Conference PaperPDF Available

REPLACEMENT OF COPPER WIRING WITH CARBON NANOTUBES IN AEROSPACE APPLICATIONS REPLACEMENT OF COPPER WIRING WITH CARBON NANOTUBES IN AEROSPACE APPLICATIONS

Authors:

Abstract and Figures

Replacement of copper wiring with carbon-based conductors such as carbon nanotube (CNT) materials could reduce the weight of wire conductors by up to 90%. CNT fiber conductors offer game-changing design possibilities over traditional copper-based electrical distribution systems. With respect to copper, CNT could provide improved reliability, higher current capacity and enhanced thermal stability. This paper provides a detailed review and technology gap analysis on CNT as a replacement for copper conductors. Low conductivity and a low technology readiness of CNT presently make its use challenging as a replacement for copper. There are a number of approaches that will be discussed which can improve CNT to a level where it could replace copper in certain aerospace wiring applications. INTRODUCTION A detailed review was conducted using technical papers and government-funded reports on metallic and semi-conductive CNT research and development. Metallic CNT has highly conductive electrons that move almost resistance free as opposed to a semiconducting CNT. Key CNT researchers from government, universities, and aerospace OEMs, as well as CNT materials companies, were also consulted. Analysis of the findings, show the most intrinsically conductive CNT fibers are currently within 4% of the conductivity of a nickel-plated ultra-high strength copper conductor at room temperature. While the mechanical break load strength would be similar to nickel-plated copper, CNT conductor would be expected to have a far higher flex life than copper, and its weight would be up to ten times less than a copper conductor. Compared to copper, CNT fibers would have a higher temperature capability, a lower resistance increase as the temperature is increased, higher strength and higher thermal conductivity. Highly conductive CNT fiber is near Technical Readiness Level TRL 3 1 , and the cost is estimated to be over 1000 times the cost of copper. As the economy of scale is developed, materials cost should be reduced, and improved manufacturing processes should further lower CNT costs dropping to within 10 times the cost of copper. Improved conductivity would also be expected.
Content may be subject to copyright.
REPLACEMENT OF COPPER WIRING
WITH CARBON NANOTUBES
IN AEROSPACE APPLICATIONS
9 Oct 2019
2019 AEROSPACE ELECTRICAL INTERCONNECT SYSTEMS SYMPOSIUM
San Deigo, CA
Blayne Lum
Aircraft Wiring Specialist
NAVAIR WIRING SYSTEMS 4.4.5.3
Patuxent River
240-808-0004
blayne.lum@navy.mil
George Slenski
Senior Engineer NAVAIR Consultant
Eagle Systems Inc.
937-241-5556
G.Slenski@ameritech.net
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
2 of 34
2019 AEROSPACE ELECTRICAL INTERCONNECT SYSTEMS SYMPOSIUM
REPLACEMENT OF COPPER WIRING WITH CARBON NANOTUBES
IN AEROSPACE APPLICATIONS
Blayne Lum
Aircraft Wiring Specialist
NAVAIR WIRING SYSTEMS 4.4.5.3
Patuxent River
240-808-0004
blayne.lum@navy.mil
George Slenski
Senior Engineer NAVAIR Consultant
Eagle Systems Inc.
937-241-5556
G.Slenski@ameritech.net
ABSTRACT
Replacement of copper wiring with carbon-based conductors such as carbon nanotube (CNT) materials could
reduce the weight of wire conductors by up to 90%. CNT fiber conductors offer game-changing design
possibilities over traditional copper-based electrical distribution systems. With respect to copper, CNT could
provide improved reliability, higher current capacity and enhanced thermal stability. This paper provides a
detailed review and technology gap analysis on CNT as a replacement for copper conductors. Low conductivity
and a low technology readiness of CNT presently make its use challenging as a replacement for copper. There are
a number of approaches that will be discussed which can improve CNT to a level where it could replace copper in
certain aerospace wiring applications.
INTRODUCTION
A detailed review was conducted using technical papers and government-funded reports on metallic and semi-
conductive CNT research and development. Metallic CNT has highly conductive electrons that move almost
resistance free as opposed to a semiconducting CNT. Key CNT researchers from government, universities, and
aerospace OEMs, as well as CNT materials companies, were also consulted. Analysis of the findings, show the
most intrinsically conductive CNT fibers are currently within 4% of the conductivity of a nickel-plated ultra-high
strength copper conductor at room temperature. While the mechanical break load strength would be similar to
nickel-plated copper, CNT conductor would be expected to have a far higher flex life than copper, and its weight
would be up to ten times less than a copper conductor. Compared to copper, CNT fibers would have a higher
temperature capability, a lower resistance increase as the temperature is increased, higher strength and higher
thermal conductivity. Highly conductive CNT fiber is near Technical Readiness Level TRL 3 1, and the cost is
estimated to be over 1000 times the cost of copper. As the economy of scale is developed, materials cost should be
reduced, and improved manufacturing processes should further lower CNT costs dropping to within 10 times the
cost of copper. Improved conductivity would also be expected.
1 TRL 3 research and development that includes analytical and experimental critical function and/or characteristic proof of concept
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
3 of 34
METHODOLOGY
The objectives of this technology gap analysis task are to (1) review the technology readiness level of highly
conductive grade Carbon Nano Tube (CNT) conductors determine if CNT is capable of directly replacing copper
in aircraft wiring shielding, and signal and power distribution applications (3) identify potential technology gaps
and what would be required to develop a CNT conductor that could replace copper. This study focused on
assessing the performance, technology, and cost required for CNT wire to achieve a Technical Readiness Level
(TRL) and Manufacturing Readiness Level (MRL) of 8 2. Methodology for identifying the performance,
technology and cost gaps included the following:
Review published technical papers, and government reports on metallic based CNT and CNT fibers
designed to replace copper conductors. This provided an assessment of CNT as a conductor with respect to
conductivity, mechanical properties, stability, availability, and cost.
Conduct technical Interchange Meetings (TIM) with stakeholders in Carbon Nanotube (CNT) technology.
This included CNT material suppliers, CNT cable manufacturers, wire and cable manufacturers, aerospace
OEMs, government agencies, and universities.
Explore solutions to address technology gaps.
A modern aircraft Electrical Wiring Interconnection System (EWIS) is primarily comprised of round wire
insulated multi-conductor copper alloy conductors and fiber optic cables. EWIS has become a critical aircraft
system on all-electric aircraft such as the F-35, modern commercial aircraft, and Unmanned Aircraft Vehicles
(UAVs). Today, EWIS provides power, command, and control of all vital systems. Aircraft such as the F-35
generate and distribute power and most control via copper conductor. While fiber optics has replaced copper in
many communication systems, there is still a large amount of EWIS that will continue to depend on electron as
opposed to photon conduction. Electron conduction through metals like copper is limited by the conductance of
the material which is dependent on the geometry of the conductor. The size of the conductors is based on the
required current capacity of the application and required mechanical integrity. Disadvantages of copper include its
high density (weight), increasing resistance as temperature increases and susceptibility to breakage as a result of
flexing and loading. The move to all-electric aircraft has significantly challenged designers to meet EWIS
distribution requirements while keeping aircraft within their weight budgets. Technologies and materials that can
reduce the weight of wiring will improve fuel economy, increase payload capability and increase flight time/
distance. A Boeing 787 has about 310 miles (500 kilometers) of wiring which is about 3% of the aircraft weight 3.
This equates to approximately 7,935 pounds of wiring4. Military transport aircraft have over 100 miles of wiring
and fighter aircraft over 20 miles of wiring. Modern aircraft (F-35) and Unmanned Aircraft Vehicles (UAVs) are
all electric aircraft with the electrical system powering and controlling flight surfaces, providing access to sensors
and location and powering and controlling all weapon systems. One method of reducing EWIS conductor weight
is to replace copper conductors with carbon-based materials such as CNT which can provide up to a 10:1 weight
reduction and also provide increased reliability by improved flex life and break load strength of the conductors.
BACKGROUND
As part of this study, the types of wiring and amount used on aerospace systems were identified using
government, Original Equipment Manufacturers (OEM’s), and wiring industry sources.
2 A TRL 8 is an actual system completed and qualified through test and demonstration.
3 War on wiring, web article, HENRY CANADAY, MAY 2017
4 http://www.modernairliners.com/boeing-787-dreamliner/boeing-787-dreamliner-specs (21)
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
4 of 34
Primary wires for power account for about 10% of the wiring on a military fighter aircraft. These conductors
typically range from 8 gauge to 20 gauge. Wire gauge sizes are based on American Wiring Gauge (AWG) sizes
where a smaller number corresponds to a larger diameter conductor. The majority of wiring on modern aircraft is
typically shielded to provide some level of protection against electronic interference and minimize damage from a
lightning strike. Currently, pure CNT conductors do not have sufficient conductivity to meet shielding and
lightning protection requirements. Therefore, CNT is an unlikely candidate for a 1:1 replacement. However,
metalizing CNT or adding copper strands to the conductor construction may make this a more practical and cost-
effective option.
Signal wires account for about 80% of wiring on a military aircraft and range from 22 to 26 gauge for military
aircraft and distribute critical and non-critical electrical signals for command and control. On an aircraft such as an
F-16, well over 80% of the signal wiring is silver plated copper 26-gauge conductor. Much of the primary wiring is
shielded with braided nickel-plated copper conductor which conforms to ANSI/NEMA WC 27500. A basic list of
primary wiring sizes for silver coated high strength copper alloy conductors and properties from AS29606 is given
in Table 1.
Table 1. Conductor properties from AS29606 TABLE 4C (High Strength Copper Alloy Conductors)
Wire
Size
Conductor Area
(circular mils)
Stranding
No. X AWG
of strands
Size of a
Strand
(inches)
Conductor
Diameter
(inches)
Ohms/1,00
0 Ft.
Breakin
g
Strength
lbs.
