Diffusion Controlled Research Articles

Gasification and kinetic study on metallurgical cokes in CO2-N2-H2O and CO2-N2 atmosphere

ABSTRACT A high-temperature gas-solid reaction device was used to simulate the gasification of coke in a hydrogen-rich blast furnace, with the gasification reaction of water/anhydrous bulk cokes studied. CO2 and H2O effects on coke gasification kinetics were analyzed in CO2-N2-H2O and CO2-N2 with the experimental temperature of 1173–1523 K, the CO2 content of 15–60%, and the H2O content of 15%. Compared with those of CO2-N2, the gasification reaction rate and carbon conversion rate of cokes in the CO2-N2-H2O mixture were significantly higher. Carbon conversion rates of the CO2-N2-H2O mixture at different temperatures were about 30% higher than those of CO2-N2 on average, and the gasification reaction rate was about 50% higher on average. There were two temperature regions for gasifying cokes in CO2-N2-H2O and CO2-N2 mixtures. At 1,273 K, the gasification reaction is transformed into diffusion control, which is from chemical reaction control. The aggravation of coke gasification by H2O generated after hydrogen reduction of iron ores was mainly reflected at the lower temperature. Besides, the kinetic model analysis showed that random pore model was optimal in describing the gasification reaction of cokes in CO2-N2-H2O and CO2-N2, and the addition of H2O improved the gasification reaction’s activation energy.

Recover value metals from spent lithium-ion batteries via a combination of in-situ reduction pretreatment and facile acid leaching

The pretreatment of cathode material before leaching is crucial in the spent lithium-ion battery hydro-metallurgical recycling. Here research demonstrates that in-situ reduction pretreatment could dramatically improve the leaching efficiencies for valuable metals from cathodes. Specifically, calcination under 600 °C without oxygen using alkali treated cathode can induce in-situ reduction and collapse of oxygen framework, which is ascribed to the carbon inherently contained in the sample and promote the following efficient leaching without external reductants. The leaching efficiencies of Li, Mn, Co and Ni can remarkably reach 100%, 98.13%, 97.27% and 97.37% respectively. Characterization methods, such as XRD, XPS and SEM-EDS, were employed and revealed that during in-situ reduction, high valence metals such as Ni3+, Co3+, Mn4+ can be effectively reduced to lower valence states, conducive to subsequent leaching reactions. Moreover, leaching processes of Ni, Co and Mn fit well with the film diffusion control model, and the reaction barrier is in accordance with the order of Ni, Co and Mn. In comparison, it is observed that Li was leached with higher efficiency regardless of the various pretreatments. Lastly, an integral recovery process has been proposed and economic assessment demonstrates that in-situ reduction pretreatment increases the benefit with a negligible cost increase.

Controlling diffusion in gold bonding materials for high reliability via microalloying of trace rare earth metals

Diffusion plays a vital role in regulating microstructure evolution and properties of metallic materials. However, understandings of how microalloying affects diffusion kinetics in gold bonding materials remain far from comprehensive, which severely threatens the reliability of microelectronic devices in the big-data era. This problem persists challenging due to enormous difficulty in accurate and cost-effective experimental measurements. Here, first-principle based theoretical computations are performed to explore the control of diffusion at elevated service temperatures by trace rare earth (RE) microalloying in gold bonding materials. We identify the light lanthanides can stably bind excess vacancies and the efficacy to modulate vacancy/solute-vacancy evolution depends on the RE concentrations and ambient temperatures. Above critical doping concentrations, self- and impurity-diffusion can be simultaneously hindered. These findings successfully point to a rational microalloying strategy to withstand heat and a novel perspective on improving the service life-time of microelectronics packaging materials.

Optimal Control of Information Diffusion in Temporal Networks

Effective control of information diffusion is quite a significant and universal task in information science and control engineering. The diffusion process and network evolution often share a common time scale. However, previous studies mainly focus on fixed topological structures, ignoring the temporal property of real networks. To fill this gap, we comprehensively investigate the optimal control of information diffusion in temporal networks. First, activity-driven networks (ADNs) are introduced to represent realistic temporal networks. Meanwhile, the node-based susceptible-infected-recovered-susceptible (SIRS) model is employed to describe the diffusion dynamics from a microcosmic perspective. Second, we propose two synergistic optimal control approaches to suppress negative diffusion and enhance positive diffusion, respectively. Then, the optimal control problems of minimizing cumulative system cost and maximizing total system revenue are formulated. Subsequently, the optimal control signals are obtained using the optimal control theory and Pontryagin’s minimum principle. Third, we exploit an implementation framework with a multi-layer hybrid feedback control scheme for large-scale temporal networks. This framework utilizes centralized and distributed techniques to implement different control strategies. Finally, experimental results on various real-world datasets validate the efficiency of the proposed synergistic optimal control approaches and implementation framework.

