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1.
The relationship between heat capacity (C
p) and linear thermal expansion (α) derived from the Lennard–Jones potential is C
p=Aα(U
0–E), where U
0 is the heat of sublimation at T=0, E is the enthalpy and A is the coefficient. The values of A for different solidified inert gases coincide with one another within the limits of experimental error (±2%).
The relationship is shown to be valid for various substances: solidified rare gases, diamond, halite and copper.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Summary The effect of perchlorate anion as mobile phase modifier on the separation factor, α, forN-(dansyl)-dl-norvaline andN-(dansyl)-dl-tryptophan on a human serum albumin (HSA) column was studied by varying the concentration,c, of the chaotropic agent and the column temperatureT. Gibbs-Helmholtz parameters Δ(ΔH) and Δ(ΔS) between thed andl enantiomers were determined from linear van't Hoff plots of lnα against 1/T. Thermodynamic results indicated that the enhancement of the separation factor observed asc was increased was enthalpically controlled owing to stereoselective H-bonding interactions. Such behavior was used to optimize
the chromatographic conditions for separation ofN-(dansyl)-amino acids on HSA. 相似文献
3.
H. -X. Gao F. -Q. Zhao R. -Z. Hu H. -A. Zhao H. Zhang 《Journal of Thermal Analysis and Calorimetry》2009,95(2):477-482
A method for estimating the critical temperatures (T
b) of thermal explosion for energetic materials is derived from Semenov’s thermal explosion theory and the non-isothermal kinetic
equation dα/dt=A
0
T
B
f(α)e−E/RT using reasonable hypotheses. The final formula of calculating the value of T
b is $
\left( {\frac{B}
{{T_b }} + \frac{E}
{{RT_b^2 }}} \right)
$
\left( {\frac{B}
{{T_b }} + \frac{E}
{{RT_b^2 }}} \right)
(T
b−T
e0=1. The data needed for the method, E and T
e0, can be obtained from analyses of the non-isothermal DSC curves. When B=0.5 the critical temperature (T
b) of thermal explosion of azido-acetic-acid-2-(2-azido-acetoxy)-ethylester (EGBAA) is determined as 475.65 K. 相似文献
4.
In this paper, evaluation of kinetic parameters (the activation energy – E,the pre-exponential factor – A and the reaction order – n) with simultaneous determination of the possible reaction mechanism of thermal decomposition of calcium hydroxide (portlandite),
Ca(OH)2 formed during hydration of commercial Portland-slag cement, by means of differential scanning calorimetry (DSC) in non-isothermal
conditions with a single heating–rate plot has been studied and discussed. The kinetic parameters and a mechanism function
were calculated by fitting the experimental data to the integral, differential and rate equation methods.
To determine the most probable mechanism, 30 forms of the solid-state mechanism functions, f(αc) have been tried. Having used the procedure developed and the appropriate program support, it has been established that the
non-isothermal thermal decomposition of calcium hydroxide in the acceleratory period (0.004<αc<0.554) can be described by the rate equation: d αc/dT=A/βexp(−E/RT)f(αc), which is based on the concept of the mechanism reaction:f(αc)=2(αc)1/2.
The mechanism functions as well as the values of the kinetic parameters are in good agreement with those given in literature.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
P. Slobodian 《Journal of Thermal Analysis and Calorimetry》2008,94(2):545-551
Volumetric thermal analysis of semicrystalline poly(ethylene terephthalate), PET, with different content of crystalline phase
was carried out using mercury-in-glass dilatometry. The effect of crystals on the thermal properties of amorphous phase (glass
transition temperature, T
g, thermal expansion coefficients, α) were determined. At cold-crystallization (106°C, up to 4 h), crystalline content of 2.4–25.3
vol.% was achieved. Increasing content of crystalline phase broadens the glass transition region and increases T
g. The change of thermal expansion coefficient during glass transition is lower than that predicted by the two-phase model,
which indicates the presence of a third fraction — rigid amorphous fraction (RAF), whose content steadily increases during
crystallization. However, its relative portion (specific RAF) is significantly reduced. Further significant decrease in specific
RAF appears after annealing at a higher temperature. 相似文献
6.
