Regelation in Physics: Definition, Process & Real-World Examples

Regelation is a phenomenon in which the freezing point of water is lowered by the application of pressure. Regelation is defined as the phenomenon in which at below 0°C temperature, on the application of pressure the ice melts to water, and on the removal of pressure refreezes back to ice. It is demonstrated by the process of compressing the ice under pressure and turning it into the water, and when the pressure is removed it solidifies again.

That's why the refreezing of water is derived from the melting of ice under pressure when the pressure is relieved. Meaning that as a liquid changes into a solid when heat and pressure are released, freezing is almost always an exothermic process. Glaciers act as a source of a river due to regelation.

Regelation of Ice

The ability of water molecules to coalesce together after being separated by solid matter is called the regelation of ice. This process is what enables ice cubes in a drink to form and eventually melt; the water molecules on the outside of the cube will freeze onto the sides of the cube, while those on the inside will continue to flow until they reach the bottom. The longer an ice cube is left in a drink, the more Regelation that will occur and the smaller it will become.

Examples of Regelation

Here are a few examples:

1. Glaciers act as a source of the river due to regelation. The mass of the glacier exerts pressure on the lower surface, which lowers the melting point of the ice at its base. This results in the melting of ice and propels the glacier to slide over the liquid. Under appropriate conditions, liquid water flows from the base of the glacier to lower altitudes when the temperature of the air is above the freezing point of water.

2. Preparation of an ice ball: The ice slab is shredded into pieces and the shredded pieces are pressurized around the tip of a stick to prepare the ice ball. If two small pieces of ice are taken and pressed against each other, they stick to each other.

3. Glaciers act as a source of a river due to regelation.

4. Skating is possible on snow due to the formation of water only for the regelation. Water is formed due to the increase of pressure and it serves as a lubricant.

5. This process is often observed in the Arctic and Antarctic regions, where ice sheets are exposed to warmer air temperatures. It's also sometimes seen with thin pieces of sea ice that have broken off into chunks; these can melt away if they're left out on land, but regelation may occur when they come back into contact with one another or other objects (e.g., rocks) at lower elevations. 

If you've ever put an object onto a block of ice and had it stick there for a while before sinking down below its surface, this was likely due to regelation happening right above your hand.

6. Regelation is observed in plants when the water droplets on their leaves freeze. The tiny ice crystals that form grow and spread, until eventually, they take over the entire leaf. This happens during cold weather conditions and is one-way plants can protect themselves from losing too much water.

7. Regelation can be seen when the temperature of a material is below the freezing point but there is still liquid water present. The water droplets on the surface will freeze and create an ice layer. This happens when frost forms on objects like grass, metal wires, or leaves.

8. Regelation moreover occurs in animals like frogs and toads, who use this process as a way of surviving the winter. It's not an active type of behaviour; rather, it occurs automatically whenever these amphibians are exposed to cold air temperatures for extended periods (e.g., during hibernation).

9. Regelation is also similar to another process called nucleation, which can cause ice crystals to form in water. Nucleation happens when the temperature of a liquid or gas phase decreases below its normal freezing point but doesn't quite reach 0 degrees Celsius yet; this triggers an increase in molecular activity and forces some molecules to become locked together through ionic bonds (i.e., they start forming solid material).

Experiment on Regelation of Ice

Using a metallic wire by performing an experiment on an ice slab, the regelation of ice can be better understood. The procedure of the experiment is as follows:

1. Take a slab of ice.

2. Take a wire and fix two blocks, say 5 kg each, at its ends.

3. Put the wire over the slab.

4. If you observe, you can see that the wire passes through the ice slab. 

5. Due to the fact that just below the wire, ice melts at a lower temperature, this happens due to an increase in pressure.

6. Water above the wire freezes again when the wire has passed.

7. Thus the wire passes through the slab and the slab doesn't split. This process of refreezing is called regelation.

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Here, the melting point of the ice becomes lower than 0°C due to the applied pressure. This implies that at 0°C ice is converted into water and as soon as the pressure is removed the melting point is restored back to 0°C and the water is converted back to ice again.

Skating is possible on snow due to the formation of water only for the regelation. Water is formed due to the increase of pressure and it serves as a lubricant.

Fun Facts

1. Microscopy, Astrid Döppenschmitt, and Hans-Jürgen Butt, (These all are research works) measured the thickness of the liquid-like layer on ice using atomic force which is roughly 32 nm at −1°C, and 11 nm at −10°C, in 1998. 

2. For normal crystalline ice, its melting point is far below,  there will be some relaxation of the atoms near the surface. Near its melting point, the simulations of ice show that there is significant melting of the surface layers rather than asymmetric relaxation of atom positions. Evidence for a liquid layer on the surface of ice is being provided by Nuclear magnetic resonance.

3. The surface melting can account for the low coefficient of friction of ice, as experienced by skaters, ease of compaction of ice, high adhesion of ice surfaces.

4. A glacier can exert a sufficient amount of pressure on its lower surface to lower the melting point of its ice. It allows it to move from a higher elevation to a lower elevation with the melting of the ice at the glacier's base. at lower elevations when the temperature of the air is above the freezing point of water the Liquid water may flow from the base of a glacier.

5. Glaciers act as a source of a river due to regelation.

Conclusion

This is what the regelation of ice stands for. Understand the concept by following the simpler explanation. Learn how this natural phenomenon occurs and can be used in different ways.