Argon . Chemical element with atomic number 18 and symbol Ar, renamed since 1959 , since its symbol was A. It is the third of the noble gases, colorless and inert like them. It constitutes 0.934% of dry air. Its name comes from the Greek αργος, which means inactive (because it does not react).
Summary
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- 1 History
- 2 Applications
- 3 Abundance and obtaining
- 4 Isotopes
- 5 Related Links
- 6 Reference
- 7 Sources
History
Henry Cavendish , in 1785 , exposed a Nitrogen sample to repeated electrical discharges in the presence of Oxygen to form Nitrogen Oxide which he subsequently removed and found that about 1% of the original gas could not be dissolved, stating then that not all ‘air phlogisticate ‘was nitrogen.
In 1892 Lord Rayleigh discovered that atmospheric nitrogen had a higher density than pure nitrogen obtained from nitro. Rayleigh and Sir William Ramsay demonstrated that the difference was due to the presence of a second, slightly reactive gas heavier than nitrogen, announcing the discovery of argon (from the Greek αργóν, inactive, vague or lazy) in 1894 , an announcement that was welcomed with quite skepticism by the scientific community.
In 1904 Rayleigh received the Nobel Prize in Physics for his investigations of the density of the most important gases and the discovery of the existence of argon.
Applications
It is used as a fill gas in incandescent lamps since it does not react with the filament material even at high temperature and pressure, thus prolonging the useful life of the bulb, and as a replacement for neon in fluorescent lamps when a green color is desired -blue instead of neon red . Also as a substitute for molecular nitrogen (N2) when it does not behave as an inert gas due to operating conditions.
In the industrial and scientific field, it is universally used in the recreation of inert (non-reactive) atmospheres to avoid unwanted chemical reactions in many operations:
- Arc welding and gas welding.
- Manufacture of titanium and other reactive elements.
- Manufacture of single crystals – cylindrical pieces formed by a continuous crystalline structure – of silicon and germanium for semiconductor components.
Argon-39 is used, among other applications, for the dating of ice cores, and groundwater (see the Isotopes section).
In technical diving, argon is used for the inflation of dry suits – those that prevent the contact of the skin with the water unlike the typical wet ones of neoprene – both because it is inert and because of its small thermal conductivity, which provides the Thermal insulation necessary for long dives to a certain depth.
The argon laser has medical uses in dentistry and ophthalmology ; the first intervention argon laser, by Francis L’Esperance , to treat retinopathy was conducted in February of 1968 .
Abundance and obtaining
The gas is obtained by means of the fractional distillation of liquefied air, in which it is found in a proportion of approximately 0.94%, and subsequent elimination of residual oxygen with hydrogen. The Martian atmosphere contains 1.6% Ar-40 and 5 pm Ar-36 .; that of Mercury 7.0% and that of Venus traces.
Isotopes
The main argon isotopes present on Earth are Ar-40 (99.6%), Ar-36 and Ar-38. The K-40 isotope, with a half-life of 1,205 × 109 years, decays, 11.2% to stable Ar-40 by electron capture and β + decay (emission of a positron), and the remaining 88.8% to Ca-40 by β- decay (emission of an electron). These disintegration ratios allow determining the age of rocks.
In the Earth’s atmosphere, Ar-39 is generated by cosmic ray bombardment mainly from Ar-40. In unexposed underground environments, it is produced by neutron capture of K-39 and α-decay of calcium. Ar-37, with a half-life of 35 days, is the product of the decay of Ca-40, the result of underground nuclear explosions.
