"We wanted to get larger amounts of cerium 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 silica 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 ultraviolet light. 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 glass 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).
The National Science Foundation and the U.S. Air Force Research Laboratory supported this work.
A'ndrea Elyse Messer | EurekAlert!
Custom sequences for polymers using visible light
22.03.2018 | Tokyo Metropolitan University
The search for dark matter widens
21.03.2018 | American Institute of Physics
An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.
The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...
In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.
Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...
Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.
They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...
A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...
For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.
In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...
19.03.2018 | Event News
16.03.2018 | Event News
13.03.2018 | Event News
22.03.2018 | Materials Sciences
22.03.2018 | Health and Medicine
22.03.2018 | Earth Sciences