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1.
Yuanjing Cui Guodong Qian Lujian Chen Zhiyu Wang Minquan Wang 《Journal of Sol-Gel Science and Technology》2008,47(3):252-259
A series of organically modified sol–gel films with various acceptor groups were prepared and characterized. All the chromophores
exhibit much larger microscopic optical nonlinearity compared with the classical chromophore DR1 in solvatochromic measurement. Using in situ second harmonic generation (SHG) technique, the optimal poling temperatures
(T
opt) for sol–gel films were obtained. The second harmonic coefficients (d
33) of hybrid films at the wavelength of 1,064 nm were in the range of 50.1–70.3 pm/V after corona poling under their T
opt. The NLO stabilities of these poled films were also investigated by tracing the d
33 value as a function of temperature and time. One of the hybrid films, which was prepared from chromophore 2,4-dinitro-4′-(N,N-dihydroxyethyl) aminoazobenzene exhibited a combination of large optical nonlinearity and high NLO stability. Furthermore,
the effects of molecular structure on the NLO property and thermal stability of the hybrid films were also discussed. 相似文献
2.
The present work demonstrates application of electrical conductivity (σ)–temperature (T) cycles to investigate thermal properties viz., crystallization and glass transition kinetics in AgI–Ag2O–V2O5–MoO3 superionic glasses. The σ–T cycles are carefully performed at various heating rates, viz., 0.5, 1, 3, 5, and 7 K/min. The conductivity in Ag+ ion conducting glasses exhibit anomalous deviation from Arrhenius behavior near glass transition temperature (T
g) followed by a drastic fall at crystallization (T
c). The temperature corresponding to maximum rate of crystallization (T
p) is obtained from the derivative of σ–1/T plots. With increasing heating rates, the characteristic temperatures (T
g, T
p) are found to be shifting monotonically toward higher temperatures. Thus, activation energy of structural relaxation E
s, crystallization E
c and other thermal stability parameters have been obtained from σ–T cycles using Kissinger equation and Moynihan formulation. For a comparative study, these kinetics parameters have also been
calculated from differential scanning calorimetry plots. The parameters obtained from both the methods are found to be comparable
within experimental error. 相似文献
3.
Hélio Salvio Neto Jivaldo do Rosário Matos 《Journal of Thermal Analysis and Calorimetry》2011,103(1):393-399
In this work, TG/DTG and DSC techniques were used to the determination of thermal behavior of prednicarbate alone and associated
with glyceryl stearate excipient (1:1 physical mixture). TG/DTG curves obtained for the binary mixture showed a reduction
of approximately 37 °C to the thermal stability of drug (
T\textdm/\textdt = 0 \textDTG\textMax T_{{{\text{d}}m/{\text{d}}t = 0\,{\text{DTG}}}}^{\text{Max}} ). The disappearance of stretching band at 1280 cm−1 (νas C–O, carbonate group) and the presence of streching band with less intensity at 1750 cm−1 (νs C–O, ester group) in IR spectrum obtained to the binary mixture submitted at 220 °C, when compared with IR spectrum of drug
submitted to the same temperature, confirmed the chemical interaction between these substances due to heating. Kinetics parameters
of decomposition reaction of prednicarbate were obtained using isothermal (Arrhenius equation) and non-isothermal (Ozawa)
methods. The reduction of approximately 45% of activation energy value (E
a) to the first step of thermal decomposition reaction of drug in the 1:1 (mass/mass) physical mixture was observed by both
kinetics methods. 相似文献
4.
Thermodynamic stability of CdMoO4 was determined
by measuring the vapor pressures of Cd and MoO3 bearing
gaseous species. Th vaporization reaction could be described as CdMoO4(s)+MoO2(s)
=Cd(g)+2/n(MoO3)n
(n=3, 4 and 5). The vapor pressures of
the cadmium (p
Cd)
and trimer (p
(MoO3)3)
measured in the temperature range 987≤T/K≤1111
could be expressed, respectively, as ln (p
Cd/Pa)
= –32643.9/T+29.46±0.08 and
ln(p
(MoO3)3/Pa) = –32289.6/T+29.28±0.08. The standard molar Gibbs free
energy of formation of CdMoO4(s),
derived from the vaporization results could be expressed by the equations:
°f
G
CdMoO4
(s)
0= –1002.0+0.267T±14.5 kJ mol–1
(987≤T/K≤1033) and °f
G
CdMoO4 (s)
0
= –1101.9+0.363T±14.4 kJ mol–1
(1044≤T/K≤1111). The standard enthalpy
of formation of CdMoO4(s)
was found to be –1015.4±14.5 kJ mol–1
. 相似文献
5.
