Co-Precipitation Studies on Lead Azide with Tetrazole Derivatives-a search for lead azide substitute

Propellants, Explosives, Pyrotechnics 17,241-248 (1992) 24 1

Co-Precipitation Studies on Lead Azide with Tetrazole Derivatives - A Search for Lead Azide Substitute

G. Om Reddy*

INBRI, Division of IDL Chemicals Ltd., Malleswaram, Bangalore 560 003 (India)

Untersuchungen iiber die Mitfallung von Bleiazid rnit Tetrazolde- rivaten - eine Suche nach einem Bleiazid-Ersatz

Die Mitfallung von Bleiazid mit verschiedenen Tetrazol- und Nitro- phenolderivaten wird diskutiert. Das thermische Verhalten voii Blei- azid vor und nach der Mitfallung wird untersucht mittels DSC. Die thermischen Untersuchungen zeigten, daB die Mitflllung von Bleiazid mit anderen flammempfindlichen Verbindungen eine feste Mischung des Bleiazid rnit den Bleisalzen der Tetrazol- und Nitrophenolderivate aber keine einheitliche Verbindung gebildet hat.

Die Auswertung der Sprengstoffeigenschaften zeigte, daR die Mit- fallung nicht nur die Flammempfindlichkeit von Bleiazid verbessert sondern auch die Gefahrlichkeit beim Mischen von Bleiazid rnit flammempfindlichen Materialien eliminiert. Eine gute Korrelation zwischen der thermischen Empfindlichkeit und Flammempfindlichkeit wird beobachtet, beide nehmen ab.

Summary

Co-precipitation of lead azide with various tetrazole and nitrophen- 01 derivatives is discussed. Thermal behaviour of lead azide before and after co-precipitation is studied using DSC. Thermal study indicated that the co-precipitation of lead azide with other flame sensitive compounds produced an intimate mixture of lead azide and lead salts of tetrazole and nitrophenyl derivatives but not a single compound.

Explosive properties evaluation indicated that the co-precipitation process not only improves the flame sensitivity of lead azide but also eliminates the hazardous process of physical mixing of lead azide with flame sensitive materials. A good correlation between thermal sensitivity and flame sensitivity is noticed. Both thermal and flame sensitivity decreased.

1. Introduction

Among initiators, lead azide (LA) is a very powerful initiatory explosive with a high sensitivity to friction. Its flame sensitivity is not sufficient to use it alone in detonators. Therefore, it is often mixed with lead styphnate (LS) and powdered aluminium. Thus prepared composition com- monly known as ASA mixture, has all qualities required for a good initiator including flame sensitivity. Another draw- back of LA is its tendency to form copper azide, a highly sensitive material, in copper shells. Though the addition of LS to LA improves the flame sensitivity, it also enhances the possibility of copper azide formation. Many research- ers(') have tried to overcome this problem. Research has been continued in the past to find an alternative initiator to replace ASA composition but no satisfactory candidate has been found so far for commercialization. Robensteid2) co- precipitated LA and lead 2,4-dinitroresorcinate to improve the LA performance.

A similar attempt is made and LA is co-precipitated with various flame sensitive materials and the results are dis-

Etudes sur la coprecipitation de I'azoture de plomb avec des deri- ves de tetrazone - Recherche d'un substitut d'azoture de plomb

On examine la coprtcipitation de I'azoture de plomb avec differents dCrivCs de tttrazole et de nitrophCnol. Le comportement thermique de l'azoture de plomb est CtudiC au moyen de la DSC avant et aprbs co- prkcipitation. Les Ctudes thermiques ont montrk que la coprecipitation de l'azoture de plomb avec dautres composes sensibles aux flammes a form6 un melange solide dazoture de plomb avec les sels de plomb des dtrivCs tCtrazol et nitrophenol mais pas de composk homogkne.

