Platinum is a shiny, silvery metal and is much rarer than both gold and silver — so rare, in fact, that all the platinum ever mined could fit into your home. The name originates from Spanish word platina, meaning ‘little silver’. It is one of the most stable metals and is resistant to corrosion, even at high temperatures, making it ideal for electronic components, laboratory equipment and jewellery. The stable properties of platinum make it ideal for applications where absolute size or weight must be maintained despite changes of temperature or pressure over time. It is also a good catalyst – meaning that it enables chemical reactions to proceed at a faster rate or lower temperature than otherwise possible.
As Platinum is one of the rarest and most precious metals, it is used to represent 70 year celebrations, such as birthdays, anniversaries and royal jubilees.
Density: 21.5 g/cm3 compared with water: 1 g/cm3 (platinum is nearly 22 times denser than water!), gold: 19.3 g/cm3, silver: 10.5 g/cm3 or lead: 11.3 g/cm3
Boiling point: 3,825 °C compared with water: 100 °C, gold: 2,970 °C, or silver: 2,162 °C
Melting point: 1770 °C compared with water: 0 °C, gold: 1,064°C, lead: 328 °C or tungsten: 3,400 °C
Atomic number: 78 compared with gold: 79 or lead: 82
Rarity: (parts per million abundance in the earth’s crust): 0.005 ppm compared with iron: 56,300 ppm
Where is platinum found? South Africa and Russia compared with gold which is found in China, Australia and Russia
Platinum powder is used as a catalyst to reduce the exhaust emissions from motor vehicles. It converts unburned hydrocarbons into carbon dioxide and water vapour. It is the catalyst in catalytic converters.
A platinum resistance thermometer is a piece of platinum wire which determines the temperature by measuring its electrical resistance. It is referred to as a temperature sensor and offers an excellent combination of sensitivity, range and reproducibility. Platinum resistance thermometers are a common way to measure the temperature over a wider range of temperatures – used in applications from industry to weather stations. NPL calibrates the thermometers to make sure they are as accurate as possible.
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Find out more about measuring the temperature of the earth
The stability, both chemically and physically, of platinum means that is can be used as a ‘standard’ which other objects can be compared with. The kilogram used to be defined using a single standard weight made of platinum-iridium alloy.
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In 1875 the Metre Convention was signed by participating nations and the International Bureau of Weights and Measures (BIPM) was established.
In 1880 three platinum-iridium standard weights were manufactured from material provided by the British firm Johnson-Matthey. One of these weights was selected as the master kilogram (Le Grand K). Further copies, calibrated against Le Grand K, were manufactured in 1889. By the same year a number of platinum-iridium metre bars had been produced, and one was then selected as the International Prototype metre. Certified, calibrated copies of both the kilogram and metre were distributed to the member countries of the Metre Convention. Lots were drawn and Britain received kilogram number 18 and metre bar number 16.
The candela is the SI unit for measuring the visual intensity of light sources, such as light bulbs or torches. In the past, the unit used to measure visual intensity was called the candle, however this lacked sufficient accuracy and reproducibility. A new standard, proposed in 1937, and ratified in 1948, was based upon a perfect ‘black body’ at the freezing point of platinum and gave the name ‘candela’ to the unit of luminous intensity.
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NPL is actively researching measurement techniques for polluting airborne particles, particularly metal particles including platinum. We provide services and give advice to companies and researchers to help them understand how to make measurements and understand the results.
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Cobalt-platinum permanent magnets are quite exceptional. They are one of the most powerful permanent magnetic materials available and are readily fabricated. They are used in miniaturised circuits where space is limited and can be made into strips or wires. NPL calibrates cobalt-platinum magnets to ensure they work effectively.
Find out more about measuring magnetic materials
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