Elongatio
n
%
30
112
7X38
0.004
0.0124
5.2
6
28
175
7X36
0.005
0.0154
8.2
6
26
304
19X38
0.004
0.0204
14.2
6
24
475
19X36
0.005
0.0254
22.4
6
22
754
19X34
0.0063
0.0324
35.8
6
20
1216
19X32
0.008
0.0404
58.1
6
About 10% of signal wiring is double shielded controlled impedance cable. As the need for higher speed signal
propagation increases with higher processing speed, higher quantities of controlled impedance and coax cable is
expected. Many of these cables are defined in MIL-DTL-17 and may weigh over 1lbs./ft. with the shielding almost
50% of the weight (see Figure 4). High-speed data transfer cables include MIL-STD-1553, IEEE 1394
(FireWire™), twisted pair, Twinax, and Local Area Network (LAN) Cables (CAT 5 and 6).
The quantity of wiring used on aircraft is measured in miles; typical examples are below:
Large aircraft 150-200 miles; most wire shielded
Fighter Aircraft over 15-20 miles; most wire shielded
Spacecraft 5-10 miles; most wire shielded
Large Unmanned Aircraft Vehicles (UAVs) 5-20 miles; with double shielding
Aircraft Carrier Gerald Ford 190 miles of wiring; most shielded5
5 The USS Gerald R. Ford: By the Numbers, ABC News Mar 2, 2017
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
5 of 34
The Global Hawk UAV contains about 850 pounds of cable (1). Using a CNT shield in place of a metallic one
could reduce aircraft weight by 300 lbs. An all-CNT cable might save an additional 100 lbs. (1). A 300 lb. savings
would be significant for a glider based vehicle such as a Global Hawk. This can be challenging since all composite
aircraft such as the Global Hawk require highly conductive wiring to provide the majority of electrical shielding
and lightning strike protection. As already noted, most CNT replacement weight savings are concentrated in the
shield. Examples of the impact of replacing copper shield or primary conductor with a carbon based conductor on
large aircraft is shown in Figure 2. These calculations were based on replacing the copper with metalized aramid
fiber (Aracon) which is about 50% heavier than a CNT based conductor and has a thermal rating of 150˚C versus
a 200˚C rating for a CNT conductor. Military aircraft typically use double shielded cables to meet Electro-
Magnetic Pulse (EMP) and hostile electronic countermeasure protection requirements.
In the case of the B-1B, replacing one shield layer with a carbon based conductor could save over 11,000 lbs. As a
modern aircraft example, replacing one layer of copper shielding with a carbon based conductor on the New Air
Force tanker (a modified 767) could save almost 2,000 lbs.
B1B aircraft has over 150 miles of wiring similar to a transport with 80% signal level double shielded
wiring
o Replacing one shield layer with an Aracon (metalized Aramid) could provide 11,470 lbs.
weight savings (77%)
KC-46 Tanker (Boeing 767-200) has 117 miles of wiring with double shielding added to meet
EMP/EMI and other military requirements
o Replacement of one shield layer with Aracon conductor is estimated to save 1,900 lbs.
Aircraft electrical shielding effectiveness is dominated by its low DC resistance value below 100 MHz
frequencies. DC conductor resistance must be within copper conductor values to meet low frequency shielding
and lightning strike aircraft requirements. Above 100 MHz, CNT and metalized carbon based conductor shield
attenuation can exceed copper due to its tight braiding geometry. A comparison of CNT and copper shielded cable
shield effectiveness from Minnesota Defense/Minnesota Wire is shown in Figure 1.
Figure 1. Example of shield attenuation in a twisted pair CNT shielded controlled impedance cable which
exceeds the attenuation of copper above 100 Mhz. Shielding results for a CNT (red and gray lines) compared
with a commercial off the Shelf (COTS) copper cable (black line). (2)
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
6 of 34
Reductions in weight can lead to better fuel economy, increased payloads and increased flight time/ distance.
CNT has the potential for reducing wire/cable weight and improving wire reliability through longer flex life and
higher break loads compared to copper conductors. A 2011 study by The Center for Strategic and Budgetary
Assessment report: Sustaining Critical Sectors of the U.S. Defense Industrial Base, provides documented cost
savings associated with weight reduction in aircraft (Figure 2). As noted in Figure 3, an F-35 costs about $4,500
per pound in 2011 dollars as a total cost to procure and operate this would be $5,000 in 2018 dollars. A
procurement of 2,456 aircraft is planned, replacing a copper FireWire (IEEE 1394B cable) with CNT conductors
could result in a 75 lb. savings/aircraft for a total savings of $921 million. (See Case Study below)
Figure 2. Graph from 2011 study by The Center for Strategic and Budgetary Assessment report: Sustaining
Critical Sectors of the U.S. Defense Industrial Base.
CASE STUDY: CNT Wire Technology Insertion in a Fighter Aircraft
IEEE 1394B (FireWire™ Cable) is a high-speed communications cable with a 200 Mbit/s half-duplex data
rate. It is a double shielded cable with four 24 gauge primary wires. These cables are very stiff and have
experienced failures due to tight bend radiuses and flexing during flight. A representative fighter aircraft has an
estimated 3,500 Ft. of FireWire™ cable which at 37 lbs./1,000 Ft. would have a weight of 125 lbs. As part of
aircraft weight reduction program, over $1 million has been spent to save one pound of weight. In addition to
weight savings, aircraft availability and reliability could be increased with improved flexibility and bending
performance. A wire company building CNT cable has reported replacing one shield with CNT could result in a
30% weight savings. A cable was also built with a CNT primary conductor and one CNT and one copper shield
resulting in a 60% weight savings (2). While impressive, the CNT based cables did not meet all electrical
requirements due to the low conductivity of the CNT conductor. Potential weight savings of replacing one shield
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
7 of 34
layer with CNT could save 37.5 lbs. on each aircraft. Furthermore, if all copper conductors could be replaced
with CNT of sufficient conductivity the potential weights savings per aircraft would be 75 lbs. Controlled
impedance cables failures have resulted from excessive flexing and exceeding the cable’s allowable bend radius.
Replacement of copper with CNT also could improve cable flexibility and allow for a tighter cable bend radius.
Replacement of a failed cable requires opening and resealing a Low Observable (LO) surface which one a military
aircraft was reported to take several days; impacting aircraft readiness.
Several controlled impedance cables (1553, 1394, RG142, RG213, Coax, Twisted pair) have been built and
electrically tested and evaluated for weight savings using CNT based conductors (Table 2). Potential weight
savings for a typical controlled impedance cable (MIL-DTL-17) is shown in Figure 3. To meet electrical and
system requirements, some copper will most likely be needed in a CNT based cable to provide low frequency
shielding (below 100 MHz) and lightning strike protection. Conservatively, weight savings of 20-30% can be
expected for most cable designs with savings as high as 70% for some cable constructions. As noted earlier, most
weight savings are in the shield and even one layer of shield replacement can provide a 20% weight savings with
the inner core and one layer of shield copper. Cables based on MIL-STD-1553 have been built with CNT
shielding and primary conductors and been able to the cable electrical requirements. The CNT based cable was
reported to have provided a 50% weights savings or about 9 lbs. savings per 1,000 ft. of cable. Most 1553 cables
are limited to 10-15 ft. in length due to the high attenuation of the cable. Military aircraft OEM’s have evaluated
CNT based cables as a potential replacement of copper based cables. Low conductivity, variability in material,
high cost, termination concerns, lack of field experience, and inability to pass lightning strike protection
requirements are some of the reasons OEM’s have not installed CNT on aircraft. Metalized carbon fiber such as
Aracon™ and Amberstrand™ have been used on spacecraft and aircraft.
Figure 3. Example of weight savings (51%) when Copper is replaced with CNT fiber. (2)
A review of wiring technical literature (specifications, Government/OEM wiring requirements and material
from current suppliers of CNT materials) indicates, some of the best candidates for conversion to CNT conductors
are controlled impedance cables and shielded primary wiring such as twisted pairs as specified in NEMA
WCS27500™. A list of the common MIL-DTL-17 cables used by the military services for a one-year period are
shown below (Table 2). Included in the table is cable type, weight, and basic electrical requirements. The Defense
Logistics Agency (DLA) is the engineering and qualification authority for MIL-DTL-17. Over 1.2 million ft. of
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
8 of 34
M17 type cables are being procured for military uses. Some of these cables are used in ground and shipboard
applications. Cables in red have been built and tested using CNT conductors for shielding and primary conductors.
Two cables that have built and extensively evaluated with CNT shield and even CNT primary conductors are 1553
and FireWire™ (IEEE 1394B) data cables. The most procured cables in Table 2 are M17/183 and M17/184 cables
which are coaxial cables of 50 and 75 ohms respectively and could be made with CNT shielding.
Table 2. High volume procurement (descending order) of MIL-C-17 cables used on DoD systems showing
key electrical requirements, weight, quantity used, and cost provided by DLA as of Aug 2018.
NSN
PART No.
