Fluorescence emission sensing in coatings: Method for defects detection in coated surfaces of structural elements

We suggest a method for detecting defects in coated surfaces by utilizing fluorescence emission. Fluorescent material was added to the coating layer prior to the curing stage. The fluorescent material used was characterized experimentally to measure absorption coefficient and observe the absorption and emission wavelength range. The tests were then made for fluorescence emission in coated layers prepared either by draw down blade or sprayed with an airless spray gun. The concentration of fluorescent material in a coated layer is the main parameter studied. Fluorescence emission is suggested as a probe to enhance the visual inspection of coated layers because it has a distinctive emission signal. It was found that for a homogeneous distribution of fluorescent material within a layer of coating, the emission increased up to a certain concentration limit. This limit was found to be around 0.5 wt%; further increase of fluorescent material leads to emission signal decrease due to self absorption phenomenon.