Tannic Acid

Last updated: May 4, 2017

What Does Tannic Acid Mean?

Tannic acid is a weak acid and a commercial form of tannin, which is also one type of polyphenol. The chemical formula for tannic acid is C76H52O46. Its weak acidic nature is due to the many phenol groups in its structure. This acid is found naturally in nutgalls (the swelled areas of trees) and in a tree’s twigs, especially in oak and chestnut trees. Tannic acid is an organic acid and sometimes known as “cola water” due to its black-brown appearance.


Corrosionpedia Explains Tannic Acid

Tannic acid is a useful acid having a pH value of less than 7 and a molar mass of 1,701 g/mol. The many uses of tannic acid include:

  • Protects wood from chemical stains, fire, insects and bacteria.
  • Used in the dyeing process for cellulose.
  • Imparts anti-staining properties in polyamide yarns and carpet materials.
  • Corrosion mitigation in iron-based metallic surfaces. Tannic acid reacts with corrosion products to form a stable compound, thereby forming a protective covering over a corroded area and curbing further corrosion deterioration. Thus, it acts as a corrosion inhibitor, but is limited to ferrous metal objects.
  • The residue that remains after a corroded surface is treated with tannic acid also helps to slow the corrosion process because it absorbs moisture.

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