IMPACT, THERMAL, AND SHOCK SENSITIVITY OF

MOLTEN TNT AND OF ASPHALT-CONTAMINATED MOLTEN TNT

by

Richard J. Mainiero and Yael Miron

U.S. Department of the Interior

Bureau of Mines, Pittsburgh Research Center

P.O. Box 18070, Pittsburgh, Pennsylvania, USA

Solin S. W. Kwak, Lewis H. Kopera, and James Q. Wheeler

U.S. Army Defense Ammunition Center and School (USADACS)

Savanna, Illinois, USA

ABSTRACT

The research reported here was part of the effort to evaluate the safety of a process to

recover TNT from MK-9 depth bombs by the autoclave meltout process. In this process

the depth bombs are heated to 121oC so that the TNT will melt and run into a vat. 

Unfortunately, asphalt lining the inside surface of the bomb also melts and flows out with

the TNT. It is not known what effect the asphalt contamination and the higher than

normal process temperatures (121oC) would have on the sensitivity of the TNT. 

Testing was conducted on molten TNT and molten TNT contaminated with 2 pct asphalt at

90, 100, 110, 120, 125, and 130oC. In the liquid drop test apparatus with a 2 kg weight, the

molten TNT yielded a 50 pct probability of initiation at a drop height of 6.5 cm at 110oC,

decreasing to 4.5 cm at 130oC. Asphalt-contaminated TNT was somewhat less impact

sensitive than pure TNT at temperatures of -110 to 125oC, but became more sensitive at

130oC; 50 pct probability of initiation at a drop height of 7.8 cm at 110oC, decreasing to 3.3

cm at 130oC. In the card gap test, the molten TNT detonated at high velocity for a gap of

0.25 inches at 90 to 125oC and detonated at high velocity for a gap of 0.5 inches at 130oC. 

For gaps of 0.5 to 3 inches at 90 to 125oC and 0.75 inches to 3 inches at 130oC, the TNT did

not detonate at high velocity but produced a violent explosion that caused significant

damage to the test fixture. For gaps of 4 inches the TNT did not react. In the gap test

there was no significant difference between the pure and asphalt-contaminated TNT. The

thermal analysis test results showed that when asphalt is present in TNT, it greatly

accelerates the exothermic decomposition of TNT, starting at temperatures near 200oC.

The research demonstrated that asphalt-contamination of recovered TNT does not appear

to have a significant effect on TNT shock sensitivity, but does adversely affect impact and

thermal sensitivity. The results also showed that molten TNT seems to be more shock

sensitive than previously suspected. It appears that at relatively low shock stimulus levels,

the molten TNT may be undergoing a low velocity detonation, wherein the shock wave

traveling through the gap test pipe cavitates the molten TNT, greatly increasing its

sensitivity.
INTRODUCTION

The Army is continually faced with the problem of what to do with unneeded or outdated

munitions. Traditionally, these munitions were open-burned or detonated but these

options are being discouraged, and there is a move to recover explosives and make them

available for commercial use. The research reported here was part of the effort to evaluate

the safety of a process to recover TNT from MK-9 depth bombs by the autoclave meltout

process. In this process the depth bombs are heated to 121oC so that the TNT will melt and

run into a vat. Unfortunately, asphalt lining the inside surface of the bomb also melts and

flows out with the TNT. It is not known what effect the asphalt contamination and the

higher than normal process temperatures (121oC) would have on the sensitivity of the TNT. 

Three of the primary considerations in evaluating the safety of an explosive are its impact,

shock, and thermal sensitivities. We decided to evaluate the impact sensitivity of pure and

asphalt-contaminated TNT through the application of the drop weight impact test and

their shock sensitivity (or explosion-by-influence) through the application of the card gap

test, while differential scanning calorimetry was used for the evaluation of the thermal

sensitivity. Comparison of the behavior of the contaminated and pure TNT will elucidate

any additional hazards that must be considered when asphalt is present.

SAMPLES AND SAMPLE PREPARATION

Three types of TNT were utilized in this research program, crystalline TNT from the

Bureau of Mines' inventory (designated Key Number M-7601), flaked TNT supplied by the

Army, (Key Number X-4530A), and a mixture of flaked TNT with 2 pct asphalt (Key

Number X-4530C), also supplied by the Army. The mixture of flaked TNT with asphalt

was prepared by an Army ammunition plant to simulate the asphalt-contaminated TNT

recovered from the depth bombs. The mixture was prepared by mixing flaked TNT with

asphalt in a large steam kettle and heating it to above 120oC with continuous stirring. The

asphalt did not mix with the TNT and floated on top. When the mixture was processed to

produce flaked TNT, the product was nonhomogeneous, and varied in color from yellowbrown to light gray. Utilizing the asphalt-contaminated TNT in testing was not

straightforward since the composition of the sample was not uniform. Preparing a 45 mg

sample of the TNT contaminated with 2 pct asphalt for the liquid drop tester was especially

difficult; for these tests we assumed that the discolored flakes of TNT in the sample were

essentially pure TNT and what appeared to be chunks of asphalt were essentially pure

asphalt. We prepared test samples by weighing out 44 mg of the discolored, flaked TNT

and adding a 1-mg piece of asphalt shaved off one of the asphalt chunks. For the gap test,

we scooped a sample out of the box and assumed that since the sample size was relatively

large (-700g), its overall composition was 2 pct asphalt. Preparation of samples for the

thermal testing is discussed in the section of this paper on that work. The Army also

supplied a quantity of asphalt, designated Key Number X-4530B. 

