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1.
Light scattering by monodisperse solutions of rigid rod-like anisotropic macromolecules, with linear dimensions l of the order of incident wavelength λ, oriented in an external d.c. electric field, → E has been analysed. The relative variations δ VEv, δ HEv, δ VEh, δ HEh of the scattered light components are discussed for the three values [ l/λ] = 1, 0·5, 2, and various reorientation parameters, p = [μE/kT] of the permanent dipole moment μ and q = [( 3 − 1) E2/2 kT] of the moment induced by the principal polarizabilities 1 = 2 ≠ 3. The saturation orientation field strength has been calculated for certain macromolecules with the aim of determining their optical anisotropy numerically. 相似文献
2.
The melt viscosity of polycaprolactam can be enhanced by incorporation of chromium (III) ions into the resin. As a possible interpretation of this phenomenon, formation of a mixed complex is suggested by X-ray diffraction, infrared and uv. absorption spectroscopic studies. By comparison with a model compound, it was found that the carbonyl oxygen and the water occurring in the polymer appear to be the coordination centres of chromium (III) ions. The hypothetical composition of the mixed complex is [Cr(CO amide) n(H 2O) 6−n] 3+ where 2 n 6. 相似文献
3.
Fine powders of submicron-sized crystallites of BaTiO 3 were prepared at 85–130°C by the hydrothermal method, starting from TiO 2.ξH 2O gel and Ba(OH) 2 solution. The products obtained below 110°C incorporated considerable amounts of H 2O and OH − in the lattice. As-prepared BaTiO 3 is cubic and converts to the tetragonal phase after heat treatment at 1200°C, accompanied by the loss of residual OH − ions. Hydrothermal reaction of SnO 2.ξH 2O gel with Ba(OH) 2 at 150–260°C gives rise to the hydrated phase, BaSn(OH) 6.3H 2O, due to the amphoteric nature of SnO 2.ξH 2O which stabilises Sn(OH) 62− anions in basic media. On heating in air or releasing the pressure in situ at 260°C, BaSn(OH) 6.3H 2O converts to BaSnO 3 through an intermediate, BaSnO(OH) 4. Solid solutions of Ba(Ti,Sn)O 3 are directly formed from (TiO 2 + SnO 2)..ξH 2O gel up to 35 mol% SnO 2. At higher Sn contents, the hydrothermal products are mixtures of BaSn(OH) 6.3H 2O and BaTiO 3, which on annealing at 1000°C result in monophasic Ba(Ti,Sn)O 3. The sintering characteristics and the dielectric properties of the ceramics prepared out of these fine powders are presented. The dielectric properties of fine-grained Ba(Ti,Sn)O 3 ceramics are explained on the basis of the prevailing diffuse phase transition behaviour. 相似文献
4.
Periodic current/potential curves were taken potentiostatically at 30 mV/sec on smooth platinum in 1 N HClO 4 with different additions of HCl, HBr, and HI, in the potential range between hydrogen evolution and deposition of oxygen or of the respective halide ion. The effect of increasing halide ion concentration, starting at 10 −6 M, on hydrogen adsorption and oxygen adsorption was studied systematically. Impedance measurements were made at 1000 c/s under the same conditions as the measurements of the current/potential curves. It is concluded from the dependence of the double layer capacitance upon the bulk concentration of halide ions in the double layer region that nearly a monolayer of adsorbed ions is present there for 0cCl− ≈ 10 −2 M, 0cBr ≈ 10 −4 M, and 0cHI ≈ 10 −5 M. The measurements at larger concentrations, especially for I −, show additional effects which are due to the deposition of halides and to the reverse reaction. 相似文献
5.