L'evaluation des propriCtCs des explosifs a montrC que la coprkcipi- tation n'amkliore pas seulement la sensibilite aux flammes de I'azoture de plomb mais Climine aussi le caractkre dangereux du mklange de I'azoture de plomb avec des matCriaux sensibles aux flammes. On ob- serve un bonne corrklation entre la sensibilitC thermique et la sensibi- lit6 aux flammes; touts deux diminuent.

cussed in this paper. The compounds which are screened for better flame sensitivity are lead azotetrazole (Pb-AzTz, l ) , lead hydrazotetrazole (Pb-HzTz, 2), lead salt of 2-hydroxy- 3,5-dinitrobenzaldehyde (Pb-2H-3,5-DNBA, 3), lead salt of 4-hydroxy-3,5-dinitrobenzaldehyde (Pb-4H-3,5-DNBA, 4) , lead salt of 2-hydroxy-3,5-dinitrobenzaldehyde- 1 H-tetrazol- 5-yl-hydrazone (Pb-2H-3,5-DNBA-SHzTz, 5 ) and lead salt of 4-hydroxy-3,5-dinitrobenzaldehyde - 1 H-tetrazol-5-yl- hydrazone (Pb-4H-3,5-DNBA-SHzTz, 6). The structures of all these compounds are displayed in Scheme - 1.

This paper discusses the method of co-precipitation of LA with various compounds listed in Scheme-1, and the thermal and explosive properties of all those co-precipitated compounds.

2. Experimental

2.1. Instrumentation

Mettler TA-2000 C and Perkin-Elmer DSC- I B were used for recording TG-DSC thermograms. Non-isothermal study was carried out under helium purge gas. The instru- ments were calibrated with appropriate standards. Emery paper friction test apparatud3) developed by ERDE, Eng- land was employed for testing the friction sensitivity. A load of 15 kg applied on the roller when an arm with a 4 kg weight, suspended from its end, was lowered into position. Oakey grade "0" emery paper was used. Perkin-Elmer-577 grating infra-red spectrophotometer (IR) was used and Jeol DX-300 double focussing magnetic sector mass spectrome- ter was used for mass spectral study. The efficiency of co- precipitated samples was determined by evaluating minimum quantity of initiator explosive required for base

* Present address: Standard Research Centre, Dr. Reddy's Group, Hyderabad - 500016 (India).

0 VCH Verlagsgesellschaft, D-6940 Weinheim, 1992 0721-31 15/92/0510-241 $3.50+.25/0

242 G. Om Reddy

Scheme- 1

Propellants, Explosives, Pyrotechnics 17,241-248 (1 992)

scneme - z

1 2

0 'N=O

H ';c+O-Pb

N =O O=N

od 4 Lo .NO2

charge (PETN) initiation by adopting lead plate test. No. 6 detonator with 30 cg of PETN as base charge was used and the results were compared with standard 80:20 ASA mixture. Ball drop tested4) was used to determine the impact sensitivity of co-precipitated samples. Material was spread on a steel base and a steel ball (28 g) was dropped from a pre-determined height with the help of an electromagnet. Bruceton up-and-down method was used to obtain the so called 50% height i.e. the height of the drop for which 1/2 trials are "go" and 1/2 trials are "no-go". The No Fire Level (NFL) was also determined. Safety fuse was employed for initiation to assess the flame sensitivity.

2.2. Material

Dextrinated lead azide (DLA) was prepared as reported(". Azo and hydrazotetrazoles were prepared and de- scribed in our previous publication(@. 2-Hydroxy-3,5-dinitro benzaldehyde (7) and 4-hydroxy-3,5-dinitro benzaldehyde (8) were prepared('). The compounds 2-hydroxy-35 dinitrobenzaldehyde- I H-tetrazol-5-yl-hydrazone (9) and 4- hydroxy-3,5-dinitrobenzaldehyde- 1H-tetrazol-5-yl-hydrazone (10) are new and were not reported earlier. The procedure is given below.

The alcoholic solution of 2-hydroxy-3,5-dinitrobenzaldehyde was mixed with 5-hydrazinotetrazole hydrochloride (ZZ) in aqueous medium and refluxed for one hour. The re- action mass was cooled, filtered and washed. The yield was quantitative. The same procedure was used to prepare the hydrazone of 4-hydroxy-3,5-dinitrobenzaldehyde. The reactions are shown in Scheme-2.

