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j.mtcomm.2018.06.014

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Materials Today Communications 16 (2018) 250–257
Contents lists available at ScienceDirect
Materials Today Communications
journal homepage: www.elsevier.com/locate/mtcomm
Wustite-induced formation of sp3-rich faceted carbon foam: The key role of
cooling rate on sp3-abundance (and oxide crystal-habit) control
T
Xiaotian Zhanga,b, Daniel Medrandaa,b, Omololu Odunmbakua,b, Ayoub Taallaha,b,
⁎
Filippo S. Boia,b,c,
a
College of Physical Science and Technology Sichuan University, Chengdu, China
Sino-British Joint Materials Research Institute, Sichuan University, Chengdu 610064, China
c
School of Physics and Astronomy Queen Mary University of London, London, UK
b
A R T I C LE I N FO
A B S T R A C T
Keywords:
Carbon Foam
sp3-rich
Carbon onions
Fusion
Iron-oxide
Alpha-Fe
We report the formation of a novel faceted carbon-foam (CFM) phase by re-crystallization of recently discovered
sp3-rich α−Fe filled CFM. The formation of this novel carbon material is found by increasing the cooling-rate
factor after the annealing stage. High cooling rates can therefore create the right thermodynamic conditions for
FeO crystallization with consequent modification of the carbon-surface-characteristics and sharp increase in the
sp3-carbon content. In addition a possible dependence of the sp3 content on the crystal-habit of the encapsulated
oxide is found. This observation is confirmed by additional measurements in CFM-samples filled with variable
quantities of maghemite/hematite phases obtained with slow cooling experiments. This method has a crucial
importance since it can allow the control of surface-carbon-characteristics by modification of the encapsulated
oxide crystal-habit phases.
1. Introduction
Recently, extensive theoretical and experimental efforts have been
focused on searching for new carbon polymorphs or on understanding
structurally unknown carbon-phases under conditions of high pressure.
Several carbon allotropes have been proposed, such as M-carbon [1],
W-carbon [2], X-carbon [3], R-carbon [4], H-Carbon [5], O-carbon [8],
oC16-I [9], bct-C4 [10], Y-carbon [3], C-carbon [11], S-carbon [5], Jcarbon [12], F-carbon [13], T12-carbon [14], Cco-C8 [15], oC16-II [9],
Z-carbon [16], Z4-A3B1 [17], V-Carbon [7] and many others [18,23].
An important attention has been posed also on the use of carbon based
allotropes such as fullerenes or pea-pods for the fabrication of sp3-rich
carbon systems. Fabrication of carbon systems with very important
mechanical properties have been indeed recently reported by B.B. Liu
et al. [6,7]. In these experiments structural transitions from sp2-rich
carbon systems into a sp3 rich-one have been demonstrated [6,7]. While
these processes involve mainly the use of hollow carbon structures as
precursor materials, little is still known about the mechanism of such
transitions in presence of metal/alloys-filled carbon nano-onions
⁎
Corresponding author.
E-mail address: f.boi@scu.edu.cn (F.S. Boi).
https://doi.org/10.1016/j.mtcomm.2018.06.014
Received 28 April 2018; Accepted 29 June 2018
Available online 30 June 2018
2352-4928/ © 2018 Elsevier Ltd. All rights reserved.
(CNOs) as precursors. Recently, we have reported the preliminary observations of a novel structural transition involving an unusual spontaneous process of CNOs-fusion during annealing experiments of Fe3C
filled CNOs [19]. Such an unusual fusion mechanism was found to
trigger the formation of a carbon foam material (CFM) filled with a
continuous phase of α-Fe and characterized by a sp3-rich surface arrangement, with sp3/sp2 ratios up to the value of 0.99 [21]. Being interested in gathering a deeper understanding on the formation mechanism of such new family of CFM systems we re-investigated the
dynamics of such fusion process by changing two key parameters in the
synthesis/annealing experiments, namely 1) the deposition zone: a
quartz boat was added within the synthesis reactor, as a substrate for
the filled CNOs deposition and 2) the wall-thickness of the reactor: the
thickness of the quartz-tube reactor was reduced from 2.5 mm to 2 mm
in order to achieve a higher cooling rate.
