In the nineties, the first generation of organic thin film coatings for corrosion protection of zinc-coated thin sheet steel have been introduced. The coating typically consists of a suspension of small zinc particles, embedded in a polymer matrix. In the scope of quality control, the characterisation of the resulting layer structure is of great interest, comprising not only a constant layer thickness and a local homogeneity of the coating, but also the depth distribution of the particles within the layer. Especially the latter parameter does have a direct influence on the spot weldability of the steel sheets. The present work shows, how photothermal methods like modulated infrared radiometry and photoacoustics can be used for a successful depth profiling of the thin film coatings. The sample surface is periodically heated using an intensitymodulated laser beam, and a thermal wave is induced in the layer system. By variation of the modulation frequency of the laser beam, the thermal diffusion length and, as a consequence, the penetration depth of the thermal wave can be adjusted. By a suitable evaluation of the amplitude and phase lag signals as a function of the modulation frequency, accurate depth profiling has been realized which can be used for a very reliable prediction of the welding properties of the product. In the first investigations, artificial samples with well defined extreme distributions of the particles have been analyzed, and in a second step, an evaluation strategy has been developed for real production samples.


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    Title :

    Characterisation of organic thin film coatings on automobile steel sheets by photothermal methods


    Additional title:

    Charakterisierung organischer Dünnschichten auf Auto-Stahlblechen mittels photothermischer Verfahren


    Contributors:
    Orth, T. (author) / Flügge, W. (author) / Gibkes, J. (author)


    Publication date :

    2006


    Size :

    14 Seiten, 9 Bilder, 1 Tabelle, 5 Quellen



    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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