Americium(III) hydroxide

Americium(III) hydroxide is a radioactive inorganic compound with the chemical formula Am(OH)3. It consists of one americium atom and three hydroxide groups. It was first discovered in 1944, closely related to the Manhattan Project. However, these results were confidential and were only released to the public in 1945. It was the first isolated sample of americium, and the first americium compound discovered.

Americium(III) hydroxide
Names
IUPAC name
Americium(III) hydroxide
Systematic IUPAC name
Americium(3+) trihydroxide
Other names
Americium hydroxide
Americium trihydroxide
Identifiers
3D model (JSmol)
ChemSpider
Properties
Am(OH)3
Molar mass 294.084 g/mol
Hazards
Main hazards Radiation
NFPA 704 (fire diamond)
Flammability (red): no hazard codeHealth (blue): no hazard codeReactivity (yellow): no hazard codeSpecial hazard RA: Radioactive. E.g. plutonium
Related compounds
Other anions
 Americium(III) oxide
Americium(III) chloride
Americium(III) bromide
Other cations
 Curium(III) hydroxide
Europium(III) hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Properties

Americium hydroxide is a pink solid[1] which is sparingly soluble in water.[2] Due to self-irradiation the crystal structure of 241Am(OH)3 decomposes within 4–6 months, while for curium(III) hydroxide 244Cm(OH)3 the same process takes less than a day.

Synthesis

Americium metal can be converted to Am(OH)3 in a four step process. As described by the Oak Ridge National Laboratory, americium is added to hydrochloric acid, then neutralized using ammonium hydroxide (NH4OH). A saturated oxalic acid solution is added to the now neutralized solution. This causes large americium oxalate crystals to begin to grow. Once complete precipitation is achieved, oxalic acid is once again added, to attain a slurry of americium oxalate and oxalic acid. The americium oxalate is then filtered out, washed with water, and is partially dried by allowing exposure to air.

Am + (COOH)2 → Am(COO)2

The americium oxalate is then added to a platinum combustion boat to undergo calcination. The americium oxalate is dried in a furnace and will begin to decompose at 350 °C. When decomposition begins to occur, the oxalate will turn into the desired black americium dioxide. To ensure no oxalate remains in the americium dioxide, the oven temperature is increased to and held at 800 °C then slowly allowed to cool to room temperature.

Am(COO)2 → AmO2

The americium dioxide is heated once more, to about 600 °C, in the presence of hydrogen, to produce americium(III) oxide.

2AmO2 + H2O → Am2O3 + O2 + H2

The final step involves the hydrolysis of the americium(III) oxide, to produce the final product, americium(III) hydroxide.[3]

Am2O3 + 3H2O → 2Am(OH)3

Reactions

When ozone is bubbled through a slurry of americium(III) hydroxide in 0.03 M potassium bicarbonate at 92 °C, hexagonal KAmO2CO3 (potassium dioxoamericium(V) carbonate) can be obtained. Potassium carbonate can also be used. The resulting KAmO2CO3 reacts with dilute acids to produce americium dioxide.[4]

O3 + Am(OH)3 + KHCO3 + H2O → KAmO2CO3 + 3H2O + O2

In a dilute base such as sodium hypochlorite, Am(OH)3 gets oxidised to Am(OH)4, which is black in solution. Further oxidation using ozone and sodium hydroxide can produce yellow Am(OH)6.

See also

References
  1. Krivovichev, Sergey; Burns, Peter; Tananaev, Ivan (2006-12-08). Structural Chemistry of Inorganic Actinide Compounds. Elsevier. ISBN 978-0-08-046791-7.
  2. Runde, Wolfgang (2011), "Americium and Curium: Radionuclides", Encyclopedia of Inorganic and Bioinorganic Chemistry, American Cancer Society, doi:10.1002/9781119951438.eibc0438, ISBN 978-1-119-95143-8, retrieved 2020-03-21
  3. Morss, L. R.; Williams, C. W. (1993-12-31). "Synthesis of crystalline americium hydroxide, Am(OH){sub 3}, and determination of its enthalpy of formation; estimation of the solubility-product constants of actinide(III) hydroxides". 4. international conference on chemistry and migration behavior of actinides and fission products in the geosphere,Charleston, SC (United States),12-17 Dec 1993. Retrieved 2020-03-21.
  4. Penneman, R. A.; Keenan, T. K. (1960-01-01). "THE RADIOCHEMISTRY OF AMERICIUM AND CURIUM". OSTI 4187189. Cite journal requires |journal= (help)
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