Free «A Brief History of Chemical Explosives: Types and Characteristics» Essay
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The study of the history of chemical explosives may help every scientist and engineer to create a broader and more correct view of the laws of explosives’ development and their place among other sciences. An explosion is now one of the world’s most powerful sources of pulsed power loads on the various objects of nature and technology. It means an extremely rapid release of energy in a small space with the active zone, which leads to compaction, displacement, and destruction of the surrounding area. Even putting aside physics, every man has a clear idea of what explosion is at least visually. However, it took humanity centuries to understand the nature of an explosion and put the destructive force on the right track. Gunpowder, dynamite, and TNT marked the turning point in the history of chemical explosives.
In ancient times, namely the 7th century BC, someone in the Byzantine Empire invented the so-called ‘Greek fire,’ which represented an incendiary mixture of potassium nitrate, sulfur, and oil (Partington, 2009). It was designed to destroy enemy ships and forts. An ignition of this mixture in the closed metal vessel led to a sharp pressure increase with the rapid combustion and formation of hot gases. The pressure allowed throwing flames through a narrow opening in a vessel over long distances.
Before this invention, people of that period already knew that, for example, a wood impregnated with an aqueous solution of potassium nitrate and ignited in the air will continue to burn under water. This phenomenon was widely used by swimmers and treasure hunters. Much later, the chemists found that the process of burning was conditioned by the decomposition of potassium nitrate and the release of oxygen necessary to maintain a burning of wood under water.
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Subsequently, the crushing of potassium nitrate and such combustible materials as sulfur and charcoal allowed creating black powder or gunpowder, which became the first chemical explosive in the history. It is believed that the inventor of this powder is a Chinese medical scientist Sun Simiao (Deng & Wang, 2011). He made this explosive material from sulfur, potassium nitrate, and charcoal mixed in a certain proportion. Although the Chinese people were unable to explain scientifically the explosive chemical reaction, they soon started to use gunpowder in combat. It is known that the Chinese used black powder in the 11th century in hand grenades and incendiary bombs, launched towards the enemy by a catapult. In the 12th century, the Chinese used black powder as an inner warhead and began to make powerful explosive bombs with thick hulls made of cast iron and filled with shrapnel. The Chinese army actively used gunpowder as a chemical explosive in the defense of Beijing from the onslaught of the Mongol armies of Genghis Khan in 1226.
There is no exact information about the way gunpowder got to Europe. On the one hand, modern historians believe that black powder got to Central Asia at first, and then – to the European part of the continent along the Silk Road. On the other hand, gunpowder was most likely invented in several places simultaneously. In the 13th century, Roger Bacon described the exact composition of the black powder in his treatise ‘Epistolae de Secretis Operibus.’ He indicated that one needs seven parts of potassium nitrate, five parts of carbon, and five parts of sulfur to produce black powder (Partington, 2009). Potassium nitrate acted as an oxidant. Coal was needed as the primary fuel. Sulfur was a cementing substance that it reduced the hygroscopicity of gunpowder and facilitated its ignition. Oxygen released potassium nitrate when it heats up, so coal was burnt extremely fast.
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Scientists carried out attempts to improve the quality of gunpowder constantly. Finally, at the end of the 18th century, the French scientists Lavoisier and Berthelot found the optimal composition of black powder, which remained almost unchanged up to the present time – 75% saltpeter, 10% sulfur, and 15% carbon. At the same time, gunpowder ceased to meet the growing demands on the increase in destructive power, sensitivity to initiation, and combustion rate. Therefore, the creation of a new and more powerful explosive material became a matter of urgency.
The new compounds enormous destructive power were found in the 19th century. In 1838, the French chemist Theophile-Jules Pelouze conducted the first experiments on the nitration of organic substances. The essence of this reaction was that many carbonaceous materials release hydrogen when treated with a mixture of concentrated nitric and sulfuric acids (Seymour, 2012). Then, these materials take an NO2 nitro group and transform into a powerful explosive. The German chemist Christian Schönbein applied nitration to the cotton wool and found pyroxyline, which is used for the production of smokeless powder (Seymour, 2012).
Later, in 1847, the Italian chemist Ascanio Sobrero worked in the same way with glycerin. The result of the experiment was the invention of nitroglycerin. This substance could explode at the slightest shock or heat. The explosion of nitroglycerin decomposes it to CO2, CO, H2, CH4, N2, and NO (Bettelheim, Brown, Campbell, Farell, & Torres, 2015). The gases interact with each other, releasing a huge amount of heat. After heating to very high temperatures, these gases rapidly expand and exert tremendous pressure on the environment. This explains the enormous explosive force of nitroglycerine. The latter would seem a perfect replacement to gunpowder. However, the storage and transportation of this compound were associated with extreme danger. It was clear that the reduction of sensitivity to detonation is necessary for the successful use of nitroglycerin (Bettelheim et al., 2015).
