Surface treatments of vapor-grown carbon fibers produced on a substrate: Part II: Atomic force microscopy

doi:10.1016/S0008-6223(99)00055-X

Carbon

Volume 37, Issue 11, 1999, Pages 1809-1816

https://doi.org/10.1016/S0008-6223(99)00055-X Get rights and content

Abstract

Vapor-grown carbon fibers (VGCF) were produced from a methane–hydrogen mixture on a substrate seeded with an iron catalyst. The fibers thus produced were submitted to different oxidative treatments: nitric acid, oxygen plasma and partial gasification with air or carbon dioxide. These fibers have been previously characterised by X-ray diffraction, SEM, nitrogen adsorption, XPS and ToF–SIMS. In the present paper we report on the examination of their surface nano-topography by atomic force microscopy (AFM).

Introduction

Surface oxidation of carbon fibers is commonly used to improve the adhesion between fiber and matrix in composites [1], [2], and the activation of carbon fibers to produce an adsorbent material relies on carbon dioxide or steam gasification, in order to develop an adequate porous texture [3], [4].

In a comparative study of the oxidation of different types of fibers (in air, at 973 K), the peculiar behavior of the VGCF was evidenced [5]. In particular, it was found that these fibers were attacked by a pitting mechanism, which was not observed either with PAN or with pitch fibers. Later, this phenomenon was investigated in more detail, and it was tentatively proposed that such a mechanism was due to the catalytic action of iron traces on the surface of the VGCF [6]. The presence of iron was not unexpected, as it was the catalyst used for fiber growth, but it could not be detected either by XPS or by EDS.

In Part I of this investigation [7] we were able to confirm the presence of iron by time-of-flight secondary ion mass spectrometry (ToF–SIMS). It was also shown that the metal could be eliminated by HCl washing. This procedure originated a clear change in the gasification mechanism, as the large pits were no longer formed. Furthermore, the fibers were submitted to different post-production treatments in order to obtain modifications of their texture and/or surface chemistry, and characterized by SEM, XPS and nitrogen adsorption. These previous studies are complemented here with an investigation of the surface topography of the same VGCF samples by atomic force microscopy. Although the usefulness of scanning probe microscopy and derived techniques for the study of carbon fiber surfaces has been recognized [8], the authors are unaware of any investigation of VGCF by AFM.

Section snippets

Experimental

Vapor-grown carbon fibers were grown from a methane–hydrogen mixture on a Grafoil^® support seeded with an iron catalyst, Fe₃(CO)₁₂ being used as the catalyst precursor. The experimental method used for fiber growth was previously described [9]. The fibers as produced were submitted to different oxidative treatments: Oxidation with nitric acid (70 wt. %) was performed in a Soxhlet at 80°C during 5 h on 2 g of material (ACF1). Oxygen plasma treatments (ACF2) were realized at INCAR, Oviedo, Spain,

Results and discussion

Typical surface compositions of the VGCF obtained by XPS before and after the oxidative treatments are given in Table 1, together with their BET surface areas. The effect of oxidation is obvious, as indicated by the increase in the surface oxygen concentration.

The VGCF are produced with a variety of morphologies, and frequently show numerous crenulations [10]. As the fibers were not submitted to any graphitisation treatment, and the size of the ordered domains was small (L_c of the order of 4

Conclusions

AFM examination of the surface of VGCF revealed a granular texture which is not observed on the other fiber types (pitch, PAN). Nitric acid oxidation does not change this surface topography, but the plasma treatment increases the size of the grains.

Examination of the fibers after partial gasification by carbon dioxide revealed the presence of holes or pits in the sub-micrometer scale; at the bottom of each pit a particle of about 10 nm height was clearly visible. Both the large pits and the

Acknowledgments

Financial support by the EC through the Human Capital and Mobility programme (contract number CHRX-CT94-0457) is gratefully acknowledged. The authors are indebted to Drs. J.M.D. Tascón and A. Martı́nez-Alonso (INCAR, Oviedo, Spain) for the plasma treatments, and to UCAR (USA) for providing the Grafoil^®.

