mV SHE Research Articles

Diagram for the Electrochemical Stability of Water

According to the electrochemical stability diagram of water (Fig. 1), Ox/Red pairs displace hydrogen and oxygen respectively, when equilibrium potentials E Ox/Red < E H+/H2 (line a ) and E Ox/Red > E O2/OH- (line b ). However, if this is theoretically possible, the fact is that only pairs with E Ox/Red > ~ +0.5 V SHE ( E o I2/I- = + 0.535 V SHE; E o NiO2/Ni(OH)2,OH- = + 0.49 V SHE) displace oxygen from alkaline solutions and only pairs with E Ox/Red < ~ +0.5 V SHE ( E o Cu/Cu2+ = +0.34 V SHE; E o Co/Co3+ = +0.4 V SHE) can displace hydrogen from acid solutions. There will be no displacement of oxygen by ions Cu2+ (Ox-form) and hydrogen by ions I- (Red-form) at the appropriate pH (Fig.1) [1,2].The reason for this is that Red-forms (I-ions) with E Red/Ox > ~+0.5 V SHE and Ox-forms (Cu2+, Co3+ ions) with E Red/Ox < ~+0.5 V SHE is already thermodynamically stable in solutions, their transitions to conjugated forms (I2, Cu) are not spontaneous. With the theoretical possibility of H2 displacement, ions I-will form acids (HI) with H+ ions. With the theoretical possibility of O2 displacement, ions Cu2+, Co3+ will form hydroxides (Cu(OH)2) with OH- ions. These reactions are more thermodynamically probable. Accordingly, electrodes displace either hydrogen or oxygen from water.Between pairs with low oxidizing and reducing activities, there should be a pair of zero activity, in which Ox + ne and Red-forms are chemically equilibrium (line c , Fig.1) [1-3]. Its average potential is E Red/Ox ~ +0.44 V SHE between E o I2/I- = + 0.535 V SHE and E o Cu/Cu2+ = +0.34 V SHE and E Red/Ox ~ +0.47 V SHE between nearest E o NiO2/Ni(OH)2,OH- = +0.49 V SHE and E o Ru/Ru3+ = +0.45 V SHE determined opposite activities [1,2].The intersection of line c with lines a (pH = -8; point d ) and b (pH=12.8; point e) should also correspond to zero activity of H+/H2 - and O2/OH- - electrodes (Fig.1). The differenceΔpH =12.8 – (-8) = 20.8 determines emf of H+/H2//O2/OH- element (20.8 x 0.0 59 = 1.227 V) [1]. The instability of metal ions reflects itself in the decomposition of hydroxides 2CuOH→ Cu2O + H2O; 2AuOH → Au2O +H2O. Unstable metal ions (Cu+, Te4+, Ag+, Au+) can polarize hydroxyl ions without the formation of the pair OH-/O2[2]. Indeed, the boundary at E Red/Ox ~+0.47 V SHE separates stable and unstable hydroxides (Table). Me/Men+ E o, V SHEHydroxide/Oxide Pb/Pb2+ -0.126 Pb(OH)2 Cu/Cu 2+ +0.34Cu(OH)2 Co/Co 3+ +0.4 (+0.46)Co(OH)3 Ru/Ru 2+ +0.45Ru(OH)2 Cu/Cu+ +0.52Cu2OTe/Te 4+ +0.568TeO2 Hg/Hg2 2+ +0.789Hg2OAg/Ag+ +0.799Ag2O Absolute values |-E H+/H2 | = |+E O2/OH- | = 1.227 V/ 2 = ~ 613.6 mV (10.4 x 59 mV) are equal at pH = 10.4 (line f , Fig.1), where 1.227 V is the distance between lines a and b (emf H2/H+//OH-/O2 element).Line f divides the horizontal distances (as g - i ) from pH = 0 to pH = 14 (14 x 59 mV= 826 mV) into parts 1227 mV / 2 = 613.6 mV ( g - h ) and 212.4 mV (3.6 pH x 59 mV; h - i ). Their ratio is 613.6 mV / 212.4 mV = ~ 2.89. Thus, presented613.6 mV = (212.4 mV + 0.89 x 212.4 mV) + 212.4 mV == 401.2 mV + 212.4 mV = 2.89 x 212.4 mV ==2.89 (ψ O2/OH-, pH=14 + ψ O2/OH-,pH=10.4)where ψ O2/OH-, pH=14 + ψ O2/OH-,pH=10.4 are the sum of external potential drops (not Galvani potentials) arising in half-reactions between oppositely charged particles in double-electrical layers on electrodes.Both sides are equal to 212.4 mV. Therefore, dividing 212.4 mV (left) / 2.89 = 73.5 mV should give the smallest actual component ψ O2/OH-,pH=14of equal 212.4 mV (right).Then, its second component ψ O2/OH-,pH=10.4 is 401.2 mV (left) / 2.89 =138.8 mV or 212.4 mV - 73.5 mV = 138.9 mV. Close ψ O2/OH-, pH=14 (14 - 12.8) x 59 mV = 70.8 mV and ψ O2/OH-, pH=10.4 - (12.8 - 10.4) x 59 mV =141.6 mV calculated relative to pH=12.8 (point e , Fig.1) [1].The potential of pairs of zero activity (line c , Fig.1) is calculated as E O2/OH-,pH=10.4 - ψ O2/OH-,pH=10.4 = 613.6 mV SHE - 138.8 mV = + 474.8 mV SHE. The potential drops ψ H +/H2,pH=0 = - 474.5 mV; ψ O2/OH-,pH=0 = + 752.4 mV and ψ H +/H2= ψ O2/OH- at pH = 2.4 are calculated (Fig.1).Reference1.A.I.Chernomorskii, Zh. Fiz. Khim., 51,924 (1977).2.A.I.Chernomorskii, Dokl. Akad.Nauk Uzb.SSR, 3,37(1989).3.A.I.Chernomorskii, Journal of The Electrochemical Society,2021,168,116514. Figure 1