A. I. Kazakov Yu. I. Rubtsov G. B. Manelis L. P. Andrienko 《Russian Chemical Bulletin》1997,46(12):2015-2020
Kinetic regularities of thermal decomposition of dinitramide in aqueous and sulfuric acid solutions were studied in a wide
temperature range. The rate of the thermal decomposition of dinitramide was established to be determined by the rates of decomposition
of different forms of dinitramide as the acidity of the medium increases: first, N(NO2)− anions, then HN(NO2)2 molecules, and finally, protonated H2N(NO2)2
+ cations. The temperature dependences of the rate constants of the decomposition of N(NO2)− (k
an) and HN(NO2)2 (k′ac) and the equilibrium constant of dissociation of HN(NO2)2 (K
a) were determined:k
an=1.7·1017 exp(−20.5·103/T), s−1,k′ac=7.9·1016 exp(−16.1·103/T), s−1, andK
a=1.4·10 exp(−2.6·103/T). The temperature dependences of the decomposition rate constant of H2N(NO2)2
+ (k
d) and the equilibrium constant of the dissociation of H2N(NO2)2
+ (K
d) were estimated:k
d=1012 exp(−7.9·103/T), s−1 andK
d=1.1 exp(6.4·103/T). The kinetic and thermodynamic constants obtained make it possible to calculate the decomposition rate of dinitramide solutions
in a wide range of temperatures and acidities of the medium.
In this series of articles, we report the results of studies of the thermal decomposition of dinitramide performed in 1974–1978
and not published previously.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2129–2133, December, 1997. 相似文献
6.
Nurhidayatullaili Muhd Julkapli Hazizan Md. Akil Zulkifli Ahmad 《Journal of Thermal Analysis and Calorimetry》2012,107(1):365-376
The 4,4,-oxydiphthalic anhydride-chitosan (ODAC) filler at composition of 2–12 wt/v% was selected to reinforce the Cs matrix
by solution casting method. The thermal properties of the bio-composites were then evaluated by thermogravimetry analysis,
differential scanning calorimetry, and dynamic mechanical analysis. The addition of ODAC filler in Cs matrix up to 10 wt/v%
had increased the thermal stability of the bio-composites by increasing the thermal degradation (T
d) and glass transition temperature (T
g) of the bio-composites. Good interfacial bonds of electrostatic interactions and inter-hydrogen bonds of the bio-composite
components significantly influenced the thermal properties of the bio-composites. 相似文献
7.
The delay time τ has been measured for the formation of the ·OH radical in igniting hydrogenoxygen mixtures diluted with argon (79–97%). The experiments have been carried out under incident
shock wave conditions at temperatures of 900–3000 K, pressures of 0.5–2.5 atm, and H2/O2 ratios of 0.2–20. The dependence of τ on the pressure P
s of the stoichiometric part of the combustible mixture (2H2-O2) has been investigated for different mixture compositions. Under the above conditions, τ depends practically linearly on
1/P
s at P
s = 0.02−0.1 atm, irrespective of the mixture composition. This allows the measured τ data to be converted to one quantity,
τP
s. The temperature dependence of τP
s in the P
s range from 0.02 to 0.1 atm is Arrhenius-like. For the hydrogen-rich mixtures (H2/O2 = 2–20), this dependence appears as τP
s= 0.057 + 0.0256exp(7470/T) μs atm; for the lean mixtures (H2/O2 = 0.125–1), τP
s = 0.021 + 0.0069exp(7470/T) μs atm. The length of the shock-heated gas plug in the incident shock wave poses limitations on the ignition delay time
measurements at T < 900 K. 相似文献
8.
