Monetary metal: zinc

There is little zinc in the earth's crust, in terms of prevalence among metals, it takes 16th place. But still, he is five times more than lead, 30 times more than tin, and even less copper than zinc. Many saw beautiful zinc crystals on a new galvanized bucket (Fig. 1). But basically zinc is used for the manufacture of various alloys.

“Metal zinc ... it turns out to be mostly oxygen ores, i.e., from a Galma, sometimes in whole layers ... In Sweden, in the 15th century, Galmey was processed in a zinc alloy with copper (brass, or yellow copper), and from Galma Paracelsles received a zinc; But the technical mining of the metal itself, known since ancient times in China, began in Europe only in 1807, in Belgium, when Abbot Doni discovered that Zinc was a flying, ” said Dmitry Mendeleev in the Basics of Chemistry. Historians of science believe that the ancient Egyptian alchemists could be the first to get brass (“artificial gold”).

Zinc is a rather active metal, it reacts with moisture and carbon dioxide air, and its surface is irreversibly covered with a dark gray layer of oxidation products. Therefore, zinc is poorly suitable for minting coins. Nevertheless, during the Second World War, when copper became strategic material, coins were minted from zinc in many countries (Fig. 2) [1]. The coinage lasted for some time after the war.

From zinc, for example, 1, 5 and 10 Austrian pennies (1947-149), 1 and 2 Swiss Rappen (1942–1946), small Albanian coins - Lex (1947–1957), Romanian lei of the war years, Belgian coins to 5 francs to 5 francs from the times of the I and II world wars, small Danish Danish are minted. Coins until 1971 (Fig. 3) and others. The last time minting coins from zinc took place in Austria in 1994. True, these coins were released not for circulation, but for collectors: a small circulation and improved quality (Fig. 4).

Zinc is half the cheaper than copper - about $ 7,000 and $ 7,000 per ton, respectively (in March 2018). Therefore, in order to save on October 1982, the small coins of the United States - cents began to be minted not from brass, as before (copper with 5% zinc), but from zinc (with an addition of 0.8% copper), covering them with a galvanically very thin layer of clean copper. As a result, the total content of copper in the coin was reduced from 95 to 2.5%; The mass of the coin also decreased significantly: from 3.11 to 2.50 g.

Knowing the mass of copper in new coins and measuring its area, you can calculate the thickness of the copper coating: it is approximately 5.2 microns. The coating really turned out to be very thin. And a significant difference in the mass of old and new cents allows us to conduct a curious experiment: by accurately weighing a handful of coins, the percentage of “old” and “new” cents can be calculated. What are the chemistry teachers in the USA to illustrate the “isotopic analysis” of elements with two natural isotopes (this refers, for example, Bor, Chlorine, Copper, Gallium, etc.).

Zinc is chemically much more active than copper. Therefore, if you slightly scrape off the edges of such a coin and put it in diluted salt or sulfuric acid, then for several days the acid will dissolve the zinc gut, without touching the shell until a light copper cover remains. You can also, having selected a suitable reagent, partially remove a copper coating from the surface of the coin, while a zinc gut will be exposed (Fig. 5).

It is interesting that since 2006, coins have also been produced in South Korea, in which copper content has been significantly reduced to save. Only, unlike American cents, their core is not zinc, but aluminum (aluminum is slightly cheaper than zinc), and the coin is placed on the outside, and, also, unlike the cents, the coins of the coin remains unnecessary (Fig. 6). Diluted hydrochloric acid quickly dissolves aluminum, leaving only two thin copper plates (Fig. 7).

The weighing of such a record and the measurement of its area showed that in Korea the thickness of the copper coating is much larger than in the USA: about 110 microns. Obviously, this is explained by the way of applying copper: galvanic in the USA and placer (hot rolling of sheets) in Korea. Crying of zinc coins with copper was used in the manufacture of single -centric coins in Canada in 1997-2003 (Fig. 8).

Ilya Lenson,
cand. chem. sciences, associate professor of the Higher Chemical College of RAS

In the next number of the TRV-hobby, we will tell you about another monetary metal-iron.

1. Gelfand M., Leleson I. Coins of war // TRV-NAUKA, No. 250 of March 27, 2018.