Inhibition glycol solutions

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. 

Differences in low temperature emission spectra of benzil in methylcyclohexane and in isopentane have been ascribed to inhibition of the conformational changes involved in the skewed to planar relaxation in isopentane 33). Emission spectra were identical in both solvents at temperatures above the glass-forming temperature. Preference for an s-cis conformation in ethylene glycol solution has been suggested 33b) to account for anomalous emission spectra of benzil in that medium. Other aspects of benzil emission have been examined 33c). 

All-weather ethylene glycol-type solutions that automobile radiators require complex mixtures of additives, including corrosion inhibitors, stabilizers, and buffering agents. Without proper commercial inhibition, a 40 percent glycol solution at 70°C would corrode iron and steel at 250 to 500 jim/y, while also attacking the copper, brass, solder, and/or aluminum components at 25 to 50 pimly. 

The inhibition effect of fluorides has also recently been observed on AZ91 in an ethylene glycol solution [30]. However, the effect is not as evident as on pure magnesium. This could be due to the content of alnminium in the alloy. Fluorides cannot inhibit the dissolution of aluminium. 

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. 

E. Slavcheva, G. Petkova, P. Andreev, Inhibition of corrosion of AZ91 magnesium alloy in ethylene glycol solution in presence of chloride anions . Materials and Corrosion 56 (2005) 83-87. 

For temperatures lower than about -40 F, glycol injection is impractical because of the high viscosity of glycol solutions at such low temperatures. Methanol s low viscosity and other favorable characteristics make it the fluid of choice for hydrate inhibition in very low... 

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. 

Microtubules can be reconstituted in vitro at 37 °C from a solution that contains a physiological mixture of brain tubulin, MAPs, small amounts of guanosine 5 -triphosphate (GTP), magnesium ions, and the calcium-chelating agent EGTA [ethylene glycol-bis(2-aminoethyl ether) N, N -tetraacetic acid]. Tubulin assembly is inhibited by low temperature and by the presence of calcium ions. 

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