| Identification | More | [Name]
Rhodium | [CAS]
7440-16-6 | [Synonyms]
Rh
rh-945
Rhodiu
RHODIUM
RH000270
RH000225
RH000170
RH000212
RH000180
RH000220
RH004600
RH005120
RH005130
RH004500
RH000205
RH000301
RH005110
RH005105
RH000201
RH000210
RH000203
RH000235
RH000190
RH000160
RH000230
RH004700
ESCAT 3401
Rhodium, 5%
Rhodium Foil
RhodiuM Rh/C
RhodiuM
rhodium atom
Rhodium(10%)
RHODIUM METAL
RHODIUM BLACK
ESCAT(TM) 3401
RHODIUM SPONGE
RhodiumpowderN
Rhodium (0.5%)
Rhodium powder
RHODIUM-SCHWARZ
RHODIUM, 99.99%
RHODIUM-ALUMINA
RHODIUM CATALYST
RHODIUM STANDARD
Rhodium black 3N
Rh5%Rhodium atom
METALLIC RHODIUM
Rhodium solution
CUPRIC CITRATE TS
RHODIUM ON SRTIO3
RHODIUM ON CARBON
Rh/Rhodium/Carbon
RHODIUM ON ALUMINA
RHODIUMBLACK,POWDER
Rhodium 5% on Al2O3
Rhodium foil25x25mm
Rhodium foil50x50mm
Rhodiumpowder(99.8%)
rhodium(metalfumeand
RHODIUM ICP STANDARD
Rhodium,99.9%,powder
Rhodiumpowder(99.95%)
Rhodium, 5% on carbon
Rhodium,0.5%onalumina
Rhodiumoncarbonpowder
Rhodium black (99.9%)
Rhodium, Rh 1000μg/mL
Rhodium Powder, Sponge
Rhodium, Powder, 99.9%
Rhodiumonaluminapowder
RHODIUM, SPONGE, 99.9%
RhodiuM/AluMinuM oxide
RHODIUM, 99.90%, POWDER
Rhodium, powder, 99.90%
Rhodium, 5 % on alumina
Rhodium, on carbon, dry
Rhodium, Powder 22 Mesh
Rhodium, Sponge 20 Mesh
RHODIUM ICP/DCP STANDARD
RHODIUM BLACK: 99.9%, 3N
Rhodiumonaluminaxpellets
RhodiumblackNblackpowder
RhodiuM on carbon(5wt.%)
RhodiuM, 60 Mesh, Powder
Rhodium Powder, -100 Mesh
Rhodium Powder, -200 Mesh
Rhodium Powder, -325 Mesh
ROYER(R) RHODIUM CATALYST
RHODIUM/ACTIVATED CHARCOAL
RHODIUM, 5% ON CARBON, DRY
Rhodium Powder < 60 micron
RHODIUM POWDER: 99.8%, 2N8
RHODIUM(METALFUMEANDDUSTS)
RHODIUM POWDER: 99.95%, 3N5
Rhodium ISO 9001：2015 REACH
Rhodium Wire/Φ0.25mm/99.95%
Rhodium Wire/Φ0.50mm/99.95%
Rhodium Wire/Φ1.00mm/99.95%
Rhodium Wire 0.5 mm diameter
Rhodium Wire 1.0 mm diameter
Rhodium Wire 0.25 mm diameter
Rhodium soluble salts (as Rh)
Rhodium on carbon (55% water)
RHODIUM, AAS STANDARD SOLUTION
Rhodium Wire 0.125 mm diameter
Rhodium, Sponge 20 Mesh 99.95%
Rhodium, Powder 22 Mesh 99.99%
Rhodium,0.5%on3mmaluminapellets
RHODIUM SINGLE ELEMENT STANDARD
Rhodium Black, S.A. 15 m2/g min
Rhodium on activated wood carbon
Rhodium Foil/0.10x50x50mm/99.95%
Rhodium Foil/0.10x25x25mm/99.95%
RHODIUM INTERNAL ICP-MS STANDARD
RHODIUM PLASMA EMISSION STANDARD
RHODIUM, PLASMA STANDARD SOLUTION
RHODIUM, FOIL, 0.1MM THICK, 99.9%
RHODIUM, WIRE, 1.0MM DIAM., 99.9%
RHODIUM WIRE 0.5MM DIAM. 99.9%
RHODIUM FOIL 0.25MM THICK 99.9%
Rhodium,1%onPolyethyleneimine/SiO2
RHODIUM ATOMIC ABSORPTION STANDARD
Rhodium on activated carbon, 5% Rh
Rhodium wire, 0.5mm (0.02 in.) dia.