The synthesis of a novel 3D aluminophosphate is described. The thermal properties of the material were investigated, and the existence of three high-temperature variants was revealed. The crystal structures of the as-synthesized material (UiO-26-as) and the material existing around 250°C (UiO-26-250) were solved from powder X-ray diffraction data. UiO-26-as with the composition [Al 4O(PO 4) 4(H 2O)] 2−[NH 3(CH 2) 3NH 3] 2+ crystallizes in the monoclinic space group P2 1/c (no. 14) with a=19.1912(5), b=9.3470(2), c=9.6375(2) Å and β=92.709(2)°. It exhibits a 3D open framework consisting of connections by PO 4 tetrahedra with AlO 4 tetrahedra, AlO 5 trigonal bipyramids and AlO 5(H 2O) octahedra forming two types of layers stacked along [1 0 0] and connected by Al–O–P bondings. The structure possesses a 1D 10-ring channel system running along [0 0 1], in which doubly protonated 1,3-diaminopropane molecules are located. UiO-26-250 with the composition [Al 4O(PO 4) 4] 2−[NH 3(CH 2) 3NH 3] 2+ crystallizes in the monoclinic space group P2 1/c with a=19.2491(4), b=9.27497(20), c=9.70189(20) Å and β=93.7929(17)°. The transformation to UiO-26-250 involves removal of the water molecule which originally is coordinated to aluminum. The rest of the structure remains virtually unchanged. The crystal structures of the two other variants existing around 400 (UiO-26-400) and 600°C (UiO-26-600) remain unknown. 相似文献
6.
The electrosorption properties of p-norborn-2-yl phenolate ions in alkaline solutions were investigated by ac polarographic and electrocapillary measurements. Two adsorption regions were found. At low bulk surfactant concentrations the adsorption at the positively charged electrode (−0.2 E −0.6 V) is predominant while at higher surfactant concentrations the adsorption at the negatively charged electrode (−0.6 E −1.0 V) is more pronounced. At E = −0.40 V the adsorption parameters were determined (a ≈ 2; ΔG°A = −32.5 ± 1 kJ mol−1. Between −0.6 E −1.0 V one potential of maximum adsorption for all concentrations does not exist and therefore the adsorption parameters could not be calculated. At E = −0.40 V progressive two-dimensional nucleation with a nucleation order of 3 was observed which corresponds well with the high attraction constant. The electrode reaction S2O2−8 + 2e− → 2 SO2−4 is inhibited by norborn-2-yl phenolate ions in the potential range −0.2 E −0.6 V. In the second potential range of capacity decrease the electrode process is much less retarded. At E = −0.40 V, in a similar manner as described for neutral molecules, a linear dependence of the log ks (ks apparent rate constant) on ln cA and π (π = surface film pressure), respectively, has been found. 相似文献
7.
To clarify the effect of substitutional electron doping on the thermoelectric figure of merit ( ZT = S2σTκ−1) of Ruddlesden–Popper phase SrO(SrTiO 3) n (or Sr n+1Ti nO 3n+1), measurements were conducted for several thermoelectric parameters, e.g. electrical conductivity ( σ), Seebeck coefficient ( S) and thermal conductivity ( κ), of (Sr 1−xREx) n+1Ti nO 3n+1 ( n = 1 or 2, RE (rare earth): La or Nd, x = 0.05 and 0.1) dense ceramics prepared by a conventional solid-state reaction and hot-pressing technique. Crystal structures of the resultant ceramics were represented as (Sr 1−xREx) n+1 Ti nO 3n+1 evaluated by powder X-ray diffraction followed by the Rietveld analysis. All the ceramics exhibited electrical conductivity and the σ values simply depended on the dopant concentration, indicating that both La 3+ and Nd 3+ ions act as electron donors. The | S| values increased with temperature due to decrease in the chemical potential. Significant reduction of the κ values was observed as compared to cubic-perovskite SrTiO 3. The ZT value increased with temperature and reached 0.15 at 1000 K for (Sr 0.95La 0.05) 3Ti 2O 7. 相似文献
8.
The entropy theory of glasses is used to derive the glass temperature, Tg, of a binary polymer blend in terms of the glass temperatures of the two substituents. The formula is Tg = B1Tg1 + B2Tg2, where Bi is the fraction of flexible bonds of substituent i. A bond is flexible if rotation about it changes the shape of the molecule. Bonds in side groups as well as in the backbone are to be counted. This formula assumes that the free volume, taken here to be the volume fraction of empty lattice sites, is the same for each of the three materials. It has no parameters. The above equation expressed in weight fractions, Wi, is ( Tg − Tg1) W1(γ 1/ω 1) + ( Tg − Tg2) W2(γ 2/ω 2) = 0, where ω i is the weight of a monomer unit and ggi is the number of flexible bonds per monomer unit. A more general treatment is given. One variation of the more general treatment which expresses the properties of the blend in purely additive terms gives Tg = B1Tg1 + B2Tg2 + KB1B2( Tg1 − Tg2)( V01 − V02), where V0i are the free volume fractions of the homopolymers at their glass temperatures and K is a constant. The added term is usually small. The most general form of the equation requires the energy of interaction between the two unlike molecules, which can be estimated by volume measurements on the blend. 相似文献
9.