HCI + H2N-HN-C '/"'F; ".N

H NO2 11

7 R 1 = O H , R 2 = H

8 R l = H , R 2 = O H I 9 R , = O H , R 2 = H

10 R , = H I R 2 = OH

After screening several compounds for their explosibility only four compounds (7-10) are converted into lead salts. The reactions are shown in Scheme-3.

A typical co-precipitation procedure is given below. All other co-precipitations were carried out using the same procedure.

Scheme - 3

ti

)c =o N\02

7 i i ) p b ' 2 i ) NaOH ' O Z N G O - P b - O e - 'NO2 O=C

3 'H

i) NaOH

i i ) Pb" 9

Propellants, Explosives, Pyrotechnics 17,241-248 (1992) Co-Precipitation Studies on Lead Azide with Tetrazole Derivatives 243

The following stock solutions were prepared: Solution A: 5% solution of sodium salt of the flame

sensitive material. Solution B: 5% solution of sodium azide Solution C: 10% solution of lead acetate Solution D: 1 % solution of dextrin Solution E: 1 % solution of carboxymethylcellulose

The quantity of these solutions used were such that ap- proximately 2-3 g of co-precipitated product was obtained.

Typical procedure: Solution C was taken into a 500 ml stainless steel beaker which was clamped firmly on a water bath. The temperature of the bath was maintained at 60 _+

1.O"C. Solution D was added to solution C and stirred for a few minutes. The solutions A, B and E were mixed together and added from a dropping funnel to a solution of C and D at 60°C over a period of 20 min while stirring. After com- pletion of addition, the stirring was continued for 10 min at the same temperature before cooling to room temperature. The supernatant solution was decanted. The settled precipi- tate was filtered and washed with demineralized water to make it free from water soluble impurities and finally with

(CMC)

S c heme - 4

14

95% ethyl alcohol. The material was dried at 60°C in a hot air oven. The reactions are shown in Scheme-4.

3. Results and Discussion

3.1. Physical properties

Table 1 lists the decomposition and explosion temperatures, bulk density, colour and lead content of all the compounds (1 -6) and co-precipitated compositions with lead azide (Scheme-4). For comparision, dextrinated lead azide (DLA) was also studied. All these compounds were yellow to orange in colour and bulk densities were low when compared with DLA. The percentage of lead was used as a ba- sis for determination of molar percentage of the constituents present in the co-precipitated compositions. As the percentage of LA decreased in the composition, the bulk density also decreased. All explosives listed in Table 1 were highly sensitive to heat and exploded while heating on a spatula in the flame.

Though the bulk density was low, the free flowing pro- perty was satisfactory. The crystals without crystal modi-

A r\

0 'c

Dextrinated lead

18

12

az i de (DLA)

17

15

244 G. Om Reddy Propellants, Explosives, Pyrotechnics f 7,241 -248 (1 992)

Table 1. Physicochernical Properties

Compound Lead [%.I Colour Bulk Decomposition/Explosion obs. calc. Density [g/cm'] Temp (TP) I"C1

Pb-AzTz ( I ) Pb-HzTz (2) Pb-2H-3,S-DNBA (3) Pb-4H-3,S-DNBA (4) Pb-2H-3,S-DNBA- 5HzTz (5)

SHzTz (6) Pb-4H-3,5-DNBA-

LA-Pb-AzTz (12) LA-Pb-HZTL (13) LA-Pb-2H-3,S- DNBA (14)

DNBA (15) LA-Pb-4H-3.5-

LA-Pb-2H-3,S- DNBA-~HzTz (16) LA-Pb-4H-3,S- DNBA-SHZTL (17) DLA (18)

Note:

