Rhodium nanoparticles entrapped in aluminum hydroxide matrix preparation

Application

At ordinary temperatures rhodium is stable in air. When heated above 600°C, it oxidizes to RH₂O3, forming a dark oxide coating on its surface. The gray crystalline sesquioxide has a corundom-like crystal structure. The sesquioxide, RH₂O3 , decomposes back to its elements when heated above 1,100°C. However, on further heating the metal starts to lose its weight similar to platinum, probably due to loss of its volatile oxide RhO2 dissolved in the metal. The molten metal readily absorbs gaseous oxygen.

The metal in powder form absorbs hydrogen when heated. When heated with carbon monoxide under pressure rhodium forms carbonyl, Rh4(CO)12. The metal combines with halogens at elevated temperatures. When heated with fluorine at 500 to 600°C, it forms a trifluoride, RhF3, a red rhombohedral crystalline powder insoluble in water, dilute acids, or alkalis. Also, a blue tetrafluoride, RhF4, is formed as a minor product. When heated with chlorine gas above 250°C, the brown-red trichloride, RhCl3, forms. It is hygroscopic, decomposing at 450°C.

Rhodium is attacked by fused caustic soda or caustic potash. Also, fused sodium or potassium cyanide and sodium bisulfate attack the metal.