Mechanical, thermal and ablative properties of zirconia, CNT modified carbon-phenolic composites

Mechanical, thermal and ablative properties of zirconia, CNT modi?ed

carbon/phenolic composites

I. Srikanth a ,c ,?,N. Padmavathi b ,Suresh Kumar a ,P. Ghosal b ,?,Anil Kumar a ,Ch. Subrahmanyam d

a

Advanced Systems Laboratory, DRDO, Hyderabad 500 058, India

b

Defence Metallurgical Research Laboratory, DRDO, Hyderabad 500 058, India c

Department of Material Science and Engineering, Indian Institute of Technology, Hyderabad, India d

Department of Chemistry, Indian Institute of Technology, Hyderabad, India

a r t i c l e i n f o Article history:

Received 15 November 2012

Received in revised form 26 February 2013 Accepted 2March 2013

Available online 14 March 2013 Keywords:

A. Polymer matrix composites (PMCs)A. Oxides

B. Mechanical property

B. High temperature property B. Thermomechanical properties

a b s t r a c t

Zirconium oxide (Zirconia)coating on carbon fabric (C-fabric)was developed by using zirconia sol. C-fabrics having different weight percentages (wt%)of zirconia namely 0wt% (Blank),3.5 wt%, 6.5 wt% and 9.5 wt% were used to make Zirconia–Carbon–Phenolic (Zr–C–Ph)composites. Similarly, 0.5 wt% multiwalled carbon nanotube (CNT)dispersed phenolic resin was used to make CNT–C–Ph composite .Thermal conductivity, ILSS and ?exural strength were measured for the prepared composites. Based on the initi a l results, subsequently a functionally graded carbon–phenolic composite (FG -C–Ph)having CNT–C–Ph composition up to certain thickn e ss followed by Zr–C–Ph composition for the remaining thickness was made .Thermal insulation and ablative properties for blank C–Ph,Zr–C–Ph, FG-C–Ph were

studied using plasma arc jet test which was carried out at a heat ?ux of 4.0 MW/m

2

for 30 s. Results from the plasma arc jet test show that, the temperature drop across the Zr–C–Ph composite was found to be highest while it was least for the blank. However the ablation rate was found to be highest for the FG-C–Ph while it was least for the blank .Ablation mechanisms for all the tested composites are proposed based on the SEM and XRD studies.

ó2013 Elsevier Ltd. All rights reserved.

1. Introduction

Rayon carbon fabric reinforced phenolic (C–Ph)composites are widely used as thermal protection systems (TPSs)for aerospac e applications due to the low thermal conductivity of the rayon based carbon fabric and the high char yielding properties of the phenolic matrix [1–3].Many research groups attempted to reduce the ther- mal conductivity of the C–Ph composites further, as it can offer sig- ni?cant weight saving for the aerospace systems. It is reported that, the spun yarn carbon ?bers carbonized at low temperature can bring down the thermal conductivity of C–Ph composites signi?-cantly besides imparting better interfacia l and ablative properties [4].Silicone based anti-ablation coatings on TPS, which can form oxidation resistant silica layer during ablation and silicone polymer based ablative composites which can undergo cermetisation during ablation forming tough oxidation resistant ceramic layer were explored by different research groups [5,6].On the other hand, addition of various nano materials like, nano silica, montmorilloni t e (MMT)nanoclays, polyhedral oligomeric silsesquiox a ne (POSS)to C–Ph composites are widely reported to reduce the thermal con- ductivity of the Phenolic composites besides reducing the ablation rate [7,8].Though, zirconia (ZrO 2)is known as better thermal insulator than silica, it was not explored much, as additive to C–Ph composites to reduce thermal conductivi t y. Recently, Chen et al. reported that addition of zirconium diboride to C–Ph compos- ites can signi?cantly improve their thermal insulation propertie s during ablation. This is primarily due to formatio n of insulating zirconia layer in the C–Ph composite during oxidative decompo s i- tion of zirconium diboride [9].Though, it is now well established that, ceramic additives can bring down the thermal conductivi t y of C–Ph composites, they pose new problems such as poor inter laminar shear strength (ILSS)especiall y at higher loadings which results in the delamination of the composites [7].It is essential for TPS to have a good inter laminar shear strength to resist the mechanical erosion due to high velocity aerodynamic shearing ex- erted by the harsh environments that they are generally exposed to. On the other hand, carbon nanotubes (CNTs)and nano-?bers are re- ported to enhance ILSS of the C-?ber reinforced polymer matrix composites [10,11].So far, limited studies have been reported on the effect of the ceramics and CNTs addition to C–Ph composites on their thermomechan i cal and ablative performanc e [7,12–14].Developing zirconia coating on C-fabrics and using them as rein- forcements to obtain low thermal conductive TPS is a novel concept

