By Isabelle Robinson, M.Sc.Feb 6 2018
Research into self-crack-healing structural ceramics has uncovered a novel way of using 3D networks of healing activators as a design approach.
A scientific report published by Toshio Osada on December 19th, 2017, outlines a new approach for self-healing design - using an activator on a fracture path, which can accelerate the healing time by more than 6000x. This is a significant improvement and could have a number of applications, inlcuding aerospace engineering.
Self-healing structural ceramics have long been the focus of material research groups due to the high commercial demand. Despite their unparalleled superior strength at high temperatures, structural ceramics remain brittle. Therefore, there are obvious advantages to self-healing ceramic materials that can increase the work-life of a component by protecting the structural integrity of the material.
In addition to this, self-healing ceramics are more efficient at a lower cost because the self-healing can take place after the component has been fabricated and the full material strength is regained if the component is healed when in use. These factors mean that self-crack-healing structural ceramics also improve the safety of the components they are used for.
Presently, strict safety requirements in the industry limit the use of advanced structural ceramics in aircraft as turbine blades, despite the fact that they could significantly increase fuel efficiency due to their lightweight nature. Damage by foreign object collision could reduce the work life of the component and have catastrophic results. Osada and his team hope that new research into self-crack-healing design strategy can be used to develop new structural ceramics that can be used in turbine blades for aircraft engines.
Interestingly, self-healing ceramics take inspiration from bone regeneration. Full recovery can be split into three stages, inflammation, repair and remodeling. Blood is circulated into the crack of the bone and recruit osteoclasts for repair and regeneration of the bone. The new design technique mimics the networks of capillary blood vessels that deliver the fundamentals for regeneration.
Currently, self-healing of structural ceramics is achieved via oxidation reactions. This is done by exposing a high strength healing agent, such as silicon carbide, to high temperatures. This triggers a reaction and allows the ceramic to recover.
The new design approach enhances this strategy by utilizing an additional network of healing applicators which increases the efficiency of oxygen delivery and allows faster repair times, as well as decreasing the temperature required to initiate an oxidization reaction. In addition to this, the activator promotes crystallization to form a strong healing oxide.
The addition of manganese oxide as an activator is applied to the fracture path of the base material; in this case, an alumina ceramic increases the healing time significantly. In their research, a 110μm crack was fully healed in 10 minutes at 1273K, while using current methods at the same temperature the crack would heal in 1000 hours. It should also be noted that the MnO doping method can be activated using the temperature of a normal gas lighter, making it much more practical for industrial application.
This is only the first step for research into bio-inspired ceramic repair. Osada and his team conclude that they are currently investigating further into high-temperature mechanical properties of the self-healing structural ceramics. You can read their full report here.
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