(Digital Presentation) Experimental Results on the Determination of the Billiter Potential

The experimental effects at the Billiter potential are measured in narrow intervals of the equilibrium potentials (A, B). The Billiter potential + 0.475 V SHE [1-3] is confirmed by the following experimental results [4,5,7- 9]. The change in the direction of the current between a dropping mercury and a mercury bottom in solutions of redox systems Fe(CN)6 3 - - Fe(CN)6 4 - and quinone-hydroquinone at a given potential E equil . = + 475 V SHE has been established with exactness ± 1-2 mV [4, 5]. This result was confirmed in [6]. At E equil. > +0.475 V SHE, the current flows from a mercury bottom to dropping electrode and at E equil. < +0.475 V SHE - in the opposite direction. Electrocapillary curves have been found by drop-weight method in these solutions in narrow range E equil. ~+0.4 ÷+0.55 V SHE with a maximum at E equil. ~ + 0.475 V SHE [4].A self-recording galvanometer was used to record the reversal of the current between a mercury bottom and a dropping electrode in solutions of redox systems [7-9]. In a solution of quinone-hydroquinone redox system, a recorded positive current decreases exactly to zero at E = + 228 mV SCE (+ 475 mV SHE), and then a negative current increases with continuous dropping of mercury. E equil. changes by itself since an adsorbed quinone on mercury drops are removed from solution onto mercury bottom (A).The current reversal at E ~+ 0.22 ÷ + 0.23 V SCE (~+0.475 V SHE) has been recorded by a recorder between a mercury bottom and a dropping electrode in acidified Hg2(NO3)2 solutions with the addition of complexing agents (triethanolamine, sodium ethylenediaminetetraacetate, thiocarbamide, others) [7-9].The electrocapillary curves (ECC) have been measured by weight-drop method in these solutions (B; with sodium ethylenediaminetetraacetate). After passing the electrocapillary maximum for reversible Hg2 2+/ Hg electrode at E ~ + 0.22 ÷ + 0.23 V SCE, we have obtained an ascending branch of ECC of an ideally polarizable electrode at E equil. < ~+0.190 ÷ +0.210 V SCE. A registered second current reversal at these E equil. corresponds to the transition from a small descending branch of ECC of Hg2 2+/Hg electrode to an ascending branch of ECC of an ideally polarizable electrode. The electrocapillary maximum was also obtained using diluted acidified solutions of Hg2(NO3)2.An increase in a polarization resistance and a change in polarization capacitance have been detected when impedance measuring with reversible electrodes at Ee ~ +0.475 V SHE. These effects were also measured on mercury drops in the diluted 10-10 N solution of Hg2(NO3)2 + 0.1÷ 0.001 N KNO3 The increase in polarization resistance was explained by the achievement of chemical equilibrium of half-reactions at Ee quil. ~ +0.475 V SHE [6,7,16].Measurements by the immersion method with redox systems and solid electrodes of the second kind confirm the reversal of the current at E ~+ 475 V SHE. Submersible small solid electrodes must be absolutely clean and dry [5]. This method is under development.According to [8 - 10], Billiter potential corresponds to some electrode with zero chemical activity (transitional from metals to non-metals with the intermediate electron work function 5.19 eV). The same zero activity is obtained at chemical equilibrium of half-reactions when the sum of changes of chemical potentials of electrons and ions Δμion + Δμelectron = 0, and potential drops in double - electric layers are compensated. The components Δμion= 0 and Δμelectron≠ 0 correspond to potentials of zero charge Ep. z.c. For mercury, the electron work function is 4.52 eV and Δμelectron = 4.52 eV - 5.19 eV = - 0.67 eV. In order Δμion + Δμelectron = 0, Δμion should be equal + 0.67 eV. Indeed, if E p.z.c. = - 0.193 V SHE for mercury is changed by + 0.67 V we obtain the chemical equilibrium of half-reactions at ~ +0.475 V SHE. REFERENCES J.Billitzer, Methods for Determination of the Absolute Potentials, Trans. Amer. Electrochem. Soc., 1930,57, 351.The Encyclopedia of Electrochemistry, C.A. Hampel (ed.), (Reinhold,New York, NY) (1964).H.J.Oel, H Strelow,Z. Electrochem, 1954,58,665.A.I.Chernomorskii, Soviet Electrochemistry, 1981, 17, 874.A.I.Chernomorskii, Russian Journal of Physical Chemistry,1981, 55, p.206.Ya.I.Tur’yan, Redox Reactions and Potentials in Analytical Chemistry, Khimiya, Moscow, 1989.A.I. Chernomorskii,N.S.Polizan, Reports of Academy of Sciences of the Uzbekistan,1990, 6, 35.A.I.Chernomorskii, Thernodynamics of Electrodes, FAN, Tashkent, 1993.A.I.Chernomorskii, The Intermediate Electron Bond and Half-reactions, Scientific Resources, New York, 1999.A.I. Chernomorskii, Journal of The Electrochemical Society, 2021, 168,116514. Figure 1

