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1.
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
2.
Comparative method to evaluate reliable kinetic triplets of thermal decomposition reactions 总被引:1,自引:0,他引:1
Reliable kinetic information for thermal analysis kinetic triplets can be determined by the comparative method: (1) An iterative
procedure or the KAS method had been established to obtain the reliable value of activation energy E
a of a reaction. (2) A combined method including Coats-Redfern integral equation and Achar differential equation was put forward
to confirm the most probable mechanism of the reaction and calculate the pre-exponential factor A. By applying the comparative
method above, the thermal analysis kinetic triplets of the dehydration of CaC2O4·H2O were determined, which apparent activation energy: 81±3 kJ mol-1, pre-exponential factor: 4.51·106-1.78·108 s-1, the most probable mechanism function: f(α)=1 or g(α)=α, which the kinetic equation of dehydration is dα/dt=Ae-E
a
/RT.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
The aim of the present work was to provide arguments to the almost ‘hystorical’ problem of what β-tungsten is.
WO3was reduced in dry H2gas atmosphere in order to examine, whether β-tungsten formed in such a way contains oxygen as part of the lattice described
as WxO (e.g. W20O) or is a pure metallic phase of tungsten.
As a result of thermoanalytical measurements and of chemical analysis for oxygen, the assumption is supported that in the
600-800°C temperature range of metal formation not the WxO (β-W)→W(α-W) transformation but the β-W→α-W structural rearrangement of materials with identical chemical composition is
the most probable process.
The earlier opinion that the formation of the β-W structure requires the presence of oxygen atoms was not verified by our
results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Two new polyhydroxysteroids and five new glycosides were isolated from the starfishCeramaster patagonicus and their structures were elucidated: 5α-cholestane-3β,6α,15β,16β,26-pentol, (22E)-5α-cholest-22-ene-3β,6α,8,15α,24-pentol, (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β,4β, 6α,8,15β,16β,28-heptol (ceramasteroside C1), (22E)-28-O-[O-(2,4-di-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β, 6α,8,15β,16β,28-hexol (ceramasteroside C2), (22E)-28-O-[O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β,6α,8,15β,16β 28-hexol (eramasteroside C3), (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-methyl-5α-cholest-22-ene-3β,4β,6α,8, 15β, 26-hexol (ceramasteroside C4), and (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-xylopyranosyl]-5α-cholest-22-ene-3β,6α,8,15β,24-pentol (ceramasteroside C5)). Three known polyhydroxysteroids (24-methylene-5α-cholestane-3β,6α,8,15β,16β,26-hexol, 5α-cholestane-3β,6α,8,15β,16β,26-hexol,
and 5α-cholestane-3β,6β,15α,16β,26-pentol) were also isolated.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 190–195, January, 1997. 相似文献
5.
A critical analysis is presented of the use of an overall single rate reaction equation instead of the true rate equation
corresponding to a complex process consisting of two consecutive reactions. In accordance with this approximation, which is
often used in the kinetic analysis of systems in which several reactions take place, the overall process is described by apparent
activation parameters (the apparent activation energy Eap and the apparent pre-exponential factor Aap) and an apparent conversion function.
The theoretical isotherms (α=α(t), where α is the conversion degree and t is time) were simulated for a system in which two
consecutive reactions occur. In this case, the apparent activation parameters depend on (a) the considered range of temperature;
and (b) the temperature for a given conversion degree. It is shown that the apparent activation parameters are correlated
by the compensation effect relationship: ln Aap = α* + β*Eap where α* and β* are the linear regression parameters.
The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those
for which these parameters were evaluated is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
The L spectra of the elements 14 ≤ Z ≤ 22 were reinvestigated. Because of the limited energy resolution of the multilayer
reflectors neither Ll and Lη nor Lα and Lβ1 could be resolved. Nevertheless, the line Lβ3,4 = L1M2,3 was observed for all elements Z ≥ 16, but not for 14Si and 15P. Exceptions to this are 18Ar and 22Ti. For 18Ar no suitable sample is available. In the case of 22Ti the Lβ3,4 line is overlapped by the O Kα line which has its origin in the oxide surface layer of the Ti standard. In all cases the
Lβ3,4 line was observed near to the expected position which was determined by means of the known electron binding energies.
The L spectrum of 21Sc was studied for various energies of the incident electrons, E0. These measurements show that Lβ3,4 is much more strongly absorbed in Sc than Ll,η and Lα,β1. From these measurements approximate mass absorption coefficients (m.a.c.) were deduced. The relative net peak height I(Lβ3,4)/I(Lα,β1) decreases from 15% at E0 = 4 keV to 4% at E0 = 20 keV, whereas I(Ll,η)/I(Lα,β1) remains nearly constant at 90%. The peak to background ratio of Ll,η is greater than that of Lα,β1. 相似文献
7.
