This work aims at improving the oxidation resistance and dispersion of expanded graphite for low carbon refractories.Expanded graphite was modified by the hydrothermal method using MgSO₄,NH₄OH and surfactants:sodium dodecyl benzene sulfonate (SDBS),polyethylene glycol (PEG),and sodium polyacrylate (PAAS) as starting materials.The effects of the NH₄OH addition (NH₄OH and MgSO₄ mole ratios of 3∶1,2∶1 and 1∶1) and surfactants on the phase composition,the microstructure,the oxidation resistance and the sedimentation property of modified expanded graphite were discussed.The results reveal that:(1)different surfactants result in different phase composition of the hydrothermal products,and the prepared modified expanded graphites have different oxidation resisitance and sedimentation property:whisker-like magnesium hydroxide sulfate is generated with the SDBS addition;flake magnesium hydroxide is generated with the PEG addition;both whisker-like magnesium hydroxide sulfate and flake magnesium hydroxide are generated with the PAAS addition;(2)the modified expanded graphites all have improved oxidation resistance and sedimentation property than the original expanded graphite;the modified expanded graphite prepared with PEG is the optimal.

Corundum based castables were prepared using tabular corundum,α-Al₂O₃ micropowder and calcium aluminate cement as starting materials,curing at 25 ℃ in different humidities for 3 d,drying at 110 ℃ for 24 h,and firing at 800,1 100,1 450 and 1 620 ℃ for 3 h,respectively.The effects of the curing humidity (40%,70%,and 100%) on the properties,the phase composition and the microstructure of the castables were researched.The results show that,as the curing humidity decreases,the demolding strength,the drying strength and the cold modulus of rupture of the samples increase while the apparent porosity and the MOR retention ratio decrease.Moreover,with the reduction of the curing humidity,the hydration degree of the calcium aluminate cement is enhanced,and the aggregates and the matrix are bonded more closely for the castable fired at 1 620 ℃.

β-SiAlON-SiC composites were prepared using SiC particles and fines,silicon powder,AlN powder,α-Al₂O₃ micropowder and flake graphite as starting materials.The influence of the graphite (particle size of 45 and 300 μm,addition of 3.0%,5.5%,7.5%,and 10.0%,by mass) on the molten-alkali resistance was investigated.The results show that the molten-alkali resistance for the β-SiAlON-SiC sample with 7.5% of graphite (300 μm) is the optimal,showing the lowest mass change rate after corrosion,and the highest cold modulus of rupture and hot modulus of rupture retention ratio.

SiC is widely used in the field of refractories because of its excellent mechanical properties.The synthesis of SiC powder by catalytic reaction has a bright future.However,it is difficult to separate the catalysts,which act as impurities.While the influence of catalysts on the properties of SiC has not been studied.Therefore,the first-principles plane-wave pseudopotential method was used to study the catalysts (Fe,Co and Ni) and the doping concentration (1.56%,3.125%,6.25%,and 12.5%,by atom) on the thermodynamic properties,the mechanical properties and the density of states (DOS) of 3C-SiC.The results show that:(1)the structure stability of 3C-SiC crystals doped with Fe,Co and Ni atoms decreases in the order of Fe-SiC,Co-SiC and Ni-SiC.(2)When the Fe doping concentration is 1.56%,compared with the undoped 3C-SiC crystal,the changes of the elasticity modulus,the shear modulus and the Young’s modulus of Fe-SiC are 0.023%,3.57% and 2.77%,and the hardness and the brittleness do not change obviously,and DOS diagram is basically unchanged,which shows that low concentration Fe doping has negligible effect on the mechanical properties of 3C-SiC system.Therefore,SiC powder prepared by catalytic reaction method with Fe as the catalyst can be used in the field of refractories in theory.

Al₂O₃-SiC-C iron trough castables were prepared using brown corundum,silicon carbide,α-Al₂O₃ micropowder,SiO₂ micropowder,and different calcium aluminate cements as raw materials to study the influence of cements (CA50,CA70,Vical71,and Vical21) on their properties.The results show that with the Al₂O₃ and SiO₂ content increasing,CaO and other impurities content decrease in the cements,for the specimens,the apparent porosity after drying at 110 ℃ decreases gradually,and the apparent porosity after heat treatment at 1 450 ℃ decreases at first and then increases,the bulk density in the two conditions both changes slightly;the cold strengths after drying decrease firstly and then increase,the cold strength after heat treatment,the hot modulus of rupture,and the slag corrosion resistance enhance gradually.Considering both the laboratory and the industrial results,Vical21 cement is the best choice.

