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1.
Preparations and physico-chemical characterizations of NASICON-type compounds in the system Li 1+xAl xA 2−xIV(PO 4) 3 (A IV=Ti or Ge) are described. Ceramics have been fabricated by sol-gel and co-grinding processes for use as ionosensitive membrane for Li + selective electrodes. The structural and electrical characteristics of the pellets have been examined. Solid solutions are obtained with Al/Ti and Al/Ge substitutions in the range 0≤ x≤0·6. A minimum of the rhombohedral c parameter appears for x about 0·1 for both solutions. The grain ionic conductivity has been characterized only in the case of Ge-based compounds. It is related to the carrier concentration and the structural properties of the NASICON covalent skeleton. The results confirm that the Ti-based framework is more calibrated to Li + migration than the Ge-based one. A grain conductivity of 10 −3 S cm −1 is obtained at 25°C in the case of Li 1·3Al 0·3Ti 1·7(PO 4) 3. A total conductivity of about 6×10 −5 S cm −1 is measured on sintered pellets because of grain boundary effects. The use of such ceramics in ISE devices has shown that the most confined unit cell (i.e. in Ge-based materials) is more appropriate for selectivity effect, although it is less conductive.© 相似文献
2.
Layered -titanate materials, Na xM x/2Ti 1−x/2O 2 (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na 0.4Ni 0.2Ti 0.8O 2 were ca. 7×10 3 S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm −1 K −1 at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na 0.4Ni 0.2Ti 0.8O 2 and Na 0.4Co 0.2Ti 0.8O 2 was about 1.9×10 −4 and 1.2×10 −4 K −1 around 700 °C, respectively. 相似文献
3.
Na-ZSM-5 membranes were synthesized by secondary growth on the outer surface of stainless steel porous tubes. The membranes were ion-exchanged with Cs +, Ba 2+ and Sr 2+ to investigate their effect upon the separation of p-xylene from m-xylene and o-xylene. The permeation through the membranes was measured between 150 and 400 °C using each xylene isomer separately and a ternary mixture. All the membranes were selective to p-xylene in the temperature range studied. N 2 and xylene permeation measurements together with SEM observations were used to determine whether or not cracks and/or pinholes developed after exposure to the xylene isomers at high temperature (400 °C). Neither pore blockage nor extra-zeolitic pores developed after the ion exchange procedure and subsequent calcination. Furthermore, duplicate synthesized membranes of each cation form had similar separation factors and permeances. The duplicate values differ much less than the measurement error. The p-xylene permeation flux decreased in the order: Na-ZSM-5 > Ba-ZSM-5 > Sr-ZSM-5 Cs-ZSM-5 while the permeation flux of the m- and o-xylene decreased in the order Na-ZSM-5 > Sr-ZSM-5 > Ba-ZSM-5 > Cs-ZSM-5. The membrane that exhibited the best performance was Ba-ZSM-5, with a maximum p/ o separation factor of 8.4 and a p-xylene permeance of 0.54 × 10 −7 mol s −1 m −2 Pa −1 at 400 °C. 相似文献
4.
The binary adsorption characteristics of methane and ethane on dry coal to 40 atm pressure have been calculated from pure-component isotherms. In some coal seams, pressures exceeding 40 atm have been recorded and the methane sampled from the virgin coal often shows a few percent of ethane. The binary adsorption characteristics were calculated by employing the ideal adsorbed solution theory of Myers and Prausnitz, and experimentally-determined (Type I) pure gas isotherms at 0, 30 and 50 °C. The coal used in this investigation was high-volatile ‘A’ bituminous (hvab) from the Pennsylvania Pittsburgh seam. Gas nonideality was accounted for by replacing pressure with fugacity. Adsorption of methane on dry coal is purely physical; the isosteric heat of adsorption does not exceed 2.4 kcal/mol * at 30 °C on the above coal. Isobars on the resulting binary equilibrium diagram exhibited an unexpected phenomenon of intersecting each other which might be attributable to the above nonideality considerations. The region of a few percent of ethane, which is of practical importance from the viewpoint of coal seams, was expanded and reduced to an equation: V( CH4) = −21.52 + 7.18( VF) + 16.88( VF) 2 −0.395( P) − 0.00661( P) 2 + 0.824( T) − 0.00030( T) 2 + 0.928( VF)( P) − 0.858( VF)( T). V(Total) = 25.9 − 23.6( VF) + 0.655( P) − 0.00875( P) 2 − 0.795( T) + 0.743( VF)( T) where V( CH4) and V(Total) = cm 3(STP) CH4 and total gas respectively adsorbed per g dry coal; VF = vol. fraction of methane as analysed at 1 atm (0.94 VF 1.0); P = seam pressure, atm (0 P 40); T=seam temperature, °C(−10 T 50). 相似文献
5.