Cable
Weight
(lbs/100 ft)
Freq
Annual
Quantity
Sold (Ft)
Cost/ Ft
2017 Cost
6145012969856
M17/183-1
50Ω
Coaxial
3
50Mhz to 1Ghz
301,000
$0.57
$171,570
6145013832464
M17/184-1
75Ω
Coaxial
4.3
50Mhz to 1Ghz
250,959
$0.67
$168,143
6145009846262
M17/94
RG179
1
50Mhz to 3Ghz
185,175
$0.25
$46,294
6145005422773
M17/128
RG400
5
50Mhz to 12Ghz
184,100
$1
$184,100
6145009189494
M17/113
RG316
1.22
50Mhz to 3Ghz
166,318
$0.39
$64,864
6145005426092
M17/28
RG58
2.6
50Mhz to 1Ghz
157,264
$0.18
$28,308
6145006608054
M17/75
RG214
1.3
50Mhz to 11Ghz
120,500
$3.42
$412,110
6145008232544
M17/60
RG142
4.3
50Mhz to 8Ghz
105,000
$0.97
$101,850
6145012879251
M17/75
RG365
13.8
50Mhz to 11Ghz
23,000
$4.72
$108,560
6145013893427
M17/190-1
RG-214
15.4
50Mhz to 11Ghz
11,000
$4.45
$48,950
6145001499176
M17/127
RG393
16.5
50Mhz to 11Ghz
10,000
$4.10
$41,000
6145011347598
M17/139-1
RG180
1.94
50Mhz to 3Ghz
6,000
$0.79
$4,740
6145012327484
M17/176-2
1553
1.8
10Mhz
4,000
$0.78
$3,120
6145006608711
M17/74
RG213
1.11
50Mhz to 12hz
3,000
$0.59
$1,770
6145006610191
M17/29
RG59
3.5
50Mhz to 1Ghz
497
$212.79
$105,757
Total
1,527,816
$1,213,809
Cables in red have been constructed with CNT conductors resulting in a weight savings between 20-60% (3).
A modern aircraft fighter has approximately 15 miles of copper wiring. Replacing all copper shielding with
CNT would save approximately 1,180 lbs. of weight. Replacing all copper shielding and primary conductors with
CNT would save approximately 1,975 lbs. of weight. This clearly shows shield replacement has more impact on
weight savings than replacing the primary conductor. While weight savings would be the main driver to use a
CNT based cable, there are other advantages such as increased flex life and much higher tensile strength. A review
of Navy aircraft maintenance data with respect to wiring quantifies wire breakage is a common failure mode for a
fighter aircraft, Figure 4.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
9 of 34
Figure 4. Failure modes of EWIS components6. Wire breakage as a leading cause of wiring failures. (4)
High instances of conductor breakage are partially due to extensive use of 26-gauge conductor on aircraft
which can break in as little as 14 flex cycles. For this reason, the installation guide for aircraft wiring, SAE
AS50881™ prohibits use of wiring smaller than 24 gauge. Almost all military aircraft programs since the F-14
have obtained waivers to use 26 gauge conductors to save weight, this includes the F-18 and F-35. Breakage
results from flexing during maintenance or due to high vibration. A CNT based conductor would have textile
fiber qualities which can be flexed thousands of cycles and has far greater tensile strength than copper.
Typically, a carbon based conductor has well over ten times the flex endurance of a copper conductor as shown
in Figure 5.
Figure 5. Flex endurance of metalized aramid fiber compared to copper. At low loads a carbon
conductor has over 1,000 times the flex life of a copper conductor 7.
In addition to weight savings, a CNT based conductor should have a much higher reliability. Figure 6
illustrates the importance of wiring reliability and its impact on aircraft safety. Publicly available USAF
Accident Investigation Board (AIB) reports show for remotely piloted aircraft, 50% of the Class A accidents
6 Navy Safety Center Hazardous Incident Data 1980 1999 showing broken wires as a leading cause of electrically caused mishaps
Published in reference (4)
7 SAE publication AIR5464A
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
10 of 34
were attributed to an electrical failure; more than crew error as shown in Figure 7. Mishaps are identified as a
Class A accident when there is loss of life, loss of vehicle, or damages more than 2 million dollars. Over 40%
of these accidents were attributed to wiring. For manned aircraft, 8% of Class A accidents were attributed to
an electrical failure with 30% of these accidents attributed to wiring. The cost can be substantial. In 2012, a
USAF F-22 aircraft was destroyed due to a wiring failure. While the pilot ejected safely, loss of the aircraft
exceeded $150 million (left photo in Figure 7). OEMs report, stiffness of wiring as a major issue that causes
broken wires and chafing since the wiring is installed behind the avionics rack backplanes; compressing the
wires is shown in the right side photo in Figure 7. CNT flexibility would be a significant improvement, the
stiffness of copper conductor’s results in many pounds of force being applied to push avionic boxes into place.
Figure. 6. Wiring impacts aircraft safety based on analysis of data compiled from public released Air
Force Investigation Board (AIB) reports.
Figure 7. Crash site of an F-22 aircraft (left) that was attributed to a copper wire chafing against and
arcing to a hydraulic line (5). F-22 aircraft avionics bay (left) wiring behind avionics boxes required many
pounds of force to compress the copper wiring, so the boxes could be installed in the aircraft. Public released
Technologically advanced aircraft are completely dependent on the electrical wiring system to control and
command all aspects of flying the vehicle. New aircraft such as, the F-35 and UAV’s use electrical actuators and
flight computers to control and move all flight surfaces (see Figure 9). Since most modern aircraft are
aerodynamically unstable and require computer control to maintain stable flight, loss of electrical power for even a
few seconds may result in a mishap. Increased safety requirements imposed on wiring will result in more shielding
and weight since the shield protects the control wiring from interference from other systems or hostile emissions
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
11 of 34
designed to disrupt the flight controls. Advanced aircraft designs now under development, may need CNT based
conductors just to meet weight and size limitations. For these systems, electrical wiring will be a major system
responsible for flight controls, flight surface actuators, and all aspects of aircraft life support, navigation and
weapons management (Figure 8). Flight actuators and special mission loads are expected to increase power
requirements to the megawatt range; increasing wiring ampacity (current and thermal capacity). Wiring robustness
will be imperative for flight safety and all composite structure would allow embedded wiring.
Figure 8. New aircraft such as the F-35 and UAV’s use electrical actuators and flight computers to control
and move flight surfaces
In summary, the market drivers for aerospace wiring are primarily weight and volume reduction. CNT
based conductors would provide significant benefits even when cost may be much higher than copper based
conductors. One significant advantage that may not be readily apparent is use of revolutionary approaches for
conductive paths with the use of CNT conductors. CNT wiring could be imbedded in composite structure or used
in flat cables as opposed to round wire. Use of CNT based wiring will be determined by the OEMs since they
typically decide what type of wiring is used on an aerospace system.
As CNT fiber performance improves relative to copper conductors and manufacturing efficiencies lower
product costs, many new conductive path/wiring distribution applications will be possible. These multifunctional
conductive paths can greatly expand the use and exploit the benefits of CNT based conductors. CNT based
conductors have reportedly been used as shield and primary conductors in electrical cables on classified systems as
part of a 1553 data bus cable. As costs are reduced and conductivity further improves future applications could
include Coax, Ethernet and Fire Wirecables which are used for high speed data transfer. These are commonly
used cables and as noted in the DLA cable usage analysis (Table 2). Some other possible applications where
copper can be replaced by CNT conductor are given below:
CNT would offer benefits over copper in applications such as power transmission and generation cables,
windings in electric machines (generators, motors, transformers), communication cables, bus cables and
bus bars for converters. NASA is conducting CNT research for these types of applications (6)
Sonobuoys have long lengths of Kevlar and conductive metal wiring which could be replaced by CNT.
These devices are deployed extensively by naval aircraft. While a CNT cable has exceptional strength and
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
12 of 34
flex life the low conductivity of CNT increases the size of cable beyond an acceptable range and the CNT
cost makes it prohibitive at this time. Improving conductivity and lowering cost of the CNT fiber could
make it a viable alternative to the present cable system.
Flex cables are used extensively in avionic boxes and many ground applications. (Figure 9). CNT offers
superior flexibility and can be readily deposited directly on insulators such as Kapton. This could easily
be a several hundred million dollar market.
Figure 9. Flex circuits have copper metalized on Kapton film
Towed Decoys which use small copper wires with Kevlar strength members could be replaced with a CNT
conductor which would have the conductivity and strength to control decoys without the Kevlar fiber
(Figure 10)
Figure 10. Decoy towed behind aircraft using a conductive cable.
Deicing wiring is used to melt ice and contain copper conductors which could be replaced with CNT based
conductors. CNT based conductors would be far more flexible and could be embedded in composite
structure.
Flame resistant and thermocouple copper wires copper wires used in engine areas and other high
temperature applications require wiring to withstand temperatures in excess of 300°C for short durations.
CNT could replace the copper conductors by providing weight savings, increased flexibility, higher
ampacity, and a higher temperature capability.
CNT conductors could be embedded in composite structure providing protection to the conductors and
integrated into an aerospace structure some of the benefits include:
o Lightning strike protection, currently copper mesh based be able to be replaced with CNT if high
enough CNT conductivity is reached
o Distribution of electrical signal throughout the aerospace vehicle
o Up to 80% weight savings compared to copper
o Increased reliability with conductors protected in the composite structure
o Actively create a low observable surface by reduced radar cross-section through varying the
impedance of the outer composite surface
THE PROMISE OF CNT AND THEORY OF CONDUCTION
Copper exhibits one of the highest conductivities of all metals, with a conductivity of 58,000,000
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
13 of 34
Siemens/meter (58 MS/m) 8. While copper is an excellent conductor, a portion of the power or signal being carried
is lost as dissipated heat due to its finite resistivity. At the nanoscale, Single Wall Carbon NanoTubes (SWCNT’s)
can have over 17 times the electrical conductivity of copper, 7 times it’s thermal conductivity, and 1,000 times its
current density capacity (7) (8). A SWCNT type material is a single atom thick graphene sheet folded into a tube
which results in two-dimensional conduction. SWCNT fiber at the nanoscale, has a 30 times higher tensile
strength than steel (60 times higher than Copper) and is 10 times lighter than copper (7) (8). At this time, bulk
quantity SWCNT’s can reach lengths of about 1.5 microns with a diameter of 1.5 nm (9). The longest intact CNT
tube is about 2 cm; small diameter and an aspect ratio of over 1,000 of a CNT makes growth of long tubes
particularly difficult. CNT macro length yarns or fibers are created by aligning CNT’s end to end which creates
ohmic resistances between each tube reducing the conductivity of macro length CNT conductors (several centers to
over a meter). This appears to be the most significant factor in the low conductivity of the CNT yarn. At the
macro scale, the individual CNT fibers create internal ohmic resistances which lowers the aggregate conductivity.