Polycrystalline (PbS) 1.14(TaS 2) 2, a misfit layer sulfide, was used as cathodic material for lithium secondary battery. One molar LiClO 4 in propylene carbonate (PC) was used as electrolyte. The cell could be galvanostatic discharged down to x = 4.6 [Li x(PbS) 1.14(TaS 2) 2] when the current density was 65 μA cm −2 and the cell was cycled more than 100 times between 3.5 and 1.5 V at a current density of 260 μA cm −2. Lattice expansion increased linearly with lithium content and was less than that reported for the Li/TaS 2 system. Chemical diffusion coefficients were determined by a modified version of the galvanostatic intermittent titration technique and they were fairly constant in the composition range 0.2 < x < 1, and an average value of 8.1 × 10 −11 cm 2 s −1 was calculated. Sodium intercalation was also accomplished, but the uptake of this ion resulting in a significant lattice expansion compared with that observed for lithium ions. Moreover, a similar dependence of the sodium chemical diffusion coefficient on the composition was observed with an average value of 1.4 × 10 −10 cm 2 s −1, somewhat higher than that of lithium ion. We believe that differences in lattice expansion may be responsible for the differences found in the chemical diffusivity values. 相似文献
10.
SAPO-56 (framework type: AFX) has a framework topology slightly different from that of zeolite chabazite (framework type: CHA). While metal substituted aluminophosphate chabazite analogues can be prepared under a variety of experimental conditions with dozens of different amines, the synthesis of SAPO-56 type materials has been more difficult, particularly in non-SAPO compositions. Prior to this work, the growth of large crystals of the AFX-type materials suitable for single crystal diffraction has not been possible in any composition. Here we report the synthesis and single crystal structure of a magnesium aluminophosphate denoted as MAPO-AFX. This represents the first time that the AFX-type topology is made in a metal aluminophosphate composition. The synthesis was accomplished with a novel polyether diamine as the structure-directing agent. Crystal data for MAPO-AFX, (RH 2) 0.10(NH 4) 0.45[Mg 0.65Al 1.35(PO 4) 2](H 2O) where R=O[CH 2CH 2O(CH 2) 3NH 2] 2, space group P-31c (#163), Z=12, MoK radiation, 2θ max=50°, a=13.8425(6) Å, c=20.204(1) Å, V=3352.7(3) Å 3, refinement on F2, R( F)=7.94% for 131 parameters and 1218 unique reflections with I>2.0σ( I). 相似文献
11.
Non-stoichiometric V 6O 13±0.2 (VO y) prepared by thermal decomposition of NH 4VO 3 in N 2 atmosphere is investigated cathode material for Li batteries. The maximum lithium composition is found to be Li 2y-3VO y. The emf vs composition relationship of Li/Li xVO 2.144 is determined in the interval 0 < x < 1.3, yielding a theoretical energy density of 890 Wh kg −1. The kinetics and reversibility of the VO y electrode is investigated by cyclic voltammetry and cycling of test cells. The lithium diffusion coefficient and the electronic conductivity of the oxide is found to decrease with increasing lithium content. The cyclability of very thin electrodes is found to be excellent, but inferior results are obtained with practical cells, presumably due to degradation of electrode structure. 相似文献
12.
Friedels salt, the chlorinated compound 3CaO · Al 2O 3 · CaCl 2 · 10H 2O (AFm phase), presents a structural phase transition at about 30°C from a monoclinic to a rhombohedral phase. It has been studied by X-ray powder diffraction and optical microscopy in transmitted light with crossed polarisers on single crystals prepared by hydrothermal synthesis. The high temperature phase was determined at 37°C from X-ray single crystal diffraction data. The compound crystallises in the space group R
c with lattice parameters of a = 5.7358(6)Å and c = 46.849(9)Å ( Z = 3 and Dx = 2.111 g/cm 3). The refinement of 498 independent reflections with I > 2σ( I) led to a residual factor of 7.1%. The Friedels salt can be described as a layered structure with positively charged main layers of composition [Ca 2Al(OH) 6] + and negatively charged layers of composition [Cl −,2H 2O]. The chloride anions are surrounded by 10 hydrogen atoms, of which six belong to hydroxyl groups and four to water molecules. The structural phase transition may be related to the size of the chloride anions, which are not adapted to the octahedral cavity formed by bonded water molecules. 相似文献
13.
