Vera P. Pavlović

Ferroelectric nanocomposites of polyvinylidene fluoride/polymethyl methacrylate blend and BaTiO3 particles: Fabrication of β-crystal polymorph rich matrix through mechanical activation of the filler

Nanocomposites of polyvinylidene fluoride/polymethyl methacrylate (PVDF/PMMA) blend and mechanically activated barium titanate (BaTiO3) particles were prepared by melt mixing. Modification of filler by means of mechanical activation has a profound effect on the crystallization of PVDF in the blend matrix. Raman analysis showed that the modified BaTiO3 particles, due to higher specific surfaces, induce, predominantly, the crystallization of the electrically active β-phase of PVDF, while the initial micron size particles induce the formation of the most common but non-polar α-crystal form. The introduction of activated particles reduces the overall crystallinity but slightly affects the crystallization and melting temperatures of the matrix. Dielectric spectroscopy revealed that at fixed filler content the dielectric constant of the blend increases with decreasing of the particle size (increasing of the activation time). A similar trend was observed for the storage moduli in dynamic mechanical analysis; the...

Correlation Between Densification Rate and Microstructure Evolution of Mechanically Activated BaTiO3

Increasing demands on the quality of electronic ceramics requires a well-controlled correlation between particle morphology and processing conditions. Since mechanical activation is one of the methods for modification of physico-chemical properties of dispersed systems, in this study a correlation between the densification rate and microstructure evolution of mechanically activated BaTiO 3 has been analyzed. The shrinkage behaviour of mechanically activated samples, sintered under non-isothermal conditions has been analyzed by a sensitive dilatometer. Densification rate as a function of relative density for different activation times has been calculated. Microstructure investigations of sintered samples were carried out, using a scanning electron microscope (SEM). The presented results enable establishing processing parameters that are indispensable for obtaining materials with advanced properties.

Application of the Master Sintering Curve Theory to Non-Isothermal Sintering of BaTiO3 Ceramics

In this paper a practical approach to the analysis of sintering of BaTiO3 using the Master Sintering Curve concept has been presented. Non-isothermal sintering of high-purity non-doped BaTiO3 ceramics was monitored using a sensitive dilatometer at three different heating rates (10, 20 and 30 oC/min) up to 1380oC. Densification of BaTiO3 during sintering was analyzed using the Master Curve Sintering Theory. A MSC was defined characterizing the sintering behavior of barium-titanate regardless of the heating rate. Construction of the MSC enabled estimation of the process activation energy. Using defined MSC, densification behavior of BaTiO3 ceramics during sintering can be predicted for arbitrary temperature-time excursions and these predictions can be used in controlling and planning the sintering process of this material.

Structural properties of composites of polyvinylidene fluoride and mechanically activated BaTiO3 particles

Nanocomposites of electroactive ceramics and ferroelectric polymers exploit favorable features of the matrix polymer and the nanostructured filler to produce new functional materials for pressure and IR sensors. In this study, the influence of mechanical activation of barium titanate (BaTiO3) particles on the structural properties of BaTiO3/polyvinylidene fluoride (PVDF) nanocomposites was investigated. Nanocomposite films were prepared by the solution casting method and characterized by scanning electron microscopy, x-ray diffraction and Raman spectroscopy. It was found that mechanically activated fillers promote the formation of a ferroelectric ?-phase during crystallization of PVDF.

Phase Transformations and Thermal Effects of Mechanically Activated BaCO 3 -TiO 2 System

Phase transformations and thermal effects of BaTiO 3 ceramics due to influence of mechanical activation were investigated. Equimolar mixture of BaCO 3 and TiO 2 powders was activated in high energy vibromill for various grinding times. Specific surface area determinations of initial and activated powders were carried out. The phase composition and crystallographic data of initial and thermal treated powders was determined using X-ray powder diffraction method. Heating process was investigated using differential thermal analysis.

Microstructure and Dielectric Properties of Rare-Earth Doped BaTiO3 Ceramics

The specimens of BaTiO3 doped with 0.01, 0.1 and 0.5 wt% of Er2O3 or Ho2O3 used for this investigation were prepared by the conventional solid state reaction. The specimens were sintered at 1350°C in an air atmosphere for 4 hours. The grain size and microstructure characteristics for various samples and their phase composition was carried out using a scanning electron microscope SEM equipped with EDS system. SEM analysis of Er/BaTiO3 and Ho/BaTiO3 doped ceramics showed that in samples doped with a low level of rare-earth ions, the grain size ranged from 10–60μm, while with the higher dopant concentration the abnormal grain growth is inhibited and the grain size ranged between 2–10μm. We also applied the fractal method in microstructure analysis of sintered ceramics especially as influence on dielectric properties of BaTiO3 ceramics. These fractal effects have been used for better understanding of intergranular capacitors.

The Influence of Tribophysical Activation on Non-Isothermal Sintering of BaTiO3 Ceramics

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 1380oC. Dilatometric analysis was performed in air in the temperature range from room temperature to 1380oC with heating rates of 10, 20 and 30oC/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.

The Influence of Heating Rate On Sintering Process of BaTiO3 Ceramics

Ceramic materials obtained on the basis of BaTiO3 and its related compounds are of great importance for their fundamental and model aspects. In order to investigate the influence of heating rate on sintering process of BaTiO3 ceramics, tribophisicaly activated powders of 50mol% BaCO3 and 50mol% TiO2, were pressed, calcinated and sintered with different heating rates (4°C/min., 10°C/min. and 30°C/min.) up to 1300°C for 2h. Heating process was studied using dilatometer. The samples were analyzed by X-ray diffraction. Changes of dielectric properties were correlated with changes at different structural levels.