PRIPRAVA ELEKTROKERAMICKYCH MATERIALU PRO POKROCILE APLIKACE PROCESSING OF ELECTROCERAMIC MATERIALS FOR ADVANCED APPLICATIONS
The doctoral thesis is focused on processing of advanced ceramic materials with interesting physical properties. The materials were prepared by solid state resp. hydrothermal syntheses. The first investigated material described in this work is EuTiO3 perovskite ceramics. Absence of thermodynamic data of this system led to extensive experimental research of proper processing conditions. Three mixtures of different powder precursors (Eu2O3 with Ti2O3 resp. TiO2 rutile or anatase) were homogenized by planetary ball mill and formed by isostatic pressure of 300 MPa. These cylindrical green bodies were sintered conventionally in reducing atmospheres (Ar 7 H2 resp. pure H2) or by Spark Plasma Sintering (SPS) The influence of the sintering technique, temperature, atmosphere composition and dwell time on final density and phase purity was discussed. The investigation resulted in successful processing of phase pure EuTiO3 ceramic with relative density higher than 95 of theoretical density %TD) According author's best knowledge, it is up to now the best bulk EuTiO3 ceramic sample. The importance of this achievement is also declared by four publications in respected journals where the properties of these samples were presented. The infra red reflectivity spectra of prepared materials were compared with data from literature. It was proven that only single phase samples with low content of porosity are suitable for establishing their real (undistorted) physical properties. The next research was aimed on processing of Eu0.5Na0.5TiO3 ceramics by hydrothermal syntheses (HTS) The HTS were performed in highly alkaline environment of NaOH resp. KOH solution at temperature range 220 250 degC. The experiments with varied precursors (EuCl3 and TiCl4) and reductant agent concentrations led to processing of pure Eu0.5Na0.5TiO3 perovskite ceramic powder with submicron cubic particles. Another titanate MgTiO3 was synthetized by solid state reaction from MgO and TiO2 powder mixtures. The mixtures were mechanically activated in ball mill for 0, 10, 40, 80 resp. 160 min. The green bodies were formed by isostatic pressure of 300 MPa and sintered by two different approaches. The first batch of samples was sintered by two step sintering technique at 1300 degC (30 min) and 1200 degC (20 h) The second set was sintered conventionally at 1300 degC resp. 1400 degC for 30 min and post sintered by Hot Isostatic Press (HIP) at 1200 degC resp. 1280 degC. The phase pure MgTiO3 samples with relative density higher than 93 %TD were reached after post sintering by HIP at 1280 degC for 3 hours in Ar atmosphere and pressure of 200 MPa. The last studied material was Ba(Ca)Ti(Zr)O3 lead free piezoceramics, which was prepared by solid state reaction from powder mixtures milled by planetary ball mill at different conditions. The pressure less sintering of isostatically pressed bodies (300 MPa) at 1200, 1300, 1400 resp. 1500 degC for 1 h in air was performed. The processing condition needed for single phase perovskite Ba0.85Ca0.15Ti0.9Zr0.1O3 ceramics with required microstructure were studied. The single phase Ba(Ca)Ti(Zr)O3 sample with relative density 96 %TD was successfully prepared. Our results proved the importance of careful choice of the processing techniques and their variables for reaching of desired microstructure and phase composition of advanced electroceramics and therefore for proper evaluation of their physical properties. KLICOVA SLOVA Pokrocila keramika, elektrokeramika, elektromagneticke vlastnosti, synteza v tuhe fazi, slinovani