A new cement free iron trough castable was prepared with dense corundum and silicon carbide as the main raw materials and submicron SiO₂ powder (d₅₀=0.242 μm,99.9 mass% SiO₂) as the binder.The effect of the submicron SiO₂ powder addition (3%,4%,5%,6%,7%,8%,and 9%,by mass,respectively) on the properties of the prepared castables was studied.The working mechanism of submicron SiO₂ powder was analyzed from the perspectives of the particle size distribution and infrared absorption spectrum.The results show that:(1)cement free iron trough castables can be prepared using submicron SiO₂ powder alone as the binder;(2)compared with traditional castables,the cement free castables have made a breakthrough in the water addition and the hot modulus of rupture.The optimal submicron SiO₂ powder addition is 4%-6%.

Periclase-spinel bricks were prepared using sintered magnesia,flotation magnesia,fused magnesium aluminate spinel and calcined Al₂O₃ fines as starting materials and calcium lignosulfonate as the binder,mixing,shaping and firing at 1 650 ℃.Flotation magnesia particles were used to replace ordinary sintered magnesia particles and different amounts of calcined Al₂O₃ fines were extra-added (0%,3% and 5%,by mass) to investigate their effects on the properties of periclase-spinel bricks.The results show that:(1)the periclase-spinel bricks prepared with flotation magnesia particles have reduced apparent porosity and cold compressive strength,and enhanced bulk density,thermal shock resistance,hot strength and hot toughness;(2)in the periclase-spinel bricks prepared with flotation magnesia particles,as the calcined Al₂O₃ fines addition increases,the apparent porosity and the cold compressive strength decrease,and the bulk density,the thermal shock resistance,the hot strength and the hot toughness are improved.

First,walnut shell powder (WSP) was impregnated with different impregnating reagents:5% ZrO₂ sol,7% Al₂O₃ sol,and 3% SiO₂ sol.Then,porous Al₂O₃ materials were prepared using α-Al₂O₃ micropowder as the main starting material and the treated WSP as the pore forming agent.The effects of the sol impregnated WSP on the pore structure,the thermal conductivity and the mechanical properties of the porous Al₂O₃ materials were investigated.The results show that the morphological changes of WSP are clearly observed in the pores of the porous Al₂O₃ materials,which is an important factor in optimizing the pore structure of ceramics.Porous Al₂O₃ ceramics of low thermal conductivity (0.297 W·m ^-1·K ^-1 at 200 ℃) and high compressive strength (43.5 MPa) can be obtained adopting the WSP impregnated with 3% SiO₂ sol.Furthermore,mullite cross network structure is also found in the pores of the material.

Oxidation behavior of SiC castables at 1 000 ℃ in static air and steam atmospheres (according to ASTM C863-2000) for 50,100,and 150 h,respectively,was researched through SEM and XRD.The results show that (1)the mass and volume change rates of the castables in pure water steam are obviously larger than those in static air;(2)compared to static air,steam oxidation damages the structure of SiC castables more seriously,which may be caused by the lack of a protective film formed with the extension of the time,leading to continuous oxidation;when the volume continues to expand,the internal structure of the castables is destroyed,resulting in cracking,spalling and failure;(3) the oxidation resistance difference of SiC castables in static air and steam is related to the destruction of hydrogen bonds to the oxidation film.

Using zircon,boric acid and carbon black as starting materials,ZrB₂-ZrO₂-SiC composite powder was synthesized by calcining at 1 500 ℃ in flowing argon atmosphere.The effects of the soaking time (3,6 and 9 h) and the addition of additive AlF₃ (0,0.5%,1.0%,1.5%,2.0% and 2.5%,by mass) on the phase composition and the microstructure of the synthesized products were investigated.The results show that:(1)ZrB₂-ZrO₂-SiC composite powder can be synthesized by carbothermal reduction at 1 500 ℃ in flowing argon atmosphere;ZrB₂ and ZrO₂ are granular-like,and SiC crystals are fiberous;(2)with the soaking time increasing,the amount of ZrB₂ increases,the amounts of m-ZrO₂ and SiC decrease,and the total amount of non-oxides ZrB₂,SiC and ZrC gradually increases;(3)compared with the specimen without AlF₃,the specimen with 0.5% AlF₃ has decreased m-ZrO₂ amount,noticeably increased ZrB₂ amount but decreased SiC amount;however,when the amount of AlF₃ increases from 0.5% to 2.5%,the m-ZrO₂ amount increases,the ZrB₂ amount decreases,and the SiC amount changes slightly;the optimum AlF₃ addition is 0.5%.

