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In this article the influence of ball miling process on structure of MgO-TiO2 system, as well as the electrical properties of samples after sintering, was investigated. The mixtures of MgO-TiO2 powders were mechanically activated in a planetary ball mill for the time period from 0 to 120 min. The influence of mechanical activation and sintering on the lattice vibrational spectra was studied by Raman spectroscopy at room temperature. Structural investigations have been performed on produced powders. Nitrogen adsorption method was used to determine the BET specific surface area and pore size distribution. Unusual results have been obtained: specific surface area continuosly decreased up to 40 min of activation and increased after that, reaching its minimun value of 5.5 m(2)/g. The Raman spectra of activated powders have shown that anatase modes have been decreasing in intensity and broadening as the time of activation extended. Also, the additional modes attributed to TiO2 II, srilankite and rutile phases started to appear as a consequence of activation. The small differences noticed in the Raman spectra of sintered samples have been explained by structural modification of MgTiO3 phase due to the presence of defects. The effects of activation and sintering process on microstructure were investigated by scanning electron microscopy (SEM). The electrical measurements showed difference in dielectric constant (epsilon(r)), loss tangent (tg delta) and specific resistance (rho) as a function of time of mechanical treatment.

Mixtures of BaCO3, ZnO and TiO2 powders, with molar ratio of 1:2:4, were mechanically activated for 20, 40 and minutes in a planetary ball mill. The resulting powders were compacted into pellets and isothermally sintered at 1250 degrees C for 2h with a heating rate of 10 degrees C/min. X-ray diffraction analysis of obtained powders and sintered samples was performed in order to investigate changes of the phase composition. The microstructure of sintered samples was examined by scanning electron microscopy. The photoacoustic phase and amplitude spectra of sintered samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled determination of photoacoustic properties including thermal diffusivity. Based on the results obtained correlation between thermal diffusivity and experimental conditions, as well the samples microstructure characteristics, was discussed.

Starting mixtures of BaCO3, ZnO, and TiO2 powders are mechanically activated in a planetary ball mill for various periods of time. The powders obtained are sintered isothermally at 1100A degrees C for 120 min. Non-isothermal sintering process is followed by measurements with a sensitive dilatometer, as well. Results of microstructure characterization using SEM analyses along with DTA analyses are provided. These results are correlated with the values of electric resistivity, capacitance, and loss tangent of the samples, and it is found that with increasing milling time, the increase in values of electrical properties is noticed.

The aim of this work was an investigation of structural and electrical properties of sintered barium-zinc-titanate ceramics. Mixtures of BaCO(3), ZnO and TiO(2) were mechanically activated in a planetary ball mill up to 80 minutes and sintered isothermally in air for 120 minutes at 1300 degrees C. The phase composition in the BaCO(3)-ZnO-TiO(2) system after milling and sintering was analyzed using the XRD method. The existence of pure barium-zinc-titanate has been registered. Microstructure analyses were performed using SEM. The results of electric resistivity, capacitance and loss tangent of the sintered samples were correlated with the XRD and SEM results.

Mixtures of BaCO(3)-ZnO-TiO(2) were mechanically activated using high-energy planetary ball mill during 20, 40 and 80 min. As the time of mechanical activation increased, the decrease in particle size was observed. The effect of milling on microstructure was investigated by scanning electron microscopy, as well. Sintering process was performed in air at 1100 and 1200 C for 2 h. Various phases are present within mixtures sintered at 1100 and 1200 degrees C, and almost pure BaZn(2)Ti(4)O(11) phase was obtained after 80 min of milling and sintering at 1200 degrees C for 2 h. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Mixtures of MgO-TiO2 were mechanically activated using high-energy planetary ball mill during 5, 10, 20, 40, 80 and 120 minutes. Sintering process was preformed in air at 1100 degrees-1400 degrees C for 2h. The decrease in powders particle size was noticed as the time of mechanical activation increased and confirmed by particle size analyzer. XRD analyses were performed in order to acquire the information about phase composition. Different ratio mixtures of MgTiO3 and Mg2TiO4 are present within all sintered samples. The effect of tribophysical activation on microstructure was investigated by scanning electron microscopy. The differential thermal gravimetric analysis has been performed in order to investigate thermal behaviour of the mixtures.

Densification rate and phase structure changes during sintering of nanosized ZnTiO3 were studied. Sintering was performed in a dilatometer in two regimes: the first to 900 degrees C (heating rates 5, 10 and 15 degrees C/min) and the second to 1200 degrees C (heating rates 3, 5 and 10 degrees C/min). XRD analysis of samples sintered at both temperatures combined with Rietveld structure refinement enabled determination of all phases present and their structure parameters. Samples sintered to 900 degrees C contained ZnTiO3 and Zn2TiO4 with traces of r-TiO2 (rutile) and Zn2Ti3O8, while samples sintered to 1200 degrees C contained only r-TiO2 and Kn(2)TiO(4). A master sintering curve was defined for sintering to 900 degrees C enabling determination of the sintering process activation energy as 3 13 kJ/mol.

