Главная – Журналы – Химия в интересах устойчивого развития 2007 номер 2

The mechanochemical reduction of copper sulphide (Cu₂S) and lead sulphide (PbS) with elemental Fe as well as reduction of copper sulphide (Cu₂S) with silicon are studied. Metallic Cu and Pb are obtained due to the reducing power of iron and silicon, respectively. The obtained particles are characterized by XRD, VSM, SEM and TEM methods. While for Cu₂S and PbS the reduction by iron is rather straightforward leading to Cu and Pb metals in 10-23 nm dimensions, the process of Cu₂S reduction by silicon is more intricated. In this case the overall process proceeds via complicated mechanism with several overlapping steps. Phase transformations in copper sulphide phases, the formation of elemetal nanocopper with X-ray determined particle size of 23 nm and formation of ternary sulphide Cu₈SiS₆ with anomalous surface area values are the main products of the mechanochemical reaction.

A combination of First Principle Calculations (FPC) and statistical thermodynamics, i.e., the Cluster-Site Approximation (CSA), is applied to describe the bcc-based Fe-Al phase diagram. The formation energies of ordered compounds are calculated using Full-Potential Linearised Augmented Plane Wave (FP-LAPW) results, and the entropy term is evaluated using the so-called modified Cluster Variation Method (CVM). The CSA model has been used to model the bcc bases in the Fe-Al system. The results obtained from this combination are compared with those obtained from the irregular tetrahedron approximation of the CVM, with the same FP-LAPW total energies.

Mechanochemical (MC) treatment for degrading recalcitrant harmful PAH compounds (namely, anthracene and benzo[a]pyrene) adsorbed on marine sediments was investigated in laboratory. Optimal operating conditions (i.e., mill rotation speed, milling time, milling-to-milled mass ratio), together with explanation of their physical effects on sediment particle size and specific surface area were assessed, leading to fast (30-60 min) and very effective (>98 %) degradation of both contaminants under the experimental conditions investigated. Attempts carried out through HPLC analysis and DTA checks before and after MC treatment permitted to envisage likely pathways for chemical reactions occurring during the process, yielding amorphous carbon as final product. Further research is planned to exclude the formation of noxious gaseous by-products.

Results of a laboratory investigation aimed at determining technical efficiency as well as kinetics of chemical degradation of PCBs contaminating marine sediments by mechanochemical treatment with NaBH₄ are presented. Optimization of operating conditions allowed PCBs degradation to be achieved in very effective (>98 %) and fast (<30 min) manner. A kinetic approach to PCBs degradation accounting for variation of reaction rates for different PCB congeners was developed and a mathematical model useful for scaling-up MC treatment was convincingly achieved.

In the field of mechanochemistry, the exact nature of the atomistic processes underlying physical and chemical transformations under mechanical processing conditions is a long-standing problem. Far from being satisfactorily solved, the lively debate associated has constantly stimulated the development of conceptual frameworks alternative to the defect-enhanced thermal diffusion scenarios initially proposed. Different approaches laying emphasis on the capability of mechanical forces to induce atomic scale mixing phenomena independent of thermal contribution were thus investigated. Along this line of inquiry, molecular dynamics simulations were here employed to gain deeper insight into the atomic-scale processes induced at the phase boundary between crystalline Ni and Zr metal lattices by the application of a shear stress. The numerical findings show that the application of shear stresses determines the deformation of the crystal and the formation of a sliding interface. Atoms with defective coordination appear at the interfacial region and gradually arrange into complex aggregates, the dynamics of which promotes the migration of atomic species and their gradual mixing near the interface. Chemical disordering processes take place at the interface, resulting in the formation of an amorphous domain.

