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Questions and answers

What is platinum?

One of the rarest and most precious metals

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, recently, the Queen’s Jubilee.  

Platinum at a glance

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

How is platinum used in everyday life?

  • Platinum is strong, hard wearing and withstands both heat and extreme cold. This makes it ideal for jewellery, where it retains its good looks even when worn regularly.

  • 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.  

  • Platinum-based drugs can treat a wide range of cancers, as they can slow or stop the division of living cells. The first platinum-based chemotherapy drug was discovered more than forty years ago.
  • Platinum catalysts are used to manufacture plastics, synthetic rubber and polyester fibres for clothes and blankets from petrochemical feed stocks.
  • Platinum-cured silicones are used to coat and protect automotive air bags from their explosive systems. The platinum treatment keeps the air bags stable so that they can be kept folded up for long periods of time without deteriorating.  
  • Platinum-cured silicone is non-toxic so can be used in a range of personal care products including lipsticks, shampoos, contact lenses and medical applications.
  • Platinum is an effective catalyst in hydrogen-powered electric cars. The platinum means the fuel cell works instantly and at low temperatures, as well as emitting only water.

NPL uses platinum for metrology and measurements

Measuring temperature  

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.

Find out more about platinum resistance thermometers

Find out more about measuring the temperature of the earth


Accurate mass and length standards

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.

Find out more about calibrating weights

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.

Find out more about SI units


Measuring light

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.

Find out more about the candela


Platinum particles in the air

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.

Find out more about measuring airborne particles


Platinum as a powerful magnet 

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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