Search

Nickel oxide was supported on MCM-41 using the precipitation method. Reduction kinetics of supported and unsupported nickel oxide was studied using non-isothermal methods to investigate the change in activation energy and the reduction reaction mechanism. Activation energy was determined using the Kissinger's method and Straink's method. Model discrimination was done using the Hancock-Sharp analysis and Malek's method. The support influenced the reduction kinetics by increasing the activation energy. The reaction mechanism shifted from Avrami-Erofeev model in the unsupported to three-dimensional diffusion-controlled model in the supported nickel oxide. The higher activation energy and the model discrimination in the case of nickel oxide supported on MCM-41 indicates the diffusion of vacancies is the rate limiting step. The reduction mechanism of nickel oxide supported on MCM-41 was proposed in agreement with literature and current study. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AA) is the most widely used reductant for noble metal nanoparticle (NP) synthesis. Despite the synthetic relevance, its aqueous chemistry remains misunderstood, due in part to various assumptions about its reduction pathway which are insufficiently supported by experimental evidence. This study aims to provide an understanding of the complex chemistry associated with AA under aqueous conditions. We demonstrate that (i) AA undergoes appreciable degradation in alkaline solution on a timescale relevant to NP synthesis, (ii) contrary to popular belief, AA does not degrade into dehydroascorbic acid (DHA), nor is DHA the oxidized product of AA under noble metal NP synthetic conditions, (iii) DHA, which readily degrades under alkaline conditions, can also effectively reduce metal salt precursors to metal NPs, (iv) neither ascorbate nor dehydroascorbate act as surface capping agents post‐synthetically on the NPs (v) AA degradation time greatly affects the morphology and polydispersity of the resultant NP. Results from our mechanistic investigation enabled us to utilize purposefully‐aged reductants to achieve control over shape yield and monodispersity in the seed‐mediated synthesis of Au nanorods. Our findings have important implications for achieving monodispersed products in the many metal NP synthesis reactions that make use of AA as a reducing agent. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AA) is the most widely used reductant for noble metal nanoparticle (NP) synthesis. Despite the synthetic relevance, its aqueous chemistry remains misunderstood, due in part to various assumptions about its reduction pathway which are insufficiently supported by experimental evidence. This study aims to provide an understanding of the complex chemistry associated with AA under aqueous conditions. We demonstrate that (i) AA undergoes appreciable degradation in alkaline solution on a timescale relevant to NP synthesis, (ii) contrary to popular belief, AA does not degrade into dehydroascorbic acid (DHA), nor is DHA the oxidized product of AA under noble metal NP synthetic conditions, (iii) DHA, which readily degrades under alkaline conditions, can also effectively reduce metal salt precursors to metal NPs, (iv) neither ascorbate nor dehydroascorbate act as surface capping agents post‐synthetically on the NPs (v) AA degradation time greatly affects the morphology and polydispersity of the resultant NP. Results from our mechanistic investigation enabled us to utilize purposefully‐aged reductants to achieve control over shape yield and monodispersity in the seed‐mediated synthesis of Au nanorods. Our findings have important implications for achieving monodispersed products in the many metal NP synthesis reactions that make use of AA as a reducing agent. [ABSTRACT FROM AUTHOR]

The oxide scale on the surface of hot‐rolled low‐carbon steel strips is subjected to isothermal reduction in 10 vol%H2–Ar and 20 vol%H2–Ar environments to simulate the reduction process that occurs in a continuous annealing furnace. The influence of hydrogen concentration on the reduction kinetics and the microstructural evolution of the oxide scale after reduction at temperatures ranging from 450 to 850 °C for a duration of 20 min are investigated in detail. The mass changes of the oxide scale in the two gases are quantified using a thermogravimetric analyzer. This data is then employed to calculate the reduction rate constant and the apparent activation energy. To examine the microstructure and element distribution, electron probe microanalysis and energy‐dispersive spectrometry are employed. An novel approach is also undertaken to assess the reduction degree of the oxide scale by measuring surface microhardness. In the findings, it is indicated that an increase in hydrogen concentration served primarily to accelerate the reduction reaction within the temperature ranges of 450–550 and 800–850 °C. Meanwhile, the mechanism of physical transformation of oxide scale, the microstructure of reduction layer, and hydrogen concentration on reduction efficiency under different reaction stages are proposed. [ABSTRACT FROM AUTHOR]

Organic pollutants negatively impact the environment, including air, water, soil, and living organisms. These pollutants come from various sources, including industrial, agricultural, and domestic activities. Removing organic pollutants from the environment is a difficult task and requires a combination of prevention and innovative strategies. Herein a novel nanocomposite consisting of beta‐cyclodextrin (β‐CD) modified silver (Ag@β‐CD) and gold (Au@‐β‐CD) nanoparticles (NPs) attached on the surface of Fe3O4@TiO2 core–shell structure with an average 530 nm diameter in an eco‐friendly environment is presented. In the first step, Au@‐β‐CD and Ag@‐β‐CD are synthesized, and the core–shell structure is modified by these nanoparticles. The catalytic activities of the synthesized nanocomposite are investigated for the reduction of RhB and 4‐NP and the photodegradation of MB. The synthesized composite shows the highest catalytic performance in the reduction of RhB and 4‐NP and photodegradation of MB, and the reactions are completed in 75, 45 s, and 16 min with a rate constant (k) 0.03 ± 0.005 s−1, 0.07 ± 0.01 s−1, and 0.25 ± 0.07 min−1, respectively. The reduction and photodegradation reactions follow the first‐order rate law. The catalyst is reused for six cycles after separation from the reaction system by an external magnetic field. [ABSTRACT FROM AUTHOR]

