International Journal of Science and Advanced Technology (ISSN 2221-8386) Volume 2 No 12 December 2012 http://www.ijsat.com 68 Effect of Mineral Acids on Corrosive Propensity of Metals Alka Sharma, Arpita Sharma, Guddi Choudhary, Swati Yadav Department of Chemistry, University of Rajasthan, Jaipur (Rajasthan) INDIA Email: sharma_alka21@yahoo.com Abstract – The corrosive propensity of mild steel, aluminium and copper in various concentrations of mineral acids viz. HCl and H 2 SO 4 has been studied by employing weight loss method. The effect of acid strength on the metal corrosion has been investigated at room temperature at different immersion periods. In H 2 SO 4 media, the corrosion rate of mild steel has been observed to be higher than that of aluminium and copper; while in HCl, aluminium has been observed to get corroded fast. The thermodynamic as well as kinetic parameters have also been evaluated. The surface morphological analysis has been carried out by Optical micrographs. Keywords: metal corrosion, mineral acids, corrosion parameters, thermodynamic and kinetic parameters, optical micrograph I. INTRODUCTION Regardless of all the recent advances in polymer technology and the development of high strength plastics, industry and civilization would grind to a halt without the metals. Unfortunately all metals are subject to corrosion, a continuous process that consumes increasingly scarce raw materials. Corrosion is the deterioration of materials by chemical interaction with their environment, resulting in to a less desirable material from the original metal [1]. Metals are usually exposed to the action of bases or acids in the industries. Acid being corrosive causes severe damage to properties of metal resulting in sudden failure of material in service [2-4]. The corrosion costs in most of the countries are in the range of 2-4 % of the gross national product [5]. Consequently, it is needed to investigate the trend of the metal-dissolution on their exposure to various mineral acids, as this is an important factor in material selection that determines the service life of the material [6-7]. The present work has been focused to study the corrosive tendency of passive and active metals viz aluminium, copper and mild steel in various concentrations of hydrochloric acid and sulphuric acid by employing weight loss method. II. EXPERIMENTATION A. Specimen (coupon) preparation Rectangular specimen (coupons) of industrially used metals viz aluminium, copper and mild steel having the compositions as: Aluminium: (Al) 97.6%, (Mn)1.3%, (Fe)0.87%, (Cu)0.11%, (Zn)0.11%; Copper: (Mn)0.51%, (Fe)0.19%, (Cu)93.6%, (Zn)5.7%, and Mild Steel: (Mn) 0.3%, 0.01% (Mo), 0.039% (Cr), Fe 99.7. These specimens have been mechanically pressed cut to form different coupons, each of dimension exactly (3 cm x 2.4 cm x 0.16 cm) with a hole about 0.12 mm diameter drilled at one end for free suspension. The specimens have been mechanically polished, degreased with acetone, washed with distilled water and well polished with emery paper, cleaned, rinsed and dried then stored in desiccators [8]. B. Test Solutions Mineral acids viz. hydrochloric acid and sulphuric acid each of 2 N and 0.5 N strengths have been prepared using standard procedures. For the preparation of all solutions double distilled water was used and all reagents used were of analytical grade. C. Chemical (Weight loss) Measurements The pre-treated (raw) coupons were introduced in the test solutions. The weight of coupons was measured before and after each immersion. The mass loss was taken as the difference in weight of the coupons before and after immersion. Since weight loss is not uniform with time, thus average loss is reported [9-10]. From the experiment data, various corrosion parameters such as corrosion rate (ρ corr ) (mmy -1 ), percentage inhibition efficiency (IE %), apparent activation energy (E a ) were evaluated. D. Surface morphological analysis To scan morphology of metal surface, the optical micrograph of the coupons were taken before and after immersion in different concentrations of aggressive media, viz. HCl and H 2 SO 4 solutions [7]. III. RESULT AND DISCUSSIONS Corroding process of all three metals in acidic media, viz. HCl and H 2 SO 4 was investigated. As an established fact, aluminium is more corrosion resistant than other materials due to a compact, strongly adherent and continuous microscopically thin film of aluminium oxide, Al 2 O 3 ; but this film is resistive to corrosion in the pH range from 4-9 [11-12]. Figures 1-4 reveal that weight loss of Aluminium is found to be more in the HCl media as compared to H 2 SO 4 . This is because of the anion effect