Characterization of ethylene homo- and copolymers

Summary For the estimation of molecular mass distribution and average molecular masses of (norbornene ethylene) copolymers a size exclusion chromatography method is described. The validity of the universal calibration function of Benoit et al. based on polystyrene molecular mass standards was confirmed by comparing with the number average molecular masses obtained by osmometry. The constants of the Mark-Houwink equation are a = 0.535, K = 1.00·10^–1 (Xylene, 90 °C) and a=0.589, K=4.93·10^–2 (diethylbenzene, 120°C,[] in cm³g^–1).Part IV: Plaste u. Kautschuk 32, 12, 444 (1985)     

Etude des propriétés électriques et électrochimiques d'un réseau de polyuréthanne à base de polyéther chargé de perchlorate de lithium

Résumé Nous avons étudié les propriétés électriques et électrochimiques de réseau de polyuréthanne à base de copolymère triblocs poly(oxyde d'éthylène)/poly(oxyde de propylène) contenant du perchlorate de lithium. La conductivité électrique de ce réseau est supérieure à 10^{–5 –1} cm^–1 à 20°C. Le domaine de stabilité électrochimique de cet électrolyte polymère est de 4V. Des accumulateurs tout solide RuO₂/polyuréthanne chargé de LiClO₄/Li ont été réalisés et testés à 60°C. Les rendements expérimentaux sont respectivement de 96.6% à la première décharge, 90% à la première charge et 83% à la deuxième décharge. Ces valeurs sont en accord avec les rendements théoriques correspondant à ces conditions de cyclages.

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The electrical and electrochemical properties of triblock copolymer (poly(ethylene oxide)-b-poly(propylene oxide))-based polyurethane were studied. The electrical conductivity of this material was up to 10^{–5 –1} cm^–1 at 20°C. The redox stability domain of the electrolyte was about 4V. Solid secondary batteries with RuO₂/polyurethane containing LiClO₄/Li have been prepared and tested at 60°C. The coulombic efficiencies were successively 96.6% at the first discharge, 90% at the first charge and 83% at the second discharge. These values agree with theoretical data.

     

First In Situ Raman Study of Vanadium Oxide Based SO2 Oxidation Supported Molten Salt Catalysts

In situ Raman spectroscopy at temperatures up to 500°C is used for the first time to identify vanadium species on the surface of a vanadium oxide based supported molten salt catalyst during SO₂ oxidation. Vanadia/silica catalysts impregnated with Cs₂SO₄ were exposed to various SO₂/O₂/SO₃ atmospheres and in situ Raman spectra were obtained and compared to Raman spectra of unsupported model V₂O₅–Cs₂SO₄ and V₂O₅–Cs₂S₂O₇ molten salts. The data indicate that (1) the V^V complex V^VO₂(SO₄)₂ ^3– (with characteristic bands at 1034 cm^–1 due to (V=O) and 940 cm^–1 due to sulfate) and Cs₂SO₄ dominate the catalyst surface after calcination; (2) upon admission of SO₃/O₂ the excess sulfate is converted to pyrosulfate and the V^V dimer (V^VO)₂O(SO₄)₄ ^4– (with characteristic bands at 1046 cm^–1 due to (V=O), 830 cm^–1 due to bridging S–O along S–O–V and 770 cm^–1 due to V–O–V) is formed and (3) admission of SO₂ causes reduction of V^V to V^IV (with the (V=O) shifting to 1024 cm^–1) and to V^IV precipitation below 420°C.     

Preparation and electrochemical characteristics of a new Li-Mn-V-O system formed from heat-treatment of a MnO2, NH4VO3 and LiNO3 mixture

New quarternary oxides (Li₂O) _x · MnO₂ · yV₂O₅ (x = 0.125 0.25, y = 0.125 0.25), formed by heating mixtures of MnO₂, NH₄VO₃ and LiNO₃ at various Li/Mn and V/Mn atomic ratios and at different temperatures (300 400 °C in air, have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy (ESCA) and infrared spectroscopy. The quarternary oxide with x = 0.25 and y = 0.25 showed a discharge capacity of 220 A h (kg oxide)^–1 and an energy density of ca. 600 W h (kg oxide)^–1 at a current density of 0.20 mA cm^–1 in 1 m LiClO₄-propylene carbonate at 25 °C. When charge-discharge cycling with the (Li₂O) · MnO₂ · 0.25V₂O₅ electrode was performed at a constant capacity of 30 A h (kg oxide)^–1 and at a constant current density of 0.10 0.20 mA cm^–2, the electrode sustained over 100 cycles at a high mean discharge potential of ca. 3 V vs Li/Li⁺.This paper was originally presented at the 183rd meeting of the Electrochemical Society (Honolulu, Hawaii, 1993).     