The reduction of hematite with ammonia is a potentially environmentally friendly method of ironmaking. Previous studies on ammonia reduction of pellets typically involved samples weighing only 2.8 g and lacked detailed activation energy analysis for the ammonia-hydrogen co-reduction of pellets. Therefore, to further investigate the reduction thermodynamics and kinetics of NH3–H2 reduction of pellets, this study uses 50 g pellets for reduction experiments. By increasing the pellet mass, the study expands the scope of kinetic research on ammonia reduction of pellets. The results indicate that nitrogen gas produced from ammonia decomposition reduces the equilibrium components of the reducing gas. In the temperature range of 700–850 °C, the formation of iron nitride exhibits a narrow range during ammonia reduction of hematite. In the reduction of 50 g of pellets, the reduction rate using 100% NH3 is lower than that using a 50% NH3 and 50% H2 mixed gas, which is, in turn, slower than using 100% H2. As temperature increases, the reduction effect of 50% NH3 and 50% H2 approaches that of 100% H2. Among common gas-solid reaction mathematical models, the Phase-boundary-controlled model with the Contracting Cylinder Model is selected as the most plausible mechanistic function. For the reduction of 50 g of pellets, the activation energies for reactions using 100% NH3, 50% NH3 and 50% H2, and 100% H2 are 65.42, 54.37, and 29.17 kJ/mol, respectively. The decomposition of NH3 has a negative effect on the reduction of Fe2O3. XRD analysis and electron microscopy element line scanning show that Fe4N is formed during the reduction of Fe2O3 with 100% NH3. The use of a 50% NH3 and 50% H2 mixture significantly reduces the formation of Fe4N during the reduction of the pellets. [ABSTRACT FROM AUTHOR]

Hydrogen-based smelting reduction has received widespread attention as an important technology for realizing low-carbon development in hydrogen metallurgy. In this study, the thermodynamics of smelting reduction was firstly analyzed by using FactSage 8.1 thermodynamic software, on the basis of which smelting reduction experiments of iron oxides by using bottom-blown hydrogen were carried out. The experiments used oxidized pellets as experimental materials, and the effects of the reduction process were analyzed in terms of the reduction temperature, the reduction time, and the hydrogen flow rate. The experimental results show that under the experimental conditions of a temperature of 1550 °C and a hydrogen flow rate of 0.2 Nm3/h, the reduction rate of iron oxides in the process of reducing iron oxides by hydrogen is significantly faster in the first 10 min than after 10 min. The hydrogen utilization rate reached a maximum of 41.87%, then decreased continuously and finally maintained at about 20%. Using the method of model fitting, it was found that the hydrogen-based molten reduction conformed to the phase boundary reaction model ( G α = 1 − (1 − α) 1 / 2 ), the corresponding mechanism function is f α = 2 (1 − α) 1 / 2 , where α stands for the reduction conversion, and the reaction rate constant k (T) is 2.37 × 10−4 s−1 under the experimental conditions. [ABSTRACT FROM AUTHOR]

Nickel oxide reduction kinetics and formation of the electric potential of anode-supported solid oxide fuel cell (SOFC) were studied using in situ Raman spectroscopy (RS) and conventional electrochemical techniques. It was shown that the time dependence of the electric potential and the intensity of the Raman spectra during anode substrate reduction can be conditionally divided into two stages. At the initial stage, in the first seconds after hydrogen supply, the open circuit voltage (OCV) quickly rises and stabilizes at a value of about 0.85 V. This stage is not accompanied by noticeable changes in RS. Then, there is a more gradual rise, requiring tens of minutes, to the OCV equilibrium value. The beginning of the second stage of the increase in the OCV coincides with a sharp change in the intensity of the specific spectral line in the Raman spectrum. An increase of the OCV in the first seconds after hydrogen supply is explained by an increase in the hydrogen concentration at the outer boundary of the SOFC anode. The sharp change in the intensity of the Raman spectrum, in turn, can be explained by the reduction of NiO to the metallic state in the near electrolyte region. In this work, a detailed reduction model of the NiO-YSZ (yttria-stabilized zirconia) cermet composite supporting substrate of an anode-supported SOFC was constructed. The model was developed on the assumption that the rate of the nickel oxide reduction reaction at each point of the sample depends only on the partial pressure of hydrogen, the fraction of oxidized nickel, and temperature. In the case of repeated reduction and at high temperatures, it can be assumed that the reaction has first-order kinetics, i.e., reaction rate is proportional to the fraction of oxidized nickel. At primary reduction and temperatures of 400–600 °C, the reaction is described by Avrami-Erofeev kinetics. [ABSTRACT FROM AUTHOR]

For the performance optimization strategies of hard carbon, heteroatom doping is an effective way to enhance the intrinsic transfer properties of sodium ions and electrons for accelerating the reaction kinetics. However, the previous work focuses mainly on the intrinsic physicochemical property changes of the material, but little attention has been paid to the resulting interfacial regulation of the electrode surface, namely the formation of solid electrolyte interphase (SEI) film. In this work, element F, which has the highest electronegativity, was chosen as the doping source to, more effectively, tune the electronic structure of the hard carbon. The effect of F‐doping on the physicochemical properties of hard carbon was not only systematically analyzed but also investigated with spectroscopy, optics, and in situ characterization techniques to further verify that appropriate F‐doping plays a positive role in constructing a homogenous and inorganic‐rich SEI film. The experimentally demonstrated link between the electronic structure of the electrode and the SEI film properties can reframe the doping optimization strategy as well as provide a new idea for the design of electrode materials with low reduction kinetics to the electrolyte. As a result, the optimized sample with the appropriate F‐doping content exhibits the best electrochemical performance with high capacity (434.53 mA h g−1 at 20 mA g−1) and excellent rate capability (141 mA h g−1 at 400 mA g−1). [ABSTRACT FROM AUTHOR]

Magnetization reduction roasting is an important method for the utilization of oolitic magnetite. In this study, the magnetization reduction behavior and kinetics of oolitic hematite in gas-based roasting were systematically investigated by X-ray photoelectron spectroscopy (XPS). The results revealed that under optimal roasting conditions of 650 °C, a roasting time of 60 min, and a CO concentration of 30%, the magnetization reduction rate of the roasted product reached 44.34%. Furthermore, the weak magnetic separation concentrate presented a TFe of 58.09% and a concentrate iron recovery of 94.3%. The results of the XPS spectrum indicated that the peak area ratio (Fe2+/Fe3+) gradually increased with an increase in roasting temperature, roasting time, and CO concentration, while over-reduction occurred when the roasting temperature exceeded 750 °C. The investigation of magnetization roasting kinetics for varying particle sizes demonstrated that the magnetization reduction process is controlled by chemical reaction, with a corresponding activation energy range of 42.96 kJ/mol to 63.29 kJ/mol, indicating the particle size has little effect on the magnetization reduction of oolitic hematite. [ABSTRACT FROM AUTHOR]

