Redox Potential Of Solution Research Articles

Influence of slag composition on the stability of steel in alkali-activated cementitious materials

Among the minor elements found in metallurgical slags, sulfur and manganese can potentially influence the corrosion process of steel embedded in alkali-activated slag cements, as both are redox-sensitive. Particularly, it is possible that these could significantly influence the corrosion process of the steel. Two types of alkali-activated slag mortars were prepared in this study: 100% blast furnace slag and a modified slag blend (90% blast furnace slag + 10% silicomanganese slag), both activated with sodium silicate. These mortars were designed with the aim of determining the influence of varying the redox potential on the stability of steel passivation under exposure to alkaline and alkaline chloride-rich solutions. Both types of mortars presented highly negative corrosion potentials and high current density values in the presence of chloride. The steel bars extracted from mortar samples after exposure do not show evident pits or corrosion product layers, indicating that the presence of sulfides reduces the redox potential of the pore solution of slag mortars, but enables the steel to remain in an apparently passive state. The presence of a high amount of MnO in the slag does not significantly affect the corrosion process of steel under the conditions tested. Mass transport through the mortar to the metal is impeded with increasing exposure time; this is associated with refinement of the pore network as the slag continued to react while the samples were immersed.

Electrochemical Potential Gradient As a Quantitative Test Platform for Cellular Oxidative Stress

Oxidative stress (OS), involved in many biological phenomena, such as aging, carcinogenesis and inflammation, is defined as an imbalance between reactive oxygen species (ROS) and organism’s antioxidant defenses. The consequences of this imbalance lead to the disruption of cellular redox homeostasis and oxidative damage to DNA, proteins and lipids.(1) One metric of the relative strengths of oxidizers implicated in causing pathogenic oxidative damage via ROS production is the effective redox potential experienced by the cells. Therefore, establishing the relationship between the strength of the oxidative action, characterized by redox potential, and the biomolecular consequences is critical to elucidating the thermodynamic framework of oxidative damage. Experiments with OS in the lab environment require subjecting the study object to a given level of oxidative bias relative to biosystem’s natural equilibrium, preferably in a well-defined, reproducible and quantitative fashion. Popular in vitro OS inducers include exogenous chemical agents (hydrogen peroxide, paraquat, menadione, and t-butyl hydroperoxide), ionizing radiation or heat shock. In addition to disrupting redox homeostasis, each of these agents will also have a specific chemical interaction with cell components, which have to be accounted for during interpretation.(2) Here, we describe a novel way to create an OS environment for surface attached Chinese Hamster Ovary (CHO) cells by exposing them to an electrochemical potential gradient. With this technique we can apply a stable linear potential profile over a cell monolayer, thus providing an efficient method to screen live cell response to an exogenous redox background. It is based on a bipolar electrode configuration (3), adapted for a rectangular cell growth flask. A constant current is produced in cell media, thus generating an electric field and potential drop over the mammalian cell monolayer. Surface attached cells experience varying electrochemical potential, depending on their location along the current axis. Subsequently, cell viability gradients were produced within a range of treatment levels. The live-dead assay fluorescence image of the flask bottom slide shows the CHO cell condition following incubation under the redox potential gradient for a fixed time interval (see Figure). Images contain a rather uniform live, dead and a narrow changeover region ( magnified view in the lower panel of Figure ), consistent with a commencement of cell death at increasingly positive solution redox potential. The cell viability ratio was calculated from integrated pixel density using a custom ImageJ software macro. Therefore, the sigmoidal cell viability curve shape, produced when cells are exposed to the electrochemical potential gradient , is consistent with a two state conversion model and could be numerically characterized by a half maximum effective potential. This concept is widely used to describe dose-response curves in toxicology. Such numerical values would be useful to compare cell viability when subjected to oxidative stress in diverse experimental circumstances. That way, the higher effective potential value would indicate the increase in cell viability or the efficacy of the antioxidant. We have compared CHO cell response when exposed to three hydrogen peroxide concentrations (20 mM, 50 mM, and 100 mM) with the exposure to electrochemically induced potential gradient. Redox potential values of these H2O2 preparations were measured in separate experiments 1h after hydrogen peroxide was diluted into the cell growth media. Remarkably, cell viability vs solution redox potential dependencies are very close suggesting that exogenous hydrogen peroxide causes CHO cell OS largely by a positive shift in the solution redox potential, at least in this concentration range. Our test platform allows for direct imaging and analysis of cell viability, exposed to a range of electrochemical potentials. The slide vessel system can readily be adapted for other cellular assays such as ROS detection, apoptosis, etc. The system is particularly useful for providing a linear range of oxidative and reductive potentials in a single experiment. By replacing the vessel contents before during and after treatment a wide range of solution conditions can be tested and cell images can be acquired during oxidative treatment. This is particularly useful for in vitro testing of the effectiveness of additives such as anti-oxidants as it enables monitoring a real time cellular response. In addition, various cell types including cancer cell lines can be compared in their resistance to oxidative potentials and effectiveness of various drugs. References (1) Halliwell, B. Trends Pharmacol Sci 2013, 34, 301. (2) Buettner, G. R.; Wagner, B. A.; Rodgers, V. G. J. Cell Biochem Biophys 2013, 67, 477. (3) Fleischmann, M.; Ghoroghchian, J.; Rolison, D.; Pons, S. J Phys Chem-Us 1986, 90, 6392. Figure 1

