Most discoveries born in the university laboratory never make it into the marketplace. They may add to the sum total of scientific knowledge, but the road from idea to product is a long and torturous one. That has certainly been the case with Penn State’s research on textured ceramics, which the Messing lab has worked on since the late nineties. But recently, with the help of the Navy and Penn State Applied Research Lab, the road ahead has become much more promising.
Ceramics have multitudinous uses, but the Navy’s interest is mainly in underwater sonar. Both sonar and medical ultrasound use a property of certain types of material called piezoelectricity. When an electric voltage is applied to these ceramic materials, the result is a small mechanical transformation. Conversely, when mechanical pressure is applied, the result is a small electrical response. This piezoelectric effect is used in a variety of sensors, energy harvesters, ultrasonic cleaning and welding, as well as the aforementioned sonar and ultrasound.
“It is especially useful anytime you are sensing what’s under the ocean,” says Gary Messing, Distinguished Professor of Materials Science and Engineering at Penn State and the lead author of a recent review article in the Journal of Materials Research describing a number of advantages of ceramics with piezoelectric and other properties and new ways to make them. “We are talking about mineral discovery, oil and gas discovery, deep well monitoring, and energy harvesting.”
Messing’s lab has been developing an intriguing approach to making high-performance ceramics for these applications called texture engineering. By texture, he is not referring to patterns on the surface of the ceramic, but rather engineering the crystal orientation throughout the material. The properties of a ceramic are determined by two things: the intrinsic crystal arrangement of the material and the microstructure. In polycrystalline ceramics made from powder, the arrangement of crystals is random and the piezoelectric response is relatively low. At the opposite end of response are single crystals which are essentially one grain aligned in one direction.
For some applications, polycrystalline ceramics are sufficient. They are cheaper and more robust than single crystal ceramics. But there is great interest in improving on polycrystalline performance, if the cost and robustness can be retained. Enter textured ceramics.
“That’s the reason anyone would even consider going in this direction,” Messing explains. “There are key advantages of making a material that falls between single crystal and polycrystalline ceramics, with performance close to single crystal performance. For one, it is much easier and less expensive to make large parts. To make a large part from single crystals, you need to tile smaller pieces together. Very expensive. Our method of textured growth uses tape casting, which is a standard industry process.”
Textured ceramics use a process called templated grain growth. Small crystal particles are oriented in a particle matrix and when the mixture is heated, the particles tend to induce the rest of the mixture to grow in a single direction. The result is very similar to the uniformity of single crystal.
In the lab, thin strips or tapes of the ceramic mixture are stacked on top of one another by hand, typically by a graduate student, and then heated to induce the grain growth. The process is tedious, even to make small samples for testing.
The Applied Research Lab scales up the process
Richard Meyer is an associate professor of materials science and engineering and a senior scientist at the Penn State Applied Research Lab (ARL). Meyer has studied the properties of single crystals in detail for his work with the Navy.
Messing says, “We had been working in the area of textured ceramics for a long time with funding from the Navy. Then, for whatever reason, the funding went away and the work slowed down. Then Dr. Meyer came along.”
“We needed to take it out of the lab,” Meyer says, “and into the hands of the people who can do something with it.”
Messing and Meyer made some pieces of the textured ceramic in the lab that had good performance in a Navy transducer (the heart of the sonar device), and the Navy asked the Applied Research Lab to do the research on the processing requirements to take this material to the pilot-scale production level, Meyer says. “Our niche is being able to produce parts that are outside the form factor and beyond the quantity that are viable in single crystal.”
In their facilities in Freeport, Pennsylvania, 30 miles northeast of Pittsburgh, a group led by Dr. Mark Fanton is spearheading the effort to produce quantities of high quality textured ceramics capable of being handed off to manufacturers for potential device production on an industrial scale.
“This material is approaching single crystal performance,” Meyer says, “and we are getting closer every day. We’ve gone to great lengths to scale the processing conditions from grams to kilograms.”
With funding from the Defense University Instrumentation Program (DURIP), the Freeport facility has purchased a system that automates the stacking and lamination process. “With this machine, you program the shape you want and it will stack and make parts 24/7,” Meyer says.
Messing adds, “That’s why the Freeport operation is so important. Typically, the customer is buying 10-100 parts so they can put it in their transducer design. There is no way in an academic environment that we could ever upscale to that.”
In the process of scaling up to manufacturing level, a constant feedback loop has developed between Freeport and the Meyer and Messing labs at University Park. “What we are learning on the scaling side leads back to the lab. But also, what they are learning on the lab scale is leading back to improve the pilot-scale program,” Meyer remarks.
They are working with a number of perovskite ceramics, including lead indium niobate, lead magnesium niobate, lead titanate, collectively known as PIN-PMN-PT. A key advantage to the textured ceramic process is the ability to maintain chemical homogeneity in the multicomponent single-phase ceramic, something that is near impossible to achieve in growth of large single crystals. This is a key advantage of texture-engineered ceramics, because properties such as piezoelectricity are highly sensitive to chemical composition.
The next step
The goal of the program, says Meyer, is to simultaneously create both supply and demand. This requires getting the material to the point where they can hand it off to industry to build devices and evaluate performance.
“We have enough data to know there is interest. It’s just a matter of getting the material and processing information into the hands of the vendors,” he says.
Penn State has an open door policy when it comes to industry. If companies want to see the process in action, they are welcome to come to either the Freeport facility or to Penn State’s University Park campus. “They can tap our resources to facilitate adoption of this technology to the commercial side,” Meyer says.
In the review article in the Journal of Materials Research, Messing and Meyer, along with their collaborators, shared the technology with the research community in order to extend the oriented ceramics technique beyond piezoelectrics.
“The other part of this story is that there is opportunity to make other kinds of property sets by making textured materials, including mechanical, thermal, electrical, and ion conducting materials,” Messing. “There are many applications for this approach, both including piezoelectrics and beyond.”
Original article: “Texture-engineered ceramics – Property enhancements through crystallographic tailoring” DOI: 10.1557/jmr.2017.207
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the Office of Naval Research that sponsored some of this work.