-~

54.84 55.00 31.12 3 1.98 25.80

24.98

67.12 67.52 58.00

64.98

61.85

61 50

69.81

55.79 55.49 32.90 32.90 26.10

26.10

67.99 66.68 59.66

65.39

62.12

62.32

71.10

Yellow Light yellow Orange Orange Yellow

Yellow

Yellow Yellow Orange

Dark yellow

Yellow

Reddish yellow

White

0.85 0.80 0.30 0.45 0.52

0.65

0.95 0.84 0.67

0.58

0.57

0.70

1.30

180.0 143.0 320.0

280.0, 320.0 278.0

264.0

200.0, 343.0 195.0, 325.0

325.00

285.0, 340.0

280.0, 335.0

266.0, 328.0

315.0

Tp= DSC peak temperature, DLA= Dextrinated lead azide

fiers (dextrin and CMC) were of irregular shape. The modifiers improved the crystal shape and gave globular crystals but did not increase the bulk density. High concentration of dextrin or CMC gave sticky and non-free flowing crystals.

The IR spectra of (3) and (4) showed the absence of OH frequency and indicated the lead salt formation through phenolic group. The IR spectra of (5 ) and (6) had also shown the absence of OH frequency, near 3600 c m ' however, showed a broad peak at 3400 cm-' - 3200 cm-' due to tetrazole proton (NH). This suggests that the lead salt formation is through phenolic -OH but not through tetrazole nitrogen. The co-precipitated compositions showed a strong peak at 2100 cm-', corresponding to azide (N,) frequency.

3.2. Thermal study

Before handling explosives in gram quantities they were subjected to thermal study to assess the thermal sensitivity and explosibility for safe handling. Both differential scan- ning calorimeter (DSC) and thermogravimetry (TG) tech- niques were employed. Small quantities (a few mg) of the samples were dried in the air oven at 80°C for 2 h and then in a desiccator over P,O,.

(a) Lead azotetrazole ( I ) co-precipitated with lead azide to produce LA-Pb-AzTz, (12)

The co-precipitation of LA and ( I ) carried out using var- ied molar proportions of azide, sodium azotetrazole and lead acetate so as to obtain 80% of LA and 20% of ( I ) in a final composition. Table 1 gives the physical properties of LA-Pb-AzTz. A detailed thermal study on ( 1 ) using TG and DSC was reported earlier('"). The peak temperature (Tp) of this compound was 180°C. The DSC thermograms of co- precipitated samples were recorded and are shown in Fig. 1. These co-precipitated samples gave two separate exotherms at 200°C and 343°C when the sample size was below 0.4

mg and the heating rate was 10 deg.min-'. The same sample size when heated at 64 deg.min-I rate, gave only one exotherm at 215°C corresponding to compound ( I ) (see Fig. l(c)). When the sample size was increased to 1.0 mg, the sample exploded at 200°C even at 10 degrees.min-' heating rate. This observation clearly suggests that when the sample size is small and heating rate is low (< 10) the constituents of co-precipitated material (LA-Pb-AzTz) exhibit their individual exotherms corresponding to ( I ) and LA. It is to be noted that pure DLA on heating at 10 deg.rnin-' rate exploded under helium atmosphere at 315°C. Therefore the low temperature decomposition peak (200°C) is due to ( I ) and the high temperature decomposition peak (343°C) is due to LA. The shift in the second exotherm (corresponding to LA) to a higher temperature in a co-precipitated sample

WEIGHT 0.38 mg

b

1Y)'C Ln 1 1 1

I I 1 1 1 I )

C T p 215'C

i WEIGHT 1 0 rng

SCAN SPEED lO*/mm

Tp 3,5.c WART SPEED (ornrnlmm DSC RANGE 20 v

WEIGHT 0 29 mg : 150'C

TEMPERATURE, ["Cl +

Figure 1. DSC traces of (a) Pb-AzTz, (b) LA-Pb-AzTz, (c) Pb-AzTz, (d) LA.

