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1.
A. Parvathy Rao A. Venkateswara Rao Uzma K. H. Bangi 《Journal of Sol-Gel Science and Technology》2008,47(1):85-94
The experimental results on the preparation of low thermal conductivity and transparent ambient pressure dried silica aerogels
with the sodium silicate solution, TMCS silylating agent with methanol, isopropyl alcohol, hexane and xylene solvents, are
reported. This study is focussed on the effect of preparation conditions such as varying the number of preparation steps,
pH of the hydrosol and hydrogel ageing temperature, for the production of the low thermal conductive silica aerogels and the
results are analysed. Density, thermal conductivity, % of optical transmission and contact angle of the aerogels were measured.
The Fourier Transform Infrared Spectroscopy (FTIR) studies revealed the presence of Si–C and C–H along with the Si–O–Si and
OH bonds and their intensities strongly depend on the processing steps, pH of the hydrosol and gel ageing temperature. The
UV–Visible spectra indicated the % of optical transmission of the aerogels decreased with increasing the number of processing
steps, increase in the pH of the hydrosol from 3 to 8 and decreased for ageing temperature up to 50 °C. Further increase in
temperature >50 °C, the % of optical transmission of the aerogels increased. The TGA-DTA data showed the thermal stability
of the aerogels with respect to hydrophobicity is 325 °C. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy
(SEM) analyses revealed the nanostructure of the aerogels. The porosity of the aerogels was studied using the pore size distribution.
Silica aerogels with low density (0.051 g/cc), low thermal conductivity (0.049 W/m K), optical transmission (65%), high hydrophobicity
(159°) and resistance to humid atmosphere >1 year was obtained in the present studies. 相似文献
2.
Thermal and chemical stability of Romanian bentonite 总被引:1,自引:0,他引:1
A. V. Ursu G. Jinescu F. Gros I. D. Nistor N. D. Miron G. Lisa M. Silion G. Djelveh A. Azzouz 《Journal of Thermal Analysis and Calorimetry》2011,106(3):965-971
Ca–bentonite originating from a Romanian deposit was leached in 0.5–8.0 M HCl solution at 90 °C for 4 h. This material was
fully characterized through BET, thermogravimetry, X-rays diffraction, and elemental analysis. The acid treatment at high
temperature altered the crystallinity, but produced an increase in the surface area and thermal stability. The resulting acid-treated
bentonite turned out to be an efficient adsorbent in both liquid and gaseous media. The changes of the clay mineral properties
were discussed in terms of structural modification of the bulk material and increase in the number of edge terminal aluminol
and silanol sites. The kinetic parameters of first dehydration step, reaction order (n), apparent activation energy (E
a) and pre-exponential factor (ln A) were calculated by the Freeman–Carroll method. 相似文献
3.
Preparation and characterization of zirconium titanate fibers with good high temperature performance
Zirconium titanate (ZT) precursor fibers were prepared via sol–gel technique by dry-spinning method using polyacetylacetonatozirconium
(PAZ) and tetrabutyl titanate (TBOT) as starting materials. PAZ and TBOT were added into methanol with vigorous stirring at
room temperature for 2 h and mixed together homogenously. The mixture came into being a new and complicated polymerization
system, and PAZ and TBOT were connected through –O– bridge forming the –O–Zr–O–Ti–O– linear chains. The evolutions from the
precursor fibers to polycrystalline oxide fibers were characterized by Fourier transform infrared (FT–IR) and thermal gravimetry/differential
thermal analysis (TG/DTA). The surface of the ZT fibers was smooth, dense in cross-section without cracks by scanning electronic
spectroscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The size of the nanocrystals was less than 50 nm and arranged
compactly by atomic force microscopy (AFM). The fibriform was still kept and the size of the grains was up to 400–500 nm due
to the grain growth with increasing temperature and the ZT fibers were with good high temperature performance. 相似文献
4.
DMSO-kaolinite complexes of low- and high-defect Georgia kaolinite (KGa-1 and KGa-2, respectively) were investigated by thermo-XRD-analysis.
X-ray patterns showed that DMSO was intercalated in both kaolinites with a d(001)-value of 1.11 nm (type I complex). The samples were gradually heated up to 170°C and diffracted by X-ray at room-temperature.
