Definition - What does Alkali mean?

Alkali refers to the ionic salt or basic of alkali elements and metals. It can also be defined as dissolved base in water with a pH higher than 7.0.

Alkali that causes corrosion is called a base. These are typically water soluble and generate solutions that can be very corrosive, such as caustic soda. These solutions turn litmus paper blue. One common example is sodium hydroxide.

Corrosionpedia explains Alkali

Alkali's major characteristic is its ability to produce hydroxide ions once dissolved in liquids such as water. Aqueous solutions that are alkaline in nature usually have the following properties:

  • Mildly concentrated solutions that have a pH of more than 7.1
  • Highly concentrated caustic solutions that can cause chemical burns
  • Tendency to be soapy and slippery to the touch, as its fatty substance could go through saponification when exposed to the skin's surface
  • Typically soluble in water with the exception of some alkalis such as barium carbonate that are soluble with an aqueous solution that is acidic in nature

Understanding alkalis is important as alkali corrosion is a major problem in many boiler and chemical units, cement plants, incinerators and other industrial plants. Alkalis can cause refractory wear when the alkali reacts with the matrix.

In order to limit corrosion brought about by alkalis, industries can make use of products such as zirconium compounds as well as silicon carbide compounds. Such products can provide great resistance to corrosion caused by alkalis.

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