The Mechanical and Reaction Behavior of PTFE/Al/Fe under ...fields of the PTFE/Al composites if the Al/Fe2 O3 reac-tion can be triggered. But to the best of our knowledge, few researchers

Research ArticleThe Mechanical and Reaction Behavior of PTFEAlFe2O3 underImpact and Quasi-Static Compression

Jun-yi Huang Xiang Fang Yu-chun Li Bin Feng Huai-xi Wang and Kai Du

College of Field Engineering PLA University of Science and Technology Hou Biaoying Road No 88 Nanjing Jiangsu 210007 China

Correspondence should be addressed to Xiang Fang fangxiang3579163com

Received 19 April 2017 Accepted 10 July 2017 Published 8 August 2017

Academic Editor Jun Liu

Copyright copy 2017 Jun-yi Huang et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Quasi-static compression and drop-weight test were used to characterize the mechanical and reaction behavior of PTFEAlFe2O3composites Two kinds of PTFEAlFe2O3 composites were prepared with different mass of PTFE and the reaction phenomenonand stress-strain curves were recorded the residuals after reaction were analyzed by X-ray diffraction (XRD) The results showedthat under quasi-static compression condition the strength of the materials is increased (from 371Mpa to 772Mpa) with theincrease of PTFE and the reaction phenomenon occurred only in materials with high PTFE content XRD analysis showed thatthe reaction between Al and Fe2O3 was not triggered with identical experimental conditions In drop-weight tests PTFEAlFe2O3specimens with low PTFE content were found to be more insensitive by high-speed photography and a High Temperature MetalSlag Spray (HTMSS) phenomenon was observed in both kinds of PTFEAlFe2O3 composites indicating the existence of thermitereaction which was confirmed by XRD In PTFEAlFe2O3 system the reaction between PTFE and Al precedes the reactionbetween Al and Fe2O3

1 Introduction

Reactive materials (RMs) or impact-initiated materials andtheir applications have attached great interest in recent yearsdue to their uniquely mechanical and chemical propertiesThe mixture of polytetrafluoroethylene (PTFE) and alu-minum (Al) is one of the typical RMs andhas been extensivelystudied because of its high energy density and a favorablecombination of properties of PTFE such as low friction coef-ficient high thermal stability high electrical resistance highchemical inertness high melting point (327∘C) high thermalenergy release when decomposed and the easiness to deform[1] A lot of experiments have been conducted to probe themechanical and reaction behavior of PTFEAl compositesby different means In order to improve the density andstrength of the materials many researchers have tried toadd tungsten (W) the most common ldquoheavyrdquo metal intothe PTFEAl composites Dynamic compression experimentswere performed by Cai et al on a pressed PTFEAlWmixture to understand the mechanical response and failureat high-strain and high-strain rate [1] The results showedthat failure was proceeded by extensive plastic deformation

concentrated mainly in the PTFE matrix and the initiationas well as the propagation of cracks was caused by theseparation of the W particle-PTFE interface Herbold et alinvestigated the particle size effect on the strength failureshock behavior and dynamic properties of PTFEAlWcomposites combining simulation and experiments [2 3]They found that the increased strength of the sample with finemetallic particles is due to the formation of force chains underdynamic loading Numerical modeling of shock loadingof this granular composite material demonstrated that theinternal energy specifically thermal energy of the soft PTFEmatrix can be tailored by the W particle size distribution Xuet al tested four kinds of PTFEAlW with different contentsand sizes ofWparticles [4]The tensile and impact propertiesof PTFEAlW reactive energetic composites were probedusing a universal materials testing machine and an improvedpendulum impact tester at room temperature The resultsrevealed that the failure behavior of PTFEAlW includeddeformation fracture disorganization and reaction Theyalso drew the conclusion that the addition of 30wt ofcoarse W particles improved the impact strength of thematerial but led to the increase of reactive activity and

HindawiAdvances in Materials Science and EngineeringVolume 2017 Article ID 3540320 9 pageshttpsdoiorg10115520173540320

2 Advances in Materials Science and Engineering

(a) (b)

Figure 1 Samples of PTFEAlFe2O3 composites (a) for quasi-static compression and (b) for drop-weight tests

the decrease of perfectibility of the reaction Other scholarsalso carried out in-depth study of PTFEAlW from otherperspectives using different techniques including quasi-staticand dynamic compression (both drop-weight test and Split-Hopkinson Pressure Bar) scanning electron microscopy(SEM) X-ray diffraction (XRD) and differential scanningcalorimetry (DSC) [5ndash9]

As can be seen above much attention has been put to theaddition of W particles to increase the strength and densityof PTFEAl while literatures about the addition of metaloxides such as CuO and Fe2O3 are scarce In the aboveexperiments about PTFEAlW no reaction between Al andW was observed only a small amount of WC and W2Cformed which were activated by the high heat as a result offluorination of Al [7] But the heat generated by the reactionbetween Al and metal oxides (thermite) cannot be neglectedZhou et al studied the reactions of AlCuO AlFe2O3and AlZnO systems using T-Jumptime-of-flight mass spec-trometer [10] They found the temperatures of the reactionscan reach 2837K 3135 K and 1822K respectively And theenthalpy of combustion is minus60405 kJmol minus4251 KJmoland minus3121 KJmol (per mol of Al) correspondingly AlsoWang et al revealed that the heat generated from the reactionbetween Al and Fe2O3 can raise thematerial to a temperatureof ca 3000∘C higher than the melting point of Fe (1535∘C)and Al2O3 (2059