Rhodium AA Standard,1000 ppm in HCl
Rhodium 5% on Carbon, 50%-70% Water
Rhodium wire, 1.0mm (0.04 in.) dia.
rhodium(metalfumeandinsolublecompou
RHODIUM, FOIL, 0.025MM THICK, 99.9%
RHODIUM ATOMIC SPECTROSCOPY STANDARD
Rhodium, insoluble compounds (as Rh)
Rhodium wire, 0.25mm (0.01 in.) dia.
RhodiuM, 1% on 2.5MM aluMina spheres
Rhodium, 5% on carbon paste, Type 594
RhodiuM on aluMina, 5% Rh, powder 5GR
RhodiuM on aluMina, 5% Rh, powder 25GR
Rhodium wire, 0.127mm (0.005 in.) dia.
Rhodium, 5% on alumina powder, Type 526
Rhodium Carbon/ Rhodium on Carbon/ Rh/C
KIT OXYGEN MAINT BOD/DO PROBES SYMPHONY
5% on Carbon (wetted with ca. 55% Water)
RHODIUM ICP STANDARD TRACEABLE TO SRM FR
RHODIUM 5 WT. % (DRY) ON CARBON WET DE&
Rhodium, 5% on alumina powder, C301099-5
RHODIUM ON ACTIVATED WOOD CARBON, REDUCED
RHODIUM ATOMIC ABSORPTION STANDARD SOLUTION
Rhodium, 1% on Polyethyleneimine/SiO2 powder
RhodiuM on carbon(wetted with ca. 55% water)
Rhodium metal fume and dust (also see metal)
Rhodium, AAS standard solution, Rh 1000μg/mL
Rhodium, plasma standard solution, Rh 10μg/mL
RhodiuM, 0.5% on 3MM (0.12in) aluMina pellets
Rhodium, 0.5% on 1mm(.040in) alumina spheres
RHODIUM PLASMA EMISSION SPECTROSCOPY STANDARD
RhodiuM, 0.5% on 1MM (0.040in) aluMina spheres
Rhodiumwire,0.5mm(0.02in)dia,99.8%(metalsbasis)
Rhodium plasma standard solution, Rh 10000μg/mL
Rhodium standard solution, 1 mg/ml Rh in 10% HCl
RHODIUM ON ACTIVATED CARBON, 5% RH, REDUCED, DRY
Rhodium 5% on Carbon (wetted with ca. 65% Water)
Rhodium 5% on Carbon (wetted with ca. 55% Water)
Rhodium, 1% on Polyethyleneimine/SiO2
Rhodium on activated carbon, 5% Rh, unreduced, dry
Rhodium sponge, -20 mesh, 99.9% trace metals basis
Rhodium wire, 1.0mm dia., 99.5% trace metals basis
Rhodium wire, 0.25mm dia., 99.5% trace metals basis
Rhodium powder, -325 mesh, 99.95% trace metals basis
Rhodium,5%onactivatedcarbon(50%wettedpowder)EvonikG1
Rhodium powder, Precious metals typically <20ppm each
Rhodium, 1% on Polyethyleneimine/SiO2 powder
Rhodium, plasma standard solution, Specpure, Rh 10g/ml
Rhodium foil, 0.25mm (0.01in) thick, 99.8% (metals basis)
Rhodium, AAS standard solution, Specpure(R), Rh 1000μg/ml
ROYERRHODIUM CATALYST BEADS 1% Rh on Polyethylenimine/SiO2
Rhodium foil, thickness 0.025 mm, 99.9% trace metals basis
