Researchers have used 3-D printing to create ceramic structures from silicon polymers.
Scientists at HRL Laboratories LLC in Malibu, Calif., announced their process overcomes the limitations of traditional ceramic parts to yield high-strength parts able to resist temperatures exceeding 3,000° F.
Researcher Zak Eckel said in a phone interview that he and colleagues were working on making ceramics from prepolymers such as siloxane-type materials with silicon-oxygen backbones.
“We discovered this system should work with 3-D processes to give a material with low density and high strength,” Eckel said from his laboratory in Malibu. “We get unique lattice micro-structures.”
HRL scientists initially are focusing on aerospace applications, not a surprise given that HRL is jointly owned by airplane manufacturer Boeing Co. and General Motors Co. HRL is looking for a commercial partner to develop the technology commercially.
Materials under study at HRL are relatives of silicone rubbers similar to those used to injection mold disposable parts for medical and other markets. Such polymeric molded components are soft and flexible, bringing their elastomeric properties to end uses such as syringe components.
HRL researchers, however, are making products at the other end of the materials-properties spectrum, where silicon and oxygen-based molecules lead to hard, temperature-resistant ceramics.
Eckel, a senior development engineer, and his associates reported their startling discovery in the Jan 1 issue of sciencemag.org published by the American Association for the Advancement of Science.
The secret to the discovery is the composition of a resin formulation that can be 3-D printed into parts of virtually any shape. The 3-D printed resin is UV-cured in the 3-D printer and then fired at elevated temperatures of about 1,800° F to give a fully dense ceramic that is ten times stronger than comparable materials. The typical route to make ceramic parts is to sinter powder raw materials at high temperatures, but the process usually is plagued by porosity and low strength for the finished part.
“Our team has surmounted the challenges inherent in ceramics to develop an innovative material that has myriad applications in a variety of industries,” noted Tobias Schaedler, a senior scientist with HRL's Sensors and Materials Laboratory in a news release.
New ceramics made at HRL have a silicon oxycarbide backbone arranged in a micro-lattice. They also created similar ceramics with silicon-carbon and silicon-nitrogen raw materials.
“With our new 3-D printing process, we can take full advantage of the many desirable properties of this oxycarbide ceramic,” Schaedler added. He envisions applications as diverse as jet engine and hypersonic vehicle components, intricate parts in miniature electromechanical systems and electronic packaging.
Eckel said the HRL-developed process works with conventional 3-D printing machines.
Normally one doesn't associate ceramics with polymers except as rivals, along with metals, competing for thousands of end-uses in the materials universe. Polymers of course are very large molecules with repeating links in the backbone. Polymers called plastics typically have carbon-carbon or carbon-oxygen linkages.
3-D printing technology has so far focused on using thermoplastics such as nylon and polylactic acid or metals to make parts with complex geometries. Thermoplastics are already well established in custom-making medical shapes such as prostheses. 3-D-printed metal parts are finding use in exotic applications such as high-performance jet engine components.
Eckel and his team attached groups such as vinyls, acrylates and thiols to chemicals like siloxane so that the resultant pre-ceramic monomers can be cured by UV light to give a pre-ceramic polymer part. The UV-cured polymer part is fired to drive off the unwanted groups to create a cross-linked ceramic matrix.
