Luminescence studies of the penetration of diffusants into epoxy coatings

• V.A. Shchelkov and A.B. Il’in

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: Diffusion studies on the penetration of phosphoric acid solutions into modified amine-cured epoxies with stoichiometric and non-stoichiometric curing were conducted over an exposure period of more than one year. Using local X-ray spectral and luminescence analysis, the penetration depths were determined and the concentration profiles of the diffusion penetration of a 60% acid solution at +50°C were built. The studies confirmed that the distribution profile in the diffusion zone has a two-step shape, with no smooth Fickian precursor before the sharp step front of acid penetration, and the kinetics of penetration and the increase in sample dimensions ΔL for non-stoichiometric epoxies at relative depths of 2X/L = 0.44–0.83 are nonlinear in the coordinates X ~ √t and X ~ t during long-term exposures. The combination of X-ray and optical fluorescence observation methods makes it possible to evaluate the emergence of features of the diffusion behavior of the phosphoric acid/amine epoxide system under the effect of internal stresses arising in the polymer during intense swelling (ΔL > 10%).

Keywords: epoxy coatings, internal stresses, phosphoric acid, concentration profile, diffusion model, hydrate number, fluorescence spectrum, phosphorescence time

Int. J. Corros. Scale Inhib., 2025, 14, no. 4, 2111-2132
doi: 10.17675/2305-6894-2025-14-4-20

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