In the present study, we have examined sulfation of cerium oxide via impregnation of (NH 4) 2SO 4, followed by heating in the temperature range of 220–720°C, using Raman Spectroscopy. Based on the SO and SO stretching frequencies in the range of 900–1400 cm −1, a wide range of surface oxysulfur species and bulk cerium-oxy-sulfur species are identified. At 220°C, a mixture of (NH 4) 2SO 4 crystals, SO 2−4(aq) and HSO 1−r(aq) is found to have formed on ceria's surface, whereas complete conversion of (NH 4) 2SO 4 to SO 2−4(aq) and HSO 1−4(aq) occurs at 280°C. At 350°C, formation of a mixture of surface pyrosulfate S 2O 2−7(surf.0, consisting of two SO oscillators and a bulk type compound identified as Ce(IV)(SO 4) x(SO 3) 2−x (0 < x < 2) have been observed. Upon introduction of moisture, the former transforms to HSO 1−4(surf.), whereas the latter remains unchanged. At 400°C, only the bulk type compound can be observed. At 450°C, only Ce 2(SO 4) 3 is generated and remains stable until 650°C. Further increase in the temperature to 720°C results in the formation of CeOSO 4. The present study not only provides a more thorough understanding of the sulfation of cerium oxide at a molecular level, but also demonstrates that Raman spectroscopy is a highly effective technique to characterize sulfation of metal oxides. 相似文献
6.
The dynamic mechanical spectrum of cellulose acetate (CA) from −130°C to 240°C has been determined at different frequencies (from 0.1 to 30 Hz). Three relaxations, designated , β and γ in order of decreasing temperature, and one shoulder (β*) above room temperature were found. Comparison with calorimetric and thermogravimetric measurements yields the conclusion that the relaxation (197°C at 3 Hz) is related to the glass-to-rubber transition and the β* shoulder (50°C–100°C) is due to loss of moisture. The β relaxation (−38°C at 3 Hz, Δ H = 100 kJ mol −1) is tentatively assigned to local motions of the main chain (glucopyranose rings). The low-temperature γ relaxation (−88°C at 3 Hz, Δ H = 46 kJ mol −1), is humidity-dependent: its intensity decreases when the samples are dried to moisture contents lower than that obtained by normal room conditioning (about 3%). Higher water contents shift the relaxation to lower temperatures without increasing the intensity of the mechanical loss. It is suggested that water associated with the unesterified methylol groups of cellulose acetate is responsible of the dynamic mechanical γ dispersion. 相似文献
7.
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
8.
