Phys. Status Solidi B 248, No. 11, 2704–2707 (2011) / DOI 10.1002/pssb.201100054 p s sb

statu

s

soli

di

www.pss-b.comph

ysi

ca

basic solid state physics

Ultra-fast efficient synthesisof one-dimensional nanostructures

Agnieszka Dabrowska*,1, Andrzej Huczko1, Michał Soszynski1, Badis Bendjemil2, Federico Micciulla3,Immacolata Sacco3, Laura Coderoni3, and Stefano Bellucci3

1Department of Chemistry, Warsaw University, 1 Pasteur str., 02-093 Warsaw, Poland2Department of Physics, University of Badji-Mokhtar, LEREC, BP. 12, 23000 Annaba, Algeria3Laboratori Nazionali di Frascati, Via E. Fermi 40, 00044 Frascati, Roma, Italy

Received 22 April 2011, revised 13 July 2011, accepted 1 August 2011

Published online 27 September 2011

Keywords carbonates, CNT, nanocomposites, nanofibres, nanomaterials, nanowires, SHS, SiC

*Corresponding author: e-mail aggy-dab@wp.pl, Phone þ48-22-8222375

Self-propagating high-temperature synthesis (SHS) can be

regarded as an efficient method to obtain new nanomaterials.

Different starting mixtures of magnesium powder with various

carbonates (Li2CO3, Na2CO3, CaCO3, FeCO3, (NH4)2CO3)

were tried and the auto-thermal reactionswere carried out under

both reactive (air) and neutral atmosphere (argon)with an initial

pressure of 1 or 10 atm to yield novel nanomaterials. Both SiC

nanofibres and novel branched SiC nanostructures were also

obtained from Si/polytetrafluoroethylene (PTFE) mixtures and

their synthesis and purification have been optimized. The

application of those one-dimensional (1-D) SiC nanostructures

as a composite filler is presented.

� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1 Introduction In a search for new methods toproduce novel nanomaterials we propose the combustionsynthesis [self-propagating high-temperature synthesis(SHS)], a thermal-explosion, autogenous mode of fast redoxreaction between the strong reducing agent and oxidant. Acareful selection of powdered reactants, which are very basicchemicals, can result in the efficient formation of novelnanostructures. The process takes place usually under far-from-equilibrium conditions so itmay lead to productswith anewmorphology and stoichiometry. It is known that the one-dimensional (1-D) nanostructures (nanowires, nanotubes)often show distinct properties from their bulk counterpartsbecause of the radial confinement. Here, we present a fast,simple, easy to operate and one-step chemical synthesis ofbranched 1-D SiC nanostructures, SiC nanofibres and 1-Dnanocarbons from carbonates via an SHS route. The processcan be easily escalated by using a bigger reactor chamber.Finally, a possible application of those nanomaterials innanocomposites is proposed.

2 Experimental The combustion was carried out in ahigh-pressure reactor, the modified calorimetric bombprovided with a polycarbonate window (Fig. 1) to performin situ spectral registration of the emitted light. The details ofthe experimental procedure have been outlined elsewhere[1]. The effect of process parameters, such as: reactant

composition (powderedMg/carbonate, Si/PTFE or Si/PTFE/NaN3 mixture), initial combustion pressure (1–20 atm) andatmosphere (air, argon, nitrogen) was studied. The productswere characterized using X-ray diffraction (XRD), scanningelectron microscopy (SEM), transmission electron micro-scopy (TEM) and Raman spectroscopy [2]. The protocol forthe chemical purification of sought products was proposed.The powder mixture of the reactants was placed in a quartzcrucible (with the immersed carbon tape), the reaction wasinitiated by Ohmic heating and terminated usually withinless than 2 s.

3 SHS process in carbonate systems Differentstarting homogenous mixtures of Mg powder (Sigma–Aldrich, >99%) with various carbonates (Li2CO3 from‘POCh’, Na2CO3 from Sigma–Aldrich,>99%, CaCO3 fromSigma–Aldrich, >99%, FeCO3 from Polish Institut ofGeology, (NH4)2CO3 from Sigma–Aldrich, >99%), as asource of elemental carbon, were tried. Reactions werecarried out under reactive (air) or neutral atmosphere (argon)at an initial pressure of 1 or 10 atm. Fe, Co and Ni powderswere used as catalysts (�325mesh).