DROP WEIGHT IMPACT TESTING

Many types of drop weight impact apparatus are available and it was uncertain which one

would prove useful in evaluating the impact sensitivity of molten pure and asphalt-
(1)The Bureau of Mines Drop Weight Impact Tester employs a 5 kg drop weight

with drop heights up to 320 cm and the Bureau of Explosives Machine employs a 3.63 kg

drop weight with drop heights up to 84 cm.

(2)"Standard Test Method for Drop-Weight Sensitivity of Liquid

Monopropellants", ASTM Designation D2540-93.

(3)Mason, C.M. and E.G. Aiken "Methods for Evaluating Explosives and

Hazardous Materials", Bureau of Mines Information Circular 8541, 1972.

contaminated TNT. The initial drop weight impact testing was conducted with two impact

testers, namely, the Bureau of Mines Drop Weight Impact Tester and the Bureau of

Explosives Machine(1); each apparatus was modified to permit the testing of molten TNT

at the temperature range of 90 to 130oC. In this series of tests the TNT would not initiate

at the maximum drop heights available, probably because in both instruments the sample

is not confined in the sample cup. During impact the sample was free to escape from the

cup. The next series of tests was conducted in a liquid drop tester according to the

procedure described in ASTM Method D2540-93(2). In this method a 2 kg drop weight is

used and the sample is confined in a sealed sample cell. Since this impact tester is intended

for liquids at ambient temperature, the test procedure does not require heating of the

sample. To test molten TNT, the sample and portions of the equipment had to be heated,

and maintained, at the desired test temperature. Procedures were developed to allow this. 

Testing was conducted at 90, 100, 110, 120, 125, and 130oC on flaked TNT and flaked TNT

contaminated with 2 pct asphalt (Key Numbers X-4530A and X-4530C, respectively) using

the Bruceton Up-and-Down method(3). Test results were used to calculate H50 values, the

height corresponding to a 50 pct probability of a positive result; H50 values were

determined for each temperature. 

The results of the impact sensitivity tests for pure TNT and TNT-asphalt mixtures are

presented in Tables 1 and 2 and Figure 1. The results show that impact sensitivity

increases with temperature for TNT and for TNT with asphalt. The H50 values obtained at

90oC, and perhaps even at 100oC, may be out of line. These temperatures are close to the

melting point of TNT, of -81oC. During preparation and transfer of the sample from the

oven to the impact tester, the sample, or a portion of it, might have solidified. If this were

the case, unreliable H50 values would be obtained. At the temperatures above 100oC, a

trend is observed whereby, initially the H50 values for the TNT-asphalt samples are higher

than the respective values for the pure TNT, and then at 125 and 130oC the H50 values for

the TNT-asphalt mixtures decrease more dramatically. These results suggest that at first

asphalt can act as a soft wax, and lower sensitivity of the TNT, but at the higher

temperatures, some reaction occurs between the two ingredients, and as a result the

sensitivity of contaminated TNT increases.

Thermal Analysis of TNT and TNT-Asphalt Mixtures

The literature indicates that impact sensitivities of organic high explosives are primarily a

function of the rates of thermal decomposition processes occurring in the temperature
(4)J.C. Dacons, H.G. Adolph, and M.J. Kamlet, "Some Novel Observations

Concerning the Thermal Decomposition of 2,4,6-Trinitrotoluene", Journal of Physical

Chemistry, v. 74, 1970, pp. 3035-3040.

(5)Reference to specific products does not imply endorsement by the Bureau of

Mines or USADACS.

range generated under the impact hammer. Thus, the thermal decomposition of TNT and

of TNT-asphalt mixtures, as determined by thermal analysis are of interest to this study.

The thermal decomposition of TNT was studied by various researchers, using different test

methods. These methods included gas evolution techniques (such as the modified Taliani

test or other off-gas tests), weight loss measurements, time to explosion (such as the Henkin

or modified Henkin test), and isothermal tests at different temperatures, among others. 

Results, as measured by values of activation energies, by products of decomposition, or by

other parameters vary, depending on test instrumentation used, on test procedures, on

sample size, and on other factors. Dacons, Adolph, and Kamlet(4) discuss the reasons for

some of the differences in the results.

Samples of TNT, of asphalt, and of TNT-asphalt mixtures were tested in the differential

scanning calorimeter (DSC), and the results are reported. The effect of rust on the thermal

behavior of TNT was also evaluated.

