V. Balek

Thermal behaviour of ground and unground acid leached vermiculite

Acid leaching of vermiculite is an interesting procedure to prepare high surface area porous silica. Thermal behaviour of unground and ground vermiculite leached with HCl solutions has been studied by TG, DTA, ETA and high temperature XRD. Important differences have been observed in the thermal behaviour of unground and ground vermiculite after the acid treatments. Thus, for the acid-treated unground vermiculite, dehydrated vermiculite, enstatite and cristobalite were formed during the heating, while for the acid-treated ground vermiculite only iron oxides and cristobalite phases were observed. Structural modifications due to acid treatment were responsible for changes in the transport properties determined by ETA for the vermiculite samples.

Thermal analysis methods in the characterization of photocatalytic titania precursors

A new method for the preparation of titania photocatalyst was proposed. Precursors of the photoactive titania were prepared from TiOSO4·nH2O solution by precipitation with ammonia and addition of H2O2 or HNO3, respectively. Methods of TG, DTA, ETA, EGA/MS detection and FTIR were used to characterize the thermal degradation of the titania precursor and to determine the optimal temperature to obtain the photoactive titania. ETA made it possible to characterize the microstructure development of the samples in the heating conditions.

Characterisation of α-FeOOH Grinding Products Using Simultaneous DTA and TG/DTG Coupled with MS

Effects induced by grinding in synthetic goethite samples were studied. The products of α-FeOOH grinding were characterised by means of DTA, TG/DTG coupled with EGA (Mass spectrometry detection), powder X-ray diffraction analysis, and surface area determination.

USE OF EMANATION THERMAL ANALYSIS IN CHARACTERISATION OF NANOSIZED HEMATITE PREPARED BY DRY GRINDING OF GOETHITE

Hematite nanoparticles of narrow size distribution were prepared by grinding of goethite. Intermediate and final products of grinding were characterised by different techniques, including the less-common emanation thermal analysis (ETA). ETA was shown to be a useful technique for characterising processes of surface annealing, initial sintering and growth of hematite particles under in situ conditions of thermal treatment. A good agreement was found between results of ETA, TG, XRD, IR spectrometry, transmission electron microscopy and scanning electron microscopy, used for characterisation of thermal behaviour of the goethite samples ground for varying time (0–70 h).

Thermal Behavior of Nanostructured Powder

Diffusion structural analysis (DSA), based on the measurement of the release of radon previously incorporated into the samples, was used to characterize thermal behavior of N-doped titania powder prepared by heat treatment of anatase in gaseous ammonia at and the reference powder prepared from the ST-01 anatase titania powder (Ishihara Ltd., Japan). The results of DSA, surface area and porosity measurements by nitrogen adsorption, SEM micrographs, XPS, and XRD are presented and discussed. The results of DSA are in agreement with the results of other methods and indicated the annealing of the subsurface structure irregularities of the samples. Transport properties of the samples were determined from the mobility of radon atoms released on sample heating in air. The decrease of radon permeability in the porous titania powders in the temperature range 850– due to annealing of the subsurface structure irregularities, that served as radon diffusion paths in the samples, was evaluated from the DSA results.

Thermal behaviour of advanced composite materials based on SiC fibres

Emanation thermal analysis (ETA) was used for characterization of thermal behaviour of SiCf/SiC composites on heating in argon and air, respectively. Effect of gas environment (argon, air) and helium ions implantation on the microstructure development of the SiCf/SiC composite prepared by chemical vapour infiltration (CVI) from Nicalon CG fibres was investigated under in situ conditions of heating. The annealing of near surface structure irregularities was observed in the range 280-700°C and evaluated by means of the mathematical model, assuming that the structure irregularities served as diffusion paths for radon. The ETA reflected the formation of amorphous silica and its subsequent crystallization to crystoballite. Morphology of the SiCf/SiC samples before and after the heat treatments was characterized by means of SEM.