development and characterization of nanoparticlee
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University of Central Florida University of Central Florida
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Electronic Theses and Dissertations, 2004-2019
2013
Development And Characterization Of Nanoparticlee Development And Characterization Of Nanoparticlee
Enhancements In Pyrolysis-derived High Temperature Enhancements In Pyrolysis-derived High Temperature
Composites Composites
James McKee University of Central Florida
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STARS Citation STARS Citation McKee, James, "Development And Characterization Of Nanoparticlee Enhancements In Pyrolysis-derived High Temperature Composites" (2013). Electronic Theses and Dissertations, 2004-2019. 2833. https://stars.library.ucf.edu/etd/2833
DEVELOPMENT AND CHARACTERIZATION OF NANOPARTICLE ENHANCEMENTS
IN PYROLYSIS-DERIVED HIGH TEMPERATURE COMPOSITES
by
JAMES RICHARD MCKEE
B.S. University of Central Florida, 2011
A thesis submitted in partial fulfillment of the requirements
for the degree of Master of Science
in the Department of Material Science and Engineering
in the College of Engineering and Computer Science
at the University of Central Florida
Orlando, Florida
Fall Term
2013
Major Professor: Jihua Gou
ii
©2013 James McKee
iii
ABSTRACT
Thermal protection systems, which are commonly used to protect spacecraft during
atmospheric entry, have traditionally been made of materials which are traditionally high in
manufacturing costs for both the materials needed and the manufacturing complexity, such as
carbon-carbon composites and aerogels. [1] In addition to their manufacturing costs, these
materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles
as opposed to single structures because they are not capable of supporting larger structures. [2]
The limitations of polymer reinforced composites have limited their entry into these applications,
except for pyrolyzed composite materials, such as carbon-carbon and ceramic composites. These
materials have been successfully demonstrated their utility in extreme environments, such as
spacecraft heat shields, but their high costs and the difficulty to manufacture them have limited
their use to similarly high performance applications where the costs are justifiable.
Previous work by others with “fuzzy fiber” composites have shown that aligned carbon
nanotubes (CNTs) grown on fibers can improve their thermal conductivity and wettability. To
this end vertically aligned CNTs were studied for their potential use, but found to be difficult to
process with current conventional techniques. A composite material comprised of basalt, a
relatively new reinforcing fiber, and phenolic, which has been used in high-temperature
applications with great success was made to attempt to create a new material for these
applications. To further improve upon the favorable properties of the resulting composite, the
composite was pyrolyzed to produce a basalt-carbon composite with a higher thermal stability
than its pristine state. While testing the effects of pyrolysis on the thermal stability, a novel
iv
technique was also developed to promote in-situ carbon nanotube growth of the resulting basalt-
carbon composite without using a monolithic piece of cured phenolic resin in place of the
standard aromatic hydrocarbon-catalyst precursor. [3, 4] The in-situ growth of carbon nanotubes
(CNTs) was explored as their thermal stability [5] and effectiveness in improving performance
has been previously demonstrated when used as a resin additive [6].
The specimens were examined with SEM, EDS, and TGA to determine the effects of
both pyrolysis and CNT growth during pyrolysis of the basalt phenolic composites. These tests
would confirm the presence of CNTs/CNFs directly grown in the composite by pyrolysis, and
confirm their composition by EDS and Raman spectroscopy. EDS would additionally confirm
that the surface of the basalt fibers possess a composition suitable for CNT growth, similar to the
parameters of CVD processing. Additional testing would also show that the growth behavior of
the CNTs/CNFs is dependent on temperature as opposed to composition, indicating that there is
a threshold temperature necessary to facilitate the availability of catalysts from within the basalt
fibers. The thermal stability shown by TGA indicates that the process of pyrolysis leaves the
newly formed composite with a high degree of thermal stability, making the new materials
potentially usable in applications such as turbines, in addition to large-scale thermal protection
systems.
v
For Jade and my family.
vi
ACKNOWLEDGMENTS
Dr. Jihua Gou, my research advisor and director of the Composite Materials and
Structures Laboratory (CMSL) at UCF, deserves a great deal of thanks for taking the chance to
bring me into the research family as an undergraduate and giving me the amazing opportunity to
be a part of the groundbreaking research in nanocomposites through the years. This opportunity
gave me a better picture of the world than an education alone could have ever provided at both
levels of my academic career to date, and I believe has prepared me for a career and lifetime of
learning and expanding the world of composites he introduced me to.
I would like to thank my thesis committee members Dr. Jayanta Kapat and Dr.
Chengying Xu for their interest in my work, insights, and support in completing this work. I
would like to extend a special thanks to Dr. Qingwen Li and her research team at Suzhou
Institute of Nanotechnology and Nano-Bionics for their hospitality and sage counsel this past
summer when I was a visitor in their lab and they taught me more about carbon nanotubes than I
could ever have hoped to learn on my own. I would also like to thank and acknowledge the
National Science Foundation for their support with the EAPSI Program that afforded me an
opportunity to experience another culture and see the world in a way I could not have imagined.
I would like to extend my thanks to Mr. Donovan Lui, my irreplaceable friend and
invaluable partner in so many of the research projects I have worked on in graduate school. Dr.
Fei Liang, whose advice on the adventures of graduate school, including this thesis have been
invaluable. Mr. Gregory Freihofer, a friend and researcher whose knowledge of Raman has
helped immeasurably with this work. Dr. Jason Gibson, whose work prepared me for the rigors
of this work and providing composite industry insights that helped me along the way.
vii
Above all, I would like to thank my beloved Jade for her unwavering support and
encouragement through the entirety of this adventure, and her constant belief in me in all of the
endeavors I have undertaken at every level of my career. I would like to thank my loving parents,
Robert and Deborah McKee, my brother Robert, and my grandparents, Dr. Richard and
Catherine Michalec for their patience and support in every level of my education. I would also
like to give my thanks to Mr. James McKee and Mrs. Ann McKee, my uncle and aunt, for their
love and encouragement.
