Ceramic Industry

Advancing Ceramic & Glass Technology

August 1, 2008
CI’s annual Ceramic and Glass R&D Overview highlights technology advances from around the globe.

A self-healing ceramic, crystals grown from aqueous solutions, lunar construction materials produced through a self-propagating high-temperature synthesis reaction-these are but a few of the technology advances being made at universities and research laboratories around that world that are detailed in this year’s Ceramic and Glass R&D Overview.

In yttria-stabilized zirconia (top), the defects produced by radiation are few and far between, having less impact on the properties of the material. In zircon (bottom), the defects are clustered, which could compromise the material’s integrity.

Self-Healing Ceramic

A new computer simulation has revealed a self-healing behavior in a common ceramic that may lead to the development of radiation-resistant materials for nuclear power plants and waste storage. Researchers at the Department of Energy’s (DOE) Pacific Northwest National Laboratory (PNNL) found that the restless movement of oxygen atoms heals radiation-induced damage in yttria-stabilized zirconia.

Scientists Ram Devanathan and Bill Weber modeled how well that ceramic and other materials stand up to radiation.1 “If you want a material to withstand radiation over millennia, you can’t expect it to just sit there and take it,” said Devanathan. “There must be a mechanism for self-healing.”

“This research raises the possibility of engineering mobile defects in ceramics to enhance radiation tolerance,” Weber said. He noted that materials capable of handling high-radiation doses also “could improve the durability of key equipment and reduce the costs of replacements.”

Although the self-healing activity does not completely repair the material, the defects are less apt to cause problems because they are spread out. This characteristic indicates that yttria-stabilized zirconia, which is used today in such items as solid oxide fuel cells and oxygen sensors, might be suitable for nuclear applications.

The researchers also simulated the impact of radiation on zircon, a ceramic that is a candidate for immobilizing high-level nuclear waste. The scientists are now refining the simulations and applying them to other materials.

The DOE’s Office of Basic Energy Sciences funded the research, which was performed on massively parallel supercomputers in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) at PNNL and the National Energy Research Scientific Computer Center at Lawrence Berkeley National Laboratory.

For more information, visit www.pnl.gov

Cross-section of a PWHGM.

Hollow Glass Microspheres with Unique Porous Walls

Porous glasses have been prepared by various means and in many forms. Their purposes have included catalysis and filtration, for example. Recently, the Savannah River National Laboratory (SRNL) developed a new geometric form: hollow glass microspheres (HGMs) with unique porous walls-PWHGMs. The glass porosity of this material is in the range of hundreds to thousands of angstroms and has permitted the introduction of materials to the interior of the HGMs.

In general, a glass composition prone to amorphous phase separation is used to produce an HGM. The HGM is heat-treated to develop the interconnected microstructure. The heat-treated HGM is then subjected to a leaching process, which results in a sponge-like network structure consisting mainly of silica.

SRNL developed a matrix of six glass compositions based on a composition from previous research that was successfully proven to form PWHGMs. Two critical parameters were varied: the silica concentration and the B2O3/alkali molar ratio. HGMs were produced by a flame process that utilizes an experimental apparatus developed at SRNL. Various heat treatment conditions (temperature and time) were used to develop the microstructure in the HGMs prior to acid leaching.

Heat treatment temperature rather than composition was determined to be most effective in changing the porosity of PWHGMs. Pore diameter in a non-heat-treated sample (prior to acid leaching) was approximately 100 Å. With heat treatment at 600°C for eight hours, the diameter was increased tenfold to approximately 1000 Å. A considerable increase in pore volume was also observed in heat-treated samples.

The capability to control pore size of PWHGMs through heat treatment temperature and potentially composition can possibly meet various end user needs such as hydrogen storage, molecular sieves, drug and bioactive delivery systems, and environmental, as well as chemical and biological indicators.

Information provided by Fabienne C. Raszewski, Erich K. Hansen, Steven D. Mann, Ray F. Schumacher, and David K. Peeler of the Savannah River National Laboratory. For more information, visit srnl.doe.gov.

The SHS reaction reaches its maximum when all favorable mineral and glass constituents within the regolith simulant have been reduced by oxidation-reduction reactions with aluminum.

Ceramic Lunar Construction Materials Produced Utilizing SHS

The NASA Constellation program plans to return humans to the moon by 2020. In-situ resource utilization is essential to establish a permanent settlement on the moon. A process for transforming a mixture of JSC-1AF lunar regolith simulant into a coherent ceramic material has been discovered. The transformation is accomplished by means of a self-propagating high-temperature synthesis (SHS) reaction. This reaction is initiated by heating a portion of the sample to the ignition temperature. Once ignition occurs, the reaction continues without any further application of external heat.

During the SHS reaction, aluminum reduces some of the constituents of the regolith simulant, which produces a large quantity of heat. Methods to harness this heat in order to liberate volatiles-along with any ice present on the lunar surface-are being investigated. The reaction product retains the shape of the crucible used for the reaction. In addition, the nature of the SHS reaction allows this reaction to be scaled to any size.

Gibbs free energies were calculated for the reduction of the oxides present in the regolith simulant through interaction with aluminum. The oxides used in these calculations were determined using bulk compositional analysis. Regolith, however, is an assemblage of minerals and glass, not simple oxides. The Gibbs free energies indicate that iron oxides, silicon oxides and titanium oxides are the most likely compounds to undergo reduction. XRD analyses have indicated that elemental silicon, iron and possibly titanium are present in the reaction product.

The product of this reaction has potential for use as a lunar habitat construction material, a habitat radiation and micro-meteorite shield, a paving material for lunar roads and landing sites, a source for elements in their reduced states, and a heat source to either liberate water and volatiles from lunar regolith or be used in a system to produce electrical power.

For more information, contact Eric J. Faierson at (757) 325-6822 or faierson@vt.edu, or Kathryn V. Logan at (757) 325-6820 or kvlogan@vt.edu.

NASA's 64-tile shuttle array mounted atop the Solar Tower.

NASA Tests HYTHIRM at Sandia's Solar Tower

NASA recently turned to Sandia’s National Solar Thermal Test Facility-a.k.a. the Solar Tower-to help evaluate new technology for future space shuttle missions. NASA’s most recent testing series in early March evaluated the HYpersonic AeroTHermodynamic InfraRed Measurements (HYTHIRM) systems.

HYTHIRM is a collection of systems NASA wants to use to plan and execute missions. It includes a suite of radiometric infrared imaging systems, mission planning capabilities such as a radiance prediction methodology, and other systems with an understanding of atmospheric effects. NASA test director Kamran Daryabeigi says planners will use HYTHIRM to evaluate the performance of the participating sensor systems and associated image processing algorithms.

Sandia test engineer Cheryl Ghanbari says NASA expects the new instruments to provide more accurate thermal and radiological monitoring data on the conditions on the shuttle’s surface during re-entry. NASA also hopes, Ghanbari says, that these monitoring systems will help scientists understand the overheating of the shuttle surface due to unexpected boundary layer transition from laminar to turbulent flow that is caused by anomalies (like protruding gap filler).

The Solar Tower testing involved the coordination of infrared imaging assets from five locations: three land imagers, one flown on a Navy P2 and one space-based. A 4 x 4-ft array of 64 shuttle LI-900 ceramic tiles was placed on the test arm at the top of the 200-ft-high tower, Ghanbari says. Then thermocouples internally installed in some of the tiles on the array and an infrared imager located close to the test target provided actual surface temperature conditions.

NASA’s Scott Splinter (left) and Sandia’s J.J. Kelton examine shuttle tiles used for the Tower experiment.

A solar beam, made from reflections of 40 of the field heliostats, was focused on the test array of shuttle tiles. The array was subjected to uniform and nonuniform heating to obtain radiometric data of a known radiation source at temperatures up to 2000°F. This high temperature, Ghanbari says, simulated surface temperatures of the shuttle during re-entry into Earth’s atmosphere, allowing NASA to calibrate and evaluate HYTHIRM.

The test results will be used to evaluate the readiness of multiple monitoring systems, and will help NASA determine the relative priority for deployment in support of future hypersonic boundary layer transition flight experiments on the shuttle orbiter in 2009.

Subsequent analysis of the imagery will be used to evaluate the performance of the participating sensor systems and associated image processing algorithms. For more information, visit www.sandia.gov.

Single crystals of scandia grown hydrothermally at Clemson University.

Exploring Crystal Growth Technology

The sesquioxides of scandium, yttrium and lutetium are promising hosts for eye-safe, high-average-power lasers because of their isotropic structure, favorable ligand field properties, and high thermal conductivities, among other properties. Growing large, high-quality single crystals is a challenging problem since the extremely high melting points of these materials severely limit possible crystal growth techniques and introduce a number of complications affecting size and purity. The Advanced Materials Research Laboratory (AMRL) at Clemson University has addressed this task using a novel hydrothermal approach where crystal growth occurs from aqueous solutions at approximately 1800°C below the melting points of the oxides.

In its preliminary studies, AMRL has grown optically clear crystals of Sc2O3 and Er: Sc2O3 with dimensions up to 1 cm at rates of about 1 mm/side/week. This represents a significant breakthrough in crystal growth technology as it pertains to scandia. Single crystals of Er: Sc2O3 having various shapes have been fabricated and optically polished from these hydrothermally grown pieces. Advanced optical and thermal conductivity measurements on these crystals are presently underway. Scale-up of the hydrothermal growth process for scandia and proof of concept studies of the growth of lutetia are also being performed. For more information, visit www.ces.clemson.edu.

Figure 1. Resistance change of ε-WO3 with exposure to acetone at 400°C.

Acetone Nanosensor for Non-Invasive Diabetes Detection

Diabetes is a common disease worldwide, and acetone in exhaled breath is a known biomarker of Type-1 diabetes. The Center for Nanomaterials and Sensor Development in Stony Brook University, N.Y., has developed an exhaled breath analyzer with the potential to diagnose diabetes as a non-invasive alternative to currently used blood-based diagnostics.

The device utilizes a chemiresistor based on ferroelectric tungsten oxide ceramic nanoparticles. Ferroelectric WO3 (ε-WO3) nanoparticles were synthesized using a method called flame spray pyrolysis using the facilities at the Particle Technology Laboratory of Professor Sotiris E. Pratsinis in ETH Zurich. Cr dopants were added to stabilize the polymorph of interest, which would otherwise transform to common γ , β-WO3 phases at high temperatures.

The ε-WO3 phase is a type of ferroelectric material that has a spontaneous electric dipole moment. On the other hand, acetone has a much larger dipole moment than most other gases commonly found in human breath. As a consequence, the interaction between the ε-WO3 surface dipole and acetone molecules may be stronger than any other gas, enabling selective acetone detection.

The obtained nanosensor sensitivity suits the detection requirements of acetone in human breath with concentrations of < 0.8 ppm for a healthy person and > 1.8 ppm for a diabetic patient (see Figure 1). In addition, the sensor responds to acetone exposure in less than 10 seconds. Therefore, the ε-WO3 nanoparticle-based sensor is capable of real-time, fast-response, stable and highly sensitive detection of acetone gas.

The relative response of this sensor to a series of interfering gases commonly found in human breath (including CO, NH3, methanol, ethanol, CO2, NO and NO2) was also tested. The sensor demonstrates very good selectivity to acetone at 400°C. To make the portable breath analyzer, the sensor was attached onto a heater and then embedded into a circuit board. For more information, contact P. I. Gouma, Ph.D., at pgouma@notes.cc.sunyb.edu.

Editor’s note: This article was compiled from information submitted by laboratories and universities, and it is not intended to be a comprehensive overview of all ceramic and glass research currently in progress.