SPECIAL REPORT/R&D OVERVIEW: Advanced Ceramic & Glass Technology

August 1, 2007
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CI's Ceramic and Glass R&D Overview highlights technology advances from around the globe.

Phosphate cements, ceramic nano-islands, bio-resorbable scaffolds-this year's Ceramic and Glass R&D Overview has it all. Following is a selection of technology advances being made at universities and research laboratories around the globe.

Polished surface of a sintered glass ceramic.

Glass and Glass-Ceramic Matrix Composites

Several types of inorganic waste can be dissolved in glasses. Though these glasses are chemically stable, they are economically advantageous only with the transformation in added-value products. This concept may also be applied to hardly recycled glasses, which represent a form of industrial waste themselves, like glasses from dismantled cathode ray tubes (largely landfilled), which have been the subject of several studies.

Glass-ceramic materials for paving applications and cellular glasses (glass foams) for thermal and acoustic insulation have been developed. In addition, attention has been given to glass sintering. Sintering leads to glass objects at particularly low temperatures, and, above all, allows the mixing of glass with reinforcements, yielding strong glass matrix composites, or, in the case of simultaneous crystallization, innovative sintered glass-ceramics (stronger than common glass-ceramics and with a simpler and cheaper treatment). Recent studies have combined these last aspects, thus leading to innovative glass-ceramic matrix composites.

At Universita' di Padova's Dipartimento di Ingegneria Mechanica (Padova, Italy), glass matrix composites can be obtained from pre-ceramic polymers as an alternative to sintering. The advantage is obtaining a homogenous dispersion of the reinforcement by using molding processes at moderate temperatures; the polymer/reinforcement composite is thermally treated for the polymer/ceramic conversion.

One interesting type of preceramic polymer is that of silicone resins, which yields oxycarbide (SiOC) glasses upon pyrolysis. SiOC glasses possess extraordinary properties, but they are hardly available as monoliths since the pyrolysis causes notable shrinkage and gas evolution, forming pores and cracks. The introduction of a secondary phase by reducing the "transforming mass" compensates the shrinkage and yields monoliths. If chemical interactions between resin and secondary phase occur, advanced ceramics (mullite, wollastonite, SiAlON, etc.) may be obtained.

For more information, visit www.dim.unipd.it/materiali/Personale/Bernardo.

SEM micrograph of the self-ordered microstructure on the (001) surface of YSZ.

Self-Assembled, Pseudo-Periodic Array of Ceramic Nano-Islands

The Department of Materials Science and Engineering at The Ohio State University, Columbus, Ohio, has developed an array of nano-islands that self-assembles following a single deposition and does not utilize lithography. A meta-stable planar film of Gd-doped ceria (GDC) is deposited on a single crystal substrate of yttria stabilized zirconia (YSZ-9 mol% yttria) and breaks up into islands upon annealing due to the instability of a strained thin film.

The islands are all aligned to the substrate in the same orientation, and there is significant periodicity in their 2-D spacing. Intrinsic self-ordering occurs, and there is great potential to improve the ordering through thermal processing optimization. The materials and processing are inexpensive, and the structure can be scaled to cover large areas. Comparable work has been done with semiconductor quantum dots in the past, though the degree of self-ordering seen here has not been achieved in those systems without using lithography or multilayer depositions to guide the pattern.

In light of its interesting properties (high-temperature stability, oxygen ion conductivity and transparency to visible wavelengths), the GDC-YSZ system may have intrinsic usefulness for a range of potential optical and electronic applications. Also, due to the morphology of the structure, additional biological nano-fluidic applications such as DNA and protein separations are attractive.

Using polymer imprint pattern transfer techniques, it is conceivable that the nanostructure could even be used as a template to produce the pattern in other materials of interest. Or, the isolated nano-islands could be capped with another material, which is the approach used with semiconductors to produce structures with interesting optical and field-emission properties. In general, because the self-patterned structure is extremely inexpensive to manufacture and the features are self-organizing, a range of nanotechnology-based applications could be impacted by this process. For more information, contact Mike Rauscher at Rauscher.4@osu.edu.

Figure 1. Sintered SiC armor ceramic specimen (a) reflected signal amplitude ultrasound C-scan images at 5, 75, and 125 MHz showing varying levels of material inhomogeneities; and (b) elastic modulus, shear modulus, and bulk modulus maps showing subtle variations in elastic properties.