Thermal behavior of xGa2O3–(50 − x)PbO–50P2O5 (x = 0, 10, 20, and 30 mol.% Ga2O3) and xGa2O3–(70 − x)PbO–30P2O5 (x = 0, 10, 20, 30, and 40 mol.% Ga2O3) glassy materials were studied by thermo-mechanical analysis (TMA) and differential thermal analysis (DTA). Replacement of
PbO for Ga2O3 is accompanied by increasing glass-transition temperature (263 ≤ T
g/°C ≤ 535), deformation temperature (363 ≤ T
d/°C ≤ 672), crystallization temperature (396 ≤ T
c/°C ≤ 640) and decreasing of coefficient of thermal expansion (5.1 ≤ CTE/ppm K−1 ≤ 16.7). Values of Hruby parameter were determined (0.1 ≤ K
H ≤ 1.3). The thermal stability of prepared glasses increases with increasing of concentration of Ga2O3. 相似文献
9.
Poly(p-arylene sulfide ketone/Schiff base) copolymers(PASK/SB) were prepared by solution polycondensation of 4,4’-diflurobenzophenone(DFBP) and N-phenyl(4,4’-diflurodiphenyl) ketimine(DFBI) with sodium sulfide in the presence of sodium hydroxide under normal pressure.Elemental analyses,FT-IR,NMR,DSC,TGA and XRD were used to characterize the resultant copolymers.It was found that the copolymers had good thermal properties with glass transition temperature(T_g) of 155.0-172.0°C,melting temperature(T_m) of 298-344°C,5%weight loss temperatures(T_d) of 471.0-501.5°C.These copolymers were almost amorphous with the content of DFBI beyond 30%.The polymer with 100% DFBI had excellent solubility,and it could dissolve in some solvents such as tetrahydrofuran(THF) and N-methyl-2- pyrrolidone(NMP).The processability of polymers was improved.Meantime the viscosity of PASK made from hydrolysis of PASK/SB(H-PASK/SB) was greatly improved from 0.135 dL/g to 0.605 dL/g. 相似文献
10.
C. -H. Tang 《Journal of Thermal Analysis and Calorimetry》2007,89(3):941-951
The thermal properties of buckwheat (Fagopyrum esculentum Moench) proteins with different lipid contents (2.5, 6.5 and 17.8%) were studied by differential scanning calorimetry (DSC)
under various medium conditions. From DSC curves, many DSC characteristics including denaturation temperature (T
d), enthalpy change (ΔH) and the width at half peak height (ΔT
1/2) of endothermic peaks were obtained and evaluated. The DSC curves of various buckwheat proteins (BWPs) in the 0.05 M phosphate
buffer (pH 7.0) showed a major endotherm at about 102°C and a minor endotherm at about 80°C, attributed to thermal transitions
of 13S and 8S globulins, respectively. T
d and ΔH of the globulins of BWPs were independent of their lipid contents, while the presence of high lipid content (17.8%) to some
extent increased the ΔT
1/2. The progressive increase in T
d of 13S globulins with increase in NaCl concentration, suggests a more compact conformation with higher thermal stability.
The influence of chaotropic salts on the DSC characteristics of 13S globulins was also independent of their lipid contents.
Thermal analysis of the 13S globulins in the presence of protein perturbants (including urea, sodium dodecyl sulfate, ethylene
glycol, dithiothreitol and N-ethylmaleimide) indicated that hydrophobic and hydrogen bondings are the major interactions for
stabilizing protein conformation of buckwheat 13S globulins and the SS-SH interchange also attributes to the stabilization
of the protein conformation. 相似文献
11.
《印度化学会志》2021,98(10):100175
Carboxyl-terminated hyper-branched polyester is extensively used as high exhaustion chrome tanning auxiliary owing to its strong coordination ability with trivalent chrome. Owing to lower electronegativity of N than O, the coordination ability with trivalent chrome for hyper-branched polyamide is stronger than polyester. Herein, in this paper, an amino-terminated hyper-branched polyamide (HBPN) is synthesized and used as high exhaustion chrome in tanning of pickling pigskin (HBPN–Cr). The effects of utilization of HBPN in denaturation temperature, shrinkage temperature, chrome uptake, and microstructure structure of wet-blue leather are studied. Moreover, the anti-oxidation stability of wet-blue leather is preliminary studied by heat treatment. The results show that incorporation of 1% HBPN in pickling process can significantly improve chrome uptake to 83.32%. The hydrothermal stability of wet-blue leather is improved due to the formation of higher crosslinking degree of collagen fibers. In addition, for the wet-blue leather without unsaturated fatliquoring agent, through heat treatment, hexavalent chrome does not appear after 24 h heat treatment. On the contrary, the chrome complex changes from hydroxyl copolymerization to more stable oxygen copolymerization or chrome oxide for C–Cr and HBPN-Cr tanned leather, respectively. These results will build a data support for the further study of hyper-branched polymer chrome tanning auxiliaries. 相似文献
12.
