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1.
V2O3(OH)4(g), Proof of Existence, Thermochemical Characterization, and Chemical Vapor Transport Calculations for V2O5(s) in the Presence of Water By use of the Knudsen-cell mass spectrometry the existence of V2O3(OH)4(g) is shown. For the molecules V2O3(OH)4(g), V4O10(g), and V4O8(g) thermodynamic properties were calculated by known Literatur data. The influence of V2O3(OH)4(g) for chemical vapor transport reactions of V2O5(s) with water ist discussed. ΔBH°(V2O3(OH)4(g), 298) = –1920 kJ · mol–1 and S°(V2O3(OH)4(g), 298) = 557 J · K–1 · mol–1, ΔBH°(V4O10(g), 298) = –2865,6 kJ · mol–1 and S°(V4O10(g), 298) = 323.7 J · K–1 · mol–1, ΔBH°(V4O8(g), 298) = –2465 kJ · mol–1 and S°(V4O8(g), 298) = 360 J · K–1 · mol–1. 相似文献
2.
V. D. Živanović S. R. Grujić M. B. Tošić N. S. Blagojević J. D. Nikolić 《Journal of Thermal Analysis and Calorimetry》2009,96(2):427-432
The crystallization of K2O·TiO2·3GeO2 glass under non-isothermal condition was studied. In powdered glass with particle sizes less than 0.15 mm, surface crystallization
was dominant and an activation energy of crystal growth of E
a,s=327±50 kJ mol−1 was calculated. In the size range 0.15 to 0.45 mm, both surface and volume crystallization occurred. For particle sizes >0.45
mm, volume crystallization dominated with spherulitic morphology of the crystals growth and E
a,v=359±64 kJ mol−1 was calculated. 相似文献
3.
Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount
of CaO and MgO in Li2O-Al2O3-2SiO2 were investigated. With CaO and MgO addition, the crystallization temperature (T
p) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol−1 to 537±5 kJ mol−1. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk
crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength
and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated
with crystallization and morphology of glass ceramics. 相似文献
4.
Sergey Vyazovkin Nicolas Sbirrazzuoli Ion Dranca 《Macromolecular rapid communications》2004,25(19):1708-1713
Summary: An advanced isoconversional method has been applied to determine the effective activation energies (E) for the glass transition in polystyrene (PS), poly(ethylene terephthalate) (PET), and boron oxide (B2O3). The values of E decrease from 280 to 120 kJ · mol−1 in PS, from 1 270 to 550 kJ mol−1 in PET, and from 290 to 200 kJ mol−1 in B2O3. It is suggested that a significant variation in E should be observed for the fragile glasses that typically include polymers.
5.
《无机化学与普通化学杂志》2018,644(15):833-837
In order to enhance the thermal stability of the barium salt of 5,5′‐bistetrazole (H2BT), carbohydrazide (CHZ) was used to build [Ba(CHZ)(BT)(H2O)2]n as a new energetic coordination compound by using a simple aqueous solution method. It was characterized by FT‐IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction. The crystal belongs to the monoclinic P21/c space group [a = 8.6827(18) Å, b = 17.945(4) Å, c = 7.2525 Å, β = 94.395(2)°, V = 1126.7(4) Å3, and ρ = 2.356 g · cm–3]. The BaII cation is ten‐coordinated with one BT2–, two shared carbohydrazides, and four shared water molecules. The thermal stabilities were investigated by differential scanning calorimetry (DSC) and thermal gravity analysis (TGA). The dehyration temperature (Tdehydro) is at 187 °C, whereas the decomposition temperature (Td) is 432 °C. Non‐isothermal reaction kinetics parameters were calculated by Kissinger's method and Ozawa's method to work out EK = 155.2 kJ · mol–1, lgAK = 9.25, and EO = 158.8 kJ · mol–1. The values of thermodynamic parameters, the peak temperature (while β → 0) (Tp0 = 674.85 K), the critical temperature of thermal explosion (Tb = 700.5 K), the free energy of activation (ΔG≠ = 194.6 kJ · mol–1), the entropy of activation (ΔS≠ = –66.7 J · mol–1), and the enthalpy of activation (ΔH≠ = 149.6 kJ · mol–1) were obtained. Additionally, the enthalpy of formation was calculated with density functional theory (DFT), obtaining ΔfH°298 ≈ 1962.6 kJ · mol–1. Finally, the sensitivities toward impact and friction were assessed according to relevant methods. The result indicates the compound as an insensitive energetic material. 相似文献
6.
