Comparative study of lithium ion conductors in the system Li1+xAlxA2−x (PO4)3 with A=Ti or Ge and 0≤x≤0·7 for use as Li sensitive membranes

Preparations and physico-chemical characterizations of NASICON-type compounds in the system Li_1+xAl_xA_2−x^IV(PO₄)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(PO₄)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.©     

Separation and enrichment of carbon dioxide by capillary membrane module with permeation of carrier solution

A novel facilitated transport membrane for gas separation using a capillary membrane module is proposed in which a carrier solution is forced to permeate the membrane. Both a feed gas and a carrier solution are supplied to the lumen side (high pressure side, feed side) of the capillary ultrafiltration membrane and flow upward. Most of the carrier solution which contains dissolved solute gas, CO₂ in the present case, permeates the membrane to the permeate side (low pressure side, shell side), where the solution liberates dissolved gas to form a lean solution. The lean solution is circulated to the lumen side. This type of capillary membrane module was applied to the separation of CO₂ from model flue gases consisting of CO₂ and N₂. Monoethanolamine (MEA), diethanolamine (DEA) and 2-amino-2-methyl-1-propanol (AMP) were used as carriers or absorbents of CO₂. The feed side pressure was atmospheric and the permeate side was evacuated at about 10 kPa. CO₂ in the feed gas was successfully concentrated from 5–15% to more than 98%. The CO₂ permeance was as high as 2.7×10⁻⁴ mol m⁻² s⁻¹ kPa⁻¹ (8.0×10⁻⁴ cm³ cm⁻² s⁻¹ cmHg⁻¹) when the CO₂ mole fraction in the feed was 0.1 and temperature was 333 K. The selectivity of CO₂ over N₂ was in the range from 430 to 1790. The membrane was very stable over a discontinuous one-month testing period.     

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.     

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.     

Variation of the aerosol charge neutralization coefficient in the entire particle size range

The rate at which the mean charge on aerosol particles relaxes to its steady-state value under bipolar charging is characterized by the neutralization rate constant, β (s⁻¹). It is an important parameter for fixing the nt product in charge neutralizers as well as in the theory of charging-induced diffusion. Here we compute the neutralization coefficient, β/n (where n is the mean ion density), as a function of particle size through the use of ion-particle combination coefficients provided by the recent theories. The results indicate that β/n decreases from a continuum limit value of 3.1 × 10⁻⁶ cm³ s⁻¹, to a free molecular limit value of 1.4 × 10⁻⁶ cm³ s⁻¹. The changeover occurs rapidly in the transitional regime (10–100 nm). This clearly indicates that the nt product required to attain steady state is higher for nano particles than for larger ones. The paper also presents the variations of the mean square variance of charge, the coefficients of charging-induced drift and diffusion, as a function of particle size.     

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.     

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.     

Ion conduction in crosslinked β-cyclodextrin gels

Gels of crosslinked β-cyclodextrin have been prepared using dimethylacetamide containing lithium, sodium and potassium triflate salts.

Compositions were adjusted to produce materials with dry surfaces that showed no evidence of solvent leakage. Alternating current conductivity (σ) measurements of ion transport in these systems were made over the temperature range 290–360 K. Systems containing KCF₃SO₃ exhibited the best range of conductivity values from σ=10⁻⁴ S cm⁻¹ (293 K) to σ=1.8×10⁻³ S cm⁻¹ (360 K). These systems also show a linear dependence of log conductivity on 1/temperature, with activation energies for ion transport in the range 32–48 kJ mol⁻¹.     

Mechanism of gas flow through coal

Coals are fossilized plant material plus inorganic silt deposited in irregular layers and containing 1–20% void space which provides a medium which is porous to gas flow. Gas flows have been measured using discs of coal cut from several coal seams. Observed flow phenomena include molecular diffusion (low gas pressure, small pores) and bulk diffusion (higher gas pressure, larger pores). In the examples investigated, methane flows ranged from 1.2 × 10⁻¹⁰ cm² s⁻¹ atm⁻¹ for Pittsburgh-seam attrital coal to 2.0 cm² s⁻¹ atm⁻¹ for Oklahoma Hartshorne coal. Flow characteristics have been compared with gas flows observed by Knudsen through glass capillaries. This information can be applied to mine safety and to coal utilization studies.     

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.     

