Energy Release Characteristics and Reaction Mechanism of PTFE/Al/Bi2O3 Reactive Materials under Drop-Hammer Test
Abstract
:1. Introduction
2. Materials and Methods
2.1. Formulations and Preparation
2.2. Drop-Hammer Test
2.3. Thermal Analysis
3. Results and Analysis
3.1. Energy Release Characteristics of PAB under Drop-Hammer Impact
3.1.1. Shock-Induced Chemical Reaction Phenomenon
3.1.2. Impact Sensitivity
3.1.3. Ignition Delay
3.2. Shape of the Specimen before and after the Reaction
3.2.1. Macroscopic Appearance of Specimens
3.2.2. Microscopic Morphology of Specimens
3.3. Ignition and Reaction Mechanism of PAB under Drop-Hammer Impact
3.3.1. Hot-Spot Formation
3.3.2. Thermal Decomposition Process
3.3.3. Microscopic Morphology of Reaction Products
3.3.4. Ignition and Reaction Propagation Process
3.3.5. Ignition of Aluminum Particles
4. Conclusions
- (1)
- At a drop height of 150 cm, PABs can react vigorously under drop-hammer loading. The ratio influenced the reaction duration and intensity. As the Bi2O3 content increased to 9%, the reaction duration increased and the reactivity increased, and when the content continued to increase, the reaction duration decreased and the intensity of the reaction decreased. When the Bi2O3 content was 9%, the reaction was the most intense, and the duration was the longest at 1300 μs. With the increase in Bi2O3 content in the system, the sensitivity of the material first increased, and then fell. When the Bi2O3 content was 9%, the highest impact sensitivity was achieved with a characteristic drop height H50 of 130.5 cm.
- (2)
- Under impact loading of the drop hammer, ignition occurs at the tips of open cracks. PAB undergoes several physicochemical processes such as PTFE melting, a PTFE/Bi2O3 reaction, an Al/ Bi2O3 reaction, molten PTFE pyrolysis, and a C2F4/Al reaction during the local temperature rise. The presence of Bi2O3 results in a lower reaction onset temperature of the reactive material, a lower excitation threshold of the reactive material, and a higher degree of reaction, improving the overall energy release of the reactive material.
- (3)
- The ignition process and propagation process in PAB can be roughly divided into three stages: local PTFE melting (mush zone); the reaction of the active component and thermal decomposition of the matrix to produce gas (multiphase zone); and violent combustion of Bi2O3 and Al particles in strong oxidizing C2F4 gas (flame zone). With a appropriate amount of Bi2O3, the reaction of molten PTFE and Bi2O3 and the thermit reaction between Al/Bi2O3 will occur more easily in the multiphasic zone; this will release a large amount of energy and promote diffusion in the multiphasic zone, thus promoting the propagation of the overall reaction and improving the reactivity of PAB.
Author Contributions
Funding
Conflicts of Interest
References
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Formulation Codes | Al/Bi2O3 Additive Content/(wt.%) | Content/(wt.%) | Theoretical Density /(g∙cm−3) | Theoretical Calorific Value/(kJ∙g−1) | ||
---|---|---|---|---|---|---|
PTFE | Al | Bi2O3 | ||||
1 | 0 | 74 | 26 | - | 2.32 | 8.42 |
2 | 5 | 70 | 25 | 5 | 2.41 | 8.11 |
3 | 10 | 67 | 24 | 9 | 2.48 | 7.79 |
4 | 15 | 63 | 24 | 13 | 2.57 | 7.48 |
5 | 20 | 59 | 23 | 18 | 2.68 | 7.16 |
Formulation Codes | Bi2O3 Content/(%) | Theoretical Density /(g∙cm−3) | Actual Density /(g∙cm−3) | Relative Density /(%) | Porosity Ratio /(%) |
---|---|---|---|---|---|
1 | 0 | 2.32 | 2.19 | 94.92 | 5.08 |
2 | 5 | 2.41 | 2.27 | 93.59 | 6.41 |
3 | 9 | 2.48 | 2.32 | 92.77 | 7.23 |
4 | 13 | 2.57 | 2.33 | 90.66 | 9.34 |
5 | 18 | 2.68 | 2.38 | 88.43 | 11.67 |
Bi2O3 Content/(%) | Characteristic Drop Height H50/(cm) |
---|---|
0 | 138.4 |
5 | 135.8 |
9 | 130.5 |
13 | 137.5 |
18 | 143.6 |
Formulation | Peak | Start Temperature /(°C) | Peak Temperature /(°C) | End Temperature /(°C) | Energy Release /(J/g) | Physicochemical Changes |
---|---|---|---|---|---|---|
PTFE-Al | A | 325 | 343 | 360 | −36.0 | Melting of PTFE |
B | 522 | 561 | 576 | −243.8 | Decomposition of PTFE | |
C | 564 | 590 | 605 | 344.4 | PTFE/Al reaction | |
D | 645 | 658 | 668 | −35.4 | Melting of Al | |
E | 755 | 825 | 877 | −380.4 | Sublimation of AlF3 | |
PTFE-Al-Bi2O3 | F | 329 | 342 | 354 | −23.6 | Melting of PTFE |
G | 385 | 422 | 446 | 61.4 | PTFE/Bi2O3 reaction | |
H | 472 | 574 | 602 | 1042.2 | Al/Bi2O3 reaction, Decomposition of PTFE, and PTFE/Al reaction | |
I | 642 | 656 | 661 | −7.5 | Melting of Al |
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Jiang, C.; Hu, R.; Mao, L.; Wang, Z.; Xu, W.; Hu, W. Energy Release Characteristics and Reaction Mechanism of PTFE/Al/Bi2O3 Reactive Materials under Drop-Hammer Test. Polymers 2022, 14, 1415. https://doi.org/10.3390/polym14071415
Jiang C, Hu R, Mao L, Wang Z, Xu W, Hu W. Energy Release Characteristics and Reaction Mechanism of PTFE/Al/Bi2O3 Reactive Materials under Drop-Hammer Test. Polymers. 2022; 14(7):1415. https://doi.org/10.3390/polym14071415
Chicago/Turabian StyleJiang, Chunlan, Rong Hu, Liang Mao, Zaicheng Wang, Wenyu Xu, and Wanxiang Hu. 2022. "Energy Release Characteristics and Reaction Mechanism of PTFE/Al/Bi2O3 Reactive Materials under Drop-Hammer Test" Polymers 14, no. 7: 1415. https://doi.org/10.3390/polym14071415