Investigation of Microstructure and Phase Composition of Chromic Oxide, AZS/Cr and High-alumina Refractories after Exposure of Basalt and Aluminaboronsilicate Glasses Melts

The microstructure and phase composition of high-alumina,chromic oxide,and AZS/Cr refractories containing 30%and 60%(by mass)Cr_(2)O_(3) after exposure to aluminaboronsilicate glasses and basalt melts depending on the type of melts and temperature have been studied.The mechanisms of refractory corrosion by the used melts and the factors contributing to the inhibition of corrosion development have been investigated by the method of petrographic analysis.On the basis of obtained results,the use of high-alumina,chromic oxide,and AZS/Cr refractories in the sections of glass furnace linings,experiencing the intensive impact of aluminaboronsilicate glasses and basalt melts,has been confirmed and scientifically substantiated.

How Marie Sklodowska-Curie Doctoral Networks Can Support European Refractory Ecosystem in Context of The European Green Deal

The movement of the Iron&Steelmaking(I&S)industry towards Net-Zero emissions and digitalized processes through disruptive,breakthrough technologies will be achieved through the use of Hydrogen.The biggest challenge for the refractory industry is to continue to meet the performance expectations while,at the same time,moving to a more sustainable production direction.The complexity and urgency of these technological changes,highlighted by the European Green Deal,requires ambitious,international,interdisciplinary and intersectoral projects,bringing together institutes from across the global value chain,to carry out cutting edge research.The European Union,through its flagship doctoral training program,MSCA,has,and continues to support research and development as well as the promotion of the refractory industry in Europe.An introduction to two MSCA projects and some of the results achieved are highlighted within this article.

Effect of Slag Basicity on Alumina Dissolution and Diffusivity:A High-temperature Confocal Laser Scanning Microscopy Study

Alumina is one of the crucial and extensively utilized refractory components.As the refractory wear due to dissolution at elevated temperatures during operation is a major threat to refractory lifespan,quantifying dissolution is important for developing cost-effective and resource-efficient refractories.This study investigated the dissolution of alumina particles in two silicate and one calcium aluminate slags at 1450,1500,and 1550°C using high-temperature confocal laser scanning microscopy(HT-CLSM).Dissolution was quantified in terms of diffusivity,with all influencing factors,including Stefan flow and bath movement,incorporated into the determination process.The trends observed in total dissolution time and diffusivity in three slags at three experimental temperatures could not be explained solely on the basis of slag basicity.Two parameters,considering the influencing factors,were introduced to explain these trends.Furthermore,the linear trend observed in Arrhenius plots of diffusivities supports the diffusivity results.Additionally,good agreement between the diffusivities of alumina in one silicate slag obtained via CLSM and rotating finger test investigations verified the reliability of the results.

Effect of ZrC Modified Graphite on Structure and Properties of Low-carbon Al_(2)O_(3)-C Refractories

To address the issues of reduced performance and shortened lifespan during the low-carbonizating process of Al_(2)O_(3)-C refractories,nano-crystalline ZrC modified graphite was prepared using Zr powder and flake graphite as raw materials,with NaCl and NaF mixed salt serving as the medium.The flake graphite was gradually replaced by ZrC modified graphite in the preparation of Al_(2)O_(3)-C refractories,and its impact on the material’s structure and properties was investigated.The results indicate that,compared to samples with only flake graphite,the introduction of 1 mass%to 5 mass%nano-crystalline ZrC modified graphite can significantly enhance the mechanical performance of low-carbon Al_(2)O_(3)-C refractories.When 5 mass%ZrC modified graphite is added,the mechanical properties of the samples are optimal,with the cold modulus of rupture and elastic modulus reaching 22.5 MPa and 65.0 GPa,respectively.