An improved version of the Hewitt (differential) electric mobility analyzer was developed and its classifying characteristics were determined theoretically. The central mobility of the classified aerosol was found to be ( qc + qm)/4 πΛV, where qc and qm are the clean air and main outlet flows, respectively, Λ is a geometric factor, and Λ is the center rod voltage. The half-width of the mobility band was found to be ( qa + qs)/4 πΛV, where qa and qs are the aerosol and sampling outlet flows, respectively. These expressions were verified by the tests with a monodisperse aerosol of known size and low charge. A major advantage of this device is that the classified aerosol fraction remains airborne, ready for further use or analysis. Thus, one application of the device is the production of monodisperse test aerosols of known size, charge, and concentration by classification of a polydisperse aerosol. Other current applications include accurate measurement of particle electric mobility moments and high-resolution particle size analysis for polydisperse aerosols in the 0.005–1.0 μm size range. 相似文献
14.
We have obtained mass spectra of negative ions produced by rays in artificial air at atmospheric pressure (N 2: 80%, O 2: 20%, H 2O: 20–1500 ppm, CO 2: 0.2–300 ppm, NO, NO 2 0.02 ppm). We observed two main categories: hydrates built on simple ions (O 2−, O 3−, OH −, CO 3−, CO 4−, HCO 3−, NO 2−, NO 3−), hydrates built on complex ions (NO x−, HNO γ, HCO 3−HNO x, x = 2,3; Y = 2, 3). For high values of hygrometry, CO 2 content and ageing time (5 msec) we observe the disappearance of O 2−, O 3−, OH − hydrates whereas the major part of the spectrum consists of complex ions. 相似文献
15.
A relation was obtained between electro-chemical properties of sodium salts (NaCl, NaBr, and Na 2SO 4), and the thermodynamic property of permeability in symmetrical cellulose acetate membranes, the distribution coefficient K and the kinetic property, the overall diffusion coefficients D. K and D were obtained by the method we proposed using measured unsteady- and steady-state dialysis data. The K values increase with the increase of water content and are in the range of 10 −2 for sodium halides and 10 −3 for Na 2SO 4. D is found to increase with the increase of the solute concentration, and the extrapolated values of D to zero concentration D (0) are obtained as 0.015–0.03 μm 2/s and increase with the increase of water content in the membrane. D can be divided into the concentration independent diffusion coefficients in the dense part of the membrane Dd and in the porous Dp, applying a two-part (perfect or dense and imperfect or porous) model of the membrane. Contrary to Dd, Dp increases with the increase of Ww and can be correlated as Dp,c =
d exp (γ × Ww). It is shown that the averaged Dd,
D increases with the increase of the quantity of the ionic mobility u of the solutes at infinite dilution divided by valence, and that the parameter γ increases with the increase of the ionic mobility u. The value of K increases slightly with the increase of water content and decreases with the increase of the Flory—Huggins parameter χ. The Flory—Huggins parameter χ is calculated from the measured values of distribution coefficients and data obtained from the literature. And it was found that the gradient of linear decrease of χ (λ cation) depends on equivalent ionic conductivity of anion of salt, λ an. 相似文献
16.
Three compounds, K 2(H 2O) 4H 2SiMo 12O 40 · 7H 2O (1), K 2Na 2(H 2O) 4SiW 12O 40 · 4H 2O (2), and Na 4(H 2O) 8SiMo 12O 40 · 6H 2O (3) have been synthesized and structurally characterized by single-crystal X-ray analysis, IR, and thermogravimetry. Compounds 1 and 2 both show the high symmetry trigonal space group P3 221 and a novel 3D network structure. The Keggin anions [SiM 12O 40] 4−(M = Mo, W) are linked by potassium or sodium cations to generate hexagon-shaped channels along the c-axis, in which water molecules are accommodated. Compound 3 is tetragonal, space group P4/mnc constructed from [SiMo 12O 40] 4− anions and Na ions. 相似文献
17.
