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Manganese doped SrTiO3 powders with various manganese dioxide weight percentages in the range of 1.5, 3 and 6 wp% were prepared by a solid-state method in the presence of mechanical activation (10, 30 and 120 minutes). A systematic investigation by X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size analisys (PSA), Brunauer-Emmett-Teller (BET) methods and Raman spectroscopy has been undertaken to evaluate the role of dopants on the microstructural and morphological study of the perovskite oxide obtained. The optical properties of the different manganese doped and activated SrTiO3 powders have been also evaluated. Mn insertion in SrTiO3 is discussed considering the possibility for Mn ions to occupy both Ti4+ and Sr2+ sites as well as manganese segregation and Mn incorporation-related non-homogeneities. The results demonstrated that Mn has substituted into the lattice and surface layers of the particles of SrTiO3 powders and the absorption onset shifted to higher values of wavelengths with increasing time of activation and dopant concentration. The lowest value of the band gap (Eg=3.10 eV) was registered with the longest activation for 120 minutes and the highest concentration of dopant (6 wp%). Combining doping with mechanical activation lower values of band gap can be achieved and that fact could be used in subsequent studies to make Mn-SrTiO3 more suitable visible-light photocatalysts.

The research is based on the synthesis and characterization of polymer nanocomposites based on Poly(vinylidene fluoride) (PVDF) polymer and mechanically activated zinc oxide powder. In order to produce the polymer nanocomposite with enchanced electrical and mechanical properties different amount of the mechanicaly activated zinc oxide powder was used as a filler in PVDF polymer. PVDF (Mw∼530 000) was used without further purification. Mechanical activation of the powder was performed in a planetary mechanochemical activator (mill) with tungsten carbide balls. Activation times were 10 and 30 minutes. Ball to sample mass ratio was 40:1, while the rotation speed was 390 rpm. After the mentioned procedure, PVDF and nanocomposite films (50 μm) were obtained by casting the solutions into Petri dishes. The percentage of ZnO powder inside the polymer matrix was 5% for powder mechanically activated for 30 minutes, while for powders activated for 10 minutes the percentages were 2.5%, 5% and 10%. From the obtained results it can be concluded that the bigger amount of powder as a filler inside polymer matrix can be substituted with the prolonged time of mechanical activation time and have enhanced electrical properties also saving material and making the production of nanocomposites more economical.

In recent years, a lot of interest has been shown in obtaining materials with predetermined properties. The aim is to establish a functional dependence between the synthesis parameters, structural characteristics, and properties of the material. Ceramic materials based on strontium titanate (SrTiO3) are of special interest due to their unique physical-chemical properties. Having in mind the importance of examining the influence of synthesis parameters on the process of obtaining and properties of functional electroceramic materials, and the importance of SrTiO3 as a perovskite material, the motive was to analyze and consider the influence of mechanical activation. It has been established that the time of mechanical activation (0, 10, 30, 60, 90, and 120 minutes) of SrTiO3 powders indirectly affects on electrical properties of SrTiO3 ceramics. It was noticed that in SrTiO3 ceramics the values of relative dielectric permittivity in the radio frequency range (0,3 MHz-3 GHz) are stable, which is important for the fabrication of electronic components. Microstructural SEM analysis showed that the increase in mechanical activation time results in less porous samples. It was found that the value of the relative dielectric permittivity of ceramic samples at room temperature changes following the combined effect of changes in sample density, grain size, as well as changes in the grain boundary region. The maximum value of dielectric permittivity was observed in the sample activated for 10 minutes. Also, the sample activated for 10 min exhibits relatively low values of loss tangent, compared to the other mechanically activated samples, providing the best overall dielectric performance compared to other samples.

