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The Chemistry of Explosives - Noor Zuhair

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Noor Zuhair

on 1 May 2015

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Transcript of The Chemistry of Explosives - Noor Zuhair

Safety
How to use explosives to Rock Blast in Mines
The Chemistry of Explosives
Rock Blasting
What are Explosives?
Types of Explosives used in Mining
The main explosives most commonly used in mines around the world are:

- ANFO (Ammonium Nitrate Fuel Oil ) often with TNT
- Primers / cast boosters
- Detonating cord
- Slurrry/ Water Gel Explosives
- Ammonium Nitrate Emulsion
- Detonators
An explosive is a substance, which when initiated, converts to gases at a rapid rate at a high pressure and temperature.

Rock blasting is the process by which explosives are used break down rock. Explosives are used as it eases and reduces the time to reach to the resources Mining companies are after.
References
Water gel explosives is one type of explosives used in many mines worldwide, as they are not as toxic nor as hazardous as explosives like dynamite to transport, store and manufacture. They tend to be quite safe and are not hard to use, and are often used in the mining industry. They are also often preferred use as they produce less noxious fumes.


Basic Classifications of Explosives
Why Mining Companies should use Explosives in excavation.
Using explosives during excavation is very important as it uses previous companies have noted the vast difference in using them as opposed to using older methods of excavation, as displayed in the graph below.
Explosive reactions need oxidation reactions in order to release energy. Therefore, the oxygen balance, which is how much oxygen is in the system, is directly related to the energy the explosion releases. More energy is released (due to a higher concentration of oxygen), as the oxygen balance nears 0.

Oxygen Balance Equation:
Oxygen Balance
OB% = -(100 %) * ((Molar Mass of O2) / (Molar Mass of Explosive)) *
( (2 * Moles of carbon) + (1/2 * Moles of Hydrogen) - (Moles of Oxygen))
Application:
Find the Oxygen Balance of TNT (Molar mass: 227 g/mol, C7H5N3O6)
OB% = -(100 %) * ((Molar Mass of O2) / (Molar Mass of Explosive)) * ( (2 * Moles of carbon) + (1/2 * Moles of Hydrogen) - (Moles of Oxygen))
OB% = -(100 %) * ((16) / (227.1)) * ( (2 * 7) + (1/2 * 5) - (6))
OB% of TNT = -74%
Given its low oxygen balance, TNT is often added to Ammonium nitrate (ANFO) which produces a balance of +20% to make the balance closer to zero, in order to create a more powerful explosive.
The following must be exhibted for a chemical to be considered an Explosive:

• Rapidty of reaction
• Production of heat
• Rapid expansion (of gases)
• Initiation of reaction

When molten ammonium nitration solution is sprayed, dense nitrate crystals are created. This causes the formation of spherical particles called ‘prills’. These are used together with nitroglycerine, and are non absorbent. To create an absorbent form of ammonium nitrate, 95% solution of hot ammonium nitrate is sprayed into a high tower.The spheres that form are dried and cooled to stop breakage while handling, and are then added to fuel oil.

Ammonium nitrate is one of the most cost effective sources of oxygen available for explosives. It is used alone, or with fuels or, to increase its efficiency further, with other fuels.
The injection of gaseous ammonia into 40-60% nitric acid at 150 °C, as depicted below,
How ANFO (Ammonium Nitrate Fuel Oil) is created
Nitration
Nitration makes up a major part of the preparation of explosives. It is a chemical reaction wherein nitro (NO) groups are added to organic compounds. It is primarily a substitution /double exchange reaction wherein 1 or more groups of the compound being nitrated are replaced by 1 or more groups of the NO groups of the nitrating agent.

The nitration reaction may be categorised into three classes as displayed by the next image.

Given WA’s abundant mining land with mines such as Collie Coal and The Super Pit, WA plays a major role in Australia’s mining industry. For this reason, we require the most up to date and effective facilities required to make use of our land's natural resources. Rock blasting is an essential part of excavating mining material, and given its dangers, good explosives are required as it is essential to abide by safety measures to successfully complete rock blasting. The first explosive to be used in the world was gunpowder, accidentally created by Chinese alchemists in 220BC. Since then, better explosives have been developed, with many different types now being used in many different fields, including the mining industry. This is particularly of interest to the mining industry as it makes up an essential part of their excavation process, where ‘Rock blasting’ occurs.
Many chemical reactions release energy, and are called exothermic reactions. In explosions, a large amount of energy can be accumulated into a rather small volume, then manifest itself by a hot gases rapidly expanding, which often pushes fragments out at a high speed.

Exothermic Reactions
Global mining explosives industry market 2015, finds new report. (2015, Feb 17). M2 Presswire Retrieved from: http://search.proquest.com/docview/1655505946?accountid=10382

Sir Thomas Oliver, M.D., LL.D. GLASG., D.SC., F.R.C.P. LOND. (PHYSICIAN TO THE ROYAL VICTORIA INFIRMARY, NEWCASTLE-UPON-TYNE.)
doi:10.1016/S0140-6736(00)78273-0

Konya, Calvin J. Walter, Edward J.. Rock Blasting and Overbreak Control - 1. (2010) Explosives Engineering. U.S. Department of Transportation.
Retrieved from:http://app.knovel.com/hotlink/pdf/id:kt008J9G14/rock-blasting-overbreak/explosives-engineering

Davis, Tenney Lombard. (1984). The Chemistry of Powder and Explosives. Hollywood, CA: Angriff Press.

Meyer, Rudolf, Josef Köhler, and Axel Homburg. (2007). Explosives. Weinheim: Wiley-VCH.

Akhavan, Jacqueline. RSC Paperbacks, (2004). Chemistry of Explosives. Cambridge, 35. Royal Society of Chemistry.

Australian Centre for Geomechanics (2012, Oct 23) Underground Drilling and Blasting Training DVD - ACG. Retrieved from:https://www.youtube.com/watch?v=G2Hs51QDszcTNT

Akhavan, Jacqueline. RSC Paperbacks, (2004). Chemistry of Explosives. Cambridge, 35. Royal Society of Chemistry. [Image] Retrieved from: http://site.ebrary.com.dbgw.lis.curtin.edu.au/lib/curtinuniv/reader.action?docID=10621221
There are many different types of explosives, and some are deemed too weak or too strong to be used in Rock Blasting in mines. Explosive reactions are exothermic reactions and therefore produce energy. Due to the rapidity of these reactions in a relatively small volume, a shockwave is created causing an explosion. Explosive reactions rely on oxidation reactions for their energy release. As a result, the oxygen balance is directly related to the energy released by the explosion. The closer the oxygen balance is to 0, the more energy will be released as a result of a higher oxygen concentration.
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