Measurements on the temperature dependence of the cationic polymerization of styrene in CH2Cl2 with CF3SO3H as catalyst

Summary The cationic polymerization of styrene in CH₂Cl₂ with CF₃SO₃H as catalyst and at low monomer concentrations shows, at –15°C, –45°C and –60°C, the same formal dependence on monomer concentration. The dependence on the catalyst concentration is approximately but not exactly of a third order.The unimodal molecular weight distributions at [M]_o<0.2 mol·1^–1 become broader with decreasing polymerization temperature and increasing monomer concentration and change to bimodal or trimodal distributions at [m]_o>0.2 mol·1^–1. The addition of (Bu)₄N⁺CF₃SO₃ ^– to the polymerization system shows that the two higher molecular peaks are produced by free ions. The activation energy of the total reaction is found to be 3.5 kcal·mol^–1.I thank Prof. G. V. Schulz for interesting discussions and the possibility to work in his group, G. Greschner for a computer program and the Alexander von Humboldt Stiftung for their financial help.     

On the kinetic mechanism of the reaction of NH2 with O2 in O-, H-, and N-containing flames. 1. Kinetic parameters of the NH2+O2=NHO+OH reaction

The reaction pathways for NH₂+O₂Products are considered on the basis of experimental data on the ignition of an NH₃/O₂/Ar mixture in reflected shock waves (p=1–10 atm, T=900–2160 K) and on the NH₃/O₂/Ar flame structure (p=35 torr, T=1050–2600 K) using a multistage kinetic mechanism. The rate constants of the NH₂+O₂=HNO+OH reaction, obtained from a comparison of experimental and calculated data, are reported (k=3·10¹¹ exp (–15,000/RT) cm³/(mole·s) at T1500–2160 L and k=3·10⁹ cm³/(mole·s) at T900–1400 K).Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 1, pp. 60–65, January–February, 1994.     

Electrochemical behaviour of manganese in the aluminium electrorefining bath

The study of the mechanism of the electrode reaction Mn(II)/Mn in the aluminium electrorefining bath free of aluminium fluoride (1·48 NaF-1·05 BaCl₂) has been carried out by chronopotentiometry with an inert graphite electrode, a manganese electrode and a platinum electrode; this study was supplemented by utilizing anodic chronopotentiometry with current reversal from a stationary state. The tests carried out at 800° C show that the exchange mechanism of Mn(II)/Mn is reversible, involves the exchange of two electrons and that the diffusion coefficient D_Mn(II)=(1·9±0·5)×10^–5 cm² s^–1.     

Electrochemical characteristics and structural changes of molybdenum trioxide hydrates as cathode materials for lithium batteries

Several characteristics of MoO₃·2H₂O and MoO₃·H₂O, such as thermal behaviour and conductivity and the electrochemical behaviour and structural changes associated with discharge and charge have been investigated. The suitability of these substances as new cathode materials for non-aqueous lithium batteries has been assessed. MoO₃·H₂O, having only one coordinated water molecule, showed a discharge capacity of about 400 Ah kg^–1 of acid weight and a discharge potential around 2.5 V vs Li/Li⁺. This capacity was much higher than the 280 Ah kg^–1 of anhydrous MoO₃.MoO₃·H₂O showed good charge-discharge cyclic behaviour at a capacity below l e^–/Mo while keeping the original layered lattice on cycling. In addition, the crystal system of MoO₃·H₂O was found to be changed from a monoclinic system to orthorhombic with lattice parameters ofa=0.5285 nm,b=1.0824 nm,c=0.5237 nm on discharge to 0.5 e^–/Mo.This paper was originally presented at the Fall 1987 Meeting of the Electrochemical Society, Inc. held at Honolulu, Hawaii (Proceedings of the Symposium on Primary and Secondary Ambient Temperature Batteries, PV88-6, p. 484–493 (1987).     

