US 3886010 A
A stabilized and aerated blasting slurry is made up of an aqueous or partly aqueous solution of inorganic oxidizer salt, preferably comprising ammonium, sodium and/or calcium nitrate, in which a suspension of finely divided fuel, such as metallic aluminum, carbonaceous material, and/or TNT or other self-explosive is suspended. The suspension is stabilized by adding a gelling agent, e.g. guar gum, to the solution, adding a further thickener, such as starch, to the suspension, and incorporating a gas generating chemical, e.g. ammonium nitrite, or nitrous acid, along with an oxidizer-reducer cross-linking system.
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Description (OCR text may contain errors)
United States Patent [191 Thornley et al.
STABILIZED AND AERATED BLASTING SLURRY CONTAINING THIOUREA AND A NITRITE GASSING AGENT Inventors: Gary M. Thornley, Bountiful; Lex L.
Udy, Salt Lake City, both of Utah Assignee: Ireco Chemicals, Salt Lake City,
Filed: July 5, 1973 Appl. No.: 376,874
Related US. Application Data Continuation of Ser. No. 274,236, July 24, 1972, abandoned, which is a continuation of Ser. No. 816,770, April 16, 1968, abandoned.
US. Cl. 149/60; 149/42; 149/43; 149/44; 149/60; 149/61; 149/74; 149/73; 149/76; 149/83; 149/85; 149/92; 149/98;
149/105 Int. Cl C06b 1/04 Field of Search 149/82, 83, 73, 61, 44,
References Cited UNITED STATES PATENTS 5/1969 Knight 149/60 [451 May 27, 1975 3,660,181 5/1972 Clay et al 149/44 X 3,695,948 10/1972 Clark 149/2 X 3,713,919 1/1973 Tomic 149/60 X Primary ExaminerStephen J. Lechert, Jr. Attorney, Agent, or Firm-Robert A. Bingham [5 7] ABSTRACT 5 Claims, No Drawings STABILIZED AND AERATED BLASTING SLURRY CONTAINING THIOUREA AND A NITRITE GASSING AGENT This is a continuation, of application Ser. No. 274,236, filed July 24, 1972 now abandoned, which is a continuation of Ser. No. 816,770, filed Apr. 16, 1968, now abandoned.
BACKGROUND AND PRIOR ART It has been known for some time that slurry explosives may be improved in several respects by thickening them with a gelling agent and stabilizing the gelling agent. In U.S. application Ser. No. 733,319, filed May 31, 1968, U.S. Pat. No. 3,485,686 for example, the advantages of reduction-oxidation type cross-linking agents are set forth in some detail and a number of very effective thickener systems are disclosed. Since blasting slurries depend on intimate contact and reaction between oxidizer material, which is in liquid solution to a large extent, and solid particles of fuel (or sensitizer material) such as powdered aluminum and/or carbonaceous fuel, e.g. powdered coal, finely ground gilsonite, and the like, if these solid particulate fuel-sensitizer ingredients are not effectively and stably held in homogeneous suspension throughout the mass of the slurry, partial or complete detonation failure may occur. Write various cross-linking agents have been suggested, some of these are quite specific for use with particular gelling agents. Some are effective for short storage time, such as a few minutes or even an hour or two, but lose their effectiveness on extended storage. Some are of the migrating linkage type, which tend to maintain an elevated viscosity over sustained time periods but this sort of linkage is not effective to keep the denser fuel or sensitizer particles in suspension. Consequently, the slurry heterogeneous so the heavier particles settle out; lighter particles on the other hand, may rise to the top in some cases. The general problem is mentioned in U.S. Pat. No. 3,378,235, for example.
