Chemical Properties
Germanium is a grayish-white, lustrous, brittle metalloid. When crystalline, it exists in a diamond-cubic structure. It has a very low vapor pressure and is insoluble in water.
Germanium is never found in a pure state in the environment. In the refined state, it is a gray– white metalloid. Like its counterparts in group 14 of the periodic table (carbon, silicon, tin, and lead), germanium has both metallic and nonmetallic properties. It has a valence of +2 or +4; the atom usually is quadrivalent.
Germanium is a true semiconductor, is highly transparent to infrared light, and has a high index of refraction. Germanium and its compounds or alloys have found wide use in the optical and electronics industries. In electronic applications, it often is alloyed with antimony, gallium, indium, or arsenic.
Germanium is a low production volume chemical.
History
The existence of this element was predicted by Mendeleev in 1871 in his periodic scheme. He predicted that it should belong to the carbon group and occupy the position just below silicon. He therefore named it ekasilicon.
Fifteen years later in 1886, the predicted element was discovered by Clemens Winkler who isolated it from the mineral argyrodite. It was named in honor of Germany.
Germanium occurs in nature mostly as sulfide ores. It is found in the minerals germanite, 7CuS•FeS•GeS2; argyrodite, 4Ag2S•GeS2; renierite (Cu,Ge,Fe,Zn,As)S; and canfieldite, 4Ag2S. It also is found in small quantities in many zinc blende ores from which it is commercially extracted in the United States. Trace quantities of germanium are also found in many coals. Its abundance in the earth’s crust is about 1.5 mg/kg and concentration in sea water is 0.05 µg/L.
Uses
The most important uses of germanium are in electronic industries. It is a semiconductor material exhibiting an exponential increase of conductivity with increasing temperature. The element can be prepared in extreme purification with a high degree of crystalline perfection so as to yield highly characterized surfaces. Other applications of germanium are in infrared detectors, microscopes and various optical instruments; as a phosphor in fluorescent lamps; as an alloying agent; and as a catalyst.
Production Methods
In the United States, germanium is obtained as a by-product of zinc production from zinc blende ores. The ore is concentrated by the flotation process. Concentrated ore is then roasted, converting zinc and the impurity metals to their oxides. Heating the crude oxides with sodium chloride and coal converts germanium and other impurity metal oxides into their volatile chlorides. The chloride vapors are condensed and germanium chloride, GeCl4, is separated from the condensate by fractional distillation.
Germanium also is recovered from coal that contains this metal at trace concentrations. Coal ash and fine dusts are mixed with sodium carbonate, copper oxide, calcium oxide, and coal dust, and smelted. The crude oxide products are converted to their volatile chlorides. Germanium chloride is isolated from the condensate products by fractional distillation.
High purity (99.9999%) germanium may be produced by fractional distillation of the chloride in the presence of hydrochloric acid and chlorine in quartz stills, followed by hydrolysis of the purified chloride with double distilled water to produce germanium oxide, GeO2. The oxide is reduced with hydrogen at 1,000°C. Exceedingly high purity germanium for semiconductor applications may be obtained from the high purity grade material by the zone refining process. Impurities present in germanium are more soluble in its melt than the solid metal. Thus, repeated passes of a molten zone along the impure ingot of germanium effectively removes trace impurities from the solid metal ingot.
Doping of the metal for its solid state electronic use may be carried out either by adding trace amounts of doping agents into the melts before a single crystal is grown from the melt or into the prepared single crystal by solid state diffusion. Single crystals up to a few inches in diameter may be prepared from the melt by the Czochralski technique, which involves contacting the melt with a seed crystal under an inert atmosphere and controlled conditions of temperature and seeding.
Reactions
The chemical properties of germanium fall between those of silicon and tin. It forms both the divalent and tetravalent compounds, the oxidation state +4 being more stable than the +2 oxidation state. The metal is stable in air and water at ambient temperatures. However, it reacts with oxygen at elevated temperatures forming divalent and tetravalent oxides, GeO and GeO2.
While no reaction occurs with dilute mineral acids, the compound is attacked by concentrated HNO3 and H2SO4. Also, no reaction occurs with caustic alkalies.
