Argon

{ syn. }

0.336 %

{ syn. }

0.063 %

In traces

99.6 %

{ syn. }

{ syn. }

Attention

Argon is a chemical element with the symbol Ar ( until 1957 only A) and atomic number 18 in the periodic table it is in the 8 main group ( group 18) and therefore is one of the noble gases. Like the other noble gases, it is a colorless, extremely inactive, monatomic gas. In many properties, such as melting and boiling point or density, it is between the lighter neon and the heavier krypton.

Argon is the most common occurring on earth noble gas, the proportion of the atmosphere is about 0.934 %. This Argon is the third most common component of the Earth's atmosphere, after nitrogen and oxygen. This is largely due to the decomposition of the potassium isotope 40K, is formed in the 40Ar.

Argon was the first noble gas - was discovered on Earth - after the discovery of helium in the solar spectrum. It was founded in 1894 by Lord Rayleigh and William Ramsay found by fractional distillation of liquid air. Cheapest inert gas as argon is used in large quantities as a protective gas such as in welding and in the production of some metals, as well as a filling gas of incandescent lamps.

History

The first evidence for the later discovered argon was Henry Cavendish, the 1783 explored the reactivity of the air. He produced electric discharges in a given amount of air enriched with oxygen in a ratio of 5:3. Nitrogen, and oxygen react with each other, and the resulting nitrogen oxides could be washed out. It always remained a small residual non- reacted gas. Cavendish, however, did not realize that this is dealt to another element and did not continue his experiments.

After John William Strutt, 3rd Baron Rayleigh in 1892 had determined the density of nitrogen isolated from air, fell on him, that of ammonia -derived nitrogen having a lower density. There have been various speculations about this finding; so said James Dewar, it must, therefore, be a N3, a nitrogen analogue of ozone. Rayleigh repeated Cavendish's experiments, generated by electric sparks in an air-filled glass ball and as nitrogen and oxygen brought to reaction. After confirmation of Cavendish's result of an unreactive residue William Ramsay examined this in 1894 by passage over hot magnesium detail. Since magnesium reacts with nitrogen to nitride, he was able to escape the mixture further nitrogen. He found an increase in the density and finally found a previously unknown, inactive gas. On January 31, 1895 Ramsay and Rayleigh gave finally the discovery of new element known, that led them to the ancient Greek ἀργός, argos, " sluggish " called argon. When William Ramsay in 1898, the isolated from the air argon further investigated, he discovered it three more elements, the noble gases neon, krypton and xenon.

First technical applications found the gas in the electrical industry, in which, among other rectifiers were made on the basis of glow discharges in argon, which were based on " Tungar tubes ".

Occurrence

Argon is one of the more common elements in the universe, in its abundance, it is comparable to that of sulfur and aluminum. It is the third most abundant noble gas by helium and neon. It is the primordial argon, which is found approximately in the sun or gas planets like Jupiter, only the isotopes 36Ar and 38aR, while the third stable isotope 40Ar does not occur. The ratio of 36Ar to 38aR is about 5.7.

On Earth, argon, however, is the most abundant noble gas. It makes 0,934 % of the volume of the atmosphere ( without water vapor) and is thus controlled by nitrogen and oxygen the third most common atmospheric constituent. The composition of the terrestrial argon is considerably different from that of the primordial argon in the universe. It consists of more than 99% of the isotope 40Ar, which is caused by decomposition of the potassium isotope 40K. The primordial isotopes, however, are present only in small quantities.

Since the argon is produced by the decay of potassium in the earth's crust, it is also found in rocks. Upon melting of rocks in the mantle argon, but also formed during other decays helium is degassed. It therefore accumulates primarily in the basalts of the oceanic crust. From the rock, the argon is delivered to the ground. Therefore, in spring water, especially when it comes from a greater depth, argon solved.

Production and representation

The pure argon is exclusively from the air, usually in the context of air liquefaction in the Linde process. The argon is not isolated in the main rectification column of the process of the main components of air, but in a separate argon column. In the crude argon is produced by first rectification, which still contains about 3-5 % of oxygen and 1% nitrogen.

Subsequently, the crude argon is purified in further stages. The gas mixture is first warmed to room temperature and compressed to 4-6 bar. To remove residual oxygen and then hydrogen is injected responsive to noble metal catalysts with the oxygen to form water. After this has been removed, in a further column, the argon, which accumulates at the lower end of the column, separated from the rest of nitrogen, so that argon can be produced at a purity of 99.9999 %.

Other sources for the extraction of argon are the production of ammonia in the Haber- Bosch process and the synthesis gas production, such as for methanol production. In these methods, the use of air as a raw material to argon and other noble gases in the production process accumulate and can be isolated from the gas mixture. The different gases also be separated by adsorption or rectification of each other and thus obtained pure argon as the Linde process.

