- Limescale
Limescale is the hard, off-white, chalky deposit found in kettles, hot-water boilers and the inside of inadequately maintained hot-water central heating systems. It is also often found as a similar deposit on the inner surface of old pipes and other surfaces where “
hard water ” has evaporated.These types of limescale differ slightly due to their origins.
The type found deposited on the heating elements of water heaters etc. has a main component of
calcium carbonate , precipitated out of the (hot) water.Hard water containscalcium (and oftenmagnesium )bicarbonate and/or similarsalt s.Calcium bicarbonate is soluble in water, however at temperatures above 70 °C the soluble bicarbonate is converted to poorly-soluble carbonate, leading to deposits in places where water is heated. [Centre for Water Science — Cranfield University. [http://www.cranfield.ac.uk/sas/water/scale/calcium.htm Calcium Carbonate] . Last accessed April 19, 2007.] Local boiling “hot spots” can also occur when water is heated, resulting in the concentration and deposition of salts from the water.Calcium
cation s from hard water can also combine withsoap , which would normally dissolve in soft water. This combination often forms scum which precipitates out in a thin film on the interior surfaces of baths, sinks, and drainage pipes. Soap usually contains salts ofanion s from neutralizedfatty acid s or similarchemical compound s. The calcium salts of these anions are lesssoluble in water.The type found on air-dried cooking utensils, dripping taps and bathroom tiling consists of calcium carbonate mixed with all the other salts that had been dissolved in the water, prior to
evaporation .It can also be found on taps where
hard water has been continually running through and has depositedcalcium carbonate . This can be a help to start with by protecting the inside of the tap, but can build up and eventually block the tap.See also
*
Fouling
*Descaling agent
*Water softener
*Hard water
*Magnetic water treatment
*Limestone References
External links
* [http://www.scalewatcher.co.uk/pages/lime-scale-removal.asp Scale problems]
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