LONG TERM MASS LOSS STUDIES OF PROPELLANTS USED IN AGEING ANALYSIS

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1 LONG TERM MASS LOSS STUDIES OF PROPELLANTS USED IN AGEING ANALYSIS Moritz Heil, Manfred A. Bohn Fraunhofer ICT, D Pfinztal, Germany Presentation on the 7th International NC-Symposium 2016 May 31 to June 1, 2016, Montréal, Canada Hosted and organized by General Dynamics - Ordnance and Tactical Systems (GD-OTS), Valleyfield, Canada

2 Motivation Long term stability of NC-based gun propellants is of never-ending concern. In the past there have been intensive discussions on the methods to determine long-term stability. Some discrepancies between laboratory ageing at higher temperatures and the typical surveillance testing of GPs by (continuous) storage at 65.5 C ( = 150 F) have finally caused ICT ( Dr. Fred Volk) to start a real long-term ageing with selected gun propellants at quite low temperatures: 30 C, 35 C, 40 C, 45 C, 50 C, each with four samples and also at higher temperatures, 70 C, 80 C, 90 C. This was more than 36 years ago, beginning in the years 1979 / 1980 Because of lack of other sensitive measurement methods at that time and because of economical reasons (because of the quite big amount of samples at a lot of temperatures to be kept there for long times) mass loss was taken as method.

3 OUTLINE Motivation Overview Single base GP A5020, 20 mm machine gun Double base GP JA-2 (L5460), 120 mm tank gun Double base GP NK1074, 105 / 90 mm / howitzer / tank gun Kinetic description of data Theoretical models for mass loss Results Conclusions

4 Overview on the propellants presented here A5020 JA-2 (L5460) NK1074 single base, one hole, 20 mm grain size 2mm x 1mm, cylindric. double base, 7 hole, 120 mm cut rod to size 18-22mm x 8mm double base, 7 hole, 105 / 90 mm grain size 12mm x 9mm, cylindric. NC (13.2 % N) 95 % NC (13.0 % N) 59.5 % NC (13.1 % N) 51.8 % Centralite I 1 % Nitroglycerine 14.9 % Nitroglycerine 40.5 % DBP / DOP 2.6 % Diglycol dinitrate 24.8% DPA 1.0 % DPA 0.8 % Akardite II 0.7 % Centralite I 1.5 % Sodiumoxalate 0.6 % MgO 0.05 % Ethylphenylurethane 3.7% Graphite Graphite 0.05 % DNT 1.5 % Lead stearate 1.4 % sb: single base, db: double base

5 Ageing in PID-controlled and regularly checked aluminum block ovens 30 mm Mostly used vials with ground stoppers, loosely inserted (without grease and clamps) About 50 ovens in operation. 40 with a capacity of 26 small vials each. 10 with a capacity of 15 large vials each.

6 Mass loss measurement results: overview for A5020

7 Overview on mass loss of L5460 (JA-2)

8 Overview on mass loss of NK1074

9 Single base GP A5020, 20mm machine gun At end of storage 35 C, 31 years grain size 2mm x 1mm, cylindrical, graphitized At end of storage 40 C, 28 years At end of storage 45 C, 31 years At end of storage 50 C, 31 years

10 Mass loss curves of A5020

11 Mass loss curves of A5020

12 DB GP NK1074, 105 / 90 mm / howitzer / tank gun At end of storage 30 C, 36 years grain size 12mm x 9mm Ø, cylindrical, graphitized. At end of storage 35 C, 36 years At end of storage 45 C, 36 years At end of storage 50 C, 36 years

13 Mass loss curves of NK1074

14 Mass loss curves of NK1074

15 Double base GP L5460 (JA-2), 120 mm tank gun At end of storage 30 C, 36 years At end of storage 35 C, 36 years At end of storage 40 C, 36 years cut rod to length: 18-22mm x 8mm Ø cylindrical; smoothly graphitized. At end of storage 45 C, 36 years At end of storage 50 C, 36 years