The Effect of the Redox Potential of Aqua Regia and Temperature on the Au, Cu, and Fe Dissolution from WPCBs

Constant growth in waste electrical and electronic equipment (WEEE) levels necessitates the development of new, commercially viable recycling processes. Waste printed circuit boards (WPCBs) are a sub-group of WEEE that are of increasing interest due to their relatively high level of valuable metal content including Au, Ag, and platinum group metals (PGMs). Currently, precious metals like gold are mainly recycled from WEEE streams through copper smelting/refining; however, the possibility to peel gold from WPCBs prior to smelting, could offer advantages for recycling. In this study, the suitability of aqua regia for selective or partially selective gold leaching from un-crushed WPCBs was investigated. The redox potential of aqua regia solutions and the dissolution efficiencies of Au, Cu, and Fe from WPCBs were investigated at different temperatures (40–80 °C) and concentrations (2–32%) in batch leaching tests. The redox potential of aqua regia solution was found to depend on concentration and temperature. It is suggested that Au dissolution in aqua regia requires dissolved Cu2+ ions originating from the WPCB material to work. Au extraction (>50%) was shown to require a redox potential >700 mV with [Cu2+] > 2500 ppm, as a potential >850 mV alone was insufficient without cupric ions. Significant amounts of Au and Cu could be dissolved with only minor Fe dissolution at ≥8% aqua regia at 80 °C. Results suggest that leaching of uncrushed WPCBs in 8% aqua regia (T = 80 °C) can provide the opportunity for partial Au recovery prior to further processing.

Limited role of sessile acidophiles in pyrite oxidation below redox potential of 650\u2009mV

Pyrite oxidation by mixed mesophilic acidophiles was conducted under conditions of controlled and non-controlled redox potential to investigate the role of sessile microbes in pyrite oxidation. Microbes attached on pyrite surfaces by extracellular polymeric substances (EPS), and their high coverage rate was characterized by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). The dissolution of pyrite was negligible if the redox potential was controlled below 650 mV (near the rest potential of pyrite), even though the bacteria were highly active and a high coverage rate was observed on pyrite surfaces. However, with un-controlled redox potential the rate of pyrite oxidation increased greatly with an increasing redox potential. This study demonstrates that sessile microbes play a limited role in pyrite oxidation at a redox potential below 650 mV, and highlight the importance of solution redox potential for pyrite oxidation. This has implications for acid mine drainage control and pyrite oxidation control in biometallurgy practice.

