I must have known copper was something amazing when I used it as one of the colors to my wedding décor back in 2006. That was before using metallic at weddings was considered fashionable, so I felt far ahead of the trend, using copper, as it were.
But what makes copper so fantastic on a pure, elemental level? What makes it such a perfect conductor of heat, or metal that bonds beautifully?
First, let’s start with the copper on the periodic table and it’s material science.
Copper’s atomic number on the table is 29, and it’s symbol is Cu (which I never understand, as there’s no “u” in the word copper…it’s like having a US state abbreviation that doesn’t completely match). The atomic mass of copper is 63.546 u + 0.003 u. The melting point of copper is 1,984 F (or 1,085 C), and the thermal conductivity rate is 386 W/m K. Copper’s coefficient of thermal expansion is 17 per degree C x10^-6. Pure copper rates dead soft on the Rockwell C hardness scale, and is under the “non-ferrous” metal heading, meaning it does not contain any molecules of iron.
Whew. So, if that information helped you out, you’re welcome. I feel smarter just writing it all out in one place!
Copper, compared to other metals, is not highly reactive. That means it doesn’t react to other natural elements the same way iron does, for example. Attacks of oxygen and hydrogen (or water, for that matter) are usually futile – copper needs to be heated to at least 300 C to change it’s molecular make-up and become copper oxide. Iron, on the other hand, just needs to be exposed to air to make iron oxide (aka rust).
Copper can change/bond to other metals with the exchange of electrons. Elements are constantly forming covalent bonds between other elemental atoms (when an element may share electrons with other atom) or losing electrons to become positively charged. When that happens, the lost electrons move to another element, which is then negatively charged (that middle school science class coming back to you yet?), creating an electric (like a magnet) attraction between the two atoms, which is called an ionic bond.
Most metal elements/atoms lose electrons when they form the ionic bonds with other elements. However, copper is unique as it can form two ionic bonds. That is to say, once electrons are exchanged and the atom becomes less stable, it can combine with other elements (such as oxygen, for example) in two ways instead of one. This means deep molecular change can occur at a faster and higher rate when copper comes into contact with other elements. Take, for example, an item sitting outside in the rain. It’s a brass item (containing copper) and as it rains, the oxygen and carbon dioxide create a copper carbonate as the copper reacts with the rain in multiple ways. The brass item is covered with the greenish copper carbonate, thereby protecting the brass item from further corrosion.
For all the numbers above, copper certainly doesn’t come out of Mother Earth so pure and beautiful. We have to mine it out, and it comes out as copper ore, which usually contains only 1% of metal, so the ore needs to be floated. The refineries will pulverize the ore, mix it with water, and then pass it through water-filled tanks.The chemicals used in the water produces foam, which traps the copper minerals on the surface so they can be skimmed off, leaving the remaining ore. This is the part where the type of chemicals (or lack thereof) can determine how a copper is deoxidized, or whether it might turn into an alloy of copper instead of remaining pure. The finished “product” of this process is now about 25 – 35% copper, which is sent to be smelted.
Smelting uses high temperatures to finish purifying the copper. The first stage removes more copper from the ore by heating it with oxygen gas. From there, the “blister” copper goes through a fire refining and electrorefining stage, which results in a 99.99% pure copper.
When you have pure copper, the bonding abilities of those electrons are at a very high peak. Copper is conducting heat at nearly the perfect level of 386, and it is able to bond with silver or tin easily (depending on the chemicals/elements used to extract the copper from the ore – certain ones actually hinder the copper’s bonding ability), creating a molecular bond that lasts, at least in cookware, for a good chunk of time.
And that, all that science put into one place, is probably (now that I know way more about copper than I did at my wedding) what makes copper cookware, to me, so incredibly cool (and, of course, beautiful).