Reaction monitoring of rose bengal photodegradation in alcohols using multivariate frequency-domain dynamic fluorescence

• Photodegradation of rose bengal (RB) exposed to simulated solar radiation evaluated. • Reaction progress monitored using matrix-formatted frequency domain fluorescence. • RB and photoproduct(s) spectra and kinetics resolved by multivariate data mining. • Facile RB dehalogenation in methanol; no photoproducts observed in cyclohexanol. • Multivariate approach insulates results from distortion by unknown concomitants. The photodegradation of rose bengal (RB) by simulated solar radiation in several air saturated alcohols, monitored using wavelength-resolved frequency-domain dynamic fluorescence measurements, is described. This work illustrates a novel strategy for characterizing photochemical reactions of fluorophores using a combination of reaction monitoring by multichannel frequency domain fluorescence measurements and data mining. Kinetic and mechanistic details of RB photodegradation in the selected alcohols are obtained by resolving the spectra and frequency domain decays of unreacted RB and its fluorescent photoproducts from the multivariate measurements. The analysis indicates that RB exhibits photochemical activities and photodegradation rates that are strongly dependent on solvent properties. An associated benefit of the data mining is the insulation of rate calculations from distortions produced by spectral overlap of undiscovered concomitants. This was most evident in RB photodegradation rates in methanol, which paradoxically, is a common solvent choice for photosensitizer efficiency measurements using RB as the standard reference. RB photodegradation in methanol was not only the fastest of all the solvents investigated at 10.0±1 μM/min, methanol supported the formation of three fluorescent photoproducts that had emission properties consistent with RB dehalogenation. In the remaining alcohols, the rates of RB degradation decreased with decreasing solvent relative polarity and increasing solvent viscosity and only one dehalogenated RB derivative was observed. In octanol, the photodegradation rate was faster than expected based on its dielectric constant at 0.249±0.006 μM/min. In cyclohexanol, no photoproduct formation was detected. These results suggest a role for diffusion control in photoinitiated RB dehalogenation.

Acid pressure oxidation leaching of arsenopyrite in the presence of pyrite: Oxygen consumption kinetics

In the process of extraction of gold from refractory sulphide ores, arsenopyrite and pyrite represent two of the major hosts for gold in solid solution. In this study, the pressure oxidation of arsenopyrite and arsenopyrite-pyrite mixtures in a H2SO4–O2 system have been investigated, with the aim of using the oxygen consumption kinetics to probe the oxidation mechanisms. The effects of temperature (180–220 °C), acidity (pH 0.5–2.5), dissolved iron concentration (10 and 30 g/L) and molar ratios (0:1–3:1) of pyrite-to-arsenopyrite (Py/Aspy) were evaluated. Kinetic analysis of arsenopyrite dissolution at 180–220 °C via a shrinking core model indicated an activation energy (Ea) of 48.46 kJ/mol, suggesting a mixed interface reaction and diffusion control. The order of the reaction to acidity was 0.16 at 200 °C, suggesting that [H+] is likely not the rate-limiting factor under typical reaction conditions. The addition of Fe(II) ions to the feed enhanced arsenopyrite oxidation, due to the formation of Fe(III) as a surrogate oxidant to drive the reaction.The Ea for Py/Aspy of 1:1 exhibited two behaviours, calculated to be 77.32 kJ/mol below 200 °C and decreasing to 34.59 kJ/mol above 200 °C. The former was attributed to surface control due to the oxidation of elemental sulphur, followed by a switch to mixed control at elevated temperatures. As Py/Aspy was increased to 2:1 and 3:1, a single behaviour was observed, with Ea values of 56.01 kJ/mol and 43.35 kJ/mol respectively. These values imply a mixed control and begin to approximate literature values for pyrite oxidation. A time-to-a-given-fraction method was also used to examine changes in Ea with reaction extent. Arsenopyrite was found to be under mixed control for most of the reaction extent. At increasing pyrite fractions, oxidation was observed to be reaction-limited at the initial stage of reaction, potentially reflecting the kinetics of sulphur oxidation.

