This invention relates to a slurry explosive composition for open cast mines and other excavation works and a process for making a slurry explosive from the said composition.
The slurry explosive made from the slurry explosive composition is expected to be a commercially viable product which will find wide usage for excavation particularly in open cast mines and also for other excavation works.
Nitroglycerine (NG) explosives are available for use in underground blasting and other rock excavation works. The velocity of detonation and detonation pressure are very high which causes safety problems. The density varies from 1.10 to 1.30 g/cm3. Reference may be made to the Encyclopedia of Explosives Vol. 9, pp T415. The NG based explosives are highly sensitive to impact and friction, thus there is increased danger during operation. The commercial NG- based explosives are going to be obsolete in India due to safety precaution.
In India large diameter cartridge explosives are available in 83mm, 125mm and 200mm with different weights of 2.76kg, 6.25 kg and 12.5kg respectively. These cartridge explosives are packed in the plastic tube with copper clip or blow molded tube. Reference may be made to: Engineering Index Annual -1993, Vol. 92, Part III, Development in explosives (050974). These are cap sensitive compositions and the velocity of detonation varies from 3000 to 4500 m/sec in unconfined condition.
The large diameter slurry explosives are the mixtures of oxidizers, fuels and sensitizer resulting high degree of sensitivity and velocity of detonation. The velocity of detonation in slurry compositions varies from in the range of 3000 - 4500m/s. These explosives have poor shelf life and high energy content that are suitable for blasting in hard rock. The use of these products in soft and medium hard rock is the wastes of explosive energy.
A survey of available literature provides a list of publications in various journals and seminars proceedings in blasting related areas :

(Table Removed)
A search of EPO and US patent databases for slurry explosive compositions reveals a number of patents. The details are as follows:
Reference maybe made to patent no.: GB1321731, wherein a slurry explosive composition comprises an inorganic oxygen-supplying salt, a solvent for the salt, a polysaccharide thickener, a fuel, and, for aeration of the composition, a nitrogen com- pound having a specified formula and.an oxidiz- ing agent reactable with the nitrogen com- pound to produce gas. Suitable nitrogen com- pounds are hydroxylamine and hydrazine and their hydrochlorides, sulphates and nitrates, phenylhydrazine and its hydrochloride and nitrate, 2, 4-dinitrophenylhydrazine, phenyl- sulphonyl hydrazide, semicarbazide and its hydrochloride and nitrate, phenyl thiosemi- carbazide, and benzoyl hydrazide. Preferred oxidising agents are potassium iodate, potassium periodate, copper sulphate, potassium ferri- cyanide, lead dioxide, ceric ammonium nitrate, potassium permanganate, potassium dichro-mate, mercuric oxide, hydrogen peroxide, and peroxysulphuric acid. The oxygen-supplying salt may be ammonium, sodium, potassium, barium or calcium nitrate or mixtures thereof. Suitable solvents are water, formamide, di- methylsulphoxide, and ethylene glycol. Fuels referred to are Al, Al Alloy, Si, ferrosilicon, ferrophosphorus, sulphur, carbon, sugar, urea, thiourea, TNT, PETN, RDX, smokeless powder, nitrocellulose, and nitrostarch. Suitable thick- eners are carboxymethyl cellulose, guar gum, carob seed gum, karaya gum, locust bean gum, hydroxyethyl cellulose, tamarind flour, and starch. Cross-linking agents may be added, for example potassium pyroantimonate, zinc chro- mate, or sodium or potassium dichromate in conjuction with potassium antimony tartrate. Other ingredients used in examples are iso- propyl nitrate and ethyl centralite.
