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Register a new userA Convection Chamber for Measuring Ice Crystal Growth Dynamics
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Added by
Kenneth G. Libbrecht
Publication date
2008
fields
Physics
and research's language is
English
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We present the design of a general-purpose convection chamber that produces a stable environment for studying the growth of ice crystals from water vapor in the presence of a background gas. Crystals grow in free fall inside the chamber, where the temperature and supersaturation are well characterized and surprisingly uniform. As crystals fall and land on a substrate, their dimensions are measured using direct imaging and broad-band interferometry. We also present a parameterized model of the supersaturation inside the chamber that is based on differential hygrometer measurements. Using this chamber, we are able to observe the growth and morphology of ice crystals over a broad range of conditions, as a function of temperature, supersaturation, gas constituents, gas pressure, growth time, and other parameters.
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We present a series of experiments investigating the growth of ice crystals from water vapor in the presence of a background gas. We measured growth dynamics at temperatures ranging from -2 C to -25 C, at supersaturations between 0.5 and 30 percent, and with background gases of nitrogen, argon, and air at a pressure of one bar. We compared our data with numerical models of diffusion-limited growth based on cellular automata to extract surface growth parameters at different temperatures and supersaturations. These data represent a first step toward obtaining precision ice growth measurements as a function of temperature, supersaturation, background gas pressure and gas constituents. From these investigations we hope to better understand the surface molecular dynamics that determine crystal growth rates and growth morphologies.
Ice growth has attracted great attention for its capability of fabricating hierarchically porous microstructure. However, the formation of tilted lamellar microstructure during freezing needs to be reconsidered due to the limited control of ice orientation with respect to thermal gradient during in-situ observations, which can greatly enrich our insight into architectural control of porous biomaterials. This paper provides an in-situ study of solid/liquid interface morphology evolution of directionally solidified single crystal ice with its C-axis (optical axis) perpendicular to directions of both thermal gradient and incident light in poly (vinyl alcohol, PVA) solutions. Misty morphology and V-shaped lamellar morphology were clearly observed in-situ for the first time. Quantitative characterizations on lamellar spacing, tilt angle and tip undercooling of lamellar ice platelets provide a clearer insight into the inherent ice growth habit in polymeric aqueous systems and are suggested exert significant impact on future design and optimization in porous biomaterials.
I describe an adaptable apparatus for making precision measurements of the growth of faceted ice prisms from water vapor as a function of temperature, supersaturation, and background gas pressure. I also describe procedures for modeling growth data to disentangle a variety of physical effects and better understand systematic errors and measurement uncertainties. By enabling precise ice-growth measurements over a broad range of environmental conditions, this apparatus is well suited for investigating the molecular attachment kinetics at the ice/vapor interface, which is needed to understand and model snow crystal growth dynamics.
I examine a variety of snow crystal growth measurements taken at a temperature of -5 C, as a function of supersaturation, background gas pressure, and crystal morphology. Both plate-like and columnar prismatic forms are observed under different conditions at this temperature, along with a diverse collection of complex dendritic structures. The observations can all be reasonably understood using a single comprehensive physical model for the basal and prism attachment kinetics, together with particle diffusion of water vapor through the surrounding medium and other well-understood physical processes. A critical model feature is structure-dependent attachment kinetics (SDAK), for which the molecular attachment kinetics on a faceted surface depend strongly on the nearby mesoscopic structure of the crystal.
I examine a variety snow crystal growth experiments performed at temperatures near -2 C, as a function of supersaturation, background gas pressure, and crystal morphology. Although the different experimental data were obtained using quite diverse experimental techniques, the resulting measurements can all be reasonably understood using a single comprehensive physical model for the basal and prism attachment kinetics, together with particle diffusion of water vapor through the surrounding medium and other well-understood physical processes. As with the previous paper in this series, comparing and reconciling different data sets at a single temperature yields significant insights into the underlying physical processes that govern snow crystal growth dynamics.
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