ROYERRHODIUM CATALYST POWDER 1% Rh on Polyethylenimine/SiO2
Rhodium, plasma standard solution, Specpure(R), Rh 1000μg/ml
Rhodium, plasma standard solution, Specpure(R), Rh 10,000μg/ml
RHODIUM, 5% ON ACTIVATED CARBON (50% WETTED POWDER) DEGUSSA G1
Rhodium foil, 0.025mm (0.001 in.) thick, certified pinhole free
Rhodium, 0.5% on alumina spheres, 1mm (0.040 in.) alumina spheres
Rhodium,5%onactivatedwoodcarbon,reduced,50%waterwetpaste(Escat3401)
Rhodium, 5 wt. % (dry) on carbon, wet, Degussa type G106B/W, reduced
RhodiuM, 5% on activated carbon (50-70% wetted powder) Evonik Noblyst P3053
Rhodium, 5% on activated carbon (50-70% wetted powder) Evonik G 106 N/W 5% Rh
Rhodium, 5% on activated carbon (50-70% wetted powder) Evonik Noblyst(R) P3053
Rhodium nanoparticles entrapped in aluminum hydroxide matrix preparation
Rhodium, 5% on activated carbon powder, standard, reduced, nominally 50% water wet
Rhodium, 5% on activated wood carbon, reduced, 50% water wet paste (Escat(TM) 3401)
RhodiuM, 5% on activated carbon powder, Type C101038-5, reduced, noMinally 50% water wet
RhodiuM nanoparticles, pure, (<20nM) in acetone at 100Mg/L (surfactant and reactant-free)
RhodiuM, 5% on activated carbon powder, Type 23, standard, reduced, noMinally 50% water wet
RhodiuM nanoparticles, pure, (<20nM) in isopropanol at 100Mg/L (surfactant and reactant-free)
Rhodium powder, -22 mesh, Premion, 99.97% (metals basis), precious metals typically <20ppm each
Rhodium powder, -22 mesh, Premion(R), 99.97% (metals basis), precious metals typically <20ppm each
RhodiuM nanoparticles, pure, (<20nM) in water at 100Mg/L (surfactant and reactant-free, stabilized with < 0.01 MMol/l of citrate)
RhodiuM nanoparticles, pure, (<20nM) in water at 500Mg/L (surfactant and reactant-free, stabilized with < 0.01 MMol/l of citrate)
ROYER RHODIUM CATALYST BEADS, 1% Rh on Polyethylenimine/SiO2ROYER RHODIUM CATALYST BEADS, 1% Rh on Polyethylenimine/SiO2ROYER RHODIUM CATALYST BEADS, 1% Rh on Polyethylenimine/SiO2 | [EINECS(EC#)]
233-397-6 | [Molecular Formula]
Rh | [MDL Number]
MFCD00011201 | [Molecular Weight]
102.91 | [MOL File]
7440-16-6.mol |
| Chemical Properties | Back Directory | [Definition]
Metallic element having
atomic number 45, group VIII of the periodic table,
aw 102.9055, no isotopes, valence = 3.
