A Materials Take on Going for Gold

goldAs the 2012 Olympics open in London this week, athletic achievements, and gold medals in particular, are drawing everyone’s attention. At the original Olympics in ancient Greece, the winner simply received an olive wreath: when the games first restarted in 1894, winners received a trophy. For most of the recent Olympic history, however, the crowning glory of any athletic career has been the Olympic Gold Medal. But behind the excitement of                                             sporting prowess, we wanted to know more about the gold in the medals                                         themselves.

The first surprise was that the last Olympic medals to be made of solid gold were awarded in 1912. All subsequent first-place medals have merely been gold-plated. Today, both gold and silver medals are 92.5% silver. This year’s medals are reported to be the biggest ever designed: the 85mm diameter far exceeding the minimum requirements of the International Olympic Committee (at least 3mm thick and 60mm in diameter). But this doesn’t mean there is more gold than ever before: the standards only specify that there must be six grams of high quality gold on each.

Perhaps it should be no surprise in the current economic climate that these medals aren’t solid gold. Gold’s rich color, its malleability, its resistance to almost all corrosion, and its sheer scarcity combine to make it the most desirable of metals. It is the one thing investors around the world have turned to whenever investments are insecure: as US President Herbert Hoover said, “We have gold because we cannot trust Governments.” So some 90% of the global production of gold gets squirreled away as bullion and jewelry. The remaining 10% plays vital roles in the electronics industry as interconnects and as surface layers on connectors: its high electrical conductivity and resistance to attack allow extreme miniaturization.

At today’s prices, ore grades as low as 0.5 ppm are economic. Gold occurs as a native metal, usually in very small particles. The metal is isolated from sand or silt by “panning”—shaking in a water-filled sieve—using its high density to separate it. Chemical processes are also used: it is soluble in mercury (from which it is recovered by distilling) and also dissolves in alkaline cyanide solutions (from which it can be recovered by precipitation). The concentration of gold in some consumer electronics means that old mobile phones and portable computers are a viable resource for the metal.

So should medalists be trying to recover the gold from their medals? While the raw materials have been costed at just over £400 per medal, it isn’t the cost of the gold that gives them their value. The ‘king of metals’ is used—even if only as an external coating—to symbolize the highest of achievements. So with athletes participating for the glory and the honor, there should be no danger of anyone wanting to melt down their medals.

Granta’s MaterialUniverse is an outstanding resource for materials scientists and engineers, the result of many man-years of effort. In a searchable electronic format, it contains complete sets of material property data for 3,500 unique data records covering virtually all purchasable engineering materials, and 240 records covering related processes. A selection of material properties for Gold, representing some of the information available in CES EduPack, are presented below.

General properties
Density 1.93e4 1.94e4 kg/m^3
Mechanical properties
Young’s modulus 77 81 GPa
Tensile strength 180 220 MPa
Hardness – Vickers 50 70 HV
Thermal properties
Melting point 1.06e3 °C
Thermal conductivity 305 319 W/m.°C
Thermal expansion coefficient 13.5 14.5 µstrain/°C
Electrical properties
Electrical conductor? Good conductor
Optical properties
Transparency Opaque
Eco properties
Embodied energy, primary production 2.4e5 2.65e5 MJ/kg
CO2 footprint, primary production 2.54e4 2.81e4 kg/kg
Recycle True
Typical uses: Jewelry; Interconnects, Printed circuit board edge connectors; Electrical contacts; Lining for chemical equipment; Coinage; Bullion; Plating for space satellites; Toning silver images in photography.
Palladium, platinum, and silver may substitute for gold.

Granta Design provides no warranty for the accuracy of this material property data

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