Home – Home – Jornals – Chemistry for Sustainable Development 2014 number 1

Various mechanochemical approaches to improving the sorption properties of metal materials accumulating hydrogen are discussed. Some experimental results illustrating the possibilities of each approach are presented. It is established that the sorption characteristics of known metal accumulators of hydrogen can be improved by affecting their structure, morphology and surface properties with the help of the mechanical activation and mechanical alloying with various kinds of additives. The possibility to search for new hydrogen-absorbing materials through the mechanochemical synthesis of metastable composites of components of various natures including thermodynamically immiscible components was demonstrated. These composites may possess a high reactivity with respect to hydrogen and serve as precursors for the synthesis of new phases. The synthesis of intermetallic compounds and hydride phases directly during the mechanochemical treatment also opens opportunities for the preparation of new materials promising for hydrogen storage.

Synthesis method is based on grinding coarse aluminium powder in the planetary centrifugal mill in the presence of a surface-active organic substance that promotes a decrease in the size of aluminium particles and covers the resulting products with a film that is impermeable for oxygen. The synthesis is carried out in the flow of high-purity nitrogen. At a temperature of 300–400 °C, the organic film is evaporated from the precursor particles, aluminium surface, active toward nitriding, shows up, and the reaction takes place at a temperature of about 750 °C. The yield of the product is about 100 %, its oxygen content is less than 0.6 mass % (the detection limit for the method used). Because of low temperatures, the resulting powder is weakly agglomerated; particle size varies within the range 350–500 nm.

The products of the joint mechanical activation of kaolinite with polymers (Sevilen, poly-N-vinylpyrrolidone and polyamide PA-6) in a high-energy ball mill were studied by means of IR spectroscopy and X-ray phase analysis. It was established that for definite polymer content of the initial mixture the mechanochemical interaction of kaolinite with polymer occurs, and the chemical bond is formed between them.

Mechanocomposites composed of tungsten and zirconiums interacting with the former according to the equilibrium diagram of states were studied. The composition, structure and morphology of the samples obtained at the stages of mechanical activation are considered. The effect of the introduction of organic compounds into W/Zr mechanocomposites is studied.

Mechanical milling is widely used for the purpose of efficient mixing of the components of particle-reinforced composite materials, which are further obtained in a bulk form by consolidation of the milled powder mixtures. Using the Ti₃SiC₂–Cu system as an example of a metal matrix composite with a ductile matrix and a reinforcement phase prone to chemical interaction with the matrix at elevated temperatures, we show that the effect of the preliminary mechanical milling of the components is seen not only in the uniformity of distribution of the reinforcing particles in the matrix but also in the consolidation behavior of the powders. The influence of the presence of composite agglomerates in the milled mixture on the processes induced by heating during consolidation is demonstrated by detonation spraying of the mechanically milled and mixed Ti₃SiC₂–Cu powders in comparative experiments and Spark Plasma Sintering of the Ti₃SiC₂–Cu agglomerates of different morphology. Interparticle interactions that are affected by the presence/absence of composite agglomerates and their morphology are the interfacial chemical reactions, the degree of transformation and melting of the copper matrix in the contact regions.

Glauconite and glauconite sand were used as starting materials. To prepare adsorbents on the ground of glauconite, mixtures of glauconite sand and sodium dihydrophosphate NaH2PO4 at various weight ratios (1 : 1, 2 : 1, 3 : 1, 4 : 1) were subjected to the mechanical activation (MA) in a planetary mill. MA products were studied by methods of X-ray phase and thermal analysis. Degrees of sorption for ions of manganese, cuprum, nickel and zinc were determined from appropriate solutions of sulphates within the concentration range of 60–1000 mg/L.

Thermal decomposition of the samples of cold-weather storage bitumen (heating with water vapour) was studied by means of thermogravimetric analysis. Bitumen was treated to remove water according to the regulations and with higher temperature and treatment time than those stated in the regulations. The effect of mechanically activated mineral additive and the additive imitating pyrobitumen on thermolysis was considered. Calculated activation energies of thermal decomposition of bitumen samples are reported.

Radiation-thermal synthesis of ferrite Ni_0.75Zn_0.25Fe₂O_4. was investigated. Comparative analysis of the reactivity of mechanically activated mixtures obtained from commercial oxides and from metal nanooxides was carried out. It was shown that the formation of mechanocomposite was necessary for the efficient reaction.

