Methods for depositing sol-gel derived coatings on substrates to form film coated substrates with low water content.
Sol-gel processing is a common method for the production of glass or ceramic material. The first and still one of the largest applications for sol-gel technology is for the formation of thin films, generally 0.5 micrometers or thinner. The films are generally produced on substrates that have been coated with the sol. Traditional sol-gel processes generally involve water as a reagent to form the sol, resulting in materials with high affinity for water. The water must be removed to avoid unwanted efficiency loss due to absorption. Moreover, coatings for certain infrared applications should be substantially free of water to avoid absorption of certain wavelengths, such as 2950 nm. Absorption at this wavelength due to water has been a problem for numerous infrared applications, such as thermal imagery and infrared positioning, regarding either spatial or distance acuity. In both of these systems multiple lenses are generally needed, and multiple lenses further degrade the transmission by increasing absorption. The current technique used for preparing coatings that display little water absorption is physical vapor deposition (PVD), which aside from the significant cost and complexity introduced by this process, PVD transfers significant energy into the substrate material. These energy sources as well as the thermal energy of the drying can adversely affect the material, causing some partial crystallization, resulting in scattering and lowered transmittance. Thus, there is a need for a low temperature method for forming low water content thin film coatings on substrates.
UCF researchers have developed a method of depositing sol-gel derived coatings on substrates, which permits high water removal efficiencies at near normal room temperature. The relatively thin coatings, generally <110 nm, promote continued porosity throughout the layer. This property helps to avoid forming encapsulated water pockets within the material. The water removal from this procedure reduces the absorption due to water down to 1%, avoiding efficiency losses and resulting in long-term corrosion protection. In addition, the resulting coatings can be formed on temperature sensitive substrates, such as certain chalcogenide glasses, for optical applications, including infrared optics.
- Significantly reduces unwanted absorption due to water (all the way down to 1%), increasing the quality of the material
- Long-term corrosion protection due to low water absorption, resulting in a cost effective and low maintenance product
- Coatings can be formed at lower temperatures to include substrates that cannot handle high temperatures, such as certain chalcogenide glasses used in sensitive infrared optical lenses