Cumulative chemical composition of atmospheric cloud condensation nuclei

Condensation nuclei (CN) separated during winter 1982–1983 in Colorado consisted mostly of sulfates and chlorides, with nitrates practically absent. Nitrates were present in all precipitation (rain and snow). CN condensate collected in the presence of haze contained the largest amounts of SO₄²⁻ (1.7 × 10⁻⁷ moles/ml), Cl (> 1.4 × 10⁻⁷), and NO₃⁻(2.1 × 10⁻⁸) recorded; the concentrations of the cations were > 2.2 × 10⁻⁷ moles/ml of Na⁺, > 1.1 × 10⁻⁷ of NH₄⁺, and > 2.6 × 10⁻⁷ of K⁺. Nitrates were present in low concentrations in CN separated in the presence of fogs.

The pH of the separated CN varied from 5.2 to 6.6; the pH of rain samples was between 4.6 and 5.3, and that of the snow samples was between 3.9 and 4.9.

Analysis of single aerosol particles collected since 1979 showed the predominant anion to be sulfate. Nitrate ion-bearing aerosol particles were not detected on some days.     

Adsorption and diffusion of light alkanes on nanoporous faujasite catalysts investigated by molecular dynamics simulations

Molecular dynamics simulations were performed for ethane, propane, and n-butane in siliceous faujasite for different numbers of molecules per unit cell (loadings) at 300 K. Both the adsorbed molecules and the zeolite framework were modeled as flexible entities. A new semiempirical analytical potential function for the systems was constructed. From the mean-square displacement of the molecules, self-diffusion coefficients of 18.7 × 10⁻⁵, 13.3 × 10⁻⁵, and 4.3 × 10⁻⁵ cm²/s were calculated for ethane, propane, and n-butane, respectively at a loading of 8 molecules/unit cell. They compare well with experimental values from pulsed-field gradient NMR measurements (10 × 10⁻⁵, 9 × 10⁻⁵, and 6 × 10⁻⁵ cm²/s, respectively). Besides depending on the size of the hydrocarbon, the heats of adsorption and self-diffusion coefficients also strongly depend on the loading of adsorbate molecules. The results suggest that the new intermolecular force field can reasonably describe the adsorption and diffusion behavior of ethane, propane, and n-butane in faujasite zeolite.     

Electrocatalytic reduction of nitrate by foreign Pb adatoms

Au/Pb(ad) electrodes were prepared by the underpotential deposition of lead ions at various potentials in 1 M HClO₄ solution containing Pb(CH₃COO)₂ at concentrations of about 1 × 10⁻², 1 × 10⁻⁴ and 1 × 10⁻⁶ M, respectively. The best preparation condition was selected. These electrodes, modified by foreign metal atom were used to catalyze the reduction of nitrate in concentrated alkaline solution, and exhibited efficient electrocatalytic activity for this system.     

含CdS/偶氮分子的PMMA/SiO2纳米复合二阶非线性光学材料的制备与性能

以γ-缩水甘油醚基丙基三甲氧基硅烷(KH-560)为偶联剂,用溶胶-凝胶法合成了含4-(4′-对硝基偶氮苯)-3-氨基-苯胺(DAB)生色团的键合型有机/无机复合非线性光学材料。以掺杂的方式引入表面用AOT修饰的纳米CdS微粒。在160℃、6000 V条件下经电晕电场极化后,只含DABASD的聚合物膜极化后序参数Ф值为0.278,二阶非线性光学系数(d₃₃)值为7.784×10^-9esu,含CdS/DABASD的聚合物膜极化后序参数Ф值为0.375,d₃₃值为7.556×10^-7esu。在150℃、7000 V条件下经电晕电场极化1h后d₃₃可达8.638×10^-7esu。这种有机生色团与无机玻璃键合形成的交联网络结构中,无机玻璃的刚性三维结构能有效抑制NLO生色团的极化松弛。去极化实验结果表明,复合材料的非线性光学性能的常温稳定性好,在100℃放置400 h序参数仍保持初值的95％以上。     

Mercury-mercurous propionate electrode: standard potentials at different temperatures and related thermodynamic quantities

The standard molal potentials E°_m of the Hg/Hg₂(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.     