Barium zirconium titanate ceramics were prepared using solid state reactions of BaCO3, TiO2 and ZrO2 at elevated temperatures. The prepared BZT was mechanically activated in the planetary ball mill from 0-120 min to achieve different powder grades from micro- to nanosized particles. After the powder characterization by XRD and SEM the samples were pressed in disc shape and sintered at 1100 and 1200 °C in the air. The sintered samples were characterized by SEM. After that the silver epoxy electrodes were deposited on sintered disc samples. The disc samples capacitance and resistivity were measured in the low frequency region from 1 Hz to 200 kHz using a low frequency impedance analyzer. Sintering temperatures and powder grades were used as parameters. Finally, specific resistance ρ, dielectric permittivity (ε' + jε") and tgδ were obtained from the impedance measurements. The trends in electronic properties were analyzed: the relaxation effect of the space charge (inter-granular electric charges) vs. sintering temperature and ceramic grades. These show that mechanical activation has a significant effect on electrical properties, resulting in generally improved overall performance.

Magnesium aluminate and other alumina-based spinels attract attention due to their high hardness, high mechanical strength, and low dielectric constant. MgAl2O4 was produced by solid-state reaction between MgO and a-Al2O3 powders. Mechanical activation was used to increase the reactivity of powders and decrease the sintering temperatures. Mechanical activation of mixed powders was performed in a high-energy planetary ball mill in air for 30, 60, 90, and 120 minutes. The resulting powders were characterized to determine the effect of activation on surface area, particle size, and crystallinity. Mechanical activation decreased particle size, increased surface area, and increased the width of peaks in x-ray diffraction. Dilatometry was used to monitor densification behavior up to 1500 °C. For non-activated powders, sintering started at approximately 1400 °C, while for activated powders, the onset temperature decreased to about 1340 °C. Mechanical activation is an efficient method to improve the densification behaviour of MgAl2O4 produced from mixed oxide powders.

Magnesium aluminate, MgAl2O4, and other alumina-based spinels are refractory ceramics with high hardness and resistance to chemical attack while also being possible microwave dielectrics. Pure MgAl2O4 can be optically transparent when fully dense. Spinels exhibit inversion, which results in disorder among occupancy of A and B site cations. The goal of this study was to examine the effects of mechanical activation and composition on the temperature required for spinel formation and the site occupancy in the resulting spinel. MgAl2O4 was produced by solid state reaction between MgO and alpha-Al2O3. The starting powders were mixed by ball milling to homogenize the powders without significant particle size reduction. Mechanical activation of mixed powders was performed in a high-energy planetary ball mill in air for 1 h. Powders were compacted at 300 MPa. Heat treatments were performed in air, at temperatures ranging from 1200 to 1500 °C with 2 h dwell time, to determine the amount of spinel formation as a function of temperature. Phase composition and microstructure of initial powders and heated samples were determined by means of X-ray diffraction, particle size analysis, and scanning electron microscopy. The influence of milling and consolidation parameters were studied by electrical measurements and mechanical characterization. The main results of this study were that mechanical activation for 60 minutes initiated a mechano-chemical reaction, and resulted in spinel formation at much lower temperatures than within non-activated powders. Microstructures of ceramics sintered below 1400 oC indicated that final stage sintering started at much lower temperatures for activated samples than for non-activated samples. Changes in microstructure parameters, as a consequence of mechanical treatment and subsequent heating of investigated powder mixtures, strongly affect electrical and mechanical properties of the final ceramics.

The initial powder (16 % Fe2O3, 4 % BaCO3, 80 % BaTiO3) was mechanically activated in a planetary mill for 20, 80, 120, 160, 200 and 220 minutes in air. Modified Faraday method was used to perform magnetization measurements of compressed activated powder. The value of magnetization of these samples increases with increase in time of activation from 0.77 Am2kg-1 to 1.74 Am2kg-1. Thermomagnetic measurements in 20-600 °C temperature interval was used to investigate the dependence of magnetization on temperature. Multiple heating cycles of the sample activated for 120 min shows that after heating to 540 °C and 600 °C the value of magnetization increases 17 % and 62 %, respectively. Compressed powder samples were sintered for 2 hours at 1200 °C, leading to an increase in magnetization of 81 to 123 %. Thermomagnetic measurements of sintered samples in 20-450 °C temperature interval shows that sintered samples possess both ferromagnetic and ferroelectric properties. The relative dielectric constant of sintered samples at room temperature is around 8x104, depending on mechanical activation time.

