Sodium benzoate and sodium nitrite as corrosion‐inhibitors in ethylene glycol anti‐freeze solutions. I. Laboratory investigations

Abstract

AbstractThe addition of 1·5% sodium benzoate and 0·1% sodium nitrite to a 20% ethylene glycol anti‐freeze solution effectively prevents corrosion of cast iron and soldered joints in conditions of intermittent heating. In the absence of benzoate, sodium nitrite protects cast iron but increases the attack on soldered joints in glycol solutions, the intensity of attack increasing considerably over the range 0·1 to 1·5% sodium nitrite.A short initial period of heating is necessary to ensure complete protection of cast iron in 20% glycol solution containing 1·5% sodium benzoate + 0·1% sodium nitrite. At room temperature without initial heating, 0·3% sodium nitrite is required to protect machined cast iron in 20% glycol solution containing 1·0 or 1·5% sodium benzoate; with 30% glycol and 1·0 or 1·5% sodium benzoate, 0·1% nitrite is sufficient. With ‘as‐cast’ surfaces higher concentrations of sodium nitrite are required to prevent rusting.