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1.
The A1, O, AlO, A12O, Al2O2, WO2, and WO3, partial pressures in the vapor over Al2O3 in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1+, O+, AlO+, A12O+, Al2O2+, WO2+, and WO3+, ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO3(g) = WO2(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A12O2 were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Δat H o(AlO, g, 0) = 510.7 ± 3.3 kJ mol−1, Δat H o(Al2O, g, 0) = 1067.2 ± 6.9 kJ mol−1, and Δat H o(Al2O2, g, 0) = 1556.7 ± 9.9 kJ mol−1.  相似文献   

2.
Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO2 composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO2 composite and PANI are all D3, and the corresponding function is ƒ(α)=1.5(1−α)2/3[1−(1-α)1/3]−1. The correlated kinetic parameters are E a=112.7±9.2 kJ mol−1, lnA=13.9 and E a=81.8±5.6 kJ mol−1, lnA=8.8 for PANI/ZrO2 composite and PANI, respectively.  相似文献   

3.
Enthalpy of formation of the perovskite-related oxide BaCe0.9In0.1O2.95 has been determined at 298.15 K by solution calorimetry. Solution enthalpies of barium cerate doped with indium and mixture of BaCl2, CeCl3, InCl3 in ratio 1:0.9:0.1 have been measured in 1 M HCl with 0.1 M KI. The standard formation enthalpy of BaCe0.9In0.1O2.95 has been calculated as −1611.7±2.6 kJ mol−1. Room-temperature stability of this compound has been assessed in terms of parent binary oxides. The formation enthalpy of barium cerate doped by indium from the mixture of binary oxides is Δox H 0 (298.15 K)=−36.2±3.4 kJ mol−1.  相似文献   

4.
Areas of fusion and crystallization peaks of K3TaO2F4 and KTaF6 were measured using the DSC mode of a high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities, considering the temperature dependence of the calorimeter sensitivity, values of the fusion enthalpy of K3TaO2F4 at the fusion temperature of 1181 K of (43 ± 4) kJ mol−1 and of KTaF6 at the fusion temperature of 760 K of (8 ± 1) kJ mol−1 were determined.  相似文献   

5.
B3LYP method with the LANL2DZ basis for tin and aug-cc-pVDZ basis for carbon and hydrogen were used to obtain the equilibrium geometry of the main (with a positive charge on the tin) isomers in the C4H11Sn+ system and the transition states at their interconversion. As in the case of silicon and germanium, the cations of lighter elements of the 14th group, the most stable isomer is shown to be the tertiary ion, however, the energy of its complexes with ethane and propane is higher only by several kJ mol−1. Nevertheless, the formation of these complexes from the tertiary ion requires overcoming a rather high barrier (293 and 272 kJ mol−1, respectively). The barrier for isomerization of the secondary ion in the ethane complex is somewhat lower (222 kJ mol−1), but still is significantly greater than the energy gained at the appearance of the nucleogenic ion. The most probable transformation pathways of the nucleogenic stannylium ions are the formation of complexes with ethylene, which requires overcoming barriers of 130 and 117 kJ mol−1 for the tertiary and secondary ions, respectively.  相似文献   

6.
The heat capacity and the enthalpy increments of strontium metaniobate SrNb2O6 were measured by the relaxation method (2-276 K), micro DSC calorimetry (260-320 K) and drop calorimetry (723-1472 K). Temperature dependence of the molar heat capacity in the form C pm=(200.47±5.51)+(0.02937±0.0760)T-(3.4728±0.3115)·106/T 2 J K−1 mol−1 (298-1500 K) was derived by the least-squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S m0 (298.15 K)=173.88±0.39 J K−1 mol−1 was evaluated from the low temperature heat capacity measurements. The standard enthalpy of formation Δf H 0 (298.15 K)=-2826.78 kJ mol−1 was derived from total energies obtained by full potential LAPW electronic structure calculations within density functional theory.  相似文献   

7.
The two complexes, [RE(Gly)4(Im)(H2O)](ClO4)3(s)(RE = Eu, Sm), have been synthesized and characterized. The standard molar enthalpies of reaction for the following reactions, RECl3·6H2O(s)+4Gly(s)+Im(s)+3NaClO4(s) = =[RE(Gly)4(Im)(H2O)](ClO4)3(s)+3NaCl(s)+5H2O(l), were determined by solution-reaction colorimetry. The standard molar enthalpies of formation of the two complexes at T = 298.15 K were derived as Δf H mΘ {Eu(Gly)4(Im)(H2O)}(ClO4)3(s)} = = −(3396.6±2.3) kJ mol−1 and Δf H mΘ {Sm(Gly)4(Im)(H2O)}(ClO4)3(s)} = −(3472.7±2.3) kJ mol−1, respectively.  相似文献   