Study on Chrome-free Purging Plugs for Steel Ladles

Purging plug refractories in China typically contain around 3 mass% of super-fine chromium oxide in the matrix in order to improve the performance of the purging plugs, primarily, slag corrosion and wear resistance. Alternatives to chromium oxide containing refractories have gained interest due to health concerns related to the formation of soluble chromium compounds over long storage periods of refractory wastes. Super-ground reactive alumina can replace chromium oxide in purging plug refractories and this paper discussed the new reactive alumina E-SY 88 in comparison to chromium oxide in a typical purging plug castable. The mixing behaviour, wet castable properties, as well as cured, dried, and fired properties at different temperatures up to 1 600 ℃ were compared. In addition, the hot modulus of rupture, creep behaviour, thermal shock resistance and slag corrosion resistance were tested. The microstructure after slag corrosion was investigated by SEM. The results prove that E-SY 88 is an economically viable technical alternative to chromium oxide in purging plug refractories.

Regulation of Pore Structure and Hightemperature Fracture Behavior of CACbonded Alumina-Spinel Castables Based on Hydration Design

The lamellar hydrates of CAC were designed with the introduction of nano CaCO_(3)or Mg-Al hydrotalcite(M-A-H),and the effects on the green strength,pore structures,and high-temperature fracture behavior of alumina-spinel castables were investigated.The results show that nano CaCO_(3)or M-A-H stimulates rapidly the hydration of CAC and the formation of lamellar C_(4)AcH_(11)or coexistence of C_(2)AH_(8)and C_(4)AcH_(11)at 25℃.The formation of lamellar hydrates can contribute to a more complicated pore structure,especially in the range of 400-2000 nm.Meanwhile,the incorporation of well-distributed CaO or MgO sources from nano CaCO_(3)or M-A-H also regulates the distribution of CA_(6)and spinel(pre-formed and in-situ).Consequently,the optimized microstructure and complicated pore structure can induce the deflection and bridging of cracks,thus facilitating the consumption of fracture energy and enhancing the resistance to thermal stress damage.

Aluminum and Activated Alumina Powder Additions on Microwave Synthesis of Al_(4)SiC_(4)

Aiming at improving the properties of magnesia carbon materials,silicon aluminum carbide(Al_(4)SiC_(4))containing materials were prepared using industrial aluminum powder,silicon carbide powder,and graphite as raw materials,and activated alumina powder as an additive,mixing thoroughly,pressing into cylinders and then firing at 1200℃for 30 min in a carbon embedded atmosphere by the microwave method.The effects of the aluminum powder addition(20%and 24%,by mass)and activated alumina powder addition(0,3%,5%and 7%,by mass)on the microwave synthesis of Al_(4)SiC_(4) as well as the effect of the obtained Al_(4)SiC_(4) containing material on the properties of magnesia carbon bricks were studied.The results show that:compared with the samples with 20%aluminum powder,those with 24%aluminum powder generate more Al_(4)SiC_(4).With the activated alumina powder addition increasing from 0 to 7%,the amount of Al_(4)SiC_(4) generated increases first and then decreases.Compared with the sample without activated alumina powder,the samples with activated alumina powder show lower bulk density and higher apparent porosity.With the activated alumina powder addition increasing from 3%to 7%,the bulk density of the samples increases first and then decreases,while the apparent porosity of the samples shows an opposite trend.The optimal additions are 24%aluminum powder and 5%activated alumina powder,and Al_(4)SiC_(4) synthesized in this sample has a hexagonal plate structure.With the synthesized Al_(4)SiC_(4) containing material added,the magnesia carbon brick has slightly increased cold modulus of rupture,basically the same modulus of elasticity and improved oxidation resistance.

Effect of CaO Impurity on Mullite Formation from SiO_(2) Gel and Al_(2)O_(3) Powders

To broaden the application of SiO_(2) sol-bonded castables,using micro-or nano-Al_(2)O_(3) powder and SiO_(2) gel powder as the main raw materials,the effects of CaO impurity on the formation of mullite by the reaction of Al_(2)O_(3) and SiO_(2) at different temperatures(1350,1400,1500,and 1600℃)in different atmospheres(oxidation atmosphere and reduction atmosphere)were studied.The results show that in the oxidizing atmosphere,the introduction of CaO can promote the formation of mullite.When the temperature increases from 1350℃to 1600℃,the amount of mullite formed gradually increases.In the reducing atmosphere,the introduction of CaO is not conducive to the formation of mullite,and the amount of mullite decreases with the increasing temperature.The smaller the particle size of Al_(2)O_(3),the more easily it reacts with SiO_(2) gel powder to form mullite.