0266-3538/$ -see front matter ó2013 Elsevier Ltd. All rights reserved. https://www.360docs.net/doc/c610029053.html,/10.1016/https://www.360docs.net/doc/c610029053.html,pscitech.2013.03.005

?Corresponding authors. Address: CMCD/HTCC, Hyderabad, Andhra Pradesh 500 058, India. Tel.: +91 040 24306998 (I.Srikanth).

E-mail addresses: i_srikanth@https://www.360docs.net/doc/c610029053.html, (I.Srikanth),dr.parthaghosal@gmail.-com (P.Ghosal).

which is not explored so far by any research group. This study is aimed (i)To develop zirconia coating on the C-fabric, and to study the mechanical, thermal and ablative properties of phenolic composites made out of these fabrics, and (ii)To study whether en- hanced ?exural strength and shear strength of C–Ph composites due to CNTs can result into reduction in ablation rate.

2. Experimental work

2.1. Zr–C–Ph composite fabricatio n

Zirconia sol was prepared by mixing zirconium oxy chloride, ethanol and demineral i zed water in the molar ratio of 0.05:8:1.1 and stirring the mixture for one hour with a magnetic stirrer at room temperature. This sol was applied on the surface of the rayon carbon fabric (C-fabric)with the help of a spray gun and allowed to dry at room temperat u re (approximately 96 h)till the coated fabric attained the constant weight. Expected yield of the zirconia coating from the sprayed sol was calculated by using Eq. (1).

ZrOCl2tH2O!ZrO2t2HCle1TThus, four different compositions of zirconia coated C-fabrics (Zr–C-fabrics)having zirconia weight percentages (wt%)of 0.0 wt% (blank), 3.5 wt%, 6.5 wt% and 9.5 wt% were made by selecting the amount of the sol sprayed. Coating morphology on the Zr–C-fabrics was studied with scanning electron microscopy (ESEM-FEI Quanta 400, The Netherlands).Resol based phenolic re- sin was applied on the Zr–C-fabrics followed by drying at room temperature for 48 h to allow partial curing to get prepregs (Zr-C-prepregs).Zr–C-prepregs were cut into 150 mm ?150 mm pieces (approximately60 layers)and stacked up (job)followed by curing in an autoclave. Typical cure cycle involved raising the temperature of the job up to 120 °C and then soaking the job for 120 min. 5bar pressure was applied on the job at the time of gelling. Subsequentl y temperat u re was raised to 180 °C and maintained for four hours under the same load. Thus, four different Zr–C–Ph composites of approximate 20 mm thickness were pre- pared with 0.0 wt% (blank),3.5 wt%, 6.5 wt% and 9.5 wt% Zr–C-fab-rics. Representat i ve samples were collected from the laminate s to measure density and ?ber volume fraction (%V f).%V f was measured as per ASTM D3171.

2.2. CNT-C–Ph composite fabricatio n

0.5 wt% of Multiwal l ed carbon nanotubes (CNTs)which were amino functionalised were added to phenolic resin and ball milled for 3h at 250 rpm to ensure better dispersion of the CNTs in the resin. This CNT-resi n mixture was applied on the C-fabric and al- lowed to dry at room temperat u re for 48 h to allow partial curing to get prepregs (CNT-C-Prepreg).CNT-C-prepreg was cut into 150 mm ?150 mm pieces. These pieces were stacked up followed by curing similar to the curing process mentioned for Zr–C–Ph composites.