When heated with carbon dioxide at 800°C, the divalent oxide is formed:
Ge + CO2 →GeO + CO
The metal also reduces the tetravalent oxide to the divalent oxide upon heating at elevated temperatures:
Ge + GeO2→ 2GeO
Heating with chlorine at elevated temperatures yields germanium tetrachloride:
Ge + 2Cl2 →GeCl4
Description
Germanium is extracted from zinc ores in a very complicated process as it has aqueous properties similar
to those of zinc. Once the germanium/zinc mixture has been sufficiently enriched with germanium, it is
heated in HCl with Cl
2 in order to allow the formation of germanium tetrachloride (GeCl
2).
Chemical Properties
Germanium is a grayish-white, lustrous, and
brittle metalloid. The powder is grayish-black and odorless. It
is never found free and occurs most commonly in ergyrodite
and germanite. It is generally recovered as a by-product in
zinc production, coal processing, or other sources.
Physical properties
Germanium has a gray shine with a metallic silvery-white luster. It is a brittle elementclassed as a semimetal or metalloid, meaning it is neither a metal such as iron or copper nora nonmetal, such as phosphorus, sulfur, or oxygen. Germanium has some properties likea metal and some like a nonmetal. It is a crystal in its pure state, somewhat like silicon. Itwill combine with oxygen to form germanium dioxide, which is similar to silicon dioxide(sand).
Germanium is not found in its free elemental state because it is much too reactive. For themost part, it is found combined with oxygen, either as germanium monoxide or as germaniumdioxide. Also, it is recovered from the ores of zinc, copper, and arsenic and the flue depositsof burning coal.
The crystal structure of germanium is similar to that of diamonds and silicon, and its semiconductingproperties are also similar to silicon.The melting point of germanium is 938.3°C, its boiling point is 2833°C, and its densityis 5.323 g/cm
3.
Isotopes
There are a total of 38 isotopes of Germanium, five of which are stable. Thestable isotopes of germanium and their natural abundance are as follows: Ge-70 =20.37%, Ge-72 = 27.31%, Ge-73 = 7.76%, Ge-74 = 36.73%, and Ge-76 = 7.83%.Ge-76 is considered stable because it has such a long half-life (0.8×10
+25 years)All theother 33 isotopes are radioactive and are produced artificially.
Origin of Name
Germanium’s name was derived from the Latin word Germania, meaning
“Germany.”
Occurrence
Germanium, the 52nd most abundant element in the Earth’s crust, is widely distributed,but never found in its natural elemental state. It is always combined with other elements,particularly oxygen.
Germanium’s main minerals are germanite, argyrodite, renierite and canfieldite, all ofwhich are rare. Small amounts of germanium are found in zinc ore, as well as in copper andarsenic ores. It is known to concentrate in certain plants on Earth, particularly in coal: commercialquantities are collected from the soot in the stacks where coal is burned.
Characteristics
Once germanium is recovered and formed into blocks, it is further refined by the manufacturerof semiconductors. It is melted, and the small amounts of impurities such as arsenic, gallium,or antimony, are added. They act as either electron donors or acceptors that are infused(doped) into the mix. Then small amounts of the molten material are removed and used togrow crystals of germanium that are formed into semiconducting transistors on a germaniumchip. The device can now carry variable amounts of electricity because it can act as both aninsulator and a conductor of electrons, which is the basis of modern computers.
History
Germanium was predicted by Mendeleev in 1871 as ekasilicon, and discovered by Winkler in 1886. The metal is found in argyrodite, a sulfide of germanium and silver; in germanite, which contains 8% of the element; in zinc ores; in coal; and in other minerals. Germanium is frequently obtained commercially from flue dusts of smelters processing zinc ores, and has been recovered from the by-products of combustion of certain coals. Its presence in coal insures a large reserve of the element in the years to come. Germanium can be separated from other metals by fractional distillation of its volatile tetrachloride. The tetrachloride may then be hydrolyzed to give GeO2; the dioxide can be reduced with hydrogen to give the metal. Recently developed zone-refining techniques permit the production of germanium of ultra-high purity. The element is a gray-white metalloid, and in its pure state is crystalline and brittle, retaining its luster in air at room temperature. Germanium is a very important semiconductor material. Zone-refining techniques have led to production of crystalline germanium for semiconductor use with an impurity of only one part in 10
10. Doped with arsenic, gallium, or other elements, it is used as a transistor element in thousands of electronic applications. Its application in fiber optics and infrared optical systems now provides the largest use for germanium. Germanium is also finding many other applications including use as an alloying agent, as a phosphor in fluorescent lamps, and as a catalyst. Germanium and germanium oxide are transparent to the infrared and are used in infrared spectrometers and other optical equipment, including extremely sensitive infrared detectors. Germanium oxide’s high index of refraction and dispersion make it useful as a component of glasses used in wide-angle camera lenses and microscope objectives. The field of organogermanium chemistry is becoming increasingly important. Certain germanium compounds have a low mammalian toxicity, but a marked activity against certain bacteria, which makes them of interest as chemotherapeutic agents. The cost of germanium is about $10/g (99.999% purity). Thirty isotopes and isomers are known, five of which occur naturally.