References (18)

W. Kowbel et al.
The mechanism of fiber-matrix interactions in carbon–carbon composites
Carbon
(1990)
S.K. Ryu et al.
Activation of carbon fibres by steam and carbon dioxide
Carbon
(1993)
M. Suzuki
Activated carbon fiber: Fundamentals and applications
Carbon
(1994)
Ph. Serp et al.
Surface treatments of vapor-grown carbon fibers produced on a substrate
Carbon
(1998)
W.P. Hoffman
Scanning probe microscopy of carbon fiber surfaces
Carbon
(1992)
Ph. Serp et al.
A microstructural investigation of vapor-grown carbon fibers
Carbon
(1996)
F.W.J. van Hattum et al.
The effect of morphology on the properties of vapour-grown carbon fibres
Carbon
(1997)
J.-B. Donnet et al.
Study of carbon fiber surfaces by scanning tunneling microscopy, Part I. Carbon fibers from different precursors and after various heat treatment temperatures
Carbon
(1992)
J.-B. Donnet et al.
Study of carbon fiber surfaces by scanning tunneling microscopy, Part II. PAN based high strength carbon
Carbon
(1993)

There are more references available in the full text version of this article.

Cited by (24)

A review of fibrous graphite materials: graphite whiskers, columnar carbons with a cone-shaped top, and needle- and rods-like polyhedral crystals
2023, Xinxing Tan Cailiao/New Carbon Materials
Fibrous graphite materials are highly attractive due to their unique morphologies, high degree of orientation of their graphite microcrystallites, extremely good mechanical and conductive properties, fascinating growth mechanisms, diverse preparation methods and potential applications. This review summarizes the preparation methods, Raman spectra and the growth mechanisms of graphite whiskers, columnar carbons with cone-shaped top cones, and needle- and rod-like polyhedral crystals, and their optical, electrical and magnetic properties and applications are outlined.
Effect of surface functionality of PAN-based carbon fibres on the mechanical performance of carbon/epoxy composites
2014, Composites Science and Technology
The performance of composite laminates depends on the adhesion between the fibre reinforcement and matrix, with the surface properties of the fibres playing a key role in determining the level of adhesion achieved. For this reason it is important to develop an in-depth understanding of the surface functionalities on the reinforcement fibres. In this work, multi-scale surface analysis of carbon fibre during the three stages of manufacture; carbonisation, electrolytic oxidation, and epoxy sizing was carried out. The surface topography was examined using scanning electron microscopy (SEM), which revealed longitudinal ridges and striations along the fibre-axis for all fibre types. A small difference in surface roughness was observed by scanning probe microscopy (SPM), while the coefficient of friction measured by an automated single fibre tester showed 51% and 98% increase for the oxidised and sized fibres, respectively. The fibres were found to exhibit heterogeneity in surface energy as evidenced from SPM force measurements. The unsized fibres were much more energetically heterogeneous than the sized fibre. A good correlation was found between fibre properties (both physical and chemical) and interlaminar shear strength (ILSS) of composites made from all three fibre types.
Design of microwave plasma and enhanced mechanical properties of thermoplastic composites reinforced with microwave plasma-treated carbon fiber fabric
2014, Composites Part B: Engineering
Citation Excerpt :
Montes-Moran et al. [18,23] and Kowbel and Shan [24] reported that a plasma treatment improved interlaminar shear strength (ILSS). Figueiredo et al. [25] reported that the surface roughness of the CF was increased substantially after plasma treatment, while nitric acid treatment did not substantially change the morphology of the surface of the CF. In this study, CFF was treated with lab-made argon microwave plasma, and the plasma parameters were measured to specify the condition of the plasma treatment. The treated and untreated CFF were made into thermoplastic CFFRCs using a fast manufacturing process with the CBT resin, and the effect of the developed microwave plasma treatment on the mechanical property of the prepared CFFRCs was investigated.
Microwave plasma equipment was designed and manufactured to improve the interfacial bonding and mechanical interlocking between carbon fiber fabric (CFF) and the polymer matrix. Tensile specimens for the composites reinforced with the as-received and microwave plasma-treated CFFs were prepared using high-speed fabrication with a polymerizable and low-viscosity cyclic butylene terephthalate (CBT) oligomer matrix. Compared with the polymerized CBT (pCBT) matrix, the tensile strengths of the as-received and plasma-treated CFF reinforced composites (CFFRCs) were enhanced by approximately 362.5% and 436.3%, respectively. A high carbon fiber content of 70 vol.% was achieved without introducing pores and/or defects into the CFFRC due to the low viscosity and high impregnation characteristics of the CBT resin. It was confirmed that the microwave plasma can increase the surface roughness of the tested CFF without varying the chemical composition and defect level of the CFF. In addition, the interfacial bonding and mechanical interlocking between the CFF and polymer matrix were improved.
On the role of the residual iron growth catalyst in the gasification of multi-walled carbon nanotubes with carbon dioxide
