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1.
The electrical conductivity of sintered specimens of nonstoichiometric CeO2?x was measured as a function of temperature (750–1500°C) and oxygen pressure (1–10?22 atm). The isothermal compositional dependence of the electrical conductivity of CeO2?x was determined by combining recently obtained thermodynamic data, x = x(PO2, T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expression
σ=410[x]e?(0.158+x)kT(ohm cm)?1
over the temperature range 750–1500°C and from x = 0.001 to x = 0.1.This expression was rationalized in terms of the following simple relations for (a) the electron carrier concentration
ncece=8xa03
where nCe′Ce is the number of Ce′Ce per cm3 and a0 is the lattice parameter and (b) the electron mobility
μ=5.2(10?2)e?(0.158+x)kT(cm2/V sec)
.  相似文献   

2.
Yttrium self-diffusion in monocrystalline yttrium oxide (Y2O3) is studied by means of the classical radio tracer technique. The few reliable diffusion data obtained in the temperature range 1600–1700°C lead to the following diffusion coefficient
D=3.5×10?9exp?72RT(kcal/mole) m2sec?1
.Experimental errors on the above numerical values are large and give, for the preexponential and energy terms, respectively:
2.10?7<D0<3.10?10m2sec?
62<Q<82 kcal/mole
.Nevertheless these results seem in good agreement with those deduced from high-temperature and low-stress creep experiments. The theoretical aspect of self-diffusion of yttrium in Y2O3 is studied in terms of point defects and lattice disorder due to the equilibrium between the oxide and its environment. This last part is confined to the restricted range of high oxygen partial pressure in which oxygen interstitials are supposed to be majority defects. Intrinsic and extrinsic diffusion behavior are both considered on the basis of a vacancy diffusion mechanism.  相似文献   

3.
In the region of 8 GHz the rotational transition of J = 3 → 2 of both isotopic species of AgI has been investigated. The analysis of the quadrupole hyperfine structure in the vibrational states up to v = 4 resulted in the v-dependent coupling constant
eqvQ (127I) = { ? 1061.37(40) ? 2.13(20)(v + 12) } MHz
. From observations of the Stark pattern of 107AgI in its ground vibrational state we derived the electric dipole moment
O| = 5.10 (15) D
.  相似文献   

4.
The compounds Ba4Fe2S6[S23(S2)13] and Ba3.6Al0.4Fe2S6[S0.6(S2)0.4], designated I and II, were prepared by reacting BaS, Fe, and S powders and Al foils in graphite containers sealed in evacuated quartz ampoules at approximately 1100°C. The crystal structure of I was determined using 1682 independent, nonzero X-ray reflections, while 3589 were used for II. They are triclinic, Al:
a=9.002(2)A?,b=6.7086(8)A?,c=24.658(4)A?α91.49(2)°,
β=105.10(2)°y=90.74(2)°,ψcalc=4.15g/cm3,for I:
a=8.993(6)A?,b=6.708(7)A?,c=24.70(1)A?α91.11(6)°,
β=105.04(6)°y=90.90(9)°,ψcalc=3.90g/cm3,for II:
BaS6 trigonal prisms share edges to form distorted hexagonal rings which form one-dimensional chains leaving two free lateral edges. The chains link in a stairstep manner with the rings offset along the [301] direction. These stairsteps join in a complicated manner to form a three-dimensional network. Fe ions are in two sites forming isolated FeS4 tetrahedra and isolated Fe2S6 dimers by edge-sharing tetrahedra. The Al substitution occurs in the trigonal prisms which have free edges with Al replacing Ba. Room-temperature Mössbauer isomer shifts are 0.20 mm/sec. for I and 0.30 mm/sec for II. These data indicate that upon Al substitution charge compensation occurs by reducing Fe3+. Valence calculations indicate that Fe in edge-sharing tetrahedra are reduced while the Fe in the isolated tetrahedron remains unchanged. The effective charge distribution in the Al substituted compound is approximately Fe3+, Fe2.5+ with electron delocalization across the shared edge. Room temperature electrical resistivity is 105 ohm/cm. The compositions of the crystals are best represented by the formulas [Ba4Fe2S7]23·[Ba4Fe2S6(S2)]13 and [Ba3AlFe2S7]0.4·[Ba4Fe2S7]0.2·[Ba4Fe2S6(S2)]0.4. The replacement of a sulfide by a disulfide ion is thought to be strongly dependent on the sulfur activity during the preparation.  相似文献   

5.
The standard enthalpy of formation of γ-UO3 has been critically assessed; the value ?(292.5 ± 0.2) kcalth mol?1 is suggested.The enthalpies of solution of β-UO3 and γ-UO3 in 3 M H2SO4 have been measured and used to derive:
ΔHf°(β?UO3, 298.15 K) = ?(291.6 ± 0.2) kcalth mol?
  相似文献   