Reference maybe made to patent no.: GB769210, wherein the Ammonium nitrate blasting explosives described are substantially oxygen balanced, i.e. not more than 5g. oxygen surplus, or deficiency, per 100g. composition, low power blasting

explosive comprises ammonium nitrate, at least one self-explosive organic sensitizing agent, and at least one non-explosive flame suppressor of average particle size which does not exceed 20A, i.e. whose specific surface by volume is not less than 3000cm 2/cc, wherein at least part of the ammonium nitrate is contained in discrete internally coherent particles, or aggre- gates, of a mixture of ammonium nitrate with at least a portion of the flame suppressor, with or without other ingredients of the composi- tion, and at least a portion of the sensitizeris in the portion of composition external to the aggregates. The aggregates should include not less than 25 per cent, ammonium nitrate, and not less than 45 per cent, flame suppressor, should all pass No. 8 B.S.S. and be retained on No. 18 B.S.S. should be oxygen balanced and may include a portion of the sensitizer. The aggregates may be made : by mixing the flame suppressor with a hot solution of ammonium nitrate containing 5-10 per cent, water toform a slurry, casting, and breakimg up ;or by spray drying molten ammonium nitrate, or a hot solution thereof, in admixture with the flame suppressor, or by admixing the flame suppressor, ammonium nitrate and a binding agent, e.g. collodionor spirit gum.In examples : (1) aggregates ofammonium nitrate and chalk <20A,are mixed with a nitrated 80 : 20 mixture of glyceroland ethylene glycol as sensitizer.ammonium nitrate retainedon 25 B.S.S., ammonium chloride, woodflour.and sodium chloride<20A ;(2) aggregates of ammonium nitate, cryolite <20A, and wood flourare mixed with the same componentsas in (1) except cryolite <20A is used in place of sodium chloride ; (3) (4) aggregates of ammonimn nitrate, sodium chloride <20A and gum arable, are mixed with the sensitizer of (1), ammonium nitratesodium chlorideor sodium silicofluoride <20A and wood .flour or ammonium chloride; (5) (6) aggregates of T.N.T., ammonium nitrate, magnesium nitrate and sodium chloride <20A are mixed with the sensitizer of (1), ammonium nitrate, and wood- flour or bagasse, with or without sodium chloride <20A other flame suppressors mentioned are fluorspar, potassium chloride, and potassium fluoride, and it is stated that all ingredients, except the sensitizer, may be included in the agglomerates. Other sensitizers are T.N.T., nitroglycerin and ethylene glycol dinitrate, and the composition should have
a power not greater than 30 per cent, of that of blasting gelatin.
Reference maybe made to patent no.: JP2003146789, wherein the slurry explosive composition is a slurry explosive composition consisting of an oxidizer, water, foaming agent and/or unshaped inert material and viscous agent and containing a sensitizer, inflammable agent and surfactant at need, in which the amount of the water to be added is 18 to 35 wt.% in the slurry explosive composition, the amount of the unshaped inert material to be added is 0 to 15 wt.%, the specific gravity is 0.75 to 0.95 and the viscosity is 100 to 400 kPa.s. Glass microballoons, resin balloons, porous resin materials, etc., are used for the foaming agent; pearlite, sirasu microballoons, vermiculite, pumice, etc., are used for the unshaped inert material and guar gum, starch, etc., are used for the viscous agent.
Reference maybe made to patent no.: U.S.3,546,034 which discloses a slurry explosive composition containing 20-30% by weight of nitromethane as a sensitizer and 4-7% by weight of urea as a crystallization temperature-lowering agent for ammonium nitrate at low temperature. In this U.S. Pat. No. 3,546,034, the 20-30 parts by weight of nitromethane contained in the explosive composition are gelatinized by using 1.5-2.0 parts by weight of nitrocellulose, and the gelatinized nitromethane is dispersed in the gum contained in the explosive composition, whereby the nitromethane is solidified in the explosive composition. Moreover, in this U.S. Patent, urea is merely used for lowering the crystallization temperature of ammonium nitrate. In this U.S. Patent, the problem of aggregation of nitromethane at low temperature is solved by solidifying nitromethane and by lowering the crystallization temperature of ammonium nitrate, but all of the slurry explosive compositions described in the examples of this U.S. Patent are not ignited by No. 8 detonator in spite of the presence of 20-30% by weight of nitro compound in the explosive composition, and completely detonate with 10-40g of a particular booster (a mixture of
trimethylenetrinitramine and plasticizer). That is, the problem of sensitivity of explosive at low temperature is not at all solved in U.S. Pat. No. 3,546,034.
