GERMANIUM: HISTORY, PROPERTIES, STRUCTURE, OBTAINING, USES - CHEMISTRY - 2024

The germanium is a metalloid element is represented by the chemical symbol Ge and belonging to the group 14 of the periodic table. It is found beneath silicon, and shares many of its physical and chemical properties with it; so much so that once its name was Ekasilicio, predicted by Dmitri Mendeleev himself.

Its current name was given by Clemens A. Winkler, in honor of his homeland Germany. Hence, germanium is linked to this country, and it is the first image that evokes to the mind those who do not know it well.

Ultra pure germanium sample. Source: Hi-Res Images of Chemical Elements

Germanium, like silicon, consists of covalent crystals of three-dimensional tetrahedral lattices with Ge-Ge bonds. Likewise, it can be found in monocrystalline form, in which its grains are large, or polycrystalline, composed of hundreds of small crystals.

It is a semiconductor element at ambient pressure, but when it rises above 120 kbar it becomes a metallic allotrope; that is to say, possibly the Ge-Ge bonds are broken and their are arranged individually wrapped in the sea of ​​their electrons.

It is considered a non-toxic element, as it can be handled without any type of protective clothing; although its inhalation and excessive intake can lead to the classic symptoms of irritation in individuals. Its vapor pressure is very low, so its smoke is unlikely to cause a fire.

However, inorganic (salts) and organic germaniums can be dangerous for the organism, despite the fact that their Ge atoms interact in a mysterious way with biological matrices.

It is not really known if organic germanium can be considered a miracle cure for treating certain disorders as an alternative medicine. However, scientific studies do not support these claims, but reject them, and brand this element even as carcinogenic.

Germanium is not only a semiconductor, accompanying silicon, selenium, gallium and a whole series of elements in the world of semiconductor materials and their applications; It is also transparent to infrared radiation, making it useful for manufacturing heat detectors from different sources or regions.

History

Mendeleev predictions

Germanium was one of the elements whose existence was predicted in 1869 by the Russian chemist Dmitri Mendeleev in his periodic table. He provisionally called it ekasilicon and placed it in a space on the periodic table between tin and silicon.

In 1886, Clemens A. Winkler discovered germanium in a mineral sample from a silver mine near Freiberg, Saxony. It was the mineral called argyrodite, due to its high silver content, and only recently discovered in 1885.

The argyrodite sample contained 73-75% silver, 17-18% sulfur, 0.2% mercury, and 6-7% a new element, which Winkler later named germanium.

Mendeleev had predicted that the density of the element to be discovered should be 5.5 g / cm ³ and its atomic weight around 70. His predictions turned out to be quite close to those of germanium.

Isolation and name

In 1886, Winkler was able to isolate the new metal and found it similar to antimony, but he reconsidered and realized that the element he had discovered corresponded to ekasilicon.

Winkler named the element 'germanium' originated from the Latin word 'germania', a word they used to describe Germany. For this reason, Winkler named the new element germanium, after his native Germany.

Determination of its properties

In 1887, Winkler determined the chemical properties of germanium, finding an atomic weight of 72.32 by an analysis of pure germanium tetrachloride (GeCl ₄).

Meanwhile, Lecoq de Boisbaudran deduced an atomic weight of 72.3 by studying the element's spark spectrum. Winkler prepared several new compounds from germanium, including fluorides, chlorides, sulfides, and dioxides.

In the 1920s, investigations into the electrical properties of germanium led to the development of high-purity monocrystalline germanium.

This development allowed the use of germanium in diodes, rectifiers, and microwave radar receivers during World War II.

Development of your applications

The first industrial application came after the war in 1947, with the invention of germanium transistors by John Bardeen, Walter Brattain, and William Shockley, which were used in communications equipment, computers, and portable radios.

In 1954, high-purity silicon transistors began to displace germanium transistors because of the electronic advantages they possessed. And by the 1960s, germanium transistors had practically disappeared.