Electrodeposition of catalytically active Co-Ni-Tl alloy powders from dilute sulphate baths

Cobalt-nickel-thallium alloy powders were electrodeposited from dilute metal sulphate baths of composition: 0.007–0.0245 mol l^–1 CoSO₄·7H₂O, 0.0245–0.007 mol l^–1 NiSO₄·6H₂O, 0.001 mol l^–1 TlCl, 0.5 mol l^–1 (NH₄)₂SO₄, 0.07 mol l^–1 Na₂SO₄·10H₂O and 0.4 mol l^–1 H₃BO₃. The cathodic polarization curves were traced during electrodeposition and utilized in the discussion of a reaction mechanism for the electrolytic powder deposition. The alloy composition and the cathodic current efficiency were influenced to a great extent by the bath composition (I) and slightly by the deposition current density (II). Irrespective of variables (I) and (II), the electrodeposition of the alloy belonged to the anomalous type. The surface morphology and the catalytic activity, towards the decomposition of 0.4% H₂O₂ solution, of the as-deposited alloy powders were affected predominantly by the percentage of cobalt in the alloy. X-ray diffraction studies showed that the alloys consisted mainly of the face-centred cubic nickel phase either alone or with minor proportions of face-centred cubic cobalt phase and hexagonal close-packed -cobalt phase. The occurrence of the latter phases was observed only in the alloys with a higher cobalt percentage than nickel.     

Investigations in platinum metal group electrochemistry: I some iridium (IV) — iridium (III) systems

The Norbide, boron carbide, electrode has been shown to be exceptionally good in terms of its chemical inertness, rapid response and high hydrogen overvoltage. It has been applied especially in potentiometric and polarographic studies of the Ir(IV)-Ir(III) system in various media. By its means, supported by evidence from use of other cathodes, certain previous work has been confirmed and standard or formal redox potentials of the following systems have been determined: Ir(IV)-Ir(III)-ClO ₄ ^– (M HClO₄, 1·27 V; Ir (IV)-Ir(III)-SO ₄ ^2– (0·18M H₂SO₄), 1·08 V; Ir(IV)-Ir(III)-PO ₄ ^3– (0·3M H₃PO₄), provisionally 0·99 V; IrCl ₆ ^2– -IrCl ₆ ^3– (0·1M NaClO₄ or NaCl), 0·899 V; IrBr ₆ ^2– -IrBr ₆ ^2– (0·1M NaClO₄or NaBr), 0·838 V. The potentials fall in the expected sequence. The possibility of analytical application of the Norbide and rotating platinum electrode has also been examined.     

Physicochemical properties of the deposits from the circulating water at the Zaporozhe Refractory Plant

Conclusions The deposits in the study are multicomponent polydispersed suspensions characterized by a solid-phase concentration of 3.79–17.7% density 1–1.09 g/cm³, and a pH of 8.2–11.9. When the deposits are left to stand for 10 days they become compacted up to 40–70% of the original volume. The size of the aggregates of the dispersed phase change from 5 to 50 m with a predominant particle size of 5 to 20 m (64–79%). The electrokinetic potential of the phase is from –1.5 to –12.8 mV for various batches of deposits.The dispersion medium of the deposits is characterized by a pH of 8–11.5; a density of 1 g/cm³; viscosity of 0.001 Pa·sec; an electrical resistivity of 7.8·10^–4 to 44·10^–4–1·cm^–1; and a concentration of dry residue up to 1490 mg/liter.The dispersed phase of the deposits has a density of 2.16–2.52 g/cm³ and consists mainly of oxides of silicon, aluminum, calcium and a very small amount of oxides of titanium, iron, magnesium, and manganese.The addition of polyacrylamide to the original deposits in amounts of 25 to 400 mg/liter leads to a reduction in the electrokinetic potential of the particles, to their aggregation, and to spatial structure-formation.With the addition of polyacrylamide in amounts of 100–250 mg/liter to the deposits, the size of the aggregates decreases 15–30-fold by comparison with the untreated. The addition of PAA does not significantly affect the chemical composition of the dispersed phase.The data in this paper have been used to plan the cleansing equipment at the Zaporozhe Refractory Plant.Translated from Ogneupory, No. 5, pp. 30–33, May, 1984.     