Ultrasonic NDE of Armor Ceramic Materials

In a joint effort between the NSF/Industry-University Cooperative Research Center - The Ceramic and Composite Materials Center and The U.S. Army Materials Center of Excellence for Lightweight Materials for Vehicle Protection within the Department of Material Science and Engineering at Rutgers University, Piscataway, N.J., a major initiative examining the processing and performance of armor ceramics is underway. Professors Richard Haber and Dale Niesz, along with graduate student Raymond Brennan, have been examining ceramics such as silicon carbide, boron carbide and a variety of oxide-based systems for opaque and transparent armor applications. These materials have been incorporated into armor systems to reduce their weight while providing high hardness, high compressive and tensile strength, and good elastic response to high stress. However, the presence of critical-sized defects and flaws in armor ceramics, such as pores and inclusions, can lead to ballistic failure. For this reason, new ultrasonic nondestructive evaluation (NDE) studies are being conducted to locate and characterize defects and inhomogeneities in dense materials.

High-frequency ultrasound NDE is being used to locate micron-range defects, as well as to identify microstructural changes in dense armor ceramics. Ultrasound parameters like transducer frequency have been analyzed to determine the necessary system conditions for obtaining areal image maps based on differences in either the intensity of the collected ultrasound signals (reflected signal amplitudes) or the transit time of ultrasound energy through the materials, otherwise known as time-of-flight (TOF). While TOF scans (see Figure 1a) have been used to show changes in thickness, acoustic wave velocity, density and acoustic impedance, reflected signal amplitude scanning has recently been employed to analyze attenuation, or loss, through a test specimen. Novel elastic property imaging (see Figure 1b) capabilities have also been developed to plot differences in Poisson's ratio, elastic modulus, shear modulus and bulk-modulus-all necessary for design applications.

Amplitude and TOF maps can now be used to characterize area-under-the-curve values, full-width at half-maximum values, and critical tail region properties to provide a valuable means of materials comparison. These data have been utilized to establish a representative materials "fingerprint" that provides defect input data that can be further quantified and applied to property, design, and performance modeling and simulation of armor ceramic materials.

For more information, contact Center Director Richard Haber at (732) 445-5900 or visit www.cmcc.rutgers.edu.

Electron micrograph of ceramic scaffold.

Bio-Resorbable Scaffolds

At Politecnico di Torino's Materials Science and Chemical Engineering Department (DISMIC) location, the synthesis of macroporous scaffolds for tissue engineering started in 2000 through the development of innovative glass compositions. Glass and glass-ceramic can be produced in macroporous scaffold form with morphology very similar to human cancellous bone. Scaffolds that were completely resorbable in the body were successfully prepared using phosphate glasses. Moreover, due to the presence of an amorphous phase, the scaffolds can release ions with specific effects, such as magnesium that stimulates cell metabolism, or zinc, silver and copper for antibacterial purposes. The scaffolds can be reinforced with ceramic phases such as hydroxyapatite to enhance their mechanical strength.

Ceramic scaffolds based on nanostructured hydroxyapatite-tricalcium phosphate were also produced through the use of an innovative gel casting procedure in the frame of the integrated project NanoKer. For more information, visit www.composites.polito.it or www.nanoker-society.org.

Joining of Crofer 22 to anode-supported electrolyte by glass-ceramic sealant developed at Politecnico di Torino, Italy.

Joining of Ceramic Matrix Composites

Carbon fiber reinforced carbon matrix (Cf/C), carbon fiber reinforced silicon carbide matrix (Cf/SiC) and silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites are among the most promising materials for high-temperature applications. However, these new materials cannot be joined through traditional means because they do not melt, and common mechanical joints (rivets, bolts) are not effective. This presents a problem for the preparation of complex structures, which is needed in the field of high-temperature applications, energy production (i.e., solid oxide fuel cells) and thermonuclear fusion technology.

The research group at Politecnico di Torino has been involved in the development of joints for ceramic matrix composites and advanced ceramics for many years. Joining and coating materials have been designed and synthesized with coefficient of thermal expansion, wettability and reactivity compatible with the composite substrates. The method employed to obtain joined and coated composites is the slurry technique, followed by heating in conventional and/or microwave furnaces. For more information, visit www.composites.polito.it.

Figure 1. Flow diagram detailing NETL's latest research on gasification refractories.

Advanced Refractories for Slagging Gasifiers

Gasification is used to produce H2 and CO from multiple carbon sources, and is considered a critical component of future clean power generation systems (see Figure 1). Failure of the refractory materials used to line an air-cooled slagging gasifier impacts gasifier reliability and availability, and has been identified as a roadblock to greater use of this technology.

