Novel Studies of Roughening of the Prism Plane of Ice
- PDF / 1,496,041 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 76 Downloads / 255 Views
Novel Studies of Roughening of the Prism Plane of Ice
Ann-Marie Williamson & Alex Lips Unilever Research Colworth, Colworth House, Sharnbrook, Bedford, MK44 1LQ, UK
ABSTRACT
A novel technique for examining kinetic roughening of crystals is described, and applied to the study of the prism plane of ice in contact with aqueous fructose solution. The technique can be generally applied to crystals that roughen at low driving forces. Since the residual driving force for growth utilised is that due to Ostwald ripening, this technique also facilitates simultaneous quantification of ensemble growth kinetics and crystal anisotropy during ripening. The driving force required for kinetic roughening, and the step, or ledge, free energy of this plane of ice show an approximately linear variation with temperature over the experimental temperature range –13°C to –17°C. Whilst we can conclude that the thermodynamic roughening temperature (TR) is higher than –13°C, its precise value, and conformance or otherwise of the roughening transition with Kosterlitz Thouless scaling, can not be concluded from the current data set.
INTRODUCTION
The state of roughness of a crystal surface affects microstructural evolution (e.g. the size, shape and degree of connectedness of crystals) for crystal/fluid systems. This paper describes a new technique developed to determine the kinetic roughening transition for crystal interfaces that kinetically roughen at low driving forces, and involves a detailed investigation of isothermal coarsening of a dilute dispersion of crystals, with quantification of their growth morphologies during coarsening. Furthermore, since the residual driving force for growth of the crystals results solely from Ostwald ripening, this technique has the advantage that, in addition to mapping the kinetic roughening transition, the kinetics of ensemble ripening, the crystal size distribution, and the state of crystal anisotropy are simultaneously monitored. The crystal interface studied is that between the prism plane of ice and an aqueous fructose solution; fructose providing a convenient solute for controlling the dissolution temperature of ice in the temperature range of interest. This has been identified from recent work by Maruyama et al.1,2, based on the use of pressure to vary the freezing point of ice, that suggests that the thermodynamic roughening temperature (TR) of this plane of ice in contact with water lies in the range –13°C to –17°C. The technique looks for the onset of faceting of the prism plane of ice by following changes in the morphology of crystals oriented with their basal planes normal to the observation direction, i.e. crystals which start with a high degree of circularity in their 2-D profile, but develop hexagonal symmetry as the prism-plane kinetic faceting transition is traversed. Fourier analysis is used to quantify changes to the symmetry of the crystals. These changes are correlated with the measured supersaturation of the ensemble in its asymptotic ripening limit, and estimates
M9.6.1
are made
Data Loading...