A Dupont 990 DSC(5) was used in all the tests. The tests were conducted in an atmosphere

of static air, or more specifically, in a self-generated atmosphere of gaseous vaporization

and decomposition products mixed with the original air atmosphere. Various heating rates

were used, and they are cited for each test. Aluminum pans with lids were used to contain

the samples during the tests. Inert glass microspheres, likewise contained in an aluminum

pan with lid, were used as reference material. The lids were not crimped onto the pans;

they were just pressed together.

Two samples of TNT were tested, Key Numbers M-7601 and X-4530A. The first sample,

Key Number M-7601, was crystalline and a darker yellow in hue than the second sample,

Key Number X-4530A, which consisted of flakes. Each of the two TNT materials was

lightly ground in a glass mortar and pestle prior to being sampled.

The crystalline TNT was heated at 10 and 20oC/min and resultant thermograms were

essentially the same. The thermogram for the test at 20oC/min is shown in Figure 2. The

thermogram contains the melting endotherm of TNT, followed by an endotherm due to the

evaporation of the TNT. The onset temperature for evaporation is a function of the

heating rate, and increases with higher heating rates. The flake TNT sample, Key No. X4530A, was heated at 20 and 50oC/min. The resultant thermogram for the test at 50oC/min

is presented in Figure 3. The two endotherms in the figure, as in Figure 2, signify the

melting and evaporation of the TNT. Small exothermic peaks, at 325, 378, 420, and 447oC,

suggest decomposition of left-over, trace amounts of TNT that did not evaporate. To

determine the ignition/explosion temperature of TNT in the DSC, or in other analytical

instrumentation, the TNT must be hermetically sealed, or be present in large amounts. If it
is not confined, it evaporates. Results for the tests are presented in Table 3.

Asphalt, Key No. X-4530B, supplied by the Army, was tested in the DSC, at heating rates

of 10 and 20oC/min. Thermograms are shown in Figures 4 and 5, and both display the

exothermic decomposition behavior of the asphalt, including the ignition of the flammable,

volatile decomposition products, when present in sufficient quantities, as indicated by the

sharp peak at 391oC, in Figure 4. Onset of exothermic behavior is at 260 and 230oC, for the

heating rates of 10 and 20oC/min, respectively. A small endotherm, at 67oC, is indicative of

the softening of the asphalt. The cause for the second endotherm, at about 125oC, is not

known. Results for the two tests with asphalt are given in Table 4.

The flake TNT, which was a fresher and more pure sample, was used for the preparation of

mixtures with asphalt, for tests in the DSC. The amount of asphalt in the mixtures varied

from test to test, and was as high as 31 pct. Larger amounts of asphalt were used on

purpose, in order to show clearly any reactions between the two materials. The asphalt is

sticky, and it was not easy to obtain samples of a desired weight. The asphalt was placed

first in the sample pan, and the TNT powder was sprinkled on top of it. Weights, when

available, and heating rates for the tests are cited in Table 4, and thermograms are

presented in Figures 6 to 9. It is evident from these thermograms that TNT reacts with

asphalt in an exothermic fashion, and the extent of reaction appears to depend on the

amount of asphalt. Onset temperature for exothermic behavior for the test in Figure 6 is

200oC, while for Figures 7 to 9, onset temperatures are between 225 and 235oC. Some

evaporation of TNT is indicated in Figures 7 and 9 by the presence of endotherms, but the

amount of evaporation is relatively small. As the asphalt softens, it may engulf and/or hold

on to the TNT, and slow down TNT evaporation. Even with smaller amounts of asphalt, as

in Figure 6, exothermic reaction starts prior to the decomposition of the asphalt by itself.

A sample of TNT already mixed with asphalt (Key No. X-4530C), sent by the Army, was

also tested. This material is the asphalt-contaminated TNT recovered from munitions. 

Despite heating to above 120oC in a steam kettle with continuous mixing, the TNT and

asphalt did not mix significantly. The sample consisted of large chunks of either yellowbrown or gray material. The concentration of asphalt in the sample varied from chunk to

chunk, and probably within each chunk. For a test, a sample was lightly ground in a glass

mortar and pestle. Two tests, both at 10oC/min, were done. In one test only the yellowbrown portion was utilized, and the resultant thermogram is shown in Figure 10. In the

second test, the sample contained mostly the yellow-brown portion, plus a small amount of

the gray portion. The thermogram for the latter test is presented in Figure 11. A small

amount of evaporation is evident in both figures, but more so in Figure 11, and it is

followed by an exothermic behavior. Onset of exothermic behavior is at 240 to 250oC. 

Both thermograms contain a sharp endotherm, with peak temperature at 286 and 273oC,

respectively. This endotherm may be indicative of some boiling; a reaction of the sample

with the DSC surface is also possible, however, evidence of leakage onto the surface was not

observed. Melting of a compound or an adduct, formed between TNT and the asphalt

during the preparation stage, is more probable. Results are summarized in Table 4.