Germanium turned out to be a key component in the making of infrared (IR) lenses and windows. In the 1970s, silicon germanium (SiGe) voltaic cells (PVC) were produced that remain critical for satellite operations.

In the 1990s, the development and expansion of fiber optics increased the demand for germanium. The element is used to form the glass core of fiber optic cables.

Starting in 2000, high-efficiency PVCs and light-emitting diodes (LEDs) using germanium led to an increase in the production and consumption of germanium.

Physical and chemical properties

Appearance

Silvery white and shiny. When its solid is made up of many crystals (polycrystalline), it has a scaly or wrinkled surface, full of overtones and shadows. Sometimes it can even appear as grayish or black as silicon.

In standard conditions it is a semi-metallic element, brittle and metallic luster.

Germanium is a semiconductor, not very ductile. It has a high refractive index for visible light, but is transparent for infrared radiation, being used in equipment windows to detect and measure these radiation.

Standard atomic weight

72.63 u

Atomic number (Z)

32

Melting point

938.25 ºC

Boiling point

2,833 ºC

Density

At room temperature: 5.323 g / cm ³

At melting point (liquid): 5.60 g / cm ³

Germanium, like silicon, gallium, bismuth, antimony, and water, expands as it solidifies. For this reason, its density is higher in the liquid state than in the solid state.

Heat of fusion

36.94 kJ / mol

Heat of vaporization

334 kJ / mol

Molar caloric capacity

23.222 J / (mol K)

Vapor pressure

At a temperature of 1,644 K, its vapor pressure is only 1 Pa. This means that its liquid emits hardly any vapors at that temperature, so it does not imply a risk of inhalation.

Electronegativity

2.01 on the Pauling scale

Ionization energies

-First: 762 kJ / mol

-Second: 1,537 kJ / mol

-Third: 3,302.1 kJ / mol

Thermal conductivity

60.2 W / (m K)

Electrical resistivity

1 Ωm at 20 ºC

Electric conductivity

3S cm ^-1

Magnetic order

Diamagnetic

Hardness

6.0 on the Mohs scale

Stability

Relatively stable. It is not affected by air at room temperature and oxidizes at temperatures above 600ºC.

Surface tension

6 10 ^-1 N / m at 1,673.1 K

Reactivity

It oxidizes at temperatures above 600ºC to form germanium dioxide (GeO ₂). Germanium produces two forms of oxides: germanium dioxide (GeO ₂) and germanium monoxide (GeO).

Germanium compounds generally exhibit the +4 oxidation state, although in many compounds germanium occurs with the +2 oxidation state. The oxidation state - 4 occurs, for example, in magnesium germanide (Mg ₂ Ge).

Germanium reacts with halogens to form tetrahalides: germanium tetrafluoride (GeF ₄), a gaseous compound; germanium tetraiodide (GeI ₄), solid compound; germanium tetrachloride (GeCl ₄) and germanium tetrabromide (GeBr ₄), both liquid compounds.

Germanium is inert towards hydrochloric acid; but it is attacked by nitric acid and sulfuric acid. Although hydroxides in aqueous solution have little effect on germanium, it readily dissolves in molten hydroxides to form geronates.

Structure and electronic configuration

Germanium and its bonds

Germanium has four valence electrons according to its electronic configuration:

3d ¹⁰ 4s ² 4p ²

Like carbon and silicon, their Ge atoms hybridize their 4s and 4p orbitals to form four sp ³ hybrid orbitals. With these orbitals they bond to satisfy the valence octet and, consequently, have the same number of electrons as the noble gas of the same period (krypton).

In this way, the Ge-Ge covalent bonds arise, and having four of them for each atom, surrounding tetrahedra are defined (with one Ge in the center and the others at the vertices). Thus, a three-dimensional network is established by the displacement of these tetrahedra along the covalent crystal; which behaves as if it were a huge molecule.

Allotropes

The covalent germanium crystal adopts the same face-centered cubic structure of diamond (and silicon). This allotrope is known as α-Ge. If the pressure increases to 120 kbar (about 118,000 atm), the crystal structure of α-Ge becomes body-centered tetragonal (BCT, for its acronym in English: Body-centered tetragonal).