This
study discussed the phenomena on thermal polymerization of α-methylstyrene
(AMS). A curve scanned by temperature-programmed technique was performed by
differential scanning calorimetry (DSC). Heat of polymerization (ΔH) and onset temperature of exothermic (T0) behavior were determined
to be 280±10 J g-1 and about 138±1°C,
respectively. A dimer formation mechanism was proposed for initiation of the
propagating chain. Spectroscopic identification of dimer structure was conducted
by infrared (IR) spectroscopy in the wavenumber from 650 to 1100 cm-1associated
with molecular fingerprint characteristics. The mechanism of thermal polymerization
on α-methylstyrene proposed in this study was similar to that of styrene
suggested by Mayo. 相似文献
7.
A. F. Santos L. Polese M. S. Crespi C. A. Ribeiro 《Journal of Thermal Analysis and Calorimetry》2009,96(1):287-291
The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent
kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably
managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol−1, logA=14.1±0.2 s−1 for the kinetic model, and the autocatalytic model function was: f(α)=αm(1−α)n=α0.42(1−α)0.56. 相似文献
8.
Yonit Sembira-Nahum Alexander Apelblat Emanuel Manzurola 《Journal of solution chemistry》2008,37(3):391-401
Densities of aqueous solutions of L-glutamic acid and magnesium-L-glutamate were determined from T=288.15 to 333.15 K at 5 K temperature intervals. The measured densities were used to evaluate the apparent molar volumes,
V
2,φ
(m,T), the cubic expansion coefficients, α(m,T), and the changes of isobaric heat capacities with respect to pressure, (∂
C
p
/∂
p)
T,m
. They were qualitatively correlated with changes in the structure of water that occur when L-glutamic acid or magnesium-L-glutamate
are present. 相似文献
9.
H. X. Ma B. Yan Y. H. Ren Y. Hu Y. L. Guan F. Q. Zhao J. R. Song R. Z. Hu 《Journal of Thermal Analysis and Calorimetry》2011,103(2):569-575
3,3-Dinitroazetidinium (DNAZ) salt of perchloric acid (DNAZ·HClO4) was prepared, it was characterized by the elemental analysis, IR, NMR, and a X-ray diffractometer. The thermal behavior
and decomposition reaction kinetics of DNAZ·HClO4 were investigated under a non-isothermal condition by DSC and TG/DTG techniques. The results show that the thermal decomposition
process of DNAZ·HClO4 has two mass loss stages. The kinetic model function in differential form, the value of apparent activation energy (E
a) and pre-exponential factor (A) of the exothermic decomposition reaction of DNAZ·HClO4 are f(α) = (1 − α)−1/2, 156.47 kJ mol−1, and 1015.12 s−1, respectively. The critical temperature of thermal explosion is 188.5 °C. The values of ΔS
≠, ΔH
≠, and ΔG
≠of this reaction are 42.26 J mol−1 K−1, 154.44 kJ mol−1, and 135.42 kJ mol−1, respectively. The specific heat capacity of DNAZ·HClO4 was determined with a continuous C
p mode of microcalorimeter. Using the relationship between C
p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic
time-to-explosion) was evaluated as 14.2 s. 相似文献
10.
