共查询到20条相似文献,搜索用时 31 毫秒
1.
Ashis Bhattacharjee Debasis Roy Madhusudan Roy 《International Journal of Thermophysics》2012,33(12):2351-2365
Thermal decomposition of oxalate-based molecular precursors, namely ${\{{\rm N}(n{-} {\rm C}_{4} {\rm H}_{9})_{4}[{\rm Zn}^{\rm II}{\rm Fe}^{\rm III}({\rm C}_{2} {\rm O}_{4})_{3}]\}_{\infty}, \{{\rm N}(n{-}{\rm C}_{4}{\rm H}_{9})_{4}[{\rm Co}^{\rm II}{\rm Fe}^{\rm III}({\rm C}_{2}{\rm O}_{4})_{3}]\}_{\infty}}$ , and ${\{{\rm N}(n{-}{\rm C}_{4} {\rm H}_{9})_{4}[{\rm Fe}^{\rm II}{\rm Fe}^{\rm III}({\rm C}_{2}{\rm O}_{4})_{3}]\}_{\infty}}$ , abbreviated as BuZnFe, BuCoFe, and BuFeFe, respectively, are studied using thermogravimetry (TG) in the temperature range from ~300?K to ~675?K at multiple heating rates. This study also deals with how the thermal decomposition of the complexes proceed stepwise through a series of intermediate reactions. The effect of the divalent metal MII on the nature of thermal decomposition of the complexes, reflected in their TG profiles in terms of number of steps involved, is reported in this study. The temperature range of thermal decomposition steps for BuZnFe, BuCoFe, and BuFeFe with the same heating rates are studied systematically. Two different isoconversional methods, namely an improved iterative method and a model-free method are employed to calculate the kinetic parameters, and thus the most probable reaction mechanism of thermal decomposition is determined. Based on kinetic parameters, the important thermodynamic parameters such as the changes of entropy, enthalpy, and Gibbs free energy are estimated for the activated complex formation from the precursors. Considering the mass loss during the different thermal decomposition steps of BuZnFe, BuCoFe, and BuFeFe, observed in the thermogravimetry profiles, the overall reactions of the thermal decompositions are demonstrated. 相似文献
2.
Eric F. May Robert F. Berg Michael R. Moldover 《International Journal of Thermophysics》2007,28(4):1085-1110
The zero-density viscosity of hydrogen, methane, and argon was determined in the temperature range from 200 to 400 K, with standard uncertainties of
0.084% for hydrogen and argon and 0.096% for methane. These uncertainties are dominated by the uncertainty of helium’s viscosity
, which we estimate to be 0.080% from the difference between ab initio and measured values at 298.15 K. For xenon, measurements ranged between 200 and 300 K and the zero-density viscosity was determined with an uncertainty of 0.11%. The data imply that xenon’s viscosity virial coefficient is positive over this
temperature range, in contrast with the predictions of corresponding-states models. Furthermore, the xenon data are inconsistent
with Curtiss’ prediction that bound pairs cause an anomalous viscosity decrease at low reduced temperatures. At 298.15 K.
the ratios , and were determined with a relative uncertainty of less than 0.024% by measuring the flow rate of these gases through a quartz
capillary while simultaneously measuring the pressures at the ends of the capillary. Between 200 and 400 K, a two-capillary
viscometer was used to determine with an uncertainty of 0.024% for H2 and Ar, 0.053% for CH4, and 0.077% for Xe. From was computed using the values of calculated ab initio. Finally, the thermal conductivity of Xe and Ar was computed from and values of the Prandtl number that were computed from interatomic potentials. These results may help to improve correlations
for the transport properties of these gases and assist efforts to develop ab initio two- and three-body intermolecular potentials for these gases. Reference viscosities for seven gases at 100 kPa are provided
for gas metering applications. 相似文献
3.
