共查询到20条相似文献,搜索用时 31 毫秒
1.
Z. Dobkowski 《European Polymer Journal》1984,20(4):399-403
Linear and branched bisphenol A polycarbonate (PC) samples were characterized by their average molecular weights, and , polydispersity degree , and branching degree gv. The weight fraction of microgel was also determined for branched samples. The samples were amorphized and densities were measured at 23°C to obtain the values of specific volume, vsp. The dependence of vsp on molecular characteristics is described by the multivariable power function , where Δvsp = vsp ? vsp,∞, and Asp, a, apx and ab are constants. It has been confirmed that a = ?1, apn = 0 and apw = 1. It has also been found that the branching exponent ab significantly depends on microgel content. The relationships found for PC should, in principle, be valid for other polymers. Examples based on literature data are given for linear polyethylene and polydimethylsiloxane. 相似文献
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The kinetics of the interaction of hexaaquochromium(III) ion with potassium octacyanomolybdate(IV) have been studied using conductance and spectrophotometric data. The mechanism of the reaction is discussed and the effect of H+ ion and the ionic strength on the rate of the reaction determined. The reaction is found to be pseudo-first order with respect to potassium octacyanomolybdate(IV) and inverse first order with [H3O+]. The rate of the reaction increases with increase in ionic strength and temperature. Activation parameters have been calculated using the Arrhenius equation and have the values ΔE* = 1.3 × 102 kJ mol?1, ΔH* = 129 kJ mol?1, ΔS* = ?315 e.u., ΔF* = 2.3 × 102 kJ and A = 1.5 × 10?3. The mechanism proposed is based on ion-pair formation and the rate equation obtained is given by: kobs= 相似文献
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Joaquín García Juan Bartolomé Domingo González Rafael Navarro Daniel Fruchart 《The Journal of chemical thermodynamics》1983,15(12):1169-1180
The heat capacity of the solid solution Mn3.2Ga0.8N was measured between 5 to 330 K by adiabatic calorimetry. A sharp anomaly with first-order character was detected at TA = (160.5±0.5) K, corresponding to a magnetic rearrangement and a lattice expansion. No sharp anomaly was observed at Tc ≈ 260 K where the magnetic ordering takes place; instead, a smooth shoulder was detected. The thermodynamic functions at 298.15 K are , , , . At low temperatures the coefficient for the linear electronic contribution to the heat capacity was derived: γ = (0.031±0.003) J·K?2·mol?1. Moreover, the different contributions to the heat capacity were obtained and the electronic origin of the phase transitions was established. 相似文献
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Geometric constraints present in A2BO4 compounds with the tetragonal-T structure of K2NiF4 impose a strong pressure on the BOIIB bonds and a stretching of the AOIA bonds in the basal planes if the tolerance factor is , where RAO and RBO are the sums of the AO and BO ionic radii. The tetragonal-T phase of La2NiO4 becomes monoclinic for Pr2NiO4, orthorhombic for La2CuO4, and tetragonal-T′ for Pr2CuO4. The atomic displacements in these distorted phases are discussed and rationalized in terms of the chemistry of the various compounds. The strong pressure on the BOIIB bonds produces itinerant bands and a relative stabilization of localized dz2 orbitals. Magnetic susceptibility and transport data reveal an intersection of the Fermi energy with the d2z2 levels for half the copper ions in La2CuO4; this intersection is responsible for an intrinsic localized moment associated with a configuration fluctuation; below 200 K the localized moment smoothly vanishes with decreasing temperature as the d2z2 level becomes filled. In La2NiO4, the localized moments for half-filled dz2 orbitals induce strong correlations among the electrons above ; at lower temperatures the electrons appear to contribute nothing to the magnetic susceptibility, which obeys a Curie-Weiss law giving a μeff corresponding to , but shows no magnetic order to lowest temperatures. These surprising results are verified by comparison with the mixed systems La2Ni1?xCuxO4 and La2?2xSr2xNi1?xTixO4. The onset of a charge-density wave below 200 K is proposed for both La2CuO4 and La2NiO4, but the atomic displacements would be short-range cooperative in mixed systems. The semiconductor-metallic transitions observed in several systems are found in many cases to obey the relation , where and Tmin is the temperature of minimum resistivity ?. This relation is interpreted in terms of a diffusive charge-carrier mobility with at T = Tmin. 相似文献