6.
Intensity parameters of Sm3+ in borate glasses were obtained by fitting the oscillator strengths to the Judd-Ofelt formula and a study of energy transfer from gadolinium to samarium was performed. An increase of samarium fluorescence originating from the 4G52 level was observed in the presence of gadolinium, in the concentration range of 0.1–3 wt% samarium with gadolinium constant at 3 wt%. The intensity of samarium fluorescence on excitation at 273 nm increased by one order of magnitude in the presence of gadolinium. From the excitation spectrum of the double-doped glasses (Gd + Sm), it was deduced that energy absorbed by gadolinium is transferred from 6P72 gadolinium levels to the 4P32 and 4P52 samarium levels.The mechanism of this energy transfer was obtained by plotting the energy transfer probabilities as a function of samarium concentration. A linear dependence of η0η (η intensity of gadolinium in the presence of samarium) versus square of concentration of Sm + Gd is obtained. From this it is concluded that the transfer is of electric-multipolar type, mainly dipole-dipole. A small increase (about 10%) of fluorescence of samarium in the presence of gadolinium excited at levels where no energy transfer can take place is attributed to the fact that the quenching of samarium occurring by the cross relaxation (4G526F92) (6H526F92) is suppressed by the presence of gadolinium as seen from concentration dependence of samarium doped glasses compared to double-doped glasses.  相似文献   

7.
The tracer diffusion coefficient, D1O, of oxide ions in LaCoO3 single crystal was determined over the temperature range of 700–1000°C by a gas-solid isotopic exchange technique using 18O tracer. For the determination, two methods, the gas phase analysis and the depth profile measurement, were employed. Under an oxygen pressure of 34 Torr, the temperature dependence of D1O in LaCoO3 was expressed by
D1O(cm2·sec?1) = 3.63 × 104exp? (74 ± 5)kcal · mole?1RT
D1O at 950°C was found to be proportional to P?0.35O2. The diffusion of oxide ions occurs through a vacancy mechanism. The activation energy for the migration of oxide ion vacancies was estimated as 18 kcal · mole?1.  相似文献   

8.
The study of K2NiF4 and perovskite structure type by the “method of invariants” leads to the relationship: (A-X)9 212 ? (A-X)12 = constant, where (A-X)9 and (A-X)12 are the invariant values associated with cation A in coordination number 9 and 12. In the case where A = K+ and X = F?, we propose the relationship:
(K+?F)R = 2.832 R111.4
where R is the coordination number.  相似文献   

9.
The polymerization of styrene initiated by 2,2′ azobisisobutyronitrile had been studied in N,N-dimethylformamide at 60°, in the presence of Tris(phenanthroline)-iron(III) perchlorate. The complex was prepared in situ by mixing phenanthroline with hexakis (N,N-dimethylformamide) iron(III) perchlorate in the ratio 3:1. The nature of the complex formed was established by Job's method. The equilibrium constant for
Fe3+ + 3 Phen ? [Fe(Phen)3]3+
is 2·3 × 102 13 mol?3. The velocity constant at 60° for the reaction of polystyryl radical with [Fe(Phen)3]3+ is 2·93 × 104 mol?1 l s?1.  相似文献   

10.
The radiation induced solid-state polymerization and post-polymerization of crystalline acetaldehyde were studied in a diathermic calorimeter by measuring the heat evolution during polymerization. The heat of melting of crystalline acetaldehyde was found to be 1,4 ± 0,07 kcal mol?1 and the heat of polymerization 2,5 ± 0,5 kcal mol?1 at 80–150°K. Under isothermal conditions the rate of the solid state polymerization of acetaldehyde increased with irradiation time up to a maximum and thereafter it decreased. This phenomenon is connected with an increase of the concentration of active centres during irradiation. The propagation rate constant is kp ? 5 × 10?4exp(?11,000/RT) cm3 sec?1 at 130–140°K and the average time of addition of one monomer unit is 10?1–10?2 sec.  相似文献   

11.
The chlorination of PVC has been studied in a fluidized bed reactor, initiating the reaction with elementary fluorine. The reaction has been carried out at temperatures between 20° and 60° for various concentrations of chlorine and fluorine. The rate of reaction is given by the equation:
(1)x=k[Cl2]0·5[F2]t1+k[Cl2]0·5[F2]t
, temperature is given by
log k=35004·571T+0·707
.Equation (1) is satisfied also by data obtained from a small scale plant reactor. A reaction mechanism is proposed.  相似文献   

12.
Isotopic vapor-pressure differences between (CH3)2CO and (CD3)2CO have been measured by differential capacitance manometry. When combined with available absolute vapor pressures for (CH3)2CO the results may be expressed (206 to 333 K) as:
1n(pHpD) = 3642.6(K/T)2 ? 22.205(K/T) + 0.01129
  相似文献   

