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1.
V. Balek E. R. Vance V. Zeleňák Z. Málek J. Šubrt 《Journal of Thermal Analysis and Calorimetry》2007,88(1):93-98
Emanation thermal
analysis (ETA) was used to characterize the thermal reactivity of amorphous
brannerite mineral of general formula U1–xTi2+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. 相似文献
2.
Núñez-Regueira L. Rodríguez-Añón J. Proupín-Castiñeiras J. Labarta-Carreño C. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):93-101
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. 相似文献
3.
4.
V. Balek J. Šubrt E. Klosová M. Beneš 《Journal of Thermal Analysis and Calorimetry》2008,92(1):169-172
Emanation thermal analysis was used to characterize the thermal behaviour of alumina coatings as deposited on EUROFER 97 steel
surface by filtered vacuum arc technique. Temperature ranges of the healing of cracks and structure irregularities observed
by SEM were determined from the ETA results. Transport properties of the alumina coatings were assessed from the ETA results
by the evaluation of radon diffusion parameters in the temperature range from 50 to 300°C. Healing microstructure irregularities
of the alumina coatings can be expected in the range 300–700°C as indicated by the decrease of the radon release rate. From
the ETA results it followed that the onset of healing the cracks observed by the SEM on the surface of one alumina coating
sample can be expected at 430°C.
Dedicated to Dr. K. Habersberger, Past-Chairman of the thermal analysis working group of the Czech Chemcial Society, at the
occasion of his 75th birthday 相似文献
5.
Balek V. Šubrt J. Rouquerol J. Llewellyn P. Zeleňák V. Bountsewa I. M. Beckman I. N. Györyová K. 《Journal of Thermal Analysis and Calorimetry》2003,71(3):773-782
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. 相似文献
6.
L. A. Pérez-Maqueda V. Balek J. Poyato J. Šubrt M. Beneŝ V. Ramírez-Valle I. M. Buntseva I. N. Beckman J. L. Pérez-Rodríguez 《Journal of Thermal Analysis and Calorimetry》2008,92(1):253-258
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. 相似文献
7.
G. A. Zenkovets Yu. Yu. Tanashev V. V. Danilevich S. V. Tsybulya V. Yu. Gavrilov A. A. Shutilov V. N. Parmon 《Kinetics and Catalysis》2010,51(3):444-448
The physicochemical properties of titania (anatase) prepared from hydrated titanium dioxide by centrifugal thermal activation
(CTA) at 140–700°C were studied. It was found that the microstructure and the texture parameters of anatase prepared by the
above method were considerably different from those of the samples prepared by the traditional thermal decomposition of titanium
hydroxide. The conditions of centrifugal activation exerted a considerable effect on the structure and the texture parameters
of the resulting anatase. The crystal structure of anatase prepared at a temperature lower than 650°C was imperfect, and it
approached a regular structure only at a temperature of >650°C. At temperatures higher than 300°C, the samples of TiO2 prepared using CTA were characterized by higher specific surface areas, fine pore structures, and comparable mesopore volumes,
as compared with the samples prepared by commonly used synthetic methods. 相似文献
8.
E. Kraleva M. L. Saladino R. Matassa E. Caponetti S. Enzo A. Spojakina 《Journal of Structural Chemistry》2011,52(2):330-339
Pure titania, zirconia, and mixed oxides (3–37 mol.% of ZrO2) are prepared using the sol-gel method and calcined at different temperatures. The calcined samples are characterized by
Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen
adsorption porosimetry. Measurements reveal a thermal stability of the titania anatase phase that slightly increases in the
presence of 3–13 mol.% of zirconia. Practically, the titania anatase-rutile phase transformation is hindered during the temperature
increase above 700°C. The mixed oxide with 37 mol.% of ZrO2 treated at 550°C shows a new single amorphous phase with a surface area of the nanoparticles double with respect to the other
crystalline samples and the formed srilankite structure (at 700°C). The anatase phase is not observed in the sample containing
37 mol.% of ZrO2. The treatment at 700°C causes the formation of the srilankite (Ti0.63Zr0.37Ox) phase. 相似文献
9.
V. Balek Y. Zhang V. Zelenák J. Ŝubrt I. N. Beckman 《Journal of Thermal Analysis and Calorimetry》2008,92(1):155-160
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 相似文献
10.