Current refractory liners are high in Cr2O3 and fail primarily by spalling and corrosive wear caused by molten slag. Through postmortem analysis, the National Energy Technology Laboratory (NETL) has evaluated refractory/slag interactions and the causes of refractory failure. Using that information, NETL developed and patented an improved performance, high-Cr2O3 refractory containing phosphate additions (U.S. patent # 6,815,386). Through field trials conducted with an industrial partner, Harbison-Walker Refractories Co., Bromborough, UK, the refractory was found to decrease spalling wear dramatically, resulting in a service life improvement of approximately 50% vs. currently used materials.

Harbison has obtained an exclusive license to manufacture this refractory and is producing it commercially. Current refractory research at NETL is directed toward developing non-chrome oxide alternative liner materials for gasification. For more information, contact James Bennett at (541) 967-5983, e-mail James.Bennett@netl.doe.gov or visit www.netl.doe.gov.

Functional Ceramic Coatings by Plasma-Enhanced CVD

The Nanocrystalline Materials and Thin Film Systems research division at Leibniz Institute for New Material (INM), Saarbrücken, Germany, provides innovative surface-engineering solutions for different applications, and boasts several years of experience in the synthesis, modification, and application of materials using chemical nanotechnology. Specifically, INM applies thermal and plasma-enhanced CVD (PECVD) techniques to functionalize surfaces and to deposit protective coatings.

The CVD process involves absorption, accumulation and decomposition of gaseous reactants on solid surfaces under high temperature or energy conditions. Depending on the needs of its industry partners, INM offers ceramic coatings with high hardness, chemical inertness, abrasion resistance, corrosion protection and thermal stability, to name a few functional properties.

Plasma-induced decomposition of molecular precursors enables coating at reduced process temperatures (<100°C), which opens up new opportunities for temperature-sensitive substrates like polymers. Using this method, deposition cycles are drastically shortened because substrate heating (>400°C) and cooling is not required, which is essential in conventional thermal CVD procedures. The product expertise available at INM includes (but is not limited to):
  • Thin conducting and semi-conducting films
  • Barrier layers
  • Surface energy modulation
  • Wear-resistant films
  • Optical coatings
For more information, contact Sanjay Mathur, Ph.D., at Sanjay.Mathur@inm-gmbh.de or visit www.inm-gmbh.de.

Nanoparticles Advance Ceramic Technology

Research at Sandia National Laboratories is pioneering the future of superalloy materials by advancing the science behind how these superalloys are made. As part of Sandia's nanoscale research, a group of experts specializing in inorganic synthesis and characterization, modeling, and radiation science have designed a radical system of experiments using a method of radiation known as radiolysis to explore an entirely new area of research for creating composite alloys through nanoparticle synthesis, as well as advancing the science of metal and alloy nanoparticle creation.

A specialized area of superalloys, metal matrix composites, is already in use in aircraft, automotive, and biomedical applications where strength and lightness are essential. These metal/ceramic nano-composites offer magnetic and electrical functionality in addition to their enhanced mechanical properties. Satisfying the increasing demand for highly customized parts, which incorporate these new materials and push the boundaries of conventional ceramic technologies, requires precise control over the microstructure and fabrication of the metallic components.

The team of researchers is able to achieve the strict fabrication control that is demanded by this research through the precision capabilities of Sandia's in-house Gamma Irradiation Facility (GIF) and the Ion Beam Materials Research Laboratory (IBMRL). For more information, visit www.sandia.gov.

Porous Wall, Hollow Microspheres for Hydrogen Storage

An interdisciplinary team of hydrogen and glass scientists at the Savannah River National Laboratory has developed a unique form of hollow glass microspheres featuring porous walls, and demonstrated that they could fill the microspheres and use this new system for hydrogen storage applications. The team, led by George Wicks, Kit Heung and Ray Schumacher, developed porous wall, hollow glass microspheres (PW-HGMs) with average diameters of about 50 microns and one-micron-thick walls. Within those walls, the developers induced an interconnected porosity in the range of about 100 to 1000 Angstroms. This porosity was then used to fill the PW-HGMs with special absorbents for hydrogen storage, transportation and distribution.

PW-HGMs are able to act as small 'cocoons' for protecting reactive materials. Also, in the tight confines of the glass microspheres, recombination of the solid reactive materials can occur more readily. One of the most important potential advantages associated with reactive species contained within hollow glass microspheres is improved safety in handling, processing and distribution operations. In the case of hydrogen filled PW-HGMs, they can be contained in lighter, lower-pressure tanks, with or without absorbents, improving safety performance for impact events or accident scenarios.

