cr,Al)₂O₃ solid solution,and the poor direct bonding of phosphate binders and (Cr,Al)₂O₃ solid solution matrix with Al₂O₃ as well as Cr₂O₃ particles worsen the corrosion resistance of the sample;(4)if the bonding strength between matrix and particles of sintered chrome-corundum refractories is enhanced,forming similar structures as fused materials,the problem of discontinuous corrosion in molten glass will be solved,the corrosion resistance against molten glass will be improved,and the refractories are potential to be applied in ceramic electric melting furnaces.

To investigate the damage of Si₃N₄ bonded SiC bricks for the bustle pipe of OY reduction shaft furnaces,samples were taken from bricks that had been in service for two years.The appearance,phase composition,microstructure and element composition of the samples were analyzed.The results indicate that:(1)the used bricks show obvious erosion,with rough erosion surfaces and the erosion rate of 50%;(2)the bulk density and apparent porosity of the used bricks decrease,and the oxidation degree decreases with the increase of the distance from the working face;(3)Si₃N₄ bonded SiC bricks are oxidized by the gas in the OY furnaces to form SiO₂,which are not suitable as the lining materials for the bustle pipe of shaft furnaces.

The manual sorting process of fused magnesia results in low classification accuracy and has harsh working environment.The image recognition technology of artificial intelligence has the advantages of high efficiency and reliability,so the identification and classification of fused magnesia by artificial intelligence is a good solution to this problem.Based on the image recognition technology of convolutional neural network,after collecting the macroscopic characteristics of a large number of fused magnesia samples,different fused magnesia varieties were identified and classified,and 150 iterations of high calcia fused magnesia images were trained.The results show that using convolutional neural network to train the high calcia fused magnesia image,and the training accuracy is the highest at the 104^th iteration,reaching 97.2%.In actual identification,all the prediction probabilities of six fused magnesia samples are more than 99.4%,which can not only reduce labor,but also improve the classification efficiency and identification accuracy for fused magnesia.

Accounting the carbon footprint of silicon carbide-mullite bricks,which support the high-quality development of the cement industry,is of great significance to promote the low-carbon development of refractory production enterprises,and help the energy conservation and emission reduction,and low-carbon transformation of downstream cement enterprises.Taking a typical enterprise as an example,based on the life cycle assessment method,a life cycle assessment model for silicon carbide-mullite bricks through Simapro 9.5 software was built,the carbon footprint of silicon carbide-mullite bricks “from cradle to gate” was quantified,and a carbon reduction path for silicon carbide-mullite bricks was proposed.The results show that the carbon footprint of producing 1 ton silicon carbide-mullite bricks is 1 795.14 kgCO_2eq,of which the raw material and fuel acquisition stage and the production stage contribute 89.7% and 10.3%,respectively to greenhouse gas emissions within the system boundary.The main sources of greenhouse gas are the upstream silicon carbide production process,the high-temperature sintering process of bauxite (clinker),and silicon carbide-mullite bricks production.The carbon footprint of silicon carbide-mullite bricks can be effectively reduced by developing highly active silicon carbide production catalysts,increasing the proportion of green electricity application,minimizing the use of raw materials with high carbon emissions,and vigorously promoting the fuel substitution and application of oxygen-rich combustion technology.

Basic refractory materials are commonly used as linings in metallurgical equipment.However,the harsh working environment often leads to significant damage to these refractories,reducing their high-temperature service performance.The slag penetration and the dissolution of refractory materials caused by the corrosion of the molten slag to basic refractory materials are the main causes of the damage.This paper briefly summarized the test methods of slag corrosion resistance of basic refractories and their advantages and disadvantages,reviewed the research progress of the slag corrosion resistance mechanism of magnesia refractories,magnesia-chrome refractories,magnesium-aluminate spinel refractories,and magnesia-calcia refractories,and discussed their future development directions.

Cordierite ceramics,known for their low thermal expansion coefficient,good chemical stability,and high strength,have been widely applied in metallurgy,catalysts,refractories and other fields.With the advancement of the semiconductor industry,cordierite ceramics have emerged as a critical material for high-end equipment ceramic structural components.Various preparation methods of cordierite ceramics,including solid-state synthesis,sol-gel method,and melt-glass method,were briefly described.The current research status on reducing the thermal expansion coefficient of cordierite ceramics through approaches such as adjusting raw material ratios and particle sizes,doping other elements,and modifying firing processes was summarized.Additionally,the current application status of low thermal expansion coefficient cordierite ceramics in different fields was discussed,and the future research direction was prospected.

In the process of clean steel smelting,traditional carbon-containing refractory materials are vulnerable to oxidation and spalling at high temperatures due to their high carbon content,resulting in an increase in the steel carbon content and energy consumption.To address the dual needs of the smelting process and service performance,it is crucial to develop low-carbon refractories with good thermal shock resistance.This paper reviewed the collaborated regulation of low carbonization and performance enhancement of carbon-containing refractories,such as the optimization of carbon sources,the use of additives,and the introduction of composite powders,and finally discussed the problems and future development trends of low carbon refractories.

The effects of various components in used MgO-C bricks,such as magnesia,graphite,binders and antioxidants,on the regeneration of MgO-C bricks in recent years were reviewed.The treatment methods of MgO-C bricks recycling,namely directly using and carbon removal by heat treatment,were discussed.The key problems such as Al₄C₃ hydration and false particles in the recycling of used MgO-C bricks were pointed out.Some suggestions for recycling used MgO-C bricks were put forward.