Thermal and Optical Behavior of Novel Phosphate-Based Inorganic Mixtures Containing Fe and Na and Their Application as Solar Reflective Coating

Abstract

Herein, the synthesis of the novel and inexpensive phosphate mixtures, Fe3(PO4)2·0.5 Na3PO4.6 H2O· NaOH (calcined) and Fe3(PO4)2·0.5 Na3PO4·4 H2O· NaOH (non-calcined) of iron (Fe) and sodium (Na) and their application as reflective coating with building envelope materials is reported. The main objective of this work is to determine the effect of hydrated mixtures as a reflective coating. To obtain different hydrated mixtures, samples were synthesized in both calcined and non-calcined manner. Various measurement techniques were used to characterize and study the thermal behavior of mixtures. From the thermal behavior of the mixtures, it is noticed that the mixtures can be used as heat-dissipating materials. The average crystallite size was found to be 40.18 nm and 25.48 nm for the calcined and the non-calcined mixtures, respectively. The calculated band gap for the calcined mixture is 3.71 eV and the non-calcined mixture is 3.73 eV. According to Reddy's equation, the refractive index of the calcined and the non-calcined mixtures is 2.61 and 2.60, respectively. Both the calcined (1A) and the non-calcined (1B) mixtures were fabricated with commercial white paint to develop aesthetic light gray coatings. Both coatings were painted and tested on two building material slabs separately. Then, the highest reflective coating material between these two was painted on a house prototype and tested against commercial gray paint available in the market. An average temperature reduction of 3.8 K was observed in modified gray coating compared to commercial building paint. The reflective coating of the calcined mixture blended with white paint was observed to be better than the non-calcined mixture blended with white paint.