2.3. FG-C–Ph composite fabricatio n

Based on the subsequent thermal and mechanical characteriza- tion of the composites made in Sections 2.1 and 2.2 ,a FG-C–Ph composite was fabricated by using the combination of CNT-C-pre- pregs and Zr–C-prepregs made with 6.5 wt% zirconia coated C-fabric. To prepare the FG-C–Ph composite, initially nine layers of CNT-C-prepreg s were stacked up, over which approximat e ly 40 layers of Zr–C-prepregs were stacked. Curing cycle employed was similar to the curing cycle adopted for Zr–C–Ph composites. In the ?nished composite, approximately 3mm from the top was having CNT–C–Ph composition while the rest 17 mm of the com- posite was having Zr–C–Ph composition. Samples from this com- posite were tested only for ablation properties.

3. Characteriza t ion

3.1. Flexural strength and ILSS

Specimen s of size 5?10?100 mm and 5?10?50 mm were collected for ?exural strength and ILSS tests respectively from the prepared composites. Flexural strength was measured as per ASTM D790 while ILSS was measured as per the ASTM D2344 using universa l testing machine (United,Model STM 50 KN, USA). Minimum ?ve number of samples were tested for each property and the average values are shown in Table 1.Tested samples were analyzed with ?eld emission scanning electron microscope (FES-EM, Model FEI, Quanta 200, USA).

3.2. Thermal conductiv i ty

Cylindrical specimens of diameter 25 mm and height 5mm were machined from the prepared composites. Thermal conductiv- ity in the through thickness direction was measure d at 300 °C un- der steady state condition s as per ASTM E1225-99 using hot guard method. Two samples from each of the composite were tested and the average values of the thermal conductivity of the two samples is shown in Table 2.

3.3. Plasma arc jet test

Cylindrical specimens of diameter 10 mm and height 17.6 mm (±0.1mm)were machined from the blank C–Ph,Zr–C–Ph and FG- C–Ph composites. Length of the specimens was kept perpendicul a r to the direction of the fabric layup. Test specimen was encircled with the guard ring which was also machined out from the same composite. G uard ring was employed to ensure unidirecti o nal exposure of the test specimen to the plasma arc jet. ‘K’ type ther- mocoupl e was bonded to the rear surface (away from the surface facing the plasma arc jet)of each specimen to measure back face temperat u re. A schematic of the test specimen con?guration is shown in Fig. 1a. Specimen s were exposed to the plasma arc jet at a?ame velocity of about 1mach having a stagnant ?ux of 4.0 MW/m 2for 30 s(Fig. 1b).Raise in back face temperat u re is con- tinuously recorded as a function of time. Though the plasma jet was switched off after 30 s of test duration, back face temperat u re was recorded up to 70 s.In case of FG-C–Ph,test specimen was ori- ented in such a way that, CNT–C–Ph part of the composite faced the plasma jet while the back face temperature measure d was for Zr–C–Ph part of the composite. Ablation rate was determined by dividing the reduction in length of the specimen with the test duration in seconds. Average back face temperature and ablation rate was determined based on the average of two samples. Obtained values are shown in the Table 3.Microstructure of the ablated surfaces was studied with FESEM .Compositional changes resulted due to ablation was studied with X-ray diffraction Table 1

Physical and mechanical properties of the composites.

Sample description Density (g/cc)%V f a F.S (MPa)ILSS (MPa)

Blank C–Ph 1.44 53 225(22)20(1.0)

3.5 wt.%Zr–C–Ph 1.40 50 222(36)19(2.8)

6.5 wt.% Zr–C–Ph 1.25 37 146(10)14(2.9)

0.5 wt% CNT-C–Ph 1.42 51 262(21)22(2.1)

a Flexural strength, values in the parentheses are standard deviations.