These BCT crystals correspond to the second allotrope of germanium: β-Ge, where the Ge-Ge bonds are broken and arranged in isolation, as happens with metals. Thus, α-Ge is semi-metallic; while β-Ge is metallic.

Oxidation numbers

Germanium can either lose its four valence electrons, or gain four more to become isoelectronic with krypton.

When it loses electrons in its compounds, it is said to have numbers or positive oxidation states, in which the existence of cations with the same charges as these numbers is assumed. Among these we have the +2 (Ge ²⁺), the +3 (Ge ³⁺) and the +4 (Ge ⁴⁺).

For example, the following compounds have germanium with positive oxidation numbers: GeO (Ge ²⁺ O ^2-), GeTe (Ge ²⁺ Te ^2-), Ge ₂ Cl ₆ (Ge ₂ ³⁺ Cl ₆ ^-), GeO ₂ (Ge ⁴⁺ O ₂ ^2-) and GeS ₂ (Ge ⁴⁺ S ₂ ^2-).

Whereas when it gains electrons in its compounds, it has negative oxidation numbers. Among them the most common is -4; that is, the existence of the Ge ^4- anion is assumed. In germanides this happens, and as examples of them we have Li ₄ Ge (Li ₄ ⁺ Ge ^4-) and Mg ₂ Ge (Mg ₂ ²⁺ Ge ^4-).

Where to find and obtaining

Sulfurous minerals

Argyrodite mineral sample, of low abundance but a unique ore for the extraction of germanium. Source: Rob Lavinsky, iRocks.com - CC-BY-SA-3.0

Germanium is a relatively rare element in the earth's crust. Few minerals contain an appreciable amount of it, among which we can mention: argyrodite (4Ag ₂ S · GeS ₂), germanite (7CuS · FeS · GeS ₂), briartite (Cu ₂ FeGeS ₄), renierite and canfieldite.

They all have something in common: they are sulfur or sulfurous minerals. Therefore, germanium predominates in nature (or at least here on Earth), like GeS ₂ and not GeO ₂ (in contrast to its widely spread SiO ₂ counterpart, silica).

In addition to the minerals mentioned above, germanium has also been found to be found in mass concentrations of 0.3% in carbon deposits. Likewise, some microorganisms can process it to generate small amounts of GeH ₂ (CH ₃) ₂ and GeH ₃ (CH ₃), which end up being displaced towards rivers and seas.

Germanium is a by-product of the processing of metals such as zinc and copper. To obtain it, it must undergo a series of chemical reactions to reduce its sulfur to the corresponding metal; that is, to remove GeS ₂ its sulfur atoms so that it is simply Ge.

Toasted

Sulfur minerals undergo a roasting process in which they are heated together with the air for oxidations to occur:

GeS ₂ + 3 O ₂ → GeO ₂ + 2 SO ₂

To separate the germanium from the residue, it is transformed into its respective chloride, which can be distilled:

GeO ₂ + 4 HCl → GeCl ₄ + 2 H ₂ O

GeO ₂ + 2 Cl ₂ → GeCl ₄ + O ₂

As can be seen, the transformation can be carried out using hydrochloric acid or chlorine gas. The GeCl ₄ is then hydrolyzed back to GeO ₂, whereby it precipitates as an off-white solid. Finally, the oxide reacts with hydrogen to reduce to metallic germanium:

GeO ₂ + 2 H ₂ → Ge + 2 H ₂ O

Reduction that can also be done with charcoal:

GeO ₂ + C → Ge + CO ₂

The germanium obtained consists of a powder that is molded or tamped into metal bars, from which radiant germanium crystals can be grown.

