Musings on Metals: Copper
It could be argued that civilization began with the smelting of copper. Although thousands of years before, humans fired clay to make figurines and containers, smelting required several non-obvious steps. After all, the firing of clay, at some level, can be accomplished by simply dropping clay into a fire.
To smelt copper, our ancestors had to:
- Take malachite (see photo) or another copper ore, grind it up or break it into small pieces
- Mix the ground malachite with carbon
- Heat the mixture in a vessel to 1,085oC.
Achieving this temperature with a wood fire is, to me, astounding. Think about those days when you are grilling some burgers. You leave the grill on after the burgers are done, to burn off the grease. You come back 20 minutes later and the grill is at 500oF. You can feel the heat. Even touching the knob to turn the gas off is intimidating, as the heat drives you back. This temperature, 500oF, is only 260oC! The ancients reaching 1,085oC with wood and bellows is, indeed, impressive. By the way, a good rule of thumb to convert degrees C to degrees F from 100oC to 1,5000C is that 2XC=F, this fast approximation is accurate to about 10% in this range.
The confluence of the three procedures is not only non-intuitive, but think how many times the smelter of old could only reach 900oC and failed. I have argued that if copper melted at 1,200oC or so, civilization would have never gotten started. This temperature is perhaps a little too high to reach with a wood fire. The smelting of copper encouraged investigations into other metals, eventually resulting in the discovery of the processing of iron, an even less intuitive process than smelting copper. So, I believe that the success with copper was necessary to the production of steel.
Copper smelting became an industry that encouraged permanent settlements and stimulated trade, which encouraged writing and ciphering. An effective copper smelter would likely keep secret some of his craft as he wanted a competitive advantage. He could make more by smelting copper than doing anything else, so he almost certainly was an early specialist.
Considering all of this, I believe that without the discovery of copper smelting, we might still be living in huts or teepees, using stone tools, and living a nomadic existence without commerce, writing, or mathematics. Examples to support this thesis are the state of native peoples in the Americas in the 1400s. These native peoples had never learned to smelt metals and hence also lacked the follow-on aspects of civilization mentioned above.
Today, copper is a foundation material for electronics, given its excellent electrical conductivity, second only to silver. Copper’s ductility likely aids in the formation of PWB traces and plated through-holes in that it resists cracking.
Additionally, copper's ability to form an electrical and mechanical bond with solder is another trait that makes it a winner as an electrically-conductive assembly material in modern electronics.
Copper has been used for more than 10 millennia, but, as with most metals, 90 to 95% of it has been mined since 1900. About 15,000,000 metric tons (MT) are used each year, third to aluminum’s 22,000,000 MT and steel’s unequaled 1,000,000,000 MT.
In the next installment, we will discuss tin and how it forms an intermetallic with copper during soldering. Thus making solder paste, solder wire, and solder preforms critical components of electronics assembly.