Resultant conductivity, tensile strength and other properties will also be much lower than the reported values for
single continuous CNT. Most CNT fibers that are commercially available are multi-walled CNT which introduces
defects and further lowers conductivity and tensile strength compared to SWCNT fibers. Carbon atoms can form
different configurations due to its ability to connect with other atoms in four locations. Some common
configurations are graphene: a 1-D CNT a 2-D graphene sheet: referred to as a SWCNT and a 3-D structure: called
a buckminsterfullerene (Figure 11).
Figure 11. Representation of carbon atoms arranged as graphene, SWCNT and MWCNT (10).
Carbon nanotubes have a hollow cylindrical nanostructure, with typical diameters ranging from 0.1 to 1000
microns resulting in fibers with high aspect ratios. The lattice structure of SWCNT greatly influences its material
properties and the specific and discrete angles of the structure are referred to as chirality. Similarly, multi-walled
carbon nanotubes (MWCNT) are multiple layers of graphene being rolled into cylinders.
A metallic CNT is highly conductive as opposed to a semi-conductive CNT. The unique nanostructure and
chemical bonds of metallic CNT are theorized to impart novel electrical, mechanical, thermal, electrochemical, and
optical properties. With respect to electrical properties, CNT’s can behave like a metal or semiconductor
depending their designs; metallic CNT’s have armchair or Zigzag designs while most other designs result in
semiconducting CNT’s. The design depends on the way the graphene is wrapped into a cylinder such as on its edge
(zigzag) or on a corner (armchair). A single-walled nanotube’s structure is represented by a pair of indices (n,m)
called the chiral vector. The chiral vector is defined in Figure 12.
8 The International Annealed Copper Standard (IACS) established a standard for the conductivity of commercially pure annealed copper. At 20°C, annealed copper has a
resistivity of 1.7241x10-8 ohm-meter or 58 x106 Siemens/meter when expressed in terms of conductivity.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
14 of 34
Figure 12. A red solid point represents metallic nanotube and a black open circle represents semiconductor
nanotubes. The condition for the metallic nanotube is: 2n+m=3q (q: integer) (11).
In the case of a metal, electrons flow through the metal and are scattered and slowed by impurities and
defects which create an electrical resistance. The average length an electron can travel freely before a collision
that will change its momentum is called mean free path; a characteristic of a material. Electron conduction in
metallic CNT is quantized and the maximum electrical conductance is equal to that of a ballistic quantum channel.
When ballistically conducted, the electron mean free path is large and electrons travel along the CNT without
being scattered; resulting in a low resistance and very high conductivity the length of CNT. This unique property
imparts many of the impressive characteristics of metallic CNT’s. At present, the exact mechanism of ballistic
conduction in CNT is not known. For MWCNTs, it is speculated electrons travel in the spaces between graphene
layers and while there is the potential for very high conductance in these CNT’s, imperfections between the
multilayers of CNT create defects which lowers the potential conductivity of the CNT. Most lab created metallic
grade CNT is actually double and triple walled CNT’s which still have superior properties compared to MWCNT’s
which have many more layers and lead to lower conductivity (increased resistance to electronic movement). As
noted, SWCNT and MWCNT tubes can range in lengths of 1.5 nm to 1.5 mm.
Over the last 25 years, a variety of synthesis methods have been developed to create CNT’s, each having its
own advantages and disadvantages. For this discussion, synthesis techniques that are capable of creating more
than 1 g/day of CNT’s are discussed. These include arc discharge, laser oven, high pressure carbon monoxide
(HiPco), fluidized bed chemical vapor deposition (CVD), fixed bed catalyst CVD, catalytic gas flow CVD,
plasma-enhanced CVD, enhanced direct injection pyrolytic synthesis (eDIPS), and growth of vertically aligned
CNT carpets (or forests) on substrates. Each of these methods have been employed, and for a detailed
understanding of each technique (12). Table 3 from reference (12) shows the lack of high-quality CNT from USA
based companies and what are the key characteristics that result in a conductive CNT fiber which can be formed
into a macro length CNT conductor as a yarn or fiber.
One final area to discuss is the environmental impact on workers who come in contact with CNT fibers
through handling. Companies producing and fabricating products with CNT claim (with EPA certification) that
using a CNT yarn or macro sized fiber provides structural integrity, making them functionally and mechanically
different from a nanotube powder. For this reason, macro sized products don’t require personal protection during
handling.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
15 of 34
Table 3. Evaluation of CNT’s Produced by Various Manufacturers and Production Methods (12)
Bold and in red were semi-metallic CNT’s. Most sources are outside the USA.
CNT Manufacturer Production
Method
CNT
Type
Raman
Aspect
ratio
Purity
(%
carbon)
Aspect
Ratio
(L/D)
Purified by
Spun
into
a
fiber
Notes
Teijin Aramid BV
(AC 299)-1
eDIPS
DWCNT
>50
94
9610
Rice
no
insufficient material
Teijin Aramid BV
(AC 299)-2
eDIPS
DWCNT
>50
100
4400
Rice
yes
Meijo Nano Carbon
Co.-1
eDIPS
SWCNT
>50
88
6430
unpurified
no
not spinnable due to
impurities
Meijo Nano
Carbon Co.-2
eDIPS
SWCNT
43
99
4350
Rice
yes
Samsung Cheil-1
FC-CVD
DWCNT
>50
6310
Rice
no
not spinnable due to
impurities
Samsung Cheil-2
FC-CVD
DWCNT
>50
98
5150
Rice
yes
OCSiAl Group
(Tuball)-1
PE-CVD
SWCNT
>50
86
3100
Rice
no
not spinnable due to
impurities
OCSiAl Group
(Tuball)-2
PE-CVD
SWCNT
>50
97
1260
Rice
yes
purified by oxidizing for 48
h
OCSiAl Group
(Tuball)-3
PE-CVD
SWCNT
>50
97
2310
Rice
yes
purified by oxidizing for 24
h
Raymor Industries
plasma
torch CVD
SWCNT
>50
75
>2000
supplier
no
not spinnable due to
impurities
UniDym
fixed bed
CVD
DWCNT
>50
96
4010
supplier
yes
CCNI-1 (USA)
fixed bed
CVD
DWCNT
>50
94
2810
supplier
yes
CCNI-2 (USA)
fixed bed
CVD
DWCNT
>50
98
2600
supplier
yes
Linde Group
CVD
SWCNT
>50
90
3520
supplier
no
insufficient material amount
Canada Natl.
Research Council
laser oven
SWCNT
>50
80
2400
supplier
no
not spinnable due to
impurities
SWeNT-1
fluidized bed
CVD
SWCNT
30
97
4900
supplier
no
insufficient material
SWeNT-2 (USA)
fluidized
bed CVD
SWCNT
30
97
2800
supplier
yes
Rice University-1
(USA)
HiPco
SWCNT
30
80
1780
Rice
no
insufficient material
Rice University-2
(USA)
HiPco
SWCNT
11
98
440
Rice
yes
not spinnable due to
impurities
Nano-C
combustion
synthesis
SWCNT
30c
97
450
supplier
no
not spinnable due to
impurities
KH Chemicals
catalytic gas
flow CVD
SWCNT
20c
80
2000
unpurified
yes
unoptimized spinning
Nanocyl
catalytic gas
flow CVD
DWCNT
20
90
<200
supplier
no
not spinnable due to low
aspect ratio
TimesNano
CVD
SWCNT
25
95
N/A
supplier
no
not soluble
Thomas Swan
Elicarb
CVD
SWCNT
10
95
N/A
supplier
no
not soluble
Klean Carbon
CVD
SWCNT
10
90
N/A
supplier
no
not soluble
CNano
catalytic gas
flow CVD
MWCNT
1
95
N/A
supplier
no
not soluble
General Nano(USA)
Carpet growth
MWCNT
1
95
N/A
unpurified
no
not soluble
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
16 of 34
DWCNT Double Walled CNT, PE-plasma-enhanced, FC floating catalyst, CCNI continental carbon nanotechnologies, SWeNT South
West Nano Technologies
EXAMPLES OF CNT CHARACTERIZATION TECHNIQUES
Raman spectroscopy is one of the most popular techniques for characterizing the quality and ultimately the
conductivity and mechanical performance of metallic CNT’s. G mode (G from graphite). corresponds to planar
vibrations of carbon atoms and for SWCNT it is shifted to lower frequencies relative to graphite (1580 cm1). D
mode is present in graphitic materials and originates from structural defects. The ratio of the G/D modes is
commonly used to quantify the structural quality of carbon nanotubes (Figure 13). High-quality nanotubes have
this ratio significantly higher than 50. Another characterization technique is the Aspect Ratio (L/D) where L is the
length and D is the diameter with values well above 1,000 providing high conductivities and high strength are
provided in Figure 14.
Figure 13. Example of a Raman aspect ratio graph from Wikipedia. D mode is present in graphitic
materials and originates from structural defects. The ratio of the G/D modes is commonly used to quantify the
structural quality of carbon nanotubes. High-quality nanotubes have a ratio higher than 50.
Figure 14. CNT fiber tensile strength versus aspect ratio and CNT fiber conductivity versus aspect ratio for
fibers made from SWCNT’s and DWCNT’s from different manufacturers. Aspect Ratio (L/D), length (L)
and diameter (D) with values well above 1,000 providing high conductivities and high strength (12)
Transmission electron microscopy (TEM) and Scanning Electron Microscopy (SEM) can image CNT’s and
provide detailed morphological properties (length, width, shape) of individual CNT’s and TEM micrographs can
be used to distinguish between SWCNT’s and MWCNT’s (13). Thermogravimetric Analysis (TGA) can give
insight into the percentage of unstructured carbon, catalytic metals, and graphitic structured carbons (SWCNT and
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
17 of 34
MWCNT). The presence of unstructured carbon and other contaminates degrade CNT fiber properties and will
appear as the residual material in the TGA evaluation.