Amorphous solid electrolytes were synthesized in the systems Li₃N-P₂S₅ and Li₃N-P via mechanochemical route. Amorphous materials were obtained at the compositions with x = 50 and 60 in the system
xLi₃N×(100-x)P₂S₅ (mol. %), while crystalline Li₂S was obviously formed at the compositions with x = 70 and 80. The conductivity increased with increasing Li₃N content, and then decreased in the composition range x > 60. The highest conductivity of 2.2×10^-5 S/cm at room temperature was achieved at the composition with x=60. The formation of insulative Li₂S in the compositions with higher Li₃N content is responsible for the decrease of conductivity. Li₃N was reacted with P instead of P₂S₅ by milling in order to prevent the formation of Li₂S. The obtained materials were basically amorphous, but partially included crystalline materials such as Li₃P and Li₇PN₄. The 80Li₃N×20P (mol. %) material exhibited the highest conductivity of 1.0×10^-5 S/cm at room temperature in the system Li₃N-P.

The contribution describes chemical, physical and mineralogical properties of so-called Albanian (ore origin) leaching residuum from dumping ground of former Sered' Nickel Works (West Slovakia). The main mineral component of this residuum represents synthetic magnetite, which is known by its ability to sorb some substances. The changes in grain size and specific surface were studied as a function of grinding time and mill. The activation in ball mill during 25 min resulted in a two-fold increase in specific surface. Contrary to this fact, grinding in attritor led to a three-fold increase in specific surface already after 15min, i.e. from 1.31 to 3.86 m²/cm³.
For adsorption tests and following magnetic filtration the leaching residuum ground in the solution of K₄Fe(CN)₆ was applied. Obtained results point to the fact, that magnetic sorbent prepared in such a way and magnetic filtration enable substantial reduction of ion concentration of heavy metals such as copper, manganese and zinc.

High-energy ball-milling in hexane medium was employed to prepare amorphous Al-La-Fe-Ni alloys of three different nominal compositions (Al₈₂La₁₀Ni₄Fe₄, Al₈₅La₉Ni₃Fe₃ and Al₈₈La₆Ni₃Fe₃). Using a planetary ball mill (AGO-2) at a rotational speed of 300 rpm, nearly complete amorphization could be achieved for the Al₈₂La₁₀Ni₄Fe₄ alloy after milling for 350 h. In contrast, the Al₈₅La₉Ni₃Fe₃ and Al₈₈La₆Ni₃Fe₃ samples remained crystalline to a certain extent even after prolonged milling and contained fcc Al crystallites. The glass forming ability was found to increase with decreasing Al and increasing La content, which can be ascribed to the enhanced atomic size mismatch of the constituents on La addition. Amorphous Al₈₂La₁₀Ni₄Fe₄ powder undergoes two-stage crystallization with onset temperatures at 640 and 700 K and glass transition at 566 K. Differences to DSC traces of previously studied melt-spun samples are believed to be mainly due to carbon impurity incorporation and compositional changes during milling. Taking into account the DSC data, consolidation of amorphous Al₈₂La₁₀Ni₄Fe₄ powder was attempted by means of spark-plasma sintering at a temperature of 613 K and applied pressures of 400 and 600 MPa. Compacts produced under these conditions were found to have relative densities of 80 and 96 %, respectively.

Effect of LiCoO₂ support prepared by traditional ceramic and mechanochemical route on the activity of Rh and Pt catalysts in the reaction of NaBH₄ hydrolysis was studied and compared with traditional supports, such as γ-Al₂O₃, TiO₂ (anatase) and carbon (sibunit). Catalysts supported on LiCoO₂ prepared using mechanical activation were found to have the highest catalytic activity. However, the endurance tests of 1 % Rh-LiCoO₂ и 1 % Pt-LiCoO₂ catalysts showed their gradual degradation. To understand the reason of this phenomenon, the interaction of LiCoO₂ with NaBH₄ solution was studied by XRD, FTIR, DRS and TEM.

Mechanochemistry-assisted treatment (MT) was applied for the first time to extract isofraxidin from Acanthopanax senticosus using water as solvent. Six extraction variables, i.e. solvent, Na₂CO₃ content, sample granularity, extraction time, liquid/solid ratio (ml/g), extraction temperature were investigated with respect to the yield of isofraxidin. The most favourable conditions were obtained by using superfine powered plant material (D₉₅ of 47 mm) with Na₂CO₃ content of 0.5 mass %, extracted with water (liquid/solid ratio of 20:1, ml/g) for 3 min at 25 ^oC. The results obtained using the optimized conditions were compared to those with heat reflux extraction. MT extraction was found to increase the yield of isofraxidin considerably while excluding organic solvents and reducing both extraction time and temperature.

