Ice
Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 °C, 32 °F, or 273.15 K. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.
| Ice | |
|---|---|
An ice block, photographed at the Duluth Canal Park in Minnesota | |
| Physical properties | |
| Density (ρ) | 0.9167–0.9168 g/cm3 |
| Refractive index (n) | 1.309 |
| Mechanical properties | |
| Young's modulus (E) | 3400 to 37,500 kg-force/cm3 |
| Tensile strength (σt) | 5 to 18 kg-force/cm2 |
| Compressive strength (σc) | 24 to 60 kg-force/cm2 |
| Poisson's ratio (ν) | 0.36±0.13 |
| Thermal properties | |
| Thermal conductivity (k) | 0.0053(1 + 0.0015 θ) cal/(cm s K), θ = temperature in °C |
| Linear thermal expansion coefficient (α) | 5.5×10−5 |
| Specific heat capacity (c) | 0.5057 − 0.001863 θ cal/(g K), θ = absolute value of temperature in °C |
| Electrical properties | |
| Dielectric constant (εr) | ~95 |
| The properties of ice vary substantially with temperature, purity and other factors. | |
In the Solar System, ice is abundant and occurs naturally from as close to the Sun as Mercury to as far away as the Oort cloud objects. Beyond the Solar System, it occurs as interstellar ice. It is abundant on Earth's surface – particularly in the polar regions and above the snow line – and, as a common form of precipitation and deposition, plays a key role in Earth's water cycle and climate. It falls as snowflakes and hail or occurs as frost, icicles or ice spikes and aggregates from snow as glaciers and ice sheets. In the recent decades, ice volume on Earth has been decreasing due to climate change. The largest declines have occurred in the Arctic and in the mountains located outside of the polar regions.
Ice exhibits at least nineteen phases (packing geometries), depending on temperature and pressure. When water is cooled rapidly (quenching), up to three types of amorphous ice can form depending on its history of pressure and temperature. When cooled slowly, correlated proton tunneling occurs below −253.15 °C (20 K, −423.67 °F) giving rise to macroscopic quantum phenomena. Virtually all ice on Earth's surface and in its atmosphere is of a hexagonal crystalline structure denoted as ice Ih (spoken as "ice one h") with minute traces of cubic ice, denoted as ice Ic and, more recently found, Ice VII inclusions in diamonds. The most common phase transition to ice Ih occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. It may also be deposited directly by water vapor, as happens in the formation of frost. The transition from ice to water is melting and from ice directly to water vapor is sublimation.
Humans have been using ice for various purposes for thousands of years. Some historic structures designed to hold ice to provide cooling are over 2,000 years old. Before the invention of refrigeration technology, the only way to safely store food without modifying it through preservatives was to use ice. Ice also plays a major role in winter sports.