2I. Srikanth et al. /Composites Science and Technology 80 (2013)1–7

(XRD-Philips PWD, Model 1830, The Netherlands).Representative samples after the test are shown in Fig. 1b (i–iii).4. Results and discussion

4.1. Microstructu r e of the coated fabric and prepregs

Microstruct u re of the representat i ve C-fabric samples coated with zirconia are shown in Fig. 2.Thicknes s of the coating was observed to be approximately 700–900nm for 3.5 wt% zirconia coating (Fig. 2b).It can be seen from the ?gures (Fig. 2a–c)that, the liquid precursor based coating method employed in the pres- ent study can penetrate and spread to every ?lament and develop uniform coating surrounding their surface. However, as the wt% of zirconia on C-fabric was increased, lumps of zirconia coating were observed to be forming on the C-?ber surface (Fig. 2d and e).On the other hand, CNTs were observed to be well dispersed on the C-fabric surface (Fig. 2f).4.2. Density, %V f

It is observed that, as the wt% of the zirconia on the C-fabric increased, density and %V f of the composites have come down (Table 1).This is due to the increased coating thickness that is deposited over the C-fabric with increased wt% of the zirconia which seeks more space during compaction of the C-fabric layers. CNT–C–Ph composite has not shown signi?cant variation in density and %V f as compared to blank C–Ph,indicating better com- pressibility of the CNT–C–Ph prepregs. ILSS properties. Hence physical and mechanical property data can’t be generated for this composition. Reason for the reduced ILSS for Zr–C–Ph composites can be attributed to the fact that, once the zirconia layer is deposited on the C-?ber,effective interfacial inter- action area between the matrix to the ?bers is reduced. This lead to poor interfacial bond strength, resulting in lower ILSS. Signi?cantly poor ILSS at higher loading can be attributed to the large crystal- lites/lum p s of the zirconia that were observed at higher wt% of zirconia coating (Fig. 2d and e)which could have acted as defect zones in the composite. Besides this, reduction in %V f of the composites made with Zr–C-prepregs is also responsible for the reduction in the mechanical properties for the Zr–C–Ph compos- ites. On the other hand, CNT–C–Ph composite displayed enhanced ?exural and shear properties. It can be seen that, well dispersed CNTs present in C–Ph composites ,are strengtheni n g the ?ber–ma-trix interface by bridging the interfacial micro cracks (Fig. 3a)lead- ing to enhanced ILSS for the CNT–C–Ph.Similar strengthening mechanis m s for the ILSS improvement of CFRPs due to CNTs were reported previously by some other research groups [15,16].Enhanced ?exural strength due to CNTs can be attributed to the strengthening of the ?ber matrix interface (Fig. 3b)and stiffening of the matrix which can effectively resist the bending forces [17].4.4. Thermal conductiv i ty

Through thickness thermal conductivity of Zr–C–Ph composites is found to be signi?cantly less as compare d to blank C–Ph (Table 2).This is due to the fact that, signi?cant proportion of the advancing heat energy is consumed in generating lattice vibration s (phonons)in the zirconia layer which is sandwiching Table 2

Thermal conductivity values of the composites. Sample description Thermal conductivity (W/m K)Percentage change

a

Blank C–Ph

0.59(±0.05)–3.5 wt% Zr–C–Ph 0.41(±0.15)à30

6.5 wt% Zr–C–Ph 0.33(±0.10)à44

0.5 wt% CNT–C–Ph

0.69(±0.05)

+17 a

[(Sample-Blank)/Blank]?100. Values in the parentheses are maximum and minimum deviation from average value.

Schematic con?guration of the sample and the holder used for plasma arc jet testing and (b)Plasma arc jet testing under progress; (i)after test; (iii)FG-C–Ph after test.

Table 3

Ablation rate and back face temperature of composit e s in plasma arc jet test.

Sample description Ablation rate (mm/s)

Temp (°C)a

Blank C–Ph

0.054 169

3.5 wt% Zr–C–Ph 0.078 114 6.5 wt% Zr–C–Ph 0.105 104

F G

-C–Ph 0.103 135

a

Back face temperature at the end of test (30s).