Propellants, Explosives, Pyrotechnics 17,241-248 (1992) Co-Precipitation Studies on Lead Azide with Tetrazole Derivatives 245

may be due to the decomposition of (0, which must have tarnished the surface of LA and thereby decreasing the thermal sensitivity. The absence of second exotherm (corresponding to LA) when thermograms recording on co-precipitated sample with high heating rate (64 deg.min-') may be due to fast decomposition of ( I ) resulting in a quick re- lease of energy, sufficient to induce thermal decomposition in LA. The weight loss and enthalpy of decomposition indi- cate simultaneous decomposition of ( I ) and LA at high heating rates. It is also evident that when the sample size is increased (> 1 mg), the material exploded even at a low heating rate. This may be due to the fact that with increas- ing sample size the decomposition rate as well as the reac- tion energy increase, and thereby possibly occurs initiating thermal decomposition in LA. In primary explosives the critical mass plays a vital role. It is clear from the above study that the co-precipitated sample is a homogeneous mixture of LA and ( I ) and not a single compound. Thermal data obtained on physical mixture of LA and ( I ) (80:20) was not consistent and microscopic examination indicated inhomogeniety in the sample. In physical mixture, the seggregation of LA from ( I ) is observed because of large dif- ferences in densities of LA (1.3) and ( I ) (0.85). The co-precipitated sample, appeared uniform and optical microscopic examination could not distinguish individual components and no seggregation was observed. Thus, the co-precipitated technique not only produces homogeneous mixture but also eliminates the mixing operation which is a highly hazardous operation in primary explosive industry.

(b) Lead hydrazotetrazole (2) co-precipitated with lead azide to produce LA-Pb-HzTz, (13)

Compound 2 decomposes at lower temperature (Tp 143°C) when heated at 10 deg.min-' compared to (1) (Tp 180°C). The TG-DSC studies on salts of hydrazotetrazole were reported earlier(6b). This paper discusses only the thermal behaviour of lead azide co-precipitated with (2). The co-precipitated sample showed two exotherms, one at Tp 198°C and the other at Tp 325°C. The former peak corre- sponds to the decomposition of (2) and the latter peak cor- responds to the decomposition of lead azide. In this case also, the mass of the sample and heating rate markedly affect- ed the decomposition characteristics of the co-precipitated sample. When the sample size increased (> 1.0 mg) or the heating rate was high (> 20.0) only one exotherm corresponding to (2) was obtained indicating simultaneous decomposition of (2) and LA. The argument put forward for LA-Pb-AzTz, holds good in this case. An additional interesting feature in this case is that the decomposition temperature of (2) (Tp 143°C) is increased to Tp 198°C in co-precipitated sample which is close to the decomposition temperature of ( I ) . Decomposition temperature of LA is also increased by 10 degrees in the case of co-precipitated sample. The crystal modifiers, such as dextrin and CMC did not show any effect on the decomposition characteristics. The thermal study clearly demonstrates, like in the case of LA- Pb-AzTz, that the co-precipitated sample is an intimate homogeneous mixture of individual compounds, LA and (2).

(c) Pb-2H-3,5-DNBA (3) and Pb-4H-3,5-DNBA (4) TG and DSC thermograms of compounds (3) and ( 4 )

were recorded and are shown in Fig. 2 . Both the compounds showed only exothems. Compound (3) showed only one exotherm (Tp 322°C) with a shoulder and compound (4) exhibited two exotherms (Tp 282°C and Tp 320°C). The increased thermal stability of (3) compared to (4) may be due to the presence of formyl group close to hydroxyl group, which may likely be involved in the co-ordination bond with lead.

HEATING RATE l D ' C / r n # n SAMPLE WEIGHT = 0 .485 mg

I I I I _

T G RANGE I mg i-

Figure 2. Non-isothermal TG-DSC thermograms of Pb-2H-3,5- DNBA and Pb-4H-3,5-DNBA.

(d) LA-Pb-2H-3,5-DNBA (14) and LA-Pb-4H-3,5-DNBA (15)

Compound (3) was not sensitive to friction and impact test (in the range normally used for testing initiatory explosive) whereas compound (4) was sensitive to impact but was insensitive to friction. Thermal study also rated compound (3) was more thermally stable compared to compound (4). The purpose of co-precipitation of these compounds with LA is to increase the flame sensitivity and to decrease the friction sensitivity of LA.

