Study On The Bactericidal Mechanism And Corrosion Inhibition Behavior Of D-Amino Acid Enhanced Germicidal Corrosion Inhibitor

Sulfate-reducing bacteria（SRB）are anaerobic bacteria that dominate microbial corrosion（MIC）of metallic materials,and the annual economic loss from microbial corrosion is as high as 2.5～4 trillion USD worldwide.SRB biofilms secrete extracellular polymers（EPS）with the main components of proteins,DNA,polysaccharides and lipids,which can provide energy for bacterial growth,and the top biofilm restricts the carbon source consumption,resulting in the corrosion-prone Fe as the only electron donor to accelerate metal corrosion,so the decomposition and destruction of biofilm has become the core problem of attacking microbial corrosion.Therefore,in this paper,the corrosion behavior of 45#steel,N80 and P110 steel in SRB-containing environmental media under different surface states and temperatures was investigated by means of molecular biology,sterilization process evaluation,electrochemical testing and surface analysis,using a combination of quaternary phosphate salts,D-tyrosine,enhanced penetrant,antimicrobial peptide and chitosan corrosion inhibitor,to elucidate the effect of D-tyrosine decomposition in the biocide to inhibit biofilm.amino acid decomposition inhibits the role and mechanism of biofilm;screening out the best concentration ratio of biocides and corrosion inhibitors;revealing the multi-factor coupling mechanism between D-tyrosine,biocides and corrosion inhibitors to achieve a new biocidal and corrosion inhibiting treatment technology and method of biofilm desorption.The results of the study are as follows:（1）After 14d of corrosion in the SRB environment,the corrosion severity of the three steels in descending order was N80（0.0355 mm/a）>45#（0.02831 mm/a）>P110（0.02196mm/a）,all of which were moderately corrosive;and after adding the new D-tyrosine enhanced fungicide,the corrosion severity of the three steels in descending order was P110（0.01803mm/a）>45#（0.01596 mm/a）>N80（0.01496 mm/a）,all light corrosion,indicating that the new fungicide has a good sterilization effect,in which the corrosion rate of N80 steel is the largest reduction,the best inhibitory effect,a decline of 57.9%.（2）Chitosan corrosion inhibitor can effectively inhibit the corrosion behavior of N80 steel in SRB environment,with the increase of corrosion inhibitor concentration,the corrosion degree size in order of no corrosion inhibitor>0.1 g/L>0.2 g/L>0.4 g/L>0.3 g/L,and all are moderate corrosion,corrosion inhibition rate reached the maximum（70%）when the concentration of chitosan is 0.3 g/L,indicating that chitosan has excellent corrosion inhibition effect on N80 steel in SRB environment,and when the chitosan concentration reached a certain value,the corrosion inhibition rate remained basically the same.（3）In the SRB environment,with the increase in surface finish,the corrosion degree of N80 steel in different surface states is significantly reduced,are moderate corrosion,the corrosion rate of the decline of up to 52.4%,indicating that the surface corrosion of carbon steel is significantly reduced;different temperatures of N80 steel corrosion degree ranked 37℃>50℃>20℃,corrosion degree from moderate corrosion（37℃,50℃under）to Light corrosion（20℃under）,indicating that N80 steel in the SRB growth of the best temperature（37℃）under the most serious degree of corrosion.After the addition of different biocides and corrosion inhibitors,the corrosion degree of N80 steel surface were significantly reduced to light corrosion,and the biocide and corrosion inhibitor of different biocides and corrosion inhibitors were ranked as:D-tyrosine enhanced biocide+corrosion inhibitor combination>D-tyrosine enhanced biocide>chitosan corrosion inhibitor.（4）Ca²⁺in SRB environment is easy to react with CO₃^2-to generate Ca CO₃ precipitation,which will adsorb on the product film together with other products,producing uneven corrosion product film and causing local corrosion.Film coverage area and the substrate surface will form a micro-electric coupling effect,intensifying corrosion.At the same time,the carbon source and fat source to provide energy for SRB,and SRB will be SO₄^2-as the electron acceptor,relying on the carbon source to provide energy to reduce SO₄^2-into H₂S gas,the resulting sulfide,phosphide will accelerate corrosion.The weak acid environment caused by fatty acids when concentrated under the microbial corrosion deposit will also aggravate the substrate corrosion.（5）The D-tyrosine in the biocide as a signal molecule can be combined with SRB proteins,resulting in a large area of bacterial biofilm,while the lipophilic group in the biocide enters the bacterial cell membrane and destroys the cell wall,thus modifying the bacterial protein,and the oxygen concentration difference environment in solution is destroyed,slowing down metal corrosion.meanwhile,chitosan can combine with Fe²⁺on the metal surface to form an outer protective film.The anions in the solution medium are easily adsorbed by positively charged cations on the metal surface,resulting in an excessive negative charge on the metal surface,at which time the chitosan protonated amino groups will be electrostatically attracted to the negative charge on the metal surface,strengthening the adsorption effect of the protective film and reducing the degree of metal corrosion.