∘C) [11] However because of the low energyrelease rate and the difficulty to shape the application ofthe thermites is limited But experiments confirmed that theaddition of 10 wt PTFE into Fe2O3Al mixture can reducethe time to reach the exothermic peak by two orders ofmagnitude [12]

The PTFEAlFe2O3 composites are promising reac-tive materials which have the dual properties of PTFEAland AlFe2O3 and can greatly expand the applicationfields of the PTFEAl composites if the AlFe2O3 reac-tion can be triggered But to the best of our knowledgefew researchers investigated the mechanical and reactionbehavior of PTFEAlFe2O3 systematically In this paperthe mechanical and reaction behavior of PTFEAlFe2O3under impact and quasi-static compressionwere investigatedand the failure and ignition mechanism were analyzed Theinsensitivity of PTFEAlFe2O3 to impact was measuredquantitatively which is of great importance for applicationsof reactive materials

2 Experimental Setup

21 Specimens Preparation In this study two kinds ofcomposites 50PTFE-28Al-22Fe2O3 (wt) (type A speci-men) and 75PTFE-14Al-11Fe2O3 (wt) (type B specimen)were fabricated by powder mixture cold isostatic pressing(CIPing) and vacuum sintering based on the patent ofNielsonrsquos [13] The initial powers have the following averagesizes PTFE 25 um (3M Shanghai) Al 1-2 um (JT Hunan)Fe2O3 3ndash5 um (NAO Shanghai) Firstly the PTFEAlFe2O3powders were suspended in an ethanol solution and mixedby a motor-driven blender for 20 minutes and then dried ina vacuum oven for 48 hours at 60∘C followed by a screeningprocess to break up agglomeratesNext the driedmixturewascold pressed into cylinders (for quasi-static compression andfor drop-weight test Figure 1) under the pressure of 60MpaFinally specimens were sintered in a vacuum oven at thetemperature of 370∘C for 4 h with a cooling rate of 50∘Ch

22Methods Quasi-static compression tests were performedusing a SFLS-30T electrohydraulic press with a maximumloading of 30 kN The sample was placed between twohardened steel anvils and was compressed at the speed of9mmmin corresponding to a normal strain rate of 001sThe load was terminated when the sample was fractured orthe maximum load was reached All tests were conductedat room temperature and the stress-strain curves of all thesamples were recorded by the hydraulic press automaticallyTo ensure repeatability at least five specimens of each kindwere tested

Drop-weight tests were carried out with a fall hammerimpact sensitivity tester with a drop mass of 10 kg whichcan be dropped from a maximum height of 15m So themaximum speed of 55ms of the drop hammer and the strainrate of almost 1000s can be achieved In order to observe thereaction process high-speed photographywith the frame rateup to 20000 framess was adopted

Hitachi S-4800 scanning electron microscope (SEM) wasused to observe the microstructure of the materials and toanalyze the reaction and fracture mechanisms

The residues of the specimen after quasi-static compres-sion and drop-weight test were collected and characterized byX-ray diffraction (Bruker D8 ADVANCE operating at 40 kVand 40mA with unfiltered Cu K120572 radiation)

Advances in Materials Science and Engineering 3

(a) (b)

Figure 2 Samples before and after quasi-static compression (a) Type A specimen and (b) type B specimen

(a) (b)

Figure 3 The microstructures of PTFEAlFe2O3 composites (a) Type A specimen and (b) type B specimen

3 Results and Discussion

31 Mechanical Behavior under Quasi-Static CompressionTypical photographs of uncompressed and compressedPTFEAlFe2O3 reactivematerials of the two kinds are shownin Figure 2 It can be found that there are quite differencesbetween the two materials For type A specimens cracksappeared soon after the compression load was added and thespecimens were fractured at a relatively low strain level Buttype B specimens stayed intact even when they are pressed toabout 02 of their original length indicating a greater plasticdeformation The difference of the failure behavior of thetwo materials is mainly attributed to the different content ofPTFE More PTFE ensures better matrix continuity and thusleads to a great plasticity which can be confirmed from theSEM photographs in Figure 3 As can be seen from Figure 3the combination between Al Fe2O3 and PTFE matrix intype B specimens is better than that in type A specimensindicating more perfect mechanical properties for type Bspecimens The stress-strain curves of the two materials aregiven in Figure 4 and their corresponding parameters arelisted in Table 1 When compressed both types of specimenunderwent the process of elastic and plastic deformationcrack propagation and fracture As can be seen the twospecimens have almost identical elastic deformation andpossess similar yield stresses After the pressure exceeded theyield stress the strain hardening phenomenon occurred forboth types of PTFEAlFe2O3 However the strain hardeningmodulus of type B specimen (348Mpa averaged from strain

