Explosives

Explosives Explosives, highly exothermic chemical reactions that produce expanding gases were first made by Asian alchemists more than one thousand years ago when they discovered mixtures of saltpeter (KNO3) and sulfur could be detonated. Explosives are classified as:
1. Primary (Initiators): Do not burn but detonate if ignited (mercury fulminate).
2. Low (Propellants): Burn at steady speed and detonated only under extreme conditions (gunpowder).
3. High: Release large amounts of energy when detonated (nitroglycerine).


Roger Bacon (1220-1292)
Born England, Bacon studied geometry/arithmetic/music/astronomy in France. Upon returning to England in 1247, Bacon became interested in science. His experiments using lenses/mirrors resemble modern scientific approaches. In 1257 Bacon left the University of Oxford and entered the Order of Friars Minor. His interests in the sciences continued and in 1266 Bacon wrote to Pope Clement IV proposing a science encyclopedia. Pope Clement IV misunderstood what Bacon was proposing and assumed the encyclopedia already existed. So when the Pope asked to see the encyclopedia, Bacon rapidly began work on the project. The project was carried out in secret since Bacon's superiors opposed what he was doing. Bacon hoped to demonstrate that science had a rightful role in the university curriculum. But In 1268 Pope Clement IV died along with Bacon's chance to see the project accepted (only parts of the manuscript were ever published).

What is the connection between Bacon and explosives? While composing the encyclopedia, Bacon became aware of the discovery by the Asian alchemists. This prompted Bacon to experiment with mixtures of saltpeter, sulfur, and a new ingredient (charcoal); Bacon had made black powder (the early form of gunpowder).
One hundred years later friar Berthold Shwarts looked into this black powder. Schwarts took a long iron tube and closed one end except for a tiny hole. He filled the tube with black powder and stuffed a small pebble in it. He touched a flame to the tiny hole and the pebble shot through the air with great speed. Schwarts had invented the "gun."

Nitroglycerin/Nitrocellulose

Five hundred years after Berthold Schwarts invented the gun, Ascano Sobrero (Italian) mixed nitric acid and glycerin to obtain nitroglycerine--an explosive so unstable that it could be detonated by the touch of a feather. One mole of nitroglycerine (227g) releases 1427 kJ upon exploding. It's volume increases from a liquid of approximately 1/4 L to gases occupying approximately 650 L.

In 1845, Christian Schoenbein made nitrocellulose (guncotton) by dipping cotton in a mixture of nitric and sulfuric acids. However, the material obtained was too unstable to be used as an explosive. Major E. Schultze (1860) of the Prussian army produced a useful propellant. He nitrated small pieces of wood by placing them in nitric acid and impregnated the pieces with barium and potassium nitrates. The purpose of the latter was to provide oxygen to burn the incompletely nitrated wood. Schultze's powder was highly successful in shotguns but was too fast for cannon or even most rifles. In 1884 a French chemist, Paul Vieille, made the first smokeless powder as it is now known. He partially dissolved nitrocellulose in a mixture of ether/alcohol, then he rolled it into sheets and cut into flakes. When the solvent evaporated, it left a hard, dense material. This product gave satisfactory results in all types of guns.


Alfred Nobel (1833-1896)
Alfred Nobel mixed nitroglycerin and silica (SiO2) forming a paste that could be safely used as an explosive--he patented this material as dynamite (1867). Nobel also invented the blasting cap to provide a safe and dependable means for detonating. Nobel's original blasting cap consisted of 80% mercury fulminate [Hg(ONC)2] and 20% potassium chlorate. Blsting caps today are lead azide [Pb(N3)2] due to its greater stability when stored under hot conditions.
A French newspaper--thinking Alfred and not his brother had died in 1886--ran his obituary under the headline, "The merchant of death is dead." Nobel, displeased that his inventions became an instrument of war, established the Nobel Prize in categories reflecting his interests (Chemistry, Physics, Medicine, Literature, Peace).

Ballistite
In 1887 Nobel introduced ballistite, 40% nitrocellulose/60% nitroglycerin blended together with diphenylamine. When cut into flakes, this made an excellent propellant and it continued in use for over 75 years. The British refused to recognize Nobel's patent and developed a number of similar products under the generic name cordite.


Cordite
Sir James Dewar (1842-1923) is best known for his work with low-temperature--he invented the thermos and produced both hydrogen and oxygen in liquid form. Along with Sir Frederick Abel, Dewar invented cordite (1889). This smokeless gunpowder consists of nitroglycerin, guncotton, and a petroleum substance gelatinized by addition of acetone.

Trinitrotoluene (TNT)
Trinitrotoluene is a high explosive that is unaffected by ordinary shocks and therefore must be set off by a detonator. TNT is often mixed with other explosives such as ammonium nitrate to form amatol. Because it is insensitive to shock and must be exploded with a detonator, it is the most favored explosive used in munitions and construction.
Why do nitro groups (NO2) lead to unstable compounds? Nitrogen has charge of +1 and nitro group have a strong tendency to withdraw (pull) electrons from other parts of the compound. Attaching three nitro groups to a compound leads to an extremely unstable situation.

Pentaerythritoltetranitrate (PETN)
PETN is a powerful high explosive with 140% the power of TNT. Because PETN is more sensitive to shock or friction than TNT, it is primarily used in small caliber ammunition.

Cyclotrimethylenetrinitramine (RDX)
Also called RDX, Cyclotrimethylenetrinitramine is a white crystalline solid usually used in mixtures with other explosives, oils, or waxes. RDX has a high degree of stability in storage and is considered the most powerful high explosive. RDX is the main ingredient in plastic explosives.

ANFO (Ammonium Nitrate Fertilizer)

Although ammonium nitrate (NH4NO3) is a benign fertilizer, when mixed with fuel oil it becomes a deadly bomb (ANFO). Dynamite or TNT are usually used to detonate ANFO (military manuals suggest using one pound of TNT for every fifty pounds of fertilizer). The deadly Oklahoma City Bomb was ANFO.

du Pont de Nemours (1771-1834)
DuPont is one of the oldest continuously operating industrial enterprises in the world. The company was established in 1802 near Wilmington, Delaware, by a French immigrant, Eleuthére Irénée du Pont de Nemours, to produce black powder. The company was capitalized at $36,000 with 18 shares* at $2000 each. du Pont de Nemours had been a student of Antoine Lavoisier, the father of modern chemistry, and he brought to America some new ideas about the manufacture of consistently reliable gun and blasting powder. Due to increasing competition in the early 1900s, DuPont made the transition from an explosives manufacturer to a diversified chemical company.