We continue our discussion from late last year with our review of some of the most important materials in heat treatment and metallurgy.

Nitrogen (Chemical symbol: N)  

The Scottish physician Daniel Rutherford discovered nitrogen in 1772. He removed oxygen and carbon dioxide from air and showed that the residual gas (nitrogen) would not support combustion or living organisms. Nitrogen is the fifth most abundant element in the universe and makes up about 78% of the earth's atmosphere, which contains an estimated 4,000 trillion tons of the gas. Nitrogen gas (N2) is odorless and colorless.

Indispensable for life on earth, nitrogen is one of the 17 elements that are essential to plant growth and one of the three macronutrients needed in large quantities. Nitrogen must be changed into the form of ammonia or other nitrogen compounds before plants can use it effectively. Fertilizers containing nitrogen compounds are used to accelerate plant growth. Nitrogen is absorbed by roots from the soil as either nitrate or ammonium. It is then used in the leaves for producing chlorophyll, which is the pigment that gives leaves their green color and allows photosynthesis.

Nitrogen is one of the most common inert gases used in industrial processes due to its low reactivity, abundance and low cost. Although largely inert, it is not a truly inert noble gas like helium or argon. Nitrogen gas is used as a protective shield in the semiconductor industry and during certain welding and soldering operations. It is also a protective atmosphere to reduce oxidation of parts heated in industrial furnaces. High-pressure nitrogen is used by oil companies to force crude oil to the surface. Liquid nitrogen is a cryogenic liquid used for refrigeration, preservation of biological samples and for low-temperature scientific experimentation. It is also used to quickly freeze foods and help preserve their flavor, texture and moisture. Nitrogen compounds are found in foods, fertilizers, poisons and explosives. The human body is 3% nitrogen, which is a component of all proteins.

Nitrogen gas is obtained from liquefied air through a process known as fractional distillation. About 150 tons of ammonia is produced every year using the Haber process, which combines nitrogen from the air with hydrogen derived from natural gas to form ammonia.

Ironically, considering nitrogen's inert qualities as a gas, it forms extremely combustible compounds when combined with hydrogen and oxygen. As a result, ammonium-nitrate fertilizer is dangerously explosive. The explosion at the West Fertilizer Company factory in the town of West, Texas, in 2013 killed five people and injured over 150. At least 50 homes were damaged. Over 60 years earlier, in 1947 in Texas City, Texas, a ship carrying 2,300 tons of ammonium nitrate fertilizer caught fire and exploded, setting off a chain reaction that killed nearly 600 people. It has been called the worst industrial accident in U.S. history.

Here are a few important facts about nitrogen:

Atomic mass = 14.0067

Density = 1.25 gm/L

Group = diatomic nonmetal

Melting point = 63.15 K

Boiling point = 77.34 K