01 to 172) is 288 times higher than that of type A specimen(121Mpa averaged from strain 01 to 145) which causes thetoughness (the area under the stress-strain curve) of type Bspecimen to be higher than that of type A specimen Thatis in the case of quasi-static compression type B specimenscan absorb more energy than type A specimens beforefracture So type B specimens are more likely to react inthe same condition and the experiments had confirmed thishypothesis which will be discussed later As for the failureprocess type B specimens failed more suddenly than typeA specimens With the increase of compression load theaxial cracks and shear cracks in type A specimens developedgradually when the specimens cannot resist the pressurethey fractured But for type B specimens no obvious visiblemacrocracks generated until the maximum strength wasreached However once the fracture condition was met typeB specimens fractured catastrophically accompanied with asharp drop in stress and intensive reaction phenomenonTheignition point was marked in Figure 4

32 Reaction Behavior under Quasi-Static Compression Fig-ure 5 shows the initiation phenomenon of a type B specimenunder quasi-static compressionWhen the true stress reachedabout 75Mpa the initiation started from the vicinity ofthe outer surface of the cylinder where the shear force isthe strongest accompanied by explosion sound and brightlights Then the reaction propagated from the edge to theinterior of the specimen and quenched quickly the wholeignition process lasted about 1 s with about 90 of the


Table 1 Parameters of PTFEAlFe2O3 reactive material

Type PTFE Al Fe2O3(wt)

Density(gcm3)

Yield stress(Mpa)

Average strainhardening

modulus (Mpa)

Ultimate strength(Mpa) Ignition or not

A 50 28 22 223 201 121 371 NoB 75 14 11 233 199 384 772 Yes

Type AType B

Ignition

0

15

30

45

60

75

True

stre

ss (M

pa)

03 06 09 12 15 1800True strain

Figure 4 Stress-strain curves of two kinds of PTFEAlFe2O3composites

specimen unreacted Feng et al also observed the initiationphenomenon with PTFEAl composites under similar exper-imental condition [14] in which PTFE and Al had reactedwith each other to formAlF3 and C (carbon black) Howeverno initiation phenomenon was observed for any type Aspecimen which could be attributed to the low toughness asmentioned above

The specimen of type B after reaction and themicrostruc-tures of the reacted and unreacted regions are shown inFigure 6 As can be seen from Figure 6(a) the black partscorrespond to the reacted regions which is marked withldquoreacted regionrdquo And there is a clear boundary betweenthe unreacted and reacted region which can be seen moreclearly in Figure 6(b) The microstructures of the unreactedand reacted regions are given in Figures 6(c) and 6(d)In unreacted region (Figure 6(c)) PTFE has a distinctorientation and forms a dense nanofiber network with Aland Fe2O3 particles embedded in the PTFE matrix withoutsignificant deformation In reacted region (Figure 6(d)) thecrack section is covered by smooth melted PTFE and carbonblack and PTFE nanofiber network completely disappearedThe specimen after reaction is displayed in Figure 6(a) theblack part corresponds to the reacted region which ismarkedwith ldquoinitiationrdquo Moreover the opening crack and shearplane caused by compression are clearly visible which areclosely related to the ignition phenomenon [15] Althoughthere has been much controversy about the mechanicalinitiation of explosions over these years many scholars

believe that the initiation is due to the existence of ldquohotspotsrdquo Swallowe and Field found that the hot spots formedat the polymer crack tip and shear band can activate theexplosive [16] In the PTFEAlFe2O3 system PTFE is thepredominant pressure-bearing component when subjectedto compression PTFE matrix was deformed heavily causingthe crack generation and spreadThe crack propagation speedcan reach 200ms to 800ms and the temperature of the cracktip can reach 300∘C to 1000∘C [17] and the high temperaturecan greatly promote the reaction Feng et al proposed a crack-induced initiation mechanism of Al-PTFE under quasi-staticcompression which can also explain the reactionmechanismof PTFEAlFe2O3 system [15] As can be seen from the XRDanalysis in Figure 7 the reaction products showed that Fe2O3was not involved in the reaction the initiation phenomenonwas actually caused by PTFE and Al

TheXRD results of the residuals of both typeA and type Bspecimens after compression are shown in Figure 7 No otherspecies were found besides the original three components(PTFE Al and Fe2O3) in the compressed specimen of type Aspecimens which means that there was no reaction betweenPTFE Al and Fe2O3 This is due to the brittle nature ofthis material and the lower strength and toughness Whencompressed type A specimens fractured quickly before theformation of high temperature of the crack tip and thus therewas no enough energy to induce the reaction However AlF3was found in the compressed specimen of type B materialsand the black powder remaining on the anvil proved to becarbon black indicating the following reaction had takenplace

Al + (-C2F4-) 997888rarr AlF3 + C (1)