| [Appearance]
Rhodium, together with platinum, palladium,
iridium, ruthenium, and osmium, is one of the platinum-
group metals in Group VIII of the Periodic Table. Rhodium
metal is a white, hard, ductile, malleable solid with a
bluish-gray luster. | [Melting point ]
1966 °C (lit.) | [Boiling point ]
3727 °C (lit.) | [density ]
1.41 g/mL at 25 °C
| [storage temp. ]
Flammables area | [solubility ]
insoluble in acid solutions, slightly soluble in aqua regia | [form ]
wire
| [color ]
Red | [Specific Gravity]
12.41 | [Resistivity]
4.33 μΩ-cm, 20°C | [Water Solubility ]
Insoluble | [Merck ]
14,8186 | [Exposure limits]
ACGIH: Ceiling 2 ppm
OSHA: Ceiling 5 ppm(7 mg/m3)
NIOSH: IDLH 50 ppm; Ceiling 5 ppm(7 mg/m3) | [History]
Wollaston discovered rhodium in 1803-4 in crude
platinum ore he presumably obtained from South America.
Rhodium occurs native with other platinum metals in river
sands of the Urals and in North and South America. It is also
found with other platinum metals in the copper-nickel sulfide
ores of the Sudbury, Ontario region. Although the quantity
occurring here is very small, the large tonnages of nickel processed
make the recovery commercially feasible. The annual
world production of rhodium in 1999 was only about 9000
kg. The metal is silvery white and at red heat slowly changes
in air to the sesquioxide. At higher temperatures it converts
back to the element. Rhodium has a higher melting point
and lower density than platinum. Its major use is as an alloying
agent to harden platinum and palladium. Such alloys are
used for furnace windings, thermocouple elements, bushings
for glass fiber production, electrodes for aircraft spark plugs,
and laboratory crucibles. It is useful as an electrical contact
material as it has a low electrical resistance, a low and stable
contact resistance, and is highly resistant to corrosion. Plated
rhodium, produced by electroplating or evaporation, is exceptionally
hard and is used for optical instruments. It has a high
reflectance and is hard and durable. Rhodium is also used for
jewelry, for decoration, and as a catalyst. Fifty-two and isomers are now known. Rhodium metal (powder) costs
about $180/g (99.9%).isotopes | [CAS DataBase Reference]
7440-16-6(CAS DataBase Reference) | [NIST Chemistry Reference]
Rhodium(7440-16-6) | [EPA Substance Registry System]
7440-16-6(EPA Substance) |
| Safety Data | Back Directory | [Hazard Codes ]
C,Xi,F | [Risk Statements ]
R36/38:Irritating to eyes and skin .
R11:Highly Flammable.
R36/37/38:Irritating to eyes, respiratory system and skin .
R36:Irritating to the eyes.
R34:Causes burns.
R23:Toxic by inhalation. | [Safety Statements ]
S26:In case of contact with eyes, rinse immediately with plenty of water and seek medical advice .
S24/25:Avoid contact with skin and eyes .
S16:Keep away from sources of ignition-No smoking .
S22:Do not breathe dust .
S36:Wear suitable protective clothing .
S17:Keep away from combustible material .
S45:In case of accident or if you feel unwell, seek medical advice immediately (show label where possible) .
S36/37/39:Wear suitable protective clothing, gloves and eye/face protection . | [RIDADR ]
UN 3089 4.1/PG 2
| [WGK Germany ]
3
| [RTECS ]
VI9069000
| [TSCA ]
Yes | [HazardClass ]
4.1 | [PackingGroup ]
III | [HS Code ]
7110390000 | [Safety Profile]
Handle carefully. It may be a sensitizer but not to the same extent as platinum. Most rholum compounds have only moderate toxicity by ingestion. Flammable when exposed to heat or flame. Violent reaction with chlorine, bromine pentafluoride, bromine trifluoride, and OF2. A catalytic metal | [Hazardous Substances Data]
7440-16-6(Hazardous Substances Data) | [IDLA]
100 mg Rh/m3 |
| Hazard Information | Back Directory | [Hazard]
Flammable in powder form. Upper respira-
tory tract irritant. Questionable carcinogen.
| [Potential Exposure]
Rhodium has few applications by
itself, as in rhodium plating of white gold jewelry or plat-
ing of electrical parts, such as commutator slip rings, but,
mainly, rhodium is used as a component of platinum alloys.
