Characterization of special material using thermoanalytical methods

Práce shrnuje poznatky získané při studiu fázových změn ve speciálních materiálech, jakými jsou chalkogenidová skla, nanokompozity na bázi epoxidových pryskyřic, látky, vhodné pro akumulaci tepla a energetické materiály. Blíže jsou vysvětleny postupy termické analýzy a interpretace kinetických popisů dějů ve speciálních materiálech a stanovení důležité termodynamické veličiny - tepelné kapacity.The work presents summary of results obtained by studying the phase changes in special materials, such as chalcogenide glasses, nanocomposites based on epoxy resins, materials suitable for accumulation of energy and explosives. The procedures of thermal analysis are given in detail as well as their interpretation within the processed observed for special materials. Further, the determination of basic thermodynamic quantity - heat capacity is described.Katedra anorganické technologieDokončená práce s úspěšnou obhajobo

Vliv experimentálních podmínek na entalpickou relaxaci studovanou pomocí cyklických měření w konstantní rychlostí ohřevu

The cyclic experiments with constant heating rate following cooling by various cooling rates were done using DSC to be able to apply different methods of estimation of TNM model parameters. The advantage and limitation of employed experimental procedure is discussed and the composition of (GeS2)(y)(Sb2S3)(1) (-) (y) glasses for y = 0.2 and 0.3 was used as model systems.Cyklická měření s konstantní rychlostí ohřevu následující po chlazení různou rychlostí bylo provedeno pomocí DSC tak, aby bylo možno použít různé postupy určení parametrů TNM modelu. Výhody a omezení použitého postupu je diskutováno a složení (GeS2)(y)(Sb2S3)(1-y) pro y=0,2 a 0,3 bylo použito jako modelový systém

Pokroky v dopování perovskitu - SrTiO3 kobaltovými ionty

This paper supports the point of research on doping of inorganic materials – in this case pigments – with various elements. Compounds on the basis of SrTiO3 with individually substituted titanium positions for cobalt ions have been prepared by the solid state reaction which was boosted by the mechanoactivation in advance. Calcination temperature and molar ratio of reactants were varied in order to study their influence on the pigment synthesis. Powders were characterised in terms of thermal behaviour and phase composition. Particle size distribution and application possibilities in ceramic glaze and organic binder along with colour properties were subsequently determined for selected samples. Prepared set of pigments SrTi1-xCoxO3 (x = 0.1-0.9) differed in characteristic according to diverse range of substitution and conditions of the synthesis.Tento článek podporuje výzkumu dopování anorganických materiálů - v tomto případě pigmentů - různými prvky. Sloučeniny na bázi SrTiO3 s substituovanými pozicemi titanu za kobaltové ionty byly připraveny reakcí v pevné fázi, která byla podpořena mechanoaktivací. Kalcinační teplota a molární poměr reaktantů byly měněny za účelem studia jejich vlivu na syntézu pigmentu. Prášky byly charakterizovány z hlediska termického chování a fázového složení. U vybraných vzorků byla následně stanovena distribuce velikosti částic a možnosti použití v keramických glazurách a organických pojivech spolu s barevnými vlastnostmi. Připravený soubor pigmentů SrTi1-xCoxO3 (x = 0,1-0,9) se lišil charakteristikami podle různého rozsahu substituce a podmínek syntézy

Viskozita a strukturní relaxace stříbrem dotovaného (GeS2)50(Sb2S3)50

The viscosities of Agx[(GeS2)50(Sb2S3)50]100-x glasses and undercooled melts for x = 5, 7.5, and 15 are studied in the range of 10E6–10E13 Pa·s. The measurements are recorded using a thermomechanical analyzer and two experimental setups, the parallel-plate and penetration methods. The structural relaxation of the composition Ag10[(GeS2)50(Sb2S3)50]90 is studied using differential scanning calorimetry and thermomechanical analysis. The enthalpy and volume relaxation are characterized and described using the Tool-Narayanaswamy-Moynihan (TNM) model. It is verified that both the enthalpy and volume relaxation can be described using similar values of the TNM model parameters. The parameters characterizing the viscous flow and structural relaxation, and their relationship, are discussed.Viskozita Agx[(GeS2)50(Sb2S3)50]100-x skla a podchlazené taveniny pro x = 5, 7.5, a 15 byla studována v rozsahu hodnot 10E6–10E13 Pa·s. Měření bylo provedeno pomocí termomechanického analyzátoru a dvou experimentálních uspořádání, metody paralelních desek a penetrační metody. Strukturní relaxace pro složení Ag10[(GeS2)50(Sb2S3)50]90 byla studována pomocí diferenční skenovací kalorimetrie a termomechanického analyzátoru. Entalpická a objemová relaxace byla popsána pomocí TNM modelu, kde jsou získané parametry pro obě metody podobné a je diskutován vztah mezi těmito parametry a popisem viskozitního chování

Structural relaxation in terms of TNM and AGS models

In this article the structural relaxation of non-crystalline materials was studied. The materials researched in this work were the amorphous selenium, Ge2Se98, As2Se98, and poly(vinyl acetate). Two types of relaxation – volumetric and enthalpic – were studied by using mercury dilatometry and differential scanning calorimetry. The relaxation of the materials studied was described on the basis of the Tool-Narayanaswamy-Moynihan (TNM) and Adam-Gibbs-Scherer (AGS) models. The main objective of this work was to describe and compare the volume and enthalpy relaxation of glassy Se, Ge2Se98, As2Se98 and PVAc

Effect of silver addition on thermal properties of (GeS2)50(Sb2S3)50 glass

Thermal properties of the (GeS2)50(Sb2S3)50 glass without and with the addition of 10 at. % of silver has been studied using calorimetry and thermal analysis. The viscosity data were obtained in a wide temperature range and described by the appropriate model. The glass transition region and the crystallization behaviour were studied in detail

Kinetic processes in Te-Se glasses

Structural relaxation kinetics and crystallization kinetics of chosen compositions from the Se-Te glassy system were studied under non-isothermal conditions by using differential scanning calorimetry in dependence on particle size. The purpose of this contribution is to demonstrate the extent of information accessible by the present-day kinetic analysis provided by the differential scanning calorimetry and to suggest its importance and merit for the development of new high-tech PCM materials. Enthalpic relaxation was described on the basis of Tool–Narayanaswamy–Moynihan model. Single set of TNM parameters was obtained from the curve-fitting procedure for each studied glass. A comparison with our previous measurements on a-Se was made and the development of particular TNM parameters with increasing Te content was discussed in terms of changes in molecular structure of the material. The curve-fitting results were further verified by several independent non-fitting methods. The crystallization kinetics was described in terms of the nucleation-growth Johnson–Mehl–Avrami model. Complexity of the crystallization process was in this case represented by very closely overlapping consecutive competing surface and bulk nucleation-growth mechanisms. Mutual interactions of both mechanisms as well as all other observed effects were explained in terms of thermal gradients, surface crystallization centres arising from the sample preparation treatments and changing amount of volume nuclei originating from the combination of prenucleation period and the very glass preparation phase. Advanced error analysis was performed for each step of the kinetic study. A new criterion for quick determination of the dominating crystallization mechanism — surface or bulk — was introduced

Advances in perovskite doping – SrTiO3 with cobalt ions

This paper supports the point of research on doping of inorganic materials – in this case, pigments – with various elements. Compounds on the basis of SrTiO3 with individually substituted titanium positions for the cobalt ions have been prepared by the solid-state reaction boosted by the prior-to-made mechanoactivation. Calcination temperature and the molar ratio of reactants were varied in order to study their effect on the pigment synthesis. Powdered materials were characterised in terms of thermal behaviour and the phase composition. Particle size distribution and application possibilities in ceramic glaze and organic binder along with colour properties were subsequently determined for selected samples. The prepared set of pigments SrTi1–xCoxO3 (x = 0.1–0.9) differed in characteristics according to a diverse range of substitution and conditions of the synthesis

Use of Mg(NO3)2.6H2O for the thermal energy storage

Hexahydrát dusičnanu hořečnatého byl zvolen jako vhodný materiál pro akumulaci tepelné energie díky své teplotě a entalpii tání. Mnohonásobné opakování cyklu ohřev-chlazení vykazuje podchlazení 29,7 K. Z tohoto důvodu byla použita nukleační činidla snižující podchlazení (AlO(OH), BaO, BaO2, Ba(OH)2.8H2O, BaCO3, CaO, Ca(OH)2, CaCO3, MgO, Mg(OH)2, MgCO3,Sr(OH)2 a SrCO3). Jako nejvhodnější nukleátor se jeví hydroxid strontnatý.Magnesium nitrate hexahydrate is suitable compound for the thermal energy storage because of its temperature and enthalpy of fusion. The repeating of heating-cooling cycle showed supercooling of 29.7 K. That is why the group of the promising non-isostructural nucleators (AlO(OH), BaO, BaO2, Ba(OH)2.8H2O, BaCO3, CaO, Ca(OH)2, CaCO3, MgO, Mg(OH)2, MgCO3,Sr(OH)2 a SrCO3) was tested in 1% addition. The strontium hydroxide seems to be the most effective nucleator