The article presents the results of obtaining a composite material by sintering nickel-containing raw materials mixed with carbon-containing materials, namely using coke and semi-coke. The sintering process was performed at a charge layer height of 240 mm and the temperature of the lower layer was T = 1200 °C. The results of the sieve analysis showed (a fraction of 10 mm) that the yield of a suitable composite material using coke was 68.3% and with semi-coke 67.0%. The average nickel and chromium content in the composite materials was 1.42% and 3.07%, accordingly. As a result of determining the strength characteristics of the obtained composite materials with various reducing agents by dropping from a height of 2 m onto a steel pallet, it was found that the obtained composite materials have high mechanical properties in terms of strength of 81% and 89.2%. The results of the elemental composition at the studied points and the thermal analysis of the studied composite material are presented. The mineralogical composition of the composite material is presented in the form of serpentine and nontronite, and the empty rock is made of quartz and talc. The activation energy of thermal analysis by the method of non-isothermal kinetics were calculated. The results of experiments on the production of composite materials from nickel-containing raw materials will be recommended for obtaining the optimal composition of composite materials at the stage of pilot tests and industrial development of the developed technology for processing nickel ores of the Republic of Kazakhstan. For the processing of nickel-poor nickel ores, it is of great importance to obtain optimal technological and technical and economic indicators that ensure low cost of nickel in the resulting product. [ABSTRACT FROM AUTHOR]

On‐board methanol reforming is a practical solution to supply hydrogen for fuel cell vehicles (FCVs). For commonly employed Cu‐based reforming catalysts, activation has a profound influence on subsequent reaction performance. However, tailoring of this process at the reformer level has received little research attention. Herein, we present the dynamics of compact methanol reformers with Cu/ZnO/Al2O3 catalysts during in situ H2/N2 pre‐activation as a preliminary step of online catalyst activation by computational fluid dynamics simulations. Raising inlet temperatures or hydrogen fractions is demonstrated to accelerate activation while generating a high‐temperature band within the catalyst bed, which hampers effective activation. Increasing the reductant flow rates improves the homogeneity of activation thanks to enhanced convective heat and mass transfer. Notably, we revealed that inlet reductants exceeding 453 K trigger temperature runaway that may severely damage the reformer. These new insights will enlighten optimization of operation and control of on‐board methanol reforming for FCVs. [ABSTRACT FROM AUTHOR]

Generally, fossil carbon materials (coal, coke/char, and petroleum coke), biological carbon materials (charcoal, woodchips), and quartz from the earth's crust are sources of carbon and silica to synthesise silicon carbide (SiC) at temperatures between 2000 and 2200 °C. The study investigated the isothermal and non-isothermal kinetics of synthesising SiC from automotive shredder residues (ASR) and windshield glass of end-of-life-vehicle (ELVs) at 1300 °C, 1400 °C, and 1500 °C for 30 min. The kinetics of ASR and waste glass degradation were studied by relating the thermogravimetric data via the Coats–Redfern model. The reaction mechanism includes the rapid formation of a gaseous SiO intermediate, and carbon reduction of the SiO to SiC is reaction-rate-controlling. The understanding of kinetics inferred that the optimisation of SiC formation is entirely associated with the conversion of SiO2 to SiO vapour and their reaction with CO and carbon particles. The kinetic parameters of the degradation of mixed ASR and waste glass were determined, and the activation energy of mixed ASR and glass for non-isothermal conditions are 22.48 kJ mol−1, 2.97 kJ mol−1, and 6.5 kJ mol−1, and for the isothermal study to produce SiC is 225.9 kJ mol−1, respectively. The results confirmed that this facile way of synthesising SiC would conserve about 50% of chemical energy compared to the traditional way of producing SiC. A beneficial route of transforming the heterogenous ASR and glass wastes into SiC with economic and environmental benefits is recognised. [ABSTRACT FROM AUTHOR]

The understanding of oxide scale reduction mechanisms after microstructure transformation under different preheating conditions is incomplete. Herein, the reduction kinetics and microstructure transformations of hot rolled steel strip oxide scale during reduction (30% H2–N2) annealing are studied in detail using thermogravimetric and microstructure analyses, and mathematical modeling based on the gas–solid reaction. The results show that the rate‐determining steps of the reduction reaction are nucleation and growth of new phase between 500 and 600 °C, and gas–solid interface reactions between 700 and 800 °C. Microstructure transformation of the oxide scale occurs during the preheating process: at 500 °C, the eutectoid iron preferentially dissolves, and short‐range diffusion of Fe ions into adjacent Fe3O4 increases their content in the metal oxide; at 600 °C, nucleation and growth of Fe1 − yO occur, and some Fe3O4 precipitates and white α‐Fe are found in the Fe1 − yO layer, whereas the majority of the Fe3O4/iron eutectoid structure is retained; between 700 and 800 °C, the oxide scale forms outer and inner layers of Fe3O4 and Fe1 − yO, respectively. After preheating and reduction, the reduced products are porous iron over 500–600 °C, while porous and dense iron occur at 700 °C; dense iron forms as whiskers or granules between 700 and 800 °C. The surface quality of hot rolled steel strip after reduction annealing is subsequently improved as surface cracks are infilled by the newly formed dense iron. [ABSTRACT FROM AUTHOR]

Water-soluble spin probes were obtained from reduction-resistant sterically shielded pyrrolidine nitroxides by forming a 4,5-dicarboxy-1H-1,2,3-triazole fragment in the side chain by the Huisgen reaction of the azido group with acetylenedicarboxylic acid ester followed by hydrolysis. For the synthesized radicals, the reduction rate constants by ascorbate and the partition coefficient in an octanol—water system were determined. [ABSTRACT FROM AUTHOR]

The effect of different lower air inlet tube inclinations on the gas dynamics, including concentration, fluid flow profile, temperature, and heat transfer potency, to the bottom part of a rotary hearth furnace (RHF), were investigated. The lower air-inlet tube inclination was varied from 5° to 25° upwards with the horizontal to maximize the burner efficiency. The inlet tube configuration with the lower two air-inlet tubes inclined at 10° upwards emerged as the most efficient tube orientation in the present burner system. This air inlet configuration of the burner produced the maximum heat transfer efficiency in transferring the combustion heat produced in the freeboard region to the bottom pellet layer region. Moreover, it was also able to produce better CO post-combustion efficiency. [ABSTRACT FROM AUTHOR]