Biotransformation of 2-Benzoxazolinone to 2-Amino-(3<Emphasis Type="Italic">H</Emphasis>)-Phenoxazin-3-one and 2-Acetylamino-(3<Emphasis Type="Italic">H</Emphasis>)-Phenoxazin-3-one in Soil

An alternative to the use of synthetic pesticides is to exploit the natural defense chemicals produced by cereals. An important class of allelochemicals is cyclic hydroxamic acids and related benzoxazolinones. A prolonged degradation experiment of the allelochemical compound from rye 2-benzoxazolinone (BOA) was carried out for up to 90 d at 15°C at three different concentration levels, 3, 3000, and 30,000 nmol BOA· g soil^–1, respectively, in a sandy loam soil. Two main degradation products, 2-amino-(3H)-phenoxazin-3-one (APO) and 2-acetylamino-(3H)-phenoxazin-3-one (AAPO), were identified and quantified by LC-ESI-MS-MS. The half-life of BOA increased with higher levels of BOA added to the soil. Half-lives of BOA, APO, and AAPO were determined by fitting a single first-order model to the degradation data. Half-life of BOA was determined to be 0.6 d in the 3 nmol BOA g soil^–1 treatment. Half-lives of BOA, APO, and AAPO were 3.1, 2.7, and 2.1 d, respectively, in the 3000 nmol BOA· g soil^–1 treatment. In the 30,000 nmol BOA· g soil^–1 treatment, the half-lives were 31 d for BOA and 45 d for APO. The microbial community structure was not affected by addition of BOA to the soil as investigated by analysis of signature fatty acids. The results suggest that the exploitability of BOA for crop protection is dependent on the existing concentration of BOA in the soil and the timing of incorporation of hydroxamic acid synthesizing crops into the soil.     

Hydrothermal Synthesis of Novel Smectite-Like Mesoporous Materials

Hydrothermal reaction of slurries made from Si-Mg hydrous oxide and water yielded trioctahedral smectite-like mesoporous materials (SMMs). The OH anion had a marked effect on the properties of SMMs under hydrothermal condition whereas Na cation did not influence SMMs properties. With the increase in synthesis pH at 200°C, pore volume, specific surface area and average pore diameter decreased whereas methylene blue adsorption increased in the pH range of 8.5 to 11.4. Therefore, the SMMs having different layer charges could be synthesized. Both micropore and macropore formation rates decreased with increasing synthesis temperature in the range of 125–200°C and the formation of latter increased over 200°C. As a result, the SMMs synthesized at 200°C from slurries of pH 9.0–9.3 revealed the maximum mesopore formation rate: 0.98 and gave a narrow pore size distribution curve of 3–5 nm. The SMMs were characterized by specific surface areas of 243–679 m² g^-1, pore volumes of 0.20–0.48 cm³ g^-1, average pore diameters of 2.2–5.4 nm and methylene blue adsorption values of 0.16–0.96 meq · g^-1.     

Kinetic conditions for the forced transition of macromolecules of an acrylonitrile copolymer into the uncoiled state

Conclusions -- The transition of the macromolccule of an acrylonitrile copolymer into the uncoiled state in lengthwise flow of aqueous salt solutions at concentrations from 1 · 10^–3 to 5 · 10^–2 g/cm³ has been studied.-- The critical velocity gradients at which the tangled state of the macromolecules becomes unstable in a lengthwise field have been determined. It has been shown that the values of these agree well with predictions of the theory of semidilute polymer solutions.Translated from Khimicheskie Volokna, No. 2, pp. 19–21, March–April, 1993.     

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)     

Detonation Properties and Electrical Conductivity of Explosive–Metal Additive Mixtures

Detonation properties of mixtures of condensed high explosives with metal additives are studied. A scheme of measurement of high electrical conductivity of detonation products ( > 10 ^–1 · cm^–1) with a time resolution of 10 nsec is developed. It is shown that the properties of detonation products depend significantly on the content of the additive in the HE and on dispersion and density of the mixture. The electrical conductivity of detonation products of the compositions examined reaches 5 · 10^{3 –1} · cm^–1, which is more than three orders higher than the electrical conductivity of the HE without the additive. Significant variation of electrical conductivity of detonation products over the conducting region thickness has been found. The main conductivity corresponds to a sector 1 mm long near the detonation front. The overdriven state of the detonation wave has a strong effect on electrical conductivity and conducting region thickness. It is assumed that the behavior of electrical conductivity with time is caused by successive processes of shock compression of the HE, excitation of the chemical reaction (including the reaction of the additive with detonation products), and expansion of detonation products. The measurement technique used is highly informative due to the possibility of studying detonation in various regimes.     

