Microstructure and physical properties of steel-ladle purging plug refractory materials

Three different castables were prepared as steel-ladle purging-plug refractory materials:corundum-based low-cement castable (C-LCC), corundum-spinel-based low-cement castable (C-S-LCC), and no-cement corundum-spinel castable (C-S-NCC) (hydratable alumina ρ-Al₂O₃ bonded). The properties of these castables were characterized with regard to water demand/flow ability, cold crushing strength (CCS), cold modulus of rupture (CMoR), permanent linear change (PLC), apparent porosity, and hot modulus of rupture (HMoR). The results show the CCS/CMoR and HMoR of C-LCC and C-S-LCC are greater than those of the castable C-S-NCC. According to the microstructure analysis, the sintering effect and the bonding type of the matrix material differ among the three castables. The calcium hexaluminate (CA₆) phase in the matrix of C-LCC enhances the cold and hot mechanical strengths. In the case of C-S-LCC, the CA₆ and 2CaO·2MgO·14Al₂O₃ (C₂M₂A₁₄) ternary phases generated from the matrix can greatly increase the cold and hot mechanical strengths. In the case of the no-cement castable, sintering becomes difficult, resulting in a lower mechanical strength.     

In-situ fabrication of Al(Zn)-Al2O3 graded composite using the aluminothermic reaction during hot pressing

In this study, the fabrication of multilayer Al(Zn)–Al₂O₃ with different volume fractions of Al₂O₃ was investigated. Al and ZnO powders were milled by a planetary ball mill, after which five-layer functionally graded samples were produced through hot pressing at 580℃ and 90 MPa pressure for 30 min. Formation of reinforcing Al₂O₃ particles occurred in the aluminum matrix via the aluminothermic reaction. Determination of the ignition temperature of the aluminothermic reaction was accomplished using differential thermal and thermogravimetric analyses. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometery analyses were utilized to characterize the specimens. The thermal analysis results showed that the ignition temperatures for the aluminothermic reaction of layers with the highest and lowest ZnO contents were 667 and 670℃, respectively. Microstructural observation and chemical analysis confirmed the fabrication of Al(Zn)–Al₂O₃ functionally graded materials composites with precipitation of additional Zn in the matrix. Moreover, nearly dense functionally graded samples demonstrated minimum and maximum hardness values of HV 75 and HV 130, respectively.     

18wt%Cr–8wt%Ni不锈钢中增塑性MnO–Al2O3–SiO2基非金属夹杂物的演变及其浸泡性能

The properties of MnO–Al₂O₃–SiO₂-based plasticized inclusion are likely to change during soaking  process due to its low melting point. In this study, the evolution of the MnO–Al₂O₃–SiO₂-based inclusion of 18wt%Cr?8wt%Ni stainless steel under isothermal soaking process at 1250°C for different times was investigated by laboratory-scale experiments and thermodynamic analysis. The results showed that the inclusion population density increased at the first stage and then decreased while their average size first decreased and then increased. In addition, almost no Cr₂O₃-concentrated regions existed within the inclusion before soaking, but more and more Cr₂O₃ precipitates were formed during soaking. Furthermore, the plasticity of the inclusion deteriorated due to a decrease in the amount of liquid phase and an increase in the high-melting-point-phase MnO–Cr₂O₃ spinel after the soaking process. In-situ observations by high-temperature confocal laser scanning microscopy (CLSM) confirmed that liquid phases were produced in the inclusions and the inclusions grew rather quickly during the soaking process. Both the experimental results and thermodynamic analysis conclude that there are three routes for inclusion evolution during the soaking process. In particular, Ostwald ripening plays an important role in the inclusion evolution, i.e., MnO–Al₂O₃–SiO₂-based inclusions grow by absorbing the newly precipitated smaller-size MnO–Cr₂O₃ inclusions.     

Porous α-Al2O3 thermal barrier coatings with dispersed Pt particles prepared by cathode plasma electrolytic deposition

Porous α-Al₂O₃ thermal barrier coatings (TBCs) containing dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED). The influence of the Pt particles on the microstructure of the coatings and the CPED process were studied. The prepared coatings were mainly composed of α-Al₂O₃. The average thickness of the coatings was approximately 100 μm. Such single-layer TBCs exhibited not only excellent high-temperature cyclic oxidation and spallation resistance, but also good thermal insulation properties. Porous α-Al₂O₃ TBCs inhibit further oxidation of alloy substrates because of their extremely low oxygen diffusion rate, provide good thermal insulation because of their porous structure, and exhibit excellent mechanical properties because of the toughening effect of the Pt particles and because of stress relaxation induced by deformation of the porous structure.     

