Selected hydrazides and thiosemicarbazides of fatty acids with 11, 12, and 18 carbon atoms were synthesized and evaluated as corrosion inhibitors on mild steel and oil-well steel (N-80) in boiling 15% hydrochloric acid solution, by weight loss method. Potentiodynamic polarization studies carried out on mild steel and N-80 steel at room temperature showed that all the tested compounds are of mixed type. Adsorption studies showed that all the investigated compounds followed Temkin's adsorption isotherm.Paper no. J9195 in JAOCS 77, 265-268 (March 2000).
KEY WORDS:Corrosion inhibitors, fatty acid hydrazides, fatty acid thiosemicarbazides, mild steel, oil well tubular steel, potentiodynamic polarization, Temkin's adsorption isotherm.Corrosion inhibitors are widely used over a range of corrosive environments. A variety of organic compounds are effective corrosion inhibitors under acid conditions including acetylenic alcohols, aromatic α-, β-unsaturated aldehydes, α-alkenyl phenones, nitrogen-and sulfur-containing heterocyclic compounds, quaternary ammonium salts, and condensation products of carbonyls and amines (1-4). Among these compounds, acetylenic alcohols are widely used as acid inhibitors in industry because of their commercial viability and effectiveness. However, these inhibitors produce toxic vapors under acidic conditions, and are effective only at high concentration. Because of this, a need exists for development of new acidizing inhibitors.Continuing our work on development of acid inhibitors (5-8), we have synthesized a few hydrazides and thiosemicarbazides of long-chain fatty acids with a view to evaluate their corrosion inhibition properties on mild steel and N-80 steel in 15% boiling hydrochloric acid (HCl). These fatty acid derivatives were chosen because they are more environmentally benign, less toxic, and more cost effective than acetylenic alcohols.
MATERIAL AND METHODS
Weight loss measurements.Corrosion experiments were carried out using N-80 steel (2.0 × 1.0 × 0.7 cm) and cold rolled mild steel in 15% HCl. The mild steel sample (2.0 × 2.0 × 0.6 cm) had the following percent composition: C, 0.14; Mn, 0.35; Si, 0.17; S, 0.025; P, 0.03; the remainder, Fe. The experiments were performed in a 500-mL three-neck roundbottomed flask using a condenser at 105 ± 2°C as per ASTM, G 1-72 (9).Electrochemical studies. For potentiodynamic polarization studies, mild steel strips and N-80 steel of the same composition embedded in Araldite (Aldrich Chemical Co., St. Louis, MO) (a fixing material) with an exposed area of 1.0 cm 2 were used and the experiments were carried out at constant temperature of 28 ± 2°C as per ASTM G 3-74 and G 5-87 (9). Potentiodynamic polarization studies were carried out using a potentiostat/galvanostat (model 173; EG&G, Gaithersburg, MD), a universal programmer (model 175; EG&G), and X-Y recorder (model RE 0089; EG&G). A platinum foil was used as auxiliary electrode, and a saturated calomel electrode served as reference. Analyzed reagent-grade HCl (Merck India Ltd., Bombay, India) and...