Bioleaching of Copper Slag Material

Bioleaching is applied mainly for copper recovery from low-grade sulfide ores via heap leaching. The main copper processing route includes pyrometallurgy and the remaining copper slag from smelting may still contain copper in amounts found in the ore. Here bioleaching of copper slag material with a copper content of about 1 % (grain size &lt; 63 µm) and fayalite (Fe2SiO4) und magnetite (Fe3O4) as main mineral phases was tested in aerobic shake flask experiments with a mixed culture of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidiphilium spp..To additionally test for reductive bioleaching, experiments under anaerobic conditions (80% N2, 20% CO2, v/v) with or without addition of elemental sulfur were run. The pH was adjusted to &lt; 3 by addition of sulfuric acid. After the incubation period of more than 50 days at 30°C cell growth was observed in all biological assays. The redox potential was above 800 mV SHE in the aerobic biological assays and dropped to around 500 mV in the chemical control assays as well as in the anaerobic biological and chemical assays. A significant copper bioleaching was observed in the aerobic experiments with 91 % copper release (max. 35 % in the chemical controls). Anaerobic bioleaching experiments did not show a significant copper release, however the release of iron (as iron(II)) and sulfate was much higher than in the abiotic assays and several fold higher than in the classical aerobic bioleaching experiments. Overall the results show that copper bioleaching from slag material is possible, however the economic feasibility needs to be demonstrated.

X-PEEM, XPS and ToF-SIMS characterisation of xanthate induced chalcopyrite flotation: Effect of pulp potential

Abstract Synchrotron-based X-ray photoemission electron microscopy (X-PEEM), X-ray photo-electron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and ultraviolet visible spectroscopy were used to characterize the flotation behaviour of chalcopyrite with xanthate at different processing conditions. The flotation recovery of chalcopyrite decreased from 97% under oxidative conditions (Eh ~ 385 mV SHE, pH 4) to 41% at a reductive potential of − 100 mV SHE (at pH 9). X-PEEM images constructed from the metal L3 absorption edges were used to produce near-edge X-ray absorption fine structure (NEXAFS) spectra from regions of interest, allowing the variability in mineral surface chemistry of each mineral particle to be analysed, and the effect of pulp potential (Eh) on the flotation of chalcopyrite to be determined. XPS, ToF-SIMS and NEXAFS analyses of chalcopyrite particles at oxidative conditions show that the surface was mildly oxidised and covered with adsorbed molecular CuEX. The Cu 2p XPS and Cu L2,3 NEXAFS spectra were dominated by CuI species attributed to bulk chalcopyrite and adsorbed CuEX. At a reductive potential of − 100 mV SHE, an increase in concentration of CuI and FeIII oxides and hydroxides was observed. X-PEEM analysis was able to show the presence of a low percentage of CuII oxides (CuO or Cu(OH)2) with predominantly CuI oxide (Cu2O) which is not evident in Cu 2p XPS spectra.

