After integrating the concept of the process-structure-property materials triangle that we talked about in Part 1, the next most important concept in materials science for failure analysis of metal and polymeric components is related to structure and its multiple overlapping levels.

Things are different when we get into the nano world, and I don’t have experience in that arena. My working philosophy regarding materials science is related to what I commonly call structural components. We’re talking about components that have to resist mechanical forces in the presence of a constant or variable environment.

So, let’s get to the nitty-gritty of structure. As I said in the first piece, we require concepts that allow us to understand the multiple levels of structure inherent in each component (Figure 1). If we are talking about a solid material as a materials scientist, the finest level of structure that concerns us on a day-to-day basis is the atomic structure. We need to have a basic idea of what an atom is.

The ancient Greek traveler and natural philosopher (they didn’t have scientists back then) Democritus (c. 460-370 BC) was the first to formulate the idea of the atom as the smallest piece of matter that could exist. Here is a quote from Wikipedia’s article (https://en.wikipedia.org/wiki/Democritus) on the early Greek theory of atoms:

“Democritus, along with Leucippus and Epicurus, proposed the earliest views on the shapes and connectivity of atoms. They reasoned that the solidness of the material corresponded to the shape of the atoms involved. Thus, iron atoms are solid and strong with hooks that lock them into a solid; water atoms are smooth and slippery; salt atoms, because of their taste, are sharp and pointed; and air atoms are light and whirling, pervading all other materials.[32]

Using analogies from our sense experiences, he gave a picture or an image of an atom that distinguished them from each other by their shape, their size and the arrangement of their parts. Moreover, connections were explained by material links in which single atoms were supplied with attachments: some with hooks and eyes and others with balls and sockets.[33] The Democritean atom is an inert solid (merely excluding other bodies from its volume) that interacts with other atoms mechanically. In contrast, modern, quantum-mechanical atoms interact via electric and magnetic force fields and are far from inert.”

References 32 and 33 may be found in the Wikipedia link.

This was fascinating to me. Of course I learned that Democritus was the first to have a theory of the atom. But I had been unaware – until researching this post – that he also had a theory of atomic bonds. While it is obvious that his theory neglects the insights of modern physics and quantum mechanics, some aspects of his theory are not so crazy. In fact, we now understand that atoms are not spherical, that the electron clouds that surround the nucleus are not spherical, and the three-dimensional geometry of the electron cloud surrounding the nucleus of the atom is extremely important in determining which other types of atoms will be attracted to a given type of atom.

I'll have more in Part 3.