Manufacturing Bits: Sept. 28

Self-healing ceramics; space polymers; autonomous materials.


Self-healing ceramics
Texas A&M University has discovered a new self-healing mechanism for ceramics, a technology that could one day be used for jet engines, hypersonic aircraft and nuclear reactors.

Ceramics involve various materials that are neither metallic nor organic, but rather they are crystalline and/or glassy, according to the University of Maryland. One common example is clay, which is shaped and then heated in a kiln. This in turn forms bricks, pottery or tile.

Ceramic materials are also used to make spark plugs, fiber optics, artificial joints, space shuttle tiles, cooktops, race car brakes, chemical sensors, bearings, body armor, and skis, according to the University of Maryland. Ceramics are also used in the field of electronics. Certain IC packages and superconductors use these materials.

Ceramics are resilient to heat and extreme environments. The problem? They are fragile and crack easily, according to Texas A&M.

In response, Texas A&M has demonstrated a mechanism that can heal the cracks as they form in ceramics, even at room temperature. Researchers have discovered a self-healing mechanism within a type of ceramics using MAX phases. Potentially, these materials prevent catastrophic failures in ceramics. Self-healing materials that are resilient to heat and extreme environments such as MAX phases are ideal for next-generation technologies like jet engines, nuclear reactors and other systems.

The MAX phases involve a family of materials called ternary carbides. In simple terms, atomically layered ternary carbide materials are layered within the ceramics themselves.

“Imagine a plain loaf of bread, it is homogeneous, so if I slice it up, each slice will look the same – similar in idea to conventional ceramics,” said Miladin Radovic, a professor in the Department of Materials Science and Engineering at Texas A&M. “But MAX phases are layered like a peanut butter sandwich with peanut butter between two slices of bread.”

“Crystals of this class of ceramic materials readily fracture along weakly bonded crystallographic planes. However, the onset of an abstruse mode of deformation, referred to as kinking in these materials, induces large crystallographic rotations and plastic deformation that physically heal the cracks. This implies that the toughness of numerous other layered ceramic materials, whose broader applications have been limited by their susceptibility to catastrophic fracture, can also be enhanced by microstructural engineering to promote kinking and crack-healing,” explained Hemant Rathod, a doctoral student in the Department of Materials Science and Engineering at Texas A&M and the lead author in a paper in Science Advance, a technology journal.

“This kinking or self-healing mechanism can occur over and over closing the newly formed cracks, thus delaying the failure of the material,” Rathod said.

“What’s really exciting about MAX phases is that they readily form kink-bands under loading which can self-heal cracks even at room temperature, making them suitable for a variety of advanced structural applications,” said Ankit Srivastava, assistant professor in the Department of Materials Science and Engineering at Texas A&M, and a corresponding author on the study.

Space polymers
The University of Illinois Urbana-Champaign (UIUC) has developed self-healing polymer materials for use at the International Space Station National Laboratory.

Several thermoplastic materials are used in aerospace applications, such as wire insulation, thermal blankets and metal surface coatings. But these materials are known to degrade in space due to radiation and extreme temperatures.

This could be problematic for the International Space Station (ISS). The ISS serves as a research lab for companies, government agencies and universities. For some time, astronauts on the ISS have conducted a plethora of experiments at the orbiting lab from various organizations.

UIUC, meanwhile, has developed a new class of 3D-printed polydicyclopentadiene (pDCPD)-based thermosetting polymers. These materials harden when heated, which may provide a more durable option for space-based applications. A lightweight thermoset material, pDCPD is used to make automobile body panels and aviation components.

“The materials we use are novel nanocomposites, based on thermosetting polydicyclopentadiene (pDCPD)-matrix mixed with self-healing components, which can be cured in a matter of minutes to hours compared to traditional thermosetting polymers that take days to cure inside an autoclave. Also, these novel pDCPD-based materials are amenable to additive manufacturing techniques with the potential for rapid fabrication or repair of parts right where they are in space,” said Debashish Das, a postdoctoral scholar in the Department of Aerospace Engineering at UIUC.

Researchers will synthesize the test materials in ground laboratories and then launch the materials to the ISS for testing. “The innovative coupling of selective high-temperature synthesis with 3D printing by UIUC offers a pathway for utilization of space or Earth in-situ resources in the manufacturing of new materials,” said Etop Esen, commercial innovation manager at the Center for the Advancement of Science in Space (CASIS), manager of the ISS National Lab. “This project will determine if the pDCPD polymers produced by this method are more durable than conventionally manufactured polymers, such as Kapton or Teflon, currently used in harsh aerospace applications.”

Autonomous materials
The Indian Institute of Science Education and Research, the Indian Institute of Technology Kharagpur and RWTH Aachen University have discovered a self-healing piezoelectric molecular crystal.

“The ability to autonomously restore shape or self-heal are useful properties that have been incorporated into a range of materials, including metals and polymers,” according to researchers in Science. “Bhunia et al. found that both of these abilities could be achieved in piezoelectric molecular crystals, specifically bipyrazole organic crystals. When the crystals are fractured, they develop charged surfaces that attract each other, drawing the two faces together to enable self-repair as long as they remain within a critical distance of each other. The effect can also be seen in other noncentrosymmetric piezoelectric crystals.”

Science X, a web-based news service, explains how this all works.

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