Isotopes

Germanium does not possess any highly abundant isotope in nature. Instead, it has five isotopes whose abundances are relatively low: ⁷⁰ Ge (20.52%), ⁷² Ge (27.45%), ⁷³ Ge (7.76%), ⁷⁴ Ge (36.7%) and ⁷⁶ Ge (7.75%). Note that the atomic weight is 72.630 u, which averages all the atomic masses with the respective abundances of the isotopes.

The ⁷⁶ Ge isotope is actually radioactive; but its half-life is so long (t _1/2 = 1.78 × 10 ²¹ years) that it is practically among the five most stable isotopes of germanium. Other radioisotopes, such as ⁶⁸ Ge and ⁷¹ Ge, both synthetic, have shorter half-lives (270.95 days and 11.3 days, respectively).

Risks

Elemental and inorganic germanium

The environmental risks to germanium are a bit controversial. Being a slightly heavy metal, a propagation of its ions from water-soluble salts could inflict damage on the ecosystem; that is, animals and plants can be affected by consuming Ge ³⁺ ions.

Elemental germanium is safe as long as it is not powdered. If it is in dust, a current of air can carry it to sources of heat or highly oxidizing substances; and consequently there is a risk of fire or explosion. Also, its crystals can end up in the lungs or eyes, causing severe irritations.

A person can safely handle a germanium disk in his office without worrying about any accident. However, the same cannot be said for its inorganic compounds; that is, its salts, oxides and hydrides. For example, GeH ₄ or Germanic (analogous to CH ₄ and SiH ₄), is a quite irritating and flammable gas.

Organic germanium

Now there are organic sources of germanium; Among them, mention may be made of 2-carboxyethylgermasquioxane or germanium-132, an alternative supplement known to treat certain ailments; although with evidences put in doubt.

Some of the medicinal effects attributed to germanium-132 is to strengthen the immune system, thus helping to fight cancer, HIV and AIDS; regulates the functions of the body, as well as improves the degree of oxygenation in the blood, eliminates free radicals; and it also cures arthritis, glaucoma and heart disease.

However, organic germanium has been linked to serious damage to the kidneys, liver and nervous system. That is why there is a latent risk when it comes to consuming this germanium supplement; Well, although there are those who consider it a miracle cure, there are others who warn that it does not offer any scientifically proven benefit.

Applications

Infrared optics

Some infrared radiation sensors are made of germanium or its alloys. Source: Adafruit Industries via Flickr.

Germanium is transparent to infrared radiation; that is, they can pass through it without being absorbed.

Thanks to this, germanium glasses and lenses have been built for infrared optical devices; for example, coupled with an IR detector for spectroscopic analysis, in lenses used in far-infrared space telescopes to study the most distant stars in the Universe, or in light and temperature sensors.

Infrared radiation is associated with molecular vibrations or heat sources; so the devices used in the military industry to view night vision targets have components made of germanium.

Semiconductor material

Germanium diodes encapsulated in glass and used in the 60s and 70s. Source: Rolf Süssbrich

Germanium as a semiconductor metalloid has been used to build transistors, electrical circuits, light-emitting diodes, and microchips. In the latter, germanium-silicon alloys, and even germanium, by itself have begun to replace silicon, so that ever smaller and more powerful circuits can be designed.

Its oxide, GeO ₂, due to its high refractive index, is added to glasses so that they can be used in microscopy, wide-angle objectives and fiber optics.

Germanium has not only come to replace silicon in certain electronic applications, but can also be coupled with gallium arsenide (GaAs). Thus, this metalloid is also present in solar panels.

Catalysts

GeO ₂ has been used as a catalyst for polymerization reactions; for example, in the one necessary for the synthesis of polyethylene terephthalate, a plastic with which shiny bottles sold in Japan are made.

Likewise, the nanoparticles of their platinum alloys catalyze redox reactions where they involve the formation of hydrogen gas, making these voltaic cells more effective.

Alloys

Finally, it has been mentioned that there are Ge-Si and Ge-Pt alloys. In addition to this, its Ge atoms can be added to the crystals of other metals, such as silver, gold, copper and beryllium. These alloys show greater ductility and chemical resistance than their individual metals.

References

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