Chromium’s use through history

• Chromium’s most common use throughout history has been the production of various ferrous alloys (alloys containing iron) with the most common by far being the alloy ferrochromium

• Chromium is also used to make:

paint up to the 1980’s

Elevators

Escalators

Barbeques

Aeroplane Frames

And many other things…

Activity & Ease of Refinement

• In relation to Chromium’s uses:– Chromium does not react easily; it possesses

passivation, which makes it highly unreactive– It does not corrode or oxidise easily

• Therefore it is used to build & plate things to protect them from corrosion and oxidation

– Chromium ore (chromite) has a high abundance, and chromium is easy to extract

• The relative ease of refinement allows chromium to be widely used

Extraction Process of Chromium

• Chromium is extracted commercially from chromite (chromium oxide), which is found naturally

• Chromite has the formula Cr2O3

• Chromium is extracted using the Thermite Process in which a reduction/oxidation reaction takes place with aluminium

• Chromite (chromium oxide) reacts with aluminium. The chromite is reduced to form pure chromium, and the aluminium is oxidised to form aluminium oxide

• Cr2O3(s) + 2Al(s) Al2O3(s) + 2Cr(s)

Chromite

• Energy input involved:

– The Thermite Process requires substantial heat energy

– This energy ‘drives’ the reaction

– In turn the reaction produces a substantial amount of heat

– Therefore energy input is necessary to successfully extract chromium from its ore

Extraction Process of Chromium

A typical thermite reaction

Common Alloys of Chromium• Chromoly:

- A Range of low alloy steels- Advantage over aluminium is more tensile strength and malleability- Disadvantage to aluminium is extra weight and does not resist corrosion as stainless steel does - Used in bicycle frames and race-car roll cages

• Chromel:- Made up of roughly 90% nickel and 10% chromium- resists high temperatures (1100°C) and high tensile strength - used to make positive conductors for a type of temperature sensor know as a thermocouple

• Chromel A:- Variation of Chromel, contains 80% nickel and 20 % chromium and hashigh resistance to corrosion, high temperatures and oxidation

Common Alloys of Chromium• Stellite:

- Formed from a variety of cobalt-chromium alloys designed to wear resistance- Completely non-corrosive and non-magnetic- Cuts things at high temps- Expensive to produce due to extreme durablity, done by grinding rather than cutting- used in saw teeth, hard facing, acid-resistant machine parts, improved quality of poppet valves, valve seats and internal combustion engines greatly. Also used in M60 machine guns, starting from the chamber as well as jet turbine engine blades

• Ferrochrome:- This alloy of chromium is 50%-70% chromium, alloyed with iron- 80% of ferrochrome is used in the production of stainless steel- Usually used in areas of specialist productions like engineering. A high Cr to Fe ratio is needed and minimum amounts of other elements such as Sulfur, Phosophorus and titanium are important - This production is done in small furnices rather than large

Ferrochrome

Common Alloys of Chromium

• Stainless Steel:- Most common alloy which chromium is present in- Resistance to heat, malleable, resistance to corrosion, cost effective and resistance to water and oxidation - Many different types due to the ease amounts of each metal can be varied-Core metals are chromium, iron, aluminium and titanium-Stainless steel is used to make cutlery, cooking utensils, pots and pans, furniture, shelters, subway trains, fuel and chemical containers, piping and much more

Availability of Metals• The availability of metals has increased in

the past 200 years• This is due to:

– The discovery of more ores and metals

– Advances in technology• It is easier to locate ore bodies

now than 200 years ago• New processes to extract metals

from their ores have been discovered, eg the Bayer Process

• The industrial revolution– Mass production and

extraction of metals began– Due to these advances, it is easier to

extract and produce metals. Therefore their availability has increased as these advances are made

The Recycling of Chromium

• Chromium is currently not recycled on the large scale due to:– The abundance of chromium

ores and their ability to satisfy human needs for many hundreds of years

– The relative ease associated with extracting chromium

• However in the future a need may arise to recycle chromium:– as chromium ores become

depleted– as energy conservation

becomes more of an issue• But in the short term and at

present there is no need to recycle chromium