V. Balek M. Beneš Z. Málek G. Matuschek A. Kettrup S. Yariv 《Journal of Thermal Analysis and Calorimetry》2006,83(3):617-623
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. 相似文献
11.
P. Padmaja K. G. K. Warrier M. Padmanabhan W. Wunderlich 《Journal of Sol-Gel Science and Technology》2009,52(1):88-96
Alumina–titania mixed oxide nanocatalysts with molar ratios = 1:0.5, 1:1, 1:2, 1:5 have been synthesized by adopting a hybrid
sol–gel route using boehmite sol as the precursor for alumina and titanium isopropoxide as the precursor for titania. The
thermal properties, XRD phase analysis, specific surface area, adsorption isotherms and pore size details along with temperature
programmed desorption of ammonia are presented. A specific surface area as high as 291 m2/g is observed for 1:5 Al2O3/TiO2 composition calcined at 400 °C, but the same composition when calcined at 1,000 °C, resulted in a surface area of 4 m2/g, while 1:0.5 composition shows a specific surface area of 41 m2/g at 1,000 °C. Temperature programmed desorption (of ammonia) results show more acidic nature for the titania rich mixed
oxide compositions. Transmission electron microscopy of low and high titania content samples calcined at 400 °C, shows homogeneous
distribution of phases in the nano range. In the mixed oxide, the particle size ranges between 10–20 nm depending on titania
content. The detailed porosity data analysis contributes very much in designing alumina–titania mixed oxide nanocatalysts. 相似文献
12.
V. Balek T. Mitsuhashi I.M. Bountseva H. Haneda Z. Malek J. Šubrt 《Journal of Sol-Gel Science and Technology》2003,26(1-3):185-189
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. 相似文献
13.
Mesoporous titania nanoparticles (denoted as MTN) with high surface area (e.g., 252 m2 g−1) were prepared using tetrapropyl orthotitanate (TPOT) as a titania precursor and 10–20 nm or 20–30 nm silica colloids as
templates. Co-assembly of TPOT and silica colloids in an aerosol-assisted process and immediate calcination at 450 °C resulted
in anatase/silica composite nanoparticles. Subsequent removal of the silica colloids from the composite by NaOH solution created
mesopores in the TiO2 nanoparticles with pore size corresponding to that of silica colloids. Effects of silica colloids’ contents on MTN porosity
and crystallites’ growth at a higher calcination temperature (e.g., 1000 °C) were investigated. Silica colloids suppressed
the growth of TiO2 crystallites during calcination at a higher calcination temperature and controllable contents of the silica colloids in precursor
solution resulted in various atomic ratios of anatase to rutile in the calcinated materials. The mesostructure and crystalline
structure of these titania materials were characterized by transmission electron microscope (TEM), scanning electron microscope
(SEM), X-ray diffraction (XRD), differential thermal analysis (DTA)-thermo-gravimetric analysis (TGA), and N2 sorption. 相似文献
14.
V. Balek J. L. Pérez-Rodríguez L. A. Pérez-Maqueda J. Šubrt J. Poyato 《Journal of Thermal Analysis and Calorimetry》2007,88(3):819-823
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. 相似文献
15.
A. Nakaruk C. Y. Lin D. S. Perera C. C. Sorrell 《Journal of Sol-Gel Science and Technology》2010,55(3):328-334
Essentially fully dense titania thin films were spin coated on fused quartz substrates under identical conditions and subjected
to annealing over the range 750°–900°C. The films were of a consistent ~400 nm thickness. The anatase → rutile phase transformation
temperature was between 750°C and 800°C, with first-order kinetics; annealing at 900°C yielded single-phase rutile. Silicon
contamination from the fused quartz substrate was considered to be critical since it suppressed both titania grain growth
(maintaining constant grain size) and the phase transformation (occurring at an unusually high temperature); its presence
also was considered to be responsible for the formation of lattice defects, which decreased the transmittances and the band
gaps. 相似文献
16.
V. Balek L. A. Pérez-Maqueda J. Poyato Z. Černý V. Ramírez-Valle I. M. Buntseva J. L. Pérez-Rodríguez 《Journal of Thermal Analysis and Calorimetry》2007,88(1):87-91
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. 相似文献
17.
