In order to study the effect of the microsilica addition on the resistance to explosive spalling of ρ-Al₂O₃ bonded corundum castables,white fused corundum,ρ-Al₂O₃,reactive α-Al₂O₃ micropowder,etc.,were used as the main raw materials,adding microsilica with mass fraction of 0,1%,2%,3%,4%,5% and 6%,respectively,to replace fused white corundum fine powder in the matrix.After vibration casting,the cold mechanical properties,the air permeability,the pore size distribution and the resistance to explosive spalling temperature were tested,respectively.The results show that with the microsilica addition increasing,the cold mechanical properties of the specimens increase,the air permeability after demoulding and drying at 110 ℃ gradually decreases,the air permeability after heat treatment at 1 400 ℃ gradually increases,the overall pore diameter increases,and the resistance to explosive spalling first increases and then decreases.In consideration of the mechanical properties and the resistance to explosive spalling,the optimal microsilica addition is 1%-2%.

The foaming method was used to introduce pores into Si bodies to increase the volume by 0,1,2,and 3 times,respectively.Si₃N₄ fiber materials were produced by in-situ nitridation with porosity of 49%,74%,81%,and 87%,respectively.The effects of the oxidation temperature (1 150,1 350,and 1 550 ℃) and the apparent porosity on the oxidation resistance of the Si₃N₄ fiber materials were studied.The results show that:(1) the temperature is a key factor affecting the oxidation resistance of Si₃N₄ fiber materials;as the temperature increases,the amount of the SiO₂ produced by the oxidation gradually increases;since the silicon nitride fiber in the pores has large specific surface area,it is converted into beaded SiO₂ structure after oxidation at 1 550 ℃;the ideal service temperature of the silicon nitride fiber material shall be lower than 1 150 ℃;(2) the apparent porosity of the samples increases from 49% to 87%,and the amount of the SiO₂ generated after oxidation does not change much;(3) the pores introduced by the foaming method can partially absorb the volume effect generated by the oxidation of Si₃N₄ on the pore walls to avoid cracks in the pore walls during oxidation;at the same time,the volume expansion caused by the oxidation of silicon nitride can densify the pore wall structure,which is beneficial to improving the strength of the materials.

Corundum-based porous ceramic samples were prepared using white fused corundum powder as the main raw material,water-based or oily bisphenol F epoxy resin as the binder,water or ethanol as the solvent,water-based or oily fatty amine as the curing agent,batching,stirring,light ramming,drying,and holding at 150 ℃ for 2 h.The effects of the bisphenol F epoxy resin types (water-based or oil-based),the particle size of the corundum powder (100,220,800 mesh,i.e.<0.15,<0.07,<0.02 mm),and the amount of resin (3,5,8,11 g) and whether to add coupling agent on the apparent porosity,the cold modulus of rupture (CMOR),MOR retention ratio after water immersion were studied.The results show that:(1)compared with the water-based bisphenol F epoxy resin bonded samples,the oil-based bisphenol F epoxy resin bonded samples have smaller apparent porosity and higher CMOR;(2)as the particle size of the corundum powder decreases,the apparent porosity of the samples gradually decreases,and the CMOR first increases and then decreases;the overall performance of the sample prepared with <0.07 mm (220 mesh) corundum powder is good with the apparent porosity of 46.26% and the CMOR of 13.21 MPa;(3)as the amount of bisphenol F epoxy resin increases,the apparent porosity of the samples gradually decreases,and the CMOR and the CMOR after immersion in water gradually increase;the prepared sample added with 5 g of oily bisphenol F epoxy resin has the best overall performance: the apparent porosity is 36.81%,the CMOR reaches 20.98 MPa,and the CMOR retention ratio after water immersion for 48 h is 27.98%;(4)after adding 1.2 g of silane coupling agent KH-560,the CMOR retention ratio after immersion is greatly increased to 80%.

MgO-MA samples and MgO-MA-Al samples containing 5 mass% metal Al were prepared using fused magnesia,fused spinel and aluminum as raw materials and phenolic resin as the binder.After drying at 110 ℃ for 24 h,some samples were heat treated in a closed sagger at 1 600 ℃ for 5 h to analyze their phase composition and microstructure;the other samples were tested for slag resistance at 1 600 ℃ in nitrogen atmosphere for 5 h.The results show that (1)a MgO dense layer is formed on the MgO-MA-Al sample containing 5 mass% Al since the strong reducing Al promotes the transformation of MgO to Mg gas during the heat treatment in the closed sagger at 1 600 ℃ for 5 h under nitrogen atmosphere;(2)in the process of the slag resistance test at 1 600 ℃ for 5 h in nitrogen atmosphere,the outer layer of the sample is also densified,which improves the slag penetration resistance and the slag corrosion resistance of the samples.