Single-phase superfine LiCo_1–yFe_yPO₄ solid solutions were synthesized with the use of a mechanochemically stimulated carbothermal reduction of iron and cobalt oxides throughout the entire range of 0 ≤ y ≤ 1. The mechanical activation was carried out using an AGO-2 planetary mill. According to the scanning electron microscopy, the average primary particle size of the samples synthesized ranges within 200–250 nm. According to the XRD phase analysis, all the samples crystallize in the orthorhombic system, with space group Pnma. The volume of the unit cell increases with increasing the content of iron in samples. According to Mцssbauer (NGR) spectroscopy, all iron ions are in the oxidation state 2+ in an octahedral environment typical for olivine. Electrochemical properties of Li_{1 – y}Fe_yPO₄ were investigated by means of galvanostatic cycling. It has been demonstrated that with the increase of Fe content a marked shift in the potential of the Co²⁺/Co³⁺ pair toward lower voltage values occurs, whereas the potential of the Fe²⁺/Fe³⁺ pair remains almost unchanged.

A solid-phase waste-free and energy-saving synthesis with the use of mechanical activation of single-phase cathode material Na₂FePO₄F (sp. gr. Pbcn) for sodium and lithium accumulator has been implemented. It has been demonstrated that the product is formed already at the stage of mechanical activation (MA) and is crystallized in the course of subsequent annealing up to 600 °С, whereas heating up to 700 °С results in decomposing the product formed to give Na₃PO₄, Fe₃O₄, Na_0.11FeF₃ and Na₃Fe₂(PO₄)₃. Electrochemical properties of Na2FePO4F have been studied in a cell with a lithium anode and lithium electrolyte. According to results of the studies the specific capacity of Na2FePO4F surface-modified with carbon is equal to 115 mA ⋅ h/g at a rate of cycling amounting to C/10. It has been found that the process of chemical and electrochemical replacing Li by Na in the structure of Na2FePO4F is completed by the formation of a compound with the composition NaLiFePO4F (sp. gr. Pbcn).

Lithium γ–monoaluminate was obtained as a result of mechanochemical activation of the mixture of lithium carbonate and aluminium hydroxide in AGO-2 planetary activator, followed by the thermal treatment. The effect of mixture composition and humidity on the phase composition and specific surface of lithium γ–monoaluminate was studied. It was shown that in the variation of the composition and humidity of the mixture the specific surface area of the final product decreases significantly (from 13 to 0.2 m²/g).

The anomalous effect of graphite on the degree of wear of copper milling bodies was studied quantitatively. It was shown that mechanical activation of the system diamond–graphite–silicon with copper milling bodies led to the formation of copper-containing semi-products and stable coatings on the surface of milling bodies.

The temperature anomalies and long-term depressions of ozone in the stratosphere observed after large-scale volcanic eruptions are poorly explained from the point of view of modern ideas about composition of the stratospheric aerosol of the volcanogenic nature. However, such post-volcanic phenomena could occur in case when the aerosol comp its surface. The basic opportunity of forming nanosized carbon aerosol (less than 0.1 μm in size) in the stratosphere in case of powerful Plinian type volcanic eruptions is shown in the paper. Estimates of the amount and lifetime of these particles allow explaining long-term temperature anomalies and the ozone depression in the stratosphere after volcanogenic perturbations.

An effect of various concentrations of high molecular mass components of oil as wastes of petroleum production on the soil state and plant production processes was studied. From the standpoint of toxicity, its permissible concentrations values thereof for the normal vital function of plants were determined. A positive effect of oil on some agrochemical soil properties has been revealed, which opens up prospects for developing a biological method of utilization of oil wastes disposal.

Adsorption and photocatalytic oxidation kinetics for sulphide ions on zinc oxide in aqueous solutions has been studied. It has been found that the rate constants of sodium sulphide adsorption and photocatalytic oxidation on zinc oxide decrease with increasing the substrate concentration, which indicates an auto-inhibition of these processes due to blocking the surface of zinc oxide by sodium sulphide.

Integrated investigation of the thermolysis of black coal from the Tavantolgoy deposit (Mongolia) was carried out. It was discovered that coal decomposes during thermolysis within temperature range 300–500 °С with the evolution of gas, low-melting and low-boiling phases, intensively increases in volume and gets agglomerated. As a result, rather strong porous cake is formed. Its volume is 1.5–2 times larger than the volume of the initial sample. It was shown that coal from the Tavantolgoy deposit (without any binding additives) can be used for briquetting.