Light-weight, cellular β-SiAlON/SiC ceramics were produced via dip-coating of an Al/Si-powder containing preceramic polymer
slurry into corrugated cardboard. The coated cardboard preforms were pyrolyzed in Ar-atmosphere at 1200°C, where the cellulose
fibres decomposed into carbon. Simultaneously the Al/Si melt infiltrated into the porous carbon and formed β-SiC. Subsequent
nitridation at temperatures between 1200–1530°C resulted in the formation of a β-SiC-containing
composite. Different pre-oxidation treatment resulted in a variation of the oxygen content in the solid solution phase (z = 0.6–1.2). 相似文献
4.
Activation kinetics of the As acceptor in HgCdTe 总被引:1,自引:0,他引:1
The amphoteric model of As in HgCdTe is the basis of an investigation into how the transfer is achieved under Hg saturation and so obtain a method for calculating optimum annealing times for the transfer. It is concluded
that Schaake’s assumption that the transfer, or activation, process is diffusion limited, rather than reaction-rate limited,
is a better fit to experimental data. The identification of the Te self-diffusivity in HgCdTe as due to Te
i
defects is considered to be incorrect. As a result, Schaake’s activation model can only underestimate the optimum anneal
times for activation if the experimentally observed Te self-diffusivity is used. An equation based on experimental activation data
is given that permits an estimate of the optimum anneal time to be obtained in HgCdTe layers. 相似文献
5.
Mahendra Nath Roy Ashis Banerjee Pran Kumar Roy 《International Journal of Thermophysics》2009,30(2):515-528
Partial molar volumes and viscosity B-coefficients for nicotinamide in (0.00, 0.05, 0.10, 0.15, and 0.20) mol·dm−3 aqueous resorcinol solutions have been determined from solution density and viscosity measurements at (298.15, 308.15, and
318.15) K as a function of the concentration of nicotinamide (NA). Here the relation , has been used to describe the temperature dependence of the partial molar volume . These results and the results obtained in pure water were used to calculate the standard volumes of transfer and viscosity B-coefficients of transfer of nicotinamide from water to aqueous resorcinol solutions to study various interactions in the
ternary solutions. The partial molar volume and experimental slopes obtained from the Masson equation have been interpreted in terms of solute–solvent and solute–solute
interactions, respectively. The viscosity data have been analyzed using the Jones–Dole equation, and the derived parameters
B and A have also been interpreted in terms of solute–solvent and solute–solute interactions, respectively, in the ternary solutions.The
structure making or breaking ability of nicotinamide has been discussed in terms of the sign of . The activation parameters of viscous flow for the ternary solutions studied were also calculated and explained by the application
of transition state theory. 相似文献
6.
K. Zelonka M. Sayer A. P. Freundorfer J. Hadermann 《Journal of Materials Science》2006,41(12):3885-3897
Stoichiometric barium strontium titanate (BST) films of composition
with thickness >2 μm have been fabricated on Si/SiO2/Pt substrates by hydrothermal sol-gel composite processing. This film deposition technique involves the treatment of a spun-on
sol-gel composite film, formed from a suspension of a powder in an aqueous BST sol-gel, at temperatures from 100–200°C at
a pressure of 1–15 atm. An initial hydrolysis procedure eliminates dissolution of the dried sol-gel during the hydrothermal
treatment. Glancing angle X-ray diffraction shows excellent crystallinity and stoichiometry in the BST films with no evidence
of new phases created during processing. Scanning electron micrography and atomic force microscopy show densification of the
film structure and the development of a bridging microstructure. Transmission electron micrography indicates that while much
of the sol-gel derived matrix phase is amorphous a more crystalline interface occurs with the powder particles. The relative
permittivity and loss tangent of the films are measured using a parallel plate capacitor technique in the frequency range
1–100 kHz. At 100 kHz relative permittivities of the films range from ɛr = 400–1200 and loss tangents lie in the range 0.05 < tan δ < 0.10, depending on the parameters of film preparation. The film
structure and morphology and the electrical studies suggest that the microstructure of the films evolves by deposition of
the sol-gel derived BST on the underlying powder, resulting in an electrically interconnected microstructure in which the
sol-gel derived material bridges between the high permittivity powder particles. 相似文献
7.
