Isothermal reduction kinetics of Panzhihua ilmenite concentrate under 30vol% CO–70vol% N_2 atmosphere

The reduction of ilmenite concentrate in 30vol% CO–70vol% N_2 atmosphere was characterized by thermogravimetric and differential thermogravimetric(TG–DTG) analysis methods at temperatures from 1073 to 1223 K.The isothermal reduction results show that the reduction process comprised two stages;the corresponding apparent activation energy was obtained by the iso-conversional and model-fitting methods.For the first stage,the effect of temperature on the conversion degree was not obvious,the phase boundary chemical reaction was the controlling step,with an apparent activation energy of 15.55–40.71 k J·mol~(–1).For the second stage,when the temperatures was greater than 1123 K,the reaction rate and the conversion degree increased sharply with increasing temperature,and random nucleation and subsequent growth were the controlling steps,with an apparent activation energy ranging from 182.33 to 195.95 k J·mol~(–1).For the whole reduction process,the average activation energy and pre-exponential factor were 98.94~(–1)18.33 k J·mol~(–1) and 1.820~(–1).816 min~(–1),respectively.     

Isothermal reduction kinetics and mineral phase of chromium-bearing vanadium-titanium sinter reduced with CO gas at 873-1273 K

Reduction of chromium-bearing vanadium-titanium sinter (CVTS) was studied under simulated conditions of a blast furnace, and thermodynamics and kinetics were theoretically analyzed. Reduction kinetics of CVTS at different temperatures was evaluated using a shrinking unreacted core model. The microstructure, mineral phase, and variation of the sinter during reduction were observed by X-ray diffraction, scanning electron microscopy, and metallographic microscopy. Results indicate that porosity of CVTS increased with temperature. Meanwhile, the reduction degree of the sinter improved with the reduction rate. Reduction of the sinter was controlled by a chemical reaction at the initial stage and inner diffusion at the final stage. Activation energies measured 29.22-99.69 kJ/mol. Phase transformations in CVTS reduction are as follows:Fe₂O₃→Fe₃O₄→FeO→Fe; Fe₂TiO₅→Fe₂TiO₄→FeTiO₃; FeO·V₂O₃→V₂O₃; FeO·Cr₂O₃→Cr₂O₃.     

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.     

In situ reaction mechanism of MgAlON in Al-Al2O3-MgO composites at 1700℃ under flowing N2

The Al-Al₂O₃-MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M₁, M₂, and M₃, respectively, were prepared at 1700℃ for 5 h under a flowing N₂ atmosphere using the reaction sintering method. After sintering, the Al-Al₂O₃-MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M₁ was composed of MgO and MgAl₂O₄. Compared with specimen M₁, specimens M₂ and M₃ possessed MgAlON, and its production increased with increasing aluminum addition. Under an N₂ atmosphere, MgO, Al₂O₃, and Al in the matrix of specimens M₂ and M₃ reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al-Al₂O₃-MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N₂ atmosphere, the partial pressure of oxygen is quite low; thus, when the Al-Al₂O₃-MgO composites were soaked at 580℃ for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al₂O₃ diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al₂O₃ to form MgAl₂O₄. When the temperature was greater than (1640 ±10)℃, AlN diffused into Al₂O₃ and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl₂O₄ at high temperatures because of their similar spinel structures.     

Comparative study on the corrosion behavior of X52, 3Cr,and 13Cr steel in an O2-H2O-CO2 system:products,reaction kinetics,and pitting sensitivity

The corrosion behaviors of X52, 3Cr low-alloy steel, and 13Cr stainless steel were investigated in an O₂-H₂O-CO₂ environment at various temperatures and O₂-CO₂ partial-pressure ratios. The results showed that the corrosion rates of X52, 3Cr, and 13Cr steels increased with increasing temperature. The corrosion rates slowly increased at temperatures less than 100℃ and increased sharply when the temperature exceeded 100℃. In the absence of O₂, X52, 3Cr, and 13Cr exhibited uniform corrosion morphology and FeCO₃ was the main corrosion product. When O₂ was introduced into the system, various forms of Fe₂O₃ appeared on the surface of the samples. The Cr content strongly influenced the corrosion resistance. The 3Cr steel with a low Cr content was more sensitive to pitting than the X52 or 13Cr steel. Thus, pitting occurred on the surface of 3Cr when 1.25 MPa of O₂ was added; this phenomenon is related to the non-uniform distribution of Cr in 3Cr.     