A new class of polymer electrolytes, based on the interpenetrating polymer network approach, was obtained starting from functionalised macromers, of poly-ether nature, in the presence of a lithium salt (LiBF 4, LiClO 4, LiCF 3SO 3) and propylene carbonate (PC) or tetraethyleneglycol dimethylether (TGME), as plasticizers. The macromers were synthesised by living polymerisation employing a HI/I2 system as the initiator. The macromer has a polymerisable end group, which can undergo radical polymerisation, attached to a monodisperse poly-vinylether, containing suitable ethylene oxide groups for ion coordination. Monomers and macromers were characterised by FTi.r., u.v.–vis, 1H- and 13C-n.m.r. Self-consistent and easily handled membranes were obtained as thin films by a dry procedure using u.v. radiation to polymerise and crosslink the network precursors, directly on suitable substrates, in the presence of the plasticizer and the lithium salt. The electrolytic membranes were studied by complex impedance and their thermal properties determined by differential scanning calorimetry analysis. Ionic conductivities (σ) were measured for PC and TGME-based membranes at various plasticizer and salt contents as a function of T (60 to −20°C). LiClO4/PC/PE electrolytes, with 3.8% (w/w) salt and 63% PC, have the highest σ (1.15×10−3 and 3.54×10−4 S cm−1 at 20°C and −20°C, respectively). One order of magnitude lower conductivities are achieved with TGME; samples with 6% (w/w) LiClO4 and 45% (w/w) TGME exhibit σ values of 2.7×10−4 and 2.45×10−5 S cm−1 at 20°C and −20°C. 相似文献
9.
We report that ultrastable faujasite-based ruthenium zeolites are highly active catalysts for N 2O decomposition at low temperature (120–200°C). The faujasite-based ruthenium catalysts showed activity for the decomposition of N 2O per Ru 3+ cation equivalent to the ZSM-5 based ruthenium catalysts at much lower temperatures (TOF at 0.05 vol.-% N 2O: 5.132 × 10 −4 s −1 Ru −1 of Ru-HNaUSY at 200°C versus 5.609 × 10 −4 s −1 Ru −1 of Ru-NaZSM-5 at 300°C). The kinetics of decomposition of N 2O over a Ru-NaZSM-5 (Ru: 0.99 wt.-%), a Ru-HNaUSY (Ru: 1.45 wt.-%) and a Ru-free, Na-ZSM-5 catalyst were studied over the temperature range from 40 to 700°C using a temperature-programmed micro-reactor system. With partial pressures of N 2O and O 2 up to 0.5 vol.-% and 5 vol.-%, respectively, the decomposition rate data are represented by: −dN 2O/d t=itk( PN2O) ( PO2) −0.5 for Ru-HNaUSY, −dN 2O/d t=k( PN2O) ( PO2) −0.1 for Ru-NaZSM-5, and −dN 2O/d t=k( PN2O) −0.2 ( PO2) −0.1 for Na-ZSM-5. Oxygen had a stronger inhibition effect on the Ru-HNaUSY catalyst than on Ru-NaZSM-5. The oxygen inhibition effect was more pronounced at low temperature than at high temperature. We propose that the negative effect of oxygen on the rate of N 2O decomposition over Ru-HNaUSY is stronger than Ru-NaZSM-5 because at the lower temperatures (<200°C) the desorption of oxygen is a rate-limiting step over the faujasite-based catalyst. The apparent activation energy for N 2O decomposition in the absence of oxygen is much lower on Ru-HNaUSY ( Ea: 46 kJ mol −1) than on Ru-NaZSM-5 ( Ea: 220 kJ mol −1). 相似文献
10.
A detailed temperature variation (18–50 °C) FTIR/ATR study of sorption and desorption of water into a series of cured epoxy resins has been reported. For higher temperatures (35–50 °C) the data were modelled with a single Fickian diffusion equation, giving an increased D as the temperature increased and an activation energy ( EA) in the 55–60 kJ mol −1 region. At lower temperatures (18–35 °C)—well-below the Tg—a two-stage sorption equation was needed and the apparent EA was negative. This is probably associated with changes in water clustering among the distributed ‘voids’ in the glassy polymer associated with chain relaxation at extended times. The use of D 2O as a penetrant allowed diffusion coefficient measurements for highly dense epoxy matrices, where FTIR/ATR cannot detect the ν(OH) band of water over and above the residual polymer–OH groups (in the dry state). The data for the D 2O studies were notably influenced by isotopic exchange; which was found to be a diffusion controlled process, even in a polymer matrix. 相似文献
11.
