ANFO and Slurry Explosives

Picric acid [(trinitrophenol) (C6H3N307)] was found to be a suitable replacement for blackpowder in 1885 by Turpin, and in 1888 black-powder was replaced by picric acid in British munitions under the name Liddite. Picric acid is probably the earliest known nitrophenol it is mentioned in the alchemical writings of Glauber as early as 1742. In the second half of the 19th century, picric acid was widely used as a fast dye for silk and wool. It was not until 1830 that the possibility of using picric acid as an explosive was explored by Welter. 

Designolle and Brugere suggested that picrate salts could be used as a propellant, while in 1871, Abel proposed the use of ammonium picrate as an explosive. In 1873, Sprengel showed that picric acid could be detonated to an explosion and Turpin, utilizing these results, replaced blackpowder with picric acid for the filling of munition shells. In Russia, Panpushko prepared picric acid in 1894 and soon realized its potential as an explosive. Eventually, picric acid (1,2) was accepted all over the world as the basic explosive for military uses. 

Picric acid did have its problems in the presence of water it caused corrosion of the shells, its salts were quite sensitive and prone to acci- 

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Since then the use of LOX has declined greatly, as ANFO and Slurry Explosives began to replace them. An indication of the decline in the use.of LOX is given in the patent literature. For example, a 1936 review (Ref 8) lists 64 German patents on LOX. Undoubtedly by 1936 there were also many patents issued in the USA, UK and France. In the period of 1936—1960 a considerable number of patents on LOX is listed in CA. Some of these are abstracted in Section 5 below. Since 1960, however, the number of LOX patents has declined drastically. Almost none is listed in the most recent Quintennial Index of CA... 

In many ways slurries may be considered as intermediate between ANFO and nitroglycerine explosives. They are more expensive than ANFO but can be used in wet conditions they are often cheaper and safer than nitroglycerine explosives but are more critical of conditions of use if misfires are to be avoided. 

The table indicates that both.ANFO and slurries are excellent cratering explosives the effectiveness of which equals or exceeds TNT capabilities. Advantages are ease of field use, insensitivity to heat and shock — hence safe, voidless filling of holes, and low expense. Disadvantage is the need for a large booster charge for initiation... 

Table 19. Cratering Characteristics of ANFO, Slurry Explosives, and TNT ...

Inorganic oxidizers are widely used as blasting agents in mining and construction explosives and also in improvised explosive devices utilized by terrorists. Ammonium-nitrate-based explosives (e.g., ammonium nitrate and fuel oil — ANFO) have almost completely replaced the majority of dynamites. In addition, slurry and emulsion explosives, which contain mosdy ammonium nitrate and a small amount of other oxidizers, have become widely used. 

Ammonium nitrate (AN NH4NO3) is a white, crystalline material, the crystal structure of which varies with temperature.melting point is 442 K and its heat of fusion is 71.4 kj kg . Though the mass fraction of oxygen of AN is 0.5996, it is highly hygroscopic and absorbs moisture from the atmosphere to form liquid AN acid. This limits its application in propellants and pyrolants. However, AN is widely used as an oxidizer of explosives such as slurry explosives and ANFO (ammonium nitrate fuel oil) explosives. 

The physicochemical properties of explosives are fundamentally equivalent to those of propellants. Explosives are also made of energetic materials such as nitropolymers and composite materials composed of crystalline particles and polymeric materials. TNT, RDX, and HMX are typical energetic crystalline materials used as explosives. Furthermore, when ammonium nitrate (AN) particles are mixed with an oil, an energetic explosive named ANFO (ammonium nitrate fuel oil) is formed. AN with water is also an explosive, named slurry explosive, used in industrial and civil engineering. A difference between the materials used as explosives and propellants is not readily evident. Propellants can be detonated when they are subjected to excess heat energy or mechanical shock. Explosives can be deflagrated steadily without a detonation wave when they are gently heated without mechanical shock. 

R.A. Dick, The Impact of Blasting Agents and Slurries on Explosive Technology , 1C 8560, USBuMines (1972) [The shock sensitivity of ANFO (AN—fuel oil) compns increases rapidly as the AN particle size decreases. However, by compression to a density of approx 0.9g/cc, sensitivity is found to decrease and deton vel to increase]... 

Examples of very highly sensitive substances are mixture of chlorates-red phosphorus, paper cracker, lead azide, and DDNP. High sensitivity substances are dynamite(powder), PETN(powder), HMX(powder), RDX(powder), tetryKpowder), picric acid(powder), TNT(powder), and benzoyl peroxide (powder). Medium-sensitivity substances are the modem safety industrial explosives (slurry explosives, ammonium nitrate explosives), black powder, AIBN, and t-butyl-benzoate. Among low sensitivity substances are non-cap explosives dinitro benzene, dinitropentamethylenetetramine, ANFO, ammonium nitrate, nitromethane, dinitrotoluene, and cast TNT. 

One reason is that the sensitivities of dynamites were lower than those of the slurry explosives or ANFO. But one must be careful, even if insensitive slurry explosives or ANFO with detonators are misfired and remain, because impact accidents between drill bits and the explosives might still occur. 

Ammonium nitrate is the principal base material in slurry explosives and lower-cost blasting agents. It can be converted to an effective blasting agent by proper mixing with a carboniferous material such as fuel oil. Ammonium Nitrate/Fuel Oil (ANFO) mixtures are used extensively in open-pit mining and outdoor construction work because of ease of handling, availability, low cost, and safety. 

Blasting agents—explosive materials that cannot be initiated by a No. 8 Test Detonator when unconfined, but which will detonate with a stronger stimulus. Typical examples include ammonium nitrate/fuel oil (ANFO), blends, and certain emulsions, water gels, and slurries. ... 

Division 1.5—explosives that are very insensitive. Division 1.5 explosives have a mass explosion hazard but are very unlikely to initiate or detonate from burning under normal transportation conditions. Typical examples include blasting agents, ANFO, non cap-sensitive emulsions, blends, slurries, water gels, and other explosives that require a booster for initiation. 

Development of ANFO, Slurry, Emulsion and Blasting Explosives... 

Nevertheless ANFO had two significant limitations ammonium nitrate is very water-soluble, so wet boreholes readily deactivated the explosive and ANFO s low density of 0.85 g/cc limited its bulk explosive strength. Many attempts were made to waterproof the product and add densifying agents, but with only limited success. However, because of this effort the next advance in industrial explosives technology was made by the invention of slurry explosives. 

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