Mechanical activation leads to the creation of new surfaces and decrease in particle size of the initial powder particles, which affects the crystallization of PVDF matrix. In addition, prolonged mechanical activation leads to agglomeration of nanoparticles agglomerates of different sizes. Microstructural changes due to mechanical activation in ZnO, BaTiO3, SrTiO3 and TiO2 powders were investigated using electron microscopy (TEM and SEM), x-ray diffraction (XRD) and particle size analysis (PSA). These were correlated with molecular simulations of mechanical properties of PVDF-nanocluster composites with different oxide nanocluster sizes (1, 1.5 and 2 nm) Each system was simulated using a periodic system of metal oxide nanocrystal inside β-PVDF matrix. β-PVDF was chosen for its superior properties over α- and γ- phases. Geometry of each system was optimized prior to the calculation of mechanical properties using GULP v4.3 software package. Molecular simulations show that, in general, mechanical properties (Young modulus as an indication of elasticity, Shear modulus as an indication of hardness) for all systems improve with decrease in nanocluster size. This suggests that mechanical activation of fillers in PVDF-metal oxide nanoparticle composites should have a positive effect on the mechanical properties of composite systems. This suggests mechanical activation as an easy an inexpensive method of improving mechanical properties of polymer-nanocrystal composite materials. Conference abstract: [https://hdl.handle.net/21.15107/rcub_dais_882]

Cordierite 2MgO+2Al2O3+5SiO2 is frequently used ceramic material, that is commonly used as a carrier of electrical components due to its low dielectric constant (~ 5), and low temperature thermal expansion coefficient (20•10-7 ºC-1). In order to accelerate the process of sintering, 5.00 mass% TeO2 was added to the starting mixtures. System was tested in two parallel mixtures, one with no added additives, and the other one with TeO2. The mechanical activation of the both mixtures was performed in a high-energy ball mill in time intervals from 0 to 40 min with ball to powder mass ratio 1:40. The particle size analysis (PSA) was employed in order to determine the changes in the particle size of the mechanically treated powders. The phase composition of the starting powders as well as microstructures was analyzed by the means of X-ray diffraction method and SEM.

Mechanically activated powders (0, 10, 40, 80 and 160 minutes) were formed by isostatic pressure 300 MPa to cylindrical green bodies (φ 12 mm). First set of samples was sintered at 1300°C for 30 min in air (heating rate 10 °C/min, cooling rate 5 oC/min). These samples were re-sintered at 1200 oC for 20 h in air (heating rate 20 °C/min, cooling rate 10 oC/min). Samples reached almost 90 % TD. The second set of samples was sintered at 1400 °C for 30 in air (heating rate 10 oC/min, cooling rate 5 °C/min). Relative densities increased up to 93 % TD. The samples of absence of open porosity (MTO-10, 40, 80 and 160) were post-sintered by pressure assisted technique Hot Isostatic Pressing (HIP) at 1200 °C for 2 h in argon atmosphere with pressure 200 MPa. The samples increased densities up to 96 % TD for sample MT-160. Electrical measurements were performed in the microwave field of frequency. IV Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 21-23, 2015; Belgrade

The structure and lattice dynamics of mechanically activated nanocrystalline Fe/BaTiO3 is investigated in this work. The powder mixture of 60%Fe and 40% BaTiO3 was mechanically activated up to 240 min in 500 cm3 zirconium oxide beakers together with balls of 10 mm in diameter (the ratio of powder and balls was 1:20). The microstructure development has been studied by scanning electron microscope equipped with energy dispersive x-ray analysis spectrometer. Room temperature Raman spectra of the samples were obtained in the spectral range from 100 to 1650 cm-1, in the backscattering geometry, using 633 nm line of a He-Ne laser. Raman spectroscopy was employed to investigate the laser power dependence of the spectra of the activated samples as wells. Microstructural investigations showed that mechanical activation has led to the creation of new surfaces and the comminution of the initial powder particles. Raman spectroscopy analysis pointed out that activation had a pronounced influence on Fe/BaTiO3 lattice spectra, thus affecting both the stability of the crystal structure and the phase transition phenomena.

Powder mixture of 60 mass % of iron (Fe) and 40 mass % of barium titanate (BaTiO3) has been activated in planetary mill for 100, 120, 150, 180, 210 and 240 min in the air. During the activation the iron powder transits into iron oxides FeO, Fe2O3 and Fe3O4. Depending on the activation time the percentage of iron oxides varies. Simultaneously, with the content change of the activated system, magnetic properties change as well. The thermomagnetic measurements in the temperature interval from 200C up to 6200C have shown that the powder activated for 120 minutes exhibits maximum magnetization prior to annealing. After multiple annealings of the same sample it has been shown that the maximum magnetization of the cooled sample is obtained upon annealing at 5600C during 10 min for all activation times of as-cast powder sample. The sample obtained from pressed powder mixture activated for 120 min has the maximum magnetization, upon isothermal sintering of samples at 12000C during 2h, being M = 2,9 Am2/kg. With additional annealing of the same sample up to Curie temperature (TC = 4300C) and subsequent cooling of the sample in the magnetic field of H = 20 kA/m, the sample is permanently magnetized. The magnetization of sample cooled in the magnetic field with intensity of 20 kA/m being M = 10,15 Am2/kg.

Cordierite, 2MgO•2Ah03•5Si02 (MAS), is a very attractive high-temperature ceramic material. In order to accelerate the process of sintering, 5.00 mass% Mo03 was added to the starting mixtures. The mechanical activation of the starting mixtures was performed in a high energy ball mill in time intervals from 0 to 160 minutes. In following, starting mixtures were sintered at 1300 °C for 2h. In order to determine the changes in the particle size distribution, the mechanically treated powders were characterized by a laser light-scattering particle size analyzer. The phase composition of the starting mixtures and sintered samples was analyzed by the X-ray diffraction method. Differential thermal analyses (DTA) and thermo-gravimetric (TG) analysis were used in order to determine characteristic temperatures. Kissinger's equation was employed to calculate apparent activation energies of various processes that occur within the system while heating. Based on the obtained DTA results, it was established that mechanical activation along with MoO3 additive, has influence on sintering temperature which was decreased for about 150 °C.

The authors investigated the morphological characteristics of mechanically activated ZnO powder. ZnO powder was mechanically activated for 2, 5, 10 and 30 minutes in a planetary ball mill. Mechanical activation introduces lattice disorder and defects into ZnO hexagonal wurtzite structure. In order to determine specific surface area and pore volume, we performed N2 porosimetry and SEM in order to investigate the microstructure of non-activated and mechanically activated ZnO powders. Using Kubelka-Munk function, UV-Vis spectra showed the reducing in band gap with activation time. ZnO powder activated for 5 minutes has the narrowest band gap.

Materials based on ZnO structure have more frequently application as fillers in polymer ceramics nanocompozites. Performances of these materials depends on fillers morphology, surfaces texture and particles size. According to this, in this paper, the authors investigated the influence of mechanical activation of ZnO powder on crystal and micro structure. Commercially available ZnO powder was activated in a planetary ball mill for 2, 5, 10 and 30 minutes. Characterization of such obtained powders was performed using XRD, SEM and Raman spectroscopy. XRD patterns indicated at lowering of peak intensities along with its broadening wich is realted to partical fragmentation and amorphyzation. Micrographs show irregularly shaped particles at the beginning and with prolonged milling time, particles gained uniformed distibution, while after 30 minutes of activation agglomerates started forming. The results we got by investigation of dynamical structure by Raman spectroscopy are in correlation with the other results of structures analysis. Results presented here enable further optimization of, polymer nanocompozite based on ZnO and PVDF, making process. II Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 30 - October 1, 2013; Belgrade

According to its low temperature thermal expansion coefficient, low dielectric constant, also good mechanical properties, cordierite, 2MgO×2Al2O3×5SiO2, represents a very attractive hightemperature ceramic material. In this study, cordierite was prepared by solid state reaction of the MgO, Al2O3 and SiO2 mixture. One of the components from the mixture, SiO2, was mechanically activated in a high energy ball mill during 5 and 10 minutes. The applied pressure before the sintering process was 2 t/cm2. Sintering process of mixtures containing non-activated and activated SiO2 powder was performed at 1350 oC for 4h in the air atmosphere. The phase composition of starting oxides and sintered samples was analyzed by the X-ray diffraction method. Particle size analysis was performed to investigate the differences between starting components. Scanning electron microscopy was done to analyze the microstructure of both components and sintered samples. This paper investigates the influence of one mechanically activated SiO2 component on the densities of green bodies as well as on the sintered samples, along with electrical properties of cordierite ceramics.

Poster presented at the conference Advanced Ceramics and Application II – Serbian Ceramic Society, Belgrade, September 30 – October 1, 2013

In this article the influence of ball miling process on structure of MgO-TiO2 system was investigated. The mixtures of MgO-TiO2 powders were mechanically activated in a planetary ball mill for the time period from 0 to 120 minutes. The influence of mechanical activation 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 continuously decreased up to 40 minutes of activation and increased after that, reaching its minimun value of 5.5 m2/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.

Mechanical activation is widely used and relatively inexpensive procedure for sintering process sample preparation. However, the influence of pressure, which is used for compaction, has not been completely investigated. Cordierite, 2MgO⋅2Al2O3⋅5SiO2, is a very actual hightemperature ceramic material, due to its characteristics. Based on our previous investigation, the mechanical activation of the starting mixtures with 5.00 mass% TiO2 was performed in a high energy ball mill during 10 minutes. Compaction pressure varied from 0.5 to 6t/cm2 (49 MPa - 588 MPa). Sintering process was performed at 1350oC for 4h in air atmosphere. The phase composition of activated and sintered samples was analyzed by the X-ray diffraction method. Scanning electron microscopy was performed to analyze the microstructure of both compacted and sintered sample. Non-isothermal sintering up to 1400oC, with a constant heating rate, was investigated by thermal shrinkage change with dilatometer. In this paper we research green bodies and sintered samples compaction pressure influence electrical properties. II Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 30 - October 1, 2013; Belgrade

Ferroelectric ceramic barium strontium titanate (Ba0.77Sr0.23TiO3), BST, was prepared by solid-state reactions using starting powders of barium carbonate (BaCO3), strontium carbonate (SrCO3) and titanium dioxide (TiO2-anatase). Non-activated and mechanically activated mixtures with high-energy planetary ball mill (0, 5, 10, 20, 80 and 120 minutes) were sintered at 1100, 1200, 1300 and 1400 °C for two hours in air. The maximum value of ceramic density is about 86.20% TG. X-ray diffraction analysis was used to obtain information on the phase composition, as well as determining the influence of mechanical activation on the half height width of the diffraction lines (111) BST isothermally sintered samples at 1400 °C during two hours. Defects and the beginning process of sintering on the microstructure were investigated by scanning electron microscopy (SEM). Electrical measurements (loss tangent of the angle, Nyquist diagrams and influence the activation time dependence of XC = f (log ν)) are made of ceramics sintered at 1400 °C for two hours.

