Current Density on Microstructure and Thermal Control Performances of MgO-ZnO Ceramic Coatings

doi:10.15541/jim20170057

Abstract

Abstract:

MgO-ZnO thermal control coatings were prepared on AZ31 magnesium alloy using micro-arc oxidation (MAO) in the electrolyte containing Zn(H₂PO₄)₂. The influence of current density on the microstructure, composition, adhesive strength, and thermal control performances of MAO coatings were investigated, and the variation of solar absorptance (α_s) was examined at different ultraviolet irradiation time. The results show that the MAO coating is composed of MgO, ZnO and a few amorphous phases. With an increase of current density, the number of pores gradually decreases while the roughness increases. As the thickness, adhesion and emittance (ε) firstly increase and then decrease, the changing tendency of α_s shows the opposite. When the current density is set at 9 A/dm², the MAO coating exhibits a stronger adhesive strength of 12.6 MPa, a higher ε of 0.872 and a lower α_s of 0.363. Moreover, the ultraviolet irradiation test reveals that the α_s increases followed by leveling off with increasing irradiation time. This process provides a technical support for fabricating thermal control coating with excellent adhesion, low α_s/ε ratio, and good anti-ultraviolet irradiation.

Key words: micro-arc oxidation, thermal control coating, ZnO, ultraviolet irradiation

CLC Number:

TQ174

LI Hang, LU Song-Tao, QIN Wei, WU Xiao-Hong. Current Density on Microstructure and Thermal Control Performances of MgO-ZnO Ceramic Coatings[J]. Journal of Inorganic Materials, 2017, 32(12): 1292-1298.

Figures/Tables 10

Fig. 1 SEM images of coatings obtained at different current densities^(a) 3 A/dm2; (b) 6 A/dm2; (c) 9 A/dm2; (d) 12 A/dm2

Fig. 2 Section images of coatings obtained at different current densities^(a) 3 A/dm2; (b) 6 A/dm2; (c) 9 A/dm2; (d) 12 A/dm2

Fig. 3 XRD patterns of coatings prepared at different current densities

Fig. 4 XPS spectra of coatings prepared at 9 A/dm2(a) Survey scan; (b) Zn2p; (c) O1s

Fig. 5 TEM analysis of MAO coatings prepared at 9 A/dm2(a) TEM image; (b) Electron diffraction pattern

Fig. 6 Effect of current density on the roughness of coatings

Fig. 7 Effect of current density on adhesion strength of coatings

Fig. 8 Effect of current density on the emissivity of the coating

Fig. 9 Diffuse reflectance spectra of coatings prepared under different current densities

Fig. 10 Diffuse reflectance spectra of the coatings before and after ultraviolet irradiation

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