Understanding Emulsion Explosives

History of Emulsion Explosives

The history of emulsion explosives began in 1961 when Richard Egly and Albert Neckar of Commercial Solvents Corporation filed a patent application with the U.S. Patent Office for a blasting agent composed of a blend of a water-in-oil emulsion and a solid oxidizing agent such as ammonium nitrate. This was granted in 1964 as U.S. Patent 3,161,551. Rather than looking for a new type of explosive in the form of an emulsion, they were trying to make a waterproof ANFO. Subsequent developments in the 1960’s and early 1970’s resulted in emulsion explosives with explosive characteristics of minimum diameter and detonation rate comparable to the various grades of dynamite. In addition, emulsions were developed with characteristics which allowed their safe and efficient use in high-volume bulk loading systems.

ZMW’s Role in Emulsion Explosives

Charles Wade was the inventor of the first detonator sensitive and the first underground permissible emulsion explosive and several other emulsion and water gel explosives. This key emulsion explosives invention has resulted in significant improvements in blasting in tough, yet normal, wet condition resulting in enormous strides in faster and more efficient mineral extraction. This foundational invention is used worldwide and now emulsion explosives are the most common industrial explosive. Charles is credited has a number of inventions in the field of emulsion explosive compositions which form the basis of the following US Patents: 3,715,247; 3,765,964; 4,110,134; 4,149,916; 4,149,917; and 4,383,873. He was also the inventor of new technology for the metal salt catalysis of emulsion explosives. These patents have counterparts in many countries of the world.

Mike Cechanski was the inventor of the 1st commercially applied PIBSA based emulsifiers. Mike is highly skilled in emulsion explosives formulation, explosives chemistry and explosives safety, emulsion explosives plant design and commissioning, explosives safety, quality assurance, explosives packaging equipment and emulsion plant project management and construction. Mike also has numerous explosives related patents. PIBSA emulsifiers are the most efficient and the standard where high quality and stable emulsion explosives manufacturing is required.

Tom Zukovich has extensive expertise in emulsion explosives manufacturing systems, design, and construction and start up of new explosives production facilities. Tom designed, and managed the successful installation and start up of numerous emulsion explosives manufacturing plants. Tom is an expert for the design of emulsion explosives handling equipment, new processes for blending emulsions with other explosives and propellants, and new processes for packaging emulsion blends.

Bob Morhard has extensive expertise in emulsion explosives formulations manufacturing systems, design, and construction and start up of new explosives production facilities. He is also qualified in explosives safety, blasting applications, UN hazards testing and performance packaging design.

Emulsion Explosives Properties

Physical Form

An emulsion is an intimate mixture of two immiscible liquids with one liquid phase dispersed uniformly throughout the second phase. Emulsion explosives are dispersions of water solutions of oxidizers in an oil medium or “water-in-oil” emulsions. It is this unique structure and the high ratio of oxidizer to fuel that give emulsion explosives their special characteristics.

Oxidizer surrounded by fuel

The oil or fuel phase is known as the continuous or external phase because it surrounds and coats all of the oxidizer droplets.The fuel phase is generally oil or wax or a combination of the two. No. 2 diesel fuel oil (FO) is common to many emulsion explosives and certain other fuels are used in packaged emulsions explosives.

The water or oxidizer solution phase is called the discontinuous or internal phase because the microscopically fine droplets are kept apart and surrounded by the continuous fuel phase. The oxidizer phase always contains ammonium nitrate. Other salts such as sodium nitrate, calcium nitrate and ammonium may also be included.

The oxidizer remains dispersed in the fuel to form a stable emulsion through the action of a surfactant (emulsifier). For example, oil and vinegar are held together by egg yolks to form the emulsion known as mayonnaise. There are many different emulsifiers,and choosing which one to use depends on the particular requirements for the product. The emulsion formed from the fuel phase,oxidizer phase and emulsifier, before any addition of bulking agent, aluminum, or solid ammonium nitrate, is called the matrix and is the foundation for sub-sequent products.

The emulsion formed from the fuel phase, oxidizer phase and emulsifier, before any addition of bulking agent, aluminum, or solid ammonium nitrate, is called the matrix.

Structure

Because of the necessity to have close to zero oxygen balance,emulsion explosives need the volume of oxidizer to be much greater than the volume of fuel: the ratio is approximately 9 to 1. Because the relative volume of fuel is so much less than that of the oxidizer, it must be spread in a very thin layer in order to cover all of the oxidizer droplets. The size of the droplets is very small: and, due to the oxidizer/fuel ratio, the droplets are in the shape of many sided polyhedrons Droplets are usually in the range of 0.2-10 microns in diameter, or about 1 ⁄ 40th to 1 ⁄ 2000th the sizeof a grain of table salt.