采用HVOF涂层提高异种合金825和AISI 321 CO2激光焊件在900°C腐蚀盐环境中的热腐蚀性能

This study investigated the hot corrosion performance of a dissimilar weldment of Ni-based superalloy and stainless steel joined by CO₂-laser welding and improved by high-velocity oxy-fuel (HVOF) coating in a Na₂SO₄?60wt%V₂O₅ environment at 900°C. A dissimilar butt joint of AISI 321 and alloy 825 was fabricated by CO₂-laser welding with low heat input after obtaining the optimum welding parameters by bead-on-plate trials. The metallurgical and mechanical properties of the laser weldment were evaluated. The tensile test results indicated the occurrence of fracture in the base metal AISI 321 side. The HVOF process was employed to coat Ni?20wt%Cr on the weldment. To evaluate the surface morphology of the corrosion products formed on the uncoated and Ni?20wt%Cr-coated weldments, scanning electron microscopy (SEM) analysis was performed. Energy-dispersive spectroscopy (EDS) was used to determine the different elements present on the surface scales. The existence of oxide phases on the weldments was determined by X-ray diffraction (XRD). The cross sections of the weldments were characterized by SEM with EDS line mapping analysis. The results indicated that the Ni?20wt%Cr-coated weldment exhibited superior hot corrosion resistance due to the development of Cr₂O₃ and NiCr₂O₄ protective oxide scales.     

Properties of a reaction-bonded β-SiAlON ceramic doped with an FeMo alloy for application to molten aluminum environments

An FeMo-alloy-doped β-SiAlON (FeMo/β-SiAlON) composite was fabricated via a reaction-bonding method using raw materials of Si, Al₂O₃, AlN, FeMo, and Sm₂O₃. The effects of FeMo on the microstructure and mechanical properties of the composite were investigated. Some properties of the composite, including its bending strength at 700℃ and after oxidization at 700℃ for 24 h in air, thermal shock resistance and corrosion resistance to molten aluminum, were also evaluated. The results show that the density, toughness, bending strength, and thermal shock resistance of the composite are obviously improved with the addition of an FeMo alloy. In addition, other properties of the composite such as its high-temperature strength and oxidized strength are also improved by the addition of FeMo alloy, and its corrosion resistance to molten aluminum is maintained. These findings indicate that the developed FeMo/β-SiAlON composite exhibits strong potential for application to molten aluminum environments.     

Microstructure and properties of Ag–Ti3SiC2 contact materials prepared by pressureless sintering

Ti₃SiC₂-reinforced Ag-matrix composites are expected to serve as electrical contacts. In this study, the wettability of Ag on a Ti₃SiC₂ substrate was measured by the sessile drop method. The Ag–Ti₃SiC₂ composites were prepared from Ag and Ti₃SiC₂ powder mixtures by pressureless sintering. The effects of compacting pressure (100–800 MPa), sintering temperature (850–950℃), and soaking time (0.5–2 h) on the microstructure and properties of the Ag–Ti₃SiC₂ composites were investigated. The experimental results indicated that Ti₃SiC₂ particulates were uniformly distributed in the Ag matrix, without reactions at the interfaces between the two phases. The prepared Ag–10wt%Ti₃SiC₂ had a relative density of 95% and an electrical resistivity of 2.76×10-3 mΩ·cm when compacted at 800 MPa and sintered at 950℃ for 1 h. The incorporation of Ti₃SiC₂ into Ag was found to improve its hardness without substantially compromising its electrical conductivity; this behavior was attributed to the combination of ceramic and metallic properties of the Ti₃SiC₂ reinforcement, suggesting its potential application in electrical contacts.     

Fluoride evaporation and crystallization behavior of CaF2–CaO–Al2O3–(TiO2) slag for electroslag remelting of Ti-containing steels

To elucidate the behavior of slag films in an electroslag remelting process, the fluoride evaporation and crystallization of CaF₂–CaO–Al₂O₃–(TiO₂) slags were studied using the single hot thermocouple technique. The crystallization mechanism of TiO₂-bearing slag was identified based on kinetic analysis. The fluoride evaporation and incubation time of crystallization in TiO₂-free slag are found to considerably decrease with decreasing isothermal temperature down to 1503 K. Fish-bone and flower-like CaO crystals precipitate in TiO₂-free slag melt, which is accompanied by CaF₂ evaporation from slag melt above 1503 K. Below 1503 K, only near-spherical CaF₂ crystals form with an incubation time of less than 1 s, and the crystallization is completed within 1 s. The addition of 8.1wt% TiO₂ largely prevents the fluoride evaporation from slag melt and promotes the slag crystallization. TiO₂ addition leads to the precipitation of needle-like perovskite (CaTiO₃) crystals instead of CaO crystals in the slag. The crystallization of perovskite (CaTiO₃) occurs by bulk nucleation and diffusion-controlled one-dimensional growth.     