Investigation of the isothermal cure kinetics of new series of bis(trimellitimide) derived epoxy-imide resins

The isothermal curing kinetics of a newly synthesized series of trimellitimide-derived epoxy-imide resins were studied compared to their previously obtained non-isothermal results. Although the minimum isothermal curing temperature was ca. 30°C above the highest glass transition temperature of the fully cured systems, the curing processes did not complete. The absolute and relative conversions (α, α')-based values of isothermal activation energy (Ea) are extremely consistent with the non-isothermal ones in the early stages of the curing processes, but the transition to the diffusion control regime at α≈0.7 leads to the dramatic increase of the α-based Ea. We also found that utilizing α' results in physically meaningful trends. Moreover, evaluation of the reactions model showed evidence of autocatalytic behavior, although the curing processes behave like an nth-order reaction in the range of 0.1<α<0.7. The difference between non-catalytic and autocatalytic activation energies indicates that more autocatalytic feature appears in the aromatic resin system.

Reduction Kinetics of Compact Hematite with Hydrogen from 600 to 1050 °C

Reduction of iron ores with hydrogen is a solution to replace fossil fuels. For this reason, it is important to discuss previous discrepancies. Some previous studies suggest a rate minimum with respect to temperature. Our research work indicates that a rate minimum can be avoided. Thermogravimetric isothermal reduction experiments were carried out from 600 to 1050 °C with pure reagent ferric oxide and hydrogen using a tubular furnace. The morphology and chemical composition of the initial sample, consisting of particulate hematite (Fe2O3), and the final product, consisting of metallic iron (Fe°), was defined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The reduction rate for the conversion from hematite to magnetite (Fe2O3 to Fe3O4) was the highest, around 5 %/min, decreasing to around 2–5%/min for the second stage of conversion from magnetite to wüstite (Fe3O4 to FeO). This reduction rate remains almost constant from about 20–80% reduction, decreasing to 0.3–1%/min for the completion of reduction from wüstite to metallic iron (FeO to Fe°). The reduction controlling mechanism was evaluated based on the calculated apparent activation energy and fitting the experimental data to one gas-solid reaction equation. Under the experimental conditions in this work, the reduction rate of pure hematite with hydrogen linearly increased with temperatures from 600 to 1000 °C, without a rate minimum in this temperature range. Above 1000 °C, the reduction rate decreased due to sintering phenomena. This result suggests a maximum reduction temperature of 1000 °C using pure hematite and hydrogen as the reducing gas. The reduction controlling mechanisms identified using hydrogen as a reducing gas were chemical reaction for the conversion from hematite to wüstite and diffusion control for the final reduction from wüstite to metallic iron. Since the reduction rate from wüstite to metallic iron is the one that affects the overall rate of reduction, overall changes in porosity were also evaluated. Finally, the reduction of wüstite is schematically described.

A novel atropine electrochemical sensor based on silver nano particle-coated Spirulina platensis multicellular blue-green microalga

In this work, Atropine as the anticholinergic drug was measured using the environmentally friendly sensor. In this regard, Self-cultivated Spirulina platensis with electroless silver was employed as a powder amplifier in carbon paste electrode modification. Also, 1-Hexyl-3 methylimidazolium Hexafluorophosphate (HMIM PF6) ion liquid as a conductor binder was used in the suggested electrode construction. Atropine determination was investigated by voltammetry methods. According to voltammograms, the electrochemical behavior of atropine depends on pH, and pH 10.0 was used as the optimal condition. Moreover, the diffusion control process for the electro-oxidation of atropine was verified by the scan rate study, so the diffusion coefficient (D∼ 3.0136×10−4cm2/sec) value was computed from the chronoamperometry study. Furthermore, responses of the fabricated sensor were linear in the concentration range from 0.01 to 800 μM, and the lowest detection limit of the Atropine determination was obtained at 5 nM. Moreover, the stability, reproducibility, and selectivity factors of the suggested sensor were confirmed by the results. Finally, the recovery percentages for atropine sulfate ampoule (94.48–101.58), and water (98.01–101.3) approve of the applicability of the proposed sensor to Atropine determination in real samples.

Diffuse land control, shifting pastoralist institutions, and processes of accumulation in southern Kenya

ABSTRACT In East Africa, pastoralist systems are undergoing rapid transformation due to land enclosures, benefit distributions associated with new land uses, shifting social relations, and changing authority and governance structures. We apply a critical analysis of the institutions that mediate access and benefits across a complex mosaic of property relations within Ilkisongo Maasai pastoralist land in southern Kenya. Our analysis elucidates how global and national influences have interacted with shifting dynamics of socio-cultural norms and rules regarding access to create new benefit pathways, cascading patterns of accumulation and social differentiation, and diffuse institutional controls over land.