Kinetics of hydrogen oxidation reaction on Nafion-coated Pt/C electrodes under high overpotentials

The influences of the Nafion film thickness and Pt loading on the kinetics of the hydrogen oxidation reaction on Nafion-coated 20 wt% Pt/C electrodes immersed in 0.5 M H₂SO₄ were investigated using a rotating disk electrode configuration. The coating of a Nafion film (8 μm) had a negligible effect on the electrochemical surface area of an electrode. The kinetic parameters were estimated at an overpotential of 0.4 V; the values obtained were shown to vary with the method of data treatment. The diffusional resistance for H₂ in the Nafion film was negligible when the film was thinner than 0.2 μm. The permeability of H₂ in the Nafion film ranged from 2.4 × 10⁻⁵ to 4.8 × 10⁻⁵ mM cm²/s. The error analysis demonstrated that the apparent kinetic current estimated was resulted from experimental errors, instead of resulting from a chemical process as proposed by some previous investigators.     

Catalytic decomposition of nitrous oxide over Ru-exchanged zeolites

We report that ultrastable faujasite-based ruthenium zeolites are highly active catalysts for N₂O decomposition at low temperature (120–200°C). The faujasite-based ruthenium catalysts showed activity for the decomposition of N₂O per Ru³⁺ cation equivalent to the ZSM-5 based ruthenium catalysts at much lower temperatures (TOF at 0.05 vol.-% N₂O: 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 N₂O 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 N₂O and O₂ up to 0.5 vol.-% and 5 vol.-%, respectively, the decomposition rate data are represented by: −dN₂O/dt=itk(P_N2O) (P_O2)^−0.5 for Ru-HNaUSY, −dN₂O/dt=k(P_N2O) (P_O2)^−0.1 for Ru-NaZSM-5, and −dN₂O/dt=k(P_N2O)^−0.2 (P_O2)^−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 N₂O 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 N₂O decomposition in the absence of oxygen is much lower on Ru-HNaUSY (E_a: 46 kJ mol⁻¹) than on Ru-NaZSM-5 (E_a: 220 kJ mol⁻¹).     

Reversible electrochemical insertion of anions in poly-p-phenylene from aqueous electrolytes

Poly-p-phenylene (PPP) was synthesized from benzene according to the Kovacic method. Electrodes were made from this electronic insulator by cold- or hot-pressing of the loose, brown powder, under the addition of 7.5 wt. % soot (Corax L^®, Degussa AG). The electrochemical insertion and removal of anions HSO⁻₄, ClO⁻₄ in this material in aqueous solutions of the corresponding acids was investigated by slow cyclic voltammetry.

Initially, only a surface layer of about 0.1 mm thickness takes part in the electrochemical processes, which are reversible. A maximum concentration of anions in the solid of [(−C₆H₄−)⁺₇ A⁻] is attainable. The maximum degree of insertion is equal to 0.14. The insertion potential U_I shifts strongly into the negative direction with increasing concentration c of the acid. A linear U_I/c relationship is observed as in the case of graphite, where the intercalation potential is more positive by 20–200 mV for the same electrolyte. The round trip current efficiency for the insertion/removal cycle increases with increasing acid concentration attaining 100% in 14 M H₂SO₄ or 11.3 M CHlO₄. For a given concentration, increases in the same order as with graphite (H₂SO₄ < HClO₄ < HBF₄), being somewhat lower for a given electrolyte composition. From anodic current limitation (j_lim = 5–10 mA cm⁻²), a diffusion coefficient of about D = 2 × 10⁻⁷ cm² s⁻¹ is derived for the transport of anions in the bulk of PPP. The striking similarity of our results to former findings with graphite is thoroughly discussed. Some general conclusions are derived thereof.     

Dilute solution properties of carboxymethylchitins in high ionic-strength solvent

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<10⁷×D<2.9 cm² s⁻¹; the sedimentation coefficient, 2.4<s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130<k_s<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 M^0.94; D=1.87×10⁻⁴ M^−0.60; s=4.10×10⁻¹⁵ M^0.39. 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 k_s values for these substances is discussed.     

Effects of oxygen concentration on the electrical properties of ZnO films

In this paper, electrical characteristics by various oxygen content in ZnO films were studied. To control the oxygen content of ZnO films, post-thermal annealing was performed in N₂ and air ambient, led to improve crystallinity and optical properties of ZnO films. The oxygen concentration was measured by Auger electron spectroscopy. The ZnO films having the deficiency of oxygen showed the electron concentrations between 10²¹ and mid 6 × 10¹⁷ cm⁻³ and resistivity at 10⁻³–10⁻¹ Ω cm. On the other hand, when the oxygen concentration of the ZnO films was up to the stoichiometry with Zn, the ZnO films showed low electron concentration at −10¹⁷ cm⁻³ and resistivity at 10 Ω cm.     