Sintering high purity,magnesia with additions of hafnium dioxide

Conclusions The introduction of hafnium dioxide into high-purity active magnesia accelerates its sintering and with 0.1–0.3 mol % HfO₂ a ceramic with an apparent density of 99–100% of the theoretical (3.56–3.63 g/cm³) can be obtained after firing at 1300–1400°C. The optimum quantity of HfO₂ additive is close to 0.25 mol %.The calcination temperature of the mixture of magnesium hydroxide and additive obtained by precipitation from a solution of MgCl₂ and Hf(SO₄)₂ with ammonia, and the fabrication pressure do not greatly affect the final density of the ceramics.Sintering of spectrally pure MgO containing 0.25 mol. % HfO₂ begins at 950°C, then the apparent density grows rapidly with rise in firing temperature, approaching 3.40 g/cm² at 1100°C. Selective recrystallization at these low temperatures is slow and sintering is not accompanied by a substantial grain growth. At 1300°C and higher firing temperatures densification of the ceramics approaches the limit in several minutes.The mechanism of the transfer of substance during the sintering of these specimens is volume self-diffusion from the grain boundaries to the surfaces of the bridges formed between them. The energy of activation of this process [3.9 eV (6.2 × 10^–16 J) in the 1000–1300°C range] and the coefficient of self-diffusion for MgO calculated in accordance with this (6 × 10^–14 cm²/sec at 1100°C) correspond to existing data on the diffusion of magnesium into MgO.With the incorporation of 0.25 mol. % HfO₂ in less pure magnesia obtained from chemically pure MgCl₂, sintering is little different from the sintering of spectrally pure MgO, but the limiting apparent density of the ceramics in this case is somewhat lower-of the order of 99% of the theoretical.     

Monitoring of molybdenum H-ZSM5 catalyst preparation by in situ ultraviolet Raman spectroscopy

In situ ultraviolet Raman spectroscopy was used to follow the preparation of Mo/H-ZSM5 catalysts by thermal treatment of a physical mixture of MoO₃ and H-ZSM5. The Raman spectra recorded from 300 to 1800 cm^–1 during the thermal treatment showed that MoO₃ spread over the zeolite support to form dispersed molybdenum oxide species. Curve-fitting analysis of the overall spectral profile for the samples after treatment at 600°C in O₂ showed the presence of three spectral components at 962, 868 and 815 cm^–1. The band at 815 cm^–1 was assigned to the zeolite support. The most intense band at 962 cm^–1 could be attributed to terminal Mo=O groups of isolated tetrahedrally coordinated monomers and the weaker band at 868 cm^–1 to bridging Mo–O–Mo groups of dimeric species. These last two assignments are not definitive and may be due to other unique structures of oxides of molybdenum on the zeolite framework.     