CNT MACRO PROPERTY DEVELOPMENT
Continued improvement of macro CNT fiber conductivity over the last ten years indicates research labs are
approaching within 20% the conductivity of alloyed copper used as a wire conductor as shown in Figure 15 (7).
One concern is that these are university reported values which may not be thermally stable and can be expected to
degrade over time or when exposed to temperatures above 100˚C. This is most likely due to the presence of
residual acids and other dopants which are removed from the CNT fiber during heating or aging. As an example, a
CNT fiber supplier has reported macro fiber conductivity as high as 3.8 MS/m yet the conductivity was reduced to
1.9 MS/m after a 24-hour exposure to 200˚C. Pure copper conductivity is reported as 58 MS/m and silver plated
high strength alloy copper (20 to 26 AWG) has a conductivity of 44 Ms/m and nickel-plated ultra-high strength
copper alloy has a conductivity of 32 Ms/m. The highest CNT conductivity found in published reports was in a
2018 paper by researchers from DexMat and Rice University see Figures 15 and 16 (9). The 2018 paper reported a
macro CNT fiber conductivity as high as 7.7 MS/m and strength as high as 3 GPa. The benefit of metallic CNT
over copper can be best demonstrated by comparing the specific electrical, thermal conductivity and strength
(property/density) (Table 4). Graphically this is plotted in Figure 17 of this report.
Figure 15. Chart showing Macroscale CNT’s still need additional improvements in conductivity (7) and (9)
7.7 MS/m Robert J. Headrick 2018
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
18 of 34
Figure 16. Macro fiber CNT mechanical and conductivities using various processes. Tensile strength versus
electrical conductivity for fibers from CNT arrays (black circles), CVD floating catalyst CNT fibers (blue
triangles), carbon fiber (green diamonds), wet spinning CNT fiber (yellow plus signs), chlorosulfonic acid (CSA)
solution-spun CNT fiber (work reported in (9) red squares, and hand-twisted CNT fibers (work reported in (9), red
stars. The graph shows the highest CNT conductivity is 7.7 MS/m which was created using a CSA processing
technique.
Table 4. Property data for metals and semi-metallic CNT (Metals, (14)and (15), CNT, (12) and (9).
Material
Electric
conductivity
(MS/m)
Thermal
conductivity
(W/mK)
Tensile
Strength
(MPa)
Density
(Kg/m3)
Electrical
Conductivity/
Density
(KSm
2
/Kg)
Thermal
Conductivity/
Density
(mWm
2
/Kg K)
Strength/Density
(MPa/(g/cc))
Semi-
metallic
CNT
7.7
700
2,400
1,270
6.06
551
1,890
Aluminum
36.9
237
724
2,700
13.67
88
268
Copper
58.7
386
332
8,900
6.60
43
37
Silver
64.5
419
140
10,500
6.14
40
13
Gold
45.5
301
120
19,400
2.34
16
6
The specific conductivities and strength are obtained by dividing the property by the materials density. Semi-
metallic CNT has a considerably higher specific thermal conductivity and strength compared to the metals. As
electrical conductivity is improved (above 18 MS/m), metallic CNT is expected to have a higher electrical specific
conductivity than metals.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
19 of 34
GOVERNMENT STAKEHOLDERS, COMPANIES, AND UNIVERSITIES CONDUCTING CNT RESEARCH.
The Navy is developing a carbon based conductor military specification since metalized carbon fibers using
aramids and other types of Liquid Crystal Polymers (LCPs) have been used on Navy aircraft with varying degrees
of success. Developing a specification with government, OEM and materials suppliers is expected to advance
carbon based conductor technologies (including CNT) since it will provide standardized testing and performance
requirements. The carbon based conductor specification MIL-DTL-32630, CONDUCTOR, ELECTRICAL,
STRANDED, UNINSULATED CARBON BASED CONDUCTIVE FIBER, GENERAL SPECIFICATION FOR,
was recently published and can be obtained from the website https://assist.dla.mil Benefits of the specification
include:
Specified electrical requirements will include stable DC and AC resistance over the thermal operating
range including the fusing current and current rating of the fiber as a 26 AWG conductor
Documented mechanical requirements including break strength, weight, and flex life and controlled
diameters comparable to copper conductor
Requires qualification by NAVAIR which will provide a consistent qualified product over an extended
manufacturing time and deliver a continuous conductor of at least 600 feet from a US based source
The following companies along with their material have been participating in the development of the specification:
Carlisle Interconnect Technologies- produces Aracon a commercially available metalized aramid fiber
primarily used as a shield and in limited conductor applications on spacecraft and aircraft
Syscom/Glenair produces AmberStrand, a commercially available metalized PBO fiber primarily used as
a shield in aerospace applications
Minnesota Wire produces CNT based wire cables using commercially available CNT fiber
Nanocomp produces Miralon™ a commercially available CNT MWCNT fiber
Stakeholders for Carbon Based Conductor Specification for Aerospace Wiring Applications:
NAVAIR sponsoring organization
DLA
NASA
Northrup Grumman
Minnesota Wire
Carlisle Interconnect Technologies
Syscom Advanced Materials
Nanocomp
DexMat
TE Connectivity
The types of carbon based conductors being addressed in the specification are below:
Type I - Metal Coated Para-Aramid Fiber. Each fiber shall be comprised of a bundle of individually Metal
Coated Aramid Fiber (MCAF) as shields or as primary conductor
Type II. Metal Clad Poly (p-phenylene-2, 6-benzobisoxazole (PBO) Fiber. Each fiber shall be comprised
of a bundle of individually Metal Clad PBO Fiber (MCPF) as a shield or as primary conductor.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
20 of 34
Type III - Metal Clad Liquid Crystal Polymer (LCP) Fiber. Each fiber shall be comprised of a bundle of
individually Metal Coated LCP Fiber (MCLF) as a shield or as primary conductor.
Type IV - Carbon Nanotube (CNT) Fiber made up of conductive multi-walled carbon nanotubes or single
walled carbon nanotubes. Fiber does not require coating, may be metalized as a shield or as primary
conductor.
The following tests are included in the specification:
Thermal Rating
Corrosion/Material Compatibility
Thermal Stability
Flammability SAE AS4373
Thermal Shock
Smoke Density
Tensile/Elongation
Smoke Toxicity
Flex Life
DC Resistance
Outgassing ASTM E 595
Fusing Current SAE AS4373
Fluid Resistance SAE AS4373
Termination/solderability
Fungus Resistance
Weight
Salt Fog
Water Absorption
Temperature coefficient of resistance
Solderability
The specification includes several types of carbon based conductors (including CNT) and detailed properties that
will be included in the specification using a 26-gauge conductor are shown in Table 5. Metalized carbon based
fibers are within 10% of nickel-plated ultra-high strength copper conductor.
Table 5. Detailed properties in Carbon based military specification compared with copper conductors.
Part Number
26 AWG
Conductor
Conductor
Diameter
(in)
(+/-
.001)
Max. DC
Resistance
(R)(Ω/
ft) at
20˚C
Conductance
(S/m)
Min.
Break
Load
(lbs.)
Elongation
(%)
Max. Linear
Density
(lbs./1,000ft)
Rated
Current
High
Temp.
(˚C)
Min. Flex
Life
(Cycles)
M 32630/1-
00
8 Metal
Clad Aramid
Fiber)
0.018
0.67
2,770,649.11
15
1
0.185
1.25A
150
500
M 32630/2-
001 Metal
Clad Aramid
Fiber)
0.017
0.47
3,601,843.7
30
1
0.185
1.25A
150
500
M
32630/3-
0006(CNT)
0.018
1.52
1,221,272.96
21.3
5
0.090
0.88A
200
500
Nickel-plated
Ultra High
Strength
Copper Alloy
0.018
0.0584
31,786,556.52
21.5
6
0.978
4.8A
200
200
Silver plated
high strength
copper alloy
0.0175
0.0448
43,837,646.34
14.2
6
4.8A
200
50
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
21 of 34
Government and Industry CNT Research
NASA has extensive CNT research since use of CNT in space systems offers significant weights savings
with space launch costs estimated by NASA of over $10,000/lbs. CNT has been used in a number of satellites as a
charge dissipative material given only semi-conductive levels are only needed to dissipate charge.
NASA is also developing motors for hybrid electric propulsion applications for aviation. Metallic grade carbon
nanotubes and composites containing CNT are being explored as a possible way to increase wire conductivity,
increase ampacity of the conductors and lower weight of motor windings.
Rice University has a long history of CNT research ever since Dr. Richard Smalley was a co-recipient of
the Nobel prize in chemistry for the discovery of carbon-based buckminsterfullerene in 1996. In 2005, the Richard
E. Smalley Institute for Nanoscale Science and Technology was established at Rice. Historically, Rice researchers
have published some of the highest CNT conductivity levels and continue to receive extensive funding from D0D
and other government agencies. In 2010, the Rice nanotechnology group published that CNT’s could be dissolved
into a suspension using chlorosulfonic acid (16). Chlorosulfonic acid (CSA) spontaneously dissolves CNT’s at
high concentrations without introducing defects or shortening CNT’s. This allowed for densifying and aligning the
CNT fibers and in 2013, led to drawing and spinning of CNT fibers using a process similar to how Kevlarfibers
are created (Figure 18). The Ashley plots 9 in Figure 17 show the potential benefits of semi-metallic CNT over
metals such as copper. Optimized semi-metallic CNT (has superior tensile strength and conductivity by density
over copper and other metals (plot B) and for electrical and thermal conductivity by density (plot C). The 2013
paper reported a number of conductivities and it appears the Ashly plots used a 5.3 MS/m conductivity. Rice has
continued to optimize spinning of semi-metallic CNT fiber with a 2018 paper reporting conductivity as high as 7.7
MS/m with a strength of 3 GPa (9). Rice researchers have shown that contact resistance between CNT’s is highly
dependent on the presence (absence) of surface impurities and functional groups and they have developed a
number of techniques and processes to optimize CNT performance in long lengths of fibers (several meters). CNT
fiber properties such as electrical conductivity continues to improve over time (Table 6). A number of the Rice
researchers formed a company, DexMat to commercially produce semi-metallic CNT fiber and conduct CNT
research. DexMat CNT materials are discussed below.
