Chromium
On the 26th of July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in the Ural Mountains. He named this find Siberian red lead. Scientists later identified it as crocoite with a chemical formula of PbCrO4. In 1794, Louis Nicolas Vauquelin received samples of that same crocoite ore. He produced chromium trioxide by mixing the ore with hydrochloric acid. By 1797, Vauquelin discovered he could isolate metallic chromium by heating the oxide in a charcoal oven. This achievement earned him credit for truly discovering the element. The name chromium comes from the Greek word chrōma meaning color. Many compounds of this metal display intense colors ranging from yellow to green to red.
Gaseous chromium has a ground-state electron configuration of [Ar] 3d5 4s1. It is the first element in the periodic table whose configuration violates the Aufbau principle. Chromium is the third hardest element after carbon and boron. Its Mohs hardness measures 8.5 on the standard scale. This allows it to scratch quartz but not corundum. The melting point reaches 1907 degrees Celsius or 3465 degrees Fahrenheit. That temperature is relatively low compared to most transition metals. Yet it holds the second highest melting point among all period 4 elements. Only vanadium exceeds it by three degrees Celsius. The boiling point sits at 2671 degrees Celsius or 4840 degrees Fahrenheit. This value ranks fourth lowest among period 4 transition metals. Chromium shows unique magnetic properties as well. It remains the only elemental solid that displays antiferromagnetic ordering at room temperature. Above 38 degrees Celsius its magnetic behavior shifts to paramagnetic ordering.
Approximately 28.8 million metric tons of marketable chromite ore were produced globally in 2013. About two-fifths of world production came from South Africa while Kazakhstan contributed one-third. India, Russia, and Turkey also served as substantial producers. Ferrochromium represents the leading end use for this raw material. Stainless steel then becomes the primary product derived from ferrochromium. For ferrochromium production, miners reduce chromite ore in large electric arc furnaces. They use either aluminum or silicon in an aluminothermic reaction. Pure chromium requires a different process involving roasting and leaching steps. The ore heats with calcium carbonate and sodium carbonate in air presence. Iron forms stable iron oxide while chromium oxidizes to hexavalent form. Sulfuric acid converts the resulting chromate into dichromate. Carbon reduces the dichromate to chromium oxide followed by aluminum reduction. This final step yields pure metallic chromium metal.
High-speed tool steels contain between three and five percent chromium. Stainless steel forms when chromium enters molten iron at concentrations above eleven percent. Nickel-based alloys gain strength through discrete carbide particles at grain boundaries. Inconel 718 contains eighteen point six percent chromium. These nickel superalloys serve jet engines and gas turbines due to high-temperature properties. ASTM B163 relies on chromium for condenser tubes. Castings containing chromium remain standard for elevated temperature applications. AISI type 332 resists carburization and oxidation. During World War II U.S. road engineers avoided chromium in yellow paint. Officials feared it might become critical during emergencies. The United States considered chromium essential for the German war industry. They made diplomatic efforts to keep it out of Nazi hands. Chrome plating deposits a layer below one micrometer thickness for decorative surfaces. Thicker layers provide wear resistance for industrial parts. Both methods use acidic chromate or dichromate solutions.
The plus three and plus six states occur most commonly within chromium compounds. Charges of plus two appear frequently while plus four and plus five exist rarely. Chromium hexafluoride remains unknown as of 2020 despite several erroneous claims. Sodium chromate produces an equilibrium between yellow chromate and orange dichromate ions. Adding acid shifts this balance visibly from yellow to orange. Chromic acid serves as a powerful oxidizing agent for cleaning glassware. Potassium dichromate dissolves at 50 grams per liter compared to 200 grams for sodium dichromate. Dichromate cleaning solutions have phased out due to high toxicity concerns. Modern alternatives are highly effective yet free of chromium entirely. Chromium(IV) oxide functions as a magnetic compound superior to gamma iron oxide. It manufactures magnetic tape used in audio cassettes. Zinc chromate acts as an anticorrosive agent for aluminum in aerospace applications. Chrome alum serves as a mordant fixing dyes into fabric during tanning processes.
In 1950s experiments scientists controlled rat diets to test glucose metabolism. Rats on chromium-deficient diets could not respond effectively to increased blood sugar levels. A chromium-rich Brewer's yeast enabled them to metabolize glucose properly. The European Food Safety Authority concluded research did not justify recognizing dietary chromium as essential. Australia, New Zealand, India, and Japan consider it essential while the United States disagrees. The U.S. National Academy of Medicine set Adequate Intake estimates rather than strict requirements. Women ages fourteen through fifty need twenty-five micrograms daily according to these guidelines. Men require thirty-five micrograms per day from age fourteen to fifty. Hexavalent chromium remains highly toxic and mutagenic to living organisms. Ingestion links directly to stomach tumors and allergic contact dermatitis. Workers exposed to strong chromate solutions develop chrome ulcers on their skin. Acute oral toxicity ranges between one point five and three point three milligrams per kilogram. Hemolysis and liver failure result after reaching the bloodstream. Chromium compounds found in soil and groundwater often require environmental cleanup at industrial sites.
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Common questions
Who discovered chromium and when was it first identified?
Johann Gottlob Lehmann found the mineral in 1761 while Louis Nicolas Vauquelin officially discovered metallic chromium by 1797. Vauquelin produced chromium trioxide from crocoite ore samples received in 1794 before isolating the metal through heating.
What is the chemical formula for crocoite and how does chromium relate to its name?
Crocoite has a chemical formula of PbCrO4 and derives its name from the Greek word chrōma meaning color. The element chromium takes its name because many compounds display intense colors ranging from yellow to green to red.
Which countries produce the most marketable chromite ore globally as of 2013?
South Africa provided about two-fifths of global production while Kazakhstan contributed one-third in 2013. India, Russia, and Turkey also served as substantial producers alongside these leading nations.
How much chromium is required daily for women and men according to U.S. guidelines?
Women ages fourteen through fifty need twenty-five micrograms daily according to U.S. National Academy of Medicine estimates. Men require thirty-five micrograms per day from age fourteen to fifty under the same Adequate Intake guidelines.
Why was chromium considered essential during World War II by United States officials?
U.S. road engineers avoided chromium in yellow paint because officials feared it might become critical during emergencies. They made diplomatic efforts to keep chromium out of Nazi hands since they considered it essential for the German war industry.