Performance of W/MnO 2 as an Environmentally Friendly Energetic Time Delay Composition

Transcription

1 Performance of W/MnO 2 as an Environmentally Friendly Energetic Time Delay Composition Joshua T. Koenig, Anthony P. Shaw, Jay C. Poret, William S. Eck, Lori J. Groven Supplemental Information Pages: 11 Figures: 10 Tables: 1 S1

2 SEM Images of the Reactants Used in this Research Figure S1. SEM image of tungsten powder, magnified 500x. Figure S2. SEM image of tungsten powder, magnified 1000x. S2

3 Figure S3. SEM image of manganese (IV) oxide powder, magnified 500x. Figure S4. SEM image of manganese (IV) oxide powder, magnified 1000x. S3

4 Thermochemical Predictions from FactSage 7.0 The reactants tungsten and manganese (IV) oxide were simulated in FactSage 7.0, with combustion temperature and gas production results graphed below. Figure S5. Simulated adiabatic temperatures of combustion as a function of wt-% W in the W/MnO 2 system. Key Points from S5 41% fuel, 0.15% gas produced, K peak temperature solids: 67.53% (MnO)(WO 3 ), 27.41% MnO liquids: 4.91% MnO gases: 0.15% O 2 simplified equation at 41.3% fuel: W + 3MnO 2 (MnO)(WO 3 ) + 2MnO From 28-30% fuel, the temperature appears to be limited by the 6Mn 2 O 3 (s) 4Mn 3 O 4 (s) + O 2 (g) decomposition, which occurs at 1626 K. From 34-38% fuel, the temperature appears to be limited by the 2Mn 3 O 4 (s) 6MnO(s) + O 2 (g) decomposition, which occurs at 1925 K. From 41-52% fuel, the temperature is limited to 2115 K by the MnO(s-l) transition. S4

5 Figure S6. Simulated gas production of the W/MnO 2 system as a function of wt-% W. Key Points from S6 16% fuel, 4.25% gas produced, K peak gas solids: 69.40% Mn 2 O 3 (bixbyite), 26.35% (MnO)(WO 3 ) liquids: none gases: 4.25% O 2 30% fuel, 1.61% gas produced, K solids: 49.41% (MnO)(WO 3 ), 48.41% Mn 3 O 4, 0.58% Mn 2 O 3 (bixbyite) liquids: none gases: 1.61% O 2 38% fuel, 1.05% gas produced, K solids: 62.58% (MnO)(WO 3 ), 30.02% MnO, 6.35% Mn 3 O 4 liquids: none gases: 1.05% O 2 S5

6 Thermal and Reaction Characteristics as a Function of Aging as Measured by DSC-TGA wt. % (a.u.) Temperature ( C) Figure S7. Wt. % change of the 50/50 W/MnO 2 system as a function of temperature, zero (bottom) to eight (top) weeks aging Heat Flow (W/g) Temperature ( C) Figure S8. Heat flow change as a function of temperature for the 50/50 W/MnO 2 system, zero (bottom) to eight (top) weeks aging S6

7 Combustion Velocity for the W/MnO 2 System Combined with Diluents Combustion Rate (mm/s) % SiO2 5% SiO2 2.5% Fe2O3 60W/40MnO2 Composition Figure S9. Average combustion rates for the 60/40 W/MnO 2 system with varying 10 micro SiO 2 and Fe 2 O 3 wt-%. Using 4.7 mm SS housing. The 5 wt-% Fe 2 O 3 mixture failed to propagate Combustion Rate (mm/s) % SiO2 5% SiO2 2.5% Glass 5% Glass 60W/40MnO2 Composition Figure S10. Average combustion rates for the 60/40 W/MnO 2 system with varying 125 micron SiO 2 and 325 mesh soda-lime glass wt-%. Using 4.7 mm SS housing. S7

8 Experimental Procedure for Measuring M213/M228 Fuze Times Each fuze was held by an insulated clamp in a rigid assembly. To initiate the test, a steel weight was positioned approximately 60 cm above the fuze within a plastic tube and held in place by an electromagnet. The weight was dropped by turning off the power supply to the electromagnet. The action of the weight on the fuze striker initiates the fuze by firing the percussion primer. The acoustic signature produced by the weight striking the fuze was captured by an acoustic trigger (Kapture Group MD-1505 with TTL output). The striking/initiating event causes the acoustic trigger to generate a 5 V TTL pulse, used to activate an in-house-developed data collection system. The audible report produced by the output charge generated a second TTL pulse and the time difference between the two pulses was used as the fuze functioning time. The accuracy of the method was verified with a high-speed video camera (Vision Research Phantom 7.1). The delay burning time is thought to account for most of the functioning time, as the other events are rapid. Custom-built stainless steel blocks were used to hold the fuzes during hot or cold temperature conditioning. The blocks served as thermal buffers due to their large size and heat capacity. The fuzes, within the blocks, were conditioned in a hot or cold chamber overnight and transported to the testing room in an insulated container. Each fuze was tested within approximately seconds after removal from the fuze block in the container. As mentioned previously, each fuze was held by an insulated clamp during the test, to minimize heat flow to or from the surroundings. Table S1. Experimental M213/M228 Fuze Results a) temperature ( C) average (s) standard deviation (s) lowest (s) highest (s) a) Each fuze contained 1.89 grams of W/MnO 2 delay (50/50) loaded in four increments. The delay columns were consolidated to 64% of the theoretical maximum density, and were approximately 18.5 mm long. A proprietary titanium-based igniter was used as an input/output charge. At each temperature, fuzes were tested. S8