AlF3 was formed from the Al oxidized by fluorine fromthe PTFE But besides iron oxide (Fe2O3) no other ironcompounds or iron (Fe) was found in the reaction productsillustrating that Fe2O3 did not involve in the reaction Thatis the thermite reaction between Al and Fe2O3 was nottriggered under quasi-static compression Firstly the energyor temperature required to initiate the thermite reaction isrelatively highWilliams et al found the ignition temperatureof Al and Fe2O3 was 800Kndash950K by experiment [18]but Zhou et al concluded that the ignition temperatureof Al and Fe2O3 was 1100K using T-Jumptime-of-flightmass spectrometer [10] while Fan et al discovered that theexothermic peak of DSC curves of Al and Fe2O3 powdermixture appeared at 8535∘Cndash9497∘C and the exothermicpeak represented the thermite reaction [19] The differencesof ignition temperature in the three studies are attributedto the diversity of materials and the difference of heatingrate but all three studies showed that thermite reaction


(a) (b)

(c)

crack

(d)

Figure 5 The initiation process of a type B specimen (a) First sign of initiation (b) reaction propagated from the edge to the interior of thespecimen (c) violent reaction and (d) after initiation and the formed crack

Opening cracks

Shear plane Unreacted region

Reacted region

(a) (b)

(c) (d)

Figure 6 SEM photographs of the initiation region and specimen after reaction (a) Specimen after reaction (b) boundary of reacted region(right) and unreacted region (left) (c) unreacted region and (d) reacted region


PTFEAlF23

0

200

400

600

800

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

(a)

0

200

400

600

800

1000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

PTFEAl Al3

F23

(b)

Figure 7 The XRD results of specimens after quasi-static compression (a) Type A specimen and (b) type B specimen

needs high temperature (hundreds of degrees centigrade) totrigger However the temperature rise caused by quasi-staticcompression is low relatively (tens of degrees centigrade)according to the simulation result of Feng et al [14] thereforeit is not enough to trigger the reaction of Al and Fe2O3Furthermore despite the intense reaction of PTFE with Althe duration may be too short to induce thermite reactionbetween Al and Fe2O3 Besides the content of Al and Fe2O3was small and they were dispersed in the PTFE matrix theless contact of the two substances resulted in the difficulty toreact Lastly compared with other active oxides such as CuOand Cu2O the activity of Fe2O3 is relatively lower because ofits much less oxygen release since the analysis by Wang etal suggested that the initial steps of the thermite reaction arethe decomposition of the oxidizer particles to form oxygen aswell as Al diffusion through the Al2O3 shell [11]

33 Reaction Behavior under Drop-Weight Test The impactsensitivity of both type A and type B materials was inves-tigated using an impact sensitivity tester and a high-speedphotography and the sensitivity of the materials is measuredby the lowest drop height from where the drop mass isreleased to produce greater than 50 reaction which is onthe basis of an abbreviated Bruceton method [20] and thecharacteristic drop height is represented by H50 in Table 2Characteristic drop height (H50) can be used to calculateignition energy based on potential energy as in

119864119901 = 119898119892ℎ (2)

where 119864119901 is the potential energy of the drop mass 119898 isthe mass of the drop mass and ℎ is the optimal height forreaction To compare the absorbed energy of the materialsunder quasi-static compression and drop-weight test theestimated ignition energy under quasi-static compression is

Table 2 Results of ignition energy under static and dynamic load

Type Drop height(H50)cm

Ignition energy(static)J

Ignition energy(impact)J

A 80 mdash 78B 51 71 50

also calculated by the work done by the machine along thecompress direction which can be expressed as follows

119882 = sum119865119905Δ119904 (3)

where119882 is the work done by the machine 119865119905 is the transientforce and Δ119904 is infinitesimal increases of displacement both119865119905 and Δ119904 can be retrieved from the testing machine directlyThe information of the two materials under the two testconditions is listed in Table 2

As can be seen from Table 2 the ignition energy of typeB materials under quasi-static compression (71 J) is higherthan that under drop-weight impact (50 J) But if takingconsideration of the energy dissipated into the surroundingenvironment during the quasi-static compression processthey may be similar because more heat will be lost duringquasi-static compression while dynamic impact can be con-sidered as an adiabatic process Comparing the behavior ofthe two materials under dynamic impact we can concludethat type B specimens are easier to ignite than type Aspecimens More energy or higher drop height is needed fortype A specimens to react which is consistent with the resultsof quasi-static compression

Figures 8 and 9 show a sequence of images taken fromhigh-speed camera of the two kinds of PTFEAlFe2O3composites under impact loading and the drop mass wasdropped from the same height of 15m Obviously type Bspecimens reacted more violently than type A specimens


t = 0 s

(a)

t = 150 s

(b)

t = 200 s

(c)

t = 250 s

(d)

t = 300 s

(e)

t = 350 s

(f)

t = 400 s

(g)

t = 450 s

(h)

Figure 8 Selected images for a type A specimen reaction recorded by a high-speed camera (from the height of 15m)

t = 0 s

(a)

t = 100 s

(b)

t = 200 s

(c)

t = 300 s

(d)

t = 400 s

(e)

t = 500 s

(f)

t = 600 s

(g)

t = 700 s

(h)

Figure 9 Selected images for a type B specimen reaction recorded by a high-speed camera (from the height of 15m)

