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1
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Mechanochemistry and the Other Branches of Chemistry: Similarities and Differences

100%
Takacs L.
Acta Physica Polonica A
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2012
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vol. 121
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issue 3
711-714
EN
It is argued that mechanical action can induce a unique chemical reaction, if enough mechanical energy is concentrated in the bonds involved in the process to bypass the activation energy. This can happen at crack tips, at the core of dislocations, or at the asperities of colliding or sliding surfaces. A mechanical reaction is always complex, as the macroscopic work is distributed among many possible reaction sites. In comparison, an elementary photochemical reaction is induced by a single photon, while thermochemical reactions rely on the accidental concentration of energy by thermal fluctuations. The paper also compares mechanochemical synthesis in a ball mill with reactions under well-defined loading conditions and mechanochemical experiments carried out on the molecular scale. Closer interaction among those branches of mechanochemistry is urged.
2
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Deformation-Induced Structural Transformations in Molecular Crystals

100%
Rybin D., Konygin G., Porsev V., Yelsukov E., Arsentyeva I., Boldyrev V.
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vol. 126
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issue 4
1014-1018
EN
The physical mechanisms of the deformation-induced structural transformations in molecular crystals, including morphological changes, amorphization and molecular polymorphous conversions in nano-dispersed bioinorganic compounds are discussed in this work. Integrated study using direct structural and structure-sensitive spectroscopic methods allowed obtaining the data on polymorphous transformations, taking place during mechanical activation in calcium gluconate monohydrate (CG). One of the possible reasons for lattice polymorphous transformations and amorphization, observed in the course of mechanical activation of low-symmetry molecular crystals, might be the spatial molecular isomerization. In this case, the disappearance of the translational invariance of the lattice is conditioned by the simultaneous coexistence of the reactants and reaction products, which have different stereo-organization of the molecular structure.
3
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The Promising Synthetic Route Hydrothermal Synthesis of Non-Stoichiometric Cerium and Boron Containing Compounds and Characterization

100%
Çelik G., Kurtuluş F.
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vol. 125
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issue 2
325-326
EN
Cerium, the most abundant rare earth element, and boron containing mineral (lithium tetraborate pentahydrate) were used for synthesizing rare earth borates. Alternatively, for preparing rare earth borates, hydrothermal technique can be used. The non-stoichiometric cerium and boron containing compounds were synthesized by hydrothermal method using cerium sulphate and lithium tetraborate pentahydrate in appropriate molar ratio. Characterizations were done by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy/energy dispersive X-ray analysis, and thermogravimetric/differential thermal analysis.
4
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Microwave-Assisted Synthesis of CeVO_4 in the Mild Conditions, Characterization and Investigation of Luminescent Properties

100%
Çelik G., Kurtuluş F.
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vol. 125
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issue 2
357-358
EN
CeVO_4 (ICDD: 12-757) was synthesized by microwave-assisted method by using cerium sulphate and vanadium (V) oxide in an appropriate molar ratio. Characterizations were done by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet spectrophotometry and thermogravimetric/differential thermal analysis. The material is crystallized in tetragonal system with unit cell parameters a = 7.399 Å and c = 6.496 Å and space group I41/amd(141).
5
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Characterization of Structural Properties of LiM_xFe_{5-x}O_8 (M=Al, Cr, Mn), Spinel Solid Solutions

100%
Darul J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 2
367-373
EN
The structural properties of series spinel oxides with the general formula, LiM_{0.5}Fe_{4.5}O_8 (M = Mn, Cr, Al), are investigated. The effect of limited substitution of manganese, chromium and aluminum ions in the lithium ferrite samples on the order-disorder phase transition in the spinel crystal lattice at room temperature is presented. In these materials it is found that the ordered structures have not been isolated as single phases under the present experimental conditions and this fact will certainly influence the magnetic behavior of the compounds. The Rietveld refinements of the synchrotron X-ray diffraction data revealed that transition metal ions hinders the ordering process and Al^{3+} ion was shown to be least effective in removing of order.
6
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Study of the Mechanochemical Reduction of Ilmenite Concentrate by Addition of Aluminum