Rhodium-containing catalysts have been proposed for use
in automotive catalytic converters for exhaust gas cleanup. | [First aid]
If this chemical gets into the eyes, remove any
contact lenses at once and irrigate immediately for at least
15 minutes, occasionally lifting upper and lower lids. Seek
medical attention immediately. If this chemical contacts the
skin, remove contaminated clothing and wash immediately
with soap and water. Seek medical attention immediately.
If this chemical has been inhaled, remove from exposure,
begin rescue breathing (using universal precautions, includ-
ing resuscitation mask) if breathing has stopped and CPR if
heart action has stopped. Transfer promptly to a medical
facility. When this chemical has been swallowed, get medi-
cal attention. Give large quantities of water and induce
vomiting. Do not make an unconscious person vomit. If
metal fume fever develops, it may last less than 36 hours.
| [Shipping]
Flammable powder, Hazard Class: 4.1; Labels:
4.1-Flammable solid. | [Incompatibilities]
Flammable as a dust, fume, or powder
may form explosive mixture with air. Incompatible with
strong oxidizers (chlorates, nitrates, peroxides, permanga-
nates, perchlorates, chlorine, bromine, fluorine, etc.); con-
tact may cause fires or explosions. Keep away from
alkaline materials, strong bases, strong acids, oxoacids,
epoxides, bromine pentafluoride, and bromine trifluoride;
chlorine trifluoride; oxygen difluoride. | [Description]
Rhodium is one of the platinum group elements, and is found
at very low concentrations in the Earths crust. Rhodium was
discovered by William Hyde Wollaston (England) in 1804. The
origin of the name comes from the Greek word rhodon,
meaning rose. The plated solid is very corrosion resistant and
exceptionally hard. While inert in air and acids, it can produce
a violent reaction to chlorine, bromine pentafluoride, bromine
trifluoride, and fluorine monoxide. | [Chemical Properties]
Rhodium, together with platinum, palladium, iridium, ruthenium, and osmium, is one of the platinum-group metals in Group VIII of the Periodic Table. Rhodium metal is a white, hard, ductile, malleable solid with a bluish-gray luster. soluble in ether, alcohol, and water. The alloys of rhodium can also be used in high temperature conditions (i.e., thermocouples and crucibles). It also can be used in electroplating glass products due to its reflective properties.
| [Waste Disposal]
Recovery in view of the high
economic value. Recovery techniques for recycling of
rhodium in plating wastes and spent catalysts have been
described in the literature. | [Isotopes]
There are 52 isotopes of rhodium, ranging from Rh-89 to Rh-122. All are producedartificially with relatively short half-lives except one stable isotope, Rh-103, whichconstitutes 100% of the element’s existence in the Earth’s crust. | [Origin of Name]
Named after the Greek word rhodon, which means “rose,” because of
the reddish color of its salt compounds. | [Occurrence]
Rhodium is rare, but not as rare as ruthenium. It makes up only 1 part in 20 million of theelements found in the Earth’s crust. Even so, it is considered the 79th most abundant elementand is found mixed with platinum ore, and to a lesser extent, it is found with copper andnickel ores. It is found in Siberia, South Africa, and Ontario, Canada.
Rhodium is recovered from platinum and other ores by refining and purification processesthat start by dissolving the other platinum group metals and related impurities with strongacids that do not affect the rhodium itself. Any remaining platinum group elements areremoved by oxidation and bathing the mixture in chlorine and ammonia.