Typical water-in-oil emulsion as seen under a microscope. Between each number is 50 microns. Each small division is 5 microns.

The rheology or viscosity of the emulsion is controlled by the nature of the fuel phase and the droplet size. The composition (wax, oil, emulsifier) of the full fuel phase has the greatest influence on the final viscosity of the product. Low viscosity oils, such as No. 2 diesel fuel, can be used to make pumpable emulsions. Waxes and high viscosity oils are used to make thick, putty-like packaged products. The droplet size is controlled by the amount of work put into the emulsion. The faster and longer it is stirred,the greater the work input and the smaller the droplet size and size distribution. The smaller the droplet size, the thicker the emulsion.

Typical water gel showing crystallization as seen under a microscope. Between each number is 50 microns. Each small division is 5 microns.

The first emulsion production at Red Bull Powder Company who licensed ZMW emulsion technology. Shown here (left to right) Tony Van Houtte,
Plant Manager - Red Bull Powder, Peter Shapiro, Managing Director - Red Bull Powder and Tom Zukovich, ZMW

(Photo courtesy of Red Bull Powder Company, Auckland, New Zealand)

Emulsion explosives may be pumped in ranges from 100 % emulsion though to heavy ANFO blends of approximately 60 % emulsion 40 % ANFO depending on hose, temperature and other factors.

(Photo courtesy of RedBull Company, Auckland, New Zealand)

Austin Powder Company has hundreds of Hydromite ™ bulk emulsion delivery trucks capable of pumping 100 % emulsion or auguring emulsion ANFO blends.

(Photo courtesy of Austin Powder Company, Cleveland, OH USA The emulsion bulk
body was designed to Austin Powder Company specifications and manufactured by Tread Corporation, Roanoke, VA USA)

Thermochemical Energy

The addition of aluminum or ANFO to an emulsion explosive can be used to increase its energy (cal/g). Aluminum does not significantly increase the sensitivity of emulsions, so a much coarser and less costly aluminum can be used rather than the high cost paintgrade aluminum used to attain sensitivity in some water gels.Theoretically, an addition of 5% aluminum will increase the energy of the emulsion by about 25-35%. Ten percent aluminum increases the energy by about 40-60%. Above 10% the addition of aluminum may not be cost effective.

ANFO added to emulsions can increase the energy by about 5% for every 10% increment added. ANFO also has the added advantage of producing only gaseous detonation products, and therefore, an increase in gas volume is also realized. An increase in gas volume usually leads to better heave and throw of the rock being blasted.

Red Bull Powder Company Red Star ™ bulk emulsion delivery trucks are capable of adding aluminum to the emulsion matrix and pumping 100 % emulsion or auguring emulsion ANFO blends, with or without aluminum.

(Photo courtesy of Red Bull Powder Company, Auckland, New Zealand)

The ratio of the amount of energy released to the calculated thermochemical energy is the measure of the efficiency of an explosive. Water gels generally have a liquid and a solid phase.They are generally made at elevated temperatures; as the product cools, oxidizer salt crystals begin to form. The colder the product becomes, the greater the tendency for crystals to form. The longer the product is stored,the larger the crystals become.The more crystals present and the larger they are, the more insensitive and less efficient the product becomes. The components are not intimately associated with one another because a relatively large amount of oxidizer surrounds a relatively small amount of fuel. In contrast, the increased intimacy between fuel and oxidizer in emulsions, and the very small particle size of the droplets, is believed to be responsible for the greater efficiency and enhanced detonation properties of these products. The emulsions are two phase systems. In order to have a suitable oxygen balance,only a very small amount of fuel is available to spread over each individual oxidizer droplet. This results in a very intimate mixture. Because there are so many oxidizer droplets and because they are so small,the oxidizer salts,regardless of temperature, will not easily crystallize and grow. Since the oxidizer salts remain in solution, the detonation properties of emulsion explosives remain unchanged for long periods of time and over wide temperature ranges.

Safety

Emulsions fail to detonate in impact and friction tests which have been standard to the explosive industry for years. When placed against a metal plate, the emulsions fail to detonate under the impact of a 30-06 projectile. Other high velocity impact tests with larger caliber projectiles show emulsions to have a greater resistance to initiation by impact than either water gels or dynamites. Normally, emulsion explosives will not detonate during burning, but there is no guarantee of this, particularly if the material is contaminated with foreign materials such as rust, detonators, dynamites or aluminum powders. When pumping emulsions, care must be taken so that the pump does not run dry or against a closed system (“deadhead”). In either case, friction can raise the temperature of the emulsion in the pump beyond the decomposition point of ammonium nitrate or other ingredients. If this happens, a detonation can occur. Remember, it can be just as hazardous to pump unsensitized emulsion oxidizers as it is to pump sensitized ones. Although tests have demonstrated that emulsions offer a great degree of safety, they will detonate if subjected to severe conditions. They are explosives, and regardless of their degree of safety, should never be abused.