Powder characteristics of three types of reactive alumina micro-powders,the pH value of saturated solutions,the variation of the Zeta potential with the pH value of the alumina suspensions and the rheological properties of the slurries with the a solid content of 50% were investigated.The correlation between the rheological properties of slurries and the powder characteristics was discussed by Herschel-Bulkley fitting of shear stress-shear rate curves and grey correlation analysis.Effects of three types of polycarboxylate dispersants on the rheological properties of the alumina slurries with the solid content of 50% were also studied.The results show that:(1)at low shear rates the slurry of the reactive alumina with the largest d₅₀ and the widest particle size distribution presents the lowest shear stress and apparent viscosity;(2)according to the grey correlation degree analysis,the yield stress,the viscosity coefficient and the apparent viscosity of the reference slurries are highly correlated with pH and d₁₀ of the micro-powders;however,the grey correlation degrees are lower than 0.9,which indicates that the rheological behavior is influenced by multi-factors;within the range of 1-100 s ^-1,the influence of the powder characteristics on the rheological properties of the slu-rries declines with the shear rate increasing;(3)among the three types of dispersants,pure and alumina-based polycarboxylate dispersants work better while the cement-based polyacrylate dispersant is less effective.

The zirconia metering nozzle samples heat-treated at 1 300 ℃,1 410 ℃,and 1 540 ℃ for 5 h were analyzed by XRD and SEM to investigate the phase composition and microstructure for studying the effect of the temperature gradient on the damage mechanism of zirconia metering nozzles.The results show that when the samples heat treated at 1 300 ℃,1 410 ℃,and 1 540 ℃ for 5 h are water quenched,the c-ZrO₂ and m-ZrO₂ contents as well as the grain size change significantly.With the increasing heat treatment temperature,the c-ZrO₂ content increases,the m-ZrO₂ content reduces,and the grain size increases,which means that the temperature gradient during continuous casting of metering nozzles will affect the phase composition and the microstructure.In combination of the steel slag corrosion,the damage of metering nozzles will be accelerated,thereby reducing the performance and the service life.

Lightweight homogenized bauxite samples were prepared with homogenized bauxite raw powder and carbon black.The effects of the carbon black type (N990 and N774),the carbon black addition (0,4%,and 8%,by mass),and the heat-treatment temperature (1 450,1 500,and 1 550 ℃ for 3 h) on the pore structure of the lightweight homogenized bauxite were investigated.The results reveal that with the heat-treatment temperature increasing,the pore amount in the lightweight homogenized bauxite decreases but the average pore diameter increases;pores in the samples with N990 exhibit more uniform distribution and smaller average size since N990 is easy to disperse;while the average pore size distribution of the samples with N774 is less uniform and the average pore size increases with the rising N774 addition since N774 is not easy to disperse.

The hot modulus of rupture,the creep resistance and the microstructure of high purity sintered MgAl₂O₄ materials with 66%,71%,75%,85%,and 90% Al₂O₃ (by mass) and fused-rebonded MgAl₂O₄ materials with varying Al₂O₃ contents were studied.The results show that:(1)for high purity sintered MgAl₂O₄ materials,the hot modulus of rupture increases along with the increase of the Al₂O₃ content;the sample with 66 mass% Al₂O₃ is spinel-periclase composites in which the existence of periclase weakens the bonding force of grain boundaries,thus resulting in low hot strength;for the samples with 71%,75%,and 85% Al₂O₃,with the increase of the Al₂O₃ content,the grain size increases,and the bonding strength of grain boundaries increases,the main fracture mode changes from intergranular fracture to transgranular fracture,and the hot strength also increases;the sample with 90% Al₂O₃ is spinel-corundum composite which leads to lower hot strength than that of the sample with 85% Al₂O₃;(2)the sinterability of the fused-rebonded MgAl₂O₄ materials decreases with the increase of the Al₂O₃ content,while the creep resistance increases.

