Image 1: (A) TEM bright-field image of as-deposited TiO2 film on self-assembled monolayer on silicon. (B) Diffraction pattern of film.
Titanium oxide films have been shown to be effective coatings for protecting plastics, metal and glass from corrosion and ultraviolet (UV) light. But many manufacturers have shied away from this useful coating due to the costly and complicated process needed to produce it.

Researchers at the Department of Energy's Pacific Northwest National Laboratory (PNNL) have developed a simple and inexpensive process for producing titanium oxide coatings based on solution deposition.

Titanium oxide's effectiveness as a coating is well known. "Now we have a better way to apply it," said Eric Lund, a licensing associate at the laboratory. "The application process PNNL has developed will allow the film to adhere to a variety of surfaces."

Image 2: Titanium oxide film on sulfonated polycarbonate (TEM micrograph).

--Uniform, conformal film on sulfonated polycarbonate
--As deposited film is amorphous, hydrated titanium oxide

The PNNL's solution deposition method uses a titanium chelate solution, which is then decomposed, depositing titanium oxide film on the surface. First, the substrate is immersed in an aqueous solution of titanium chelate. Next, decomposition of the titanium chelate by acid, base or heat, results in the deposition of the titanium oxide film, as the oxyhydroxide, on the substrate. The immersion process produces uniform coverage and high adhesion of the coating to the substrate. The hard surface of the film may also provide scratch resistant coatings for lenses and the like. Experimental tests have shown that this technique is extremely effective in reducing yellowing and other degradation of commercially available plastic parts exposed to light (e.g., light fixtures). Although industrial scale-up has not been investigated, it is believed to be fairly straightforward since this is an aqueous solution deposition technique.

"This process is cost-effective, easy, has wide applicability and should readily scaleup because it's simple solution chemistry," Lund said. "It's also quite rapid, capable of coating most objects within 10 minutes at temperatures between 40-100 deg C." Complete dehydration, accomplished by treating the films at temperatures near 400 deg C, produces single-phase titanium oxide.

Image 3: TEM bright-field image showing the as-deposited film and the sulfonated layer on the polycarbonate. Dark regions in the polycarbonate are film debris from sample preparation.
In contrast, currently used preparation techniques, such as vapor or vacuum-based deposition, require complicated processes and expensive equipment, ultimately limiting the shape of objects the coating may be used on. Other solution methods can produce films that may shrink and crack as they harden and that typically have poorly controlled microstructures. Gas-phase methods require direct growth of materials by heterogeneous nucleation from the gas phase, requiring high temperatures at the source and a vacuum, thus increasing costs and limiting processing choices.

The laboratory's titanium oxide film was originally developed to prevent UV radiation damage to polymer components in conventional lighting. Other applications for this process may include UV-blocking coatings for plastics, photocatalysts, optical and decorative purposes, photoelectrodes, gas sensors and electrochromic display devices.

Advantages include the following.

  • Low cost easy to perform: Does not require high temperatures or vacuum.
  • Uniformly coats complex and irregular shapes.

Image 4: Optical transmittance of TiO2 films on SiO2 substrates.
The PNNL's titanium oxide coating is potentially applicable in any setting titanium oxide coatings are already used, such as self-cleaning window glass, anti-microbial coatings on cutting boards and reflectivity coatings inside light bulbs. It also can be used to coat complex, intricate structures ranging from semiconductors to aerospace components.

PNNL is a DOE research facility and delivers breakthrough science and technology in areas of environment, energy, health, fundamental sciences and national security. Battelle, based in Columbus, Ohio, has operated PNNL for DOE since 1965.

Battelle, which operates PNNL, has obtained patent protection for this novel method (U.S. Patent 5,766,784) and is seeking industrial partners, including those who may be interested in Cooperative Research and Development Agreements, to help commercially develop this titanium oxide film processing method to meet their needs. Business inquiries on PNNL research and technologies should be directed to 888/375.PNNL or

All graphics reprinted with permission of The American Ceramic Society, POBox 6136, Westerville, OH 43086-6136. Copyright 1998 by The American Ceramic Society. All rights reserved.