The effects of the oxidation treatment (in air atmosphere at 400,600 and 800 ℃ for 3 h) of Si₃N₄ powder synthesized by self-propagating combustion and the types of dispersants (sodium polyacrylate,sodium hexametaphosphate,trimerization sodium phosphate,and calcium lignosulfonate) on the anti-settling,the zeta potential and the viscosity of the Si₃N₄ slurries were investigated.The results show that:(1)after the oxidation treatment in air atmosphere at 800 ℃ for 3 h,the Si₂N₂O content in the obtained powder increases;the corresponding slurry has the best stability,large zeta potential absolute value and the smallest viscosity;(2)the Si₃N₄ slurry prepared with sodium hexametaphosphate as dispersant has good stability,the highest zeta potential absolute value and the lowest viscosity;(3)the Si₃N₄ slurry prepared with 0.021% sodium hexametaphosphate has the highest zeta potential absolute value and low viscosity.

In order to improve the service life,the MgO-C brick specimens were prepared using the fused magnesia (5-3,3-1,≤1 mm and ≤0.074 mm),flake graphite (≤0.15 mm),Si powder (≤0.044 mm),Al powder (≤0.044 mm) and calcium hexaluminate (≤0.044 mm) as raw materials and the thermosetting phenolic resin (PF5323) as the binder,mechanical pressing under 150 MPa,then carbon embedded firing at 1 200 and 1 400 ℃ for 3 h,respectively.Effects of calcium hexaluminate additions (0,3%,6%,and 9%,by mass) on the properties of MgO-C refractories were researched.The results show that:as the addition of calcium hexaluminate is 3%,the specimen performs the best cold physical properties and slag corrosion resistance.The addition of calcium hexaluminate can accelerate the sintering among particles at high temperatures,forming magnesium aluminate spinel in the refractories,improving the MOR and the crushing strength.Meanwhile,Al₂O₃ is formed,which increases the viscosity of liquid molten slag,improving the corrosion resistance of MgO-C refractories.

Magnesia ceramic specimens were prepared using high purity magnesia powder as the main starting material and polyvinyl alcohol as the binder,doping different amounts of La₂O₃ powder (0,2%,4%,6%,and 8%,by mass).The effects of uniaxial pressing,isostatic pressing and different calcination temperatures (1 400,1 500 and 1 600 ℃) on the sintering performance,the microstructure and the thermal shock resistance of La₂O₃ doped MgO ceramics were investigated.The results show that the magnesia powder is subjected to the same forming pressure from all directions and then the pressure is uniformly transferred to all directions by isostatic pressing,so as to obtain a more compact green body and significantly improve the sintering performance of magnesia ceramic.The increase of the sintering temperature is more conducive to the formation of substitution solid solution or lattice distortion when the doped La₂O₃ reacts with MgO,which promotes sintering and achieves densification.When the calcination temperature is 1 600 ℃ and the doping amount of La₂O₃ is 4%,the green body formed by isostatic pressing is the densest,and the cracks are small after thermal shock.The La₂O₃ crystals at the interface of the periclase crystal phase change the crack direction,then block and disperse part of the energy and stress,which slows down the linear extension of the cracks.

