Diffusion Structural Analysis Study of Titania Films Deposited by Sol-Gel Technique on Silica Glass

The diffusion structural analysis (DSA) was used to characterize microstructure changes of hydrous titania gel films under in situ conditions of heating. TG and DTA were used in order to elucidate the processes controlling the formation of anatase film during heating of hydrous titania gel film. The annealing of porosity and near surface structure defects of the dehydrated titania films was indicated by DSA in the temperature range 255–700°C as the decrease of radon release rate. It was demonstrated that the annealing was enhanced on heating in oxygen in comparison with heating in argon. The DSA experimental results were compared with model curves describing the radon diffusion mobility and the annealing of radon diffusion paths.     

Application of emanation and surface labelling methods in the study of thermal processes

The emanation method and the method of surface labelling have been applied to study thermal processes. Using these methods, processes which are not connected with thermal effects can be analysed. In certain cases, for example in the study of poorly crystalline, or amorphous phases, these methods are even more sensitive than thermographic and X-ray techniques. The method of surface labelling is advantageous in cases when it is impossible to activate the samples by the parent isotope of the gas during the process of their preparation. This work was performed during the author's study leave to Moscow State University, Department of Radiochemistry.     

Emanation Thermal Analysis of SiC Based Materials

Results of emanation thermal analysis (ETA) characterizing microstructure changes of SiC based materials during heat treatment in argon are demonstrated. This method made it possible to reveal fine changes of the texture of SiC nano-sized powders, SiC micro-sized powders and SiC whiskers under in situconditions of the heating. ETA curves can serve as fingerprints of the respective samples.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal behaviour of amorphous Li2ZrO3 prepared by sol-gel technique

The results of the investigations of thermal behaviour of Li₂ZrO₃, prepared in the amorphous state by means of sol-gel technique are demonstrated. The thermal treatment was carried out in air under constant heating rate of 5 deg·min^–1 and cooling rate of 2.5 deg·min^–1. The methods of DTA, TG, Emanation Thermal Analysis (ETA) and dilatometry were used, for characterization of the thermal behaviour in dynamic conditions. The X-ray diffraction patterns were used for characterization of the phase changes observed by TA Methods.

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Zusammenfassung Ergebnisse aus Untersuchungen des thermischen Verhaltens von Li₂ZrO₃, hergestellt mittels einer Sol-Gel-Technik im amorphen Zustand werden dargelegt. Die thermische Behandlung wurde in Luft bei einer konstanten Aufheizgeschwindigkeit von 5 Grad·min^–1 und einer Abkühlgeschwindigkeit von 2,5Grad·min^–1 durchgeführt. Zur Beschreibung des thermischen Verhaltens unter dynamischen Verhältnissen wurden DTA, TG, Emanationsthermoanalyse und Dilatometrie angewendet. Zur näheren Charakterisierung der bei TG beobachteten Phasenumwandlungen wurde Röntgendiffraktion verwendet.

     

Thermal behaviour of advanced composite materials based on SiC fibres

Emanation thermal analysis (ETA) was used for characterization of thermal behaviour of SiC_f/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 SiC_f/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 SiC_f/SiC samples before and after the heat treatments was characterized by means of SEM. This revised version was published online in July 2006 with corrections to the Cover Date.     

Emanation thermal analysis study of a sol-gel precursor for silica-titania waveguides

Emanation Thermal Analysis (ETA) was demonstrated as a tool for the characterization of microstructure changes of a sol-gel precursor for silica-titania layers deposited on the glass plate to be used as planar waveguides. Temperature ranges of 280-330 and 380-500°C, respectively, in which the densification of the layers took place, were determined by ETA under in situ conditions of the sample heating. Results of thermogravimetry were compared with the ETA data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal stability of new zinc acetate-based complex compounds

