Whole Life Assessment of Nitrocellulose in Double Base Propellants. Nathalie Mai Michael Isherwood Phil Gill

Transcription

1 Whole Life Assessment of Nitrocellulose in Double Base Propellants Nathalie Mai Michael Isherwood Phil Gill

2 Contents Introduction Aged DB rocket propellant analysis GPC HPLC Aged DB gun propellant analysis GPC microhardness Conclusion and future work 2

3 Whole life assessment of NC in propellants Processing parameter during manufacture viscosity Chemical ageing stabiliser depletion NC molar mass changes Mechanical ageing hardness The problem 3

4 GPC method described in STANAG 4178 Repeatable results once a month (5 months) same batch of NC was analysed in 20 replicates RSD (Mn) RSD (Mw) 5 measurements RSD % in the past 2.8% 2.8% Comparable to other analytical techniques 4

5 Validation of the GPC method Broad distributed PS standard NBS 706a Certified by NIST (previously NBS) Injected in triplicate with every set of propellant samples 5

6 Accuracy and precision of the GPC method 14 measurements of NBS 706a Mw in triplicate (5 month) Accuracy: Mw = 2.85 ± g/mol (± 8%) certified by NIST Precision: RSD < 0.9% 6

7 The aim To assess the life of DB propellants by: transferring the GPC method to formulated NC product (aged DBP) measuring the kinetic parameters (k, E a ) To perform mechanical testing and correlate results to average molar mass of NC 7

8 Propellants used Generic DB rocket propellant NG, NC, p-nma and 2-NDPA supplied by Roxel (UK Rocket Motors) Ltd DB gun propellant, 20 mm (Phalanx) NC, NG, DPA donated by DOSG MoD in addition naturally aged propellant (15 y old) was supplied 8

9 Ageing (AOP-48) 2g for DB rocket propellant / 5g for DB gun propellant were pre-conditioned 60-70% RH level, 48h, 25 o C heat sealed in polymer coated aluminium bags aged at 30, 40, 50, 60 o C (DB rocket propellant) 70, 80 o C (DB gun propellant 9

10 GPC sample preparation Simple, quick and easy with no pre-conditioning 24h in solution Automatic injection in 5 replicates 10

11 Contents Introduction Aged DB rocket propellant analysis GPC HPLC Aged DB gun propellant analysis GPC Microhardness Conclusion and future work 11

12 Mw changes for artificially aged DB rocket propellant Mw (g/mol) Thousands deg C 50 deg C 40 deg C 30 deg C Mn follows the same trend Ageing time (day) 12

13 Arrhenius plot for NC decomposition 10 8 LnK NC 6 Ea = 93.5 kj/mol /T (K) Decomposition of NC at T<60 o C dominated by low Ea process. 13

14 NC decomposition NC decomposes following 2 pathways: Thermolysis of CO-NO 2 group (producing 2 radicals) Ea = kj/mol Hydrolysis of CO-NO 2 group (producing nitric acid) Ea = 100 kj/mol Our result is consistent with hydrolysis process Ref: M. A. Bohn, J. of Thermal Analysis and Calorimetry, 2001, 65,103 14

15 Depletion of stabilisers at 60 o C 2-NDPA content, wt.% NDPA p-nma Ageing time (day) 15

16 2-NDPA depletion 2-NDPA content, wt.% deg C 50 deg C 40 deg C Ageing time (day) 16

17 Arrhenius plot for 2-NDPA depletion Ea = 175 kj/mol LnKstab /T (K) 17

18 P-NMA depletion 0.7 p-nma content, wt.% deg C 50 deg C 40 deg C 30 deg C Ageing time (day) 18

19 Arrhenius plot for p-nma depletion -3-5 Ea = 103 kj/mol -7 LnKstab p-nma 2nd Mech. p-nma 1st Mech. Ea = 113 kj/mol /T (K) 19

20 Summary Mw and Mn decrease with ageing time Low Ea (Mw) consistent with hydrolysis p-nma is consumed quicker than 2-NDPA with lower Ea 2 mechanisms involved in depletion of p-nma Material too soft to do mechanical tests 20

21 Outline Introduction Aged DB rocket propellant analysis GPC HPLC Aged DB gun propellant analysis GPC microhardness Conclusion and future work 21

22 Mw changes for artificially aged DB gun propellant Mw (g/mol) Thousands 70 deg C 80 deg C Ageing time (h) 22

23 Mn changes for artificially aged DB gun propellant Mn (g/mol) Thousands 70 deg C 80 deg C Ageing time (h) 23

24 Apparent number of chain scissions of NC artificially aged at 70 and 80 o C Scissions per molecule S = (Mn o /Mn t ) deg C 80 deg C Ageing time (h) 24

25 Vickers hardness test Easy and quick testing procedure which consists of measuring the diagonals of the impression left by a load of various magnitudes 25

26 Grain hardness changes with ageing time Hardness Vicker (Hv) deg C 80 deg C Ageing time (h) 26

27 Relationship between grain hardness and NC Mw Hardness Vickers (Hv) deg C 80 deg C Mw (g/mol) 27

28 Naturally aged propellant 15-16y Hardness Vickers (Hv) deg C 80 deg C Naturally aged Mw (g/mol) 28

29 Summary Mw and Mn decrease with ageing time Chain scission factor consistent with hydrolysis Grain hardness decreases with ageing time Good correlation between grain hardness and Mw Naturally aged material fits with the curve 29

30 Contents Introduction Aged DB rocket propellant analysis GPC HPLC Aged DB gun propellant analysis GPC microhardness Conclusion and future work 30

31 Conclusion The GPC method successfully transferred to formulated NC Ea (Mw) correlates well with published values Good correlation between the Mw and mechanical properties. 31

32 Ongoing experiments and future work Reducing sample preparation time (4h using shaker) Comparison GPC analysis, mechanical properties for aged propellants DMA, microhardness, nanoindentation Round Robin analysis of NC in propellants planned for 2011/

33 Acknowledgment AWE and DOSG for sponsoring the work Roxel (UK Rocket Motors) Ltd for providing the DB rocket propellant Cranfield University staff and students Thank you for your attention 33

34 Any question? The Defence Academy Campus 34