13.
Electron spin resonance spectra attributed to four Fe3+ centers designated Oa, Ob, Ta, Tb have been observed in crystals of muscovite and phlogopite. The results are discussed using the spin Hamiltonian
Hs=geμBH·S+D(Sz2?13S?(S+1)+E(S?x2?E(S?y2)
with ge ~ 2.002. The angular variation of the resonance lines is used to determine the ESR axes of the four different sites. Two species are octahedrally coordinated (Oa and Ob) and are assigned to two different surroundings of Fe3+ in the octahedral sheet. The remaining two species (Ta and Tb) may be assigned to the tetrahedral FeO4. The Ta sites have a symmetry axis lying along one of the FeO bonds. The symmetry axis is created by an excess of negative charge on the oxygen bound to the neighboring tetrahedral substitution. Rhombic symmetry of the Tb sites is due to the presence of fluorine anions substituting some hydroxyl ions. One of the ESR axes is directed toward the fluorine ion.  相似文献   

14.
I.N. Juchnovski  I.G. Binev 《Tetrahedron》1977,33(22):2993-2995
σ+ constants of H2Cxxx- (?11.2), HNxxx- (?7.6), C2H5OOC-HCxxx- (?5.0), NC-HCxxx- (?5.4) and some other anionic substituents were estimated on the basis of νCN of the corresponding benzonitrile anions and by using the correlations νCNσ+ for benzonitriles, in polar aprotic solvents.  相似文献   

15.
Aqueous solutions of acrylamide were dispersed with non-ionic surfactants within isoparafinic hydrocarbons to particles of approx. 1 μm and polymerized in a batch reactor by water-soluble and oil-soluble azo-initiators at 42 to 57°C. The resulting conversion-time curves are S-shaped showing a strong gel effect. For maximum rate of polymerization, the following kinetic expressions were determined for the conditions investigated:
rmax=kCI,o0.5CM,o
for water-soluble initiators;
max=kCI,oCE,o?0.2
For oil-soluble initiators, the overall rate constant k is a function of interface area and temperature. The interface area is dependent on the phase ratio, stirring speed and temperature. For constant interface areas, an activation energy of 26 kJ/mol was found. The overall activation energy of the polymerization is 88.2 kJ/mol, when temperature dependence of the interphase is not taken into account. Polymerization of acrylamide with oil-soluble initiators can be described at low conversions by a model which considers mass transfer of primary radicals, and to a lesser extent of initiator molecules, from the oil phase into the water phase as rate determining step and termination by primary radicals. The resulting molecular weights of the polymer are extremely high (106g/mol) and depend on temperature, stirring speed and concentration of initiator, emulsifier and monomer.  相似文献   

16.
Excess volumes and ultrasonic speeds have been measured for (2-ethoxyethanol + n-heptane) at 298.15 K. Isentropic compressibilities, excess isentropic compressibilities, and the partial molar excess quantities KS, iE = ?(?ViE?p)S were calculated from the results. The excess volume is positive over the entire mole-fraction range, whereas the curves for the excess isentropic compressibility is sigmoid with negative values occurring at mole fractions of 2-ethoxyethanol greater than 0.35. A qualitatitive interpretation of the results is presented.  相似文献   

17.
18.
For the polyamide Trogamid TR, good as well as θ-solvents are available. Determinations of molecular weights by ultracentrifugation, light scattering, osmometry, viscometry and gelchromatography (GPC) are reported. For DMF at 25° the relation
[η] = 0.02737 M0.706w cm3 g?1
was established, [η] = f(T) shows a maximum between ? 70° and + 120°. θ-temperatures are 142° for aniline and 62° for pyrroline, the latter having a negative temperature gradient. The unperturbed dimensions are calculated from the viscosity in θ-solvents and in DMF; for the latter, the Stockmayer-Fixman extrapolation was used. Molecular dimensions proved to be small in comparison with those of similar polymers. This effect is due to the three methyl side-groups for each chain unit sterically preventing a more stretched conformation.  相似文献   

19.
In order to elucidate the defect structure of the perovskite-type oxide solid solution La1?xSrxFeO3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, PO2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of PO2 ≥ 0.13 atm, δ in La1?xSrxFeO3?δ was found to be close to 0. With decreasing log PO2, δ increased and asymptotically reached x2. The log(PO2atm) value corresponding to δ = x2 was about ?10 at 1000°C. With further decrease in log PO2, δ slightly increased. For LaFeO3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log PO2 is interpreted on the basis of the defect equilibrium among Sr′La (or V?La for the case of LaFeO3?δ), V··O, Fe′Fe, and Fe·Fe. Calculations were made for the equilibrium constants Kox of the reaction
12O2(g) + V··o + 2FexFe = Oxo + 2Fe·Fe
and Ki for the reaction
2FexFe = FeFe + Fe·Fe·
Using these constants, the defect concentrations were calculated as functions of PO2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.  相似文献   

20.
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 τ0C ? 10?13sec for H1.71MoO3 and EA = 11 kJ mole?1 and τ0C ? 3 × 10?8sec for H0.36MoO3.  相似文献   

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