Long service life IrO2/Ta2O5 electrodes for electroflotation

Ti/IrO₂-Ta₂O₅ electrodes prepared by thermal decomposition of the respective chlorides were successfully employed as oxygen evolving electrodes for electroflotation of waste water contaminated with dispersed peptides and oils. Service lives and rates of dissolution of the Ti/IrO₂-Ta₂O₅ electrodes were measured by means of accelerated life tests, e.g. electrolysis in 0.5M H₂SO₄ at 25°C and j = 2 A cm^–2. The steady-state rate of dissolution of the IrO₂ active layer was reached after 600–700 h (0.095 g Ir h^–1 cm^–2) which is 200–300 times lower than the initial dissolution rate. The steady-state rate of dissolution of iridium was found to be proportional to the applied current density (in the range 0.5–3 A cm^–2 ). The oxygen overpotential increased slightly during electrolysis (59–82 mV for j = 0.1 A cm^–2 ) and the increase was higher for the lower content of iridium in an active surface layer. The service life of Ti/IrO₂ (65 mol%)-Ta₂O₅ (35 mol%) in industrial conditions of electrochemical devices was estimated to be greater than five years.List of symbols a constant in Tafel equation (mV) - b slope in Tafel equation (mV dec^–1) - E potential (V) - f mole fraction of iridium in the active layer - j current density (A cm^–2) - l number of layers - m _Ir content of iridium in the active layer (mg cm^–2) - r dissolution rate of the IrO₂ active layer (g Ir h^–1 cm^–2) - T _c calcination temperature (°C) - _{O 2} oxygen overpotential (mV) - _{O 2} difference in oxygen overpotential (mV) - _A service life in accelerated service life tests (h) - _S service life in accelerated service life tests related to 0.1 mg Ir cm^–2 (h) - _p polarization time in accelerated service life tests (h)     

Effects of Water and Ion-Exchanged Counterion on the FTIR Spectra of ZSM-5. II. (Cu+–CO)-ZSM-5: Coordination of Cu+–CO Complex by H2O and Changes in Skeletal T–O–T Vibrations

The 2157 cm^–1 (strong) and 2108 cm^–1 (very weak) (CO) IR bands due to Cu⁺–CO in ZSM-5 zeolite with ¹²C and ¹³C isotopes, respectively, are reversibly red-shifted by subsequent adsorption of H₂O at 293 K. On the contrary, the locally perturbed internal (T–O–T) asymmetric stretching framework vibration [ _as ^int (TOT)(Cu⁺–CO)=965 cm^–1] is reversibly blue-shifted. The courses of the band shifts revealed notable features. Charge transfers from water to Cu⁺ ions, changes in coordination spheres of Cu⁺(CO)(H₂O) _n aqua complexes and secondary (solvent-like) effects were considered to explain the results.     

Infrared spectroscopy of carbon monoxide adsorbed on Pt/L zeolite

A series of 0.6 wt% Pt/MBaL zeolites, where M is Li, Na, K, Rb or Cs, were prepared and characterized by transmission electron microscopy, chemisorption, and infrared spectroscopy of adsorbed carbon monoxide. Greater than 90% of the exposed platinum in the samples is associated with small clusters, less than 7 Å across, inside the zeolite channels. The remaining fraction of exposed platinum is on 100–500 Å crystallites outside the channels. Adsorption of carbon monoxide on the platinum at 25 °C produces a broad infrared band whose maximum shifts from 2065 to 2025 cm^–1 as the alkali cations in the zeolite are changed from Li to Cs. This shift is indicative of electron transfer between the cations and the platinum clusters. Heating the Pt/L catalysts to 225 °C produces new infrared bands at 2020–2015, 1975, and 1935–1920 cm^–1. The appearance of these low-frequency bands strongly suggests that the CO-covered platinum clusters change their structure during heating. We propose that the new structure is one in which the carbon monoxide molecules insert into spaces between the framework atoms of the L zeolite.     

Rheological and technological properties of titanium dioxide slips and the properties of the castings

Conclusions An investigation of the rheological and technological properties of titanium dioxide slips and slip castings demonstrated the presence of two castability regions. The properties of the slip and castings are optimal in the alkaline castability region (pH 8).A study of the influence of the firing temperature of the titanium dioxide starting material on the properties of the slip and castings showed that the properties are optimal when the TiO₂ had been fired at 1550° C.An analysis of the sintering of titanium dioxide slip castings showed that the properties of the sintered castings are optimal when the castings were produced from slip with pH 8 because in this case the density of the castings is at maximum.The strength of TiO₂ castings in the sintering process depends on their porosity and that of the sintered castings on the size of the crystals.Titanium dioxide fired at 1550°C yielded castings with open porosity 1.8–2.0%, apparent density 3.90–3.92 g/cm³, _b 1020–1050 kgf/cm², acid resistance 97.5%, specific inductive capacitance 90–100, and tangent of the dielectric loss angle at 20°C and 1 MHz 8·10^–4–9·10^–4 Translated from Ogneupory, No. 3, pp. 28–33, March, 1978.     