I. Srikanth et al. /Composites Science and Technology 80 (2013)1–7

3

4.5. Back face temperature and ablation rate

Observed back face temperat u res with respect to time, for the samples that were subjected to plasma arc jet test are shown in As it can be seen from the graphs shown in Fig. 4,back face temperature of the test specimens continue d to raise even after the plasma jet is switched off after 30 s of test duration. This is due to the accumulated heat energy from the ablated surface reaching the back face of the test sample. Back face temperat u re of the tested samples at the end of the test (30s after the plasma jet hit the front face of the specimen)and ablation rate of the test specimens are

Results show that, there is a signi?cant reduction in the back face temperature of the Zr–C–Ph composites as com- pared to the blank. It indicates that, the insulating coating layer of the zirconia present on the C-fabric layers is able to reduce the back face temperature signi?cantly under harsh testing environ- ment. It is observed that, as the wt% of zirconia increased in composites, there is more reduction in the back face tem- perature (Table 3)as the ceramic skin (zirconia coating)structure

present on the C-?bers,can effectively insulate the virgin material beneath the ablation surface [20].More thermal insulation capability of the Zr–C–Ph composites, is also evidenced by the low- er depth of penetration of pyrolytic decompo s ition zone (char Fig. 4. Back face temperatures of the blank C–Ph,Zr–C–Ph and FG-C–Ph composites.

coated with 3.5 wt% of zirconia showing thin layer of coating (indicated by arrows),(b)3.5 wt% zirconia coating on C-?bers

nm, (c)3.5 wt% zirconia coating on C-?bers showing coating formation on all carbon ?laments,(d)6.5 wt% zirconia coating on C-?bers

9.5 wt% of zirconia coating on C-?ber having lumps of zirconia and (f)CNT–C-prepregs showing good dispersion of CNTs.

FESEM images of the CNT–C–Ph composites failed under shear and ?exural loads (a)Image showing well dispersed CNTs bridging the matrix micro cracks at the interface (encircled zone)during shear failure and (b)Image showing CNT reinforced matrix holding the C-?bers together during ?exural

zone)in the through thickness direction from the ablated surface (Fig. 5).It can be seen that, compared to the thickness of the char zone (char depth)that is observed for the blank C–Ph composites , the char depth for the Zr–C–Ph composites has come down signif- icantly (Fig. 5).Effective thickness of the insulating Zr–C–Ph layers the ablated surfaces shown in Fig. 6indicates that the matrix char- ring and it’s subsequent removal is preceding the ?ber erosion (Fig. 6a and b).Fiber damage and their erosive losses will be signif- icantly low, when the char that is forming during ablation is re- tained for long duration. This is due to the fact that, char not

Stereo microscope images of samples after plasma arc jet test. Left end of the sample surface is the ablated surface (surface exposed to plasma).

Blank C–Ph,(b)3.5 wt% Zr–C–Ph,(c)6.5 wt% Zr–C–Ph and (d)FG-C–Ph.

I. Srikanth et al. /Composites Science and Technology 80 (2013)1–75

network formation (Fig. 6b)in the remaining matrix. Similar obser- vations regarding enhanced matrix removal for C–Ph composites in presence of zirconia (derived from high temperature oxidative decompositi o n of ZrB 2)is reported recently by Y.Chen et al. [9]. The above proposed reaction, showing consump t ion of the solid char by ZrO 2giving gaseous by products (reaction(3))is also validated by carrying out through thickness SEM studies of the char zone of the tested samples (approximately0.3 mm behind the ablated surface).It can be observed that, compare d to the blank

Fig. 6c),porosity in Zr–C–Ph composite is signif- Fig. 6d,e).Lower rate of matrix removal from the blank resulted in better protection of the ?bers as evidenced by the formation of needle like structure with less ?ber breakage Higher rate of matrix removal in Zr–C–Ph composites,

under protected from the high velocity shear forces of plasma jet, which resulted in severe breakage of lumps of ?bers(Fig. 6g,h).The cumulative effect of enhanced rates of ma- trix and ?ber removal resulted into enhanced ablation rate for Zr–C–Ph composites. As the wt% of zirconia in C-Ph increased, net reduction in solid char volume will become more prominent which resulted in more ?ber damage (Fig. 6i)with further enhancement in the ablation rate.