Sorption kinetics of ammonia and ammonium ions on gel and macroporous sulphonic acid cation exchangers

Diffusion of ammonia and ammonium ions in sulphonic acid cation exchangers (gel Purolite SGC 100 × 10 MBH and macroporous Purolite C 160 MBH) from the solutions, representing the composition of “caustic condensate” (waste of nitrogen fertilizers production) is affected by pH of initial solution and structure of the matrix of cation exchanger. In gel matrix the effective intraparticle diffusivity (D_ef) depends greatly on the solution pH because of shrinkage in alkaline and swelling in acidic medium: on decreasing the initial concentration of ammonia from 0.214 to 0.003 and increasing that of ammonium nitrate from 0 to 0.214 mol l⁻¹ instead, the effect of ion exchange leads to a decrease in pH, resulting in swelling and increase in D_ef from 0.1 to 0.34 × 10⁻¹⁰ for gel Purolite SGC 100 × 10 MBH and variation of 0.18–0.11 × 10⁻¹⁰ m² s⁻¹ for macroporous Purolite C 160 MBH (resistant to shrinkage and swelling).

In Purolite C 160 MBH both macropore diffusivity (0.07–0.29 × 10⁻¹⁰ m² s⁻¹) and gel (solid phase) diffusivity (0.06–0.19 × 10⁻¹⁰ m² s⁻¹) are higher than micropore diffusivity (0.28–0.56 × 10⁻¹⁸ m² s⁻¹).

With respect to the effective intraparticle diffusivity, resistance to nitric acid, used for the regeneration, and high concentration of ammonium nitrate in eluate (up to 110 g l⁻¹), Purolite C 160 MBH has been installed for the conversion of ammonia and ammonium ions to ammonium nitrate reusable in the fertilizers production. This allows minimizing the economic loss and preventing the environmental contamination.     

Voltammetric behavior of the C60-γ-cyclodextrin inclusion complex (1:2) on hmde in an aqueous solution

Electrochemical behavior of the water-soluble C₆₀-γ-CD (1:2) inclusion complex has been studied on the hanging mercury drop electrode. A one-electron reversible adsorptive electro-reduction and three irreversible adsorptive electro-reductions were detected by cyclic voltammetry. The amount of C₆₀-γ-CD adsorbed at saturation is 2.50 × 10⁻¹¹ mol cm⁻², the diffusion coefficient is 4.36 × 10⁻⁶cm²s⁻¹ and the standard rate constant of the surface reaction k_s are 0.745 s⁻¹, 0.612 s⁻¹ and 0.513s⁻¹, respectively.     

An evaluation of Ce-Pr oxides and Ce-Pr-Nb oxides mixed conductors for cathodes of solid oxide fuel cells: Structure, thermal expansion and electrical conductivity

Ceria doped with praseodymia and niobia has been studied in order to evaluate the possibility of applying these materials as cathodes for solid oxide fuel cells. The content of crystallographic phases and their lattice parameters have been determined by X-ray diffraction, the thermal expansion coefficient has been characterised by the dilatometry technique and the electrical conductivity has been measured by complex impedance spectroscopy and by the four probe DC technique. The results have shown the presence of one fluorite phase in binary compositions (CeO₂-PrO_2−x) for PrO_2−x concentrations up to about 20 mol% and two fluorite phases with different lattice parameters for higher PrO_2−x concentrations. The addition of 3 mol% NbO_2·5 has allowed the stabilisation of a single fluorite phase up to 50 mol% PrO_2−x. The thermal expansion coefficient varies between 0 and 30 × 10⁻⁶/K depending on composition and temperature. The electrical conductivity is mainly electronic and thermally activated. The conductivity exceeds 0·1 S/cm at 800°C for compositions with 40 to 50 mol% PrO_2−x.     

Drift mobility determination using surface-charge decay technique in polyvinylidene fluoride (PVF2)

Drift mobility of charge carriers in pure and iodine doped PVF₂, has been determined by surface-potential decay method. The mobility 8 × 10⁻¹¹cm²V⁻¹s⁻¹ and 10⁻⁸cm²V⁻¹s⁻¹ have been encountered in pure and iodine doped PVF₂ respectively. The increase in mobility with doping is attributed to the charge transfer complex formation. The existence of charge transfer complex is found from the analysis of u.v. and visible spectra of doped samples. It is concluded that charge carrier conduction in PVF₂ may be due to a hopping process.     

Electrical conductance of KI in anhydrous acetonitrile

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 Λ₀, 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.     

Influence of nitrogen doping on photoconductivity properties of a: DLC films

We present photoconductivity, photosensitivity and decay time of photocurrent measured as a function of temperature for both nitrogen-doped and undoped a:DLC films. The a:DLC films were deposited using radio-frequency (RF) glow discharge of methane gas (CH₄) as a source of carbon. Several films were doped employing nitrogen (N₂) as the doping gas. The doped and undoped a:DLC films have shown photoconductivity effects in a wide range of temperatures. All photoconductivity parameters, i.e. spectral response, photosensitivity, decay time and photocurrent, were measured for both undoped and doped films. The maximum spectral photosensitivity of doped films shifts to a higher energy, similar to the optical energy-gap measurements. The photocurrent of the doped film is larger by two orders of magnitude than that of undoped film, while the photosensitivity shows an opposite effect. The mobility of doped films (2.43 × 10⁻⁵) is larger by two orders of magnitude than that of undoped films (5.64×10⁻⁷) at room temperature. In order to provide nanoscale information about the morphological properties of the undoped a:DLC films surface, we have used atomic force microscopoy (AFM). It was found that the roughness of our films increased with increasing thickness of the films, from 0.3 to 1.5 μm.     