L. A. Yakovishin V. I. Grishkovets A. S. Shashkov V. Ya. Chirva 《Chemistry of Natural Compounds》1999,35(5):543-546
Two new minor triterpene glycosides L-G1, and L-G2b, the 3-O-α-L-arabinopyranosyl-28-O-α-L-rhamnopyranosyl-(1→4)-O-β-D-gentiobiosyl and 3-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranosyl-28-O-α-L-rhamnopyranosyl-(1→4)-O-(6-O-acetyl-β-D-glucopyranosyl)-(1→6)-O-β-D
glucopyranosyl esters of 30-norhederagenin, respectively, are isolated from the leaves of canary ivy (Hedera canariensis Willd.). The structures of the glycosides are found by chemical methods and1H and13C NMR spectroscopy.
Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 623–626, September–October, 1999. 相似文献
8.
V. I. Grishkovets A. A. Loloiko A. S. Shashkov V. Ya. Chirva 《Chemistry of Natural Compounds》1990,26(6):663-666
We have isolated from Crimean ivy berries in addition previously known triterpene glycosides — 3-O-α-L-arabinopyranosyl-28-O-[O-α-L-rhamnopyranosyl-(1
→ 4)-O-β-D-glycopyranosyl-(1 → 6)-β-D-glucopyranosyl]hederagenin, 3-O-[O-α-L-rhamnopyranosyl-(1 → 2)-α-L-arabinopyranosyl]-28-O-[O-α-L-rhamnopyranosyl-(1
→ 4)-O-β-D-glucopyranosyl-(1 → 6)-β-D-glycopyranosyl]hederagenin, the new triterpene glycosides hederoside H2-3-O-[O-β-D-glycopyranosyl-(1 → 2)-β-D-glycopyranosyl-(1 → 2)-β-D-glucopyranosyl]-28-O-[O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl]oleanolic
acid- and hederoside I-3-O-[O-β-D-glucopyranosyl-(1 → 2)-β-D-glucopyranosyl]-28-O-[O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl]hederagenin.
Details of their13C NMR spectra are given.
M. V. Frunze Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 779–783, November–December,
1990. 相似文献
9.
Abstact The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the
catalyst proceeds in two steps:
which was validated by the TPR and in-situ XRD experiments. The kinetic parameters of the reduction process were obtained with a comparative method. For the first step,
the activation energy, E
a, and the pre-exponential factor, A, were found to be 104.35 kJ mol−1 and 1.18·106∼2.45·109 s−1 respectively. The kinetic model was random nucleation and growth and the most probable mechanism function was found to be
f(α)=3/2(1−α)[−ln(1−α)]1/3 or in the integral form: g(α)=[−ln(1−α)]2/3. For the second step, the activation energy, E
a, and the pre-exponential factor, A, were found to be 118.20 kJ mol−1 and 1.75·107∼2.45 · 109s−1 respectively. The kinetic model was a second order reaction and the probable mechanism function was f(α)=(1−α)2 or in the integral form: g(α)=[1−α]−1−1. 相似文献
10.
Perlovich G. L. Hansen L. K. Bauer-Brandl A. 《Journal of Thermal Analysis and Calorimetry》2001,66(3):699-715
X-ray, DSC and solution calorimetric investigations were carried out for α-, β- and γ-modifications of glycine. Particular
attention was paid to kinetic and thermochemical aspects of γ- → α-phase transition. The temperature of this phase transition
turned out to be sensitive to a) conditions under which the crystals of the γ-modification were grown, b) tempering of crystals
c) form (geometry) of crystals. Kinetics of this phase transition of single crystals of γ-phase in rhomboedric form can be
described by the equation for two-dimension nuclei growth, whereas for crystals of triangle geometry the equation for three
dimension growth is valid. On the basis of energy parameters describing growth of α-form in γ- →α-phase transition, the kind
of structure defects, which are responsible for this phase transition, was estimated. Taking into account the Δsol
H
m, the absolute values of the lattice energies of the investigated polymorphs indescending order are follows: γ->α->β-modification.
The obtained results are discussed with respect to the peculiarity of the crystal lattice structures, particularly the network
of hydrogen bonds. The β-modification of glycine is monotropically related to the other forms, whereas γ-and α-polymorphs
are enantiotropically-related phases.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
The intensities of the Fe L lines/bands l = L3M1, η = L2M1, α1,2 = L3M4,5, β1 = L2M4, and β3,4 = L1M2,3 were measured for pure Fe and Fe3O4 using a TAP crystal as the dispersing element. The energy of the exciting electrons, E0, was varied in the range 5 ≤ E0 ≤ 25 keV.
