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The powder mixtures of calcium oxide (CaO) and silica gel (SiO2) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO3, Ca3Si2O7, Ca2SiO4 compounds and CaO/Ca2SiO4 two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV-vis diffuse reflectance spectroscopy (DRS), N-2 adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO center dot SiO2 and 3CaO center dot SiO2 calcined at 700 degrees C, and 3CaO center dot SiO2 calcined at 900 degrees C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca2SiO4 complex mixture. The effect of different amount of catalyst used for transesterification (0.2-2 wt%) was analyzed using the most active catalyst i.e. 3CaO center dot SiO2 calcined at 700 degrees C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO3, Ca3Si2O7 and Ca2SiO4, phases did not possess catalytic activity.

The effect of thermal treatment atmosphere (argon, air or oxygen) on the electret behavior of bismuth titanate (Bi4Ti3O12) ceramics was investigated. Polycrystalline ferroelectric ceramics were prepared by reactive liquid phase sintering. Sintered samples were polarized applying an electric field, Ep = 1 MV m-1 at 100 °C for 60 min. Effective surface density, σeff of free charges was determined by compensation voltage measurements. Thermally treated samples in oxygen atmosphere exhibit a significant decrease of σeff while those treated in argon exhibit an increase of σeff accompanied by the improvement in stability of electret charge. In all cases homocharge with a time independent sign was obtained. © 2009 Elsevier Ltd and Techna Group S.r.l.

Yttrium orthoferrite (YFeO3) powder was prepared by a mechanochemical synthesis from a mixture of Y2O3 and alpha-Fe2O3 powders in a planetary ball mill for 2.5 h. The obtained YFeO3 powder sample was characterized by X-ray diffraction (XRD), Raman and infrared spectroscopy. The average crystallite size calculated by the Scherrer equation was 12 nm. The Mossbauer spectroscopy at room temperature confirms the superparamagnetic character of YFeO3 orthoferrite sample.

The Auger and XPS technique has been used for investigation in the surface of bismuth titanate (Bi4Ti3O12) (BIT) ceramics obtained by reactive sintering from Bi2O3 and TiO2 oxides. All peaks characteristic for bismuth, titanium and oxygen are clearly visible in the spectrum. Oxygen vacancies are preferentially sited in the vicinity of bismuth ions observed by our X-ray photoemission data. The variation in the valence state of titanium ions is also possible. The XPS and AES measurements confirm that the surface elemental composition of bismuth titanate ceramics does not deviate from nominal bulk composition. © 2008 Elsevier B.V. All rights reserved.

A powder mixture of alpha-Bi2O3 and ZrO2, both monoclinic, in the molar ratio 2:3, was mechanochemically treated in a planetary ball mill in an air atmosphere for up to 20 h, using steel vial and hardened-steel balls as the milling medium. Mechanochemical reaction leads to the gradual formation of an amorphous phase. After 5 h of milling the starting alpha-Bi2O3 and ZrO2 were transformed fully into a non-crystalline phase. After milling for various times the powders were compacted by pressing and isothermal sintering. The pressed and sintered densities depended on the milling time. Depending on the duration of the mechanochemical treatment and sintering temperature, the phases: gamma-Bi-12(ZrxFe1-x)O-20; Bi(ZrxFe1-x)O-3 and Bi-2(ZrxFe1-x)(4)O-9 were obtained by reactive sintering, whereby the Fe originates from vial and ball debris. The dielectric permittivity of the sintered samples significantly depends on the milling time. Samples milled for 10 and 15 h and subsequently sintered at 800degreesC for 24 h exhibit a hysteresis dependence of the dielectric shift (in altering electric fields higher than 10 kV/cm at room temperature), confirming that the synthesized materials possess ferroelectric properties. (C) 2004 Kluwer Academic Publishers.

Calcium-containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 were synthesized by calcination of mechanochemically treated stoichiometric mixtures of CaCO3 and either TiO2, MnO2, ZrO2 or Fe2O3 powders. X-ray diffraction analysis revealed a pure single perovskite phase for all four samples after calcination. This study proved that the pure perovskite phase exhibited low or no catalytic activity at 60 °C for the methanolysis of sunflower oil. However, at 165 °C FAME yield of more than 90% was reached after 2 h using CaTiO3, CaMnO3 and CaZrO3 as catalyst. Contrary to inactive pure perovskites at 60 °C, the CaTiO3 and Ca2Fe2O5 samples containing a very small amount of “free” CaO also showed methanolysis activity at 60 °C. This fact can be used to explain some contradictory statements reported in literature related to the perovskites as catalyst for biodiesel synthesis at mild temperatures.