K. A. Aly A. Dahshan Yasser B. Saddeek 《Journal of Thermal Analysis and Calorimetry》2010,100(2):543-549
The present paper reports on the effect of MoO3 on the glass transition, thermal stability and crystallization kinetics for (40PbO–20Sb2O3–40As2O3)100−x
–(MoO3)
x
(x = 0, 0.25, 0.5, 0.75 and 1 mol%) glasses. Differential scanning calorimetry (DSC) results under non-isothermal conditions
for the studied glasses were reported and discussed. The values of the glass transition temperature (T
g) and the peak temperature of crystallization (T
p) are found to be dependent on heating rate and MoO3 content. From the compositional dependence and the heating rate dependence of T
g and T
p, the values of the activation energy for glass transition (E
g) and the activation energy for crystallization (E
c) were evaluated and discussed. Thermal stability for (40PbO–20Sb2O3–40As2O3)100−x
–(MoO3)
x
glasses has been evaluated using various thermal stability criteria such as ΔT, H
r
, H
g and S. Moreover, in the present work, the K
r(T) criterion has been considered for the evaluation of glass stability from DSC data. The stability criteria increases with
increasing MoO3 content up to x = 0.5 mol%, and decreases beyond this limit. 相似文献
13.
N. A. Halim Z. A. Ibrahim A. B. Ahmad 《Journal of Thermal Analysis and Calorimetry》2010,102(3):983-988
The high potential for intercalations by water and various guest molecules is induced by the exchangeable cation inside Ca2+–Montmorillonite gallery. XRD peak for Mon at 2θ = 6.04° (d
001 = 1.462 nm) shows the structural effect on the clay gallery influenced by the intercalated water layers. Further increases
in the gallery height are observed with the intercalation of octadecyl ammonium cations in OMON (d
001 = 1.840 nm) and ENR-50 matrix chains in CENR-50 (d
001 = 1.954 nm). DSC studies on the other hand reveal the thermal behaviors of intercalated molecules that are linked to the
exchangeable cations. The endothermic of Ca2+–Montmorillonite (H
Mon = 356.3 J/g) in low temperature range (30–100 °C) indicates the removal of free water and hydrogen bonded water molecules,
while the endothermic around 150 °C is related to the induced skeletal layer of water within Ca2+–Montmorillonite. The OMON endothermic (H
OMON = 47.0 J/g, T
m = 36.94 °C) tells that cation exchange had modified the water structures and content inside the renewed clay. The intercalation
of ENR-50 chains into OMON gallery reveals two endothermic with the T
m1 and T
m2 are at 86.24 and 113.80 °C, respectively. These T
ms confirm that the alkyl chain segment on octadecyl ammonium cation occupy the OMON interlayer space. 相似文献
14.
Shouhong Xu Junpei Yamanaka Isamu Miyata Masakatsu Yonese 《Colloid and polymer science》2007,285(8):899-906
Effects of denaturation and association of collagen on adsorption behavior were studied in various pH and temperature T by a quartz crystal microbalance QCM. The surface nanostructure, the adhesion force F
ad, and the local frictional coefficient μ of collagen were studied by an atomic force microscope AFM and a lateral force microscope LFM. Adsorptions of collagen were
Langmuir type in the regions of pH 3.0–5.8 and T = 25–50 °C. With increasing pH and T, adsorption mass Γ increased, and adsorbed fibrils increased in width. At interface, the association of collagen molecules in solution enhanced the formation of fibrils. The results of F
ad in the solution of pH 3.0 increased with increasing Γ and T but decreased in pH 5.8. The results of μ increased with increasing Γ and T, and those in pH 3.0, were much greater than those in pH 5.8. From comparing them with the results of bovine serum albumin
and sodium hyaluronate monolayer, we concluded that nonelectrostatic interactions and the softness of collagen layer contribute
primarily to F
ad and μ. 相似文献
15.
Glasses with compositions 60B2O3–40PbO, 60B2O3–40Bi2O3, and 60B2O3–30Bi2O3–10PbO have been prepared and studied by differential thermal analysis. The crystallization kinetics of the glasses was investigated
under non-isothermal conditions. From dependence of the glass transition temperature (T
g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the
crystallization process was determined. Thermal stability of these glasses were achieved in terms of the characteristic temperatures,
such as the glass transition temperature, T
g, the onset temperature of crystallization, T
in
, the temperature corresponding to the maximum crystallization rate, T
p, beside the kinetic parameters, K(T
g) and K(T
p). The results revealed that the 60B2O3–40PbO is more stable than the others. The crystallization mechanism is characterized for glasses. The phases at which the
glass crystallizes after the thermal process have been identified by X-ray diffraction. 相似文献
16.
V. N. Smirnov 《Kinetics and Catalysis》2011,52(2):166-169
The results of our experimental studies and an analysis of the published data on the rate constant for the reaction Fe + O2 = FeO + O in the forward (I) and reverse (−I) direction are reported. The data obtained in this work are described by the
expressions k
1 = 6.2 × 1014exp(−11100 K/T) cm3 mol−1 s−1 and k
−1 = 6.0 × 1013exp(−588 K/T) cm3 mol−1 s−1 (T = 1500–2500 K). The generalized expressions for the temperature dependences of these rate constants derived by combining
our results with the literature data can be presented as k
1 = 9.4 × 1014(T/1000)0.022exp(−11224 K/T) cm3 mol−1 s−1 (T = 1500–2500 K) and k
−1 = 1.8 × 1014(1000/T)0.37exp(−367 K/T) cm3 mol−1 s−1 (T = 200–2500 K). 相似文献
17.
M. V. Alonso M. Oliet J. C. Domínguez E. Rojo F. Rodríguez 《Journal of Thermal Analysis and Calorimetry》2011,105(1):349-356
Resol resins are used in many industrial applications as adhesives and coatings, but few studies have examined their thermal
degradation. In this work, the thermal stability and thermal degradation kinetics of phenol–formaldehyde (PF) and lignin–phenol–formaldehyde
(LPF) resol resins were studied using thermogravimetric analysis (TG) in air and nitrogen atmospheres in order to understand
the steps of degradation and to improve their stabilities in industrial applications. The thermal stability of samples was
estimated by measuring the degradation temperature (T
d), which was calculated according to the maximum reaction rate criterion. In addition, the ash content was determined at 800 °C
in order to compare the thermal stability of the resol resin samples. The results indicate that 30 wt% ammonium lignin sulfonate
(lignin derivative) as filler in the formulation of LPF resin improves the thermal stability in comparison with PF commercial
resin. The activation energies of degradation of two resol resins show a difference in dependence on mass loss, which allows
these resins to be distinguished. In addition, the structural changes of both resins during thermal degradation were studied
by Fourier transform infrared spectroscopy (FTIR), with the results indicating that PF resin collapses at 300 °C whereas the
LPF resin collapses at 500 °C. 相似文献
18.
A new method for the analysis of thermal desorption spectra is presented, based on the experimental peak maximum functions
for temperatureT
m(β) and pressureP
m(β) and a rigorous mathematical treatment. The resonant heating rate βr is determined, satisfyingT
m(βr)=T
r, whereT
r is the resonant temperature defined byA exp(−E
d/(RT
r))=1. Desorption energyE
d and frequency factorA can be determined simultaneously with relatively high robustness towards statistical experimental errors as demonstrated
by computer-simulated thermal desorption spectra. 相似文献
19.
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
20.
M. A. da Silva P. J. A. Sobral T. G. Kieckbusch 《Journal of Thermal Analysis and Calorimetry》2006,84(2):435-439
Differential scanning calorimetry (DSC) was used
to determine phase transitions of freeze-dried camu-camu pulp in a wide range
of moisture content. Samples were equilibrated at 25°C over saturated
salt solutions in order to obtain water activities (aw)
between 0.11–0.90. Samples with aw>0.90
were obtained by direct water addition. At the low and intermediate moisture
content range, Gordon–Taylor model was able to predict the plasticizing
effect of water. In samples, with aw>0.90,
the glass transition curve exhibited a discontinuity and T’g was practically constant (–58.8°C), representing the glass transition
temperature of the maximally concentrated phase(Tg
). 相似文献