The preparation of low-temperature fusion enamel coatings for corrosion control using local raw materials

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An attempt has been made in this study to formulate materials for low-temperature fusion enamel coating from local raw materials and borax that can be applied directly onto steel substrate for corrosion control. Mfensi and Afari clays, and the Mouri feldspar were mixed in various proportions with borax to form various batches. The batches were mixed with water to form slips which were used to coat already prepared steel surfaces and were allowed to dry in the open. The coated steel plates were again dried in the oven and fired at temperatures of 800oC, 850oC and 900oC to mature. The coatings were observed and also physico-chemical tests were conducted to evaluate some properties of the coatings. The coatings matured and adhered very well to the substrate at 850oC and 900oC and showed good hardness and thermal shock resistance as well as good corrosion resistance in brine and 10% nitric acid. The coatings hardness at the above temperatures were between 7 and 8 on the Mohs scale and 70-90 on the BHN(1/60). The coatings thickness at these temperatures was between 0.42mm and 0.5mm. They were able to resist fifteen cycles of heating and quenching from 400oC. The coatings prepared with the Afari clay with its higher content of iron oxide showed better results in terms of hardness and thermal shock resistance than those prepared with the Mfensi clay. However the coatings fired at 800oC did not fuse properly and hence did not show good adhesion to the substrate. They showed a hardness of 4-6 on the Mohs scale and failed on the Brinnel Hardness Tester.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Science, 2007