Abstract:

The inhibition impact of 5-((thiophen-2-ylmethylene)amino)-2-mercapto-1,3,4-thiadiazole (TMT) on mild steel corrosion in 1.0 M HCl have been Investigated. The weight loss and Scanning electron microscopy techniques were utilized in order to estimate inhibition efficiency of TMT as immersion time function. TMT shows an excellent inhibition impact in corrosive solution on mild steel. The excellent efficiency was due to the active sites blocking which were done through adsorption of MTM molecules on the steel surface. The inhibition efficiency decreases with increasing temperature.

 

 

 

 

INTRODUCTION:

Corrosion is a considerable economic issue for the industrial country. Corrosion problem impact all segments of production, processing, and transportation of the products. A $276 billion, corresponding to 3.1% of the US total local production was the yearly evaluated direct corrosion cost in the country [1]. Processing, utilizing suitable, corrosion inhibitors was the main solution in cooperation with corrosion issues triggered by exceedingly varying treatment, conditions and concentrations of water salts at various stages of the gas and/or oil production operation. Regarding to corrosion inhibition action mechanism or composition, these corrosion inhibitors from natural or synthetic origin could be categorized as barrier film, neutralizing, scavenging and other various inhibitors [2].

 

Inhibitors from organic or natural origin that action by adsorption on the surface of the metal may block the effective site through substituting of H2O molecule and forms a film as solid barrier to reduction corrosion [3-10]. This investigations represent synthesis and studied as corrosion inhibitor for mild steel in corrosive solution of inhibitor namely 5-((thiophen-2-ylmethylene)amino)-2-mercapto-1,3,4-thiadiazole (TMT).

 

EXPERIMENTAL:

Materials

NMR (Nuclear magnetic resonance) spectra have been recorded on a 600 MHz AVANCE spectrometer (Bruker, Billerica, MA, USA) with DMSO-d6 and TMS as solvent and internal reference respectively. The infrared spectra were performed on a 6700 FT-IR Spectrometer Thermo Scientific Nicolate (Thermo Fisher Scientific, Waltham, MA, USA). All reagents used in this investigation were obtained commercially from supplied by Sigma-Aldrich, Selangor, Malaysia and were utilized without further purification. In the Gravimetric experiments, Mild steel specimens which were purchased from Metal-Samples-Company” (St. Mary’s, PA, United States). Specimens composition percentages were: Iron, 99.21; Carbon, 0.21; Silicon, 0.38; Phosphorous, 0.09; S, 0.05; Manganese, 0.05; and Aluminum, 0.01. The specimens were cleaned and drying in vacuum desiccators and fully dried before experiments. The cleaning methodology has been done according to reference [30]. All experiments were done in aerated and non-stirred corrosive solution having TMT with various concentrations [11-25].

 

Corrosion Inhibitor

The Refluxing of equal molars of 5-amino-2-mercapto-1,3,4-thiadiazole and 2-thiophenaldehyde in 100 mL of ethanol for 10 h. After filtration the solvent was evaporated in vacuum and the residue crystallized from dichloromethane. Yield: 69%. M.p. 179 ^oC. Purity of TMT has been confirmed through thin layer chromatography technique. Plate’s diminutions were 0.20m by 0.10m which was silica gel recoated on aluminum 60F–254, with a approximately 0.5x10-3m thickness of stationary phase. Investigated solutions with five microliters have been applied on each plate. Plate placed in chromatographic tank that have the solvent system, ethyl acetate 25%; methanol 25% and acetone 50%. FT-IR; 2622.4 and 2549.2 (-S–H), 1629.4 cm^-1        (-C=N-); ¹H-NMR δ (ppm): 13.11 (s, 1H, -SH), 8.41 and 7.96 (d, 1H, -CH=N-). 13C NMR δ (ppm): 182.5, 161.8, 156.6, 142.1, 131.7, 128.2, 126.3 [26-43].

 

Gravimetric methodology

Efficiency for the investigated corrosion inhibitor could be calculated according to the weight of the mild steel as loss of metal substrate because of corrosion. Weight loss methodologies have been performed employing specimen with the dimension of 0.02m x 0.05m x 0.001m. The specimen was weighting accurately and immersed in corrosive solution having 1.0 M of hydrochloric acid with and without of TMT at various concentrations. After 24 h exposure, the specimens were taken out rinsed thoroughly with distilled water, dried and weighted accurately. Experiments were done triplicate in and the weight loss mean value have been reported. The corrosion rate (C_R) and inhibition efficiency (E %) were calculated using equations 1 and 2.

           w₂ - w₁

C_R=------------                                         1

               st                                                   

 

Where w₂ and w₁ were the specimen weights before and after respectively, S was the specimen area in cm² and t is the exposure time (h).

