US2297538A - Liquid oxygen explosive - Google Patents

Description

Patented Sept. 29, 1942 LIQUID OXYGEN EXPLOSIVE Arthur Russell Taylor Denues, Severna Park, Md., assignor to the Government of the United States of America, as represented by the Secretary oi the Interior No Drawing. Application January 8, 1940, Serial No. 312,906

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 15 Claims.

This invention relates to liquid oxygen explosives and to rendering fire resistant such explosives as well as the containers or wrappers therefor.

In the use of liquid oxygen explosives, a suitable quantity of a carbonaceous absorbent material is commonly placed in a bag or wrapper, usually of canvas, and a liquid often obtained from liquid air and containing a high proportion of iquid oxygen is added thereto. Such ,cartridges together with a detonating initiator are placed in a hole or bore to be blasted, the charge may be tamped and fired by detonation of the initiator by any known means. In practice, the cartridges formed as indicated may be of considerable size and they are often handled in large numbers.

An outstanding disadvantage of liquid oxygen explosives as now commonly used lies in their high infiammability. They may be ignited very readily by commonly occurring materials, such as a glowing coal or cigarette. Once ignited, these explosives defiagrate or oiten detonate. Serious hazards originating in high inflammability therefore attend the practical handling of liquid oxygen explosives.

To minimize or remove the hazards due to this infiammability, I have invented and desire to make available by Letters Patent valuable fire retardant treatments for liquid oxygen explosives. These treatments have proved capable of rendering the explosive practically non-inflammable and do not decrease materially the propulsive strength or rate of detonation nor impair seriously other useful properties of the explosive.

I am aware of the patent to Holderer, No. 2,119,050, granted May 31, 1938, and directed to the improvement of liquid oxygen explosives through the use of a solution of fireprooflng material. However, I have found that not all ordinary fireprooiing salts may be employed safely or successfully for fireprooting carbonaceous absorbent or wrappers for use in liquid oxygen explosives. Thus I have found that borax and phosphoric acid under, certain conditions do not retard the inflammation but may produce an increase in the infiammabiiity and burning rate, i. e.. they may under some circumstances sensitize the explosive with reference to the fire hazard rather than retard it. When carbon was treated with a 5% aqueous solution of borax the inflammability index as measured by a method to be detailed subsequently rose from 400 for carbon containing only water to 430 with the borax solution; coincidentiy the combustion time for standard samples decreased from 16 seconds for the basic moist carbon to 14 seconds for the treated sample. When a 10% solution of orthophosphoric acid was applied to the canvas wrapper and the wrapper then dried. the samples exhibited an extremely high surface sensitivity and high infiammability, as evidenced by practically instantaneous blazing upon application of a flame. However, when phosphoric acid is applied to the carbonaceous absorbent in a method which I have invented and which I shall describe below, it is a very effective fire retardant. Under some conditions other materials commonly recognized as fire retardants including, for example, the primary, secondary, and tertiary sodium salts of orthophosphoric acid, sodium sulphate, sodium stannate. potassium carbonate and ammonium carbonate produce appreciable sensitization. Some materials can be used efl'ectively under some conditions for the wrapper but may at the same time be ineffective for retardation of the inflammation of the carbonaceous absorbent or may even sensitize it. Dibasic ammonium prosphate, monobasic ammonium phosphate and borax exemplify such materials. It is thus not safe to assume that any of the ordinary fireproofing salts may be employed successfully for fireproofing liquid oxygen explosives. Indeed. most common fire retardants are not effective for this purpose.

In practicing my invention I prefer to apply an aqueous solution of phosphoric acid containing at least about 35 weight per cent of acid to a granular carbonaceous absorbent until the weight of acid, calculated as orthophosphoric acid, in the mixture of carbon, water and acid is at least 10 per cent of the total weight and not substantially greater than 20 per cent. If desired aqueous solutions of phosphoric acid of higher concentrations may be used. or commercial phosphoric acids, some of which have concentrations as high as percent, may be used alone.

