Study On New Al-coated Steel Enamel With Low Firing Temperature And Its Enamel Adherence Mechanism

It is well known that Al-coated steel enamels are new kinds of composite materials, which consist of Al-coated steel substrate and inorganic coat. The materials were first developed by Japanese in 1980s. However in China there have not been products yet. After consulting many domestic and oversee documents, and with the help of some advanced instruments, combined with thermodynamics and kinetics theories, we studied the new Al-coated steel enamel with low firing temperature and its enamel adherence mechanism.The Al-coated steel enamels were made successfully in our research. It was revealed by the study that the surface pretreatments of substrates would play important roles in the adherence strength between metal substrate and enamel. It showed that it had gotten better process by analysis of adherence strength of the materials in the paper.The materials must be fired at low temperature below the melting point of aluminum. The enamel composition, firing temperature, firing time, et al, would have effects on the enamel adherence strength. According to thermal and dynamics data calculated byΦFunction, it was revealed that there were spontaneous chemical reactions between SiO₂ and Al₂O₃ at low temperature, which maybe lead to form aluminum metasilicate. At the same time it showed that it was possible to lower the firing temperature of the materials. What's more, the Orthogonal Experiments revealed that the total percentages of silicon oxide and titanium oxide, firing temperature and time, have played the very important roles in the adherence strength.The materials have showed excellent acid-resistance while they were performed experiments in lemon acid condition. Linear Fitting Method was used to study relations between pH value and alkalis-resistance. It was displayed that when the enamel components stayed steady, the loss ratio in quantity of enamels is reduced as pH value increased in the specified limits and there was certain linear relativity between the former and the latter. So it was important to control the pH value.The enamel powder before and after firing was characterized by XRD method. It showed that in the pictures there was not any obvious diffract peak except for TiO₂ to exist in the form of tetragonal rutile, and TiO₂ has been proved to come from mill additions rather than enamel frits.The materials interface was characterized by SEM and XPS. It was discovered that there were steel layer, steel-aluminum layer, aluminum-enamel layer and enamel layer in the interface, some of which could decrease diversities between the enamel layer and metal and maintain stability. Not only Fe and Al could diffuse into enamel layer, but also enamel elements could diffuse into metal layer and there was mutual diffusion between Fe and Al. Therefore, all of these facts would contribute to form excellent adherence strength between metal substrate and enamel layer.Due to mutual diffusions and chemical reactions which took place in the interface, and the strong chemical bonds have been developed in the Al-coated steel enamel interface, so it was concluded that the excellent adherence strength between the enamel layer and Al-coated steel was chiefly achieved by chemical forces, partly by molecule forces.