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EUROPEAN COMMISSION

Deliverable no: D3.1 FOI designation no. FOI-2010-1487

Dissemination level: PU Date: 30/11/2011

HISP has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 262099.

Production of prilled ADN for WP6 using current methods

Niklas Wingborg, Mattias Liljedahl (FOI)

Thomas Heintz (ICT)

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Deliverable no: D3.1 Due date of deliverable: 30/11/2011 Actual submission date: 30/11/2011 Version: 1 FOI designation no. FOI-2010-1487 Responsible: Niklas Wingborg (FOI) Authors: Niklas Wingborg (FOI), Mattias Liljedahl (FOI) and Thomas Heintz (ICT) Number of pages: 19 Dissemination level: Public Start date of project: 01/03/2011 Duration: 3 years Webpage: www.hisp-fp7.eu Front page picture; Spray prilled ADN.

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Summary The ADN received from EUB has high purity but the particles have needle shaped morphology which is unsuitable for propellant formulation. For this application spherical, prilled, ADN is preferred. In this report the production of prilled ADN by two different methods are presented; i.e. spray prilling (FOI) and emulsion prilling (ICT). FOI prilled ADN will be delivered to the following project partners: ICT, TNO and AVIO. The delivery of FOI prilled ADN to international partners is handled by EUB. In order to receive prilled ADN the receiver must apply and obtain the transport permits needed and send an official order to EUB. So far (24/11/2011) only ICT has been able to obtain the permits needed and thus FOI prilled ADN has only been delivered to ICT. The status of delivery is summarised below. Partner Prilled ADN (kg) Grade Delivery status ICT 3 kg

6 kg 200 μm 200 μm

First delivery delivered 24/08/2011 Second delivery December 2011

TNO 1 kg 200 μm Ready for delivery since August AVIO 18 kg 9 kg – 50 μm

9 kg – 200 μm Not ordered. To be delivered at the earliest in January 2012

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Contents 1 Introduction.................................................................................................................................... 5

2 Spray prilling (FOI) ........................................................................................................................ 7 2.1 Description of the spray prilling process............................................................................ 7 2.2 Production and batch control ............................................................................................. 7 2.2.1 Analysis of as received ADN ............................................................................................. 7 2.2.2 Production of ADN prills..................................................................................................... 9 2.2.3 Analysis of prilled ADN .................................................................................................... 10 2.2.4 Analytical methods........................................................................................................... 11 2.2.4.1 Particle density................................................................................................................. 11 2.2.4.2 Tap density ...................................................................................................................... 11 2.2.4.3 Differential scanning calorimetry, DSC............................................................................ 12 2.3 Delivery to project partners.............................................................................................. 12

3 Emulsion prilling (ICT)................................................................................................................. 13 3.1 Description of the emulsion prilling process .................................................................... 13 3.1.1 Stabilization of ADN-Prills................................................................................................ 14 3.2 Production and batch control ........................................................................................... 15 3.2.1 Analytical methods........................................................................................................... 18 3.2.1.1 Particle size analysis ....................................................................................................... 18 3.2.1.2 Morphology ...................................................................................................................... 18 3.2.1.3 Density ............................................................................................................................. 18 3.3 Delivery to project partners.............................................................................................. 18

4 Conclusions................................................................................................................................. 19

5 References .................................................................................................................................. 19

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1 Introduction In order to obtain high specific impulse a high solid loading is required. However, high solid loading increases the viscosity of the uncured propellant. Thus, the maximum solid loading and impulse is limited by processing constrains. To obtain a castable propellant formulation with reasonable viscosity and high solid loading, particles with minimum spatial extension are required. For this reason the particles should have a low aspect ratio, or more preferably a spherical shape. Today ADN is produced by EUB in Sweden and available in larger amounts for evaluation and research. The purity of the material produced is above 99% and it has a high thermal stability. However, the particle shape of the ADN received from EUB is needle shaped and thus not suitable for formulation. In the HISP project the total amount of ADN to be used is 60 kg (batch 20119036). The production of this batch is reported in the HISP deliverable D2.1 “Production of 60 kg ADN and 20 kg GAP using current methods”. Currently two different methods to produce spherical ADN particles, prills, are used; i.e. spray prilling (FOI) and emulsion prilling (ICT). The production of prilled ADN using these methods, and the delivery of the required amount of prilled ADN to respective project partners, are described in this report.

