Mechanochemical interaction of Ca silicate and aluminosilicate minerals with carbon dioxide

Processes induced by mechanical activation (MA) in a planetary ball mill of natural diopside CaMgSi₂O₆ and plagioclase (CaAl₂Si₂O₈)_0.745·(2NaAlSi₃O₈)_0.209·(2KAlSi₃O₈)_0.046 in CO₂ atmosphere have been studied. Plagioclase like diopside consumes CO₂ during MA in the form of distorted carbonate groups resulting in appearance of the double IR absorption band in 1400-1600 cm^?1 region corresponding to the stretching vibrations of CO^2? ₃ group. The degree of spitting of the double carbonate band for plagioclase is markedly higher than that for diopside indicating increased distortion of CO^2? ₃ group in the mechanically activated plagioclase. According to the XRD data after 25 min of MA the diopside and plagioclase samples are almost totally amorphous. The carbonization degree of the plagioclase is lower than that of diopside after MA at the same conditions. The differences in the mechanically induced CO₂ sorption ability by silicates can be explained on the basis of simple thermodynamic considerations involving standard Gibbs free energies of reactions of the crystalline minerals with carbon dioxide producing crystalline carbonates, silica and alumina. The results on thermal relaxation of the activated samples have been reported.     

Mechanochemical synthesis of nanoparticles

The results of recent investigation of the mechanochemical synthesis of inorganic nanoparticles are reviewed. It was demonstrated that, by selecting suitable chemical reaction paths, stoichiometry of starting materials and milling conditions, mechanochemical processing can be used to synthesise a wide range of nanocrystalline particles dispersed within a soluble salt matrix. Selective removal of the matrix phase by washing the resulting powder with appropriate solvents can yield nanoparticles of the desired phase. This technique has been shown to have advantages over other methods of producing nanoparticles in terms of low cost, small particle sizes, low agglomeration, narrow size distributions and uniformity of crystal structure and morphology.     

Mechanochemical synthesis of Co-C materials

Using mechanochemical processing, we prepared nonequilibrium Co-C solid solutions supersaturated with carbon to above 7 at %. X-ray diffraction characterization showed that the formation of fcc Co_{1 ? x} C _x solid solutions was accompanied by an increase in the probability of deformation stacking faults. In Co + C mixtures containing more than 10 at % carbon, the fcc solid solution converted to the metastable cobalt carbide Co₃C with an orthorhombic structure. We assessed the thermal stability of the nonequilibrium Co_{1 ? x} C _x solid solutions and the heat effect of the decomposition of the cobalt carbide Co₃C: ?ΔH = 23 kJ/mol.     

Mechanochemical synthesis of chromium-based alloys

This paper presents a detailed study of the formation of chromium-based alloys, Cr–Ta–W + plasticizing additives (Nb and Zr) and Cr–Ta–Si, during milling of powder mixtures in a Fritsch (P-7) planetary mill under an Ar atmosphere. It is shown that, after milling for 18 h, all the components of the starting mixtures convert into a Cr-based BCC solid solution. The powders of chromium alloys obtained in this study are readily compacted by hot isostatic pressing (HIP) under conditions typical of the processing of powders of high-temperature nickel alloys. Heating of the powders and compacts leads to the decomposition of the supersaturated solid solution and the formation of two forms of the Cr₂M Laves phase with cubic crystal lattices. The formation of a mixed-phase fine microstructure in the chromium alloys after HIP suggests that the materials studied here are potentially attractive as a base of next-generation chromium-based high-temperature alloys.     

Mechanochemical modification and synthesis of drugs

Various aspects of the application of mechanochemistry and mechanical activation in the study of pharmaceutical materials are presented including the use of mechanical activation for modification of the physical and chemical properties of drugs and solid state synthesis of the drugs by mechanochemical methods. It is necessary to take the mechanochemical factors into account during grinding and tabletting the drugs.     