Skuban S. J. Skuban F. Lukić S. R. Cvejić ž 《Journal of Thermal Analysis and Calorimetry》2003,71(2):439-444
The object of the paper is an investigation of the glasses of the (As2S3)x(AsSe0.5Te0.5I)100-x. type for 65≤;x≤;95, using methods of thermomechanical analysis. Values of the thermal coefficients of linear expansion in solid and visco-plastic
phase were determined. it was shown that introducing arsenic-sulfide in glass-matrix AsChI, i.e. (AsSe0.5Te0.5I), leads to an increasing stability of these glasses. The characteristic temperatures of softening Tg and the temperature of the beginning of deformation tw increase by increasing content of As2S3. The analytical forms of dependence of four significant physical values αg, αl, Tg, Tw, as a function of As2S3 content in the structure of glasses were fitted.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
T. Furuki R. Abe H. Kawaji T. Atake M. Sakurai 《Journal of Thermal Analysis and Calorimetry》2008,93(2):561-567
The phase transitions of α,α-trehalose dihydrate (T
h) were investigated by either differential thermal analysis (DTA) with an in-house apparatus of variable-pressure type equipped
with an open sample holder or commercially available TG (thermal gravimetry)-DTA apparatus for comparison under the same experimental
conditions as to the heating rate (2°C min−1), the type of pan (open), and the particle size of T
h (63 μm). The former DTA measurements were carried out under five different total pressures, 101, 75, 61, 48 and 35 kPa, which
provided quite helpful information necessary for confirmative assignments of the endothermic peaks due to either melting or
dehydration of T
h. The usage of largely different amount of T
h, 126 and 14 mg for the DTA and TG-DTA measurements respectively, led to their different DTA traces, showing that there were
largely different extents of the influence by the measured sample surface exposed to the surrounding atmosphere on its dehydration
behavior. In addition the high thermal sensitivity achieved with such mass of T
h gave rise to an interesting discovery of an unidentified thermal event at 92°C prior to either melting or dehydration of
T
h. 相似文献
12.
Pet'kov V. I. Orlova A. I. Kazantsev G. N. Samoilov S. G. Spiridonova M. L. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):623-632
A5–4xZrxZr(PO4)3 (A=Na, K;0≤x≤1.25), Na1-xCd0.5xZr2(PO4)3 (0≤x≤1), Na5–xCd0.5xZr(PO4)3 (0≤x≤4) compositions which belong to the NZP structural family were synthesized using the sol-gel method. The lattice thermal
expansion of members of these rows were determined up to 600°C by high-temperature X-ray diffractometry. The axial thermal
expansion coefficients change from -5.8·10-6to 7.5·10-6 °C-1 (αa) and from 2.6·10–6 to 22·10–6 °C-1 (αc). These results, in addition to those for other NZP compounds allow us to explain their low thermal expansion. The mechanism
can be attributed to strongly bonded three-dimensional network structure, the existence of structural holes capable to damp
some of the thermal vibrations and anisotropyin the thermal expansion of the lattice.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
Summary Two different methods were used to determine the separation factor α at different temperatures and the Gibbs-Helmholtz parameters
(Δ(ΔH), Δ(ΔS)) of two adjacent benzodiazepines on a chromatogram were obtained from plots of lnα versus 1/T. We first studied each factor (fraction of water ϕ in the ACN/water mixture and column temperatureT), which controls the retention mechanism, and then we examined the simultaneous variation of all these factors. The changes
in Δ(ΔH) and Δ(ΔS) in relation to a volume fraction of water ϕ in an ACN/water mixture were examined. In the ACN/water system, Δ(ΔH) was fairly constant in the acetonitrile region of ϕ≤0.52 and appears to be a roughly linear function of ϕ for ϕ≥0.52. In
this system Δ(ΔS) is approximately a parabolic function of ϕ with an optimum at ϕ≊0.52. The retention mechanism of ten benzodiazepines was
found to be significantly different in the methanol/water and ACN/water mixtures. The separation optimization of these ten
benzodiazepines was then considered. A fraction of water of 0.43 in the ACN/water mixture and a column temperature of 44 °C
gave the most efficient separation conditions in the ACN/water mixture. 相似文献
14.
High energy ball-milling methods were employed in the synthesis of anatase-doped hematite xTiO2(a) · (1−x)α-Fe2O3 (x = 0.1, 0.5, and 0.9) ceramic system. The thermal behavior of as obtained ceramic system was characterized by simultaneous
DSC–TG. The pure anatase phase was found to be stable below 800 °C, but there is a 10.36% mass loss due to the water content.
