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Monday, 10 August 2020
Raw materials & technologies, Applications, Industrial coatings

Sol-gel perfectly substitute chromate conversion coatings on Al-substrates

Monday, 17 December 2012

To substitute chromate conversion coatings always lead to a laughing and a crying eye. Chromate coatings were simple and easy to apply and furthermore highly efficient and permanent. Just the environmental impact was bad enough to gain a smile substituting it. A recent research found one more way to dry the tears because of performance.

Sol-gels are an alternative for chromate conversion coatings

Source: Huber, München

Sol-gels are an alternative for chromate conversion coatings

Source: Huber, München

Akbar Hojjati Najafabadi and his colleagues from Malek Ashtar University of Technology, Iran deposited the coatings derived from hydrolysis and condensation of polymerizable silane precursors tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) on AA5083 substrates by a dip coating technique.

Best adhesion property was obtained with higher inorganic and hydrolysis water content

Adhesive strength of sol–gel coatings to the substrate was evaluated using pull off and tape tests. Bending, impact resistance and pencil scratch tests were employed to characterize mechanical properties of different coatings. The surface morphology and chemical composition of the hybrid films were studied by atomic force microscopy (AFM) and Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR/FTIR), respectively. Optical microscopy (OM) and field emission scanning electron microscopy (FE-SEM) were used to investigate structure of the coatings.

The sol–gel films with optimum conditions show excellent mechanical properties

The results show an increase of the hydrolysis water content at a constant organic/inorganic molar ratio and other variable parameters increases adhesion of coatings to substrate, and optimum coatings exhibit excellent mechanical properties as well as adhesive to the substrate.

Taguchi method has been found to be an effective tool in optimization of parameters

Statistical design of experimental (DoE) methodology based on Taguchi orthogonal design has been used to study and optimize compositional and process parameters using multifactor analysis of variance (ANOVA) analysis method and the adhesion strength of coatings to the substrate as per pull off test has been used as a response.

Read more in the next Progress in Organic Coatings Journal,Volume 76, Issue 1, January 2013, Pages 293–301

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