The Use of the f-block Metals in Industry – Cerium
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erium is one the element in the f-block of the periodic table. The symbol for cerium is Ce and their atomic number is 58. Cerium is an iron-grey lustrous metal, and is malleable and oxidises very readily at room temperature, especially in moist air. Cerium was named after the dwarf planet Ceres. Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is very reactive and it oxidizes slowly in cold water and rapidly in hot water. It also dissolves in acids. It can burn when heated or scratched with a knife.
History
Cerium was discovered by Jöns Jacob Berzelius and Wilhelm von Hisinger, Swedish chemists, and independently by Martin Heinrich Klaproth, a German chemist, in 1803. Cerium was named by Berzelius after the dwarf planet Ceres which is discovered in 1801.
Source
Cerium is found in a number of minerals including allanite (also known as orthite), monazite, bastnasite, cerite, and samarskite. Monazite and bastnasite are presently the more important sources of cerium.
Large deposits of monazite (found on the beaches of Travancore, India and in river sands in Brazil), allanite (in the western United States), and bastnasite (in Southern California) will supply cerium for many years to come.
Metallic cerium is prepared by metallothermic reduction techniques, such as reducing cerous fluoride with calcium, or using electrolysis of molten cerous chloride. The metallothermic technique produces high-purity cerium.
Physical properties
Cerium has the longest liquid range of any non-radioactive element which is from 795°C to 3443°C. It has variable electronic structure. The energy of the inner 4f level is nearly the same as that of the valence electrons and only small energy is required to change the relative occupancy of these electronic levels. This gives rise to dual valence states. Density at room temperature is 6.770 gcm-3 and at melting point (795oC) is 6.55 gcm-3. It relative atomic weight is 140.1 gmol-1.
Chemical Properties
Cerium metal tarnishes slowly in air and burns readily at 150 °C to form cerium(IV) oxide.C
Ce(s) + O2(g) ---> CeO2(s)
Cerium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form cerium hydroxide.
Ce(s) + 6H2O(l) ---> 2Ce(OH)3(aq) + 3H2(g)
Cerium metal reacts with all the halogens to form cerium halide.
Ce(s) + 3F2(g) ---> 2CeF3(s)
Ce(s) + 3Cl2(g) ---> 2CeCl3(s)
Cerium dissolves readily in dilute sulfuric acid to form solutions containing the colorless Ce(III) ions, which exist as a [Ce(OH2)9]3+ complexes.
Ce(s) + 3H2SO4(aq) ---> 3+(aq) + 3SO2−4(aq) + 3H2(g)
Applications
Cerium has many uses in the industry nowadays. A major technological application for cerium(IV) oxide is as catalytic converter for the reduction of carbon monoxide,CO emission in the exhaust gases from motor vehicles and form carbon dioxide,CO2 which is less harmful. In this case, cerium oxide is added into diesel fuels.
CeO2 + CO ---> Ce2O3 + CO2
The process is reversed and cerium(III) oxide is oxidized to cerium(IV) oxide with the existence of oxygen gas.
2Ce2O3 + O2 ---> 4CeO2
Another important use of the cerium oxide is a hydrocarbon catalyst in self cleaning ovens. The walls of self-cleaning ovens are coated with cerium (IV) oxide and acting as oxidation catalyst. It help to burn off cooking residue in the oven without using any chemical agents.
Cerium(IV) oxide is considered one of the most efficient agents for polishing of optical components. Cerium compounds are also used in the manufacture of glass, both as a component and as a decolourizer. For example, cerium(IV) oxide in combination with titanium(IV) oxide gives a golden yellow color to glass.
Cerium(IV) oxide is used in gas mantles, such as the gas mantle, where it was combined with thorium, lanthanum, magnesium or yttrium oxides. The fabric of the mantles is saturated with thorium oxide and cerium oxide. The burning of the mantles leaves a residue of thorium and cerium dioxides. This residue glows with a brilliant white luminescence when heated to a high temperature by the gas flame. The presence of the thorium makes these mantles slightly radioactive, so recent mantles have replaced these oxides with other illuminants.
The cerium(IV) oxide-cerium(III) oxide cycle use in hydrogen production. Advantage of the cerium based cycle is the separation of hydrogen gas,H2 and oxygen gas,O2 in two steps which makes high temperature gas separation redundant.
s2CeO2 ---> Ce2O3 + 0.5O2 (dissociation)
e2O3 + H2O ---> 2CeO2 + H2 (hydrolysis)
Cerium alloy are used in permanent magnet and in tungsten electrodes for gas tungsten arc welding to improves arc stability and ease of starting. It also use in carbon-arc lighting, especially in the film industry. Cerium oxalate is an anti-emetic drug that is effective against vomiting and nausea .
Cerium(IV) sulfate, also known as ceric sulfate is used extensively as a volumetric oxidizing agent in quantitative analysis. The ceric ion is a strong oxidizer, especially under acidic conditions. If ceric sulfate is added to dilute hydrochloric acid, then elemental chlorine is formed, albeit slowly. With stronger reducing agents it reacts much faster. When ceric compounds are reduced, so-called cerous compounds are formed. The cerous ion is colorless.
Ce4+ + e− -----> Ce3+.
Ceric sulfate is used in analytical chemistry for redox titration, often together with a redox indicator.
Health effects of cerium
Cerium is one of the rare chemicals, that can be found in houses in equipment such as colour televisions, fluorescent lamps, energy-saving lamps and glasses. All rare chemicals have comparable properties.
Cerium is mostly dangerous in the working environment, due to the fact that damps and gasses can be inhaled with air. This can cause lung embolisms, especially during long-term exposure. Cerium can be a threat to the liver when it accumulates in the human body.
Cerium has no known biological role, but it has been noted that cerium salts stimulate metabolism.
Environmental effects of cerium
Cerium is dumped in the environment in many different places, mainly by petrol-producing industries. It can also enter the environment when household equipment is thrown away without a systematic procedure. Cerium will gradually accumulate in soils and water soils and this will eventually lead to increasing concentrations in humans, animals and soil particles.
With water animals cerium causes damage to cell membranes, which has several negative influences on reproduction and on the functions of the nervous system.
REFERENCES
1. C. Hampel,Glass Industry, (USA), No. 2, 1960, pp 82-86, 109-113
Translated from Steklo i Keramika, Vol. 18, No. 4, pp. 48, April, 1961
2. Lauri Niinistö, "Swedish Contributions to the Discovery of Elements: Part 2: The Work of Berzelius." ERES Newsletter, vol. 10, no. 1 (31 August 1999).
3. http://en.wikipedia.org/wiki/Cerium
4. http://en.wikipedia.org/wiki/Cerium%28IV%29_oxide
5. http://en.wikipedia.org/wiki/Cerium%28III%29_oxide
6. http://elements.vanderkrogt.net/element.php?sym=Ce
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