The stability of tungsten carbide particles in iron-rich and nickel-rich liquid during the laser surface alloying (LSA) process was investigated. Kinetic calculations indicate a rapid dissolution of tungsten carbide particles in iron-rich liquid, as compared with the dissolution rate in nickel-rich liquid. Optical microscopy indicated a heterogeneous microstructure around the tungsten particles that is in agreement with concentration gradients predicted by kinetic calculations. The work demonstrates the applicability of computational thermodynamics and kinetic models for the LSA process.

6399We obtained rate constants for some of the transfer reactions by using the usual techniques for reversible kinetics6 In the first two reactions in Table I11 the forward reaction proceeds with nearly unit collision efficiency, which suggests that the internal H bond is indeed formed within the lifetime of the reaction complex of the transfer reaction.The third reaction in Table I11 constitutes an interesting case in that the forward reaction is exothermic but endoergic, while the reverse reaction is endothermic but exoergic. An unusual result is observed in that here the reverse, Le., endothermic reaction proceeds with nearly unit collision efjciency. The present result is to our knowledge the first case where an endothermic reaction proceeds essentially at the collision rate. Abstract:The development of a new experimental method for producing laser wavelengths in the Soret band region of bacteriochlorophyll (BChl) and its electrogenerated cation radical permits a more detailed study of the effect of excitation wavelength on the resonance Raman (RR) spectrum than was previously possible. Stimulated Raman scattering (SRS) from H2 or D2 under high pressure is driven with the second or third harmonics of a Nd:YAG laser. Wavelengths ranging from 396.7 to 502.9 nm are generated. The highest energy wavelength is on the shoulder of the strongest Soret transition in neutral BChl. Good quality RR spectra are obtained at this wavelength, and no evidence of photodegradation is observed. In the case of BChl cation radical, however, the effect of excitation wavelength is more dramatic because it is possible to excite near resonance with three different intense electronic transitions by using the available laser lines. In addition, the resulting spectra show clearly that one-electron oxidation of BChl causes distinctive changes in its RR spectrum. Two intense RR bands seen in the BChl'. spectrum are absent (1414 cm-I) or only weakly observed (1340 cm-I) in the corresponding spectra for BChl. These results indicate that selective RR monitoring of the formation and decay kinetics of the cation radical in vivo should be possible by using 416.0-nm excitation together with detection of the 1414-or 1340-cm-' Raman peaks. The RR spectra of BChl and BChl'. are examined in terms of recent ab initio configuration interaction calculations regarding the nature of the electronic transitions in the Soret region. The resonance enhanced Raman spectra agree qualitatively with changes in the molecular geometry which might be expected on the basis of the molecular orbital composition of the excited electronic state relative to the ground state.

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A preliminary assessment of the available options to recover soluble salts from saltcake slag material has been carried out. From limited benchscale experiments, it was demonstrated that in a semicontinuous batchmode operation, about 85% of the chlorides in a one-stage or close to 100% in a multistage series of exhaustion operations can be converted to bicarbonates through an ionexchange, resin-based option.