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Cerium Oxide

Cerium OXide Metallurgical Grade

Applications

Steel:

When cerium is added to the melt steel, it will combine with oxygen and sulfur, even reducing other oxides and sulfides present, to form high-melting, hard, Ln oxysulphides and oxides. It will not deform during rolling of the steel and will not create planes of weakness.

Cast Iron:

The lanthanides, and in particular cerium, are used to provide graphite morphology control.

The function of cerium (and all the lanthanides) is:

a) To remove free oxygen and sulfur from the melt through formation of stable lanthanide oxysulfides, key role in steel technology

b) To initiate the special carbon crystal growth by nucleation on those oxysulfide compounds

c) To fix up undesirable trace elements such as Pb and Sb perhaps through intermetallics

Lighter Flints and Getters:

Most widely associated with cerium has probably been the pyrophoric iron-mischmetal(≈60%) alloy for lighter flints.

Similar low-vapor-pressure reactive alloys based on cerium can also be the basis of getters, for electronic equipment and vacuum tubes.

Welding Electrodes:

The electrodes used in inert-gas tungsten-arc welding and plasma cutting can contain a finely dispersed oxide distributed throughout the tungsten matrix. Cerium oxide provides an alternative to thorium oxide, a common additive that is now being phased out because of environmental reasons. These oxide particles give electrodes arc-strike reliability at lower voltages than would pure tungsten.

Several commercial alloys use pure cerium to significantly improve oxidation resistance, provide creep resistance and confer a longer operating life. It removes traces of unwanted sulfur impurities from the metal crystallite boundaries plus a modification to the diffusion mechanism for oxide skin growth. If cerium is present in the alloy, it can spall of the oxide skin formed at high temperatures shows less tendency.

Aluminium Alloys:

New light weight alloys, Al-8.31Fe-4.0Ce (wt %) is the most promising material, with excellent properties in the range 230 °C to 340 °C. This alloy shows an attractive combination of creep resistance, elevated-temperature tensile-strength and corrosion resistance.

Electrowinning of Aluminium:

Currently, the production of aluminum requires carbon anodes that are consumed during the electrolysis of the cryolite. A new approach relies on a self-forming anode technology whereby cerium oxide coatings are deposited, from the molten electrolyte, onto conducting ceramic substrates.

Addition of cerium allows the formation of a protective and electrocatalytically active coating of CeO2 on to the conducting anode. If a steady concentration of the appropriate additive is maintained in the electrolyte then the equilibrium between dissolved and deposited material ensures a stable coating layer. If the cerium is added as Ce(IV)O2, the dissolved Ce species will be Ce(III) :

CeO2 + AlF3 => CeF3 + ½A12O3 + ¼O2

The deposition of the oxide at the anode:

6CeF3 + 4Al2O3 => 6CeO2 + 6AlF3 + 2Al 3+ + 6e¯

The self-forming coating, cerium oxide or more probably a cerium oxyfluoride cerium oxide solid solution, will reduce significantly the rate of wear of the anode, a doped SnO2 or ferrite, and improve the purity of the Al metal recovered.