Vol 89, No 7 (2016)

Recently published data concerning the preparation and valuable properties of organosilicon compounds of silatrane structure with carbofunctional sulfur-containing substituents (thiol, sulfide, disulfide, polysulfide) and heteroatomic sulfur-containing groups (thiourea, thiourea dioxide, dithiocarbamate, thiuram disulfide) are summarized and analyzed.

Mechanisms of ozone generation in an electrochemical system with a solid polymer electrolyte and the electrode and catalytic materials used in systems of this kind are considered. The influence exerted by the process parameters and by the type of electrolyte and electrocatalysts on the productivity of the system and on the current efficiency by ozone is analyzed.

Data on reactivities of α- and γ-Al₂O₃ finely dispersed powders in a melted carbonate eutectic (Li₂CO₃–Na₂CO₃–K₂CO₃)_eut and carbonate-chloride mixture 0.72(Li₂CO₃–Na₂CO₃–K₂CO₃)_eut–0.28NaCl were obtained. The methods of synchronous thermal and X-ray phase analyses and Raman spectroscopy confirmed that, in contrast to γ-Al₂O₃, α-Al₂O₃ does not chemically interact with the melted carbonate eutectic and carbonate-chloride mixture (Li₂CO₃–Na₂CO₃–K₂CO₃)_eut–NaCl can be recommended as a thickening agent for a carbonate fuel cell.

New approach to processing of the apatite concentrate is suggested and substantiated. The approach includes treatment of the concentrate with a phosphoric acid solution at room temperature in the presence of a sulfo cation exchanger in the NH₄⁺ or H⁺ form. The phosphoric acid solution and the sorbent saturated with metal cations are separated and processed into target products by the known methods. The advantages and disadvantages of the approach are discussed.

Effect of methanol on the reduction kinetics of oxygen on highly dispersed catalysts 60Pt/C (HiSPEC 9100), 40Pt/carbon nanotubes, and CoFe/carbon nanotubes for the cathode of a direct methanol-oxygen fuel cell was studied. It was shown that the CoFe/carbon nanotubes catalyst surpasses the platinum systems in tolerance to the alcohol. It was found that the tolerance of the cathode catalyst strongly affects the current–voltage characteristics of the fuel cell, which is the principal result of the study and constitutes its scientific novelty. The maximum power density of an alkaline methanol-oxygen fuel cell with nonplatinum cathode (260 mW cm^–2) exceeds the characteristics of similar fuel cells with platinum cathode catalysts, both obtained in the present study and described in the literature, which points to the practical importance of the study.

Possibility of performing deep purification of concentrated sodium molybdate solutions to remove vanadium(V) impurity by selective sorption of vanadium(V) from the solutions with fixed pH values on a strong base anion exchange resin Purolite A500/2788 was demonstrated.

Specific features of oxidation of unsymmetrical dimethylhydrazine on a Pt-containing catalyst were studied. The temperature dependence of the unsymmetrical dimethylhydrazine conversion was determined, and the main intermediate and final reaction products were identified. Platinum behaves in the process as a multifunctional catalyst participating in dehydrogenation, hydrogenolysis, and oxidation. A new method was suggested for detecting unsymmetrical dimethylhydrazine in air. It consists in catalytic conversion of unsymmetrical dimethylhydrazine and detection of the nitrogen dioxide formed with semiconductor gas sensors. The method was successfully used for detecting unsymmetrical dimethylhydrazine in air at concentrations in the range 0.1–10 mg m^–3.

Preparation of a polyelectrolyte complex of chitosan with the oxidized form of Siberian larch arabinogalactan at the component ratio from 0.05: 1 to 1: 1 was studied by spectrometry and laser scattering. Water-insoluble films based on this complex were prepared. These films were used as a matrix for drug immobilization. The possibility of controlling the rate and degree of the drug release from the film by variation of the polysaccharide ratio, modification of the polymer film with a sodium dodecyl sulfate solution, or heat treatment was demonstrated with cefazolin antibiotic as example. The films obtained exhibit high bactericidal activity.

Comparative analysis of the curing performance of epoxy-containing cross-linking agents of different structure in vulcanization of a promising binder for energetic systems, poly-N-methyl-5-vinyltetrazole prepared by the modification procedure and containing residual N–H-unsubstituted tetrazole fragments, was made. Cross-linking of polymer chains of the binder is a result of alkylation of the residual N–H-unsubstituted tetrazole rings in poly-N-methyl-5-vinyltetrazole macromolecules with oxirane rings of the second reactant. Curing of poly-N-methyl-5-vinyltetrazole in the presence of macromolecular curing agents, carbon-chain polymers containing oxirane rings in pendant chains, at temperatures lower than 100°С occurs in a considerably narrower time interval compared to curing with low-molecular-mass epoxy resin.

