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Co-Inhibition Characteristics of Sodium Tungstate with Sodium Nitrate on Low Carbon Steel in 0.085M Hcl

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Co-Inhibition Characteristics of Sodium Tungstate with Sodium Nitrate on Low Carbon Steel in 0.085M Hcl Emirates Journal for Engineering Research, 17 (2), 1-6 (2012) (Regular Paper) CO-INHIBITION CHARACTERISTICS OF SODIUM TUNGSTATE WITH SODIUM NITRATE ON LOW CARBON STEEL IN 0.085M HCL. Ogundare, O.1, Umoru, L.E.2, Olorunniwo, O. E. 2, Ige, O. O. 2 1 Engineering Materials Development Institute, Akure Nigeria. 2Department of Materials Science and Engineering, Obafemi Awolowo University, Ile- Ife, Nigeria (Received January 2012 and Accepted September 2012) ﻗﻴﻤﺖ هﺬﻩ اﻟﻮرﻗﺔ the co-inhibitive characteristics ﻟﺘﻨﺠﺴﺘﺎت اﻟﺼﻮدﻳﻮم ﻣﻊ ﻧﺘﺮات اﻟﺼﻮدﻳﻮم ﻓﻲ ﺣﺎﻣﺾ اﻟﻬﻴﺪروآﻠﻮرﻳﻚ M.0.085 وﻗﺪ أﺟﺮﻳﺖ اﻟﺪراﺳﺔ ﺑﺎﺳﺘﺨﺪام ﺗﻘﻨﻴﺔ اﻟﺠﺎذﺑﻴﺔ. ﺗﻢ دراﺳﺔ ﺗﺄﺛﻴﺮ إﺿﺎﻓﺔ single inhibitor and co-inhibitors ﻓﻲ ﻣﻌﺪﻻت اﻟﺘﺂآﻞ. أﻇﻬﺮت اﻟﻨﺘﺎﺋﺞ أن ﺗﻨﺠﺴﺘﺎت اﻟﺼﻮدﻳﻮم وﺣﺪﻩ أﻋﻄﻰ 47IE٪ وﻧﺘﺮات اﻟﺼﻮدﻳﻮم اﻧﺘﺠﺖIE 57٪ ﻋﻨﺪﻣﺎ ﺗﺴﺘﺨﺪم وﺣﺪهﺎ ﺑﻌﺪ 336 ﺳﺎﻋﺔ ﻣﻦ اﻟﺘﻌﺮض. ﺗﻢ اﻟﺤﺼﻮل ﻋﻠﻰ آﻔﺎءة 54٪ ﻋﻨﺪ 150 ﺟﺰء ﻓﻲ اﻟﻤﻠﻴﻮن ﻣﻦ ﻧﺘﺮات اﻟﺼﻮدﻳﻮم، و 50 ﺟﺰء ﻓﻲ اﻟﻤﻠﻴﻮن ﻣﻦ اﻟﺼﻮدﻳﻮم ﺗﻨﺠﺴﺘﺎت ﺑﻌﺪ 336 ﺳﺎﻋﺔ ﻣﻦ اﻟﺘﻌﺮض. اﺳﺘﻨﺎدا إﻟﻰ اﻟﻨﺘﻴﺠﺔ اﻟﺘﻰ ﺗﻢ اﻟﺤﺼﻮل ﻋﻠﻴﻬﺎ ﻳﺠﺐ ان ﻳﻜﻮن ﺗﺮآﻴﺰ ﺗﻨﺠﺴﺘﺎت اﻟﺼﻮدﻳﻮم أﻗﻞ ﻣﻦ ﺗﺮآﻴﺰ ﻧﺘﺮات اﻟﺼﻮدﻳﻮم ﻟﻠﺤﺼﻮل ﻋﻠﻲ آﻔﺎءة ﻣﺎﻧﻊ ﻓﻌﺎﻟﺔ. This paper has evaluated the co-inhibitive characteristics of sodium tungstate with sodium nitrate in 0.085 M hydrochloric acid. The inhibition study was carried out using the gravimetric technique. The uninhibited solution of 0.085 M hydrochloric acid served as the control. The effect of addition of single inhibitor and co-inhibitors at 50 (parts per million) ppm, 100 ppm, and 150 ppm on corrosion rates (CR) (mpy) and inhibition efficiencies (IE) was investigated. The results showed that sodium tungstate alone gave 47% IE and sodium nitrate produced 57% IE when used alone after 336 hours of exposure. The inhibitive efficiency of 54% was obtained at 150 ppm of sodium nitrate and 50 ppm of sodium tungstate after 336 hours of exposure. Based on the result obtained sodium tungstate must be in lower concentration than sodium nitrate for effective inhibitive efficiency. Keywords: Corrosion, inhibition, co- inhibitors and corrosion inhibition efficiency. 1. INTRODUCTION potential and high cost[2]. This is due to the fact that tungstate ions alone cannot shift the potential of the Corrosion is the reaction between a material and its metal into the passive region substantially[3-5]. This environment that produces a deterioration of the fact justifies the small quantity of sodium tungstate material and alters its mechanical properties. The (50 ppm) used throughout this work. Hence, its actual corrosion process that takes place on a piece of inhibitive potential can be fully maximized when bare mild steel is very complex due to factors such as used in the presence of oxidizing inhibitor such as variations in the composition or structure of the steel, sodium nitrate, sodium silicate, sodium chromate and presence of impurities due to the high instances of the sodium nitrite. recycled steel, uneven internal stress, or exposure to a non-uniform environment[1]. Co-inhibitive effects have been investigated on molybdate and phosphate as inhibitors in synthetic Inhibitors are substances