100%
Achimovičová M., Gock E., Turianicová E., Kostova N., Velinov N., Kaňuchová M., Baláž P.
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vol. 126
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issue 4
867-870
EN
Mechanochemical reduction of ilmenite concentrate (FeTiO_{3}) with elemental aluminum powder was performed by high-energy milling in an industrial eccentric vibratory ball mill ESM 656-0.5 ks (Siebtechnik, Germany). The mechanochemically reduced ilmenite with various times of milling was characterized by X-ray diffraction analysis, which confirmed the presence of the Al_2O_3 and Fe_2Ti phases after 120 min of milling. Thermal analysis evidenced the completion of a mechanochemical reduction during milling. After 360 min of milling, the Fe_2Ti phase decomposed to α-(Fe,Ti) alloy, which was proven by ^{57}Fe Mössbauer spectroscopy. X-ray photoelectron spectroscopy detected the amorphous TiO phase in product after mechanochemical reduction, which is in accordance with thermodynamic prediction. Decreasing of specific surface area after 60 min of milling resulted from growing layers of the solid products of FeTiO_3 mechanochemical reduction.
7
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What Is Unique About Mechanochemical Reactions?

100%
Takacs L.
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vol. 126
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issue 4
1040-1043
EN
Mechanochemical reactions can provide compounds, phases, and microstructures that are essentially different from the products of ordinary reactions. In this paper, the origin of this uniqueness is discussed in light of the recent advances of the field. It is claimed that the local availability of large batches of energy, well above kT, is the key feature of mechanochemical reactions. As a consequence, reactions that cannot occur thermally become possible, similarly to the reactions induced by the energy of photons in photochemistry. However, the situation is more complex, as macroscopic deformation affects many defect sites simultaneously. The direction of the mechanical load relative to the orientation of a molecule or the crystallographic axes of a solid can be important. Many mechanochemical reactions of organic compounds take place at low milling energy that is not sufficient to break primary bonds, but the gentle mechanical grinding can influence the relative position of macromolecules, leading to the formation of unique cocrystals and compounds. In inorganic systems, unusual products form due to forced mixing and the high defect density generated by intense milling.
8
Content available remote

Low-Loss Microwave Dielectrics for Different Frequency Ranges

75%
Belous A., Ovchar O.
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issue 1
221-227
EN
Depending on the operating frequency range of modern communication systems various microwave elements are required for effective operation of radio equipment. In this work potential ways of developing the microwave dielectric materials for different frequency ranges are discussed. It has been shown that temperature stable dielectrics with the permittivity of about 100, which are intended for the utilization in the decimetre wavelength band, can be developed by means of alio- and isovalent substitution in the cation sublattices of barium lanthanide titanates (BLTss) Ba_{6-x}Ln_{8 + 2x/3}Ti_{18}O_{54} (Ln = La-Gd). The temperature behaviour of the permittivity and dielectric loss in the BLTss has been discussed in terms of both harmonic and anharmonic contributions to the phonons of the BLT crystal lattice. It has been shown that a slight deviation from the compositional stoichiometry in both A-site and B-site deficient perovskites Ba(M_{1/3}^{2+}Nb_{2/3})O_{3} (M = Co, Zn, Mg) allows a prominent enhancement of their microwave quality factor (Q). As a consequence, new dielectrics with the extremely high quality factor (Qxf = 90000-150000 GHz), which are intended for the utilization in the centimetre wavelength band, can be developed. Some examples of the possible implementation of the developed materials are also discussed.
9
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Novel Route to Prepare Magnetic Material Co_3V_2O_8 and Structural Characterization

63%
Celik G., Kurtulus F., Guler H.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1
203-204
EN
Co_3V_2O_8 is a member of kagomé staircase oxides, represented by general formula M_3V_2O_8 (M = Ni, Co, Mn). It attracted great attention due to strong magnetic anisotropy, magnetic phase transition, genuine macroscopic quantum effects, strong quantum fluctuations, low-temperature ferroelectricity, field-induced magnetic transitions, complicated phase diagram and displays long-range magnetic order because of geometrical frustration. Different routes to prepare the frustrated magnetic material was reported such as floating zone technique and conventional high temperature method. Co_3V_2O_8 (International Centre for Diffraction Data (ICDD): 16-675) was synthesized with Co_3O_4 (ICDD: 80-1536) as binary phase by microwave assisted preparation using Co(NO_3)_2 ·6H_2O and NH_4VO_3. The synthesized material was characterization by powder X-ray diffraction, the Fourier transform infrared spectroscopy, and thermogravimetric-differential thermal analysis.
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