9 The Hao-Tanaka Model Hao, Ouchiyama, and Tanaka published a series of papers 1-5 which focused on formulating a microstructure model for determining reaction conversion as a function of time. The first paper 1 focused on determining the average number of contacts between randomly mixed solid particles, only valid for binary mixtures. The second paper 2 analyzed the currently existing Jandar model, concluding that the Jandar model was not accurate due to the variation of the rate constant with the molar ratio. Hao and Tanaka also determined that other models were not accurate, and concluded that a new microstructure model needed to be created. In their third paper 3, Hao and Tanaka discuss the role of contact points between particles and how these points impact the reactivity of solids. They express the reactivity of solids in terms of molar ratio, particle size ratio, and the nature of the reacting system. This theory was then confirmed with experimental results. Hao and Tanaka then propose a new experimental method to specify the diffusion component in a reacting particulate packing 4. The method proposes that the diffusing component can be determined based upon the difference in the dependence of the reaction rate upon the particle size ratio. Lastly, in their final paper, analysis of solid-solid reactions controlled by uni-directional diffusion 5, Hao and Tanaka are able to overcome defects in previous models by separating the reaction into two stages, which includes the moments before and after contact between two reactant layers. The model, which relates reaction conversion to physical parameters, is shown in Equations 1-4. = (1) = (2) = (3) = (4) Where α A is the extent of reaction, R r is the radius ratio of R B /R A, is the porosity of the mixture, is ratio of the number of A particles to B particles, N A /N B, N AB is the number of B particles surrounding A particles, X A are the number fraction of A particles, D B is the diffusivity of component B, K = (b/a)(ρ A /ρ B ), with b and a the stoichiometry coefficients and ρ A and ρ B the densities of particles A and B, r Ao is the initial radius of particle A, X 1 the dimensionless S9

10 thickness of a contact point, t the time, and is the dimensionless time. The Hao-Tanaka model assumes that the particles are equidistant, that no change in the number or positions of contact points exists, that the cross-sectional area at a contact zone is constant during reaction, and that the formation of the product layers does not change the total volume of a particle. Conduction, Convection, and Percentage of Theoretical Maximum Density (%-TMD) in Pyrotechnic Pellets As any type of powder is pressed at increasingly higher %-TMD, the amount of air voids in that powder will decrease. In fact, the definition of void spacing can be considered to be 100 %-TMD, and is a measure of how much of the pellet is void space. In general, that void space will generally be filled with the same atmosphere that the pellet was pressed in, resulting in a pellet that has both parts gas and solid. If there are less gases in the pressed pellet, during combustion preheating and convection of those gases through the pellet will be lessened. This then results in reduced convective thermal transport, and is independent of the gas production of the pyrotechnic system (though gas production of a pyrotechnic system will impact convective thermal transport). However, another phenomenon that is inversely related to that of void spaces in the system is particle contact, or thermal conductivity. As powder is pressed at increasingly higher %-TMD, thermal conductivity of the pellet increases due to increased particle contact. Therefore, one can also say that at higher %-TMD, thermal conductivity of the pellet will be increased, which will result in higher rates of conductive thermal transport. With these two phenomena in mind, one can consider the combustion of a high %-TMD pellet to be primarily dominated by conductive effects mainly the fact that conduction plays a larger role in thermal transport during combustion than convection. The inverse is also true for combustion of a low %-TMD pellet, with convection being the dominant mode of thermal transport, over that of conduction. Somewhere between those %-TMD ranges will fall the critical %-TMD (a maximum or minimum), which can be considered to be the ideal %-TMD for thermal transport if a maximum, or the worst case %-TMD for thermal transport if a minimum. For the W/MnO 2 system, a thermal transport maximum is reached around 60%-TMD, with thermal transport decreasing at both higher and lower %-TMD due to the inverse impacts of S10

11 better particle-particle contact (increased thermal conductivity) and greater pore volume (increased thermal convection). References [1] Ouchiyama, N.; Tanaka, T. Estimation of the Average Number of Contacts between Randomly Mixed Solid Particles. Ind. Eng. Chem. Res., 1980, 19, [2] Hao, Y. J.; Tanaka, T. Some Problems Encountered in the Proposed Solid-Solid Reaction Models. J. Soc. Powder Technol. Jpn. (Funtai Kogaku Kaishi), 1987, 24, [3] Hao, Y. J.; Tanaka, T. Role of the Contact Points Between Particles on the Reactivity of Solids. Can. J. Chem. Eng., 1988, 66, [4] Hao, Y. J.; Tanaka, T. A New Experimental Method to Specify the Diffusion Component in a Reacting Particulate Packing. Can. J. Chem. Eng., 1990, 68, [5] Hao, Y. J.; Tanaka, T. Analysis of Solid-Solid Reactions Controlled by Uni-directional Diffusion. Int. Chem. Eng., 1990, 30, S11