he morning breeze brings music from the wind chimes outside your window. You wake up, and as you enter the bathroom, you are jolted when your bare feet touch the cold tile floor. Your feet are warmed in the bathtub during your shower. You become fully awake while sipping coffee from a mug. As you scoop cereal from a bowl, you daydream as you gaze at the brick hearth and the decorative figurines and flower vase on the mantel. Welcome to the world of traditional ceramics, products made by baking mixtures of nonmetallic minerals. These conventional ceramics are made from natural raw materials such as clay. Ceramics were probably discovered when someone accidentally dropped into fire a clay pot or bowl shaped by hand and allowed to dry; the resulting object was observed to be hard and dense. Today some ceramics are still formed at a potter's wheel, which was invented 5000 years ago by the Sumerians, while others are made by slip-casting before being fired in a kiln. For centuries, ceramics have been used to hold food for cooking and eating, store beverages, and provide forms for artistic expression and decoration. In the 20th century, a new kind of ceramics emerged. These ceramics are less visible, but they play an important role in today's technologiesthe space shuttle, jet aircraft, power plants, and some cars and trucks. Americans call them "engineering ceramics" and the Japanese call them "fine ceramics." These advanced ceramics are formed by using high temperatures to process or densify inorganic, nonmetallic compounds, such as oxides, nitrides, borides, carbides, silicides, and sulfides. These materials are also known as "structural ceramics" because they are strong enough to bear weight.
"Engineering ceramics are not made from clay or other minerals," says Ray Johnson, leader of DOE's Ceramic Technology Project in ORNL's Metals and Ceramics (M&C) Division. "They are made from highly controlled, artificially produced raw materials. They are formed and densified by controlled processes such as hot isostatic pressing. They are used for products that have unusually demanding requirements, such as turbine blades and parts for rockets, nuclear reactors, and aircraft and automobile engines. Their microstructure is highly controlled. In short, they are appreciably different from traditional ceramics in their properties and in the way they are manufactured.
Ogbemi Omatete shows a ceramic turbine rotor formed by gelcasting at AlliedSignal Ceramic Components in Torrance, California.
"I have a ceramic hammer in my office that I use to show that engineering ceramics are much stronger and tougher than traditional ceramics," Johnson continues. "I encourage visitors to drive nails into a piece of wood with my hammer, which is made from transformation-toughened zirconia. You wouldn't strike a nail with a porcelain vase."
In the Ceramic Technology Project, funded by DOE Energy Efficiency's Office of Transportation Technologies, Oak Ridge National Laboratory is developing technology for the cost-effective manufacture of reliable, lightweight ceramic parts for advanced engines. These engines will enable cars and trucks to use fuel more efficiently and reduce emissions. Our ceramic industry may someday be using advanced techniques to manufacture ceramic engine parts for cars and trucks and design even better ones for the future, thanks to ceramic-forming processes being developed in the M&C Division. The Laboratory's innovation in ceramic forming may be molding the future of ceramics manufacture.
Gelcastingan advanced process for forming ceramicswas originally developed at ORNL to make complex-shaped automotive parts such as turbines. It is now receiving industrial and government support for early commercialization. The reason: this new process for making high-quality, complex-shaped ceramic parts shows promise for manufacturing ceramics at a lower cost than conventional forming techniques. In addition, gelcasting appears attractive for an increasing number of applications ranging from accelerator magnets to artificial bone.
"We developed gelcasting to produce small, complex-shaped turbomachinery for our sponsors," says Mark Janney of the M&C Division, who had the original idea for gelcasting. "Now, the applications are expanding to include simpler but larger shapes such as ring-shaped magnets for particle accelerators. Once we thought the largest shape we'd ever make would be the size of a loaf of bread. Now, we're being asked to make parts as large as a chair."
Consider the comments from Randall M. German, Brush Chair Professor in Materials at Pennsylvania State University. In a recent letter, German called gelcasting an "important advancement in ceramic-forming technology." He described gelcasting as "an innovative process for the production of ceramics" and as "an enabling technology that provides an avenue for implementing the use of ceramics in many advanced systems."