Catalyzing a cycloaddition with molecularly imprinted polymers obtained via immobilized templates

Polymeric catalysts to be applied in the Diels–Alder cycloaddition of hexachlorocyclopentadiene and maleic acid have been prepared via molecular imprinting with template molecules immobilized on silica particles. These enzyme mimicking polymers exhibit specific catalytic effects compared to non-imprinted control polymers or polymer-free solutions. It could be demonstrated that the activity of the molecularly imprinted material rises when increasing the temperature. By this means, the reduction of the activation energy (as expected for catalysts) from 63 to 55 kJ mol⁻¹ could be observed. Furthermore, the reaction was characterized based on the Michaelis–Menten model. For the diene compound a Michaelis constant of K_M=5.8 mmol l⁻¹ and an effective reaction rate of r_max,eff=0.4 μmol l⁻¹ s⁻¹, leading to a reaction rate constant k_eff=1.1×10⁻³ s⁻¹, were determined.     

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.     

Longitudinal volume viscosity of 1,2 syndiotactic polybutadiene

The volume flow of 1,2 syndiotactic polybutadiene (1,2 s-PB) ( , T_m = 373 K and T_g = 262 K) has been measured. The elastic modulus of the longitudinal wave, the longitudinal volume viscosity, the initial longitudinal volume viscosity and retardation times are described at compression rates of 1.0 × 10⁻⁵–200.0 × 10⁻⁵ s⁻¹, and at temperatures of 403–423 K and pressures up to 150 MPa. Longitudinal volume viscosity decreases with increasing compression rate, and with decreasing volume deformation, the behaviour being in all cases typical non-equilibrium behaviour. Longitudinal volume viscosity increases with increasing temperature, the volume flow activation energy being 56.3 kJ mol⁻¹.     

Preparation and characteristics of natural rubber/poly(ethylene oxide) salt hybrid mixtures as novel polymer electrolytes

Poly(ethylene oxide) (PEO) of molecular weight 1000 (PEO₁₀₀₀) containing lithium benzenesulfonate (LiBs) (PEO₁₀₀₀/LiBs), PEO derivatives having benzenesulfonate groups on both chain ends (PEO₁₀₀₀–(BSLi)₂), or 1-ethyl-2,3-dimethylimidazolium bromide (ImB), were each blended with natural rubber (NR). The ionic conductivity was measured from AC impedance values. The ionic conductivity of the mixture of NR and PEO₁₀₀₀/LiBs (40 wt%) was about 10⁻⁶ S cm⁻¹ at 50°C; this mixture retained rubbery physical characteristics. At NR content of 10 wt%, the ionic conductivity of the mixture (NR/PEO₁₀₀₀/LiBs) was 2.7×10⁻⁵ Scm⁻¹ at 50°C, approximately 10 times higher than that of the bulk PEO/LiBs mixture. For mixtures of NR and PEO₁₀₀₀–(BSLi)₂, no improvement in ionic conductivity by mixing was found. The ionic conductivity of the mixture of NR and ImB was about 10 times higher than for the bulk of PEO₁₀₀₀–(BSLi)₂ at a NR content of 10 wt%. We propose that the ionic conductivity of the mixture increases when an ion conducting matrix containing simple salt is added. On the other hand, the DSC curve for NR/PEO derivatives showed two T_gs based on the separate components, suggesting phase separation of the PEO derivative in the NR phase.     

Selective permeation and separation of steam from water–methanol–hydrogen gas mixtures through mordenite membrane

Separation properties of a mordenite membrane for water–methanol–hydrogen mixtures were studied in the temperature range from 423 to 523 K under pressurized conditions. The mordenite membrane was prepared on the outer surface of a porous alumina tubular support by a secondary-growth method. It was found that water was selectively permeated through the membrane. The separation factor of water/hydrogen and water/methanol were 49–156 and 73–101, respectively. Even when only hydrogen was fed at 0.5 MPa, its permeance was as low as 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹ up to 493 K, possibly suggesting that water pre-adsorbed in the micropores of mordenite hindered the permeation of hydrogen. The hydrogen permeance dramatically increased to 6.5 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 503 K and reached to 1.4 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 523 K because of the formation of cracks in the membrane. However, the membrane was thermally stabilized in the presence of steam and/or methanol.