The Influence of Biomass Cokes on the Microstructure and Thermal Shock Resistance of MgO-C Refractories

In this study,biomass cokes from sunflower seed hull(SFSH)and wood pellets(WP)were added to a MgO-C batch(3 mass%C)to replace 1.1 mass%of graphite.After hardening and carbonizing the samples,the influence of the biomass cokes on the microstructure and thermal shock resistance was investigated.The replacement of flaky graphite by carbonized WP and SFSH reduced the bulk density and increased the apparent porosity after pressing and carbonization,but the degree was only marginal.This was confirmed by SEM investigations,where the biomass-coke containing samples exhibited a microstructure with a higher amount of pores between the fine MgO grains.The thermal shock resistance of the porous wood pellet coke containing MgO-C is at the same level as the reference sample but not superior to it.

Effects of Al_(2)O_(3)-SiO_(2) Raw Material Types on Properties of Anorthite Based Insulation Refractories

To optimize their Al_(2)O_(3)-SiO_(2) raw materials,anorthite based insulation refractories were prepared by the in-situ sintering process combined with the foaming method after sintering at 1350℃for 3 h,using green and pollution-free kaolin,kyanite,andalusite and sillimanite as Al_(2)O_(3)-SiO_(2) raw materials,respectively,and industrial CaCO_(3) as the CaO source.Effects of Al_(2)O_(3)-SiO_(2) raw material types on the physical properties,phase composition and microstructure were investigated.The results are as follows.All samples prepared by different Al_(2)O_(3)-SiO_(2) raw materials have hexagonal flake anorthite and a small amount of mullite and corundum.Their bulk density and thermal conductivity decrease in the order of using kaolin,andalusite,kyanite and sillimanite as the Al_(2)O_(3)-SiO_(2) raw material,but their apparent porosity increases.Moreover,in the sample with kaolin,the bonding between anorthite crystals on the pore walls is closer than that of the other samples,which is conducive to increasing the cold crushing strength.The bonding between anorthite crystals on pore walls gradually decreases in the order of using kyanite,andalusite and sillimanite as the Al_(2)O_(3)-SiO_(2) raw material,thus their cold crushing strength decreases accordingly.In comprehensive consideration,the properties of the sample from kyanite are the optimal.Its apparent porosity,thermal conductivity and cold crushing strength are 84.6%,0.141 W·m^(-1)·K^(-1) and 1.89 MPa,respectively.

Investigation on Effect of Composition on the Drying of Castables with Cement Binder

Monolithic refractory castables comprising a hydraulic bond are still used in a vast majority of cases because of their flexibility and robustness,despite many developments for chemical as well as non-cement castable binders.The drying can however be a challenge,in particular for deflocculated dense castables of the low cement castable range.Many publications have been released on this topic for the last ten years,but they often focused on the drying mechanisms or on the addition of drying aids.This paper presents some experimental results on the effect of the composition on the drying properties,especially on the effect of silicon carbide,used for its high thermal conductivity,and on the matrix system.It also introduces two laboratory tests to study and iteratively improve the drying schedule of a given castable lining.The results show that the spalling resistance and the vapor pressure build-up are significantly influenced by the formulation.It is also shown that the castable properties after drying can be altered if the heating rate is very high.