Reference maybe made to patent no.: US 3,966,516, which discloses a slurry explosive composition comprising an inorganic oxidizing acid salt, water, a combustible material, a thickener, a nitroparaffin and an amide is very sensitive and stable, and can be detonated at low temperature without the use of primer.
Reference maybe made to patent no.: US 4,055,449 wherein a fuel oil sensitised aqueous slurry explosive is prepared by dispersing fuel oil in hot concentrated ammonium nitrate solution containing crystal habit modifier and allowing the solution to cool. Long needle-like ammonium nitrate crystals are formed as a matrix which inhibits migration and coalescence of the dispersed oil droplets. Slurry explosive compositions prepared by this method are still significantly less sensitive than ANFO explosive and their preparation involves the undesirable handling of hot ammonium nitrate solution.
Reference maybe made to patent no.: US 4,141,766 which describes a slurry explosive composition comprising inorganic oxidizing salt and a liquid solvent, dispenser or carrier for the salt, which liquid is emulsified with a sensitizing liquid aliphatic mononitrate containing from 3 to 8 carbon atoms per molecule. The composition preferably comprises from 4 to 20% w/w of liquid alkyl mononitrate and from 5 to 25% w/w of liquid solvent, disperser or carrier, from 0.1 to 3.5% w/w of emulsifier, from 25 to 85% w/w of ammonium nitrate, from 0 to 35% w/w of other inorganic oxidising salt and optionally up to 20% of solid fuel.
Reference maybe made to patent no.: US 4,384,903 which discloses an aqueous slurry explosive blasting composition comprising an aqueous suspension of water-soluble crystalline oxidizing salt consisting predominantly of ammonium nitrate, which salt has been comminuted in a saturated aqueous solution in the presence of a water-
soluble crystal-growth inhibiting surfactant having a hydrophobic portion and a hydrophilic portion in its molecule, in intimate admixture with liquid water-immiscible hydrocarbon fuel sensitizer. The surfactant maintains the oxidizer salt in a finely divided state and also ensures that the liquid hydrocarbon remains uniformly distributed throughout the explosive mass as a stable coating of droplets on the salt particles thereby enhancing the explosive sensitivity of the composition. The preferred fuel is diesel oil and preferred surfactants include sodium carboxymethyl cellulose, long chain aliphatic amines, polyacrylic acids, sulphonated nuclear aromatic compounds, sulphonated dyes, sulphonated polymers and long chain alcohol sulphonates and phosphonates.
A number of United States Patents were filed for surface blasting and they are commercially available. The details are as follows:
(a) TOVEX ® BLASTRITE ™ 3 Rs is a cap sensitive cartridged watergel explosive, specially designed for surface mines and is required where the high energy is required. It is available in 50mm diameter cartridge and density of the product is 1.18g/cc. The velocity of detonation reported was 4800m/s. This product is acceptable for use under 24 metres hydrostatic pressure head or 241.32 kPa with a standard blasting cap (Ref. ETI Canada Inc., © 1998-2000).
(b) TOVEX ® EL- 930™ is another Canadian patent booster sensitive water-gel explosive designed for surface mines and underground use and available in 50mm and larger. The density of the product is 1.30g/cc and its velocity of detonation is 6000 m/s. The product in diameter in between 50mm -70mm is used with 90gram cast booster whereas diameter in between 75mm - 125mm the required booster charge is 150 gram. The diameters 125mm and up required 454 gram of cast booster. This product is not a cap sensitive explosive and acceptable for use under 30 metres (50psi) hydrostatic pressure head (Ref. ETI. Canada Inc., © 1998-2000).
The Canadian explosives referred herein above are available in 50mm to 125mm diameter and the velocity of detonation and detonation pressure of product are very high in the range of 4800 to 6000 m/sec, which may causes ground vibration, back break and fly rock problem in blasting. The densities of the products were very high ranging from 1.15 to 1.30g/cm3, and in unconfined it is generally found density at above 1.25 g/cm3 misfire or poor detonation occurred.
The reference is made from the Encyclopedia of Explosives and Related items. Vol. 9 (1980), p. SI24-147, US Patent No. 3380333 is a pumping slurry explosive and it is non-cap sensitive. Another US Patent No. 3926698 is slurry explosive composition sensitized with metallic fuel particles, which is high energy and high velocity of detonation product. This product is not suitable for soft and medium hard rock blasting.