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《The Journal of chemical thermodynamics》2002,34(12):2083-2092
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D.J. Ruben S.G. Kukolich L.A. Hackel D.G. Youmans S. Ezekiel 《Chemical physics letters》1973,22(2):326-330
Very high resolution measurements of hyperfine structure on the P(13) and R(15), 43?0, transitions in iodine 127 were made using laser molecular beam spectroscopy. The observed linewidth was 300 kHz (fwhm) giving a resolution of 5 × 10?10 The observed spectrum was fitted to obtain a quadrupole coupling strength difference of ΔeQq = 1906 ± 2 MHz and a spin rotation interaction strength difference of ΔCI = 181 ± 7 kHz between the upper and lower levels of the P(13) transition. For the R (15) transition ΔeQq = 1905 ± 2 MHz and ΔCI = 167 ± 5 kHz. 相似文献
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The kinetics, mechanism, and activation energy of the isothermal decomposition of CuCrO4 was studied using an isothermal TG method and an X-ray high-temperature diffraction technique in either air or a flowing atmosphere of N2. The enthalpy change ΔH of the decomposition reaction was determined by DSC analysis. The mechanism of the thermal decomposition of CuCrO4 is well represented by the standard Avrami-Erofeev kinetic equation . According to this mechanism, the reaction rate is controlled by the formation and growth of nuclei on the surface of the reactant. The activation energy EA of the process in air is EA = (248 ± 8) kJ mole?1, in flowing atmosphere of nitrogen EA = (229 ± 8) kJ mole?1. ΔH in air is 110 kJ mole?1, in flowing nitrogen 67 kJ mole?1. The lower values of ΔH and EA in the flowing atmosphere of nitrogen are due to the fast elimination of O2 from the reaction interface. However, the decay of the crystalline portion of CuCrO4 during its thermal decomposition, studied by the X-ray diffraction, is controlled by a different reaction mechanism (first-order kinetics). The reaction mechanism is discussed in the relation to the crystal structure of the reactants. 相似文献
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Proton NMR relaxation times (T2T1, and T1?) and absorption spectra are reported for the compounds H1.71MoO3 (red monoclinic) and H0.36MoO3 (blue orthorhombic) in the temperature range 77 K < T < 450 K. Rigid lattice dipolar spectra show that both compounds contain proton pairs, as OH2 groups coordinated to Mo atoms in H1.71MoO3 and as pairs of OH groups in H0.36MoO3. The room temperature lineshape for H1.71MoO3 shows that the average chemical shielding tensor has a total anisotropy of 20.1 ppm. The relaxation measurements confirm that hydrogen diffusion occurs and give EA = 22 kJ mole?1 and for H1.71MoO3 and EA = 11 kJ mole?1 and for H0.36MoO3. 相似文献
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Gel permeation chromatography (GPC) and viscometry (V) methods have been combined for determination of long-chain branching in bisphenol-A polycarbonate (PC) by means of a branching factor , where and are the apparent viscosity-average molecular weights calculated from GPC data and from intrinsic viscosities [η] of the samples respectively. A linear dependence of gv on molar % of branching agent has been obtained. The GPC data on PC samples have also been applied for verification of an earlier [η]?M relationship for branched polydisperse polymers. 相似文献
13.
Emilio Aicart M.K. Kumaran Carl J. Halpin George C. Benson 《The Journal of chemical thermodynamics》1983,15(12):1189-1197
Ultrasonic speeds were determined for binary mixtures of 2-methylpentan-1-ol with n-hexane and each of its four isomers. Measurements were made over the whole mole-fraction range with particular attention given to the region of high dilution with respect to the alcohol. The results were combined with excess molar volumes reported previously to obtain values of the excess molar quantity and the corresponding partial molar derivatives. 相似文献
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Enthalpies of reaction, ΔHr, of the monouranates of lithium, potassium, and rubidium with 1 mol dm?3 HCl have been measured calorimetrically. From these measurements, and auxiliary determinations of the enthalpies of solution in acid of the chlorides of lithium, potassium, and rubidium and of uranyl chloride, the standard enthalpies of formation of the uranates, ΔHfo, have been derived. The results obtained are as follows:
α-Li2UO4 | ?(41.77±0.02) | ?(463.31±0.84) |
K2UO4 | ?(42.07±0.05) | ?(451.39±0.83) |
Rb2UO4 | ?(41.30±0.05) | ?(452.00±0.85) |