In addition to asphalt, TNT may come in contact with rust, during the recovery phases. 

Therefore, it was desired to find out if these two ingredients interact thermally. The effect

of rust on the thermal behavior of both TNT samples was thus determined. In the case of
(6)A.J.B. Robertson, "The Decomposition, Boiling, and Explosion of Trinitrotoluene

at High Temperatures", Trans. Faraday Soc., v. 44, 1948, pp. 977-983.

(7)J. Harris, "Autoignition temperatures of Military High Explosives by Differential

Thermal Analysis", Thermocheimica Acta, v. 14, 1976, pp. 183-199.

(8)T.B. Joyner, "Thermal Decomposition of Explosives, Part 2. Effect of Asphalt on

the Decomposition of TNT", Report No. NWC-TP-4709, Part 2, April, 1969, 17 pp.

the crystalline TNT (Key No. M-7601), the TNT was weighed first, and rust was then

sprinkled on it, with the idea of slowing down the evaporation of the TNT somewhat. In

the case of the flake TNT (Key No. X-4530A), the rust was placed first in the pan, and the

TNT was then placed on top of the rust. Both tests were conducted at a heating rate of

50oC/min in the temperature range of interest, in an attempt to minimize vaporization, and

have a sufficient amount of TNT for reaction. Figures 12 and 13 display the thermograms

for the crystalline and flake samples, respectively. As can be seen in the thermograms, the

presence of the rust contributed to the exothermic behavior of the mixture, either

catalytically or due to a chemical reaction between TNT and the rust. Additionally, the

rust may have slowed down the evaporation of the TNT so that enough TNT was available

for reaction. Onset temperature of exothermic reaction in Figure 12 is not easy to

determine exactly; the endotherm due to evaporation masks the exothermic initiation. 

However, at 300oC exothermic behavior is clearly visible. In Figure 13, onset of exothermic

behavior is seen at 280oC. The addition of small amounts of many diverse materials has

been found to accelerate the thermal decomposition of TNT. Strong promoters of

decomposition include iron compounds(6). According to Robertson, ferric oxide, present to

the extent of 10 pct in TNT caused ignition at 300oC with no perceptible prior

decomposition, probably as a result of a reaction between the TNT and the ferric oxide. 

The temperatures of the first exothermic peak in the thermograms in Figures 12 and 13 are

both at 310oC. Within experimental variation these temperatures agree with the

temperature quoted by Robertson. At the termination of the tests with the rust, the sample

pans contained a black residue. Charring of the TNT is probable. The rust, (Fe2O3@XH2O),

originally brown in color, may have converted to FeO or Fe3O4 (both black), or to ferrous

and/or ferric nitrate. The latter two salts are not black, but would be masked by the char. 

All test results are summarized in Table 4.

Onset temperatures for exothermic decomposition of flake TNT-asphalt mixtures, prepared

individually for each test in the DSC varied from 200 to 235oC. The onset temperatures for

the mixtures prepared by the army were slightly higher at 240 to 245oC. In all of these

tests, the samples were not confined or hermetically sealed. In comparison, corresponding

onset temperatures, obtained in DTA tests for confined TNT samples heated at 10 and

20oC/min, were about 296 and 308oC, respectively(7). These results present clear evidence

that asphalt affects the thermal decomposition of TNT, and lowers its initiation

temperature, and its presence will, likewise, affect the sensitivity of TNT in impact tests at

elevated temperatures.

The effect of asphalt on the decomposition of TNT was evaluated by T.B. Joyner(8). In his

tests, isothermal runs were made at 10-degree intervals over the range of 160 to 270oC. The
(9)Ribovich, J., R.W. Watson, and F.C. Gibson, "Instrumented Card-Gap Test",

AIAA Journal, vol. 6, no. 7, 1968, pp. 1260-1263.

runs utilized 10- and 25-mg samples of TNT and asphalt, respectively, and were conducted

under nitrogen pressure to minimize evaporation of the TNT. The progress of reaction was

followed by pressure increase. Joyner found that asphalt greatly accelerated the

decomposition of TNT. The percent of asphalt in his test samples was high, 71.4 pct. 

Asphalt by itself was also tested at 250oC for 16 h, and decomposition was not observed. 

Although the reason for the proportions of TNT and asphalt chosen by Joyner is not given,

it seems that there was a similar desire to easily observe the possibility of reaction between

the two compounds. 

The results of the tests with the rust mixtures, likewise show that the decomposition of TNT

is sensitized by the rust, and onset temperature is lowered. DSC tests of TNT mixtures,

with rust or with asphalt, at lower heating rates could possibly indicate still lower onset

temperatures for decomposition.