In our co-pending Indian patent application No. 2642/DEL/96, we have described and claimed a coal base composition for surface blasting for dry holes. The composition claimed was (g/100) (i) ammonium nitrate=92.00, coal powder = 6.4, guar gum = 0.8, sodium nitrite = 0.40 and potassium dichromate = 0.4. (ii) ammonium nitrate =73.6, sodium nitrate =15.8, coal powder = 8.8, guar gum = 1.3, sodium nitrite = 0.2 and potassium dichromate = 0.3. This explosive composition was in a powdery form and it cannot be used in watery holes due to poor water resistance.
In another co-pending Indian patent application No 3836/DEL/98, we have described a composition useful for excavation work such as blasting in coal and non-coal surface mines. The compositions claimed were in the range of (g/100) ammonium nitrate 73.79 to 74.67, diesel 1.76 to 1.78, wax 2.02 to 2.04, urea 2.35 to 2.37, thio -urea 0.10 to 0.11, sorbitan mono-oleate 1.58 to 1.60, acrylamide 0.05 to 0.08, sodium nitrite 0.05 to 0.08 and water 18.00 to 19.00. This composition is bulk emulsion product and suitable for hard bench shovel blasting depth up to 15-20m and poor water resistant properties.
The main object of the present invention is to provide a slurry explosive composition for open cast mines and other excavation works, which obviates the above noted drawbacks.
Another object of the present invention is to provide a process for making a slurry explosive from the novel explosive composition, which obviates the above noted drawbacks.
Yet another object of the present invention is to provide a low energy and low velocity of detonation explosive for blasting in soft and medium hard rock.
Still another object is to provide a synergistic composition for preparing a slurry explosive having velocity of detonation in the range of 3000 to 3800 m/s in unconfined; explosion energy in the range of 1660 to 2000 KJ/kg with excellent water resistant properties, which is sufficient to break the soft and medium hard rock with proper fragmentation.
A further object is to provide a novel explosive composition for preparing the slurry explosive, which would be cap- sensitive with No. 6 strength detonator.
Slurry explosive of the present invention is a novel explosive with low velocity of detonation and explosion energy, which is cap sensitive in 50mm and larger. This low velocity of detonation and energy product is suitable for soft and medium hard rock blasting which helps in reduction of back break and ground vibration. The product has excellent water resistant property and the shelf life is more than six months. The composition of the present invention is safe in handling and non - hazardous during preparation.
The synergistic composition of the present invention for making a slurry explosive utilizes ingredients of oxidizing phase consisting of agents such as ammonium nitrate, reducing agents such as sugar, guar gum, aluminium powder and thiourea, cross-
linking agents such as potassium dichromate, potassium pyro-antimonate or mixture thereof and sodium nitrite as a gassing agent to produce zero oxygen balance to provide a slurry explosive composition cap-sensitive in 50mm diameter and larger. The function of thiourea is to provide stability to the explosive composition.
In our earlier co-pending Indian patent application no. 2642/DEL/96, the oxidizing agents like ammonium nitrate, sodium nitrate were used in the range of 73.6 to 92.00 wt % and 15.80 wt % respectively. Reducing agents were used in the range of carbon 6.4 to 8.8 wt %. In another co-pending patent no. 3836/DEL/98 the oxidizing agents used were in the range of ammonium nitrate 73.79 to 74.67 weight % and reducing agents used were in the range of diesel 1.76 to 1.78, wax 2.02 to 2.04, thiourea 0.10 to 0.11 and urea 2.35 to 2.37 weight % respectively. The emulsifier (SMO) was used in the range of 1.58 to 1.60 wt%. The gassing agents were used in the range of acrylamide 0.05 to 0.08 and sodium nitrite 0.05 to 0.08 wt%. The solvent for oxidizer i.e., water was used in the range of 18 to 19 wt%.
