US3536544A - Trinitrotoluene explosive compositions containing a polycyclic aromatic hydrocarbon - Google Patents

Description

3,536,544 TRINITROTOLUENE EXPLOSIVE COMPOSI- 'I'IONS CONTAINING A POLYCYCLIC AROMATIC HYDROCARBON Otis K. Pennington and Harold J. Gryting, China Lake, and Louis McDonald, Altadena, Califi, assignors to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed Nov. 13, 1953, Ser. No. 392,073 Int. Cl. C06b 9/04 US. Cl. 149-405 Claims This invention relates to explosives and explosive compositions and more particularly to explosive compositions containing trinitrotoluene which exhibit improved physical properties under variations of temperature and pressure.

Trinitrotoluene is well-known for properties which make it especially useful in making cast explosives. It is relatively insensitive to shocks and blows, highly stable over extended periods of storage and forms no sensitive explosive compounds by reaction with metals. The relatively low melting temperature of trinitrotoluene makes it well adapted for forming cast explosive charges, since fusion may be brought about by the use of hot water or steam.

Although trinitrotoluene, hereinafter referred to as TNT, enjoys the foregoing desirable properties, TNT and explosive compositions containing TNT exhibit three distinct objectionable characteristics which are especially deleterious and evident under storage conditions and in handling and manufacturing. TNT and TNT compound explosives such as tritonal, torpex, Composition B, baratol,

and baronex exhibit (1) irreversible dimensional instability, (2) exudation and (3) poor thermal shock resistance.

The objectionable behavior referred to hereinbefore may be typified by cast TNT (grade 1, having a set point of approximately 80.2" C.). In the course of normal temperature variation under uncontrolled storage conditions or in thermal cycling from approximately 70 F. to 140 F. the cast charge or grains of TNT grow irreversibly each time the temperature undergoes a cycle. Thus, a rise in temperature increases the dimensions of the cast charge but the subsequent decrease in temperature does not produce an equal amount of contraction, so that there is a steady and graduated growth in the dimensions of the cast charge.

TNT also exudes products known to be composed of dinitrotoluene and certain other impurities normally found in commercial TNT. The dinitrotoluene along with these other impurities form eutectic mixtures with TNT which exhibit very low melting points. The presence of these eutectic mixtures in the grain, or charge, makes it possible for the material to liquefy and exude at the more elevated temperatures of storage. The exudation and irreversible growth is frequently sufficiently adverse under military storage conditions as to render the ammunition or explosive unsafe or unsuitable for military use.

Explosive compositions, such as those mentioned hereinbefore which contain TNT as one of the components, exhibit surveillance properties similar to those of TNT; that is, cast charges of these explosives 'will undergo irreversible dimensional changes or distortion and will exhibit exudation when exposed under confinement to ther mal cycles in the same manner as cast charges of TNT. In general, the magnitude of growth of the binary explosive charges such as baratol greatly exceeds that of cast TNT, although exudation tendencies are lessened due to adsorption on the fine barium nitrate crystals. Increases in volume of the order of three to five percent are frequently observed where binary explosive charges are made with TNT having a set point as high as 804 C. In general, the

3,536,544 Patented Get. 27, 1970 magnitude of irreversible growth also increases with the percentage by weight, or total surface area, of the infusible dispersed component of the binary explosive mixture. Accordingly, baratol containing 71 percent barium nitrate grows less than baratol containing 76 percent barium nitrate when the same TNT is used as the fusible component.

The third deleterious eifect encountered in cast TNT and cast explosive compounds containing TNT is poor thermal shock resistance leading to the formation of cracks or fissures in the cast or poured charge or grain of the explosive. The appearance of cracks, fissures and cavities is especially prevalent and objectionable during manufacturing when machining of a charge is necessary after casting.

It is an object of the present invention to provide explosive compositions containing TNT which have physical properties superior to TNT-containing explosives heretofore known to the art.

It is another object of the present invention to provide explosive compositions which exhibit no objectionable, irreversible dimensional growth, exudation or cracking.

It is a further object of the present invention to provide a class of additives for TNT and explosive compositions containing TNT which form high melting temperature eutectic mixtures with TNT to prevent cracking of cast charges Without increasing exudation or irreversible dimensional growth.