The thermal sensitivity of LA was not altered by co-pre- cipitating with these compounds. Compound (3) gave only one sharp exotherm while the sample co-precipitated with LA gave a broad exotherm (Tp 325°C) when a small size sample (0.5-0.7 mg) was heated with 10°C heating rate. The sample exploded when the same sample size was heated at 64 degrees.min-'. Compound (4) which exhibited two exotherms (Tp 280°C and Tp 320°C), also showed two exotherms when co-precipitated with LA, at slow heating rate, but gave only one exothem at Tp 290°C when heated at 64 deg.min-'. Fast heating rate advances the decomposition of LA and both compounds (4) and LA undergo decomposition corresponding to the first exotherm of (4).

(e) Pb-2H-3,5-DNBA-SHzTz (5) and Pb-4H-3,5-DNBA- 5HzTz (6)

Compounds 2H-3,5-DNBA-SHzTz ( 9 ) and 4H-33- DNBA-5HzTz (10) were synthesized for the first time and

246 G. Om Reddy Propellants, Explosives, Pyrotechnics 17,241 -248 (1 992)

characterized by infrared and mass spectral data in an effort to make a series of high nitrogen organic compounds with high energy. TG-DSC thermograms of these compounds were recorded and are displayed in Fig. 3. They have good thermal stability and do not decompose before 250°C. Compounds (9) and (10) decomposed in a single step at Tp 252°C and 265°C respectively. Lead salts of these two compounds (5 and 6) were also prepared and TG-DSC thermograms were recorded. An interesting feature is that compound (5) showed better stability (Tp 278°C) compared to compound (9) whereas the thermal stability of (6) is unal- tered. This may be due to the presence of exocyclic nitrogen in close promixity of lead, which may co-ordinate with lead and induce the thermal stability in compound ( 5 ) whereas such arrangement is not possible in the case of compound (6) (see Scheme 3).

(f) LA-Pb-2H-3,S-SHzTz (16) and LA-Pb-4H-3,S-SHzTz (1 7)

Compounds (5) and (6) were co-precipitated with LA. The non-isothermal TG-DSC thermograms were recorded under non-isothermal conditions and the peak temperatures are tabulated in Table 1. Compound (5) when co-precipitated with LA exhibited two exotherms (Tp 280°C and Tp 320°C) whereas compound (6) when co-precipitated with LA also showed two exotherms (Tp 266°C and Tp 328°C). These compounds exploded when they were heated at 20

Figure 3. TG-DSC thermograms of 2H-3,S-DNBA-SHzTz (9) and 4H-3,S-DNBA-SHzTz (10).

Table 2. Explosive Sensitivity Results

Compound Friction Sensitivity Impact Sensitivity Height [ft/sl [4 kgwtl [cm] (28 g ball) NFL w,, NFI- w50

I 2.5 3.0 5.0 6.5 2 2.0 2.5 10.0 11.5 3 NS NS NS NS 4 NS NS 20.0 22.5 5 7.5 8.0 10.0 11.5 6 4.0 4.5 9.0 10.5 12 4.0 4.5 7.0 7.5 13 3.0 3.5 8.0 8.5 14 5.0 5.6 15.0 16.5 15 3.5 4.2 10.0 12.0 16 3.5 4.0 15.0 16.0 17 4.0 4.5 8.0 9.0 18 3.0 3.5 15.0 17.0

Note: NS = Not sensitive; NFL = No Fire Level; W,, = 50% Proba- bility

deg/min (0.5 mg). The explosion temperature was corresponding to the decomposition temperatures of compounds (5) and (6). These compounds were found to possess more energy and better thermal sensitivity among all the samples studied so far.

3.3. Explosive properties

All compounds were tested for explosive properties like flame sensitivity, friction sensitivity, impact sensitivity and efficiency.