The coal slag corrosion resistance of SiC-CA₆ composites was tested using the static crucible method under carbon embedded atmosphere at 1 500 ℃ for 3 h.The corrosion mechanism of coal slag on SiC-CA₆ composites was studied by means of XRD,SEM and EDS.The results show that:(1)in the reducing atmosphere,no obvious corrosion layer is found in the SiC-CA₆ composites;the formed permeation layer is relatively thin and dense,indicating that SiC-CA₆ composites have good slag corrosion resistance;(2)the corrosion mechanism of coal slag on SiC-CA₆ composites mainly includes two aspects: the oxidation of SiC particles at the slag/sample interface by iron oxide in the slag and the reaction of CA₆ in sample matrix with the SiO₂,Al₂O₃ and CaO in the slag to form CAS₂;the formed CAS₂ can dissolve into the slag and increase the viscosity of the local slag at the slag/sample interface,therefore suppressing the further penetration of the slag into the material.

Magnesia-calcia refractory is an ideal refractory for smelting clean steel,but the free calcia in it is easy to hydrate,which limits its wide application.In this paper,the adsorption behavior of H₂O molecules on CaO(100) face was studied by first-principle calculation.On this basis,the effect of applied electric field on the adsorption behavior of H₂O on CaO(100) face was studied.The results show that H₂O molecules are the most easily adsorbed on the bridge sites of CaO(100) face with perpendicular-up and perpendicular-down.The distance and adsorption energy between H₂O and CaO(100) face increase with the increase of the applied electric field intensity.At the same time,the bond angle of H₂O keeps decreasing,and it tends to be single H₂O.The results of charge transfer show that with the increase of the negative electric field intensity,the electrons transferred from Ca atom to O atom are less and less,which indicates that the interaction between H₂O and CaO(100) face is weakening.Under the action of positive electric field,the distance between the H₂O and the CaO(100) has little change with the increase of electric field intensity,but the adsorption energy gradually changes from negative to positive.The applied electric field can inhibit the adsorption of H₂O on CaO(100) face,providing a new method for the waterproofing of magnesia-calcia refractory materials.

Reaction-sintered silicon carbide specimens were prepared using SiC,carbon black,and thermosetting phenolic resin as raw materials,extra adding metal Al powder (0,and 4 mass%),mixing,shaping,curing at 180 ℃,and carbonizing at 800 ℃,and firing in vacuum at 1 550 ℃,1 600 ℃,1 650 ℃ and 1 700 ℃,respectively,in graphite crucibles embedded by Si powder.The results show that:(1)the main phases of the specimens with 4% or without Al powder are α-SiC,β-SiC and free Si;(2)the specimen with 4% Al powder has lower permanent linear change;after firing at 1 600 ℃,the specimen has the lowest residual Si content and the highest SiC content,and performs the best properties;(3)Al has great plasticity;the specimen with 4% Al powder has high density and low porosity;during the reaction sintering process,the resistance of liquid Si infiltration is greater,the amount of infiltration is less,so the final residual amount is less,so the hot strength of the specimen is higher;after firing at 1 700 ℃,Al₄SiC₄ forms,increasing the bonding among the particles.

Al₂O₃-SiC-C based castables were prepared with brown corundum,SiC,aluminate cement,α-Al₂O₃ micropowder,and SiO₂ fume as starting materials.Effects of pitch types (spherical pitch,high temperature modified pitch,spherical+high temperature modified pitch),compounds of pitch and graphite (or carbon black) on the flowability of the castables and the properties of the specimens hot treated at 110,1 100,and 1 450 ℃ were researched.The results show that the flowability and the oxidation resistance of the castables can be improved by introducing the spherical+high temperature modified pitch.With temperature rising,the bulk density,the modulus of rupture and the crushing strength of the castables firstly decrease and then increase,the change of the apparent porosity is inversely correlated.Addition of composite carbon source results in the increase of water demand of the castables and obvious improvement of oxidation and slag corrosion resistance.The castables with the addition of pitch+carbon black perform the best oxidation resistance and slag resistance.

The specimens were prepared using low grade magnesite as the raw material,added with 0-3 mass% La₂O₃,calcined at 1 600 ℃ for 3 h.The bulk density,the apparent porosity and the cold modulus of rupture of the specimens were measured.The composition and microstructure of the calcined specimens were analyzed.The results show that adding La₂O₃ into magnesite can form lanthanum calcium silicate,which is dendritic and interlaces at MgO grain boundaries,and the dendrite toughens the specimen and increases the modulus of rupture.When 2 mass% La₂O₃ is added,the mechanical properties of the specimen are the best,and the modulus of rupture of the specimen reaches 103.1 MPa.La₂O₃ can promote the growth of periclase grains.When the La₂O₃ addition exceeds 2 mass%,the growth of periclase grains slows down,which may be due to the large number of second phases presenting at grain boundaries,inhibiting the growth of periclase grains,thus partly offsetting,the promotion of grain growth by La₂O₃.