Far infrared reflectivity spectra of sintered Pb0.9Sn0.1Te doped with 0.2 and 2 at.% Pd are measured. The experimental results are analyzed using a fitting procedure based on a modified plasmon-phonon interaction model. The values of calculated parameters are compared with literature data for PbTe and PbSnTe single crystal samples doped with palladium and nickel, with the purpose of determining whether the sintered samples can be used in different devices instead of single crystals.

Zinc-titanate ceramics were obtained by initial mechanical activation in a high-energy planetary mill for 15 min followed by sintering at temperatures 900-1100 degrees C for 2 h. Room temperature far infrared reflectivity spectra for all samples were measured in the range 1001200 cm(-1). The same ionic oscillators were present in the measured spectra, but their intensities increased with the sintering temperature in correlation with the increase in sample density and microstructure changes. Optical parameters were determined for seven oscillators belonging to the spinel structure using the four-parameter model of coupled oscillators. Born effective charges were calculated from the transversal/longitudinal splitting.

In this article the solid state reaction of BaTiO3 formation from a mechanically activated BaCO3-TiO2 system has been investigated. An equimolar mixture of BaCO3 and TiO2 powders was activated in a planetary ball mill in a continual regime for 0, 30 and 90 min, pressed and thermally treated up to 1200 degrees C. The eject of the milling and firing regime on the phase formation was investigated by the X-ray diffraction (XRD) method and differential thermal analysis (DTA). Deconvolution of the experimental DTA curve corresponding to the BaTiO3 synthesis process has been performed. The influence of the activation time on the change of characteristic temperature for each elementary step in the complete solid-state reaction of BaTiO3 formation, was analyzed. These results were correlated with the ones obtained by SEM characterization and by XRD analysis.

The effects of Bi2O3 addition on the phase composition, microstructure and optical properties of ZnO-SnO2 ceramics were investigated. Starting powders of ZnO and SnO2 were mixed in the molar ratio 2:1. After adding Bi2O3 (1.0 mol.%) this mixture was mechanically activated for 10 min in a planetary ball mill, uniaxially pressed and sintered at 1300 degrees C for 2 h. Far-infrared reflection spectra were measured (100-1000 cm(-1)). To investigate the occurred differences in FTIR spectra, the Bi2O3-doped sample was examined more carefully with a Perkin-Elmer FTIR spectrometer (Perkin Elmer, Waltham, MA, USA) connected with a Perkin-Elmer FTIR microscope and itemized points of interest were also studied with SEM-EDS.

Powder mixtures of zinc oxide and tin oxide in the molar ratio, ZnO:SnO2 = 2: 1, were mechanically activated in a planetary ball mill in the time intervals of 0-160 min. The adsorption-desorption isotherms, specific surface area, pore volume and pore size distribution spectra of mechanically activated powder mixtures were established by N-2 adsorption at 77 K. Microstructure analysis was performed using scanning electron microscopy (SEM) and digital pattern recognition (DPR) microstructure quantity analysis. The phase composition of the mixed powders was determined by Xray analysis. Mechanochemical activation of the ZnO-SnO2 system resulted in fine grinding of the starting particles and generation of contacts between them, mass transfer at contacts zones and formation of Zn2SnO4 spinel, which was observed after 40 min of activation.

The aim of this work was analysis of isothermal sintering of zinc titanate ceramics doped with MgO obtained by mechanical activation. Mixtures of ZnO, TiO2 and MgO (0, 1.25 and 2.5%) were mechanically activated 15 minutes in a planetary ball mill. The powders obtained were pressed under different pressures and the results were fitted with a phenomenological compacting equation. Isothermal sintering was performed in air for 120 minutes at four different temperatures. Structural characterization of ZhO-TiO2-MgO system after milling was performed at room temperature using XRPD measurements. DTA measurements showed different activation energies for pure and doped ZnO-TiO2 systems. Thus addition of MgO stabilizes the crystal structure of zinc titanate.

Semi-quantitative methods of X-ray diffraction and FTIR-spectroscopy, accompanied by electron microscopy, X-ray microanalysis and others were used to monitor structural-phase reorganizations occurring in a smectite-gypsum mixture (bentonite) subjected to NaOH treatment with the subsequent addition of quaternary ammonium salt (TMA) in conditions of water deficiency. The interaction of bentonite with NaOH breaks up large bentonite aggregates, saturates smectite with Na cations, and yields Ca(OH)(2). The addition of TMA is accompanied by its penetration into the interlayer space and adsorption on the surface.

