Rhodium
Rhodium (lat. Rhodium; denoted by the symbol Rh) is
an element of a secondary subgroup of the eighth group of the fifth
period of the periodic system of chemical elements of D. I. Mendeleev,
atomic number - 45. In appearance, compact rhodium is a beautiful
silvery metal with a bluish tint.
Rhodium belongs to the noble metals of the platinum group. Compared to
other metals in this group, it is brighter and harder - it becomes
plastic only when heated.
The name of the element, translated from ancient Greek, means "rose". He
got this name from the color of his typical compounds - they are red,
like roses.
Rhodium is a very rare and trace element. Its average content in the
earth's crust is 1 o 10-7% by weight. It does not have its own minerals.
Contained in nickel and platinum ores as a simple compound. It is also
contained in isomorphic admixtures of minerals of the osmous iridium
group (up to 3.3%), in copper-nickel ores. The rarest variety of osmist
iridium is also known - the native nevyanskite. It contains up to 11.3%
rhodium. It is the richest mineral in rhodium.
Rhodium was discovered in England in 1803 by the remarkable scientist of
his time, William Hyde Wollaston. While studying native South American
platinum, he drew attention to a bright pinkish-red filtrate, which he
obtained from a solution of native platinum in aqua regia. The solution
acquired this color after the precipitation of platinum and palladium.
From this solution, Wollaston isolated a dark red powder, calcined it in
a hydrogen atmosphere and obtained a heavy white metal - rhodium.
PHYSICAL PROPERTIES OF RHODIUM
In appearance, compact rhodium is a beautiful silvery metal with a
bluish tint. It has a face-centered cubic lattice, the unit cell
parameter is a = 0.3803 nm. Density at 20 ° C 12.41 g / cm3. Melting
point 1963 ° C, boiling point 3727 ° C. Unlike gold and platinum,
rhodium is difficult to machine. Therefore, it can be rolled or pulled
into a wire only at 800 ... 900 ° C. Shows the properties of a
paramagnet. The reflectivity of the surface of rhodium is 80% for the
visible spectrum.
Other characteristics:
- heat of fusion - 21.8 kJ / mol;
- heat of vaporization - 494 kJ / mol;
- specific heat - 0.244 J / (K o mol);
- thermal conductivity - 150 W / (m o K).
Rhodium occurs naturally in the form of a stable isotope, 103Rh. Its
longest-lived isotopes with half-lives are: 101Rh (3.3 years), 102Rh
(207 days), 102mRh (2.9 years), 99Rh (16.1 days).
Compact rhodium is extremely resistant to any kind of chemical attack.
However, if you take an alloy of rhodium with zinc or cadmium and
dissolve it in hydrochloric acid, and then filter it off, you get a fine
rhodium precipitate that can explode in air.
CHEMICAL PROPERTIES OF RHODIUM
Rhodium is a noble metal, superior to platinum in chemical resistance in
most corrosive environments. Neither acids nor alkalis act on compact
rhodium. Only finely crushed rhodium dissolves slowly in hot aqua regia
or concentrated sulfuric acid. Rhodium is very resistant to the action
of halogens: it reacts with chlorine, bromine and even fluorine only
after prolonged heating. In this case, depending on the reaction
temperature, halides of various compositions are obtained. In
particular, chlorine forms chlorides of one-, two- and trivalent rhodium
RhCl, RhCl2, RhCl3. At high temperatures, rhodium slowly reacts with
sulfur, turning into sulfides RhS, RhS2, Rh2S5.
Finely ground rhodium is only slowly oxidized at temperatures above 600
° C:
4Rh + 3O2 = 2Rh2O3.
Rhodium, when heated in air, has a peculiar behavior. At temperatures
from 600 to 800 degrees, an oxide film - Rh2O3 - forms on its surface.
When the temperature rises from 800 to 1000 degrees, the oxide film on
the surface of rhodium decomposes again to metal.
Deposits and mining of rhodium
Less than 30 tons of rhodium are mined in the world annually. The main
exporter of this metal is South Africa (approximately 80%). Industrial
mining of rhodium is difficult as the metal occurs in ores mixed with
other metals such as palladium, silver, platinum, and gold.
From the mines, crude platinum goes to a refinery, where it is loaded
into porcelain kettles and processed with aqua regia. The process takes
place when heated during the day. As a result, rhodium goes into
solution.
APPLICATION OF RHODIUM
The price of rhodium is high, not only because the element is precious,
but also because there are more industries where it is needed than the
metal itself. However, it is used only where there is no cheaper and
more widespread alternative to it.
The lion's share of the rhodium mined is consumed by the automotive
industry. Excellent catalytic properties of the metal make it possible
to manufacture exhaust gas neutralizers from its alloys.
Rhodium-platinum alloy is a very effective catalyst in the production of
nitric acid by oxidizing ammonia with air. It is in this area that
rhodium as a metal catalyst has no analogues.
Rhodium in alloys with iridium and / or platinum is used in the
manufacture of thermocouples, which are used to effectively measure high
temperatures up to 2200 degrees Celsius.
