What makes chromium unique

Chromium-plated car and lorry parts, such as bumpers, were once very common. It is also possible to chromium plate plastics, which are often used in bathroom fittings.

However, the waste effluent is toxic so alternatives are being investigated. Chromium compounds are used as industrial catalysts and pigments in bright green, yellow, red and orange colours. Rubies get their red colour from chromium, and glass treated with chromium has an emerald green colour.

Biological role. Chromium is an essential trace element for humans because it helps us to use glucose. However, it is poisonous in excess. We take in about 1 milligram a day. Natural abundance. Chromium is found mainly in chromite. Chromium metal is usually produced by reducing chromite with carbon in an electric-arc furnace, or reducing chromium III oxide with aluminium or silicon. Help text not available for this section currently.

Elements and Periodic Table History. He was intrigued by a bright red mineral that had been discovered in a Siberian gold mine in and was referred to as Siberian red lead. It is now known as crocoite and is a form of lead chromate.

Vauquelin analysed it and confirmed that it was a lead mineral. Then he dissolved it in acid, precipitated the lead, filtered this off, and focused his attention on the remaining liquor from which he succeeded in isolating chromium.

Intrigued by the range of colours that it could produce in solution, he named it chromium from the Greek word chroma meaning colour. He then discovered that the green colouration of emeralds was also due to chromium. Atomic data. Glossary Common oxidation states The oxidation state of an atom is a measure of the degree of oxidation of an atom.

Oxidation states and isotopes. Glossary Data for this section been provided by the British Geological Survey.

Relative supply risk An integrated supply risk index from 1 very low risk to 10 very high risk. Recycling rate The percentage of a commodity which is recycled. Substitutability The availability of suitable substitutes for a given commodity. Reserve distribution The percentage of the world reserves located in the country with the largest reserves. Political stability of top producer A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.

Political stability of top reserve holder A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators. Supply risk. Relative supply risk 6. Young's modulus A measure of the stiffness of a substance. Shear modulus A measure of how difficult it is to deform a material. Bulk modulus A measure of how difficult it is to compress a substance. Vapour pressure A measure of the propensity of a substance to evaporate.

Pressure and temperature data — advanced. Listen to Chromium Podcast Transcript :. You're listening to Chemistry in its element brought to you by Chemistry World , the magazine of the Royal Society of Chemistry.

This week an element that adds sparkle and value to minerals, through the colourful characteristics of its compounds. In the Western world, the colourful history of chromium begins, suitably enough, at the far end of the visible spectrum with a red-orange mineral that was named "Siberian red lead" by its discoverer, the 18th-century geologist Johann Lehmann.

It was in the middle of this surge of discovery, over 35 years after Siberian red lead was first found that the French chemist Louis Vauquelin showed that this mineral, now known as crocoite, contained a previously unknown chemical element.

It took Vauquelin several steps to isolate chromium. First he mixed the crocoite solution with potassium carbonate to precipitate out the lead. Then he decomposed the lemon yellow chromate intermediate in acid, and finally removed the compounded oxygen by heating with carbon - leaving behind elemental chromium.

The name for this new element was debated among his friends, who suggested "chrome" from the Greek word for colour because of the colouration of its compounds. Although he objected to this name at first because the metal itself had no characteristic colour, his friends' views won out. When Vauquelin exhibited his pale grey metal to the French Academy of Sciences, he commented on the metal's brittleness, resistance to acids and incapability of being melted. He thought these properties made it overly difficult to work with and thus limited its applications as a metal.

He did suggest, however, that chromium's compounds would be widely used as beautiful, brilliantly coloured pigments. A browse through images of chromium compounds on Wikipedia shows a whole spectrum of colours: dark red chromium VI oxide, orange-red lead chromate, bright yellow sodium chromate, brilliant chrome green that's chrome III oxide , light blue chromium II chloride, and violet anhydrous chromium III chloride.

The last of these compounds shows an amazing property when hydrated. Its colour changes between pale green, dark green and violet depending on how many of the chromium ion's six coordination sites are occupied by chloride rather than water. Of all these pigments, one of them stands out.