Suitable carbonaceous materials comprise those which are essentially hydrophilic, that is, they tend to absorb and coat themselves readily with water and with aqueous solutions. Certain carbonaceous materials do not possess this property, but are oily in character and tend to cause aqueous solutions to segregate as films of water do when placed on oily surfaces; such hydrophobic carbons are not suitable for the purpose of this invention. The weight of the untreated carbon to be used in the mixture should always be greater than the sum of the weights of the ivator and acid.

These treatments may be made by applying to the carbonaceous absorbent a finely divided spray of the aqueous solution of orthophosphoric acid while this absorbent is agitated mechanically so that the aqueous solution is distributed substantially uniformly throughout the entire mass of the carbonaceous absorbent. I have found that treatment of the carbonaceous material throughout is necessary for safety. If the carbon already contains a known amount of water, this can, of course, be compensated for by adding a correspondingly stronger solution of phosphoric acid to give substantially the same end product. It will be understood that the proportions of phosphoric acid, water and carbonaceous absorbent may be varied somewhat and still give a liquid oxygen explosive which has marked fire-resistance. The treatment described gives a product of about the following composition:

Conszitucnt Weight, per cent Dry, untreated granular carbonaceou absorbent 67.3 Water 22.5 Orthophosphoric acid 10.0

Another effective composition is:

Weight, per cent Dry, untreated granular carbonaceous absorbent 68 Water 17.0 Orthophospheric acid 15.0

A third effective composition is:

Weight, per cent Dry, untreated granular carbonaceous absorbent 63.8 Water 21.3 Orthophosphoric acid 15.0

A fourth composition which is not so desirable but which may lead to an explosive of high fire resistance is:

Weight, per cent Dry, untreated granular carbonaceous absorbent 57.0 Water 38.0 Orthophosphoric acid 5.0

bonaceous absorbent that I have discovered to be optimum.

If desired, the treated carbonaceous absorbent may then-be charged into an ordinary untreated wrapper, such as a canvas bag and saturated with liquid oxygen in the usual way. While I prefer a canvas wrapper, other fabric materials, such as burlap, or; other fibrous material, such as'suitable papers, may be used. The resultant explosive possesses marked advantages over the untreated product. While the bag may be inflamed readily by an ordinary spark or flame and burned off, the explosive proper, consisting of the treated carbonaceous material and liquid oxygen, does not burn or detonate from this action.

However, I prefer to treat also the wrapper to retard its inflammation. For this purpose I use aqueous solutions without subsequent drying. Eilective agents for this purpose include aqueous solutions of primary or secondary ammonium salts of phosphoric acid, ammonium chloride or orthophosphoric acid. Some other agents are not so effective but give some retardation; examples are sodium silicate, borax, ammonium borate and ammonium sulphate.

If the procedure above indicated is not followed and the bags are allowed to dry, the retardation is in general much less effective and in some cases sensitization may follow; in addition, marked decreases in the strength of the canvas will result. weakened bags may lead to more burst cartridges and increased hazards.

In treating the bag, I prefer to use aqueous solutions containing approximately twenty weight per cent of the dissolved retardant. I use sufiicient of this solution to saturate the canvas. Should some of this drain away before use, it is desirable to replace it. It will be understood that some latitude in the concentration of th aqueous solution is permissible; effective treatments may be obtained with concentrations as low as approximately 5 per cent or as high as the limitations in solubility will permit. I may saturate the canvas bags before carbonaceous absorbent is charged into them or I may dip the charged bags in the. tardant solution or spray these with the soluti either before or after treatment with liquid oxygen. Some additional protection is obtained by arranging the operations so that an excess of the retardant solution is frozen on the surface of the cartridge. In the application of the retardant to the charged bag, I take care to prevent excessive penetration of the solution into the carbon by controlling carefully the duration of such treatments. This care avoids wastage and prevents undue contamination of the carbonaceous absorbent by a material which when on the carbonaceous absorbent may be ineffective or may even sensitize the absorbent, as previously pointed out herein.