8.
Quantum-chemical calculations of the geometry and energies of nine possible isomers of 12-vertex cobaltacarborane CpCoC2B9H11 (1) were carried out by the DFT method (PBEPBE/DGDZVP/DGA1). Thermodynamic stability of the isomers increases with increasing distance between the carbon atoms in the cage and is virtually independent of the position of the CpCo vertex. The relative stabilities of the 1,2,3-(17.57 kcal mol−1), 1,2,4-(3.72 kcal mol−1), and 1,2,9-isomers of 1 (0 kcal mol−1) are similar to the corresponding values for the ortho (17.61 kcal mol−1), meta (3.21 kcal mol−1), and para isomers (0 kcal mol−1) of carborane C2B10H12. The results of the present study confirm a close similarity of the CpCo and BH fragments in metallacarborane chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1557–1559, July, 2005.  相似文献   

9.
Yttrium orthoborate crystallizes in the vaterite-type structure and has two polymorphous forms, viz. a low- und a high temperature one. DTA measurements of YBO3 confirmed a reversible phase transition with a large thermal hysteresis. The phase transition has been accurately characterized by the application of different heating and cooling rates (β). Consequently, the extrapolation of the experimental data to zero β yields the transition points at 986.9°C for the heating up and at 596.5°C for the cooling down cycle. These values correspond to samples just after treatment at 1350°C. For samples with a different ‘thermal history’ other phase transition temperatures are observed, (e.g. after having performed several heating and cooling cycles). The linear relationship between the associated DTA signal ΔT=T onsetT offset and the square root of the heating rate β was confirmed, but the relation between T onset and square root of β is not found here. From the empirical data a good linear fitting between T onset and ln(β+1) can be derived. From the kinetic analysis (Kissinger method) of the phase transformation of YBO3 an apparent activation energy of about 1386 kJ mol–1 for heating and of about 568 kJ mol–1 for cooling can be determined  相似文献   

10.
Temperature dependence of viscosity of title glasses (x=0, 2, 4, 6, 8, 10, abbreviated as M0, M2, M4, M6, M8, and M10, respectively) was measured by rotational viscometry (high temperature region: 102−106.5 dPas) and thermomechanical analysis (low temperature region: 108.5−1011.5 dPas) and described by the Vogel-Fulcher-Tammann equation. The MgO/CaO equimolar substitution (i.e. the increasing x value) smoothly shifts the high temperature viscosity to higher values. In the low temperature region the mixed alkali effect is demonstrated, and the highest viscosities are observed for the glasses M0 and M10. In the low temperature range the activation energy of viscous flow linearly decreases with the increasing x value (E act/kJ mol−1=479−9.0x). No significant dependence of activation energy on x was found in the high temperature range (E act/kJ mol−1=238.1±4.2). The structural relaxation was measured by thermomechanical experiment and theoretically interpreted in the frame of Tool-Narayanaswamy-Mazurin’s model. The broadening of the relaxation time spectrum was observed for the calcium-magnesium glasses in comparison with the pure calcium or magnesium glasses.  相似文献   

11.
Homogeneous manganocolumbite (MnNb2O6) was synthesized from Nb2O5 and MnO oxides. Powder sample was orthorhombic with unit cell parameters: α = 0.5766 nm, b = 1.4439 nm, c = 0.5085 nm and V = 0.4234 nm3. Heat capacity over the temperature range of 313–1253 K was measured in an inert atmosphere with combined thermogravimetry and calorimetry using NETZSCH STA 449C Jupiter thermoanalyzer. Melting point was 1767 ± 3 K, enthalpy of melting was 144 ± 4 kJ mol−1. Experimental heat capacity of MnNb2O6 is fitted to polynomial C pm = 221.46 + 3.03 · 10−3 T + −39.79 · 105 T −2 + 40.59 · 10−6 T 2.  相似文献   