3.1 Product characterization Under the appliedconditions the presence of crystalline MgO in productsconfirmed by XRD analysis (not presented here), even for

� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Phys. Status Solidi B 248, No. 11 (2011) 2705

Original

Paper

Figure 1 (online colour at: www.pss-b.com) Modified calorimet-ric bomb as a high-pressure reactor with polycarbonate window.

the reaction under neutral atmosphere, points to the deepconversion of carbonates. For producing fibrous productsthe Na2CO3 system proved to be the most promising one(in other of tested carbonate systems, except Li2CO3, thecontent of fibrous phase was insignificantly small). SEMimages (Fig. 2, upper row) show the morphology of theproducts with some 1-D nanostructures resembling carbonnanotubes. In fact, Szala showed earlier [3] that condensingcarbon vapours, produced via SHS, can yield CNTs. Also,Bendjemil [4] produced carbon nanotubes by combustiondecomposition of carbonates under low pressure. One shouldmention here that CO2, which is, in fact, an intermediatereactant of our carbonate decomposition under SHSconditions, can be reduced to CNTs by metallic Li [5].

4 SHS process in Si/PTFE/NaN3 systems Using thesame SHS procedure and the initial mixtures of reactantscomposed of Si (Sigma–Aldrich, <43mm, 99%), PTFE(Sigma–Aldrich, 1mm, powder) and NaN3 (Sigma–Aldrich,>99.5%) in different proportions, the variety of interestingnanomaterials was obtained. Mainly, the SiC nanofibres

Figure 2 Products obtained from carbonate (upper row) and siliconNa2CO3/Mg/PTFE/Fe, 1 atm, air; FeCO3/Mg, 10 atm, air; Si/PTFE/N

www.pss-b.com

have been efficiently produced (Fig. 2, lower row) and duringthe parametric studies the optimal synthesis conditions werefound: the stoichiometric composition of reactants (36wt%Si and 64wt% PTFE), air atmosphere (as the oxygen seemsto play an important role in SiC growth [6]), and the initialpressure equal to 10 atm.Optimal NaN3 content was found tobe 55wt% of reactants.

4.1 SiC nanofibres from Si/PTFE system andtheir purification SiC nanofibres (as the filler for polymernanocomposites) with the aspect ratio well above 102 wereefficiently synthesized (Fig. 2; lower row, right; conversionefficiency to raw solid products was about 35wt%) andpurified by 4 h boiling in 30% KOHaq (un-reacted Siremoval) and 4.5 h of thermal treatment in air (650 8C) toburn the elemental carbon. This procedurewas confirmed notto be harmful for the SiC nanofibres structure. Purifiedproduct is equal to 20wt% of the raw material.

4.2 SiC branches from Si/PTFE/NaN3 system Thebasic composition of reactants was modified by the additionof NaN3. Its content varied between 0.1 and 85wt% inSi/PTFE mixture. Under initial air pressure equal to 10 atmthe efficient formation of novel nanostructures, the branches(bundles) of SiC fibres, was observed (Fig. 2, lower row, leftand in the middle). The smaller crystallite outgrowthswere found on branches surface. The content of thosenanostructures increases with the decreasing initial pressure.TheXRD allowed to identify the following compounds: SiC,SiO2, Na2SiF6 and Si3N4.

5 Applications in nanocomposites Due to theremarkable mechanical, thermal and chemical properties,the SiC nanoparticles [7, 8] and, specifically, nanofibresseem to be the promising fillers in composites. The previous

carbide (lower row) systems, from left: Na2CO3/Mg/Co, 1 atm, air;aN3, 10 atm, air; Si/PTFE, 10 atm, air.

� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2706 A. Dabrowska et al.: Ultra-fast efficient synthesis of one-dimensional nanostructuresp

hys

ica ssp st

atu

s

solid

i b

Figure 3 (online colour at: www.pss-b.com) The relationship between the measured tensile stress (MPa) and tensile strain; the Youngmodulus was calculated from fitting the linear function to the experimental data; different curves represent the samples with differentSiC nanofibres filler content (phr).

Figure 4 (online colour at: www.pss-b.com) The changes in ulti-mate tensile strength (MPa) for samples with different content (phr)of SiC nanofibres (SiC in a legend) and branches (SiC� in a legend);the line marks the value for a pure resin (reference).

Table 1 The results of mechanical tests. Reference results formatrix with CNTs listed in [] obtained by Bellucci (not published

investigations [9] already showed that even less than 1 phr(between 0.1 and 0.5 phr, where phr denotes SiC parts perhundred parts of resin) content of SiC nanofibres in the epoxyresin matrix increased its flexural modulus, flexural strengthand ultimate elongation. However, those results were still farfrom the maximum theoretical values and the procedure ofpreparing nanoSiC/epoxy resin composites materials has notbeen optimized yet. That was one of the motivations of thepresent studies.

5.1 SiC nanofibres/epoxy resin and SiCbranches/epoxy resin nanocomposites In order toprepare the composite samples for mechanical testing, theSiC purified fibres and raw SiC branches were obtained fromcombustion of Si< 43mm/PTFE 1mm and Si< 43mm/PTFE 1mm/NaN3 powdered mixtures, respectively. Thefillers were dispersed in 1-propanol, 2-propanol or inisopropylic alcohol by ultrasonication and added to themodified epoxy resin EL20 (with an equivalent weight190 g). Finally, the curing agent P-900 was added. Thefollowing samples were prepared:

yet).