viii
TABLE OF CONTENTS
LIST OF FIGURES ........................................................................................................... xi
LIST OF TABLES ........................................................................................................... xiii
LIST OF ABBREVIATIONS .......................................................................................... xiv
CHAPTER ONE: INTRODUCTION ................................................................................. 1
1.1 Motivation ............................................................................................................. 1
1.2 Research Methods ................................................................................................. 2
1.2.1 Carbon Nanotube Growth Phenomenon ........................................................ 2
1.2.2 Pyrolysis Behavior of Phenolic Resins .......................................................... 3
1.2.3 Objectives ....................................................................................................... 3
1.3 Structure of the Thesis............................................................................................... 4
CHAPTER TWO: LITERATURE REVIEW ..................................................................... 6
2.1 CVD Growth of CNTs .......................................................................................... 6
2.2 Carbon Nanofiber/Nanotube Enhancements to Composites ................................. 8
2.2.1 Bulk Filler ...................................................................................................... 8
2.2.2 Carbon Nanopaper.......................................................................................... 8
2.2.3 In Situ Grown CNTs on “Fuzzy Fibers” ............................................................ 9
2.3 Properties of Basalt Fiber Composites ................................................................ 11
2.4 Pyrolysis Behavior of Phenolic Resin ..................................................................... 12
ix
CHAPTER THREE: METHODOLOGY ......................................................................... 15
3.1 Basalt Fiber Composite Preparation .................................................................... 15
3.2 Basalt Fiber Composite Pyrolysis ....................................................................... 15
3.2.1 Nomenclature of the Pyrolyzed Samples ......................................................... 16
3.3 VACNT ............................................................................................................... 16
CHAPTER FOUR: FINDINGS ........................................................................................ 20
4.1 Effects of Temperature on the Pyrolysis of BFC ................................................ 20
4.2 Morphology of the Pyrolyzed Composites.......................................................... 22
4.3 Verification of Ordered Carbon Nanostructures ................................................. 28
4.3.1 Raman Spectroscopy .................................................................................... 28
4.3.2 EDX .............................................................................................................. 31
4.4 Thermal Analysis of the Pyrolyzed Composites ................................................. 35
CHAPTER FIVE: CONCLUSIONS ................................................................................ 38
APPENDIX A: MATLAB CODE FOR TGA ANALYSIS ............................................. 40
Analysis.m ..................................................................................................................... 41
TGA_DataImport.m ...................................................................................................... 42
APPENDIX B: MATLAB CODE FOR RAMAN SPECTROSCOPY PLOTS ............... 45
Analysis.m ..................................................................................................................... 46
APPENDIX C: EDAX MICROANALYSIS REPORT .................................................... 47
x
APPENDIX D: BASALT FIBER DATA SHEETS ......................................................... 53
Characteristics of Basalt Fiber ...................................................................................... 54
Comparison of basalt fiber with other fibers ................................................................. 54
APPENDIX E: COPYRIGHT PERMISSION LETTER FOR FIGURE 4 ...................... 55
LIST OF REFERENCES .................................................................................................. 62
xi
LIST OF FIGURES
Figure 1 Typical CVD Reactor Configuration ................................................................................ 7
Figure 2 Crowding Effect from the Growth of CNTs on the Reactor Wall ................................... 8
Figure 3 Schematic of the Interface of a Fuzzy Fiber Composite ................................................ 10
Figure 4 Gas species evolved from the pyrolysis of neat phenolic resin ...................................... 13
Figure 5 VACNT Manufacturing Configuration (50mm tube) .................................................... 18
Figure 6 VACNT Manufacturing Configuration (100mm tube) .................................................. 18
Figure 7 VACNT Growth Cycle Chart in 100mm Furnace .......................................................... 19
Figure 8 Photograph of basalt-phenolic composite and pristine phenolic resin before and after
pyrolysis ............................................................................................................................ 20
Figure 9 Photograph of the two halves of a piece of PPR before and after pyrolysis factors ...... 21
Figure 10 SEM micrographs of BFC-850 (a) and PPR (b) after pyrolysis ................................... 22
Figure 11 SEM micrographs of BFC-850-CNT showing the diameter of a CNT/CNF grown by
pyrolysis ............................................................................................................................ 23
Figure 12 SEM micrograph of BFC-850-CNT samples ............................................................... 24
Figure 13 VACNT Arrays Produced in 100mm Reactor (Left) and 50mm Reactor (Right) ....... 25
Figure 14 SEM Micrograph of VACNT Array in Figure 13 ........................................................ 27
Figure 15 SEM Micrograph of VACNT Array at Higher Magnification ..................................... 27
Figure 16 Raman Spectrograph of BFC-850-CNT and Pyrolyzed PPR ....................................... 29
Figure 17 Raman Spectrograph of VACNT Sample made by CVD ............................................ 30
Figure 18 EDS Results for Pyrolyzed Carbon Matrix from the Bottom Side of BFC-850 .......... 32
Figure 19 EDS Results for Pyrolyzed Carbon Matrix from the Top Side of BFC-850 ................ 34
xii
Figure 20 TGA results for BFC-750 (left) and BFC-850-CNT (right) in Argon ......................... 35
Figure 21 TGA results for BFC-750 (left) and BFC-850-CNT (right) in Air .............................. 36
Figure 22 TGA results for pyrolysis of (a) pristine phenolic resin and (b) pristine BFC ............. 37
xiii
LIST OF TABLES
Table 1: Sample Nomenclature and Process Data ............................................................ 16
Table 2: VACNT Growth Parameters ............................................................................... 17
Table 3: Mass loss of BFC-850 Specimens ...................................................................... 20
Table 4: EDS results from the data shown in Figure 18 for the bottom of BFC-850 ....... 32
Table 5: EDS results from the data shown in Figure 19 for the top of BFC-850 ............. 33
Table 6: Effects of prolonged high temperatures in air .................................................... 36
xiv
LIST OF ABBREVIATIONS
BFC Basalt Fiber Composite
CNF Carbon Nanofiber
CNT Carbon Nanotube
CVD Chemical Vapor Deposition
EDX Energy-Dirspersive X-ray Spectroscopy
MSDS Material Safety Data Sheet
PICA Phenolic Impregnated Carbon Ablator
PMC Polymer Matrix Composite
PPR Pyrolyzed Phenolic Resin
SEM Scanning Electron Microscope
SINANO Suzhou Institute of Nanotechnology and Nano-bionics
TEM Tunneling Electron Microscope
TGA Thermogravimetric Analysis
VACNT Vertically-Aligned Carbon Nanotubes
1
CHAPTER ONE: INTRODUCTION
1.1 Motivation
Polymer composites have held an important role in modern engineering design,
particularly for aerospace structures. [5] With their high specific strength, they can easily replace
metallic components in many applications, maintaining the same strength but with a greatly
reduced weight. With their greatest asset being their strength, their disadvantages include
relatively low usage temperatures and poor electrical conductivity. The latter of these has been
greatly improved upon with the use of additives, including carbon nanotubes and other
conductive materials. The use of these additives are relatively low cost, but still introduce some
manufacturing challenges that add to production time and quality control needs, largely due to
the increased viscosity of the resin with the additives.
The thermal envelope of the composites has been more of a challenge, requiring the use
of exotic matrix materials or extensive, costly processing techniques, or sometimes both. The
traditional super-high-temperature material is referred to as a carbon-carbon composite, and
requires extensive processing, and has thus been relegated to applications where the performance
is so critical that the costs can be acceptable. [6] Single-use high temperature materials, for
applications such as atmospheric entry vehicles, have relied upon a combination of carbon-
carbon composites and ablative materials, which are sometimes based on phenolic resins.
Pyrolysis represents an effective way to improve thermal performance, as it removes many of the
volatile gases and leaves a stable carbon char that enhances the performance of the composite.
[7-10]
2
Previous research conducted with basalt fiber composites has yielded data pointing to
their excellent thermal stability and mechanical properties. [11] While a great deal of work has
been performed to investigate the mechanical properties of this naturally-derived fiber,
particularly as a friction material for brakes [11-14], there are few studies using it in thermal
protection systems. Formaldehyde phenolic resins have enjoyed use in a wide variety of
applications, and thusly have been well-studied as the first synthetic thermoset resin ever
developed. This research combined the proven properties of formaldehyde-phenolic resin and
basalt fiber to develop a new high-temperature composite that can improve on the performance
limitations of carbon-carbon composites and potentially do so at a lower cost than the pure
carbon counterpart.
1.2 Research Methods
1.2.1 Carbon Nanotube Growth Phenomenon
The since the first paper was published regarding nanotubes roughly twenty years ago,
their unique properties and multitude of uses have made them a very attractive potential solution
in many areas of science. [7] Since then, their properties have been examined for applications as
varied as solar cells and a theoretical space elevator, with a seemingly unlimited number of
potential applications to be explored. [8-10] The underlying principle for these applications is the
limitations imposed by the CNT growth behaviors. There are two growth modes for CNTs,
which differ based on the location of the catalyst particle relative to the growth, being either tip
growth or base growth. [11, 12] The differing methods for growing CNTs leads to varied
behavior and different dynamics for the growth kinetics of CNTs that will be further discussed in
the literature review.
3
1.2.2 Pyrolysis Behavior of Phenolic Resins
The experiments conducted at SINANO focused on the pyrolysis of basalt-phenolic
composites to measure their thermal stability and potential utility in thermal protection systems
and high temperature composite structures. While there has been some research into the
pyrolysis of phenolic resin [13] and basalt fiber composites [14] separately, there is little to no
direct research into the behavior of these composites when they are pyrolyzed. To evaluate the
basic structure, morphology, and thermal performance of the specimens, several analytical and
observational tools were chosen that would be best suited for the tasks. Keeping the goals of
basic evaluation in mind, the samples were examined using scanning electron microscopy
(SEM), Raman spectroscopy, and thermogravimetric analysis (TGA) to explore their properties
and behaviors following pyrolysis.
1.2.3 Objectives
With a great deal of research being done with the improvement to thermal properties and
behavior carried out in other research, novel methods for the inclusion of CNTs into a
continuously-reinforced fiber composite were sought. The lack of background research into the
particular resin and fiber combination utilized led to a preliminary investigation of the basic
thermal stability of the polymer reinforced composite and methods to improve upon the baseline
performance. Previous work within the research group has shown that the addition of a carbon
nanofibers, nanotubes, and other fillers can improve the fire retardancy of a composite
significantly. [15-18] This leads to questions as to what can be done to further improve the
thermal performance of the composite, and that leads to the process of pyrolysis, which has been
used extensively in the production of high-temperature composites, most notably carbon-carbon
composites. This research is intended to demonstrate the manufacture of basalt-carbon
4
composites produced by the pyrolysis of basalt-phenolic composites for high temperature
applications. These composites were then pyrolyzed under conditions that are demonstrably
similar to the methodology for the growth of VACNT forests by means of a CVD process.
1.3 Structure of the Thesis
This thesis explores a novel topic that has no direct literature review or background on its
subject. This thesis will first explain the theory and behavior of materials and processes that are
similar to the phenomenon that occurs with the in situ growth explained in Chapter 4. This
background research establishes the basic principle of CVD growth of CNTs and the growth
behavior of CNTs manufactured by this method, particularly VACNTs. The extension of this
process is explored with in situ grown CNTs, which have been made during the pyrolytic
conversion of PDCs from polymer to ceramics and behave similarly to the product of the work in
this thesis, but are still dependent on an external precursor.
The other extension of CVD explored is the growth of radially aligned CNTs on fiber
substrates referred to as fuzzy fibers, which appear similar to the basalt-CNT-carbon composites,
but are again the result of CVD performed on the pristine fibers that result in the CNTs
effectively being a coating. These fibers have been explored in detail since their inception and
demonstrated very desirable properties and behaviors, which are improvements over their
pristine state. The combination of the in situ growth process and fuzzy fibers as a concept form
the foundational theory for the behavior observed with the basalt composites explored in this
thesis.
The combination of these processes and behaviors is explored after observing the
properties of basalt fibers, their composites, and the pyrolytic behavior of phenolic resin. The
5
combination of these is shown to meet the requisite conditions that are similar to the processes
observed with the review work. To confirm the presence of CNTs/CNFs, a VACNT array is
fabricated using traditional CVD processing to provide a standard to compare the resulting
structural growth observed in the composite following pyrolysis. These comparisons are made,
and it is indeed shown that the structures observed within the composite can be reasonable
referred to as either CNTs or CNFs.
The observation of these structures and the confirmation of their veracity leads to
variations in their manufacture being tested to determine more optimal process parameters,
focusing on the amount or resin present and the pyrolysis temperature. The results of this
variation showed that the process is more dependent on the temperature the pyrolysis is
performed at than the resin content of the sample and effectively the hydrocarbon source.
The resulting material, now confirmed to have undergone a CNT/CNF growth process,
was then tested for thermal stability using a TGA. The results were compared to tests of the
pristine materials and the other pyrolyzed samples for comparison. The stability of the new
material showed excellent thermal stability, which performed at a level that makes the material a
good candidate for high-temperature applications. The thermal stability is coupled with an
anecdotally observed interlaminar strength that is retained or potentially improved over the
pristine material.
The thesis concludes with a summary of the findings and future work planned to expand
the data available on this new material, including the mechanical properties, thermal properties,
and optimization of the manufacturing process.
6
CHAPTER TWO: LITERATURE REVIEW
2.1 CVD Growth of CNTs
The growth of CNTs has been researched thoroughly since their discovery in the early
1990s, with several methods for their production being researched, including arc discharge,
plasma, laser ablation, and chemical vapor deposition (CVD). [4, 19-22] Among these
production methods, chemical vapor deposition stands apart for its ease of manufacture and low
costs compared to the others. CVD also holds a special advantage in that it can be performed
with a wider variety of substrates, even in-situ with other materials, such as ceramics. [23] The
inherent flexibility in this processing method has been explored, as has its ability to grow aligned
CNT “forests” for use in applications that exploit the highly anisotropic properties of the CNTs.
[3] The process for growing CNTs with CVD has been studied in-depth, and modeled by Raji, et
al providing a method to predict the growth behaviors of the CNTs and to allow for their
production. [24] In addition to the work by Raji, the Li, et al have shown the effects that the
choice of the precursor has on the CNTs grown by CVD. [4, 25]
7
VACNT Growth Substrate
Growth Zone(High Temperature)
Hydrocarbon/Ferrocene Precursor
(Syringe Pump)
Argon Gas
Preheater
Exhaust Trap
Figure 1 Typical CVD Reactor Configuration
A typical CNT growth reactor is shown in Figure 1 is commonly used for laboratory
scale growth of CNTs, including the growth of VACNTs on substrates inserted into the growth
zone of the reactor. [4, 26, 27] In many cases the substrate used for VACNT growth is quartz or
a silicon oxide that has been doped, although there are cases where the aligned CNTs are grown
on other surfaces, such as the case of fuzzy fibers, which will be discussed in a later section. The
VACNTs themselves are not a special case when using a reactor of the type pictured above. This
growth behavior leads to agglomerations of the CNTs on areas of the reactor wall as seen in
Figure 2 and means that CNTs grown in this manner need to undergo a debulking treatment in
order to facilitate their use in the manufacture of carbon nanopaper and as filler in composite
matrices.
8
CNTs
CNTs grow normal to the reactor surface and
eventually experience crowding as seen here
Figure 2 Crowding Effect from the Growth of CNTs on the Reactor Wall
2.2 Carbon Nanofiber/Nanotube Enhancements to Composites
2.2.1 Bulk Filler
The first generation of nanoparticles, fullerenes referred to as “carbon black” was first
reported by Iijima in 1980, and became the subject of study in the family of structures that would
lead to carbon nanotubes a decade later. [28] These particles have been the subject of research in
their use as additives to improve the thermal and electrical conductivity and mechanical
performance in composite structures from within the polymer matrix of the composites. [29, 30]
The previous work performed by within the laboratory has shown the improvements that can be
made to fire performance with the simple addition of CNTs and CNFs to a polymer matrix. [31]
The mechanical enhancement provided to the composite is a result of the surface area of the
fillers, which add a mechanical resistance to the distortion of the matrix as well as increasing
fracture toughness by suppressing crack propagation. [32]
2.2.2 Carbon Nanopaper
Carbon nanopaper was developed in an attempt to exploit the properties of CNTs and
CNFs in a form that is more flexible and discrete than as a bulk filler. This paper is possible
9
based on the formation of a network by the entanglement of the individual CNTs and CNFs
during processing that interlock by means of surface friction. [33] Carbon nanopaper can be
made using several methods, the one that was primarily considered for this research is direct
filtration, in which the CNTs, CNFs, or some combination of those and other particles are
suspended in a solution and then passed through a membrane filter. [16, 18, 34] As with use as a
bulk filler, the nanopaper allows the use of multiple types of nanoparticles in the composite;
however, the use of these particles in a self-supporting nanopaper allows them to be considered
as a laminate, rather than a modification to the matrix of the composite, and allow the
manufacture of selective properties in discrete layers in the composite. The fundamental
drawbacks to nanopapers is their relatively high density, which contributes to increased difficulty
in properly wetting out of the nanopaper layers. As with standard laminates, the degree of
wetting of the nanopapers can be directly tied to the mechanical performance of the completed
composite. [35]
The other fundamental challenge in the use of nanopaper in composites is the interface of
the nanopaper with the matrix and adjacent layers. The increased surface area of the individual
CNTs and CNFs in the nanopaper greatly enhance the interfacial properties of the composite
compared to standard laminar composites, however the higher areal density of the nanopaper can
lead to wetting issues that lead to poorer cross linking within the matrix.