For type A specimens when impacted only a weak fire wasproduced and the duration of reaction was only 300 120583s Butfor type B specimens intensive light was captured by high-speed photography accompanied with explosion noise Thereaction time is more than 600 120583s which is much longer

than that of type A specimens The difference in reactiontime is mainly due to the difference in completeness of thereaction For type A only a small part of the specimen wasinvolved in the reaction while most of type B specimenreacted Furthermore the ignition time of type A specimens


0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

Al3

FeAＦ23

FeO(OH)Fe2

Figure 10 XRD results of type B materials after drop-weight test

is 150 120583s while the ignition time of type B specimens is 100 120583sindicating that type A specimens are more insensitive

Interestingly we observed aHigh TemperatureMetal SlagSpray (HTMSS) phenomenon in both kinds of materialsupon dynamic compression However when PTFEAl orPTFEAlW was impacted only bright white light appearedwith no HTMSS phenomenon [4 7 21] Therefore Fe2O3 isdefinitely involved in the reaction and local thermite reactionmay be triggered and the XRD of the reaction products oftype B materials (Figure 10) confirmed this The reaction oftype A specimens is too weak to allow the products to beanalyzed effectively so the XRD results are not given here Asshown in Figure 10 Fe and Al2O3 were found in the reactionproducts demonstrating the occurrence of reaction betweenAl and Fe2O3 that is

Al + Fe2O3 = Fe + Al2O3 (4)

According to the results of quasi-static compression webelieve that the reaction between PTFE and Al occurs pref-erentially and the reaction between Al and Fe2O3 followedwhich is triggered by the huge energy generated from thereaction between PTFE and Al and from the impact ofdrop mass However a small amount of FeF2 and FeO(OH)was also found in the products of type B specimens FeF2is probably from the complex reaction between Fe2O3 andPTFE FeO(OH) may be from the following reaction

4Fe2+ +O2 + 6H2O 997888rarr 4FeO (OH) + 8H+ (5)

Fe2+ is probably derived from FeF2 when contacting withO2 and H2O in the air Fe2+ will be converted to FeO(OH)under some conditions However FeF2 and FeO(OH) are alltraceable which have little effect on the energy release of thematerial so they both can be regarded as impurity and can beignored temporarily the specific details will be studied later

4 Conclusions

In this study two kinds of PTFEAlFe2O3 composites wereprepared and their mechanical and reaction behavior underquasi-static compression and dynamic impact were investi-gated The main conclusions are shown below

(1) Under quasi-static compression with the increaseof PTFE content the strength of the materials isincreased (from 371Mpa to 772Mpa) and the frac-ture mode changes from brittle to ductile Ignitionphenomenonwas found in type Bmaterials (75PTFE-14Al-11Fe2O3) and not in type A materials (50PTFE-28Al-22Fe2O3)

(2) The residuals of the reacted specimen after quasi-static compression were analyzed and no reactionof Al and Fe2O3 was found This is due to thehigh temperature threshold of thermite reaction theinsufficient contact of Al and Fe2O3 and the lowreactivity of Fe2O3

(3) In the case of drop-weight test more energy isneeded for type A specimens to ignition than typeB specimens And it takes less time to ignite for theformer (100120583s) than the latter (150120583s) indicating thattype A specimens are more insensitive

(4) A High Temperature Metal Slag Spray (HTMSS)phenomenon had been observed in PTFEAlFe2O3composites in the drop-weight test which indicatesthat the reaction betweenAl and Fe2O3 was triggered

(5) In PTFEAlFe2O3 system the reaction betweenPTFE and Al precedes the reaction between Al andFe2O3

Conflicts of Interest

The authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

The financial support from the National Natural ScienceFoundation of China (General Program Grant no 51673213)is gratefully acknowledged

References

[1] J Cai S MWalley and R J A Hunt ldquoHigh-strain high-strain-rate flow and failure in PTFEAlW granular compositesrdquoMaterials Science amp Engineering A vol 472 no 1-2 pp 308ndash3152008

[2] E B Herbold V F Nesterenko D J Benson et al ldquoParticlesize effect on strength failure and shock behavior in poly-tetrafluoroethylene-Al-W granular composite materialsrdquo Jour-nal of Applied Physics vol 104 no 10 Article ID 103903 2008

[3] E B Herbold J Cai D J Benson and V F NesterenkoldquoSimulation of particle size effect on dynamic properties andfracture of PTFE-W-Al compositesrdquo in Proceedings of the 15thBiennial International Conference of the APS Topical Group on


Shock Compression of Condensed Matter (SCCM rsquo07) vol 955pp 785ndash788 American Institute of Physics June 2007

[4] S Xu S Yang and W Zhang ldquoThe mechanical behaviors ofpolytetrafluorethyleneAlW energetic compositesrdquo Journal ofPhysics Condensed Matter vol 21 no 28 Article ID 2854012009

[5] X F Zhang J Zhang and L Qiao ldquoExperimental study ofthe compression properties of AlWPTFE granular compositesunder elevated strain ratesrdquoMaterials Science amp Engineering Avol 581 no 10 pp 48ndash55 2013

[6] F Y Xu S B Liu Y F Zheng Q B Yu and H F WangldquoQuasi-static compression properties and failure of PTFEAlWreactive materialsrdquo Advanced Engineering Materials vol 19 no1 Article ID 1600350 2017

