Scientists discover new metal hardening technique

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Metallurgy is a science that covers all aspects of metal. It is what helps us understand how to alloy certain metallic elements and compounds, how to melt ore solidify them and even gain a better understanding of a metal’s tensile strength, durability and hardness. Recently, a group of scientists looked into ways to improve the hardness of metal, resulting in substances that are even ore resilient than they were before. The basis for this revolution? Manipulation of metallic grains.

Several researchers at Brown University discovered a hardness-enhancing technique that involves colliding nanoclusters of metal into each other. While hardly a conventional approach to raising the hardness of an item, the end result is a metal that is four times as hard as its naturally-formed counterpart.

Ou Chen, an assistant chemistry professor with the university and author of the research paper detailing this technique, remarked that all prior approaches to hardening are very top-down approaches to altering the grain structure of a metal. He also mentioned that the drawback to these known techniques is that it makes it very challenging to guide the change in size of those grains.

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Chen describes the end result of his team’s new technique as a means of creating nanoparticle blocs that fuse when squeezed. This approach allows for a uniformity to grain sizes, making the process of tuning the grains for enhancing the metal a trivial process. The team’s research project entailed nanoparticles of several types of metal, stripping those metals of a class of organic molecule known as a “ligand” and then applying pressure to induce fusion. Ligands inhibit the ability for metals to form a chemical bond with other metals.

The coins that resulted from this pressure exhibited just as much conductivity and reflectivity as their normal counterparts. The key differences were in coloration and hardness. Chen remarked that a process known as the “plasmonic effect” causes gold nanoparticles to appear a purple-black color when viewed under a microscope. However, the pressure applied to these ligand-free purple clusters resulted in them turning the iconic shade of gold known recognized by the human eye. Chen stated that the change in color was the moment the team could tell they had resulted in creating bulk gold.

Now that the technique is verified and can be recreated, the researchers have moved on to figure out how best to implement it in the commercial sector. Chen has already seen to patent the technique and has high hopes to apply it within industry and in the furthering of scientific research.

A bit more on hardness

While some people may be familiar with the Mohs scale, a 10-point scale to gauge an object’s hardness, there is more than one form of hardness.

  • Scratch hardness is the form of hardness where the Mohs scale comes into play, although only when dealing with minerals like talc, apatite and diamond. This form concerns how well an object resists fracturing or permanently changing shape when exposed to a force. The logic goes that the harder of two objects will leave scratches on the softer object when pressed against each other. While this is one of the first forms of hardness most children learn about, it is not really that relevant to the field of metallurgy and more vital to field geologists seeking to compare samples.
  • Indentation hardness is especially relevant in the fields of engineering and metallurgy. This form of hardness seeks to gauge a material’s resistance to deformation when exposed to a constant amount of pressure from something sharp.
  • Rebound/Dynamic hardness is concerned with elasticity and is tested by gauging the height of a diamond-tipped hammer after it is dropped from a fixed height and then bounces against the material in question.

Generally, the more gaps you leave in a substance’s molecular structure, the more strengthening anchor points you will create.

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