Figure 17. Multiple graphs showing CNT electrical, thermal and mechanical properties. Black denotes
literature values, blue denotes earlier wet-spun 0.5-mm CNT fibers, and red denotes fibers in the 2013 paper (14).
(A) Comparison of properties normalized to the highest value. (B) Ashby plots of specific tensile strength versus
specific electrical conductivity of metals and carbon fibers (CNT fibers from (14)(red circle). Note the red circle
CNT falls in a high-strength, high-conductivity region while metals define a high-conductivity, low-strength
9 An Ashby Plot displays two or more properties of many materials or classes of materials and are useful for comparing the ratio
between different properties.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
22 of 34
region. (C) Specific electrical conductivity versus specific thermal conductivity Ashby plot, showing the distinct
advantages of CNT (red dot).
Table 6. Rice 2018 paper (12) showing the continued improvement of macro CNT fiber properties.
The highest quality SWCNT’s are obtained from Japan.
DexMat is a company formed by Rice University researchers and is producing high quality CNT fibers for
government agencies and US based companies. This is accomplished by selecting a CNT source that has high
purity, CNT’s with high aspect ratios or low D/G ratios. DexMat CNT fiber primarily uses high quality DWCNT
and multi-wall CNT to create a continuous CNT fiber (Figure 18). They have produced CNT fiber as a braided
material which has been formed into a 26 gauge conductor and as a shield braid with a conductivity reported to be
3.8MS/m. A TRL 2 or 3 is estimated at this time for the DexMat CNT process which can produce CNT yarns and
tapes in lengths over 100 ft (Figure 19). DexMat has participated in the development of the NAVAIR carbon
based military specification and have claimed conductivity as high as 7 MS/m for a commercially available 1mm
(39 mil) diameter CNT conductor which is near the size of a 20-gauge conductor on their website. DexMat results
on RG316 Coax single shield shielding performance using CNT tape compared with silver plated copper shielding
are shown in Figure 20.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
23 of 34
Figure 18. DexMat CNT fiber process starts with DWCNTs and multiwalled CNTs which are dissolved in
Chlorosulfonic acid and spun into a fiber that is washed and dried to remove the acid. This is similar to the
method used create Kevlar fiber. (12)
Figure 19. CNT fiber can be made into a braid or tape to form into a shield at a conductivity as high as 7
MS/m for a 1mm (39 mil) diameter which is near the size of a 20-gauge conductor. (from the DexMat
company website Jun 2019)
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
24 of 34
Figure 20. DexMat results on RG316 Coax single shield shielding performance using CNT tape compared
with silver plated copper shielding (from the DexMat company website).
Minnesota Wire (MN Wire) is a US based specialty wire and cable supplier that has completed several
government and industry research programs related to CNT materials and wire conductors. MN Wire has
manufactured CNT based shielding and cables using Nanocomp, Rice, RIT, and DexMat CNT fibers for OEMs
and government agencies. They have demonstrated a TRL 610 CNT wire and cable manufacturing process using
Nanocomp MWCNT fiber. As reported, Nanocomp CNT fiber has a documented conductivity of 1.3 MS/m which
is only adequate to meet shielding requirements for selective controlled impedance cables. MN Wire has built and
tested several types of cables using CNT both as the shield and primary conductor including FireWire(IEEE
1394B), 1553 cables, shielded twist pair, and a variety of MIL-DTL-17 cables such as 50 ohm Coax (M17/183-1),
RG400, RG316, RG142 and RG939). All the M17 cables are on the DSCC list of top DoD procured cables (Table
2). Examples of production CNT conductor cables and estimated weight savings is given in Figure 3.
Considerable variability exists in CNT material which can be addressed by focusing on requirements that have
been documented in the recently released NAVAIR Military Specification for carbon based conductors (MIL-
DTL-32630). A 100 ohm CNT shielded twisted pair CNT primary conductor cable physical cross-section is
shown in Figure 21. Shield attenuation and insertion loss for the 100 ohm twisted pair cable in shown in Figures
22 and 23. Shield attenuation is superior to the copper cable while insertion is higher it is in an acceptable range
for this type of cable. Crimping and termination are challenging for a CNT shield, yet it can meet minimum
requirements (Figure 24). Thermally cycling CNT cables produced minimal change in resistance after 400 cycles.
While promising, OEMs haven’t moved forward with CNT conductors since there are technical issues such
as manufacturing variability, termination concerns, and passing lightning strike requirements. These obstacles can
be overcome with focused efforts and working with OEMs since they must be convinced CNT based cables will
meet design and field performance requirements. A final chart is offered in Figure 25 which displays how CNT
can replace copper as a conductor as the cost of CNT is reduced as a function of weight savings and indirect cost to
operate a system based on its cost per pound. At the time of this report, replacing copper with CNT conductors can
be economically viable for spacecraft and in selected cases, modern fighter aircraft. Increasing the TRL and MRL
of CNT will help move CNT from the laboratory into more the aircraft applications. There have been degraded
electrical properties in CNT conductor noted over time and temperature exposure and corrosion where connectors
10 TRL 6 is a system/subsystem model or prototype demonstration in a relevant environment.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
25 of 34
are attached to the CNT conductor. CNT fiber manufacturing involves the use of strong acids and typically some
residual acid remans in the CNT after processing. The acid contributes to conductivity and when the CNT is
heated above 100˚C the acid is off gassed; reducing conductivity. Off gassing is most likely dependent on the
degree of solvent washing and extended high temperature exposure and vacuum environments.
Figure 21. 28 gauge 100 ohm CNT shielded twisted pair cable with a CNT primary conductor and cable
cross-section. (2)
Figure 22. Shielding effectiveness of the 100 ohm twisted pair all CNT conductor cable.
CNT cable exceeds the shielding effectiveness of a copper based cable. (2)
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
26 of 34
Figure 23. Insertion loss for 100 ohm copper COTs and CNT based 100 ohm shielded twist pair cable. (2)
Figure 24. Crimping and pull force for 28 AWG CNT conductor exceeded specification requirements. (2)
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
27 of 34
Figure 25. Graph showing cost points of when CNT conductors could become economically viable for
various aerospace systems. (2)
TECHNOLOGY GAPS AND PATHWAYS FOR CNT CONDUCTOR TO REACH A TRL 8.
NANOMETAL-INTERCONNECTED CARBON CONDUCTORS (NICCS)
NICC based CNT conductors are created by deposition of metals including copper, titanium, silver or
palladium and palladium into the CNT in order to reduce intra resistances between intact CNT’s. According to
RIT published reports, depositing metal in the MWCNT matrix greatly improves conductivity with values reported
as high as 6 Ms/m the amount of copper can be between 15-70% weight percent (17). These CNT fibers are
typically called composites and with CNT volume fractional 45 vol % show densities of 5,000 Kg/m3 (vs Cu
density 8,900 Kg/m3), electrical conductivity has been measured within 50% of copper ( (18). Structurally
uniform composite wires have been created with conductivities 100 times the initial value of MWCNT’s. The
NICC fibers were more thermally stable compared to copper (temperature coefficient of resistivity 50% of Cu) and
exhibited a 28% higher current-carrying capacity than copper (18). The process for creating the CNT-CU
composite which has 10% of the electrical conductivity of copper is shown in Figure 26. The compromise is the
composite is only 2 times as light as copper compared to CNT fiber which can be ten times lighter than copper and
$10,000(s)/lbs
$1,000(s)/lbs
$100(s)/lb
2019
2020
2021
2022
2018
Space Applications
CubeSat
Military Fighters
Attack Helicopters
Large UAVs
Commercial Aviation
“CNT Wiring for Spacecraft
Applications”
This expectation is becoming closer to
reality with cost reduction of CNT
conductor
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
28 of 34
the CNT fibers have been no more than a meter in length. The copper infusion process has been accomplished
with Multiwall and single wall CNT’s.
Figure 26. Process used to create a CNT-Cu composite fiber with electrical conductivities within 10% of
copper; the resulting fiber is only 2 times lighter than copper (18).
EXTERNALLY METALIZING CNT FIBERS
Another approach for improving CNT conductivity is to electroplate or vapor deposit the carbon fiber with
a metal. This is already done commercially (TRL8) with metalized fibers such as Araconand AmberStrand™.
Conductivity levels that can be obtained by direct plating onto CNT is shown in Table 7. CNT wiring could reach
within 20% of copper conductivity by metalizing SWCNT fibers (TRL of 6-7). This conductivity level, with some
copper wiring added to the construction could possibly replace traditional copper shielding and meet and exceed
attenuation levels above 100 MHz and also meet low frequency requirements. Some laboratories have used both
infiltration and electroplating to metalize CNT fibers as shown in Figure 27 (19). Metalizing CNT allows the fiber
to reach within 50% of copper conductivity using process that are most likely at TRL 6. A summary of CNT and
plated CNT conductors compared to metalized carbon fiber (such as Aracon) and copper conductor properties
along with the estimated TRL is given in Table 8. Prior to metallization, removal of any CNT residual acid may be
needed. Most published papers have used copper to coat CNT fibers. Vapor deposition is another approach for
coating CNT yarn. It is accomplished using Chemical Vapor Deposition (CVD) or Laser Chemical Vapor
Deposition (LCVD). Chemical deposition may also result in a chemical reaction (functionalization of the CNT
surface) which could improve coating adhesion and overall electrical properties the coated CNT yarn. Future
research should consider silver or nickel as the conductive coating since both these metals are less reactive than
copper.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
29 of 34
Table 7. CNT wiring could reach within 20% of copper conductivity by metalizing SWCNT fibers using
TRL 8 technology.
26 AWG
Aracon Ni
Plated Kevlar
26 AWG
Aracon NI
Plating R
+Nanocomp
CNT R
26 AWG
Aracon Ni
Plating R
+DexMat CNT
R
26 AWG Nickel-
plated Copper
Ultra High Strength
Conductor
R1 Aracon Resistance (ohms)
0.67
0.67
R2 CNT Resistance (ohms)
1.6
0.5
Total Resistance assuming two
Resistances in Parallel (ohms)
0.67
0.47
0.29
0.0584
Conductor area (Ft
2
)
0.0000018
0.0000018
0.0000018
0.0000018
Conductance (S/m)
2,770,649.1
3,930,858.4
6,483,318.9
31,786,556.5
This conductivity level with some copper wiring added to the construction could replace traditional copper
shielding and meet and exceed attenuation levels above 100 MHz and also meet low frequency requirements.
Figure 27. Example infiltration and electroplating to metalize CNT fibers (19). Metalizing CNT allows the
fiber to reach within 50% of copper conductivity using a process most likely at TRL 6.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
30 of 34
Table 8. Property comparison of CNT conductors, metalized carbon conductors, metalized CNT, and copper conductors.
Part Number 26
AWG Conductor
Cond.
Dia.
(in)
(+/-
.001)
Cond. Area
(ft2
)
(Dia/2)2
Max. D
C Res.
(R) (Ω/f
t) at
20˚C
4
Cond. (S/ft)
(1/R)*A
Cond.
(S/m)
Min.
Break
Load
(lbs.)
Elong
(%)
Max.
Linear
Density
(lbs./1,000
ft)
Min.
Fusing
Time
(Sec.)@
Amperes
Rated
Current
(Amp.)
High
Temp.
(˚C)
Min.
Flex Life
(Cycles)
TRL
Level
M 32630/03-
0004 (CNT)
2
0.019
0.0000020
7.89
64,362
211,163
8.8
20
0.082
180@2.5A
0.6
200
500
7
M 32630/03-
0005 (CNT)
2
0.017
0.0000016
1.55
409,248
1,342,678
18.6
4
0.099
22@3.25A
0.84
200
7
M 32630/03-
0006 (CNT)2
0.018
0.0000018
1.52
372,244
1,221,273
21.3
5
0.090
22@3.25A
0.88
200
7
M 32630/01-003
Metal Clad
Aramid Fiber)
2
0.018
0.0000018
0.67
844,494
2,770,649
15
1
0.185
90@3.25A
1.25
150
500
9
TRL 3 CNT
Yarn
3
0.017
0.0000016
0.55
1,153,336
3,783,910
22.0
2
0.090
N/A
N/A
N/A
N/A
3
Plated TRL 3
CNT Fiber Best
Case (calculated)
0.018
0.0000018
0.47
1,203,853
3,949,648
3
Plated TRL 8
CNT Fiber
(Calculated)
0.038
0.0000079
0.49
259,091
30,000,000
21
5
0.86
6
Nickel-plated
Ultra High
Strength Copper
Alloy
1
0.018
0.0000018
0.0584
9,688,542
31,786,556
21.5
6
0.978
30@27A
4.8
260
200
9
silver plated
annealed copper
1
0.0175
0.0000017
0.0384
15,588,667
51,143,920
<14.2
6
200
9
silver plated high
strength copper
alloy
1
0.0175
0.0000017
0.0448
13,361,715
43,837,646
14.2
6
200
9
Bare copper
conductor
0.0159
1.37904E-06
0.0481
15,075,682
49,460,900
1From1 From AS29606, specification for stranded wire conductors,
2 Conductor values are from M-DTL-32630 and are based on Nanocomp CNT manufacturing by MN Wire commercially available materials at TRL
7 or TRL 8, 3 lab measured or calculated value needs to be independently verified
4 For TRL 7 and higher products the resistance value is based a guaranteed maximum resistance and increases no more than 15% after exposed to
1,000 hrs. at the maximum operating temperature
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
31 of 34
KEY FINDINGS
Carbon based fibers, including CNT based fibers, are currently available at TRL/MRL 8 as replacement
for copper conductors in high frequency aircraft shielding applications in which high DC conductivity is not
required. Currently, metalized non-conductive carbon fiber (such as Kevlar) has about 10% the conductivity of
nickel-plated copper and the TRL 8 CNT fiber is about 4% the conductivity of nickel-plated copper (see Table
11). With respect to a nickel-plated copper conductor, the cost of metalized carbon fiber is about 5 times its
cost while TRL 8 CNT would be over 5 to 10 times the cost of copper. Both carbon based insulations would
offer significant weight savings and enhanced flexibility over copper. CNT is 10 times lower in weight
compared to copper while metalized carbon conductor is about 5 times lower in weight than copper.
Presently, there are no commercial sources of CNT based conductors that can be a direct replacement
for most copper based aircraft wire and cable applications. As a drop-in replacement for copper conductor,
CNT is at a no more than a TRL/MRL 2 or 3.
A summary of conductivity, mechanical properties, and weight of copper and carbon based conductors
is given above in Table 8. This includes copper wiring used on aircraft, commercially available CNT
conductors, lab produced CNT conductors with and with metallization (theoretical calculation), and
commercially available metalized carbon based conductors. The table indicates metalized CNT conductivity
would most likely exceed commercially available metalized carbon fiber. Metalized CNT conductor would also
have a higher temperature capability, improved mechanical properties and provide more weight savings
compared to commercially available carbon fiber.
There are a number of techniques that may allow CNT conductors to approach copper conductivity levels
and provide significant weight savings and offer significant thermal conduction and a reliability improvement
over copper based wiring. The following approaches are offered for improving CNT conductivity and its
potential as conductors for shielding and primary wire aircraft applications.
1. Externally metalizing continuous lengths of CNT fibers using methods similar to what is used for
metalized carbon fiber such as the commercial product Aracon™.
2. Growing longer and higher quality SWCNT’s which can be aligned and formed into wire conductor
with less inter resistances between CNT tubes.
3. Infiltrating metals between the CNT tubes to reduce inter CNT tube resistances
4. Adding CNT into primarily metal conductors
One of the most serious challenges in developing CNT fibers as a replacement for copper for military use is
locating US based sources of metallic grade CNT. Another major challenge is scaling up high conductivity
CNT manufacturing processes so cost can be reduced, and the quantity and quality of the material can be
improved. The new carbon based conductor military specification recently published by NAVAIR will
significantly help government agencies and OEMs better define requirements for CNT based conductors. It will
also provide a guideline to CNT suppliers in developing CNT based products for aircraft applications.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
32 of 34
GAPS AND POTENTIAL SOLUTIONS
Low CNT conductivity, a low technology readiness and the high cost of CNT based conductors make it
unsuitable at this time as a direct replacement for most aircraft wire and cable applications. As a drop-in
replacement for copper conductor, CNT is at a TRL/MRL 2 or 3. Some of the gaps and challenges that need to
be addressed for CNT to replace copper shield or primary conductor on aircraft are as follows:
1. Low conductivity, must be at least 60% of copper (would be similar to aluminum)
2. High variability in material, need CNT qualified to a specification
3. High cost, must be no more than 10X of copper
4. Termination issues; must use standard processes and most likely include metal at the fiber interface
5. Lack of field experience using CNT based cables, CNT based cables need to be flown in non-critical
applications to gain confidence in the technology.
6. Inability to pass lightning strike requirements. Conductivity needs to be sufficient or augmented with
metal to pass lightning strike tests
7. Limited US Based CNT sources, CNT domestic CNT sources need to be developed
8. CNT conductivity stability and corrosive off gassing over time and temperature is a concern due to loss
of residual acid; remove residual acid through a baking out process and/or seal CNT to prevent off
gassing using metallization or a uniform coating.
9. Environmental impact of CNT fibers on health of workers handling the material
CONCLUSIONS
There are technology approaches such as metalizing/coating CNT and metal infiltration which could bring
CNT to within 10% to 50% of the conductivity of copper (now TRL 5 or 6). Examples of current and potential
CNT conductor properties that are achievable with one or two years of focused research is shown above in
Table 8. Applications would include controlled impedance cables, high impedance wiring applications,
shielded cables, high current battery contacts, motor windings, and in other applications that require copper
conductors.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
33 of 34
Author Biographies:
Mr. Slenski has a BS degree in Electrical Engineering from University of Florida
(1980) and a MS in Materials Engineering from University of Dayton (1995) and has
worked in the aerospace wiring area for over 39 years. He is retained as a subject
matter wiring expert by the Naval Air Systems Command Wiring System Branch
through Eagle Systems and the NASA Engineering and Safety Center Electrical
Power and Avionic Teams.
Mr. Lum is a certified rotorcraft pilot and a retired U.S. Air Force Electronic
Integrated Systems Inspector (Avionics). He has worked in the aircraft electrical
systems area over 25 years and is currently an aircraft wiring specialist and
Technical Area Expert with the Naval Air Systems Command Wiring Systems
Branch. Mr. Lum is currently attending Embry Riddle Aeronautical University.