For pure Fe the following results were obtained. The net peak height ratio Ll/Lα remains relatively constant with varying
E0 at approximately 14%. The E0 dependence of Lη is similar to that of Ll, although Lη is less intense than Ll by a factor of 7. Lβ1/Lα decreases from 20% for E0 = 5 keV to about 5% for 25 keV. Lβ3,4 behaves like Lβ1 but is weaker by a factor of 15.
For Fe3O4 a much weaker intensity of Lα was observed which can be partially explained by its stronger absorption. Again, the E0 dependence of Ll and Lη is similar with Ll/Lα = 19% and Lη/Lα = 4%. Lβ1 and Lβ3,4 show a comparable E0 dependence. Lβ1/Lα decreases from 50% for E0 = 5 keV to 34% for 25 keV. Lβ3,4 is weaker than Lβ1 by a factor of about 25.
The observed E0 dependence of the different lines was used to estimate a set of mass absorption coefficients. Our value for Lα in Fe agrees
well with other data which were deduced from variable E0 measurements but differs considerably from data given by Heinrich and Henke. 相似文献
12.
A. G. Magdalena A. T. Adorno T. M. Carvalho R. A. G. Silva 《Journal of Thermal Analysis and Calorimetry》2011,106(2):339-342
In the Cu–Al system, due to the sluggishness of the β ↔ (α + γ1) eutectoid reaction, the β phase can be retained metastably. During quenching, metastable β alloys undergo a martensitic
transformation to a β′ phase at Al low content. The ordering reaction β ↔ β1 precedes the martensitic transformation. The influence of Ag additions on the reactions containing the β phase in the Cu–11mass%Al
alloy was studied using differential scanning calorimetry and in situ X-ray diffractometry. The results indicated that, on
cooling, two reactions are occurring in the same temperature range, the β → (α + γ1) decomposition reaction and the β → β1 reaction, with different reaction mechanisms (diffusive for the former and ordering for the latter) and, consequently, with
different reaction rates. For lower cooling rates, the dominant is the decomposition reaction and for higher cooling rates
the ordering reaction prevails. On heating, the (α + γ1) → β reverse eutectoid reaction occurs with a resulting β phase saturated with α. The increase of Ag concentration retards
the β → (α + γ1) decomposition reaction and the β → β1 ordering reaction, which occurs in the same temperature range, becomes the predominant process. 相似文献
13.
Zhang J.-J. Wang R.-F. Li J.-B. Liu H.-M. Yang H.-F. 《Journal of Thermal Analysis and Calorimetry》2000,62(3):747-755
The thermal decomposition of Eu2(BA)6(bipy)2 (BA=C2H5N–
2, benzoate; bipy=C10H8N2, 2,2'-bipyridine)and its kinetics were studied under the non-isothermal condition by TG-DTG, IR and SEM methods. The kinetic
parameters were obtained from analysis of the TG-DTG curves by the Achar method, the Madhusudanan-Krishnan-Ninan (MKN) method,
the Ozawa method and the Kissinger method. The most probable mechanism function was suggested by comparing the kinetic parameters.
The kinetic equation for the first stage can be expressed as: dα/dt=Aexp(–E/RT)3(1–α)2/3.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
V. I. Grishkovets 《Chemistry of Natural Compounds》1999,35(5):547-551
Chromatographically inseparable mixtures of oleanolic and ursolic 3-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranosides (glycosides
B1 and B2) and their 28-O-α-L-rhamnopyranosyl-(1→4)-O-β-D-glucopyranosyl-(1→6)-O-β-D-glucopyranosyl esters (glycosides F1 and F2) are isolated from the leaves ofTupidanthus calyptratus Hook f. (Araliaceae). The structures of the isolated glycosides are established from chemical methods and1H and13C NMR spectra. Glycoside F2 is a new triterpene glycoside.
Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 627–633, September–October, 1999. 相似文献
15.
O. A. Veremeeva N. A. Yakovleva S. N. Klyamkin E. A. Berdonosova E. V. Shelekhov 《Russian Chemical Bulletin》2006,55(6):949-954
The first cycles of hydrogen absorption-desorption in LaNi5-H2 and LaNi4.5Cu0.5-H2 systems were studied using Tian-Calvet differential heat-conduction microcalorimetry, volumetric measurements, and powder
X-ray diffraction. The diffraction profiles were analyzed, and the microstructure characteristics of the LaNi5 and LaNi4.5Cu0.5 systems at different stages of activation were determined. The pressure-composition isotherms were plotted, and the enthalpies
of phase transitions α→β and β→α were calculated. The effect of substitution on the change in the thermodynamic parameters
and microstructure characteristics of the hydride-forming intermetallic compounds during activation was shown.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 915–920, June, 2006. 相似文献
16.