It is a still further object of the present invention to provide a class of additives for TNT and explosive compositions containing TNT which form molecular compounds with TNT which in turn form high melting temperature eutectic mixtures with TNT to prevent cracking of cast charges without increasing exudation or irreversible dimensional growth.

The present invention achieves the foregoing and other objects by the incorporation of proportionately small amounts of anthracene, or other polycyclic aromatic compounds of the class disclosed herein, into a molten mixture of high purity TNT or explosive composition containing high purity TNT.

It is possible to substantially eliminate irreversible dimensional growth or to reduce such irreversible growth to an order of magnitude that is no longer found to be deleterious by the utilization of TNT of high purity. For example, when TNT which has been purified by recrystallization from alcohol followed by a second recrystallization from a mixture of ethylene dichloride and carbon tetrachloride and finally water washed and dried to give a set point of 80.7i0.l C., is used for the preparation of a poly component explosive containing a dispersed phase, it is found that the full scale cast charges do not show irreversible changes in volume exceeding 0.9 of one percent. Frequently the growth is of a considerably lower order of magnitude, i.e., 0.5 of one percent. Also, when TNT having a similarly high set point produced by purification processes other than recrystallization from solvent is employed similar results are obtained. For example, when TNT of high purity having a set point of 80.70 C. or higher produced by rigorous nitration coupled with double Sellite treatment and water wash is employed, the resulting cast charges show a growth of the order of 1.0 percent. Also, due to the absence of impurities and lower order nitrotoluenes in such relatively pure TNT, exudation is avoided. Thus, two of the three objectionable characteristics of TNT and TNT compound explosives may be avoided by the use of sufficiently pure TNT. However, such TNT when in the form of cast explosive charges has especially poor resistance to thermal shock and such charges are accordingly subject to extensive crack failure during thermal cycling or normal stor- 3 age in which the temperature range varies on the order of 60 to 85 F.

Prior to the present invention, various additions to high purity TNT and explosive compositions containing high purity TNT have been attempted in order to alleviate the poor thermal resistance characteristics but have proved ineffective in the control of irreversible growth and exudation. For example, the addition of lower order nitrotoluenes such as a mixture of ortho-nitrotoluene and paranitrotoluene to Composition B containing high purity TNT has effectively controlled cracking by improving the thermal shock resistance but has, on the other hand, increased the irreversible growth and exudation of cast charges under temperature change and confinement.

It has been found that the addition of one of the compounds disclosed herein to a molten slurry of high purity TNT or an explosive composition containing high purity TNT will form high melting temperature eutectic mixtures with the TNT which inhibit and control cracking of cast charges by improving thermal shock resistance, but such compounds will not re-introduce the problems of exudation or irreversible growth which are avoided by the use of sufficiently pure TNT.

When a high melting point eutectic forming additive is incorporated into TNT having a set point of 80.70 C. or higher, appreciable growth and exudation does not take place until the melting temperature of the eutectic mixture is reached. Above the eutectic melting temperature growth increases rapidly with rising temperature, indicating an increasing solubility of the TNT in the eutectic matrix. It is necessary therefore that the additive introduced into the explosive compositions form eutectic mixtures with TNT which have a melting temperature above those temperatures normally encountered in thermal cycling, in addition to making the composition resistant to thermal shock and cracking in cast form.

The present invention comprises a TNT explosive or explosive composition containing a proportionately small amount of a compound from the class of polycyclic aromatic compounds comprising anthracene, napthalene, dihydroanthracene, acenaphthene, phenanthrene, triphenylcarbinol, fluorene, chrysene and pyrene. The quantity of additives incorporated into the explosive composition is within the range of 0.1 to one percent of the TNT present in the explosive mixture.

The presently preferred embodiment of the invention disclosed herein comprises a high purity (alpha, 2,4,6-trinitrotoluene having a set point of 80.7i0.l C.) TNT explosive or an explosive composition containing alpha TNT to which anthracene has been added in an amount equal to approximately 0.5 of one percent of the TNT content of the explosive composition.

The anthracene, or compound of the class described hereinbefore, can be measured either volumetrically or gravimetrically and is added to, and mixed with, the molten slurry of the explosive prior to pouring. In the case of vacuum melts, the addition can be made after breaking the vacuum on the melt. The explosive is then mixed, poured and cast.

