This study presents a process for preparation of cellulose−lignin barrier coatings for hot-dip galvanized (HDG) steel by aqueous electrophoretic deposition. Initially, a solution of softwood kraft lignin and diethylene glycol monobutyl ether was used to prepare an aqueous dispersion of colloidal lignin particles (CLPs) via solvent exchange. Analysis of the dispersion showed that it comprised submicron particles (D = 146 nm) with spherical morphologies and colloidal stability (ζ-potential = −40 mV). Following successful formation, the CLP dispersion was mixed with a suspension of TEMPO-oxidized cellulose nanofibers (TOCN, 1 and 2 g•L −1 ) at a fixed volumetric ratio (1:1, TOCN− CLPs), and biopolymers were deposited onto HDG steel surfaces at different potentials (0.5 and 3 V). The effects of these variables on coating formation, dry adhesion, and electrochemical properties (3.5% NaCl) were investigated. The scanning electron microscopy results showed that coalescence of CLPs occurs during the drying of composite coatings, resulting in formation of a barrier layer on HDG steel. The scanning vibrating electrode technique results demonstrated that the TOCN−CLP layers reduced the penetration of the electrolyte (3.5% NaCl) to the metal−coating interface for at least 48 h of immersion, with a more prolonged barrier performance for 3 V-deposited coatings. Additional electrochemical impedance spectroscopy studies showed that all four coatings provided increased levels of charge transfer resistance (R ct )compared to bare HDG steelalthough coatings deposited at a higher potential (3 V) and a higher TOCN concentration provided the maximum charge transfer resistance after 15 days of immersion (13.7 cf. 0.2 kΩ•cm 2 for HDG steel). Overall, these results highlight the potential of TOCN−CLP biopolymeric composites as a basis for sustainable corrosion protection coatings.
Corrosion inhibitive pigments, based on the cations Ce 4+ and Cr 3+ exchanged into smart release resins, are dispersed in a polyvinyl butyral (PVB) model coating and applied to a hot dip galvanised steel (HDG) substrate. An investigation is made into the influence of different pigment volume fractions (ø pig) of Ce(IV) and Cr(III) based inhibitors, used both in isolation and combination, on the kinetics and mechanism of corrosion driven cathodic coating delamination. The rate of coating delamination is obtained using scanning Kelvin probe (SKP) potentiometry and time lapse photography, and the efficiency with which each inhibitor combination is able to resist cathodic coating delamination is calculated. Isobolograms, commonly utilized within the field of drug interaction, are presented as an effective method for characterising corrosion inhibitor interactions. In some cases, the sum of the efficiencies calculated for Ce(IV) and Cr(III) based pigments is shown to be greater than the sum of their individual efficiencies. It is proposed that Ce 4+ , released upon electrolyte exposure, is able to oxidize the Cr 3+ species resulting in the formation of transient CrO 4 −2 .
SUMMARY
A method is described for high contrast staining of Araldite embedded biological material that has a high water content due to erroneous dehydration.
The role of smart-release corrosion inhibitive pigments in preventing cathodic delamination of organically coated hot-dip galvanised steel is investigated. The pigments consisted of hydrotalcite exchanged with a range of inorganic and organic anionic species and were dispersed in a model PVB coating. A scanning Kelvin probe technique was used to determine cathodic delamination rates, and the inhibition efficiencies obtained for inorganic ions increased in the order CO32- MoO42- NO3- VO43- WO42- PO43- CrO42-. The inhibition efficiencies for organic-based pigments increased in the order triazole <phenylphosphonate <trans-cinnamate <benzoate <salicylate <benzotriazole. The inhibition efficiency afforded by the best performing organic inhibitor, benzotriazole (BTA), rivalled that of HT containing stored chromate anions. Findings are consistent with HT-BTA acting to sequester anions from the underfilm electrolyte, releasing BTA- which subsequently strongly adsorbs on the underfilm metal surface but can also form an insoluble Zn-BTA precipitate at the coating-defect boundary.
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