Effect of Hydrated Calcium Aluminate Cement on the Chloride Immobilization of Portland Cement Paste

To improve the efficiency and stability of chloride immobilization of portland cement paste,hydrated calcium aluminate cement(HCAC)prepared by wet grinding of CAC was added into portland cement paste as an additive.The immobilized chloride ratio(ICR)was evaluated,and the mechanism of chloride immobilization was researched by XRD,DTG,NMR,and MIP tests.The analysis results demonstrated that HCAC could improve the chloride immobilization capacity of portland cement paste.The mechanism was attributed to the following aspects:chemical binding capacity was enhanced via producing more Kuzel’s salt;physical adsorption capacity was reduced by decreasing the C-S-H gel;migration resistance was enhanced through refining the pore structure.

Chloride Corrosion of Reinforced Calcium Aluminate Cement Mortar

This paper describes a study on the corrosion behavior of steel reinforcement in CAC mortars via electrochemical methods including corrosion potential,electrochemical impedance,and linear polarization evaluation.Results indicate that there is a non-linear relationship between the corrosion degree of steel reinforcement in CAC mortar and the concentration of NaCl solution.The electrochemical parameters of specimens immersed in 3%NaCl solution suddenly drop at 40 days,earlier than 60 days of the reference.And the charge transfer resistivity of the specimen has decreased by 11 orders of magnitude at 40 days,showing an evident corrosion on steel reinforcement.However,it is interesting to notice that the corrosion is delayed by high external chloride concentration.The specimens immersed in 9%and 15%NaCl solutions remain in a relatively stable state within 120 days with slight pitting.The great corrosion protection of CAC concrete to embedded steel bars enables its wide application in marine.

Recovery of iron and calcium aluminate slag from high-ferrous bauxite by high-temperature reduction and smelting process

A high-temperature reduction and smelting process was used to recover iron and calcium aluminate slag from high-ferrous bauxite. The effects of w（CaO）/w（SiO_2） ratio, anthracite ratio, and reduction temperature and time on the recovery and size of iron nuggets and on the Al_2O_3 grade of the calcium aluminate slag were investigated through thermodynamic calculations and experiments. The optimized process conditions were the bauxite/anthracite/slaked lime weight ratio of 100：16.17：59.37, reduction temperature of 1450°C and reduction time of 20 min. Under these conditions, high-quality iron nuggets and calcium aluminate slag were obtained. The largest size and the highest recovery rate of iron nuggets were 11.42 mm and 92.79wt%, respectively. The calcium aluminate slag mainly comprised Ca_2 SiO_4 and Ca_（12）Al_（14）O_（33）, with small amounts of Fe Al_2O_4, CaAl_2O_4, and Ca_2Al_2SiO_7.

Effect of Curing Temperature on Intermediate Temperature Properties of Calcium Aluminate Cement Bonded Corundum Castables

In order to study the effect of the curing temperature on the intermediate temperature properties of calcium aluminate cement bonded corundum castables,the prepared castables were cured at 5,10,25,40 and 50℃,respectively,dried at 110℃ for 24 h and heat treated at 800 and 1100 ℃,respectively.Then the apparent porosity,the cold modulus of rupture and the cold crushing strength were measured.The phase composition of castable matrix specimens treated under the same conditions and the influence of the curing temperature on the intermediate temperature strength of the castables were also analyzed.The results show that with the increase of the curing temperature,the hydration degree of calcium aluminate cement increases,which promotes the uniform distribution of hydration products with AI203 after decomposition,thus enhancing the intermediate temperature strength of castables.

Mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al2O3-Na2O system during high-temperature sintering

The mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al2O3-Na2O system during the hightemperature sintering process were systematically investigated using DSC-TG,XRD,SEM-EDS,FTIR,and Raman spectra,and the crystal structure of Na4Ca3(AlO2)10 was also simulated by Material Studio software.The results indicated that the minerals formed during the sintering process included Na4Ca3(AlO2)10,CaO·Al2O3,and 12 CaO·7 Al2O3,and the content of Na4Ca3(AlO2)10 could reach 92 wt%when sintered at 1200°C for 30 min.The main formation stage of Na4Ca3(AlO2)10 occurred at temperatures from 970 to 1100°C,and the content could reach82 wt%when the reaction temperature increased to 1100°C.The crystal system of Na4Ca3(AlO2)10 was tetragonal,and the cells preferred to grow along crystal planes(110)and(210).The formation of Na4Ca3(AlO2)10 was an exothermic reaction that followed a secondary reaction model,and its activation energy was 223.97 kJ/mol.

Crystallization Kinetics of Calcium Aluminate Glasses Studied by Non-isothermal Techniques

The crystallization kinetics of 38.0CaO-38.0Al2O3-10.5BaO-6.5MgO-6.0Y2O3-1.0（Na2O＋K2O） （wt%） glass was studied by differential scanning calorimeter （DSC） and X-ray diffraction （XRD） techniques. Tile results showed that DSC curves of calcium aluminate glass have a single glass transition temperature followed by one crystallization peak for the heating rates β = 5 K/min and two crystallization temperatures T1 and T2 for β≥ 10 K/min. The activation energies of crystallization obtained from the Gao-Wang model of the first exothermal peak and the second exothermal peak of calcium aluminate glass are 340 and 662 kJ/mol, respectively. The Avrami exponents of the both crystallization peaks are approximately 2, indicating the two- dimensional crystalline growth during its transformation from amorphous to crystalline. Ca12Al14O33, Ca3Al2O6 and unknown crystalline phases firstly appear when calcium aluminate glass is heat-treated. With the extending of heat-treatment duration, BaAl2O4 phase comes out.

Effect of Different Kinds of Zinc (Ⅱ) on Early Hydration of Calcium Aluminate Cement

The early hydration of calcium aluminate cement (CAC) with different kinds of zinc (II),such as ZnSO4g7H2O,ZnO,Zn(NO3)2·6H2O and ZnCl2,was analyzed.Changes in consistency,setting time,hydration heat flow,hydration heat amount,ion concentration in solution,and hydration products were found upon the addition of different Zn^2+.The water consumption of standard consistency of CAC is decreased with different Zn^2+.Zn^2+ can delay the initial hydration of CAC.The induction period of cement with Zn^2+ is longer than that of CAC,especially the reaction time of the acceleration period is extended.Zn^2+ can promote hydration hydrate of CAC at 24 h.The characteristic diffraction peaks of CA and CA2 in CAC with different Zn^2+ are significantly reduced.It can inhibit the formation of CAH10 and promote the formation C3AH6 and AH3 in hydration products at 24 h.

Preparation and characterization of calcium aluminate by chemical synthesis

Saturated Ca（OH）2 and AlCl3 solutions were used to synthesize calcium aluminate hydrate precipitates at room temperature; high purity calcium aluminate powders with stable phases were made by calcination of the precursors at a temperature as low as 1100℃. PSD and BET analysis revealed the particles with sizes ranging from submicrometer to several micrometers and with a specific area of 13 m^2/g. The measurement of hydraulic exotherm revealed that the exothennal rate is in peak for about 2 h. The exothermal quantities are 449.24 J/g at 12 h and 488.38 J/g at 24 h. Its strength development is quick and the 1 day curing strength is almost equal to 100% of the 3 days curing strength in the mortar test.

Effect of Microsilica on Chemical Bond of Calcium Aluminate Cement Bonded Corundum Castable at Low and Intermediate Temperatures

Calcium aluminate cement bonded corundum castable specimens were prepared using brown fused corundum （8 - 5, 5 - 3, 3 - 1 mm ） , white fused corundum （ ≤ 1, ≤0. 045 mm）, micro-sized α-Al2O3 and microsilica as starting materials. This work focused on investigating the relationship between the bond change in the castable matrix and the strength of the castable with 5 mass% microsilica or without microsilica after heat treatment at 110, 800 and 1 000 ℃, respectively. Chemical bond changes between the microsilica and hy- drates of calcium aluminate cement after drying at 110 ℃ or firing at 800 ℃ were investigated by XPS and FTIR. The results show that Si-O-Al bonds form be- tween the microsilica and hydrates of calcium aluminate cement after drying at 110 ℃ or firing at 800 ℃. Therefore, the increased strength of castable specimens is attributed to the formation of Si-O-Al bonds from 110 ℃ to 800 ℃.