[7] L Wang J Liu and S Li ldquoInvestigation on reaction energymechanical behavior and impact insensitivity of WndashPTFEndashAlcomposites with different W percentagerdquo Materials amp Designvol 92 no 5 pp 397ndash404 2016

[8] J Addiss J Cai S Walley W Proud and V Nesterenko ldquoHighstrain and strain-rate behaviour of ptfealuminuimtungstenmixturesrdquo in Proceedings of the 15th Biennial InternationalConference of the APS Topical Group on Shock Compression ofCondensed Matter (SCCM rsquo07) pp 773ndash776 June 2007

[9] J Cai F Jiang K S VecchioMAMeyers andV FNesterenkoldquoMechanical andmicrostructural properties of PTFEAlW sys-temrdquo inProceedings of the 15th Biennial International Conferenceof the APS Topical Group on Shock Compression of CondensedMatter (SCCM rsquo07) pp 723ndash726 June 2007

[10] L ZhouN Piekiel S Chowdhury andM R Zachariah ldquoTime-resolvedmass spectrometry of the exothermic reaction betweennanoaluminum and metal oxides the role of oxygen releaserdquoJournal of Physical Chemistry C vol 114 no 33 pp 14269ndash142752010

[11] L L Wang Z A Munir and Y M Maximov ldquoThermite reac-tions their utilization in the synthesis and processing ofmaterialsrdquo Journal of Materials Science vol 28 no 14 pp 3693ndash3708 1993

[12] St Petersberg Shock Induced Chemical Processing US armyresearch office 1997

[13] D B Nielson R L Tanner and G K Lund ldquoHigh strengthreactive materials US US6593410rdquo 2003

[14] B Feng X Fang Y-C Li H-X Wang Y-M Mao and S-Z Wu ldquoAn initiation phenomenon of Al-PTFE under quasi-static compressionrdquo Chemical Physics Letters vol 637 ArticleID 33187 pp 38ndash41 2015

[15] B Feng Y C Li and S Z Wu ldquoA crack-induced initiationmechanism of Al-PTFE under quasi-static compression and theinvestigation of influencing factorsrdquo Materials amp Design vol108 pp 411ndash417 2016

[16] G M Swallowe and J E Field ldquoIgnition of a thin layer ofexplosive by impact the effect of polymer particlesrdquo Proceedingsof The Royal Society of London Series A Mathematical andPhysical Sciences vol 379 no 1777 pp 389ndash408 1982

[17] K N Fuller P G Fox and J E Field ldquoThe temperature rise atthe tip of fast-moving cracks in glassy polymersrdquo Proceedingsof the Royal Society A Mathematical Physical and EngineeringSciences vol 341 no 1627 pp 537ndash557 1975

[18] R A Williams J V Patel A Ermoline M Schoenitz andE L Dreizin ldquoCorrelation of optical emission and pressuregenerated upon ignition of fully-dense nanocomposite thermitepowdersrdquo Combustion and Flame vol 160 no 3 pp 734ndash7412013

[19] R-H Fan H-L Lu K-N Sun W-X Wang and X-B YildquoKinetics of thermite reaction in Al-Fe2O3 systemrdquo Ther-mochimica Acta vol 440 no 2 pp 129ndash131 2006

[20] United Nations Recommendations on the Transport of Danger-ous Goods Manual of Tests and Criteria New York NY USA3rd edition 1999 STSGAC1011Rev 3

[21] WMock Jr andWHHolt ldquoImpact initiation of rods of pressedpolytetrafluoroethylene (PTFE) and aluminum powdersrdquo inProceedings of the AIP Conference vol 845 pp 1097ndash1100August 2006

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(a) (b)

Figure 1 Samples of PTFEAlFe2O3 composites (a) for quasi-static compression and (b) for drop-weight tests

the decrease of perfectibility of the reaction Other scholarsalso carried out in-depth study of PTFEAlW from otherperspectives using different techniques including quasi-staticand dynamic compression (both drop-weight test and Split-Hopkinson Pressure Bar) scanning electron microscopy(SEM) X-ray diffraction (XRD) and differential scanningcalorimetry (DSC) [5ndash9]

As can be seen above much attention has been put to theaddition of W particles to increase the strength and densityof PTFEAl while literatures about the addition of metaloxides such as CuO and Fe2O3 are scarce In the aboveexperiments about PTFEAlW no reaction between Al andW was observed only a small amount of WC and W2Cformed which were activated by the high heat as a result offluorination of Al [7] But the heat generated by the reactionbetween Al and metal oxides (thermite) cannot be neglectedZhou et al studied the reactions of AlCuO AlFe2O3and AlZnO systems using T-Jumptime-of-flight mass spec-trometer [10] They found the temperatures of the reactionscan reach 2837K 3135 K and 1822K respectively And theenthalpy of combustion is minus60405 kJmol minus4251 KJmoland minus3121 KJmol (per mol of Al) correspondingly AlsoWang et al revealed that the heat generated from the reactionbetween Al and Fe2O3 can raise thematerial to a temperatureof ca 3000∘C higher than the melting point of Fe (1535∘C)and Al2O3 (2059

