Coinage

Gold bars have become available in the past 100 years. There are three qualities of fine gold used in most bars. (1) For the international market, gold bars of about 12.5 kg (4(X) troy ounces) with a purity of at least 99.5% Au are prescribed. Each bar must be marked with the purity in 4 digits, the trademark of the refinery, and a serial number. The mark and the dimensions of the bar are registered by the London Bullion Market. The bars can then be traded worldwide without further control. Most of 

---

C (Mond process). The silver-white metal is ccp. The metal is not tarnished by air but is attacked by acids (except cone. HNO3). It is resistant to Fj. It is used extensively in alloys, particularly in steels and cast iron and as a coinage metal. Used in glass (green) in catalysts (particularly for hydrogenation). Western world production 1981 662 000 tonnes. 

Nickel is a moderately lustrous, silvery metal, and is extensively used in alloys (for example coinage, stainless steel) and for plating where a durable resistant surface is required. It is also used as an industrial catalyst, for example in the hydrogenation of unsaturated organic compounds. It is attacked by dilute aqueous acids but not by alkalis it combines readily with many non-metals on heating. 

The oxide is soluble in ammonia to give the complex [AglNHjlj] (linear). On heating, silver(I) oxide loses oxygen to give the metal (all the coinage metal oxides have low thermal stability and this falls in the order Cu > Ag > Au). 

It is used in coinage and is a standard for monetary systems in many countries. It is also extensively used for jewelry, decoration, dental work, and for plating. It is used for coating certain space satellites, as it is a good reflector of infrared and is inert. 

Much of modem life revolves around the use of the decimal system of numbers, although for many purposes it is far from ideal. This system (dec = ten) takes 10 as the basic unit of operation, and we say that we are working to base 10. However, the base 10 is not the only one possible the previous British and many other countries coinage was founded on a base of 12. The meaning of a base for purposes of calculation is illustrated in Figure 42.1. 

Perhaps the most extensive appHcation for conversion-rolled, explosion-bonded clads was for U.S. coinage in the 1960s (34) when over 15,900 metric tons of explosion-clad strip that was suppHed to the U.S. Mint helped alleviate the national silver coin shortage. The triclad composites consist of 70—30 cupronickel/Cu/70—30 cupronickel. 

Nickel—copper alloys also are used as coated electrodes or filler alloys for welding purposes. Coinage is typically an alloy of 75 wt % Cu and 25 wt % Ni. 

The words aromatherapy, aromachology, and aromakinetics are coinages of the 1990s. Aromatherapy, once based on a tradition of folklore and herbal medicine, is being investigated scientifically. 

Almost as soon as Pedersen announced his discovery of the crown ethers (see Chaps. 2 and 3) it was recognized by many that these species were similar to those prepared by Busch and coworkers for binding coinage and transition metals (see Sect. 2.1). The latter compounds contained all or a predominance of nitrogen and sulfur (see also Chap. 6) in accordance with their intended use. The crown ethers and the polyazamacrocycles represented two extremes in cation binding ability and preparation of the intermediate compounds quickly ensued. In the conceptual sense, monoazacrowns are the simplest variants of the macrocyclic polyethers and these will be discussed first. 

In the reactions of 10.13a with alkali metal terr-butoxides cage expansion occurs to give the sixteen-atom cluster 10.15, in which two molecules of MO Bu (M = Na, K) are inserted into the dimeric structure. The cluster 10.13a also undergoes transmetallation reactions with coinage metals. For example, the reactions with silver(I) or copper(I) halides produces complexes in which three of the ions are replaced by Ag" or Cu" ions and a molecule of lithium halide is incorporated in the cluster. ... 

Bronze (7%) (Cu/Sn) typically 5-10% Sn often with added P or Zn to aid casting and impart superior elasticity and strain resistance. Gun metal is 85% Cu, 5% Sn, 5% Zn and 5% Pb. Coinage metal and brass also often contain small amounts of Sn. World production of bronzes approaches SOO 000 tonnes pa. 

Ruthenium and osmium are generally found in the metallic state along with the other platinum metals and the coinage metals. The major source of the platinum metals are the nickel-copper sulfide ores found in South Africa and Sudbury (Canada), and in the river sands of the Urals in Russia. They are rare elements, ruthenium particularly so, their estimated abundances in the earth s crustal rocks being but O.OOOl (Ru) and 0.005 (Os) ppm. However, as in Group 7, there is a marked contrast between the abundances of the two heavier elements and that of the first. 

The non-ferrous alloys include the misleadingly named nickel silver (or German silver) which contains 10-30% Ni, 55-65% Cu and the rest Zn when electroplated with silver (electroplated nickel silver) it is familiar as EPNS tableware. Monel (68% Ni, 32% Cu, traces of Mn and Fe) is used in apparatus for handling corrosive materials such as F2 cupro-nickels (up to 80% Cu) are used for silver coinage Nichrome (60% Ni, 40% Cr), which has a very small temperature coefficient of electrical resistance, and Invar, which has a very small coefficient of expansion are other well-known Ni alloys. Electroplated nickel is an ideal undercoat for electroplated chromium, and smaller amounts of nickel are used as catalysts in the hydrogenation of unsaturated vegetable oils and in storage batteries such as the Ni/Fe batteries. 

Collectively known as the coinage metals because of their former usage, these elements were almost certainly the first three metals known to man. All of them occur in the elemental, or native , form and must have been used as primitive money long before the introduction of gold coins in Egypt around 3400 BC. 

About one-third of the copper used is secondary copper (i.e. scrap) but the annual production of new metal is nearly 8 million tonnes, the chief sources (1993) being Chile (22%), the USA (20%), the former Soviet Union (9%), Canada and China (7.5% each) and Zambia (5%). The major use is as an electrical conductor but it is also widely employed in coinage alloys as well as the traditional bronze (Cu plus 7-10% Sn), brass (Cu-Zn), and special alloys such as Monel (Ni-Cu). 

The fee lattice of the coinage metals has 1 valency electron per atom (d °s ). Admixture with metals further to the right of the periodic table (e.g. Zn) increases the electron concentration in the primary alloy ( -phase) which can be described as an fee solid solution... 

The selenides and tellurides of the coinage metals are all metallic and some, such as CuSe2, CuTc2, AgTe. 3 and Au3Tc5 are superconductors at low temperature (as also are CuS and CUS2). 

---