A new study by researchers at the Technion-Israel Institute of Technology and Germany has found that gold microparticles possess shape memory and self-healing properties.
Shape-memory materials have the ability to mend moderate damage they sustain and recover their original shape.
The discovery could one day lead to the development of micro- and nanorobots capable of self-repair as well as damage-tolerant machine components, to name a few.
The study, published in the journal Advanced Science, was led by Prof. Eugen Rabkin of the Technion Department of Materials Science and Engineering and with Dr. Christian Brandl of Karlsruhe Institute of Technology.
Until now, the shape memory effect has only been observed in only a few metal alloys such as nickel titanium. These alloys are characterized by polymorphism – multiplicity of possible stable crystalline phases. This is the first time the shape memory effect has been seen in gold particles.
As part of the study, researchers indented gold particles with a sharp diamond tip controlled by an atomic force microscope. Annealing the indented particles at a temperature of 600°C, which is about 65% of the absolute melting temperature of gold. This resulted in full healing of the damage and recovery of the particles’ original shape prior to deformation.
Prof. Rabkin explained that the discovery is surprising for two reasons: “First, the particles’ original shape was not perfect in terms of energy and thermodynamic equilibrium. Second, gold in its solid state is not characterized by polymorphism.”
To understand how surprising this process is, think of spilled milk jumping back from the floor into the glass, or a car that self-restores its original shape after being severely damaged in an accident.
Prof. Rabkin said that the discovery could be used for the design of mechanically stable and damage-tolerant components and devices at the submicrometer length scale.