Slurry and Emulsion Explosives

A mixture of AN and water forms a low-strength explosive referred to as a slurry or emulsion explosive. Since a mixture of AN and water cannot be detonated by initiation with a moderate detonation strength, to formulate practical slurry explosives nitrate esters such as monomethylamine nitrate, ethylene glycol mononitrate, or ethylamine mononitrate in conjunction with aluminum powder are added as sensitizers that facilitate the initiation of detonation. 

The major chemical components of emulsion explosives are fundamentally the same as those of slurry explosives, as shown in Table 9.4.[i l Instead of the sensitizers used for slurry explosives, a large number of hollow microspheres made of glass or plastics are incorporated to formulate emulsion explosives in order to obtain successive detonation propagation after the initiation of detonation. During detonation propagation into the interior of the explosives, an adiabatic compression results 

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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. 

Table 9.4 Typical chemical ingredients of slurry and emulsion explosives (mass %).

A suspected water gel is examined on a microscope slide to identify the microspheres used in slurry and emulsion explosives. The gel is directly extracted with methanol, which dissolves the amine salt, and a small amount of NH4NO3. TLC on a cellulose plate using a chloroform-methanol-water system separates the sensitizers. The plate is sprayed with ni-nhydrin and heated to visualize the amine salt. A second spray with diphenylamine in ethanol followed by long-wave UV irradiation visualizes the NFi4N03 if desired. Alternatively, the methanol extract may be evaporated to near dryness, redissolved in water, and analyzed by IC to identify the sensitizer. An intact sample can also be extracted with water using either a small homogenizer or ultrasonic agitation to disrupt the gel structure. Microspheres float on the surface and are removed for examination by SEM-EDX to characterize the manufacturer. Spot tests and IC identify ammonium, calcium, and nitrate ions in the water extract. Flake aluminum, if present, is identified as described above. 

Some generalized formulas for slurry and emulsion explosives are shown in Table 30.6. 

In the manufacture of explosives, sodium nitrate is used mainly in blasting agents. In slurries and emulsions, sodium nitrate improves stabiUty and sensitivity. It also improves the energy balance because sodium nitrate replaces water, so that more fuel can be added to the formulation. Sodium nitrate reduces crystal size of slurries, which in turn increases detonating speed. In dynamites sodium nitrate is used as an energy modifier. Typical content of sodium nitrate is 20—50 wt % in dynamites, 5—30 wt % in slurries, and 5—15 wt % in emulsions. Sodium nitrate is used also in permissible dynamites, a special type of dynamite for coal (qv) mining. 

Commercial industrial explosives such as dynamites, slurries, and emulsions are included in these categories because their major components, nitrate esters and nitrate and perchlorate salts, are listed. However, mixtures of fuels and oxygen or other gases that may be explosive at certain ratios are not covered, including the liquid oxygen explosives that saw limited application earlier in the 20th century. 

For mud-like ammonium nitrate explosives - Slurries and -< Emulsion Slurries. 

Details of the synthesis and larger-scale production of a number of molecular explosives including dynamites are given in the four-volume series by Urbanski Chemistry and Technology of Explosives Pergamon Press, 1964-84) and in various military books such as reference 8. Formulations of commercial slurries and emulsions generally are considered proprietary and are described mainly in the patent literature. Some specific... 

The emphasis of the explosives industry on safety in the manufacturing and handling of explosives has led to its being one of the safest industrial environments. A comparison of 1987 work injury rates for the explosives industry, for all industries, and for several selected industries is shown in Fig. 30.13. The data listed are OSHA recordable occupational injuries and illnesses per 100 employees as reported by the National Safety Council." The development of modern blasting agents and explosives, such as ANFO, slurries, and emulsions, that contain no self-explosive ingredients has further advanced safety of application, and has lowered costs and increased the options available to the consumer. The current level of R D effort is likely to continue this trend and also to lead to extension of this technology into military applications. 

Water-in-od emulsion explosives have been made as typified by a formulation containing 20% water, 12% oil, 2% microspheres, 1% emulsifier, and 65% ammonium nitrate. The micro droplets of an emulsion explosive offer the advantage of intimate contact between fuel and oxidizer, and tend to equal or outperform conventional water-based slurries. 

Being partly aqueous, slurry explosives are not inactivated by water or humidity, and they are essentially insensitive to mechanical shock or heat. The strength of detonation is approximately equal to that of NG-NC-based explosives. Since slurry explosives are composed of a mixture of aqueous AN and an oil, they exist as emulsions and hence are also termed emulsion explosives. 

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. 

Emulsions appear to have even a greater margin of safety than water gels and slurry explosives in impact sensitivity tests. When subjected to burning tests, emulsions generally do not detonate. As in the case of all explosives, however, results obtained from tests performed under controlled conditions do not guarantee that a given product will behave in a like manner in the field. Emulsion explosives must be handled and used with the same attention to safety afforded any explosive material. 

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

The latest significant development in industrial explosives actually was invented only a few years after slurries, but full commercialization has occurred only within about the last fifteen years. Water-in-oil emulsion explosives involve essentially the same ingredients that slurry composite explosives do, but in a different physical form. Aqueous solutions of oxidizer salts, primarily ammonium nitrate, are emulsified into a relatively small amount of oil and emulsifier. Because of oxygen-balance constraints the volume ratio of the two liquid phases is about 90 10 for the aqueous and oil phases, respectively. This... 

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