Effect of Calcium Aluminate Cement Variety on the Hydration of Portland Cement in Blended System

Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confi rming that the CA phase in CAC plays an important role in the delay of PC hydration.

Effect of ZnO Precursor on Properties of Calcium Aluminate Cement Bonded Corundum Castables

Calcium aluminate cement(CAC)bonded corundum based castables were prepared using tabular corundum and activated alumina as the starting materials,CAC as the binder,zinc hydroxide(Zn(OH)_(2))and basic zinc carbonate(BZC)as the ZnO precursors.The effects of the two ZnO precursors on the phase composition and the microstructure of the CAC bonded corundum based castable matrix specimens were analyzed,and the reasons affecting the hot performance of the castables were studied.The results show that Zn(OH)_(2) with a smaller particle size(d_(50)=1.26μm)is prone to agglomerate during sample preparation and generates ZnAl_(2)O_(4) spinel grains after firing,hindering the growth of CA_(6),thus decreasing the mechanical strength of the castables.BZC with a larger particle size(d_(50)=2.91μm),which shows a sound dispersity,in-situ generates nano-sized ZnO after firing,and ZnO or Zn^(2+)diffuses into calcium aluminates,promoting the sintering of CA_(2) and CA_(6),thereby enhancing the hot properties of the CAC-bonded corundum based castables.

Effect of Ga_2O_3 on Structure and Properties of Calcium Aluminate Glasses

The effect of Ga_2O_3 on the structure and properties of calcium aluminate glasses fabricated by vacuum melting process was investigated by Raman spectrum, differential scanning calorimeter（DSC）, and infrared spectrum methods. The results show that calcium aluminate glass network only consists of [AlO_4] tetrahedral units. With the gradual addition of Ga_2O_3, the quantity of [GaO_4] tetrahedral units increases. Substitution of Ga_2O_3 for Al_2O_3 results in a decrease in Tg, Tx, and Tp, and an increase in the thermal stable index ΔT. Similarly, the absorption band around 3.0 μm obviously reduces and the transparency in 4.0-6.0 μm rapidly increases with increasing Ga_2O_3 content. However, the chemical stability of calcium aluminate glasses decreases if Ga_2O_3 is introduced due to the increasing of [GaO_4] units in the glass network.

Dry reforming reaction over nickel catalysts supported on nanocrystalline calcium aluminates with different CaO/Al_2O_3 ratios

Nanocrystalline calcium aluminates with different CaO/Al2O3 ratios were prepared by a facile co-precipitation method using Poly（ethylene glycol）-block-poly（propylene glycol）-block-poly（ethylene glycol） （PEG-PPG-PEG, MW： 5800） as a surfactant. They were employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction （XRD）, N2 adsorption （BET）, temperature-programmed reduction and oxidation （TPR-TPO）, and scanning electron microscopy （SEM） techniques. Catalysts showed a relatively high catalytic activity and stability. TPR analysis revealed that the catalysts with higher CaO content are more difficult to be reduced. TPO analysis showed that the 5 wt%Ni/CA and 5 wt%Ni/C12A7 catalysts with higher CaO amount were effective against coke deposition.