Surprisingly, we found that for experiments performed in quartz
tubes with thickness of 2 mm an unusual re-crystallization involving the
oxidation of the α-Fe-filling comprised in the CFM into Wustite (FeO)
occurs after 18 h of annealing. This process is found to profoundly
Materials Today Communications 16 (2018) 250–257
X. Zhang et al.
Fig. 1. In A schematic of the CVS experimental system used for the growth of CNOs and annealing process. Note that the crucial factor inducing the formation of FeO
wustite is the cooling- rate.
These results have a crucial importance since they can in principle
allow accurate control of surface carbon-characteristics by directly
tuning the crystal habit of the encapsulated oxide phase at the interface.
modify the characteristics of the surface carbon-layers of the CFM, by
inducing the formation of carbon facets with high sp3 content, as confirmed by X-ray photoelectron spectroscopy (XPS). We attribute this
process to 1) interactions of the CFM layers with oxygen species in the
surface of the quartz boat during the annealing process, implying
therefore the possible presence of dandling bonds (possibly created
during the boat fabrication) and oxygen impurities which accelerate the
oxidation process [20], 2) to the very high cooling rate of the quartz
tube reactor which creates the right thermodynamic conditions for
crystallization of Wustite [22]. In addition a possible dependence of the
sp3 content on the crystal-habit of the encapsulated oxide is found. This
observation is confirmed by additional measurements in CFM-samples
filled with variable quantities of maghemite/hematite phases obtained
with slow cooling experiments (natural cooling rate of the furnace) (see
Suppl. Info. Figs. 3–6,9,11).
2. Experimental
The synthesis experiments were carried out by using a chemical
vapour synthesis (CVS) system composed of a quartz tube of length
1.5 m, one zone electric furnace and an Ar flow rate of 10–12 ml/min.
The Fe3C-filled CNOs were produced with a CVS reactor equipped with
a rail system for fast cooling, as shown in Fig. 1 inset. Precisely, the
used CVS systems consisted of a quartz tube with length of 1.5 m, a one
zone electric furnace and a rail system. As shown in Fig. 1A, the first
step consisted in the fabrication of Fe3C-filled CNOS by sublimation/
pyrolysis of ferrocene (1 g) at the local temperature of 900 °C on the top
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X. Zhang et al.
Fig. 2. Heating rates (A) and Cooling rates (B) used during the processes of CNOs fabrication (A) and FexOx foam formation (B) for quartz tubes with wall thickness of
2 mm and 2.5 mm.
the samples grown within the quartz boat. Instead a much slower
oxidation was observed in the other regions of the quartz tube or in
experiments performed without the use of quartz boats as shown in
Fig. 1 A–E in the right panels. As shown in Fig. 1 II,E in the left panel
the formation of Wustite was found only in the samples brought to
room temperature by using the cooling rate 1.
See supp. Materials for details on the equipment used for characterization and analyses of comparative annealing experiments performed in conditions of slow cooling rates.
of a custom-designed quartz boat (wall thickness of 1.4 mm). Annealing
experiments were performed immediately after the CNOs-growth in the
same reactor at the temperature of 1000 °C under Ar flow. Note that the
samples were not exposed to oxygen before annealing.
Precisely quartz tubes with controlled wall thickness of 2 mm
(inner diameter of 18 mm) and 2.5 mm (inner diameter of 15 mm)
were used in the attempt to control the cooling rate of the samples.