Conducting block copolymers. Towards a polymer pn- junction

Summary The synthesis of polyphenylacetylene (1), polypentafluorophenylacetylene (2) and the block copolymer of 1 and 2 polyphenylacetylene-polypentafluorophenylacetylene (3) using a Rhodium catalysed living polymerisation reaction is presented. Photoelectron spectroscopy of thin films of the individual polymers using 50eV photons from a synchrotron allowed for the determination of the position of the the electronic energy levels, ionisation potentials and the vacuum level shift which indicated that the block copolymer organises at the gold substrate surface such that the fluorinated part of the copolymer extends towards the air interface. Pulse radiolysis time resolved microwave conductivity (PR-TRMC) allowed for the determination of the minimum carrier mobilities and the carrier lifetimes. The sum of carrier mobilities, _min, were respectively 5.2·10^–7, 6.3·10^–7 and 3.2·10^–7m² V^–1 s^–1 and the first half life, _1/2, was 2.0, 1.5 and 1.0 s in 1, 2 and 3. The study shows that it is possible to make conducting block copolymers by the rhodium catalysed polymerisation of arylacetylenes with different electronic energies that organises at the surface giving rise to electronic properties that approach analogy to the traditional inorganic semiconductor pn-junctions.     

Generating mechanical pulses by the laser blasting of explosive coatings

For strength tests of materials and structures, a method of generating mechanical pulses over a large area (1 m²) is proposed on the basis of the laser blasting of explosive coatings. Compositions with record high levels of sensitivity (4·10^–3-4·10^–2 J/cm²) to a single laser pulse are developed, as well as technologies for producing coatings of these compositions on various materials. This approach yields submicrosecond load pulses of density 0.08–1.0 kPa sec.Mining Institute, 3200600 Dnepropetrovsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 2, pp. 106–111 March–April, 1994.     

Solid state ionics. High ionic conductivity solid in silver halide-silver sulphate system

The ionic conductivities and phase diagrams of AgI-Ag₂SO₄, AgCl-Ag₂SO₄ and AgBr-Ag₂SO₄ systems have been studied with the help of electrical conductivity, transport number, DTA and X-ray studies. In the AgI-Ag₂SO₄ system, the solid solution of -AgI with Ag₂SO₄ was quenched to room temperature to have high ionic conductivity of 5·0×10^–2 (ohm. cm)^–1 at room temperature and 1·3×10^–3 (ohm. cm)^–1 at –78°C. The quenched solid solution was stable at –20°C, but gradually decomposed to-AgI and-Ag₂SO₄ at room temperature. The transport number of silver ion in this solid solution was about 1·0. In the AgCl-Ag₂SO₄ and AgBr-Ag₂SO₄ systems, the electrical conductivity was of the order of 10^–4 to 10^–6 (ohm. cm)^–1 at room temperature.     

Anodic film on lead-arsenic alloy in sulphuric acid medium

The phase composition, anodic behaviour and semiconducting properties of the anodic film on Pb-6 at % As alloy have been investigated. The linear relationship between i and t ^–1/2 shows that the anodic film growth is controlled by a diffusion mechanism. The experimental results show that the anodic film contains t-PbO, PbO · PbSO₄, 3PbO · PbSO₄ and some arsenic compounds. The dielectric constant of the film is 2.8 × 10² obtained from the capacitance-time relationship measured at 2500 Hz. The Mott-Schottky plot shows that the film is an n-type semiconductor. The flat-band potential is –0.56 V vs Hg/Hg₂SO₄, and the donor density is 7.2 × 10¹⁵ cm^–3 for the film obtained at 0.9 V vs Hg/Hg₂SO₄ for 2 h on a Pb-6 at % As electrode.     