Forming mechanism of refined granular crystalline of Cu70Ni30 alloy by undercooled solidification

Moth glass fluxing and cyclic superheating techniques were adopted to effectively uudercool the Cu₇₀Ni₃₀ alloy in vacuum. Within the undercooling range of 21 K to 270 K, the microstructure evolution ol the alloy was investigated. When the inell was undercooled to △T > △T', (210 K) , the grain refinement took place abruptly, liascd on the observation of the solidified microstructure, the rnierocheinieal-analysis and the calculated results with UCT model, it is found that the secondary grain refinement mechanism consists of two stages. The dendrite is, firstly, broken into hag-ments owing to the stress caused by uneven shrinking during rapid solidilication, then the fragments, under the driving force of surface and strain energies, merge through the migration of l>ouinlaries, i. c. recryslallization, thus leading to the formation of secondary granular-crystalline .     

Evolution of ferronickel particles during the reduction of low-grade saprolitic laterite nickel ore by coal in the temperature range of 900–1250℃with the addition of CaO–CaF2–H3BO3

The method of producing ferronickel at low temperature(1250–1400℃)has been applied since the 1950s at Nippon Yakin Kogyo,Oheyama Works,Japan.Limestone was used as an additive to adjust the slag composition for lowering the slag melting point.The ferronickel product was recovered by means of a magnetic separator from semi-molten slag and metal after water quenching.To increase the efficiency of magnetic separation,a large particle size of ferronickel is desired.Therefore,in this study,the influences of CaO,CaF₂,and H₃BO₃ additives on the evolution of ferronickel particle at≤1250℃were investigated.The experiments were conducted at 900–1250℃with the addition of CaO,CaF₂,and H₃BO₃.The reduction processes were carried out in a horizontal tube furnace for 2 h under argon atmosphere.At 1250℃,with the CaO addition of 10 wt%of the ore weight,ferronickel particles with size of 20μm were obtained.The ferronickel particle size increased to 165μm by adding 10 wt%CaO and 10 wt%CaF₂.The addition of boric acid further increased the ferronickel particle size to 376μm,as shown by the experiments with the addition of 10 wt%CaO,10 wt%CaF₂,and 10 wt%H₃BO₃.     

Shear-thinning behavior of the CaO-SiO2-CaF2-Si3N4 system mold flux and its practical application

Satisfying the mold-flux performance requirements for high-speed continuous casting necessitates the development of a new non-Newtonian-fluid mold flux with shear-thinning behavior, i.e., a mold flux whose viscosity is relatively high under lower shear rates and relatively low under higher shear rates. In this work, a mold flux that exhibits shear-thinning behavior was developed by adding different amounts of Si₃N₄ to the CaO-SiO₂-CaF₂ mold flux. The shear-thinning behavior was investigated using a rotational viscometer. In addition, the microstructure of the newly prepared slags was studied by high-temperature Raman spectroscopy and X-ray photoelectron spectroscopy. The results showed that the mechanism of shear-thinning was attributable to a temporary viscosity loss caused by the one-way shear stress, whereas the corresponding magnitude of shear-thinning was closely related to the degree of polymerization (DP). Finally, the non-Newtonian fluid mold flux was used for laboratory casting tests, which revealed that the mold flux could reduce slag entrapment and positively affect the continuous casting optimization.     

Synthesis, Characterization and Calorimetry of Ni（C4H8N2O3）2Cl2

A coordination complex was synthesized from NiCl2 and dipeptide glycylglycine（GG）. It was characterized by element analysis, NMR and TG methods, and then was determined to be Ni（C4HsN2O3）2Cl2. Using an isoperibolic reaction calorimeter, the standard molar enthalpy of formation of Ni（GG）2Cl2（solid） has been determined to be -（1 674.66±2.02） kJ · mol^-1 at 298.15 K.     