Strontium-titanate powder was mechanically activated in a planetary ball mill for 0, 5, 10, 30, 60, 90 and 120 minutes. Non-isothermal sintering of non-activated and activated SrTiO3 powder samples in the temperature interval from 50 to 1300 0C with three different heating rates (10, 15 and 20 0C/min) was investigated on a dilatometer. X-ray powder diffraction and scanning electron microscopy (SEM) were used to determine the phase composition, lattice microstrains and microstructure morphology of the samples. XRD results showed the presence of new phases: SrCO3 (strontuim-carbonate) and TiO2 (anatase) after 30 minutes of mechanical activation. II Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 30 - October 1, 2013; Belgrade

TiO2-based materials are widely used in production of ceramic capacitors and semiconductors. The conventional method of ceramics synthesis relies on the solid-state reaction between TiO2 and other compounds (BaCO3, BaO, ZnO, MgO and SrCO3) at high temperatures. During this reaction control of final stoichiometry and powder characteristics are difficult to maintain, because of the lack of the consistency in initial raw material's mixture and the existence of local inhomogeneities in reaction product which occur as a result of incomplete mixing and incomplete reaction of the constituents. In the most cases the sintering kinetics of these ceramics are determined by several parameters, including pressed powder density, material's particle size, sintering temperature, atmosphere etc. As a result, during thermal treatment mass transport by plastic flow, bulk diffusion, surface and volume diffusion, grain boundary diffusion, or a combination of these processes may occur. In order to produce nanocrystalline powders and improve the sintering kinetics, high energy mechanical activation can be employed among other methods. DTA analyses indicated that the position of DTA exothermic peak assigned to the process of ceramics formation was shifted toward lower temperatures in activated samples. The distinction in that peak magnitude due to activation process was observed as well. These results pointed out an increase of the solid state reaction rate, due to activation process. It was concluded that mechanical activation provoked the acceleration of mass transport and enhanced the nucleation probability of a new phase, which caused the decrease of synthesis reaction temperature.

In this article the influence of mechanical activation on sintering process of barium-strontiumtitanate ceramics has been investigated. Both non-activated and mixtures treated in planetary ball mill for 5, 10, 20, 40, 80 and 120 minutes were sintered at 1100-1400 °C for 2 hours in air atmosphere. The influence of mechanical activation on phase composition and crystal structure has been analyzed by XRD, while the effect of activation and sintering process on microstructure was investigated by scanning electron microscopy. It has been established that temperature of 1100 °C was to low to induce final sintering stage for the system. Electrical measurements have been conducted for the densest ceramics sintered at 1400 °C for 2 hours. I Serbian Ceramic Society Conference - Advanced Ceramics and Application : program and the book of abstracts; May 10-11, 2012; Belgrade

Mechanical activation is widely used for sample preparation before the sintering process. However, the influence of pressure, which is used for compaction, has not been completely investigated. Cordierite, 2MgO_2Al2O3_5SiO2, is a very attractive high-temperature ceramic material, due to its outstanding electrical characteristics, such as the low temperature expansion coefficient, low dielectric constant and good mechanical properties. Based on our previous investigation, the mechanical activation of the starting mixtures with 5.00 mass% TiO2 was performed in a high energy ball mill during 10 minutes. Compaction pressure varied from 0.5 to 6 t/cm2. Differential thermal analysis (DTA) was used in order to determine characteristic temperatures within the system during heating. Sintering process was performed at 1350 °C for 4 h in air atmosphere. The phase composition of activated and sintered samples was analyzed by the X-ray diffraction method. Scanning electron microscopy was performed to analyze both compacted and sintered sample microstructure. This paper deals with the influence of compaction pressure on the densities of green bodies as well as on the sintered samples, along with electrical properties

Mixtures of MgO and TiO2 were mechanically activated in a planetary ball mill for different time intervals. Thus obtained powders were sintered in a furnace for 2 h at temperature of 1300 °C in air atmosphere. Raman scattering spectroscopy at room temperature has been used for characterization of sintered samples. Very similar spectra for all samples were observed, which indicate that there has been structure recovery during treatment at higher temperature. SEM analyses were performed in order to investigate effect of activation and sintering process on microstructure. Electrical measurements showed difference in dielectric constant (εr), loss tangent (tgδ) and specific resistance (ρ) as a function of time of mechanical treatment. The aim of this paper was to determine optimal parameters for materials preparation with a goal to obtain dense ceramic with appropriate characteristic.