It is also known, as suggested in U.S. Pat. No. 3,382,117, for example, that inclusion of a small amount of air in finely dispersed condition in an explosive slurry may be beneficial. Other references have suggested use of various additives, in small proportions, which will degenerate in the slurry environment and thereby form small and widely dispersed gas bubbles. Among agents which have been suggested for this purpose are carbonates, which decompose in presence of weak acids to form gaseous carbon dioxide, peroxides which may decompose to form gaseous oxygen, nitrites which may decompose to form gaseous nitrogen, etc. Others which are obvious to those skilled in the art include some of the hydrides which will generate hydrogen in the aqueous environment. Some of these materi' als, carbon dioxide for example, may be too watersoluble to be as effective as is desired. Others may require critical pH range in the slurry vehicle, etc. Thus the particular gassing agent needs to be chosen so as to be compatible with and effective in a particular slurry composition.
A particular object of the present invention is to combine the thickening, cross-linking, stabilizing and passing or aerating functions in a simple combination ingredients which are widely available, relatively inexpensive, and effective in small proportions. Additives may be used which serve, at least to some extent, as
cross-linkers and stabilizers, with particular thickeners, as well as gassing or aerating agents.
SUMMARY To summarize the present invention, a small amount of a thickener for the oxidizer solution is first incorporated in the solution before the particulate fuel or sensitizer materials are incorporated therein. This thickener helps hold tiny sensitizing gas bubbles in the liquid phase. Thereafter, other thickener, cross-linker and aerating or gas-generating as well as stabilizing materials, in small proportions are added, preferably but not necessarily along with the sensitize-fuel ingredients. The solution is an aqueous or partly aqueous solution of a powerful oxidizer salt such as ammonium, alkali metal, alkaline earth metal and/or other nitrate, and/or ammonium or alkali metal chlorates and perchlorates. A liquid fuel, such as a monohydric or dihydric alcohol, an amine, amide, or aldehyde, etc., may be added to the water. A small amount of guar gum in the solution may be supplemented by addition of further gum and- /or starch, along with cross-linkers, to the whole slurry; a particular improvement is obtained when a highly cross-linkable gum is used, such as xanthan gum (derived, as far as is determinable at this time, by bacterial action on guar or analogous gums). By addition of a compound which decomposes to generate a substantially insoluble gas, aeration is accomplished in situ. Nitrous acid, ammonium nitrite or other nitrates are effective for this purpose. So are some of the hydrides, e.g. the alkali metal hydrides, barium hydride, etc.
Compounds such as nitrous acid and ammonium nitrite which not only generate gaseous nitrogen but also tend to stabilize the cross-linking agents, are particularly preferred but may be replaced with others by strenghening the cross-linking in other ways, especially by reduction-oxidation cross-linker combinations.
DESCRIPTION OF PREFERRED EMBODIMENT In general terms, the invention deals with an oxidation solution, fuel-sensitizer explosive system thickened, cross-linked, aerated and stabilized to preserve effective homogeneity and impart controlled sensitivity. This is accomplished, preferably by thickening an aqueous or partly aqueous (which in broad terms may be called aqueous) solution of ammonium nitrate and- /or sodium nitrate, calcium nitrate, or one or more of the other nitrates, chlorates or perchlorates named above, by adding a small amount of well-dispersed thickener. This may be, preferably, a small amount, 0.01 to 1 percent or so of guar gum, as described in U.S. Pat. application Ser. No. 650,628 (now U.S. Pat. No. 3,453,158). This dispersion may be accomplished by using a small amount of ethylene glycol or similar liquid to first disperse the gum, then adding this dispersion to the main oxidizer solution.
Thereafter, a dry mixture of particulate solids is added to and suspended in the solution by appropriate stirring and mixing. This dry mixture usually will contain at least one particulate fuel such as finely divided aluminium, ground coal, gilsonite, flour, starch, sugar or the like. The primary fuel, in some cases. may be a liquid such as dihydric or monohydric alcohol and/or water compatible amine, amide, aldehyde, etc., as already mentioned. Ethylene glycol is a good fuel and a desirable constituent, particularly where the slurry is to be used at low temperature where it might congeal prematurely or even freeze. In most cases, enough particulate fuel will be used to contribute substantially toward oxygen balance.