Microstructure development of TiB₂-Cu nanocomposite powders during cold and detonation spraying was investigated. The powders were produced by self-propagating high-temperature synthesis (SHS) followed by mechanical milling. A computer model was developed to calculate the temperatures during detonation spraying. The change in the nanostructure of the powders during spraying was studied: due to low temperatures in cold spraying the size of TiB₂ particles in the coatings was well retained, in detonation sprayed coatings the growth of the particles was observed, the mode of spraying affecting the microstructure and the size of the particles.

The effect of BN addition on hydrogen uptake by Ti after and during mechanochemical activation under flow conditions was studied using kinetic, structural, microscopic and spectroscopic techniques. An addition of hexagonal BN significantly stimulated Ti-H₂ interaction during and after the milling process. The hydrogen uptake temperature (T_max) decreased from 960 to 590 K after mechanical treatment of Ti with h-BN in helium flow due to formation of porous BN matrix containing randomly distributed Ti nanofragments. No titanium surface or bulk modification by N (B) atoms was found. Contrary to this, new types of occupation sites available for hydrogen in Ti lattice were formed under the milling in H₂/He flow. These centres responsible for a drastic reduction of H₂ desorption temperature from 1000 to 670-610 K were attributed to the presence of interstitial N atoms. Similar effect on hydrogen distribution between the site types was observed for TiH₂/h-BN as-milled system.

A methodological approach is presented to study gas-solid interactions under mechanochemical activation. Based on a detailed analysis of bulk microstructure, surface features control of milling energy parameters, the H₂ sorption kinetics in Mg₂Ni/Ni nanostructured powders was studied. Hydriding rate and specific parameters such as turnover frequency, mechanochemical gain and instantaneous yield were used to analyze the process on an absolute scale, to elucidate the reaction mechanism and highlight mechanochemical effects.

Glassy solid electrolytes with higher Li₂S content were mechanochemically prepared in the Li₂S-P₂S₅ based multicomponent system, and showed high conductivity by the addition of glass formers SiS₂ and Al₂S₃. The 78Li₂S ×19.8P₂S₅×1.1SiS₂×1.1Al₂S₃ (mol. %) glass exhibited the conductivity of 1.2×10^-4 S/cm at room temperature, which was twice as high as the conductivity of the 78Li₂S×19.8P₂S₅×2.2SiS₂ glass without Al₂S₃. The glass ceramics obtained by crystallization of the glasses showed the same XRD patterns as superionic crystals called thio-LISICON II phase of Li_4-xGe_1-xP_xS₄, which is one of the best Li⁺ ion conducting crystals with very high conductivity over 10^-3 S/cm at ambient temperature. The conductivity of the glass ceramic prepared by heating the glass at 230 ^oC was 1.2×10^-3 S/cm, which was one order of magnitude higher than that of the corresponding glass. The precipitated thio-LISICON II analogs are responsible for the high conductivity of the glass ceramics.

In this paper, the synthesis of the C₂S cement by using reactive mixture containing fly ash (class F) from fluidized coal combustion and Ca(OH)₂ (CaO/SiO₂ ratio of 2) by mechanochemical treatment and subsequent heating is studied. Changes in structure and phase composition of milled and calcinated products of reactive mixture are compared with those of starting mixture. Two hours milling leads to mechanochemical decomposition of portlandite and to the structural and compositional metastability of mixture. The formation of the new compounds as C₂S precursors (CSH and a-C₂SH gels with low degree of ordering and a- and b-C₂S nanocrystalline phases) was confirmed after 2 h milling by X-ray diffraction and infrared spectroscopy. Creation of a- and b-C₂S and gehlenite in milled reactive mixture takes place at lower temperature (600^oC) compared to non-milled starting mixture (1200^oC). Mechanochemical synthesis in combination with thermal treatment offers opportunities for the increased utilization of coal fly ash as a basic raw material for belite production.