2.2.3 In Situ Grown CNTs on “Fuzzy Fibers”
Growing CNTs and CNFs on fibers for improving composite performance have been
documented for a variety of fiber types ranging including ceramic fibers, glass fibers, and carbon
fibers. [36-38] The process documented by Ci et al is highly similar to the CVD process used to
10
produce VACNT forests that was documented in Section 2.1, consisting of a hydrocarbon
source, such as xylene, and a ferrocene catalyst. [36-38] These methods rely on the “adsorption-
diffusion-deposition” model for CNT and CNF growth, and are little removed from the CVD
process used to produce VACNT forests. [39] The difference in the growth of these CNTs and
CNFs versus the VACNTs is in their orientation– a VACNT forest is by definition vertically
aligned which is normal to the flat surface of its substrate. These “fuzzy fibers” grow normal to
the substrate, which is now a fiber, and are therefore effectively radially aligned with respect to
the fiber. [40]
Figure 3 Schematic of the Interface of a Fuzzy Fiber Composite
These radially aligned CNT fibers can then be used in polymer composites to produce
composites with improved conductivity and mechanical performance. The entanglement of the
CNTs with one another and the increase surface area, as shown in Figure 3, improve the
11
interfacial properties of the resulting composite. This interface is key to the shear behavior of the
composite and presents an excellent mechanism for improving the mechanical performance of a
composite structure. The work performed by Garcia et al has shown that the addition of in situ
grown CNTs on an alumina fiber can improve the interlaminar shear strength by 69% over a
pristine alumina-polymer composite as well as increases of 106 and 108 in the laminate level
electrical conductivity in-plane and through-thickness, respectively. [41] The mechanisms for the
improvements seen in these cases rely upon the increased conductivity provided by the CNTs
linking within the composite; the CNTs also provided improved wetting routes for the resin,
which further improved the density and mechanical properties of the composites.
Current work being performed by Ahmed et al [42] is investigating the ability to grow
nanotubes in situ by doping a powdered activated carbon substrate and heating in an environment
with an acetylene hydrocarbon source and hydrogen promoter in a modified CVD process. This
process is effectively a variation of the basic CVD process that uses a dry precursor instead of a
liquid precursor, this is effectively similar to the benzene sublimation techniques traditionally
used for manufacturing CNTs.
2.3 Properties of Basalt Fiber Composites
Basalt fibers are a relatively recent reinforcing fiber in the composites industry, and there
are still many areas where they are being investigated. The properties, listed in Appendix D,
show that it is a relatively heavy fiber, but this weight comes coupled with a relatively high
strength and a high temperature range. When compared to the data for common reinforcing
fibers, basalt seems to be a poor fit, but its performance characteristics become more favorable
12
when held against ceramic fibers, whose performance envelope is more similar to basalt in
chemical and temperature resistance.
Much of the previous work has focused on basalt and epoxy composites designed to
capitalize on the thermal stability of the basalt. [6, 14, 43] In many of these applications, basalt
has been shown to be a viable alternative to more expensive carbon/epoxy composites owing to
its lower cost over carbon, but superior strength to E-glass. The body of this work is still
relatively small, and little exploration of other resin systems with the basalt fiber has been
conducted outside of the aforementioned epoxy and polymer derived ceramics.
2.4 Pyrolysis Behavior of Phenolic Resin
In this work, a novolak-type phenolic resin is utilized as both the composite matrix
material and the hydrocarbon source to facilitate CNT growth in a process that is fundamentally
similar to CVD growth that is discussed in Section 2.1. Previous work has shown that the
decomposition of the phenolic resin produces a large number of gas species, including hydrogen,
methane, and ethane. [44, 45] The evolution of these gases is shown in Figure 4, with the gas
evolution being measured by means of an FTIR during TGA analysis. The results show that there
is ample production of hydrocarbons during the pyrolysis of the resin. This process is considered
in comparison to the pyrolysis of the composite that will be explored in Section 3.2. The
hydrocarbons produced during the pyrolysis of the phenolic resin is similar to the sources that
are used during CVD growth of CNTs that was discussed earlier. The species produced are
produced of interest are primarily methane, ethane, and hydrogen; the two hydrocarbons
generated are capable of promoting growth, especially with the presence of hydrogen, which
tends to behave as a catalyst for CVD growth of CNTs. [46]
13
Figure 4 Gas species evolved from the pyrolysis of neat phenolic resin
Source: Trick, K.A. and T.E. Saliba, Mechanisms of the pyrolysis of phenolic resin in a
carbon/phenolic composite. Carbon, 1995. 33(11): p. 1509-1515.
The body of work for phenolic pyrolysis is fairly well-explored, with the use of phenolic
resin dating back over 100 years. [1] The use of phenolic as the matrix material in thermal
14
protection systems, most notably PICA has facilitated an understanding of its decomposition at
high temperatures and demonstrated its strength retention following exposure to these conditions.
[2, 47, 48]
15
CHAPTER THREE: METHODOLOGY
3.1 Basalt Fiber Composite Preparation
Samples of pristine basalt-phenolic composite panels, as well as a monolithic piece of
pristine cured formaldehyde phenolic were prepared at the. These panels were made from a
(0/90)4 basalt fiber layup with a Momentive® Durite SC-1008 matrix at a fiber volume fraction
of approximately 20%. The panels were manufactured by hand laying the resin and fiber
preform, then B-staging the preform as a whole. The B-staged preform was then cured in an
autoclave using the curing parameters provided by the supplier, which utilized a consolidation
temperature of 93°C and a curing temperature of 162°C. Since the samples were intended to
undergo pyrolysis, no post-cure was performed.
The panels were then cut into pieces small enough for placement into a quartz tube
furnace for pyrolysis using an Argon atmosphere with varied pyrolysis temperatures and times.
The samples are designated in Table 1, and were processed individually, except for BFC-850-
CNT and PPR, which were processed during the same pyrolysis cycle.
3.2 Basalt Fiber Composite Pyrolysis
The pyrolysis temperatures were chosen arbitrarily to be 750°C and 850°C, and were
performed in an Argon atmosphere using a quartz tube furnace. The initial pyrolysis temperature
utilized was 750°C, and yielded a mild degree of pyrolytic carbon formation, but much of the
resin was not pyrolyzed. The second trial increased the temperature of the resin to 850°C, to fully
pyrolyze the composite, and a piece of pristine phenolic resin was placed in the furnace with the
composite to examine the effects of the temperature of the unreinforced resin. This trial yielded a
pyrolyzed basalt composite specimen with in-situ grown nanotubes, a matter which will be
16
further discussed later. The final 850°C trial was a repeat of the first 850°C trial, to test the
degree of CNT growth that the composites can be expected to experience.