Solid TNT is not very sensitive to impact (relatively speaking), unless confined by sand

paper discs. Molten TNT, at temperatures near and above the melting point, is more

sensitive to impact. The presence of asphalt desensitizes the TNT to a small extent. This is

to be expected. Materials such as wax (CxHy) are used to desensitize explosives to impact

and friction. Asphalt may contain wax, and it itself can act as a desensitizer, but if the

mixture is heated to a higher temperature, such as 120oC or 130oC, and it reacts and forms

a small amount of active intermediates, and then the impact hammer raises the

temperature of the test sample to the range where TNT and asphalt interact much more

rapidly, the temperature will rise and overall reaction in the impact test will be accelerated. 

Extent of reaction can be observed and assessed by the degree of damage to the test

instrument. Indeed, the combined results from the impact and thermal tests support this

hypothesis.

CARD GAP TESTING

Card gap testing was conducted to evaluate the sensitivity of TNT and TNT contaminated

with asphalt to shock stimulus. The apparatus for the Bureau of Mines Gap Test is shown

in Figure 14. The test sample was contained in a cylinder consisting of a 16-inch length of

11⁄2-inch schedule 80 black seamless steel pipe. A mild steel witness plate 6 inches square

and 0.125 inches thick was mounted at the upper end of the sample pipe and separated

from it by Lucite spacers 0.062 inches thick. A 2-inch diameter, 2-inch long cast Pentolite

booster placed against the bottom of the pipe provided the shock stimulus to the sample; a

2-inch diameter Lucite cylinder of different lengths, varying from 0.25 to 4 inches, was

placed between the booster and the pipe to attenuate the shock to the desired stimulus level

and acted as the gap. The Lucite cylinder was cemented to the pipe with high-temperature

silicone rubber cement. A continuous probe of fine wire, which measured the velocity of

detonation(9) was mounted on the inside wall of the sample pipe. The Pentolite booster

was initiated by a No. 8 strength instantaneous detonator. 
(10)Recommendations on the Transport of Dangerous Goods: Tests and Criteria,

Second Edition, Test 1 (a)(iii), "Gap Test for Solids and Liquids", published for the United

Nations by Labelmaster, Chicago, IL, pp 19-23, 1990.

The U.N. test protocol(10) calls for the use of a bubbler in testing liquids, 

but no bubbler was employed here since it was expected that due to its high viscosity, the

molten TNT would not be agitated to the point where it would contain fine bubbles. In

addition, since card-gap tests are generally not conducted at elevated temperatures, a

procedure for doing this was developed by trial and error. Initially the gap test pipe was

wrapped with nichrome heating ribbon with the intent of heating and melting the TNT

directly in the pipe. Preliminary trials with wax showed, however, that a significant

temperature gradient developed within the melt in the pipe and this technique was

abandoned. The wraps of nichrome heating ribbon around the pipe did prove useful for

preheating the pipe and were retained for this purpose. Pipe insulation was placed around

the pipe-nichrome heating ribbon assembly to minimize heat loss. At the beginning of the

test series, the TNT was heated in a large Pyrex beaker in a Fisher Isotemp Forced Draft

Oven, Model 800. For this procedure the pipe was preheated to the test temperature using

the nichrome heating ribbon and the TNT was heated to several degrees above the chosen

test temperature. The TNT was poured into the pipe and the temperature was monitored

using a thermocouple. It was surmised that by heating the TNT in the oven to several

degrees above the test temperature, the TNT would be close to the test temperature after it

was poured into the pipe and the shot could be fired immediately. This procedure worked

quite well, however, due to evaporation TNT crystals precipitated on the outside of the

oven. Due to the possibility of TNT crystals also being deposited within the oven, and the

associated hazard, this procedure was also abandoned. Instead, a steam-heated kettle was

used to heat the TNT. The steam heat heated the TNT to a temperature of 105-115oC. The

heated, molten TNT was poured into the pipe and then the nichrome heating ribbon

wrapped around the pipe was used to heat the filled pipe up to the test temperature. This

procedure proved satisfactory. Testing was conducted on pure TNT and TNT

contaminated with 2 pct asphalt (Key Numbers X-4530A and X-4530C, respectively) at 90,

100, 110, 120, 125, and 130oC.

Test results for the pure TNT and asphalt-TNT mixture were essentially the same, and will

be discussed together. Three criteria were used in evaluating the results of the tests: a hole

in the witness plate, fragmentation of the pipe, and the measured velocity of detonation. 

The results fell into one of three types. At small gaps, less than 1/2 inch, there was a clean

hole in the witness plate, the pipe was fragmented into a hundred or more small pieces, and

the detonation velocity was about 6,400 m/sec; all clear indications of a high velocity

detonation. For gaps of 4 inches or more there was no damage to the pipe or witness plate,

indicating that the TNT did not react. For the mid-range gaps, 1/2 to 3 inches, the witness

plate suffered varying degrees of damage ranging from undamaged to being domed, bent,

or torn, and the pipe was peeled open and sometimes fragmented into up to 43 pieces. It

was clear that the TNT was not detonating at high velocity in the 1/2- to 3-inch gap range

but a very energetic reaction was occurring. The violence of this reaction was further

evidenced by the observation that the 8- by 8- by 24-inch logs set up around the card gap

test assembly to stop shrapnel, were torn apart. Reaction velocities between 1,300 and
(11)Hay, J.E. and R.W. Watson, Description of a Shock Sensitivity/Detonation

Propagation Test for Defining Class 1 Explosive Substances Which are Liquids, Pittsburgh

Research Center Report No. 4301.