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Alfred Nobel was the first who managed to do this. He found that the resistance to detonation increases if nitroglycerine is dissolved in alcohol. Nevertheless, the required safety was not achieved, and the problem was resolved only when Nobel impregnated the porous natural absorbent material diatomite with nitroglycerin, preserving its explosive properties at the same time. In this state, it did not explode by neither weak hit nor burning. However, the ignition of a small amount of mercury fulminate in the metal cap caused an explosion of the same force as the same amount of pure nitroglycerine did (Bettelheim et al., 2015). Dynamite immediately found wide application in the construction of highways, tunnels, canals, and railroads.
During World War I, dynamite was used in the blasting work and the production of shells. In some countries, it was used during World War II and after it in mines and quarries up to the 60s of the 20th century (Bettelheim et al., 2015). Nevertheless, its use was fraught with danger despite the best efforts of Nobel. The sensitivity of dynamite to detonation increased sharply at low temperatures. In some cases, it led to the rupture of the shells in the barrel. At high temperatures and insufficient tightness of the projectile body, nitroglycerin began to separate from diatomite and flow out, leading to explosions of shells storage sites. This often occurred due to a violation of production technology.
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The manufacture of dynamite was finally stopped in the 1970s. Today, it is a very important milestone in the history of explosives. TNT became the substance which replaced dynamite.
A German chemist, Julius Wilbrand, prepared trinitrotoluene or simply TNT for the first time in 1863, but no actual usage have been conducted beyond laboratory experiments (Krehl, 2009). At that time, many chemical explosives had various disadvantages but greater explosive force than TNT. Its potential as an explosive was not appreciated for several years mainly because it was so difficult to detonate since it was less powerful than alternatives. For example, hexogen was much more sensitive to detonation, while melinite was very toxic and reacted with metals (Krehl, 2009). Manufacturers began to make mechanical mixtures based on TNT to combine the advantages of various explosives and neutralize their weaknesses. The mixture of trinitrotoluene with hexogen lowered sensitivity of the latter, while the mixture with ammonium-based explosives increased their explosive properties, enhanced chemical resistance, and reduced the absorbability (Akhavan, 2011).
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Pure TNT has almost fallen into disuse because mechanical TNT mixtures with other substances began to get more and more popularity. At first, it was replaced by an explosive called torpex, which was a mix of TNT, RDX, and aluminum. One of the most powerful chemical explosives – HMX – was then developed. It is commonly used in combination with TNT. The most common mixture comprises of 70% HMX and 30% TNT (Krehl, 2009).
TNT ignites only at temperature 2900°C (Akhavan, 2011). Thus, one can melt it and give it any shape or fill any container and the cavity of ammunition in particular. Pressed TNT is easily machined. It is possible to cut, rasp, and drill it. TNT is very chemically inert, it does not react with metals, and does not react with water. Even when it ignited, TNT does not explode but burns with a yellow smoky flame. Long-term (60 to 70 years) stay in the water, land, or ammunition does not change the explosive properties of trinitrotoluene (Akhavan, 2011).
TNT is prepared by nitration of toluene, which is a hydrocarbon with the formula C6H5CH3. It is a colorless volatile liquid with a pungent odor. Toluene is a waste product of oil processing and the preparation of coke. A mixture of toluene is nitrated with nitric acid and sulfuric acid in a special process for the manufacture of TNT. Upon completion of the nitration and purification process, TNT takes the form of a yellow crystalline solid (Akhavan, 2011).
Trinitrotoluene was removed from the mass production in the last decade of the previous century. Until that time, it was the most popular explosive in most countries. Moreover, the ton of TNT is the unit of quantifying the energy released in explosions. Trinitrotoluene became so widespread due to chemical stability, insensitivity to almost all external influence, the reliability of activation, as well as safety in production and use.
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Gunpowder, dynamite, and TNT are the most important phases of the explosives history. No invention based on chemical processes had greater potential to affect the human development than chemical explosives. The invention of gunpowder, dynamite, and trinitrotoluene marked a new era in the history of humankind. Many scientists faced the greatest difficulties trying to improve the efficiency of the explosion, the levels of mechanization and the safety processes during the manufacture and use of explosives. The historical path of development of chemical explosives was driven by diligence to combine these three essential requirements. Although gunpowder, dynamite, and TNT are not used in their pure form now, they are an important landmark in the history of chemical explosive materials.