3.2.1 Nomenclature of the Pyrolyzed Samples
The samples that were pyrolyzed under the methodology in the previous section were
given the designations in Table 1 to facilitate their use in subsequent sections. These
designations are based the presence or
Table 1: Sample Nomenclature and Process Data
Specimen Designation Pyrolysis
Temperature
(°C)
Pre-
Pyrolysis
Mass (g)
Post-
Pyrolysis
Mass (g)
Mass
Loss
(g)
Loss
(wt. %)
Basalt-
Phenolic
BFC-850-CNT 850 4.9955 4.5909 0.4046 8.10%
Basalt-
Phenolic
BFC-750 750 N/A N/A N/A N/A
Basalt-
Phenolic
BFC-850 850 11.528 10.5036 1.0244 8.89%
Pristine
Phenolic
PPR 7.8252 4.0167 3.8085 48.67%
3.3 VACNT
VACNTs were grown using a CVD process as described in Section 2.1. This process was
carried out using a Taurine/Ferrocene solution with 6 wt. % ferrocene. The VACNT forest was
grown on a SiO2 substrate inside a tube furnace using an argon atmosphere. The growth phase
was carried out at 750°C at an injection rate of 10mL/hour for a period of two hours. The tube
was flushed with argon and the argon was flowed continuously at a rate of 2L/min from the start
until the furnace temperature decreased to below 300°C following the growth phase to prevent
any oxidation of the CNTs.
17
Table 2: VACNT Growth Parameters
Nominal
Tube
Diameter
(mm)
Furnace Heated
Length
(mm)
Argon
Flow Rate
(L/min)
Precursor
Injection
Rate
(mL/hour)
Dwell
Time
(hours)
Typical
Precursor
Used per
Cycle (mL)
100 KMT
OTF-
1200X
440 2 10 2 20
50 Carbolite
MTF 12
400 1 5 5 10-15
The basic temperature parameters, seen in Figure 7, are followed by all the growth cycles
performed, with the hold temperature being determined as optimal from the literature review. [3]
The process was repeated using two different reactors of varying diameters, with the exact cycles
being listed in Table 2. The original process, shown in Figure 7, was designed for the larger
diameter tube furnace was scaled and modified through experimentation for the smaller furnace.
The furnace is configured with a syringe filled with the growth media, the hydrocarbon/ferrocene
mixture discussed earlier with a predetermined volume based on the desired parameters. In each
process, the mixture is preheated to vaporize the hydrocarbon source and sublimate the ferrocene
at a temperature of 140°C, in Figure 5 the injector assembly is seen on the right and on the left in
Figure 6. The argon gas is flowed in with the vaporized precursor, and flowed into the hot
section of the furnace, the hot section of the furnace is used to determine the amount of
precursor, as the CNT growth can only occur at temperatures high enough to crack the
hydrocarbon bonds.
18
Figure 5 VACNT Manufacturing Configuration (50mm tube)
Figure 6 VACNT Manufacturing Configuration (100mm tube)
This process yields an array of VACNTs on the surface of the SiO2 substrate, but also
yields a large amount of CNTs on the surface of the reactor (quartz tube) walls. These CNTs, as
with the VACNTs on the surface of the SiO2 substrate, always grow normal to the tube walls.
These radially aligned CNTs tend to form agglomerations when removed from the furnace
sidewalls that can be debulked for use as fillers or in nanopaper production. The excess amount
of CNTs must be removed from the walls every few runs or they can detach under their own
mass damage the VACNT sample.
19
Figure 7 VACNT Growth Cycle Chart in 100mm Furnace
The samples produced by CVD from both processes were taken and examined using
SEM and Raman spectroscopy. These techniques were used to confirm the alignment of the
VACNT array and the veracity of the nanotubes grown for the newer configuration with the
smaller furnace diameter. These samples were additionally used as a reference material for the
CNT/CNF growth observations made in the pyrolyzed basalt-phenolic composites.
0
100
200
300
400
500
600
700
800
0 50 100 150 200 250 300
Tem
per
atu
re (°C)
Time (minutes)
VACNT Growth Cycle
20
CHAPTER FOUR: FINDINGS
4.1 Effects of Temperature on the Pyrolysis of BFC
Figure 8 Photograph of basalt-phenolic composite and pristine phenolic resin before and after
pyrolysis
The samples were photographed prior to and following their pyrolysis to observe any
changes in the appearance and size. Figure 8 shows the appearance of all the basalt-phenolic
composite (BFC) samples and the appearance of the pristine phenolic resin (PPR) prior to
pyrolysis.
These samples were subjected to differing pyrolysis temperatures and rates, some
processes taking over 24 hours to complete. The basic pyrolysis results for these samples are
recorded in Table 3, with the sample designations that will be used to refer to them in this report.
Table 3: Mass loss of BFC-850 Specimens
Specimen Pre-Pyrolysis
Mass (g)
Post-Pyrolysis Mass (g) Mass Loss (g) Loss (wt. %)
BFC-850-CNT 4.9955 4.5909 0.4046 8.10%
BFC-850 11.528 10.5036 1.0244 8.89%
PPR 7.8252 4.0167 3.8085 48.67%
21
It should be noted that due to a procedural mistake, the mass data for BFC-750 is absent
due to a measurement mistake on the part of the researcher, where the masses were not properly
recorded during the process. The results seen in Figure 10 show the appearance of the PPR and
BFC-CNT-850 following pyrolysis, where it can be seen that the specimens have produced a
good carbon structures following the pyrolysis.
Figure 9 Photograph of the two halves of a piece of PPR before and after pyrolysis factors
The volumetric loss of the phenolic resin is visibly significant during pyrolysis, as seen in
Figure 9, and is also visible in the BFC samples, with the severity seeming to depend on several
namely temperature and the degree of nanotube growth in the composite panels. An unexpected
result arose from the first 850°C experiment, where one of the samples spontaneously grew
carbon nanotubes without the use of a gaseous precursor as has been shown to cause nanotube
growth in certain polymer-derived ceramics during pyrolysis. [23] The temperature effects can
be compared to the work performed in growing VACNT arrays and general CVD of CNTs,
where the temperature is vital for cracking the hydrocarbons and creating the CNT structure.
Given that the pyrolysis experiments were conducted above 650°C, which is typically the
minimum temperature used in CNT growth.
22
4.2 Morphology of the Pyrolyzed Composites
Figure 10 SEM micrographs of BFC-850 (a) and PPR (b) after pyrolysis
The discovery of in-situ grown carbon nanotubes was revealed when the BFC-850-CNT
sample was examined under a scanning electron microscope (Hitachi S-4800). The structure
revealed an abundance of what appeared to be carbon nanotubes grown from the surface of the
basalt fibers into the pyrolytic carbon, as seen in Figure 12. These nanotubes are not seen in the
same amount in the other samples, and do not appear at all in the PPR samples. Figure 10(a)
shows a nanotube grown on from the pyrolysis of the BFC-850 sample and Figure 10(b) shows
the absence of carbon nanotube growth from pyrolysis of the PPR sample. The diameter of the
structures grown was observed to be between roughly 70nm and 80 nm, as seen in Figure 11. In
both Figure 11 and Figure 12, it can be seen that the process left the surface of the basalt fiber is
left largely undamaged from the pyrolysis, which means that the strength of the fiber should be
largely retained following the growth process.
a b
23
Figure 11 SEM micrographs of BFC-850-CNT showing the diameter of a CNT/CNF grown by
pyrolysis
24
Figure 12 SEM micrograph of BFC-850-CNT samples
(a)
(b)
Carbon Matrix
Basalt Fiber
Basalt Fiber
Carbon Matrix
25
Figure 13 VACNT Arrays Produced in 100mm Reactor (Left) and 50mm Reactor (Right)
For comparison, VACNT arrays were prepared by CVD with the methodology discussed
earlier. These arrays were produced using only a ferrocene and a hydrocarbon source, which
simulates the environment generated during phenolic pyrolysis. These arrays, as seen in Figure
13, maintain a highly consistent surface quality and an average CNT length of 300-500 µm, as
seen in Figure 14. Compared to this, the length of the CNTs and CNFs observed in Figure 12(a)
are extremely short at roughly 10 µm, although there is a possibility that the CNTs are longer,
but were possibly broken during sample preparation. Another possibility can be seen in Figure
12(b), where they appear to be connected to both the basalt fiber and the carbon matrix created
by the pyrolysis process. This matrix appears to be a strong factor in limiting the CNT/CNF
growth, but this phenomenon is unique in that the heterogeneous composite now has structural
connections between the matrix and the reinforcing fiber.
26
This interface should be stronger than a simple traditional composite, and should possess
properties similar to the fuzzy fibers discussed earlier. The key difference being the method by
which the CNFs/CNTs were grown on the fiber– the pyrolysis grown CNTs were spontaneously
grown from the available catalyst particles located on the fiber surface, which are still chemically
a part of the fiber structure, as opposed to the coating method used to produce the fuzzy fibers,
where the CNTs, fibers, and matrix remain discrete components of the composite.
27
Figure 14 SEM Micrograph of VACNT Array in Figure 13
Figure 15 SEM Micrograph of VACNT Array at Higher Magnification
28
4.3 Verification of Ordered Carbon Nanostructures
4.3.1 Raman Spectroscopy
The nanotubes observed in the BFC-850-CNT sample were confirmed using Raman
spectroscopy, where the peaks associated with highly ordered carbon were observed very clearly,
as seen in Figure 16, although the quality of the nanotubes is not as high as is seen in pure carbon
nanotubes grown using standard growth processes such as chemical vapor deposition (CVD).
[49] The observation of the clear G, D, and G’ peaks coupled with the SEM micrographs
confirmed that the structured observed in the SEM observations of all the BFC samples are
indeed carbon nanotubes and carbon nanofibers. The relatively low G/D ratio observed in the
Raman spectrograph in Figure 16 do indicate that the purity and concentration of the nanotubes
is relatively low [50], and higher on the bottom of the sample than the top side of the sample.
This difference is still somewhat difficult to explain, but is likely linked to the ability of the
pyrolytic gases to escape from the top side of the specimen without being impinged upon since
the bottom is resting on a plate in the furnace. Regardless of the side, the presence of the 𝐺′ peak
strongly indicates the presence of the carbon nanotubes in the specimens.
29
Figure 16 Raman Spectrograph of BFC-850-CNT and Pyrolyzed PPR
To verify the presence of the nanotubes, the Raman spectra of a VACNT array produced
with the methodology described in Section 3.3 and shown in Figure 13(b); the results of this
examination are shown in Figure 17. The presence of the three peaks indicate the strong presence
of CNTs show that the specimen observed in Figure 16 does contain CNTs, or at least CNFs,
based on the spectrograph observed. [51] The spectra shown in Figure 17 does show that the
VACNT array does contain higher quality CNTs than those observed in the BFC-850-CNT
specimen, evidenced by the higher G/D ratio observed in the VACNT sample. The ratio of the
VACNT sample is still relatively low, with some CNTs exhibiting ratios in the 60s. The ratio
0 500 1000 1500 2000 2500 30000
50
100
150
200
250Laser Raman Spectroscopy
eV
BCC-850-CNT Top
BCC-850-CNT Bottom
PPR
D G
𝐺′
30
reduction in the VACNT sample might be a result of the laser being aligned with the longitudinal
axis of the CNTs, resulting in fewer potential counts for the G band, which is the in-plane mode
of the CNTs, due to scattering away from the collector, relatively short CNT length (this sample
had an expected length of 100-200 µm), or simply missing the CNT walls which would be
coupled with a lower density array. [52]
Figure 17 Raman Spectrograph of VACNT Sample made by CVD
The presence of the carbon nanotubes is expected to positively and strongly affect the
interlaminar properties of the composite, as the increased interfacial area is critical to the
0 500 1000 1500 2000 2500 3000 35000
1
2
3
4
5
6
7x 10
4 VACNT Raman Spectroscopy
Wavelength (cm-1)
Location 1
Location 2
Location 3
Si D G 𝐺′
31
properties of any composite material. The performance increases seen with “fuzzy fiber”
composites might be an indicator of what gains can be expected with the mechanical, electrical,
and thermal properties. [6, 53-55] These “fuzzy fibers” are often made by use of a coating on the
fibers that have been used as a substrate for CNT growth, which differs significantly from the
process used in this case, which relies on the fiber itself to serve as a growth substrate for the
CNTs and may possess a better bond to the fiber that would further improve the mechanical
properties.
4.3.2 EDX
To confirm the composition of the nanostructures observed, as well as the surface
composition of the fibers following pyrolysis and the assumed diffusion of particles that would
facilitate CNT and CNF growth specimens were examined using EDX (EDAX® TEAM™
EDS). The specimen chosen for analysis was the BFC-850 sample, which exhibited limited
CNF/CNT growth, but otherwise followed the same process parameters as the BFC-850-CNT
specimen. This sample was chosen for the presence of a small number of CNTs/CNFs, which
indicated favorable conditions for CNT growth, but an inadequate hydrocarbon source to
facilitate growth.
The results confirmed the presence of a predominately carbon matrix following pyrolysis
that would be expected from the decomposition of the phenolic resin, as seen in Figure 18 and in
Table 4. This confirms that the pyrolysis of the matrix is complete, and it has been converted into
pyrolytic carbon, which does not have a strong crystalline character, but does retain many of the
advantageous properties of carbon. The lack of a crystalline structure in pyrolytic carbon does
32
lower its overall thermal stability and mechanical strength, but still represents an improvement in
thermal performance over the pristine resin material.
Table 4: EDS results from the data shown in Figure 18 for the bottom of BFC-850
Element Wt% At%
CK 87.09 92.07
OK 06.12 04.86
SiK 06.79 03.07
Matrix Correction ZAF
Figure 18 EDS Results for Pyrolyzed Carbon Matrix from the Bottom Side of BFC-850
The low amounts of oxygen present, combined with the small presence of oxygen to
silicon indicate that most, if not all of the oxygen present was lost during pyrolysis, as was
predicted by previous research. [13] The presence of the silicon, and possibly some of the
remaining oxygen can be attributed to some diffusion from the basalt fiber into the matrix, given
33
the high concentration of SiO2 in the basalt fiber. The low amount of oxygen present indicates
that there is little oxidation on the surface of the fibers and little chance for oxidation to occur
within the pyrolytic carbon matrix.
