Search

The kinetics of the hydrogen evolution reaction on nickel silicide NiSi (fabricated by Czochralski method) in solutions of 0.5 M H2SO4 and 1 М КОН has been studied by polarization measurements and electrochemical impedance spectroscopy. In an acid solution two Tafel slopes have been observed on the polarization curve for NiSi: the slope b is equal to 0.105 V/decade at E > –0.33 V (SHE) and b = 0.18 V/decade at E < –0.33 V. In an alkaline solution one linear region of the Tafel line has been observed, b = 0.13 V/decade. The exchange current density i0 is 4.45·10–6 A cm–2 and 4.2·10–6 A cm–2 in acidic and alkaline solution respectively. In an acidic solution the Nyquist plots consist of a single semicircle at not high cathodic polarizations and of two well-resolved capacitive arcs at higher cathodic polarizations. An equivalent circuit considering the hydrogen absorption reaction was used at high cathodic polarizations. In an alkaline solution the Nyquist plots consist of a single capacitive semicircle. The potential dependences of equivalent circuit elements R1, R2, C2 and time constant R2C2 have been discussed. The conclusion was made that hydrogen evolution on NiSi in a sulfuric acid solution proceeds via a two-route Volmer–Heyrovsky–Tafel mechanism (with hydrogen absorption reaction in parallel) and in an alkaline solution via the Volmer–Heyrovsky mechanism with unequal transfer coeffi cients for the steps. The obtained results show that the adsorbed atomic hydrogen on an NiSi electrode obeys the Langmuir isotherm in both solutions.

AgI-SiO2 hybrid powders (HPs) based on SBA-15, MCM-41, and MCM-48 have been prepared by template co-condensation of silica and silver iodide under hydrothermal conditions. The effect of the [Ag]/[Si] ratio and the type of silica matrix on the textural, structural, morphological, and rheological properties of the HPs has been studied. The formation of the target phase of iodargyrite (β-AgI) is dependent both on the ratio of the main components [Ag]/[Si] and on the pore arrangement in the silica matrix, as detected by XRD. The small-angle XRD and low-temperature nitrogen adsorption data have shown the textural and structural properties of AgI-SiO2 hybrid powders to be similar to the porous structure of the initial silica matrices—SBA-15, MCM-41, or MCM-48. A uniform distribution of silver iodide in all silica matrices, SBA-15, MCM-41 and MCM-48, has been demonstrated by energy dispersive microanalysis (EDAX). For AgI-SiO2 powders with various types of pore arrangement, a high fluidity degree has been demonstrated using the data on the natural angle of repose. It has been shown that MCM-48 based β-AgI-SiO2 powders are characterized by the smallest crystallite sizes (~6 nm), and average size of particles (50 nm) and average size of particle aggregates (13 μm), the highest specific surface area (up to 860 m2/g) and the best fluidity. Highlights: The formation of the target β-AgI phase, iodargyrite, in AgI-SiO2 hybrid powders (HP) depends both on the component [Ag]/[Si] ratio and on the pore arrangement type of the silica matrix. Crystal phase, corresponding to iodargyrite, was detected in HPs samples prepared using the [Ag]/[Si] ratios within the range from 0.04 to 0.08. In AgI-SiO2 powders prepared by hydrothermal template synthesis via а co-condensation route, the ordered pore arrangement was found to be similar to that of the initial silica matrices—SBA-15, MCM-41 or MCM-48. The smallest crystallites (~6 nm), average size of particles (50 nm) and average size of particle aggregates (13 μm), the highest specific surface area (up to 860 m2/g), and the best fluidity was found in the case of β-AgI-SiO2 powders based on the MCM-48 matrix. [ABSTRACT FROM AUTHOR]

We assess the feasibility of using struvite as a component of a fire-extinguishing powder agent. A fine-particle crystalline MgNH4PO4⋅6H2O hydrate (struvite) has been synthesized in the presence of different surfactants. We have optimized conditions for the preparation of a fine-particle crystalline hydrate so as to exclude a comminution step, without distorting its crystal structure. The thermal decomposition of the crystalline hydrates synthesized in the presence of the surfactants has been shown to be accompanied by a considerable heat absorption, which can be used to lower the temperature of a fire source. [ABSTRACT FROM AUTHOR]

The contents of Na+, K+, water, and dry matter were measured in leaves and roots of euhalophytes Salicornia europaea L. and Climacoptera lanata (Pall.) Botsch featuring succulent and xeromorphic cell structures, respectively, as well as in saltbush Atriplex micrantha C.A. Mey, a halophyte having bladder-like salt glands on their leaves. All three species were able to accumulate Na+ in their tissues. The Na+ content in organs increased with elevation of NaCl concentration in the substrate, the concentrations of Na+ being higher in leaves than in roots. When these halophytes were grown on a NaCl-free substrate, a trend toward K+ accumulation was observed and was better pronounced in leaves than in roots. Particularly high K+ concentrations were accumulated in Salicornia leaves. There were no principal differences in the partitioning of Na+ and K+ between organs of three halophyte species representing different ecological groups. At all substrate concentrations of NaCl, the total content of Na+ and K+ in leaves was higher than in roots. This distribution pattern persisted in Atriplex possessing salt glands, as well as in euhalophytes Salicornia and Climacoptera. The physiological significance of such universal pattern of ion accumulation and distribution among organs in halophytes is related to the necessity of water absorption by roots, its transport to shoots, and maintenance of sufficient cell water content in all organs under high soil salinity. [ABSTRACT FROM AUTHOR]