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2 Spray prilling (FOI)

2.1 Description of the spray prilling process In the spray prilling process crude ADN is melted in a vessel equipped with a bottom valve. To improve the heat transfer and hence shorten the melting time, the vessel is equipped with a stirrer. The molten ADN is then sprayed through a nozzle into a container containing a liquid medium. The melted ADN droplets solidify into particles (prills) in the liquid medium. The process is schematically shown in Figure 1. Currently the prills are produced using up to 250 g ADN per batch. The particle size can be controlled, to some extent, by varying spray nozzle size and spray pressure. After spraying, the prills are dried in two steps; first by vacuum filtration, using a glass filter funnel, and then, to fully dry the prills, using a fluidized bed. 0.5-1.0 weight-% fumed silica (Cab-O-Sil) is added to the dried prills to prevent caking.

Figure 1. Schematic illustration of the ADN spray prilling process.

2.2 Production and batch control

2.2.1 Analysis of as received ADN The ADN used in this study was produced by EUB in Sweden, batch number 20119036. The production of this batch is reported in HISP deliverable D2.1 “Production of 60 kg ADN and 20 kg GAP using current methods”. As a standard procedure it was subjected to the following analysis:

• Particle density measurements at 25°C

• DSC (25 to 300°C at a heating rate of 10 K/minute) The apparatuses and the experimental procedures used are further described in section 2.2.4.

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The results from the analysis are presented in Table 1, Table 2 and in Figure 2. The density of the material was 1.814 g/cm3 which is in agreement with previous studies [1]. The melting point (93.4°C), heat of melting (148 J/g) and the estimated purity (99.9 mol%) all indicate the material to be very pure and in accordance to previous studies [1]. Table 1. Results from the particle density measurements performed at 25°C. Material Sample ID Density (g/cm3) Average (g/cm3) a ADN 20119036 #7517:1

#7517:10 #7517:11 #7517:12

1.8168 1.8115 1.8132 1.8125

1.814 (0.002)

a) standard deviation within parenthesis.

Figure 2. DSC thermogram for ADN, batch 20119036, at a heating rate of 10 K/min.

Table 2. Results from DSC analysis of ADN 20119036. Sample ID #7520:11 #7520:12 #7520:13 #7520:20 Average a ΔHm (J/g) 142.27 150.14 150.14 148.45 148 (4) Mp (°C) 93.33 93.37 93.33 93.55 93.4 (0.1) Purity (mol%) 99.88 99.95 99.94 99.99 99.9 (0.05) a) standard deviation within parenthesis.

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2.2.2 Production of ADN prills Crude ADN batch 20119036 from EUB was used. One large batch of 4296 g ADN was manufactured, sieved and homogenized. Each spraying of ADN was made using 250 g ADN. In total 18 spraying rounds were made. After prilling and drying, the whole batch was sieved using a 1000 µm sieve. After sieving, 0.5% Cab-o-Sil was added as an anti-caking agent. The batch was then homogenized, weighed and put into 1000 ml polyethylene cans with air-tight lids. The cans were put in black ESD bags together with silica gel. The manufactured batch has batch number FP11013, and the production parameters for the whole process can be seen in Table 3 to Table 5. Table 3. Batch information. Crude ADN batch 20119036 Prilled ADN batch FP11013 Amount prilled ADN 4296 g Additive Cab-o-Sil M5 (0.5%) 21 g Table 4. Spray prilling process parameters. Melt time 7 min Each spray 250 g Number of runs 18 (17x250g+ 195g) Losses 3.3% (including particles >1000 µm) Temperature of recirculating heating batch

105ºC

Spraying pressure 1.6 bar Spray nozzle SU5 Room temperature and humidity during production

22-23ºC 19-23% RH

Medium for solidification dried n-Heptane Temperature of medium 22-23ºC Drying agent for medium Molecular Sieve, 4Å Table 5. Sieving and packing. Sieving <1000 µm Can 1000 ml Drying agent Silica gel with moisture indicator Temperature and humidity during sieving and packing

21ºC, 12% RH (relative humidity)

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2.2.3 Analysis of prilled ADN Prilled ADN batch number FP11013 was subjected to the following analysis:

