Inert Gases Uses and Application
Inert gases are gases which are chemically inactive, so will not undergo chemical reactions with many materials. Inert gases are used for many purposes in a wide range of industries - for example in welding, chemical processing, and as filler gases in light sources. You can use these gases to create inert atmospheres (such as within a glove box) where you can handle air sensitive materials and samples. You can also use inert gases to "blanket" samples, which is where you surround your material with an inert gas to prevent oxidization and prolong material lifetime. Blanketing is often used in the food industry, as well as in chemical storage.
The term inert gas is often used interchangeably with the term "noble" gases (helium, argon, xenon) - which refers to atoms in Group 18 of the periodic table. However, nitrogen gas (N2) is also very unreactive so is also considered an inert gas in many fields. The reactivity of an atom depends on its electronic configuration. Inert atoms or molecules have full outer orbitals. This means they have no free electrons or vacancies to interact with other molecules. Noble gas atoms have full outer electrons inherently. These atoms are therefore stable alone. Other atoms can form stable compounds by forming bonds with like atoms, such as nitrogen.
The choice of which inert gas is suitable for your application will depend on:
- What materials you are using (and will these react with any inert gases).
- The cost of the gas (which is related to its relative abundance).
- The levels of inertness you require in your environment (relates to the density and purity of gas you need).
The term noble gas refers to atoms that are in group 18 of the periodic table. These all exist as gases at standard temperature and pressure. These include:
These gases have full outer orbital layers, so they neither want to take electrons from or donate electrons to other atoms. This means they will not take part in chemical reactions, and it takes a large energy input to create molecules using these atoms. Noble gases are therefore optimum choices to use for inert processing conditions.
We have discussed helium and argon, as these are primarily used for their inert properties.
Helium is the simplest noble gas, holding only two electrons in one electronic orbital. This is a noble gas so it can be used to create an inert environment.
It is one of the most abundant gases in the universe, but only the 71st most abundant element on earth, with most of it being found under the Earth's crust. Helium is a lot less dense than most of the elements in the earth's atmosphere. Upon being released into the air, it will quickly escape terrestrial atmosphere into space. Helium liquifies at 4.18 K (or -268.97 ℃) so storage of liquid helium requires extremely low temperatures or high pressures.
One use of liquid helium is to cool certain materials enough so that they exhibit superconductivity. Submerging these materials in liquid helium basically eliminates all electrical resistance. Therefore, these superconductors can be used to create powerful magnets that can used in nuclear magnetic resonance (NMR) imaging.
The stability of helium makes it a good material to conduct air sensitive experiments in. However, due to the low abundance of helium on earth and the high temperatures/high pressures needed to store liquid helium, it is an expensive choice - especially for high purity helium. However, there are some materials which require this level of inertness - such as lithium. For example, helium glove boxes are sometimes used to conduct studies involving lithium batteries.
Argon has an atomic number of 18 and has an outer shell containing eight electrons. It is the 3rd most abundant gas on earth and is much heavier than helium.
Argon is most commonly used to process air sensitive materials. By filling a contained space with argon, air-sensitive compounds can be handled without reacting with the environment. Additionally, you can use solid argon to trap extremely air sensitive material within a solid matrix in order to study them. Argon is also used in combination with nitrogen in filament bulbs as it decreases burn out rate of the filament.
Argon is the most popular noble gas used in glove boxes. It is heavier than both nitrogen and helium, so will be the most effective inert gas at displacing air within a confined space. It will liquify at -186 ℃, so argon gas is cheaper than helium to store. However, it is significantly more expensive than using nitrogen gas as argon is much less abundant.
There are situations where it may be worth the extra money though, for example if you are working with very sensitive materials. Additionally, argon is a noble gas, unlike nitrogen. If you are working with materials that can react with nitrogen (such as lithium, magnesium, and calcium carbide) you may wish to use Argon gas. Also, for applications such as welding, nitrogen is not a great choice as it will become reactive in the presence of an electric arc.
Other Noble Gases
Noble gases are often used as a filler gas within arc or filament lamps. By surrounding light sources with noble gas, manufacturers can reduce the rate at which the filament burns, increasing lamp lifetime. The choice of noble gas used can change the colour of light that can be produced. Bulbs filled with neon for example will produce light with an orange-red colour, but you can change this emission with the use of phosphor additives. Xenon produces a nearly continuous spectrum that mimics sunlight well, so it is a popular choice for solar simulators. Noble gases can also be used to produce excimer lasers, especially in combination with halogens.
Nitrogen gas (in the form of N2) can also be used as an inert gas. It is the most abundant element in the Earth atmosphere, making up 78% of air. The nitrogen atom has an atomic number of 7, and has 5 electrons in its outer shell (3 short of being a full orbital). This makes the lone atom extremely reactive, therefore it quickly seeks to be in a more stable compound. Therefore, two nitrogen atoms form triple covalent bonds between them, sharing 6 electrons to make 3 covalent bonds. This gives both nitrogen atoms a full outer orbital, with a triple bond between them to secure it - in fact, this bond is one of the strongest bonds in chemistry and it requires large amounts of energy to break N2 molecules apart. Therefore, the N2 molecule is very stable N2 gas, and is almost as chemically unreactive as noble gases.
This inertness combined with its chemical abundance make nitrogen a popular choice for inert atmosphere processing. N2 gas is used in the food industry to prevent oxidation, prolonging sell-by-dates and reducing food rotting. It is also used in chemical processing to handle air-sensitive or hygroscopic materials.
Nitrogen gas is significantly cheaper than both argon and helium. It is therefore the most popular choice for inert atmosphere processing. However, as it is not a noble gas (meaning it doesn't have a full outer shell of electrons), there are a few situations where it is not appropriate. Nitrogen gas can react with some metals at high temperatures and can react with magnesium and lithium. However, for working with most organic materials, nitrogen will most likely be fine.
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