SiC-TiC composite powders were prepared at 1 550 ℃ for different durations by the carbothermic reduction method,using silica sol,starch and TiO₂ as the starting materials.The influences of the holding time (1 h,2 h and 3 h) on the phase composition and the microstructure of the synthesized powders were discussed by XRD,SEM and EDS.The results show that the synthesis reaction of the SiC-TiC composite powder at 1 550 ℃ for 2 h is relatively complete.In addition to a certain amount of flake particles and many approximately spherical particles (with particle diameter of 50-100 nm),some SiC-based whiskers with uniform sizes and the diameter of 50-100 nm exist.

Forsterite-spinel composite materials were prepared using high-carbon ferrochrome slag as the starting material.Effects of the heat treatment temperatures (1 150,1 200,and 1 250 ℃) on properties of the prepared materials were researched.The results show that there are well developed forsterite and spinel in the high-carbon ferrochrome slag,which can act as the support skeleton for forsterite-spinel composite materials.Heat treatment temperatures can significantly affect the contents of the phases in the composites,and the net-structured spinel crystal in the composite materials can improve the thermal shock resistance of the specimens.The spinel favors the solid-solution of the free chromium ions,their leaching concentration decreases as the heat treatment temperature increases.When the temperature is 1 200 ℃,the composite materials have the best comprehensive performance,with the CCS of 108.8 MPa,the thermal shock resistance of 8 cycles,and the total chromium ion (Cr³⁺ and Cr⁶⁺) leaching mass concentration of 0.14 mg·L^-1.

In order to further improve the strength and thermal shock resistance of Al₂O₃-C materials for steel ladle slide gates,the effects of four kinds of alumina micropowder (unimodal active alumina micropowder 07RAL,unimodal active alumina micropowder 15RA,bimodal active alumina micropowder 22RABL,and calcined alumina micropowder 40CA) on the density,the strength and the thermal shock resistance of Al₂O₃-C materials were studied.The results show that the density,the strength and the thermal shock resistance of Al₂O₃-C materials can be improved with the introduction of active alumina micropowders.Among them,the specimen with bimodal active alumina micropowder shows the best comprehensive performance,especially the hot modulus of rupture.Its actual application results in steel mills show that the average service life of the Al₂O₃-C slide plate prolongs,and the problems of casting hole expansion,the oxidizing and brushing of the plate surface,and cracking are obviously improved.

For improve the high value-added utilization of fly ash floater,porous mullite ceramic materials were prepared by adhesion method and solid-phase sintering using fly ash floater as the template,bauxite as the aluminum source,AlF₃ and V₂O₅ as the additives.Effects of the calcination temperature (1 100,1 200,1 300,and 1 350 ℃,respectively) on the phase composition,the microstructure and the properties of the prepared materials were studied.The results show that: when the temperature changes from 1 100 ℃ to 1 350 ℃,the diffraction peaks of the mullite gradually increase,and these of the quartz gradually weaken until disappear,the apparent porosity of the specimens increases firstly and then decreases,while the bulk density and the compressive strength are on the contrary;when the calcination temperature is 1 300 ℃,the specimen has the apparent porosity of 68.4%,the bulk density of 0.72 g·cm^-3,and the compressive strength of 14.6 MPa.

In order to reasonably control the preparation cost of ceramic membrane,the ceramic membrane support was prepared using the low-cost loess and fly ash as the raw materials,carboxymethyl cellulose as the binder,roll forming and atmospheric sintering.Effects of the loess/fly ash mass ratio,and the sintering temperature on the properties of the support were studied.The results show that the support with the loess/fly ash mass ratio of 6∶4,sintered at 1 100 ℃ for 2 h,has the water flux of 1 832 L·m^-2·h^-1,and the modulus of rupture of 28.3 MPa.

The quality statistics of a basic brick shaping plant was comprehensively researched using R language+WPS,and the analysis tools such as data perspective table,correlation analysis,association analysis,cluster analysis,linear models,decision trees,random forests,and artificial neural networks.The winner from the above tool family was selected to analyze the effects of refractory equipment,refractory brick variety,type and yield on green brick qualified rate,and to discuss the internal connection between various shaping defects.According to the found causes of the defects and the harm degree,the targeted governance was adopted,significantly improving the product qualified rate and enhancing the economic benefits.