Polymerization of surface-active monomers: 5. Syntheses and polymerizations of anionic surface-active monomers: sodium di(10-undecenyl)sulphosuccinate and sodium n-undecyl 10-undecenylsulphosuccinate

Novel, anionic surface-active monomers, sodium di(10-undecenyl)sulphosuccinate (DUSS) and sodium n-undecyl 10-undecenylsulphosuccinate (MUSS) were prepared. The monomers were soluble in both water and apolar organic solvents on heating. DUSS and MUSS in water exhibited Kraft points at about 39°C and 48°C, respectively. The critical micelle concentrations for aqueous solutions of DUSS and MUSS at 50°C were determined to be 2.4 × 10⁻⁵ and 1.2 × 10⁻⁵ mol l⁻¹, respectively. Polymerization of the monomers in darkness and under u.v. irradiation at 50°C were studied using three different solvents, namely water, n-hexane and dioxane, giving aqueous micelles (or vesicles), reversed micelles and isotropic solution, respectively. Only traces of polymers were formed for the polymerizations in darkness, while the polymerizations under u.v. irradiation gave polymers, except for the polymerization of MUSS in dioxane. The solvents used for the polymerization were observed to exert an effect on the solubility of the polymers of DUSS and only the polymer obtained from the polymerization in water was soluble in solvents such as water and N,N-dimethylformamide. Thus, the monomer aggregation, especially for the aqueous system, was found to affect the structure of the resulting polymers.     

Voltammetric behavior study of folic acid at phosphomolybdic-polypyrrole film modified electrode

The electrochemical behavior of folic acid at the Keggin-type phosphomolybdate (PMo₁₂) doped polypyrrole (PPy) film modified glassy carbon electrode (PMo₁₂-PPy/GCE) was studied. PMo₁₂ doped PPy modified electrodes were achieved during the electrochemical preparation of the polymer films in aqueous solution. The redox behavior of the modified electrode was described by cyclic voltammetry. The electrochemical behavior of folic acid at PMo₁₂-PPy/GCE was studied by 0.5 order differential voltammetry. Numerous factors affecting the reduction peak currents of folic acid at PMo₁₂-PPy/GCE were optimized to maximize the sensitivity. The results showed that folic acid had high inhibitory activity toward the reduction of modified electrode in 0.01 M H₂SO₄. The reduction peak currents were directly proportional to the concentration of folic acid from 1.0 × 10⁻⁸ to 1 × 10⁻⁷ M with correlation coefficient of 0.9976, a detection limit of 1.0 × 10⁻¹⁰ M of folic acid was estimated. From the inhibitory effect of folic acid on PMo₁₂-PPy/GCE, the apparent formation constant of folic acid with the modified film was estimated. This modified electrode showed excellent sensitivity and stability for the determination of folic acid. The response mechanism of folic acid at PMo₁₂-PPy/GCE was discussed in detail.     

Methacryl-terminated macromers by living polymerization as precursors of IPN polymer electrolytes

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 (LiBF₄, LiClO₄, LiCF₃SO₃) 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.     

Poly-(3-methylthiophene)/carbon nanotubes hybrid composite-modified electrodes

The preparation of poly-(3-methylthiophene)—multi-walled carbon nanotubes hybrid composite electrodes is reported. The hybrid electrode shows a synergic effect of the electrocatalytic properties, and high active surface area of both the conducting polymer and carbon nanotubes, which gives rise to a remarkable improvement of oxidation of NADH with respect to polymer-modified electrodes, and CNTs-modified electrodes. SEM showed that carbon nanotubes served as nanosized backbone for P3MT electropolymerization. The amperometric NADH detection at +300 mV provided fast responses, a range of linearity between 5.0 × 10⁻⁷ and 2.0 × 10⁻⁵ mol l⁻¹, and a detection limit of 1.7 × 10⁻⁷ mol l⁻¹, which compares advantageously with those reported for other NADH CNT-based amperometric sensors. Furthermore, the direct electrochemistry of cytochrome c and FAD at the hybrid electrode is also checked.     

