Formation of oxygen atoms in the reaction of chlorine atoms with ozone

Oxygen atoms are detected by NO + O + M chemiluminescence as a secondary product of the reaction between Cl and O₃. The mechanism Cl + O₃ → ClO + O₂(¹Σ⁺_g), O₂(¹Σ⁺_g) + O₃ → O₂ + O₂ + O is proposed to account for the oxygen atom formation. The branching ratio to the O₂(¹Σ⁺_g) product in the reaction of Cl with O₃ is estimated to be in the range (0.1–0.5) x 10^?2.     

Micromechanics of fatigue crack propagation in glassy thermoplastics

By the aid of the optical interference method the size of the craze zone at the crack tip has been measured during fatigue crack propagation (FCP) in two glassy thermoplastics thus giving a basis to re-examine proposed models. In contrast to previous assumptions it has been found, that in PMMA of high molecular weight crack propagation occurs only during a short interval of the loading cycle when the fibrils are stretched most severely and it is not limited by crack tip blunting; between the dimensions of the craze zone and the crack advance per cycle which is also reflected by markings on the fracture surface no simple correlation has been found. In PVC first the craze grows continuously during many loading cycles up to its final size and then the crack propagates by a jump separating the craze zone only partly. Thus at all stress intensity levels investigated the length of the final craze zone has been found to be distinctly larger than the jump spacing on the fracture surface. By aid of SEM-photography it is shown that in PVC during FCP cracking occurs by separation of fibrils instead of void coalescence.     

Photoelectric evidence for a neutral excited state in fully polymerized polydiacetylene-p-(toluenesulfonate) single crystals

The intensity dependence of photocurrent transients excited by the 1.06 μ line of a Nd laser has been measured. Observation of an I² and an I³ branch indicate that charge carriers can be generated via two-quantum absorption and that at high intensities photoionization of a neutral excited state with a lifetime of the order 10^?10 s dominates.     

Seawater—A test of multicomponent electrolyte solution theories. II. Enthalpy of mixing and dilution of the major sea salts

In a continuing effort to predict the physicochemical properties of seawater from the properties of single aqueous electrolyte solutions, the pairwise heats of mixing at constant molal ionic strength,I=1.0 ional, have been determined for the six possible pairs of salts from the set (NaCl, Na₂SO₄, MgCl₂, MgSO₄) at 30°C. In addition, heats of dilution for two aqueous solutions formed from these salts and havingI=1.0 ional have been determined at 30°C. In order to present the most thermodynamically consistent results, it was found necessary to apply a correction term to the relative apparent equivalent enthalpies given in the literature at 30°C. These correction terms derived from a consideration of published results on heats of dilution at very low concentrations. Further, in order to make predictions for seawater at 25°C, it was deemed desirable to refit existing heat-capacity data. The heats relative apparent equivalent enthalpies for the two mixtures mentioned as well as for seawater. The estimates are based on the theoretical equation of Reilly and Wood for charge-asymmetric mixtures which derives from the work of Friedman. In the most applicable cases, the estimates agree with experimental relative apparent equivalent enthalpies to within 5%. In general, the results substantiate the theoretical equation.Taken in part from the Ph.D. dissertation of W. H. Leung, University of Miami, Miami, Florida 33149.     

Zur Kinetik der Spinellbildung von β-Ga2O3 mit zweiwertigen Oxiden. IV. Reaktionen 2. Art im System CoO-β-Ga2O3

The solid-state reaction of the second kind in a sandwich type diffusion couple of $\text{Co}{}_{\mathrm{1?z}}\text{Ga}{}_{\mathrm{<mtext>2z</mtext><mtext>3</mtext>}}\text{O}$ and β-Ga₂O₃ has been investigated between 1249 and 1550°C in air. The quantity z, which corresponds to the saturation concentration of β-Ga₂O₃ in CoO, was determined as a function of temperature by X-ray methods and the optical microscope; the homogeneity range of the spinel phase $\text{Co}{}_{\mathrm{1?y}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2y</mtext><mtext>3</mtext>}}\text{O}{}_4$ was investigated also. The growth of the thickness of the reaction layer follows a parabolic rate law; the activation energy is 71.6 kcal/mole. A comparison of reaction rate constants of the first and second kind in connection with experimental results, achieved with a modified marker technique, leads to confirmation of the Wagner mechanism for the formation of CoGa₂O₄ spinel as supposed before by Laqua. Reaction rate constants of the second kind, calculated from interdiffusion profiles in CoO-β-Ga₂O₃ diffusion couples, are in good agreement with experimental values. Presented data are used for estimating interdiffusion coefficients for the CoO-β-Ga₂O₃ system according to theoretical aspects developed by Pelton, Schmalzried, and Greskovich.     

