Economy stain
A sparing stain is a pickling agent made from a strongly acidic solution (usually from sulfuric or hydrochloric acid) for cleaning metal surfaces .
In addition, pickling inhibitors ( saving pickling additives) are added to the saving stains in order to keep the rate of dissolution of the metal as low as possible without affecting the rate of dissolution or detachment of the deposits to be removed, which usually consist of oxides of the metal in question or of other compounds (e.g. scale ) persist is noticeably delayed. Complete protection of the metal is not possible.
Citric acid and formic acid are also used as acids. Aldehydes, amines, nitriles, nitrogen-containing heterocycles, mercaptans and thioethers are known as pickling inhibitors, as are compounds in which nitrogen and sulfur are bonded to a common carbon atom.
When pickling unalloyed and low-alloy steels, hexamethylenetetramine is often used in hydrochloric acid , and dibenzyl sulfoxide is often used in sulfuric acid . To accelerate the dissolution of the coverings, organic wetting agents are added to the economy stains . The choice of the appropriate economy pickling agent depends on the type and composition of the pickling agent and the metal present.
After pickling, careful rinsing with water is required, if necessary with the addition of sodium hydroxide for neutralization, in order to avoid damage from remaining acid residues.
Individual evidence
- ↑ Otto Vogel. Hermine Vogel u. Alfred Keller (edit.): Handbook of metal pickling II. Iron materials. 2nd, expanded edition .
- ^ Sparbeizen - Lexicon of Chemistry
- ↑ Arthur Splittgerber: Water treatment in steam power plant .