The variation of the critical temperature and of the superconductive gaps as functions of doping (Al, C) in the diboride MgB has been studied in the framework of the two-band Eliashberg theory and traditional phonon coupling mechanism. We have solved the two-band Eliashberg equations using first-principle calculations or simple assumptions for the variation of the relevant physical quantities. We have found that the experimental curves can be exactly explained only if the Coulomb pseudopotential changes with x by tuning the Fermi level toward the σ band edge. We also found that a small amount of impurities changes the structural properties of the material, so we cannot treat the Mg and MgB systems as a contamination with Al or C of MgB, but as new materials. Finally, we compare the predictions of our theory with the available experimental data. 相似文献
8.
Excess molar volumes, , excess molar isentropic compressibilities, , and deviations of the speeds of sound, u
D, from their ideal values u
id in an ideal mixture for binary mixtures of 1-octanol, C8H17OH, with hexadecane, C16H34, and squalane (2,6,10,15,19,23-hexamethyltetracosane), C30H62, at T = (298.15, 303.15, and 308.15) K and at atmospheric pressure were derived from experimental density, ρ, and speed-of-sound data, u. Viscosity measurements were also carried out for the same mixtures. The Prigogine-Flory-Patterson (PFP) theory has been
applied to analyze of these systems. Furthermore, the apparent molar volumes, and apparent molar compressibility, of the components at infinite dilution have been calculated. 相似文献
9.
M. L. McCombie V. R. Tarnawski G. Bovesecchi P. Coppa W. H. Leong 《International Journal of Thermophysics》2017,38(2):21
The paper reveals the experimental procedure and thermo-physical characteristics of a coarse pyroclastic soil (Pozzolana), from the neighborhoods of Rome, Italy. The tested samples are comprised of 70.7 % sand, 25.9 % silt, and 3.4 % clay. Their mineral composition contained 38 % pyroxene, 33 % analcime, 20 % leucite, 6 % illite/muscovite, 3 % magnetite, and no quartz content was noted. The effective thermal conductivity of minerals was assessed to be about \(2.14\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\). A transient thermal probe method was applied to measure the thermal conductivity (\(\lambda \)) over a full range of the degree of saturation \((S_{\mathrm{r}})\), at two porosities (n) of 0.44 and 0.50, and at room temperature of about \(25\,^{\circ }\hbox {C}\). The \(\lambda \) data obtained were consistent between tests and showed an increasing trend with increasing \(S_{\mathrm{r}}\) and decreasing n. At full saturation (\(S_{\mathrm{r}}=1\)), a nearly quintuple \(\lambda \) increase was observed with respect to full dryness (\(S_{\mathrm{r}}=0\)). In general, the measured data closely followed the natural trend of \(\lambda \) versus \(S_{\mathrm{r}}\) exhibited by published data at room temperature for other unsaturated soils and sands. The measured \(\lambda \) data had an average root-mean-squared error (RMSE) of \(0.007\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\) and \(0.008\,\hbox {W}{\cdot } \hbox {m}^{-1}{\cdot } \hbox {K}^{-1}\) for n of 0.50 and 0.44, respectively, as well as an average relative standard deviation of the mean at the 95 % confidence level \((\hbox {RSDM}_{0.95})\) of 2.21 % and 2.72 % for n of 0.50 and 0.44, respectively. 相似文献
10.
A layered cuprate TaSr2
Cu2
for x = 0.4–0.8 has been successfully synthesized by solid state reaction. X-ray powder diffraction analysis indicates that nearly
all the peaks from the samples can be indexed to a single phase of Ta-1222. The sample with nominal composition TaSr2Gd1.6Ce0.4Cu2
showed a tetragonal structure with lattice parameters a = 3.858 Å, c = 28.81 Å with space group most likely I4/mmm. The TaSr2
Cu2
compound exhibits a narrow superconducting region near x = 0.6 with Tc-onset = 30 and Tc-zero=10 K as determined by d.c. electrical resistance versus temperature measurements. 相似文献
11.
