INHIBITORY EFFECTS OF CALCIUM SULPHATE CONCENTRATIONS ON COOKWARE ALUMINIUM CORROSION IN HIGHLY ACIDIC AND ALKALINE MEDIA AT ELEVATED TEMPERATURES

Corrosion of aluminium cookware is unavoidable. It has been an issue of great concern for decades now due to the toxicological, mutagenic, and carcinogenic effects of the corrosion substances in the human body system, with the ability to cause many chronic ailments. The aim of this paper is to present an inquiry into the inhibitory effects of calcium sulphate as a cheap, worldwide-available, environmentally friendly, biocompatible, and inorganic food substance on corrosion of cookware aluminium in highly acidic and alkaline media. Coupons were produced from the aluminium 6061 alloy as a common cookware aluminium and immersed for 1-3 hours in sequentially treated acidic media of 2.5, 2.7, and 3 pH and alkaline media of 10.5, 10.7, and 11 pH with calcium sulphate (anhydrite) concentrations of 0, 0.2, 0.25, 0.3, and 0.35 parts per unit mass of the media at the temperature conditions of 30, 50, and 70°C. Corrosion penetration rates, inhibition efficiencies, and micro-topographical changes of the coupons were evaluated relative to coupons immersed in the untreated media. Results show appreciable corrosion rates of 0.121-1.579 in the acidic and 0.101-1.105 mm/yr in the alkaline media, which increase with the exposure temperatures and durations as well as acidity and alkalinity levels. The highest corrosion inhibition efficiency of 74.34% occurred in the acidic media after a 3-hour immersion in the 2.7-pH medium at 30°C, treated with 0.35 parts per unit mass of the medium, while the highest value in the alkaline media was 72.95% after a 3-hour immersion in the 10.5-pH medium at 30°C, treated with 0.3 parts per unit mass of the medium. SEM micro-topographical analysis indicates that higher concentrations of anhydrite facilitated the coupons’ corrosion inhibition in the media by coating formations on them