Investigations into precipitation membrane growth.

The catalytic activity of copper electrodes coated with nickel foam and metal oxides and hydroxides in highly alkaline alcoholic media was investigated. It has been found that the most promising catalyst is one coated with iron and cobalt oxides. The presence of cobalt oxides in nickel foam leads to easier oxidation of ethanol and reduction of oxygen. At the same overvoltage, in the alcohol layer at a potential of 100 mV, the current density on nickel foam with cobalt oxides is at least 2 times higher. In the salt layer, the process of releasing oxygen on nickel foam with cobalt oxides begins at potentials 250 mV more negative than on pure nickel foam. The use of a copper support as a support for the catalyst is justified due to its good electrical.

Spheroidal weathering, one of the important rock weathering styles, has been attributed to chemical weathering by the water from joint surfaces, and mechanical aspects of the weathering have not been well addressed. We made an investigation on spheroidal weathering of Miocene granite porphyry with well‐developed columnar joints and found that this spheroidal weathering proceeds through chemical processes and accompanying mechanical processes. The investigation of the textures, physical properties, mineralogy, and chemistry of the porphyry revealed the presence of a brown band on the surface margins of corestones, representing the oxidation of pyrite and chlorite, and the precipitation of iron hydroxides, and the consequent generation of micro‐cracks within the band. During weathering, oxidation progresses inwards from joints that surround the rindlets, including both high‐angle columnar and low‐angle planar joints, and causes rounding of the unweathered interior portion of the rock. Microscopic observations of the brown band embedded with fluorescent resin show that pores are first filled with iron hydroxides, and that micro‐cracks then form parallel to the oxidation front in the outer portion of the brown band. Iron hydroxide precipitation increases the P‐wave velocity in the brown band, while micro‐crack formation decreases the tensile strength of the rock. Where the brown band has thickened to ~6 cm, the micro‐cracks are connected to one another to create continuous cracks, which separate the rindlets from the corestone. Micro‐crack formation parallel to the corestone surface may be attributed to compressive stresses generated by small amounts of volumetric expansion due to the precipitation of iron hydroxides in the brown band. Earth surface is under oxidizing environments so that precipitation of iron hydroxides commonly occurs; the spheroidal weathering in this paper is a typical example of the combination of chemical and mechanical processes under such environments. Copyright © 2016 John Wiley & Sons, Ltd.

Stratiotes aloides L. is an aquatic macrophyte that occurs in waters on reduced peaty sediments which have a relatively narrow range of free-iron content in the sediment. Comparison of different aquatic macrophytes reveals that species from reducing sediments have much lower oxidizing ability than do species from oxidizing sediments. Compared with those other species from reducing sediments, the oxidizing ability of Stratiotes aloides is very low and probably makes the species very vulnerable to sulphide toxicity and internal precipitation of iron hydroxide. Apoplastic iron contents were determined for Stratiotes roots growing in sediments with different free-iron concentrations. Roots collected from sediment with a low free-iron content appeared to have a relatively low apoplastic-iron content whereas roots from sediments with a relatively high free-iron concentration had a relatively high apoplastic-iron content. In sediments with low free-iron levels, sulphide levels are generally high. Using light microscopy, iron hydroxide precipitates were observed around the endodermis and cortical air spaces of the roots of Stratiotes aloides growing in iron-rich sediments. Internal iron oxidation outside the endodermis can prevent iron toxicity inside the stele and thus enable root apices to survive. The root hairs, however, die because of iron hydroxide precipitation at their base; the dead roots have the highest visible iron hydroxide content. Excessive internal iron hydroxide precipitation and the consequential early death of the roots probably explains the absence of Stratiotes aloides in locations with high free-iron levels in sediment pore water.

Fe(III) hydroxide nanoparticles are an essential carrier for aqueous heavy metals. Particularly, iron hydroxide precipitation on mineral surfaces can immobilize aqueous heavy metals. Here, we used grazing-incidence small-angle X-ray scattering (GISAXS) to quantify nucleation and growth of iron hydroxide on quartz in 0.1 mM Fe(NO3)3 solution in the presence of Na(+), Cu(2+), Pb(2+), or Cr(3+) at pH = 3.7 ± 0.1. In 30 min, the average radii of gyration (R(g)) of particles on quartz grew from around 2 to 6 nm in the presence of Na(+) and Cu(2+). Interestingly, the particle sizes remained 3.3 ± 0.3 nm in the presence of Pb(2+), and few particles formed in the presence of Cr(3+). Quartz crystal microbalance dissipation (QCM-D) measurements showed that only Cr(3+) adsorbed onto quartz, while Cu(2+) and Pb(2+) did not. Cr(3+) adsorption changed the surface charge of quartz from negative to positive, thus inhibiting the precipitation of positively charged iron hydroxide on quartz. Masses and compositions of the precipitates were also quantified. This study provided new insights on interactions among quartz, iron hydroxide, and metal ions. Such information is helpful not only for environmental remediation but also for the doping design of iron oxide catalysts.

