Mechanochemical Transformations Research Articles

Mechanochemical solid-state transformations from a 3D lead(ii) chloride triazole carboxylate coordination polymer to its bromide/thiocyanate analogs via anion-replacements: precursors for the preparation of lead(ii) chloride/bromide/sulfide nanoparticles

Irreversible crystal-to-crystal transformations of 3D lead(II) coordination polymers with the ligand 1H-1,2,4-triazole-3-carboxylic acid (HL), from [Pb(L)(μ2-Cl)(H2O)]n (1) to [Pb(L)(μ2-Br)(H2O)]n (2) and [Pb(L)(μ1,1-NCS)(H2O)]n (3) by solid-state anion-replacement processes under mechanochemical reactions, have been studied. The thermal stabilities of compounds 1–3 were studied by thermogravimetric and differential thermal analyses. These irreversible solid-state structural transformations of compound 1 to compounds 2 and 3, have been verified by PXRD measurements. PbCl2, PbBr2 and PbS nanoparticles were obtained by thermal decomposition of compounds 1, 2 and 3 in oleic acid as surfactant at 200 °C under air atmosphere, respectively. These nanoparticles were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM).

Mechanochemical transformation of an organic ligand on mineral surfaces: The efficiency of birnessite in catechol degradation

The aim of this work is to investigate the efficiency of the phyllomanganate birnessite in degrading catechol after mechanochemical treatments. A synthesized birnessite and the organic molecule were grounded together in a high energy mill and the xenobiotic-mineral surface reactions induced by the grinding treatment have been investigated by means of X-ray powder diffraction, X-ray fluorescence, thermal analysis and spectroscopic techniques as well as high-performance liquid chromatography and voltammetric techniques. If compared to the simple contact between the birnessite and the organic molecule, mechanochemical treatments have revealed to be highly efficient in degrading catechol molecules, in terms both of time and extent. Due to the two phenolic groups of catechol and the small steric hindrance of the molecule, the extent of the mechanochemically induced degradation of catechol onto birnessite surfaces is quite high. The degradation mechanism mainly occurs via a redox reaction. It implies the formation of a surface bidentate inner-sphere complex between the phenolic group of the organic molecules and the Mn(IV) from the birnessite structure. Structural changes occur on the MnO 6 layers of birnessite as due to the mechanically induced surface reactions: reduction of Mn(IV), consequent formation of Mn(III) and new vacancies, and free Mn 2+ ions production.

Mechanochemical transformations in NaNH 2-MgH 2 mixtures

Mechanochemical transformations occurring during ball milling of sodium amide (NaNH 2) with magnesium hydride (MgH 2) taken in 2:3 and 2:1 molar ratios have been investigated using X-ray powder diffraction (XRD) and solid-state nuclear magnetic resonance (SSNMR) techniques. For the 2NaNH 2–3MgH 2 system the mechanochemical reaction proceeds via the formation of MgNH as an intermediate, whereas magnesium nitride (Mg 3N 2), sodium hydride (NaH) and hydrogen (∼5 wt%) form as the final products. The overall solid state reaction for this system is 2NaNH 2 + 3MgH 2 → Mg 3N 2 + 2NaH + 4H 2. However, the mechanochemical transformation of the 2NaNH 2–MgH 2 system proceeds through the reaction: 2NaNH 2 + MgH 2 → Mg(NH 2) 2 + 2NaH, without any hydrogen release. Comparison of the mechanochemical transformations with the previously studied thermochemical transformations reveals that the two approaches lead to the same final products via different reaction pathways.

Mechanochemical Polymorphic Transformation of Photocatalyst Material TiO<sub>2</sub> and its Dependence on the Milling Operation

Some dry and wet grinding experiments have been respectively conducted on titanium dioxide which is a noble photocatalyst material in a mortar, a tumbling mill and a planetary mill. Anatase is apt to transform to rutile via a metastable phase brookite in every kind of mills in the case of dry grinding. And it hardly takes place for phase transformation from rutile to other forms. It is shown that the kind of mill has not decisive effect on the mechanochemical polymorphic transformation of titanium dioxide, which merely influences the rate of phase transformation. On the other hand, the addition of other liquid media, such as water and acetone, is helpless for phase transformation of anatase. Only anatase can transform to metastable phase brookite by wet grinding. When ground titanium dioxide is heated, the amorphous phase is easier to transform to rutile than metastable phase brookite at lower temperature.