Chemometric and Multivariate Statistical Analysis of Time-of-Flight Secondary Ion Mass Spectrometry Spectra from Complex Cu–Fe Sulfides

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) spectra of mineral samples are complex, comprised of large mass ranges and many peaks. Consequently, characterization and classification analysis of these systems is challenging. In this study, different chemometric and statistical data evaluation methods, based on monolayer sensitive TOF-SIMS data, have been tested for the characterization and classification of copper-iron sulfide minerals (chalcopyrite, chalcocite, bornite, and pyrite) at different flotation pulp conditions (feed, conditioned feed, and Eh modified). The complex mass spectral data sets were analyzed using the following chemometric and statistical techniques: principal component analysis (PCA); principal component-discriminant functional analysis (PC-DFA); soft independent modeling of class analogy (SIMCA); and k-Nearest Neighbor (k-NN) classification. PCA was found to be an important first step in multivariate analysis, providing insight into both the relative grouping of samples and the elemental/molecular basis for those groupings. For samples exposed to oxidative conditions (at Eh ~430 mV), each technique (PCA, PC-DFA, SIMCA, and k-NN) was found to produce excellent classification. For samples at reductive conditions (at Eh ~ -200 mV SHE), k-NN and SIMCA produced the most accurate classification. Phase identification of particles that contain the same elements but a different crystal structure in a mixed multimetal mineral system has been achieved.

Cu and Fe chalcopyrite leach activation energies and the effect of added Fe 3+

The leaching kinetics of chalcopyrite (CuFeS 2) concentrate in sulfuric acid leach media with and without the initial addition of Fe 3+ under carefully controlled solution conditions ( E h 750 mV SHE, pH 1) at various temperatures from 55 to 85 °C were measured. Kinetic analyses by (i) apparent rate (not surface area normalised), and rate dependence using (ii) a shrinking core model and (iii) a shrinking core model in conjunction with Fe 3+ activity, were performed to estimate the activation energies ( E a) for Cu and Fe dissolution. The E a values determined for Cu and Fe leaching in the absence of added Fe 3+ are within experimental error, 80 ± 10 kJ mol −1 and 84 ± 10 kJ mol −1, respectively (type iii analyses E a are quoted unless stated otherwise), and are indicative of a chemical reaction controlled process. On addition of Fe 3+ the initial Cu leach rate (up to 10 h) was increased and Cu was released to solution preferentially over Fe, with the E a value of 21 ± 5 kJ mol −1 (type ii analysis) suggestive of a transport controlled rate determining process. However, the rate of leaching rapidly decreased until it was consistently slower than for the equivalent leaches where Fe 3+ was not added. The resulting E a value for this leach regime of 83 ± 10 kJ mol −1 is within experimental error of that determined in the absence of added Fe 3+. In contrast to Cu release, Fe release to solution was consistent with a chemical reaction controlled leach rate throughout. The Fe release E a of 76 ± 10 kJ mol −1 is also within experimental error of that determined in the absence of added Fe 3+. Where type (ii) and (iii) analyses were both successfully carried out (in all cases except for Cu leaching with added Fe 3+, <10 h) the E a derived are within experimental error. However, the type (iii) analyses of the leaches in the presence of added Fe 3+ (>10 h), as compared to in the absence of added Fe 3+, returned a considerably smaller pre-exponential factors for both Cu and Fe leach analyses commensurate with the considerably slower leach rate, suggestive of a more applicable kinetic analysis. XPS examination of leached chalcopyrite showed that the surface concentration of polysulfide and sulfate was significantly increased when Fe 3+ was added to the leach liquor. Complementary SEM analysis revealed the surface features of chalcopyrite, most likely due to the nature of the polysulfide formed, are subtly different with greater surface roughness upon leaching in the absence of added Fe 3+ as compared to a continuous smooth surface layer formed in the presence of added Fe 3+. These observations suggest that the effect of Fe 3+ addition on the rate of leaching is not due to the change in the chemical reaction controlled mechanism but due to a change in the available surface area for reaction.

The flotation of millerite — A single mineral study

While pentlandite is the dominant nickel sulphide mineral recovered from nickel ores, other nickel sulphide minerals can often be present. One such rare but important nickel sulphide mineral is millerite (NiS). There is very little information in the literature about the flotability of millerite, in particular its flotation behaviour relative to that of pentlandite under different flotation conditions. This paper details a single mineral investigation into the flotability of millerite, and compares its flotability with that of pentlandite and other nickel arsenides often present in nickel sulphide ores. Millerite was found to be strongly flotable with xanthate collector at pH 9 but there was a noticeable decrease in recovery at pH 10 and a further decrease at pH 10.5. Size-recovery data suggests the recovery of millerite decreases at sizes above 75 μm and below 10 μm. In particular, fine millerite floats poorly in a similar fashion to fine pentlandite. At pH 9 with xanthate collector millerite exhibits a lower limiting threshold potential at about − 100 mV SHE, about 300 mV below the lower limiting threshold potential for pentlandite. Millerite is not readily depressed by cyanide at pH 9 and further, cyanide doses required to affect depression are much higher than those required to depress the nickel arsenide mineral gersdorffite. Cyanide should therefore be a suitable depressant for the separation of gersdorffite from other nickel sulphide minerals such as millerite and pentlandite.

A microelectrochemical scanning flow cell with downstream analytics

The combination of a capillary based microelectrochemical flow cell system and downstream UV–vis analytics allows obtaining synchronized electrochemical and spectroscopic data in a fully automated mode. This method combination can be generally applied to microelectrochemical studies in which an electrochemical species is released or consumed during the electrochemical reaction. For the example of pure zinc surfaces, the characterization of the integrated spectroscopic system is presented with a Zn 2+ detection limit below 0.1 μmol l −1 using Zincon as complexing agent. A parameter screening of the effect of pH in the range of 6.6–9.0 in borate buffer reveals a linear increase in zinc dissolution with proton concentration but a distinct step in the open circuit potential from the active state (around −700 mV SHE, pH 6.6–7.1) to the passive state (around −300 mV SHE, pH 7.4–9.0) indicating the formation of a closed passive layer. This mechanism is strongly influenced by sulfate anions which increase the dissolution rate of the passive film and promote the active state as monitored by the dissolution profile and OCP (open circuit potential) values. Within the scope of this parameter variation, the congruency between OCP transients, potentiodynamic sweeps and time resolved dissolution profiles is discussed.

Leaching behavior of copper using electro-generated chlorine in hydrochloric acid solution

The leaching behavior of metallic copper has been investigated using chlorine electro-generated at the anode in 1.0 mol/L HCl solution. An electrochemical reactor divided into two compartments by an anion exchange membrane was employed for these experiments. Various parameters, viz., current density, chloride concentration, leaching temperature and time, and agitation speed, were studied to understand the mechanism of copper leaching. The leaching rate of copper increased with increasing current density, from 10 to 40 mA/cm 2, increasing agitation speed, from 200 to 600 rpm, and increasing temperature, from 25 to 50 °C. The addition of Cl − ions enhanced the leaching efficiency of copper remarkably by dissolving CuCl precipitated on the surface of the copper plate. Based on the results of the leaching experiment, the leaching of copper by electro-generated chlorine is proposed to proceed through three stages: stage I (ORP of leach solution ≈ 1300 mV SHE), stage II (380 mV SHE < ORP < 490 mV SHE), and stage III (ORP > 490 mV SHE).

The flotation of gersdorffite in sulphide nickel systems — A single mineral study

The flotation response of gersdorffite has been determined in a series of batch flotation tests in which a sulphide sample containing about 76% gersdorffite was floated from mixtures with quartz. Using xanthate as collector, the arsenide floated strongly at pH 9, irrespective of whether lime, sodium hydroxide or sodium carbonate was used as pH modifier. When the pH was raised further to 10 or more using lime, the flotability decreased sharply. Changing the pulp potential at pH 9 also strongly affected the flotation response. Above about − 230 mV SHE, the mineral floated strongly, but below this potential it was essentially non-flotable. As far as it was tested (up to + 400 mV SHE), no upper limiting potential was found. Adding cyanide to the grinding mill brought about only a weak depressant effect on subsequent gersdorffite flotation at both pH 9 and 10. However, adding the same amount of cyanide to the flotation cell produced a strong depressant effect at the same pH values. At both pH 9 and pH 10, a threshold cyanide addition existed below which gersdorffite floated strongly, and above which it did not. For the conditions used in this study, this addition equates to about 100 g/t at pH 9 and about 80 g/t at pH 10. A hypothesis for the depression effect is presented which is consistent with both the available flotation data and a series of diagnostic analyses of grinding and flotation pulps completed during the test work.

Single Crystalline Molybdenum Nanowires, Nanowire Arrays and Nanopore Arrays in Nickel-Aluminium

This work describes a novel fabrication method of single crystalline Mo nanowires and nanowire arrays. The method utilizes directional solidification (ds) of a NiAl-Mo eutectic alloy and its subsequent electrochemical processing. In the first step, a self-organized array of Mo nanowires embedded in a NiAl matrix is obtained. By combining the Pourbaix diagrams of the three elements involved, a strategy for selective removal of either of the two phases is derived. An oxidizing acidic solution of pH 0.2 dissolved the matrix and released an array of long and uniform Mo wires. Even a complete extraction of the wires is possible through entire dissolution of the matrix. On the other hand, electrodissolution of the Mo with a simultaneous passivation of the NiAl matrix at the pH 6 and the potential of 200 mV SHE yielded nanopore arrays with rectangular pores. This method has several advantages. First of all, it is one of the few top-down methods that allow the production of large amounts of nanostructures. In addition, both the wires and the matrix are single crystalline which makes them favorable for various applications. Further, the obtained nanostructures exhibit extremely high aspect ratios (> 1000), unreachable by most other techniques. This technique has the potential for the production of nanowire arrays either for employment in sensors or in field emission.

Nanostructuring of NiAl–Mo eutectic alloys by selective phase dissolution

A technique for the electrochemical structuring of directionally solidified NiAl–Mo eutectic by selective phase dissolution is presented. Local matrix dissolution at 200 mV SHE in 1 M HCl of pH 1 yielded the grid of Mo nanowires spanning along the central part of the sample. On the other hand, the dissolution of the fibrous minor phase while passivating the continuous NiAl matrix resulted in continuous nanopore arrays. Initially, mechanical polishing and electropolishing were employed to thin the samples. Etching time was optimized by plotting the etch time until hole formation as a function of initial sample thickness, along with plotting sample thickness versus etching time. As a next step, an investigation into the passivation behaviour of the NiAl was performed in order to determine the optimal potential for wire dissolution. A potential scan from 0 to 2500 mV SHE on a bulk sample of pure NiAl in an electrolyte of 0.1 M acetate buffer pH 6.0 indicated that a potential of 500 mV SHE, just below the breakdown potential would provide maximum driving force for wire dissolution process. Different parameters within the electrochemical system are varied in order to optimize the wire dissolution. The extent of wire dissolution is measured both quantitatively (total charge transfer) and qualitatively (optical and SEM imaging).

Strain-induced corrosion cracking behaviour of low-alloy steels under boiling water reactor conditions

The strain-induced corrosion cracking (SICC) behaviour of different low-alloy reactor pressure vessel (RPV) and piping steels and of a RPV weld filler/weld heat-affected zone (HAZ) material was characterized under simulated boiling water reactor (BWR)/normal water chemistry (NWC) conditions by slow rising load (SRL) and very low-frequency fatigue tests with pre-cracked fracture mechanics specimens. Under highly oxidizing BWR/NWC conditions (ECP ⩾+50 mV SHE, ⩾0.4 ppm dissolved oxygen), the SICC crack growth rates were comparable for all materials (hardness <350 HV5) and increased (once initiated) with increasing loading rates and with increasing temperature with a possible maximum/plateau at 250 °C. A minimum K I value of 25 MPa m 1/2 had to be exceeded to initiate SICC in SRL tests. Above this value, the SICC rates increased with increasing loading rate d K I /d t, but were not dependent on the actual K I values up to 60 MPa m 1/2. A maximum in SICC initiation susceptibility occurred at intermediate temperatures around 200–250 °C and at slow strain rates in all materials. In contrast to crack growth, the SICC initiation susceptibility was affected by environmental and material parameters within certain limits.

Effect of corrosion potential on the corrosion fatigue crack growth behaviour of low-alloy steels in high-temperature water

The low-frequency corrosion fatigue (CF) crack growth behaviour of different low-alloy reactor pressure vessel steels was characterized under simulated boiling water reactor conditions by cyclic fatigue tests with pre-cracked fracture mechanics specimens. The experiments were performed in the temperature range of 240–288 °C with different loading parameters at different electrochemical corrosion potentials (ECPs). Modern high-temperature water loops, on-line crack growth monitoring (DCPD) and fractographical analysis by SEM were used to quantify the cracking response. In this paper the effect of ECP on the CF crack growth behaviour is discussed and compared with the crack growth model of General Electric (GE). The ECP mainly affected the transition from fast (‘high-sulphur’) to slow (‘low-sulphur’) CF crack growth, which appeared as critical frequencies ν crit = f(Δ K, R, ECP) and Δ K-thresholds Δ K EAC = f( ν, R, ECP) in the cycle-based form and as a critical air fatigue crack growth rate d a/d t Air,crit in the time-domain form. The critical crack growth rates, frequencies, and Δ K EAC-thresholds were shifted to lower values with increasing ECP. The CF crack growth rates of all materials were conservatively covered by the ‘high-sulphur’ CF line of the GE-model for all investigated temperatures and frequencies. Under most system conditions, the model seems to reasonably well predict the experimentally observed parameter trends. Only under highly oxidizing conditions (ECP ⩾ 0 mV SHE) and slow strain rates/low loading frequencies the GE-model does not conservatively cover the experimentally gathered crack growth rate data. Based on the GE-model and the observed cracking behaviour a simple time-domain superposition-model could be used to develop improved reference CF crack growth curves for codes.

The separation of arsenic from copper in a Northparkes copper–gold ore using controlled-potential flotation

In order for the high-arsenic regions of the Northparkes copper–gold orebody to be beneficiated economically, tennantite ((Cu,Fe) 12As 4S 13) present in the ore needs to be rejected to enable copper concentrates to meet the typical smelter penalty level of 2000 ppm As. Using a composite sample of high-arsenic drill cores from Northparkes it was possible to selectively separate tennantite from chalcopyrite (CuFeS 2) and bornite (Cu 5FeS 4) using controlled-potential flotation. The separation was made on a bulk copper–arsenic concentrate after reducing the pulp potential to about − 150 mV SHE at pH 12 and floating the tennantite from the other copper minerals. The basis of the separation relies on findings that the lower limiting pulp potential threshold for tennantite is lower than that for chalcopyrite such that there is a potential window in the reducing region where tennantite is strongly floatable but chalcopyrite is not. Little or no selectivity between tennantite and chalcopyrite was found in the oxidising pulp potential region for the range examined. From the composite sample tested, which had a head grade of 0.11% As and 1.2% Cu, it was possible to produce a low-arsenic high-copper concentrate containing 52% of the non-tennantite copper and assaying 2600 ppm As. Computer simulations have shown that for a feed containing a more typical arsenic and copper level (200 ppm As and 1% Cu) the efficiency of separation should be sufficient to concentrate about 61% of the copper in a product assaying less than 2000 ppm As. A conceptual flowsheet for arsenic rejection from Northparkes copper–gold ore, based on the findings from this study, is presented and discussed in this paper.

Effect of oxidation potential and zinc sulphate on the separation of chalcopyrite from pyrite

The effects of oxidation potential (Eh) and zinc sulphate on the separation of chalcopyrite from pyrite were investigated at pH 9.0. The flotation recovery of these minerals is Eh dependent with maximum separation obtained at 275 mV SHE. Zinc sulphate addition improved this mineral separation at an Eh value of 275 mV by selectively depressing pyrite flotation. A different result was obtained at lower Eh values where zinc sulphate addition improved chalcopyrite flotation but had no or little effect on pyrite flotation. These opposite effects of zinc sulphate on mineral flotation were reconciled by examining the surface species of these minerals. The selective depression of pyrite flotation by zinc sulphate was also confirmed in the flotation of two copper ores.