The relation between electric and redox potential: evidence from laboratory and field measurements

Formation of iron(III) hydroxides from homogeneous solutions

Zn-doped nickel iron (oxy)hydroxide nanocubes passivated by polyanions with high catalytic activity and corrosion resistance for seawater oxidation

An electric potential probe was constructed so that simultaneous, multiple measurements of electric potential could be made in a six-in-line electric furnace for smelting nickel calcine having a maximum transformer capacity of 36 MVA. When the electric potential distributions were compared with those calculated from the solution of the Laplace equation, it was evident that there was significant electric potential drop at the electrode surface, 100 to 120 V for an applied potential of 180 to 230 V and currents of 20 to 30 kA. The Soderberg electrodes were continuously oxidized in the slag, likely creating carbon monoxide. The electric potential drop at the surface was attributed to arcing through the carbon monoxide. Thus, heat was released in the immediate vicinity of the electrode due to arcing, as well as in the bulk of the slag by Joule heating. The proper distribution of heat dissipation is required for the transport model, developed in Part II of this series.

With the development of micro chemical and medical analysis in MEMS, micro-fluid-control chip becomes more and more popular. Based on discrete droplet control system, chemical and medical analysis is applied in the micro chip lab. The change of voltage between the dielectric layer of the electrode controls the wettability of a droplet on a dielectric solid surface and then makes it possible to create,transport,merge and cut the micro droplets. This paper presents a numerical method to simulate the droplet motion by electrowetting on dielectric (EWOD). The second-order projection method is carried out to solve N-S equations and level set function. The interface is captured as zero level set. Dynamic contact angle for fluid contacting a solid surface by the electric potential is used to evaluate the wettability of fluid by EWOD. The numerical scheme is based on staggered MAC grid. Numerical simulations are used to capture the interface between two kinds of fluids in micro channels, the shapes of micro droplets resting on the horizontal solid surface under different electric potential and the transportation of a micro droplet in a parallel-plate channel when electrodes are activated.

Reusable superparamagnetic nanocomposite particles for magnetic separation of iron hydroxide precipitates to remove and recover heavy metal ions from aqueous solutions

This paper describes a radiochemical method for the determination of99Tc in large volumes of rain, river and seawater. The procedure is based on the reduction of technetium to the +4 oxidation state with potassium disulfite in a slightly acidic medium, followed by iron hydroxide precipitation. After oxidation to the +7 oxidation state, the technetium fraction is purified with iron hydroxide and calcium carbonate precipitations. Technetium (+7) is extracted with TBP (xylene) in 3M H2SO4, back extracted in 2M NaOH or ammonia, and the electrodeposition is made in 2M NaOH or H2SO4/NH4OH medium at pH 5–6. The radiochemical yield is determined by gamma counting of the 140 keV gamma ray from99Tcm.99Tc is counted on an anti-coincidence shielded GM-gas flow counter. The purity of the99Tc plated samples is checked by alpha and beta spectrometry using surface barrier detectors and by gamma spectrometry on Ge(HP) detector. The radiochemical yield of 50–150 l water samples is around 20–60%.

Detailed thermal demagnetization experiments have been carried out on 31 samples (93 specimens) of fore-reef limestones from the northern Canning basin, Western Australia. Samples are from a condensed sequence composed of deep-water (over 100 m) stromatolites in the marginal-slope facies of the Virgin Hills Formation. These stromatolites are made up of shrublike cyanobacterial filaments of Frutexites, an organism that probably precipitated iron hydroxide from seawater. Under the oxidizing conditions created by extremely slow sedimentation rates, it is likely that iron hydroxides were converted to hematite at or near the sediment-water interface. When plotted within the microstratigraphic framework for the study area, the observed characteristic directions from the sampled interval (14.5 cm thick) lie in five discrete normal and reversed polarity zones. The measured northeast-southwest declinations and shallow inclinations in these polarity zones probably record Late Devonian magnetostratigraphy on a centimeter scale. Using sedimentation rates from detailed conodont studies, a 56,000-year periodicity is calculated for Late Devonian polarity reversals. This value assumes no breaks in sedimentation, and is comparable to minimum lengths of late Mesozoic and Cenozoic polarity reversals. However, this study shows that iridium is present over the span of five magnetic reversals. Evidence therefore favors a biologic, rather thanmore » extraterrestrial, origin for anomalous iridium concentrations.« less

Precambrian banded iron formations in the North China Craton: Silicon and oxygen isotopes and genetic implications

PO43− adsorption in a complex solution by nickel–cobalt hydroxide, and its cytotoxicity on bovine aortic endothelial cells

Non-contact imaging of electric potentials with micro-metre resolution can provide relevant insights in material characterisation, electrostatic charge imaging and bio-sensing applications. However, scanning electric potential microscopes have been confined to rigid and single-probe devices, making them slow, prone to mechanical damage and complex to fabricate. In this work, we present a novel 5-element flexible array of electric potential probes with spatial resolution down to $20 \mu \mathrm{m}$ which reduces the scanning time by a factor of 5 when compared to a single probe device. This was achieved by combining flexible thin-film probes for active guarding and shielding with state-of-the art discrete conditioning circuits. The potential of this approach is showcased by using the fabricated array to image latent fingerprints deposited on an insulating surface by contact electrification. This is the first example of a micro-scale array of electric potential sensors.