The role of iron in cement hydration process: From perspective of chemical admixture

The post-peak decelerating hydration progress plays a significant role for concrete technology to assure durability of concrete. The effect of chemical admixture on cement hydration, hydration products, pore structure and moisture diffusion process are conducted by various experiments and the controlling factor on deceleration period of cement hydration and the effect of iron ion on microstructure are revealed. When the chemical admixture is added into cement paste, more ferrite phase is consumed and the iron dissolved in the pore solution modifies the initial hydration product layer and accelerate the hydration process, causing more C-S-H gel generated and denser microstructure. In addition, it is also proved that single diffusion control factor occurs at 80 h for the later deceleration period of cement hydration.

Evaluation of chemical structure and Si segregation of Al/Si(111)

Control of diffusion and segregation of Si atoms through a thin metal layer from a stacked Si structure is one of the effective techniques to grow two-dimensional (2D) or ultrathin Si crystals. We have studied the formation of the Al layer with a flat surface and high crystallinity on a wet-cleaned Si(111) wafer by thermal evaporation in order to use it as a growth template for ultrathin Si crystals. Then, the impacts of the annealing in N2 ambient on the surface flatness, the Al crystallinity, and the chemical bonding features for the Al/Si(111) structure were investigated. A formation of a sub-nanometer Si layer on the Al(111) surface using Si segregation with keeping surface flatness was demonstrated by the control of annealing temperature.

Effect of Cr2O3 on the Kinetics Mechanism and Microstructure of Pellet During Oxidation Roasting Process

The oxidation process of iron ore with different Cr2O3 contents is separated into two stages. The Coats–Redfern method is applied to conduct the kinetic analysis, and the restriction links between stages I and II correspond to diffusion control. The apparent activation energy (E) progressively decreases at all stages as the contents of Cr2O3 increase, which is favorable for improving the oxidation kinetics. The fluctuation amplitudes of E in stages I and II are 5.450 and 16.021 kJ mol−1, respectively. The interaction of Fe2O3 and Cr2O3 during oxidation forms a Fe–Cr solid solution, which loosens the internal structure of the pellet and thus increases the number and diameters of the inner pores. This phenomenon facilitates the internal diffusion of oxygen and lowers its concentration inside and outside the pellet. Therefore, the utilization of chromium‐bearing iron ore should be comprehensively considered in terms of its kinetics and microstructure.

Structural Evolution and Transitions of Mechanisms in Creep Deformation of Nanocrystalline FeCrAl Alloys.

FeCrAl alloys have been suggested as one of the most promising fuel cladding materials for the development of accident tolerance fuel. Creep is one of the important mechanical properties of the FeCrAl alloys used as fuel claddings under high temperature conditions. This work aims to elucidate the deformation feature and underlying mechanism during the creep process of nanocrystalline FeCrAl alloys using atomistic simulations. The creep curves at different conditions are simulated for FeCrAl alloys with grain sizes (GS) of 5.6-40 nm, and the dependence of creep on temperature, stress and GS are analyzed. The transitions of the mechanisms are analyzed by stress and GS exponents firstly, and further checked not only from microstructural evidence, but also from a vital comparison of activation energies for creep and diffusion. Under low stress conditions, grain boundary (GB) diffusion contributes more to the overall creep deformation than lattice diffusion does for the alloy with small GSs. However, for the alloy with larger GSs, lattice diffusion controls creep. Additionally, a high temperature helps the transition of diffusional creep from the GB to the dominant lattice. Under medium- and high-stress conditions, GB slip and dislocation motion begin to control the creep mechanism. The amount of GB slip increases with the temperature, or decreases with GS. GS and temperature also have an impact on the dislocation behavior. The higher the temperature or the smaller the GS is, the smaller the stress at which the dislocation motion begins to affect creep.

Improvement of utilization efficiency of magnesite by (NH4)2SO4 roasting–water leaching process

(NH4)2SO4 roasting–water leaching process was studied as a method for improving the utilization efficiency of magnesite. Transformation of the mineral phases during roasting was evaluated by X-ray diffraction (XRD) analysis, combined with thermogravimetry−differential thermal analysis (TG−DTA). The data were compared with the phase transformation of MgO during roasting using (NH4)2SO4. The experimental results demonstrated that at a (NH4)2SO4/ magnesite (MgO in ore) molar ratio of 1.6:1, roasting temperature of 475 °C, and roasting time of 2 h using a particle size of ~74 μm, the magnesium extraction rate reached a maximum of 98.7%. The phase transformation during roasting could be summarized as follows: MgCO3 was transformed into (NH4)2Mg2(SO4)3, and then decomposed into MgSO4. The reaction followed the mixed control mechanism involving chemical reaction control and diffusion control, with an apparent activation energy of 33.02 kJ/mol.

