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1.
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
2.
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
3.
4.
We have determined the parameters of the Arrhenius equation (E, log A) for reactions between
\textNO2+ {\text{NO}}_2^{+} ions and C3-C8 alkanes in HNO3–93 wt.% H2SO4 solutions at 277–353 K, and we have also estimated the activation parameters E
j
, log A
j
for secondary and tertiary C—H bonds of these alkanes. We show that the following compensation relations are satisfied: E = 2.3R βlog A + C with isokinetic temperature β = 360 ± 65 K, and also E
j
=2.3Rβ
j
log A
j
+ C
j
, for secondary C—H bonds, β2 =300 ± 60, and for tertiary C—H bonds, β3 =310 ± 50. 相似文献
5.
1. Results of thermodynamic and kinetic investigations for the different crystalline calcium carbonate phases and their phase
transition data are reported and summarized (vaterite: V; aragonite: A; calcite: C). A→C: T
tr=455±10°C, Δtr
H=403±8 J mol–1 at T
tr, V→C: T
tr=320–460°C, depending on the way of preparation,Δtr
H=–3.2±0.1 kJ mol–1 at T
tr,Δtr
H=–3.4±0.9 kJ mol–1 at 40°C, S
V
Θ= 93.6±0.5 J (K mol)–1, A→C: E
A=370±10 kJ mol–1; XRD only, V→C: E
A=250±10 kJ mol–1; thermally activated, iso- and non-isothermal, XRD
2. Preliminary results on the preparation and investigation of inhibitor-free non-crystalline calcium carbonate (NCC) are
presented. NCC→C: T
tr=276±10°C,Δtr
H=–15.0±3 kJ mol–1 at T
tr, T
tr – transition temperature, Δtr
H – transition enthalpy, S
Θ – standard entropy, E
A – activation energy.
3. Biologically formed internal shell of Sepia officinalis seems to be composed of ca 96% aragonite and 4% non-crystalline calcium carbonate.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Lang SM Claes P Neukermans S Janssens E 《Journal of the American Society for Mass Spectrometry》2011,22(9):1508-1514
Structural information on free transition metal doped aluminum clusters, Al
n
TM
+ (TM = Ti, V, Cr), was obtained by studying their ability for argon physisorption. Systematic size (n = 5 – 35) and temperature (T = 145 – 300 K) dependent investigations reveal that bare Al
n
+ clusters are inert toward argon, while Al
n
TM
+ clusters attach one argon atom up to a critical cluster size. This size is interpreted as the geometrical transition from
surface-located dopant atoms to endohedrally doped aluminum clusters with the transition metal atom residing in an aluminum
cage. The critical size, n
crit
, is found to be surprisingly large, namely n
crit = 16 and n
crit = 19 – 21 for TM = V, Cr, and TM = Ti, respectively. Experimental cluster–argon bond dissociation energies have been derived as function of cluster size from
equilibrium mass spectra and are in the 0.1–0.3 eV range. 相似文献
7.
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
8.
Glassy selenium matrix alloyed with up to 10% indium, namely Se0.95In0.05 and Se0.9In0.1, was prepared by the melt quenching technique. Differential thermal analysis (DTA) has been used to study the glass transition
kinetics of the two binary Se–In alloys in comparison with that of pure Se. DTA scans were recorded at different constant
heating rates (β = 1:20 °/min). The glass transition temperature (T
g) is found to be shifting to a higher value with increasing of both β and In-content. Such a configurationally response is related to the observed increase of the stability parameters accompanied
with the introduction of In into the Se matrix. The activation energy of glass transition (E
g) has been determined using two different non-isothermal models (Moynihan and Kissinger) where a good coincidence is obtained.
The compositional dependence (0:10% In) of all considered parameters is discussed in terms of the introduced structural matrix. 相似文献
9.
10.
J. Pablo Tomba Daniel Portinha Walter F. Schroeder Mitchell A. Winnik Willie Lau 《Colloid and polymer science》2009,287(3):367-378
This paper describes experiments that investigate the use of low glass transition temperature (T
g) latex particles consisting of oligomer to promote polymer diffusion in films formed from high molar mass polymer latex.
The chemical composition of both polymers was similar. Fluorescence resonance energy transfer (FRET) was used to follow the
rate of polymer diffusion for samples in which the high molar mass polymer was labeled with appropriate donor and acceptor
dyes. In these latex blends, the presence of the oligomer (with M
n = 24,000 g/mol, M
w/M
n = 2) was so effective at promoting the interdiffusion of the higher molar mass poly(butyl acrylate-co-methyl methacrylate; PBA/MMA = 1:1 by weight) polymer (with M
n = 43,00 g/mol, M
w/M
n = 3) that a significant amount of interdiffusion occurred during film drying. Additional polymer diffusion occurred during
film aging and annealing, and this effect could be described quantitatively in terms of free-volume theory.
This paper is dedicated to Professor Haruma Kawaguchi to honor his many contributions to the field of latex particles and
their applications. 相似文献
11.
Phase behavior and crystal morphology in poly(ethylene succinate) biodegradably modified with tannin
Siti Nurkhamidah Eamor M. Woo I-Han Huang Chean C. Su 《Colloid and polymer science》2011,289(14):1563-1578
Specific interactions, growth kinetics, and dendritic morphology in poly(ethylene succinate) (PESu) biodegradably modified
with various contents of tannic acid (TA) were characterized using differential scanning analysis, Fourier-transform infrared
(FTIR) spectroscopy, polarized-light optical microscopy, and atomic force microscopy. Strong interactions and highly retarded
growth between PESu and a macromolecular ester with polyphenol groups, TA, interaction-induced highly retarded growth rates
for the PESu/TA (80:20) composition are proven to lead to single-crystal-like dendrites when crystallized at high crystallization
temperature (T
c). At T
c = 70 °C, the growth rate for neat PESu is 12 μm/min while it is dramatically depressed to one tenth-fold at 1.5 μm/min with
20 wt.% TA in the blend. Strong specific interactions between the carbonyl group of polyesters and the phenolic hydroxyl group
of TA are confirmed by (1) the blend’s glass transition temperature (T
g)–composition relationship exhibits a sigmoidal curve, well fitted by the Kwei T
g model for miscible blends with large negative q = −90; (2) thermal analysis on crystal melting revealed an interaction parameter χ = −0.64 between PESu and TA; and (3) IR peak shifting analyzed using two-dimensional FTIR technique. A comparative blend
of another polyester poly(hexamethylene sebacate) with TA, lacking the specific interactions, does not exhibit such single
crystals upon similar melt crystallization. 相似文献
12.
A number of samples of sodium and silver phosphate glasses doped with
various compositions of some transition metals viz. iron, manganese and zinc
chlorides alongwith undoped samples of sodium and silver phosphate glasses
were synthesized and characterized by X-ray diffraction, IR spectral, electrical
conductivity and differential scanning calorimetry (DSC). The glass transition
temperature (T
g)
and crystallization temperature (T
c)
values obtained from DSC curves were found to increase with increasing concentration
of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses
and the following sequence is observed:
T
g(–FeCl3)>T
g(–MnCl2)>T
g(–ZnCl2)
T
c(–FeCl3)>T
c(–MnCl2)>T
c(–ZnCl2)
The increase in T
g
and T
c values indicate
enhanced chemical durability of the doped glasses. The electrical conductivity
values and the results of FTIR spectral studies have been correlated with
the structural changes in the glass matrix by the addition of different transition
metal cations as dopants. 相似文献
13.
Marta Worzakowska 《Journal of Thermal Analysis and Calorimetry》2010,100(2):685-693
A series of N-alkyl-N-alkyl′-pyrrolidinium-bis(trifluoromethanesulfonyl) imide (TFSI−) room temperature ionic liquids (RTILs) has been investigated by means of thermogravimetric analysis (TG), differential scanning
calorimetry, FT-IR spectroscopy, and X-ray diffraction analysis. These compounds exhibit a thermal stability up to 548–573 K.
The mass loss starting temperature, T
ml, falls in a narrow range of temperatures: 578–594 K. FT-IR spectra, performed before and after 24 h isothermal experiments
at 553 and 573 K, have confirmed their great thermal stability. Below the ambient temperature, these compounds exhibit a complex
behavior. N-methyl-N-propyl-pyrrolidinium-TFSI is the sole liquid which crystallizes without forming any amorphous phase even after quenching
in liquid nitrogen. Its crystalline phase has a melting point, T
m, of 283 ± 1 K. When the amorphous solid is heated, the N-butyl-N-ethyl-pyrrolidinium-TFSI presents a glass transition temperature, T
g, at 186 K followed by a cold crystallization, T
cc, at 225 K, and a final T
m at 262 K. The N-butyl-N-methyl-pyrrolidinium-TFSI exhibits a T
g between 186 and 181 K, its cold crystallization leading to two different solid phases. Solid phase I has a melting point
T
I,m = 252 K and phase II, T
II,m = 262 K. When the amorphous phase is obtained at a cooling rate of 10 K/min, its T
cc is 204 K, and a metastable solid phase (III) is obtained which transforms into the phase II at 226 K. However, when the sample
is quenched, the amorphous phase transforms into phase II at T
cc = 217 K and phase I at 239 K. P15-TFSI exhibits the most complicated pattern as, on cooling, it leads to both a crystallized phase at 237 K and an amorphous
phase at 191 K. On heating, after a T
g at 186 K and a T
cc at 217 K, two solid–solid phase transitions are observed at 239 K and 270 K, the final T
m being 279 K. 相似文献
14.
15.
Ulrich Englich Ingo Prass Karin Ruhlandt-Senge Thorsten Schollmeier Frank Uhlig 《Monatshefte für Chemie / Chemical Monthly》2002,133(7):931-943
Summary. Hydrido substituted stannasilanes of the type or (Z = H, Me, Ph; R, R′ = alkyl, Ph) are accessible by reaction of either alkali metal stannides (MSn(Z)R
2; M = Li, Na) with halogen substituted silanes (; X = F, Cl) or chlorostannanes (R
2SnCl2, Ph3SnCl) and fluorosilanes in the presence of magnesium. Stannasilanes with halogen substituents at the silicon as well as the tin atom are formed by
treatment of the hydrido substituted stannasilanes with CHCl3 or CCl4. The hydrido substituted stannasilanes decompose in contact with air to distannanes and siloxanes or to the linear (
t
Bu2Sn(–O–
t
Bu2Si–OH)2) and cyclic ((–
t
Bu2Sn–O–
i
Pr2Si–O–)2) stannasiloxanes.
Received November 29, 2001. Accepted (revised) January 16, 2002 相似文献
16.
Franke AA Custer LJ Morimoto Y Nordt FJ Maskarinec G 《Analytical and bioanalytical chemistry》2011,401(4):1319-1330
Estrogens and other endogenous steroids are known risk markers for cancer. Gas chromatography (GC) with mass spectrometry
(MS) has traditionally predominated the analysis of estrogens and other endogenous steroids, but liquid chromatography (LC)
MS is increasingly favored. Direct comparisons of the two technologies have hitherto not been performed. Steroids were analyzed
from 232 urine samples of 78 premenopausal women in a blinded fashion by benchtop orbitrap LCMS and single quadrupole GCMS.
Sixteen steroidal estrogens including oxidized metabolites could be analyzed by LCMS. LCMS–GCMS Spearman rank correlations
of the major estrogens E1, E2, E3, 16α-OHE1, and 2-OHE1 were very high (r = 0.72–0.91), and absolute concentrations also agreed (<5% difference for E1, E2, E3, 16α-OHE1). LCMS allowed reinterrogation of the acquired data due to orbitrap technology, which permitted post-analysis quantitation
of progesterone, cortisol, and cortisone (LCMS–GCMS Spearman rank correlations = 0.80–0.84; absolute difference, <7%; n = 137). GCMS allows the measurement of a wide range of steroids including non-polar analytes that escape the presented LCMS
assay. In contrast, orbitrap-based LCMS can detect more estrogens, is faster, less costly, allows post-data acquisition reinterrogation
of certain analytes that had not been targeted a priori, and requires much less urine. 相似文献
17.
Kiyoshi Sawada Eiji Takahashi Tomokazu Horie Keiichi Satoh 《Monatshefte für Chemie / Chemical Monthly》2001,132(11):1439-1450
Summary. The distribution of tetraalkylammonium ions (C
n
H
2n+1
)4N+ (R
+, TAAn
+, n = 4–7) with picrate ion (pic
−) and inorganic anions X
−, (Cl−, Br−, ClO−
4), into various inert organic solvents was studied at 25.0°C. The distribution data were analyzed by taking into consideration
the distribution of ion pairs, R
+ · X
−, and the dimerization of the ion pairs, (R
+ · X
−)2, in the organic phase. The ion-pair, distribution constant, K
dist, increases with increasing chain length of the tetraalkylammonium ion and with increasing ionic radius of the anion. The
values of K
dist show a good correlation with the E
T value of solvent, i.e. the solvation ability with respect to the anion, and smoothly increase with increasing E
T. The effect of the solvent on the dimerization constants, K
dim, is markedly different between the ion pairs of picrate ion and inorganic anions. In the case of picrate, K
dim significantly decreases with decreasing length of the alkyl chain of the tetraalkylammonium ion, but hardly changes by changing
the solvent. On the other hand, in the case of ion pairs of inorganic anions the value of K
dim decreases with decreasing E
T and is almost constant for all anions. These results were reasonably explained by the difference of the solvation of the
anion moieties of the monomeric and dimeric ion pairs.
Received May 15, 2001. Accepted (revised) July 18, 2001 相似文献
18.
Ana B. Gaspar M. Carmen Mu?oz Nicolás Moliner Vadim Ksenofontov Georgii Levchenko Philipp Gütlich José Antonio Real 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):285-294
Summary. The monomeric compounds [Fe(abpt)2(NCX)2] (X = S (1), Se (2) and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) have been synthesized and characterized. They crystallize in the monoclinic
P21/n space group with a = 11.637(2) ?, b = 9.8021(14) ?, c = 12.9838(12) ?, β = 101.126(14)°, and Z = 2 for 1, and a = 11.601(2) ?, b = 9.6666(14) ?, c = 12.883(2) ?, β = 101.449(10)°, and Z = 2 for 2. The unit cell contains a pair mononuclear [Fe(abpt)2(NCX)2] units related by a center of symmetry. Each iron atom, located at a molecular inversion center, is in a distorted octahedral
environment. Four of the six nitrogen atoms coordinated to the Fe(II) ion belong to the pyridine-N(1) and triazole-N(2) rings
of two abpt ligands. The remaining trans positions are occupied by two nitrogen atoms, N(3), belonging to the two pseudo-halide ligands. The magnetic susceptibility
measurements at ambient pressure have revealed that they are in the high-spin range in the 2 K–300 K temperature range. The
pressure study has revealed that compound 1 remains in high-spin as pressure is increased up to 4.4 kbar, where an incomplete thermal spin crossover appears at around
T
1/2 = 65 K. Quenching experiments at 4.4 kbar have shown that the incomplete character of the conversion is a consequence of
slow kinetics. Relatively sharp spin transition takes place at T
1/2 = 106, 152 and 179 K, as pressure attains 5.6, 8.6 and 10.5 kbar, respectively.
Corresponding author. E-mail: jose.a.real@uv.es
Received June 12, 2002; accepted July 1, 2002 相似文献
19.
Kiyoshi Sawada Eiji Takahashi Tomokazu Horie Keiichi Satoh 《Monatshefte für Chemie / Chemical Monthly》2001,36(4):1439-1450
The distribution of tetraalkylammonium ions (C n H 2n+1 )4N+ (R +, TAAn +, n = 4–7) with picrate ion (pic −) and inorganic anions X −, (Cl−, Br−, ClO− 4), into various inert organic solvents was studied at 25.0°C. The distribution data were analyzed by taking into consideration the distribution of ion pairs, R + · X −, and the dimerization of the ion pairs, (R + · X −)2, in the organic phase. The ion-pair, distribution constant, K dist, increases with increasing chain length of the tetraalkylammonium ion and with increasing ionic radius of the anion. The values of K dist show a good correlation with the E T value of solvent, i.e. the solvation ability with respect to the anion, and smoothly increase with increasing E T. The effect of the solvent on the dimerization constants, K dim, is markedly different between the ion pairs of picrate ion and inorganic anions. In the case of picrate, K dim significantly decreases with decreasing length of the alkyl chain of the tetraalkylammonium ion, but hardly changes by changing the solvent. On the other hand, in the case of ion pairs of inorganic anions the value of K dim decreases with decreasing E T and is almost constant for all anions. These results were reasonably explained by the difference of the solvation of the anion moieties of the monomeric and dimeric ion pairs. 相似文献
20.
C. Ramírez M. J. Abad J. Cano J. López P. Nogueira L. Barral 《Colloid and polymer science》2001,279(2):184-189
Enthalpy relaxation in a system containing the diglycidyl ether of bisphenol A (DGEBA) resin and a diamine, 1,3-bisaminomethylcyclohexane
(1,3-BAC) as curing agent, has been investigated by differential scanning calorimetry (DSC). Samples fully cured were annealed
at temperature Tg–15 °C for periods of time from 1 h to a maximum of 168 h. The enthalpy relaxation is analyzed by the peak shift method, in
which the sample is heated at 10 °C/min following cooling at various rates through the glass transition region. The key parameters
of structural relaxation determined were the non-linearity parameter x=0.47 ± 0.02, the apparent activation energy Δh*=1264 ± 48 kJ/mol or Δh*/R=152 ± 6 kK and the non-exponentiality parameter β ≈ 0.3. The results, obtained by the same method, were compared with those for other systems based on fully cured DGEBA. The
correlations among these parameters with the peak shift model should be considered with caution. However, the results show
that a correlation between crosslink lengths and the value of Δh* can be considered. The relaxation process for DGEBA/1,3-BAC proves to be highly cooperative.
Received: 28 June 2000 Accepted: 6 September 2000 相似文献