• Particle density measurements at 25°C

• Tap density measurements at 25°C

• DSC (25 to 300°C at a heating rate of 10 K/minute) The apparatuses and the experimental procedures used are further described in section 2.2.4. The results from the analysis are presented in Table 6 to Table 8 and in Figure 3. The particle and the tap density of the material was 1.775 g/cm3 and 1.11 g/cm3 respectively, which is inline with previous studies [1]. The melting point (93.1°C), heat of melting (146 J/g) and the estimated purity (99.9 mol%) all indicate the material to be very pure and is in accordance to previous studies [1]. Table 6. Results from the particle density measurements performed at 25°C. Material Sample ID Density (g/cm3) Average (g/cm3) a ADN FP11013 #7517:6

#7517:7 #7517:8 #7517:9

1.7749 1.7765 1.7743 1.7736

1.775 (0.001)

a) standard deviation within parenthesis. Table 7. Results from the tap density measurements. Material Sample ID Density (g/cm3) Average (g/cm3) a ADN FP11013 #4643:1

#4643:2 #4643:3

1.10 1.12 1.10

1.11 (0.01)

a) standard deviation within parenthesis. Table 8. Results from DSC analysis of FP11013. Sample ID #7520:14 #7520:15 #7520:16 Average a ΔHm (J/g) 146.39 145.40 145.96 145.9 (0.5) Mp (°C) 93.19 92.98 93.10 93.1 (0.1) Purity (mol%) 99.97 99.94 99.95 99.9 (0.02) a) standard deviation within parenthesis.

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Figure 3. DSC thermogram for prilled ADN, batch FP11013, at a heating rate of 10 K/min.

2.2.4 Analytical methods

2.2.4.1 Particle density Density measurements were performed at room temperature using a Micromeritics AccuPyc 1330 gas pycnometer, operating in a helium atmosphere (99.996%, AGA Gas). The density of each sample was determined by five consecutive runs, each purged five times before analysis. Prior to analysis the calibration of the apparatus was checked using the Micromeritics AccuPyc 1330 calibration standard (6.37203). Ammonium chloride (Sigma-Aldrich #11209, Lot# SZBA1950V) was used to verify the calibration. The results are shown in Table 9, showing excellent agreement with the literature value [2]. Table 9. Results from the particle density measurements performed at 25°C. Material Sample ID Density (g/cm3) Average (g/cm3) a NH4Cl Lot # SZBA1950V

#7517:03 #7517:04 #7517:05

1.5277 1.5270 1.5268

1.527 (0.0004) Lit dat 1.5274 [2]

a) standard deviation within parenthesis.

2.2.4.2 Tap density The tap density was determined using a 25 ml glass measuring cylinder. The cylinder was filled with 20 to 25 ml of powder. The amount of powder was weighed and the cylinder was tapped repeatedly until a constant volume was obtained. The volume was then read and the tap density calculated.

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2.2.4.3 Differential scanning calorimetry, DSC A Mettler Toledo DSC 822 differential scanning calorimeter was used to determine phase transitions and related changes in enthalpies. The apparatus was purged with nitrogen (80 ml/min) and the heating rate was 10 K/minute. The samples, approximately 2 mg, were put in 40 μl aluminium cups with pierced lids. The temperature and heat flow was calibrated using indium (ME-29749 Mettler-Toledo) and gallium (no. 203319 Sigma-Aldrich). The calibration was verified using the same materials. The results are presented in Table 10 and shows excellent agreement with literature data. Table 10. DSC calibration verification. All literature values from reference [3]. Material Number of

analyses Measured ΔHm (J/g)

Lit data ΔHm (J/g)

Measured Mp (°C)

Lit data Mp (°C)

In 6 28.5 (0.13) 28.58 156.6 (0.04) 156.6 Ga 7 79.8 (0.25) 79.97 30.0 (0.07) 29.77 The purity of ADN was estimated using the Mettler Toledo STARe software v 8.10. The method is based on analysis of the DSC melting peak by using the van’t Hoff equation, as described in the literature [4].

2.3 Delivery to project partners The delivery of FOI prilled ADN to international partners is handled by EUB. In order to receive prilled ADN the receiver must apply and obtain the transport permits needed and send an official order to EUB. So far (24/11/2011) ICT and TNO has sent orders to EUB but not AVIO.

• The delivery to ICT has been divided in two. In the first delivery, sent in August 2011, 3 kg prilled ADN (batch FP11013) was delivered. The second delivery was ordered 25/10/2011 and will be delivered in December 2011.