In order to reduce the burning loss and the spalling and to improve energy efficiency,the mullite composite lining plates were used to replace cast steel or alloy lining in the dry quenching rotary coke tank.The results show that:the dense mullite composite lining plate in the cone part has the density of 2.2 g·cm^-3 and the loss of 4.08 cm³,and the light weight mullite composite lining plate in the straight cylinder part has the density of 1.95 g·cm^-3 and the loss of 17.6 cm³.After using,there is no internal shrinkage gap,no burn loss or holes,indicating good sealing of the mullite composite lining plate.The lining plate for the cone part has good burn loss resistance,without spalling for more than half a year.The outer surface temperature of coke tanks adopting the cast steel or the alloy lining is 480 to 570 ℃,that of the one adopting mullite composite lining plate is 120 to 170 ℃,showing largely improved insulating property.Adopting mullite composite lining plates on the basis of the current coke tank cage,the lining plate can be timely treated and wholly changed,improving the service life and reducing the maintenance workload.

TRIZ theory was applied to analyze the problem of stuffing sand pollution to molten steel in the design of casting system of continuous casting ladles,and the key points were confirmed through functional analysis and causal chain analysis.The design of the continuous casting process was improved by TRIZ tools,such as material-field model,physical conflict and cutting,producing five solutions.After comprehensive evaluation,two optimal solutions were determined.(1)Replace the traditional solid stuffing sand with liquid metal stuffing sand of low melting point and high density,and adopt the hollow and/or vacuum treatment sliding plate,which can increase the insulation of the stuffing sand in the upper nozzle and avoid solidification,thus ensuring good drainage.(2)Design the long shroud outlet with combination structure,the bottom for intercepting stuffing sand and the side walls for molten steel running,extracting the stuffing sand that pollutes molten steel into the bottom of the long shroud for storage.

To improve the tundish life and metal yield,and ensure the production stability,the stopper,the current stabilizer,the tundish working layer,the submerged entry nozzle,the upper nozzle and the pocket brick were improved.The service life of a single tundish was prolonged from 24 h to 60.6 h,creating conditions for efficient continuous casting.

Quality control chart,a widely proven effective quality control tool,has been gradually known and applied by refractories enterprises.To supervise whether the calcium oxide content of refractories for clean steel smelting was stably controlled during production,the calcium oxide content was determined for many times and the mean-range(X-R) control chart of calcium oxide content was established.The calcium oxide content of the refractories was stably controlled within the range of the required technical data through the analysis and judgment.The X-R control chart plays a good control and prevention role during the refractories production.

Liquid phase is produced during solid-liquid phase transition of high-temperature phase change heat storage materials,corroding the vessels.The research progress and the existing problems on the package of the high-temperature phase change heat storage materials were reviewed,and the future applications of the materials were prospected.

The causes,the formation process,and the prevention of submerged entry nozzle (SEN) clogging were introduced.The influence of electric field on the SEN clogging was focused on,including the basic theory and measurement of SEN charging,the preliminary research on SEN charging,the influence of molten steel on the wetting behavior of refractory materials in electric field,and the influence of electric field on the oxide inclusions in molten steel.Based on the influence of the hydrodynamics,chemistry and other factors on refractory materials,structure,inclusion particle transfer and adhesion,many anti-clogging researches have been carried out,such as optimizing process conditions,compositing anti-clogging inner lining materials,innovating SEN structure and applying physical fields,which solve the problem of SEN clogging to a certain extent.However,the problems of weak adaptability and superficial study on clogging mechanism are still prominent.The electric field control is a new technology to prevent clogging.Although it has achieved certain results in on-site continuous casting trials,some problems such as the method of applying electric field,the electric field parameters and the equipment still need to be gradually improved,and the surface characteristics of inclusions and SEN materials at high temperatures need to be further studied.It was pointed out that the combination of materials and applied electric field will become an important direction for SEN anti-clogging technology.

The classification of bonding systems and bonding modes of refractory castables was introduced.The research progress on new-type cements of the cement bonding system was expounded in detail.The characteristics and the application progress of sol (gel),hydration alumina,magnesia binders,phosphate (phosphoric acid),other binders that can replace cement,and new additives were illuminated.It was pointed out that the new-type cement has good application effect,but it is of high cost.The non-cement bonded castables are not easy to construct,but they are easy to bake,which is suitable for gunning mixes and precast products.The new additives greatly improve the placing performance of castables and have a broad application prospect.

Combined with the production processes,the main equipment and the key technologies of refractory intelligent manufacturing were discussed,including the intelligent stereoscopic warehouse of raw materials,automatic batching system,automatic molding production line,automatic temperature control of ultra-high temperature tunnel kiln,intelligent on-line detection during production,and intelligent on-line monitoring during service.The development suggestions on refractory intelligent manufacturing were also put forward.

The influences of the raw materials and the elements doping on the properties of porous mullite ceramics were summarized.On this basis,the problems during the preparation and application of the porous mullite ceramics were pointed out,and the future development direction was prospected.