Reducibility and reduction kinetics of hardened pellets prepared from a novel, lean-grade multimetallic magnetite ore was investigated in the present study. The hardened pellets were reduced between the temperature range of 1223–1423 K for 30–120 min in a bed of non-coking coal. The highest reducibility and metallization of 80% and 92% were obtained at 1373 K at a reduction time of 120 min. The kinetic model "[(1 − α)−1/3 − 1]2 = kt" was found to be the best fit for the reduction of pellets. Activation energy calculated for the pellets was 165.38 kJ/mole. A metallization of up to 85% was achieved on pellets reduced at 1373 K for 90 min. [ABSTRACT FROM AUTHOR]

Chemical looping reforming of methane is a novel and effective approach to convert methane to syngas, in which oxygen transfer is achieved by a redox material. Although lots of efforts have been made to develop high-performance redox materials, a few studies have focused on the redox kinetics. In this work, the kinetics of SrFeO3−δ−CaO·MnO nanocomposite reduction by methane was investigated both on a thermo-gravimetric analyzer and in a packed-bed microreactor. During the methane reduction, combustion occurs before the partial oxidation and there exists a transition between them. The weight loss due to combustion increases, but the transition region becomes less inconspicuous as the reduction temperature increased. The weight loss associated with the partial oxidation is much larger than that with combustion. The rate of weight loss related to the partial oxidation is well fitted by the Avrami—Erofeyev equation with n = 3 (A3 model) with an activation energy of 59.8 kJ·mol−1. The rate law for the partial oxidation includes a solid conversion term whose expression is given by the A3 model and a methane pressure-dependent term represented by a power law. The partial oxidation is half order with respect to methane pressure. The proposed rate law could well predict the reduction kinetics; thus, it may be used to design and/or analyze a chemical looping reforming reactor. [ABSTRACT FROM AUTHOR]

Long duration energy storage (LDES) is an economically attractive approach to accelerating clean renewable energy deployment. The newly emerged solid oxide iron–air battery (SOIAB) is intrinsically suited for LDES applications due to its excellent low‐rate performance (high‐capacity with high efficiency) and use of low‐cost and sustainable materials. However, rechargeability and durability of SOIAB are critically limited by the slow kinetics in iron/iron‐oxide redox couples. Here the use of combined proton‐conducting BaZr0.4Ce0.4Y0.1Yb0.1O3 (BZC4YYb) and reduction‐promoting catalyst Ir to address the kinetic issues, is reported. It is shown that, benefiting from the facilitated H+ diffusion and boosted FeOx‐reduction kinetics, the battery operated under 550 °C, 50% Fe‐utilization and 0.2 C, exhibits a discharge specific energy density of 601.9 Wh kg–1‐Fe with a round‐trip efficiency (RTE) of 82.9% for 250 h of a cycle duration of 2.5 h. Under 500 °C, 50% Fe‐utilization and 0.2 C, the same battery exhibits 520 Wh kg–1‐Fe discharge energy density with an RTE of 61.8% for 500 h. This level of energy storage performance promises that SOIAB is a strong candidate for LDES applications. [ABSTRACT FROM AUTHOR]

Isothermal thermogravimetric analysis was used to study the reduction process of solid/liquid wustite by hydrogen. Results show that wustite in both states can be reduced entirely at all temperatures. The thermal and kinetic conditions for the hydrogen reduction of molten phases are better than those when the reactants and products are in the solid state, with a higher reaction rate. The hydrogen reduction of different wustite phases fits the Mampel Power model (power exponent n = 1/2) well, and this model is independent of the phase state. The average apparent activation energies of the reduction process calculated by the iso-conversional method are 5.85 kJ·mol−1 and 104.74 kJ·mol−1, when both reactants and products are in the solid state and the molten state, respectively. These values generally agree with those calculated by the model fitting method. [ABSTRACT FROM AUTHOR]

With Pd as an example, a set of quantitative analyses is designed to shed light on the bromide‐mediated reduction kinetics and oxidative etching in determining the twin structure and facet of Pd nanocrystals. The success of this work relies on the kinetic measurements of Pd(II) precursor reduction and the close examinations of resultant Pd seeds and nanocrystals at different stages of synthesis. We observe there is a clear trend where low, moderate, and high initial Pd(II) reduction rates regulated by Br− ions correspond to the formation of Pd seeds with singly‐twinned, multiply‐twinned, and single‐crystal structures in the nucleation stage, respectively. Our quantitative analyses also suggest the oxidative etching induced by oxygen/Br− pair can selectively remove the multiply‐twinned Pd seeds from the products in the growth stage while leaving behind singly‐twinned or single‐crystal Pd seeds for the evolution into Pd nanocrystals with well‐defined facets in high purity. The mechanistic insights obtained in this work can be extended to the synthesis of Pd@Pd−Pt core−shell nanocubes with high‐index facets, which can be used as excellent electrocatalysts and photocatalysts for hydrogen generation. [ABSTRACT FROM AUTHOR]

Red mud is a potential iron resource that needs to be urgently exploited and utilized. However, due to the properties of high alkalinity, fine particle size and complex mineral composition, the utilization of red mud is difficult. Focusing on red mud's prominent feature of high alkalinity, this paper studies the influence of NaOH content on the reduction kinetics of hematite, which is the main component of red mud. The results show that the conversion degree of hematite was strongly inhibited by NaOH, and the magnetization and specific magnetic susceptibility of reduction products was significantly decreased with the increase in NaOH content. Meanwhile, the results of the calculation of kinetics parameters demonstrate that the addition of NaOH did not affect the control step of the reduction of hematite, while it dramatically decreased the reduction rate of hematite. Moreover, thermodynamic analysis and SEM-EDS detection were conducted to uncover the inhibited mechanism of NaOH on the reduction of hematite, which indicated that sodium ferrite could be produced spontaneously under the experimental conditions and that it is hard for it to be further reduced by CO. Furthermore, the produced sodium ferrite formed a dense film, which covered the surface of the hematite particles, inhibiting the diffusion of CO and thereby hindering the reduction of the interior hematite. [ABSTRACT FROM AUTHOR]

