WHAT IS ZINC?

 

Zinc is a hard silver-grey metal with an atomic weight of approximately 65, compared with hydrogen at 1, carbon at 12, oxygen at 16 and gold at 197. Its density is 7.1 compared with water at 1, and it is one of the metals called a “heavy metal”.  The densities of other common metals are aluminium at 2.7, copper at 9, lead at 11.3 and iron at 7.9. Thus it feels quite heavy, being a little lighter than iron but much heavier than aluminium. Zinc melts at 420 degrees C and boils at 907 degrees C, both these figures being quite low for a metal.

 

Compared to the most commonly found elements in the earth’s crust, zinc is quite rare.  For example silicon is approximately 3000 times, iron 600 times and calcium 450 times as abundant as zinc. But zinc is not a precious metal. Like all metals in the service of man zinc has unique properties that make it useful. Its representation in alchemy is something like the following:

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Metals are usually found in an oxidised state in nature, i.e. as a compound, not as the metal itself, although there are several noble metals such as silver, gold and platinum which are all rather un-reactive and do not readily corrode or tarnish in air or water and can be found as metals in nature. Most metals, including zinc, are found in an oxidised state because they are reactive by nature.  Iron, for example, is always happy to “rust” or oxidise to brown iron oxide, a form in which it is found in nature, and to which, given half a chance, it likes to revert. We are lucky that zinc is available to look after all our steel structures.

 

It follows that most metals have to be “reduced” from their natural state back to metal. Traditionally metals were “smelted” (that is to say treated by heat in the presence of carbon) from the ores and minerals in which they were found. However, whereas copper was first smelted from its ores about 5000BC, lead about 4000BC and iron about 2000BC, zinc has always been much more difficult to extract.  The problem arises from the fact that, at normal smelting temperatures which are close to or higher than 1000 degrees C, zinc exists as a vapour, and zinc vapour is very reactive. Thus, as soon as zinc oxide is reduced to zinc vapour, it has a powerful desire to oxidise back to zinc oxide. It was not until the 14th century AD that zinc metal was produced, first in India and later in China. Brass, an alloy of zinc and copper was, however, produced much earlier, possibly as early as 200BC. By heating copper, zinc oxide and carbon together, zinc that was produced in this way was immediately absorbed into the copper before it could oxidise. Zinc is therefore a relatively new metal.

 

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