I'm a chemist who was born, raised and schooled in the Midwestern United States, so the iconic yellow school buses in North America were familiar sights. Chrome yellow, also known as "school bus yellow", was adopted in for all U. However, the presence of both toxic lead and hexavalent chromium of Erin Brockovitch fame has led to it being largely replaced by a family of azo dyes, known as Pigment Yellows, though chrome yellow is still used in some marine and industrial applications. Of all chromium's natural occurrences, my favourites are gemstones, where a trace of the element adds a blaze of colour.

As corundum, beryl, and crysoberyl, these metal oxides are colourless and obscure minerals. But add a dash of chromium, and they become ruby, emerald and alexandrite. The chemist's tool of crystal-field theory, which models the electronic structure of transition metal complexes, provides a surprisingly accurate way of describing and predicting the source and variability of colour in chromium's compounds. In ruby - which is aluminium oxide with a few parts per thousand of the aluminium ions are replaced by chromium III ions - the chromium atoms are surrounded by six oxygen atoms.

This means that the chromium atoms strongly absorb light in the violet and yellow-green regions. We see this as mainly red with some blue, giving, in the best cases, the characteristic pigeon-blood colour of the finest rubies. So, when more chromium is added to aluminium oxide, the octahedral environment around the chromium becomes distorted and the two bands of absorption shift towards the red.

My next gem, the emerald, in an oxide of silicon, aluminium and beryllium. It has the same substitution of a chromium ion for an aluminium ion and a similar distorted octahedral arrangement of oxygen around chromium, giving emeralds their characteristic green colour, like that from green sapphires.

Of the chromium gemstones, alexandrite is the most fascinating to me. Its stones are strongly pleochroic. That is, they absorb different wavelengths depending on the direction and polarisation of the light that's hitting them. So, depending on a gem's orientation, alexandrite's colour ranges from red-orange to yellow and emerald green.

Its colour also changes depending on whether it is viewed in daylight or under the warm red tones of candlelight. When moved from daylight to candlelight, the best specimens turn from a brilliant green to a fiery red.

Lesser gems turn from dull green to a turbid blood red. Outside this rainbow of chromium compounds, chromium helps prevent a particularly undesirable colour: rust brown. The alloyed chromium reacts with oxygen to form a transparent nanoscopic layer of oxide that forms a barrier to further oxygen penetration and so prevents the ruddy, flaky products of iron oxidation.

Given these widespread uses of chromium complexes, it should come as no surprise when I tell you that under one-half of a per cent of chromium produced is chromium in its elemental form. So, to some extent, Vauquelin's prediction from two centuries ago about the limited usefulness of elemental chromium was spot on.

On the other hand, the first picture in my mind for chromium after gemstones, of course is when it is in its metallic form, such as for the mirrored corrosion and wear-resistant "chrome" surfaces of ball bearings and the shiny silvery trim on car parts.

So it's shiny and colourful as well as corrosion and wear resistant. I don't think I would say chromium had limited uses, would you? She has taught science courses at the high school, college, and graduate levels.

Facebook Facebook Twitter Twitter. Updated November 08, Featured Video. Cite this Article Format. Helmenstine, Anne Marie, Ph. Physical Properties of the Element Chromium. Copper Facts: Chemical and Physical Properties. Chemical Element Pictures - Photo Gallery. Vanadium Facts V or Atomic Number Get 10 Interesting Facts About Oxygen.

Your Privacy Rights. To change or withdraw your consent choices for ThoughtCo. At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. Chemical reactions in the charge separate the metal from the waste product slag and the purified metal collects in the crucible.

Usually the slag floats on top and the metal is poured from a spout in the bottom of the crucible. While in operation the blast furnaces are extremely hot. These high temperatures are necessary to facilitate the chemical reactions that separate metal from ore. But this heat could potentially enable the ore to react with materials in the walls of the blast furnace and the lining of the crucible, contaminating the metal being refined.

And if the walls expand under this heat, the structural integrity of the tower could be challenged. For these reasons, the walls must have an appropriate chemical composition. Standard building materials like concrete and cement cannot stand up to these conditions and clearly any steel used in the building must be shielded or it will melt like the metal inside the furnace.

For these reasons, refractories are indispensable to the steel-making process. Refractories, or refractory materials, have high melting points and are chemically stable. This makes them ideal for insulating blast furnaces that extract pig iron from iron ore and for lining the large crucibles that hold molten steel.

