查看更多>>摘要：In order to enhance the service life of refractories for melting and casting of titanium alloy,preparation of yttrium oxide coatings on the refractories surface is an effective solution.The improvement of thermal shock stability of the coating is beneficial to its spalling resistance during the high-temperature service,and the available slurry with good performance is the prerequisite.The effects of the varieties and contents of dispersant(sodium tripolyphosphate,sodium hexam-etaphosphate,sodium pyrophosphate,citric acid and polycarboxylate ammonium salt)and binder(aluminum dihydrogen phosphate,zirconium acetate and yttria sol)on the stability,rheological and thixotropic properties of yttrium oxide water-based slurry were investigated,and the effects of slurry composition design on the thermal shock resistance of the coating were focused.The results showed that the introduction of polycarboxylate ammonium salt as dispersant significantly improved the stability of the slurry,and the varieties of the binders had significant effects on the dispersibility of the slurry.When aluminum dihydrogen phosphate and polycarboxylate ammonium salt were used as binder and dispersant,respectively,the slurry had better stability,suitable rheological and thixotropic properties.By using aluminum dihydrogen phosphate as binder,the coating had good thermal shock resistance and no obvious cracks were observed for the coating after thermal shock,which was attributed to the yttrium aluminate binding phase generated in the coating.An effective method was provided for preparing yttrium oxide coatings with enhanced thermal shock resistance applied in the process of titanium alloy melting and casting.
查看更多>>摘要：Ti(C,N)concentration was found to be lower on the hearth sidewall of a blast furnace and increased gradually toward the bottom of the blast furnace.The Ti(C,N)protective layer in a blast furnace is thin.Therefore,the formation of a Ti(C,N)protective layer was promoted by studying the heterogeneous nucleation principle of titanium compounds on different substances and regulation measures for the deposition process of titanium compounds on refractories or impurities.The lattice disregistry between the titanium compounds and the main components in the refractory or the main impurities in the protective layer was calculated using a two-dimensional disregistry equation to study the heterogeneous nucleation principle of titanium compounds.The results revealed that in refractory materials,the heterogeneous nucleation of carbonitride is weak when C,SiO2,and Al2O3 are used as heterogeneous nucleation substrates,and the heterogeneous nucleation of carbonitride is strong when TiO2 and SiC are used as heterogeneous nucleation substrates.As nucleation phases,TiC,TiN,Ti(C0.3,N0.7),and Ti(C0.5,N0.5)have similar heterogeneous nucleation ability in single component refractory,and the type of carbonitride has little effect on the lattice disregistry.The impurities in the protective layer as the substrate phases are not conducive to the heterogeneous nucleation of carbonitride.When CaS was used as the substrate phase,the heterogeneous nucleation ability of carbonitride was the worst.Both carbon and alumina were not conducive to the heterogeneous nucleation of carbonitride,but carbon was more unfavourable than alumina.
查看更多>>摘要：Conventional MgO-C bricks(graphite content＞14 wt.％)produce a great deal of greenhouse gas emission,while low-carbon MgO-C bricks have serious thermal shock resistance during high-temperature service.To enhance the high-temperature mechanical property and thermal shock resistance of low-carbon MgO-C bricks,a novel route of introducing ZrSiO4 powder into low-carbon MgO-C bricks was reported in such refractories with 2 wt.％flaky graphite.The results indicate that the low-carbon MgO-C brick with 0.5 wt.％ZrSiO4 addition has the maximum hot modulus of rupture at 1400 ℃ and the corresponding specimen fired in the carbon embedded atmosphere has the maximum residual strength ratio(98.6％)after three thermal shock cycles.It is found that some needle-like A1ON and plate-like Al2O3-ZrO2 composites were in situ formed in the matrices after the low-carbon MgO-C bricks were coked at 1400 ℃,which can enhance the high-temperature mechanical property and thermal shock resistance due to the effect of fiber toughening and particle toughening.Moreover,CO2 emission of the newly developed low-carbon MgO-C bricks is reduced by 58.3％per ton steel after using them as the working lining of a 90 t vacuum oxygen decarburization ladle.
