Useful news and interesting research:

Washington Mills decodes particle size conversion in fused minerals

Washington Mills has developed a particle size conversion chart to assist in selecting the correct grit size based on the American National Standards Institute (ANSI) and Federation of European Producers of Abrasives (FEPA) guidelines for grading and sizing fused minerals. The particle size conversion chart compares millimeters, microns, and inches to sieve sizes and matches them to the corresponding grit size. For convenience, a PDF version is available for download. For questions regarding grit sizes, contact us the company directly at info@washingtonmills.com or 800-828-1666.

Global pigments market is expected to reach USD 14.7 Billion in terms of revenue and 4.4 million tons in terms of volume by 2018

According to a new market report published by Transparency Market Research “Pigments (Organic, Inorganic & Specialty) Market - Global Industry Analysis, Size, Share, Trends, Growth and Forecast, 2012 - 2018,” the global pigments market revenues are expected to reach USD 14.7 billion in 2018, growing at a CAGR of 4.5% from 2013 to 2018. In terms of volumes, pigments demand is expected to reach 4.4 million tons by 2018. Specialty pigments market is expected to have fastest growth potential among the global pigments market, growing at a CAGR of 5.4% during the analysis period. Availability of large variety of products and ability to encompass high and unique visual effects is primarily fueling the growth of the specialty pigments market. Increasing demand for paints and coatings, particularly from key end-use industries such as construction, is expected to drive demand over the next five years. Fluctuating and volatile prices of key raw materials including benzene and toluene coupled with an increasingly stringent regulatory environment are critical challenges to this industry.

Alta Devices achieves 30.8% efficiency record with new generation solar cell technology

Alta Devices disclosed that it has reached 30.8 percent solar cell efficiency. This new National Renewable Energy Laboratory-verified record resulted from the company’s first implementation of a new generation “dual junction” solar cell technology, which augments the company’s “single junction” technology. Higher efficiency directly translates into more electricity generated from smaller surface areas. Therefore, applying Alta’s highly efficient, very thin and flexible mobile power technology to consumer devices can extend the battery life of everyday products such as smartphones, tablets, keyboards, mouses, remote controls, and more. To help device manufacturers understand the benefits of using Alta’s material on their products, Alta created a calculator to compute the battery life extension for a variety of consumer mobile devices (http://www.altadevices.com/calculator.php). According to the calculator, a typical outdoor worker could realize 80 percent more battery life each day for their mobile phone. Or a student can get over 60 percent more battery life for his or her tablet device. These results can be achieved with minimal weight or form-factor penalty on the device design.

World’s first conceptual nuclear reactor design of high plutonium breeding by light-water cooling

Yoshiaki Oka, professor at Waseda University (Japan), and his research team developed a conceptual nuclear reactor design of high plutonium breeding by light water cooling for the first time. He devised a new fuel assembly where fuel rods are closely packed for reducing reactor coolant to fuel volume fraction for high breeding. With computational analysis he achieved high plutonium breeding with light water cooling. The study will open the way of commercialization of fast reactor and nuclear fuel cycle for nuclear energy based on mature light water cooling technologies. The results from the study were published in January issue of the Journal of Nuclear Science and Technology of Atomic Energy Society of Japan, entitled “Plutonium breeding of light water cooled fast reactors.”

Electronic sensors printed directly on the skin

(Technology Review) Taking advantage of recent advances in flexible electronics, researchers have devised a way to “print” devices directly onto the skin so people can wear them for an extended period while performing normal daily activities. Such systems could be used to track health and monitor healing near the skin’s surface, as in the case of surgical wounds. So-called “epidermal electronics” were demonstrated previously in research from the lab of John Rogers, a materials scientist at the University of Illinois at Urbana-Champaign; the devices consist of ultrathin electrodes, electronics, sensors, and wireless power and communication systems. In theory, they could attach to the skin and record and transmit electrophysiological measurements for medical purposes. During the two weeks that it’s attached, the device can measure things like temperature, strain, and the hydration state of the skin, all of which are useful in tracking general health and wellness. One specific application could be to monitor wound healing: if a doctor or nurse attached the system near a surgical wound before the patient left the hospital, it could take measurements and transmit the information wirelessly to the health-care providers.