2012, Catalysis Today
Citation Excerpt :
It was found that these processes can be reversed suggesting that they both involve the diffusion of carbon through the metal nanoparticles. Serp, Figueiredo and coworkers [21,22] performed detailed studies on the surface properties of vapor-grown carbon fibers after gasification with CO2 or air, which were found to be strongly influenced by the presence of traces of iron. Green and coworkers made use of the Boudouard reaction to open and cut CNTs [23].
The gasification of carbon with CO₂ was applied to examine the role of the residual iron growth catalyst in multi-walled carbon nanotubes (CNTs), which were pre-treated either by refluxing in nitric acid at 120 °C or by nitric acid vapor at 200 °C. Temperature-programmed desorption (TPD) and surface reaction (TPSR) experiments were performed in He and CO₂, respectively. The Fe nanoparticles were retained after the treatment in HNO₃ vapor, whereas the liquid HNO₃ treatment was able to remove the accessible residual Fe catalyst. The exposed Fe nanoparticles were found to catalyze the gasification of CNTs with CO₂ according to the reverse Boudouard reaction C + CO₂ = 2CO. In case of the CNTs pretreated in HNO₃ vapor, evolving CO₂ formed due to the decomposition of oxygen-containing functional groups during the TPD experiments was fully converted above 750 °C into desorbing CO, and the addition of 2000 ppm CO₂ in the feed gas during the TPSR experiments resulted in full conversion at 1000 °C. X-ray photoelectron spectroscopy studies show that the treatment in HNO₃ vapor at 200 °C favors the formation of oxygen species doubly bound to carbon (CO groups). During the TPSR experiments, CO₂ as a weak oxidant partially oxidized the CNTs leading to the formation of CO groups, and a much higher amount of these groups was detected on HNO₃ vapor-treated CNTs with residual Fe catalyst. Their presence suggests that CO groups are reaction intermediates of the CNT gasification with CO₂, which is considered an effective test reaction for the presence of residual catalytically active nanoparticles.
New hybrid method for simultaneous improvement of tensile and impact properties of carbon fiber reinforced composites
2011, Carbon
Citation Excerpt :
Specifically, Kowbel et al. [26] reported that oxygen plasma treatment was the best way to improve the interlaminar shear strength (ILSS) of CF filled phenolic resin (Fiberite 6055) among surface treatments of CF such as oxygen plasma, oxygen and argon plasma, nitric acid, and nitric acid and argon plasma treatments. Figueiredo et al. [27] observed that plasma treatment increases the surface roughness of CF while nitric acid treatment does not change the topography of the surface of CF. However, according to Jang et al. [28], nitric acid treatment was the best way to improve the ILSS of CF filled polybenzoxazine composite. Zhang et al. [25] compared experimental results on mechanical properties of epoxy composites filled with liquid nitrogen treated CF or oxidation treated CF, and found that the effects of the cryogenic treatment were larger than those of the oxidation treatment.
For weight savings of automobiles to improve fuel efficiency, tensile and impact strengths of carbon fiber reinforced composites (CFRC) are important properties required for substitution of metallic or ceramic automotive parts by CFRC parts. Effect of surface treatments of carbon fiber (CF) such as plasma, nitric acid, and liquid nitrogen treatments on interfacial bonding and mechanical properties of CF reinforced thermoplastic composites was investigated and nitric acid treatment was the best method to improve the interfacial affinity between the used CF and thermoplastic polymer matrix since the treatment induced acidic functional groups on the surface and increased surface roughness simultaneously. A new hybrid fabrication method was suggested by applying a bi-component two-layer structure to the film insert molding to improve tensile and impact strengths of CFRC simultaneously. Compared with tensile and impact strengths of the base polymer, those of the new hybrid composites filled with rubber particles and CF were improved by about 41.3% and 105.7%, respectively. In particular, tensile and impact strengths of the composite specimen prepared by the hybrid fabrication method were improved by about 15.0% and 36.0%, respectively when compared with those of the composite specimen prepared by the conventional melt mixing.
Interface property of carbon fibers/epoxy resin composite improved by hydrogen peroxide in supercritical water
2009, Materials Letters
Carbon fibers were treated by hydrogen peroxide in supercritical water and the surface morphologies of treated carbon fibers were observed by atomic force microscopy. It was found that surface roughness of the treated carbon fiber was improved obviously. Furthermore, X-ray photoelectron spectroscopy (XPS) was used to analyze surface functional groups of carbon fibers. It was found that functional groups containing oxygen were significantly increased compared with untreated carbon fibers. The maximal interlaminar shear strength (ILSS) of treated carbon fibers/epoxy resin composite was 110.5 MPa, which was higher than 63.5 MPa for untreated carbon fibers/epoxy resin composite. It also indicated that interface property of carbon fibers/epoxy resin composite was improved by hydrogen peroxide in supercritical water.

View all citing articles on Scopus

View full text