• The delivery to TNO has been ready for transport since August 2011 but unfortunately

TNO has not yet (24/11/2011) obtained the transport permits needed.

• AVIO has (11/11/2011) not obtained the transport permits needed. It is expect that it will take additional 1 to 1.5 month to obtain the permits and then an official order can be sent to EUB. Prilled ADN can thus not be delivered to AVIO before January 2012.

A summary of the delivery status is presented in Table 11. Table 11. Delivery status of FOI prilled ADN. Partner Prilled ADN (kg) Grade Delivery status ICT 3 kg

6 kg 200 μm 200 μm

First delivery delivered 24/08/2011 Second delivery December 2011

TNO 1 kg 200 μm Ready for delivery since August AVIO 18 kg 9 kg – 50 μm

9 kg – 200 μm Not ordered. To be delivered at the earliest in January 2012

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3 Emulsion prilling (ICT)

3.1 Description of the emulsion prilling process The ADN-Prilling Process [1], which is using the emulsion crystallization technology, was developed at Fraunhofer-ICT at the end of the 1990th. The goal of the ADN-Prilling process is the reshaping of irregular ADN crystals, as obtained from synthesis, into spherical particles (ADN-Prills), as they are needed for further processing, e.g. in solid rocket formulations. The prilling process comprises principally the three steps as they are illustrated in Figure 4:

• Step 1: Suspension of neat ADN (irregular shaped from synthesis) in a non-polar liquid at ambient temperature.

• Step 2: Melting and emulsifying of ADN at ϑ ≈ 95 °C (at least ϑmelt, ADN ≈ 93 °C)

• Step 3: Recrystallization of molten droplets into spherical solid particles (ADN-Prills) by cooling down to ambient temperature and simultaneous stirring.

After treatment steps like washing and drying of the ADN-prills are necessary.

Figure 4. Principle steps of the ADN-prilling process.

Step 1

Step 3

200 µm

200 µm

Step 2

heating

cooling

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Figure 5 shows the experimental setup that is currently used for the production of ADN-prills in semi-kilogram scale. The emulsion crystallization process (European patent EP 0 953 555 B1) has the following properties:

• Batch size: 500 g ADN (used raw material: EURENCO, lot No. 20027031, 20057014 and 20079003)

• Continuous phase: n-decane with different additives • Double jacket vessel: Volume 5 l • Propeller mixer: 400 – 450 1/min • Guide tube, necessary for homogeneous mixing

Figure 5. Process equipment of the emulsion crystallization process.

3.1.1 Stabilization of ADN-Prills Thermal decomposition of ADN starts at temperatures around the melting point of ADN approx. 93 °C. This results in pores of decomposition gases (e.g. nitrous oxide), which can be included inside the ADN-Prills. Stability and compatibility investigations [2, 3, 4] have also shown that it is necessary to stabilize ADN-Prills for further processing and application. So ICT made a further development by using a pre-stabilized intermediate product for the prilling process.

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Goal of this stabilization is to increase the thermal and chemical stability, to produce pore-free ADN-prills (see Figure 10) and herewith increase the density of ADN-prills (see Table 13).

3.2 Production and batch control The starting material and the produced ADN-Prills (former batches) are investigated by SEM (see Figure 6) and particle size analysis (see Table 12). The apparatuses and the experimental procedures used are further described in section 3.2.1. It is to be seen that 12 kg ADN-Prills could be fabricated in a reproducible quality according to particle size, particle size distribution and morphology.

Figure 6. SEM pictures of the raw ADN from synthesis and the spherical ADN-Prills Table 12. Overview of results (from former batches) of the particle size analysis measured by laser light diffraction. Particle size analysis of three experimental series Starting material EURENCO

20057014 EURENCO 20027031

EURENCO 20079003

Total quantity (number of batches)

5 kg (10 Batches) 3 kg (6 Batches) 4 kg (8 Batches)

Mean particle size x50.3

121 µm 106 µm 107 µm

Particle size distribution, K

0.36 [-] 0.41 [-] 0.45 [-]

According to VDI guideline (Association of German Engineers, Number 3491) the particle size distribution K is a dimensionless ratio with the following meaning:

• K ≤ 0.14 monodisperse

• 0.14 < K ≤ 0.41 quasi-monodisperse

• 0.41 < K polydisperse

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The typical mean particle size of ADN-Prills made by emulsion crystallization is 100 – 120 µm. Particle size fractions of e.g. 60 µm or 140 µm, with narrow particle size distribution, are currently achieved by sieving (see Figure 7 and Figure 8).

