Interfacial reaction between quartz and potassium silicate glass was studied at both 900 °C and 1000 °C. The results showed that no phase transformation was observed for the pure quartz at 900 °C or 1000 °C. Instead, for quartz particles in K2O-SiO2 glass, the transformation from quartz to cristobalite occurred at the quartz/glass interface at first, and then the cristobalite crystals transformed into tridymite. The tridymite formed at the interface between particles and glass became the site of heterogeneous nucleation, which induces plenty of tridymite precipitation in potassium silicate glass. The influential mechanism of firing temperature and size of quartz particles on transformation rate was discussed.
A SiO2–Al2O3 glass composite coating was prepared on Ti60 alloy via air spraying slurry and then a suitable baking process. It was composed of potassium silicate glass, alumina and quartz powders. The high temperature oxidation performance of the alloy with and without coating was evaluated in static air at both 800 °C and 900 °C. The results show that catastrophic oxidation occurs for Ti60 bare alloy. It had a mass gain of about 2 mg/cm2 after oxidation at 800 °C and 17 mg/cm2 at 900 °C for 100 h. On the contrary, the oxidation resistance of alloy coated with composite coating was much improved with the mass gain about 0.36 mg/cm2 and 0.95 mg/cm2 at 800 °C and at 900 °C, respectively. The microstructure evolution of the composite coating and the alloy was analyzed by scanning electron microscope and electron probe microanalyzer. The effect of the composite coating on the oxidation performance of the alloy is discussed especially in terms of oxygen diffusion and interfacial reaction.
Due to green development in recent years, water-borne epoxy resins (WBE) have become increasingly popular since they generate the lowest level of volatile organic compounds (VOC) during curing. However, because of the large surface tension of water, it is easy to produce voids and cracks during the curing process of the coating. An electrochemical strategy was used in this study to assess the impact of different SiO2 content on the corrosion performance of a WBE coating, in which micron spherical SiO2 particles were synthesized in a liquid phase reduction. The results showed that the synthesized micron spherical SiO2 particles were about 800 ± 50 nm in diameter and in an amorphous state. By hydrophilizing the surfaces of these SiO2 particles, uniform dispersion in an aqueous solvent and a WBE can be achieved. It is important to note that adding a small or excessive amount of SiO2 to a coating will not improve corrosion resistance and may even reduce corrosion resistance. With the appropriate modification of SiO2, corrosion resistance of composite coatings is greatly enhanced, as is the adhesion between the coatings and the metallic substrates. Because the appropriately modified SiO2 can effectively fill the pores that are formed during the curing process, a corrosive medium is less likely to react with the matrix when the medium comes into contact with the matrix. Based on their incorporation content of 3 wt.%, their corrosion resistance is the best after 16 cycles of AC-DC-AC accelerated corrosion tests.
9 November 2018 in Acta Metallurgica Sinica (English Letters)