Fluorescent Polypyrrole Nanospheres – Synthesis and Properties of “Wireless” Redox Probes

AbstractIn this work a novel concept of monitoring of occurrence of redox reactions between conducting polymer nanospheres and redox species in a solution is proposed. The redox process is monitored in the emission mode (without wiring of the probe to an electrochemical measuring set‐up) as a change in emission spectrum of a dye (not participating in the redox process itself) but reporting the alteration of properties of highly sensitive conducting polymer nanoparticles. This approach is possible due to applied unique method of synthesis of conducting polymers nanospheres of highly active, unblocked surface. Thus the nanospheres redox state is affected by the solution redox potential, leading to change of their properties. If solvatochromic probe of sufficiently high brightness (pyrene) is present in nanospheres, a redox reaction between the conducting polymer and solution can be observed as change of emission spectrum of the probe. Thus a localized redox potential optical probe can be obtained. The emission properties of the dye incorporated were preserved in the nanospheres, moreover, the emission spectrum of the probe was affected by the change in redox potential of the solution, thus influencing the redox state and ultimately the properties of the conducting polymer. The emission changes observed were dependent on ion‐exchange properties of polypyrrole, i.e. depending on the dopant ions present in the polymer, the sensitivity of the optical probe can be tuned.

A Review of Thiosulfate Leaching of Gold: Focus on Thiosulfate Consumption and Gold Recovery from Pregnant Solution

Thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high thiosulfate consumption and the difficult recovery of dissolved gold. In this review, the four solutions to reduce the consumption of thiosulfate, including the control of reaction conditions, the use of additives, the generation of thiosulfate in situ, and the replacement of traditional cupric-ammonia catalysis, are introduced and evaluated after the presentation of background knowledge about thiosulfate consumption. The replacement of cupric-ammonia catalysis with other metals, such as nickel- and cobalt-based catalysts, is proposed. The reason is that it not only reduces thiosulfate consumption observably via decreasing the redox potential of leach solution significantly but also is beneficial to gold recovery mainly owing to eliminating the interference of cuprous thiosulfate [Cu(S2O3)3]5−. Based on the comparative analysis for five common recovery techniques of rare-noble metals from pregnant leach solution, ion-exchange resin adsorption is considered to be the most appropriate to recover aurothiosulfate [Au(S2O3)2]3− because the resin can be employed in the form of resin-in-leach/pulp and, furthermore, is able to be eluted and regenerated simultaneously at ambient temperature. At last, how to reduce the process cost of the resin adsorption technique is discussed. In order to simplify the complex two-stage elution process for loaded resins, the traditional catalysis is suggested to be replaced.

Pyrite oxidation in column at controlled redox potential of 900 mV with and without bacteria

Comparisons on the bioleaching and sterile oxidation of pyrite were performed at controlled redox potential of 900 mV (vs. SHE) and different temperatures of 30 and 60 °C. For sterile experiments, the redox potential of irrigation solution was controlled by adding hydrogen peroxide solution (15 wt%), while the redox potential of irrigation solution for bioleaching was elevated by flowing through the packed bed in which bacteria were activated and colonized. The rate of pyrite bioleaching is faster than that of sterile oxidation at temperature of 30 °C. The reason is that the potential gradient of leaching solution in bioleaching column is much smaller than that in sterile column. The redox potentials of irrigation solution and leaching solution are similar for bioleaching; however, the redox potential difference of irrigation solution and leaching solution for sterile oxidation is about 150 mV. When temperature increases to 60 °C for sterile oxidation, the rate of pyrite leaching is faster than that of bioleaching at temperature of 30 °C, even though the redox potential gradient of leaching solution is great. The mineralogy analyses of pyrite residue were performed by scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. The results confirm that pyrite oxidation might only occur at specific sites with high surface energy on surface and obeys the “indirect mechanism” whether there are bacteria or not. The pyrite oxidation rate is not inhibited by inert sulfur on residue surface at elevated redox potential. According to the conclusions, the way to accelerate pyrite oxidation is proposed.