∘C) [11] However because of the low energyrelease rate and the difficulty to shape the application ofthe thermites is limited But experiments confirmed that theaddition of 10 wt PTFE into Fe2O3Al mixture can reducethe time to reach the exothermic peak by two orders ofmagnitude [12]

The PTFEAlFe2O3 composites are promising reac-tive materials which have the dual properties of PTFEAland AlFe2O3 and can greatly expand the applicationfields of the PTFEAl composites if the AlFe2O3 reac-tion can be triggered But to the best of our knowledgefew researchers investigated the mechanical and reactionbehavior of PTFEAlFe2O3 systematically In this paperthe mechanical and reaction behavior of PTFEAlFe2O3under impact and quasi-static compressionwere investigatedand the failure and ignition mechanism were analyzed Theinsensitivity of PTFEAlFe2O3 to impact was measuredquantitatively which is of great importance for applicationsof reactive materials

2 Experimental Setup

21 Specimens Preparation In this study two kinds ofcomposites 50PTFE-28Al-22Fe2O3 (wt) (type A speci-men) and 75PTFE-14Al-11Fe2O3 (wt) (type B specimen)were fabricated by powder mixture cold isostatic pressing(CIPing) and vacuum sintering based on the patent ofNielsonrsquos [13] The initial powers have the following averagesizes PTFE 25 um (3M Shanghai) Al 1-2 um (JT Hunan)Fe2O3 3ndash5 um (NAO Shanghai) Firstly the PTFEAlFe2O3powders were suspended in an ethanol solution and mixedby a motor-driven blender for 20 minutes and then dried ina vacuum oven for 48 hours at 60∘C followed by a screeningprocess to break up agglomeratesNext the driedmixturewascold pressed into cylinders (for quasi-static compression andfor drop-weight test Figure 1) under the pressure of 60MpaFinally specimens were sintered in a vacuum oven at thetemperature of 370∘C for 4 h with a cooling rate of 50∘Ch

22Methods Quasi-static compression tests were performedusing a SFLS-30T electrohydraulic press with a maximumloading of 30 kN The sample was placed between twohardened steel anvils and was compressed at the speed of9mmmin corresponding to a normal strain rate of 001sThe load was terminated when the sample was fractured orthe maximum load was reached All tests were conductedat room temperature and the stress-strain curves of all thesamples were recorded by the hydraulic press automaticallyTo ensure repeatability at least five specimens of each kindwere tested

Drop-weight tests were carried out with a fall hammerimpact sensitivity tester with a drop mass of 10 kg whichcan be dropped from a maximum height of 15m So themaximum speed of 55ms of the drop hammer and the strainrate of almost 1000s can be achieved In order to observe thereaction process high-speed photographywith the frame rateup to 20000 framess was adopted

Hitachi S-4800 scanning electron microscope (SEM) wasused to observe the microstructure of the materials and toanalyze the reaction and fracture mechanisms

The residues of the specimen after quasi-static compres-sion and drop-weight test were collected and characterized byX-ray diffraction (Bruker D8 ADVANCE operating at 40 kVand 40mA with unfiltered Cu K120572 radiation)


(a) (b)


(a) (b)









Density(gcm3)

Yield stress(Mpa)


modulus (Mpa)


A 50 28 22 223 201 121 371 NoB 75 14 11 233 199 384 772 Yes

Type AType B

Ignition

0

15

30

45

60

75

True

stre

ss (M

pa)

03 06 09 12 15 1800True strain






Al + (-C2F4-) 997888rarr AlF3 + C (1)



(a) (b)

(c)

crack

(d)


Opening cracks


Reacted region

(a) (b)

(c) (d)



PTFEAlF23

0

200

400

600

800

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

(a)

0

200

400

600

800

1000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

PTFEAl Al3

F23

(b)




119864119901 = 119898119892ℎ (2)






A 80 mdash 78B 51 71 50


119882 = sum119865119905Δ119904 (3)





t = 0 s

(a)

t = 150 s

(b)

t = 200 s

(c)

t = 250 s

(d)

t = 300 s

(e)

t = 350 s

(f)

t = 400 s

(g)

t = 450 s

(h)


t = 0 s

(a)

t = 100 s

(b)

t = 200 s

(c)

t = 300 s

(d)

t = 400 s

(e)

t = 500 s

(f)

t = 600 s

(g)

t = 700 s

(h)





0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

Al3

FeAＦ23

FeO(OH)Fe2




Al + Fe2O3 = Fe + Al2O3 (4)




4 Conclusions









Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



(a) (b)


(a) (b)









Density(gcm3)

Yield stress(Mpa)


modulus (Mpa)


A 50 28 22 223 201 121 371 NoB 75 14 11 233 199 384 772 Yes

Type AType B

Ignition

0

15

30

45

60

75

True

stre

ss (M

pa)

03 06 09 12 15 1800True strain






Al + (-C2F4-) 997888rarr AlF3 + C (1)



(a) (b)

(c)

crack

(d)


Opening cracks


Reacted region

(a) (b)

(c) (d)



PTFEAlF23

0

200

400

600

800

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

(a)

0

200

400

600

800

1000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

PTFEAl Al3

F23

(b)