The dry mix usually will include a supplemental thickener, in addition in that already incorporated in the solution. Guar gum and/or pre-gelled starches or flours are preferred, along with cross-linking agents of the types described in copending application Ser. No. 733,319, mentioned above. These comprise oxidizing agents such as ammonium and alkali metal dichromates and permanganates, and reducing agents such as the hydroxyl-bearing compounds described in further detail in said application. These are mentioned more particularly below.
In its preferred form the invention involves the combination of oxidizer and fuel-sensitizer materials, along with the necessary thickener, aeration and stabilizer components mentioned above. Along with the dry ingredients added to and suspended in the solution of a primary oxidizer salt, there may be added further and substantial proportions of the same or another oxidizer in particulate or solid state. This may or may not dissolve, or may dissolve only partially, in the solution, depending on the extent of its saturation with primary oxidizer.
In respect to thickening and stabilizing, the reduceroxidizer ingredients mentioned above in particular effective. The reducers are generally hydroxyl-bearing organic compounds selectedfrom the aliphatic and aromatic or alkylaromatic acids and their salts, particularly those containing plural hydroxyl groups. Materials such as gallic acid, particularly, and tannic acid, tartaric acid, or hydroxylated benzenes such as catechol or 1.2-benzenediol are useful. It appears that those hydroxylated compounds, either aliphatic or aromatic, which have their hydroxyl groups in ortho or other close positions, are superior. This may possibly be due to steric hindrance, although this is not positively known. The observed superiority of gallic acid over tannic acid may be due to the close positioning of three hydroxyl groups on the benzene ring. The salts of these materials appear to be generally as satisfactory as the acids and in some cases they are superior. An example is the marked superiority of potassium antimony tartrate over simple tartaric acid, due probably to the particular metals involved. Citric acid, with its single hydroxyl group, appears to be less effective than polyhydroxylated organic compounds, but some of its salts appear to be more useful.
The thickened gel compositions, in general, will contain aqueous solution of various water solubles. For explosives, at least part of their strong soluble primary oxidizer salts will be in aqueous solution; enough solution is employed in such to form a substantially continuous liquid phase in the finished slurry. Fuels and sensitizers, particulate in character and undissolved to a substantial extent, are suspended in the explosive gels or slurries with at least reasonable homogeneity. These energy-contributing materials should be used in proportions suitable to bring overall oxygen balance of the explosive gel within about +25 to -50 percent, more preferably within $20 percent. The main oxidizer salts which can be used may comprise any one or more of the following and may be used in total proportions from about 40 percent to 89.9 percent, preferably 45 to 65 percent by weight of total compositions: ammonium nitrate, sodium nitrate, barium nitrate, and the ammonium and alkali metal chlorates and perchlorates. The fuels which make up the bulk of the pre-mix and are sensitizers by nature, may comprise one or more ingredients including fine or paint grade aluminum powder in very small quantities, granulated or flaked aluminum of larger particle size than paint grade, in larger proportions, sulfur, up to 10 percent or more, carbonaceous materials such as finely ground or granulated gilsonite, coke, role, carbon black, wood particles, sugar, and starches or flours in proportions up to 10 or 12 percent, or even more. As thickeners the organic and argillaceous flours and starches, and/or galactomannan gums and their equivalents, including such materials as carboxymethyl cellulose, etc., may be used singly or in combination, but preferably incorporated in the solution and hydrated, i.e. pre-incorporated, before the dry pre-mix of fuels and other solids is added. When a fine grade of aluminum is used, the quantity may be as little as 0.1 percent or less, for example, or total fuel may amount to as much as 40 percent or more of the total composition. The solvent, usually a preponderantly aqueous solution or emulsion of an organic liquid, preferably water compatible, such as the lower aliphatic alcohols, glycols, amines, or amides such as formamide, or the like, as known in the art, preferably comprises about 10 to about 25 percent by weight of the total gel or slurry. Thickener and cross-linkers will comprise at least 0.01 and preferably about 0.05 to 5 percent of the total, as previously indicated, but the cross-linker material per se may be only a trace or as little as 0.0001 percent or less, up to 1 percent in some cases.