Insight into the sound field during a Direct Field Acoustic Test (DFAT)

Over the past 2 decades acoustic testing for the space industry has evolved from the ubiquitous reverberant chambers to using loudspeakers in what has been defined as Direct Field Acoustic Testing (DFAT). The initial need was to create a versatile system to provide a portable test facility to qualify space hardware on site as opposed to go to a dedicated test facility. Since that initial test carried out by MSI in the late '90s equipment and control strategies have improved and today it is possible to recreate an acoustic field which is very similar to that of a reverberant chamber. Using Multi-Input-Multi-Output (MIMO) control strategy has solved many of the initial issues. And it allows for control of the field's diffusivity. However, unlike a test in a reverberant chambers, the acoustic fields produced in a DFA test is dependent on the parameters used by the controller, its specific technology, and the whole sound generation system. This paper attempts to provide a qualitative overview and insight in the acoustic field generated by a set of loudspeakers set around a test item. Particular focus is placed on the diffusivity of the field as this is a characteristic that is linked to the structural response of the device under test.

Numerical Study on Smoke Diffusion and Smoke Control in Urban Underground Curved Tunnel

Effects of the radius and fire heat release rate on the smoke propagation and smoke control in curved tunnel are studied by the numerical methods. Six radiuses as 70 m, 150 m, 200 m, 250 m, 300 m and 400 m and two different fire sizes as 5 MW and 30 MW are involved. Numerical results show that comparing with the smoke flow in the straight tunnel, smoke temperature distributions across the cross-section is not symmetry with the centerline in the curved tunnel, and the smoke diffusion close to the outside boundary appears to be fast. At the higher level of the curved tunnel, such as 3 m above the tunnel floor, the smoke temperature would decrease with the distance from the fire increasing. However, at the lower level of the tunnel, the temperature would increase firstly and then decrease, maximum temperature would occur in the bend region of the curved tunnel. When the fire heat release rate is big, this temperature might be high enough to injure the people. Smoke ventilation system would run in time under this condition. Critical velocity in curved tunnel is larger than that in the straight tunnel.

Oxygen diffusion in the fluorite-type oxides CeO2, ThO2, UO2, PuO2, and (U, Pu)O2

This study evaluates the self-diffusion and chemical diffusion coefficients of oxygen in the fluorite-type oxides CeO2, ThO2, UO2, PuO2, and (U, Pu)O2 using point defect chemistry (oxygen vacancies and interstitials). The self-diffusion coefficient changed in proportion to the 1/n power of oxygen partial pressure, similar to the defect concentration. All parameters used to represent the diffusion coefficients were determined, and the experimental data were accurately stated. The defect formation and migration energies of the oxides were compared, and the change in Frenkel defect concentration was found to affect the high-temperature heat capacities of CeO2 and ThO2. The oxygen chemical diffusion was evaluated in the oxides, excluding the line compound ThO2, and the coefficients increased dramatically around the stoichiometric composition, i.e., the chemical diffusion coefficient was much higher at stoichiometric composition, with the oxygen-to-metal ratio equal to 2.00, than in low oxygen-to-metal oxides. This difference altered the mechanism of the reduction and oxidation processes. In the reduction process, the chemical diffusion control rate was dominant and a new phase with the oxygen-to-metal ratio equal to 2.00 was formed, which then expanded from the surface in the oxidation process from a low oxygen-to-metal ratio to the stoichiometric composition.

Improved Interfacial Interactions of Dip Coatings by In Situ Introducing Silica to Enhance Corrosion Resistance and Metal Bonding Strength

Corrosion is an irreversible phenomenon in nature that has been a major source of metal degradation. We herein provide a unique approach for embedding nanoparticles into epoxy resins via hydrogen bonding adsorption of in situ hydrophilic silica. Based on this adsorption action, a super-anticorrosive epoxy-based Teflon (MEP-PTFE) coating for usage on metals such as aluminum alloys was developed utilizing one-step dip coating, with promising engineering and public applications. It should be noted that the binding strength between the resultant MEP-PTFE coating and the substrate was 13.5 N. This coating had an impedance modulus of over 8 × 109 Ω·cm2 at 0.01 Hz and an impressive corrosion inhibition efficiency of 99.999%. The anticorrosion barrier from the diffusion control to the charge transfer control was revealed for the future good design of resin matrix coatings with excellent corrosion resistance.

Ti, F Codoped Sodium Manganate of Layered P2-Na 0.7 MnO 2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

Ti, F Codoped Sodium Manganate of Layered P2-Na _0.7 MnO _2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery