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
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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.