(a) Friction and Impact Sensitivity The friction and impact sensitivity of all explosive sub-

stances were determined and are displayed in Table 2. Compound (12) showed less friction sensitivity than LA and (1 ) whereas the impact sensitivity was found to be greater than LA and less than (1). Compound (13) exhibited more sensitivity to friction and less sensitivity to impact when compared to (12). Compounds (3) and (4) were not sensitive to friction but co-precipitated compounds (14) and (15) showed reduced friction sensitivity, when compared to LA. An interesting feature is that, though the friction sensitivity decreased, the impact sensitivity increased consider- ably. Compounds (5) and (6) showed less friction sensitivity compared to DLA but showed more impact sensitivity. When these compounds were co-precipitated with LA, the resulting compound (16) showed marginally reduced friction sensitivity and similar impact sensitivity compared to DLA whereas compound (17) showed reduced friction sensitivity and enhanced impact sensitivity. The crystal modifiers, like dextrin and CMC, reduced the friction and the impact sensitivity of all the compounds.

(b) Flame sensitivity Lead salts of hydrazotetrazole (2) and azotetrazole ( 1 )

could be initiated by a safety fuse. For this test, aluminium shells were taken and 30 cg of PETN was pressed at the base (base charge) and about 20 cg of (1) or (2) was pressed

Propellants, Explosives, Pyrotechnics 17,241 -248 (1992) Co-Precipitation Studies on Lead Azide with Tetrazole Derivatives 247

Table 3. Minimum Value Evaluation

Com- uound 30 25

Priming Charge Weight [cg]

20 15 10 8 6

12 F F 13 F F 14 F F 15 F F 16 F F 17 F F 18 F F

F F F F F F F F F PF F F F PF PF F F F F PF F F F F F F F F F F F F F F F

5

F PF NF PF F F F

4

PF PF NF NF PF NF F

- 3

NF NF

NF NF NF PF

-

(Electrical detonators are used. PETN is used as base charge (20 cg). Lead Plate Test (LPT) is adopted. Priming charge weight is in cg)

NOTE: F = Fire (complete initiation of PETN). PF = Partial fire (partial initiation of PETN). NF = No fire (no initiation of PETN).

over PETN as priming charge and the detonators were fired with a safety fuse. No single misfire was noticed about of 20 shots. These lead salts were as sensitive as lead azide, to friction and impact, but more sensitive to flash or spark. Power of these salts, however was less than that of lead azide. When these salts are co-precipitated with lead azide (12 and 13) not only the flame sensitivity was retained but also improved the power of initiation. The lead salts of nitrophenolic aldehydes (3 and 4) could not be initiated by a safety fuse. This observation is in accordance with the thermal sensitivity. The resultant compounds of co-precipitation of these compounds, with lead azide (14 and 15) could be however initiated by a safety fuse. When the priming charge is more than 15 cg, a complete initiation of PETN was observed. The lead salts of hydrazones of nitrophenolic aldehydes (5 and 6) were found to be flame sensitive but power was not sufficient to initiate PETN completely when the initiating charge was less than 10 cg. The co-precipitated compounds of these hydrazones with LA (16 and 17) not only gained strength (due to lead azide) but also produced initiatory composition with good flame sensitivity.

(c) Efficiency The strength of lead salts, other than co-precipitated, was

not sufficient to initiate PETN base charge. The efficiency/power of co-precipitated compositions is mainly dependent on the percentage of LA. The higher the percentage of LA, the lesser the quantity of primary charge required for initiating PETN as it is evidenced by Lead Plate Perforation Test (LPT). For the purpose of comparison with DLA, only 80% LA and 20% other components are discussed here and the results are shown in Table 3. The compounds (12) and (13) were powerful and the minimum value required for the complete initiation of PETN (30 cg) in No. 6 detonator was 5-6 cg compared to 3.0 cg of DLA. Compounds such as (14) and (15) (8-10 cg) priming base charge was required to initiate PETN base charge completely. The strength of (16) and (17) was slightly more than (12) and (13) and marginally less than DLA (18). It is apparent that the power of initiation is mainly dependent on the percentage of LA in CO-

Table 4. Minimum Value Evaluation at Various Molar Percentage of Lead Azide in Co-Precipitated LA-P~-~H-~,~-DNBA-~-HzT

Mole % of Lead azide (LA) 30

100 F 90 F 80 F 70 F 60 F 50 F 40 F

25

F F F F F F F

- 20

F F F F F F PF

-

Weight of Initiator [cg]

15 10 8 6 4 3 2

F F F F F F F F F P F F F F F N F F F F PF NF F PF NF NF -

PF NF NF - -

PF NF NF - -

PF NF NF NF NF -

NF - - - . -

- .