Mixtures of MgO-TiO2 powders were mechanically activated in a planetary ball mill for time interval from 0 to 120 minutes. On thus obtained powders, structural investigations have been performed. N2 adsorption method was used to determine the BET specific surface area and pore size distribution. Unusual results are obtained: specific surface area continuously decreases up to 40 minutes of activation and after that increases, reaching its minimum value of 4.4 m2/g. The influence of mechanical activation on lattice vibrational spectra was examined by Raman spectroscopy at room temperatures. The differential thermal analysis has been performed in order to investigate thermal behavior of the mixtures, indicating at several endothermal peaks in range of RT to 1100oC. SEM gave information about changes in microstructures, showing the clear decrease in particle size.

Mixtures of MgO-TiO2 powders were mechanically activated in planetary ball mill for time interval from 0 to 120 minutes. The influence of mechanical activation on phase composition and crystal structure was analyzed by XRD, while the effect of activation and sintering process on microstructure was investigated by scanning electron microscopy. Using a data obtained by XRD microstructure parameters, values of crystallite size (D), density of dislocation (ρD) and lattice strain (ehkl) were calculated. Dielectric measurements are performed in order to show difference in dielectric constant as a function of time of mechanical activation.

According to its exceptional electrical characteristics, such as low temperature expansion coefficient, low dielectric constant and good mechanical properties, cordierite, 2MgO⋅2Al2O3⋅5SiO2, represents very attractive ceramic material in the field of high temperatures. In order to accelerate the process of sintering, 1 mass% Bi2O3 has been added to starting mixtures. Liquid phase sintering caused by presence of bismuth-oxide leads to lowering temperature of cordierite formation. Mechanical activation of starting mixtures (0-56 minutes in vibro-mill) additionally leads to lowering sintering temperatures. Process of sintering was performed at 1200, 1300 and 1400 oC, for 2h. BET and PSA were employed in order to follow the changes in specific surface area and particle size of mechanically treated powders. Phase composition of starting powders and sintered materials was analyzed by X-ray diffraction method. Moreover, SEM analysis was used for analysis of powders morphology and sintered pallets microstructure.

In this paper the influence of mechanical activation on MgO-TiO2 system has been investigated. Mixtures of MgO-TiO2 were mechanically activated using high-energy planetary ball mill during 0, 5, 10, 20, 40, 80 and 120 minutes. XRD analyses were performed in order to give information about phase composition and to determine variety of microstructure parameters using approximation method. The decrease in powder’s particle size was noticed as the time of mechanical activation increased. Also, the effect of tribophysical activation on microstructure was investigated by scanning electron microscopy.

The influence of mechanical activation on BaO-ZnO-TiO2 sistem was observed. Mixtures of BaO-ZnO-TiO2 were mechanically activated using high-energy planetary ball mill during 0,5, 10, 20, 40 and 80 minutes. XRD analyses were imployed in order to give information about powder’s phase composition. Microstructure parameters were revealed from an approximation method. 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.

