Catalog Number
ACMA00003165
Product Name
Rhodium on alumina
Category
Fuel Cell Catalysts
Description
Rhodium metal fume is a reddish-gray to black dust-like powder. mp: 1966° C, bp: 3727°C. Insoluble in water. Bulk rhodium is a white or blueish-white, hard, ductile, malleable metal. The appearance and other properties of insoluble Rh compounds varies depending upon the specific compound.;DryPowder, OtherSolid;GREY-TO-BLACK POWDER.;Appearance and odor vary depending upon the specific soluble rhodium compound.;Metal: White, hard, ductile, malleable solid with a bluish-gray luster.
Molecular Weight
102.9055g/mol
InChI Key
MHOVAHRLVXNVSD-UHFFFAOYSA-N
Boiling Point
6741 °F at 760 mm Hg (NIOSH, 2016);3695 °C;3695 °C;6741°F
Melting Point
3571 °F (NIOSH, 2016);1964 °C;1965 °C;3571°F
Density
12.41 (metal) (NIOSH, 2016);12.41 g/cu cm @ 20 °C;12.4 g/cm³;12.41 (metal)
Solubility
Insoluble (NIOSH, 2016);Insoluble in acids and aqua regia; soluble in fused potassium bisulfate.;Insoluble in hot or cold water; soluble in concentrations of sulfuric acid and in sulfuric acid + hydrochloric acid.;Solubility in water: none;Insoluble
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.
Color/Form
Silvery-white, soft, ductile, malleable metal; face-centered cubic structure;...In air, it occurs in the form of gray fume or dust.
Covalently-Bonded Unit Count
1
MeSH Entry Terms
Rhodium;Rhodium 103;Rhodium-103
Monoisotopic Mass
102.90549g/mol
Other Experimental
Atomic number 45; valences 1-6; most common states 1, 3; One naturally occurring isotope:103; artificial radioactive isotopes: 97-102; 104-110;Electrical resistivity 4.51 microohm-cm @ 0 °C; Brinell hardness: 100; Not attacked by acids even aqua regia when in compact form; the finely divided metal reacts with aqua regia; Absorbs oxygen when melted; at a read heat is slowly oxidized to the sesquioxide; Converted to the trihalide by chlorine or bromine at a red heat; not attacked by fluorine.;Enthalpy of formation: 556.9 kJ/mol (gas); Heat capacity: 25.0 J/mol K (crystal); 21.0 J/mol K (gas);Enthalpy of fusion: 26.59 kJ/mol;Magnetic susceptibility: 9.9X10-7 cu cm/g; Vickers' hardness: 100-120;High surface reflectivity;Solid phase-temperature of transition (deg K): 2240; liquid phase-temperature of transition (deg K) 4150; heat of transition (Kcal/g mole): solid phase 5.2; liquid phase 127; entropy of transition (EU): solid phase 2.3; liquid phase 30.7; entropy at 298 deg K (EU): solid phase 7.6.;Magnetic susceptibility (Temp K= 298 deg) 111.0X10-6 CGS; (Temp K= 723 deg) 123.0X10-6 CGS;Oxidizes slowly at 6 °C
Stability
Absorbs oxygen when melted; at a red heat is slowly oxidized to the sesquioxide.;Converted to trihalide by chlorine or bromine at a red heat; not attacked by fluorine.
Vapor Pressure
0 mm Hg (approx) (NIOSH, 2016);1 Pa @ 2015 °C; 10 Pa @ 2223 °C; 100 Pa @ 2476 °C; 1 kPa @ 2790 °C; 10 kPa @ 3132 °C; 100 kPa @ 3724 °C;0 mmHg (approx)