Americium(III) hydroxide


Americium hydroxide is a radioactive inorganic compound with the chemical formula Am3. 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.

Properties

Americium hydroxide is a pink solid which is sparingly soluble in water. Due to self-irradiation the crystal structure of 241Am3 decomposes within 4–6 months, while for curium hydroxide 244Cm3 the same process takes less than a day.

Synthesis

Americium metal can be converted to Am3 in a four step process. As described by the Oak Ridge National Laboratory, americium is added to hydrochloric acid, then neutralized using ammonium hydroxide. 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 + 2 → Am2
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.
Am2 → AmO2
The americium dioxide is heated once more, to about 600 °C, in the presence of hydrogen, to produce americium oxide.
2AmO2 + H2O → Am2O3 + O2 + H2
The final step involves the hydrolysis of the americium oxide, to produce the final product, americium hydroxide.
Am2O3 + 3H2O → 2Am3

Reactions

When ozone is bubbled through a slurry of americium hydroxide in 0.03 M potassium bicarbonate at 92 °C, hexagonal KAmO2CO3 can be obtained. Potassium carbonate can also be used. The resulting KAmO2CO3 reacts with dilute acids to produce americium dioxide.
O3 + Am3 + KHCO3 + H2O → KAmO2CO3 + 3H2O + O2
In a dilute base such as sodium hypochlorite, Am3 gets oxidised to Am4, which is black in solution. Further oxidation using ozone and sodium hydroxide can produce yellow Am6.