Uses
The product can serve as one of the precursors for the formation of highly porous ZrO
2:Tb
3+ nanophosphor with excellent tunable photoluminescence and photocatalytic activities.
Uses
In electronics: manufacture of rectifying devices (germanium diodes), transistors, in red-fluorescing phosphors; in dental alloys; in the production of glass capable of transmitting infrared radiation. Review of uses: Aldington, Cumming, Endeavour 14, 200-204 (1955); New Uses for Germanium, F. I. Metz, Ed. (Midwest Research Institute, 1974) 120 pp.
Uses
By far, the most common use for germanium is in the semiconductor and electronicsindustries. As a semiconductor, germanium can be used to make transistors, diodes, andnumerous types of computer chips. It was the first element that could be designed to act asdifferent types of semiconductors for a variety of applications just by adding variable amountsof impurities (doping) to the germanium crystals.
Germanium is also used as a brazing alloy, for producing infrared transmitting glass andother types of lenses, and for producing synthetic garnets (semiprecious gemstones) that havespecial magnetic properties.
Definition
germanium: Symbol Ge. A lustroushard metalloid element belonging togroup 14 (formerly IVB) of the periodictable; a.n. 32; r.a.m. 72.59; r.d.5.36; m.p. 937°C; b.p. 2830°C. It isfound in zinc sulphide and in certainother sulphide ores, and is mainlyobtained as a by-product of zincsmelting. It is also present in somecoal (up to 1.6%). Small amounts areused in specialized alloys but themain use depends on its semiconductorproperties. Chemically, it formscompounds in the +2 and +4 oxidationstates, the germanium(IV) compoundsbeing the more stable. Theelement also forms a large numberof organometallic compounds. Predictedin 1871 by Mendeleev (ekasilicon),it was discovered by Winklerin 1886.
Production Methods
The concentration of germanium in the earth’s crust is
approximately 7 ppm. Germanium is not found in the free state, but in combination with other elements as a mineral,
such as in the mineral argyrodite (Ag8GeS6, 5–7% Ge) and
germanite (7CuS–FeS2–GeS2, 8.7% Ge). Enargite, a Cu–As
sulfide, is found in the western United States and contains as
much as 0.03% Ge; however, none of these minerals are
utilized for recovery of germanium because of the small
quantities available. The principal domestic source of germanium
is from the residues of cadmium derived from zinc
ores. Commercial recovery of germanium has been chiefly
from zinc and Zn–Cu–Pb ores, germanite, and flue dusts from
coals. Some silver and tin ores contain germanium, as do
many types of coal. Oak and beech humus in one locality in
Germany reportedly contain 70 ppm germanium.
Definition
A hard brittle gray metalloid element belonging to group 14 (formerly IVA) of the periodic table. It is found in sulfide ores such as argyrodite (4Ag
2S·GeS
2) and in zinc ores and coal. Most germanium is recovered during zinc or copper refining as a by-product. Germanium was extensively used in early semiconductor devices but has now been largely superseded by silicon. It is used as an alloying agent, catalyst, phosphor, and in infrared equipment. Symbol: Ge; m.p. 937.45°C; b.p. 2830°C; r.d. 5.323 (20°C); p.n. 32; r.a.m. 72.61.
Hazard
Many of the chemicals used in the semiconductor industries are highly toxic. For example,germanium-halogen compounds are extremely toxic, both as a powder and in a gaseous state.Precautions should be taken when working with germanium as with similar metalloids fromgroup 14 (IVA).