Analysis of active sites for N2 and H^＋ reduction on FeMo-cofactor of nitrogenase

Dinitrogen (N2) and proton (H ),which act as physiological substrates of nitrogenase,are reduced on FeMo-co of the MoFe protein. However,researchers have different opinions about their exact reduction sites. Nitrogenases were purified from the wild type (WT) and five mutants of Azotobacter vinelandii (Av),including Qα191K,Hα195Q,nifV-,Qα191K/nifV- and Hα195Q/nifV-; and the activities of these en-zymes for N2 and H reduction were analyzed. Our results suggest that the Fe2 and Fe6,atoms closed to the central sulfur atom (S2B) within FeMo-co,are sites for N2 binding and reduction and the Mo atom of FeMo-co is the site for H reduction. Combining these data with further bioinformatical analysis,we propose that two parallel electron channels may exist between the 8Fe7S cluster and FeMo-co.     

Mineral-phase evolution and sintering behavior of MO-SiO2-Al2O3-B2O3 (M=Ca,Ba) glass-ceramics by low-temperature liquid-phase sintering

In this work, network former SiO₂ and network intermediate Al₂O₃ were introduced into typical low-melting binary compositions CaO·B₂O₃, CaO·2B₂O₃, and BaO·B₂O₃ via an aqueous solid-state suspension milling route. Accordingly, multiple-phase aluminosilicate glass-ceramics were directly obtained via liquid-phase sintering at temperatures below 950℃. On the basis of liquid-phase sintering theory, mineral-phase evolutions and glass-phase formations were systematically investigated in a wide MO-SiO₂-Al₂O₃-B₂O₃ (M=Ca, Ba) composition range. The results indicate that major mineral phases of the aluminosilicate glass-ceramics are Al₂₀B₄O₃₆, CaAl₂Si₂O₈, and BaAl₂Si₂O₈ and that the glass-ceramic materials are characterized by dense microstructures and excellent dielectric properties.     

Spheroidization of silica powders by radio frequency inductively coupled plasma with Ar-H2 and Ar-N2 as the sheath gases at atmospheric pressu

Amorphous spherical silica powders were prepared by inductively coupled thermal plasma treatment at a radio frequency of 36.2 MHz. The effects of the added content of hydrogen and nitrogen into argon (serving as the sheath gas), as well as the carrier gas flow rate, on the spheroidization rate of silica powders, were investigated. The prepared silica powders before and after plasma treatment were examined by scanning electron microscopy, X-ray diffraction, and laser granulometric analysis. Results indicated that the average size of the silica particles increased, and the transformation of crystals into the amorphous state occurred after plasma treatment. Discharge image processing was employed to analyze the effect of the plasma temperature field on the spheroidization rate. The spheroidization rate of the silica powder increased with the increase of the hydrogen content in the sheath gas. On the other hand, the spheroidization rate of the silica power first increased and then decreased with the increase of the nitrogen content in the sheath gas. Moreover, the amorphous content increased with the increase of the spheroidization rate of the silica powder.     

Electrical conductivity optimization of the Na3AlF6-Al2O3-Sm2O3 molten salts system for Al-Sm intermediate binary alloy production