With the rise in temperature, due to the thermal evolution of the guest molecules, the relative intensity of the 1.11 nm peak
decreased and that of the 0.72 nm peak (neat kaolinite) increased indicating that the fraction of the non-intercalated tactoids
increased. The 1.11 peak disappeared at 130–140°C. During the thermal treatment of both complexes two additional peaks appeared
at 110 and 120°C, respectively, with d-values of 0.79–0.94 and 0.61–0.67 nm in DMSO-KGa-1 and 0.81–0.86 and 0.62–0.66 nm in DMSO-KGa-2, indicating the formation
of a new phase (type II complex). The new complex was obtained by the dehydration of type I complex and was composed of intercalated
DMSO molecules which did not escape. The new peaks disappeared at 150–160°C indicating the complete escape of DMSO. 相似文献
5.
F. Yakuphanoglu A. Karadağ M. Şekerci 《Journal of Thermal Analysis and Calorimetry》2006,86(3):727-731
Thermal properties of the single crystals have been investigated by
thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques.
The thermodynamic parameters such as activation energy and enthalpy and thermal
stability temperature of the samples were calculated from the differential
thermal analysis (DTA) and TG data. The activation energies for first peak
of DTA curves were found as 496.65 (for Cd–Pd) and 419.37 kJ mol–1
(for Zn–Pd). For second peak, activation energies were calculated 116.56
(for Cd–Pd) and 173.96 kJ mol–1 (for
Zn–Pd). The thermal stability temperature values of the Cd–Pd
and Zn–Pd compounds at 10°C min–1
heating rate are determined as approximately 220.7 and 203°C, respectively.
The TG results suggest that thermal stability of the Cd–Pd complex is
higher than that of the Zn–Pd complex. 相似文献
6.
Arturo Rodriguez Mohini Sain Robert Jeng 《Journal of Thermal Analysis and Calorimetry》2009,98(1):317-323
The thermal behavior of modified starches (MS) produced by biosynthetic pathway is described based on a comparative analysis
with native starches (NS). MS were produced by fermentation in presence of Ophiostoma spp. cultures. Thermogravimetric analysis (TG) with successive derivatives (DTG) and differential scanning calorimetry (DSC)
were used for this study. NS results showed a single peak dominating both the TG (DTG) and DSC plots. A double thermal transition
event was detected in samples of MS. The procedural decomposition temperature (T
i–T
f; lowest onset temperature of initial and final mass change) was carried out within a narrow interval of temperatures for
NS (610–640 °C). This interval could not be reached within the 1,000 °C range in MS. Residues higher than 10% were recorded
for MS at this temperature. The presence of the double thermal transition in MS is discussed. 相似文献
7.
Aouad A. Bilali L. Benchanâa M. Mokhlisse A. 《Journal of Thermal Analysis and Calorimetry》2002,67(3):733-743
The natural phosphate and its demineralization products from Moroccan deposit were pyrolysed in a thermogravimetric analyser
(TG) to examine the influence of the heating rate and mineral matter on their thermal decomposition. The heating rates investigated
in the TG were 5–100°C min−1 to final temperature of 1200°C. The integral method was used in the analysis of the TG to determine the kinetic parameters.
It has been found that for the natural phosphate and corresponding kerogen analysed in the TG, the increase of the heating
rate shifts the maximum rate loss to higher temperature. A first order reaction was found to be adequate for pyrolysis in
the range 150–600°C which was attributed to kerogen decomposition. In addition, the results indicate that the removal of mineral
matter affected the kinetic parameters found for kerogen in the natural phosphate.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Chourashiya M. G. Bhardwaj S. R. Jadhav L. D. 《Journal of Solid State Electrochemistry》2010,14(10):1869-1875
Solid oxide fuel cells (SOFCs) with comparably low operating temperature play a critical role in its commercialization and
reliability by allowing low-cost fabrication and a promised longer life. Recently, 10%Gd-doped ceria (GDC) has revealed its
importance as solid electrolytes for intermediate temperature SOFCs. Additionally, if GDC is employed in thin film form, rather
higher ionic conductivity at further lower temperatures can be obtained and thereby allowing its use in low temperature SOFC.
