Influence of addition of hard particles on the mechanical and chemical behavior of vitreous enamel

The vitreous enamel coatings present very interesting properties for several industrial applications due to the glassy nature of the matter. Their chemical resistance and corrosion protection properties result very high due to the glassy nature of deposits. A good wear behavior is also requested in some applications. The use of composite layer obtained by the addition of hard particles to enamel could be a possible solution to increase the deposits hardness. In literature, there are some work about the chemical nature of the added particles, but the influence of the dimension and quantity of these particles are not well studied. The aim of this work is the study of composite enamel layers deposited on low carbon steel substrate with addition of Al2O3 particles characterized by macro and micro dimensions with different concentration (5, 10 and 20 wt.%). After the microstructure characterization, the abrasion resistance behavior is evaluated by Taber Test following ASTM C501 for 1500 cycles. Mass loss, gloss and roughness changes are collected. The protection properties change is evaluated by Electrochemical Impedance Spectroscopy measurements. The addition of micro dimension particles produces the best behavior. On the contrary, the presence of macro dimension particles reduces the abrasion resistance, probably caused by the increase of porosity level during firing treatment. Finally, the corrosion protection properties are evaluated by Kesternich test (aggressive fog with the presence of SO2), simulating an industrial environment. In this case the presence of the micro- particles shows a limited resistance. Probably the presence of the particles produces an increase of surface roughness and a presence of higher quantity of particles in surface, which favor the start of enamel degradation with a loss of protection properties. Increasing the quantity of particles, a reduction of chemical resistance is observed.