Figure 7. Micrograph of prilled ADN (example without stabilizer). Sieve fraction with mean particle size 59 µm.

Figure 8. Micrograph of prilled ADN (example without stabilizer). Sieve fraction with mean particle size 137 µm. The micrographs Figure 9 and Figure 10 are showing the irregular shape neat material and pore free ADN-Prills with high density (see Table 13). Due to the use of stabilizers the decomposition and gas evolution of ADN during the prilling process is reduced and a density very close to the basic material can be achieved.

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Figure 9. Micrograph of neat ADN (Eurenco, lot 20119036) for use in HISP project.

Figure 10. Micrograph of stabilized, pore-free ADN-Prills.

Table 13. Density of different ADN products. Sample Density (g/cm3) Neat ADN, Eurenco Lot 20119036 1.793 ADN-Prills (delivered from FOI) 1.769 ADN-Prills without stabilizer (ICT) 1.754 ADN-Prills stabilized (ICT) 1.795 Different kinds of stabilizers have been tested. The stabilized ADN-Prills have been passed over ICT-internally for further testing in propellant formulations. These stabilized materials may be allocated to other partners within the framework of HISP project.

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3.2.1 Analytical methods

3.2.1.1 Particle size analysis Method: Laser light diffraction Model: Mastersizer 2000 Manufacturer: Malvern Instruments

3.2.1.2 Morphology Method: Light microscopy Device type: Leica Z16 APO Manufacturer: Leica Microsystems

3.2.1.3 Density Method: Helium gas pycnometry Device type: Ultrapycnolmeter 1000 Manufacturer: Quantachrome Instruments

3.3 Delivery to project partners The emulsion prilled ADN will be used by ICT only and it will thus not be transported to any other project partner.

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4 Conclusions Prilled ADN has been produced using two different methods; i.e. spray prilling (FOI) and emulsion prilling (ICT). The emulsion prilled ADN will only be used by ICT. FOI prilled ADN will be delivered to the following project partners: ICT, TNO and AVIO. In order to receive FOI prilled ADN the receiver must apply and obtain the transport permits needed. So far (24/11/2011) only ICT has been able to obtain the permits needed and thus FOI prilled ADN has only been delivered to ICT.

5 References Chapter 2. 1. Wingborg, N.; Andreasson, S.; de Flon, J.; Johnsson, M.; Liljedahl, M.; Oscarson, C.;

Pettersson, Å.; Wanhatalo, M., Development of ADN-based Minimum Smoke Propellants. In 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Nashville, TN, USA, 2010.

2. Merck Index. 11th ed.; 1989. 3. CRC Handbook of Chemistry and Physics. 83rd ed.; 2003. 4. Standard Test Method for Mol Percent Impurity by Differential Scanning Calorimetry;

E 928-85; ASTM: 1985. Chapter 3. 1. European patent EP 0 953 555 B1, Title: “Process for preparing particles of meltable

propellants and explosives”, Publication Date: 21.09.2005, Inventors: Heintz, Thomas; Teipel, Ulrich; Krause, Horst; Leisinger Karlfred, Applicant: Fraunhofer Gesellschaft zur Förderung der angewandten Forschung e.V.

2. Pontius, H, Bohn, M.A., Aniol, J.: Stability and compatibility of a new curing agent for binders applicable with ADN evaluated by heat generation rate measurements, Energetic Materials - Processing and Product Design, 39th. International Annual Conference of ICT, 2008, Karlsruhe.

3. Bohn, M.A, Pontius, H., Hürttlen, J.: Thermal Stability and Stabilization of ADN-Water Gels, Energetic Materials - Characterisation and Performance of Advanced Systems; 38th International Annual Conference of ICT, June 26 - 29, 2007, Karlsruhe.

4. Bohn, M.A. (ed.): Heat Flow Calorimetry on Energetic Materials; Proceedings of the 6th International Heat Flow Calorimetry Symposium on Energetic Materials, 2008, p. 247-280 Fraunhofer ICT, Pfinztal-Berghausen.