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Chromium

ChromiumThis is one of the most decorative elements in the periodic table. Many of its compounds are used to create colour, but it also has vast industrial uses.

By far the largest of the industrial uses of Chrome is within stainless steel – the most common alloy being composed of 8% Ni and 18% Cr with balance iron. In common parlance, it is called 18/8. Next time you pick up a knife, fork or spoon at a restaurant look at the back and it should read 18/8. Sometimes, it will say 18/0 which means there is no chrome in the alloy used to make the cutlery. This could also mean, when placed in a dishwasher it will, over time, corrode i.e show some appearance of rust. Why?

In stainless steel Chrome causes an adherent and insoluble oxide layer to form. This film seals the iron from oxygen in the atmosphere, preventing oxidation and thus the steel from corroding or rusting. That is why, when you look further at the back of the cutlery you may also see the word “Inox” (the french word for stainless steel).

Although 18/8 is the standard for many applications, stainless steel is essentially an alloy with many variants (maybe more than 150), some of which have precise inclusions of titanium, molybdenum and other elements in variable proportions to produce different properties. But, the most important quality that Chrome brings is corrosion resistance. The greater the Chrome content alloyed with nickel, the greater the corrosion resistance.

To give a sense of proportion, it is thought that 3.5 million mt of Chrome is consumed per year within the steel industry via high carbon and low carbon ferrochrome as well as charge Chrome. Lipmann Walton focuses on the smaller, low volume / high value fraction of the market made up of electrolytic Chrome flakes / powder (circa 5,000 mt per year) and aluminothermic Chrome (circa 25,000 mt per year). Both these forms of Chrome are used within numerous alloys of which LW’s focus is the super alloy industry where a degassed product is imperative.

On the more decorative side, we are all aware of ‘chrome-finished’ products. This is in fact a plating which produces a hard, beautiful surface in order to prevent corrosion. One of the great examples of this is the facing plates of the Chrysler building in New York. In a sense, Chromium almost defines the Art Deco age, the period of stream-lining, speed and style exemplified by the fins and bumpers of the Cadillac or the engine and exhaust pipes of a Harley Davidson motorcycle.

It has a variety of colours to its repertoire, as it is used in glass to give an emerald green colour. I wonder how many people know that this element is responsible for the green colour of emeralds and the red colour of rubies! Lead chromate is a yellow pigment and various other compounds are used as dyes in the textile industry.

Chromium FACTS
Chromium was discovered and isolated in 1798 by Nicholas Louis Vauquelin in Paris, France. It comes from the mineral chromite, FeCr2O4. The metal is hard, silvery in colour and has a body centred cubic (BCC) structure.

The metal is very resistant to oxidation although it dissolves in non-oxidizing acids and reacts with O2, halogens and S, at high temperatures. It is widely used in electroplating and as an additive for steel.

It can be used as a decorative finish when plated on top of nickel in the form of a very thin cracked deposit. The coating is so thin that unless the undercoat is highly polished, the chromium will appear dull.

Its main uses are in alloys, chrome plating and metal ceramics.

Chromium is a human poison by ingestion, it is also a suspected carcinogen. Chromates have a corrosive action on the skin.

Atomic no.
Relative atomic mass
Melting point
Boiling point
Density
Electrical resistivity
Young’s modulus
Heat capacity
Abundance
Thermal conductivity
24
52.00
1907°C
2671°C
7190 kgm-3
130 nΩm
279 Gpa
23.35 J/K/mol
100 ppm
93.7 W /m/K