Rhodium is usually produced as a powder and can be formed by either casting or powdermetallurgy. | [Characteristics]
Rhodium is one of the six platinum transition elements that include Ru, Rh, Pd, Os, Ir, andPt. Of these metals, rhodium has the highest electrical and thermal conductivity. Although arelatively scarce metal, rhodium makes an excellent electroplated surface that is hard, wearswell, and is permanently bright—ideal for plating the reflectors in automobile headlights. | [Uses]
As an alloy with platinum; as a corrosion-resistant electroplate for protecting silverware from tarnishing; for making high-reflectivity mirrors for cinema projectors, searchlights. Spongy or black rhodium is used as a catalyst in various organic hydrogenation and oxidation reactions. | [Uses]
Rhodium is a transition metal catalyst used in a multitude of inorganic synthesis. | [Uses]
Rhodium is commercially used as an alloy metal with other metals to form durable hightemperatureelectrical equipment, thermocouples, electrical contacts and switches, and laboratorycrucibles.
Because of its high reflectivity, it is used to electroplate jewelry, silverware, optical instruments,mirrors, and reflectors in lighting devices.
When rhodium is combined with platinum and palladium, the elements together form theinternal metals of automobile catalytic converters, which convert hot unburned hydrocarbonexhaust gases to less harmful CO2 and H2O. Similar alloys are used to manufacture hightemperatureproducts such as electric coils for metal refining furnaces and high-temperaturespark plugs. | [Production Methods]
Pure rhodium is prepared by the reduction of its ammonium
salt (dichloropentaaminorhodium). | [General Description]
We are committed to bringing you Greener Alternative Products, which adhere to one or more of The 12 Principles of Greener Chemistry. This product has been enhanced for energy efficiency. Find details here. | [Health Hazard]
There are no data demonstrating
acute or chronic rhodium-related diseases;
irritation and sensitization have occasionally
been reported in humans from exposure to the
salts of rhodium. Solutions of insoluble salts
splashed in the eye may cause mild irritation. | [Flammability and Explosibility]
Notclassified | [Industrial uses]
Metallic rhodium is the whitest of the platinum metals and does not tarnish under atmospheric conditions. It is insoluble in most acids, including aqua regia, but is attacked by chlorine at elevated temperatures and by hot fuming sulfuric acid. Liquid rhodium dissolves oxygen, and ingots are made by argon-arc melting. At temperatures above 1200 C, rhodium reacts with oxygen to form rhodium oxide, Rh2O3. Rhodium is used to make the nibs of writing pens, to make resistance windings in high-temperature furnaces, for high-temperature thermocouples, as a catalyst, and for laboratory dishes. It is the hardest of the platinum-group metals; the annealed metal has a Brinell hardness of 135. Rhodium is also valued for electroplating jewelry, electric contacts, hospital and surgical instruments, and especially reflectors.
The most important alloys of rhodium are rhodium platinum. They form solid solutions in any proportion, but alloys of more than 40% rhodium are rare. Rhodium is not a potent hardener of platinum but increases its high-temperature strength. It is easily workable and does not tarnish or oxidize at high temperatures. These alloys are used for thermocouples and in the glass industry. | [Carcinogenicity]
Chick embryos exposed to rhodium on the
eighth day of incubation were stunted; mild
reduction of limb size and feather growth inhibition
were also observed. A number of
rhodium compounds have tested positive in
bacterial assays for genetic altering capability. | [Environmental Fate]
The most common route by which rhodium enters the environment
is as a component of automobile exhaust resulting
from use of catalytic converters. Rhodium is insoluble in water
and all acids, with the exception that very finely separated
material may be dissolved in concentrated sulfuric acid and
aqua regia.
Being largely inert, rhodium can undergo long-range
transport, and particulate phase matter generally leaves the
atmosphere by wet or dry deposition. In an aqueous environment,
rhodium can form complexes with halide and
nitrogen donor ligands, which may be water soluble, but
reactions can be dictated by pH, redox potential, and what
material is available for creating ligands. Reactions in soil can
depend on these same factors, as well as chloride concentrations, and rhodium is seen to be mobile only in
highly acidic soils.