In drilling and production process, the barite powder serving as weighting agent is added to ensure operation safety when overflow occurs, that results in reservoir pollution and pore blockage. The main component of barite is BaSO₄, so ammonium carboxy chelating agents can be injected into formation to form stable chelates with Ba²⁺, BaSO₄ will be eliminated from wellbore with flowback fluid easily. In this experiment, the weight method and the atomic absorption spectrometry method were utilized to study descaling ability and an action mechanism of descaling agents. Firstly, DTPA was selected from three descaling agents: NTA, EDTA, DTPA; then OT1 was screened out to synergize with DTPA and studied its descaling mechanism; eventually, the descaling system STD was determined, and its composition was 6% DTPA + 5% OT1 + 1% antiswelling agent + 100 ppm corrosion inhibitor. And the STD’s performance evaluation experiment results suggested that it had an excellent resistance to temperature and demonstrated a good descaling ability at 170°C. Furthermore, the descaling ability of STD was almost not affected by calcium and magnesium ions and its corrsion rate is lower than standard value. Moreover, STD could descale efficiently at lower dosage. So STD can be widely applied to descale in oilfield.

Vanadium, bismuth, and copper loaded ZnO crystals were synthesized and characterized by FTIR, XRD, DRUV, SEM-EDS, and BET techniques. XRD and adsorption–desorption analysis shows that the structure of ZnO remains intact after various modifications, while spectral technique shows the successful immobilizing of the metal on the support. The effect of loaded metals (V, Bi, and Cu) of the same concentration on the photocatalytic and structural characteristics of metal loaded ZnO nanoparticles (NPs) were then investigated. The obtained band gap values were in the 3.33–3.37 eV range. The photoefficiency of this nanosized M/ZnO in photodegradation of Malachite Green (MG) was studied.

The LiFePO₄/carbon fiber (LFP/CF) cathodes were prepared by using activated carbon fiber cloth as current collector in place of conventional Al foil. The electrochemical properties of LFP/CF electrodes were analyzed by the cyclic voltammetry and galvanostatic charge/discharge tests. The results indicate that the activated carbon fiber cloth with high specific surface area and high porosity makes the LFP/CF electrode that possesses higher mass loading of 18–21 mg cm^–2 and stronger redox reaction ability compared with Al foil-based electrode. The LFP/CF electrode shows excellent rate performance and cycle stability. At 0.1C, the discharge capacity is up to 190.1 mAh g^–1 that exceeds the theoretical capacity due to the combination effect of battery and capacitor. Furthermore, the LFP/CF electrode shows an initial capacity of 150.4 mAh g^–1 at 1C with a capacity retention of 74.7% after 425 cycles, which is higher than 62.4% for LFP/Al foil electrode, and an initial discharge capacity of 130 mAh g^–1 at 5C with a capacity retention of 61.5% after 370 cycles. But this composite electrode is not suitable for charging/discharging at higher rate as 10C due to too much mass loading.

In the study the organic/inorganic chemical leaching and enrichment technology were used for selective extraction of the dolomite which co-existed in the Zhijin low-grade phosphate ore for beneficiation phosphorous and rare earths (RE) by using citric acid as leaching agent. The effects of acid concentration, reaction time, reaction temperature, liquid/solid ratio, and particle size on P₂O₅ and rare earths grade and the recovery ratio of them were investigated. The results show that under the optimized experimental conditions (acid concentration 9%, reaction time 240 min, reaction temperature 40°C, liquid/solid ratio 50: 1, and ore particle size 0.18–0.125 mm) the P₂O₅ grade can be increased from 15.47 to 34.82%, and P₂O₅ recovery rate comes up to 88.02%. The rare earths are mainly enriched in the leaching residues. Meanwhile, the recovery rate of rare earths is 72.08%. ΣREO grade can be increased from 978.06 × 10^–4 to 1998 × 10^–4%. In addition, the reaction kinetics of the chemical reaction between citric acid and dolomite are also discussed, the results show that the leaching process is controlled by chemical reaction. The activation energy for leaching was found to be 36.6337 KJ mol^–1 and k₀ was 3.67×104 s^–1, and the rate of the leaching based on the chemical reaction-controlled process could be expressed as 1–(1–a)^1/3 = 3.67 × 10⁴e^–36.63/RTt. Compare to the conventional process, the method provided in this study not only has advantages including higher phosphate concentration and rare earth grade, and higher recovery rate, but also using less amount of chemicals. Meanwhile, the citric acid can be recycled, avoiding discharge wastewater.

The efficiency of using a fluoropolymer dispersion in preparation of sheet lime chemisorbent was demonstrated. The surface morphology and the thermal and sorption properties of the СО₂ absorbent were studied. The use of the fluoropolymer dispersion as a component of the sorption material allows elimination of alkali from the formulation, improvement of the sorption, moisture retention, and strength characteristics, and expansion of the application field of the material.