Intenzivan razvoj elektronike najvećim delom zavisi od razvoja novih materijala, koji se pored strogo određenog sastava odlikuju i tačno određenom raspodelom defekata i primesa. Sa sve rasprostranjenijom primenom tehnike u svakodnevnom ljudskom životu javlja se sve veća potreba za novim materijalima koji zadovoljavaju sve strožije zahteve savremene tehnologije kako po pitanju karakteristika, tako i po pitanju funkcionalnosti a u novije vreme sve više i pitanje ekonomičnosti. Materijali koji imaju značajnu ulogu u savremenoj elektrotehnici su keramički materijali zbog svojih izuzetnih funkcionalnih svojstava. Pomenuta svojstva u najvećoj meri zavise od načina pripreme i obrade materijala. Elektronska keramika se najčešće dobija procesom sinterovanja. U najopštijem smislu, može se reći da sinterovanje predstavlja oblik kompaktiranja disperznih smeša materijala, ili ispresaka dobijenih njihovim hladnim oblikovanjem, na temperaturama nižim od temperature topljenja jedne od bazičnih komponenati, u cilju konsolidacije disperznog sistema i obezbeđivanja određenog skupa fizičko-hemijskih, mehaničkih i električnih svojstava. Aktuelnost i značaj istraživanja u oblasti proučavanja elektronskih keramika iskazuje i niz naučnih časopisa u stručnoj literturi. Među materijalima koji su od posebnog interesa zbog svoje primene u elektronici su svakako keramike na bazi titanata. Ubrzani razvoj mobilne telefonije kao i drugih telekomunikacionih sistema zahtevaju upotrebu dielektrika koji se koriste u mikrotalasnoj oblasti. Zbog svojih dobrih električnih svojstava magnezijum titanatna keramika se koristi u izradi mikrotalasnih frekventnih rezonatora i antena, u filterima i oscilatorima za aplikaciju u komunikacionim sistemima. Još se primenjuje za izradu integrisanih kola i aktuatora, a predstavlja i bazični materijal pri izradi višeslojnih kondenzatora. Uslove koji ovi materijali treba da zadovolje su prvenstveno što niže vrednosti dielektričnih gubitaka (tj. tangensa ugla gubitaka tgδ, odnosno što veći faktor dobrote Q) i visoke vrednosti dielektrične konstante. Navedena svojstva elektrokeramike zavise prvenstveno od uslova i načina pripreme polaznih komponenti. Postoji više različitih metoda za sintezu magnezijum titanata koji su do sada poznati iz literture. Među njima su najčešće korišćeni sol-gel tehnike, koprecipitacija, sprej piroliza. Od reakcija u čvrstoj fazi poslednjih godina najzastupljenija je metoda mehaničke aktivacije. Mehanička aktivacija je često korišćena tehnika promena fizičko-hemijskih svojstava disperznih sistema. Često je korišćena tehnologija za dobijanje prahova zbog svoje jednostavnosti i mogućnosti dobijanja većih količina materijala što utiče na nižu cenu konačno proizvedenih komponenti. Ovakvim tretmanom polaznih prahova dolazi do kontrolisane destrukcije materijala kao i do intezivnog prenosa mehaničke energije na prahove. Dobro je poznato da je reakciona sposobnost materijala posledica strukturnih svojstava. Stoga mehaničkom aktivacijom narušena prvobitna struktura sistema dovodi do ubrzavanja procesa sinteze i sinterovanja materijala u kojima se koristi aktivirani prah. U ovom radu smeša prahova je mehanički aktivirana u visoko energetskom planetarnom mlinu sa kuglama u različitim dužinama vremena. Cilj istraživanja je ispitivanje mikrostrukturnih svojstava polaznih i u različitim vremenskim periodima mehanički aktiviranih prahova, procesa generacije strukturnih defekata, formiranje i evolucija faznog sastava i mikrostrukture u procesu dobijanja funkcionalnih elektrokeramičkih materijala. Za formiranja dielektrika sa najboljim električnim svojstvima i najvećom gustinom određeno je optimalno vreme mehaničke aktivacije i temperatura sinterovanja. Takođe, ispitan je uticaj režima mehaničke aktivacije na temperaturu sinterovanja i utvrđen tok reakcije u čvrstoj fazi u izotermskim uslovima sinterovanja sistema MgO-TiO2.