A review of near infrared reflectance properties of metal oxide nanostructures

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Fang, F.; Kennedy, J.V.; Futter, R.J.; Manning, J. 2013 A review of near infrared reflectance properties of metal oxide nanostructures. Lower Hutt: GNS Science. GNS Science report 2013/39 20 p.

Abstract: The light that reaches the Earth’s surface ranges over a broad spectrum of wavelengths (295 – 2500 nm): ultraviolet (UV) radiation that you can’t see or feel, visible light that you see, and infrared radiation that you feel as heat. Almost half of the sun’s energy is from infrared and near infrared radiation. However, these radiations on absorption result in heating up of the surface. Significant amount of heat is absorbed into the surface by means of conduction. With such increasing heat, there is a need for variable energy in the form of air-conditioning to keep the interiors of the building cool for people to work and live inside. To reduce the increasing demand for energy consumption for air conditioning, there is a need for cooler roofs. Reflecting the sun’s radiation minimizes the amount of energy absorbed by the building. A cool coating reflects a high percentage of incident near infrared (NIR) radiation, while transmitting high levels in the visible spectra. This will reduce the amount of solar energy entering buildings which results on a cool surface when exposed to the sun. In hot summer time, cool coatings will help to keep the roof temperature down, minimizing the energy required to keep homes and buildings maintained at a comfortable temperature. NIR reflective pigments have been used in military, construction, plastic, and ink industries. A particular class of such pigment is based on mixed metal oxides. Recently, the NIR reflective pigment with nanocrystalline metal oxides has shown remarkable NIR reflectance with better colour choices. In this report, studies devoted to the preparation of cool paint with NIR reflectance properties of metal oxides have been reviewed. The NIR reflectance of metal oxide nanostructures (such as TiO2 and ZnO) synthesized in-house has also been studied and presented in this report. Powders of TiO2 and ZnO nanostructures were synthesized using an arc discharge method with in-house apparatus at GNS Science. Morphology analyses revealed that both TiO2 and ZnO have nano sized structures and the arc discharge current has an effect on the structure size. TiO2 nanostructures synthesized at 74 A arc current show diffuse reflectance from 49 % to 45 % in the NIR range (700 – 2500 nm). ZnO nanostructures show diffuse reflectance from 57 % to 14 % in the NIR range (700 – 2500 nm). (auth)

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