Preparation and properties of high emissivity Fe–Mn–matrix coatings by air plasma spraying

Abstract

In this study, two kinds of high emissivity Fe–Mn–matrix feedstock powders were synthesised by spray drying and sintering using oxides of Fe, Mn, Ti, Cu, Co, and ZrO₂/HfO₂. The complex oxide coatings with these two powders were prepared by air plasma spraying. The emissivity of two coatings was measured at 800∼1200°C. The phase structure and microstructure of the powders and coatings were also characterised. The results show that the synthesised powders perform superior flowability after spray drying and sintering. The emissivity of Hf–Fe–Mn coating is about 0·85 at the temperature range from 800 to 1200°C, and that of Zr–Fe–Mn coating is 0·86 at the similar temperature range. The high emissivity can be attributed to the spinel phases such as FeCoCrO₄, FeMn₂O₄, CoFe₂O₄ and Ti_0·5Zr_0·5O_0·5, existed in the coatings and the high emissivity phases of HfO₂ and ZrO₂. The optimal sintering temperature of Hf–Fe–Mn powder is 1300°C to get the synthesised powders with best flowability and the coating with high emissivity.

Keywords:

• Fe–Mn–matrix coating
• Oxides
• Plasma spraying
• Emissivity