Application of Niobium Enriched Ormosils as Thermally Stable Coatings for Aerospace Aluminium Coatings

The aim of this experimental research is to study the ability of niobium rich sol-gel coatings to withstand thermal stress, while remaining impermeable to corrosive agents for the protection of aerospace alloys. The coating material is developed via polymeric sol-gel synthesis employing 3-(trimethoxysilyl)propylmethacrylate (MAPTMS) and niobium ethoxide precursors as a source of silicon and niobium, respectively. The beneficial effect of niobium inclusion within coating was characterised spectroscopically, calorimetrically and electrochemically. The thermal cycling effects of the coating were studied using microscopic and accelerated test methods. Electrochemical tests showed that corrosion current of the material was 2 orders lower in magnitude than MAPTMS coating. The neutral salt spray test results of thermal stressed samples prove that inclusion of niobium nanoparticles within the silane matrix considerably improves the corrosion resistance performances in salt spray test resulting in better ability to resist thermal shock failure when compared to the MAPTMS coating alone

Protective Properties of Functionalised Tetrazine on an Aerospace Aluminium Alloy (AA 2024-T3)

Environmental health concerns over conventional chromium based surface treatments on aluminium substrates are well known. Current research efforts have concentrated on developing protective technologies for multiple applications. Such properties would enable manufacturers to address both corrosion and bacterial threats in areas such as fuel tanks and delivery systems. The present study explores the anticorrosion properties of 1,2-dihydro 1, 2, 4, 5 tetrazine-3, 6-dicarboxylic acid (H2DCTZ) on a copper rich aerospace aluminium alloy (AA 2024-T3). Furthermore the antimicrobial activity of the tetrazine is evaluated against Gram-positive and Gram-negative bacteria, both capable of inducing corrosion. The protective action of the tetrazine was investigated at different concentrations in a chloride ion rich environment (3.5% (w/v) NaCl) utilising electrochemical impedance spectroscopy (EIS). Results over a 72 h period proved that an optimum concentration was 500 ppm. FTIR and SEM elemental mapping of the surface confirmed the nitrogen rich tetrazine affinity for the copper rich intermetallic sites, through coordinate bonds, which delayed corrosion onset and reduced pit formation. Moderate antibacterial tetrazine activity was observed against Escherichia coli and 100% efficacy against Staphylococcus aureus at 250 ppm was achieved. The damage of the bacterial cell envelope at the critical concentrations (250 ppm) is proposed as a possible mechanism for antibacterial action

Corrosion Protection of AA 2024-T3 Aluminium Alloys Using 3, 4-Diaminobenzoic Acid Chelated Zirconium-Silane Hybrid Sol-Gels

Organic-inorganic polymers formed by hydrolysis/condensation reactions of alkoxide precursors, such as organically modified silanes (Ormosils) have found applications as electronic, optical and protective coatings. Such coatings possess important characteristics such as chemical stability, physical strength and scratch resistance. Further performance improvement is achieved through the incorporation of zirconium and titanium based nanoparticles, also formed through the sol-gel process. However due to the inherent difference in the reactivity of the precursors, the hydrolysis of each precursor must be carried out separately before being combined for final condensation. Zirconium precursors are commonly chelated using acetic acid or acetyl acetonate prior to hydrolysis, to lower the hydrolysis rate. In this body of work, 3,4-diaminobenzoic acid (DABA) and acetyl acetonate (acac) were compared as chelating ligands for controlling the hydrolysis reactions of zirconium n-propoxide to form nanoparticles within a silane sol matrix. The sols were applied as coatings on aerospace grade aluminium alloy AA 2024-T3 and characterised spectroscopically, electrochemically and calorimetrically. The results correlated with neutral salt spray evaluations which indicate that the novel use of DABA as a chelating ligand significantly improved the sol-gel protective performance over the traditional acac equivalent. The data indicates the anticorrosion properties of the nitrogen rich chelate have a key role in protecting the alloy

An Investigation of the Biochemical Properties Of Tetrazines as Potential Coating Additives

1,2,4,5-Tetrazine and its 3,6-disubstituted derivatives are currently used for a range of industrial and medical applications as they exhibit particular coordination chemistries, characterized by electron and charge transfer phenomena. The aim of the present work is to describe the synthesis of two tetrazine derivatives, namely 3,6-dihydrazino-1,2,4,5-tetrazine (DHDTZ) and 1,2,4,5-tetrazine dicarboxylic acid (DCTZ), and determine their antibacterial, antioxidant and anticorrosion characteristics as additives in a sol-gel coating on SS316L steel. The structure of the tetrazines was confirmed by NMR and FTIR while the surface morphology of bacterial cells in their presence was observed by AFM. Their ability to inhibit corrosion on 316L stainless steel was electrochemically determined using a potentiodynamic scanning (PDS) technique. The corrosion inhibition results showed that the acidic DCTZ provided the best corrosion protection. The concentration-dependent antioxidant capacity of the tetrazines was confirmed by both DPPH radical scavenging activity and FRAP assays, showing higher activity for DHDTZ than DCTZ. Furthermore, a DHDTZ doped sol-gel solution was prepared and curing parameter (temperature and time) was optimised for coating on microtitre wells and stainless steel panel. The antibacterial activity of the coated surfaces against P. aeruginosa ATCC 27853 and the biofilm forming bacteria S. epidermidis CSF 41498 was determined. DHDTZ showed significantly higher antibacterial activities with MIC as low as 31 ppm compared to 250ppm for DCTZ