12.
Three samples of silicon dioxide were syhthesized and their surface areas were measured. A thermo-chemical cycle was designed to calculate the molar formation enthalpy. The molar formation enthalpy, Δf H mΦ, for three amorphous silica with the Langmuir surface area 198.0854, 25.1108 and 11.9821 m2 g−1 gave −895.52, −910.86 and −915.67 kJ mol−1, respectively. With the increasing surface area, the values of Δf H mΦ increased accordingly. The results suggest that the silica with larger surface area is more unstable. The wetting heat was also measured by adding the silica powder into water. With the rehydration of the more SiOH groups on the surface, the larger surface areas of silica lead to the more wetting heat. A smaller particle has the more unstable hydroxyl groups and surface energy.  相似文献   

13.
Phase transition and thermal decomposition of hexadimethylsulfoxidealuminium chloride were studied by differential scanning calorimetry (DSC), thermogravimetry (TG) and simultaneous differential thermal analysis (SDTA). The gaseous products of the decomposition were on-line identified by a quadrupole mass spectrometer (QMS). In the temperature range of 95–300 K, [Al(DMSO)6]Cl3 indicates one phase transition at T ch=244.96 K (on heating) and at T cc=220.87 K (on cooling). Large thermal hysteresis of the phase transition (∼24 K) indicates its first order character. Large value of transition entropy (ΔS≈40 J mol−1 K−1) suggests its configurational character. Thermal decomposition of the title compound proceeds in four main stages. In the first stage, which starts just above ca. 300 K, the compound loses two DMSO molecules per one formula unit and undergoes into [Al(DMSO)4]Cl3. In the second stage, the next three DMSO ligands are released and simultaneously decomposed. The third stage, which continues up to ca. 552 K, is connected with a loss of the last DMSO ligand and the formation of AlCl3. In the fourth stage AlCl3 reacts with carbon monoxide that originates from the decomposition of DMSO, and first aluminium oxychloride and next solid Al2O3 plus carbon are created.  相似文献   

14.
Areas of fusion and crystallization peaks of K3NbO2F4 were measured using the DCS mode of a high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities, considering the temperature dependence of the calorimeter sensitivity, the value of the fusion enthalpy of K3NbO2F4 of (98 ± 6) kJ mol−1 was determined at the fusion temperature of 1257 K.  相似文献   

15.
Summary As part of a larger study of the physical properties of potential ceramic hosts for nuclear wastes, we report the molar heat capacity of brannerite (UTi2O6) and its cerium analog (CeTi2O6) from 10 to 400 K using an adiabatic calorimeter. At 298.15 K the standard molar heat capacities are (179.46±0.18) J K-1 mol-1 for UTi2O6 and (172.78±0.17) J K-1 mol-1 for CeTi2O6. Entropies were calculated from smooth fits of the experimental data and were found to be (175.56±0.35) J K-1 mol-1 and (171.63±0.34) J K-1 mol-1 for UTi2O6 and CeTi2O6, respectively. Using these entropies and enthalpy of formation data reported in the literature, Gibb’s free energies of formation from the elements and constituent oxides were calculated. Standard free energies of formation from the elements are (-2814.7±5.6) kJ mol-1 for UTi2O6 and (-2786.3±5.6) kJ mol-1 for CeTi2O6. The free energy of formation from the oxides at T=298.15 K are (-5.31±0.01) kJ mol-1 and (15.88±0.03) kJ mol-1 for UTi2O6 and CeTi2O6, respectively.  相似文献   

16.
Monomeric extracellular endoglucanase (25 kDa) of transgenic koji (Aspergillus oryzae cmc-1) produced under submerged growth condition (7.5 U mg−1 protein) was purified to homogeneity level by ammonium sulfate precipitation and various column chromatography on fast protein liquid chromatography system. Activation energy for carboxymethylcellulose (CMC) hydrolysis was 3.32 kJ mol−1 at optimum temperature (55 °C), and its temperature quotient (Q 10) was 1.0. The enzyme was stable over a pH range of 4.1–5.3 and gave maximum activity at pH 4.4. V max for CMC hydrolysis was 854 U mg−1 protein and K m was 20 mg CMC ml−1. The turnover (k cat) was 356 s−1. The pK a1 and pK a2 of ionisable groups of active site controlling V max were 3.9 and 6.25, respectively. Thermodynamic parameters for CMC hydrolysis were as follows: ΔH* = 0.59 kJ mol−1, ΔG* = 64.57 kJ mol−1 and ΔS* = −195.05 J mol−1 K−1, respectively. Activation energy for irreversible inactivation ‘E a(d)’ of the endoglucanase was 378 kJ mol−1, whereas enthalpy (ΔH*), Gibbs free energy (ΔG*) and entropy (ΔS*) of activation at 44 °C were 375.36 kJ mol−1, 111.36 kJ mol−1 and 833.06 J mol−1 K−1, respectively.  相似文献   