                  Wcorr - Wcorr(inh)

E %  = --------------------------  X 100            2

                            Wcorr

 

Wcorr and Wcorr(inh) were the values of corrosion weight losses in untreated and treated solutions, respectively. The variation of the CR with the temperatures (303– 343 K) have been investigated for 6 h as immersion time in presence and absence of highest concentration.

 

RESULTS AND DISCUSSION:

Synthesis

To synthesize 5-amino-2-mercapto-1,3,4-thiadiazole and 2-thiophenaldehyde as a corrosion inhibitor, sequence of the reaction was summarized in Figure 1 as succeed, starting from commercially obtainable or synthesize 5-amino-2-mercapto-1,3,4-thiadiazole. The synthesis have been performed through refluxing of 5-amino-2-mercapto-1,3,4-thiadiazole.with 2-thiophenaldehyde in ethanol. The molecular weight of the 5-((thiophen-2-ylmethylene) amino)-2-mercapto-1,3,4-thiadiazole (TMT) as corrosion inhibitor is 226, that was calculated regarding to molecular formula C7H5N3. TMT dissolved in, dichloromethane, dimethylsulfoxide and dimethylformamide in addition to other polar solvents. TMT as organic compound shows FT-IR spectrum absorption bands at 2622.4 and 2549.2 for mercapto group and azomethine stretching at 1629.4 cm⁻¹. The 1H-NMR spectrum exhibits a singlet at δ13.11 ppm due to the mercapto proton in addition to δ8.41 and 7.96 as doublet for one proton regarding to  azomethine group. From 13C-NMR, a band appears at 182.5, ppm due to the Carbon of thio group, in addition to bands at 161.8 and 156.6 ppm are from carbon atoms in the azomethine groups.

 

Figure 1. Chemical synthesis of TMT.

 

Effectiveness of concentration

The  effectiveness of increasing of TMT in etching solution on the corrosion of mild steel have been investigated according to weight loss technique for a times (1, 2, 3, 4, 5, 10 and 24 h) at 303 K. The corrosion rate values in addition to inhibition efficiencies in absence and presence of TMT have been showed in Figures 2 and 3.

 

Fig. 2: Corrosion rate vs time on corrosion rate at 303 K with TMT concentrations.

 

 

Corrosion rates for the inhibitor TMT have been noticeable diminished in parallel with enhancing of inhibition efficiency depending on increasing TMT concentration. The protection of mild steel depends on increasing of TMT concentration and this prosperity of inhibition efficiency.

 

Fig. 3: Inhibition efficiency vs time on corrosion rate at 303 K with TMT concentrations.

 

 

Effectiveness of temperature

The inhibition efficiency of various concentrations of TMT in corrosive solution  for mild steel at deffernt temperatures (303, 313, 323 and 333 K) indicat that IE decreased with higher temperature as shown in Figure 4.

 

 

Fig. 4: Inhibition efficiency vs TMT concentrations at various temperatures for 24h.

 

Scanning Electron Microscopy (SEM) Morphologies

Surface of mild steel have been investigated by Scanning electron microscopy in corrosive in presence and absence the studied inhibitor for 4 h at 30 °C, as displayed in Figure 5. Surface of mild steel without the studied inhibitor became damaged because of the decay of iron due to hydrochloric acid. In addition, a barrier film has been shown on the Surface of mild steel when inhibitor was added to the media.

 

Fig. 5: Scanning electron microscopy images of Surface of mild steel after immersion in a corrosive solution without and with inhibitor at 30 °C.

 

CONCLUSION:

Mild steel corrosion inhibitor has been synthesized, with structure fully characterization by spectroscopical methods. Corrosion inhibitor has the ability to inhibit mild steel corrosion in corrosive solution. Inhibitor, namely 5-((thiophen-2-ylmethylene)amino)-2-mercapto-1,3,4-thiadiazole showed perfect corrosion inhibition performance, and maximum inhibition efficiency of 92% was observed for synthesized inhibitor, at an inhibitor concentration of 5 mM. The inhibition efficiency increased with increasing inhibitor concentration, whereas it decreased with increasing temperature. The inhibition efficiencies were measured by the weight loss method, and scanning electron microscopy was used to investigate the inhibition mechanism.

 

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Received on 25.04.2017       Modified on 09.05.2017

Accepted on 25.05.2017      ©A&V Publications All right reserved