As shown in Fig. 2. three types of cooling rates were used in this
work; these consisted into two fast cooling approaches and one slow
cooling method. The fast cooling approaches were achieved by removing the furnace along the rail system after the annealing stage. A
schematic of the experimental process involving the formation of
carbon facets on the CFM surface in conditions of fast cooling rates
after annealing for a timescale of 18 h is shown in Fig. 1II. Note that
after the formation of Fe3C-filled CNOs (stage I), the as grown samples were directly annealed for long timescales. As shown in Fig. 1
IIC,D,E in the left panel a faster oxide formation was found only in
3. Results and discussion
The morphology of the faceted CFM obtained after the annealing
stage (18 h of annealing) was firstly revealed by scanning electron
micrographs (SEM) in secondary electron (Fig. 3A,C,D), backscattered
electron modes (Fig. 3B) and by cross-sectional transmission electron
micrographs (TEM), in Fig. 6. The carbon facets shown in Fig. 3A,C and
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X. Zhang et al.
Fig. 3. SEM micrographs showing the morphology of the faceted CFM obtained after the annealing stage (18 h of annealing) with secondary electrons (A,C,D) and
backscattered electrons (B).
Fig. 4. XRD analyses in the range between approximately 5–55 2θ degrees of
the faceted CFM sample obtained after 18 h of annealing with the cooling rate 1
approach. Note that Wustite has a prismatic/pyramidic crystal habit.
Fig. 5. XRD analyses of the faceted CFM sample obtained after 18 h of annealing with the cooling rate 1. Note that Wustite has a prismatic/pyramidic
crystal habit.
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X. Zhang et al.
Fig. 6. TEM micrographs showing the cross sectional morphology of the faceted CFM filled with FeO. Note in A–D the characteristic morphology of the facets. The
grey areas represent the amorphous-like carbon layers while the black areas represent the faceted oxide phase.
CFM samples obtained in conditions of slower cooling rates was then
considered. As shown in Fig. 8 and in sup. Info. for the case of Cooling
rate 2, also in this case an increase in the sp3/sp2 ratio is found with the
increasing of the annealing time.
The increase in sp3/sp2 content may correspond to the formation
of the α-Fe2O3 for the cooling rate 2 and maghemite/hematite mixtures for cooling rate 3. Such oxide crystallization condition is in
agreement with literature-works, where cooling rates as high as
70 °C/min were suggested for the crystallization of iron oxide in the
form of Wustite [11], and lower cooling rates were reported for the
crystallization of Fe2O3 phases. This difference in the oxide re-crystallization dynamics underlines the importance of cooling rates in 1)
the mechanism of CFM-surface formation and 2) in the control of
sp3/sp2 CFM characteristics for future applications. These observations are further confirmed by XPS analyses performed in slowcooled CFM samples containing the only maghemite (blue) or mixture of hematite and maghemite (red and blue) phases after magnetic
separation (see Figs. Supp. 3–6,9,11) performed with the use of a bar
magnet. See also ESI for Raman S. and FTIR measurements. Note also
that a shift of the C1s peak toward higher binding energies is found
in slow cooled samples implying possible changes in the C1s characteristics as a function of the used cooling rate.
D appear to replicate the morphological characteristics (i.e. prismatic
crystal habit) of the encapsulated Wustite phase (see Fig. 3B for morphology of the encapsulated wustite phase). This interpretation is further confirmed by the TEM analyses of Fig. 6A,B,C,D where the presence of facets was found in all the areas of this type of sample. Typical
XRD diffractograms showing the presence of Wustite are shown in
Figs. 4 and 5. Note that no peak corresponding to 002 reflection of
graphite was found in the region of 26 degrees 2θ. In the attempt to
investigate the sp3/sp2 characteristics of the faceted carbons layers, the
use of XPS was considered.
XPS analyses performed in the samples extracted from the reactor
after 9 h and 18 h of annealing with the cooling rate 1 are shown in
Fig. 7. It can be noticed that after annealing for a timescale of 9 h only a
partial conversion of the as grown Fe3C-filled CNOs into CFM is found
(Fig. 7D-F). Instead, after 18 h of annealing (Fig. 7A-C) a complete
conversion is achieved. Observing the C1s spectra in Fig. 7A and
Fig. 7D, we can clearly find a sharp increase in the sp3-carbon content
with the increase of annealing time.