2,000 m/sec were recorded for these tests with mid-range gaps but it was not clear whether

these values represented reaction of the TNT or the shock produced by the booster; this is

discussed in more detail the next sections.

For comparison, a series of tests on an essentially inert aqueous solution of sodium nitrate

at 80oC, with a density similar to that of molten TNT (55 pct sodium nitrate in water with a

density of 1.44 g/cc) were conducted at gaps of 1/2, 1, and 2 inches. In the tests of the

aqueous sodium nitrate solution the witness plate was relatively undamaged; dome depths

in the witness plate were 1/8 inch or less as compared to dome depths of up to 1/2 inch

with broken or torn witness plates for TNT tests at a larger 3-inch gap. For tests with the

sodium nitrate solution with a 1/2-inch gap, up to 6 inches of the pipe was split with no

damage beyond minor flaring at gaps of 1 and 2 inches. Figure 15 presents a comparison

of pipe and witness plate damage for TNT and the sodium nitrate solution at 100oC; it is

quite apparent from these photographs that in the 1/2- to 3-inch gap range, the damage

wrought by TNT is well beyond that expected from the booster alone. 

Test results for all of the gap tests are summarized in Tables 5 and 6. At 90 to 125oC, the

pure and asphalt-contaminated TNT detonate at high velocity for gaps of 1/4 inch or less,

and undergo a low order reaction for gaps of 1/2 to 3 inches, inclusive. At 130oC both the

pure and contaminated TNT detonate at high velocity for a 1/2-inch gap but do not

detonate at high velocity for gaps of 3/4 to 3 inches.

It is possible that the molten TNT is undergoing low velocity detonation for gaps of about

1/2 to 3 inches. In a low velocity detonation the shock wave travels through the walls of the

pipe ahead of the shock wave in the molten TNT, causing the TNT to cavitate and hence

sensitizing the molten TNT. It is of interest to note that the pure and asphalt-contaminated

TNT change from low order reactions to no reactions in the 3- to 4-inch gap range, which is

similar to the gap range Hay and Watson(11) found for molten TNT at 85oC with added

bubbles in an identical test configuration going from detonation to no detonation; at 3.5

inches the molten TNT with added bubbles detonated but at 4 inches it did not detonate. 

The molten TNT in the steel pipe seems to behave as if it were sensitized with added

bubbles.

The origin of the recorded velocities for the tests of TNT at mid-range gaps (1/2 to 3 inches)

is not clear; is this an indication of a reaction in the TNT or merely the booster-generated

shock wave traveling through the molten TNT? Figure 16 presents velocity probe

oscilloscope traces for tests of molten TNT at 100oC for gaps of 0.25 to 4 inches, as well as

analogous traces for tests of the aqueous sodium nitrate solution. Comparison of results for

TNT tests HGT-39 and HGT-38 (gaps of 0.5 and 0.75 inches, respectively) with results for

aqueous solution tests HGT-84 and HGT-85 (gaps of 0.5 and 1 inches, respectively) reveal

that there is no great difference between the velocity traces of the TNT and the solution. In

both TNT and the sodium nitrate solution at gaps of 0.5 to 1 inches velocities are relatively

high, at 2,100 to 2,550 m/sec, and then they decay to 1,400 to 1,500 m/sec at about a third
of the way down the length of the pipe. The above results indicate that the velocities

recorded for the TNT tests at gaps of 0.5 to 3 inches (with the exception of 130oC TNT at a

0.5-inch gap, which undergoes high velocity detonation) cannot be unambiguously

attributed to a low-velocity detonation reaction in the molten TNT. The velocity probe

may be recording the low-velocity detonation of the TNT or merely the booster-produced

shock wave. It is possible that the velocity of the low-velocity detonation and that of the

booster-produced shock wave are so close that we cannot discern the difference without

further study. In the 1/2- to 3-inch gap range the molten TNT is clearly reacting very

energetically, as evidenced by the damage to the test pipe and witness plate.

As mentioned above, the pure TNT and the TNT contaminated with 2 pct asphalt behaved

similarly in these tests. Since the asphalt did not mix well with the molten TNT but rather

floated on the top when loaded in the gap test pipe, this result is not too surprising . Some

component of the asphalt had mixed with the TNT since the color of the TNT was changed

from yellow to light brown but this was apparently not enough to change the shock

sensitivity significantly.