Behavior of cobalt-containing phases in hydrochloride decomposition of sulfide Cu–Ni materials

Effect of the solution redox potential on the behavior of cobalt-containing phase components of sulfide copper-nickel concentrates in the Cu(II)/Fe(III)–Cl––HCl–Cl2 system was studied. It was shown that, at solution redox potentials in the range 350–650 mV, phases based on heazlewoodite, pentlandite, cobaltous pentlandite, and cobalt pentlandite are transformed to thiospinels from the linneite group (M3S4, where M = Ni, Fe, Co). The resulting thiospinels are dissolved, with the exception of Co3S4, at solution redox potentials of 450 mV and less. The Co3S4 thiospinel is a stable compound in concentrated chloride solutions up to 650 mV, which, in the system under study, may be a reason for the poor cobalt recovery from sulfide concentrates.

Assessing the electrochemical properties of polypyridine and polythiophene for prospective applications in sustainable organic batteries.

Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, the key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties.

Electrochemical Applications in Metal Bioleaching.

Biohydrometallurgy comprises the recovery of metals by biologically catalyzed metal dissolution from solids in an aqueous solution. The application of this kind of bioprocessing is described as "biomining," referring to either bioleaching or biooxidation of sulfide metal ores. Acidophilic iron- and sulfur-oxidizing microorganisms are the key to successful biomining. However, minerals such as primary copper sulfides are recalcitrant to dissolution, which is probably due to their semiconductivity or passivation effects, resulting in low reaction rates. Thus, further improvements of the bioleaching process are recommendable. Mineral sulfide dissolution is based on redox reactions and can be accomplished by electrochemical technologies. The impact of electrochemistry on biohydrometallurgy affects processing as well as analytics. Electroanalysis is still the most widely used electrochemical application in mineralogical research. Electrochemical processing can contribute to bioleaching in two ways. The first approach is the coupling of a mineral sulfide to a galvanic partner or electrocatalyst (spontaneous electron transfer). This approach requires only low energy consumption and takes place without technical installations by the addition of higher redox potential minerals (mostly pyrite), carbonic material, or electrocatalytic ions (mostly silver ions). Consequently, the processed mineral (often chalcopyrite) is preferentially dissolved. The second approach is the application of electrolytic bioreactors (controlled electron transfer). The electrochemical regulation of electrolyte properties by such reactors has found most consideration. It implies the regulation of ferrous and ferric ion ratios, which further results in optimized solution redox potential, less passivation effects, and promotion of microbial activity. However, many questions remain open and it is recommended that reactor and electrode designs are improved, with the aim of finding options for simplified biohydrometallurgical processing. This chapter focuses on metal sulfide dissolution via bioleaching and does not include other biohydrometallurgical processes such as microbial metal recovery from solution.

New insights into the influence of redox potential on chalcopyrite leaching behaviour

Chalcopyrite (CuFeS2) is the most economically important and most refractory copper mineral when treated in conventional sulphate media leaching systems. In this study, the effect of solution redox potential on leaching of a pure and a pyritic chalcopyrite concentrate was investigated using concentrates with fresh and aged surfaces. In experiments using concentrates with fresh surfaces, the response to redox potential depended on the presence of pyrite: fresh pyritic concentrate leached more effectively at low redox potential (in agreement with reductive leaching mechanisms), while the leaching efficiencies from fresh pure concentrate were similar at high and low redox potentials. The data suggested that the reductive leaching mechanism does not necessarily result in higher and faster recoveries in the absence of the galvanic interaction induced by the presence of pyrite. It was also found that exposure of chalcopyrite to atmospheric oxidation prior to leaching (ageing) had an effect on leaching behaviour in response to redox potential: copper recoveries in leaching of aged concentrates were higher at high redox potentials. This behaviour was attributed to the presence of iron–oxyhydroxides on the surface of aged concentrates. Based on the data from this investigation and previous surface studies, it is proposed that iron–oxyhydroxides play an important role in triggering the hindered dissolution of chalcopyrite.