查看更多>>摘要：Lightweight refractory materials with thermal insulation properties and erosion resistance are advantageous for high-temperature applications.Lightweight zirconia refractories were prepared using starch as a pore-forming agent,basic magnesium carbonate as a stabilizer,and nano-zirconia as an additive.The effects of the nano-zirconia content on the pore and thermal insulation properties of the lightweight zirconia refractories were investigated based on the porosity,phase composition,microstructure,and thermal conductivity.Nano-zirconia was shown to have a high surface energy,and its addition effectively increased the driving force for sintering,reduced the sintering temperature,and promoted the sintering reaction,thereby reducing the apparent porosity and improving the density of the prepared material.Owing to the superplasticity of nano-zirconia,the surface stress caused plastic deformation between particles,which increased the migration rate of grain boundaries and trapped more gas inside the material before it diffused to the surface,thereby enhancing the closed porosity of the material.The presence of closed pores could extend the thermal conduction path,decrease the conduction rate,and hinder the conduction effect to effectively reduce the thermal conductivity of the material.At a nano-zirconia content of 0.75 wt.％,the prepared lightweight zirconia had the highest closed porosity and the lowest thermal conductivity.The apparent porosity,closed porosity,and total porosity of the material were 2.8％,7.0％,and 9.8％,respectively,and the thermal conductivity at 800 ℃ was 1.37 W m-1 K-1.
查看更多>>摘要：Magnesia-chrome porous purging plugs are crucial functional components to remove inclusions and stabilize the flow field during iron and steel smelting.However,practical applications of magnesia-chrome porous purging materials are still hampered by the poor scouring resistance to molten steel and unstable air permeability owing to their low mechanical properties and uncontrollable pore structure.Therefore,the particle-packing type magnesia-chrome porous purging mate-rials reinforced by in situ formed spinel were prepared using fused magnesia-chrome particles and Al powders as major raw materials.The results show that in situ formed spinel solid solutions in bonding phase led to the decreased median pore size and increased pore surface fractal dimension from the reactions between Al powders and magnesia-chrome particles and along with high-temperature sintering,bonding between magnesia-chrome particles and the resultant mechanical properties of materials were greatly elevated.Besides,the results of air permeability tests and polynomial fitting indicated that the formation of spinel solid solutions was the main contributing factor for controllable air permeability,and pressure drop of porous purging materials was positively correlated with surface fractal dimension of pores.Moreover,the as-prepared porous purging materials added with 6 wt.％Al powders obtained the maximum cold crushing strength(54.2 MPa)and hot modulus of rupture(12.9 MPa)with median pore size of 24.06 μm and fitting non-Darcian permeability coefficient of 0.97 × 10-6 m.
查看更多>>摘要：A systematic experimental study was conducted on the similarities and differences in the reactions between commonly used rare earth elements(REEs)and frequently used refractories in the steelmaking industry.The results indicate that the reaction behaviors of La,Ce,and Y with MgO,Al2O3,and MgO·Al2O3 crucibles differed significantly.The consumption rates of La,Ce,and Y in the molten steel were in descending order of La＞Ce＞Y for smelting with all three kinds of crucibles.As the REEs reacted with the crucible,the contents of Mg and Al showed a trend of first increasing and then decreasing.Under laboratory-scale smelting conditions,the reactions related to REEs were dominated by steel-crucible reactions,and the contact area between the unit mass of molten steel and refractory materials mainly determined the consumption rates of REEs.La-and Ce-crucible reactions generated loose and porous reaction interfaces;however,Y-crucible reactions generated a dense Y2O3 layer,dramatically suppressing the consumption rate of Y.Dynamic cal-culation indicated that the reactions between rare earth and different refractory materials were first-order reactions.The crucible materials significantly affected the product type and morphology of the steel-crucible reaction interfaces,thereby influencing the consumption rate of REEs.The reactions between REEs and refractories must be seriously considered,especially for small-scale smelting.
查看更多>>摘要：In order to explore the corrosion mechanism of Al2O3-C refractories in the mold flux bearing MnO,the immersion test of Al2O3-C refractories in CaO-SiO2-CaF2-MnO slag with different MnO contents was carried out at 1550 ℃.The results show that Mn particles were observed in the slag after experiment,due to the reduction of MnO by graphite in refractories.Large amounts of graphite were observed at the interface between refractories and slag,indicating that the oxidation of graphite is limited by the poor contact between graphite and molten slag.Therefore,the oxidation of graphite is not the main cause of damage to refractories.A small quantity of CaO·2Al2O3(CA2)and CaO·6Al2O3(CA6)adjacent to Al2O3 grain was detected at the slag/reaction layer interface.CA2 and CA6 possess relatively high melting points,which is beneficial to hindering the further penetration of slag.However,the dissolution of Al2O3 into slag is still the main cause for refractories damage.The increase in the MnO content of mold slag decreases the viscosity and then results in the severe corrosion of Al2O3-C bricks.
查看更多>>摘要：Refractories have an important effect on the cleanliness of molten steel.The interaction between CeAlO3 refractories and Ce treated steel was explored and compared with that between Al2O3 refractories and Ce treated steel.The results show that the Ce content in steel decreases sharply after contact with Al2O3 refractories and the pick-up of dissolved Al occurs.Compared with the test of Al2O3 refractories,the loss of Ce content is less in the test of CeAlO3 refractory,and the total oxygen content and dissolved Al content in steel increase less.The dense and continuous Ce2O2S interface layer is observed at the CeAlO3 refractories/steel interface,which can serve as the metallurgical isolation layer and hinder the further interaction between refractories and steel.Therefore,the higher steel cleanliness and less penetration of refractories by molten steel are obtained in the test of CeAlO3 refractories.The CeAlO3 refractories show a promising prospect in the production of clean Ce treated steel.
查看更多>>摘要：ZrB2-based ceramic composites were prepared by spark plasma sintering using ZrB2 powder prepared by molten salt method as raw material and SiC and nano-graphite as additives.The effects of nano-graphite addition on the physical properties and oxidation resistance of ZrB2-based ceramic samples were investigated.The results show that the addition of an appropriate amount of nano-graphite can effectively improve the density of ZrB2-based ceramic composites and improve the physical properties of the materials.The flexural strength of the ceramic sample with 8 vol.％nano-graphite reached 418.54 MPa,which was 53.14％higher than that of ZrB2-SiC ceramic material(273.31 MPa),and its oxidation resistance was also significantly improved.It demonstrats that the addition of an appropriate amount of nano-graphite can effectively improve the physical properties and oxidation resistance of ZrB2-SiC ceramic composites.Via prolonging its service life in application and promoting the development of ZrB2-based ceramic composites,it is of great significance for clean steel smelting.
查看更多>>摘要：ZrO2-strengthened porous mullite insulation materials were prepared by foaming technology utilizing ZrSiO4 and Al2O3 as primary materials and Y2O3 as an additive.The effects of Y2O3 contents on the phase composition,microstructure,mechanical properties,and heat conductivity of the porous mullite insulation materials were investigated.A suitable Y2O3 content could promote phase transition of monoclinic ZrO2(m-ZrO2)to tetragonal ZrO2(t-ZrO2),reduce pore size,and improve the strengths of as-prepared specimens.The cold crushing strength and bending strength of as-prepared specimens with a 119 μm spherical pore size using 6 wt.％Y2O3 were 35.2 and 13.0 MPa,respectively,with a heat conductivity being only 0.248 W/(m K).
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