Inhibition Of Corrosion Of Zinc By Two Schiff Basecompounds: L-Phenyl-2,3-Dimethyl-4- (Benzylamino) Pyrazole-5-One And (2z)-2- Benzylidenehydrazinecarbothioamide In Hc1 Medium:- Eberendu, Kizito O

ABSTRACT

The inhibition efficiencies of two Schiff bases derived from benzaldehyde namely; l-phenyl-2, 3- dimethyl(benzylamino)pyrazole-5-one (PD(B)PO and (2z)-2-benzylidenehydrazinecarbothioamide (2Z)-2-BHC) and their mechanism of adsorption on zinc metal surface in HC1 medium have been studied. Studies were carried out by weight loss and hydrogen evolution techniques and the morphology of the surface characterized by infrared spectroscopic and scanning electron microscopic analyses. Results show that Schiff bases derived from benzaldehyde are highly efficient inhibitors for the corrosion of zinc in HC1 acid environment. Experimental data proved that the lowest corrosion rates were observed for the higher concentrations ofinhibitor solutions. PD(B)PO showed better inhibition efficiency than (2Z)-2 BHC. In the case of PD(B)PO, an efficiency of —33.33% was achieved for a comparatively lower concentration of 0.001M and a maximum efficiency of 91.65% at concentration of 0.007 M while in the case of(2Z)-2 BHC, 19.99% efficiency was attained at 0.001 M and a maximum efficiency of45.00% at 0.0IM. The mechanisms of inhibition of corrosion by the two Schiff bases compounds were found to be through the adsorption oftheir molecules onto the zinc metal surface. They built up protective hydrophilic films and adsorbed molecules on the metal surface, which provided a barrier to the dissolution ofthe metal into HC1 acid electrolyte. In the thermodynamic studies, AGads values (-71.14 and -66.70 KJ/mol for the PD(B)PO and (2Z)-2-BHC respectively) obtained were more negative than -20 kjmoT1 indicating that zinc corrosion inhibition using 0.007 M solutions of PD(B)PO and (2Z)-2-BHC Schiff base inhibitors follow the physiosorption mechanism and further revealed the spontaneous nature of the process; The AS values obtained (148.12 and 234.76, J K1 mol-1, for the Schiff base compounds respectively) also indicate that the processes were spontaneous; AH values were negative for the inhibited systems indicating exothermic reactions while Ea values obtained (20.37 and 27.52 kJmoF1 for the two Schiff base inhibitors respectively), are lower than 40 kJmoT1 indicating that the processes follow physiosorption mechanisms as well. Experimental data fitted well into the Freundlich adsorption isotherms with R2 values of 0.917 and 0.892 for the two Schiff base inhibitors respectively.