"Ten years from now," Janney says, "we believe gelcasting will be used as widely as slip casting, pressure casting, die pressing, extrusion, and injection molding are used today. Gelcasting will be part of the culture."
Not surprisingly, three industrial firms have obtained licenses to use ORNL's gelcasting technology, and the ORNL researchers are working with various companies in seven cooperative research and development agreements (CRADAs) and five informal collaborations. In addition, the technology has won prestigious awards.
Mark Janney (left), Claudia Walls, Steve Nunn and Ogbemi Omatete received an R&D 100 Award for their gelcasting process, a new method for making high-quality, complex-shaped ceramic parts. Photograph by Bill Norris.
In 1995, ORNL's gelcasting technology received an R&D 100 Award from R&D magazine, one of 79 R&D 100 Awards that ORNL has won since the competition began. The ORNL developers who were honored are Mark Janney, Ogbemi Omatete, Stephen Nunn, and Claudia Walls, all in the Ceramic Processing Group of the M&C Division. This was not their first award. In 1992, Janney and Omatete received an International Hall of Fame Award from the Inventors Clubs of America. Most recently, Omatete and Walls received a Federal Laboratory Consortium Award of Excellence for Technology Transfer.
Janney is a ceramic engineer with a Ph.D. degree from the University of Florida. Omatete is a chemical engineer and professor from Nigeria with degrees from Princeton University and the University of California at Berkeley. Nunn is a ceramic engineer with a Ph.D. degree from the University of Michigan; he has been involved with several CRADAs and is especially interested in machining gelcast ceramics before they are hardened.
Walls joined ORNL after earning an associate degree in mechanical engineering at a local community college. While working with researchers Robert Lauf and Terry Tiegs, both in the M&C Division, she became interested in ceramics. In 1988, Walls joined the team that was working on gelcasting. She has done much of the lab work that led to the rapid development of gelcasting. She received a Technology Transfer Award from Martin Marietta Energy Systems in 1989 for her early machining studies. She received a Technical Achievement Award from Lockheed Martin Energy Systems in 1994 for her overall contributions to gelcasting.
Ceramics in the 20th Century
In the 20th century, it was discovered that ceramics produced in a controlled way from artificial raw materialsalumina, silicon nitride, zirconiapossess useful properties besides their resistance to heat. Some of these engineering ceramics achieve melting temperatures as high as 4000°F. They exhibit extreme mechanical hardness; for example, cubic boron nitride is almost as hard as diamond. They are resistant to corrosive chemicals. They are light. They are intrinsically strong. Unfortunately, like traditional ceramics, the use of engineering ceramics has been limited by their brittleness; but, thanks to recent developments in altering ceramic compositions, engineering ceramics are now much less brittlelike Ray Johnson's hammer.
In the late 20th century, new needs for ceramics have arisen. Shortages of fuel, energy price increases, and pollution have motivated the development of engines and power plants that use less fuel to operate. Gas turbine engines have been developed for power plants and aircraft and are being developed for automobiles because they use fuel more efficiently than spark-ignition engines. However, because these engines run at high temperatures and recover engine heat to minimize their use of fuel, they require parts that retain their strength at high temperatures. Only ceramics, not metals or even superalloys, can withstand the temperatures required for efficient automotive gas turbines.
Why are we not yet driving cars with high-temperature ceramic engines? Two problems have had to be solved. The first was that ceramics are normally brittle. Although they resist high temperatures, they can shatter when subjected to rapid and large changes in temperaturethermal shockand other stresses. Can their chemical composition and structure be altered to allow them to hold up under such harsh conditions? Can reliable ceramic parts for cars be made?
The second problem is that the cost of manufacturing ceramic parts for the automobile industry has been much higher than the cost of making steel parts. Is there a low-cost method for manufacturing reliable ceramic parts that is competitive with mass production of steel parts for autos? Can we devise some way to make low-cost ceramic components?