Electrode heat balances of electrochemical cells: application to NaCl electrolysis

This paper deals with a method of estimating single electrode heat balances during the electrolysis of molten NaCl-ZnCl₂ in a cell using a-alumina diaphragm. By measuring the thermoelectric power of the thermogalvanic cells: (T) Na/-alumina/NaCl-ZnCl₂/-alumina/Na(T+dT) and (T) C,Cl₂/NaCl-ZnCl₂/Cl₂,C(T+dT) the single electrode Peltier heat for sodium deposition and for chlorine evolution at 370° C were estimated to be –0.026±0.001 JC^–1 and+0.614±0.096 J C^–1, respectively.     

Pulse electrodeposition of titanium on carbon steel in the LiF–NaF–KF eutectic melt

Electrodeposition of titanium was carried out in the K₃TiF₆–LiF–NaF–KF melt using both direct (DC) and unipolar pulse current (PC) techniques. Dense and smooth titanium coatings were obtained by PC plating at 750 °C whereas DC plating led to rough and dendritic deposits. The best results were obtained using a 100C cm^–2 pulse charge and a cathodic current density of 50 and 75mA cm^–2. The cathodic current efficiency was in the range 60–65%. The titanium deposits obtained under such conditions behaved similarly to CP-titanium in NaCl and HNO₃ solutions at room temperature.     

Electrochemical machining of refractory materials

The feasibility of the electrochemical machining (ECM) of pure TiC, ZrC, TiB₂ and ZrB₂ has been established. In addition, the ECM behaviour of a cemented TiC/10% Ni composite has been investigated and compared to that of its components, TiC and nickel. ECM was carried out in 2M KNO₃ and in 3 M NaCl at applied voltages of 10–31 V and current densities of 15–115 A cm^–2. Post-ECM surface studies on the TiC/Ni composite showed preferential dissolution of the TiC phase during machining.Nomenclature E ₀ thermodynamic equilibrium potential (V) - F Faraday's constant (96 500 Coul mol^–1) - toolpiece feed rate (cm s^–1 or mm min^–1) - I current (A) - i current density (A cm^–2) - k electrolyte conductivity (^–1 cm^–1) - l interelectrode gap (mm) - mass removal rate (g s^–1 or g min^–1) - M formula weight (g mol^–1) - Q electrolyte flow rate (l min^–1) - t electrolyte temperature (°C) - V applied voltage (V) - V _IR ohmic drop through electrolyte (V) - z apparent valence of dissolution (eq mol^–1) - _i overvoltages (V) - density of refractory materials (g cm^–3)     

Acid-base properties and the directions of oxidative transformation of methane over nickel-based catalysts

The reactions of dry (CO₂) reforming and partial oxidation of methane have been investigated in a membrane reactor. The membrane is composed of a dense thin silica (SiO₂) film supported on porous Vycor tubes and was synthesized by chemical vapor deposition. The hydrogen permeance of the membrane was 0.2–0.3 cm³/(cm² min atm) at 600°C combined with a H₂/N₂ selectivity of 200–300. Significant increases in methane conversion were attained in both reactions at 500–750°C, albeit at very low space velocities. The membrane permeance declined by 50% after exposure to feeds containing H₂O, but otherwise exhibited excellent stability under reaction conditions.     

Computer simulation of high-discharge-rate battery systems

Simulations were carried out for a proposed two-dimensional high-discharge-rate cell under load with an interelectrode gap of the order of 100 m. A finite difference program was written to solve the set of coupled, partial differential equations governing the behaviour of this system. Cell dimensions, cell loads, and kinetic parameters were varied to study the effects on voltage, current and specific energy. Trends in cell performance are noted, and suggestions are made for development of cells to meet specific design criteria. Modelling difficulties are discussed and suggestions are made for improvement.Nomenclature A surface area of unit cell (cm²) - A _k conductivity parameter (cm^{2 –1} mol^–1) - b Tafel slope (V) - c concentration (mol cm^–3) - c ₀ concentration of bulk electrolyte (mol cm^–3) - D diffusivity (cm² s^–1) - D _h lumped diffusion parameter (J s cm^–2 mol^–1) - D _s lumped diffusion coefficient (A cm² mol^–1) - E rest potential of electrode (V) - F Faraday constant (96 500 C mol^–1) - i current density (A cm^–2) - I total current for unit cell (A) - i ₀ exchange current density (A cm^–2) - N flux of charged species (mol cm² s^–1) - R gas constant (8.314 J mol^–1 K^–1) - R _ext resistance external to cell () - t time (s) - T temperature (K) - t ₀ transference number - u mobility (cm² mol J^–1 s^–1) - V volume of an element in the cell (cm³) - V _ext voltage external to cell (V) - z charge on an ion - _c concentration overpotential (V) - _s surface overpotential (V) - conductivity (^–1 cm^–1) - stoichiometric coefficient - electric potential in solution (V)     