Another aspect of this invention concerns the aeration of the slurry to control its density and its sensitivity to detonation. It has been proposed to add air and other gases to slurry. In fact, in many cases, some gas, especially air, is entrapped in the normal manufacture of the slurry. See US. Pat. No. 3,382,l l 7. Proposals have been made also for adding gas generating materials, such as peroxide, nitrites, carbonates etc.
In connection with the oxidation-reduction thickeners described above, there are certain advantages in the use of particular gas producing additives in small quantities. Thus, the use of a small amount of nitrous acid, to generate nitrogen as it decomposes, is not only effective for aerating the slurry but it helps to stabilize the thickener system. Nitrogen is inert and, unlike carbon dioxide, it is not soluble in the aqueous liquid that makes up the continuation phases of the slurry. When the gas is generated from reactants which are soluble in the liquid phase, the gas bubbles evolved are extremely small and are readily trapped, especially when the liquid is thickened slightly before the particulate fuel or sensitizer, such as aluminum or carbonaceous particles, or even particles of self-explosives such as TNT, RDX, smokeless powder, etc., are suspended therein.
Nitrous acid, ammonium nitrite, etc., are reducers in acidic solutions. Hence, in slurries of low pH, they assist in the oxidation-reduction cross-linking of guar gum, starch, and similar thickeners when used with appropriate oxidizers.
Nitrous acid, or ammonium nitrite, may be added directly to the slurry, or can be added to its aqueous phase before the particulate solids are introduced. In basic solutions, nitrous salts, such as ammonium nitrite are quite stable and little or no gas evolution is detected. It appears that it is really nitrous acid, produced by decomposition of ammonium nitrite or other nitrous salts, that produces the desired evolution of nitrogen. Thus, evolution of gas in basic solutions from such salts as ammonium nitrite and various metal nitrites can be obtained by merely acidifying the solution, that is, reducing the pH by addition of nitric acid. Other acids, such as acetic or analogous organic acids, or sulfuric or hydrochloric acid, may be used but nitric acid is preferred because it contributes energy as a powerful oxidizer of any fuels present in the slurry.
Decomposition of the nitrous acid, when such is used, can be accelerated by use of urea or thiourea. The use of such is a further specific feature of the present invention. The following reaction is indicated:
The reaction is speeded up slightly by substituting thiurea (H NCSNH for urea. This has another distinct advantage. Thiourea may be introduced into the solution prior to making the slurry, and it has the property of stabilizing and slightly enhancing the thickening of the gums in solution, i.e. the gum in solution maintains its viscosity better with the addition of slight amounts of thiourea.
Nitrous acid (HNO is formed directly in the slurries by the addition of nitrite salts into the acidic slurry environment. In practice, this nitrite is added by blending it into the pre-mix or by introducing it as a separate component at the time of slurry manufacture. The pH of the solution is adjusted on the acidic side; usually from 5.5 to 3. The nitrite forms nitrous acid in this environment and then the nitrous acid decomposes forming nitrogen gas. If the pH of the mix is relatively low, pH 3, and the solution temperature quite hot, approximately 65C or greater, the nitrous acid decomposes without the addition of thiourea. However, at higher pHs and/or lower temperatures, the rate of nitrogen evolution is controlled by the addition of the thiourea, usually pre-blended into the solution. It has been found effective to add the nitrite by means of blending concentrated solution of ammonium nitrite into the premix. The amount of water introduced into the pre-mix in this manner does not significantly wet it. Alternatively, nitrite solutions may be added directly into the mixing funnel of the truck at the time of slurry manufacture. This latter method has the advantage of allowing more control over the density from borehole to borehole. Nitrite concentrations on the order of from 0.001 to 1.0 percent may be useful in producing the desired final density.
When urea nitrate is used in place of thiourea or urea, it is not essential to lower the solution pH, because of the already acid character of the urea nitrate.
