Synthesis and Characterization of Transparent Oxide Coatings with Enhanced Near Infrared Reflectance.

摘要

The heating of the exterior and interior of vehicles such as cars and planes is directly dependent on the absorption of electromagnetic radiation from the sun. The energy that is incident on these surfaces is approximately equally divided between UV/visible light (300--800 nm) and near infrared radiation (800--2500 nm). If the near infrared (NIR) portion of radiation were reflected instead of absorbed by the surface, the exterior and interior cabin temperatures of these bodies could be significantly reduced, leading to reduced energy usage due to vehicle cooling and smaller environmental control system (ECS) packs.;Titanium dioxide coatings are transparent to visible light and easy to synthesize using techniques such as magnetron sputtering and sol-gel chemistry. The primary goal of this research is to add metal particles or dopants to the TiO2 matrix in order to enhance the reflectance in the NIR range without significantly affecting the visible transparency of the film.;Titanium dioxide films with copper and gold nanocomposite particles were synthesized by magnetron sputtering. The maximum reflectance of these films in the infrared region (800--2500 nm) is > 50%, compared with 30% for pure TiO2. The Maxwell-Garnett equation does not model the reflectance data well. Instead, by assuming that the contribution of gold or copper particles is proportional to a projected area fraction in an effective medium approximation, we were able to fit the observed reflectance data. Magnetron sputtering was also used to create niobium-doped titanium dioxide films. These films were shown to have an enhanced reflectance compared to pure TiO2.;Sol-gel synthesis was explored as a means of bulk fabrication of niobium-doped titanium dioxide films. Coatings made by the sol-gel process were amorphous as-deposited and required additional heat treatment above 450C in order to crystallize. The grain size of pure TiO2 was less than 10 nm as-deposited and decreased with increasing niobium content. At temperatures below 650C, niobium diffused too slowly throughout the TiO2 matrix in order to dope the lattice. At temperatures above 650C, niobium reacted to form oxide phases. Niobium-doped films made by sol-gel did not exhibit a reflectance enhancement compared to TiO2.