A review of the results in terms of high-velocity detonation reveals a small effect of

temperature on the shock sensitivity of molten TNT. At 90 to 125oC, the molten TNT will

detonate at high velocity for gaps of 0.25 inches and less, but will not detonate at high

velocity for gaps of 0.5 inches and greater. At 130oC, however, the molten TNT will

detonate at high velocity at a gap of 0.5 inches. TNT at 130oC is more sensitive to shock

than it is at the lower temperatures.

Conclusions

This project was initiated due the concerns over the safety of the autoclave meltout

operation for recovering TNT from Mk-9 depth bombs. In melting out TNT from the

depth bombs, the asphalt liner material would also melt and contaminate the TNT, possibly

sensitizing the TNT and creating a hazardous situation. Based on the research reported

here we see that contamination by asphalt somewhat adversely affects the thermal and

impact sensitivity of the TNT at higher temperatures, above -110oC. Gap test results

indicate that the shock sensitivity of molten TNT, though not affected by asphalt

contamination, must also be considered. Hay and Watson(12) have shown that molten

TNT will detonate at gaps of up to 3.5 inches with the addition of bubbles and we have

shown that molten TNT can explode at gaps up to 3 inches without added bubbles. These

results put molten TNT in the sensitivity range of nitromethane and monomethylamine

nitrate solutions (detonations at 2.5 and 4.5 inches, respectively, with added bubbles), both

of which have been involved in serious accidental explosions. 

Care must also be taken in controlling the temperature of the TNT because the asphalt

affects its thermal sensitivity. The thermal analysis test results show that when asphalt is

present in TNT, it greatly accelerates the exothermic decomposition of TNT, starting at

temperatures near 200oC. In the thermoanalytical tests reported here, asphalt was

deliberately used in excess, to assure good contact with TNT. It is quite probable that

during loading of the original explosive devices, some of the TNT mixed with the asphalt

coating and formed intimate mixtures of high asphalt concentration. If, somehow, the

molten TNT heated to temperatures near 200oC, it may undergo accelerated reaction.
Table 1. Impact sensitivity test results for pure TNT (Key Number X-4530A). (Each value

of H50 is based on 10 trials.)

Temperature,

oC

H50,

cm

Standard Deviation,

cm

90 7.8 1.2

100 7.8 1.2

110 6.5 1.3

120 4.9 1.2

125 4.2 1.8

130 4.5 1.4

Table 2. Impact sensitivity test results for TNT contaminated with 2 pct asphalt (Key

Number X-4530C). (Each value of H50 is based on 10 trials. 

Temperature,

oC

H50,

cm

Standard Deviation,

cm

90 7.9 1.2

100 7.4 1.1

110 7.8 1.2

120 6.8 1.1

125 5.4 1.5

130 3.3 1.1

Table 3. DSC test results for TNT. 

Sample Figure

No.

Heating

rate,

oC/min

Sample,

weight,

mg

Weight

loss,

pct

Final test

temperature

oC

M-7601 2 10 2.4 100 280

M-7601 N.S. 20 4.4 95 347

M-7601 N.S. 20 2.5 100 351

X4530AN.S. 20 3.7 100 435

X4530AN.S. 50 5.5 100 477

N.S.: Not Shown.
Table 4. DSC test results for asphalt and for TNT-asphalt mixtures.

Sample Figure

No.

Heating

rate,

oC/min

Sample

Weight,

mg

Weight

loss,

pct

Onset

temp,

oC

Final

test

temp, oC

Comments

Asphalt,

X-4530B

4 10 2.6 - 260 405 Sample leaked

out

Asphalt,

X-4530B

5 20 4.0 - 230 485 Sample leaked

out

Flake

TNT

+ asphalt

6 10 - - 200 402 -

Flake

TNT

+ asphalt

7 10

(to 135oC)

then 50

-

- 230 497 -

Flake

TNT

+asphalt

8 10

(to 130oC)

then 20

8.1 TNT

3.6 asphalt

(30.8 pct)

- 235 389 -

Flake

TNT

+ asphalt

9 5

(to 165oC)

then 10

7.1 TNT

1.0 asphalt

(12.4 pct)

65 225 296 -

TNT

+ asphalt

10 10 2.5 84 240 304

TNT

+asphalt

11 10 3.9 72 245 294

M-7601

+ rust

12 50 3.3

0.7

88 300 407 TNT weighed first;

rust sprinkled on top

X-4530A

+ rust 13

10

(to 90oC)

then 50

- - 280 435

Rust placed first; TNT

on top of rust
Table 5. Summary of gap test results for TNT (X-4530A).

