Dr. Dan Miracle described a glass as a material with no symmetry, “A material that not only has no micro structure, it doesn’t even have an atomic structure.” These amorphous materials are actually made out of metals and are known as bulk metallic glasses (BMGs) because they can be produced in large quantities. BMGs are incredibly versatile and uses for them include anti-theft devices, cell phone cases, and even products allowing the processing of metals as if they were plastics.
BMGs hardness is twice their metallic alloy counterparts. For example, with a BMG of Cu-Zr and a metallic alloy of Cu-Zr, the BMG would be twice as hard and more resistant to corrosion. Miracle explained, “properties come from structure.” This means that even though two substances can have the same material compositions, they can have drastically different properties because their atoms are arranged differently. If the BMG has an iron base constituent, it will be magnetic. These materials have such amazing magnetic abilities that when used in transformers, they have a 99.3% efficiency as compared to the 97% efficiency of their metallic counterparts.
BMGs are vastly different from any other metal because of their micro-structure. A micro-structure is what an object’s surface looks like at a distance of only a few microns away from that surface. When Miracle began working on BMGs, he was surprised by the number of differences he found. “I learned that about 80% of what I learned in graduate school was no longer relevant,” claimed Miracle. The micro-structure of BMGs has no structure that any crystallized solid can relate too. Crystallized solids include materials like metals and have a uniform arrangement of atoms.
BMGs do have some major drawbacks. The ductility of BMGs is a lot like silicate glasses, meaning it can fracture. It is also very difficult to actually make a BMG because once the metals are melted down into a liquid state, they must also be cooled fast enough that no crystals are able to form. If crystals did begin to form, then these BMGs would be nothing more than metallic alloys.
Much of the molecular arrangement of BMGs comes from the atomic packing and arrangement of atoms. The easiest way to visualize this scenario is to imagine a cube with a lot of different-sized marbles in it. If the BMG was made of two metals, this cube would have two different marble sizes inside it. Because not all of the marbles are the same size, there would be differently sized gaps as some marbles of the same size would group together and other groups of marbles would intermix with those of the other size.
The method by which the atoms are packed into the cube is a subject of much debate in the scientific community. This debate arises from the question, “What is the most efficient way to pack spheres into an area?” Miracle has developed a simple, static, and understandable model to describe the atomic packing capabilities of BMGs. “The greatest strength of atomic simulations is that you get the x, y, and z coordinates of every atom in the structure… the biggest deficiency is that you get the coordinates of every atom in the structure,” laughed Miracle. Knowing the complete structure of BMGs is far too much information to retrieve any amount of relative data. That is where Miracle’s computational work is useful because he is able to simplify this data.
Overall, BMGs have many practical modern day uses, a unique molecular structure and offer a chance to explore in great depth the mysteries of metals without a atomic arrangement.
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