Pradeepan Periyat K. V. Baiju P. Mukundan P. Krishna Pillai K. G. K. Warrier 《Journal of Sol-Gel Science and Technology》2007,43(3):299-304
Nanocrystalline sol–gel derived titania doped with ceria (1, 2, 5 and 10-mole%) has been prepared from titanyl oxysulphate.
The titania doped with 5-mole% CeO2 after calcining to 500 °C, possesses specific surface area of 97 m2 g−1 and has anatase phase stability up to 900 °C. Moreover it retains a surface area of 37 m2 g−1 at 700 °C. In comparison, the undoped calcined material has anatase stability only up to 700 °C and specific surface area
only 48 m2 g-1 and 6 m2 g-1 at 500 °C and 700 °C, respectively. The diffuse reflectance spectra show that, as the cerium content increases, the absorption
undergoes a red shift and reaches the visible range. The exceptionally high phase stability, crystallinity and high surface
area are due to the extremely fine particle size and effective doping achieved by the specific synthesis method. The results
based on X-ray diffraction, specific surface area and diffuse reflectance spectra indicated that the maximum threshold limit
of doping is up to a value of 5-mole%. 相似文献
18.
Summary The chromatographic properties of titania have been compared with those of zirconia and alumina, by comparison of their relative
Lewis acidities whenp-substituted benzoic acids were chromatographed with aqueous mobile phases. The retention behavior ofp-substituted benzoic acids on titania was found to be similar to that on zirconia; the slopes of plots of retention factors
against solute pK
a were approximately parallel for all pH values and the slopes obtained were similar to the average slope for zirconia. The
shapes of solute peaks on titania were more symmetrical than on alumina and zirconia. The effect of calcination temperature
on the chromatographic properties of titania was examined by use of titania prepared at different temperatures. The results
obtained clearly showed that the preparation temperature affected the chromatographic properties of titania. It seemed, for
example, that titania dried at 40°C behaved as a cation-exchanger, titania heated at 200°C behaved as an amphoteric exchanger,
and titania calcined at 600°C behaved as an anion-exchanger in the pH range 4.1–6.5 It was found that the control of the preparation
temperature enabled us to make effective use of titania. 相似文献
19.
N-doped TiO2 has been prepared by use of sol–gel systems containing titanium alkoxide, with nitric acid as the nitrogen source. The time
needed for gelation of the systems was drastically reduced by ultrasonic irradiation. The peaks assigned to the nitrate and
nitrous ions were observed by FT-IR measurement during the sol–gel reaction. The N-doping was confirmed by the observation
of N–O peaks in the XPS spectrum of the sample heated at 400 °C. The nitrate ion acted as an oxidizer of the ethanol solvent
and titanium species. The TiO2 became doped with nitrogen oxide species as a result of reduction of nitrate ion incorporated into the dried gel samples.
These results indicated that the added nitric acid was reduced during the sol–gel transition and heating process, and the
resulting NO species were situated in the titania networks. The UV and visible photocatalytic activity of the samples was
confirmed by the degradation of trichloroethylene. 相似文献
20.
Carina Gargori García Roberto Galindo Llorach Mario Llusar Vicent Maria Angeles Tena Gómez Guillermo Monrós Tomás Jose A. Badenes March 《Journal of Sol-Gel Science and Technology》2009,50(3):314-320
Glasses on SiO2–CaO–ZnO–B2O3–K2O–Al2O3 oxide system modified by addition of titania (0, 3, 5, 12, and 20% w) have been prepared by sol–gel method. The obtained
gels were aged, dried and fired at 600 °C/1 h in order to stabilise the glass. The resulting fired powders were characterised
by UV–Vis–NIR spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD).
Their photocatalytic capacity on the degradation of Orange II dye has been studied. The XRD and TEM studies indicate that
system becomes amorphous with a nanostructured microstructure. From UV–Vis–NIR results the band gap calculated is around 3.5 eV
for all modified glasses. Photoactivity of powders depends on amount of titania in glass composition and the specific surface
area of prepared samples. The sample with highest surface area and lowest addition of titania (3% w sample) shows similar
activity than commercial anatase used as reference. 相似文献