added in small tap water environments[6] and on potassium concentrations to particular environments with the permanganate with sodium tungstate for the aim of slowing down the rate of corrosion at such protection of carbon steel[3]. They proposed that due sites. Co- inhibition is achieved when two or more to the similarity in chemical structure and periodicity inhibitors are used at the same time to effect better between chromates and other group VI ions, inhibition efficiency than a single inhibitor used molybdate and tungstate are to be reliable separately. replacement. Among the non–oxidizing passivating The major use of inhibitors in acid solutions is in inhibitors, tungstate seems to be better than pickling processes, oil well cleaning, descaling and molybdate in terms of its inhibition efficiency and industrial acid cleaning. Anodic Inhibitors such as applicability under wide experimental condition, sodium tungstate are found to be the most effective including pH. This was reported in their research and readily available but for its low oxidizing work[3,4]. To improve the inhibitive capacity of 1 Ogundare, O., Umoru, L.E., Olorunniwo, O. E. and Ige, O. O. molybdate, it must be in co-inhibition with other The inhibitive property of palm kernel oil (PKO), inhibitors (including organic and inorganic)[6]. For an inorganic inhibitor, on crude oil pipeline has been tungstate ions to act as anodic inhibitors (due to its investigated and modeled (non-linear regression low oxidizing ability and high cost); it must be in the analysis) to forecast and predict it[13]. presence of dissolved oxygen or oxidizing agent or The aim of this study is to evaluate the corrosion inhibitor. It should be noted that tungstate ions alone inhibition efficiencies of sodium tungstate and cannot shift the potential of the metal into the passive sodium nitrate and their co-inhibitive characteristics region substantially and this view was supported by as it relates to their application in acid pickling, oil earlier findings[3-6]. However, tungstate has been well cleaning, descaling and industrial acid cleaning. adjudged to be highly effective even in highly reducing environment[5,7]. A recent work by[11] has reported the evaluation the co-inhibitive 2. EXPERIMENTAL characteristics of sodium tungstate with sodium The low carbon steel sheet and the HCl used for this silicate in 0.085 M hydrochloric acid. The effect of research work were obtained commercially. The low palm oil as corrosion inhibitor on ductile iron and carbon steel was spectrometrically analyzed at the mild steel has been successfully reported Materials laboratory, Ajaokuta Steel Complex recently[12]. It was concluded that palm oil, being Limited, Ajaokuta, Nigeria and the composition of non-toxic, has met one of the stringent requirements the steel was as presented in Table 1. for corrosion inhibitors and its application. Table 1: Chemical Composition of experimental low carbon steel Element Fe C Si Mn P S Co Mo Ni Al Cu % Wt 99.00 0.117 0.033 0.011 0.0258 0.014 0.005 0.014 0.19 0.59 0.055 One hundred and seventy five coupon samples were cut from the low carbon steel sheet using the 3. RESULTS cutting saw into 50 mm X 30 mm X 0.5 mm each and In Fig.1 the inhibition efficiencies of low carbon steel a hole of 4mm diameter was drilled at the center top immersed in 0.085M HCl with