Table 5: EDS results from the data shown in Figure 19 for the top of BFC-850
Element Wt% At%
CK 09.51 16.33
OK 36.33 46.83
FeL 07.89 02.91
NaK 03.51 03.15
MgK 01.64 01.39
AlK 09.66 07.38
SiK 26.31 19.32
KK 02.70 01.42
CaK 02.45 01.26
Matrix Correction ZAF
34
Figure 19 EDS Results for Pyrolyzed Carbon Matrix from the Top Side of BFC-850
The surface of the actual basalt fiber within the BFC-850 specimen was examined with
EDS to determine if the surface chemistry would be amenable to the growth of CNTs and CNFs
during the pyrolysis process. While the composition of basalt fibers is known to contain a
presence of iron that is comparable to the ratio in the ferrocene-based growth precursor used in
CVD, it needed to be demonstrated that enough of the iron was present at the surface to facilitate
CNT/CNF growth under the proper conditions. It can be seen in Figure 19 and Table 5 that the
surface of the basalt fiber contains an ample amount of iron to facilitate growth, but requires a
high amount of carbon from the hydrocarbon source to reach levels comparable to CVD
processing of roughly 0.75 at. % iron. [3] The presence of so much iron would also work toward
explaining the relatively small amount of CNT/CNF growth observed in this specimen, which
was not pyrolyzed with an extra resin piece that functions as an extra hydrocarbon source. Given
the proper temperature for hydrocarbon cracking and the high amount of atomic iron present,
there should be a high potential for growth on the surface of the pristine basalt fibers.
35
4.4 Thermal Analysis of the Pyrolyzed Composites
The samples were also tested using TGA to determine their thermal stability, and this was
tested using both the previous samples and a pristine BFC sample and a pristine phenolic sample
for comparison. The samples were conducted both in Argon and in Air (20% Oxygen 80%
Nitrogen) to explore the pure thermal decay and the behavior in an oxidative environment. The
results showed that despite the CNT presence, the BFC-750 outperformed the BFC-850-CNT in
both environments. This was an unexpected result, as CNTs typically exhibit excellent thermal
stability up to very high temperatures. [56, 57]
Figure 20 TGA results for BFC-750 (left) and BFC-850-CNT (right) in Argon
There is a possibility that some of the consistent differences in the mass loss between the
BFC-750 and BFC-850-CNT in Figure 20 and Figure 21 are due to the possible additional
growth of the CNTs in Figure 20 and oxidation leading to thermal breakdown of the CNTs in
Figure 21. A more plausible explanation is that the BFC-750 specimen had more mass to lose
and the similar behavior is simply offset by this factor. This second theory is more plausible
when examining the results of leaving specimens of each in air at a temperature of 550°C
36
overnight to fully oxidize and remove any remaining resin. The results of this experiment, shown
in QOWDJQ, would indicate that there is a higher volatile content remaining in the BFC-750
sample that would mean any mass loss at a similar rate would affect the BFC-750 sample less
than the BFC-850-CNT sample.
Table 6: Effects of prolonged high temperatures in air
Specimen Initial Mass (g) Final Mass (g) Loss (g) Loss (wt. %)
BC-CNT 0.3797 0.3414 0.0383 10.09%
BC750 0.64407 0.57206 0.072 11.18%
Figure 21 TGA results for BFC-750 (left) and BFC-850-CNT (right) in Air
The behaviors of the pristine components were also examined to gain insight into the
behaviors of the BFC specimens during the pyrolysis process. These results, seen in Figure 22,
show that there is an inherent stability in both the resin and the pristine composite, which is a
defining characteristic of phenolic resins. It can also be seen that there is an improvement in the
thermal stability of the composite over the resin that is visible below 400°C. There the thermal
stability is again improved above 600°C where is the mass loss slows down more that is seen in
37
the curve for the pristine resin. It is also within this range that CNT growth is expected to occur,
based on the behaviors of CVD grown CNT that have been well-documented as well as the
development of pyrolytic carbon species. [4, 25, 58] These decreases in the mass loss rate,
coupled with the very low rates seen in Figure 20 and Figure 21 indicate that the pyrolyzed BFC
composites have a greatly improved performance over the pristine sample.
(a) (b)
Figure 22 TGA results for pyrolysis of (a) pristine phenolic resin and (b) pristine BFC
Despite the apparently better thermal performance of the BFC-750, it should also be
noted that the mechanical, thermal, and electrical improvements possible in the BFC-850-CNT
might compensate for the slightly decreased thermal performance. The increased thermal
stability of the sample without CNTs/CNFs present might also be attributable to a growth
process occurring within the sample, since the surface chemistry can allow for the growth of
CNTs. The observed behavior of both samples at elevated temperatures open the possibility of
using this material in many high-temperature applications. One potential application is in the
high-creep, high-stress environment of jet and gas turbines, where the compressor section
reaches temperatures of 500°C or less.
38
CHAPTER FIVE: CONCLUSIONS
This thesis discusses theory behind CVD growth of CNTs in various forms, including
VACNTs, in situ within a matrix, and radially aligned fuzzy fibers that are grown on pristine
fibers by means of CVD. These related processes are included to understand the process that is
being experienced by the BFC-850-CNT sample when it experiences in situ CNT/CNF growth
without a vapor hydrocarbon precursor being externally introduced. The literature review also
demonstrates some of the advantages and processing techniques commonly used with CNTs to
improve composites. The research is completed with a review of the standard properties of basalt
reinforced polymer composites, and with a review of the behavior of phenolic resin during
pyrolysis. This behavior has been shown to generate methane and ethane, which are commonly
used carbon sources for CNT growth, as well as hydrogen, which is used as a promoter for CVD
growth of CNTs.
The results of the pyrolysis process were additionally explored for any variations in the
results, and to determine the role of temperature and phenolic content in the growth of
CNTs/CNFs by pyrolysis of the basalt-phenolic composites. The results of these trials were
determined by means of SEM observation of the pyrolyzed samples. It was determined that the
temperature was the dominant factor in determining if growth will occur, with growth being
observed regardless of the amount of resin present at 850°C. The CNTs/CNFs grown in the
BFC-850-CNT sample were confirmed to be organized carbon structures by a combination of
SEM observation and Raman spectroscopy. These CNTs/CNFs were compared to reference
samples of VACNTs grown by CVD to provide a baseline, as well as a standard for comparison
with Raman spectroscopy.
39
The confirmation of the CNT/CNF structure made with Raman spectroscopy and SEM
analysis led to analysis of the surface of the fibers on the sample that was processed at the same
temperature without the presence of excess resin. The results of the EDS analysis of the carbon
structures in the composite showed that the pyrolysis left a highly carbonaceous residue on the
fibers, whose surface chemistry was demonstrated to be similar to the parameters used for CVD
growth, with an appropriate amount of iron on the surface, which only necessitated a carbon
source in the form of the pyrolytic gases to grow CNTs/CNFs. The materials were finally
examined by TGA to explore their thermal stability. These results showed that the pyrolysis
improved the thermal stability and mass retention of the pyrolyzed composites substantially. The
results showed that there was little variation within the pyrolysis range, with the BFC-750
sample performing nearly as well as the BFC-850-CNT sample. This performance difference
was slightly less varied than expected, however, the increased interlaminar properties of the
BFC-850-CNT would still make it a preferred choice for its expected strength retention.
The materials in this work were manufactured using a relatively standard process to yield
a novel material. Preliminary examination of the samples has been performed that confirmed the
presence of CNTs/CNFs, which were confirmed to be presence using several analytical
techniques. The analysis and rough parameterization of the process have been completed, leaving
the macro scale testing to be performed in the future. This work should demonstrate any
mechanical enhancements attained by this processing technique. Additional future work should
also demonstrate the efficacy of this material in its ultimate intended use in thermal protection
systems, as well as other potential applications, such as turbine engine compressors.