Although the present invention is not meant to be limited by theory, the following probable explanation is presented for clarity. The anthracene, or polycyclic aromatic compound of the clas described herein, added to TNT reacts with certain lower nitrotoluenes to form molecular compounds which have a high melting temperature and which in turn form high melting eutectic mixtures with TNT. For example, anthracene and 2,4-dinitrotoluene react in equimolecular proportions to form a molecular compound which melts in the region of 90 C. to 92 C. This TNT compound in turn dissolves into TNT of the molten slurry and reacts with alpha-TNT to form a eutectic mixture which melts in the region of 60 C. to 65 C. This eutectic composition is the last material to solidify in the casting and in the case of anthracene very fine crystalline structure may be observed. The forces between TNT and anthracene molecules are stronger than those between TNT molecules themselves, and the intercrystalline forces between the eutectic and TNT are also apparently stronger than TNT-TNT crystalline forces. Thus, cracking is controlled and a higher resistance to thermal shock is provided. Irreversible dimensional changes and exudation are not encountered unless the melting temperature of the lowest melting eutectic present is exceeded. In practice, with high purity TNT (having a set point of 80.70 C.) this temperature is a few degrees below the eutectic of pure TNT and the anthracene-TNT compound.

The thermal shock resistance of cast charges, prepared in accordance with the present invention is measured experimentally by subjecting cast sections of the explosive to the temperature of Dry Ice and then in sequence to various elevated temperatures as established in a temperature controlled bath containing petroleum naptha. On the basis of such tests and in comparison to controlled specimens and specimens containing additive materials, anthracene and polycyclic aromatics of the class described are found to be exceptionally good additives for the control of crack failure. Furthermore, an overall irreversible dimensional change in volume after exposure to fourteen thermal cycles in the range of 70 F. through F. is found to be less than one percent and exudation products are negligible.

In addition to high purity TNT and explosive compositions containing high purity TNT it has been discovered that anthracene, and the additives described herein, because of their ability to form molecular compounds with lower nitrotoluenes such as 2,4 dinitrotoluene, will inhibit and lessen irreversible growth and exudation in addition to eliminating cracking of commercial grade TNT of good purity and TNT-containing explosives such as tritonal, torpex, Composition B, baratol and baronex made from commercial grade TNT of good purity. As an example, the resistance to crack failure of Composition B containing 40 percent TNT is vastly improved by the addition of anthracene to the molten slurry in the amount of 0.20 percent of the mixture or 0.5 percent of the TNT. This inhibitory behavior of anthracene as an additive to Composition B is further indicated by an examination of certain of the physical properties of Composition B containing such anthracene. The strength in compression is increased from approximately 1200 psi. at failure to approximately 1700 psi. at failure. There is a similar increase in the modulus of elasticity at rupture with the addition of said 0.20 percent of anthracene. The overall dimensional growth of Composition B, containing commercial grade TNT to which 0.20 percent of anthracene has been added, when subjected to thermal cycling in the range of 70 F. to 140 F. is found to be less than one percent. Further, anthracene does not affect Composition B disadvantageously with respect to exudation characteristics; resistance to exudation is approximately the same for Composition B and Composition B with anthracene added. This behavior is contrary to that of other additives of the prior art which have been used for the control of cracking of TNT-containing explosives by forming low melting eutectic mixtures with TNT which increase irreversible growth and cause exessive exudation.

Although anthracene incorporated into high purity TNT or explosives containing high purity TNT has been described as a preferred embodiment and anthracene incorporated into Composition B has been used in illustration, similar results are achieved in TNT-base explosives containing either a dispersed inorganic oxdizing salt or a similarly dispersed organic explosive. Such TNT base explosives include, among others, tritonal, torpex, Composition B, baratol and baronex. Similar results are also achieved by using an additive of the polycyclic aromatic class described within the limits of operability given herein. Such limits range from 0.1 percent to one percent of the TNT present in the explosive mixture.

In addition to those compounds discussed hereinbefore, it has also been found that the incorporation of trinitrometaxylene or 1,3,8-trinitrnaphthalene to TNT or TNT- containing explosives in an amount equal to 0.1 to one percent by weight of the TNT present will eliminate objectionable crack failure without promoting irreversible growth or exudation of the cast explosive. These compounds directly form high melting eutectic mixtures with the TNT of the composition. The use of TNT of high purity, i.e., TNT having a set point of approximately 80.70 C. is essential however to the satisfactory performance of explosives containing either of these two compounds.