Reliable ceramic parts can be made for cars, and ORNL has played an important role in the solution. Norton, AlliedSignal, and other ceramic companies have come up with new compositions and microstructures for silicon nitride that make the ceramic very reliable. Silicon nitride is the ceramic of choice for high-temperature engines because it is highly resistant to wear, deformation, oxidation, thermal shock, and decomposition at high temperatures. Matt Ferber and Ted Nolan, researchers with the M&C Division, have worked with Norton to test the reliability of its improved silicon nitride compositions at high temperatures and to determine the changes in microstructure that account for its improved properties.
ORNL's gelcasting is promising for lowering ceramic part manufacturing costs to a competitive level. The reason: it may allow industry to reduce the use of diamond tools to cut, shape, and finish ceramic products. Gelcast ceramics can be shaped by molding or machining before they are hardened by sintering in a hot furnace. Half the expense of ceramic manufacturing today comes from machining sintered ceramics by diamond tools. Machining itself must be done slowly to avoid damaging the ceramic. Although the expensive diamonds are harder than ceramics, they wear out quickly, requiring frequent replacement. And costs of labor and tools add up.
Gelcast ceramics can be formed in molds to get the precise shape desired because, unlike ceramics formed by other processes such as slip casting, gelcast ceramics shrink uniformly. Thus, the mold can be designed to compensate for shrinkage so that a ceramic part of the desired shape and size can be produced. "As a forming process," Omatete says, "gelcasting is limited only by the quality of the molds."
If machining is desired to improve on the final shape, gelcasting offers another advantage. After a gelcast part is molded and dried, it is strong enough not to crumble when manipulated yet soft enough to be machined quickly by less costly carbon steel tools. This process is called "green-machining" because it is applied to gelcast ceramics at the "green body" stage. After the gelcast parts are machined, they are hardened in a sintering furnace. The amount of final machining after firing is minimized, thus greatly reducing the need for machining with expensive diamond tools.
Green-machining of gelcast materials can be particularly useful for producing prototypes rapidly, providing custom manufacturing, and adding features to a cast part that would be too difficult or too costly to include in the mold.
Because the cost of machining ceramics could be significantly reduced using gelcasting, low-cost manufacture of ceramic components for engines may be feasible. Reducing manufacturing costs is critical to introducing ceramic manufacturing into the automobile industry. Efforts to determine the feasibility of commercializing gelcasting are now being pursued by the ceramic industry and the U.S. government.
Origin of Gelcasting
When Mark Janney was studying for his doctoral degree in ceramic engineering at the University of Florida, he learned about several ceramic processing techniques. Among them was injection molding, in which ceramic powder is mixed with wax or a polymer and forced into a mold. Polymers are used in ceramic processing because they bind ceramic powders together. Later in the process, the polymer (or binder) must be burned out. Because of the large amount of organic binder used in injection molding, the binder must be burned out very slowly to prevent cracking, significantly increasing the cycle time for producing ceramic parts by injection molding.
Illustrating a step in the gelcasting process, Omatete prepares to pour a ceramic slurry into a turbine rotor mold as Janney watches.
Janney was looking for a way to avoid steps in the injection-molding process (such as binder burnout) that lead to defects. He had experimented with methylcellulose, which is used in paints and ceramic glazes. When he mixed it with water, the mixture formed a gel when heated, just the opposite of JelloTM, which forms a gel when cooled. "The gels were not very strong," Janney says, "but these experiments started me thinking about a solution-based process in which the initial material can be poured rather than forced into a mold."
Janney worked for a year and a half at Kennametals, Inc., in Greensburg, Pennsylvania, in the development of ceramics for cutting tools. Then he joined ORNL's M&C Division in 1983.
In 1984, Janney started research that eventually led to gelcasting. He knew the ceramics community at that time had a dire need for a forming method to replace injection molding for making large complex shapes such as turbine rotors. Many companies were trying to make silicon nitride and silicon carbide rotors by injection molding for DOE's Advanced Gas Turbine program. Rotors could be made by injection molding, but the yield of good product from this process was very low.
