Synthesis and Analysis of Composite Oxide Ceramics in Presence of Nonconventional Energetic Fields

Práce se zabývá syntézou a analýzou složených oxidových materiálů, zejména keramik s perovskitovou a perovskitovou-defektní strukturou.Syntézy uvedených keramických materiálů byly prováděny za nekonvenčních podmínek s využitím vysokoenergetických polí - MW pole za hydrotermálních podmínek, mechanochemickou cestou a polykondenzačními technikami. Ke komplexnímu popisu struktury syntetizovaných produktů byly využity tyto metody - rentgenová difrakce (XRD), Rietveld analýza, mikroanalýza pomocí EDS-SEM, rastrovací mikroskopie (SEM), stanovení specifického měrného povrchu pomocí BET metody, měření velikosti částic laserovou difrakcí (LD), infračervená spektroskopie (IR), termická analýza (TG). U definovaných struktur (perovskity typu La-Sr-Fe-Ti-O) byly prostudovány i elektrochemické vlastnosti. Část práce tvořilo studium chemické analýzy syntetizovaných kompozitních oxidových materiálů. Pozornost byla věnována využití nekonvenčních polí při rozpuštění těžko rozložitelných produktů.Synthesis and bulk analysis of composite ceramic oxide materials and materials with perovskite-defect structure is presented within this work. Syntheses of these advanced ceramics materials were carroed out by using of nonconventional techniques (microwave-assisted hydrothermal synthesis and polycondensation techniques) and by conventional mechanochemical activation followed by high temperature solid state reaction. X-Ray difraction (XRD), Rietveld analysis, scaning microscopy (SEM), microalysis EDS-SEM, thermal analysis (TG), infrared spectroscopy (IR), determination of particles size and specific surface area were used for description of synthesized products. In case of perovskite system based on La-Sr-Fe-Ti-O electrochemical properties were studied. Part of work was focused on chemical analysis of synthesized composite oxide materials and decomposition hard structured products by using of nonconventional fields.

Influence of Active Alumina on the Hydration Process of Portland Cement

The work is interested in the study of the hydration process by means of the isothermal calorimetry method. The Portland cement hydration process led to gradual consumption of contained calcium sulfate. This sulfate depletion is observed on the calorimetry curve as a shoulder of main silicate peak. The addition of hydratable alumina to Portland cement was studied in order to determine its influence on hydration process. Experimental results showed the shifted position of this shoulder according to alumina and calcium sulfate content. It was also observed that the overall hydration process was almost unaffected by alumina addition

The formation of feldspar strontian (SrAl2Si2O8) via ceramic route: Reaction mechanism, kinetics and thermodynamics of the process

The reaction mechanism, the equilibrium composition, the temperature range of stability of formed intermediates as well as the kinetics and thermodynamics of activated state during the formation of monoclinic strontium-aluminum-silicate feldspar stroncian (SrAl2Si2O8) via the ceramic route from the mixture of SrCO3, Al2O3 and SiO2 is described in this work. Strontian does not appear up to the temperature of 1150 degrees C and is the only stable phase at the temperature >= 1600 degrees C. Three independent reactions lead to two parallel reaction pathways, i.e. the formation of strontian from single or binary oxides (1) and with Sr-gehlenite as the intermediate (2). Since the reaction rate constants ratio is higher than one (k(1)/k(2) > 1), the first reaction route is favored according to the Wegscheider principle. The kinetics of chemical reaction of 1.5 order corresponding to the kinetic function F-2/3 ((1 - alpha)(-1/2) - 1) was determined as the rate determining the mechanism of formation of strontian. The integral and differential methods show that the process requires average apparent activation energy of 229.3 kJ mol(-1). The determined average value of frequency factor is 2.1 x 10(5) S-

Synthesis and Analysis of Composite Oxide Ceramics in Presence of Nonconventional Energetic Fields

Synthesis and bulk analysis of composite ceramic oxide materials and materials with perovskite-defect structure is presented within this work. Syntheses of these advanced ceramics materials were carroed out by using of nonconventional techniques (microwave-assisted hydrothermal synthesis and polycondensation techniques) and by conventional mechanochemical activation followed by high temperature solid state reaction. X-Ray difraction (XRD), Rietveld analysis, scaning microscopy (SEM), microalysis EDS-SEM, thermal analysis (TG), infrared spectroscopy (IR), determination of particles size and specific surface area were used for description of synthesized products. In case of perovskite system based on La-Sr-Fe-Ti-O electrochemical properties were studied. Part of work was focused on chemical analysis of synthesized composite oxide materials and decomposition hard structured products by using of nonconventional fields

The ash from fluidized bed combustion as a donor of sulfates to the Portland clinker

The paper deals with possibilities of using solid residues from fluidized bed combustion of coal, bed and filter ash in the production of composite Portland cements. The ash from fluidized bed combustion contains a high amount of CaO, in the form of free lime or CaSO4 (anhydrite), so it could be used as a possible donor of sulfates to the Portland clinker instead of usually used gypsum. At first, the chemical composition of collected ashes was determined by X-Ray Fluorescence and the ongoing hydration process was monitored by isoperibolic calorimetry. Then samples containing mixtures of Portland clinker and ash were prepared. Their respective compressive strength and flexural strength were analyzed and observations were made on the hydration and composition of products of the hydration reaction detected by X-Ray diffraction. Finally, the results of selected mixtures were verified with prepared standardized mortars

The field of solid solutions in ternary system of synthetic apatite-type alkaline earth element-yttrium-silicate oxybritholite phases of the composition: AEE(delta)Y(10-delta)[SiO4](6)O3-0.5 delta, where AEE=Ca, Sr and Ba

This contribution deals with the synthesis, properties and investigation of the field of solid solutions formed between the three end-members of apatite-type alkaline earth element-yttrium-silicate oxybritholites with the hexagonal structure (P6(3)/m). The stoichiometric composition of these compounds corresponds to the formula AEE(delta)Y(10-delta)(SiO4)(6)O3-0.5 delta, where AEE=Ca, Sr and Ba and parameter delta -> 2. These compounds and their solid solutions crystallize from non-equilibrium high temperature flux as the main product of sinter-crystallization process. Increasing ionic radius of AEE cations has significant effect to the lattice parameters, properties and miscibility of apatite phases. While there is non-limited miscibility of solid solutions formed between Ca2Y8[SiO4](6)O-2 and Sr2Y8[SiO4](6)O-2, the highest content of barium in the binary solution with these species is limited to 28% and 38%, respectively. The connecting line of these points marks out the borderline for the field of solid solutions in the ternary system. All attempts for the preparation of pure Ba2Y8[SiO4](6)O-2 end-member via the ceramic method were not successful