Rhodium has been seen to bioaccumulate in both fresh and
salt water species, and has the potential to biomagnify. | [storage]
Color Code—Red (powder): FlammabilityHazard: Store in a flammable materials storage area. Priorto working with this material you should be trained on itsproper handling and storage. Store in tightly closed containers in a cool, well-ventilated area away from strong oxidizers and sources of ignition. Where possible, automaticallytransfer material from drums or other storage containers toprocess containers. Sources of ignition, such as smokingand open flames, are prohibited where this chemical is handled, used, or stored. Metal containers involving the transferof this chemical should be grounded and bonded. Whereverthis chemical is used, handled, manufactured, or stored, useexplosion-proof electrical equipment and fittings. | [Toxicity evaluation]
Enzymes that have essential sulfhydryl groups in or near the
activation sites are completely inhibited. It is thought that
rhodium compounds bond to DNA, RNA, or the corresponding
purines and inhibit their synthesis. |
| Questions And Answer | Back Directory | [History, Occurrence, and Uses]
Rhodium was discovered by W. H. Wollaston in 1803-04 in the aqua regia platium hexachloride, (NH4)2PtCl6, from the aqua regia extract, the resulting filtrate contained two new metals, palladium and rhodium. The element was named rhodium, derived from the Greek word rhodon for the beautiful rose color of its chloro salt and its aqueous solution.
Rhodium occurs in nature in trace quantities, always associated with other platinum metals. It is found in native form. Its average abundance in the earth’s crust is estimated to be 1mg/kg. Rhodium is used as a precious metal for making jewelry and decorative. Other important applications of this metal or its compounds are in making glass for mirrors or filtering light; in catalytic reactions to synthesize a number of products; as an alloying element for platinum; as a hardening agent for platinum and palladium at high temperatures; in electrical contact plates in radioand audio-frequency circuits. Rhodium alloyed with platinum is used in thermocouples. A 10% Rh-Pt alloy was introduced by LeChatelier in 1885 for use in thermocouples. Also, rhodium alloys are used in laboratory crucibles, electrodes, optical instruments, furnace linings, and making glass fibers.
| [Physical Properties]
Grayish-white metal; face-centered cubic crystals; density 12.41 g/cm3; hardness, annealed 100-120 Vickers units; melts at 1,964°C; vaporizes at 3,695°C; electrical resistivity 4.33 microhm–cm at 0°C; tensile strength, annealed 50 tons/in2; Young’s modulus, annealed 2.3×104 tons/in2; magnetic susceptibility 0.99×10–6 cm3/g; thermal neutron absorption cross section 156 barns; insoluble in water; soluble in concentrated sulfuric or hydrochloric acid under boiling conditions; the metal in massive form is slightly soluble in aqua regia, but in small quantities or in thin plates it partially dissolves in aqua regia; forms solid solutions with platinum, palladium and iridium.
| [Reactions]
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.
| [Recovery]
Wollaston’s earliest method involved recovery of rhodium from native platinum. Pt was digested with aqua regia. Rhodium in bulk form is slightly soluble in aqua regia. However, when present as a minor constituent in platinum alloys, the metal may be extracted with aqua regia. Platinum was precipitated from aqua regia extract as ammonium hexachloroplatinate, (NH4)2PtCl6. Addition of mercurous cyanide, Hg2(CN)2, to the filtrate separated palladium as yellow palladium cyanide, Pd(CN)2. Excess mercurous cyanide in the remaining solution was decomposed by evaporating the solution with hydrochloric acid. The residue was treated with ethanol. A dark red solid residue that remained after alcohol treatment was a double chloride, sodium chlororhodite, Na3RhCl6•18H2O. Heating this rhodium complex with hydrogen decomposed the double chloride forming sodium chloride, hydrogen chloride and rhodium metal:
2Na3RhCl6 + 3H2 → 6NaCl + 6HCl + 2Rh
Sodium chloride was removed by leaching with water. Rhodium powder was left as residue.
|
|
|