Kinetics and Mechanisms of Chalcopyrite Dissolution at Controlled Redox Potential of 750 mV in Sulfuric Acid Solution

To better understand chalcopyrite leach mechanisms and kinetics, for improved Cu extraction during hydrometallurgical processing, chalcopyrite leaching has been conducted at solution redox potential 750 mV, 35–75 °C, and pH 1.0 with and without aqueous iron addition, and pH 1.5 and 2.0 without aqueous iron addition. The activation energy (Ea) values derived indicate chalcopyrite dissolution is initially surface chemical reaction controlled, which is associated with the activities of Fe3+ and H+ with reaction orders of 0.12 and −0.28, respectively. A surface diffusion controlled mechanism is proposed for the later leaching stage with correspondingly low Ea values. Surface analyses indicate surface products (predominantly Sn2− and S0) did not inhibit chalcopyrite dissolution, consistent with the increased surface area normalised leach rate during the later stage. The addition of aqueous iron plays an important role in accelerating Cu leaching rates, especially at lower temperature, primarily by reducing the length of time of the initial surface chemical reaction controlled stage.

4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxyl as a model organic redox active compound for nonaqueous flow batteries

Abstract Nonaqueous redox flow batteries (NAqRFBs) that utilize redox active organic molecules are an emerging energy storage concept with the possibility of meeting grid storage requirements. Sporadic and uneven advances in molecular discovery and development, however, have stymied efforts to quantify the performance characteristics of nonaqueous redox electrolytes and flow cells. A need exists for archetypal redox couples, with well-defined electrochemical properties, high solubility in relevant electrolytes, and broad availability, to serve as probe molecules. This work investigates the 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxyl (AcNH-TEMPO) redox pair for such an application. We report the physicochemical and electrochemical properties of the reduced and oxidized compounds at dilute concentrations for electroanalysis, as well as moderate-to-high concentrations for RFB applications. Changes in conductivity, viscosity, and UV–vis absorbance as a function of state-of-charge are quantified. Cyclic voltammetry investigates the redox potential, reversibility, and diffusion coefficients of dilute solutions, while symmetric flow cell cycling determines the stability of the AcNH-TEMPO redox pair over long experiment times. Finally, single electrolyte flow cell studies demonstrate the utility of this redox couple as a platform chemistry for benchmarking NAqRFB performance.

Electrochemical Potential Gradient as a Quantitative in Vitro Test Platform for Cellular Oxidative Stress.

Oxidative stress in a biological system is often defined as a redox imbalance within cells or groups of cells within an organism. Reductive-oxidative (redox) imbalances in cellular systems have been implicated in several diseases, such as cancer. To better understand the redox environment within cellular systems, it is important to be able to characterize the relationship between the intensity of the oxidative environment, characterized by redox potential, and the biomolecular consequences of oxidative damage. In this study, we show that an in situ electrochemical potential gradient can serve as a tool to simulate exogenous oxidative stress in surface-attached mammalian cells. A culture plate design, which permits direct imaging and analysis of the cell viability, following exposure to a range of solution redox potentials, was developed. The in vitro oxidative stress test vessel consists of a cell growth flask fitted with two platinum electrodes that support a direct current along the flask bottom. The applied potential span and gradient slope can be controlled by adjusting the constant current magnitude across the vessel with spatially localized media potentials measured with a sliding reference electrode. For example, the viability of Chinese Hamster Ovary cells under a gradient of redox potentials indicated that cell death was initiated at approximately 0.4 V vs. standard hydrogen electrode (SHE) media potential and this potential could be modified with antioxidants. This experimental platform may facilitate studies of oxidative stress characteristics on different types of cells by enabling imaging live cell cultures that have been exposed to a gradient of exogenous redox potentials.

