Synthesis And Corrosion Inhibition Of Di-Schiff Bases Corrosion Inhibitors For Acidification

Eight bis-Schiff bases as acidizing corrosion inhibitor were prepared by condensation of aromatic aldehydes（cinnamic aldehyde,benzaldehyde,para-dimethylaminobenzaldehyde and salicyic aldehyde）with ethyenediamine or hydrazine hydrate,which are 1,1’-dicinnamylidene-hydrazine（DH-C）,1,1’-dibenzylidene-hydrazine（DH-B）,1,1’-bis（4-dimethylaminobenzylidene）-hydrazine（DH-D）,1,1’-disalicylidene-hydrazine（DH-S）,N,N’-dicinnamylidene-1,2-diaminoethane（NE-C）,N,N’-dibenzylidene-1,2-diaminoethane（NE-B）,N,N’-disalicylidene-1,2-diamino-ethane（NE-D）,N,N’-bis（4-dimethylamino benzylidene）-1,2-diaminoethane（NE-S）.The structures were characterized by elementary analysis,Fourier transform infrared（FI-RT）and nuclear magnetic resonance spectroscopy（NMR）.The effects of concentration of the bis-Schiff bases,corrosive temperature and concentration of hydrochloric acid on the corrosion inhibition were researched by static weight loss measurement.The results indicated that the corrosion inhibition were ordered（increasing corrosion inhibition）as DH-C>DH-B>DH-D>DH-S for bis-Schiff bases of hydrazine hydrate and NE-C>NE-B>NE-D>NE-S for bis-Schiff bases of ethylenediamine.The corrosion inhibition of bis-Schiff bases of hydrazine hydrate was more effective than that of bis-Schiff bases of ethylenediamine.For all the bis-Schiff bases corrosion inhibitors,the inhibition efficiency increase with the increase of concentration of the inhibitors and decrease with the increase of corrosive temperature or the concentration of hydrochloric acid.The relationship between the structure and the corrosion inhibition was discussed.The results from electrochemical methods showed that bis-Schiff bases of hydrazine hydrate were mixed-type inhibitors,affecting both anodic and cathodic sites.Adsorption isotherm analysis showed that the adsorption behavior of bis-Schiff bases of hydrazine hydrate obeyed the Langmuir adsorption isotherm.The free energy of adsorption(?⁰₍（6（9））of DH-C,DH-B,DH-D and DH-S were﹣50.61 kJ·mol^-1,﹣31.10kJ·mol^-1,﹣29.58 kJ·mol^-11 and﹣26.05 kJ·mol^-1,respectively,which indicated that the adsorption process was chemisorption for DH-C and physisorption/chemisorption for DH-B,DH-D and DH-S.SEM results showed that the corrosion traces on steel surface in the inhibited hydrochloric acid significantly reduced,which indicated the forming of protective film on N80 surface.The corrosion inhibition of DH-C meets the first grade specification in SY/T5405-1996 when the congcentration of DH-C is1.5×10^-2 mol·L^-1（0.36 wt.%）in 15%hydrochloric acid.