119864119901 = 119898119892ℎ (2)






A 80 mdash 78B 51 71 50


119882 = sum119865119905Δ119904 (3)





t = 0 s

(a)

t = 150 s

(b)

t = 200 s

(c)

t = 250 s

(d)

t = 300 s

(e)

t = 350 s

(f)

t = 400 s

(g)

t = 450 s

(h)


t = 0 s

(a)

t = 100 s

(b)

t = 200 s

(c)

t = 300 s

(d)

t = 400 s

(e)

t = 500 s

(f)

t = 600 s

(g)

t = 700 s

(h)





0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

Al3

FeAＦ23

FeO(OH)Fe2




Al + Fe2O3 = Fe + Al2O3 (4)




4 Conclusions









Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of





Density(gcm3)

Yield stress(Mpa)


modulus (Mpa)


A 50 28 22 223 201 121 371 NoB 75 14 11 233 199 384 772 Yes

Type AType B

Ignition

0

15

30

45

60

75

True

stre

ss (M

pa)

03 06 09 12 15 1800True strain






Al + (-C2F4-) 997888rarr AlF3 + C (1)



(a) (b)

(c)

crack

(d)


Opening cracks


Reacted region

(a) (b)

(c) (d)



PTFEAlF23

0

200

400

600

800

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

(a)

0

200

400

600

800

1000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

PTFEAl Al3

F23

(b)




119864119901 = 119898119892ℎ (2)






A 80 mdash 78B 51 71 50


119882 = sum119865119905Δ119904 (3)





t = 0 s

(a)

t = 150 s

(b)

t = 200 s

(c)

t = 250 s

(d)

t = 300 s

(e)

t = 350 s

(f)

t = 400 s

(g)

t = 450 s

(h)


t = 0 s

(a)

t = 100 s

(b)

t = 200 s

(c)

t = 300 s

(d)

t = 400 s

(e)

t = 500 s

(f)

t = 600 s

(g)

t = 700 s

(h)





0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

Al3

FeAＦ23

FeO(OH)Fe2




Al + Fe2O3 = Fe + Al2O3 (4)




4 Conclusions









Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



(a) (b)

(c)

crack

(d)


Opening cracks


Reacted region

(a) (b)

(c) (d)



PTFEAlF23

0

200

400

600

800

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

(a)

0

200

400

600

800

1000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

PTFEAl Al3

F23

(b)




119864119901 = 119898119892ℎ (2)






A 80 mdash 78B 51 71 50


119882 = sum119865119905Δ119904 (3)





t = 0 s

(a)

t = 150 s

(b)

t = 200 s

(c)

t = 250 s

(d)

t = 300 s

(e)

t = 350 s

(f)

t = 400 s

(g)

t = 450 s

(h)


t = 0 s

(a)

t = 100 s

(b)

t = 200 s

(c)

t = 300 s

(d)

t = 400 s

(e)

t = 500 s

(f)

t = 600 s

(g)

t = 700 s

(h)





0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

Al3

FeAＦ23

FeO(OH)Fe2




Al + Fe2O3 = Fe + Al2O3 (4)




4 Conclusions









Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



PTFEAlF23

0

200

400

600

800

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

(a)

0

200

400

600

800

1000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

PTFEAl Al3

F23

(b)




119864119901 = 119898119892ℎ (2)






A 80 mdash 78B 51 71 50


119882 = sum119865119905Δ119904 (3)





t = 0 s

(a)

t = 150 s

(b)

t = 200 s

(c)

t = 250 s

(d)

t = 300 s

(e)

t = 350 s

(f)

t = 400 s

(g)

t = 450 s

(h)


t = 0 s

(a)

t = 100 s

(b)

t = 200 s

(c)

t = 300 s

(d)

t = 400 s

(e)

t = 500 s

(f)

t = 600 s

(g)

t = 700 s

(h)





0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

Al3

FeAＦ23

FeO(OH)Fe2




Al + Fe2O3 = Fe + Al2O3 (4)




4 Conclusions









Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



t = 0 s

(a)

t = 150 s

(b)

t = 200 s

(c)

t = 250 s

(d)

t = 300 s

(e)

t = 350 s

(f)

t = 400 s

(g)

t = 450 s

(h)


t = 0 s

(a)

t = 100 s

(b)

t = 200 s

(c)

t = 300 s

(d)

t = 400 s

(e)

t = 500 s

(f)

t = 600 s

(g)

t = 700 s

(h)





0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

Al3

FeAＦ23

FeO(OH)Fe2




Al + Fe2O3 = Fe + Al2O3 (4)




4 Conclusions









Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



0

2000

4000

6000

8000

10000

12000

14000

16000

18000

Inte

nsity

(cou

nts)

40 60 80202 (degrees)

Al3

FeAＦ23

FeO(OH)Fe2




Al + Fe2O3 = Fe + Al2O3 (4)




4 Conclusions









Acknowledgments


References































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of





























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Documents

The Mechanical and Reaction Behavior of PTFE/Al/Fe under ...fields of the PTFE/Al composites if the Al/Fe2 O3 reac-tion can be triggered. But to the best of our knowledge, few researchers