There is an advantageous relationship between nitrites or nitrous acid, dichromates, gallic acid and thiourea in a composite thickening-density control system, as a function of pH, particularly in slurries which contain ethylene glycol and calcium nitrate.
In compositions of low pH, i.e. less than about 4.0, 0.014 percent KNO gives Mixes A and B below a final density of 0.55 gm/cc at atmospheric pressure and a density of 1.21 and 1.26 gm/cc respectively, at 50 psi. At low pH the gallic reducer is not required in the redox or oxidizer-reducer thickening system because acidic KNO acts as the reducer to give rapid initial thickening. Thiourea at 0.05 percent added in the solution produces a convenient gassing rate.
At high pH, above 4.0 and up to about 5.5, 0.014 percent KNO gives Mix A a final density of 0.63 gm/cc but 0.5 percent is required to give Mix B the same density at atmospheric pressure. At 50 psi 0.5 percent KNO gives a final density of 1.22 and 1.34 gm/cc respectively, for Mix A and Mix B. At high pH, gallic acid of somewhat higher concentrations on the order of 0.05 percent are required for rapid initial thickening.
A series of compositions were prepared using aqueous solutions of ammonium nitrate, sodium nitrate, and/or calcium nitrate as oxidizer, with a small amount of guar gum dispersed in ethylene glycol to thicken the liquid phase somewhat, preferably prior to adding particulate fuels. Generally speaking, the liquid materials and the ingredients in the main solution are shown in Table V-A. In two cases a sriiall amount of nitric acid was included. Except where otherwise indicated, proportions are shown as percentage weight.
TABLE V-A Guar Nitric MIX AN CN SN H O Gum E.G. Acid A 33.1 38 5.6 5.6 0.2 10 B 30.6 34.5 5.2 5.2 0.18 9.5 C 33.35 38 5.6 5.6 0.2 10.3 0.2 cc D 30.77 35.2 5.2 5.2 0.2 9.5 0.18cc E 42 30.05 15 0.6 0.4 F 40.2 28.91 14.4 0.5 0.4 G 37.78 27.5 13.7 0.36 0.36 H 60.15 l5 15 0.6 0.4 I 57.44 14.4 14.4 0.5 0.4 J 54.17 13.5 13.5 0.4 0.35 K 51.44 16.8 14.9 0.43 0.50 L 51.44 16.8 14.9 0.43 0.50
TABLE V-B Thio- R MIX urea Al 5 Gil Starch ducer NaC Nitrite A 0.3 3 3 0.5 0.3 cc 0.4 B 0.3 10 3 .6 0.3 cc 0.6 C 0.05 3 3 0.3 Co 0.4 D 0.05 10 3 0.3 cc 0.4 E 0.1 6 5.6 0.01 0.2 gm 0.04 F 0.1 7 4.3 4 0007* 0.15gm 0.03 G 0.09 15 2.6 2.5 0.004* 0.09gm 0.016 H 0.1 3 5.5 0.01 0.2 gm 0.04
I 0.1 7 2 3.6 0.007 0.13gm 0.025 J 0.09 15 1 1.9 0.003 007gm 0.014 K 0.1 12.43 1.3 2 0.004 008gm 0.017 L 12.43 1.3 2 0.004 008gm 0.017
The fuels and sensitizers, as well as gassing and gel stabilizing ingredients are shown in Table V-B. In most of there, a small amount of thiourea was used, for reasons already mentioned. ln compositions E, F, G, H, I, and 1*, densities were recorded in grams per cc. as 1.10, 1.16, 1.17, 1.07, 1.08 and 1.07 respectively. In compositions K and L, the aluminum was a mixture, consisting of 0. 1 3 per cent by weight of paint grade fine flaked aluminum coated with stearic acid, 1.1 percent of atomized aluminum, and l 1.2 percent of ground aluminum**.
Mixes A and B had solution pH between 4.0 and 5.5. These were light, frothy slurries, having densities, after sitting, of 0.61 and 0.69 grams per cc, respectively. At 50 psig, these densities increased to 1.20 and 1.30, respectively. Both detonated in 2% inch diameter charges at 5C under 50 psi, approximately equivalent to pressure of the bottom charge in a borehole feet deep. Compositions A and B, above, showed good water resistance and have consistencies which will resist penetration of stemming materials very soon after placement in a borehole.