The effectiveness of the above described treatments was demonstrated in a number of ways. In some experiments, I determined the inflammability index of samples by exposing them to a standard flame for a controlled time in a device consisting essentially of a hydrogen-oxygen flame of known characteristics from a small weldin blowpipe and of a rotating disc. The sample, disc and flame were placed so that the disc prevented flame impingement on the sample except through a slot in a portion of the disc. The disc was rotated at a known speed and the time of impingement could be controlled by varying the length of the slot and the speed of the disc. A shutter was arranged to allow this impingement only during one revolution of the disc. The "inflammability index was obtained by averaging the maximum. time of exposure, in seconds, that gave no inflammations in several trials and the minimum time of exposure, in seconds, that consistently gave propagating inflammations and dividing this average into 100.

Under standard conditions the explosive prepared from the untreated granular carbonaceous absorbent exhibited an inflammability index of 2500. The explosives prepared from the treated carbonaceous absorbents described above were iulness oi the explosive.

canvas wrapper gave a cartridge the wrapper of which could not be ignited by prolonged exposure to the intense hydrogen-oxygen flame in the testing device.

Mixtures of the treated carbonaceous absorbent with liquid oxygen, of the treated canvas with liquid oxygen, as well as the liquid oxygen explosive prepared from the treatedabsorbent and canvas provedimmune to several igniting agents that are practical hazards of ignition or are more violent. than such hazards. These igniting agents included, in addition to the intense standard hydrogen-oxygen flame mentioned. lighted matches.

burning cigarettes, (lame and hot metal from lead sputter fuses burning in an atmosphere of oxygen. and violent igniting cartridges I devised to provide an especially rigorous test of the fire resistance of the treated explosive.

The treatmentsdo not impair seriously the use- The non-infiammable explosive is less sensitive to impact than the imtreated explosive and the presence oi the pho..- phoric acid does not reduce to unimportant extent the propulsive strength, rate of detonation, and life of the cartridge. Thus with the explosive prepared from the treated carbonaceous absorbent of the composition indicated by the third example cited, thephosphoric acid reduced the propulsive strength only 5.7 percent as measured in a Bureau of Mines ballistic pendulum; the initial oxygen ratio by only 6 per cent; and the life of cartridges 1 A in. in diameter and 8 in. long to a practical oxygen condition by approximately 10 per cent.

The invention described herein, if patented. may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

I claim:

1. A liquid oxygen explosive comprising carbonaceous absorbent and water and including phosphoric acid equivalent at least to one part by weight of orthophosphoric acid for each 19 parts by weight of carbonaceous material and water and at least one part by weight of water ior each 50 parts by weight of dry carbonaceous absorbent.

' 2. A liquid oxygen explosive comprising a carbonaceous absorbent approximately two parts by weight and an aqueous solution containing at least weight per cent of phosphoric acid ap proximately one part by weight.

3. A liquid oxygen explosive comprising substantially nine parts by weight carbonaceous ab sorbent, substantially three parts water, and substantially two parts by weight phosphoric acid.

4. A liquid oxygen explosive comprising substantially 63.8 to substantially 67.5 weight per cent carbonaceous absorbent and substantially 36.3 to substantially 32.5 weight per cent an aqueous solution oi phosphoric acid containing between 30.8 and about 46.9 weight per cent orthophosphoric acid.

5. A liquid oxygen explosive comprising approximately two parts by weight carbonaceous absorbent and approximately one part by weight an aqueous solution of phosphoric acid, the weight of the acid, calculated as orthophosphoric acid, in the mixture of carbon, water and acid, being at least 10 per cent of the total weight and not subill stantially greate than 20 per cent of the total weight.

