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 to 6 months (241Am has a half-life of 432.2 years); for 244Cm(OH)3 the same process takes one day (244Cm has a half-life of 18.11 years).[1]
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 and then slowly allowed to cool to room temperature.
Am(COO)2 → AmO2
The americium dioxide is heated again, 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]
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 hydroxy species of Am(VI).