This implies the presence of a structural-transition which can be
attributed to the progressive formation of the Wustite phase in minor
quantities after annealing for 9 h, and major quantities after annealing
for 18 h within the CFM. A direct comparison with the characteristics of
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X. Zhang et al.
Fig. 7. XPS analyses showing the evolution of the surface characteristics with the annealing time for the case of FeO filled faceted CFM obtained with Cooling Rate 1.
Note that a sharp increase in the sp3-content is found in this type of material, as indicated by the fitting in Fig. 7A and D with the achievement of sp3/sp2 ratios of 10.8
and 3.61 respectively (after annealing for timescale of 18 h and 9 h). See also Supp. Info. Fig. 1 for XRD measurements of the residual CNOs analyzed in G.
surface-characteristics and sharp increase in the sp3-carbon content.
A possible dependence of the sp3 content on the crystal-habit of the
encapsulated oxide is also found. This observation was confirmed by
additional measurements in CFM-samples filled with variable quantities of maghemite/hematite phases. The observed differences in the
crystallization dynamics of the encapsulated-oxides underlines the
importance of cooling rates in 1) the mechanism of CFM-surface
formation and 2) in the control of sp3/sp2 CFM characteristics for
future applications.
4. Conclusion
In summary we have reported the formation of a novel facetedcarbon-foam (CFM) in experiments involving the fusion of Fe3C-filled
CNOs with controlled cooling rates. The formation of this novel
carbon material is found by decreasing the thickness of the quartz
tube reactor and therefore increasing the cooling-rate factor. High
cooling rates are found to create the right thermodynamic conditions
for FeO crystallization with consequent modification of the carbon-
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X. Zhang et al.
Fig. 8. XPS analyses showing the evolution of the surface characteristics with the annealing time for the case of α-Fe filled CFM obtained with the Cooling rate 2.
Note that an increase in the oxygen content is found from the value of 1.8 atomic % to values higher than 31%, indicating the formation of a α-Fe2O3 phase within the
CFM (see also supp. Fig. 2 for complete spectra-set).
Acknowledgements
C70 solvates, Adv. Mater. 26 (2014) 7257–7263.
[7] X. Yang, M. Yao, X. Wu, S. Liu, S. Chen, K. Yang, R. Liu, T. Cui, B. Sundqvist, B. Liu,
Novel superhard sp3 carbon allotrope from cold-compressed C70 peapods, Phys.
Rev. Lett. 118 (2017) 245701.
[8] J. Wang, C. Chen, Y. Kawazoe, Orthorhombic carbon allotrope of compressed
graphite: Ab initio calculations, Phys. Rev. B: Condens. Matter Mater. Phys. 85
(2012) 033410.
[9] D. Selli, I.A. Baburin, R. Martonˇk, S. Leoni, Superhard sp3 carbon allotropes with
odd and even ring topologies, Phys. Rev. B: Condens. Matter Mater. Phys. 84 (2011)
161411.
[10] K. Umemoto, R.M. Wentzcovitch, S. Saito, T. Miyake, Body-centered tetragonal C4:
a viable sp3 carbon allotrope, Phys. Rev. Lett. 104 (2010) 125504.
[11] D. Li, K. Bao, F. Tian, Z. Zeng, Z. He, B. Liu, T. Cui, Lowest enthalpy polymorph of
cold-compressed graphite phase, Phys. Chem. Chem. Phys. 14 (2012) 4347.
[12] J. Wang, C. Chen, Y. Kawazoe, Phase conversion from graphite toward a simple
monoclinic sp3-carbon allotrope, J. Chem. Phys. 137 (2012) 024502.
[13] F. Tian, X. Dong, Z. Zhao, J. He, H.-T.J. Wang, Superhard F-carbon predicted by ab
initio particle-swarm optimization methodology, Phys. Condens. Matter. 24 (2012)
165504.
[14] Z. Zhao, F. Tian, X. Dong, Q. Li, Q. Wang, H. Wang, X. Zhong, B. Xu, D. Yu, J. He,
H.T. Wang, Y. Ma, Y. Tian, Tetragonal allotrope of group 14 elements, J. Am. Chem.
