Metallic nanophases - Definitions, processing and properties

Metal nanophases are found in applications as diverse as electrical engineering, electronics, digital and information technology, chemistry, and healthcare. Their use is either intentional—to exploit the specific properties of the nanoscale—or unintended, as a result of the ever-increasing trend toward product miniaturization. The objective of this article is to demonstrate and explain why new properties emerge when a material becomes what is known as a nanomaterial. We will focus on metals and metal alloys in the solid state, but the approach can be generalized to all types of phases. To illustrate this point, reference is sometimes made to ceramics and polymers, as well as to the liquid state. One might think that this is simply a matter of changing the nature of the chemical bond. However, this has significant implications: for example, metals are ductile, while ceramics are brittle. The advantage of limiting our discussion to metals is that most of their properties can be addressed from the perspective of classical physics, as opposed to quantum physics.

Underlying the main objective, the aim here is for the reader to gain a clear understanding of what nanophases and nanomaterials are, to provide a clear definition of them, and thus to acquire a method for identifying the transition from the standard state of matter to the nano state. Before addressing this aspect, it is reasonable to ask whether there is any value in discovering new materials, which include most nanomaterials. The article will only be relevant if it is convincing on this point.

It should also be noted that another way to approach nanophases –—other than the search for new properties– —is simply to experience them firsthand. We all know that technologies are trending toward ever-greater miniaturization. The components of our computers, our phones, and even the windshield wiper motors in our vehicles (!) are becoming increasingly smaller. The transition to the nanophase sometimes results in new behaviors. Ashby demonstrated in the 1970s why a ductile metallic object becomes brittle at very small dimensions. In 1949, Taylor observed that window glass, when reduced to very small...