Perovskite oxides with the composition LaFe1-xCrxO3 (x = 0.5 and 0.75) have been studied. The samples have been prepared using the mechanochemical treatment. A mixture of crystalline La(OH)3, Fe2O3 and Cr2O3 powders in stoichiometric ratio was mechanochemically treated in a planetary ball mill up to 40 h of milling. The mechanochemical formation of the LaFe1-xCrxO3 perovskite phase was followed by X-ray diffraction and magnetization measurements. The Rietveld refinement of the XRD data shows that the compounds crystallize in an orthorhombic perovskite structure with a random distribution of the Fe and Cr cations at the B sublattice. All structural and microstructural parameters were analyzed. In addition, magnetic measurements for LaFe0.5Cr0.5O3 show clear antiferromagnetic ordering bellow 250 K, which supports above conclusion of random distribution of Fe and Cr cations.

Correlation between high-temperature electrical response and microstructural properties of dense hydroxyapatite with average grain size from micrometer to nanometer level in heating/cooling cycle was investigated. Grain interior and grain boundary contributions to overall conductivity were determined. Nanostructured hydroxyapatite exhibited enhanced grain interior conductivity, with significantly higher activation energy (∼2.4 eV) than that of coarsed microstructures (∼1.7 eV). This difference in activation energies is explained by the possible influence of dehydroxylation during materials fabrication procedure, which affected the amount of OH- ions as the main charge carriers. Grain boundary conductivity was similar for all microstructures, with activation energy above ∼2 eV, implying the OH- ions migration across grain boundaries. Electrical response in cooling cycle confirmed the trends found during heating. © 2014 Elsevier B.V. All rights reserved.

The goal of this study was to prepare a CaO·ZnO catalyst containing a small amount of K2CO3 and analyze its activity for biodiesel synthesis. The catalyst was prepared using the following procedure: CaO and ZnO (mole ratio of 1:2), water and K2CO3 (in various amounts) were mechanochemically treated and after milling heated at 700°C in air atmosphere for obtaining mixed CaO·ZnO/xK2CO3 oxides (x = 0, 1, 2 and 4 mol of K2CO3 per 10 mol of CaO). All the samples were characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), scanning electron microscopy/ energy-dispersive spectroscopy (SEM/EDS), particle size laser diffraction (PSLD) distribution, solubility measurement of Ca, Zn and K ions in methanol as well as by determination of their alkalinity (Hammett indicator method). Prepared CaO·ZnO/xK2CO3 composite powders were tested as catalysts for methanolysis of sunflower oil at 70 °C using mole ratio of sunflower oil to methanol of 1:10 and with 2 mass% of catalyst based on oil weight. The presence of K2CO3 in prepared samples was found to increase the activity of catalyst, and that such effect is caused by homogeneous-heterogeneous catalysis of biodiesel synthesis., Cilj ovih istraživanja bio je da se pripremi CaO·ZnO katalizator koji sadrži malu količinu K2CO3 i analizira njegova aktivnost u sintezi biodizela. Katalizator je pripremljen prema sledećoj proceduri: CaO i ZnO (molski odnos 1:2), voda i K2CO3 (u različitoj količini) su tretirani mehanohemijski i nakon mlevenja zagrevani na 700 °C u atmosferi vazduha da bi se dobila smeša oksida CaO·ZnO/xK2CO3 (x = 0, 1, 2 i 4 mol K2CO3 na 10 mol CaO). Karakterizacija pripremljenih katalizatora izvršena je metodama rendgenske difrakcije (XRD), indukovane kuplovane plazme (ICP), spektroskopije fotoelektrona dobijenih X-zracima (XPS), termogravimetrijske analize (TGA), infracrvene spektroskopije (FTIR), skenirajuće elektronske mikroskopije i energetske disperzione spektroskopije (SEM/EDS), raspodele veličine čestica (PSLD), merenjem rastvorljivosti katalizatora odnosno Ca, Zn i K jona u metanolu, kao i određivanjem njihove baznosti (metodom Hametovih indikatora). Pripremljeni CaO·ZnO/xK2CO3 kompozitni prahovi testirani su kao katalizatori u reakciji metanolize suncokretovog ulja na 70 °C, pri molarnom odnosu suncokretovog ulja i metanola od 1:10 i sa 2 mas.% katalizatora u odnosu na masu ulja. Pokazano je da prisustvo K2CO3 u pripremljenim uzorcima povećava aktivnost katalizatora i da je takav efekat posledica homogeno-heterogene katalize u sintezi biodizela.

