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1.
The dynamic mechanical spectra of cellulose acetate (CA) with various amounts of diethylphthalate (DEP), from 3 to 50 wt%, have been obtained over a range of temperatures (−130°C to 240°C) and frequencies (0.1 to 30 Hz). The effect of DEP addition on the main () relaxation is to shift the dispersion and corresponding modulus drop to lower temperatures. The depression of the transition temperature is smaller than commonly found for polymer-diluent mixtures. The influence of DEP on the secondary β and γ relaxations is quite different: while the low-temperature γ dispersion is progressively depressed by DEP addition, the intensity of the β relaxation increases strongly at DEP contents higher than 15%. The dynamic modulus increases with γ peak depression and shows a more intense drop with the strengthening of the β relaxation. The activation energy of the β dispersion remains fairly constant up to 15% DEP content, then increases to approach, at 50% DEP, the Δ H value of the relaxation of the pure diluent. At high DEP contents, active participation of the diluent molecules in the motion responsible for the β relaxation is suggested. 相似文献
2.
USY (ultrastabilized Y) and Ce/USY (5 wt.% supported) zeolite acidities were characterized by microcalorimetric and adsorption studies of pyridine using liquid phase (Cal-Ad), thermogravimetry, and infrared analysis. The average adsorption enthalpies determined by microcalorimetry were −125.0 kJ mol −1 for USY and −97.2 kJ mol −1 for Ce/USY. A heterogeneous distribution of acid sites with heats of adsorption ranging from −134.0 (maximum heat value for USY) to −73.5 (minimum heat value for Ce/USY) kJ mol −1 was found for both zeolites. A two-site model was best fitted by the Cal-Ad method for HUSY ( n1 = 0.1385 mmol g −1 with Δ H1 = −134.0 kJ mol −1, and n2 = 0.7365 mmol g −1 with Δ H2 = −101.5 kJ mol −1) and Ce/HUSY ( n1 = 0.0615 mmol g −1 with Δ H1 = −117.6 kJ mol −1, and n2 = 0.7908 mmol g −1 with Δ H2 = −83.6 kJ mol −1). DRIFTS measurements after pyridine adsorption showed that USY zeolite possesses only Brønsted acidity and that cerium impregnation leads to the appearance of Lewis sites. Based on these results, three families of acid strength were distinguished: (i) strong Brønsted sites (Δ H > −130 kJ mol −1); (ii) Brønsted sites with intermediate strength (−100 < Δ H < −130); and (iii) weak Brønsted and Lewis sites (Δ H < −100). Thermogravimetric analysis showed that the strongest sites were able to retain pyridine up to 800 °C and that cerium incorporation leads to a more stable zeolite. A loss of strength was observed after impregnation. The total number of sites desorbed after gas adsorption (0.88 and 0.95 mmol for HUSY and Ce/HUSY, respectively) supports the Cal-Ad results (0.88 and 1.19 mmol for HUSY and Ce/HUSY, respectively) and indicates that not all Al sites are available to pyridine. The methodology used in this work for solid acid characterization (Cal-Ad) proved to be efficient in the evaluation of acid strength, total number and distribution of acid sites. XRPD, ICP-AES, 27Al NMR, and FTIR were used for additional structural characterization. 相似文献
3.
Adsorption of dihydrogen onto the zeolites Na-ZSM-5 and K-ZSM-5 renders the fundamental H–H stretching mode infrared active. The corresponding infrared absorption bands were found at 4101 and 4112 cm −1 for H 2/Na-ZSM-5 and H 2/K-ZSM-5, respectively. Thermodynamic characterization of the adsorbed state was carried out by means of variable-temperature infrared spectroscopy; simultaneously measuring integrated band intensity, temperature and equilibrium pressure of the gas phase. For the H 2/Na-ZSM-5 system, the standard adsorption enthalpy and entropy resulted to be Δ H° = −10.3 (±0.5) kJ mol −1 and Δ S° = −121 (±10) J mol −1 K −1. For H 2/K-ZSM-5 corresponding values were −9.1 (±0.5) kJ mol −1 and −124 (±10) J mol −1 K −1, respectively. 相似文献
4.
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
5.
The heats of solution at infinite dilution, Δ Hs, of more than 40 solvents of widely different structure and polarity (from n-hexane to 2,2,2-trifluoroethanol) in liquid poly (ethylene oxide) PEO, derived from gas-liquid chromatography, were quantitatively analysed within the general framework of linear solvation energy relationships: −Δ Hs(kcal mol −1) = 0.48 × 10 24P + 1.725μ + 4.29, R(26 solvents) = 0.9566. This linear multiparametric approach allows us to separate the contributions of dispersion-cavitation forces (probe polarizability P), of dipolar interactions (probe dipole moment μ) and of hydrogen bonding (H-bond donating power of the probe measured by the Taft empirical parameter). It affords reliable values for the heat of H-bonding formation between protic probes and PEO. The potential value of such a correlation analysis as a general strategy to quantify solute-polymer interactions in polar systems at a molecular level is emphasized. 相似文献
6.