"It was not unusual," Janney says, "for a company to make 20 rotors in order to get one good one. Although this situation is common in a research environment, it was not encouraging to industrial people looking ahead to production.
In the mid-1970s, Janney had worked on injection molding of ceramics at the General Electric Company's Corporate Research and Development Center. Based on this experience and his observation at the University of Florida, Janney began thinking about alternative forming approaches. Says he: "I thought that a solution-based forming process could eliminate most of the problems associated with injection molding, especially the problems of binder removal and burnout."
Janney initially focused on developing gel chemistry because it is central to gelcasting. "My background in organic chemistry was limited," Janney says. "I did know that some polymers, such as poly (methyl methacrylate), could be made by polymerizing a monomer in an organic solvent. I conducted a series of trial-and-error experiments using several different monomers and solvents. I was able to make some gels, but they were not very strong."
A monomer is a relatively light and simple molecule that can combine with other molecules to form a polymer. A polymer is one of many natural and synthetic compounds that have a high molecular weight because they consist of up to millions of repeated linked units, or monomers.
In 1985, Janney learned about a new group of monomers, called multifunctional acrylates. These are widely used in making printing inks (as on plastic cups and cereal boxes) and other coatings. He observed that gels made using the multifunctional acrylates were stronger than anything he had made so far.
"They were fantastic," Janney says. "The gels were hard and stiff, sort of like a hard rubber sole on your shoe. I mixed aluminum oxide (alumina) powder with the gel precursor solution, or premix, to make a ceramic slurry. I could get more than 50 volume percent alumina into the premix, an acceptable level of ceramic for the molding applications I was working on. When the slurry was gelled, it was very strong. You could drop a gelled part on the floor, and it would not deform or crack."
Janney dried the parts, burned out the binder, and then fired them at a high temperature. "They came out of the furnace looking great," he says. "I knew then that the concept of gelcasting would work. Next it was a matter of developing a water-based system."
In August 1987, Janney gained a collaborator in the gelcasting work. Ogbemi "Omats" Omatete, a professor of chemical engineering at the University of Lagos in Nigeria, came to ORNL on a 3-month sabbatical visit. During Omatete's visit, he and Janney worked to develop a water-based gelcasting system.
"Industrial ceramic manufacturers are used to working in water-based systems," says Janney, "so a water-based system would be accepted more readily as an industrial process." Says Omatete: "Water is easy to use, it's cheap, and it's environmentally friendly."
During his visit, Omatete tried to make water-based gels using more than 150 different compositions. Unfortunately, none of these made good gels. Finally, when they tried making gels based on the monomer acrylamide, they achieved instant success.
"We chose acrylamide because we knew it was used by biologists to make gels for electrophoresis for DNA fingerprinting," Omatete says. The acrylamide gels were quite strong and stiff. In addition, when Janney and Omatete tried to make ceramic slurries using the acrylamide gel premix, they discovered that the slurries were even more fluid than if they had made them in water alone. Recalls Janney: "Making a solids slurry that was 55 or 60 volume percent alumina was easy."
During the final 2 weeks of Omatete's sabbatical, the two engineers cast and fired an alumina rotor using the acrylamide-based gelcasting process. "The first rotor we made came out of the furnace in great shape," Janney says. "We knew we had a winning process. It was unheard of to make a good rotor the first time by injection molding. Gelcasting had proven itself, at least in concept."
Over the next 3 years, Janney, Omatete, and Albert Young, worked out the engineering details of the process and tried it on a variety of materialsalumina, quartz, silicon, silicon carbide, silicon nitride, sialon, zirconia, and ceramic composites.
Albert Young played a key role in the development of the gelcasting process.
"High solids loading is important," Omatete says, "because it minimizes shrinkage during firing of the part. The idea is to make the slurry as highly loaded with ceramic powder as possible and yet still be able to pour it into the mold," Omatete says. "We make it about the consistency of paint. Fortunately, gelcasting is a very forgiving process, and it will work over a range of solids loadings."
The key to the process is to add monomers, not polymers, to the
initial solvent-ceramic powder mix. Here is the gelcasting "recipe," or flow chart.