CCTO powders were prepared by solid state reaction and mechanochemically, respectively. Synthesized powders were characterized by XRD, FE-SEM and PSA techniques. The sinterability of CCTO powders was investigated by heating microscopy. Powders were uniaxially pressed into pellets and sintered up to 1100 °C, with heating rates of 2, 5, 10 and 20 °/min. The recorded shrinkage curves were used for choosing conventional and two step sintering (TSS) conditions. By TSS the samples were heated up to 1070 °C and after retention for 10 min cooled down to 1020 °C and kept for 20 h. The microstructure of CCTO ceramics sintered by conventional and TSS techniques was examined by FE-SEM method; the electrical properties were investigated in medium frequency (MF) range (42 Hz-5 MHz) and in the microwave (MW) range of frequencies. Electrical properties of the sintered CCTO ceramics were correlated to the samples microstructure. Finally, we have shown that appropriate choice of sintering conditions is important for preparation of high-quality CCTO ceramics with high dielectric permittivity in the kilohertz range as well as at the resonant frequency.

NiFe2O4 and ZnFe2O4 ferrites have been prepared by soft mechanochemical synthesis. The formation of spinel phase and crystal structure of sintered powders were analyzed by X-ray diffraction, Raman spectroscopy, and transmission microscopy. In order to confirm phase formation and cation arrangement, Mossbauer measurements were done. Investigation of the magnetization as a function of magnetic field confirms an expected change of the degree of inversion in the spinel structure with the sintering. The electrical DC/resistivity/conductivity was measured in the temperature range of 298-423 K. Impedance spectroscopy was performed in the wide frequency range (100 Hz-10 MHz) at different temperatures. (C) 2 013 AIP Publishing LLC

We present a study of the structural and magnetic properties of (Mn,Fe)(3-delta)O-4 nanoparticles synthesized by soft mechanochemistry using Mn(OH)(2) x 2 H2O and Fe(OH)(3) powders as starting compounds. The resulting nanoparticles with a composition of the (Mn,Fe)(3-delta)O-4 type are found to have a core/shell structure with different Mn/Fe ratios in the core and at the surface. XPS analysis points to valences of +2, +3, and +4 for Mn and +3 for Fe at the particle surface. Combined results of XRPD, Mossbauer spectroscopy, and EDX analysis suggest that there is a deviation from stoichiometry in the nanoparticle core compared to the shell, accompanied by creation of cation polyvalence and vacancies. The value of saturation magnetization, M-S, of 73.5 emu/g at room temperature, is among the highest reported so far among nanocrystalline ferrite systems of similar composition. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3700228]

Nano-sized titanium monoxide (TiO) powder was prepared by mechanochemical synthesis. A mixture of commercial Ti and TiO2 (rutile) powders with the molar ratio of 1:1 was milled in a planetary ball mill for 5, 10, 20, 30 and 60 min under argon atmosphere. The final single-phase titanium monoxide sample was characterized by X-ray diffraction (XRD), magnetic measurements using a superconducting quantum interference device magnetometer (SQUID) and thermogravimetric analysis (TGA). The temperature dependency of the magnetic susceptibility is characterized by significant contribution of Pauli paramagnetism due to conduction electrons.

Nanosized perovskite YTiO3 with mean crystallite size of 18 nm was synthesized for the first time by mechanochemical treatment. The mechanochemical solid state reaction between commercial Y2O3 powder and mechanochemically synthesized TiO powder in molar ratio 0.5:1 was performed over 3 h in a high-energy planetary ball mill in argon atmosphere. Heating in vacuum at 1150 degrees C for 12 h transforms nanosized YTiO3 to a well-crystallized single-phase perovskite YTiO3. Both samples were characterized by X-ray diffraction (XRD) and thermogravimetric (TGA/DTA) analyses, as well as superconducting quantum interference device magnetometer (SQUID) measurements.

Manganese ferrite, MnFe2O4 have been prepared by a soft mechanochemical route from mixture of (a) Mn(OH)(2) and alpha-Fe2O3 and (b) Mn(OH)(2) and Fe(OH)(3) powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the MnFe2O4 spinel phase was followed by X-ray diffraction, Raman spectroscopy, scanning and transmission microscopy and magnetization measurements. The spinel phase formation was first observed after 12 h of milling and its formation was completed after 25 h in both cases. The synthesized MnFe2O4 ferrite has a nanocrystalline structure with a crystallite size of about 40 and 50 nm respectively for cases (a) and (b). There are five Raman active modes. Measurements after 25 h of milling show magnetization values of 70.4 emu/g and 71.1 emu/g respectively for cases (a) and (b). In order to understand better the whole process of phase formation, Mossbauer measurements were done. (C) 2011 Elsevier B.V. All rights reserved.