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
7.
Some of the properties of glasses obtained in the systems TeO2–MoO3 and TeO2–MoO3–V2O5 had been studied. A good correlation between the properties and the phase diagram of the TeO2–MoO3 system was established. The glass resistance-composition function varied between 6.85 · 109 ohm · cm and 2.93 · 1010 ohm · cm. The isolines of the properties (softening temperature, density, resistance at room and higher temperatures and activation energy) of the glasses obtained from the TeO2–MoO3–V2O5 system were ploted. The electrical resistance is influenced by the concentration of V2O5 and MoO3 and by temperature. The glass absorption characteristics of thin layers were determined in the visible range. 相似文献
8.
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
9.
The energetic complex, [Cd(HTRTR)2(H2O)4](HTNR)2 {HTRTR = 4‐[3‐(1,2,4‐triazol‐yl)‐1,2,4‐triaozle; HTNR– = styphnic acid anion) was synthesized and characterized by FT‐IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction. It crystallizes triclinic in space group P$\bar{1}$ [a = 8.156(2) Å, b = 8.374(2) Å, c = 13.267(4) Å, α = 84.925(11)°, β = 87.016(11)°, γ = 63.683(5)°, V = 808.9(4) Å3, ρ = 1.940 g · cm–3]. The CdII ion is six‐coordinate with two HTRTRs and four water molecules. The thermal stabilities were investigated by differential scanning calorimetry (DSC). Non‐isothermal reaction kinetic parameters were calculated by Kissinger's and Ozawa‐Doyle's methods to obtain EK = 144.0 kJ · mol–1, lgAK = 14.22, and EO = 144.3 kJ · mol–1. The values of thermodynamic parameters, the peak temperature while β→0 (Tp0), free energy of activation (ΔG≠), entropy of activation (ΔS≠), and enthalpy of activation (ΔH≠) were obtained. Additionally, the enthalpy of formation was calculated by Hess's law on the basis of the experimental constant‐volume heat of combustion measured by bomb calorimetry, obtaining ΔfH°298 = 4985.5 kJ · mol–1. Finally, the sensitivities toward impact and friction were assessed according to relevant methods. The result indicates it as an insensitive energetic material. 相似文献
10.
Summary The third-law method has been applied to determine the enthalpies, ΔrHT0, for dehydration reactions of kaolinite, muscovite and talc. The ΔrHT0values measured in the equimolar (in high vacuum) and isobaric (in the presence of water vapour) modes (980±15, 3710±39 and
2793±34 kJ mol-1, for kaolinite, muscovite and talc, respectively) practically coincide if to take into account the strong self-cooling effect
in vacuum. This fact strongly supports the mechanism of dissociative evaporation of these compounds in accordance with the
reactions (primary stages): Al2O3·2SiO2·2H2O(s)→Al2O3(g)↓+2SiO2(g)↓+2H2O(g); K2O·3Al2O3·6SiO2·2H2O(s) →K2O(g)↓+3Al2O3(g)↓+6SiO2(g)↓+2H2O(g) and 3MgO·4SiO2·H2O(s) →3MgO(g)↓+4SiO2(g)↓+H2O(g). The values of the Eparameter deduced from these data for equimolar and isobaric modes of dehydration are as follows: 196 and 327 kJ mol-1for kaolinite, 309 and 371 kJ mol-1for muscovite and 349 and 399 kJ mol-1for talc. These values are in agreement with quite a few early results reported in the literature in 1960s. 相似文献
11.
