Carbon nanotubes act as mini heat sinks

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News

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Carbon nanotubes act as mini heat sinks New research from the Uni\'-

technology world - 100 times

under the motors' intense heat.

crsiry of Pennsylvania. USA. incli-

as strong as steel and capable

'111(' tiny structures could also

erials science and engineering

cates thai carbon n:lJ10111bes, fiI:unClllS of pure carbon less than one (cll-lhollS;:\nchh the width

of far greater eleurical conductiviry than other carbon-based

be embedded in materials regu-

in Penn's Laboratory for Reselr-

larly called upon 10 withstand

ch on the Structure of Maner.

materials. Researchers have tht.: miniature t.:nvisioned

extreme heat, such :IS those that

"Our experiments show that

form the exterior panels of air-

even within bundks of n:UlO-

strands

cr.tft and rockets.

tubes. sound waves remain remarkably one
of a

hUll1:1Il

hair. mar Ix: the bCSl

heat-conducting malerial lllan has ever known. -n,e research

bulking

up

briltle

plastics and conducting curn:nt in ever-smaller elt.:ctrical cir-

says Fischer, a professor of mat-

could lead to their :lJ)plkation as mini heat sinks in a variety of

cuits, among dozens of 0I11er

lied by sound waves; in m:ueri-

"'111e sound \vaves don't f:m OUl

dc\'iccs from future generations

possibilities.

als that are optimal conduclOrs of heat. these waves mO\'e very

and dissipate because the bonds benveen n:UlOfubes in a

Carbon nanorubes' newfound

rapidly in an essentially one-

ability 10 conduct heat suggests

dimensional

bundle are so weak," Johnson adds. ~ln terms of bonding

of

computers

to

electric

motors.

-n,C findings suggest

Heat energy in nanotubes is car-

direction.

Drs.

that these

applications far beyond those

Fischer and Johnson fOllnd that

strength. you can think of nan-

exotic strands. already heralded for their unparalleled sm:ngth and unique ability to adopt the eleClriGu properties of either semiconductOrs or perfect melals. may someday also tind applicalions as miniature heal conduits in a host of devices and m:llcria.ls. A Penn team led by m:ueria.ls scientist Dr John E. Fischer. and physicist Dr AJ:ln T Johnson, offers these t1rsl details on carbon nanotubes' ther-

that call on t.heir strength and electrical cOll(luctiviry, says

sound waves bearing thermal

Otubes in a bundle almost like

energy tr.lvel slraiglu down individual carbon nanotubes at

dried spaghetti sliding freely back and tonh \vhen you shake

of physics at Penn. As comput-

roughly 10 ()()() m/sec, behav-

its box."

ing power has skyrockt.:ted, the

iour consistent with superior

Johnson, an assistant professor

infinitesimal heat gener.ned by

thermal conductivity. BUl they

Ironically, the same weak link·

each circuit on a microchip has

also unexpectedly determined

ages that make carbon nanotubes superior for heat condo uctance could deflate scientists'

proved a headache tor compul-

that even when carbon nano

er designers and manufacturers, who have few ways to dissi-

l"ubes are bundled together like individual filamems welded

earlier e:"pectation that bundles

pate the considerable heat thaI results from millions of circuits

together inlO the giant '--abIes

of them would provide tum-

that support suspension bridges - the bonds berween

v:lled mechanical strength. While the individual nanOl"ubes

operating in tandem. Next-gen-

mal propenies in a paper app-

eration computer designs might

the

nanotubes

are extremely strong, the weak

eating in the journal Science.

circumvent this problem with

remain so weak that heat essen-

judiciously placed carbon nano-

tially docs not transcend them.

bonding Fischer and Johnson obsel"'l"('d between nanot'ubes

For some time. scienlists have

rubes 10 direct heat away from

been imrigued by carbon nan-

sensitive circuitry.

olllbcs, pure carbon cylinders with walls just one alOm thick. First created a decade ago by

indi\'idual

would need to be overcome 10 "Scientists had predicted that

lr.lnslale this strength to a

Iwo-dimensional or tlm:e
thicku structure.

Similarly, carbon ll
ensional

of

arr.lys

carbon

nanol"ubes would permit the

For further infomrarion: Stne

l..capping graphite with lasers. Ihe structures have become

motors could allow for the

sollnd waves carrying heat to

Br.ldl. Univeristy of Pennsyl-

introduCtion of plastic parts

scarter in all directions. greatly

vania: tel: + 1-215-573-6604: e-

one of the marvels of the n:mo-

that

reducing thermal conductivity,"

mail: [email protected]

might

othenvise

melt

Aerospace approvals soon for natural fibre composites Approval from the US Federal and UK Ci\"il Avi:ttion Auth-

their way into interior components such as parcel shelves,

CAA approval by the end of

polyurethane has also resulted

this year (2000). According

in

orities (FAA/CAt\) is immincnt

headliners and interior lrim

t'O a spokesman

they were

Kal'us and its customers have

for the tor the llse of natur.t1

panels. Even

fibre composites in aerospace

fibre suppliers like DwellS

85% compliant at first pass. with Ihe vertical burn tcst as

developed techniques for recovering trim waste and

structures, says manufactun:r

Corning are exploring joint venture opportunities with

the main stumbling block. Since then. he claims, Kafus

converting it back into sheet stock, \vhich can then be

producers of natur.ll (planl

has developed an effective

remanufactured into compo-

derived) fibres so as to broad-

:l.I1swer.

Kafus Biocompositcs Inc.

leading glass

Natural fibre composites of thermoplastics and ther-

en their automotive compos-

commercial

nents using standard low pressure moulding equipment.

Most development work is

mosets have already been

ites repertoires. Kafus, \vhose

embr.lCed by car makers hav-

fibres are made from fast·

focused

ing

growing kenaf. a rdativc of

(PP)-based

conon, illlends that thiS trend

produced

will soon spread to aviation.

moulding or thermoforming

I1lCllt

extruded sheet, or co-mingled

at

\0

comply with recycling

requiremenls

that

more stringent

become

with

each

passing Yt.:ar. Fibres based on

products.

on

polypropylenc

As weU as their recyclability

compOSites

advalllage. natural fibres are

compression

said 10 offer stiffness enh:mc-

by

and

sound

lower cost

damping

and density

flax, jUle, hemp. SiS:ll and

The company tells Materials

mats of PP and plalll fibres.

lh:m conventional glass fibre

kenaf are, for instance, making

Today that it hopes for FAA/

Natural

technolob')'·

Materials Today

fibre

reinforced

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