A series of composites of polycarbonate (PC) with 23 different contents of multiwalled carbon nanotubes (MWNT) was produced by melt mixing using the masterbatch dilution method. In dielectric measurements, AC conductivity and complex permittivity data obtained in the frequency range between 10 −3 and 10 7 Hz at room temperature indicated the electrical percolation threshold at about 1.0 wt%. The dynamic mode melt rheological measurements for the same samples at eight temperatures between 170 and 280 °C showed a visible change in the frequency dependence of dynamic moduli and the absolute value of the complex viscosity |η*| particularly at low frequencies. In literature these changes are sometimes related to so called ‘percolation threshold concentration’. Applying this picture to our experimental data we have to assume that the percolation threshold is strongly dependent on the measurement temperature. It changes from about 5 to 0.5 wt% MWNT by increasing the measurement temperature from 170 to 280 °C, respectively. This temperature dependence cannot be explained by a classical liquid-solid transition but may be related to the existence of a combined nanotube-polymer network. 相似文献
12.
A new brownmillerite-related compound. Ca 2Cr 2O 5, has been prepared. It has been indexed according to an orthorhombic lattice a = 5·750 Å, b = 14·398 Å and c = 5·483 Å. A series of experiments was performed in order to find the appropriate firing temperature. The total conductivity was measured by a four-point method in the range of 690–911°C. Impedance spectroscopy was also employed in the temperature range 343–785°C. Conductivity measurements at different oxygen pressures at 500°C suggest that Ca 2Cr 2O 5 is a predominantly ionic conductor at P o2 = 1–10 −2atm. 相似文献
13.
The hydrodynamic characteristics in aqueous solution at ionic strength I=0.2
of carboxymethylchitins of different degrees of chemical substitution have been determined. Experimental values varied over the following ranges: the translational diffusion coefficient (at 25.0°C), 1.1<10 7× D<2.9 cm 2 s −1; the sedimentation coefficient, 2.4< s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130< ks<680 mL g −1; the intrinsic viscosity, 130<[ η]<550 mL g −1. Combination of s with D using the Svedberg equation yielded ‘sedimentation–diffusion' molecular weights in the range 40 000< M<240 000 g mol −1. The corresponding Mark–Houwink–Kuhn–Sakurada (MHKS) relationships between the molecular weight and s, D and [ η] were: [ η]=5.58×10 −3 M0.94; D=1.87×10 −4 M−0.60; s=4.10×10 −15 M0.39. The equilibrium rigidity and hydrodynamic diameter of the carboxymethylchitin polymer chain is also investigated on the basis of wormlike coil theory without excluded volume effects. The significance of the Gralen ks values for these substances is discussed. 相似文献
14.
The electrical conductivity of KI solutions in anhydrous acetonitrile has been determined at 0, 25 and 35°C in the concentration range 0·9– 600 × 10 −4 mole/l. The values of Λ 0, K and a calculated from the results are, respectively: 145·9 mho/cm, 0·95 × 10 −2 and 1·72 Å at 0°C; 186·2 mho/cm, 8·98 × 10 −2 and 4·6 Å at 25°C; and 204·8 mho/cm, 5·17 × 10 −2 and 3·5 Å at 35°C. The phoreograms at all the three temperatures are catabatic at lower concentration, but become anabatic at 0·017, 0·022 and 0·024 respectively, at 0, 25 and 35°C. 相似文献
15.
The electrochemical behaviour of the polymer-based cell Pb/(PEO) 40. Pb(ClO 4) 2/Pb has been investigated over the temperature range 20–160°C by means of impedance spectroscopy and dc polarization methods. The bulk resistance and the charge transfer resistance display a linear trend in an Arrhenius plot. The transference numbers have been evaluated by an electrochemical method, and compared with those obtained from a preliminary experiment with Tubandt's method. These measurements indicate that both cations and anions are mobile, with a transference number for Pb 2+ lower than 0.1 between 70 and 130°C. 相似文献
16.