Comparison of various calibration techniques for the direct spectroscopical analysis of SiC powders

Techniques for the direct analysis of powdered advanced ceramics provide an advantageous alternative to methods using wet digestion in sample preparation. The direct spectrochemical methods based on electrothermal vaporization (ETV-ICP-OES, solid-ETV-AAS, etc.) show a great similarity to the classical method of d. c. arc excitation. The calibration procedure is the major difficulty of all techniques applied for direct solid sample analysis, as there is a lack of suitable reference materials of ceramics. Consequently, it was necessary to verify various possibilities of preparation and application of model calibration samples. The results of such a calibration are compared with those using within-laboratory standards.     

Thermodynamics of the Laminar Donnan System

Thermodynamic quantities of a polyelectroyte immersed in salt solution are derived modeling the polyelectrolyte by a sequence of charged parallel flat plates. The starting point for the analysis is the derivation of the Gibbs free enthalpy in its canonic variables pressure (p) and temperature (T), i.e., as a thermodynamic potential. From this, further thermodynamic quantities such as Helmoltz free energy, entropy, internal energy, compressibility, isobar and isochor heat capacities, and expansive force are derived in analytical expressions by differentiation. All these formulas contain the parameter plate surface charge density (sigma) that provides a measure of the discontinuity of the polymer charge distribution that can be used to fit the theory to experimental data. Thermodynamic quantities are also known from the classical Donnan equilibrium that treats the polyelectroyte charge network as a charge continuum. A limiting process is used to perform the transition from the laminar Poisson- Boltzmann model to the continuous Donnan equilibrium. In general, the expressions of the Donnan system are recovered for plate charge density sigma-->0, number of plates Z-->infinity, and sigma Z=constant. Copyright 2000 Academic Press.     

Computer simulation of ion recombination in irradiated nonpolar liquids

A review of the results of computer simulation of the diffusion controlled recombination of ions is presented. The ions generated in clusters of two and three pairs of oppositely charged ions were considered. The recombination kinetics and the ion escape probability at infinite time with and without external electric field have been computed. These results are compared with the calculations based on the single-pair theory.     

A continuous flow instrument with flow regulation and automatic sensitivity range adaptation for the determination of atmospheric H2S

A set-up for continuous measurements of atmospheric H₂S concentrations in the range between 0.138 g/m³ and 17.5 g/m³ is described. All flows are regulated by flow sensors which are connected to the respective pump by a feed back circuit. The instrument is working in two sensitivity ranges. One is provided for low H₂S concentrations (lower than 1.75 g/m³) and the other for higher levels (higher than 1.75 g/m³). During continuous measurements the set-up enables an automatic adaptation of one of the sensitivity ranges to ambient H₂S concentrations. The critical step of absorption of gaseous H₂S into the liquid phase of the continuous flow system could be stabilised by the development of a new fluid level control system. After numerous test measurements under laboratory conditions the instrument was tested for the first time in June 1993 during field measurements in the tropics. These measurements took place in the environment of natural and industrial sources of H₂S in the vicinity of Salvador da Bahia in Brazil. Data are presented which prove the ability of the instrument.Dedicated to Professor D. Dieter Klockow on the occasion of his 60th birthday     

Absorption spectra and photochemistry of the toluene cation and benzyl radical in solid argon

Toluene diluted in argon subjected to continuous argon discharge radiation during condensation at 21 K revealed absorptions at 310.5 and 449.6 nm due to benzyl radical, and 317 nm due to a C₇7H₉ radical. A photosensitive 430 nm band, in agreement with photodissociation spectra of the toluene parent cation, is assigned to this species.