Effect of Calcium Aluminate Cement Addition on Properties of Al_(2)O_(3)-SiO_(2) Based Gunning Mixes

Al_(2)O_(3)-SiO_(2) based gunning mixes were prepared with electric porcelain waste,silica fume,bauxite,quartz powder,and calcium aluminate cement(CAC)of different additions as raw materials firing at different temperatures to research the effect of the CAC addition on their phase change and properties.The results show that:from theoretical analysis of the phase diagram,with the CAC addition increasing from 8%to 14%,anorthite increases from 40.0%to 77.7%,by mass.With the rising CAC addition,the permanent linear change on heating of specimens increases;for the specimens dried at 110℃or hot-treated at 1000℃,the bulk density and the mechanical properties increase,and the apparent porosity decreases;and for those hottreated at 1300℃,the bulk density and the mechanical properties firstly increase,and then decrease,while the apparent porosity shows an opposite trend.Taking into account the phases at high temperatures and the properties,the optimal CAC addition of Al_(2)O_(3)-SiO_(2) based gunning mixes is 12%.

Agglomeration behavior of alumina inclusions and calcium aluminate inclusions on molten nickel-based superalloy surface

Understanding the interactive forces of inclusions on the surface of molten nickel-based superalloys and finding methods to disperse these inclusions help improve performance and service life.The aggregation behavior of aluminum oxide(Al_(2)O_(3))and calcium aluminate inclusions with different sizes and spacings on the surface of molten nickel-based superalloys was observed in-situ using a high-temperature confocal laser scan microscope.The attractive force acted on Al2O3 inclusions with radii of 3.5-6μm was found ranging from 6.2×10-18 to 3.6×10-15 N,and that of CaO·2Al2O3(CA2)inclusions with radii of 3-5.5μm ranging from 3.5×10-19 to 8.3×10-15 N.The capillary force acted on inclusions on the surface of nickel-based superalloy was calculated based on the Kralchevsky-Paunov model and investigated as a function of inclusion size,spacing,and composition.The calculated results were in the same trend as the experimental results.The capillary force acted on inclusions was also affected by their contact angle,the density,surface energy,and oxygen content of the molten alloy.It decreased with increasing alloy density and decreasing contact angle between inclusion with alloy.Thus,the attractive force acted on Al2O3 inclusions was smaller on the surface of molten nickel-based superalloy than that of molten steel.Decreasing the oxygen content in the molten nickel-based alloy could increase its surface energy,and the attractive force acted on the inclusions would decrease.When the oxygen content in the molten nickel-based alloy decreased from 0.05 to 0.0001 wt.%,the capillary force acted on the Al2O3 inclusions decreased from 1.7×10-18 to 3.6×10-19 N,reduced by 79%(1.4×10-18 N).

Mineral Transition of Calcium Aluminate Clinker during High-Temperature Sintering with Low-lime Dosage

The mineral transition mechanism and physicochemical property of calcium aluminate clinker sintered at 1350 ℃ were systematically studied using analytical reagent α-Al 2O 3,CaCO 3 and SiO 2 when the molar ratio of CaO to Al 2O 3 is 1.0.The results show that the formation of Ca 2SiO 4 accelerates the diffusion of CaO and Al 2O 3,which promotes the formation of CaAl 2O 4 determined by dilatometer,X-ray diffraction,Fourier transform infrared spectroscopy and scanning electron microscopy methods.CaAl 4O 7,Ca 3Al 2O 6,Ca 3SiO 5 and Ca 2Al 2SiO 7 only exist in the initial stage of reactions,the amounts of which decrease with the increase of sintering duration.Ca 3Al 2O 6 and Ca 12Al 14O 33 react with Al 2O 3 and CaAl 4O 7 to form CaAl 2O 4,while Ca 2Al 2SiO 7 reacts with CaO and Ca 12Al 14O 33 to form Ca 2SiO 4 and CaAl 2O 4.The sintered clinker contains CaAl 2O 4 and γ-Ca 2SiO 4 as well as some Ca 12Al 14O 33 when the sintering duration is longer than 1.0 h.The differential scanning calorimetry results reveal that Ca 2SiO 4,Ca 2Al 2SiO 7 and CaAl 2O 4 are formed at985 ℃,1045℃ and 1339 ℃,respectively.Increasing the sintering duration contributes to the transition of β-Ca 2SiO 4 to γ-Ca 2SiO 4,which improves the pulverization and alumina leaching property of the sintered clinker.