Soc. 134 (2012) 12362.
[15] Z. Zhao, B. Xu, X.F. Zhou, L.M. Wang, B. Wen, J. He, Z. Liu, H.T. Wang, Y. Tian,
Novel superhard carbon: C-centered orthorhombic C8, Phys. Rev. Lett. 107 (2011)
215502.
[16] J.A.F.-L.M. Amsler, L. Lehtovaara, F. Balima, S.A. Ghasemi, D. Machon, S. Pailhe`s,
A. Willand, D. Caliste, S. Botti, A.S. Miguel, S. Goedecker, M.A.L. Marques, Crystal
structure of cold compressed graphite, Phys. Rev. Lett. 108 (2012) 65501.
[17] C. He, L. Sun, C. Zhang, X. Peng, K. Zhang, J. Zhong, Four superhard carbon
We are grateful to the international NSFC grant number
0020205401178 and to prof. Shanling Wang.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mtcomm.2018.06.014.
References
[1] Q. Li, Y. Ma, A.R. Oganov, H. Wang, Y. Xu, T. Cui, H.K. Mao, G. Zou, Superhard
monoclinic polymorph of carbon, Phys. Rev. Lett. 102 (2009) 175506.
[2] J. Wang, C. Chen, Y. Kawazoe, Low-temperature phase transformation from graphite to sp3 orthorhombic carbon, Phys. Rev. Lett. 106 (2011) 75501.
[3] Q. Zhu, Q. Zeng, A.R. Oganov, Systematic search for low-enthalpy sp3 carbon allotropes using evolutionary metadynamics, Phys. Rev. B: Condens. Matter Mater.
Phys. 85 (2012) 201407.
[4] H. Niu, X.Q. Chen, S. Wang, D. Li, W.L. Mao, Y. Li, Families of superhard crystalline
carbon allotropes constructed via cold compression of graphite and nanotubes,
Phys. Rev. Lett. 108 (2012) 135501.
[5] C. He, L. Sun, C. Zhang, X. Peng, K. Zhang, J. Zhong, New superhard carbon phases
between graphite and diamond, Solid State Commun. 152 (2012) 1560.
[6] W. Cui, M. Yao, S. Liu, F. Ma, Q. Li, R. Liu, B. Liu, B. Zou, T. Cui, B. Liu, A New
carbon phase constructed by long-range ordered carbon clusters from compressing
256
Materials Today Communications 16 (2018) 250–257
X. Zhang et al.
allotropes: a first-principles study, Phys. Chem. Chem. Phys. 14 (2012) 8410.
[18] A.R. Oganov, C.W. Glass, Crystal structure prediction using ab initio evolutionary
techniques: principles and applications, J. Chem. Phys. 124 (2006) 244704.
[19] X. Zhang, S. Wang, Y. He, F.S. Boi, Mapping the transition from carbon-onions filled
with Fe3C to carbon-foam completely filled with α-Fe: unlocking mass-production
of ferromagnetic carbon foam, Mater. Today Commun. 14 (2018) 72–76.
[20] J.W. Hastie, 10th. Materials Research Symposium on Characterization of High
Temperature Vapors on Gases: NBS Special Publication 561 N.1, (1978).
[21] F.S. Boi, X. Zhang, D. Medranda, Evidence of sp3-rich nano-diamond-like characteristics in amorphous carbon foam continuously filled with α-Fe, Diam. Relat.
Mater. 84 (2018) 190–195.
[22] X. Yu, Z. Jiang, J. Zhao, D. Wei, C. Zhou, Effect of cooling rate on oxidation behaviour of microalloyed steel, Appl. Mech. Mater. 395 (2013) 273–278.
[23] M. Zhang, H. Liu, Y. Du, X. Zhang, Y. Wang, Q. Li, Orthorhombic C32: a novel
superhard sp3 carbon allotrope, Phys. Chem. Chem. Phys. 15 (2013) 14120.
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