40
APPENDIX A: MATLAB CODE FOR TGA ANALYSIS
41
Analysis.m
clc
clear all
close all
[ExpDat_20130716CB_PH] = TGA_DataImport('Test Data\Inert\20130716-
TGA','ExpDat_20130716CB&PH');
[ExpDat_20130716CB] = TGA_DataImport('Test Data\Inert\20130716-
TGA','ExpDat_20130716CB');
[ExpDat_20130716CB750] = TGA_DataImport('Test Data\Inert\20130716-
TGA','ExpDat_20130716CB750');
[ExpDat_20130716CB_CNT] = TGA_DataImport('Test Data\Inert\20130716-
TGA','ExpDat_20130716CB-CNT');
[ExpDat_20130716PPH] = TGA_DataImport('Test Data\Inert\20130716-
TGA','ExpDat_20130716PPH');
[ExpDat_20130719CB750] = TGA_DataImport('Test Data\Air\20130719-
TGA','ExpDat_20130719-CB750');
[ExpDat_20130719CB_CNT] = TGA_DataImport('Test Data\Air\20130719-
TGA','ExpDat_20130719-CB850CNT');
[ExpDat_20130719PyPH] = TGA_DataImport('Test Data\Air\20130719-
TGA','ExpDat_20130719-PPH850');
42
TGA_DataImport.m
function [TGA_Data_Matrix] = TGA_DataImport(directory,DatasetName)
% This data import function was written by Ricky McKee for use with the
CSV
% output of a Netzsch Libra TG 209 F1. This fuction is designed to take
% the CSV data from the control software and provide a working
analytical
% matrix in MATLAB as well as a Microsoft Excel(R) file to use for
% further analysis or data interpretation and publishing.
%
========================Documentation====================================
% dir is the directory that the data set is located in, must be a
% subfolder of the active directory of the file the function is being
% called from (e.g.: ..\Analysis.m\"Target Folder")
%
% Dataset is the file name using single quotes with appropriate
extension
% for a text file, in a column-based arrangement
% format double %Define long format to allow for full resolution
oldFolder = cd(directory); %Marking active folder to return to after
% moving to 'dir' where the data is stored
%-------------------------------------------------------------------------
-
% This section imports the data from the CSV file and extracts the data
% from it. The layout is based on the Netzsch column format of
Temperature,
% Time, and Mass Remaining, respectively.
RData = importdata([DatasetName,'.csv'],',',29); %Imports the Raw CSV Data
WData = RData.data; % extracts the data matrix from the raw CSV file
[imax,jmax] = size(WData); %Finds the size parameters for the working
% matrix
% ------------------------------------------------------------------------
-
% This section writes the outputs for Temperature and MassRemaining for
the
% function from the working data matrix WData
Temperature = WData(:,1);
43
MassRemaining = WData(:,3);
Time = WData(:,2);
% ------------------------------------------------------------------------
-
% This section calculates the mass loss rate using a first order,
% forward differential from the built-in MATLAB diff() function. It then
% writes the equation into the working data matrix WData and sends it out
% to the "Rate" output of the function
Rate = zeros(imax,1);
Rate(2:imax) = diff(MassRemaining)./diff(Time);
TGA_Data_Matrix = [Temperature,MassRemaining,Rate];
% ------------------------------------------------------------------------
-
% This section prepares the formatted data for export into an Microsoft
% Excel(R) file with the data arranged for easier access by others and
% publishing considerations
for i = 1:imax+1
if i==1
for j = 1:4
Labels = {'Time (min)','Temperature (C)','Mass Remaining
%','Mass Loss Rate (%/min)'};
EData(i,j) = Labels(j);
end
elseif i>1
ii=i-1;
EData(i,:) = {Time(ii), Temperature(ii),
MassRemaining(ii),Rate(ii)};
end
end
xlswrite([DatasetName,'_calc.xls'], EData);
% ------------------------------------------------------------------------
% This section creates two-axis plots of the TGA results with the Mass
% Remaining on the Left Axis and Mass Loss Rate on the right Axis then
% exports the plots to image files for publishing
h1 = figure;
[AX1,H1,H2] = plotyy(Temperature,MassRemaining,Temperature,Rate);
hold on
title(['TGA Results for ',DatasetName])
xlabel('Temperature ({\circ}Celsius)')
44
set(get(AX1(1),'Ylabel'),'String','Mass Remaining %')
set(get(AX1(2),'Ylabel'),'String','Mass Loss Rate %/minute')
set(H1,'LineWidth',2)
set(H2,'LineStyle',':','LineWidth',2)
hold off
print(h1, '-dtiff', [DatasetName, '_ResultPlot.tif']);
% ------------------------------------------------------------------------
cd(oldFolder) %return to working folder
45
APPENDIX B: MATLAB CODE FOR RAMAN SPECTROSCOPY PLOTS
46
Analysis.m
clc
close all
clear all
bfc_bot_1 = importdata('bfc-bottom-1.txt','\t');
bfc_bot_2 = importdata('bfc-bottom-2(with laser filter).txt','\t');
bfc_bot_3 = importdata('bfc-bottom-3(with laser filter).txt','\t');
bfc_top_1 = importdata('bfc-top-1.txt','\t');
bfc_top_2 = importdata('bfc-top-2(with laser filter).txt','\t');
bfc_top_3 = importdata('bfc-top-3(with laser filter).txt','\t');
pph = importdata('pph.txt','\t');
figure
plot(bfc_bot_1(:,1),bfc_bot_1(:,2),'g')
hold on
title('Unfiltered Laser Raman Spectroscopy')
plot(bfc_top_1(:,1),bfc_top_1(:,2),'r')
plot(pph(:,1),pph(:,2),'k')
hold off
figure
plot(bfc_bot_2(:,1),bfc_bot_2(:,2),'g')
hold on
title('Filtered Laser Raman Spectroscopy')
plot(bfc_top_2(:,1),bfc_top_2(:,2),'r')
plot(pph(:,1),pph(:,2),'k')
% plot(bfc_bot_3(:,1),bfc_bot_3(:,2),'g--')
% plot(bfc_top_3(:,1),bfc_top_3(:,2),'r--')
xlabel('eV')
hold off
figure
plot(bfc_bot_1(:,1),bfc_bot_1(:,2),'g')
hold on
title('Laser Raman Spectroscopy')
plot(bfc_top_1(:,1),bfc_top_1(:,2),'r')
plot(pph(:,1),pph(:,2),'k')
xlabel('eV')
L = legend('BCC-850-CNT Top','BCC-850-CNT Bottom','PPR');
set(L,'Interpreter','none')
hold off
47
APPENDIX C: EDAX MICROANALYSIS REPORT
48
49
50
51
52
53
APPENDIX D: BASALT FIBER DATA SHEETS
54
Characteristics of Basalt Fiber
Thermal
Working temperature -452 – 1292 ºF
Felting temperature 1922 ºF Thermal coefficient 0.03 – 0.038 w/m ºK
Phisical
Diameter of filament 7 – 15 µm
density 165 Lb/Cubic Foot
Elastic modular 100—110 Gpa
Tensile strength 600 – 696 ksi
Tensile strength @
68 ºF 100%
392 ºF 95%
752 ºF 82%
Chemical
Weight loss after 3h boiling
2N HC1 2.2%
2N NaOH 6%
H2O 0.2%
Comparison of basalt fiber with other fibers
Type of fiber Density
(Lb/cubic foot)
Tensile
(ksi)
Elastic
modular
(Gpa)
Elongation
(%)
Glass fiber
A style
C style
E style
S-2 style
153
153
162
155
480
480
500
700
69
69
76
97
4.8
4.8
4.76
5.15
Silica fiber 135 30 – 60
Quartz fiber 137 499
Carton fiber
large tow
medium tow
small tow
108
112
112
525
740
900
228
241
297
1.59
2.11
2.2
aromatic polyamide
fibre
Kevlar 29
Kevlar 149
90
92
525
505
41
186
3.6
1.5
Polypropylene fiber 57 39 – 94 38 15 – 18
Polyolefin fiber 74 72 – 132 75 11 – 20
Basalt fiber 165 600 -- 696 100 -- 110 3.3
55
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