The above noted explosive composition of Indian patent application no. 2642/DEL/96) is a powder explosive and poor water resistant and cannot be used in the watery holes. In another Indian patent application no. 3836/DEL/98 is for bulk emulsion explosive with high energy for rock fragmentation, where as the novel composition of the present invention has low energy and low velocity of detonation for rock blasting with excellent water resistant properties and suitable for soft and medium hard rock. The velocity of detonation of the novel composition is in the range of 3000 to 3800m/s in unconfined condition and explosion energy 1660 to 2000KJ/kg. The shelf life of the developed composition is more than six months and it is a cap-sensitive composition.
In table 1 is given the comparison of the ingredients of the present invention and earlier co-pending Indian patent applications.Table 1
Comparative ingredients (g/100)
(Table Removed)
Accordingly, the present invention provides a slurry explosive composition for open cast mines and other excavation works, which comprises an aqueous suspension consisting of:
Oxidizing agent(s) such as: Ammonium nitrate 59.29 to 69.33 wt %;
Reducing agent(s) such as: Sugar 5.90 to 7.24 wt %;
Aluminium powder 3.34 to 3.50 wt %;
Thiourea 0.10 to 0.18 wt%;
Guar gum 1.00 to 1.03 wt%;
Cross-linking agent(s) such as:
Potassium pyro-antimonate, Potassium dichromate 0.04 to 0.05 wt%;
Solvent for oxidizer(s) such as: Water 18.77 to 30.00 wt %;
Gassing agent(s) such as: Sodium nitrite 0.04 to 0.05 wt %.
(Table Removed)
In an embodiment of the present invention the oxidizing agent is essentially ammonium nitrate.
In another embodiment of the present invention the reducing agent is selected from sugar, flake grade aluminium powder, thiourea and guar gum or is a mixture thereof.
In still another embodiment of the present invention the cross-linking agent is selected from potassium pyro-antimonate or potassium dichromate or is a mixture thereof.
In yet another embodiment of the present invention the gassing agent is essentially a solution of sodium nitrite.
In still yet another embodiment of the present invention the oxidizing agent is of 99% purity.
In a further embodiment of the present invention the reducing agent(s) is of 99 % purity.
In a still further embodiment of the present invention the gassing agent is of 99 % purity.
In another embodiment of the present invention, the slurry explosive composition

(Table Removed)
It is a feature of the present invention that the slurry explosive composition is not a mere admixture but a synergistic mixture having properties, which are distinct and different to the mere aggregation of the properties of the individual ingredients and there is no chemical reaction in the composition.
Accordingly the present invention provides a process for making a slurry explosive from the composition of the present invention, which comprises dissolving the oxidizing agent in water at a temperature in the range of 60 to 70 °C and maintaining pH of the solution in the range 4.40 to 4.70, adding to the solution so obtained reducing agents such as sugar, thiourea, guar gum or mixture thereof to obtain a zero oxygen balanced composition in the slurry form, sensitizing the said slurry by using flake grade aluminum powder followed by treatment with gassing and cross-linking agents by conventional methods.
In an embodiment of the present invention the pH of the solution is maintained using an acid/base such as nitric acid/sodium hydroxide.
In another embodiment of the present invention the reducing agent (s) is added to the oxidizing solution at a temperature of around 52 to 55 °C.
In yet another embodiment of the present invention the gassing and cross-linking agents are added at the gumming point of the slurry.
In still another embodiment of the present invention the slurry is sensitized by adding flake grade aluminium powder at a temperature of around 40°C.
During the process with aluminium powder no gaseous product are formed, the product formed is AI2O3 (alumina), which is a solid and heat of formation of AI2O3 is very high (396 kcal/mole) and the explosive becomes sensitive to detonate with N0.6 detonator {Ref. R. Meyer, pp.13}.
The composition prepared is sensitized enough to be initiated with copper detonator (N0.6) consisting of lead azide, lead styphante, aluminium (ASA) 0.20 gm and pentaerythritol tetranitrate (PETN) 0.22 gm.