Reductive Dechlorination of Tetrachloroethene in a Sand Reactor Using a Potentiostat

In this study, an electrochemical system was investigated to enhance abiotic dechlorination of chlorinated solvents in contaminated soil in situ. A potentiostatic electrolysis sand reactor was developed and tested to evaluate tetrachloroethene (PCE) dechlorination in saturated sand. When operated with recirculating nutrient-supplemented water the reactor sustained a low oxidation reduction potential (ORP) at the cathode (<-400 mV standard hydrogen electrode [SHE]), a pH less than 9.4, and electric current >5 mA at room temperature with the cathodic potential controlled at -950 mV SHE. Tetrachloroethene in the electrolysis reactor had a half-life of 6.8 d compared with the control bioreactor without electrolysis, which had a PCE half-life of 16.4 d. Ethane and ethene were the main dechlorination products in the test reactor, while trichloroethene (TCE) accumulated in the nutrient-amended control reactor without electrolysis. An electrolysis reactor operated with water not amended with nutrients showed a PCE half-life of 7.6 d, suggesting that most of dechlorination activity in the reactor was abiotic. Since complete dechlorination can be achieved under moderate pH and temperature, this type of electrolysis technology is attractive as a remedial method for subsurface chloroethene contamination.

Corrosion behavior of steel under wet and dry cycles containing Cr 3+ ion

The corrosion behavior of mild steel has been investigated during the wet and dry cyclic transitions containing Cr 3+ ion added as sulfate in order to gain a better understanding of the influence of Cr on the atmospheric corrosion of steels. The corrosion rate during drying is greatly suppressed by the existence of Cr 3+ ion in the electrolyte covered with the surface. Lower corrosion rates are observed during drying even if the surface have been polarized to negative potentials below −200 mV SHE during the wet corrosion conditions in which the surface-covered electrolyte contains Cr 3+ ion. This corrosion behavior is identical to the case of Cr-containing steel for the wet and dry cyclic transitions without the addition of Cr 3+ ion. The composition of rust layer after the wet and dry cyclic transitions is composed of α-FeOOH, γ-FeOOH and Fe 3− δ O 4 for both cases of non-Cr 3+ and Cr 3+-containing condition, and no significant difference in the mass fraction of the above rust substances between two conditions is observed by means of Mössbauer spectroscopy. The only difference in the rust layer is that the rust formed under the wet and dry cyclic transitions containing Cr 3+ ion contains a certain amount of Cr near the steel/rust interface. Those results suggest that the role of Cr during the wet and dry cyclic transitions is the inhibition of the rust reduction and the formation of Fe 2+-state intermediate by the existence of Cr in the rust layer. This can lead to the inhibition of the oxygen reduction during drying.

Corrosion and wear properties of TiC/Ni–Mo composites produced by direct consolidation during a self-propagating high-temperature reaction

TiC/Ni–Mo composites were prepared by one-step direct consolidation during a self-propagating high-temperature synthesis reaction and their corrosion and wear properties were studied. The composites reached 99.8% of theoretical density after the direct consolidation. Corrosion potentials and rates of the composites in a 50% NaOH solution were −982.7 mV SHE and 3.6×10 −6 A cm −2 for TiC/50% Ni and −1074.8 mV SHE and 8.12×10 −6 A cm −2 for TiC/46.5% Ni–3.5% Mo, respectively. Wear resistance determined by abrasive wear increased with molybdenum addition. Electron probe microanalysis revealed that δ-phase was formed around titanium carbide in the TiC/Ni–Mo composites. Transmission electron microscopy revealed that the dislocation density around the carbide in the composites was high. The improved wear resistance was associated with increases of the interfacial bonding strength due to the formation of δ-phase and the high dislocation density around carbide due to the difference of thermal expansion coefficient between carbide and matrix.

Potential-pH region for environment-assisted cracking of gamma titanium aluminide

Environment-assisted cracking (EAC) of γ-TiAl has been investigated from electrochemical viewpoint. The material whose potential was controlled was tested in aqueous sulfate solutions of various pHs at room temperature by using a slow strain rate tensile testing apparatus. The TiAl forged at 1373 K and annealed at 1073K for 7.2 ks was used in the EAC test. It was found in the alkaline and the natural solution that maximum stress was independent of the potential in higher potential region, and decreased with decrease in the potential in the lower potential region. In acidic solution, the maximum stress changed with the potential as follows; the maximum stress was independent of the potential above −200 mV SHE, decreased with decrease in the potential between −200 and −1000 mV SHE, and increased with decrease in the potential below −1000 mV SHE. The experimental EAC results was discussed on the basis of the potential-pH diagram of Al and Ti/water system. It was revealed that the diagram of Ti/water system can predict the EAC susceptibility of TiAl, although the diagram of Al/water system shows almost no relation to the susceptibility. Therefore, the EAC of TiAl is controlled by the stability of Ti oxide, hydride, and ion on the solution/base material interface, which affect the entry of hydrogen into the material.