Calculations of low-density transport property collision integrals are used to obtain the high-temperature transport properties
of silver atoms as a function of temperature. The collision integrals depend on the two-body interaction potentials between
silver atoms in various electronic states. Contributions are included from the ground and excited molecular electronic states of the silver dimer that dissociate to two ground-state silver atoms and from the excited molecular state that dissociates to a ground state and an excited state silver atom. Spectroscopic constants are available
for these three electronic states, and these spectroscopic constants have been used to determine the Hulburt–Hirschfelder
(HH) potentials for these three states. The HH potential is perhaps the best general-purpose potential for representing atom–atom
interactions. This potential depends only on the spectroscopic constants, and can be used to calculate the viscosity and diffusion
collision integrals for the three molecular electronic states. The collision integrals are then degeneracy averaged over the
three states. The heat capacity of silver atoms is also calculated at high temperatures. These results provide the information
required to obtain the thermal conductivity, viscosity, and self-diffusion coefficients of silver atoms over a wide temperature
range from the boiling point of silver to temperatures at which ionization becomes important. 相似文献
12.
V. Doquet Q. H. Bui G. Bertolino E. Merhy L. Alves 《International Journal of Fracture》2010,165(1):61-76
Fatigue crack growth tests in mixed-mode II + III were performed on maraging steel and Ti-6Al-4V. The 3D evolutions of the crack fronts -measured by SEM after interrupted tests- were analyzed, taking into account the reduction in effective crack driving force by the interlocking and friction of the asperities of the crack surface. Under small-scale yielding conditions, the mixed-mode crack growth rates were found to correlate best with \({\sqrt{{\Delta {\rm K}}_{\rm II}^{{\rm eff}^{2}}+1.2\Delta {\rm K}_{\rm III}^{{\rm eff}^{2}}}}\) in maraging steel, while for Ti-6Al-4V, \({\sqrt{\Delta {\rm K}_{\rm II}^{{\rm eff}^{2}}+0.9\Delta {\rm K}_{\rm III}^{{\rm eff}^{2}}}}\) appeared suitable. For extended plasticity, a crack growth prediction method is proposed and validated for Ti-6Al-4V. This method is based on elastic-plastic F.E. computations and application, ahead of each node of the crack front, of a shear-dominated fatigue criterion. 相似文献
13.
The electrical conductivity and hydrogen permeation properties of membranes were studied as a function of temperature and gradient. The bulk conductivity of was an order of magnitude higher than the grain boundary conductivity over the temperature range 100–250 °C in feed gas of
4% H2/balance He (pH2O = 0.03 atm). The significantly lower grain boundary conductivity indicates that larger-grained materials might be more suitable
for proton transport. The hydrogen flux through the membranes is proportional to thickness down to 0.7 mm. The hydrogen permeation
flux increases with an increase in gradient where the increase in hydrogen flux was explained by an increase in electron conduction as a function of temperature.
The ambipolar conductivity calculated from hydrogen permeation fluxes shows the same and dependence as electron concentrations. The hydrogen and oxygen potential dependence of the ambipolar conductivity (, ) was understood from the defect structure. From this, it was confirmed that hydrogen permeation might be limited by electron
transport at wet reducing atmosphere. From the temperature dependence of the electronic conductivity, the activation energy
calculated at wet reducing conditions is 0.63 eV. 相似文献
14.
The Transport Properties of Sodium Atoms and the Heat Capacity of Sodium Dimers at High Temperatures
Including the contribution of excited state atoms can improve calculations of dilute gaseous transport properties at high temperatures. For sodium, experimental and/or theoretical information is available about the potential energy curves associated with each of ten low-lying states of the sodium dimer. These include the ${{\rm X}^{1}\Sigma_{\rm g}{}^{+}}$ and ${^{3}\Sigma_{\rm u}{}{}^{+}}$ states that dissociate to two ground state 2S sodium atoms and the four ${^{3}\Sigma_{\rm g,u}{}^{+},\,^{1}\Sigma _{\rm g,u}{}^{+},\,^{1}\Pi _{\rm g,u},\,^{3}\Pi _{\rm g,u}}$ gerade/ungerade pairs of states that dissociate to a ground state 2S atom and an excited state 2P atom. Nine of these are bound states and have been fitted with the Hulburt–Hirschfelder potential, a very good general purpose atom–atom potential. The 3Πg state is not bound and has been fitted with the exponential repulsive potential. We have used these potentials to calculate viscosity collision integrals as a function of temperature, and employed degeneracy-weighted averaging to determine the viscosity and translational contribution to the thermal conductivity of the sodium atoms. These same potentials have been used to calculate the heat capacity, ${C_{p}^{\rm o}}$ , of the sodium dimer using an approach that depends on the second virial coefficient and its first two temperature derivatives. Again, the inclusion of molecular states that dissociate to an excited state atom allows ${C_{p}^{\rm o}}$ to be determined with improved accuracy at higher temperatures. Thus, thermophysical property calculations for sodium have been extended to 25,000 K. These results are compared with previous results, including heat capacities given in the NIST-JANAF Thermochemical Tables. 相似文献
15.