Two exothermic peaks on DSC curves of pure anatase indicate the different crystallization rates. The pure hematite partially
decomposed upon heating under argon atmosphere. Ball-milling has a strong effect on the thermal behaviors of both anatase
and hematite phases. For x = 0.1 and 0.5, there is gradual Ti substitution of Fe in hematite lattice, and the decomposition of hematite is enhanced
due to the smaller particle size after ball-milling. The crystallization of hematite was suppressed as the enthalpy values
decreased due to the anatase-hematite solid–solid interaction. For x = 0.9, most of the anatase phase converted to rutile phase after long milling time. The thermal behavior of xTiO2(a) · (1−x)α-Fe2O3 showed smaller enthalpy value of the hematite transformation to magnetite and anatase crystallization due to the small fraction
of hematite phase in the system and hematite–anatase interaction, while the mass loss upon heating increased as a function
of milling time due to more water content absorbed by the smaller particle size. 相似文献
15.
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
16.
The interactions of nicotinic acid with α-D-glucose and maltose, and with α-, β-, hydroxypropyl-α- and hydroxypropyl-β-cyclodextrins were studied by using solution calorimetry at T = 298.15 K and pH = 3.4. The thermodynamic parameters (log10 K, Δ G∘c, Δ H∘c and Δ S∘c) were calculated for the systems in which complex formation was observed. Systems with weak interparticle interactions lacking
complex formation were characterized by enthalpic virial coefficients calculated on the basis of the McMillan–Mayer theory.
It was found that the complexation affinity of α-cyclodextrin to nicotinic acid is stronger in comparison to β-cyclodextrin and the mono- and disaccharides. The influence of different factors, such as the availability of the macrocyclic
hydrophobic cavity, the relationship of the sizes of guest molecule to the host cavity, the presence of bulky hydroxypropyl
substitutes and their structure, and the solvation of guest molecules on the stability of complexes and their thermodynamic
parameters of interaction is discussed. 相似文献
17.
Thermal behaviors of trehalose dihydrate (T
h) and β-anhydrous trehalose (T
β) have been investigated by in-situ laboratory parallel-beam X-ray powder diffraction. Data indicate that both phases show
essentially the same volume expansion but expansion of the anhydrous form is markedly anisotropic due to the features of the
hydrogen-bond network. Under the present experimental conditions, dehydration starts at 66 °C and within the 75 < T < 114 °C the presence of the T
α anhydrous polymorphic form has been detected. 相似文献
18.
L. Rong N. Binke W. Yuan Y. Zhengquan Hu Rongzu 《Journal of Thermal Analysis and Calorimetry》1999,58(2):369-373
Two methods for estimating the critical temperature (Tb) of thermal explosion for the highly nitrated nitrocellulose (HNNC) are derived from the Semenov's thermal explosion theory and two non-isothermal kinetic equations, d/dt=Af()e–E/RT and d/dt=Af()[1+E/(RT)(1–To/T)]e–E/RT, using reasonable hypotheses. We can easily obtain the values of the thermal decomposition activation energy (E), the onset temperature (Te) and the initial temperature (To) at which DSC curve deviates from the baseline of the non-isothermal DSC curve of HNNC, and then calculate the critical temperature (Tb) of thermal explosion by the two derived formulae. The results obtained with the two methods for HNNC are in agreement to each other.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
19.
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
20.
Iwona Zięborak-Tomaszkiewicz P. Gierycz 《Journal of Thermal Analysis and Calorimetry》2008,93(3):693-699
The change of thermal functions (ΔH
0(T), ΔS
0(T), ΔG
0(T)) and formation functions (ΔH
f0(T), ΔG
f0(T), K
f(T)) with temperature for gallium nitride and indium nitride have been formulated based on the reliable experimental data obtained
by the use the same equipment in one laboratory. 相似文献