Optical probe measurements of the temperature of burning particles in fluidized beds

The temperatures of freely moving petroleum coke particles burning in the interior of a fluidized bed of sand have been measured. An optical probe technique, employing two-wavelength pyrometry with wavelengths centred at 800 and 1000 nm, was used for the measurements over a wide range of operating conditions. Measurements were conducted in bubbling fluidized beds of 1.82 × 10⁻⁴ m and 1.09 × 10⁻³m sand particles maintained at bed temperatures of 973 and 1200 K. Batches of petroleum coke particles having average diameters in the range 7.5 × 10⁻⁴ to 8.1 × 10⁻³ m were charged into the hot fluidized bed combustor, and upon the passage of a burning particle across the optical probe's field of view, a pulsed signal was generated. Signals from the interior of the bed were continuously monitored by a pair of radiometers interfaced to a high speed data acquisition system and were processed off-line for particle temperature calculations. The average particle temperatures exceeded the bed temperature by 60–360 K for the operating conditions considered. It was found that particle temperatures in the bubble phase were on average, higher than in the emulsion phase. Further, the temperatures of particles were lower closer to the distributor as a consequence of particle circulation and combustion-assisted attrition within the bed.     

Diffusion of methane through coal

Both methane and helium flow through solid coal by Knudsen diffusion, even at relatively high pressures. Knudsen permeabilities were determined for samples of Pittsburgh, Pocahontas No.3, and Oklahoma Hartshorne coals. The average permeability for dry methane was 1.3 × 10⁻⁶ cm²/s for Pittsburgh coal, 20 × 10⁻⁶ for Pocahontas No.3 coal, and 13.8 × 10⁻⁶ for Oklahoma Hartshorne coal. A molecular-sieve effect exists for methane in all three coals examined and it is very strong in Pittsburgh coal. If the methane is saturated with water vapour the permeability decreases by a factor of 3 to 25, depending on the coal. The Knudsen permeability of solid coal discs seems to bear no relation to coalbed permeability. Lag-time measurements indicate systems of both larger and finer pores and the presence of blind pores. This effect is again more pronounced in the Pittsburgh coal.     

Photocrosslinked polymer and interpenetrating polymer network for nonlinear optics

Two photocrosslinkable NLO polymers of poly(glycidyl methacrylate) substituted with 4‐nitro‐4′‐hydroxyl stilbene (PGMAS) and acryloyl‐functionalized epoxy‐based polymer (PENAA) carrying 4‐nitroaniline moieties were synthesized and characterized. By using the sulfonium salt cationic photoinitiator BDS · 2PF₆ which can induce cationic or/and radical polymerization, the photocrosslinking of PGMAS and the interpenetrating polymer network (IPN) formed by the photocrosslinking of PGMAS and PENAA simultaneously were reported. The poled and photocrosslinked polymer films and IPN films exhibit relatively stable second‐order nonlinear optical activity. The influence of stilbene isomerization in PGMAS films with different crosslink densities on the SHG stability was also investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1081–1087, 1999     

Thermoelectric characterization of NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe) polycrystalline materials

Layered -titanate materials, Na_xM_x/2Ti_1−x/2O₂ (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_0.8O₂ were ca. 7×10³ 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_0.8O₂ and Na_0.4Co_0.2Ti_0.8O₂ was about 1.9×10⁻⁴ and 1.2×10⁻⁴ K⁻¹ around 700 °C, respectively.     

Phase transition phenomena of the adsorbed 1-dodecanol monolayer at the air–water interface

Phase transition phenomenon of the 1-dodecanol monolayer at the air/water interface was studied by the dynamic γ(t) curves and the adsorption isotherm obtained by ellipsometry at 20 °C. The surface-concentration adsorption isotherm clearly showed three abrupt increases at bulk concentration C of 1.3 × 10⁻⁹, 2 × 10⁻⁹ and 3.7 × 10⁻⁹ mol/mL, respectively. The 1st and the 3rd transitions observed herein, that were typical 2D first-order transitions, were consistent with the gas to liquid expanded (G–LE) and the liquid expanded to liquid condensed (LE–LC) phase transitions observed in a previous tensiometry study. The 2nd transition that occurred at C = 2 × 10⁻⁹ mol/mL was not identified from any previous dynamic surface-tension profiles. Judging from the substantial increase in the film thickness of the transition, it was believed that the orientation change of the adsorbed molecule was involved in the LE phase. A LE_h and a LE_v phase, that denoted the “lie-down” and “stand-up” types of adsorption, respectively, was used to describe this transition and a cusp, instead of a constant surface-tension region, was observed in the dynamic γ(t) curves for this transition. This suggested that, since the surface tension varied during the transition process, the newly identified LE_h and LE_v transition might not be the typical first-order type of phase transition.