16 Mass loss curves of L5460 (JA-2)

17 Mass loss curves of L5460 (JA-2)

18 Stabilizer content [%] Stabilizer content [%] Stabilizer content [%] Stabilizer consumption NK Temperature [ C] NK 1074 shows no DPA at all and only the samples with lowest ageing temperature contain residual Centralite I A5020 contains bit DPA and Centralite at I lower ageing temperatures with much larger consumption of DPA JA-2 shows consumption of Akardite II increasing with temperature Solid lines indicate the starting stabilizer content A Temperature [ C] JA-2 (L5460) Temperature [ C] DPA [%] Centralit [%]

19 Final stabilizer content Propellant A5020 Storage temperature [ C] Ageing time [years] Stabilizer DPA Centralite I DPA Centralite I DPA Centralite I DPA Centralite I Stabilizer content [mass-%] Not detected Not detected Not detected Not detected JA-2 (L5460) Akardit II 0.5 NK Akardit II 0, Akardit II Not detected Akardit II 0, Akardit II Not detected DPA Centralite I DPA Centralite I DPA Centralite I DPA Centralite I Not detected 1.09 Not detected Not detected Not detected Not detected Not detected Not detected

20 Theoretical models [1] M. Bohn, Ageing Analysis by mass lass measurements of single-base-propellants used as gas generants in high thermal load environments, in International Annual Conference of ICT on Energentic Materials - High Performance, Insensitive Munitions, Zero Pollution, Karlsruhe, 2010.

21 rel. Massenverlust rel. Massenverlust rel. Massenverlust Data processing These two models are used to fit the mass loss data by a generalised fit, meaning that all curves of one specific temperature were fitted allowing different offset values for each individual curve but using one shared decomposition/ evaporation rate for all curves. This process was repeated for all propellants and all temperatures. 0,010 rel. Massenverlust MLRkt0_mit_Rkt1 (User) Fit of Sheet1 B"rel. Massenverlust" 0,020 0,015 rel. Massenverlust MLRkt0_mit_Rkt1 (User) Fit of Sheet1 F"rel. Massenverlust" 0,010 rel. Massenve MLRkt0_mit_R 0,005 0,015 0,010 0,005 0,005 0,000 0, Lagerdauer [d] 0, Lagerdauer [d] Lagerdauer [d] Mass loss curves of A5020 aged at 45 C

22 Results of kinetic descriptions Both models provide similar results Good correlations are obtained with data from elevated temperatures (i.e. 50 C) Modelling of ML at lower ageing temperatures results in lower correlation coefficients A5020 JA-2 (L5460) NK1074 T [ C] formal simpl. # of curves formal simpl. # of curves formal simpl. # of curves

23 Results Arrhenius plot for A5020

24 Results Arrhenius plot for JA-2 (L5460)

25 Results Arrhenius plot for NK1074

26 Results Arrhenius plot for A5020

27 Results kinetic modelling Chemical decomposition according to zero order Propellant Kinetic model (formal) Simplified description Std. dev. Std. dev. E A, k0 [kj/mol] R² E A, k0 [kj/mol] R² [kj/mol] [kj/mol] A JA NK Evaporation according to a first order formalism Propellant Kinetic model (formal) Simplified description Std. dev. Std. dev. E A, k0 [kj/mol] R² E A, k0 [kj/mol] R² [kj/mol] [kj/mol] A JA NK

28 A5020 special observation

29 Conclusions Long term mass loss data at low temperatures provide with consistent information about activation energies of decomposition processes. However: ageing at temperatures below 45 C for mass loss measurements are affected by significant noise to signal ratio. To reduce this, higher amounts of propellants must be used, at least 10 to 20 g. Mass loss measurements contain periodic oscillations with cycles of about one year especially at low storage temperatures; slight influence of ambient temperature on the temperature control of storage ovens? slight influence of change in relative humidity in sample container? These periodic oscillations can be averaged, but mass loss measurements over at least four years are necessary. One question to clarify was the double mechanism found with A5020 also in standard surveillance. It seems that mass loss data over the whole temperature range confirm this findings.

30 Thank you for your attention Questions?