PW-HGMs can take on the shape of most any tank, pipe or irregular container, and filled microspheres can also be made into a very flowable, water-like medium.  This could be helpful if using existing equipment and infrastructures. Pneumatic handling equipment has long been used to collect and transfer material of this type with minimal breakage.

PW-HGMs offer the potential of easier loading and unloading than some systems, due to the interconnected wall porosity. Other options also exist, such as coating the microspheres and filling or closing the pores. Unloading can be achieved by conventional means, such as heat, or through other stimuli, such as photo-enhanced outgassing. For more information, visit srnl.doe.gov.

Trial house built in Venezuela using Argonne-invented phosphate cement.

Phosphate Cements

Researchers at the U.S. Department of Energy's (DOE) Argonne National Laboratory are currently working on the future of chemically bonded phosphate ceramics, or simply phosphate cements. Though these cements were developed as an alternative to Ordinary Portland Cement (OPC) and were designed to remediate the problem of radioactive waste generated from nuclear energy, they are now meeting other cementing needs.

The benefits of phosphate cements are:
  • They do not limit users to a single formulation, therefore their chemistry and components are adaptable to local needs and applications.
  • They are ideal for recycling utility and mineral solid (and sludge) waste.
  • They offer a low total application cost.
  • They offer reduced environmental damage when compared to cement use.
  • They may be recycled or disposed of as low-grade fertilizer at the end of service life.
"One ton of CO2 is produced per ton of OPC," says Arun Wagh, Ph.D., ceramist in the Energy Systems division of Argonne. "Two billion tons of annual cement production equals 6.25% of global greenhouse gases. Phosphate cements produce less than one-third the CO2 per ton of cement, leading to a reduction of at least 67% of CO2 released by the cement industry. This implies that phosphate cements have the potential to reduce global greenhouse gases by at least 4.2% annually (1.35 billion tons), which is nearly equal to greenhouse gases produced by all homes in the U.S. (1.4 billion tons), and more than the total produced by U.S. businesses (1.2 billion tons)."

In the future, Argonne plans to secure funding to further develop a range of phosphate cements, thus overcoming industry inertia while motivating the scientific, academic and technical communities.

Wagh is the key inventor of these cements. He is currently directing projects and their application in collaboration with various American industries. The scientific research in these novel materials includes solution chemistry of formation and predicting novel compositions. Applications include the use of phosphate cements (as superior structural materials) in radioactive waste stabilization and containment at various DOE sites, as well as at various Russian nuclear sites (as materials for safe transport and storage of nuclear materials). Phosphate cements are also used as oil field cements. For more information, visit www.anl.gov.

Solvothermal Crystallization Laboratory

The Solvothermal Crystallization Laboratory (SCL) at Rutgers University features a state-of-the-art capability for direct precipitation of oxide and non-oxide materials such as coatings, thin films, ceramic powders, and single crystals. Solvothermal reactions offer industry a low-cost means to prepare materials, relative to conventional solid state and advanced synthesis routes, which involve vapor-phase, aerosol or molten-salt methods.

Solvothermal reactions utilize conventional oxides (as well as other types of low-cost precursors) to directly crystallize the ceramic phase of interest with controlled size and morphology. Typically, either water is employed as the crystallization medium or organic solvents and water-organic solvent mixtures are used. Direct crystallization eliminates the need for the heat treatment or post-process milling normally associated with other solution synthesis methods.

Solvothermal processes are intelligently designed with process simulation tools that utilize principles of thermodynamics and kinetics. This unique approach enables researchers to rapidly find experimental conditions suitable for the scientific and technical needs of the sponsor.

A range of stirred reactors capable of achieving up to 450°C with volumes from 125 to 3785 ml is available. Continuous reactors offer temperatures up to 300°C, flow rates up to 200 ml/min, and slurry and solution feed systems. Washing facilities for purifying powders are available that can handle laboratory and pilot-scale processes for micron, submicron, and nanopowders. A range of powder characterization instrumentation is available to fully analyze the physics and chemistry of any materials prepared in the SCL.

For more information, contact Professor Richard E. Riman at Materials Science and Engineering, Rutgers University, 607 Taylor Rd., Piscataway, NJ  08854; e-mail riman@rci.rutgers.edu; call (732) 445-4946; or fax (732) 445-6264.

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.

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