Mechanochemical synthesis of nanocrystalline titanium monoxide

Nanocrystalline cubic titanium monoxide, TiO_x (0.92 < x < 1.19), with mean crystallite size of ≈ 6 nm, was synthesized by mechanochemical treatment of Ti and TiO₂ (rutile) powder mixtures with molar ratios of 1:1, 1.10:1 and 1.25:1. The mechanochemical solid state reaction in a high-energy planetary ball mill was completed for 2 h in either air or argon atmosphere. During heating in vacuum at 900 and 1000 °C for 24 h, nanocrystalline TiO_x transforms to a well-crystallized, cubic or monoclinic TiO_x. The materials prepared were characterized by XRPD, TGA/DSC and SEM/EDS analysis.     

Mechanochemical synthesis of cobalt oxide nanoparticles

Cobalt oxide (Co₃O₄) nanoparticle was synthesized by thermal treatment of the precursor obtained via mechanochemical reaction of Co(NO₃)₂·6H₂O with NH₄HCO₃. Calcination of the precursor at 300 °C resulted in the formation of Co₃O₄ nanoparticles of 13 nm in crystal size. The precursor was examined by simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The Co₃O₄ nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Effect of calcination temperature on Co₃O₄ crystal size was discussed. The activation energy (E) of Co₃O₄ nanoparticle formation during thermal treatment was calculated to be 15.9 kJ/mol.     

Mechanochemical synthesis of ultrafine ZrO2 powder

The synthesis of ultrafine zirconia powders by mechanochemical reaction of ZrCl₄ with CaO has been investigated using x-ray diffraction, TEM and DSC measurements. Mechanical milling resulted in a nanoscale mixture of CaO and amorphous ZrCl₄. with no evidence of any reaction having occurred. Subsequent heat treatment at temperatures above 300 °C resulted in the formation of separated particles of cubic ZrO₂,5–10 nm in diameter, within an CaCl₂ matrix. Measurements of the effect of particle size on the crystal structure of ZrO₂ are also reported.     

Holographic image storage in eu(3+)-doped alkali aluminosilicate glasses

We demonstrate that holographic information can be stored in Eu(3+)-doped alkali aluminosilicate glasses. The holograms were developed by a two-beam mixing configuration with a write-beam wavelength (465.8 nm) corresponding to the (7)F(0) ? (5)D(0) transition of the Eu(3+) ions. The images were reconstructed either with the wavelength used to record them or with wavelengths below this transition (543.5 and 632.8 nm). We stored clear holographic images using a total writing power of 5 mW and an exposure time of 20 s. In addition, clear holograms were recorded with an exposure time of 200 ms when 100 mW of the writing power was used. The exposure time and the writing power required to obtain clear holographic images are dependent on the Eu(3+) concentration.     

Mechanochemical synthesis of NaNbO3

The mechanochemical synthesis of NaNbO₃ is studied. It is shown that NaNbO₃ can be prepared by milling the constituents, i.e. Na₂CO₃ and Nb₂O₅ in the planetary mill. After 40 h of mechanochemical treatment NaNbO₃ nanoparticles in the range of 10-20 nm are obtained. Furthermore, the high-energy milling leads to the mechanochemically-triggered carbonate decomposition, which has been observed for a few cases in the open literature.     

Mechanochemical assisted synthesis of B4C nanoparticles

The present work reports on the preparation of boron carbide nanoparticles by the reduction of boron oxide with magnesium in the presence of carbon using the mechanochemical processing. The phase transformation and microstructure of powders during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during ball milling the B₂O₃–Mg–C reacted with a self-propagating combustion mode producing MgO and B₄C compounds. To separate B₄C from the milled powder mixture, an appropriate leaching process was used. After leaching, the purified powder mixture was characterized using XRD and transmission electron microscope (TEM). XRD studies indicated that the prepared particles were single phase crystalline B₄C. Moreover, TEM studies showed the size of B₄C particles were ranging from 10 to 80 nm.     