Inasmuch as anthracene and the polycyclic aromatics of the class described form equimolecular compounds with lower nitrotoluenes which in turn form high melting eutectic mixtures with the TNT it is possible to vary the process for obtaining the final explosive mixture. Although the process described herein of adding the proper amount of anthracene or the selected compound to a molten slurry of the explosive is preferable, it is also possible to first form the equimolecular compound of anthracene and nitrotoluene and add the compound to the TNT or TNT-base explosive to form the eutectic mixture. Thus, the alternative process includes forming an equimolecular compound of anthracene, or one of the polycyclic aromatics described herein, and dinitrotoluene and adding the molecular Compound to a molten slurry of high purity TNT explosive composition in an amount within the limits of operability described herein.

While there have been described what are considered to be preferred embodiments of the present invention, it is to be understood that the invention of this application is not limited to the specific examples herein recited but that numerous modifications and variations thereof may be made without departing from the scope of the invention as set forth in the appended claims.

What is claimed is:

1. The process of preparing cast trinitrotoluene and trinitrotoluene-base high explosives resistant to cracking,

'exudation and irreversible dimensional growth comprising heating the explosive to a molten condition, adding thereto an amount of polycyclic aromatic hydrocarbon of -'the class consisting of anthracene, naphthalene, dihydroanthracene, acenaphthene, phenanthracene, fluorene, chrysene and pyrene, the amount of said polycyclic aromatic hydrocarbon being from about 0.1 percent to about one percent of the trinitrotoluene present, mixing the explosive and added compound and casting the resulting melt into the desired shape.

2. The process according to claim 1 wherein the polycyclic aromatic hydrocarbon is anthracene.

3. Trinitrotoluene and trinitrotoluene-base explosive comprising from about 0.1 percent to about one percent based on the weight of the trinitrotoluene present of a polycyclic aromatic hydrocarbon of the class consisting of anthracene, naphthalene, dihydroanthracene, acenaphthene, phenanthracene, fluorene, chrysene and pyrene.

4. The trinitrotoluene and trinitrotoluene-base explosive according to claim 3 wherein the polycyclic aromatic hydrocarbon is anthracene.

5. Trinitrotoluene and trinitrotoluene-base explosive comprising trinitrotoluene having a set point of about 807 C.:0.l C., and anthracene in an amount equal to about 0.5 percent by weight of said trinitrotoluene whereby said explosive is rendered resistant to thermal shock, exudation and irreversible thermal growth.

References Cited UNITED STATES PATENTS 850,589 4/1907 MOtte 521l 911,019 1/1909 Motte 52-11 FOREIGN PATENTS 7,837 1907 Great Britain. 282,739 8/1952 Switzerland.

S. I. LECHERT, JR., Primary Examiner U.S. Cl. X.R.

Claims (2)

1. THE PROCESS OF PREPARING CAST TRINITROTOLUENE AND TRINITROLUENE-BASE HIGH EXPLOSIVE RESISTANT TO CRACKING, EXUDATION AND IRREVERSIBLE DIMENSIONAL GROWTH COMPRISING HEATING THE EXPLOSIVE TO A MOLTEN CONDITION, ADDING THERETO AN AMOUNT OF POLYCYCLIC AROMATIC HYDROCARBON OF THE CLASS CONSISTING OF ANTHRACENE, NAPHTHALENE, DIHYDROANTHRACENE, ACENAPTHENE, FLUORENE, CHRYSENE AND PYRENE, THE AMOUNT OF SAID POLYCYCLIC AROMATIC HYDROCARBON BEING FROM ABOUT 0.1 PERCENT TO ABOUT ONE PERCENT OF THE TRINITROTOLUENE PRESENT, MIXING THE EXPLOSIVE AND ADDED COMPOUND AND CASTING THE RESULTING MELT INTO THE DESIRED SHAPE.

3. TRINITROTOLUENE AND TRINITROTOLUENE-BASE EXPLOSIVE COMPRISING FROM ABOUT 0.1 PERCENT TO ABOUT ONE PERCENT BASED ON THE WEIGHT OF THE TRINITROTOLUENE PRESENT OF A POLYCYCLIC AROMATIC HYDROCARBON OF THE CLASS CONSISTING OF ANTHRACENE, NAPHTHALENE, DIHYDROANTHRACENE, ACENAPHTHENE, PHENANTHARACENE, FLUORENE, CHRYSENE AND PYRENE.