Flammability and Explosibility
Not classified
Industrial uses
A rare elemental metal, germanium (Ge) has agrayish white crystalline appearance and hasgreat hardness: 6.25 Mohs. Its specific gravityis 5.35, and melting point is 937°C. It is resistantto acids and alkalies. It has metallic-appearingcrystals with diamond structure, givesgreater hardness and strength to aluminum andmagnesium alloys, and as little as 0.35% in tinwill double the hardness. It is not used commonlyin alloys, however, because of its rarityand great cost. It is used chiefly as metal inrectifiers and transistors. An Au–Ge alloy, withabout 12% germanium, has a melting point of359°C and has been used for soldering jewelry.
Germanium is obtained as a by-productfrom flue dust of the zinc industry, or it can beobtained by reduction of its oxide from the ores,and is marketed in small irregular lumps. Germaniumcrystals are grown in rods up to 3.49cm in diameter for use in making transistorwafers. High-purity crystals are used for both P and Nsemiconductors. They are easier topurify and have a lower melting point than othersemiconductors, specifically silicon.
Industrial uses
Germanium lenses and filters have been usedin instruments that operate in the infraredregion of the spectrum. Windows and lenses ofgermanium are vital components of some laserand infrared guidance or detection systems.Glasses prepared with germanium dioxide havea higher refractivity and dispersion than docomparable silicate glasses and may be used inwide-angle camera lenses and microscopes.
Potential Exposure
Because of its semiconductor proper ties, germanium is widely used in the electronic industry in
rectifiers, diodes, and transistors. It is alloyed with alumi num, aluminum magnesium, antimony, bronze, and tin to
increase strength, hardness, or corrosion resistance. In the
process of alloying germanium and arsenic, arsine may be
released; stibine is released from the alloying of germanium and antimony. Germanium is also used in the manufacture
of optical glass for infrared applications; red-fluorescing
phosphors; and cathodes for electronic valves; and in elec troplating; in the hydrogenation of coal; and as a catalyst,
particularly at low temperatures. Certain compounds are
used medically. Industrial exposures to the dust and fumes
of the metal or oxide generally occur during separation and
purification of germanium, welding, multiple-zone melting
operations, or cutting and grinding of crystals. Germanium
tetrahydride (germanium hydride, germane, and monoger mane) and other hydrides are produced by the action of a
reducing acid on a germanium alloy.
Environmental Fate
Metals are recalcitrant to degradation; therefore, no biodegradation studies have been performed on germanium compounds. Naturally occurring germanium exists in mineral ores; therefore, the levels of free germanium are expected to be low and of low concern for bioaccumulation in aquatic and terrestrial species, due to negligible exposures.
Shipping
UN3089 Metal powders, flammable, n.o.s.,
Hazard Class: 4.1; Labels: 4.1-Flammable solid. UN1759
Corrosive solids, n.o.s., Hazard class: 8; Labels:
8-Corrosive material, Technical Name required.
Purification Methods
Copper contamination on the surface and in the bulk of single crystals of Ge can be removed by immersion in molten alkali cyanide under N2. The Ge is placed in dry K and/or Na cyanide powder in a graphite holder in a quartz or porcelain boat. The boat is then inserted into a heated furnace which, after a suitable time, is left to cool to room temperature. At 750o, a 1mm thickness of metal requires about 1minute, whereas 0.5cm needs about half hour. The boat is removed from the furnace, and the solid samples are taken out with plastic-coated tweezers, carefully rinsed in hot water and dried in air [Wang J Phys Chem 60 45 1956, Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 712 1963]. Care with the use of cyanide.
Incompatibilities
A strong reducing agent and flammable
solid. Finely divided metal is incompatible with oxidizing
and nonoxidizing acids, ammonia, bromine, oxidizers, aqua
regia, sulfuric acid, carbonates, halogens, and nitrates.
Explosive reaction or ignition with potassium chlorate,
potassium nitrate, chlorine, bromine, oxygen, and potas sium hydroxide in the presence of heat. Violent reaction
with strong acids: aqua regia, nitric, and sulfuric.
Incompatible with oxidizers (chlorates, nitrates, peroxides,
permanganates, perchlorates, chlorine, bromine, fluorine,
etc.); contact may cause fires or explosions.
Waste Disposal
Recovery and return to sup pliers for reprocessing is preferable.