4.5.2. Ablation mechanism in FG-C–Ph composite

FG-C–Ph composite which was exposed to the plasma jet to- wards the surface having CNT–C–Ph compositi o n, has shown high- est ablation rate among the tested composites. Considerable damage to the ?bers on the ablated surface is observed (Fig. 8).It is clearly visible that, the ?bers near the crossover points eroded higher than the ?bers from the other areas (Fig. 8a).This could be explained as follows. CNT reinforceme n t in the C–Ph composite has increased the thermal conductivity of the composite (Table 2). Enhanced thermal conductivi t y of the composite resulted in faster rate of the heat front advancement which in turn led to accelerated charring and degradation of the matrix along the thickness. Similar observati o ns on enhanced rate of matrix pyrolysis for CNT rein- forced phenolics was reported recently by Natali et al. [14].As the crossover points which are matrix rich areas in composites will become char rich areas during the ablation, degradation at the crossove r points is observed to be more severe. Accelerat e d charring and subsequent erosion of the matrix resulted in en- hanced ?ber breaking (Fig. 8b)resulting in enhanced ablation rate.

[21].Enhanced ?exural,shear strength of C–Ph due to CNTs could

SEM images of samples after plasma arc jet test (a)Blank C–Ph showing matrix removal ahead of ?ber damage (pockets of matrix removed zones indenti?ed

3.5 wt% Zr–C–Ph showing more matrix removal up to considerable depth, (c)Blank C-Ph showing low matrix porosity in the char zone (approximately

behind the ablated surface, (d)and (e)3.5 wt% Zr–C–Ph showing high level of matrix porosity in the char zone, (f)Blank C-Ph showing needle like structure formation for

3.5 wt% Zr–C–Ph showing broken ?bers without needle like structure formation, (h)Magni?ed view of the encircled zone of Fig.g. showing initiation of ?ber

6.5 wt% Zr–C–Ph showing lumps of broken ?bers.

Fig. 7. XRD of the ablated surface of Zr–C–Ph composite showing formation of ZrC.

not result into enhanced resistance to erosive loss of composite, primarily due to the fact that, the room temperature mechanical property improvements due to CNTs, lost their signi?cance in the charred matrix.

5. Conclusions

(i)Carbon–Phenolic (C–Ph)composites fabricated with zirconia

coated carbon fabrics can show low thermal conductivity ,

leading to reduced back face temperature when exposed to

high temperature and high ?ux environments.

(ii)Presence of zirconia in C–Ph composites has increased the ablation rate. This is due to enhanced conversion of solid char into zirconium carbide (ZrC)and carbon monoxide (gaseous product)leading to under protectio n of the carbon

?bers facing the plasma jet.

(iii)CNTs can improve the room temperature ?exural and shear strength of C–Ph composites. However enhancem e nt in these properties lost their prominence in the charred matrix.

Enhanced thermal conductivity due to CNTs improved the

ablation rate of C–Ph composites.

References

[1] Savage G. Carbon–carbon composites. London: Chapman &Hal; 1993.

[2] D’Aelio G F, Parker JA. Ablative plastics. New York: Marcel Dekker; 1971.

[3] Trick KA, Saliba TE. Mechanisms of the pyrolysis of phenolic resin in a carbon/

phenolic composite. Carbon 1995;33:1509–15.

[4] Park JK, Cho D, Kang TJ. A comparison of the interfacial, thermal and ablative

properties between spun and ?lament yarn type carbon fabric/phenolic composites. Carbon 2004;42:795–804.

[5] Xiao J, Chen JM, Zhuo HD, Zhang Q. Study of several organic resin coatings as

anti-ablation coatings for supersonic craft control actuator. Mater Sci Eng A 2007;452-453:23–30.

[6] Koo Joseph H, Miller Mark J, Weispfenning Jon, Blackmon Charles. Silicone

polymer composites for thermal protection of naval launching system. J spacecraft rockets 2001;48:904–19.https://www.360docs.net/doc/c610029053.html,/10.2514/1.46534.

