Transport properties and microstructure changes of talc characterized by emanation thermal analysis

Thermal behavior of talc samples (from locality Puebla de Lillo, Spain) were characterized by emanation thermal analysis (ETA), DTA and TG. The ETA, based on the measurement of radon release rate from samples, revealed a closing up of surface micro-cracks and annealing of microstructure irregularities of the talc samples on heating in the range 200–500°C. For ground talc sample a crystallization of non-crystalline phase formed by grinding, into orthorhombic enstatite was characterized as a decrease of radon mobility in the range 785–825°C and by a DTA exothermal effect with the maximum at 830°C. ETA results characterized the microstructure development of the talc samples on heating and served to evaluate their radon mobility and transport properties on heating and cooling. Transport properties of the talc samples were evaluated by using ETA experimental data measured during heating to 600 and 1300°C, respectively, and subsequent cooling to room temperature.     

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 synthetic gibbsite

Emanation thermal analysis (ETA) was used for thermal characterization of microstructure changes taking place during heating of synthetic gibbsite sample in argon in the range of 25–1200°C. Microstructure development and the increase of the surface area under in-situ conditions of the sample heating were characterized. The increase of the radon release rate from 130–330°C monitored the increase of the surface area due to the dehydration of Al(OH)₃. During heating of the sample in the range 450–1080°C the ETA results characterized the annealing of surface and near surface structure irregularities of intermediate products of gibbsite heat treatment. The mathematical model for the evaluation of the ETA experimental results was proposed. From the comparison of the experimental ETA results with the model curves it followed that the model is suitable for the quantitative characterization of microstructure changes taking place on heating of gibbsite sample. This revised version was published online in July 2006 with corrections to the Cover Date.     

Use of emanation thermal analysis to characterize thermal reactivity of brannerite mineral

Emanation thermal analysis (ETA) was used to characterize the thermal reactivity of amorphous brannerite mineral of general formula U_1–xTi_2+xO₆ (locality El Cabril, near Cordoba, Spain). It was demonstrated that on sample heating up to 880°C microstructure changes taking place in the sample were accompanied by the formation of new radon diffusion paths, followed by their closing up during the final transformation of amorphous to crystalline brannerite in the range 900–1020 °C. Relative changes in structure irregularities that served as radon diffusion paths during heating and subsequent cooling of the sample to temperatures of 300, 550, 750, 880, 1020 and 1130°C, respectively, were determined from the ETA results. Mass losses in temperature ranges of 230–315, 570–760 and 840–1040°C were observed by thermogravimetry. Mass spectrometry indicated the release of CO2 mainly due to the decomposition of minor carbon amount in the brannerite mineral sample.     

Emanation thermal analysis study of N-doped titania photoactive powders

Thermal behaviour of N-doped titania powders prepared by heat treatment of anatase in gaseous ammonia at 550 and 575°C, respectively, was characterized by emanation thermal analysis (ETA). The ETA results were used to assess transport properties of the samples subsurface using the mobility data of radon atoms previously incorporated into the samples to the depth of 60 nm. It was demonstrated that the radon permeability of anatase in the temperature range 50–500°C was enhanced for the N-doped titania as compared to the non-doped titania powder. Microstructure changes accompanying the anatase-rutile transition were pointed out from the decrease of the radon release rate in the temperature range 850–1000°C. The results of surface area and porosity measurements, DTA results as well XRD patterns supported the ETA results.     

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.     

Thermal characterization of commercial alumina with different preparation histories by emanation thermal analysis using Ra-226 parent isotope

Emanation thermal analysis (ETA) using the Ra-226 parent isotope, was applied in the range 25–1450°C for the characterization of commerical alumina powders with various preparation histories. The gas-release stages in the ETA curves for α-alumina prepared by a Bayer process were broadly grouped into two parts: peak I maximizing at 100–550 °C (Ia at about 270–300°C and Ib at 450–500°C) and peak II starting at about 800°C (IIa maximizing at 950°C and IIb at about 1200°C). The effects of Na ions, heating and grinding on the ETA behaviors were discussed.     

Effect of Na+ and NH 4 + Cations on Microstructure Changes of Natural Vermiculite During Heat Treatment

Emanation thermal analysis (ETA), DTA, SEM, and XRD were applied for the characterization of the effect of Na⁺ and NH ₄ ⁺ ions used for saturation of natural Mg-vermiculite on the microstructure during heating. The microstructure changes were characterized by ETA under in situ conditions of samples heating in air in the temperature range 20–1300°C. It was found that Na⁺ and NH ₄ ⁺ ions have a significant effect on the microstructure changes during heat treatment of the natural Mg-vermiculite sample saturated with these ions. For Mg-vermiculite and Na⁺ saturated vermiculite thet emperatures of the onset of the collapse of interlaminar space were determined by ETA. Differences in thermal stability of the microstructure of dehydrated vermiculite samples were observed by ETA: the microstructure of dehydrated Mg-vermiculite, and Na-vermiculite was found stable until 650 and 350°C, respectively. For dehydrated NH₄-vermiculite the annealing of the microstructure started at 730°C. The onset temperatures of the formation of new crystalline phases were indicated by ETA as the increase of the radon release rate. The onset temperatures of the ordering of the vermiculite structure or sintering under presence of the glassy stage (for Na-vermiculite), respectively, were determined from the decrease of the radon release rate. The ETA results were confirmed by DTA, XRD and SEM.This revised version was published online in November 2005 with corrections to the Cover Date.     