Possible mechanism of oil formation in a flow of supercritical fluid (using carbon dioxide as an example)

An experimental study of the supercritical fluid extraction of the organic substance with carbon dioxide from rock and soil showed that a supercritical (SC) fluid can dissolve, transfer, and accumulate petroleum-like hydrocarbons including relict ones. It was hypothesized that during the supercritical extraction, the dissolution of organic substances is accompanied by their mechanochemical transformation in the micropores and microcracks of the solid. The resulting changes in the composition, structure, and distribution of the individual hydrocarbons are similar to those in petroleum-mother rocks. We can therefore assume that fast mechanochemical transformation of the dispersed organic matter of sedimentary rocks takes place in a flow of a deep supercritical fluid. This, in turn, would allow one to revise the time scale of oil accumulation from millions to possibly hundreds of years.

Mechanochemically driven nonequilibrium processes in MNH 2–CaH 2 systems (M = Li or Na)

Mechanochemical transformations of lithium and sodium amides with calcium hydride have been investigated using gas volumetric analysis, X-ray powder diffraction, and residual gas analysis. The overall mechanochemical transformations are equimolar, and they proceed as the following solid state reaction: MNH 2 + CaH 2 → CaNH + MH + H 2, where M = Li or Na. The transformation kinetics of the lithium containing system is markedly faster compared to the system with sodium. The difference in the rates of solid state transformations, and therefore, in hydrogen release kinetics can be explained by difference in mobility of lithium and sodium atoms. Total energies and enthalpies of formation for different reaction products during the dehydrogenation of CaH 2–MNH 2 mixtures were calculated using density functional theory. Compared to thermochemical transformations, which proceed in accordance with thermodynamic equilibrium, reactions induced by mechanical energy drive the MNH 2–CaH 2 systems to nonequilibrium configurations with different final products.

Effect of Ca/P ratio and milling material on the mechanochemical preparation of hydroxyapaptite

The mechanochemical transformation of Ca(OH)(2)-(NH(4))(2)HPO(4) with different Ca/P ratios 1; 1.5; 1.67 and 1.75 was carried out for different periods of time from 10 min to 24 h in a horizontal vibration mill using steel and agate vials and balls. The phase transformations obtained at each milling stage were characterized by X-ray diffraction, infrared spectroscopy and transmission electron microscopy. Complete transformation to hydroxyapatite took place during the first 5 h of milling, for Ca/P ratios 1.5 to 1.7, when milling was carried out with steel vials and balls. The contamination was not significant for the periods of milling studied for both milling media.

Mechanochemical transformations of natural gas hydrates

Chemical transformations of hydrates of natural gas from the Irelyakh gas and oil field of the Republic of Sakha (Yakutia) upon vigorous mechanical treatment were studied. It was found that a general feature of mechanochemical transformations of natural gas hydrates is an increase in the carbon chain length of hydrocarbons forming the hydrates. It was shown that the constitution of the products of mechanical activation of gas hydrates depends on both their synthesis and mechanical treatment conditions.