Chromite was initially used as a refractory in France along with magnesite and dolomite other refractory minerals. Up until the s, bricks of solid chromite cut straight from the mine were used without further refinement or processing. These are called dressed blocks of ore. As the steel industry grew in the US and England, manufacturers developed refractory bricks made of crushed chromite or magnesite. These were cheaper to manufacture than the dressed blocks because broken pieces of ore were as useful as the large solid blocks required for dressing.

The crushed ore was mixed with a resin and pressed into brick shapes. Alternatively, they were fired at low temperatures like clay. In the s refractories made from mixtures of chromite and magnesite in various percentages were produced for different applications. In , four million metric tons of chromite were mined worldwide. The US consumes around 90, tons a year. In , 11 percent of chromite was used in refractory materials, but in the proportion had dropped to 7 percent.

Because of technological advances, chromite is less important today as a refractory than it was at the beginning of the 20th century. However, it is still irreplaceable as the critical alloy in stainless steel. Even before the value of chromium in steel-making was widely appreciated, the discovery of the ore in the United States made one family extremely wealthy and established the country as a leader in the chrome industry. With the advent of these chromium-based industries, chromium ore was in high demand.

As an amateur geologist, Isaac Tyson was one of few Americans who had studied chromite and knew its value and its commercial potential. In the summer of , he was standing in a Baltimore marketplace when he noticed a cart carrying barrels of apple cider. Heavy black stones were wedged between the barrels to keep them from rolling. Intrigued, Tyson quickly found that the stones originated from the Reed farm, 27 miles northeast of Baltimore in Harford County. Convinced that the Baltimore area held more ore, he searched in wider and wider circles.

His hunch was right; in he found ore on the Wood farm in Pennsylvania. Tyson turned the property into the Wood mine, which eventually yielded , tons of ore. Soon, Tyson owned mineral rights on all the ore-bearing sites in Pennsylvania, Virginia and Maryland. As the Siberian deposits waned, his company enjoyed a growing international monopoly in chromium ore.

However, when chromium was discovered in Turkey in , Tyson lost his monopoly. Like Kurtz in England, he turned to other products and began producing chromium chemicals for the textile industry.

In this way, he became a pioneer of the U. This process produces a great deal of dust and air-born chromium. Unfortunately, it was the workers in these industries that discovered first-hand the health risks associated with air-borne chromium dusts.

During the first half of the 20th century, dust levels in the air during ore processing were so high it was said that one could not see the opposite wall across the factory floor during peak production hours. Workers were breathing dusts containing a very high level of airborne chromium.

In the s, industrial hygienists in Germany began to notice that the incidence of respiratory cancers such as lung cancer was higher for workers in the chrome ore industry than for other similar occupations. In autopsies years later, the lungs of workers exposed to these dusts over a lifetime were shown to contain as much as 10 percent chromium by weight.

Cigarette smoking was uncommon in the general population between and and lung cancer was still relatively rare in middle-aged men. Physicians therefore noted the increased lung disease in these workers as being unusual.

Based on these observations, the Germans began a series of steps to reduce dust levels and personal exposure in the chromium industry, marking the beginnings of what are now modern industrial hygiene practices. The onset of World War II kept these observations from becoming widely disseminated or adopted by other countries, but after the war the rest of the western world began to investigate chromium-related illness and to initiate their own industrial hygiene programs.

These studies also suggested that certain forms of chromium dust, particularly compounds of intermediate solubility in water such as calcium chromate, were of greatest concern. The most water-soluble forms such as sodium or potassium chromate and the highly insoluble forms such as lead chromate were not closely associated with health effects. During this period there was a concerted effort to reduce worker exposure, by altering manufacturing processes, substituting forms of chromium, using personal protective clothing, and other measures.

Government agencies set acceptable levels for exposure, which were continually revised as new information was gained from additional studies. This led to greatly reduced dust levels and reduced worker exposure. Recent studies indicate that workers who began in these industries from the s on, after these practices were in place, have levels of respiratory cancer that are not significantly different from the general population. In the film Erin Brockovich , Universal Studios Pacific Gas and Electric is portrayed as a corporate giant that poisoned the water of the small town of Hinkley, California.

Modern petrochemical plants and refineries have large cooling towers that remove excess heat produced by generators, refrigerating units and other machines.

Over time, coolant fluids in the towers can accumulate corrosion or mineral deposits.