The total conductivity (σT) in bcc γ-Bi2O3 doped with V2O5 system has been measured in the composition range between 1 and 7 mol% V2O5 at different temperatures. Phase transitions for different addition amounts depending on the temperature were investigated
by quenching the samples. According to the XRD and DTA/TG results, this bcc type solid solution was stable up to about 720°C and the solubility limit was found at ˜7 mol% V2O5 in γ-phase. This system showed predominantly an oxide ionic conduction. As the V2O5 addition increased, the ionic conduction increased up to 5 mol% V2O5 at which the highest conductivity was found to be 8.318·10-2 Ω-1 cm-1 at 700°C and then decreased. It has been proposed that γ-Bi2O3 phase contains a large number of oxide anion vacancies and incorporated vanadium cations at tetrahedral sites which affect
the oxygen sublattice of the crystal structure.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
The relative enthalpies, ΔHo (0) and ΔHo (298.15), of stationary points (four minimum and three transition structures) on the •O3H potential energy surface were calculated with the aid of the G3MP2B3 as well as the CCSD(T)–CBS (W1U) procedures from which
we earlier found mean absolute deviations (MAD) of 3.9 kJ mol−1 and 2.3 kJ mol−1, respectively, between experimental and calculated standard enthalpies of the formation of a set of 32 free radicals. For
CCSD(T)-CBS (W1U) the well depth from O3 + H• to trans-•O3H, ΔHowell(298.15) = −339.1 kJ mol−1, as well as the reaction enthalpy of the overall reaction O3 + H•→O2 + •OH, ΔrHo(298.15) = −333.7 kJ mol−1, and the barrier of bond dissociation of trans-•O3H → O2 + •OH, ΔHo(298.15) = 22.3 kJ mol−1, affirm the stable short-lived intermediate •O3H. In addition, for radicals cis-•O3H and trans-•O3H, the thermodynamic functions heat capacity Cop(T), entropy So (T), and thermal energy content Ho(T) − Ho(0) are tabulated in the range of 100 − 3000 K. The much debated calculated standard enthalpy of the formation of the trans-•O3H resulted to be ΔfHo(298.15) = 31.1 kJ mol −1 and 32.9 kJ mol −1, at the G3MP2B3 and CCSD(T)-CBS (W1U) levels of theory, respectively. In addition, MR-ACPF-CBS calculations were applied
to consider possible multiconfiguration effects and yield ΔfHo(298.15) = 21.2 kJ mol −1. The discrepancy between calculated values and the experimental value of −4.2 ± 21 kJ mol−1 is still unresolved.
Note added in proof: Yu-Ran Luo and J. Alistair Kerr, based on the discussion in reference 12, recently presented an experimental
value of ΔfHo(298.15) = 29.7 ± 8.4 kJ mol−1 in the 85th edition of the CRC Handbook of Chemistry and Physics (in progress). 相似文献
13.
Stefan Perişanu Iulia Contineanu Mircea D. Banciu Hui Zhao Nigam Rath James Chickos 《Structural chemistry》2006,17(6):639-648
Condensed and gas phase enthalpies of formation of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1, (−199.1 ± 16.4), (−70.5 ± 20.5) kJ mol−1, respectively) and 3,4,6,7-dibenzobicyclo[3.2.1]nona-3,6-dien-2-one (2, (−79.7 ± 22.9), (20.1 ± 23.1) kJ mol−1) are reported. Sublimation enthalpies at T=298.15 K for these compounds were evaluated by combining the fusion enthalpies at T = 298.15 K (1, (12.5 ± 1.8); 2, (5.3 ± 1.7) kJ mol−1) adjusted from DSC measurements at the melting temperature (1, (T
fus, 357.7 K, 16.9 ± 1.3 kJ mol−1)); 2, (T
fus, 383.3 K, 10.9 ± 0.1) kJ mol−1) with the vaporization enthalpies at T = 298.15 K (1, (116.1 ± 12.1); 2, (94.5 ± 2.2) kJ mol−1) measured by correlation-gas chromatography. The vaporization enthalpies of benzoin ((98.5 ± 12.5) kJ mol−1) and 7-heptadecanone ((94.5 ± 1.8) kJ mol−1) at T = 298.15 K and the fusion enthalpy of phenyl salicylate (T
fus, 312.7 K, 18.4 ± 0.5) kJ mol−1) were also determined for the correlations. The crystal structure of 1 was determined by X-ray crystallography. Compound
1 exists entirely in the enol form and resembles the crystal structure found for benzoylacetone. 相似文献
14.
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
15.
16.
D. D. Agarwal K. L. Madhok H. S. Goswami 《Reaction Kinetics and Catalysis Letters》1994,52(1):225-232
The vapor phase catalytic aerial oxidation of toluene to benzaldehyde (BzH) was carried out over La2MoO6 containing the same kind of layered structure as Bi2MoO6. The overall kinetic analysis indicated the oxidation of toluene to BzH to be first order with a frequency factor of log 0.63 and activation energy (Ea) of 26.3 kJ mol–1 and 34.0 kJ mol–1, respectively, for Bi2MoO6 and La2MoO6 catalysts. A relation between the activity and activation energy of conduction (E) is shown. 相似文献
17.