This gelcasting flow chart shows how the process turns ceramic powder into a finished product.
Mix and mill ingredients. Mix ceramic powder with water (or a nonaqueous solvent), a dispersant, and gel-forming organic monomers (later linked together to form a "binder," or polymer-water gel that binds the ceramic particles together).
Deair. Place the mixture under a partial vacuum to remove air from it (otherwise bubbles could form, causing flaws in the final product).
Add catalyst. Add a "polymerization initiator" that kicks off the gel-forming chemical reaction.
Cast. Pour the ceramic slurry into molds made of metal, glass, plastic, or wax to cast it into desired shapes. "It's as simple as pouring muffin batter into a muffin pan," Omatete says.
Create a gel. Heat the molds in a curing oven. The catalyst will cause the monomers to form large cross-linked polymer molecules that trap water, creating a rubbery polymer-water gel. The gel permanently immobilizes the ceramic particles in the desired shape defined by the molds. It is this setting step that gives gelcasting its name.
"By separating the mold-filling operation from the setting operation," Janney says, "gelcasting overcomes many of the problems associated with injection molding that can cause defects in the molded part."
Unmold. Remove the ceramic from the mold.
Dry. Let the cast ceramic dry thoroughly to remove most of the solvent, preferably at a high relative humidity (90%) to minimize warping and cracking. "During drying," Omatete says, "a ceramic slurry that is half solids should shrink uniformly about 3%. To speed up drying, wait until the shrinkage stops and then decrease the humidity and increase the air temperature."
Machine, if desired. The molded and dried material looks and feels like chalk. It has very high strength. At this stage of the process, this "green body ceramic" is stronger than a green body ceramic made by any conventional technique before sintering. But the gelcast ceramic is soft enough to be "green-machined" by carbide steel tools.
Burn out binder and sinter. The last two steps can be combined into one step. It involves firing, or baking, the ceramic at 550°C and then as high as 1800°C in a furnace. This heating process accomplishes two goals. At the lower temperature, it "burns out" the polymer remaining in the ceramic; this polymer must be removed carefully or else the final product may have defects and cracks. At the higher temperature, the furnace's intense heat sinters the ceramic, making it hard and dense.
"The slurry can be processed in an entirely closed system to keep the contaminants out," Janney says. "The equipment used in gelcasting is similar to that used in conventional ceramic processing.
"The advantages of gelcasting over conventional ceramic processing methods," he adds, "are that its products are consistently defect free, uniformly dense, and very strong and that the process is able to form very large parts."
On August 18, 1989, Martin Marietta Energy Systems (now Lockheed Martin Energy Systems) licensed ORNL's gelcasting technology to Coors Ceramics Company of Golden, Colorado. However, the ORNL ceramic engineers soon realized they had a problem with their water-based gelcasting recipe. Several ceramic companies had expressed concern about using the monomer acrylamide because it was known to be toxic to the human nervous system. To solve the problem, Omatete and Janney selected seven different monomers as possible substitutes for acrylamide.
Omatete found that methacrylamide is relatively safe because it is not easily absorbed through the skin, as is acrylamide. Says Omatete, "Methacrylamide is rated as safer than common chemicals like gasoline. We decided to use it as our monomer for future industrial applications."
Three patents have been issued for gelcasting. The first was to Janney for nonaqueous gelcasting; it was issued in 1990. Two others were issued to Janney and Omatete for aqueous gelcasting in 1991 and 1992.
Gelcasting Passes an Industrial Test
In 1990, AlliedSignal Ceramic Components entered into a
cooperative research agreement with the ORNL ceramists. The company sent
ceramic powders to ORNL for gelcasting, and the gelcast parts were returned
to AlliedSignal for its evaluation. In mid-1991, AlliedSignal approached
the ORNL ceramists about making a joint proposal to the National Institute
of Standards and Technology's (NIST's) Advanced Technology Program
(ATP). The partners submitted the proposal in September 1991, and
AlliedSignal received an ATP grant in June 1992.