[7] Srikanth I, Alex Daniel, Suresh Kumar, Padmavathi N, Vajinder Singh, G hosal P,

et al. Nano silica modi?ed carbon –phenolic composites for enhanced ablation resistance. Scripta Mater 2010;63:200–3.

[8] Koo Joseph, Stretz Holly, Bray Alan, Weispfenning Jon, Luo ZP, Blanski Rusty.

Nanostructured materials for rocket propulsion system: recent progress. In: 44th AIAA/ASME/ASCE/AHS structures, structural dynamics and materials conference. 7-10th 2003 April Norfolk, Virgenia. AIAA paper no: AIAA; 2003. p.

1769.

[9] Chen Yaxi, Chen Ping, Hong Changqing, Baoxi Zhang, Hui David. Improved

ablation resistance of carbon–phenolic composites by introducing zirconium diboride particles. Composites Part B2013;47:320–5.

[10] Lubineau G, Rahaman A. A review of strategies for improving the degradation

properties of laminated continuous ?ber/epoxy composites with carbon based nanoreinforcements. Carbon 2012;50:2377–95.

[11] Park JM, Wang ZJ, Kwon DJ, Gu GY, Lee WI, Park JK. Interfacial properties and

self sensing of single carbon ?ber reinforced CNT–Phenolic nanocomposites using electro-micro mechanical and wettability tests. Composites Part B 2012;43:1171–7.

[12] Natali Maurizio, Monti Marco, Kenny JoséMaria, Torre Luigi. A nanostructured

ablative bulk molding compound: development and characterization.

Composites Part A2011;42:1197–204.

[13] Patton RD, Pittman CU, Wang Jr L, Hill JR, Day A Ablation, et al. Mechanical and

thermal conductivity properties of vaporgrown carbon?ber/phenolic matrix composites. Composites Part A2002;33:243–51.

[14] Natali M, Monti M, Puglia D, Kenny JM, Torre L. Ablative properties of carbon

black and MWNT/phenolic composites: a comparative study. Composites Part A2011;43:174–82.

[15] G reen KJ, Dean DR, Vaidya UK, Nyairo E. Multiscale ?ber reinforce composites

based on a carbon nano?ber/epoxy nanophased polymer matrix: Synthesis, mechanical, and thermo mechanical behavior. Composites Part A 2009;40:1470–5.

[16] Cho J, Daniel IM, Dakin DA. Effects of block copolymer dispersant and

nanotube length on reinforcement of carbon/epoxy composites. Composites Part A2008;39:1844–50.

[17] G ojny FH, Wichmann MHG, Kopke U, Fiedler B, Schulte K. Carbon nanotube-

reinforced epoxy –composites: enhanced stiffness and fracture toughness at low nanotube content. Compos Sci Technol 2004;64:2363–71.

[18] G au C, Chen SY, Tsai HL, Jenq Syh-Tsang, Lee Cheng-Ching, Chen Yu-Der, et al.

Synthesis of functionalized carbon nanotubes/phenolic nanocomposites and its electrical and thermal conductivity measurements. Jpn J Appl Phys 2009;48. 06FF10-1–4.

[19] Kim YA, Kamio S, Tajiri T, Hayashi T, Song SM, Endo M, et al. Enhanced thermal

conductivity of carbon ?ber/phenolic resin composites by the introduction of carbon nanotubes. Appl. Phys. Lett. https://www.360docs.net/doc/c610029053.html,/10.1063/1.2710778.

[20] Ho WK, Koo JH, Ezekoye OA. Thermo plastic polyurethane elastomer

nanocomposites: morphology, thermo physical and ?ammability properties.

J Nanomater 2010. https://www.360docs.net/doc/c610029053.html,/10.1155/2010/58323.

[21] Cho Donghwan. Byung Il Yoon. Microstructural interpretation of the effect of

various matrices on the ablation properties of carbon-?ber-reinforced

composites. Compos Sci Technol 2001;61:271–80. SEM images of FG-C–Ph samples after plasma arc jet test. (a)Signi?cant erosive loss at the crossover points (indicated by arrows)and (b)