Mixes C and D included a nitrite salt (KNO in these cases) as a source of gaseous nitrogen for density control. This material served also as a reducer for the reduction-oxidation type thickening discussed above. Nitric acid was used to lower the pH to about 3.0, which produced a nitrous acid in situ. This was a reducing component. Thiourea caused part of the nitrous acid to decompose to release nitrogen gas. Density at atmospheric pressure was 0.65 to 0.67, increasing to 1.21 to 1.26 gm/cc when placed under 50 psig pressure. Sodium nitrite or ammonium nitrite are equally suitable in lieu of postassium nitrite, or nitrous acid can be added directly.
Mixes A and B were less acidic than C and D, so the reducing effect of the nitrate was less. Hence, a small amount of another reducer of the type mentioned above (gallic acid or other hydroxyphenol compound) is added to help the redox thickening.
Mixes E to J show use of dichromate (NaC 50/50 H O/Na Cr O nitrite (or nitrous acid), gallic acid and thiourea. It is noted particularly that the combination of nitrite and thiourea increases the effectiveness of the redox cross-linking systems described above. In addition, they generate gas (N for density control. Typically, all these products will detonate in diameter column, unconfined, at C. Sensitivity can readily be adjusted by using a little more or a little less paint grade aluminum.
In general, for reduction-oxidation cross-linking, gallic acid is preferred but tannic acid, pyrogallol, catechol or other orthohydroxybenzenoic phenols are useful, as well as the antimony compounds already referred to.
The gassing agent may be hydrogen peroxide or any of several carbonates, etc., but nitrites or nitrous acid are preferred because of their cooperation with the cross-linking mechanism for the gum or starch thickener. Almost any nitrite salt can be used. Ammonium, sodium or potassium nitrites are easier to use and are often preferred for this reason.
Mixes K and L, above, were identical except that the latter contained no thiourea. For this reason, its crosslinking was less effective and its water resistance was lower than is usually desired.
It will be appreciated that the various ingredients may be used in various proportions and that substitutions of ingredients may be made within the spirit of the invention by those skilled in the art. The claims which follow are intended to cover the invention as broadly as is proper in view of the state of the art.
What is claimed is:
1. In a blasting composition of the aqueous gel or slurry type employing a decomposable nitrite gassing agent and containing oxidizer salt selected from the group which consists of the ammonium, alkali metal and alkaline earth metal nitrates and the ammonium and alkali metal chlorates and perchlorates, a sufficient amount of fuel of liquid or solid type or both to bring the overall oxygen balance of the composition within the range of +25 to 50 percent, an aqueous fluid phase containing at least part of the oxidizer salt in a concentrated solution, and an organic colloidal galactomannan thickener, the improvement which comprises including thiourea to accelerate decomposition of the nitrite gassing agent while concomitantly stabilizing the thickening effectiveness of the glactomannan thickener.
2. A composition according to claim 1 in which the thiourea is present in proportion of about 0.05 percent to about 0.3 percent by weight, based on the total composition.
3. Composition according to claim 1 in which said gassing agent is a nitrous compound.
4. Composition according to claim 1 in which said gassing agent is a nitrous acid.
5. Composition according to claim 1 which comprises 10 to 25 percent by weight of water, 40 to 65 percent of at least one strong oxidizer which is selected from the group which consists of ammonium nitrate, sodium nitrate and the ammonium and alkali metal chlorates and perchlorates, 10 to 50 percent of solid particulate fuel which is insoluble to a substantial extent in said water, and a gel-forming material which includes at least 0.01 percent of guar gum, a small amount of cross-linking salt selected from the alkali metal chromates, dichromates and permanganates, and a small amount of polyhydroxylated organic material capable of forming a redox reaction with said crosslinking salt to stabilize the formed gel.