Poly(3-octylthiophene) nanoparticles for turn-on fluorescent sensor

A novel concept of optical fluorescent sensing using conducting polymer nanostructures poly(3-octylthiophene) as an optical receptor is proposed. A conducting polymer was encapsulated within polymeric nanospheres obtained from poly(maleic anhydride-alt-1-octadecene) in a simple procedure, resulting in formation of core-shell nanostructures. In the presence of carboxyl groups at the outer shell of nanospheres the conducting polymer undergoes spontaneous oxidation (e.g. by oxygen dissolved in the solution), leading to decrease of native fluorescence of poly(3-octylthiophene). Thus obtained core-shell nanospheres are sensitive to changes of the solution redox potential, due to dependence of poly(3-octylthiophene) emission spectra on its oxidation state. The decrease in redox potential is accompanied with increase of emission intensity of the conducting polymer core, which allows application of nanospheres as turn-on probe for reducing agents. The sensitivity and selectivity of obtained nanoprobes can be fine-tuned taking the advantage of the presence of charged groups in the shell layer of the nanostructures obtained. As a model analyte, ascorbic acid was chosen. A linear response was recorded, with increase of emission intensity for increasing ascorbic acid concentration, within the range from 10−6 to 0.1M.

Soil solution chemical attributes, rice response and water use efficiency under different flood irrigation management methods

The water availability is the main limiting factor of global rice production under flood irrigation. In this context, water suppression during the rice growing cycle (intermittent irrigation) arises as an alternative to traditional continuous irrigation. However, the intermittent irrigation may affect the dynamics of soil solution chemical attributes, the water use and the rice yield. Thus, our study aims to evaluate the electrochemical characteristics and nutrient availability in soil solution during the growing cycle, the plant response and the water use efficiency of irrigated rice under different flood irrigation management methods. For this, a field experiment was conducted in Southern Brazil, with three treatments: 1) continuous irrigation; 2) one water suppression (between V6–V8); and 3) two water suppressions (between V6–V8 and V8–V10). Regarding soil solution electrochemistry, the pH and redox potential (EH) were affected by the water suppression, increasing and decreasing due to soil reoxidation, respectively. The electrical conductivity (EC) decreased during the rice growing cycle, accompanying the plant development. The nutrients (except the potassium) were affected by water suppression, diminishing their availability. However, when the water layer was reestablished, there were no differences on soil solution electrochemistry among the irrigation methods. Regarding rice response, no differences were observed and the amounts produced were, in average, 9.9 and 13.4Mgha−1 of grains and shoot dry matter, respectively. The same occurred for the water amount utilized and water use efficiency (WUE) and the values observed were, in average, 9094m3ha−1 and 1.1kgm−3, respectively. More studies regarding different flood irrigation management methods are necessary to encourage the adoption of intermittent irrigation by rice farmers of Southern Brazil and increase the sustainability of rice production.

Electrochemical Potential Gradient As a Quantitative Test Platform for Cellular Oxidative Stress

