Particle Characterisation and Depletion of Li2CO3 Inhibitor in a Polyurethane Coating

Abstract

The distribution and chemical composition of inorganic components of a corrosion-inhibiting primer based on polyurethane is determined using a range of characterisation techniques. The primer consists of a Li 2 CO 3 inhibitor phase, along with other inorganic phases including TiO 2 , BaSO 4 and Mg-(hydr)oxide. The characterisation techniques included particle induced X-ray and γ-ray emission spectroscopies (PIXE and PIGE, respectively) on a nuclear microprobe, as well as SEM/EDS hyperspectral mapping. Of the techniques used, only PIGE was able to directly map the Li distribution, although the distribution of Li 2 CO 3 particles could be inferred from SEM through using backscatter contrast and EDS. Characterisation was also performed on a primer coating that had undergone leaching in a neutral salt spray test for 500 h. Overall, it was found that Li 2 CO 3 leaching resulted in a uniform depletion zone near the surface, but also much deeper local depletion, which is thought to be due to the dissolution of clusters of Li 2 CO 3 particles that were connected to the external surface/electrolyte interface.

Li leaching from Lithium Carbonate-primer: An emerging perspective of transport pathway development

“…The Li (PIGE -red), Ti (PIXE -green) and Ba (PIXE -blue) distributions (Figure 7, right) show the distribution of the TiO 2 and BaSO 4 with respect to the Li 2 CO 3 , thus, both sides of Figure 7 capture all the major inorganic phases within the primer. As reported previously the TiO 2 particles appear to be unaltered by the exposure to NSS, thus its distribution can be used to estimate the primer thickness and by comparison to the other elemental distributions, can be used as a measure of their level of depletion [77]. In the PIXE there appears to be a "Ti-rich" outer layer in the 0h NSS, although it is most obvious in the 500h NSS sample.…”

“…The particle density in the region within the Bénard cells was a few orders or magnitude larger than the pore density indicating that there were many particles that did not dissolve due to perhaps low solubility or being covered by a thin layer of polyurethane. the BaSO 4 particles which also contain some Sr [77]. Smaller bright particles are either small BaSO 4 or TiO 2 particles.…”

“…From the combined EDS elemental colour mixing the BaSO 4 is a light olive-green, MgO is purple to blue (with the colour variation reflecting a changing composition), the Li 2 CO 3 is red because it only has an oxygen contribution since Li cannot be detected using standard EDS (and C is not selected). This identification has previously been established using a combination of PIXE and EDS [77]. The small TiO 2 particles are a salmon-pink colour.…”

Influence of TiO2 pigment particles on chromate ion transport in epoxy films

“…Pigmented resins were shaken on a Skandex ® paint shaker with solvent and Zirconox ® pearls (1.7-2.4 mm) to aid dispersion (the pearls were removed by filtration after mixing), then the hardener was added, and the samples were applied on the substrate and cured as described above. The pigment used was commercially available titanium dioxide TIOXIDE TR92 which contains Al and Zr additives, as reported elsewhere 37 .…”

Chromate replacement: what does the future hold?

“…87-89 This compact polycrystalline layer was able to impart significant corrosion resistance to Al alloys and pass a 168-hour salt spray test. 18 More recently, the utilization of Li salts loaded in a polyurethane organic coating as a replacement for SrCrO 4 primers became of interest, demonstrating effective corrosion inhibition after a neutral salt spray test (ASTM B-117) exposure as reported by Visser et al 90,91 Nowadays, the selfhealing and barrier properties of Li coatings are extensively documented [90][91][92][93] and are illustrated in Fig. 2a.…”