In the process of the present invention oxidizing agent was first taken with water and heated up to 65-70°C and pH of the solution was maintained in between 4.40 to 4.70 by adding acid/base. It was stirred for at least 5 minutes and reducing agents such as sugar, thiourea, guar gum or mixture thereof were added in the oxidizing solution at 53-55°C and at gumming point the gassing and cross-linking agents added. The composition was sensitized with the help of flake grade aluminum powder at around 40°C. This product can be easily transferred into the blow molded tube or polythene tube where the product is completely cross-linked and gassed within 24 hours. The velocity of detonation of the synergistic composition was in the range of 3000 -3800 m/s. the explosion temperature of the synergistic composition was in the range of 1967 to 2500 Kelvin and its explosion energy 1660 -2000 KJ/kg._The strength of the composition was 60-65% of BG.
The following examples are given by way of illustration of the present invention in actual practice and should not be construed to limit the scope of the present invention in any way.
Example 1

(Table Removed)
The oxidizing agent such as ammonium nitrate (1386.60g) was dissolved in required quantity of water (375.40g) at 65 + 5 ° C. The pH of the solution was maintained by adding acid/base at 4.40 to 4.70. At this pH the process of cross-linking and gassing rate is slow and the product gets stability due to formation of micron size air bubbles. The required fuels such as (2g) thiourea, sugar (144g) and guar gum (20g) were added to oxidizing solution.
The product is near to zero oxygen balanced in the slurry form. The composition was sensitized by using flake grade aluminum powder (70g) followed by treatment with gassing and cross-linking agents such as sodium nitrite (1g) and potassium pyro-antimonate (1g) respectively. In a single batch 2000g of explosive was prepared and its explosive properties were studied.
The prepared explosive was packed in the polythene tube which was cap-sensitive at 50mm diameter and the velocity of detonation measured by Dautriche method was 3800m/s. For continuity of detonation the cartridges were placed in line one after one up to 1m lengths and fired with No.6 detonator and found all cartridges were
detonated. Two cartridges were placed at a distance of 20 in a line and one cartridge was primed with No.6 detonator called donor. Another, which was not primed, is called acceptor. On detonation the acceptor was not fired. This experiment was repeated with at a distance of 15cm and found the acceptor was fired. Maximum distance at which detonation is transmitted between two explosives when kept in line is called as air gap sensitivity test. The slurry composition passed the 15cm of air gap sensitivity test. 10 kg. of weight was dropped by the fall hammer method at the height of 3m and observed no detonation behavior in the explosive. The strength of the explosive was measured by the Ballistic Motor method that was 65% of BG. The value of explosion energy and detonation temperature was theoretically calculated. The detonation behavior of the composition was tested upto more than six months and detonation was found after six months of storage periods.
Explosive properties as obtained in example 1 are given in the table below:

(Table Removed)

(Table Removed)
The oxidizing agents such as ammonium nitrate (1361.80g) was dissolved in required quantity of water (401.20g) at 65 ± 5 ° C. The pH of the solution was maintained by adding dilute nitric acid/sodium hydroxide at 4.40 to 4.70. The required fuels such as thiourea (3.0g), sugar (144.80g), and guar gum (20.40g) were added to the oxidizing solution at 53 -55°C.
The product is near to zero oxygen balanced in the slurry form. The composition was sensitized by using flake grade aluminum powder (66.8g) followed by treatment with gassing and cross-linking agent, sodium nitrite (1g) and potassium pyro-antimonate (1g) respectively. In a single batch 2000g of explosive was prepared and explosive properties were studied.
The prepared explosive was packed in the polythene tube which was cap-sensitive at 50mm diameter and the velocity of detonation measured by Dautriche method was 3707m/s. Dautriche method and Fiber Optic method were used for the measurement of velocity of detonation. 10 kg of weight was dropped by the fall hammer method at the height of 3m and observed no detonation behavior in the explosive. The strength
of the explosive was measured by the Ballistic Motor method and found 64% of BG. For continuity of detonation the cartridges were placed one after one up to 1m and fired with No.6 detonator. It was found that all the cartridges were detonated. The two cartridges were placed at a distance of 20 cm and another experiment was conducted at a distance of 15 cm. First cartridge was initiated with No.6 detonator and found that acceptor cartridge of 15cm was fired whereas the 20cm distance acceptor cartridge was misfired. The slurry composition passed the 15cm of air gap sensitivity test. The values of explosion energy and detonation temperatures were theoretically calculated. The detonation behavior of the composition was tested up to more than six months and detonation was found after six months of storage periods.