Simple Summary: NADPH-cytochrome P450 reductase (CPR) enzymes are known to undergo an ample conformational transition between the closed and open states in the process of their redox cycling. To explore the conformational landscape of CPR from the potential biofuel crop Sorghum bicolor (SbCPR), we incorporated a FRET donor/acceptor pair into the enzyme and employed rapid scanning stop-flow and pressure perturbation spectroscopy to characterize the equilibrium between its open and closed states at different stages of the redox cycle. Our results suggest the presence of several open conformational sub-states differing in the system volume change associated with the opening transition (ΔV0). Although the closed conformation always predominates in the conformational landscape, the population of the open conformations increases by order of magnitude upon the two-electron reduction and the formation of the disemiquinone state of the enzyme. In addition to elucidating the functional choreography of plant CPRs, our study demonstrates the high exploratory potential of a combination of the pressure-perturbation approach with the FRET-based monitoring of protein conformational transitions. NADPH-cytochrome P450 reductase (CPR) from Sorghum bicolor (SbCPR) serves as an electron donor for cytochrome P450 essential for monolignol and lignin production in this biofuel crop. The CPR enzymes undergo an ample conformational transition between the closed and open states in their functioning. This transition is triggered by electron transfer between the FAD and FMN and provides access of the partner protein to the electron-donating FMN domain. To characterize the electron transfer mechanisms in the monolignol biosynthetic pathway better, we explore the conformational transitions in SbCPR with rapid scanning stop-flow and pressure-perturbation spectroscopy. We used FRET between a pair of donor and acceptor probes incorporated into the FAD and FMN domains of SbCPR, respectively, to characterize the equilibrium between the open and closed states and explore its modulation in connection with the redox state of the enzyme. We demonstrate that, although the closed conformation always predominates in the conformational landscape, the population of open state increases by order of magnitude upon the formation of the disemiquinone state. Our results are consistent with several open conformation sub-states differing in the volume change (ΔV0) of the opening transition. While the ΔV0 characteristic of the oxidized enzyme is as large as −88 mL/mol, the interaction of the enzyme with the nucleotide cofactor and the formation of the double-semiquinone state of CPR decrease this value to −34 and −18 mL/mol, respectively. This observation suggests that the interdomain electron transfer in CPR increases protein hydration, while promoting more open conformation. In addition to elucidating the functional choreography of plant CPRs, our study demonstrates the high exploratory potential of a combination of the pressure-perturbation approach with the FRET-based monitoring of protein conformational transitions. [ABSTRACT FROM AUTHOR]

Pyrrolidine nitroxides with four bulky alkyl substituents adjacent to N–O group are known for their high resistance to bioreduction. The 3,4-unsubstituted 2-tert-butyl-2-ethylpyrrolidine-1-oxyls were prepared from the corresponding 2-tert-butyl-1-pyrroline-1-oxides via either the addition of ethinylmagnesium bromide with subsequent hydrogenation or via treatment with ethyllithium. The new nitroxides showed excellent stability to reduction with ascorbate with no evidence for additional large hyperfine couplings in the EPR spectra. [ABSTRACT FROM AUTHOR]

The kinetics of the reduction of magnetite concentrate particles by H2+CO mixtures have been investigated in drop-tube reactors (DTRs) to obtain rate expressions for the design of novel flash ironmaking reactors. The experimental temperature varied from 1423 K (1150°C) to 1873 K (1600°C). The H2/CO ratio was varied from 0.5 to 2, which is the typical composition range of the product gas from the partial oxidation of natural gas. The experimental data were analysed separately in two temperature ranges 1423 K (1150°C)–1623 K (1350°C) and 1623 K (1350°C)–1873 K (1600°C), as the magnetite concentrate particles tend to fuse and melt at temperatures above 1623 K (1350°C) changing the reduction mechanism. CFD (Computational Fluid Dynamics) simulations were used to more accurately account for temperature and concentration variations. Synergistic effects were observed in the reduction by H2+CO mixtures compared with the simple summation of contributions of the individual component gases. [ABSTRACT FROM AUTHOR]

A CDF model for simulating gas dynamics, heat and mass transfer in the freeboard of a pilot-scale Rotary Hearth Furnace (RHF) is developed in conjunction with an independent solid reduction model at the bottom of the hearth. The effect of air-inlet configuration and inlet fuel composition on the fuel requirement, exit gas composition, fluid flow, temperature, and gaseous composition distribution have been investigated using this model. The lower air-inlet tubes orientated at 5° upwards keeping remaining air and fuel tubes horizontal emerged as the most recommended burner configuration. Various alternative fuels categorized in terms of calorific values, demonstrated that the fuel with high calorific value required less fuel and produced less CO2 emission. Interestingly, it was found that for the same calorific value a combination of blast furnace gas and coke oven gas (BF+COG) produced less CO2 emission compared to a combination of COG+BF+NG (Natural gas). [ABSTRACT FROM AUTHOR]

As an important powder material for scandate cathode, Sc2O3-doped WO3 powder together with hollow spherical WO3 for comparison was prepared by spray-drying method. The reduction behavior and kinetics of pure WO3 and Sc2O3-doped WO3 were studied by temperature-programmed reduction (TPR) method. It is found that scandia doping can decrease the reduction activation energy of WO3 and thus lower the reduction temperature and increase the reduction rate. Based on the kinetics results, the reduction techniques are presented. The obtained powder has a narrow size distribution in the range of 0.6–0.8 μm. [ABSTRACT FROM AUTHOR]

Cobalt is a critical, high-value metal used extensively in batteries and other sustainable technologies. To secure its supply in future, it is utmost important to recover cobalt efficiently from industrial wastes and recycled End-of-Life batteries. This study aims at finding ways to improve the reduction of cobalt as well as valuable metals nickel and copper in nickel slag cleaning furnace conditions by using both traditional fossil-based coke and a more sustainable option, low-CO2 footprint biochar, as reductants. A cobalt-rich fraction of battery scrap (25.5 wt% Co) was also used as a secondary feed. The experimental technique consisted of reduction experiments with different times at 1400 ffiC under inert atmosphere, quick quenching and Electron Probe X-ray Microanalysis. The use of biochar resulted in faster reaction kinetics in the reduction process, compared to coke. Moreover, the presence of battery scrap had a clear impact on the behavior and reduction kinetics of the elements and/or enhanced settling and separation of matte and slag. The addition of scrap increased notably the distribution coefficients of the valuable metals but consequently also the iron concentration in matte which is the thermodynamic constraint of the slag cleaning process. [ABSTRACT FROM AUTHOR]