Conventional mechanical alloying (MA) is used to process mixtures of powders and generates a product that is also in powder form. MA can also be adapted to the preparation of coatings. For example, if a plate is attached to the wall of the milling container, the impacts by the milling balls activate the surface of the plate, deliver particles from the powder charge and pound them onto or into the surface. The structure and properties of the coating depend on the milling conditions and the properties of the components. In this paper, some aspects essential to the preparation of coatings are discussed. In particular, the importance of the relative hardness of the components is demonstrated by comparing the deposition of aluminium on steel and nickel on aluminium. Mechanical deposition is a promising method that may be utilized to produce a variety of coatings, but its successful application requires detailed understanding and control of the process.

M₃H(SO₄)₂ (M = Na, K, Rb) crystals, which are known to undergo superprotonic phase transition in the case of M = K and Rb, were prepared via mechanochemical process from equimolar M₂SO₄ and MHSO₄. The phase transitions of M₃H(SO₄)₂ prepared by mechanical milling using a high energy ball mill apparatus were confirmed from DTA-TG and conductivity measurements, although the phase transition temperatures were slightly lower than that of M₃H(SO₄)₂ prepared via solution process. The Rb₃H(SO₄)₂ prepared by mechanical milling showed reproducible ionic conductivity of 1×10^-3 S/cm at 230 ^oC under dry N₂ atmosphere.

Bismuth vanadate (BiVO₄) can be synthesized by mechanochemical reaction between bismuth oxide (Bi₂O₃) and vanadium oxide (V₂O₅) by using a planetary ball mill at ambient temperature. The following solid state reaction takes place mechanochemically during the milling: Bi₂O₃ + V₂O₅ ® 2BiVO₄. The particles of the sample look like agglomerates of fine grains with sizes less than 200 nm, and the agglomerates seem to be consisting of primary particles with several microns. The mechanochemical reaction ratio between Bi₂O₃ and V₂O₅ is saturated around 90 %. Heating treatment above 300^oC leads to the formation of homogeneous BiVO₄ with an increase in reaction ratio up to about 99.4 %. The mechanochemical method enables us to synthesize other bismuth complex oxides (BiAO₄; A = P, Nb and Sb).

We developed a method for narrowing the band gap in an oxide powder such as ZnO by doping other components such as S (sulphur) and N (nitrogen). The method consists of grinding a mixture of ZnO powder and non-metal element in air, followed by heating the milled sample at 400 ^oC. The former enables us to cause mechanochemical reaction between the components, and the latter allows us to enhance the bonding strength, as well as to remove the unreacted starting samples away from the surface of the oxide particles. The temperature has to be chosen in the heating operation so as to avoid any decomposition of the doped sample. The detailed information on doping S and N into ZnO powder, as well as its photo-catalytic reactivity, is shown in this report.

The objective of the present work was to show the beneficial effects of mechanochemical treatment of CuO-Al system for fabrication of composites consisting of Cu(Al) solid solution and Al₂O₃ ceramic with ultrafine grain microstructures. In particular, our research focused on explanation of the mechanism and kinetics of mechanochemically induced reactions in metal oxide-active metal system.

In the present investigation, the powder mixture of Al (70 at. %), Ni (15 at. %) and Cu (15 at. %) was mechanically milled in an attritor ball mill for 10, 20, 40, 60, 80 and 100 h in hexane medium at 400 rpm. The isothermal annealing of 100 h mechanically milled powder was done at 700 ^oC for 20, 40 and 60 h. The powders were characterized using X-ray diffraction, differential thermal analysis and transmission electron microscopy techniques. It was observed that mechanical alloying led to the formation of nano vacancy ordered (t₃) phase after 80 h of milling. In the case of 100 h mechanical milling (MM) and subsequent annealing at 700 ^oC for 20, 40 and 60 h, powder exhibited the formation of ordered and perfect t₃ phase with larger grain sizes. The phase formation and transformations in the above systems were discussed.