Emanation thermal analysis study of Na-montmorillonite and montmorillonite saturated with various cations

Emanation thermal analysis (ETA) and thermogravimetry measured in the range 20–1000°C was used to characterize the thermal behaviour of Na-montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite samples prepared by saturation with cations Li⁺ , Mg²⁺ , Al³⁺ , respectively. It was confirmed that the presence of cations used for montmorillonite saturation (Li⁺ , Mg²⁺ , Al³⁺ ) influenced the thermal behaviour of the samples. The results that indicated the decrease of radon release rate corresponding to a collapse of the interlayer space between the silicate sheets after water release and the crystallization of meta-montmorillonite in the respective temperature intervals were compared. From the ETA results it followed that the thermal stability of intermediate microstructure depends on the type of exchanged cation. A mathematical model was used to evaluate the ETA data.     

Emanation thermal analysis study of brannerite ceramics for immobilization of hazardous waste

Brannerite based ceramics, designed as a matrix for immobilization of high level radioactive waste (HLW), was investigated from the viewpoint of microstructure changes and atomic transport properties caused by leaching of the ceramics at pH 2 and 11, respectively. Scanning electron microscopy (SEM) and emanation thermal analysis (ETA) techniques were used for this purpose. Surface morphology, microstructure changes and transport properties of both ‘as-leached’ and ‘as-prepared’ samples were compared and the effect of leaching on the thermal behavior of the ceramics samples heated in the temperature range from 20 to 1250°C was characterized. The mobility of radon in the brannerite ceramics was evaluated by mathematical modeling from ETA results. The thermal behavior of the non-leached brannerite ceramics sample and its natural analogue brannerite mineral was compared using the ETA. On leave from the Institute of Chemical Sciences, Faculty of Sciences, P. J. Ŝafárik University, 041 54 Koŝice, Slovak Republic     

Thermal behaviour of ground vermiculite

Thermal behaviour of natural vermiculite (Santa Olalla, Huelva, Spain) was investigated by TG, DTA, emanation thermal analysis (ETA) and high temperature XRD on heating in the temperature range from 30 to 1100°C before and after vibratory mill grinding. Microstructure changes of natural and ground vermiculite samples were characterized by using ETA under in situ conditions of heating. By comparing the ETA and XRD results it was demonstrated that a decrease of radon release rate measured by ETA characterized the decrease in the interlayer spacing of the vermiculite samples that followed the dehydration. Dedicated to the memory of Professor Dr. Ferenc Paulik who passed away on October 12, 2005.     

Use of bomb calorimetry to assess recovery of waste industrial mineral oils through regeneration

Emanation thermal analysis (ETA), based on the measurement of the release of radon previously incorporated into the sample, was used to characterize the differences in the thermal behavior porous titania film (thickness 200 nm),when heated in argon and in oxygen, respectively, in the range from 20 to 800°C. It was observed that the annealing of porosity and structure defects in the near surface layers of the porous titania film (anatase) was enhanced on heating in oxygen in comparison to the heating in argon. ETA results were compared with SEM micrographs and XRD patterns of the titania film samples heated to 500 and 800°C, respectively. A mathematical model was used for the evaluation of the temperature dependence of the titania films microstructure development.This revised version was published online in November 2005 with corrections to the Cover Date.     

Study of natural and ion exchanged vermiculite by emanation thermal analysis,TG, DTA and XRD

Emanation thermal analysis (ETA), thermogravimetry, DTA and XRD were used in thermal characterization of natural vermiculite (Santa Olalla, Huelva, Spain) and of Na^+- and - exchanged vermiculite samples during heating in air in the range 25-1100°C. A good agreement between the results of these methods was found. Changes in the radon release rate measured by ETA, which reflected the decrease and collapse of the interlayer space after the release of water as well as the formation of new crystalline phases were evaluated using a mathematical model. The model used for the evaluation was found suitable for the quantitative characterization of microstructure changes during in situ conditions of heating of vermiculite samples. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Characterization of AlPO<Subscript>4</Subscript>/ZSM-5 Catalyst for Methanol Conversion to Dimethyl Ether

A catalyst based on zeolite was synthesized using the hydrothermal method, and alumina phosphate was embedded in its structure. The correspondent reactor tests were carried out to assess the synthesized catalyst where methanol with a purity of 99.9% was used. The results indicated that alumina phosphate is considerably effective on catalyst functionality. Given the results, the best performance was obtained when the ratio of alumina phosphate to alumina is 0.7 weighted in catalyst and fixed-bed reactor serves in a temperature of 300°C and WHSV of 0.8 h^?1. Structure and morphology of synthesized catalyst were characterized by BET, XRF, SEM, and XRD. The catalyst was evaluated in the process of converting methanol to dimethyl ether in a fixed-bed reactor under operating conditions of 300°C, 1 atm and 0.5 mL min^?1 of feed (pure methanol). The results of test indicated by increasing the amount of alumina phosphate to alumina, the conversion rate of methanol was increased to a constant value and does not change in ratios higher than 0.7. Moreover, the methanol conversion rate will reach temperature 300°C at 84%.     