In order to maximize the performance of nanocrystals in a specific application, it is necessary to control both their size and shape. Here we report a one‐pot protocol that allows us to separate growth from nucleation for achieving better control over the size and shape of Pd nanocrystals. The two processes are temporally separated from each other, although the synthesis is carried out in the same reaction container. Size control is achieved by simply varying the ratio between the amounts of precursor allocated to the growth and nucleation processes. With the involvement of seeds at a fixed number, increasing the amount of precursor for growth leads to increasingly larger nanocrystals. Shape control is made possible by varying the capping agent, with bromide leading to a cubic shape and citrate inducing the formation of an octahedral shape. The synthesis can also be scaled up by at least tenfold without compromising the quality. [ABSTRACT FROM AUTHOR]

Anion transporters have shown potential application as anti‐cancer agents that function by disrupting homeostasis and triggering cell death. In this research article we report switchable anion transport by gold complexes of anion transporters that are "switched on" in situ in the presence of the reducing agent GSH by decomplexation of gold. GSH is found in higher concentrations in tumors than in healthy tissue and hence this approach offers a strategy to target these systems to tumors. [ABSTRACT FROM AUTHOR]

Anion transporters have shown potential application as anti‐cancer agents that function by disrupting homeostasis and triggering cell death. In this research article we report switchable anion transport by gold complexes of anion transporters that are "switched on" in situ in the presence of the reducing agent GSH by decomplexation of gold. GSH is found in higher concentrations in tumors than in healthy tissue and hence this approach offers a strategy to target these systems to tumors. [ABSTRACT FROM AUTHOR]

The study of Pt(IV) antitumor prodrugs able to circumvent some drawbacks of the conventional Pt(II) chemotherapeutics is the focus of a lot of attention. This paper reports a thorough study based on experimental methods (reduction kinetics, electrochemistry, tandem mass spectrometry and IR ion spectroscopy) and quantum–mechanical DFT calculations on the reduction mechanism of cisplatin-based Pt(IV) derivatives having two hydroxido (1), one hydroxido and one acetato (2), or two acetato ligands (3) in axial position. The biological reductants glutathione and ascorbic acid were taken into consideration. The presence of a hydroxido ligand resulted to play an important role in the chemical reduction with ascorbic acid, as verified by 15N-NMR kinetic analysis using 15N-enriched complexes. The reactivity trend (1 > 2 > 3) does not reflect the respective reduction peak potentials (1 < 2 < 3), an inverse relationship already documented in similar systems. Turning to a simplified environment, the Pt(IV) complexes associated with a single reductant molecule (corresponding to the encounter complex occurring along the reaction coordinate in bimolecular reactions in solution) were characterized by IR ion spectroscopy and sampled for their reactivity under collision-induced dissociation (CID) conditions. The complexes display a comparable reduction reactivity ordering as that observed in solution. DFT calculations of the free energy pathways for the observed fragmentation reactions provide theoretical support for the CID patterns and the mechanistic hypotheses on the reduction process are corroborated by the observed reaction paths. The bulk of these data offers a clue of the intricate pathways occurring in solution. Graphic abstract [ABSTRACT FROM AUTHOR]

This article reports a facile method for the synthesis of Pd‐Ru nanocages by activating the galvanic replacement reaction between Pd nanocrystals and a Ru(III) precursor with I‐ ions. The as‐synthesized nanocages feature a hollow interior, ultrathin wall of ≈2.5 nm in thickness, and a cubic shape. Our quantitative study suggests that the reduction rate of the Ru(III) precursor can be substantially accelerated upon the introduction of I‐ ions and then retarded as the ratio of I‐/Ru3+ is increased. The Pd‐Ru nanocages take an alloy structure, with the Ru atoms in the nanocages crystallized in a face‐centered cubic structure instead of the hexagonal close‐packed phase taken by bulk Ru. Using Pd nanocubes with different edge lengths, the dimensions of the nanocages in the range of 6−18 nm can readily be tuned. When tested as catalysts toward the electro‐oxidation of ethylene glycol and glycerol, respectively, the Pd‐Ru cubic nanocages prepared from 18 nm Pd cubes exhibit 5.1‐ and 6.2‐fold enhancements in terms of mass activity relative to the commercial Pd/C. After 1000 cycles of accelerated durability test, the mass activities of the nanocages are still 3.3 and 3.7 times as high as that of the pristine commercial Pd/C catalyst, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Mineral Processing & Extractive Metallurgy Review is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Suspension magnetization roasting followed by magnetic separation is an innovative and effective way to recover iron from refractory iron ores, and the particle size of the ore greatly affects the roasting index. To identify the effect of particle size on the reduction kinetics for the transformation of hematite to magnetite, a high-purity hematite ore with different size fractions were isothermally reduced using a suspension roaster. The pure hematite ore was divided into -1000+500 µm, -500+150 µm, -150+74 µm, -74+37 µm and -37 µm size fractions, while the gas mixture of CO and CO2 with a volume ratio of 1:4 was used as reductant. The results showed that the most suitable mechanism function for the reduction of -37 µm size fraction hematite ore is the Avrami-Erofeev model. In the case of -500+37 µm size fraction, the reduction process can be described by first-order chemical reaction model. For -1000+500 µm size fraction, the reduction of hematite ore is restricted by the second-order chemical reaction. In addition, scanning electron microscopy (SEM) analysis results demonstrated that the transformation of hematite particles to magnetite is in accordance with the characteristics of shrinking core model. The phase transformation primarily occurs at the edge of hematite particles and then develop towards the inner side of particles. The findings of this paper provide a theoretical basis for the development and utilization of refractory hematite ore via suspension magnetization roasting technology. [ABSTRACT FROM AUTHOR]

A series of nanosized CeO2–Fe2O3 mixed-oxide nanocomposites with different Ce4+/Fe3+ molar ratios were successfully prepared by a co-precipitation technique. The surface area increased with Fe2O3 content increasing up to 60 wt% in the composite. However, with further increase in Fe2O3 content, the surface area began to decrease. The reduction processes of the CeO2–Fe2O3 nanocomposites were studied in a hydrogen atmosphere at 300–600 °C. The reduction rates increased by increasing both the temperature and Fe2O3 content in the nanocomposites. The microstructure of the reduced composites at 500 °C illustrated the presence of a considerable number of macro- and micro-pores. The activation energy values were calculated which were in the range of 3.56–5.37 kJ·mol−1 at the initial stages (up to 35% reduction) and 5.21–10.2 kJ·mol−1 at the final stages (up to 80% reduction) of reduction. The rate-controlling mechanisms in both the initial and final reduction stages were determined, and the initial reaction stage was controlled by combined gaseous diffusion and interfacial chemical reaction mechanisms for all the composites except for pure CeO2, which was controlled by a chemical reaction mechanism. The final reaction stage was controlled by a gaseous diffusion mechanism for some composites, while for the others it was controlled by combined gaseous diffusion and interfacial chemical reaction mechanisms. The hydrogen sorption properties of the nanocomposites were studied by pressure composition isotherms using a volumetric method. Hydrogen storage in the nanocomposites increased by increasing the temperature because of the formation of oxygen vacancies which enhance atomic H adsorption and function as strong adsorption sites forming more metal hydride covalent bonds. [ABSTRACT FROM AUTHOR]