The Role of the Size Effect on the Drying of Refractory Castables—How Its Under-standing Could Narrow the Gap between Laboratory Studies and Industrial Reality

Refractories have unique capabilities such as sustaining their shape and properties at extreme conditions such as the combination of high temperatures and thermal shock,contact with molten metals and slags and in some circumstances resistance to erosion from abrasive particles.Given the large processing output of the heavy industries such as the cement and steel ones which both require high temperature processes,the refractories structures span various meters and weight of several tons.As the water removal stage of hydraulic bonded castables in industrial sites takes hours(10-60 h)due to the risk of explosive spalling,efforts to mitigate it are commonly studied.This has provided theoretical understanding of the general aspects of drying and important tools,such as the thermogravimetry analysis(TGA),for the design of refractory compositions with higher explosive spalling resistance.However,the optimization of this process is still far from the industrial reality especially because the actual linings that require the drying are orders of magnitude larger than the samples considered in the laboratory tests.Therefore,this study proposed the analysis of the sample volume effect on the water removal dynamics through TGA of high alumina castables with calcium aluminate cement.Conventionalφ5 cm×5 cm cylindrical samples were assessed in a laboratory scale equipment whereas macro TGA were carried out considering 20 cm×20 cm×20 cm and 30 cm×30 cm×30 cm cubic samples.Additionally,the effect of polymeric fibers was also considered.It was found out that the different thermal gradients within the macro TGA samples resulted in an inflection on the sample’s heating rate and that the mass loss was affected by the volume considered,especially for the composition without additives.These findings highlight the requirement of carefully taking into consideration the different dimensional sizes and thermal gradients in the samples when analyzing and interpreting the laboratory studies,and especially when trying to extrapolate such results to the industrial reality.

Application of Thermodynamic Database to Corrosion of ZrO_(2) Containing Submerged Entry Nozzle in Steel Continuous Casting Process

The CALPHAD thermodynamic databases are very useful to analyze the complex chemical reactions happening in high temperature material process.The FactSage thermodynamic database can be used to calculate complex phase diagrams and equilibrium phases involving refractories in industrial process.In this study,the FactSage thermodynamic database relevant to ZrO_(2)-based refractories was reviewed and the application of the database to understanding the corrosion of continuous casting nozzle refractories in steelmaking was presented.

Exploring Dry-out Behaviour and Explosion Resistance of Microsilica-gel Bonded No-cement Castables

Cement-free castables have attracted significant attention due to their superior thermal-mechanical properties and rapid dry-out in comparison to cement-bonded refractory castables.However,drying industrial-scale specimens can pose more challenges than lab-scale samples.In this study,the dry-out behavior and explosion resistance of microsilica-gel bonded nocement castables(NCCs)were investigated on both lab-and industrial-scale specimens,employing various drying agents.First,the fast dry-out mechanism was assessed using thermogravimetric analysis(TGA),differential scanning calorimetry(DSC),and scanning electron microscopy(SEM)on lab-scale small samples.Then,the drying behavior of industrial-scale large samples(300 mm×300 mm×300 mm cubes,approximately 80 kg)was studied using a unique macro-thermo-balance(macro-TGA).The results showed that EMSIL-DRY^(®)reduced the temperature level for maximum dewatering rate and effectively prevented explosions during heat-up,compared to other polymer fibres.The use of a specialty drying agent(EMSIL-DRY^(®))significantly improved the explosion resistance,as demonstrated by the production of a perfect 400 kg block fired to 850℃at a rate of 50℃·h^(-1).This research contributes to the understanding and application of cement-free castables in industrial settings.

Thermomechanical Modelling of Industrial Vessels that Contain Refractory Masonry Linings

Some refractory linings that protect metallic vessels from the hot temperature of the products they contain are made of masonries with or without mortar.The joints play an important role,reducing the stresses in the masonries during heating.Furthermore,the presence of these joints makes the behaviour of the masonry nonlinear and orthotropic.To perform a thermomechanical simulation using a finite element method of an industrial vessel that contains hundreds or thousands of bricks and joints,microscopic models are not suitable due to the high computational time and the management of the behaviour of the joints(opening/closing)which affects the convergence.To overcome these problems,it is proposed to replace the masonry by a homogeneous material that has a behaviour equivalent to the set of bricks and joints,using a periodic homogenization technique.Since the joints can be closed or open,the equivalent material will have a different behaviour according to the joint state.Furthermore,refractory materials have an elastic-viscoplastic behaviour at high temperatures.So,the equivalent material will have an orthotropic elastic-viscoplastic behaviour,requiring a nonlinear homogenisation technique.An overview of this approach developed at University of Orléans is presented with two industrial applications(blast-furnace and steel ladle).