Mineral induced mechanochemical degradation: The imazaquin case

The potential role of mechanochemical processes in enhancing degradation of imazaquin by soil components is demonstrated. The investigated components include montmorillonite saturated with Na +, Ca 2+, Cu 2+and Al 3+, Agsorb (a commercial clay mix), birnessite and hematite. The mechanical force applied was manual grinding of mixtures of imazaquin and the minerals, using mortar and pestle. The degradation rates of imazaquin in these mixtures were examined as a function of the following parameters: time of grinding, herbicide load (3.9, 8.9, 16.7 and 26.6 mg imazaquin per g mineral), temperature (10, 25, 40 and 70 °C), acidic/basic conditions, and dry or wet grinding. Dry grinding of imazaquin for 5 min with Al-montmorillonite or with hematite resulted in 56% and 71% degradation of the imazaquin, respectively. Wet grinding slightly reduced the degradation rate with hematite and entirely cancelled the enhancing effect of grinding with Al-montmorillonite. Wet grinding in the presence of the transition metals: Ni 2+, Cu 2+, Fe 3+ added as chlorides was carried out. Addition of Cu 2+ to Na-montmorillonite loaded with imazaquin was the most effective treatment in degrading imazaquin (more than 90% of the imazaquin degraded after 5 min of grinding). In this treatment, Cu-montmorillonite formation during the grinding process was confirmed by XRD and accordingly, grinding with Cu-montmorillonite gave similar degradation values. LC–MS analysis revealed that the mechanochemical transformation of imazaquin resulted in the formation of a dimer and several breakdown products. The reported results demonstrate once again that mechanochemical procedures offer a remediation avenue applicable to soils polluted with organic contaminants.

Role of metal additives in mechanochemical phase transformation of zirconia

Reasons for a phase transition in zirconia subjected to intensive mechanical treatment in planetary mill have been considered. If steel balls and vials are used for milling the comminution is accompanied by oxidation of wear metal particles and successive mechanochemical reaction with ZrO2. Aluminum has been shown to behave similarly and, being deliberately added to zirconia powder, to form solid solutions. Foreign metal cations introduced into the lattice stabilize a modification with higher crystal symmetry thus increasing the threshold size above which the monoclinic modification is stable. An increase of surface energy contribution to the Gibbs’ energy of zirconia plays an important role in phase transformation at the initial stages of mechanical treatment, while henceforth thermodynamic stability is more and more determined by the stabilizing effect of the impurity cations. Under the conditions that rule out contamination of ZrO2 with wear material or other metal additives, dynamic equilibrium sets in between the direct transition to the tetragonal phase and the reverse transition to the monoclinic form.

Mechanistic inferences on the synthesis of Co 50Fe 50 solid solution by mechanical alloying

An equiatomic Co–Fe solid solution was synthesized by mechanical processing. A dissolution process of Co in Fe was observed. Its kinetic characterization permitted a reliable estimate of the number of Co atoms dissolved in collision events. This number was then compared with the corresponding quantity observed in Co–Fe diffusion couples under thermal activation conditions. The data support a mechanistic hypothesis for mechanochemical transformations alternative to the ones based on thermal diffusion.

Mechanochemical transformations in Li(Na)AlH 4–Li(Na)NH 2 systems

Mechanochemical transformations of tetrahydroaluminates and amides of lithium and sodium have been investigated using gas volumetric analysis, X-ray powder diffraction, solid-state nuclear magnetic resonance (NMR) and transmission electron microscopy. In a transformation of LiAlH 4 and LiNH 2 taken in an 1:1 molar ratio, the amount of released hydrogen (6.6 wt.% after 30 min ball milling) was higher than in any known one pot mechanochemical process involving a hydrogen-containing solid. A total of 4.3 wt.% of hydrogen is released by the NaAlH 4–NaNH 2 system after 60 min ball milling; and 5.2 wt.% H 2 is released when LiAlH 4 and NaNH 2 or NaAlH 4 and LiNH 2 are ball milled for 90 min and 120 min, respectively. All transformations proceed at room temperature. The mechanism of the overall transformation MAlH 4(s) + MNH 2(s) → 2MH(s) + AlN(s) + 2H 2(g) was identified based on detailed spectroscopic analysis of the intermediate (M 3AlH 6) and final products of the ball milling process.

Study of initial stage of mechanochemical transformation in pyrite

The initial stage of transformation of pyrite to Fe(II)-sulfate as a result of mechanical milling is studied by X-ray powder diffraction (XRD), Moessbauer spectroscopy (MS), Infrared (IR) and X-ray photoelectron spectroscopy (XPS) techniques. A degree of conversion of 0.071 is achieved in the time interval of 0 36 min. The kinetic data satisfy the equation of a shrinking core reaction 1-(1-?)1/3=kt. The reaction is of the first order. The calculated rate constant is k=6.434.10-4 min-1. .