Explosive properties as obtained in example 2 are given in the table below:

(Table Removed)
Example 3

(Table Removed)
The oxidizing agents such as ammonium nitrate (1272.80g) was dissolved in required quantity of water (505.60g) at 65 ± 5 ° C. The pH of the solution was maintained by adding dilute nitric acid/sodium hydroxide at 4.40 to 4.70. The required fuels such as thiourea (3.20g), sugar (128g), and guar gum (20.60g) were added to the oxidizing solution at 53 -55°C.
The product is near to zero oxygen balanced in the slurry form. The composition was sensitized by using flake grade aluminum powder (68g) followed by treatment with gassing and cross-linking agent, sodium nitrite (0.80g) and potassium pyro-antimonate (1g) respectively. In a single batch 2000g of explosive was prepared and explosive properties were studied.
The prepared explosive was packed in the polythene tube which was cap-sensitive at 50mm diameter and the velocity of detonation measured by Dautriche method was 3333m/s. Dautriche method and Fiber Optic method were used for the measurement of velocity of detonation. 10 kg of weight was dropped by the fall hammer method at the height of 3m and observed no detonation behavior in the explosive. The strength
of the explosive was measured by the Ballistic Motor method and found 62% of BG. For continuity of detonation the cartridges were placed one after one up to 1m and fired with No.6 detonator. It was found that all the cartridges were detonated. The two cartridges were placed at a distance of 15 cm and another experiment was conducted at a distance of 12 cm. First cartridge was initiated with No.6 detonator and found that acceptor cartridge of 12cm was fired whereas at 15cm distance acceptor cartridge was misfired. The slurry composition passed the 12cm of air gap sensitivity test. The values of explosion energy and detonation temperatures were theoretically calculated. The detonation behavior of the composition was tested up to more than six months.
Explosive properties as obtained in example 3 are given in the table below:

(Table Removed)
Example 4

(Table Removed)
The oxidizing agents such as ammonium nitrate (1185.80g) was dissolved in required quantity of water (600g) at 65 + 5 ° C. The pH of the solution was maintained by adding dilute nitric acid/sodium hydroxide at 4.40 to 4.70. The required fuels such as thiourea (3.60g), sugar (118g), and guar gum (20.60g) were added to the oxidizing solution at 53 -55°C.
The product is near to zero oxygen balanced in the slurry form. The composition was sensitized by using flake grade aluminum powder (70g) followed by treatment with gassing and cross-linking agent, sodium nitrite (1g) and potassium pyro-antimonate (1g) respectively. In a single batch 2000g of explosive was prepared and explosive properties were studied.
The prepared explosive was packed in the polythene tube which was cap-sensitive at 50mm diameter and the velocity of detonation measured by Dautriche method was 3000m/s. Dautriche method and Fiber Optic method were used for the measurement of velocity of detonation. 10 kg of weight was dropped by the fall hammer method at the height of 3m and observed no detonation behavior in the explosive. The strength
of the explosive was measured by the Ballistic Motor method and found 60% of BG. For continuity of detonation the cartridges were placed one after one up to 1m and fired with No.6 detonator. It was found that all the cartridges were detonated. The two cartridges were placed at a distance of 15 cm air gap test and another two experiments were conducted at a distance of 12 cm and 10 cm. First cartridge was initiated with No.6 detonator and found that acceptor cartridge of 10cm was fired whereas the distance of 12cm and 15cm acceptor cartridge were misfired. The slurry composition passed the 10cm of air gap sensitivity test. The values of explosion energy and detonation temperatures were theoretically calculated. The detonation behavior of the composition was tested up to more than six months and detonation behavior was also found after six months of storage periods.
Explosive properties as obtained in example 4 are given in the table below:

(Table Removed)
From the above described examples illustrating the present invention in actual practice it is observed that the synergistic composition is a slurry product, cap-sensitive in the 50mm, diameter and larger which can be used in soft and medium hard rock blasting in surface mines. The velocity of detonation of synergistic composition is in the range of 3000- 3800 m/s in unconfined condition. The composition passed the 10 -15cm air gap sensitivity tests in unconfined. The explosion energy and explosion temperature of the composition are in the range of 1660 to 2000 KJ/Kg and 1967 to 2500 Kelvin respectively. The water resistance properties of the developed product are excellent and shelf life of the product is more than six months.