In the present investigation, the preparative parameters of spray pyrolysis technique (SPT) were optimized to deposit dense
and adherent films of GDC on ceramic substrate. NiO–GDC was used as ceramic substrate, which also acts as a precursor composite
anode for GDC-based SOFCs. Prepared half cells (GDC/NiO–GDC) were characterized using XRD, SEM, and electrochemical impedance
spectroscopy. The surface and fractal SEM observations of post heat-treated (at 1,000 °C) GDC/NiO–GDC structure revealed that
GDC films were uniform in thickness with improved adherence to substrate. The relative density of post heat-treated films
was of the order of 96%, which was attributed to the presence of nano-granules in the thin films. Maximum thickness of the
GDC film prepared with optimized preparative parameters (in single run) was of the order of 13 μm. Fractal SEM of post heat-treated
GDC/NiO–GDC system showed homogenous interface, which was further analyzed by electrochemical impedance spectra and found
that it does not affect electrical properties of structure significantly. 相似文献
9.
Prieto A Zuloaga O Usobiaga A Etxebarria N Fernández LA 《Analytical and bioanalytical chemistry》2008,390(2):739-748
A method for the determination of polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs) in water samples
is proposed. The method involving stir bar sorptive extraction (SBSE) and thermal desorption followed by gas chromatography
coupled with mass spectrometry was optimised using statistical design of experiments. In the first place, the influence of
different polydimethylsiloxane stir bars was studied. A Plackett–Burman design was chosen to estimate the influence of five
factors on the efficiency of the SBSE process: desorption time (5–10 min), desorption temperature (250–300 °C), desorption
flow (50–100 mL min−1), cryofocusing temperature (-130 to 40 °C) and vent pressure (0–12.8 psi). Afterwards, two central composite designs were
used to find the optimal process settings that were applied to the optimisation of both desorption and extraction efficiency.
In the case of the desorption parameters, long desorption times (10 min) and desorption flows lower than 70 mL min-1 yielded the best signals for the majority of compounds. However, different behaviour among the analytes was observed for
the vent pressure and we decided to fix it at an intermediate value (7 psi). In the case of extraction parameters, the sample
volume and the addition of NaCl did not have a significant effect, while the addition of methanol yielded better extraction
responses. Remarkable recovery (82–106%) and repeatability (less than 18%) were attained. Furthermore, excellent regression
coefficients (r
2 = 0.991–0.999) and low detection limits (1.1–6.0 ng L−1) were also achieved for the congeners studied. The proposed method was applied to the analyses of PBDEs and PBBs in waters
from the Basque Country, Spain. 相似文献
10.
Zou Hantao Yi Changhai Wang Luoxin Liu Hongtao Xu Weilin 《Journal of Thermal Analysis and Calorimetry》2009,97(3):929-935
Thermogravimetric (TG), differential thermal analysis (DTA) and thermal degradation kinetics, FTIR and X-ray diffraction (XRD)
analysis of synthesized glycine–montmorillonite (Gly–MMT) and montmorillonite bound dipeptide (Gly–Gly–MMT) along with pure
Na–MMT samples have been performed. TG analysis at the temperature range 25–250 °C showed a mass loss for pure Na–MMT, Gly–MMT
and Gly–Gly–MMT of about 8.0%, 4.0% and 2.0%, respectively. DTA curves show the endothermic reaction at 136, 211 and 678 °C
in pure Na–MMT whereas Gly–MMT shows the exothermic reaction at 322 and 404 °C and that of Gly–Gly–MMT at 371 °C. The activation
energies of the first order thermal degradation reaction were found to be 1.64 and 9.78 kJ mol−1 for Gly–MMT and Gly–Gly–MMT, respectively. FTIR analyses indicate that the intercalated compounds decomposed at the temperature
more than 250 °C in Gly–MMT and at 250 °C in Gly–Gly–MMT. 相似文献
11.
Je Kyun Lee George L. Gould Wendell Rhine 《Journal of Sol-Gel Science and Technology》2009,49(2):209-220
Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and
supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure
by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity
of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and
equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO2) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity
values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature
to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity
values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property
and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated
with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications
and as a thermal insulation component of spacesuits. 相似文献
12.