6. A liquid oxygen explosive comprising carbo- .naceous absorbent and water and including phosphoric acid equivalent at least to one part by weight of orthophosphoric acid ior each 19 parts by weight of carbonaceous absorbent and water and at least one part by weight of water for each parts by weight of dry carbonaceous absorbent. together with a wrapper impregnated with an aqueous solution containing at least 5 weight per cent of fire retardant material of theclass consisting of primary and secondary ammonium salts of orthophosphoric acid, ammonium chloride, phosphoric acid, sodium silicate. borax, ammoniun. borate and ammonium sulphate, and used without subsequent drying.

7. A liquid oxygen explosive comprising carbonaceous absorbent and water and including phosphoric acid equivalent to at least one part by weight of orthophosphoric acid for each 19 parts by weight of carbonaceous material and water and at least one part by weight of water for each 50 parts by weight of dry carbonaceous absorbent, together with a wrapper impregnated with an aqueous solution of at least live weight per cent of salt containing the ammonium radical and acid radical of an oxygen acid 0! an element whose atomic weight is not less than thirty nor greater than thirty-three and used without subsequent drying.

8. A liquid oxygen explosive comprising carbonaceous absorbent and water and including phosphoric acid equivalent to at least one part by weight of orthophosphoric acid for each 19 parts by weight of carbonaceous absorbent and water and at least one part by weight of water for each 50 parts by weight of dry carbonaceous absorbent. together with a. wrapper impregnated with an .aqueous solution of at least five weight per cent of salt containing the ammonium radical and the acid radical of phosphoric acidand usri without subsequent drying.

9. A liquid oxygen explosive comprising a carbonaceous absorbent nine parts by weight, water three parts by weight, phosphoric acid two parts by weight; contained in a wrapper impregnated with an aqueous solution containing at least 5 weight per cent of an ammonium phosphate and used without subsequent drying.

10. A liquid oxygen explosive comprising carbonaceous absorbent and water and including phosphoric acid equivalent to at least one part by weight 01 orthophosphoric acid for each 19 parts by weight of carbonaceous absorbent and water and at least one part by weight of water for each 50 parts by weight of dry carbonaceous absorbent, together with a wrapper impregnated with an aqueous solution of at least five weight per cent of salt consisting oi the ammonium radical and a halogen and used without subsequent drying.

11. A liquid oxygen explosive comprising carbonaceous absorbent and water and including phosphoric cid equivalent. to at least one part by weight of orthophosphoric acid for each 19 parts by weight of carbonaceous absorbent and water and at least one part by weight of water for each 50 parts by weight of dry carbonaceous absorbent, together with a wrapper impregnated with an aqueous solution of phosphoric acid, the

weight of the acid, calculated as orthophosphoric acid, in the mixture of carbon, water and acid being at least 10 per cent of the total weight and not substantially greater than 20 per cent of the total weight.

12. A liquid oxygen explosive comprising carbonaceous material and a wrapper, said wrapper being impregnated with an aqueous solution containing at least 5 weight per cent of fire retardant material of the class consisting of primary and secondary ammonium salts of orthophosphoric acid, ammonium chloride, phosphoric acid, sodium silicate, bcrax, ammonium borate and ammonium sulphate, and used without subsequent drying.

13. A liquid oxygen explosive comprising carbonaceous material and a wrapper, said wrapper being impregnated with an aqueous solution of at least flve weight per cent of salt containing the ammonium radical and the acid radical of an oxygen acid 0. an element whose atomic weight is not less than thirty nor greater than thirty-three and used without subsequent drying.

14. A liquid oxygen explosive comprising carbonaceous material and a wrapper, said wrapper being impregnated with an aqueous solution of at least five weight per cent of salt consisting oi the ammonium radical and a halogen and used without subsequent drying.

Y 15. A liquid oxygen explosive comprising carbonaceous material and wrapper, said wrapper being impregnated with an aqueous solution of phosphoric acid equivalent to at least live weight per cent of orthophosphoric acid and used without subsequent drying.

ARTHUR RUSSELL TAYLOR DENUES.