Oxidative stress (OS), involved in many biological phenomena, such as aging, carcinogenesis and inflammation, is defined as an imbalance between reactive oxygen species (ROS) and organism’s antioxidant defenses. The consequences of this imbalance lead to the disruption of cellular redox homeostasis and oxidative damage to DNA, proteins and lipids.(1) One metric of the relative strengths of oxidizers implicated in causing pathogenic oxidative damage via ROS production is the effective redox potential experienced by the cells. Therefore, establishing the relationship between the strength of the oxidative action, characterized by redox potential, and the biomolecular consequences is critical to elucidating the thermodynamic framework of oxidative damage. Experiments with OS in the lab environment require subjecting the study object to a given level of oxidative bias relative to biosystem’s natural equilibrium, preferably in a well-defined, reproducible and quantitative fashion. Popular in vitro OS inducers include exogenous chemical agents, ionizing radiation or heat shock. In addition to disrupting redox homeostasis, each of these agents will also have a specific chemical interaction with cell components, which have to be accounted for during interpretation.(2) Here, we describe a novel way to create an OS environment for surface attached Chinese Hamster Ovary (CHO) cells by exposing them to an electrochemical potential gradient. With this technique we can apply a stable linear potential profile over a cell monolayer, thus providing an efficient method to screen live cell response to an exogenous redox background. It is based on a bipolar electrode configuration (3), adapted for a rectangular cell growth flask. A constant current is produced in cell media, thus generating an electric field and potential drop over the mammalian cell monolayer. Surface attached cells experience varying electrochemical potential, depending on their location along the current axis. Subsequently, cell viability gradients were produced within a range of treatment levels. The live-dead assay fluorescence image of the flask bottom slide shows the CHO cell condition following incubation under the redox potential gradient for a fixed time interval (see Figure). Images contain a rather uniform live, dead and a narrow changeover region ( magnified view in the lower panel of Figure ), consistent with a commencement of cell death at increasingly positive solution redox potential. The cell viability ratio was calculated from integrated pixel density. Therefore, the sigmoidal cell viability curve shape, produced when cells are exposed to the electrochemical potential gradient , is consistent with a two state conversion model and could be numerically characterized by a half maximum effective potential. This concept is widely used to describe dose-response curves in toxicology. Such numerical values would be useful to compare cell viability when subjected to oxidative stress in diverse experimental circumstances. That way, the higher effective potential value would indicate the increase in cell viability or the efficacy of the antioxidant. We have compared CHO cell response when exposed to three hydrogen peroxide concentrations (20 mM, 50 mM, and 100 mM) with the exposure to electrochemically induced potential gradient. Redox potential values of these H2O2 preparations were measured in separate experiments 1h after hydrogen peroxide was diluted into the cell growth media. Remarkably, cell viability vs solution redox potential dependencies are very close suggesting that exogenous hydrogen peroxide causes CHO cell OS largely by a positive shift in the solution redox potential, at least in this concentration range. Our test platform allows for direct imaging and analysis of cell viability, exposed to a range of electrochemical potentials. The slide vessel system can readily be adapted for other cellular assays such as ROS detection, apoptosis, etc. The system is particularly useful for providing a linear range of oxidative and reductive potentials in a single experiment. By replacing the vessel contents before during and after treatment a wide range of solution conditions can be tested and cell images can be acquired during oxidative treatment. This is particularly useful for in vitro testing of the effectiveness of additives such as anti-oxidants as it enables monitoring a real time cellular response. In addition, various cell types including cancer cell lines can be compared in their resistance to oxidative potentials and effectiveness of various drugs. Figure 1. Overlay of the fluorescence images of the cell growth flask bottom following the application of the electrochemical potential gradient and live-dead staining (left-live, right-dead). References (1) Halliwell, B. Trends Pharmacol Sci 2013, 34, 301. (2) Buettner, G. R.; Wagner, B. A.; Rodgers, V. G. J. Cell Biochem Biophys 2013, 67, 477. (3) Fleischmann, M.; Ghoroghchian, J.; Rolison, D.; Pons, S. J Phys Chem-Us 1986, 90, 6392. Figure 1

Conversion of ferric oxide to magnetite by hydrothermal reduction in Bayer digestion process

Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production. The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation. The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution. The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration, suggesting that Fe(OH)3− and Fe(OH)4− form by dissolving Fe and Fe2O3, respectively, in alkaline aqueous solution and further react to form Fe3O4. Moreover, aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution, and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.

Behavior of Nickel Deposition on Silicon Wafers from TMAH and Ammonia based SC1 Cleaning Process