Cornelia Marinescu Ancuta Sofronia Cristina Rusti Roxana Piticescu Viorel Badilita Eugeniu Vasile Radu Baies Speranta Tanasescu 《Journal of Thermal Analysis and Calorimetry》2011,103(1):49-57
The aim of the article is to investigate the influence of particle size on titanium dioxide phase transformations. Nanocrystalline
titanium dioxide powder was obtained through a hydrothermal procedure in an aqueous media at high pressure (in the range 25–100 atm)
and low temperature (≤200 °C). The as-prepared samples were characterized with respect to their composition by ICP (inductive
coupled plasma), structure and morphology by XRD (X-ray diffraction), and TEM (transmission electron microscopy), thermal
behavior by TG (thermogravimetry) coupled with DSC (differential scanning calorimetry). Thermal behavior of nanostructured
TiO2 was compared with three commercial TiO2 samples. The sequence of brookite–anatase–rutile phase transformation in TiO2 samples was investigated. The heat capacity of anatase and rutile in a large temperature range are reported. 相似文献
13.
We studied thermal transitions and physical stability
of oil-in-water emulsions containing different milk fat compositions, arising
from anhydrous milk fat alone (AMF) or in mixture (2:1 mass ratio) with a
high melting temperature (AMF–HMT) or a low melting temperature (AMF–LMT)
fraction. Changes in thermal transitions in bulk fat and emulsion samples
were monitored by differential scanning calorimetry (DSC) under controlled
cooling and reheating cycles performed between 50 and –45°C (5°C
min–1). Comparison between bulk fat samples
and emulsions indicated similar values of melting completion temperature,
whereas initial temperature of fat crystallization (Tonset)
seemed to be differently affected by storage temperature depending on triacylglycerols
(TAG) composition. After storage at 4°C, Tonset
values were very similar for emulsified and non-emulsified AMF–HMT blend,
whereas they were lower (by approx. 6°C) for emulsions containing AMF
or mixture of AMF–LMT fraction. After storage at –30°C, Tonset values of re-crystallization
were higher in emulsion samples than in bulk fat blends, whatever the TAG
fat composition. Light scattering measurements and fluorescence microscopic
observations indicated differences in fat droplet aggregation-coalescence
under freeze-thaw procedure, depending on emulsion fat composition. It appeared
that under quiescent freezing, emulsion containing AMF–LMT fraction
was much less resistant to fat droplet aggregation-coalescence than emulsions
containing AMF or AMF–HMT fraction. Our results indicated the role of
fat droplet liquid-solid content on emulsion stability. 相似文献
14.
Sharif Abdullah Al-Mamun Yasunori Tanaka Yoshihiko Uesugi 《Plasma Chemistry and Plasma Processing》2010,30(1):141-172
Here the authors developed a two-dimensional two-temperature chemical non-equilibrium (2T-NCE) model of Ar–CO2–H2 inductively coupled thermal plasmas (ICTP) around atmospheric pressure (760 torr). Assuming 22 different particles in this
model and by solving mass conservation equations for each particle, considering diffusion, convection and net production terms
resulting from 198 chemical reactions, chemical non-equilibrium effects were taken into account. Species density of each particle
or simply particle composition was also derived from the mass conservation equation of each one taking the non chemical equilibrium
effect into account. Transport and thermodynamic properties of Ar–CO2–H2 thermal plasmas were self-consistently calculated using the first order approximation of the Chapman–Enskog method at each
iteration point implementing the local particle composition and temperature. Calculations at reduced pressure (500 and 300 torr)
were also done to investigate the effect of pressure on non-equilibrium condition. Results obtained by the present model were
compared with results from one temperature chemical equilibrium (1T-CE) model, one-temperature chemically non equilibrium
(1T-NCE) model and finally with 2T-NCE model of Ar–N2–H2 plasmas. Investigation shows that consideration of non-chemical equilibrium causes the plasma volume radially wider than
CE model due to particle diffusion. At low pressure with same input power, presence of diffusion is relatively stronger than
at high pressure. Comparison of present reactive model with non-reactive Ar–N2–H2 plasmas shows that maximum temperature reaches higher in reactive C–H–O molecular system than non-reactive plasmas due to
extra contribution of reaction heat. 相似文献
15.
Gjurova K. Bogdanov B. Zagortcheva M. Uzov Chr. 《Journal of Thermal Analysis and Calorimetry》1999,55(1):77-84
The influence of a wide range of concentrations (0.1–40 mass%) of Na(K)I on both the thermal behaviour and melt indexes of
polyoxyethylene (POE) in a broad temperature interval was investigated by combined dynamic thermal analysis and with an extrusion
plastometer.
