Spectrally selective and adaptive surfaces for protection against radiative heating: ITO and VO₂

Abstract

SUMMARY Two surface materials for reducing absorptivity of heat radiation from fires have been investigated. The first is VO2, which is a thermochromic material. When the temperature of a VO2 surface increases over a certain temperature, it switches, ideally, from infrared (IR)‐absorbing to IR‐reflecting. VO2 window coatings are still on a research level, yet to be commercialized. In this study, VO2 powder available on the market was investigated. The thermochromic effect could be identified but was not large enough to significantly improve the fire properties of treated surfaces. Some thoughts concerning how to improve the performance of VO2 are discussed. The second investigated material is indium tin oxide (ITO), which is a so called low‐e coating, which means that it has low emissivity and absorptivity in the IR part of the spectrum. ITO is spectrally selective in the sense that it transmits visible light while reflecting a large fraction of the IR radiation, which is a rare property for surfaces in general but a typical property of thin electrically conducting non‐metallic films. It is shown that the application of ITO to poly(methyl methacrylate) (PMMA) significantly improves its fire properties. ITO coating is a mature technology already in widespread use today in the electronics industry. Copyright © 2012 John Wiley & Sons, Ltd.

Controlled Emissivity Coatings to Delay Ignition of Polyethylene

“…Moreover, the absorption coefficient changes with the thickness as shown by Linteris et al [ 21 ] even if this change is small for polyethylene. Finally, the absorption depends on the spectral distribution of the radiation which changes with the temperature of the heat source [ 16 , 21 , 22 , 24 ]. As a result, the absorptivity of the materials should change when heat flux changes.…”

“…Försth et al, have developed a thin coating based on indium tin oxide. This coating reduces the absorptivity of PMMA from 0.93–0.96 to 0.58–0.73 depending to the heat source and the type of PMMA [ 16 ]. The TTI in a cone calorimeter test at 25 kW/m 2 is significantly increased.…”

Deposition condition influence on optical properties of indium tin oxide

“…One of the most promising TCOs is indium tin oxide (ITO), which combines high transparency and conductivity. ITO is widely used for fabrication of transparent electrodes of liquid crystal screens [2], organic light emitting diodes (OLEDs) [3], touch screens and solar cells [4], as well as for heat [5] and electrostatic protection [6]. One of the mostly exploited ITO structures possesses the form of thin film, which can be fabricated via several techniques, e.g.…”

Low-Emissivity Metal/Dielectric Coatings as Radiative Barriers for the Fire Protection of Raw and Formulated Polymers

“…They showed that applying a low-emissivity coating (Cr/Cu/SiO 2 ) less than 1 μm thick increased the TTI of PC and PA6.6 substrates by several orders of magnitude in MLC testing and considerably reduced their flammability indexes . Experiments on transparent conductive oxides on PMMA and thermochromic materials on steel and glass , were then reported but without reaching the low emissivity obtained with copper. Sonnier et al have proposed polyethylene composite coatings filled with aluminum flakes; however, in their case, the top layer was thicker (from 65 to 100 μm), which might not be necessary to reach low emissivity and may limit its impact by introducing more flammable material .…”