The evolution of the cathode material of Li/V 2O 5 cells upon lithium intercalation is studied by Electron Paramagnetic Resonance (EPR) spectroscopy. Below one lithium per V 2O 5( x < 1), where the electrochemical process is completely reversible, V IV ions of the - and δ-Li x V 2O 5 phases are detected by EPR. Within this intercalation range, the shape of the EPR signal is dominated by the strong exchange interactions between magnetically concentrated V IV ions of the Li x V 2O 5 phases. The intercalation range x > 1 is characterized by a new EPR signal attributed to magnetically diluted vanadyl ions VO 2+. It is shown that these species do not belong to the Li x V 2O 5 matrix, but most probably originate from the liberation of surface vanadyl ions during the irreversible transformation of δ-Li x V 2O 5 into γ-Li x V 2O 5. On the basis of these results, a mechanism to explain the partial irreversibility of the electrochemical processes is proposed. A third EPR signal is also observed for x 1. This signal is attributed to an electron-hole defect in Li x V 2O 5, originating from a local charge compensation of the vanadyl vacancies. 相似文献
18.
Ammonium polyacrylate (NH 4PA) was introduced into powdered mixtures consisting of anatase-structured TiO 2 nanoparticles and silicon alkoxide precursors at the sol level, and the rheological behavior of the mixtures was examined under various solid loadings (φ=0.05–0.13 in volumetric ratios), shear rates (
s −1) and NH 4PA concentrations. The alkoxide precursors were mixtures of tetraethyl orthosilicate (TEOS, Si(OC 2H 5) 4), ethyl alcohol (C 2H 5OH), H 2O and HCl in a constant [H 2O]/[TEOS] ratio of 11. The nanoparticle–sol mixtures generally exhibited a pseudoplastic flow behavior over the shear-rate regime examined. The NH 4PA appeared to serve as an effective surfactant which facilitates the suspension flow by reducing the flow resistance at low NH 4PA concentrations. At φ=0.10, a viscosity reduction ca. 85% was found at
s −1 when the NH 4PA concentration was held at 2.5 wt.% of the solids. As the NH 4PA exceeded a critical level, e.g., [NH 4PA]≥3.0 wt.%, the NH 4PA acted as a catalyst which quickly turned the TiO 2–silica sol mixtures (φ=0.10) into a gelled structure, resulted in a pronounced increase of mixture viscosity. The maximum solids concentration ( φm) of the mixtures was experimentally determined from a derivative of relative viscosity, i.e., (1−η r−1/2)– φ dependence. The estimated φm increased from 0.127 to 0.165 when NH 4PA of 0.5 wt.% was introduced into the TiO 2–silica sol mixtures. 相似文献
19.
The divalent selective electrode together with high precision solid state, digital pH -mv -meter makes broader application of potentiometry in physical and inorganic chemistry a certainty. The above set-up is used to determine the stoichiometric constants, K, for Ca and Mg ions association with formates, acetates, propionates and butyrates at 25°, 35° and 45°C in aqueous media. The K-values were converted to infinite dilution KA values were found to be 8.4 LM −1, 10.4 LM −1, 19.1 LM −1 and 19.3 LM −1 for calcium salts of formate, acetate, propionate and butyrate respectively. Also KA values for Mg salts of formate, acetate, propionate and butyrate were found to be 7.8 LM −1, 9.5 LM −1, 13.1 LM −1 and 13.1 LM −1 respectively. Other thermodynamic parameters such as ΔG°, ΔH° and ΔS° are also obtained from the variation of KA with temperature for each salt. The data are interpreted relative to each other on basis of p Ka of the corresponding organic acid. Their temperature behaviour is similar to those salts derived from strong acids such as sulphates, rather than weak acids. 相似文献
20.
The impedance of electrode reactions under polarization with direct current ( idc) is theoretically analysed for the reaction where a first- or second-order chemical reaction on the electrode surface follows the charge-transfer process: A → νB + n e −, B → C. Discussion is developed upon the dependence of impedance on ac frequency and dc cd or electrode potential, for the cases of either of the above steps being rate-determining. It is shown that the plot of reactance (1/ωCs) υs resistance (Rs), which are the components of impedance in the series equivalent circuit, gives a semi-circle on the complex plane, irrespective of the rate-determining step in the reaction. The value of RT/nF, the rate constant of the surface chemical reaction, and also the double-layer capacitance, can be determined by analysing the semi-circle. The dependence of angular frequency corresponding to the maximum mf 1/ωCs on idc can be taken as a criterion for the determination of the rate-determining step. 相似文献
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