Effect of sodium silicate binder on the performance of ceramic coatings on copper prepared by the slurry method

Abstract

Low melting point metals, such as copper, are often used as high-temperature cooling equipments and endure harsh environments during operations. This usually leads to reduced service life and reliability. To address this problem, a protective coating was prepared on copper via a slurry method. However, due to the low melting point of copper, solid-state sintering was applied. Therefore, during this process, the defects generated in the ceramic coating could affect the performance of the coating. To reduce the defects, a series of ceramic coating samples using sodium silicate water glass (SSWG) as the binder were prepared, changing the SSWG-to-aggregate mass ratio (SAMR) for each sample. The results showed that they were all related to the SAMR, and there was an optimal SAMR with minimum defects and favourable performance. The non-optimized SAMR lead to more internal defects, that is, microfractures and pores in the coating, resulting to a decline in the coating performance. By identifying the types of defects and quantifying them, the relationship between the SSWG and the generation of defects was studied, and the effect of the defects on the performance of the ceramic coating was analysed in detail. The research presented in this paper provides a method for the improvement of ceramic coatings by optimising the key factors that is the SAMR in solid-state sintering. The effect of thermal stress on the formation of microfracture defects during the sintering was investigated by experiments and simulation. It is found that with increase of sintering temperature, the thermal stress inside the coating increases gradually, resulting in more generation of microfracture defects inside the coating. The inhibition effect of SSWG on thermal stress during the sintering process was verified.