Metal Sm has been widely used in making Al-Sm magnet alloy materials. Conventional distillation technology to produce Sm has the disadvantages of low productivity, high costs, and pollution generation. The objective of this study was to develop a molten salt electrolyte system to produce Al-Sm alloy directly, with focus on the electrical conductivity and optimal operating conditions to minimize the energy consumption. The continuously varying cell constant (CVCC) technique was used to measure the conductivity for the Na₃AlF₆-AlF₃-LiF-MgF₂-Al₂O₃-Sm₂O₃ electrolysis medium in the temperature range from 905 to 1055℃. The temperature (t) and the addition of Al₂O₃ (W(Al₂O₃)), Sm₂O₃ (W(Sm₂O₃)), and a combination of Al₂O₃ and Sm₂O₃ into the basic fluoride system were examined with respect to their effects on the conductivity (κ) and activation energy. The experimental results showed that the molten electrolyte conductivity increases with increasing temperature (t) and decreases with the addition of Al₂O₃ or Sm₂O₃ or both. We concluded that the optimal operation conditions for Al-Sm intermediate alloy production in the Na₃AlF₆-AlF₃-LiF-MgF₂-Al₂O₃-Sm₂O₃ system are W(Al₂O₃) + W(Sm₂O₃)=3wt%, W(Al₂O₃):W(Sm₂O₃)=7:3, and a temperature of 965 to 995℃, which results in satisfactory conductivity, low fluoride evaporation losses, and low energy consumption.     

Preparation and radar-absorbing properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> composite powder

Al₂O₃/TiO₂/Fe₂O₃/Yb₂O₃ composite powder was synthesized via the sol-gel method. The structure, morphology, and radar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes (100-200 nm) and the other is spherical Al₂O₃ particles (smaller than 80 nm). Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 (at 15.68 GHz) in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increasing matching thickness. The effective absorption band covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.     

Study on reduction of MoS<Subscript>2</Subscript> powders with activated carbon to produce Mo<Subscript>2</Subscript>C under vacuum conditions

A method of preparing Mo₂C via vacuum carbothermic reduction of MoS₂ in the temperature range of 1350-1550℃ was proposed. The effects of MoS₂-to-C molar ratio (α, α=1:1, 1:1.5, and 1:2.5) and reaction temperature (1350 to 1550℃) on the reaction were studied in detail. The phase transition, morphological evolution, and residual sulfur content of the products were analyzed by X-ray diffraction, field-emission scanning electron microscopy, and carbon-sulfur analysis, respectively. The results showed that the complete decomposition of MoS₂ under vacuum is difficult, whereas activated carbon can react with MoS₂ under vacuum to generate Mo₂C. Meanwhile, higher temperatures and the addition of more carbon accelerated the rate of carbothermic reduction reaction and further decreased the residual sulfur content. From the experimental results, the optimum molar ratio α was concluded to be 1:1.5.     

Structural and electrical properties of HCl-polyaniline-Ag composites synthesized by polymerization using Ag-coated (NH4)2S2O8 powder

Ag nanoparticles were sputter-deposited on ammonium persulfate ((NH₄)₂S₂O₈) powder to obtain (NH₄)₂S₂O₈-Ag powder, which was used to synthesize the HCl-doped polyaniline-Ag (HCl-PANI-Ag) composite via a polymerization procedure. The Ag nanoparticles were dispersed in the HCl-PANI matrix, and their sizes mainly ranged from 3 to 6 nm. The Ag nanoparticles did not affect the structure of emeraldine salt in the composite, and they increased the ordered crystalline regions in the HCl-PANI matrix. The HCl-PANI-Ag composite had a conductivity of (6.8 ±0.1) S/cm, which is about four times larger than that of the HCl-PANI. The charge transport mechanism in the composite is explained by the three-dimensional Mott variable-range hopping (3D-Mott-VRH).     

Intense laser induced field ionization of C<Subscript>2</Subscript>H<Subscript>2</Subscript>, C<Subscript>2</Subscript>H<Subscript>4</Subscript>, and C<Subscript>2</Subscript>H<Subscript>6</Subscript>

Using HOMO Field Ionization Model, the tunneling probabilities and the theoretical threshold intensities of the field ionizations of acetylene, ethylene, and ethane in intense laser field are calculated. C2H2, C2H4, and C2H6 were irradiated by 800 nm, 100 fs laser pulses with the intensity range of 10^13-10^14 W/cm^2. A TOF-mass spectrometer was coupled to the laser system and used to experimentally investigate the field ionization of these molecules. The experimental ionization threshold intensities are obtained. The calculating results of the three molecules agree well with the experimental results, indicating that HOMO Field Ionization Model is valid for the ionization of polyatomic molecules in intense laser field.