SiC powder was prepared using silica fume by carbothermal reduction in order to recycle silica fume.Effects of temperatures (1 550,1 650,1 750,and 1 850 ℃) on the smelting effect without adding cutting waste were studied.Based on the better smelting temperature,the effect of cutting waste addition (accounted for 5%,15%,25%,35%,and 50% of the silica fume addition,by mass) on the preparation of silicon carbide powder was studied.The results show that the optimal smelting temperature is 1 750 ℃,and the SiC content in the product is 92.47 mass%;the optimal addition of cutting waste is 25% of the silica fume addition,and the SiC content in the obtained product is 95.36 mass%.With 25% cutting waste,the purity of SiC in the product is significantly improved,which is of great significance for the recycling of these two kinds of solid waste,environmental protection and solving the problem of resource waste.

Al₂O₃-MgO gunning mix was prepared using tabular corundum,fused magnesia,α-Al₂O₃ micropowder and SiO₂ miropowder as main starting materials,calcium aluminate cement,SiO₂ sol and Al₂O₃ sol as binders.Effect of binders on the properties of the gunning mix was studied.The results show that:(1)the specimen with SiO₂ sol as the binder after baking has a higher strength,forming forsterite at high temperatures,which reduces the apparent porosity;with 4% SiO₂ sol,the specimen obtains the high retention ratio of modulus of rupture after thermal shock;(2)specimen with Al₂O₃ sol as the binder has a lamellar structure,good thermal shock resistance,but high apparent porosity and low strength.

In order to improve the resource utilization of fly ash,different amounts of fly ash fine powder (0,5,10,20 and 30 g per 100 g of mixture) were added into the mixture powder of m(fly ash cenosphere)∶m(Al(OH)₃)∶m(V₂O₅)∶m(AlF₃)=45∶55∶4∶3,and PVA solution was used as the binder.Mullite porous ceramic specimens were obtained after dry mixing,mud stirring,mud decaying,extrusion shaping and insulating at 1 100 ℃ for 2 h.The density,the strength and the thermal shock resistance of the specimens were tested,and the phase composition and the microstructure were analyzed.The results show that:(1)the total porosity and the open porosity of the specimens gradually decrease,while the bulk density and the compressive strength gradually increase,and the closed porosity and the thermal shock resistance firstly increase and then decrease with the fly ash fine powder addition increasing;(2)specimen M10 has the best comprehensive performance,with an open porosity of 62.20%,a closed porosity of 13.45%,a total porosity of 75.65%,a bulk density of 0.76 g·cm ^-3,a compressive strength of 16.7 MPa,a compressive strength after thermal shock of 14.3 MPa,and a residual strength ratio of 85.63%.

The firing quality statistics of a basic brick plant were comprehensively researched using R language+WPS,and the analysis tools such as data perspective table,correlation analysis,association analysis,cluster analysis,principal component analysis,linear models,decision trees,random forests,and artificial neural networks.The association between cause and intermediate variables was studied and the main influencing factors were found.The winner from the above tool family was selected to analyze the relations among the cause,intermediate and output variables.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.

The abnormal corrosion of hot iron ladles was investigated.The performance,the composition and the structure of bricks for the hot iron ladles were analyzed.The results show that (1)compared with the alumina-silicon carbide-carbon bricks for the ladle bottom,those for the ladle wall have more pyrophyllite and the Al₂O₃ content of 36.32 mass%;their bulk density,apparent porosity and compressive strength are all lower than the requirement of industry standards;they have poor oxidation resistance and are oxidized to form a porous layer during service,which loosens the brick lining structure thus leading to fracture,local wear and structural damage of bricks;(2)without heating,steel scrap is not completely melted,resulting in slag or steel attachment at the mouth or the bottom of ladles thus increasing damage of ladles;(3) and the residual bricks react with the attached slag to form low melting point phase affecting their hot properties.The refractories for the lining of hot iron ladles must be improved in combination with process changes,not entirely by raw materials replacement to reduce costs.