The kinetics of the chlorination of pyrite in two Turkish lignites in water and water-carbon tetrachloride media at ambient pressure ( 610 mm Hg) are investigated. The effects of speed of stirring (5–20 s −1), particle size (74–88, 150–180 and 250–425 μm), temperature (13–70°C) and reaction time (0–18 000 s) were studied. The experimental data were analyzed on the basis of the unreacted shrinking core model. The fine pyrite particles are assumed to be embedded inside the coal particles. The rate-controlling step was found to be diffusion of chlorine through the ash (the coal matrix). The activation energies were calculated as 25.1 kJ mol −1 for Dada
i coal in water medium and 25.0 kJ mol −1 for Mengen coal in water-carbon tetrachloride medium. 相似文献
7.
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
8.
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
9.
Silver-silver selenocyanate electrode has been prepared and the standard electrode potential determined to be −(0·02975 ± 0·0002), −(0·03022 ± 0·0003), −(0·03105 ± 0·0003) and −(0·03151 ± 0·0005) V at 35, 40, 45 and 50°C respectively (IUPAC convention). The thermodynamic quantities: Δ G°, Δ H° and Δ S° of the cell reaction and the solubility product of AgSeCN have also been calculated at the above temperatures. 相似文献
10.
The kinetics of the second calcination step in the formation of PZT solid solution (with perovskite ABO 3 lattice) has been investigated by using two different particle sizes of the B-site precursor (1.91 and 5.08 μm), the finer size being obtained by prolonged milling. In-situ analysis performed by high-temperature X-ray diffractometry in a non-isothermal mode (20–800 °C) revealed a reduction of the calcination temperature by 100 °C with a decrease in particle size of the precursor. In order to clarify the mechanism of the solid-state reaction to PZT, isothermal heat treatment of the mixtures was performed in the temperature range 540–700 °C. The activation energies for the fine and the coarse powders were estimated as 150 and 210 kJ mol −1 respectively, and the reaction was found to follow the Jander model for diffusion-controlled solid-state reaction kinetics. 相似文献
11.
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
12.
The essential properties of polyimide films of importance in microelectronic applications are thermal and thermo-oxidative stability, dimensional stability, glass transition behaviour and the relative permittivity (dielectric constant ′). A segmented rigid-rod polyimide was synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) in order to develop new materials for microelectronic applications. The thermal and thermo-oxidative stability were investigated by determining the thermal degradation activation energy in air (210 kJ mol −1) and in nitrogen (303 kJ mol −1). The thermal stability was further studied through thermogravimetry-mass spectroscopy. The coefficient of thermal expansion, which indicates the dimensional stability, was measured via a tension mode of a thermomechanical analyser and doubly extrapolated to zero stresses, and was 6.98 × 10 −6°C −1 for the BPDA-PFMB films. The glass transition temperature, measured thermomechanically, was found to be 287°C. The dielectric constant for the films, measured after ageing at 50% relative humidity for 48 h at 23°C, was between 2.8 and 2.9 in a frequency range from 0.1 kHz to 1 MHz. The temperature and frequency dependence of the dielectric behaviour is also discussed. 相似文献
13.
The transported entropy and the Thomson coefficient for charge conducting ions are needed to predict reversible heat effects in batteries. Transported entropies and Thomson coefficients have been calculated from Seebeck coefficients of the cell Fe(s, T1)|Me| β″ alumina | Me | Fe(s, T2) for Na and K (Me). The result is S* Na+ = 56 ± 3 J K −1 mol −1 at 500 K, with a Thomson coefficient τ Na+ = 30 ± 2 J K −1 mol −1 in the temperature interval 333–773 K. The transported entropy of Na + did not change by freezing Na at 370. The results for K + are identical to those of Na + within the accuracy of the experiments. The Thomson coefficient derived from measurements at different values of T1 was consistent with the observed variation in emf with Δ T for a given T1. The reversible heat changes at the electrodes have been calculated for sodium sulphur and potassium sulphur batteries. During discharge both batteries produce a net reversible heat, the production always being largest at the alkali metal anode. At the cathode, the heat effect becomes relatively small when the composition of Na and S is within the one phase region. A change in composition from the one phase to the two phase region is expected to lead to changes in local temperature gradients. The systems were described by the electric work method, a method which has practical advantages compared to other electrochemical methods. 相似文献
14.