Kinetic study of the electroreduction of nitrobenzene

A reaction kinetic study has been performed for the reduction of nitrobenzene on a Cu electrode in 1m H₂SO₄ in a 5050 (Vol%) mixture of water and 1-propanol at 27°C. The study was carried out on a rotating disc electrode for which the current-potential data were supplemented with product-concentration measurements. The resulting rate expressions represent a reaction mechanism for the reduction of nitrobenzene to aniline and p-aminophenol through the common intermediate phenylhydroxylamine, and incorporate the dependence on reactant concentration and potential for the three predominant reaction pathways. The three major reaction steps were studied independently by performing experiments in which phenylhydroxylamine only was used as the reactant to complement those experiments in which nitrobenzene was used. The kinetic expressions found from measuring the rates of the individual reactions were consistent with the results of experiments in which all the reactions were carried out simultaneously. The expressions obtained are suitable for use in reactor design, modelling and control, and of equal importance, the methodology outlined to extract kinetic parameters from the current and concentration data serves as a model for application to other reaction systems.Nomenclature A electrode area (cm²) - D diffusion coefficient (cm² s^–1) - E electrode potential (V) - F Faraday's constant, 96485 (C mol^–1) - i _H current density due to the hydrogen evolution reaction (A cm^–2) - I current (A) - I _k kinetic current (A) - I _L limiting current (A) - k ₁ rate constant for the reduction of nitrobenzene to phenylhydroxylamine (cm s^–1) - k ₂ rate constant for the reduction of phenylhydroxylamine to aniline (cm s^–1) - k ₃ rate constant for the rearrangement of phenylhydroxylamine to p-aminophenol (s^–1) - n number of electrons per equivalent - T temperature (K) - X fractional conversion of phenylhydroxylamine to p-aminophenol Greek _i diffusion layer thickness of speciesi (cm) - conductivity (cm^–1 ohm^–1) - viscosity (g cm^–1 s^–1) - kinematic viscosity (cm² s^–1) - density (g cm^–3) - rotation speed of electrode (s^–1)     

Sintering and recrystallization of high-purity magnesia-alumina spinel during hot pressing

Conclusions A study was made of the densification and recrystallization of magnesia — alumina spinel of high dispersion during hot pressing in the temperature range 1200–1600°C, a pressure of 60–300 cm², and a holding time of 10–30 min.The relative density of 92–98% theoretical was achieved at 1300–1400°C, a pressure of 300 kg/cm², and a soaking of 10 min. The spinel of theoretical density with a finely crystalline homogeneous structure was obtained by hot pressing at 1450–1600°C.Intensive recrystallization of the spinels during hot pressing occurs in the temperature range ensuring maximum rate of densification (1450–1600°C).The rate of recrystallization of the spinel grains during hot pressing at 1400°C and a pressure of 300 kg/cm² and soakings of 10 and 30 min, has the order of 10^–6 cm/sec and the maximum for the grains of diameter from 2 to 6.Report read at a symposium on pure oxide sintering, Khar'kov, 1968.Deceased.Translated from Ogneupory, No.6, pp. 32–36, June, 1970.     

