Chemical element variation in fungi-induced coating degradation using laser-induced breakdown spectroscopy combined with Raman spectroscopy, mass spectrometry, and multivariate analyses

Abstract

Traditional coating products for hindering fungal growth are environmentally hazardous. As regulations become increasingly stringent, environmentally benign coating materials are becoming more prevalent. However, due to these new, lower-toxicity coating materials, the growth of mold, mildew, and other fungus begins to cause detrimental effects on materials. Thus, it is important to develop an understanding of the fungal survival and material degradation mechanisms of such low-toxicity coating materials. This study explored the fungal degradation mechanisms of coating materials by developing an approach combining laser-induced breakdown spectroscopy (LIBS), Raman spectroscopy, and mass spectrometry (MS). The coating systems tested in this study were MIL-PRF-23377, Type I, with chromate (class C) and non-chromate (class N). Aspergillus niger (A. niger) was used for fungal growth. The LIBS results indicate a chemical change/exchange (Mg, Ca, Ti, C, and N) during fungi-induced corrosion. In the Raman study, chemical bond changes at Raman peaks 748, 812, 976, 1006, 1041, 1184, and 1610 cm⁻¹ were identified in the class N coatings after fungal growth. In the MS study, organic acids (oxalic and acetic) produced by fungi were detected. Based on the results, degradation mechanisms of non-Cr coating materials were proposed.