Descaling agent

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Limescale build-up inside a pipe reduces both liquid flow and thermal conduction from the pipe, so will reduce thermal efficiency when used as a heat exchanger. Limescale-in-pipe.jpg
Limescale build-up inside a pipe reduces both liquid flow and thermal conduction from the pipe, so will reduce thermal efficiency when used as a heat exchanger.

A descaling agent or chemical descaler is a liquid chemical substance used to remove limescale from metal surfaces in contact with hot water, such as in boilers, water heaters, and kettles. Limescale is either white or brown in colour due to the presence of iron compounds. Glass surfaces may also exhibit scaling stains, as can many ceramic surfaces present in bathrooms and kitchen, and descaling agents can be used safely to remove those stains without affecting the substrate since both ceramics and glass are unreactive to most acids. [1]

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Descaling agents are typically acidic compounds such as hydrochloric acid that react with the calcium carbonate and magnesium carbonate compounds present in the scale, producing carbon dioxide gas and a soluble salt. [2]

CaCO3 (s) + 2 H+ (aq) → Ca2+ (aq) + CO2 (g) + H2O (l)
MgCO3 (s) + 2 H+ (aq) → Mg2+ (aq) + CO2 (g) + H2O (l)

Strongly acidic descaling agents are usually corrosive to the eyes and skin and can also attack and degrade clothing fibres, so appropriate protection such as rubber gloves and plastic aprons should be used in cleaning operations.

Descaling can also cause erosion and dezincification of brass, causing the brass to leach lead which is thereby released into potable water lines. Descaling of steam boilers such as those found in espresso machines can be difficult as the boilers do not fill completely and the descaling agent is unable to reach the top of the boiler. If this problem occurs the device's safety valves, probes, and pressure sensors may not be cleared of limescale.

Acids used

Notable descaling agents include acetic acid, citric acid, glycolic acid, formic acid, lactic acid, phosphoric acid, sulfamic acid and hydrochloric acid. The calcium salts are soluble and thus washed away during dissolution or solvation. The speed of the descaling action depends on the concentration and acidity or pH of the solution provided. Hydrochloric acid is much stronger than acetic acid, for example, and therefore tends to remove scale faster. Weak acids such as acetic or citric acids may be preferred, however, where damage to the substrate is to be minimised.

Many companies offer inhibited or "buffered" acids that inhibit the corrosive effect of the acids on various materials. Approximately 10% concentrated hydrochloric acid with a corrosion inhibitor and some added penetrating and wetting agents added is typical. This allows for a better cleaning of machinery and especially heat exchangers because often the scale is mixed with silica and other contaminants. These additives reduce the corrosion on the metals and cut through and loosen these other materials mixed with the scale for faster and more thorough cleaning.

See also

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An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid.

<span class="mw-page-title-main">Carbonate</span> Salt or ester of carbonic acid

A carbonate is a salt of carbonic acid, H2CO3, characterized by the presence of the carbonate ion, a polyatomic ion with the formula CO2−3. The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate groupO=C(−O−)2.

<span class="mw-page-title-main">Calcium carbonate</span> Chemical compound

Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. Materials containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is produced when calcium ions in hard water react with carbonate ions to form limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.

<span class="mw-page-title-main">Sodium hydroxide</span> Chemical compound with formula NaOH

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<span class="mw-page-title-main">Sodium carbonate</span> Chemical compound

Sodium carbonate is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water. Historically, it was extracted from the ashes of plants grown in sodium-rich soils, and because the ashes of these sodium-rich plants were noticeably different from ashes of wood, sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process, as well as by carbonating sodium hydroxide which is made using the Chlor-alkali process.

<span class="mw-page-title-main">Limewater</span> Calcium hydroxide solution

Limewater is a saturated aqueous solution of calcium hydroxide. Calcium hydroxide, Ca(OH)2, is sparsely soluble at room temperature in water (1.5 g/L at 25 °C). "Pure" (i.e. less than or fully saturated) limewater is clear and colorless, with a slight earthy smell and an astringent/bitter taste. It is basic in nature with a pH of 12.4.

<span class="mw-page-title-main">Sodium hypochlorite</span> Chemical compound (known in solution as bleach)

Sodium hypochlorite is an alkaline inorganic chemical compound with the formula NaOCl. It is commonly known in a dilute aqueous solution as bleach or chlorine bleach. It is the sodium salt of hypochlorous acid, consisting of sodium cations and hypochlorite anions.

<span class="mw-page-title-main">Magnesium carbonate</span> Chemical compound

Magnesium carbonate, MgCO3, is an inorganic salt that is a colourless or white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.

<span class="mw-page-title-main">Hard water</span> Water that has a high mineral content

Hard water is water that has high mineral content. Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbonates and sulfates.

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<span class="mw-page-title-main">Barium carbonate</span> Chemical compound

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<span class="mw-page-title-main">Limescale</span> Hard, chalky deposit of calcium carbonate

Limescale is a hard, chalky deposit, consisting mainly of calcium carbonate (CaCO3). It often builds up inside kettles, boilers, and pipework, especially that for hot water. It is also often found as a similar deposit on the inner surfaces of old pipes and other surfaces where hard water has flowed. Limescale also forms as travertine or tufa in hard water springs.

Calcium bicarbonate, also called calcium hydrogencarbonate, has the chemical formula Ca(HCO3)2. The term does not refer to a known solid compound; it exists only in aqueous solution containing calcium (Ca2+), bicarbonate (HCO
3
), and carbonate (CO2−
3
) ions, together with dissolved carbon dioxide (CO2). The relative concentrations of these carbon-containing species depend on the pH; bicarbonate predominates within the range 6.36–10.25 in fresh water.

<span class="mw-page-title-main">Sulfamic acid</span> Chemical compound

Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, sulphamic acid and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colourless, water-soluble compound finds many applications. Sulfamic acid melts at 205 °C before decomposing at higher temperatures to water, sulfur trioxide, sulfur dioxide and nitrogen.

Calcium magnesium acetate (CMA) is a deicer and can be used as an alternative to road salt. It is approximately as corrosive as normal tap water, and in varying concentrations can be effective in stopping road ice from forming down to around −27.5 °C (−17.5 °F) (its eutectic temperature). CMA can also be used as an H2S capture agent.

<span class="mw-page-title-main">Cleaning agent</span> Substance used to remove dirt or other contaminants

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<span class="mw-page-title-main">Byne's disease</span> Mollusk disease

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<span class="mw-page-title-main">Concrete degradation</span> Damage to concrete affecting its mechanical strength and its durability

Concrete degradation may have many different causes. Concrete is mostly damaged by the corrosion of reinforcement bars due to the carbonatation of hardened cement paste or chloride attack under wet conditions. Chemical damages are caused by the formation of expansive products produced by various chemical reactions, by aggressive chemical species present in groundwater and seawater, or by microorganisms. Other damaging processes can also involve calcium leaching by water infiltration and different physical phenomena initiating cracks formation and propagation. All these detrimental processes and damaging agents adversely affects the concrete mechanical strength and its durability.

<span class="mw-page-title-main">Lead compounds</span> Type of compound

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References

  1. "Descaler", Wiktionary, Accessed January 14, 2014
  2. Stanga, Mario (2010). Sanitation: Cleaning and Disinfection in the Food Industry. John Wiley & Sons. pp. 571–572. ISBN   9783527629466.