Thermal behaviour of synthetic pyroaurite-like anionic clay

Thermal behaviour of synthetic pyroaurite-like anionic clay with molar ratio Mg/Fe=2 was studied in the range of 60-1100°C during heating in air. TG/DTA coupled with evolved gas analysis, emanation thermal analysis (ETA), surface area measurements, XRD, IR and Mössbauer spectroscopy were used. Microstructure changes characterized by ETA were in a good agreement with the results of surface area measurements and other methods. After the thermal decomposition of the pyroaurite-like anionic clay, which took place mainly up to 400°C, a predominantly amorphous mixture of oxides is formed. A gradual crystallization of MgO (periclase) and Fe₂O₃ (maghemite) was observed at 400-700°C by XRD. The MgFe₂O₄ spinel and periclase were detected at 800-1100°C. The spinel formation was also confirmed by Mössbauer spectroscopy.     

Emanation Thermal Analysis of Intercalated Montmorillonitic clay

Emanation Thermal Analysis (ETA), based on the measurement of the release of radon from previously labelled samples, has been used for 'in-situ’ characterisation of the morphology changes of intercalated montmorillonitic clay. The thermal behaviour of hydroxyaluminium intercalated montmorillonite was monitored in course of the preparation of alumina pillared montmorillonite, making possible to determine optimal temperature for the isothermal treatment of the intermediate product. Moreover, the thermal stability of alumina pillared montmorillonite porous structure was determined from the ETA data. A good agreement of ETA data and surface area, XRD patterns. DTA, and TG resulted was found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ion transport in Ca2+, Sr2+, Ba2+, and Pb2+ beta″ aluminas

Single crystals of Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺ beta″ alumina were prepared from sodium beta″ alumina by ion exchange. The ionic conductivities of Ca²⁺, Sr²⁺, and Ba²⁺ beta″ alumina are comparable, about 3 × 10^?2 (ohm-cm)^?1 at 300°C. Surprisingly, Pb²⁺ beta″ alumina is much more conductive, 1.5 × 10^?1 (ohm-cm)^?1 at 300°C and 4.6 × 10^?3 (ohm-cm)^?1 at 40°C. Its conductivity approaches that of sodium beta″ alumina at temperatures below 25°C. The diffusion coefficient for Sr²⁺ in beta″ alumina at 600°C was estimated from radiotracer experiments. It is consistent with that expected from conductivity measurements.     

Theory of Emanation Thermal Analysis: XI. Radon diffusion as the probe of microstructure changes in solids

The theoretical background for the use of radon diffusion as a probe of microstructure changes in solids is given. The high sensitivity of the emanation thermal analysis (ETA) in the study of solid state processes especially interactions taking place on surfaces and in the near surface layers is described. The increasing sensitivity of the method towards bulk processes with rising temperature is theoretically shown. The background considerations to be used in the mathematical modeling of temperature dependences of the radon release from solids on heating (i.e. simulated ETA curves) are presented. Various models for radon diffusion and various functions describing the annealing of structure irregularities, which served as diffusion paths for radon, were used in the modeling. It was shown, that ETA is able to characterize microstructure changes in the surface layers of the thickness from several nanometers to several micrometers.This revised version was published online in November 2005 with corrections to the Cover Date.     

Atomic layer deposition (ALD) as a coating tool for reinforcing fibers

Layers of alumina were deposited on to bundled carbon fibers in an atomic layer deposition (ALD) process via sequential exposure to vapors of aluminium chloride and water, respectively. Scanning electron microscopic (SEM) images of the coated fibers revealed that each individual fiber within a bundle was coated evenly and separately, fibers are not bridged by the coating. SEM and transmission electron microscopic (TEM) images indicate that the coating was uniform and conformal with good adhesion to the fiber surface. Average deposition rate, measured from SEM images, was 0.06 nm per cycle at 500 °C. SEM also revealed that at deposition temperatures of 500 °C few of the fibers were damaged. At temperatures of 300 °C, no damaged fibers were observed, the average deposition rate decreased down to 0.033 nm per cycle. Oxidation resistance of the alumina-coated fibers was characterized by thermogravimetric analysis (TGA). The alumina coating improved oxidation resistance of the carbon fiber significantly. Oxidation onset temperature was 600 °C for fibers coated with a 45 nm thick alumina. Uncoated fibers, on the other hand, started to oxidize at temperatures as low as 250 °C.