Rare earth metal enhances phosphate glass

December 15, 2009

(PhysOrg.com) -- Adding cerium oxide to phosphate glass rather than the commonly used silicate glass may make glasses that block ultraviolet light and have increased radiation damage resistance while remaining colorless, according to Penn State researchers. These cerium-containing phosphate glasses have many commercial applications for use in windows, sunglasses and solar cells.

"We wanted to get larger amounts of into glass, because of its beneficial properties, and then investigate the properties of the glasses," said Jen Rygel, graduate student in materials science and engineering.

Cerium exists in two states in glasses -- cerium (III) and cerium (IV) -- both states strongly absorb ultraviolet light. For years cerium has been added to silicate glass to enhance its ultraviolet absorbing capacity. The problem has always been that silicate glass can only dissolve so much cerium before it becomes saturated and can hold no more. Also, with high concentrations of cerium, silicate glass begins to turn yellow -- an undesirable characteristic for such things as windows or sunglasses.

Phosphate glasses have a more flexible structure then silicate glasses, which allow higher percentages of cerium to be incorporated before it begins to color. Rygel, working with Carlo Pantano, distinguished professor of materials science and engineering, and director of Penn State's Materials Research Institute, synthesized and compared 11 glasses with varying concentrations of cerium, aluminum, phosphorus and silica.

They found that they could make phosphate glasses with 16 times more cerium oxide than silicate glasses while maintaining the same coloration and ability to absorb ultraviolet light. They published their work in today's (Dec. 15) issue of Non-Crystalline Solids.

"We were able to get a lot more cerium into our phosphate glass without sacrificing the optical transmission -- they both still looked clear," said Rygel.

The researchers could get more cerium into phosphate glass compared to silicate because of the different bonding networks and phosphorus form when made into glasses.

One explanation for why phosphate glass can incorporate more cerium than silicate glass without yellowing may be that the absorbing ranges for the two cerium states -- cerium (III) and cerium (IV) -- are shifted to absorb less blue light in phosphate glasses.

"A good example is in solar cells," said Rygel. "The wavelengths that solar cells use aren't ultraviolet, and actually ultraviolet radiation can cause damage to the electronics of a solar cell. If you add cerium to the glass you can prevent the ultraviolet from getting down to the photovoltaic cells, potentially increasing their lifetime."

To synthesize their glasses the researchers used a procedure called open-crucible melting. Raw materials such as phosphorus pentoxide, aluminum phosphate, cerium phosphate and silicon dioxide were combined in a crucible and heated in a high-temperature furnace to a temperature of 3000 degrees Fahrenheit melting the contents to a liquid.

"After it's all melted, we pull it out of the furnace and pour it into a graphite mold," said Rygel. "The glass is then cooled down slowly so it doesn't break due to thermal stress."

Cerium additions do not just block . Increasing a glass' cerium concentration can also increase its resistance to radiation damage from x-rays and gamma rays by capturing freed electrons.

"Radiation can kick electrons free from atoms," said Rygel. "You can see this by looking at what happens to a Coke bottle over time. It darkens because of radiation exposure."

The proposed mechanisms for cerium's ability to block radiation are all based on cerium's two states and their ratio within the glass. Because of these implications Rygel wanted to know what percentages of each existed within her glasses.

Using X-ray photoelectron spectroscopy Rygel could determine whether the cerium in the was mostly in the cerium (III) or cerium (IV) oxidation state, or a ratio of the two. She found that all of her glasses contained approximately 95 percent cerium (III).

Explore further: Scientists see benefits of nanoceria

Related Stories

Scientists see benefits of nanoceria

November 1, 2006

A U.S. study suggests cerium oxide -- used in polishing glass and in car exhaust systems -- might be used to treat various eye disorders and other diseases.

An impossible alloy now possible

February 26, 2009

What has been impossible has now been shown to be possible - an alloy between two incompatible elements. The findings are being published in this week's edition of Proceedings of the National Academy of Science, USA.

Under pressure, atoms make unlikely alloys

March 11, 2009

(PhysOrg.com) -- Ever since the Bronze Age, humans have experimented with combining different metals to create alloys with properties superior to either metal alone. But not all metals readily form alloys - for some pairs ...

Recommended for you

CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...

Exploring the physics of a chocolate fountain

November 24, 2015

A mathematics student has worked out the secrets of how chocolate behaves in a chocolate fountain, answering the age-old question of why the falling 'curtain' of chocolate surprisingly pulls inwards rather than going straight ...

'Material universe' yields surprising new particle

November 25, 2015

An international team of researchers has predicted the existence of a new type of particle called the type-II Weyl fermion in metallic materials. When subjected to a magnetic field, the materials containing the particle act ...

Biomedical imaging at one-thousandth the cost

November 23, 2015

MIT researchers have developed a biomedical imaging system that could ultimately replace a $100,000 piece of a lab equipment with components that cost just hundreds of dollars.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.