Effect of Iron Oxides on Activity of Calcium Aluminate Clinker in CaO-Al_2O_3-SiO_2 System

The sintering characteristics at 1350℃ and leaching property at 80℃ of calcium aluminate clinkers in the CaO-Al2O3-SiO2 （C-A-S） system with different additions of FeO and Fe2O3 were investigated. FeO inhibits the conversion of β-Ca2SiO4 to γ-Ca2SiO4 and makes the clinker not pulverizable. FeO and Fe2O3 inhibit the formation of CaAl2O4, but promote the formation of Ca12Al14O33. The interplanar spacing at （2 1 1） crystal face of Ca12 Al14O33 in the clinker increases with the increase of FeO addition, which indicates that FeO forms solid solutions in Ca12Al14O33. The clinkers with Fe2O3 addition form a new phase Ca2Fe2O5, and the amount of Ca2Fe2o5 increases with the in crease of Fe2O3 addition. Both FeO and Fe2O3 do not affect the Al2O3 leaching rate of calcium aluminate clinker in sodium carbonate solution, but they increase the molar ratio of caustic Na2O to Al2O3 in the leached liquor.

Desulphurization of Hot Metal and Ferronickel With Calcium Aluminate Fluxes

Traditionally, fluxes containing calcium fluoride and other additives are used for the treatment of hot metal and molten steel. Recently, magnesium powder or lime-Mg mixture is used more popularly in hot metal desulphurization. However, the use of calcium fluoride has been restricted due to environmental concerns, and the supply of magnesium is uncertain for the countries, which are short of magnesium resource. For those reasons, calcium aluminate fluxes are a possible alternative to replace slags containing calcium fluoride or magnesium. Calcium aluminate fluxes can be produced from three different raw materials: (1) high-quality bauxite, (2) residuals from aluminum dross treatment processes and (3) waste products from alumina production. Due to the limited amount and high cost associated with high-quality bauxite, the other two sources are preferred based on both economic and environmental considerations. The objective of this paper is to examine the use of waste slags and by-products from the aluminum industry as potential refining fluxes for the steel industry so that waste disposal from the aluminum industry can be reduced with economical and environmental benefits for both industrial sectors.

Fluoride Ion Adsorption Effect and Adsorption Mechanism of Self-Supported Adsorbent Materials Based on Desulfurization Gypsum-Aluminate Cement

The adsorption method has the advantages of low cost,high efficiency,and environmental friendliness in treating fluorinated wastewater,and the adsorbent material is the key.This study combines the inherent anion-exchange adsorption properties of layered double hydroxides(LDHs).Self-supported porous adsorbent materials loaded with AFm and AFt were prepared from a composite cementitious system consisting of calcium aluminate cement(CAC)and flue gas desulfurization gypsum(FGDG)by chemical foaming technique.The mineral composition of the adsorbent material was characterized by X-ray diffraction(XRD)and Scanning electron microscopy(SEM).Through the static adsorption experiment,the adsorption effect of the mineral composition of the adsorbent on fluoride ions was deeply analyzed,and the adsorption mechanism was revealed.XRD and SEM showed that the main hydration phases of the composite cementitious system consisting of CAC and FGDG are AFm,AFt,AH_(3),and CaSO_(4)·2H_(2)O.FGDG accelerates the hydration process of CAC and inhibits the transformation of AFt to AFm.The AFt content increased,and the AFm content decreased or even disappeared as the amount of FGDG increased.Static adsorption experiment results showed that AFm and AFt in adsorbent materials could significantly enhance the adsorption of fluoride ions.The adsorption of F^(−)in aqueous solution by PAG tends more towards monolayer adsorption with a theoretical maximum capacity of 108.70 mg/g and is similar to the measured value of 112.77 mg/g.

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.