Surface capping has been shown to play a pivotal role in controlling the evolution of metal nanocrystals into different shapes or morphologies. With the synthesis of Au@Pd concave nanocubes as an example, here we demonstrate that the capping agent can also impact the reduction kinetics of a precursor, and thereby its reduction pathway, for the formation of metal nanocrystals with distinct morphologies. A typical synthesis involves the reduction of a PdII precursor by ascorbic acid at room temperature in the presence of Au nanospheres as seeds, together with the use of hexadecyltrimethylammonium chloride (CTAC) or hexadecyltrimethylammonium bromide (CTAB) as the capping agent. In the case of CTAC, the PdII precursor prevails as PdCl42−, leading to the formation of Au@Pd concave nanocubes with a rough surface because of the fast reduction kinetics and thus the dominance of solution reduction pathway. When switched to CTAB, the PdII precursor changes to PdBr42− that features slow reduction kinetics and surface reduction pathway. Accordingly, the Au@Pd concave nanocubes take a smooth surface. This work demonstrates that both reduction kinetics and surface capping play important roles in controlling the morphology of metal nanocrystals and these two roles are often coupled to each other. [ABSTRACT FROM AUTHOR]

Reduction leaching behaviors of Fe and Mn from an iron-rich manganese oxide ore using waste tobacco stem concrete as reducing agent were investigated in this paper with a view to determining the feasibility of tobacco stem concrete used in reduction leaching of Mn from iron-rich manganese oxide ore. Results indicated that the leaching processes of Fe and Mn were both dominated by internal diffusion, but the effects of leaching parameters on leaching ratios of Fe and Mn were different based on established leaching kinetic equations. The leaching ratio of Mn reached up to 96.18% while that of Fe kept a lower concentration (17.66%) under optimal leaching conditions, which achieved high selectivity recovery of Mn from iron-rich manganese oxide ore. In addition, the leached solution can be used as electrolytic stock solution in the production of electrolytic manganese. Characterization of the obtained electrolytic manganese product indicated that the quality of electrolytic manganese fully met the standards of YB/T 051-2003, which disclosing a novel recycling approach of utilizing the resource coming from the tobacco industry. [ABSTRACT FROM AUTHOR]

This study aims to reduce zinc ferrite using carbon monoxide in the temperature range of 25–1000 °C using temperature-programmed reduction. The kinetic parameters were evaluated using the Friedman isoconversional method, and multi-step reaction models were determined by nonlinear regression methods. The reduction of zinc ferrite is a stepwise process according to the thermodynamic calculation and the variation of the activation energy Ea. Ea generally remained between 100 and 120 kJ mol−1 during the reduction process. The mechanism was determined based on an F-test of the fit quality. The corresponding kinetic parameters were obtained and employed to predict the isothermal reduction of zinc ferrite. The experimental data were found to be consistent with the predicted data, suggesting that the reduction can be satisfactorily described by the presented mechanism. [ABSTRACT FROM AUTHOR]

In this study the fixation of nano zero valent iron (nZVI) on a polymeric matrix applying an environmentally friendly technique and the performance of this material for the treatment of Cr(VI) contaminated groundwater were evaluated. The investigated method could be applied in a pump & treat groundwater remediation system. A macroreticular cationic resin was selected as porous host material. It was found that green tea polyphenols were able to penetrate within the macroporous resin matrix and obtain the reduction of Fe(III) to the elemental state. The effectiveness of this composite material in removing Cr(VI) contaminated waters was evaluated by conducting batch tests. It was found that the reduction of Cr(VI) follows a kinetics law of first order with respect to the concentration of Cr(VI) and to the amount of nZVI per liter of solution. The kinetic constant varied between 5·10−3 and 0.5·10−3 per min and per mM of nZVI in the pH range 3.5-7.5. [ABSTRACT FROM AUTHOR]

A mechanism for the thermal reduction of graphite oxide is proposed. The process begins with the homolysis of the C-C bond in the basal plane of graphite oxide with subsequent reactions of isomerization of the formed radicals. The formation of both CO and a significant amount of CO2 was explained to occur via the cleavage of 1,3-dioxetane, which forms by the disproportionation and recombination of free radicals. [ABSTRACT FROM AUTHOR]

Herein, the authors reported a carbon dots mediated synthesis of gold nanoparticles (AuNPs) at room temperature. Transmission electron microscopy revealed that the AuNPs are spherical in shape with a size of 10 nm. As‐prepared AuNPs was immobilised on carbon paste electrode and subjected to electrochemical sensing of an important neurotransmitter dopamine. Differential pulse voltammetry studies revealed sensitive and selective determination of dopamine in the presence of commonly interfering ascorbic acid and uric acid. The linear detection range was 10–600 μM and the limit of detection was 0.7 ± 0.18 μM. The practical application was demonstrated by measuring dopamine in human blood serum and urine samples. The catalytic activity of AuNPs was evaluated by sodium borohydride mediated reduction of nitroaromatic compounds. The reduction kinetics was found to be pseudo‐first‐order kinetics. All the tested nitroaromatics reduced to corresponding amines in <10 min. [ABSTRACT FROM AUTHOR]