The mechanochemical treatment of europium nitrate with 1,10-phenanthroline

The reactions that occur during the mechanochemical treatment of europium nitrate with 1,10-phenanthroline were studied by X-ray electron, infrared, and luminescent spectroscopy. Two minutes of mechanical activation resulted in the formation of europium nitrate, 1,10-phenanthroline, and water. According to the X-ray electron spectroscopy data, the coordination of 1,10-phenanthroline to europium nitrate was accompanied by a decrease in the Eu 4d5/2 binding energy. Intense mechanochemical transformations caused changes in the composition of the surface of samples. Changes in the shape and size of reaction mixture particles and the morphology of sample surfaces after mechanical treatment in a ball mill compared with the initial mixture were studied.

Mechanochemical transformation of mixtures of Ca(OH) 2 and (NH 4) 2HPO 4 or P 2O 5

A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH) 2–(NH 4) 2HPO 4 and Ca(OH) 2–P 2O 5, milled in a mortar dry grinder for different periods of time was carried out. The phase transformations obtained at each milling stage were studied by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis. The transformations taking place during the first periods of milling are very different for both mixtures. However, prolonged milling, over nearly the same period, causes amorphization of both mixtures. DSC analysis of the milled powders showed the temperature of crystallization of hydroxyapatite and tricalcium phosphate (β-TCP). Calcinations of all the different milled powders at 800 °C for 2 h, results in the formation of hydroxyapatite and β-TCP.

The Kinetics and Energy Balance of Mechanochemical Transformations

AbstractFor Abstract see ChemInform Abstract in Full Text.

Preparation of Nanocrystalline Copper and Copper Silicon Sulphide by Mechanochemical Route

The composition and properties of powders prepared by high-energy milling of copper sulphides with silicon have been studied by methods of X-ray diffractometry and surface area measurement. The combination of several methods was utilized to develop a coherent picture of the process. The overall process of mechano-chemical transformations in copper sulphide-silicon system 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 creation of ternary sulphide Cu8SiS6 with anomalous surface area values are the main products of the mechanochemical reaction.

Highly coupled ATP synthesis by F1-ATPase single molecules

F1-ATPase is the smallest known rotary motor, and it rotates in an anticlockwise direction as it hydrolyses ATP. Single-molecule experiments point towards three catalytic events per turn, in agreement with the molecular structure of the complex. The physiological function of F1 is ATP synthesis. In the ubiquitous F0F1 complex, this energetically uphill reaction is driven by F0, the partner motor of F1, which forces the backward (clockwise) rotation of F1, leading to ATP synthesis. Here, we have devised an experiment combining single-molecule manipulation and microfabrication techniques to measure the yield of this mechanochemical transformation. Single F1 molecules were enclosed in femtolitre-sized hermetic chambers and rotated in a clockwise direction using magnetic tweezers. When the magnetic field was switched off, the F1 molecule underwent anticlockwise rotation at a speed proportional to the amount of synthesized ATP. At 10 Hz, the mechanochemical coupling efficiency was low for the alpha3beta3gamma subcomplex (F1-epsilon)), but reached up to 77% after reconstitution with the epsilon-subunit (F1+epsilon)). We provide here direct evidence that F1 is designed to tightly couple its catalytic reactions with the mechanical rotation. Our results suggest that the epsilon-subunit has an essential function during ATP synthesis.

The Kinetics and Energy Balance of Mechanochemical Transformations

The kinetic theory of strength formulated by Zhurkov is expanded to include an energy consumption analysis of the processes of deformation and fracture of solids and their compounds. The dependence of the kinetics of the structure defect formation and of chemical reactions in the processes of deformation and fracture of solids on the energy expended is found. Experiments and calculations concerning energy yields of the defect formation, deformational mixing, and mechanochemical reactions are discussed.

Effect of ultrasound on the properties of the rapeseed oil?monoethanolamine system

The effect of an ultrasound field on the rheological properties and thermal stability of rapeseed oil (RO) in the presence of monoethanolamine (MEA) and the dispersing properties of the RO-MEA system were investigated. The extremal character of the change in the dispersing effect of RO with an increase in the concentration of MEA was established. Ultrasound vibrations cause mechanochemical transformations that decrease the thermal stability at high temperatures.