Melek Erol 《Chemical Papers》2010,64(4):482-490
In this study, bioactivity of glass in the system SiO2-CaO-Al2O3-P2O5-Na2O-MgO-CaF2 was investigated. For this purpose, a glass sample was prepared by the traditional melting method. Crystallization behavior
of bioactive glass was also investigated using differential thermal analyses. The Avrami constant of bioactive glass sample
calculated according to the Ozawa equation was 3.72 ± 0.4, which indicates bulk crystallization. Using the Matusita-Sakka
and the Kissinger equations, activation energy of crystal growth was determined as (394 ± 17) kJ mol−1 and (373 ± 12) kJ mol−1, respectively. These results indicate that the crystallization activation energy data of bioactive glass obtained in this
study are accurate and reliable. Bioactivity of the resultant glass sample was analyzed by immersion in simulated body fluid.
Scanning electron microscopy, thin film X-ray diffraction, ultraviolet spectroscopy and inductively coupled plasma techniques
were used to monitor changes in the glass surface and the simulated body fluid composition. The results revealed that a hydroxyapatite
layer was formed on the glass surface after 21 days of immersion in SBF. Formation of the hydroxyapatite layer confirmed the
bioactivity of the glass in the system SiO2-CaO-Al2O3-P2O5-Na2O-MgO-CaF2. In addition, physical and mechanical properties of the sample were measured to determine changes in the properties with
the immersion time. The results show that bioactive glass maintained its strength during the immersion in a simulated body
fluid solution. 相似文献
18.
Martin Palou Eva Kuzielová Martin Vitkovič Maha S. M. Noaman 《Central European Journal of Chemistry》2009,7(2):228-233
Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesised in the Li2O-SiO2-CaO-P2O5-CaF2 system with P2O5: CaO: CaF2 ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics
of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller
particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle
sizes. Inclusion of FA in the LS2 favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism
is at about 0.3 mm for pure LS2 glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (299 ± 1 kJ mol-1 for pure LS2 glass and 288 ± 7 kJ mol−1 for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS2 glass and 303 ± 8 kJ mol-1 for glass containing FA according to Ozawa) indicate that the tendency of the glasses to crystallize
is supported by the FA presence. Bioactivity of all samples has been proved in vitro by the formation of new layers of apatite-like
phases after soaking in SBF.
相似文献
19.
Tien The Nguyen Thang Minh Le Duc Duc Truong Rasmus Fehrmann Anders Riisager Isabel Van Driessche 《Research on Chemical Intermediates》2012,38(3-5):829-846
In this work, the possible synergy effects between Bi2O3, MoO3 and V2O5, and between Bi2Mo3O12 and BiVO4, were investigated. The catalytic activity of the ??mechanical mixture?? of these compounds was measured. The mixture containing 36.96?mol% Bi2O3, 39.13?mol% MoO3 and 23.91?mol% V2O5 (21.43?mol% Bi2Mo3O12 and 78.57?mol% BiVO4), corresponding to the compound Bi1?x/3V1?x Mo x O4 with x?=?0.45 (Bi0.85V0.55Mo0.45O4), exhibited the highest activity for the selective oxidation of propylene to acrolein. The mixed sample prepared chemically by a sol?Cgel method possessed higher activity than that of mechanical mixtures. 相似文献
20.
L. Stradella 《Journal of Thermal Analysis and Calorimetry》1984,29(2):301-308
Oxygen depletion and reoxidation of bismuth molybdates (2∶1; 2∶3) have been studied by means of isothermal thermogravimetry and DTA measurements. From the isothermal curves, Arrhenius energies were obtained between 411 and 683 K. The activation energies for oxygen depletion from Bi2O3·MoO3 were lower than those for Bi2O3·3MoO3. Two kinetically different types of oxygen release were identified for both molybdates. Arrhenius plots were also obtained from reoxidation experiments: Bi2O3·MoO3 was more easily reoxidable than Bi2O3·3MoO3. The substantial closeness of the respective activation energies suggests that depletion and reoxidation follow the same mechanistic steps. Some DTA measurements confirm the existence of at least two types of reoxidation sites for both oxysalts. 相似文献