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Properties of Ice I

Properties of Ice I. Why Worry about Ice?. Engineers and Ice. Types of Ice Commonly Found in Nature. Lake and river ice (freshwater ice) Sea ice Glacial ice Atmospheric ice Sea spray ice Snow??. Molecular Structure. Water molecules 1 Oxygen + 2 Hydrogen atoms

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Properties of Ice I

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  1. Properties of Ice I

  2. Why Worry about Ice?

  3. Engineers and Ice

  4. Types of Ice Commonly Found in Nature • Lake and river ice (freshwater ice) • Sea ice • Glacial ice • Atmospheric ice • Sea spray ice • Snow??

  5. Molecular Structure • Water molecules • 1 Oxygen + 2 Hydrogen atoms • covalent chemical bonds between • dipolar moment of 105 • electrical polarity

  6. Hydrogen Bonds • Electrical polarity causes attraction between molecules • Weak, but significant “Hydrogen bonds” can form between molecules • Polarity and hydrogen bonds account for unique properties

  7. Hydrogen Bond Effects • Hydrogen bonds cause water to have: • High heat capacity: can absorb a lot of heat energy with little increase in temperature • energy required to break hydrogen bonds • highest heat capacity of all solids and liquids, except liquid ammonia • High latent heat of fusion (energy loss necessary for freezing): highest except ammonia

  8. Hydrogen Bond Effects • Hydrogen bonds cause water to have: • High latent heat of evaporation (energy necessary to evaporate): highest of all substances • High surface tension: highest of all liquids; important in formation of droplets and capillary waves

  9. Phase Changes

  10. Water and Ice Structure Water has a partially ordered structure where hydrogen bonds are constantly being formed and broken up Ice has a rigid lattice structure - each molecule is bonded to 4 other molecules

  11. Hexagonal Structure

  12. Ice Density • Ordered crystalline structure of Hydrogen-bonded ice fills more volume than randomly oriented water mole-cules at their closest spacing (at 4° C) Water Ice

  13. Water Density

  14. Water-Ice Density Change

  15. Density of liquid water: T = degrees Celsius  = kg/m3 T = degrees Fahrenheit  = lbs/ft3 Water Density

  16. Density of Freshwater Ice • Density of freshwater ice at 0 °C is 916.8 kg/m3 (57.2 lb/ft3) • Ice contracts with cooling, like most substances; at -30 °C the density is 920.6 kg/m3 (57.4 lb/ft3) • Bulk ice density is most affected by air bubbles and pockets of unfrozen water • for most engineering, use  = 915-917 kg/m3 (57.1-57.2 lb/ft3)for freshwater ice

  17. Ice Floats! Conclusion

  18. Freshwater Ice Growth • Static Ice Formation (Thermal Ice Growth) • Freezing directly to the bottom of the ice sheet • Quiescent (no wind or turbulence) ice growth • Heat loss from the ice/water interface to the atmosphere • Frazil Ice • Turbulent water associated with streams or rivers • Slight supercooling (<0.1° C) generally associated with open water forms disk shaped crystals • Form from seed crystals such as snow or ice crystals • Snow Ice • Freezing of water-saturated snow

  19. Lake Freezing • Lakes freeze primarily by static (thermal) ice growth • Freshwater lakes must completely “turn over,” i.e., reach 4°C over the entire volume, before further cooling can cause freezing to occur. • Surface water at 4°C sinks, being replaced by warmer water from below • Once all the water is < 4°C, colder water stays at the surface and warmer water stays below – ice can form when most of the water column is above the freezing point • Turbulent currents can overcome stratification

  20. Lake Freezing • Once an ice cover forms on a lake, further freezing is retarded by insulation from ice and snow cover

  21. River Freezing Rivers freeze with a combination of thermal and frazil ice growth Frazil nearly always precedes thermal or static ice growth

  22. Frazil Ice Frazil Flocks or Pans Frazil Crystals

  23. River Ice Evolution

  24. Lake and River Ice Crystal Structure Frazil Ice Snow Ice Vert. C-axis Vert. C-axis Horz. C-axis Lake Ice River Ice

  25. Glacier Ice • Compaction of snow into ice • Vertical sequence of snow, firn, ice • Usually more dense than lake or sea ice • Flows outward under its own weight and downslope • Calves at seaward terminus - icebergs

  26. Glacial Ice Structure Antarctic Ice Core – 194 m depth

  27. Iceberg!! • Icebergs are calved from ice sheets and glaciers • A reminder: Since the densities of ice and water are close, 85 - 90% of an ice mass is beneath the surface

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