Sintered products were prepared using coal gasification slag as the main raw material.Based on the comprehensive differential thermal analysis of dry mixture and the firing shrinkage pre-tests of green bodies as well as experience,the experiment was conducted according to orthogonal table L₉(3 ³),selecting the heating rate,the firing temperature,and the holding time as factors,2,3,and 4 ℃·min ^-1,1 100,1 150,and 1 200 ℃ as well as 2,4,and 6 h as the corresponding levels,while the bulk density,the water absorption,the compressive strength and the thermal conductivity as evaluation indexes.The results show that:(1)the order of the influence degree of the firing system factors on the compressive strength,the bulk density and the water absorption of the sintered products is the firing temperature>the holding time>the heating rate,and that for the thermal conductivity is the firing temperature>the heating rate>the holding time;(2)generally,the optimal firing system is the heating rate of 2 ℃·min ^-1,the firing temperature of 1 200 ℃,and the holding time of 6 h,and the prepared sample has the bulk density of 1.84 g·cm ^-3,the compressive strength of 112 MPa,the water absorption of 1.44%,and the thermal conductivity of 1.239 W·m ^-1·K ^-1.

Taking a 5.42 m ³ shuttle kiln for firing silicon carbide products as the research object,the temperature field and the thermal loss of the kiln body with three different lining configurations were numerically simulated,compared and analyzed using ANSYS finite element analysis software.The results show that:(1)with the fixed total thickness of the kiln body,reducing the working layer thickness and simultaneously increasing the thermal insulation layer thickness can greatly reduce the thermal loss of the kiln body;(2)when only the thermal insulation layer thickness is increased,the thermal dissipation decreases and the thermal storage increases,resulting in basically unchanged total thermal loss;(3) when only the working layer thickness is decreased,the thermal storage loss declines,while the external surface temperature of the kiln body increases leading to increased thermal dissipation.By comprehensive comparison,based on the premise of fixed total thickness of the kiln body,reducing the working layer thickness and simultaneously increasing the thermal insulation layer thickness are optimal for energy saving,which can reduce the total thermal loss of the lining materials by about 8.1%,achieving a good energy saving effect.

Recycled SiO₂ micropowder solid waste (SiO₂<85 mass%) was heat treated at 400,500,600,700,800,900,and 1 000 ℃ for 5 h,respectively,and then the heat treated powders were analyzed.The results show that the samples are gradually sintered as the heat treatment temperature increases.Below 800 ℃,the original structure of granular and spherical SiO₂ aggregates remains.However,at 500 ℃ or below,the aggregates strength is low.Above 800 ℃,SiO₂ micropowder agglomerates seriously and cristobalite is precipitated.When the heat treatment temperature is in the range of 600-800 ℃,the spherical SiO₂ micropowder with a certain strength and the bulk density of 0.73-0.95 g·cm ^-3 and a core-shell structure can be prepared,which can be used as a lightweight raw material for low temperature insulation castables and as a filler for other industries.

Reaction sintered silicon carbide is a high-density,low-cost and net-shape forming material with excellent mechanical properties,corrosion resistance and oxidation resistance.However,free silicon often remains due to the special process of the reaction sintering method,seriously damaging its hot properties.The research status of the hot mechanical properties,the oxidation resistance,the thermal conductivity and the thermal shock resistance of the reaction sintered silicon carbide was expounded.The main measures to reduce the free silicon and to improve the mechanical properties in recent years were summarized,including the optimization of the preparation process as well as the introduction of the reinforcement and toughening phases.The future research direction of the reaction sintered silicon carbide was prospected.

Porous cordierite ceramics are used as the catalyst carrier of vehicle exhaust owning to their high porosity,excellent mechanical strength and good thermal shock resistance.Therefore,the correlation between the preparation methods as well as the doping elements and the properties of the porous cordierite ceramics (such as the pore structure,the thermal shock resistance and the mechanical strength) was reviewed,the existing problems during preparation were pointed out,and their future development direction as the catalyst carrier of vehicle exhaust was prospected.

The extensive application of dolomite in the fields such as refractories and magnesium smelting was reviewed.The challenges and in-depth research direction of dolomite in the future were pointed out.