Mechanochemical synthesis of amorphous and crystalline magnesium diboride

We have studied the phase composition of materials obtained by mechanochemical processing and subsequent heat treatment of mixtures of magnesium and boron powders in the atomic ratio 1: 2. Differential dissolution, differential scanning calorimetry, and X-ray diffraction data indicate that, during mechanical processing, some of the magnesium reacts with boron to form amorphous magnesium diboride. During annealing of the activated powder mixture, X-ray amorphous magnesium diboride forms at 340°C and crystallizes at 480°C. As shown by high-resolution transmission electron microscopy, the unreacted crystalline magnesium is covered with an amorphous layer consisting of magnesium diboride and boron. The amorphous material obtained by milling contains nuclei of MgB₂ crystallites 3–5 nm in size. During subsequent heating of the activated mixture, magnesium and boron react further to form amorphous magnesium diboride and the amorphous phase crystallizes. Heating of mechanically activated mixtures to just below the crystallization temperature allow MgB₂ nanoparticles to be produced. The formation of nanocrystalline magnesium diboride nuclei along with the amorphous phase during mechanochemical processing facilitates mechanochemical synthesis compared to thermal synthesis.     

Mechanochemical synthesis of sodium tungsten bronze nanocrystalline powders

Nanocrystalline powders of sodium tungsten bronze Na_xWO₃ (x∼0.88) have been prepared by mechanochemical process using starting materials of Na pieces and WO₃ powders in a planetary ball mill. The synthesis reactions proceed with increasing milling time and are almost completed after 44 h. Phase-pure nanoparticles of Na_xWO₃ with average size of 17 nm were directly obtained after a simple washing process to remove the by-product of Na₂WO₄. The resistivity was measured in the temperature range from 77 to 300 K. The sample displays semiconducting behavior and can be characterized by three-dimensional variable-range hopping. The mechanochemical process seems to be an attractive route to fabricate tungsten bronzes because of several advantages such as easy preparation, less cost, operating at low temperature and suitability for a large-scale production.     

Mechanochemical synthesis of granulated LTA zeolite from metakaolin

LTA zeolite can be prepared from dry mixes in a vibratory mill with an impact-shear loading conditions. For the synthesis of LTA zeolite, it is necessary to use the anhydrous ingredients (Al₂Si₂O₇–metakaolin, γ-Al₂O₃). The process of synthesis is controlled by X-ray diffraction, IR-spectroscopy, and atomic-force microscopy. The presence of structural water in the initial ingredients (Al₂Si₂(OH)₄–kaolin or Al(OH)₃) leads to the formation of feldshpatoids (nepheline, sodalite). It was established that the process of mechanical activation requires the synthesis of sodium aluminate of cubic and/or tetragonal crystal systems with a lattice parameters close to those for LTA zeolite. These sodium aluminate acts as a steric template for an “assembly” of the zeolite. The presence of sodium aluminate with some other crystal structure results in the formation of sodalite. There is an optimal time of mechanochemical activation, which is determined by the synthesis of sodium aluminate with cubic or tetragonal crystal structure. A model of the mechanochemical synthesis of LTA zeolite was proposed.     

Mechanochemical synthesis of crystalline compounds in the Bi-V-O system

The phase composition of crystalline mechanochemical synthesis products in the Bi₂O₃-V₂O₅ system is determined by x-ray diffraction. The phases identified are sillenite, clinobisvanite, a fluorite phase, the high-temperature form of the Aurivillius phase -Bi₂VO_5.5-x , and new, metastable tetragonal fluorite-like solid solutions. The same compounds are obtained at other Bi : V ratios using Bi₂O₄ and VO₂ as starting reagents. Structural analysis of the synthesized compounds reveals high vacancy concentrations and substitutional disordering. The room-temperature ESR spectra of the samples show V⁴⁺ signals at g 2 and 4. The phase transitions characteristic of clinobisvanite and -Bi₂VO_{5.5 -x} are not detected by thermal analysis, in line with the structural data. Mechanical activation of high-purity -Bi₂O₃ converts it into the form; in the presence of impurities, the resulting phases have fluorite or slightly distorted fluorite-like structure.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 201–209.Original Russian Text Copyright © 2005 by Zyryanov.