Match Made in the Heavens

First, Understand Atomic Oxygen

Oxygen comes in three different forms. The oxygen that we breathe is called O2, that is, it is comprised of two atoms of oxygen bonded together. O3 is ozone, such as occurs in Earth's upper atmosphere, and O (one atom), is atomic oxygen.

Atomic oxygen doesn't exist naturally for very long on the surface of Earth, as it is very reactive. Oxygen does not like to be just atomic oxygen. It likes to be O2, CO, CO2, O3, etc. But in space, where there is plenty of ultraviolet radiation, O2 molecules are more easily broken apart to create atomic oxygen. The atmosphere in low Earth orbit is comprised of about 96% atomic oxygen. In the early days of NASA's space shuttle missions, atomic oxygen caused problems.

"In the first few shuttle flights, materials looked frosty because they were actually being eroded and textured," says Bruce Banks, "Atomic oxygen reacts with organic materials on spacecraft exteriors, gradually damaging them."

"These individual atoms don't have many opportunities to recombine into either ozone or O2 up there," says Banks. "They're like people in a desert. They don't bump into each other because there aren't many of them." Given the opportunity, however, atomic oxygen reacts quickly with other unattached or weakly bonded atoms, such as those in the hydrocarbons within the polymer sheets that hold the space station's solar arrays in place. Without protection, the sheets would disintegrate into carbon monoxide and carbon dioxide gases within a year.

NASA Glenn Research Center was asked to investigate the damage caused to NASA spacecraft by atomic oxygen. When spacecraft travel in low Earth orbit (where Space Shuttle and the International Space Station fly), the atomic oxygen formed from the residual atmosphere can react with spacecraft surfaces, causing damage to the vehicle. When the solar arrays were designed for the Space Station, there was a concern that the solar array blankets, which are made of polymers, would quickly erode due to atomic oxygen. NASA developed the solution. The team at Glenn designed a thin-film coating for the solar arrays, which was immune to the reaction with atomic oxygen. Silicon dioxide, or glass, has already been oxidized so it cannot be damaged by atomic oxygen. The researchers created a coating of a clear silicon dioxide glass that is so thin, it is flexible. This protective coating adheres to the polymers of the array and protects the arrays from erosion, while not sacrificing any thermal properties. The coatings continue to successfully protect the Space Station arrays and Mir.
"It has been successfully flying in space for more than a decade," Banks says. "It was designed to be durable."

The researchers not only invented methods to protect spacecraft from atomic oxygen; they also discovered a way to harness the potentially destructive power of atomic oxygen and use it to improve life on Earth.

Back to Earth

"We became aware of how the surface chemistry changes, how atomic oxygen removes organic materials… it can remove anything organic that's a hydrocarbon, that might not be easily removed by normal chemicals," Banks says.

The NASA team discovered a wealth of ways atomic oxygen might be employed. They learned how to enhance materials used on aircraft and spacecraft, and benefit humans through a number of biomedical applications.

There are different ways of applying atomic oxygen to surfaces. Most frequently, a vacuum chamber is used. These chambers range from the size of a shoebox to a chamber that is 4 feet by 6 feet by 3 feet. Microwaves or radiofrequency waves are used to break the oxygen into oxygen atoms—atomic oxygen. A sample of polymer is placed in the chamber and its erosion is measured to determine the level of atomic oxygen inside the chamber.

Another method of applying atomic oxygen is to use a portable, pencil beam machine that directs a flow of atomic oxygen to a specific target. It might be possible to create a bank of these beams to cover a larger surface area.

A variety of surfaces can be treated using these methods. As research into atomic oxygen has continued, various industries have learned of the work. Restoration Technology is a now a commercially available version of NASA’s atomic oxygen work.

Restoring Art

When works of art are damaged, atomic oxygen can be used to remove the organic contaminants without damaging the actual painting. The process removes all organic materials, such as carbon or soot, but it typically doesn't affect the paint. The pigments in paint are mostly inorganic, and have already been oxidized, meaning that atomic oxygen doesn't damage them. Pigments that are organic can also be preserved, through carefully timing the exposure to atomic oxygen. The canvas is also safe, as the atomic oxygen only reacts on the surface of the painting.

Artwork can be placed in a vacuum chamber where atomic oxygen is created. Depending on the amount of damage, the painting can remain in the chamber anywhere from 20 hours to 400 hours. The pencil beam can also be used to specifically target a damaged area in need of restoration, eliminating the need to place the artwork in a vacuum chamber.

Museums, galleries and churches have used this process to save and restore their works of art. Atomic oxygen restoration has demonstrated the ability to repair a fire-damaged painting by Jackson Pollack, removed lipstick from an Andy Warhol painting and saved smoke-damaged paintings at St. Stanislaus Church in Cleveland. The atomic oxygen process was used to restore a piece that was previously thought to be irreparable, a centuries-old, Italian copy of a painting by Raphael called "Madonna of the Chair," which belongs to St. Alban's Episcopal Church in Cleveland.

This process has been patented (U.S. Patents #5,560,781 and #5,693,241) and the process has been tested to determine its ability to safely treat the range of media typically used by artists (oil paint, acrylic paint, acrylic gesso, watercolors, pen and ink, and others). In 2001 validation testing was completed, and the process was deemed to be acceptable for functional art restoration. Atomic oxygen is now safe for cleaning artwork where conventional techniques have not been or are not effective.