sodium tungstate are of each coupon to facilitate its suspension. The presented. It must be emphasized that the corrosion samples were mechanically polished using emery rate is inversely related to the percent inhibition papers with 240, 320, 400 and 600 grits. This was to efficiencies (%IE). It is evident that as the amount of eliminate scaling, surface contaminant and oxide film the inhibitor increases the inhibition efficiencies on the surface of the metal. Subsequently, the sample decrease that is the concentration of the inhibitor is surfaces were degreased by swabbing with acetone. independently proportional to the inhibition The degreased surface is then air- dried. efficiencies. Interestingly at 144 hours of exposure The dimension of each coupon sample was the percent inhibition efficiencies are the same with a carefully taken and recorded in order to take care of value of about 57%IE. It is noted that before the minutest difference in the exposed surface area. The period the efficiencies increases but immediately after coupons were afterwards rinsed under tap water, the performance was decreasing after 144 hours. This dried, weighed on digital mettler balance and then may be attributed to the dissolution of the barrier immersed in the 0.085 M HCl already prepared. formed by the inhibitor. The concentration of the sodium tungstate at 50 ppm showed the highest IE Immersion tests during fourteen days using which is about 45% after 288 hours of exposure and gravimetric technique were carried out according to about 40% and 35% respectively for 100 ppm and ASTM G 1-90, by complete immersion of the seven 200 ppm. samples in the media using a large labeled plastic bowl and suspending them on sample rack. A coupon was removed from each solution medium at intervals of 48 hours, held under a stream of tap water and the surface scrubbed with a rubber stopper to remove the corrosion product. This was followed by cleaning with acetone to halt the minute electrochemical reactions and form a barrier against atmospheric corrosion. The coupon was finally air-dried and re- weighed. 2 Emirates Journal for Engineering Research, Vol. 17, No.2, 2012 Co-inhibition characteristics of sodium tungstate with sodium nitrate on low carbon steel in 0.085M HCl. 60 50 40 30 20 100ppm Na2WO4 50ppm Na2WO4 Percent Inhibition Efficiencies (%IE) 10 150ppm Na2WO4 0 0 100 200 300 400 Time of exposure (hrs) Figure 1. Percent Inhibition Efficiencies of low carbon steel immersed in 0.085 M hydrochloric acid inhibited with sodium tungstate relationship between the concentration and the While Fig. 2 shows the inhibition efficiencies of efficiency. Hence samples with 150 ppm have the mild steel as immersed in the medium and inhibited highest efficiencies and the lowest occurred at 50 with sodium nitrate. It is observed that the ppm. The efficiency also increases with the period of efficiencies increase as the concentration of the exposure but the corrosion rate is almost the same at inhibitor which shows that there is a linear 50ppm NaNO3 100ppm NaNO3 90 80 150ppm NaNO3 70 200ppm NaNO3 60 50 40 30 Percent Inhibition efficiencies (%IE) 20 10 0 0 100 200 300 400 Time of exposure (hrs) Figure 2. Percent Inhibition Efficiencies of low carbon steel immersed in 0.085 M hydrochloric acid inhibited with sodium nitrate.
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