Thermodynamic analysis and preparation of β-SiC/ZrO2 composites

A predominance area diagram for the Zr-Si-C-O system at 1773 K was plotted according to correlative thermodynamic data. β-SiC/ZrO₂ composites were prepared based on the phase diagram by carbothermal reduction of zircon (ZrSiO₄) in argon atmosphere. Zircon and carbon black were mixed according to the C/ZrSiO₄ mass ratio of 0.2, and with 0, 1wt% and 2wt% extra addition of La₂O₃. Phase evolution of the mixture was investigated at 1723-1803 K by X-ray powder diffraction, and the microstructure of the product prepared at 1803 K for 4 h was examined by scanning electronic microscope. The results show that the decomposition of ZrSiO₄ and the formation of β-SIC can be promoted by increasing the heating temperature and adding La₂O₃. The β-SiC/ZrO₂ composites can be prepared at 1803 K for 4 h in a mixture of zircon, carbon black and La₂O₃, and the contents of β-SIC and m-ZrO₂ in the product sample with 2wt% La₂O₃ reach the highest values of 10.8wt% and 89.2wt%, respectively. The crystal size of the products is about 200 nm.     

Sol-gel preparation and characterization of Co3O4 nanocrystals

A new citrate acid-hydrazine sol-gel route for preparation of Co₃O₄ nanoparticles has been developed. Co₃O₄ nanoparticles with different particle-sizes and morphology were prepared at different heat-treatment temperatures and the pure cubic nanocrystals of Co₃O₄ were obtained at 600℃. The synthesis process was monitored by infrared spectroscopy (IR), thermal gravimetric and differential thermal analysis (TG-DTA). The structure and morphology of Co₃O₄ nanocrystals were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray-photoelectron spectroscopy (XPS). The infrared absorption bands blue-shifted with particle size decreasing, which could be attributed to increasing surface effect. XPS results showed that predominant species at surface layers of Co₃O₄ nanocrystals are octahedral Co (Ⅲ).     

Roasting and leaching behaviors of vanadium and chromium in calcification roasting–acid leaching of high-chromium vanadium slag

Calcification roasting–acid leaching of high-chromium vanadium slag (HCVS) was conducted to elucidate the roasting and leaching behaviors of vanadium and chromium. The effects of the purity of CaO, molar ratio between CaO and V₂O₅ (n(CaO)/n(V₂O₅)), roasting temperature, holding time, and the heating rate used in the oxidation–calcification processes were investigated. The roasting process and mechanism were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetry–differential scanning calorimetry (TG–DSC). The results show that most of vanadium reacted with CaO to generate calcium vanadates and transferred into the leaching liquid, whereas almost all of the chromium remained in the leaching residue in the form of (Fe_0.6Cr_0.4)₂O₃. Variation trends of the vanadium and chromium leaching ratios were always opposite because of the competitive reactions of oxidation and calcification between vanadium and chromium with CaO. Moreover, CaO was more likely to combine with vanadium, as further confirmed by thermodynamic analysis. When the HCVS with CaO added in an n(CaO)/n(V₂O₅) ratio of 0.5 was roasted in an air atmosphere at a heating rate of 10℃/min from room temperature to 950℃ and maintained at this temperature for 60 min, the leaching ratios of vanadium and chromium reached 91.14% and 0.49%, respectively; thus, efficient extraction of vanadium from HCVS was achieved and the leaching residue could be used as a new raw material for the extraction of chromium. Furthermore, the oxidation and calcification reactions of the spinel phases occurred at 592 and 630℃ for n(CaO)/n(V₂O₅) ratios of 0.5 and 5, respectively.     

(NH4)2SO4焙烧?浸出法从氧化锌矿石中提取锌

An improved method of (NH₄)₂SO₄ roasting followed by water leaching to utilize zinc oxidized ores was studied. The operating parameters were obtained by investigating the effects of the molar ratio of (NH₄)₂SO₄ to zinc, roasting temperature, and holding time on zinc extraction. The roasting process followed the chemical reaction control mechanism with the apparent activation energy value of 41.74 kJ·mol?1. The transformation of mineral phases in roasting was identified by X-ray diffraction analysis combined with thermogravimetry–differential thermal analysis curves. The water leaching conditions, including the leaching temperature, leaching time, stirring velocity, and liquid-to-solid ratio, were discussed, and the leaching kinetics was studied. The reaction rate was obtained under outer diffusion without product layer control; the values of the apparent activation energy for two stages were 4.12 and 8.19 kJ·mol?1. The maximum zinc extraction ratio reached 96% while the efficiency of iron extraction was approximately 32% under appropriate conditions. This work offers an effective method for the comprehensive use of zinc oxidized ores.     

