Waste to Wealth: Cenospheres as Promising Thermal Insulation Coating Material for Protection Against Impinging Hot Air

Abstract

Saving thermal energy in a sustainable way is one of the important aspects of global energy conservation. Therefore, conservation of thermal energy by different means has been a topic of applied research in the last several years. In this direction, low-density, low-thickness, cost-effective, and easily scalable thermal insulation paint coating containing power plant waste cenosphere has been developed in the present work. Cenospheres having low thermal conductivity are used as fillers in an epoxy matrix. The coating has been developed using simple spray coating method. Morphology, phase, and particle size of cenospheres have been characterized by field emission scanning electron microscopy, X-ray diffractometry, and particle size analysis, respectively. Cenospheres show spherical morphology with mainly quartz and mullite phases. Chemical bonding and surface nature of the as-prepared coating have been evaluated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The coating contains C–O, C–O–C, C–C, C=C, –CH₃, C–N, N–H, –OH, Al–O–Si, Al–O–Al bonds, as well as Si³⁺, Si⁴⁺, C–O, C=O, O–C=O, Ca²⁺, Na⁺, and Al³⁺ species on the surface of the coating. The thermal conductivity of epoxy-cenospheres coating is in the range of 0.24 to 0.35 W m⁻¹ K⁻¹ for temperatures of 20 °C–200 °C. The thermal insulation property of the coating has been assessed using an indigenously built setup and the coating shows a temperature drop of 20 °C–27 °C, when the coating has been subjected to 200 °C hot air exposure for 5 to 20 min.