%SiC Young ultimate tensile

(i) 0 ‘fibres’ (phr) modulus (GPa) strength (MPa)

� 2011

.1, 0.25, 0.5, 0.75, 1, 2, 4 and 6 phr (for purified SiCnanofibres)

(ii) 0

.25, 1 and 2 phr (for raw SiC branches) 0 2.9 [2.9] 69.76 [62.26]

(iii) p

ure resin without a filler (as a reference sample). 0.1 2.8 59.48 0.25 3.2 42.13 [47.37]0.5 3.0 [3.0] 30.90 [58.22]0.75 3.0 31.10 [53.80]1 3.0 [2.6] 38.06 [54.43]2 – 27.184 4.2 52.936 2.9 41.21%SiC‘branches’ (phr)

Youngmodulus (GPa)

ultimate tensilestrength (MPa)

0.25 3.1 72.331 3.1 65.072 3.0 59.08

5.2 Mechanical properties As obtained sampleswere subjected to the testing of mechanical properties.Using Lloyd T20000 Instrument, the Young modulus, thetensile stress (Fig. 3) and the ultimate tensile strength (Fig. 4)were estimated. The results (Table 1) show that already lessthan 1wt% of the nanofiller changes the mechanicalproperties of the matrix. For the majority of samples theincrease in Young modulus was observed (up to 45%increase for 4 phr content of SiC). The enhancement ofultimate tensile strength was observed for matrix with0.25 phr content of SiC branches. To determine the material

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.pss-b.com

Phys. Status Solidi B 248, No. 11 (2011) 2707

Original

Paper

Figure 5 (online colour at: www.pss-b.com) The nanocompositessamples with, from left: SiC branches, neat resin, increasingSiC nanofibres content.

toughness, the well-known Charpy method (v-notch test)was adopted to measure the amount of energy absorbed by amaterial during its fracture. Failure surfaces show charac-teristics of brittle fracture. The 0.1, 0.5 and 1 phr contents ofSiC nanofibres increase the composite toughness respect-ively for 35, 35 and 5%. Interestingly, as shown in Table 1,the mechanical properties of SiC-reinforced composites(Fig. 5) are very close (or even better) to those with carbonnanotubes.

In conclusion, a variety of 1-D nanostructures (1-Dnanocarbons and different 1-D SiC) have been successfullyproduced by SHS technique, characterized and tested (SiC)as fillers in resin matrix. One of them, branches of SiCnanofibres, has not been produced before as a compositefiller (in contradistinction to SiC particles) and because of itshigh structural organization it seem promising for furtherdetailed investigations. The mechanical properties ofobtained nanocomposites were improved and possibleapplications are currently considered. The already reportedpositive ultrasonication influence on material properties [7]has been confirmed. As the Young modulus of purified SiC

www.pss-b.com

reach the level of 450GPa, there is still a place for asignificant improvement inwhich finding the resin providingan optimal interaction with filer and an efficient dispersionmethod are crucial.

Acknowledgements This project is co-financed by theEuropean Regional Development Fund within the InnovativeEconomy Operational Programme 2007-2013 (title of the project‘Development of technology for a new generation of the hydrogenand hydrogen compounds sensor for applications in abovenormative conditions’ No UDA-POIG.01.03.01-14-071/08-06).Theworkwas partially supported by the ItalianMinistry PRIN2008research programDevelopment andElectromagnetic Characterizationof Nano Structured Carbon Based Polymer CompositEs (DENSE)and by the EU FP7 project FP7-266529 BY-NanoERA. The resinEL20 was provided to our group by Prof. Gilberto Rinaldi, who wealso thank for his help in carrying out mechanical tests.

References

[1] A. Huczko, M. Osica, A. Rutkowska, M. Bystrzejewski,H. Lange, and S. Cudziło, J. Phys.: Condens. Matter 19,395022 (2007).

[2] M. Soszynski, A. Dabrowska, M. Bystrzejewski, and A.Huczko, Cryst. Res. Technol. 45, 12 (2010).

[3] M. Szala, Int. J. SHS 17, 106 (2008).[4] B. Bendjemil, Int. J. Nanoelectron. Mater. 2, 173 (2009).[5] Z. Lou, Q. Chen, W. Wang, and Y. Zhang, Carbon 41, 3063

(2003).[6] A. Huczko, A. Dabrowska, V. Savchyn, A. I. Popov, and

I. Karbovnyk, Phys. Status Solidi B 246, 2806 (2009).[7] N. Chisholm, H. Mahfuz, V. K. Rangari, A. Ashfaq, and

S. Jeelani, Compos. Struct. 67, 115 (2005).[8] K. Kueseng and K. I. Jacob, Eur. Polym. J. 42, 220 (2006).[9] V. Poornima, S. Thomas, and A. Huczko, Composites 10, 11

(2010).

� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim