Ceramics and Glass of the Future
Advanced Refractory Liners for Slagging Gasifiers
Gasifiers are the heart of Integrated Gasification Combined Cycle (IGCC) power system being developed as part of the U.S. Department of Energy's (DOE) Near Zero Emissions Advanced Fossil Fuel Power Plant. They are also used to produce chemicals that serve as feedstock for other industrial processes, and are considered a potential source of H2 in applications such as fuel cells. An IGCC gasifier is a high-pressure/high-temperature reaction vessel used to contain a mixture of O2, H2O and carbon (typically from coal or petroleum coke) while it is converted into thermal energy and chemicals (H2, CO and CH4). In a slagging gasifier, the reaction chamber operates at temperatures between 1250-1575ºC and pressures up to 1000 psi, and it is lined with refractory materials (dense firebrick composed of Cr2O3 as the primary component, along with smaller quantities of oxides such as Al2O3 and/or ZrO2). Gasifiers provide the ability to meet or exceed current and anticipated environmental emission regulations, and they are expected to play a dominant role in meeting the nation's future energy needs.However, slagging gasifiers currently have performance issues affecting their affordability, reliability and online availability, which have prevented them from wider use by industry. A recent survey of gasification industry stakeholders identified refractory service life as the most important research and development need. Slag attack from liquified ash in the carbon feedstock and the service environment of the gasifier are the main causes of a short service life. Refractory failure is typically by corrosive slag dissolution or by spalling, leading to the need for a brick relining within three to 24 months.
Through laboratory research, the DOE's Albany Research Center has developed an improved performance high Cr2O3 refractory material containing phosphate additions, produced in cooperation with a refractory manufacturer. The material is currently being evaluated in field trials at a commercial gasifier.
For more information, contact Cynthia Powell at (541) 967-5803, e-mail powellc@alrc.doe.gov or visit http://www.alrc.dow.gov.
Ceramic Membranes, Sprayable Building Materials and SOFCs
Ceramic experts and materials scientists at Argonne National Laboratory are working on several promising new technologies for energy and construction applications.In Argonne's Energy Technology Division, a research team led by Balu Balachandran has developed a ceramic membrane that can extract highly pure hydrogen from methane, the chief component of natural gas. Such high purity is possible because of the density of the membrane material-only electrons and individual ions can pass through it.
"Just as conventional cars need gas stations, fuel cells will need an infrastructure to support them. Ceramic membranes could eliminate the need for costly refineries-they are small enough and efficient enough to have one at every gas station," Balachandran said.
Argonne is also working on fuel cell technologies. A new rugged solid oxide fuel cell (SOFC) called TuffCell, invented by materials scientist J. David Carter, is designed to provide higher mechanical strength, easier fabrication and increased performance at a lower cost than current solid-oxide fuel-cell designs. The innovation replaces the traditional costly, fragile ceramic cell support with a less-expensive, stronger, metallic bipolar plate, and could be ready for commercialization in five years. The new design also simplifies manufacturing. The traditional cells built with ceramic supports require up to four separate high-temperature sinterings-one for each layer. The Argonne method spreads four thin layers of the oxide and metal materials needed-one on top of the other-and sinters only once. The new SOFCs are expected to overcome the cost and durability issues that have been barriers to introducing solid-oxide fuel cells as auxiliary power units for tractor-trailers and other portable power applications.
In the construction industry, a team of Argonne researchers working with Casa Grande LLC has invented a tough new ceramic material that is almost twice as strong as concrete may be the key to providing high-quality, low-cost housing throughout developing nations. Called Grancrete, the material is sprayed onto a rudimentary Styrofoam frame and dries to form a lightweight but durable surface. The material is based on an Argonne-developed material called Ceramicrete, which was developed in 1996 to encase nuclear waste.
Experiments have shown that Grancrete is stronger than concrete, is fire-resistant and can withstand both tropical and sub-freezing temperatures, making it ideal for a broad range of geographic locations. It insulates so well that it keeps dwellings in arid regions cool and those in frigid regions warm. The product is made from an environmentally friendly mix of locally available chemicals-50% sand or sandy soil, 25% ash and 25% binding material. The binding material is composed of magnesium oxide and potassium phosphate, the latter of which is a biodegradable element in fertilizer. The cost of building a Grancrete home, estimated at about $6000 U.S. for labor and materials, is several times less expensive than a home built using conventional building materials.
For more information, visit http://www.anl.-gov/Media_Center/Frontiers/2003/d2ee.html (ceramic membranes), http://www.transportation.anl.gov/research/fuel_cells/tuffcell.html (fuel cells), or http://www.grancrete.net (Gancrete).
Armor for the Future Combat Systems Vehicle
For more than a decade, Idaho National Laboratory (INL) has been the sole manufacturer of heavy armor for the Army's M1 A1 Abrams tanks. Today, new research and development involving the use of ceramics to develop next-generation, lightweight armor for the Army's Future Combat System vehicle is also being conducted at the lab.Researchers at INL, led by Defense Systems manager Gary Thinnes, have focused their efforts on the development of silicon carbide compounds to develop lightweight vehicle armor tiles that, when engaged by armor-piercing rounds, cause the bullets to erode and break apart as they come in contact with the ceramic plates. Similarly, researchers are developing joining methods and tools such as roll-bonding, friction stir welding bits and brazing techniques to create and facilitate ceramic armor solutions for the Future Combat System vehicle.
Armor researchers at INL are also developing ways to bond ceramic plates to titanium structures to enhance survivability and to encapsulate ceramic tiles with aluminum and titanium to withstand multiple local impacts without failing.
For more information, contact Ethan Huffman at (208) 526-0660 or e-mail ethan.Huffman@inl.gov.
Metal Oxide Powders for Ceramic Manufacturing
The Advanced Materials Synthesis Group in the Chemistry and Materials Science Directorate at Lawrence Livermore National Laboratory (LLNL) has developed an inexpensive method of making high-surface-area metal oxide powders for ceramic manufacturing. The method allows for the bulk production of single-phase metal oxides, as well as mixtures containing multiple oxide phases. Using this method, extremely fine dispersions of multiple phases can be achieved, often on scales of less than 20 nanometers. According to LLNL, these nanostructured powders display increased toughness over existing commercial powders when processed into ceramic materials.
For more information, contact Anne Starck at (925) 422-9799 or e-mail stark8@llnl.gov.
Characterization and Testing of SOFCs
YSZ and nickel or cobalt are commonly used as anodes and Sr-doped LaMnO3 as cathode. The commercial success and large-scale deployment of SOFCs in distributed power generation and mobile applications will depend on their cost, durability and reliability. These requirements constitute a significant challenge because the materials used in SOFCs are brittle, and because they possess dissimilar thermoelastic properties they will be subjected to residual stresses. Furthermore, during service these materials will experience temperature gradients, which will also result in stresses, thermal cycles, transients and long-term exposure to elevated temperatures.Researchers at the Oak Ridge National Laboratory's High Temperature Materials Laboratory are collaborating with SOFC manufacturers in the U.S. to implement probabilistic-based methodologies, which account for the stochastic nature of the strength of materials, to design SOFCs. Using advanced characterization tools they have identified the microstructural features that act as strength-limiting flaws in SOFC materials and their rate of growth with time, stress, temperature and environment. Such information is essential because it can be used to both predict the service life of SOFCs and to improve the processing, microstructure and properties of SOFC materials. ORNL researchers have also been involved in the development and implementation of test methods to evaluate the thermomechanical and thermophysical properties of SOFC materials as a function of temperature and environment. The research work at ORNL has been sponsored in part by the Core Technology Program of DOE's Solid State Energy Conversion Alliance (SECA) Program.
For more information, contact Edgar Lara-Curzio at (865) 574-5123 or e-mail laracurzioe@ornl.gov.
High-Strength Ceramics Based on Wood
Materials scientists at the DOE's Pacific Northwest National Laboratory (PNNL) have developed a chemical process to create two new ceramic materials that are laboratory versions of petrified wood. These materials combine the hardness of metal with the high surface area of carbon to form metal carbides that are stronger than steel and can withstand temperatures to 1400°C."The original cellulose structure of the wood acts as a template," explains Yongsoon Shin, the PNNL scientist who invented the process. Using a simple chemical process, Shin soaked the wood in acid, then infused it with a source of either titanium or silicon and baked it in an argon-filled furnace. In the resulting petrified wood, the silica and titanium take up permanent residence with the carbon left in the cellulose to form the silicon carbide (SiC) and titanium carbide (TiC). The intricate network of microchannels and pores in plant matter that provides enormous surface area in wood is maintained in the new materials. For this reason, the most promising applications are as catalysts in industrial chemical separations or as filters for pollutants from gaseous effluents. The new materials also offer possibilities for the cutting tools industry, where they can be used to form templates into which metal can be infused, resulting in stronger, harder blades, rotors and other cutting tools. To form tougher and longer-lasting abrasives using the PNNL process, wood flour could be infused with silicon and titanium. The process is currently available for licensing.
For more information, contact Eric Lund at (509) 375-3764 or eric.lund@pnl.gov, or visit http://www.pnl.gov/news/2005/05-38.stm.
Customized Bone Substitute
Researchers at Sandia National Laboratories have created a ceramic prosthesis that can simplify jaw reconstruction procedures and improve patient outcomes. The device was used recently during a reconstruction procedure conducted at Carle Hospital in Urbana, Ill., where it was temporarily fitted into the mouth of an elderly patient who had lost most of her teeth and a portion of her jaw. The fitting was intended to determine whether the implant, created at Sandia, had been accurately designed using only a CAT scan of the women's skull as a reference. Because scientists have performed only lab studies of the device's strength and permeability, and FDA approval has not yet been obtained, the woman then had to endure the standard method of bone replacement, which involves transplanting bone from the pelvis.Since that fitting, similar devices were implanted in goats at the University of Illinois. Complete bone ingrowth occurred in eight weeks-a very promising result.
If approved by FDA for in vivo testing, the scaffold-like structure, made of layered mesh that is as strong as bone but porous, could be used to replace a portion of the mandible. The mesh material would be gradually replaced by healthy, newly grown bone and blood vessels. The researchers believe the ceramic scaffolding could reduce patient trauma and chances of infection.
The device is built mainly of hydroxyapatite, a material already approved by the FDA for bodily implants, so approval of the new device is expected to be straightforward.
"Surgeons and patients would love to eliminate both the bone retrieval and implant preparation processes," says Sandia scientist Joe Cesarano, whose team fashioned the new implant. "This test showed we can customize artificial porous implants prior to surgery that will fit perfectly into the damaged region. The reconstructive procedure would then only require attaching the implant and closing the wound."
The Sandia-patented process, called Robocasting, was developed to fabricate defense components out of ceramics in a way no ordinary mold or machining procedure could achieve. Situated on a truck, the system can be used to make replacement parts on a battlefield, eliminating the need to carry an inventory of parts onto a site. Another goal of the project is to develop a way to form advanced catalyst supports that operate like a maze (rather than straight channels) to maximize chemical reactivity.
To cast a part, a computer-controlled machine dispenses liquefied ceramic paste-much like toothpaste squeezed from a tube-to form shapes of varying complexity along a prearranged path. To create the simulated bone scaffolding, the machine dispenses a hydroxyapatite mixture arranged in cross-laid slivers, each about as thick as the diameters of ten human hairs.
For more information, contact Michael Padilla at (505) 284-5325 or e-mail mjpadil@sandia.gov.
Hydrogen Storage in Glass Microspheres
Research headed by James Shelby, Ph.D., and Matthew Hall at the New York State College of Ceramics (NYSCC) at Alfred University is demonstrating that hollow glass microspheres produced using the sol-gel method can be used to design an operational hydrogen generator. Previous research supported by Alfred University's Center for Environmental and Energy Research (CEER) proved the validity of photo-enhanced hydrogen diffusion through glasses doped with optical activators. Results of the current study are expected to provide the "reduction to practice" needed to patent the hydrogen storage device, and to convince potential funding agencies and automobile manufacturers of the viability of this technique. The researchers believe the work will ultimately lead to a revolutionary new method for storing, transporting and delivering hydrogen on demand.
For more information, visit http://ceer.alfred.edu/Research/glassdiffusion.html.
Optical Fiber and Photonic Technologies
The School of Materials Science and Engineering (MSE) and its allied Center for Optical Materials Science and Engineering Technologies (COMSET) at Clemson University are advancing numerous inorganic materials for optical fiber and related photonic technologies. Professor Kathleen Richardson, Ph.D., school director, recently joined Clemson from the University of Central Florida and is pioneering non-oxide glasses and ceramics. Richardson's group uses ultra-fast lasers to induce structural and chemical modifications into chalcogenide glasses in order to "write" optical structures and affect optical functionality into planar and fiber devices. Professor John Ballato, Ph.D., COMSET director, leads the optical fiber effort within COMSET, which operates a state-of-the-art optical fiber draw tower and commercial production-level MCVD lathe. Ballato's research activities include the fabrication of polymeric, oxide, and non-oxide optical fibers for sensor and laser applications. Most recently, this work has focused on the fabrication of phosphate and telluride glass fibers for high-power fiber lasers.
For more information, contact John Ballato at (864) 656-1035 or e-mail jballat@clemson.edu.
Vapor Phase Sintering
Sintering ceramics in a reactive atmosphere can enhance gas transport that precludes shrinkage and densification but leads to strong interparticle bonding as predicted by simple sintering models. In addition, enhanced vapor transport gives rapid grain growth and pore growth. Therefore, sintering in a reactive atmosphere to enhance gas transport (called "vapor phase sintering," or VPS) leads to ceramics with controlled pore size and particle size.Research on vapor phase sintering has been pursued at Colorado School of Mines for several years and has produced a range of applications and patents, as well as an improved fundamental understanding of the sintering process. Controlled porosity and pore size ceramics can themselves be used as lightweight, corrosion-resistant high-temperature filter materials. Several patents have been obtained on ceramic-metal composites with unique properties and applications made by infiltrating porous VPS ceramics with molten metals. Finally, many porous oxides, such as Fe2O3 and NiO, can be reduced after VPS to produce porous lightweight metals that, in addition to being low-density structural materials, also have unique filter properties and applications-a process that also has been patented.
For more information, contact Dennis W. Readey at (303) 273-3437, e-mail dreadey@mines.edu or visit http://www.mines.edu.
Glass Resists for Lithography
Lithography is a process that rapidly replicates a micro pattern or an electronic circuit. A lithographic system consists of exposure (irradiation) source, mask, resist, and the processing steps that would accomplish pattern transfer from a mask to a resist and then to devices. The creation of mask or use of resist is based on materials that are sensitive to some specific radiation. Thus, one may transfer complicated patterns into a resist by irradiating its selected regions. Due to its radiation sensitivity, the chemical reactivity of exposed regions is modified with respect to the unexposed regions. A developer chemical than preferentially etches out either the exposed (positive resist) or unexposed (negative resist) region, thus faithfully transferring the original pattern into the resist.The highest resolution that is attained in a lithographic process is often determined by the properties of the resist material. With the currently used polymeric resists, a resolution of better than 100 nm has been achieved under manufacturing conditions, but the future nanoscale devices will require a ten times superior resolution. In principle, inorganic resists should have higher limiting resolution than polymer resists due to smaller fundamental structural units and stronger bonds in the former.
Researchers Himanshu Jain, Miroslav Vlcek and Andriy Kovalskiy at Lehigh University's Department of Materials Science & Engineering and International Materials Institute for New Functionality in Glass, in collaboration with the Army Research Laboratory, have developed chalcogenide glass-based photo and electron beam resists, which also have the advantages of greater hardness, resistance to acids, easy fabrication in thin film form, and the unique phenomena like radiation enhanced diffusion. Figure 1 shows a ‘nanowheel' created in an arsenic sulfide glass film by electron beam lithography. These wheels have demonstrated a resolution of 14 nm, and researchers believe that several times better resolution should be achievable.
For more information, contact Professor Himanshu Jain at (610) 758-4217 or e-mail H.Jain@lehigh.edu.
Nanostructured Ceramics by Gas-Phase Reaction
The widespread use of nanostructured materials is often complicated by the conflicting demands for precise control of fine features (down to the nanometer scale) and large-scale mass production. Recent work by Sehoon Yoo in Sheikh Akbar's laboratory at The Ohio State University has led to the development of a novel and inexpensive technique creating oriented nanofiber arrays of single crystal titania (TiO2) by gas phase reaction with hydrogen. The nanofibers are created by a selective and anisotropic etching process called "nano-carving". Unlike other nanostructure forming techniques, nano-carving doesn't require any sophisticated patterning technology, expensive precursors, or rigorously trained operators and can be easily scaled up. All one needs to produce the structure is a furnace for sintering the TiO2 powder compacts (at 1200°C for 6 h) and a controlled atmosphere furnace for a subsequent heat treatment (5% H2/N2 for 8 hours at 700°C). The diameters of nanofibers range from 15 to 50 nm with lengths varying from 1 to 5 μm and are oriented along the [001] direction (Fig.1). The phase of nano-fiber is confirmed to be stoichiometric rutile TiO2 from x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), as well as selected area electron diffraction.This new process provides an economical way to mass-produce high surface area nano-structures that are already attached to a substrate. This makes them ideal platforms for catalytic, gas-sensing, and a variety of environmental, biomedical, transportation, and chemical manufacturing applications. Sehoon Yoo has already demonstrated that the process works for titanium oxide, an important engineering material that has been used in chemical sensors, catalytic supports and dye-sensitized solar cells. In addition, some initial effort with tin oxide elucidate the possibility of applying the process to other technologically important ceramics. Given the novelty of the process, there are tremendous opportunities for basic research involving advanced materials characterization techniques as well as computer modeling and simulation. Moreover, this process opens a new avenue for micro- and nano-machining of ceramics, which is not a trivial task. The flexibility of the process has been demonstrated by fabricating other nano-structures such as nano-channels, nano-whiskers and nano-lamellar by gas-phase reaction.
This invention has led to the filing of a patent application (Application No. 10/678,772) and couple of distinctions for Sehoon Yoo: he was one of nine graduate finalists for the highly competitive 2004 Collegiate Inventors Award and a winner of the 2005 MRS Graduate Student Silver Award. His work also got coverage in popular media.
For more information, contact Sheikh Akbar at (614) 292-6725 or e-mail akbar@matsceng.ohio-state.edu.
Ceramic Nanocomposites and Hot Pressed SiC
Faculty (Professors Dale Niesz, Bernard Kear and W. Roger Cannon), students and post-doctorate students at Rutgers are developing a cost-effective, scalable processing for HIPping ceramic nanocomposites for armor and other applications. For example, commercial Al2O3 and MgAl2O4 are consolidated by spray drying followed by quenching in water from a DC-arc plasma torch to yield a metastable structure, which develops into a fine-grained or nanostructure during HIPping. When using materials with a high spinel content, hardness values of 20 GPa (at 2 Kg) and Kolsky-bar yield points of 5.5 to 6.7 GPa have been achieved. Forging studies of as-quenched spherical particles have emphasized the excellent green densities that can be achieved using spherical powder (see Figure 1), and the superplastic nature of the powder, which aids in densification without requiring powder milling.Faculty (Haber and Niesz) and students at Rutgers are also developing an improved technology for processing hot-pressed, armor-grade SiC. An aqueous based colloidal process has been developed that utilizes an aqueous source for B and C additions. This surfactant based additive technology has dramatically reduced the required addition levels of B and C. This has resulted in high hardness values of 22 GPa (at 2 Kg)and in hot pressed densities of 3.2 g/cm3 with fine grain microstructures, less than 3 microns.
For more information, contact W. Roger Cannon at (732) 445-4718 or e-mail cannon@alumina.rutgers.edu.
Nanostructured WC/Co Cermets
Researchers at the University of Connecticut (UConn) have developed a novel process for making low-cost, high-performance nanostructured WC/Co cermets. The process, which was patented in September 2004 (U.S. Patent No. 6,793,875), combines mechanical and thermal activation to reduce processing steps, lower reaction temperatures and shorten reaction times, thereby decreasing costs. The process is readily scaleable, and the resulting WC/Co powder has an average particle size of 300 nm and is composed of nano-WC grains with crystallite sizes ranging from 20 to 40 nm. Because of the submicrometer particle sizes, the powder is not pyrophoric, and its handling and storage can be conducted in air. This further decreases the cost of WC/Co cermets by reducing the cost of subsequent powder sintering and densification processes. The sintered bodies fabricated from this nanostructured WC/Co powder exhibit high hardness and superior toughness simultaneously, which is reportedly rare.
For more information, contact Professor Leon L. Shaw at (860) 486-2592 or
e-mail Leon.Shaw@UConn.Edu.
Ultra-High-Temperature Ceramics
Ultra-high temperature ceramics (UHTCs) are a unique class of materials that can be used at high temperatures (above 2000°C) and in reactive environments, such as air. Recent research activity related to UHTCs has been driven by NASA and military interests in hypersonic technology such as the X43, which is a hypersonic vehicle being tested by NASA. New materials are essential for the thermal protection systems and scramjet engines of hypersonic vehicles. UHTCs are candidates for these applications because of their strength at high temperature and resistance to creep, oxidation, and thermal shock. Most UHTCs are borides, carbides, or nitrides of the early transition metals such as ZrB2, HfB2, ZrC, HfC, HfN, and TaC.Research at the University of Missouri-Rolla's Materials Science and Engineering Department focuses on fundamental microstructure-processing-property relationships in UHTCs. The UMR team, led by William G. Fahrenholtz and Gregory E. Hilmas, has developed ZrB2-SiC and ZrB2-MoSi2 ceramics with room temperature flexural strengths in excess of 1000 MPa. While most UHTCs must be processed by hot pressing or similar pressure-assisted densification techniques, the researchers have devised a pressureless sintering route for ZrB2. The UMR team is also investigating the effect of structure on properties in conventional powder processed UHTCs, such as ZrB2, ZrB2-SiC, ZrC, and TaC, as well as materials with engineered meso-scale architectures, such as ZrB2-based fibrous monolithic ceramics. Research at UMR is currently supported by the Air Force Office of Scientific Research, the U.S. Army Space and Missile Defense Command, the National Science Foundation, the Air Force Research Laboratory, and the Naval Surface Warfare Center.
For more information, contact William Fahrenholtz at (573) 341-6343, e-mail billf@umr.edu; Gregory E. Hilmas at (573) 341-6102, e-mail ghilmas@umr.edu; or visit http://mse.umr.edu/files/UHTC_research.pdf or http://web.umr.edu/~uhtm.
Polysiloxane-Type Preceramic Polymers
Processing with preceramic polymers and filler-loaded preceramic polymers has become an intensive area of R&D during the past 15 years. Among them, polysiloxane-type materials bearing Si, O, C and H in their molecular structure are of interest due to their low costs and chemical stability in air. They are available as solids and liquids, are mixable with organic solvents and leave behind a ceramic residue often higher than 80 wt % after thermal conversion. Advantages include low processing temperatures and compatibility with plastic shaping processes. The fabrication of ceramic tapes, tubes, foams, coatings and composites (including carbon nanotube reinforced ceramics) have been demonstrated.In the Materials Science and Engineering Department at the University of Washington, Seattle, several liquid preceramic polymer systems have been developed for applications such as coatings, joining and pressureless room temperature casting. One of the systems comprises a low-cost polyhydrosiloxane that can be crosslinked under the influence of water at 100-200 °C with a precious metal catalyst. This system was filler-loaded and coated on stainless steel substrates. Pyrolysis at 600 to 800°C results in excellent adherence on the substrates (see the cross-section of the coating in the SEM).
Another system is based on a polysiloxane bearing active methoxy groups. When water and a catalyst are present it can be crosslinked at room temperature. Here, the water is supplied by hydroxy-terminated polysiloxane, which is mixable with the aforementioned compound. This system shows a very low viscosity of 20-30 mPas at room temperature and can be filler-loaded. Crosslinking times at room temperature vary from minutes to tens of minutes, and the ceramic residue is higher than 50 wt % after thermal conversion.
For more information, contact Professor Rajendra K. Bordia at (206) 685-8158, e-mail bordia@u.washington.edu or visit http://depts.washington.edu/rkbgroup.
Editor's note: This article was compiled from information submitted by national laboratories and universities, and is not intended to be a comprehensive overview of all ceramic and glass research that is currently in progress.