Phosphate enrichment mechanism in CaO–SiO2–FeO–Fe2O3–P2O5 steelmaking slags with lower binary basicity

The addition of silica to steelmaking slags to decrease the binary basicity can promote phosphate enrichment in quenched slag samples. In this study, we experimentally investigated phosphate enrichment behavior in CaO–SiO₂–FeO–Fe₂O₃–P₂O₅ slags with a P₂O₅ content of 5.00% and the binary basicity B ranging from 1.0 to 2.0, where the (%Fe_tO)/(%CaO) mass percentage ratio was maintained at 0.955. The experimental results are explained by the defined enrichment degree R_C2S-C3P of solid solution 2CaO·SiO₂–3CaO·P₂O₅ (C₂S–C₃P), where R_C2S-C3P is a component of the developed ion and molecule coexistence theory (IMCT)–N_i model for calculating the mass action concentrations N_i of structural units in the slags on the basis of the IMCT. The asymmetrically inverse V-shaped relation between phosphate enrichment and binary basicity B was observed to be correlated in the slags under applied two-stage cooling conditions. The maximum content of P₂O₅ in the C₂S–C₃P solid solution reached approximately 30.0% when the binary basicity B was controlled at 1.3.     

Fabrication of Fe–TiC–Al2O3 composites on the surface of steel using a TiO2–Al–C–Fe combustion reaction induced by gas tungsten arc cladding

The aim of the present study was to fabricate Fe–TiC–Al₂O₃ composites on the surface of medium carbon steel. For this purpose, TiO₂–3C and 3TiO₂–4Al–3C–xFe (0 ≤ x ≤ 4.6 by mole) mixtures were pre-placed on the surface of a medium carbon steel plate. The mixtures and substrate were then melted using a gas tungsten arc cladding process. The results show that the martensite forms in the layer produced by the TiO₂–3C mixture. However, ferrite–Fe₃C–TiC phases are the main phases in the microstructure of the clad layer produced by the 3TiO₂–4Al–3C mixture. The addition of Fe to the TiO₂–4Al–3C reactants with the content from 0 to 20wt% increases the volume fraction of particles, and a composite containing approximately 9vol% TiC and Al₂O₃ particles forms. This composite substantially improves the substrate hardness. The mechanism by which Fe particles enhance the TiC + Al₂O₃ volume fraction in the composite is determined.     

TiO2对含铬高钛熔分渣熔化性能和黏度的影响

A study on the melting and viscosity properties of the chromium-containing high-titanium melting slag (CaO–SiO₂–MgO–Al₂O₃–TiO₂–Cr₂O₃) with TiO₂ contents ranging from 38.63wt% to 42.63wt% was conducted. The melting properties were investigated with a melting-point apparatus, and viscosity was measured using the rotating cylinder method. The FactSage 7.1 software and X-ray diffraction, in combination with scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS), were used to characterize the phase equilibrium and microstructure of chromium-containing high-titanium melting slags. The results indicated that an increase in the TiO₂ content led to a decrease in the viscosity of the chromium-containing high-titanium melting slag. In addition, the softening temperature, hemispheric temperature, and flowing temperature decreased with increasing TiO₂ content. The amount of crystallized anosovite and sphene phases gradually increased with increasing TiO₂ content, whereas the amount of perovskite phase decreased. SEM observations revealed that the distribution of the anosovite phase was dominantly influenced by TiO₂.     

Characterization and photoluminescence properties of ultrafine copper molybdate (α-CuMoO4) powders prepared via a combustion-like process

We report a simple method for preparing copper(II) molybdate (CuMoO₄) powders via a combustion-like process. A gel was first prepared by the polymerizable complex method, where citric acid was used as a complexing and polymerizing agent and nitric acid was used as an oxidizing agent. The thermal decomposition behavior of the (CuMo)-precursor gel was studied by thermogravimetry–differential thermal analysis (TG–DTA), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). We observed that the crystallization of CuMoO₄ powder was completed at 450°C. The obtained homogeneous powder was composed of grains with sizes in the range from 150 to 500 nm and exhibited a specific surface area of approximately 5 m2/g. The average grain size increased with increasing annealing temperature. The as-prepared CuMoO₄ crystals showed a strong green photoluminescence emission at room temperature under excitation at 290 nm, which we mainly interpreted on the basis of the Jahn-Teller effect on [MoO₄2- ] complex anions. We also observed that the photoluminescence intensity increased with increasing crystallite size.     