A large consumer of rhodium is the glass industry. From an alloy of
rhodium with platinum (usually 7% Rh), vessels are made for melting
glass melt and obtaining the finest glass and quartz threads. Rhodium is
also practically irreplaceable here.
The surface of rhodium is highly reflective (80%) to the visible
spectrum. The reflectivity of rhodium is less than that of silver (95%),
but its resistance to the action of corrosive gases and high
temperatures is much greater. Rhodium-plated surfaces do not tarnish
even in a voltaic arc atmosphere. Therefore, the reflectors of
searchlights and technical mirrors of precision measuring instruments of
various purposes are coated with rhodium.
Metallic rhodium is used for the production of mirrors subject to strong
heating (incandescence) for high-power laser systems (for example,
hydrogen fluoride lasers), as well as for the production of diffraction
gratings for devices for the analysis of matter (spectrometers).
Precious metal and LCD monitor filters. The need for them is growing
every year. More and more rhodium is required for this industry.
Rhodium detectors are used in reactors to measure neutron flux.
There are precious minerals whose crystals grow under artificial
conditions only on filters made of platinum and rhodium alloy.
Rhodium plating
Rhodium has a beautiful silvery-white hue, for which it is highly prized
in the jewelry industry. Its reflectivity is very high, the metal
sparkles and shimmers, its brilliance is magnificent. Therefore, rhodium
plating is becoming an increasingly popular procedure in jewelry
workshops.
Rhodium plating is the application of a thin layer of rhodium (0.1 -
0.25 microns) to the surface of jewelry. The coating improves not only
the appearance of metals, giving the surface a platinum luster, but also
their chemical and mechanical properties. In addition, rhodium does not
tarnish over time.
Advantages of rhodium plating:
- brilliant platinum color;
- resistance of the product to mechanical damage, scratches, etc.
Disadvantages of rhodium plating: - Do not clean the jewelry with
abrasives, as you can damage the coating;
- after each repair of the product, it will have to be re-plated with
rhodium.
Rhodium plating does not last forever, but its lifespan depends on
several factors, the main of which is thickness. According to the
experience of use, the renewal of the rhodium layer on rings, earrings,
chains is required every five years and less often - depending on the
intensity of use of the product. In many cases, high-quality rhodium
plating has adorned the metal for decades.
PRICE OF RHODIUM ON THE WORLD MARKET
Everyone knows that precious metals cannot be cheap. And since rhodium
also belongs to this category, the price per gram of metal, which is
also quite rare, is also quite high.
.
Rhodium (lat. Rhodium; denoted by the symbol Rh) is
an element of a secondary subgroup of the eighth group of the fifth
period of the periodic system of chemical elements of D. I. Mendeleev,
atomic number - 45. In appearance, compact rhodium is a beautiful
silvery metal with a bluish tint.
Rhodium belongs to the noble metals of the platinum group. Compared to
other metals in this group, it is brighter and harder - it becomes
plastic only when heated.
The name of the element, translated from ancient Greek, means "rose". He
got this name from the color of his typical compounds - they are red,
like roses.
Rhodium is a very rare and trace element. Its average content in the
earth's crust is 1 o 10-7% by weight. It does not have its own minerals.
Contained in nickel and platinum ores as a simple compound. It is also
contained in isomorphic admixtures of minerals of the osmous iridium
group (up to 3.3%), in copper-nickel ores. The rarest variety of osmist
iridium is also known - the native nevyanskite. It contains up to 11.3%
rhodium. It is the richest mineral in rhodium.
Rhodium was discovered in England in 1803 by the remarkable scientist of
his time, William Hyde Wollaston. While studying native South American
platinum, he drew attention to a bright pinkish-red filtrate, which he
obtained from a solution of native platinum in aqua regia. The solution
acquired this color after the precipitation of platinum and palladium.
From this solution, Wollaston isolated a dark red powder, calcined it in
a hydrogen atmosphere and obtained a heavy white metal - rhodium.
PHYSICAL PROPERTIES OF RHODIUM
In appearance, compact rhodium is a beautiful silvery metal with a
bluish tint. It has a face-centered cubic lattice, the unit cell
parameter is a = 0.3803 nm. Density at 20 ° C 12.41 g / cm3. Melting
point 1963 ° C, boiling point 3727 ° C. Unlike gold and platinum,
rhodium is difficult to machine. Therefore, it can be rolled or pulled
into a wire only at 800 ... 900 ° C. Shows the properties of a
paramagnet. The reflectivity of the surface of rhodium is 80% for the
visible spectrum.
Other characteristics:
- heat of fusion - 21.8 kJ / mol;
- heat of vaporization - 494 kJ / mol;
- specific heat - 0.244 J / (K o mol);
- thermal conductivity - 150 W / (m o K).
Rhodium occurs naturally in the form of a stable isotope, 103Rh. Its
longest-lived isotopes with half-lives are: 101Rh (3.3 years), 102Rh
(207 days), 102mRh (2.9 years), 99Rh (16.1 days).
Compact rhodium is extremely resistant to any kind of chemical attack.
However, if you take an alloy of rhodium with zinc or cadmium and
dissolve it in hydrochloric acid, and then filter it off, you get a fine
rhodium precipitate that can explode in air.
CHEMICAL PROPERTIES OF RHODIUM
Rhodium is a noble metal, superior to platinum in chemical resistance in
most corrosive environments. Neither acids nor alkalis act on compact
rhodium. Only finely crushed rhodium dissolves slowly in hot aqua regia
or concentrated sulfuric acid. Rhodium is very resistant to the action
of halogens: it reacts with chlorine, bromine and even fluorine only
after prolonged heating. In this case, depending on the reaction
temperature, halides of various compositions are obtained. In
particular, chlorine forms chlorides of one-, two- and trivalent rhodium
RhCl, RhCl2, RhCl3. At high temperatures, rhodium slowly reacts with
sulfur, turning into sulfides RhS, RhS2, Rh2S5.
Finely ground rhodium is only slowly oxidized at temperatures above 600
° C:
4Rh + 3O2 = 2Rh2O3.
Rhodium, when heated in air, has a peculiar behavior. At temperatures
from 600 to 800 degrees, an oxide film - Rh2O3 - forms on its surface.
When the temperature rises from 800 to 1000 degrees, the oxide film on
the surface of rhodium decomposes again to metal.
Deposits and mining of rhodium
Less than 30 tons of rhodium are mined in the world annually. The main
exporter of this metal is South Africa (approximately 80%). Industrial
mining of rhodium is difficult as the metal occurs in ores mixed with
other metals such as palladium, silver, platinum, and gold.
From the mines, crude platinum goes to a refinery, where it is loaded
into porcelain kettles and processed with aqua regia. The process takes
place when heated during the day. As a result, rhodium goes into
solution.
APPLICATION OF RHODIUM
The price of rhodium is high, not only because the element is precious,
but also because there are more industries where it is needed than the
metal itself. However, it is used only where there is no cheaper and
more widespread alternative to it.
The lion's share of the rhodium mined is consumed by the automotive
industry. Excellent catalytic properties of the metal make it possible
to manufacture exhaust gas neutralizers from its alloys.
Rhodium-platinum alloy is a very effective catalyst in the production of
nitric acid by oxidizing ammonia with air. It is in this area that
rhodium as a metal catalyst has no analogues.
Rhodium in alloys with iridium and / or platinum is used in the
manufacture of thermocouples, which are used to effectively measure high
temperatures up to 2200 degrees Celsius.
A large consumer of rhodium is the glass industry. From an alloy of
rhodium with platinum (usually 7% Rh), vessels are made for melting
glass melt and obtaining the finest glass and quartz threads. Rhodium is
also practically irreplaceable here.
The surface of rhodium is highly reflective (80%) to the visible
spectrum. The reflectivity of rhodium is less than that of silver (95%),
but its resistance to the action of corrosive gases and high
temperatures is much greater. Rhodium-plated surfaces do not tarnish
even in a voltaic arc atmosphere. Therefore, the reflectors of
searchlights and technical mirrors of precision measuring instruments of
various purposes are coated with rhodium.
Metallic rhodium is used for the production of mirrors subject to strong
heating (incandescence) for high-power laser systems (for example,
hydrogen fluoride lasers), as well as for the production of diffraction
gratings for devices for the analysis of matter (spectrometers).
Precious metal and LCD monitor filters. The need for them is growing
every year. More and more rhodium is required for this industry.
Rhodium detectors are used in reactors to measure neutron flux.
There are precious minerals whose crystals grow under artificial
conditions only on filters made of platinum and rhodium alloy.
Rhodium plating
Rhodium has a beautiful silvery-white hue, for which it is highly prized
in the jewelry industry. Its reflectivity is very high, the metal
sparkles and shimmers, its brilliance is magnificent. Therefore, rhodium
plating is becoming an increasingly popular procedure in jewelry
workshops.
Rhodium plating is the application of a thin layer of rhodium (0.1 -
0.25 microns) to the surface of jewelry. The coating improves not only
the appearance of metals, giving the surface a platinum luster, but also
their chemical and mechanical properties. In addition, rhodium does not
tarnish over time.
Advantages of rhodium plating:
- brilliant platinum color;
- resistance of the product to mechanical damage, scratches, etc.
Disadvantages of rhodium plating: - Do not clean the jewelry with
abrasives, as you can damage the coating;
- after each repair of the product, it will have to be re-plated with
rhodium.
Rhodium plating does not last forever, but its lifespan depends on
several factors, the main of which is thickness. According to the
experience of use, the renewal of the rhodium layer on rings, earrings,
chains is required every five years and less often - depending on the
intensity of use of the product. In many cases, high-quality rhodium
plating has adorned the metal for decades.
PRICE OF RHODIUM ON THE WORLD MARKET
Everyone knows that precious metals cannot be cheap. And since rhodium
also belongs to this category, the price per gram of metal, which is
also quite rare, is also quite high.
.