Mixtures of ZnO and SnO2 powders, with molar ratio of 2:1, were mechanically activated for 40, 80 and 160 minutes in a planetary ball mill. The resulting powders were compacted into pellets and non-isothermally sintered up to 1200 degrees C with a heating rate of 5 degrees C/min. X-ray diffraction analysis of obtained powders and sintered samples was performed in order to investigate changes of the phase composition. The microstructure of sintered samples was examined by scanning electron microscopy. The photoacoustic phase and amplitude spectra of sintered samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled determination of photoacoustic properties including thermal diffusiviiy. Based on the results obtained a correlation between thermal diffusivity and experimental conditions as well the samples microstructure characteristics was discussed.

Ceramic materials with a perovskite related structures such as non-doped and doped barium titanate ceramics are attracting much interest for their application as capacitor dielectrics, resistors, thermal sensors, etc. Since mechanical activation can be used in order to modify properties of these materials, in this study microstructure evolution and electric properties of mechanically activated BaTiO3 have been analyzed. The sintering process of high purity non-doped mechanically activated BaTiO3 was monitored using a sensitive dilatometer with a heating rate of 10 degrees C/min. Investigation of the microstructure evolution of mechanically activated BaTiO3 was performed using scanning electron microscope (SEM) and digital pattern recognition (DPR) methods. A dielectric study of the paraelectric-ferroelectric phase transition in the barium titanate ceramics was performed by recording the temperature dependence of dielectric permittivity.

Far infrared reflection spectra of NiO polycrystals sintered at 1100 degrees C for various times (30-240 min) were measured at room temperature using a FTIR Spectrometer-Brucker 113V. The measured spectra depended on the sintering time due to differences in the microstructural morphology of the material and were compared with the NiO single crystal reflectivity diagram. Numerical analyses of the experimental spectra were performed using Kramers-Kronig analysis, a four-parameter model of coupled oscillators and the effective medium modeling theory. In the three-component effective medium model based on Bruggeman's theory we assumed the presence of pores, intergranular material and crystalline grains. The intergranular material and crystalline grains were defined as single and coupled ionic oscillators.

Room temperature far infrared reflectivity spectra of single phase spinel zinc-stannate thin films, prepared by rf magnetron sputtering on a glass substrate, and bulk sintered samples were measured. The sintered samples were obtained by mechanical activation of starting ZnO and SnO2 powders for 10 min followed by sintering at 1300 degrees C for 2 h. The reflectivity diagrams obtained for bulk samples were numerically analyzed using the four-parameter model of coupled oscillators. The optical parameters were determined for six observed ionic oscillators belonging to the spinel structure and two additional oscillators originating from the sintering procedure resulting from pores and grain boundaries. The reflectivity diagrams obtained for thin film samples were analyzed using the four-parameter model for optical phonons with a standard optical multi-layer technique.

The effects of small amounts (0.5; 1.0 and 1.5 mol. %) of bismuth oxide on the microstructure and electrical properties of ZnO-SnO2 ceramics have been studied. Starting powders of ZnO and SnO2 were mixed in the molar ratio 2:1. After adding Bi2O3 this mixture was mechanically activated for 10 minutes in a planetary ball mill, uniaxially pressed and sintered at 1300 degrees C for 2h. The phase composition of the sintered samples was analyzed by X-Ray Diffraction (ARD) and by Energy Dispersive Spectrometer (EDS). Morphologies were examined by Scanning Electron Microscopy (SEM). An ImpedancelGain Phase Analyzer (HP 4194A) was used to measure the impedance spectra (100Hz - 10MHz) at different temperatures. The electrical DC resistivity/conductivity at different temperatures was measured using a High Resistance Meter (HP 4329A).

Mechanical activation was used as a method for modification of the structural and optical properties of commercial ZnO powder. For this purpose zinc oxide powder was mechanically treated by grinding in a high-energy vibro-mill in a continual regime in air up to 300 minutes. Starting and modified ZnO samples were characterized using XRD, BET and TEM measurements. Optical properties of these samples were investigated by Raman and photoluminescence (PL) spectroscopy. The color of commercial ZnO powder was white while mechanically activated ZnO powder was dark yellow, indicating the presence of nonstoichiometry. In the Raman spectra of non-activated sample Raman modes of bulk ZnO were observed, while the spectra of modified samples point out structural and stoichiometric changes. The PL spectra of modified samples excited by 325 and 442 nm lines of a He-Cd laser show great difference with respect to the spectra of the original sample. This study confirms that change in the defect structure of the ZnO crystal lattice introduced by mechanical activation affects the optical properties of this material.

In this paper the influence of tribophysical activation on non-isothermal sintering of barium titanate has been investigated. BaTiO3 Powders were tribophysically activated in a planetary ball mill for 0, 60 and 120 min., pressed and non-isothermally sintered up to 1380 degrees C. Dilatometric analysis was performed in air in the temperature range from room temperature to 1380 degrees C with heating rates of 10, 20 and 30 degrees C/min. The samples were analyzed by the X-ray powder diffraction method. Investigation of the morphology of microstructure constituents was performed using the scanning electron microsocopy method. With the purpose of optimizing technological parameters the results obtained by microstructure analysis were correlated with the results of quantitative dilatometric analysis.