It was found that addition of 2–5 mass% of alkali salts resulted in the optimum thermal stability of POE and increased the
melt index of high molecular POE, regardless of the mode of introduction of the additives into the polymer.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
The size effect of silica nanoparticles (SiO2) on thermal decomposition of poly(methylmethacrylate) (PMMA) was investigated by the controlled rate thermogravimetry. Thermal
degradation temperature of PMMA–SiO2 composites depended on both fraction and size of SiO2, the thermal degradation temperature of 23 nm (diameter) SiO2–PMMA (6.1 wt%) was 13.5 °C higher than that of PMMA. The thermal stabilities of 17 nm SiO2–PMMA (3.2 wt%) and 13 nm SiO2–PMMA (4.8 wt%) were 21 and 23 °C, respectively, higher than that of PMMA without SiO2. The degree of degradation improvement was increased linearly with the surface area of SiO2. The number of surface hydroxyl group in unit volume of SiO2 particle increased with increasing the specific surface area of SiO2, and the interaction between hydroxide group of SiO2 and carbonyl group of PMMA had an important role to improve the thermal stability of PMMA. 相似文献
17.
In situ
developments of platelike spodumene–diopside grains were obtained by
controlled devitrification of the complex system Li2O–CaO–MgO–Al2O3–SiO2 glass. The crystallization mechanisms
of spodumene–diopside glass were measured by isothermal and non-isothermal
processes using classical and differential thermal analysis techniques. The
Avrami constant n was 2.0–2.1, indicating
two-dimensional crystal growth and platelike grains. The crystalline phases
precipitated first were high-quartzs.s., then transformed
to β-spodumene and diopside. The Flexural strength, fracture toughness
and thermal shock resistance (in 20°C water) increased from 145 MPa, 1.3
MPa m1/2, 800°C (pure spodumene) to 197 MPa,
2.9 MPa m1/2 and 920°C (spodumene–diopside)
with low thermal expansion coefficient (from 3∼9·10–7
to 11.8·10–7 K–1).
This mean in situ developments of platelike spodumene–diopside grains
reinforced the low thermal expansion coefficient glass-ceramics. 相似文献
18.
19.
M. Rieu P. Lenormand F. Ansart F. Mauvy J. Fullenwarth M. Zahid 《Journal of Sol-Gel Science and Technology》2008,45(3):307-313
In this work, we propose the preparation of a duplex anodic layer composed of both a thin (100 nm) and a thick film (10 μm)
with Ni–YSZ material. The support of this anode is a metallic substrate, which is the interconnect of the SOFC unit cell.
The metallic support limits the temperature of thermal treatment at 800 °C to keep a good interconnect mechanical behaviour
and to reduce corrosion. We have chosen to elaborate anodic coatings by sol–gel route coupled with dip-coating process, which
are low cost techniques and allow working with moderate temperatures. Thin films are obtained by dipping interconnect substrate
into a sol, and thick films into an optimized slurry. After thermal treatment at only 800 °C, anodic coatings are adherent
and homogeneous. Thin films have compact microstructures that confer ceramic protective barrier on metal surface. Further
coatings of 10 μm thick are porous and constitute the active anodic material. 相似文献
20.
S. C. Mojumdar L. Raki N. Mathis K. Schimdt S. Lang 《Journal of Thermal Analysis and Calorimetry》2006,85(1):119-124
A non-ionic polymer (poly(vinyl
alcohol) (PVA)) has been incorporated into the inorganic layers of calcium
silicate hydrate (C–S–H) during precipitation of quasicrystalline
C–S–H from aqueous solution. C–S–H and a C–S–H-polymer
nanocomposite (C–S–HPN) material were synthesized and characterized
by X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS), 29Si
magic angle spinning nuclear magnetic resonance (29Si
MAS NMR) and 13C cross-polarization nuclear magnetic
resonance (13C CP NMR) spectroscopy, atomic force
microscopy (AFM), thermal conductivity, thermogravimetric analysis (TG) and
differential thermal analysis (DTA). Thermal conductivity of PVA, C–S–H
and C–S–HPN material was studied in the temperature range 25–50°C.
C–S–HPN materials exhibited the highest thermal conductivity at
25 and 50°C. The thermal conductivity increases from 25 to 50°C are
7.03, 17.46 and 14.85% for PVA, C–S–H and C–S–HPN
material, respectively. Three significant decomposition temperature ranges
were observed on the TG curve of C–S–HPN material. 相似文献