Effect of Ni20Cr alloy on infrared emissivity of inorganic silicate heat-resistant composite coatings

• Ni20Cr powders are used as low infrared emissivity pigment for the first time.
• The emissivity of composite coatings depends on the ball milling time of Ni20Cr.
• The emissivity of composite coatings relies on the annealing temperature of Ni20Cr.
• The emissivity of composite coatings at 3–5 μm waveband could be reduced to 0.49.
• The composite coatings exhibit favorable thermal stability property.

Low infrared emissivity coating with good thermal resistance was prepared by using Ni20Cr alloy particles and inorganic silicate as pigments and binders, respectively. The effects of size, shape, and annealing temperature of Ni20Cr alloy particles on infrared emissivity of the coatings were systematically investigated. The results indicate that the composite coatings can exhibit low emissivity (0.49) and good thermal stability property. Ni20Cr alloy particles with tens of micron-sized, flaky, and fine crystal structure can be propitious for decreasing the infrared emissivity of the composite coatings. In addition, the thermal stability properties of the composite coatings were measured in air to explore the effect of high-temperature environment on the infrared emissivity. The measured results show that the composite coatings can exhibit a favorable thermal stability property below 800 °C and still possess low emissivity when the test temperature is below 500 °C, due to the Si–O–Si cross-linking network structure and the mechanical interlocking between the coating and substrate.

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