Velocity

It is an established fact that the smaller the particle size of the ingredients of an explosive, the higher the velocity of detonation (VOD). Since the droplet size of emulsions is so fine, the VOD of explosive emulsions is very high - close to theoretical. The VOD does decrease somewhat as the charge diameter decreases or as solids such as aluminum or AN prills are added, but the VOD generally remains relatively high when compared to most water gels.

Detonation Pressure

Since emulsions have a high velocity of detonation and a reasonable density, they also have a relatively high detonation pressure. Emulsion detonation pressures measured by the “aquarium” technique are found to be between 100 and 120 Kbar/ (1.45 - 1.74 x 10⁶psi). As a result, emulsions are particularly well-suited for improving fragmentation in hard massive rock,for breaking hard bottom rock,and for use as a booster for ANFO mixtures and other blasting agents.

Sensitivity

Because emulsions have a very fine particle size and are an extremely intimate mixture of fuel and oxidizer, only a density reducing agent needs to be added to make them detonable. It is not necessary to use high explosives or chemical sensitizers for sensitivity. The density can be reduced by occluded air, chemically generated gas, perlite, expanded plastic, hollow glass or phenolic microspheres, or even AN prills. The sensitivity of the emulsions can be made to vary from that of a No. 8 strength detonator (or less) for a high explosive classification at 68F (-20C) to booster sensitivity for blasting agent 1.5D products. The emulsions are sensitive over a wide temperature range, and they also maintain their sensitivity over a wide range of diameters 22mm and up for “Explosive, Blasting, type E 1.1D” and 38mm and up for “Explosive, Blasting type E 1.5D”. Different density reducing agents are used for different reasons, but the glass microspheres are the most common, although chemical gassing is becoming popular. Because certain glass microspheres will withstand high pressures,they are especially useful in sensitizing emulsion products for use in deep boreholes or close borehole spacing where high hydrostatic or shock pressures are likely to be encountered. Generally, the lower the density of an emulsion explosive, the more sensitive it becomes. Also, the lower the water content of the emulsion explosive, the more sensitive it becomes. The water content of blasting agents is usually higher than that of 1.1D emulsions, but so is the density. This keeps the overall bulk strength energy level of blasting agents close to that of the high explosive emulsions.

Water Resistance

Water-in-oil emulsions have a continuous, water-immiscible oil phase and are extremely water resistant. They do not depend upon the integrity of the package for water resistance. Emulsions are a good choice when wet holes are encountered, because they will perform successfully after sleeping underwater for weeks or even months.

References

ISEE Blasters Handbook, 18 th Edition, 2010
Bampfield, Howard A. and Cooper, John, Encyclopedia of Emulsion Technology, Chapter 7,
Emulsion Explosives, Marcel Dekker, Inc., New York and Basel, 1988.
Bluhm, H.F., Ammonium Nitrate Emulsion Blasting Agent and Method of Preparing Same
U.S. Patent No. 3,447,978 Washington D.C., U.S. Patent Office, (June 1969).
Clay. R.B., Water Resistant Blasting Agent and Method of Use, U.S. Patent 4,181,546, Washington, D.C. U.S. Patent Office (Jan. 1980)
Egly; R.S. and Neckar, A.E.; Ammonium Nitrate-Containing Emulsion Sensitizers for Blasting Agents, U.S. Patent Office 3,161,551,Washington, D.C. Patent Office, (Dec. 1964).
Morhard, Robert C., Explosives and Rock Blasting, Atlas Powder Co., 1987.
Sudweeks, Walter B., IQEC Product Research & Development; Physical and Chemical
Properties of Industrial Slurry Explosives; 24, 432;American Chemical Society, 1985.
Van Ommeren, Catharine L., A Consumer’s Guide to Bulk Emulsions and Emulsion/ANFO Blends; Proceedings of the 15th Conference on Explosives and Blasting Technique, Feb. 5-10, 1989. Society of Explosives Engineers, pp 271-285.
Wade, C.G.,Water in Oil Emulsion Explosive Composition, U.S. Patent 4,110,134,Washington, D.C. U.S. Patent Office (Aug. 1978).

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