Oxidative coupling of methane to C2-hydrocarbons over La-promoted CaO catalysts

La₂O₃ promoted CaO [La/Ca (mol/mol) = 0.05] catalyst shows very high activity and selectivity (methane conversion: 25%, C₂-selectivity: 66% and C₂-space-time-yield: 864 mmol ·g^–1 (cat.)·h^–1) with no catalyst deactivation in oxidative coupling of methane to C₂-hydrocarbons at 800 ° C.     

Investigation of hydrophobic porous electrodes. II. Pseudocapacitance changes during underpotential copper deposition

Differential capacitance measurements in 96%o-phosphoric acid at 160° C have been used to follow the underpotential deposition of copper on supported platinum in a porous electrode. At a potential in the range 0·2–0·3 V versus RHE the capacitance,C, increased as copper deposition proceeded and a plot ofC versust ^1/2 was linear during a substantial part of the deposition process. The slope dC/dt ^1/2 was proportional to the copper concentration in solution, suggesting that the Cu/Cu²⁺ pseudocapacitance reflected the quantity of copper deposited and that copper deposition was diffusion controlled. The effective diffusion coefficient estimated from the results was 10^–7 cm² s^–1 — some 40 times smaller than the copper ion diffusion coefficient measured separately. At potentials of 0·4 V and above, capacitance measurements could not be used to follow copper deposition because the Cu/Cu²⁺ pseudocapacitance decayed with time.     

Thermal and chemical ionization in flames

Conclusions We have determined the rate constants of the potassium ionization process AA⁺+e^– in the flames of 2H₂+O₂+X (Ar, He) mixtures on the temperature interval 1500–2500° K. The activation energy of this process is close to the ionization potential of potassium (100 kcal).In our experiments the rate of ion formation in the front of a hydrogen flame seeded with potassium exceeded the purely thermal ionization rate by 0.5–2 orders. The presumed cause is recombination ionization of the potassium in the flame front, for example, K+O+OK⁺+O₂+e^–. This is confirmed by the intensification of ionization in the reaction zone in the presence of an excess of oxygen in homogeneous H₂-air and H₂–O₂–(He, Ar) mixtures with alkali impurities.At T=1700° K the recombination coefficient for electrons and potassium ions is close to 1·10^–8 cm³·sec^–1. For a more precise determination it is necessary to know the frequency of electron capture by molecules and atoms under the experimental conditions.Experiments on thermal ionization in turbulent flames confirm the earlier conclusion concerning the important role of mass transfer in the chemi-ionization of hydrocarbon flames.Fizika Goreniya i Vzryva, Vol. 6, No. 1, pp. 37–48, 1970     

Electrochemical studies on gold electrodes in acidic solutions of thiourea containing gold (I) thiourea complex ions

Electrochemical studies were made of the behaviour of gold electrodes in degassed acidic solutions containing between 0.00l to 0.03 M thiourea and between 10^–5 to 10^–3 M gold(I)thiourea. At anodic overpotentials of up to 0.3 V the dissolution of gold was rapid, and nearly reached the maximum diffusioncontrolled rate. The exchange current density was greater than 10^–6 A cm^–2, and dissolution proceeded at 100% efficiency. At higher anodic potentials, thiourea was oxidized to formamidine disulphide and other sulphur-containing compounds and the dissolution of gold became partly inhibited, while the current efficiency decreased markedly.The reduction of gold(I)thiourea was diffusion-controlled at cathodic overpotentials between –0.15 to –0.35 V, after which slight inhibition was observed. Thiourea itself did not contribute to the cathodic reaction, but formamidine disulphide could be reduced on a freshly deposited gold surface; in the absence of gold(I)thiourea in the solution, the reduction of formamidine disulphide caused rapid passivation of the gold surface. In 0.01 M thiourea and 0.1 M sulphuric or perchloric acid, the diffusion coefficient of the Au(CS(NH₂)₂) ₂ ⁺ ion was 1·1 x 10^–5 cm² s^–1 at 30°C.The standard reduction potential at 30° C of the redox couple Au(CS(NH₂)₂) ₂ ⁺ ¦Au on a fresh gold surface wasE ₀=0.352 V, but on a passivated gold surface this value increased to as much asE ₀=041V.