Shape-controlled synthesis of Pt−Cu alloy nanocrystals (NCs) with unique geometries is of great importance in the rational design and deterministic synthesis of highly active electrocatalysts. Herein, Pt−Cu alloy NCs with concave octahedron (COH), porous octahedron (POH), yolk-shell (YSH), and nanoflower (NOF) structures were fabricated by altering the sequential reduction kinetics in a one-pot aqueous phase. The effect of the reaction kinetics on the formation of Pt−Cu bimetallic NCs with different morphologies was analyzed quantitatively. The concentrations of glycine and metal cation are demonstrated to play a key role in the reduction of Pt(IV) and Cu(II) ions; these significantly affected the morphology of Pt−Cu NCs. These Pt−Cu alloy NCs exhibit substantially enhanced catalytic activity and durability for methanol and formic acid oxidation compared to the commercial Pt/C catalyst. Specifically, the COH and NOF Pt−Cu NCs with more step atoms, intragranular dislocations, and protrusions showed superior electrochemical properties than those of POH and YSH Pt−Cu NCs. The structure-property relationship between the Pt−Cu NCs and their electrochemical performances was also investigated in depth. [ABSTRACT FROM AUTHOR]

The kinetics of reduction of a 10 wt %Fe2O3‐MgAl2O4 spinel were investigated using XRD and time resolved Fe‐K QXANES. The Rietveld refinement of the XRD pattern showed the replacement of Al with Fe in the spinel structure and the formation of MgFeAlOx. The XANES pre‐edge feature was employed to study the reduction kinetics during H2‐TPR (Temperature Programmed Reduction) up to 730°C. About 55% of the Fe3+ in MgFeAlOx was reduced to Fe2+. A shrinking core model, which takes into account both solid‐state diffusion via an oxygen diffusion coefficient, and gas‐solid reaction through a reaction rate coefficient, was applied. The activation energy for chemical reaction showed a linear dependence on the conversion, increasing from 104 to 126 kJ/mol over the course of material reduction. The good accordance between the shrinking core model description and the experimental data indicates that XANES pre‐edge features can be used to correlate changes in material structure and reaction kinetics. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1339–1349, 2018 [ABSTRACT FROM AUTHOR]

The reduction of the molecular iron-molybdenum-nanocluster, [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y](FeMoC), was studied using model free isoconversional methods. The reduction kinetics were evaluated using the non-isothermal thermogravimetric measurements at four different heating rates from 5 to 20 °C/min in a 5% hydrogen atmosphere (argon balance). The apparent activation energy dependence on conversion derived from the isoconversional Kissinger–Akahira–Sunose (KAS) and Vyazovkin methods reveals a complex multi-step process with values ranging from 60.8 ± 13.3 to 183 ± 6.3 kJ/mol. The kinetic results were validated by isothermal predictions. The results herein are useful for optimization and development of FeMoC derived Fe–Mo nanoalloy systems. [ABSTRACT FROM AUTHOR]

Cobalt nanopowder is very promising for use in science, engineering, industry, and medicine. The present study focuses on the kinetics of nanopowder production by the reduction of cobalt oxide with hydrogen in an electromagnetic field, under the action of a bed of ferromagnetic particles rotating in the electromagnetic field. Cobalt oxide (Co3O4) nanopowder is obtained by the thermal decomposition of cobalt hydroxide Co(OH)2 deposited from 10% ionic solutions of cobalt nitrate Co(NO3)2 and sodium hydroxide NaOH at 20°C, with pH 9. Cobalt nanoparticles are produced from Co3O4 nanopowder in a modified UAP-3 vortical bed system with a built-in furnace and flow-through reactor. The amplitude of the magnetic induction within the reactor is 0.16 T. The experimental reduction temperature is selected on the basis of thermogravimetric analysis of the initial Co(OH)2 sample. The kinetic parameters of hydrogen reduction with linear heating and in isothermal conditions are calculated on the basis of the Freeman-Carroll and McKewan models, respectively. The rate of cobalt- nanopowder production slows in an electromagnetic field (by up to 14% at 250°C), on account of hindrance to the adsorption of hydrogen atoms at the surface of the metallic nanoparticles formed. However, mechanical stimulation in a vortical bed increases the rate of the process by a factor of 4-5 as a result of activation. The properties of the initial material and the products are studied by thermogravimetric analysis, X-ray diffraction analysis, scanning electron microscopy, and measurement of the specific surface by low-temperature nitrogen absorption. In the reduction of the samples, smaller cobalt nanoparticles are produced in the presence of an electromagnetic field. Mechanical stimulation in a vortical bed results in aggregation of the cobalt nanoparticles and the formation of microgranules. [ABSTRACT FROM AUTHOR]

The mechanism and kinetics of the reduction of hematite to magnetite in a laboratory-scale, micro-fluidized bed reactor were isothermally investigated. The procedure consisted of the isothermal heating in a flow of a 20%CO-80%CO2 mixture at temperatures from 500 °C to 600 °C. It was found that the Avrami-Erofe'ev model of nucleation and 1D growth (n = 1.58) successfully described the phase transition of hematite to magnetite, and the value of activation energy ΔEa of the reaction was estimated to be 48.70 kJ/mol. The microstructure properties for specimens with different conversion degrees were analyzed using the Brunauer, Emmett and Teller (BET) method and scanning electron microscopy (SEM). The results showed that the magnetite nuclei were needle-like, and the hematite specimens became thoroughly porous after complete reduction to magnetite. The physical and chemical processes of the reaction were also discussed. [ABSTRACT FROM AUTHOR]

The effect of mechanical activation on the reduction kinetics of magnetite concentrate by hydrogen was studied. The magnetite concentrate was milled for 8 h in a planetary ball mill. After 8 h of milling, the average particle size was reduced from 14 to 4.4 µm, resulting in a lattice microstrain of 0.3. Isothermal reduction experiments were conducted by thermogravimetry to focus on the chemical reaction as the rate-controlling factor by eliminating external mass transfer effects and using a thin layer of particles to remove interstitial diffusion resistance. Thus, about 2 mg of magnetite powder was reduced at different temperatures under a sufficient flow of hydrogen. The magnetite concentrate and reduction products were analyzed by SEM and XRD. It was found that the onset reduction temperature decreased from 587 to 500 K (314-227 °C) due to the mechanical activation. The activation energy for hydrogen reduction of the activated concentrate decreased about 10% compared with the as-received concentrate. In view of the results, a reaction rate expression was established based on the nucleation and growth model with an Avrami parameter n = 2.5. [ABSTRACT FROM AUTHOR]

The reduction of ilmenite concentrate in 30vol% CO-70vol% N 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 kJ·mol. 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 kJ·mol. For the whole reduction process, the average activation energy and pre-exponential factor were 98.94-118.33 kJ·mol and 1.820-1.816 min, respectively. [ABSTRACT FROM AUTHOR]