V. I. Grishkovets L. A. Yakovishin I. N. Shchipanova A. S. Shashkov V. Ya. Chirva 《Chemistry of Natural Compounds》1998,34(6):694-698
The leaves of Algerian ivyHedera canariensis Willd. (Araliaceae) have yielded two new triterpene glycosides — caulophyllogenin 3-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranoside (L-F2) and its 28-O-α-L-rhamnopyranosyl-(1→4)-O-β-D-gentiobiosyl ester (L-I2) - and also the previously known hederagenin 3-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-glucopyranoside (L-F1). The structures of the glycosides were established on the basis of chemical transformations and1H and13C NMR spectroscopy.
Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 777–781, November–December, 1998. 相似文献
17.
V. V. Brei 《Theoretical and Experimental Chemistry》2009,45(3):186-188
The feasibility of using the equation log k = const – αH
0s was examined for solid acid catalysts. Data for the thermoprogrammed dealkylation of cumene showed that the temperature dependence
of the strength of the acid sites of the catalyst H
0s(T) should be considered in calculating the coefficient α. In this case, α→1.
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 3, pp. 173-175, May-June, 2009. 相似文献
18.
Le Xin Song Chuan Feng Teng Peng Xu Hai Ming Wang Zi Qiang Zhang Qing Qing Liu 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):223-233
The present work revealed there was a conceptual difference in the thermal decomposition behaviors between the complexed β-cyclodextrin
(CD) in an inclusion system and the β-CD complex of guest. The thermal decomposition behaviors of the solid inclusion complexes
of β-CD with ethylenediamine (Eda), diethylenetriamine (Dta) and triethylamine (Tea) were investigated using nonisothermal
thermogravimetry (TG) analysis based on weight loss as a function of temperature. In view of TG profiles, a consecutive mechanism
describing the formation and thermal decomposition of the three solid supermolecules of β-CD was presented. Heating rate has
very different effects on the thermal decomposition behaviors of these complexes. The faster the heating rate is, the higher
the melting-decomposition point of the complexed β-CD in an inclusion system is, and on the whole the bigger the rate constant
(k) of the thermal decomposition reaction of the complexed β-CD is. The thermal decomposition process of the complexed β-CD
for each inclusion system is determined to be simple first-order reaction using Ozawa method. The apparent activation energies
(E
a) and frequency factors (A) of the thermal decomposition reactions of the complexed β-CD molecules have been also calculated. It is found that when
the decomposition reaction of the complexed β-CD encountered a large value of E
a, such as that in Dta–β-CD system, an apparent compensation effect of A on E
a can provide enough energy to conquer the reaction barrier in prompting the k value of thermal decomposition reaction of the complexed β-CD according to Arrhenius equation. 相似文献
19.
V. A. Drebushchak Tatiana N. Drebushchak N. V. Chukanov Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2008,93(2):343-351
Five polymorphs of chlorpropamide (α, β, δ, γ, and ε) were investigated near the melting point by using DSC. Structure of
samples was tested by X-ray powder diffraction. Four first polymorphs were found to transform into ε-polymorph, which melts
at T
m=128°C, Δm
H=24 kJ mol−1. Enthalpy of the polymorph transitions ranges from +3 kJ mol−1 for α→ε to −0.8 kJ mol−1 for β→ε.
Structure of three first polymorphs was published elsewhere, and the structure of δ-polymorph is published for the first time.
XRPD patterns for all polymorphs are reported, together with the atomic coordinates for the δ-polymorph. 相似文献
20.
Z. Fengqui H. Rongzu S. Jirong G. Hongxu 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(7):1034-1036
The kinetic parameters of the exothermic decomposition of the title compound in a temperatureprogrammed mode have been studied
by means of DSC. The DSC data obtained are fitted to the integral, differential, and exothermic rate equations by the linear
least-squares, iterative, combined dichotomous, and least-squares methods, respectively. After establishing the most probable
general expression of differential and integral mechanism functions by the logical choice method, the corresponding values
of the apparent activation energy (E
a), preexponential factor (A), and reaction order (n) are obtained by the exothermic rate equation. The results show that the empirical kinetic model function in differential
form and the values of E
a and A of this reaction are (1 − α)−4.08, 149.95 kJ mol−1, and 1014.06 s−1, respectively. With the help of the heating rate and kinetic parameters obtained, the kinetic equation of the exothermic
decomposition of the title compound is proposed. The critical temperature of thermal explosion of the compound is 155.71°C.
The above-mentioned kinetic parameters are quite useful for analyzing and evaluating the stability and thermal explosion rule
of the title compound.
The text was submitted by the authors in English. 相似文献