Adverse affect of surface contamination, including metal, on silicon wafer resulted into continuous evolution of RCA cleaning process.1 Deposition behavior of nickel on silicon wafer from SC1 solution, based on TMAH, is investigated here. A number of process parameters like chemical concentration, process time and temperature on deposition behavior of nickel from SC1 solution are considered. The mechanism of nickel deposition is discussed along with possible formation of some nickel silicide on the surface. Increased level of nickel deposition, as a function of TMAH concentration, from TMAH based SC1 solution is shown in Fig. 1. Time dependency of nickel deposition is carried out by exposing wafer into a nickel-contaminated SC1 solution with incremental period of time. The level of deposited nickel is found to increase with time as shown in Fig. 2. In other words, the non-equilibrium nickel deposition is observed, for the nickel contamination level used here and the period of investigation. Additional nickel deposition study is performed by exposing wafer to TMAH based SC1 and ammonia based SC1 solution as a function of temperatures separately. Higher nickel deposition tendency, from SC1 bath, is observed in TMAH based SC1 solution compared to ammonia-based SC1 solution. Furthermore, the amount of deposited nickel from SC1 solution increases with temperature. The increased level of nickel deposition from TMAH based SC1 solution compared to ammonia- based SC1 solution is likely influenced by the increased stability of the nickel ion in ammonia with the formation of ammonia-nickel complex. 1 Characterization of surface nickel from nickel-contaminated TMAH-based SC1 solution is carried out by dippingsilcon wafers in SC1 that contains 1ppb Nickel for 4.5 min., 9 min and 18 mins. respectively. This is shown in Figure 3. Amount of deposited nickel in chemical oxide was first analyzed with VPD-ICPMS. Subsequently, non-removable surface nickel on the surface was analyzed by ICP/MS following etching with surface with mixture of hydrofluoric and nitric acid. The mechanism of nickel deposition can be considered to proceed by the reduction of Ni+2 ion via electrochemical oxidation of silicon in the alkaline solution.2 In other words the growth of chemical oxide on silicon is due to high redox potential of the SC1 solution containing peroxide. As indicated above the amount of metal oxide is expected to increase with treatment time observed in a similar study with copper.3 Furthermore, the observation of silicon oxide between the deposited nickel and substrate in alkaline solution is observed in an EDX analysis of the interface.4 The oxide layer is proposed to be produced by reaction of oxidized silicon with OH- ion promoted by Ni+2ion. Part of Ni adsorbed on wafer from SC1 (TMAH+H2O2) possibly form nickel silicide, which may be difficult to remove in traditional low pH metal cleaning step. Fig. 1 Amount of Nickel deposited on the wafer following SC1 traetment from SC1 solution with increasing ratio of TMAH to H2O2 concentration. Fig. 2. Nickel adsorption from SC1 solution contaminated with 1 ppb of nickel. Figure 3. Nickel adsorption from TMAH-based SC1 solution and NH3-based SC1 solution as a function of temperature is shown below. Elevated nickel deposition is observed in TMAH-based solution. Figure 4. Removal and non-removal nickel deposited on the wafer surface treated with dilute hydrochloric acid following depostion from from SC1 solution. Increased amount of non-removable nickel is observed with time.

REACTION ABILITY OF THE SULFITE LIQUORS AS A BASIS FOR OBTAINING THE DRILLING COMPONENTS

The comparative analysis of the sulfite liquor properties (technical lingosulfonatov), obtained by wood lignin sulfonation in relatively acidic and neutral environments, was conducted. During the research by electrochemical method there was obtained the dependence between redox potentials of lingosulfonatov solutions and pH value, and there was conducted the comparative analysis of redox potentials values depending on the method for producing sulfite liquor. There was significant distinction among liquor solutions conductivity values of different methods for producing. Differentiated determination of acidic functional groups of the structural units of lignosulfonate-fenipropanovogo link was conducted by the conductometric titration method, and there was the significant sulfogroups excess in the liquors obtained by the neutral sulphite method of wood lignin boiling. Moreover, the complexing ability of neutral sulphite and sulphite liquors for producing was researched by the potentiometric titration method. As a result, there were obtained potentiometric titration liquors solutions curves by salts of polyvalent cations (Fe II and Fe III). These studies have been allowed a comparative evaluation of reactivity and an opportunity of lingosulfonatov liquors polymeric matrix application as bases for producing of chemical reagents used in drilling technology. It was found that the drilling reagents on bases of liquors by the neutral and sulphite boiling method have several advantages since their obtaining base on the modification of lingosulfonatov matrix by less expensive reagents modifiers. The above mentioned studies in conjunction with relatively low cost, low foaming power and high resistance to high temperature were allowed to recommend the liquors of the neutral and sulphite boiling method as the perspective raw material for the drilling reagents production.