Effect of Al Powder and Si Powder Additions on Structure and Properties of Unburned Magnesium Aluminate Spinel Refractories

Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material,phenolic resin as the binder,aluminum powder(2%,4%,and 6%by mass)and silicon powder(when Al powder addition is 4%,Si powder addition varies:1%and 2%,by mass)as additives.The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures(1000,1400,and 1600℃for 3 h)were studied.The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1000 or 1400℃,and meanwhile AlN reinforcement phase forms in the matrix,which greatly improves the hot modulus of rupture of the samples at 1400℃;however,the heat treatment at 1600℃has little influence on the strength;the addition of Al powder and Si powder results in the formation of low melting point phases,greatly reducing the hot modulus of rupture.However,the low melting point phases promote sintering,which enhances the density and the cold modulus of rupture,and decreases the volume change during heating.The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only.

Effect of Sc_2O_3 addition on densification and microstructure of different spinelized magnesium aluminate spinels

The densification and microstructure of different spinelized magnesium aluminate spinels（MAS） were studied adding Sc_2O_3 as additive. Sintered products were then characterized in terms of densification, phase analysis, quantitative elemental analysis and microstructure. The results show that Sc_2O_3 is found to be beneficial for the densification of MAS. Sc_2O_3 has a more significant effect on the densification of partially spinelized MAS batch than that of fully spinelized MAS batch. At the sintering temperature of 1650 °C, the bulk density of sintered products of partially spinelized powders increases by 0.243 g/cm3 as the Sc_2O_3 content increases from 0 to 4%（mass fraction） and that of fully spinelized powder increases by 0.14 g/cm3. Compared with the sintered samples prepared from the fully spinelized powder, the sintered samples using the partially spinelized powders as raw materials have more compact microstructures.

Two-step sintering of magnesium aluminate spinels and their corrosion in Na_3AlF_6-AlF_3-CaF_2-Al_2O_3 bath

New types of refractory materials need to be developed for designing the man-made ledge of the Hall-Heroult cell for aluminum electrolysis, which are currently constructed by frozen ledge.Magnesium aluminate spinel （MAS） as potential candidate materials was prepared by two-step sintering. The densification and grain growth of the MAS wereinvestigatedbytheArchimedes drainage method and scanning electron microscope （SEM）. All the specimens were corroded in aNa3AlF6-AlF3-CaF2-Al2O3bath to assess the corrosion resistance. The results show that a MAS material with a high relative density of 99.2% and ahomogeneous microstructure is achieved under two-step sintering conditions. The corrosion mechanisms of MAS inNa3AlF6-AlF3-CaF2-Al2O3 bathare mainly proposed by dissolution of MAS, formation of aluminum oxide, and diffusion of fluorides. The MAS prepared by two-step sintering exhibits good corrosion resistance to theNa3AlF6-AlF3-CaF2-Al2O3bath.

Role of Calcium Magnesium Aluminate in Carbon-containing Bricks for Steel Ladle

Calcium magnesium aluminate,with the commercial name of MagArmour,is a synthetic material consisting of 70 mass%Al_(2)O_(3),20 mass%MgO and 10 mass%CaO,approximately.It is characterized by porous microstructure,intergranular aluminates phases and micro-crystalline spinel.Since globally launched in 2017,MagArmour has been successfully applied to various carbon-containing refractories serving for steel refining process.Lots of cases have demonstrated the role of MagArmour in enhancing the service life of carbon containing bricks for ladle lining.The benefits embody in formation of protective coating on hot surface,relief of drilling corrosion in joint positions,and elimination of grooves or cracks caused by mechanical stress concentration.In addition,MagArmour is effective in protecting graphite from deep oxidization so as to be capable of replacing the metallic or carbide anti-oxidants in carbon-containing bricks entirely.By means of chemical analysis and microstructural dissection,postmortem investigations on the used MgO-C bricks from both metal and slag zones of 120t steel refining ladle were conducted to clarify the working mechanism of MagArmour.The formation of protective coating on hot face is attributed to the dissolution of micro-crystalline spinel into contacting slag,which changes the slag chemistry so as to enhance viscosity.The improvement in corrosion/erosion resistance is highly related to the porous microstructure and dispersive aluminates.As well known,evaporation of Mg,Al and SiO,and/or internal migration,occurs in MgO-C bricks at elevated temperatures.The gaseous phases are absorbed by MagArmour particles due to the high surface area of porous microstructure and condense as corresponding oxides.These oxides react with the intergranular calcium aluminates forming liquid phase.With increasing temperature,the liquid phase seeps into the matrix under capillary force.The increased liquid amount improves the flexibility of the matrix and thus releases the internal stresses concentration resulting from mechanical stress and temperature gradient.Meanwhile,densification of the matrix microstructure occurs under the static pressure generated by liquid steel and molten slag,which blocks the channels of oxygen infiltration.

Development of Magnesium Aluminate Spinel Castable for Roof of EAF with High Molten Iron Charging Ratio

Specimens of magnesium aluminate spinel castable and calcium aluminate cement bonded bauxite based castable were prepared using special bauxite （particle size ≤8 mm ） and sintered magnesia as aggregates, SiO2 micropowder, α-alumina micropowder and calcium aluminate cement as binders, drying, firing at 1 350 ℃ and 1 500 ℃ for 3 h, respectively. The bulk density, cold modulus of rupture, cold crushing strength, permanent change in dimensions on heating, thermal shock resistance and slag resistanee were determined. The results show that compared with calcium aluminate cement bonded bauxite based castable, the magnesium aluminate spinel castable has higher cold crushing strength after drying, better slag resistance but worse thermal shock resistance. Magnesium aluminate spinel based roof of EAF with high molten iron charging ratio has a longer service life.

Chinese Standards on Refractories Magnesium Aluminate Spinel

1 Scope This standard specifies the terms, definitions, classifications, technical requirements, test methods, inspection rules, packing, marking, transportation, storage, and quality certificate of magnesium aluminate spinel. This standard is applicable to the magnesium alu- minate spinel prepared by sintering method or electric mehing method with raw materials of industrial alumina or bauxite, and light burnt magnesia.

Synthesis of Magnesium Aluminate Spinel-corundum Composite with Waste Slide Plate and Magnesia Carbon Brick

Magnesium aluminate spinel -corundum composite was prepared with waste slide plate and magnesia carbon brick. Microstructure and sintering ability of as-prepared magnesium aluminate spinel -corundum composite were investigated with XRD, SEM, and DSC/TG. With the addition of waste slide plate increasing or synthesis tem- perature rising, the bulk density of the specimen increases and the apparent porosity decreases, but the crystallinity of the specimen decreases and the magnesium alaminate spinel phase increases. The obtained composite contains 72% spinel and 26% corundum. Primary phase and secondary phase are bonded by glass phase. The results show that it is feasible to synthesis magnesium aluminate spinel - corundum material with waste slide plate and magnesia carbon brick.

Capture of carbon dioxide over porous solid adsorbents lithium silicate, lithium aluminate and magnesium aluminate at pre-combustion temperatures

The capturing process for carbon dioxide over porous solid adsorbents such as lithium silicate,lithium aluminate,and magnesium aluminate at pre-combustion temperatures was studied.Lithium silicate was prepared by the sol gel and solid fusion methods.The lithium silicate adsorbent was characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),scanning elec-tron microscopy(SEM),nuclear magnetic resonance(NMR),and surface area.The capturing of carbon dioxide over lithium silicate,lithium aluminate,and magnesium aluminate was explored at different experimental condi-tions such as exposure time,temperature variation,and exposure carbon dioxide pressure.The capturing process for carbon dioxide was investigated over these adsorbents with variation of their metal mole ratios.The effect of the addition of(promoter)sodium,potassium,and cesium in the lithium silicate adsorbent was explored to investigate the variation of the capture of carbon dioxide over these adsorbents.

CO_2 reforming of methane over nickel catalysts supported on nanocrystalline MgAl_2O_4 with high surface area

In this paper dry reforming of methane （DRM） was carried out over nanocrystalline MgAl2O4-supported Ni catalysts with various Ni loadings. Nanocrystalline MgAl2O4 spinel with high specific surface area was synthesized by a co-precipitation method with the addition of pluronic P123 triblock copolymer as surfactant, and employed as catalyst support. The prepared samples were characterized by X-ray diffraction （XRD）, N2 adsorption, H2 chemisorption, temperature-programmed reduction （TPR）, temperature-programmed oxidation （TPO）, temperature- programmed desorption （TPD） and transmission and scanning electron microscopies （TEM, SEM） techniques. The obtained results showed that the catalyst support has a nanocrystalline structure （crystal size： about 5 nm） with a high specific surface area （175 m2 g-1） and a mesoporous structure. Increasing in nickel content decreased the specific surface area and nickel dispersion. The prepared catalysts showed high catalytic activity and stability during the reaction. SEM analysis revealed that whisker type carbon deposited over the spent catalysts and increasing in nickel loading increased the amount of deposited carbon. The nickel catalyst with 7 wt% of nickel showed the highest catalytic activity.

Preparation and Luminescent Properties of BAM Blue Phosphor for PDP and CCFL

The Ba x-0.05MgAl 10O 16+x∶Eu 2+ 0.05 (0.88≤x ≤1.02) phosphors with different Ba 2+ content and the Ba 0.85MgAl 10O 16.94∶Eu 2+ 0.09 phosphors with different fluxes (BaF 2, MgF 2, AlF 3, BaCl 2, MgCl 2, AlCl 3, H 3BO 3) were prepared by high temperature solid-state reaction method and their luminescence characteristics were studied under 254 nm excitation and vacuum ultraviolet (VUV) excitation. With the increase of the Ba 2+ content, there is an increase in the emission intensity, and when x=0.94, it reaches a maximum. Then, as the Ba 2+ content increases, the emission intensity slowly falls. The fluorides have better flux-effects than chlorides and H 3BO 3. The possible mechanism in the process of particle growth was discussed when fluorides were used as fluxes. The effect of the activator concentration on this system was also investigated. The quenching concentration is 0.13 mol in per mole host.

Crystallization Characteristic of Periclase in Clinker and Effect of Mg2+ on Hydrate of Cement Pastes

Crystallization characteristic of periclase in clinker and effect of Mg^2+ on hydrate of cement pastes were investigated. Morphologies and relative content of periclase were characterized with scanning electron microscopy and X-ray diffraction. Derivative thermogravimetry analysis and backscattered electron imaging were used to characterize the effect of Mg^2+ on hydrate of cement pastes. The experimental results show that in ample space, periclase forms octahedron structure, and subhedral or anhedral crystal is formed in limited space. Due to the accelerated burning temperature and prolonged holding time, coarse pericalase crystals are formed. Mg(OH)2 particle thickness increases due to faster crystal growth rate along c axis at later age. Mg^2+can substitute Ca^2+ in C-S-H or C-A-H to form magnesium silicate hydrate(M-S-H) or magnesium aluminate hydrate(M-A-H), and the substitution extent for C-A-H is higher than that for C-S-H. Cured in 80 ℃ water, the decalcification rate of C-A-H in pastes is higher than that cured in 50 ℃ water. M-A-H with an atomic Mg/Al ratio of 2 is formed through substitution of Ca by Mg in C-A-H.

Synthesis of MgAl_2O_4 Powder in KCI-LiCl-KF System Molten Salt

Molten salt synthesis of MgAl204 powder from industrial alumina and light calcined MgO in KCl, LiCl, and KCl- LiCl media, and the influence of KF at 500 -1 000℃ were investigated. Synthesized powders were characterized by means of XRD, laser particle analyzer, and SEM, and the synthesis mechanism of MgAl2O4 was discussed as well. The results show that （1） the molten salt composite （ KCl - LiCl） is more .[hvorable for the synthesis of MgAl2O4 than single molten salt （LiCl or KCl）, and LiCl is more favorable than KCl; （2） KF can accelerate the formation of MgAl2O 4 and decrease its forming temperature ; （ 3 ） synthesis of MgAl204 powder in the molten salts without KF is controlled by ＂template -growth＂ mechanism, but in the molten salts with KF , it is controlled by ＂template - growth＂ and ＂dissolution -precipitation＂ mechanism.

Fabrication and Properties of Closed-pore Al_2O_3-based Refractory Aggregates

A novel Al2O3 based refractory aggregate with closed-pore structure was fabricated utilizing superplastic- ity with submicro-sized Al2O3 and MgO as raw materi- als, and SiC as a high temperature pore-forming agent. The effect of MgO on porosity, phase composition and microstructure of the refractory aggregate has been inves- tigated. For comparison, the common Al2O3-based refractory aggregates and porous ones with open-pore structure were also prepared. The results indicate that the closed porosity of Al2O3-based refractory aggregate in- creases as the content of MgO increases. When the con- tent of MgO is 15 mass%, the closed and apparent poros- ities are 14.5% and 1.1%, respectively. The main phase compositions are Al2O3 and MgAl204. The formation mechanism of closed pores is that the fine-crystalline- grain Al2O3 ceramic possesses superplastic deformation ability after adding MgO at high temperatures. When SiC powder is added to the Al2O3 ceramic, the generated gases by the reaction of SiC at the sintering temperature can provide a pressure to make grain boundaries slide. Then, the gases are enclosed by crystalline grains to form the closed pores. The slag corrosion resistance of the fabrica- ted closed-pore Al2O3-based refractory aggregate is better than the common refractory aggregate and porous ones.

Single-crystal Structure of ScAlMgO_4

Crystals of scandium magnesium aluminate, ScAlMgO4, were grown from the melt prepared from stoichiometric quantities of Sc2O3, Al2O3 and MgO. Single-crystal X-ray diffraction indicates that ScAlMgO4 crystallizes in the space group R3 m with a = b = 3.2506（9） A, c = 25.152（8）A, V= 230.16（11）A^3, Z= 3, F（000） = 234,μ = 2.424 cm^-1, the final R = 0.0381 and wR = 0.1061 for 1874 observed reflections with I 〉 2σ（I）. In ScAlMgO4, all Sc atoms are coordinated octahedrally, whereas AI or Mg atoms are forming a tetrahedron, or in a triangular bipyramid if one distant O atom is included. The structure of ScAlMgO4 is characterized by { [AlMgO4]^3-}∞^2 layers parallel to the ab plane, and they are further connected into a 3-dimen-sional framework by Sc atoms via O（1） atoms between the layers.

Thermodynamic Modeling of MgO-Al_(2)O_(3)-TiO_(2) System

This scientific paper gives consideration to the information on the structure of the triple component system,in particular MgO-Al_(2)O_(3)-TiO_(2) that serves as a basis for the production of thermal resistance materials.The structure of such binary systems as MgO-Al_(2)O_(3),Al_(2)O_(3)-TiO_(2),MgO-TiO_(2) was described and the data available for the MgO-Al_(2)O_(3)-TiO_(2) system were given.Thermodynamic data on all the system compounds were also presented and used for the computation of a change in the free Gibbs energy in the temperature range form 800 K to 1900 K for the basic exchange reactions.It was established that the triangulation of the MgO-Al_(2)O_(3)-TiO_(2) system was changed in the three temperature intervals:in the temperature range lower than 1537 K TiO_(2) existed as the polymorphous modification,i.e.anatase;in the temperature range from 1537 K to 2076 K TiO_(2) existed as a polymorphous modification in form of rutile and tialite was stable;and at the temperatures above 2076 K the availability of stochiometric compound of Al4TiO_(8) was possible.In the temperature range lower than 1537 K the two-phase equilibra of Al_(2)O_(3)-MgTi2O_(5),Mg-MgALCU MgTiO_(3)-MgAl_(2)O_(4),and Mg_(2)TiO_(4)-MgAl_(2)O_(4) were stable;in the temperature range from 1537 K to 2076 K the two-phase equilibria of MgTigO_(5)-AlgTiO_(5),MgTiO_(3)-Al_(2)TiO_(5),MgTiO_(3)-Al_(2)O_(3),MgTiO_(3)-MgAl_(2)O_(4),and Mg_(2)TiO_(4)-MgAl_(2)O_(4) were stable,and above 2076 K the MgTi_(2)O_(5)-Al_(2)TiO_(5),MgTi_(2)O_(5)-Al_(4)TiO_(8),Al_(4)TiO_(8)-MgTiO_(3),Al_(4)TiO_(8)-Mg_(2)TiO_(4),Al_(4)TiO_(8)-Mg0,and Al_(4)TiO_(8)-MgAl_(2)O_(4) systems were stable.

Effect of Y_2O_3 Addition on Sintering Properties and Microstructure of Spinel Materials

The effect of Y2O3 addition on the sintering proper- ties and microstructure of spinel was investigated using alumina-rich spinel as the raw material. The phase con- stitution and microstructure of the specimens were charac- terized by XRD and SEM, and the pore structure of the specimens was measured by a mercury porosimeter. The results indicate that a viscous melt forms wrapping around spinel crystals by adding a little Y2O3 powders （1 mass% ）, yttrium alumina garnet will crystallize around spinel crystals by adding more Y2O3 powders （ 3 mass% ） ; the sintering properties of the spinel are sig- nificantly improved by adding Y2O3 powders less than 3 mass%, while they will be relatively weakened by adding Y2O3 powders more than 3 mass%.

Research on Alkali Resistance of Alumina-rich MgAl2O4 Spinel for Alkali Recovery Furnace

Chrame containing refractories are a kind of traditional material for the lining of alkali recovery furnaces, but the formation of hexavalent chrome compounds will give rise to detrimental effect on environment and human＇s health. With the gradual awakening of people＇s comciousness about environment protection, it is urgent to prepare environmental-friendly materials for alkali recovery jurnaces with high quality and long life. In this paper, alumina-rich MgAl2O4 spinel （ AR90 ） was used to replace chromite. The physical properties of dried （110 ℃ for 24 h） or fired （1 300 ℃ for 3 h） AR90 and chromite were studied, respectively. The alkali vapor method was used to determine the alkali resistance of the two materials. The results show that： （1） after drying at 110 ℃ for 24 h, AR90 specimens show higher apparent porosity and slightly lower bulk density than chromite specimens; after firing at 1 300 ℃ for 3 h, AR90 has significantly higher apparent porosity as well as higher bulk density; （2） after the alkali attack, the AR90 specimens sintered at 1 300 ℃ exhibit smaller strength change and much higher compressive strength than the chromite specimens; meanwhile, the permeability degree of alkali salt in chromite specimens is more serious than that in AR90 specimens, which indicates that AR90 possesses better alkali resistance.

Thermal Shock Resistance of Ladle Castables

High purity alumina - spinel （ A - MA ） and alumina- magnesia （A -M） castables are widely used in steel ladles due to their resistance against slag penetration and corrosion. With a calcium magnesium alumihate bond （ CMA ） excellent slag penetration resistance can be achieved which results in high wear resistance due to reduced structural spalling. This paper investigates the impact of matrix eompositions and CMA-binder content of A -MA and A -M castables on thermal shock resistance（TSR）. Standardized thermal shock tests have been applied with sample quenching from 950 ℃ down to room temperature. Results show that all castables are significantly damaged after 5 cycles despite their differences in microstructure. However, the mix with 12% CMA gave TSR that is at similar good level as the reference mix with 6% CAC （70% alumina cement ）. While a similar strength level was achieved before and after the thermal cycling, the Jormulation with 12% CMA contains 0. 6% less total CaO. The A - MA castables perform better on average than the A - M mixes with this test method. Within the group of A - M castables the mix with 18% CMA and 0. 5% SiO2 gave superior TSR, similar good as castables of the A - MA group. The introduction of CMA in an A - M tastable allows reduction of free MgO and SiO2-addition. The reduction of SiO2 has been found beneficial for the TSR. This was also found during a thermal cycling trial at high temperature between 1100 and 1 500 ℃. Here the A -M mix with 18% CMA and 0. 5% SiO2 performed better than the SiO2-free A -MA castable.

Effect of Spinels on Properties of MgO-Al_(2)O_(3) Refractories for RH Snorkels

With satisfactory high temperature properties,thermal shock resistance and mechanical properties,refractories in the MgO-Al_(2)O_(3) system have become promising alternative to MgO-Cr_(2)O_(3) counterpart used as RH snorkel lining.High purity dead burned magnesia,fused magnesia and sintered spinel were used as raw materials and sulfite pulp waste as the binder,specimens of the refractories in the Mg0-Al_(2)O_(3) system were prepared for the purpose of investigating the influences in terms of the addition of three kinds of spinels,with Al_(2)O_(3) 50%,66% and 78%,by mass,respectively,and the size of MA50 spinel on properties of the specimens.Relatively superior comprehensive properties can be achieved when 16%of MA50 spinel with sizes under 1mm is adopted.

Effect of Al-Si Alloy Addition on Properties of Fused Spinel Carbon Materials

Fused magnesium aluminate spinel carbon materials were prepared using fused magnesium aluminate spinel and flake graphite as the main raw materials and phenolic resin as the binder.The effects of the Al-Si alloy addition(0,2%,4%,6%,8%and 10%,by mass)on the properties of fused magnesium aluminate spinel carbon materials were studied.The results show that fiber materials are generated in the samples with Al-Si alloy addition,which can significantly improve the cold and hot modulus of rupture,the cold elastic modulus,and the thermal shock resistance of the samples.When the addition of Al-Si alloy is 6%-8%,the comprehensive performance of the sample is the optimum.