The electro-oxidation of dimethyl ether (DME) on PtMe/Cs (Me = Ru, Sn, Mo, Cr, Ni, Co, and W) and Pt/C electro-catalysts were investigated in an aqueous half-cell, and compared to the methanol oxidation. The addition of a second metal enhanced the tolerance of Pt to the poisonous species during the DME oxidation reaction (DOR). The PtRu/C electro-catalyst showed the best electro-catalytic activity and the highest tolerance to the poisonous species in the low over-potential range (<0.55 V, 50 °C) among the binary electro-catalysts and the Pt/C, but at the higher potential (>ca. 0.55 V, 50 °C), the Pt/C behaved better than PtRu/C. The apparent activation energy for the DOR decreased in the order: PtRu/C (57 kJ mol −1) > Pt 3Sn/C (48 kJ mol −1) ≈ Pt/C (46 kJ mol −1). On the other hand, the activation energy for the MOR showed a different turn, decreased in the following order: Pt/C (43 kJ mol −1) > Pt 3Sn/C (35 kJ mol −1) ≈ PtRu/C (34 kJ mol −1). The temperature dependence of the DOR was greater than that of the oxidation of methanol (MOR) on the PtRu/C. 相似文献
15.
Saxena and co-workers have made extensive study on the complexing tendencies of several thiols and some of the aminoacids with various metals[1–4]. This paper reports the determination of composition and stabilities of La(III), Ce(III), Pr(III) and Sm(III) complexes of N-Glycylglycine at 30° C and 40° C by applying potentiometric and conductometric titration techniques and also the values of Δ G, Δ H and Δ S at 30° C accompanying the complexation reactions. There is however, no reference in the literature on the study of the present system. 相似文献
16.
The adsorption of quinoline, acridine, indole, and carbazole on the well-defined NiMoS hydrotreating catalyst edge surface has been studied by means of density-functional theory (DFT) using a periodic supercell model. Quinoline and acridine, the basic nitrogen-containing molecules present in heavy oils, are preferably adsorbed on the Ni-edge surface through the lone pair electrons of the nitrogen atom, which produces relatively high adsorption energies (−Δ Ea = 16–26 kcal mol −1). Indole and carbazole, the non-basic nitrogen-containing molecules, primarily interact with the NiMoS catalyst edge surface through the π-electrons of the carbon atoms. While indole preferentially adsorbs on the NiMoS surface through the β-carbon of the pyrrolic ring (−Δ Ea = 19 kcal mol −1), carbazole primarily interacts with the NiMoS surface through the phenyl rings (−Δ Ea = 13 kcal mol −1). The relative adsorptivities and energetically preferred adsorption modes of the nitrogen-containing molecules in heavy oils can provide insights into experimental observations about hydrodenitrogenation (HDN) kinetics and reaction pathways. 相似文献
17.
Algal cells of Dunaliella tertiolecta with a moisture content of 78.4 wt% were converted directly into oil by thermochemical liquefaction at around 300°C and 10 MPa. The oil yield was about 37% on an organic basis. The oil obtained at a reaction temperature of 340°C and holding time of 60 min had a viscosity of 150–330 mPas and a calorific value of 36 kJ g −1, comparable to those of fuel oil. 相似文献
18.
Effect of electrical ageing (EA) on the field emission parameters of thin multiwall carbon nanotube composite (t-MWCNTs-composite) was studied. Initially, t-MWCNTs were mixed with -terpineol and ethyl cellulose and subjected to three roll milling process to obtain t-MWCNTs-composite. Following this, the composite was screen printed on a conducting substrate, annealed for 10 min and employed to the electrical ageing process for a period of 6 h. The ageing, on each cathode layer, was repeated for five times and J– E characteristics have been collected before and after each ageing attempt. The analysis revealed that, the magnitude of threshold turn-on-field gradually increased from its virgin value of 1.223 to 1.968 V µm − 1 and corresponding mean field enhancement factor, γm, gradually decreased from 2700 ± 210 to 1940 ± 30 with a sequential increase in the ageing attempts. The degradation rate, δ J/δ t, estimated for untreated and EA samples, indicated that the magnitude of δ J/δ t reached to an equilibrium value of ~ 0.785 μA cm − 2 min − 1, which shows a stable emission state of the emitters. To investigate the effect of EA on the physical state of the emitters, a few virgin and all EA samples were subjected to scanning electron microscopy, micro Raman spectroscopy and X-ray photoelectron spectroscopy. The details of the analysis are presented. 相似文献
19.
The solid state reactions between 18.2% mol BaCO 3−81.8% mol TiO 2 powders were investigated in the initial stage of the process where BaTiO 3 is the only solid product. In O 2 (g) environment BaTiO 3 formation occurs in two regimes. The first one is characterized by a total apparent activation entalphy (ΔH +) of 42 kJ/mol ± 20 kJ/mol. The second one is a more activated process with ΔH + equal to 230 kJ/mol ± 25 kJ/mol. In CO 2 (g) environment and ‘In vacuo’ there was only one activated process with a ΔH + respectively equal to 222 kJ/mol ± 25 kJ/mol and to 20 kJ/mol ± 10 kJ/mol. The low activated mechanism is consisted with a layered interphase model, while the high activated step requires a bulk phenomena such as needle-like crystals BaTiO 3 grown from TiO 2 particles. 相似文献
20.
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
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