17.
The macroporous Li3V2(PO4)3/C composite was synthesized by oxalic acid-assisted carbon thermal reaction, and the common Li3V2(PO4)3/C composite was also prepared for comparison. These samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and electrochemical performance tests. Based on XRD and SEM results, the sample has monoclinic structure and macroporous morphology when oxalic acid is introduced. Electrochemical tests show that the macroporous Li3V2(PO4)3/C sample has a high initial discharge capacity (130 mAh g−1 at 0.1 C) and a reversible discharge capacity of 124.9 mAh g−1 over 20 cycles. Moreover, the discharge capacity of the sample is still 91.5 mAh g−1, even at a high rate of 2 C, which is better than that of the sample with common morphology. The improvement in electrochemical performance should be attributed to its improved lithium ion diffusion coefficient for the macroporous morphology, which was verfied by cyclic voltammetry and electrochemical impedance spectroscopy.  相似文献   

18.
The heat capacity of PbMO3 (M=Ti, Zr and Hf) at constant pressure was measured using a differential scanning calorimeter (DSC) from room temperature up to 870 K. Large anomalies were found in the heat capacity curves, corresponding to the ferroelectricparaelectric phase transition in PbTiO3 (PT), the antiferroelectric-paraelectric phase transitions in PbZrO3 (PZ) and PbHfO3 (PH). The transition entropies were estimated as 7.3 J K−1 mol−1 (PT), 9.9 J K−1 mol−1 (PZ) and 9.3 J K−1 mol−1 (PH). These values of transition entropies are much larger than that of a typical displacive-type phase transition.  相似文献   

19.
The Gibbs free energies of solvation (ΔG s) and the electronic structures of endohedral metallofullerenes M+@C60 (M+= Li+, K+) were calculated within the framework of the density functional theory and the polarizable continuum model. In water environment, the equilibrium position of K+ is at the center of the fullerene cavity whereas that of Li+ is shifted by 0.14 nm toward the fullerene cage. The Li+ cation is stabilized by interactions with both the fullerene and solvent. The equilibrium structures of both endohedral metallofullerenes are characterized by very close ΔG s values. In particular, the calculated ΔG s values for K+@C60 are in the range from −124 to −149 kJ mol−1 depending on the basis set and on the type of the density functional. Molecular dynamics simulations (TIP3P H2O, OPLS force field, water sphere of radius 1.9 nm) showed that the radial distribution functions of water density around C60 and M+@C60 are very similar, whereas orientations of water dipoles around the endohedral metallofullerenes resemble the hydration pattern of isolated metal ions.  相似文献   

20.
Nanoparticles of NiC2O4 · 2H2O were obtained within the interspheric voids of synthetic opal polycrystalline samples based on SiO2. The thermal decomposition of NiC2O4 · 2H2O inclusions within the pores of crystallites was studied by means of thermal gravimetry and differential scanning calorimetry under static conditions in atmospheres of He and air. The efficient activation energy of dehydration (180 ± 10 kJ mol−1) and dehydration enthalpy of nickel oxalate crystalline hydrate (69.9 kJ mol−1) within the pores of photonic crystals based on SiO2 were calculated. Pyrolysis of the nickel oxalate led to the formation of NiO nanoparticles within the voids and on the external surface of the photonic crystallites. The behavior of polycrystalline samples of the photonic crystals in a medium of immersion liquids was studied. It was shown that the partial population of the interspheric pores of photonic crystals with NiC2O4 · 2H2O, NiO, and Ni that diffuse visible light do not lead to a total loss of light conductivity in the immersion medium. The diffuse reflection spectra of a sample of photonic crystals populated with NiC2O4 · 2H2O and NiO phases were recorded. A sample of photonic crystals with inclusions of metallic nickel particles exhibiting magnetic properties was obtained by treating nickel oxide-containing synthetic opal based on SiO2 with molecular hydrogen.  相似文献   

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