This slurry explosive has poor impact; friction and heat sensitive and manufacturing process of the product is safe and non-hazardous. Oxidizing agent was first taken with water and heated up to 65±5°C and pH of the solution was maintained in between 4.40 to 4.70 by adding acid/base. It was stirred for at least 5 minutes and reducing agents such as thiourea, sugar and guar gum were added in the oxidizing solution at 53-55°C and at the gumming point the gassing and cross-linking agents added. The formulation was sensitized with the help of flake grade Al-powder at 40°C. This product can easily be transferred into the blow molded tube or polythene tube where the product is completely cross-linked and gassed up to detonation density with 24 hours.
The novelty of the present invention resides in the synergistic slurry explosive composition for preparing slurry explosive with low velocity of detonation and explosion energy, which is cap sensitive in 50mm and larger. This low velocity of detonation and energy product is suitable for soft and medium hard rock blasting which helps in reduction of back break and ground vibration. The product has excellent water resistant property and the shelf life is more than six months. Further, the composition of the present invention is safe in handling and non - hazardous during preparation. The novel features of the slurry explosive prepared from the composition of the present invention are summarized in the table below:
(Table Removed)
The non-obvious inventive steps of the present invention resides in the synergistic slurry explosive composition for preparing slurry explosive, which consists of a unique combination of ingredients of oxidizing phase consisting of agents such as ammonium nitrate, reducing agents such as sugar, guar gum, aluminium powder and thiourea, cross-linking agents such as potassium dichromate, potassium pyro-antimonate or mixture thereof and sodium nitrite as a gassing agent to produce zero oxygen balance to provide a slurry explosive composition for preparing slurry explosive which is cap-sensitive in 50mm diameter and larger.
The main advantages of the explosive composition of the present invention are:
1. It is a cap- sensitive composition in 50mm diameter and larger.
2. The composition would be useful for soft and medium hard rock blasting.
3. It has excellent water-resistant properties with VOD in the range of 3000-3800m/s.
4. The shelf life of the synergistic composition is more six months.
5. It is economically viable composition and safe in handling.

We Claim:
1. A slurry explosive composition for open cast mines and other excavation works, which
comprises an aqueous suspension consisting of:
Oxidizing agent(s) such as: Ammonium nitrate 59.29 to 69.33wt %;
Reducing agent(s) such as : Sugar 5.90 to 7.24 wt %;
Aluminium powder 3.34 to 3.50 wt %;
Thiourea 0.10 to 0.18 wt%;
Guar gum 1.00 to 1.03 wt%;
Cross-linking agent(s) such as:
Potassium pyro-antimonate, Potassium dichromate 0.04 to 0.05 wt%;
Solvent for oxidizers(s) such as: Water 18.77 to 30.00 wt %;
Gassing agents(s) such as: Sodium nitrite 0.04 to 0.05 wt %.
and a process for making above said composition, comprises dissolving the oxidizing agent in water at a temperature in the range of 60 to 70 °C and maintaining pH of the solution in the range 4.40 to 4.70, adding to the solution so obtained reducing agents such as sugar, thiourea, guar gum or mixture thereof to obtain a zero oxygen balanced composition in the slurry form, sensitizing the said slurry by using flake grade aluminum powder followed by treatment with gassing and cross-linking agents by conventional methods.
2. A process as claimed in claim 1, wherein the pH of the solution is maintained using an acid/base such as nitric acid/sodium hydroxide.
3. A process as claimed in claim 1, wherein the reducing agent (s) is added to the oxidizing solution at a temperature of around 52 to 55 °C.
4. A process as claimed in claim 1, wherein the gassing and cross-linking agents are added at the gumming point of the slurry.
5. A process as claimed in claim 1, wherein the slurry is sensitized by adding flake grade aluminium powder at a temperature of around 40°C.
6. A slurry explosive composition for open cast mines and other excavation works substantially as herein described with reference to the examples.