(Electrical detonators are used. PETN is used as base charge (30 cg). Lead Plate Test (LPT) is adopted. Priming charge weight is in cg).

NOTE: F = Fire (complete initiation of PETN). PF = Partial fire (partial initiation of PETN). NF = No fire (no initiation of PETN).

precipitated compositions. The other constituents in all these precipitations are not as powerful as LA. To see the effect of weight percentage of LA on the efficiency of initiation, one compound, ( I 7) was selected and was co-precipitated with LA to prepare various compositions containing varying weight percentage of LA and the efficiency test results are tabulated in Table 4. The general conclusion is that the power of initiation increases with increased LA content. The efficiency test results rated (16) and (17) as superior over other compounds. Low concentration of crystal modifiers such as CMC and dextrin showed no effect on the efficiency.

4. Conclusion

Thermal study indicates that the co-precipitation of LA with other flame sensitive compounds gave an intimate homogeneous mixture of the individual compounds. This study does not support the theory of formation of single compound.

The co-precipitation process not only improved the flame sensitivity of LA but also eliminates the hazardous process of mixing LA with lead styphnate and aluminium to improve the flame sensitivity of initiatory composition.

From both, the sensitivity and the power tests, it may be concluded that the co-precipitated compounds, discussed in this paper, can be used in detonators in the place of ASA composition.

A good correlation between thermal and flame sensitivity is noticed. Both thermal and flame sensitivity decreased in the order given below:

Pb-HzTz > Pb-AzTz > P ~ - ~ H - ~ , ~ - D N B A - ~ H z T z > Pb- ~H-~ ,~ -DNBA-SHZTZ > Pb-4H-3,5-DNBA > Pb-2H-3,5- DNBA.

5. References

(la) S.K. Sinha, R.C. Srivastava, and R.N. Surve, Proc. International Conference on Research in Primary Explosives, Vols. 1-3, pre-

248 G. Om Reddy

sentation no. 1 I (1975).

L. Rubenstein, U.S. Patent 2,633,863 (Sept. 29, 1953). ERDE, Emery Paper Friction Test Sensitiveness Collaboration Committee; Explosive Hazard Assessment Manual of Tests, Test no. 13/66 (1966). L. Avrami and R. Hutchinson in “The Sensitivity to impact and Friction of Ener<qetic Material”, Vol. 2 , H.D. Fair and R.F. Wal- ker (Eds.), Plenum Press 1977, p. 120. “Encyclopedia of Explosives and Related Items”, Edited by Bra- sil T. Fedoroff and published by Picatinny Arsenal, Dover, NJ, USA, (1960) page A546.

(6a) G.Om Reddy, B.K. Mohan Murali, and A.K. Chatterjee Thrr- mochimica Acta 66,231-244 (1983).

(6b) G.Om Reddy and A.K. Chatterjee, J . Hazardous Materials 9,

(Ib) S . Lamnevik, Zbid, presentation No. 9 (1975). (2) (3)

(4)

(5)

291-303 (1984).

Propellants, Explosives, Pyrotechnics 17,241 -248 (1 992)

(7a) G.C. Harrison and H. Diehl, fowa State College J . Sci. 21,3 I 1, (7b) ABE Lovette and E. Roberts, .I. Chem. Snc. 1978 (1928). (7c) C. Paul, Ber. 28, 2413 (1875). (7d) E.T. Borrows, et al. J . Chem. Soc. 5190 (1949).

Acknowledgements

The author wishes to thank the Management of IDL Chemicals Ltd., for the permission to publish this work. Mr. R. Vedam is thanked for his suggestions and encourage- ment. Ms. Rema Devi is thanked for typing this work.

(Received July 22, 1991; Ms 40/91)

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