Isothermal oxidation behavior and mechanism of a nickel-based superalloy at 1000℃

The oxidation behavior of a nickel-based superalloy at 1000℃ in air was investigated through X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analysis. A series of oxides, including external oxide scales (Cr₂O₃, (TiO₂ + MnCr₂O₄)) and internal oxides (Al₂O₃,TiN), were formed on the surface or sub-surface of the substrate at 1000℃ in experimental still air. The oxidation resistance of the alloy was dependent on the stability of the surface oxide layer. The continuity and density of the protective Cr₂O₃ scale were affected by minor alloying elements such as Ti and Mn. The outermost oxide scale was composed of TiO₂ rutile and MnCr₂O₄ spinel, and the growth of TiO₂ particles was controlled by the outer diffusion of Ti ions through the pre-existing oxide layer. Severe internal oxidation occurred beneath the external oxide scale, consuming Al and Ti of the strength phase γ' (Ni₃(Al,Ti)) and thereby severely deteriorating the surface mechanical properties. The depth of the internal oxidation region was approximately 35 μm after exposure to experimental air at 1000℃ for 80 h.     

Sintering Behavior and Microstructure of diphasic β-Sialon/Al2O3 Composites

Six compositions with different ratio of β-Sialon/Al₂O₃ were synthesized from Al₂O₃, Si₃N₄ and SiO₂ by sintering with 3%Y₂O₃(mass fraction) as addition under the cover with powders of SiC+C and at nitrogen atmosphere. Theeffects of atmosphere, sintering temperature and composition on the sintering behavior were studied. The results showedthat the composites reached the best sintering behavior with the highest density about 92% at 1 650℃ under the weakreduction atmosphere. Finally the relative density of diphasic β-Sialon and β-Sialon/Al₂O₃ composites were studied andpredicted using ANN (Artificial Neural Networks) method and the results were experimental examined by fore randomsamples.     

Research on application of different particle sizes of cordierite on castable refractory

Effect of different particle sizes of cordierite on properties of castable refractory by different heat treatment temperatures were investigated respectively with mullite and bauxite as raw materials,calcium aluminate cement as binders.After 24 h curing in mould and another 24 h curing at 110 ℃ after demoulding,the specimens were heat treated at 1 000 ℃,1 300 ℃ and 1 500 ℃ for 3 h,respectively.The bulk density(BD),permanent linear change(PLC),modulus of rupture(MOR)and clod crushing strength(CCS),thermal expansion coefficient and thermal shock resistance were examined.The results show that there is no obvious effect on adjusting permanent linear change and bulk density of castables by adding different particle sizes of cordierite at low temperature and intermediate temperature.Modulus of rupture of castable increase with the decreasing of the particle sizes of cordierite after heat treated by 1 000 ℃ and 1 300 ℃.In this experiment,thermal shock resistance of the castable with cordierite whose particle size is 0~1 mm is the best.     

Effects of HNO3 concentration on the pit morphologies of aluminum foil etched in HNO3–HCl and HNO3–H2SO4–HCl solutions

In this work, the effects of HNO₃ concentration on the pit morphologies of high-cubic-texture aluminum foil etched in HNO₃–HCl and HNO₃–H₂SO₄–HCl solutions were investigated. When the aluminum foil was etched in HNO₃–HCl solutions, the morphologies of pits transformed from irregular tunnels to typical tunnels (as inverted pyramids) and shallow cuboids as the HNO₃ concentration in the etchant solution was increased. However, as the HCl concentration in the etchant solution was increased, the morphologies of pits transformed from shallow cuboids to typical tunnels (as inverted pyramids) and irregular tunnels. When the aluminum foil was etched in n N HNO₃–(7.2?n) N H₂SO₄–0.8 N HCl solutions, the morphologies of the pits transformed from typical tunnels (i.e., the number of sub-tunnels formed on the main tunnels increased) to irregular tunnels (corrugated tunnels and polyline tunnels) as the HNO₃ concentration in the etchant solution was increased. These effects are attributed primarily to corrosion on the (100) and (010) faces of pits being accelerated and to the (001) faces being prone to passivation to different degrees when various concentrations of HNO₃ are added to the etchant solutions.