Omatete discusses gelcasting and efforts to transfer the technology to industry. His audience includes, from right, Secretary of Energy Hazel O'Leary, ORNL Director Alvin Trivelpiece, and Frank Munger, science reporter for the Knoxville News-Sentinel. Secretary O'Leary helped to expedite Omatete's 3-month stay in Torrance, California, so that he could guide AlliedSignal Ceramic Components in using gelcasting to form ceramic turbine rotors.
In December 1993, Omatete had a rare opportunity. As part of the ATP project, he was invited to spend 3 months at AlliedSignal Ceramic Components in Torrance, California. The purpose of the stay was to determine if gelcasting was a viable method for fabricating silicon nitride turbine rotors.
Silicon nitride was selected as the material for blades and vanes in these turbine rotors because it has the required strength and creep resistance at 1370°C. Its light weight and wear resistance are additional advantages. Such turbines are being manufactured for use in on-board engines in military and commercial aircraft. These engines provide auxiliary power when an aircraft sits idle on the tarmac and emergency power when a main engine fails.
AlliedSignal engineers were interested in investigating gelcasting and comparing it to two turbine-casting methods they had been usinginjection molding and slip casting.
In injection molding, the ceramic powder is mixed with a polymer, forming a very thick fluid. This fluid cannot be poured into a mold, as is done with gelcasting. Instead, the fluid must be forced, or injected, into the mold under high pressure.
The AlliedSignal engineers noted that gelcasting did not have two problems that plague injection molding. One problem is the removal of the binder (the polymer that binds the ceramic particles together). In injection molding, the binder can be as high as 20% of the weight of the ceramic; in gelcasting, the binder takes up only 3 to 4%. In injection molding, burning out the binder may take a week, compared to less than a day for a gelcast ceramic. Binder burnout is tricky in injection molding, because if the temperature is too high, the part can sag, warp, and crack before the binder is completely removed. Defects and cracks can also develop in other stages of the injection-molding process such as drying. Such problems are rarely seen in gelcast ceramics if they are properly dried.
"Gelcasting forms a higher percentage of defect-free parts than injection molding because the slurry is poured, not forced by high pressure, into the mold," Omatete says. "In gelcasting, the mold-filling step is separated from the setting step. The slurry doesn't solidify until the molded material is placed in the curing oven. In injection molding, the mix must be superheated so it flows easily into the mold. But then heat must be removed so that the mix cools enough to solidify in the mold. The competition between the mold-filling and heat-removing processes can form defects in the material."
In slip casting, the starting powders are suspended in water to form a "slip." The slip is poured into a porous mold made of plaster of paris or another appropriate material. The capillary action of the porous mold draws water from the slip, which forms a solid layer inside the mold. When the part is as thick as desired, the rest of the slip is poured from the mold. The part is dried partially in the mold until it has shrunk away from the mold and is rigid enough to be removed and handled.
"The AlliedSignal engineers," Omatete says, "noticed that slip-cast turbine blades had density variations, but the gelcast blades were uniform. They also were impressed that the gelcast material was stronger than the slip-cast material."
Omatete's 3-month stay involved a harrowing experience: the January 17, 1994, earthquake in southern California. "My bed shook for more than 30 seconds," Omatete says, "It was pretty scary."
The results of the gelcasting process proved anything but shaky. AlliedSignal engineers "were high on our process," Omatete says. And that was a high point for him.
Maxine Savitz, general manager of AlliedSignal Ceramic Components, wrote a letter praising Omatete's efforts to move an ORNL-invented technology into the marketplace. She states that Omatete's daily interaction was invaluable and accelerated the application of gelcasting as a potential manufacturing process at Ceramic Components.
into the Marketplace
The ORNL ceramists have demonstrated that gelcasting can be used to form parts from a variety of materials, including ceramics, superalloys, metals, and fiber-reinforced ceramic composites. They have produced gelcast ceramics that included silicon carbide, silicon, silicon nitride, aluminum titanate, and sodium zirconium phosphate. They have also made tin oxide and iron oxide (ferrite) forms.
|Complex parts made by gelcasting include, from top left clockwise, an alumina turbocharger rotor, silicon nitride tensile test bars, alumina gears, and a silicon nitride turbine wheel.|
AlliedSignal Ceramic Components now has a license to develop and use gelcasting for the manufacture of turbomachinery for aircraft. Funding for this development work comes from NIST's Advanced Technology Program and the Advanced Materials Program in the Department of Defense's Advanced Research Project Agency (ARPA). The goal of this project is to commercialize gelcasting.