Properties

Physical Properties

Argon is a monatomic, colorless, odorless gas that condenses at 87.15 K ( -186 ° C) and 83.6 K ( -189.3 ° C) solidifies at normal conditions. Like the other noble gases except helium, argon crystallizes in a cubic closest packing of spheres with the lattice parameters a = 526 pm at 4 K.

Like all noble gases argon has only closed shells ( noble gas configuration ). This can be explained that the gas monatomic always present and the reactivity is low.

At a density of 1,784 kg/m3, at 0 ° C and 1013 hPa argon is heavier than air, so it drops. In the phase diagram of the triple point is at 83.8 bar and K 0.689, the critical point at 150,86 K 4896 kPa and a critical density of 0.536 g/cm3.

In water, argon is slightly soluble. In one liter of water can dissolve at 0 ° C and atmospheric pressure up to 5.6 g argon.

Chemical Properties

As a noble gas argon is very inert and reacts almost not with other elements or compounds. So far, only one experimentally shown neutral compound of argon known. It is the Argonfluorohydrid HArF, which could be identified by photolysis of hydrogen fluoride, which are obtained in an argon matrix at 7.5 K and the light of new lines in the infrared spectrum. Above 27 K it decomposes. According to theoretical calculations and some other compounds of argon should be metastable and relatively difficult to decompose. However, these were experimentally so far not been shown. Examples include the chlorine analog of Argonfluorohydrides HArCl, but also compounds in which the proton is replaced by other groups, such as organic FArCCH argon connection and FArSiF3 with an argon -silicon bond.

Argon is some clathrates, in which it is physically entrapped in the cavities of a surrounding crystal. At -183 ° C, an argon hydrate is stable, but the rate of formation is very slow as a recrystallization must take place. Is the ice mixed with chloroform, the clathrate forms already at -78 ° C. Stable is also a clathrate of argon in hydroquinone.

Isotopes

A total of 23 isotopes and another Kernisomer of argon are known. Of these three, namely the isotope 36Ar, 40Ar and 38aR, stable and occur in nature. This far outweighs 40Ar with a share of 99.6 % of the natural mixture of isotopes. 36Ar and 38aR are rare, with a share of 0.34 % and 0.06%. Of the unstable isotopes have 39Ar 42Ar with 269 years and 32.9 years, the longest half-lives. All other isotopes have short half-lives in the range of 20 ns at 30AR to 35.04 days at 37AR.

40Ar is used for determining the age of rocks (potassium - argon dating ). This makes use of that unstable 40K, which is included in this, slowly decays to 40Ar. The more potassium decays to argon, the older the rock. The short-lived isotope 41Ar can be used for checking gas lines. Through the passage of 41Ar the performance of a ventilation or tightness can be found a line.

→ List of argon isotopes

Biological Significance

Like the other noble gases Argon due to the inertness of no biological significance and is not toxic. In higher concentrations it has an asphyxiating by displacing oxygen. At pressures greater than 24 bar it acts narcotic effect.

Use

As advantageous and available in large quantities noble gas argon is used in many areas. The production in 1998 was about 2 x 109 m3 world. The largest part of the argon is used as the protective gas. It is always used when the cheaper nitrogen is not applicable. These include in particular the welding process for metals, which react with nitrogen at high temperatures, such as titanium, tantalum and tungsten. Even when Metallinertgasschweißen and tungsten inert gas welding, which is applied for example when welding aluminum alloys or high-alloy steels, argon is used as inert gas. Furthermore, it is used in metallurgy as a protective gas, for example for the production of titanium, high-purity silicon or the melting and refining process for degassing molten metal.

Argon is a food additive (E 938 ) and is used as a propellant and inert gas in the packaging of food and wine production.

Argon can be used for its suffocating effect as gaseous extinguishing agents. It is mainly used for object protection, especially in electrical and computer equipment. This is not a pure argon, but argon - nitrogen - carbon dioxide mixture ( Inergen ) is frequently used by the remains ensured the supply of oxygen to people during the flooding of a room and no interruption of deletion is necessary.

In analytical Argon is used as carrier and an inert gas for the gas chromatography, and the inductively coupled plasma (ICP-MS, ICP -OES).

Light bulbs are often filled with argon - nitrogen mixtures. One advantage is the low thermal conductivity of gas, which allows a higher anneal temperature and thus better light yield. Even in Argon gas discharge lamps used as light gas with a typical violet color. If some mercury added, the color changes into the blue. Argon is the laser medium, further in argon -ion lasers.

In the field of argon steel production has a particularly important role to play in the secondary metallurgy. With the argon purge, the steel alloy may be degassed, and at the same time homogenized, especially while the undesired dissolved nitrogen is removed from the melt.

When diving is argon - used to fill drysuits, or to tare it - particularly in the use of helium -containing trimix as a breathing gas. In this case, the low thermal conductivity of the gas is also used to delay the cooling of the suit.