Effect of Zircon Addition on Properties of Corundum Porous Materials

This paper aims to improve the corrosion resistance of dispersive purging plugs.White fused corundum particles and fine powder,α-Al_(2)O_(3) micropowder,Cr_(2)O_(3) micropowder,Guangxi clay and zircon powder were used as the main raw materials.The mass ratio of white fused corundum particles and fine powder was fixed at 85:15,and 0,1%,2%,or 3%(by mass)of zircon fine powder was added to replace the same amount of white fused corundum fine powder.The corundum porous material was prepared by the particle stacking pore-forming method at 1650℃for 3 h.The effect of the zircon addition on the properties and microstructure of porous materials was investigated.The results show that:after adding zircon,the permeability of the porous material increases,the cold and hot strengths increase obviously,and the expansion rate after firing decreases.When the addition of zircon is 2%,the comprehensive performance of the specimen is optimal with the smallest linear change rate and the highest permeability.

Performance Assessment on Corrosion Resistance of Refractory Materials Based on High-temperature Machine Vision Technology

Refractory materials,as the crucial foundational materials in high-temperature industrial processes such as metallurgy and construction,are inevitably subjected to corrosion and penetration from high-temperature media during their service.Traditionally,observing the in-situ degradation process of refractory materials in complex high-temperature environments has presented challenges.Post-corrosion analysis are commonly employed to assess the slag resistance of refractory materials and understand the corrosion mechanisms.However,these methods often lack information on the process under the conditions of thermal-chemical-mechanical coupling,leading to potential biases in the analysis results.In this work,we developed a non-contact high-temperature machine vision technology by the integrating Digital Image Correlation(DIC)with a high-temperature visualization system to explore the corrosion behavior of Al2O3-SiO2 refractories against molten glass and Al2O3-MgO dry ramming refractories against molten slag at different temperatures.This technology enables realtime monitoring of the 2D or 3D overall strain and average strain curves of the refractory materials and provides continuous feedback on the progressive corrosion of the materials under the coupling conditions of thermal,chemical,and mechanical factors.Therefore,it is an innovative approach for evaluating the service behavior and performance of refractory materials,and is expected to promote the digitization and intelligence of the refractory industry,contributing to the optimization and upgrading of product performance.

Microwave-assisted Synthesis of Al_(4)SiC_(4) and Its Effect on Properties of MgO-C Refractories

Al_(4)SiC_(4) was synthesized from Al powder, silicon carbide, and graphite by microwave sintering, and characterized by XRD and SEM. Then the synthesized material was added to the magnesia carbon refractory brick to study its effect on the oxidation resistance, apparent porosity, bulk density, elastic modulus, and modulus of rupture. It is found that Al_(4)SiC_(4) can be synthesized by microwave sintering at 1 300 ℃ and the addition of Al_(4)SiC_(4)-containing material as an antioxidant can enhance the oxidation resistance of the magnesia carbon refractory brick.

Research Progress of Additives to Improve Hydration Resistance of Magnesia-calcium Materials

Magnesia-calcium materials have stable hot performance,good resistance to the erosion and corrosion of liquid steel and steel slag,and a special role in purifying liquid steel,so they are widely used in iron and steel industry.However,hydration of magnesia-calcium materials seriously restricts their use,so researches have been done to improve their hydration resistance,obtaining a series of achievements.In this paper,the improvements on the hydration resistance of magnesia-calcium materials by additives in recent 20 years were presented,and their mechanisms were summarized.

书信

Dear readers:The refractory industry is entering into an exciting new era.If we look back over recent decades,we see an innovative industry has responded to the needs of the refractory consuming industries,with significant reductions in refractory consumption with higher performance.