LoTEC of Salt Lake City also has a license to use gelcasting to make special automotive parts from sodium zirconium phosphate.
One of the most exciting nonautomotive applications of gelcasting, Janney says, is the development of accelerator magnets made of ferritea ceramic based on iron oxide. "Ferrite is used for soft magnets like those used in the heads of tape recorders," Janney says. "They are also used in accelerators to shape charged particle beams for research in high-energy physics."
ORNL ceramics have shown that gelcasting is well-suited for fabricating ring magnets for a particle accelerator.
The ORNL researchers are working on the magnet project in a CRADA with Ceramic Magnetics, Inc., of Fairfield, New Jersey. The goal is to use gelcasting to fabricate circular magnetsmore than 50 centimeters, or 20 inches, in diameterfrom ferrite for a high-energy physics accelerator.
Slip casting and die pressing have been considered for magnet fabrication, but it was feared that, after the large, heavy magnet parts were cast, they would break easily when moved to the sintering furnace. However, the gelcast parts are strong enough to be moved and handled without problems.
"Gelcasting," says Janney, "enables people in the ceramics industry to do things they wouldn't otherwise be able to do."
Other nonautomotive applications are being developed. Under a CRADA funded by DOE Energy Efficiency's Office of Industrial Technologies, Norton Inc. is collaborating with the ORNL group to produce complex-shaped silicon carbide parts for semiconductor wafer processing. Another application now being probed is the use of gelcasting to manufacture artificial bone to replace badly fractured human bones.
Omatete, Janney, Nunn, and Walls are extremely busy working on five gelcasting collaborations and four other gelcasting CRADAs with various industrial partners. Most of the work involves using gelcasting to develop powders or parts for automotive applications.
The ORNL researchers are serving as consultants to AlliedSignal Ceramic Components for the gelcasting commercialization project, which is receiving funding for 2 years from ARPA through the Office of Naval Research. Project participants include a consortium consisting of AlliedSignal Ceramic Components, universities, private users and manufacturers of ceramic powders and engine parts, and ORNL. They are exploring large-scale production of silicon nitride turbomachinery parts for gas turbines by gelcasting. The automobile industry will more likely be interested in building cars and trucks with gas turbines if the cost of manufacturing ceramic parts can be lowered. Gelcasting may be the key to making ceramic parts manufacturing competitive with steel parts fabrication. The goal of the $7 million ARPA project is to determine the feasibility of scaling up and commercializing ceramic production by gelcasting.
The ORNL gelcasting group also is involved in two CRADAs with Advanced Ceramic Research, Inc. of Tucson to investigate rapid prototyping. "With gelcasting," Omatete says, "we can quickly fabricate new shapes for new designs of automobile parts so they can be studied and tested."
ORNL researchers recently produced green-machined parts from gelcast ceramic billets. From top counterclockwise are a silicon nitride part green- machined on a lathe and fired; a green gelcast alumina billet (55 mm in diameter); a green gelcast alumina disk after machining using a drill press and surface grinder; and a machined, gelcast alumina disk after firing.
In one CRADA with this company, researchers will investigate how well the company's injection stereolithography process can do rapid prototyping using gelcast slurries. In the other CRADA, computer-aided design (CAD) tools will be used to green-machine gelcast parts.
"An object is designed on a computer using CAD," Omatete says, "and then the computer operates a computer numericcontrolled machine that cuts and shapes the gelcast ceramic. In this way, the ceramic is green-machined according to the computer design." You could call it high-tech pottery.
Things are shaping up well for ORNL's excellent cast of gelcasting researchers.
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