Gap, in 90oC 100oC 110oC 120oC 125oC 130oC

4.00 HGT-45 NR HGT-64 NR HGT-47 NR HGT-61 NR HGT-49 NR HGT-43/67 NR

3.00 HGT-44 EXP HGT-65 EXP HGT-46 EXP HGT-62 EXP HGT-48 EXP HGT-42/68 EXP

2.00 HGT-6 EXP

1.50 HGT-8 EXP

1.00 HGT-7 EXP HGT-15 EXP

0.75 HGT-30 EXP HGT-38 EXP HGT-32 EXP HGT-63 EXP HGT-36 EXP HGT-12/69 EXP

0.50 HGT-31 EXP HGT-39 EXP HGT-33 EXP HGT-71 EXP HGT-37 EXP HGT-11/70 DET

0.25 HGT-34 DET HGT-40 DET HGT-35 DET HGT-66 DET HGT-41 DET HGT-9 DET

NR - No Reaction

EXP - Explosion, possibly a low velocity detonation

DET - Detonation, high velocity

Table 6. Summary of gap test results for asphalt-contaminated TNT (X-4530C).

Gap, in 90oC 100oC 110oC 120oC 125oC 130oC

4.00 HGT-51 NR HGT-72 NR HGT-60 NR HGT-53 NR HGT-56 NR HGT-19/77 NR

3.00 HGT-50 EXP HGT-73 EXP HGT-52/57

NR/EXP

HGT-54 EXP HGT-55 EXP HGT-20/78 EXP

2.00 HGT-18 EXP

1.50

1.00

0.75 HGT-21 EXP HGT-24 EXP HGT-58 EXP HGT-26 EXP HGT-16/79 EXP

0.50 HGT-22 EXP HGT-74 EXP HGT-25 EXP HGT-76 EXP HGT-27 EXP HGT-17/80

DET/EXP

0.25 HGT-23 DET HGT-75 DET HGT-28 DET HGT-59 DET HGT-29 DET
Figure 1. Drop weight impact sensitivity test results for pure and

asphalt-contaminated TNT.
Figure 2. DSC thermogram for crystalline

TNT (20oC/min, 4.4-mg sample).

Figure 3. DSC thermogram for flake TNT

(50oC/min, 5.5-mg sample).

Figure 4. DSC thermogram for asphalt

(10oC/min, 2.6-mg sample).

Figure 5. DSC thermogram for asphalt

(20oC/min, 4.0-mg sample).

Figure 6. DSC thermogram for a mixture

of flake TNT with asphalt (10oC/min, not

weighed). Figure 7. DSC thermogram for a mixture

of flake TNT with asphalt (variable

heating rate, not weighed).
Figure 10. DSC thermogram for a sample

of premelted TNT with asphalt (10oC/min,

2.5-mg sample). 

Figure 12. DSC thermogram for a

mixture of crystalline TNT with rust

(50oC/min, 4.0 mg total weight).

Figure 13. DSC thermogram for a

mixture of flake TNT with rust (variable

heating rate).

Figure 11. DSC thermogram for a sample

of premelted TNT with asphalt (10oC/min,

3.9-mg sample).

Figure 8. DSC thermogram for a mixture

of flake TNT with asphalt (variable

heating rate, 11.7 mg total weight).

Figure 9. DSC thermogram for a mixture

of flake TNT with asphalt (variable

heating rate, 8.1 mg total weight).
Figure 14. Card gap test setup. 
HGT-7. TNT, 1-inch

gap, 100oC.

HGT-39. TNT, 0.5-inch

gap, 100oC.

HGT-38. TNT, 0.75-inch

gap, 100oC.

HGT-40. TNT, 0.25-inch

gap, 100oC.

HGT-86. Inert, 2-inch

gap, 100oC.

HGT-85. Inert, 1-inch

gap, 100oC.

HGT-84. Inert, 0.5-inch

gap, 100oC.

HGT-64. TNT, 4-inch

gap, 100oC.

HGT-65. TNT, 3-inch

gap, 100oC.

HGT-6. TNT, 2-inch

gap, 100oC.

HGT-8. TNT, 1.5-inch

gap, 100oC.

Figure 15. Comparison of pipe and witness plate damage for TNT and aqueous 

sodium nitrate solution at 100oC.
HGT-39. TNT, 0.5-inch

gap, 100oC.

V=2,200/1,400 m/sec.

HGT-38. TNT, 0.75-inch

gap, 100oC.

V=2,100/1,400 m/sec.

HGT-40. TNT, 0.25-inch

gap, 100oC.

V=6,400 m/sec.

HGT-86. Inert, 2-inch

gap, 100oC.

V=1,300/1,950 m/sec.

HGT-85. Inert, 1-inch

gap, 100oC.

V=2,400/1,400 m/sec.

HGT-84. Inert, 0.5-inch

gap, 100oC.

V=2,550/1,500 m/sec.

HGT-64. TNT, 4-inch

gap, 100oC.

V=1,300 m/sec.

HGT-65. TNT, 3-inch

gap, 100oC.

V=1,250 m/sec.

HGT-6. TNT, 2-inch

gap, 100oC.

V=1,300 m/sec.

HGT-8. TNT, 1.5-inch

gap, 100oC.

V=1,250 m/sec.

Figure 16. Comparison of velocity traces for TNT and aqueous sodium nitrate 

solution at 100oC.