New zinc acetate based complex compounds (of general formula Zn(CH₃COO)₂·1?2L·nH₂O) containing one or two molecules of urea, thiourea, coffeine and phenazone were prepared namely: Zn(CH₃COO)₂·2.5H₂O, Zn(CH₃COO)₂·2u·0.5H₂O, Zn(CH₃COO)₂·tu·0.5H₂O, Zn(CH₃COO)₂·2tu, Zn(CH₃COO)₂·cof·2.5H₂O, Zn(CH₃COO)₂·2cof·3.5H₂O, Zn(CH₃COO)₂·2phen·1.5H₂O. The compounds were characterized by IR spectroscopy, chemical analysis and thermal analysis. Thermal analysis showed that no changes in crystallographic modifications of the compounds take place during (heating in nitrogen before) the thermal decompositions. The temperature interval of the stability of the prepared compounds were determined. It was found that the thermal decomposition of hydrated compounds starts by the release of water molecules. During the thermal decomposition of anhydrous compounds in nitrogen the release of organic ligands take place followed by the decomposition of the acetate anion. Zinc oxide and metallic zinc were found as final products of the thermal decomposition of the zinc acetate based complex compounds studied. Carbon dioxide and acetone were detected in the gaseous products of the decomposition of the compounds if ZnO is formed. Carbon monoxide and acetaldehyde were detected in the gaseous products of the decomposition, if metallic Zn is formed. It is supposed that ZnO and Zn resulting from Zn acetate complex compounds here studied, possess different degree of structural disorder. Annealing takes place by further heating above 600°C.     

Effect of grinding on thermal reactivity of ceramic clay minerals

The effect of grinding on thermal behavior of pyrophyllite and talc as commonly used ceramic clay minerals was investigated by DTA, TG, emanation thermal analysis (ETA), B.E.T. surface area (s.a.) measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). A vibratory mill was used in this study, grinding time was 5 min. It was found that the grinding caused an increase in surface area and a grain size reduction of the samples. From TG and DTA results it followed that grinding caused a decrease of the temperature at which the structure bound OH groups released. The formation of high temperature phases was enhanced with the ground samples. For the ground talc sample the crystallization of non-crystalline phase into orthorhombic enstatite was observed in the range of 800°C. For ground pyrophyllite a certain agglomeration of grains was observed in the range above 950°C. Moreover, for both clays the ETA characterized a closing up of subsurface irregularities caused by grinding as a decrease of the emanation rate in the range 250–400°C. The comparison of thermal analysis results with the results of other methods made it possible to better understand the effect of grinding on the ceramic clays.     

Preparation and characterization of titania based nanowires

A new method for preparation of titania nanowires with diameter around 10 nm and length up to 2–3 μm is described. The precursor was prepared from sodium titanate by adding ethylene glycole (EG) and heating at temperature of 198°C for 6 h under reflux. The sodium titanate glycolate formed by this way aggregated into 1D nanostructures and was subsequently transformed into titania glycolate during a chemical treatment with 98% sulfuric acid. Titania nanowires with variable amount of anatase and rutile were prepared by heating to temperatures in the range 350–1000°C. The precursor as well as titania based samples were characterized by X-ray diffraction, Infrared spectroscopy, Scanning electron microscopy, High resolution transmission microscopy, Thermogravimetry, Differential thermal analysis, Evolved gas analysis and Emanation thermal analysis. The nitrogen adsorption/desorption was used for surface area and porosity determination. The photoactivity of the prepared titania samples was assessed by the photocatalytic decomposition of 4-chlorophenol in an aqueous slurry under UV irradiation of 365 nm wavelength.     

Thermal behaviour of titanium dioxide nanoparticles prepared by precipitation from aqueous solutions

Thermogravimetry-differential thermal analysis, emanation thermal analysis, mass spectrometry detection, Fourier transform infrared and XRD were used to characterize thermal behaviour of titanium dioxide photocatalyst precursors prepared by precipitation at various conditions from peroxotitanic acid sols. The transmission electron microscopy HRTEM technique was used to characterize the surface microstructure. The sols contained TiO₂ anatase particles of approximately 10 nm in diameter. During heating of the air dried samples, their chemical degradation took place giving rise to anatase. On further heating, the crystallization of anatase and formation of rutile phase was observed. To test the photocatalytic activity of the samples, the decomposition of 4-chlorophenol (4-CP) under ultraviolet and visible irradiation was monitored. It was shown that photocatalytic activities of the samples are comparable to the Degussa P25 photocatalyst reference material.