Liquids, surface free energy data

The natural first question to ask is whether the crystal-liquid surface free energy can be measured experimentally by some method that is independent of nucleation kinetics. In gas-liquid nucleation studies, for example, it is routine to measure the surface tension of the liquid and to use its equality with the gas-liquid surface free energy to make predictions of nucleation rates and compare them with experiment. For the liquid-solid transition, the situation is quite different, however. This is true first because the surface tension and the surface free energy are no longer strictly equal due to the possible existence of strains in the crystal. The second reason is that measurements of liquid-solid free energies or interfacial tensions are by no means simple to devise or carry out, and so are available only in certain special cases. These limited experimental data are summarized in this section. [Pg.270]

The limited temperature range of experiments which exploit viscous flow for T < Tm in connection with the scatter of the data on y does not warrant to determine experimental data on the temperature coefficient in the solid state. The scatter of surface free energy data for the solid state can be appreciated from Fig. 9. The experimental determination of the temperature dependence of y seems to be tractable only in the liquid state. A jump of Ay in passing through the melting temperature is ascribed to the heat of fusion Hf, scaled to the area per atom A Ay = Hj / A, in agreement with the experimental values of Fig. 9 [59A11]. [Pg.337]

Measurement of contact angles on solids yields data that reflect the thermodynamics of a liquid/solid interaction. These data can be used to estimate the surface tension of the solid. For this purpose, drops of a series of liquids are formed on the solid surface and their contact angles are measured. Calculations based on these measurements produce a parameter (critical surface tension, surface tension, surface free energy etc.), which quantifies the characteristic of the solid surface and its wettability. [Pg.330]

The parameters of the potential function are adjusted to give the best description of bulk properties of the ionic crystal. However, different parameters confribute differently to the surface properties as compared to the bulk properties and the choice of one parameter set might be good for bulk, but questionable for surface properties. Therefore, the results of the calculations of the surface free energies and of the surface stresses in section 4.4.7.S in Table 5 should be understood merely as estimates, although the agreement with the scarce experimental data on surface free energy of liquid salts is within 10%. [Pg.330]

Fig. 9. The surface free energy of Cu vs. temperature. The melting temperature T is indicated hy the dashed vertical Hne, data in the solid state have been obtained by the zero creep techniqne [49Udi], data of the liquid by the sessile drop technique [59All]. The jump of y at the melting temperature is ascribed to the heat of fusion. The slope of the solid line in the liquid range is -0.00031 Nm K (data from [59AH]).

In a recent paper, Pruppacher carried this analysis still ftirther in order to analyze the results of field experiments on ice nucleation in clouds. He took four additional properties for which there is no evidence of singular behavior at -45°C (heat of melting, heat of evaporation, surface tension, and liquid-solid surface free energy) and fit them to power laws that led to a vanishing of the first and the last and a divergence of the second and third of these properties. With these functional forms, he then took nucleation rate data and used them to fit the only other parameter, the activation free energy for mass transfer across the liquid-solid interface. The result was that this quantity increased as the water was cooled down to -30°C and then began to decrease sharply. [Pg.29]

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