G. A. Ummarino R. S. Gonnelli A. Bianconi 《Journal of Superconductivity and Novel Magnetism》2005,18(5-6):791-795
The variation of the critical temperature $T_{c}$ and of the superconductive gaps as functions of doping (Al, C) in the diboride MgB $_{2}$ has been studied in the framework of the two-band Eliashberg theory and traditional phonon coupling mechanism. We have solved the two-band Eliashberg equations using first-principle calculations or simple assumptions for the variation of the relevant physical quantities. We have found that the experimental $T_{c}$ curves can be exactly explained only if the Coulomb pseudopotential changes with x by tuning the Fermi level toward the σ band edge. We also found that a small amount of impurities changes the structural properties of the material, so we cannot treat the Mg $_{1-x}{\rm Al} _{x}{\rm B}_{2}$ and MgB $_{2-x}{\rm C}_{x}$ systems as a contamination with Al or C of MgB $_{2}$ , but as new materials. Finally, we compare the predictions of our theory with the available experimental data. 相似文献
16.
N. Liu M. Shi C. Wang Y. P. Yuan P. Majewski F. Aldinger 《Journal of Materials Science》2006,41(13):4205-4213
Samples of Sr- and Mg-doped LaGaO3 (LSGM) with various concentrations of Sr and Mg were prepared by using solid-state reaction method. Results show that ionic
conductivities increase with the increase of relative densities. It can also be known that the optimized concentration in
with high conductivity is LSGM1520 or LSGM2015. The results also show that, in various concentrations of LSGM, equiaxed,
rode-like, polygonal secondary phases such as LaSrGaO4 or LaSrGa3O7 were detected besides (La,Sr)(Ga,Mg)O3 by means of SEM and EDX. With the increase of doped elements, i.e. x + y, the grain size increases. 相似文献
17.
Coefficients (α) of linear thermal expansion of Rh, Ir, and Pd are reported to be respectively 8.45, 6.65, and 11.78×10?6 ° K?1 at 238°K, and 3.50, 3.43, and 6.21×10?6 °K?1 at 75°K. At temperatures below 10°K, α may be represented by $$\begin{gathered} 10^{10} \alpha = 20{\rm T} + 0.052{\rm T}^3 (Rh) \hfill \\ 10^{10} \alpha = 9{\rm T} + 0.070{\rm T}^3 (Ir) \hfill \\ 10^{10} \alpha = 40.5{\rm T} + 0.435{\rm T}^3 (Pd) \hfill \\ \end{gathered} $$ TheT andT 3terms are identifiable with electron and lattice vibrational components, respectively. Corresponding Grüneisen parameters are γ (electron)≈2.8, 2.7, and 2.22 for Rh, Ir, and Pd, and γ 0 (lattice)≈2.0, 2.3, and 2.25. 相似文献
18.