Share

An Alfred University team led by Yiquan Wu is developing methods for synthesizing anisotropic, transparent, polycrystalline ceramics for high-power applications like laser-based fast-ignition of fusion. Credit: Wu; Alfred Univ.

You need a spark to light a fire, and sometimes that’s not so easy, as anybody who’s tried to light a too-green yule log can attest. Thermonuclear reactions, too, have to be ignited, and that is definitely not easy.

The Lawrence Livermore National Laboratory has been studying the problem and is making significant progress on their laser-based “fast ignition” approach for igniting a thermonuclear reaction in a compressed hydrogen isotope fuel pellet. The conventional approach, called the “central hot spot,” involves simultaneously compressing and igniting a spherical fuel capsule in an implosion. In contrast, the FI approach separates the compression and ignition stages of the implosion, which provides advantages such as allowing for variability in fuel capsule dimensions and requiring less mass for ignition (thus less energy input and more energy gain). If the advantages of FI can be realized, the eventual development of an inertial fusion-energy power plant should be easier. Also, the ability to study these types of reactions in a controlled setting could eliminate the need for underground testing of nuclear weapons and allow scientists to study the physics and chemistry unique to the cores of stars and planets.

FI is, itself, a sophisticated technology that involves synchronizing the outputs of 192 laser beams to deliver a massive amount of energy to the fuel pellet. In May, Nature Photonics reported that LLNL successfully demonstrated the technology in March, firing the 192 beams simultaneously and delivering 1.875 megajoules of energy in 23 billionths of a second. LLNL followed-up with a successful repeat firing in July, bringing the possibility of laser-based fusion “75% of the way” to reality, according to a story on optics.org.

There are some practical problems, however. According to the LLNL website, the 192-laser array can fire off a beam only every few hours; between firings, time is needed for the thousands of optics to cool enough to endure another round. Thus, along with this technology, LLNL is working on developing a single-beam laser system in a program called “Mercury.” Mercury’s scientists have already come up with a method for cooling the optics that will allow for frequent firing of the laser. The Mercury technology uses light from diode lasers (similar to those used in commercial CD read/write players) that is amplified as it passes through a ytterbium-strontium-fluoroapatite (Yb:S-FAP) single crystal gain medium. While Yb:S-FAP is one of the most promising materials for high-efficiency, high-power laser applications, it is difficult to grow as a large single crystal, according to Alfred University assistant professor Yiquan Wu.

Wu, supported by an Air Force Office of Scientific Research Young Investigator Award, is studying the synthesis and properties of anisotropic, polycrystalline, transparent ytterbium-doped strontium fluoroapatite, the same material used now as a single crystal. (The Mercury website says that LLNL also is looking at transparent ceramic amplifier media, but does not mention composition.)

In an email Wu comments, “If polycrystalline hexagonal Yb:S-FAP transparent ceramics can be successfully developed through advanced ceramics processing, such as by spark plasma sintering, it will be possible to make large-size laser gain media with optical properties currently unattainable by the Czochralski process.” The gain media for advanced laser applications, such as these, have cross-sections of 10-40 cm².

According to Wu, laser ceramics are attractive because they last longer and can be fabricated more efficiently than single crystals, i.e., they can be formed faster with higher output production while using cost-effective manufacturing methods. He also notes that there are design opportunities that cannot be obtained with existing lasers. “Laser ceramics allow for the production of homogeneous solid solutions with high concentrations of laser-active ions and for composite laser media with complicated structures. The development of processing techniques for manufacturing laser ceramics with arbitrary geometries and with variable dopants would allow the optical and physical characteristics of ceramic lasers to be tailored, providing the opportunity to design lasers with novel properties and functions,” he reports.

His team is working with wet chemical processes and advanced ceramic processing methods to synthesize transparent ceramics. Wu says, “It would take months to grow single crystals with an appropriate size, but only several hours are needed to make these transparent ceramics.”

The image (above) shows progress the group has made synthesizing transparent Yb:S-FAP. The focus is on understanding the fundamental mechanisms that control the quality of the materials, which can be applied to a broader class of anisotropic transparent ceramics. To this end, the group is looking at other compositions, too, such as Y₃Al₅O₁₂, ZnS, Lu₂O₃, CaF₂ and Y₂O₃.

Wu will share more about his work with Yb:S-FAP and other transparent laser ceramics in the March 2013 issue of The Bulletin.

Share

According to EWI researcher Edward Herderick, the disaster at the Fukushima Daiichi nuclear power plant presents a key question to the materials community. He asks, “Are there materials innovations that can profoundly improve the safety of existing light water reactors?”

Herderick, an applications engineer in EWI’s Materials Group (Columbus, Ohio), says that, based on investigations at EWI, the answer seems to be “Yes.”

EWI has been testing the silicon carbide ceramic-matrix composites as replacements for the currently used zirconium alloy fuel cladding in light water reactors. While the SiC cladding would not have prevented the Japanese disaster, it might have prevented some of the cascading of problems seen in Japan, including the deterioration of the zirconium cladding (an event that eventually contributed to the chemical reactions that resulted in the explosions at the Fukushima reactor).

Making a SiC tube to hold nuclear fuel pellets is the relatively easy part of the solution. The difficulty has been with finding a way to join the SiC cap to the rest of the SiC tube so that the overall mechanical and thermal strength is not compromised.

“Joining” is one of the specialties of EWI, and that is how Herderick became involved. He and others at EWI perfected an approach that uses a multiphase braze alloy consisting predominately of silicon and aluminum and small amounts of alloying elements with a two-phase joined microstructure.

Samples of the EWI tubes were tested in an MIT research reactor, where they recently emerged intact, having survived six months of aggressive irradiation testing.

More testing is ahead, but Herderick says the use of the SiC tubes could lead to a substantial increase in existing reactor safety. “Transitioning from zirconium alloy nuclear fuel cladding to a silicon carbide composite cladding is fundamentally a materials challenge, and it would represent the biggest shift in light water reactor materials technology since their original design and introduction,” he says.

Share

Scintillator single crystals glowing under exposure to UV light. The compositions are (left-to-right) Lu₂SiO₅:Ce, Gd₃(Ga,Al)₅O₁₂:Ce and Lu₂SiO₅:Ce,Eu (Eu is a codopant ion). The diameter is about 30 mm, and the two taller crystals are about three inches tall. The blue colored crystal (LSO:Ce) is used in Siemens’ Positron Emission Tomographs. Credit: Zhuravleva, U. Tenn., Knoxville.

By the time you read this, I will have been to Europe and back on an airplane. I will have passed through several security checkpoints, along with millions of fellow travelers, suitcases, cargo, supplies and pretzel snacks, looking to keep out any bad guys or their stuff. It is a search for a needle in the haystack, and it has to be done accurately and quickly.

There are many other situations where radiation needs to be detected, for example, for security, monitoring nuclear materials, remote inspection (gas well logging) or medical diagnosis. Department of Homeland Security requires, for example, detecting certain kinds of radiation. Detection of radiation such as neutron and gamma rays requires instruments with materials that are sensitive to particular radiation types.

Scintillators are such materials. They are comprised of single crystal host materials doped with rare earth “activator” atoms. The host matrix is very dense, a characteristic that allows it to absorb the incident radiation and transfer it to the activator, which emits light. In the case of Eu²⁺ activator ions, for example, the luminescence comes from the 4d-5f transition. The emitted photons are captured by a photomultiplier tube, completing the radiation detection process. For some applications, the signal from the PMT is reconstructed to create an image of the original source of the radiation, and this is the principle behind medical computed tomography scans, for example.

Increasingly sophisticated applications, especially for homeland security and medicine, are driving the development of new scintillator materials with improved energy resolution and higher light outputs, according to Mariya Zhuravleva, a crystal grower and research assistant professor in the Scintillation Materials Research Center at the University of Tennessee, Knoxville. In a phone interview she said, “Especially after 9-11 there has been lots of research. People are desperate to find new materials.”

“There are several properties we are looking for depending on the application,” she says. “For medical applications we are interested in a fast scintillation decay time and high light yield.” For homeland security applications, however, the most important parameter is energy resolution because that gives the ability to detect which isotope is emitting radiation. We are looking for only traces of radiation.”

The state-of-the-art energy resolution of scintillators in use today is 3-5 percent (the lower the number, the better the resolution).

The host matrix is key, she says. “The properties are dependent on the host material. For example, if the activator is within the band gap of the host material, efficient luminescence is possible,” according to Zhuravleva. Her research program focuses on ternary alkali–metal–halide single crystals with general formulas of AM₂X₅, AMX₃ and A₄MX₆, where A is a an alkali metal, M is an alkaline earth metal and X represents the halide, either chlorine, iodine or bromine.

“By nature [halides] are much more efficient scintillators [than oxides]. The light they emit is very bright and easy to collect, which has the advantage of constructing smaller devices.” Also, these crystals are denser than silicates, which means they can stop radiation more effectively and give a better signal. There are commercially available alkali–halide scintillators, such as NaI:Tl and CsI:Na. However, Eu²⁺ is an attractive activator because it has a very efficient luminescence, which, with the right host matrix, could lead to scintillator crystals that have high light output and high-energy resolution.

Zhuravleva explained that she is studying crystal structures with a divalent cation because they have a built-in site for incorporating Eu^2+, and her new paper published the Journal of Crystal Growth reports on the properties of two new single crystal scintillators: CsCaCl₃:Eu and CsCaI₃:Eu. Other materials she has investigated over the last several years include Ce³⁺ activated scintillator crystals, such as KGd₂Cl₇:Ce, Cs₃CeCl_{6, Cs3CeBr6,} CsCe₂Cl_{7 and CsCe2Br7.}

There are significant property trade-offs between iodides and chlorides. Zhuravleva explained that iodides have the smallest band gap and are therefore more efficient. Chlorides have a wider band gap and can trap energy, which reduces efficiency. Iodides are denser and better able to stop incident gamma-ray radiation, which is important for medical applications, for example. However, chlorides are less air-sensitive, which could make them easier to work with and assemble into deployable devices.

As she considers which compounds to test as host crystals, Zhuravleva says, “I want congruent melting compounds. They are very stable and do not decompose, and we can avoid cracks that come with phase transitions during crystal growth.”

The halide family of compounds have low melting points, too, which is an advantage. She grows these crystals via the Bridgman process (most oxides are grown by the Czochralski method), however, the process in blind: She cannot see the crystal during the process. The compounds are very sensitive to growth conditions, she says, and require a lot of thermal insulation. More importantly, halides are extremely hygroscopic and are grown in sealed quartz ampoules and handled in dry boxes.

In the recent work on cesium-calcium halides, the optimal Eu dopant concentration (determined on light yield) was 10 atomic percent for the chloride and 3 atomic percent for the iodide. Interestingly, the new scintillators exhibited energy resolution that is comparable to the benchmark scintillator, NaI:Tl, which is widely used in medical and security applications.

Zhuravleva’s next goals, supported by a five-year grant from the Department of Homeland Security, are to optimize on crystal growth technology, scale up the process to grow two-inch diameter crystals and to find a matrix-activator combination that will drive the energy resolution toward one percent.

Editor’s note: Zhuravleva will provide an update on scintillator developments for homeland security and defense applications in the March 2013 issue of ACerS’ Bulletin magazine.

Share

Nuclear power plant control room. Credit: Wikipedia Commons.

When Japan’s government last week suddenly announced that it would phase out its nuclear power plants by 2040, it probably thought it would be scoring some popularity points with its population where public opinion has been strong in opposing the continued use of nuclear power since the Fukushima Daiichi disaster. But, the policy announcement clearly caught a lot of people—inside and outside the country—by surprise. Perhaps the two groups most caught off guard were Japan’s industrial sector and the communities where the nuclear power plants are located.

Thus, it isn’t totally surprising that government officials are attempting to “walk back” the policy and recast the phase-out as a general “target” rather than a specific goal.

Reuters reports, “Since the plan was announced on Friday, Japan’s powerful industry lobbies have urged the government rethink the nuclear-free commitment, arguing it could damage the economy and would mean spending more on pricey fuel imports.” The news agency goes on to say that although the Japanese Cabinet approved a new policy that would move the country to less reliance on nuclear power, a specific date for closing all reactors was omitted.

As with most reactors, the ones in Japan were designed for a 40-year lifespan. The approved policy calls for operators to adhere to that lifespan, however the same policy also permits the designed life to be exceeded if regulators certify a reactor’s safety.

There still will be a ban on new reactors, but it is not clear what the fate will be of the two reactors currently under construction

The government is also hoping that a newly launched, more credible regulatory agency will ease public concerns.

Share