Browsing by Author "Koga, Yoshikata"

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    Cooperative Interactions and Two-dimensional Ordering in the Adsorption of HBr on KBr
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (06), 1981) Harrison, Lionel G; Koga, Yoshikata; Lassau, Troy
    Adsorption isotherms of HBr gas on high surface area KBr have markedly non-ideal shapes. These are analysed using a two-layer model with repulsive interactions between molecules in the first layer. An earlier report from this laboratory of a transition in the surface layer at 20 °C, induced by adsorption, is confirmed by these data. Likewise, an apparent restriction of first-layer adsorption to no more than 25% coverage seems to correlate with the previous report from this laboratory that a ‘two-dimensional compound’ K4Br3Cl is formed in surfaces partly exchanged with HCl. Heat of adsorption is 48.5 kJ mol–1(below transition) and 30.5 kJ mol–1(above transition); mean-field repulsion constant C is ca. 40 kJ mol–1; the transition has ΔHt= 18.0 kJ mol–1 and ΔSt= 59.0 J mol–1 K–1. The remarkably large magnitudes of some of these quantities are discussed in terms of a model for adsorption involving normal weak hydrogen bonding plus additional electrostatic interactions between the Br of adsorbed HBr and adjacent K+ ions. Thereby, interactions between admolecules become intermediate-range, rather than nearest neighbour, averaging C/12 ≈ 3–4 kJ mol–1.
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    Rate of Polymorphic Transformation Between Phases II and III of Hexachloroethane
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Koga, Yoshikata; Miura, Robert M.
    The temperature dependent growth rate of the stable phase near the transition point between phases II and III of hexachloroethane (C2Cl6) was measured by dilatometry. Reproducible results were obtained by repetitive cycling of the conversions between phases II and III; these conversions being limited to 10% volume changes. The rates of volume change are considered to be proportional to the rectilinear velocity of the phase boundary. The transition temperature was determined to be Ttr= 43.59 ± 0.03°C obtained when the two phases coexisted and the growth rate was zero. The observations show the growth rate to be essentially proportional to the cube of the temperature difference T–Ttr when |T–Ttr| < 1.6°C and it appears to be diverging for |T–Ttr| > 1.6°C. The results are compared with the prediction of a stochastic theory of the kinetics of phase transitions proposed by Metiu, Kitahara and Ross. While their model equation is applicable only to the description of non-conserved variables, it is the only equation available that admits steady travelling wavefront solutions with non-zero velocity, corresponding to a moving phase boundary. Some restrictions on the model equation are indicated if one attempts to modify it to explain the observed results.