The standard molal potentials E° m of the Hg/Hg 2(OPr) 2, OPr − electrode at 15°, 20°, 25°, 30° and 35° C have been determined. The E° m values obtained are 0.5114, 0.5072, 0.5031, 0.4988 and 0.4942 V respectively, which can be fitted to the equation Edg m/V = 0.5031 −8.56 × 10 −4 (itt/°C − 25)−3.0588 × 10 −6 ( t/ °C -25) 2. The changes in standard free energy, entropy and enthalpy for the cell reaction have been calculated. 相似文献
17.
We have used a projectile impact method to estimate the flow stress of high density polyethylene at a strain rate of 3 × 10 3 sec −1. The technique was developed initially by Taylor and applied successfully by Whiffin and others to ductile metals. The data from this experiment have been compared with data obtained in more conventional compression and drop hammer tests at lower strain rates at 20° and 100°C. The flow stress of high density polyethylene deduced from the impact test at 20°C is significantly higher than that anticipated from a simple extrapolation of the low strain rate data at 20°C. The data at 100°C are however in good agreement. The technique has also been used to estimate the flow stress of high density polyethylene as a function of temperature over the range −20° to +105°C. These data indicate that the discrepancy in the data for 20°C arises from a real discontinuity in the response of the polymer rather than from an inadequacy in the theoretical analysis of the impact experiment as applied to polymeric solids. We conclude that the impact method described is a useful technique for estimating the flow stress of polymers. It is however limited to a relatively narrow range of strain rates. 相似文献
18.
The single gas H 2 and N 2 permeability of a 4 μm thick dense fcc-Pd 66Cu 34 layer has been studied between room temperature and 510 °C and at pressure differences up to 400 kPa. Above 50 °C the H 2 flux exhibits an Arrhenius-type temperature dependence with JH2=(5.2±0.3) mol m −2 s −1 exp[(−21.3 ± 0.2) kJ mol −1/( R· T)]. The hydrogen transport rate is controlled by the bulk diffusion although the pressure dependence of the H 2 flux deviates slightly from Sieverts’ law. A sudden increase of the H 2 flux below 50 °C is attributed to embrittlement. 相似文献
19.
Ten weight percent BBZS (Bi 2O 3, B 2O 3, ZnO and SiO 2) glass was added to x(Ba 4Nd 9.333Ti 18O 54) − (1 − x)(BaLa 4Ti 4O 15) (BNLT, 0 ≤ x ≤ 1) composite dielectric ceramics to lower their sintering temperature whilst retaining microwave properties useful for low temperature co-fired ceramic and antenna core technology. With the addition of 10 wt% BBZS glass, dense BNLT composite ceramics were produced at temperatures between 950 and 1140 °C, depending on composition ( x), an average reduction of sintering temperature by 350 °C. X-ray diffraction, scanning and transmission electron microscopy and Raman spectroscopy studies revealed that there was limited inter-reaction between BLT/BNT and the BBZS glass. Microwave property measurement showed that the addition of BBZS glass to BNLT ceramics had a negligible effect on r and τf, although deterioration in the measured quality factor ( Qf) was observed. The optimised composition ( xBNT − (1 − x)BLT)/0.1BBZS ( x = 0.75) had r 61, τf 38 ppm/°C and Qf 2305 GHz. 相似文献
20.
The standard exchange current densities of nine 1,4-diazines at gold electrodes were measured in DMF in the temperature range of +25 up to −59°C. From the resulting free enthalphy of activation of pyrazine as a function of temperature an activation entropy of −1.5 k is calculated. It is compared with the activation entropy of −1.1 k following from the theory of Marcus. The relative change of the free enthalpy of activation with temperature is only a property of the temperature dependences of refractive index and dielectric constant of the solvent. It is used to obtain the free enthalpies of activation for the standard temperature of 298 K. The experimental values for the compounds are compared with theoretical values, calculated from the inner and outer reorganization energies λi and λ0. For λi the bond lengths and force constants were obtained from Hückel calculations, for λo different approximations according to Marcus and Peover were used. The calculated and the measured values coincide within less than 10%. The relation between the free solvation enthalpy and the outer reorganization energy is discussed. 相似文献
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