Unburned magnesia-calcium based specimens were prepared using synthetic magnesia-calcia sand and fused magnesia as the main raw materials,anhydrous phenolic resin as the binder.Effect of the ferrocene addition (0,0.5%,1%,and 1.5%,by mass) on the specimens was researched.SEM and XRD were used to characterize the microstructure and phase composition of the specimens.The results show that:(1)the bulk density,the cold crushing strength and the hydration resistance of the specimens increase first and then decrease as the ferrocene addition increases after heat treatment at 200 ℃ and 1 650 ℃;when the ferrocene addition is 1%,the performance of the specimens is the best;(2)the introduction of ferrocene can form calcium ferrite in the specimen and some carbon remains after the heat treatment at 1 650 ℃.

In order to study the properties of zirconia products prepared from sintered porous zirconia aggregates,specimens were prepared using self-made sintered porous zirconia aggregates and municipal bubble zirconia as the aggregates,fused zirconia fine powder and zirconia micropowder as the matrix,water-soluble resin as the binder,hydraulic shaped,dried at 110 ℃,and then fired in a gas kiln at 1 800 ℃ for 6 h.The properties of the specimens were tested and the microstructure was analyzed.The results show that the specimen prepared with sintered porous zirconia aggregates has moderate bulk density and high cold crushing strength,and the hot modulus of rupture is equivalent to that of the specimens prepared using bubble zirconia as the aggregates,and the creep rate and the thermal conductivity are high.SEM analysis shows that the sintered aggregates have better bonding with zirconia matrix,which is the main reason for the strength increase,and the dispersed small pores are beneficial to blocking the heat conduction.

In order to improve the refractory material selection in the settling chamber of EAF steelmaking,the static crucible slag resistance tests of clay brick already used in the settling chamber of EAF steelmaking in Nangang,the proposed silicon nitride bonded silicon carbide brick and magnesia chrome brick were carried out using the soot from the settling chamber of EAF.The results show that:(1)the magnesia chrome brick has the best slag resistance,followed by the silicon nitride bonded silicon carbide brick,and then the clay brick;(2)at high temperatures,SiO₂ and Al₂O₃,the important components of clay brick,are easy to react with liquid soot slag and dissolve into the slag.The wettability of liquid soot slag on silicon nitride bonded silicon carbide brick is poor,and the slag is difficult to penetrate into the brick; however,the silicon nitride bonded silicon carbide brick is easy to oxidize at high temperatures,and the oxidation product SiO₂ is easy to react with the liquid soot slag and dissolves.Although liquid soot slag can penetrate into the magnesia chrome brick,periclase and magnesia chrome spinel,the main components of the magnesia chrome brick,are not easy to react with soot slag.

Hercynite powders were prepared using Fe₂O₃,Al₂O₃ and graphite powder as the raw materials,NaCl,KCl,NaCl-KCl and NaCl-Na₂CO₃ as the molten salt medium,fired at 1 000 ℃ for 3 h in high-purity nitrogen atmosphere by the molten salt method.The synthetic hercynite powders were analyzed by XRD,SEM-EDS and in terms of the particle size.The results show that hercynite is not formed using NaCl-Na₂CO₃ as the molten salt medium,because Na₂CO₃ reacts with Al₂O₃ to form Na₂Al₂O₄ at a temperature above the melting point of Na₂CO₃ (851 ℃);high-purity hercynite can be synthesized using NaCl,KCl or NaCl-KCl as the molten salt medium;when NaCl-KCl is used as the molten salt medium,the average particle size of the hercynite is larger,and the particle distribution is more uniform compared with the one using NaCl or KCl.

The research progress of MgO-ZrO₂ refractories was summarized in this paper.The emphasis was focused on the influences of the types of zirconia sources and their amount as well as additives on the performance,the composition and the microstructure of MgO-ZrO₂ refractories.It was expected to provide technical data for the production and application of MgO-ZrO₂ refractories.

The research progress of the application of various additives in MgO-MA materials was reviewed,including the improvement in sintering,strength,thermal shock resistance,and slag resistance;and the mechanism of additives on the improvement of material properties was summarized.