Inhibition glycol solution with

Where pH levels have dropped below 7.0 due to glycol degradation, there is usually little alternative but to drain, flush, repassivate, and refill with a new inhibited glycol solution. 

The inorganic nitrite used as a corrosion inhibitor in aqueous alkylene glycol or polyoxyalkylene glycol solutions can be replaced with polyoxyalkylene amines [1263,1264]. Such polyoxyalkylene amines impart corrosion inhibition to the liquid in contact with the metal and the metal in contact with the vapors of the aqueous composition. Aqueous compositions containing the glycol and the polyoxyalkylene amine also exhibit a low foaming tendency. 

The likely mechanism of the inhibitive effect of KF on AM-SCl is similar to that for pure magnesium and AZ91D in a fluoride-containing ethylene glycol solution, i.e. fluorides react with magnesium in the matrix of AM-SCl alloy, forming a low-solubility magnesium fluoride product which deposits on the alloy surface and prevents further corrosion attack to the alloy. 

Organic fluids also are mixed with water to serve as secondary coolants. The most commonly used fluid is ethylene glycol. Others include propjiene glycol, methanol (qv), ethanol, glycerol (qv), and 2-propanol (see Propyl alcohols, isopropyl alcohol). These solutions must also be inhibited against corrosion. Some of these, particularly methanol, may form flammable vapor concentrations at high temperatures. 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

In all circumstances it is important to ensure that the inhibitor is chemically compatible with the liquid to which it is added. Chromates, for example, cannot be used in glycol antifreeze solutions since oxidation of glycol by chromate will reduce this to the trivalent state which has no inhibitive properties. 

The action of salts as inhibitors is somewhat different than that of alcohols or glycols. The salt ionizes in solution and interacts with the dipoles of the water molecules with a much stronger Coulombic bond than either the hydrogen bond or the van der Waals forces that cause clustering around the apolar solute molecule. The stronger bonds of water with salt ions inhibit hydrate formation water is attracted to ions more than water is attracted to the hydrate structure. 

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