Characterization of reticulate,three — dimensional electrodes

A study has been made of the mass transfer characteristics of a reticulate, three-dimensional electrode, obtained by metallization of polyurethane foams. The assumed chemical model has been copper deposition from diluted solutions in 1 M H₂SO₄. Preliminary investigations of the performances of this electrode, assembled in a filter-press type cell, have given interesting results: with 0.01 M CuSO₄ solutions the current density is 85 mA cm^–2 when the flow rate is 14 cm s^–1.List of symbols a area for unit volume (cm^–1) - C copper concentration (mM cm^–3) - c _L copper concentration in cathode effluent (mM cm^–3) - c ₀ copper concentration of feed (mM cm^–3) - C ₀ ⁰ initial copper concentration of feed (mM cm^–3) - d pore diameter (cm) - D diffusion coefficient (cm²s^–1) - F Faraday's constant (mcoul me _q ^–1 ) - i electrolytic current density on diaphragm area basis (mA cm^–2) - I overall current (mA) - K _m mass transfer coefficient (cm s^–1) - n number of electrons transferred in electrode reaction (me_q mM^–1) - P ] volumetric flux (cm³s^–1) - Q total volume of solution (cm³) - (Re) Reynold's number - S section of electrode normal to the flux (cm²) - (Sc) Schmidt's number - (Sh) Sherwood's number - t time - T temperature - u linear velocity of solution (cm s^–1) - V volume of electrode (cm³) - divergence operator - void fraction - u/K _m a(cm) - electrical specific conductivity of electrolyte (^–1 cm^–1) - _S potential of the solution (mV) - density of the solution (g cm^–3) - v kinematic viscosity (cm²s^–1)     

Characterization of electroless Ni-Mo-P/SnO2/Ti electrodes for oxygen evolution in alkaline solution

Ni-Mo-P alloy electrodes, prepared by electroless plating, were characterized for application to oxygen evolution. The rate constants were estimated for oxygen evolution on electrodes prepared at various Mo-complex concentrations. The surface area and the crystallinity increase with increasing Mo content. The electrochemical characteristics of the electrodes were identified in relation to morphology and the structure of the surface. The results show that the electroless Ni-Mo-P electrode prepared at a Mo-complex concentration of 0.011 m provided the best electrocatalytic activity for oxygen evolution.List of symbols b Tafel slope (mV dec^–1) - b F/RT (mV^–1) - F Faraday constant (96 500 C mol^–1) - j current density (mA cm^–2) - k₁ reaction rate of Reaction 1, (mol^–1 cm³ s^–) - k ₁ = k₁C _OH ^–(mol cm^–2 s^–1) - k ₁₀ rate constant of Reaction 1 at = 0 (mol cm^–2 s^–1) - k_c1 rate constant of Reaction 2 (mol^–1 cm³ s^–1) - k _c1 = k_c1C _{H 2O} (mol cm^–2 s^–1) - k_c2 rate constant of chemical Reaction 3 (mol^–1 cm² s^–1) - k _c2 = k_c2² (mol cm^–2 s^–1) - k_c3 rate constant of Reaction 4 (mol^–1 cm² s^–1) - Q _a anodic capacity (mC) - Q _c cathodic capacity (mC) - R gas constant (8.314 J mol^–1 K^–1) - R _ct charge transfer resistance ( cm²) - R _ads charge transfer resistance due to adsorption effect ( cm²) - C _d1 double layer capacity (mF cm^–2) - _{C ads} double layer capacity due to adsorption effect (mF cm^–2) - T temperature (K) Greek symbols anodic transfer coefficient - _{O 2} oxygen overpotential (mV) - saturation concentration of surface oxide on nickel (mol cm^–2)     

Double layer capacity of graphite in cryolite-alumina melts and surface area changes by electrolyte consumption of graphite and baked carbon

The double layer (d.l.) capacity of pyrolytic graphite in cryolite-alumina melts at 1010°C was found to exhibit a minimum of 20F cm^–2 at 0·9 V positive to the aluminium electrode. The d.l. capacity attained a plateau of 60F cm^–2 at 1·1–1·4 V, while it rose steeply at potentials below 0·7 V. During electrolytic consumption involving CO₂ evolution the d.l. capacity of pyrolytic graphite remained unaffected, while that of baked carbon was changed, reflecting changes in surface area. At low current densities (cds) the surface area increased substantially and the surface was noticeably roughened, while the opposite behaviour was observed at above 2.5 A cm^–2.