V. R. Tarnawski M. L. McCombie W. H. Leong P. Coppa S. Corasaniti G. Bovesecchi 《International Journal of Thermophysics》2018,39(3):35
The thermal conductivity data of 40 Canadian soils at dryness \((\lambda _{\mathrm{dry}})\) and at full saturation \((\lambda _{\mathrm{sat}})\) were used to verify 13 predictive models, i.e., four mechanistic, four semi-empirical and five empirical equations. The performance of each model, for \(\lambda _{\mathrm{dry}}\) and \(\lambda _{\mathrm{sat}}\), was evaluated using a standard deviation (SD) formula. Among the mechanistic models applied to dry soils, the closest \(\lambda _{\mathrm{dry}}\) estimates were obtained by MaxRTCM \((\textit{SD} = \pm ~0.018\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1})\), followed by de Vries and a series-parallel model (\(\hbox {S-}{\vert }{\vert }\)). Among the semi-empirical equations (deVries-ave, Advanced Geometric Mean Model (A-GMM), Chaudhary and Bhandari (C–B) and Chen’s equation), the closest \(\lambda _{\mathrm{dry}}\) estimates were obtained by the C–B model \((\pm ~0.022\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1})\). Among the empirical equations, the top \(\lambda _{\mathrm{dry}}\) estimates were given by CDry-40 \((\pm ~0.021\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1}\) and \(\pm ~0.018\,\hbox { Wm}^{-1}\cdot \hbox {K}^{-1}\) for18-coarse and 22-fine soils, respectively). In addition, \(\lambda _{\mathrm{dry}}\) and \(\lambda _{\mathrm{sat}}\) models were applied to the \(\lambda _{\mathrm{sat}}\) database of 21 other soils. From all the models tested, only the maxRTCM and the CDry-40 models provided the closest \(\lambda _{\mathrm{dry}}\) estimates for the 40 Canadian soils as well as the 21 soils. The best \(\lambda _{\mathrm{sat}}\) estimates for the 40-Canadian soils and the 21 soils were given by the A-GMM and the \(\hbox {S-}{\vert }{\vert }\) model. 相似文献
19.
Nikos G. Tsierkezos 《International Journal of Thermophysics》2009,30(3):910-918
Surface tensions (σ) of binary liquid mixtures of acetonitrile (ACN) with 1-propanol (PrOH) were measured over the entire composition range at
eight different temperatures, 278.15 K, 283.15 K, 288.15 K, 293.15 K, 298.15 K, 303.15 K, 308.15 K, and 313.15 K. The lyophobicities
(β) of the surfactant PrOH relative to that of ACN as well as the surface mole fractions () of PrOH at various temperatures were derived using the extended Langmuir model (Langmuir 17, 4261, 2001). The β values indicate the greater affinity of PrOH for the surface, and this trend slightly increases with rising temperature.
The determined values indicate that the surface concentration of PrOH is always higher than its bulk concentration and consequently confirm
that the surface is enriched with PrOH. 相似文献
20.
Jaibir S. Yadav Dimple Sharma Satish Kumar V. K. Sharma 《International Journal of Thermophysics》2010,31(11-12):2201-2215
Excess molar volumes, ${V^{\rm E}_{ijk}}$ , and speeds of sound, u ijk , of pyrrolidin-2-one (2-Py) (i)+benzene or methyl benzene (j)+propan-1-ol (k) ternary mixtures and speeds of sound, u ij , of benzene or methyl benzene (i)+propan-1-ol (j) binary mixtures have been measured dilatometrically and interferrometrically over the complete mole fraction range at 308.15 K. Speed-of-sound data have been utilized to evaluate excess isentropic compressibilities for binary and ternary mixtures. ${V^{\rm E}_{ijk}}$ and ${\left({\kappa_S^{\rm E}}\right)_{ijk}}$ values have been fitted to a Redlich–Kister equation to predict ternary adjustable parameters and standard deviations. Topological investigations employed for predicting excess molar volumes and excess isentropic compressibilities, ${\left({\kappa _S^{\rm E}} \right)_{ij}}$ , of 2-Py + benzene or methyl benzene or propan-1-ol binary mixtures have been extended to ternary mixtures (by employing the concept of a connectivity parameter of third degree, 3 ξ, of a molecule) to obtain an expression that describes well the measured ${V^{\rm E}_{ijk}}$ and ${\left({\kappa_S^{\rm E}}\right)_{ijk}}$ values. 相似文献