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Drill & Blast

Articles from EDUCATION & TRAINING (289 Articles), BLASTING & EXPLOSIVES (147 Articles), BLAST MONITORING (120 Articles)

Figure 1. Sensitised Rioflex.
Figure 1. Sensitised Rioflex.
 











Watergel or emulsion: Which is the better bulk explosive?

In the battle between water gels and emulsions for the perfect bulk explosive, Brent Buffham explains that Maxam’s Rioflex variable density product is the best compromise.
The history of commercial explosives is relatively short. Only 140 years ago, the world was restricted to black powder and nitro-glycerine based explosives. In today’s world of resource extraction, there is an explosive for the majority of situations and applications. However, what does this mean for the user? It means choice, and with choice comes compromise - between explosive performance and cost. Is there a “perfect” explosive for your needs?

Figure 2. Unsensitised Rioflex.
Figure 2. Unsensitised Rioflex.
The explosive supply and manufacturing industry is the same as any other commercial entity that provides something for sale. The saleability of a product is based on the raw materials cost, its availability, the technology available, manufacturing costs as well as transport versus the possible returns from the sale of the product. Consider if the price of corn was raised to the same value as that of gold; we as consumers would see corn flakes disappear from our supermarket shelves overnight.

The cost of manufacturing corn flakes would negate the returns achievable. The same is true for explosives, as is the adage of “getting what you pay for”. We all want a bargain but at what cost? With explosives, that cost is available useable energy!

Many companies in the explosive industry tailor their products to suit their resources and their market. Traditionally Maxam supplies to the quarry and smaller mines in Australia and Rioflex produces exceptional results for these consumers. This robust and reliable product has seen Maxam’s quarry market share grow.

Figure 3. HDAN at 20x magnification.
Figure 3. HDAN at 20x magnification.
Rioflex, Maxam’s bulk variable density product, is placed in the category of an ammonium nitrate suspension gel. This essentially means that Rioflex is a watergel in the traditional sense. However, the watergels of yesteryear are not the same as the Rioflex matrixes of today.

Emulsions, when they first arrived on the market were hailed as the “future of explosives”, and statements and papers were produced to support the technology change. The use of electron microscopes to show the intimacy between oxidiser and fuel produced undeniably great imagery. The measurements of oxidisers in a 100 per cent emulsion phase were compared to the size of oxidisers in slurries (watergels) from the 1990s. Various companies used this as evidence that the product would have a higher velocity of detonation and therefore be a better and more advanced technology.

However, the situation in the early days of emulsion development is likely not to be as relevant to how emulsions are made in today’s market. Cost, as mentioned before, is the driving force in how products are made and marketed. Emulsions are traditionally aimed at large diameter blast hole markets in large scale mines where single blasts can consume 500 plus tonnes of bulk explosives. Although clientele now want the best deal, they remain oblivious to the rising cost of production and development of blasting products.

Thus, the key for an emulsion supplier is to make the emulsion based explosive cheaper, which is likely the reverse of the reason for their development in the first place. To do this water may be added, resulting in less energy.

Slurries or watergels get their name from being partially composed of water and containing long carbon chain molecules that are cross-linked to a gelled, semi-solid state. Thus the name “watergel”. Emulsions were derived to take the energy thief “water” out of the gel. With the expanding oil market, copious oil derivatives were produced and emulsions became cheaper to manufacture. Then the emulsion phase needed the addition of explosive grade ammonium nitrate prill (PPAN), this process is called doping.


The most common and cheapest water resistant bulk explosive is a 70 per cent emulsion with a 30 per cent ammonium nitrate dope. What the explosive suppliers realised is that emulsions needed to be made with water as well to make them more cost-effective, as water is a low cost additive. The gain of liquidising the oxidisers for intimacy is soon reduced by the addition of ammonium nitrate prill and the introduction of water to the emulsion phase. The ultimate energy thief for an explosive is water!

Therefore, to make high energy explosives, water content must be reduced. Water provides no energy to the bulk explosive when detonated. Water’s vaporisation essentially steals energy. In order to heat one kilogram of water to vaporisation, a whopping 2256 kilojoules per kilogram of energy is required. Well, now we are completely confused! Watergels have water and emulsions have water, so how is one better than the other?

Rioflex is not your usual watergel. It is made with high grade and refined short carbon chain fuels. This fuel is nitrated and normalised and along with this, ammonium nitrate is dissolved into the solution making the base suspension media of the matrix. Contrary to popular articles on watergels, water content amounts to less than 13 per cent of the final mix.

The suspension media has more ammonium nitrate prill, either high density prill or porous explosive grade, added. However, not before it is crushed and made angular. This crushing process takes the previously round ammonium nitrate and increases the surface to mass ratio and therefore drastically increases the reaction speed and in turn the velocity of detonation of the bulk product.

At this point, a very small percentage of water has been added, so where does this watergel get its name? Maybe it’s the same as when horses used to roam the streets? They weren’t called streets, they were called carriageways. Now we have dual carriageways but no horses and carts! We have watergels with less water than emulsions.

Figure 4. HDAN at 360x magnification, showing smooth edge of the prill.
Figure 4. HDAN at 360x magnification, showing smooth edge of the prill.
This is where the water plays its part in protecting and stabilising the product. The carbon chains used in gelling are long and they are all ravelled up into a little ball. They require a medium to be suspended in so that they can unravel, this is through hydration. 

In order to do this Maxam uses a small amount of water to suspend the fuel and oxidiser, and that is it. Of all the explosive phases or matrixes on the Australian explosive market, Rioflex has the least water content. Other manufacturers in the Australian market may add up to 23 per cent water to the emulsion phases of their bulk products.

It is important to understand that emulsions of any type, explosives or not, use a chemical (emulsifier) to blend two or more immiscible (non-blendable) liquids together. As emulsions in terms of explosives are waxes, oils and oxidisers in water, they have to be over-fuelled in general terms to reduce noxious fumes of nitrous oxide when doped with ammonium nitrate.

Rioflex is perfectly formulated to ensure a near neutral oxygen-fuel balance that, along with the intimate encapsulation of highly angular ammonium nitrate, produces the optimal base matrix.

The gain that the industry achieves with emulsion phase explosives creates a false economy, robbing Peter (energy) to pay Paul (procurement). What many explosive users understand is what you spend on drill and blast results in improved production in the pit as well as through the crusher or mill in orders of magnitudes. So to answer a question that was posed earlier: “Is there a perfect explosive for your needs?” The answer is yes!

Brent Buffham is the technical manager for Maxam.

Figure 5. PPAN at 19x magnification.
Figure 5. PPAN at 19x magnification.
Figure 6. PPAN at 360x magnification, showing the rough edge of the prill.
Figure 6. PPAN at 360x magnification, showing the rough edge of the prill.
Figure 7. HDAN post crushing at 21x magnification.
Figure 7. HDAN post crushing at 21x magnification.

Figure 8. HDAN at 360x magnification post-crushing.
Figure 8. HDAN at 360x magnification post-crushing.
Figure 9. PPAN at 21x magnification post-crushing.
Figure 9. PPAN at 21x magnification post-crushing.
Figure 10. PPAN at 360x magnification post-crushing.
Figure 10. PPAN at 360x magnification post-crushing.



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Tuesday, 25 September, 2018 01:42pm
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