Bibliography
1. Stefanie Harvey. Taking The Weight Out Of Data Bus Networks. SatMagazine. June 2014.
2. Tom Kukowski, Mike Matuszewski. s.l. : Minnesota Wire, 2016.
3. High-Performance Lightweight Coaxial Cable from Carbon Nanotube Conductors. Landi, Brian J. and Cress, Cory D. 4,
1103−1109, s.l. : American Chemical Society, 2012, Vols. ACS Appl. Mater. Interfaces 2012, .
4. National Science and Technology Council. Federal Programs for Wire System Safety. Washington DC : National
Science and Technology Council, 2000.
5. USAF. UNITED STATES AIR FORCE AIRCRAFT ACCIDENT INVESTIGATION Report F-22A, TIN 00-4013. TYNDALL AIR
FORCE BASE : USAF Public Released AIB Report, 2012.
6. Henry C. de Groh III. Highly Conductive Wire: Cu Carbon Nanotube. s.l. : NASA, 2017. NASA/TM2017-219480.
7. Harvey, Stefanie. CARBON NANOTUBE TECHNOLOGY PROMISES A REVOLUION IN CABLING. s.l. : TE AEROSPACE,
DEFENSE & MARINE /// WHITE PAPER, 2014.
8. A review on Carbon nano A review on Carbon nano Electronic Structure of Chiral Graphne Tubules. Das, Sudip. 3 March
2013, s.l. : International Journal of Emerging Technology and Advanced Engineering, 2013, Vol. Volume 3.
9. StructureProperty Relations in Carbon Nanotube Fibers by Downscaling Solution Processing. Robert J. Headrick,
Dmitri E. Tsentalovich. 1704482, s.l. : Advanced Materials. , 2018, Vol. 30.
NAVAIR Public Release 2019-647 DISTRIBUTION A. Approved for public release: distribution unlimited
34 of 34
10. Carbon Nanotubes for Interconnect Applications. Franz Kreupl, Andrew P. Graham. San Francisco, CA, USA : IEDM
Technical Digest. IEEE International Electron Devices Meeting, 2004.
11. Electronic structure of chiral graphene tubules. R. Saito, M. Fujita,. 2204, s.l. : Appl. Phys. Lett., 1992, Vol. 60.
12. Influence of Carbon Nanotube Characteristics on Macroscopic Fiber Properties. Dmitri E. Tsentalovich, Robert J.
Headrick, Francesca Mirri. s.l. : ACS Appl. Mater. Interfaces, 2017, Vols. 9, , p. 36189−36198.
13. Elijah J. Petersen, D. Xanat Flores-Cervantes, Thomas D. Bucheli. Quantification of Carbon Nanotubes in
Environmental Matrices: Current Capabilities, Case Studies, and Future Prospects. Environmental. Science Technology.
2016, 50, , 50, p. 4587−4605.
14. Natnael Behabtu, Colin C. Young, Dmitri E. Tsentalovich. Strong, Light, Multifunctional Fibers of Carbon Nanotubes
with Ultrahigh Conductivity. SCIENCE. 11 JANUARY 2013 , Vol. VOL 339.
15. Matweb.com. [Online]
16. A. Nicholas G. Parra-Vasquez, Natnael Behabtu,Micah J. Green. Spontaneous Dissolution of Ultralong Single- and
Multiwalled Carbon Nanotubes. ASC Nano. 2010, Vol. VOL. 4, ▪ NO. 7, pp. 39693978.
17. Andrew R. Bucossi, Cory D. Cress, Christopher M. Schauerman. Enhanced Electrical Conductivity in Extruded
Single-Wall Carbon Nanotube Wires from Modified Coagulation Parameters and Mechanical Processing. ACS Applied.
Materials. Interfaces. 2015, Vol. 7, p. 27299−27305.
18. Rajyashree Sundaram, Takeo Yamada. The importance of carbon nanotube wire density, structural uniformity,
and purity for fabricating homogeneous carbon nanotubecopper wire composites by copper electrodeposition.
Japanese Journal of Applied Physics. 2018, Vols. 57,, 04FP08.
19. . Electrical performance of lightweight CNT-Cu composite wires impacted by surface and internal Cu spatial
distribution. Sciencific Reports. 2017, Vol. 7, pp. 111.
20. Canaday, Henry. War on Wiring. Aerospace America. May 2017.
21. Boeing Commercial Airplanes. 787 Airplane Characteristics for Airport Planning. Seal Beach : Boeing Commercial
Airplanes, 2015.
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
Carbon nanotubes (CNTs) have numerous exciting potential applications and some that have reached commercialization. As such, quantitative measurements of CNTs in key environmental matrices (water, soil, sediment, and biological tissues) are needed to address concerns about their potential environmental and human health risks and to inform application development. However, standard methods for CNT quantification are not yet available. We systematically and critically review each component of the current methods for CNT quantification including CNT extraction approaches, potential biases, limits of detection, and potential for standardization. This review reveals that many of the techniques with the lowest detection limits require uncommon equipment or expertise, and thus, they are not frequently accessible. Additionally, changes to the CNTs (e.g., agglomeration) after environmental release and matrix effects can cause biases for many of the techniques, and biasing factors vary amongst the techniques. Five case studies are provided to illustrate how to use this information to inform responses to real-world scenarios such as monitoring potential CNT discharge into a river or ecotoxicity testing by a testing laboratory. Overall, substantial progress has been made in improving CNT quantification during the past ten years, but additional work is needed for standardization, development of extraction techniques from complex matrices, and multi-method comparisons of standard samples to reveal the comparability of techniques.
Article
Full-text available
The electronic structure for graphene monolayer tubules is predicted as a function of the diameter and helicity of the constituent graphene tubules. The calculated results show that approximately 1/3 of these tubules are a one‐dimensional metal which is stable against a Peierls distortion, and the other 2/3 are one‐dimensional semiconductors. The implications of these results are discussed.
Article
We present the influence of density, structural regularity, and purity of carbon nanotube wires (CNTWs) used as Cu electrodeposition templates on fabricating homogeneous high-electrical performance CNT–Cu wires lighter than Cu. We show that low-density CNTWs (<0.6 g/cm³ for multiwall nanotube wires) with regular macro- and microstructures and high CNT content (>90 wt %) are essential for making homogeneous CNT–Cu wires. These homogeneous CNT–Cu wires show a continuous Cu matrix with evenly mixed nanotubes of high volume fractions (~45 vol %) throughout the wire-length. Consequently, the composite wires show densities ~5.1 g/cm³ (33% lower than Cu) and electrical conductivities ~6.1 × 10⁴ S/cm (>100 × CNTW conductivity). However, composite wires from templates with higher densities or structural inconsistencies are non-uniform with discontinuous Cu matrices and poor CNT/Cu mixing. These non-uniform CNT–Cu wires show conductivities 2–6 times lower than the homogeneous composite wires.
Article
Single-wall carbon nanotubes (SWCNTs) synthesized via laser vaporization have been dispersed using chlorosulfonic acid (CSA) and extruded under varying coagulation conditions to fabricate multifunctional wires. The use of high purity SWCNT material based upon established purification methods yields wires with highly aligned nanoscale morphology and an over 4× improvement in electrical conductivity over as-produced SWCNT material. A series of eight liquids have been evaluated for use as a coagulant bath, and each coagulant yielded unique wire morphology based on its interaction with the SWCNT-CSA dispersion. In particular, dimethylacetamide as a coagulant bath is shown to fabricate highly uniform SWCNT wires, and acetone coagulant baths result in the highest specific conductivity and tensile strength. A 2× improvement in specific conductivity has been measured for SWCNT wires following tensioning induced both during extrusion via increased coagulant bath depth and during solvent evaporation via mechanical strain, over that of as-extruded wires from shallower coagulant baths. Overall, combination of the optimized coagulation parameters has yielded acid-doped wires with the highest reported room temperature electrical conductivities to date of 4.1-5.0 MS/m and tensile strengths of 210-250 MPa. Such improvements in bulk electrical conductivity can impact the adoption of metal-free, multifunctional SWCNT materials for advanced cabling architectures.
(1995) and has worked in the aerospace wiring area for over 39 years. He is retained as a subject matter wiring expert by the Naval Air Systems Command Wiring System Branch through Eagle Systems and the
  • Mr
Mr. Slenski has a BS degree in Electrical Engineering from University of Florida (1980) and a MS in Materials Engineering from University of Dayton (1995) and has worked in the aerospace wiring area for over 39 years. He is retained as a subject matter wiring expert by the Naval Air Systems Command Wiring System Branch through Eagle Systems and the NASA Engineering and Safety Center Electrical Power and Avionic Teams.
Taking The Weight Out Of Data Bus Networks. SatMagazine
  • Stefanie Harvey
Stefanie Harvey. Taking The Weight Out Of Data Bus Networks. SatMagazine. June 2014.
Lightweight Coaxial Cable from Carbon Nanotube Conductors. Landi, Brian J. and Cress, Cory D. 4, 1103−1109, s.l
  • High-Performance
High-Performance Lightweight Coaxial Cable from Carbon Nanotube Conductors. Landi, Brian J. and Cress, Cory D. 4, 1103−1109, s.l. : American Chemical Society, 2012, Vols. ACS Appl. Mater. Interfaces 2012,.
Highly Conductive Wire: Cu Carbon Nanotube. s.l
  • C Henry
  • Iii De Groh
Henry C. de Groh III. Highly Conductive Wire: Cu Carbon Nanotube. s.l. : NASA, 2017. NASA/TM-2017-219480.
Structure-Property Relations in Carbon Nanotube Fibers by Downscaling Solution Processing
Structure-Property Relations in Carbon Nanotube Fibers by Downscaling Solution Processing. Robert J. Headrick, Dmitri E. Tsentalovich. 1704482, s.l. : Advanced Materials., 2018, Vol. 30.
  • Andrew P Graham
Carbon Nanotubes for Interconnect Applications. Franz Kreupl, Andrew P. Graham. San Francisco, CA, USA : IEDM Technical Digest. IEEE International Electron Devices Meeting, 2004.