High-temperature microwave processing is becoming an industrial reality due to commercial microwave furnaces and process development efforts. It can provide substantial economic advantages over conventional heating methods by reducing processing times, temperatures, costs and pollution. Studies show microwave processing decreases time and energy use for applications like ceramic sintering by 50-90% compared to conventional methods. Its smaller footprint and lower emissions also make it a greener technology.

1. Rideth
he high-temperaturemlcro-
waveprocessingof materialsis
becomingan industrial realitY
with theavaiiabilityof commer-
cialmicrowavefurnacesandthe successfui
effortsto developprocessknow-how by
severaladvancedtechnologydevelopment
groupsworldwide. The impetus for this
developmentis the realizationthat high-
temperaturemicrowaveprocessingcanbe
a faster,greenerand cheaperalternativeto
conventionalelectric-andgas-basedheat-
ingtechnologies.Microwaveprocessingis
often preferredover conventionalmeth-
ods due to substantialeconomicadvan-
tagesandcomparableor betterproperties
of thefinishedproduct.
Historicaliyin the U.S.,low-temper-
ature microwaveprocessinghas been
usedextensivelyin applicationssuchas
food and wood processingand drying.
However,to datetherearefew domestic
high-temperalurecommercialmicrowave
applications.A primarychallengehasbeen
thelackof sophisticatedhigh-temperature
rnicrowavefurnaces.
Thisobstacleisbeingovercomethrough
the availabilityof new high-temperature
automatedmicrowavefurnaces,including
the latestcontinuousmicrowavepusher
system.-With a footprirrtin therangeol
2 x 6 to 2 x 18m, the sYstem'smaximum
output poweris 9-36kW. The maximum
temperatureis 1500'C,and processing
atmospherescanbe air, nitrogen'inert
gasesandmixtures.Thisindustrialmicro-
wavesystemoffers advancedindustrial
directenergytransfertechnologyandhigh
efficiencythat enablesceramicandmetal
partsto be processedat a fraction of the
time andcostof conventionalkilns.
6nl ng 6 r#en, iilipl r.,rr*rliilg {}lal'i'y
A major advantageof high-temperature
microwavesystemsis their
"green'nature.
Microwavefurnacesgenerallyheat oniy
the objectsto be processed,not the fur-
nacewallsor atmosphere.Energy-efficient
microwavefurnacesproducea substan-
tiallysmallercarbonfootprint,lesspoliut-
ants,andlower operatingand end-prod-
uctcosts.In addition,microwaveProcess-
ing caninvolveup to 90oloshorterprocess-
ing timesanda correspondingdecreaseof
up to 80o/oin energyconsumptionwhen
comparedwith conventionalmethodsfor
manycommercialProducts.
Microwavingcanalsoyield improved
product quality with finer grain size,
higher sintereddensity,increasedcorro-
sion resistance,and greaterstrengthof
finishedparts.Theseadvantagescanbe
obtainedwith ceramics,a rangeof pow-
deredmetals(suchastitanium,tungsten,
molybdenumand steels),and
"hardmet-
als"liketungstencarbide.
> High-temperature
microwaveprocessing
canbea faster,greener
andcheaperalternative
to conventiona[electric-
andgas-basedheating
technologies.
by K.Cherian,lM.KirkseY,l
P.Hu,2L. Hurtt,2J.Cheng,3
D.Agrawal3andR.RoY3
With the realizationof not only the
technicalbut alsothesubstantialeconomic
advantageshigh-temperal.uremicrowave
processingoffers,the implementationof
thisnewprocessingmethodbeganmostly
in ceramicsand relatedindustries,includ-
ing advancedceramic/carbidewearparts,
electro-ceramicsandbio-ceramics.Subse-
quently,microwaveprocessinghasbegun
to migrateto other industries'such as
powder metallurgy,wasteremediation,
andmaterialssymthesis/microwavechem-
istryapplications.
. . 1 | : ! ' ; ' i . '
In Iune 2006,PennsylvaniaStateUniver-
sityhostedthe NationalAcademy.of Engi-
neeringRegionalMeetingon
"Immediate
EnergySavingsvia MicrowaveUsagein
Maior MaterialsTechnologies."Several
leadingmicrowaveresearch,development
andapplicationgroupsfrom Asia'Europe
and the U.S.presentedreportsdetailing
the technicaland economicadvantages
andenergysavingsachievedthrough their
implementationof microwaveprocessing
technologiesin industrialapplications.
For traditional ceramic sintering,
Japan'sNational Institute of FusionSci-
encereportedthat microwaveuseenabled
the reduction of processingtime from
8 to 2 hours,energyconsumptionreduc-
tion from 335to 63 KWh, and reduction
1.SphericTechnotogies,Phoenix,Ariz.2.Syno-ThermCo.Ltd',Changsha,Hunan,PR
China'
3. MicrowaveProcessing& EngineeringCenter,PennsytvaniaStateUniversity'Pa'
16 September 2008 L www.CERAMICINDUSTRY'COM

2. ofenergycostfrom $14to $7perbatch.In the caseoflarge-part
alumina (up to 60 cm diameter),the sinteringtime wasreduced
from 96to 20hours,energyconsumptionfrom 5000to 484k,Vh
and energycostfrom $420to $70perbatch.
Successfulpilot-scale investigationshavebeencompletedin
fapanfor usingmicrowavesin steelproduction.TheU.S.Depart-
ment of Energyestimatesthat conversionof domesticsteelmak-
ing from conventionalto microwave-assistedprocessingwould
saveup to 14million tons of coalburned for energy,thus reduc-
ing pollutant emissionsby over 30 million tons of carbonmon-
oxideand carbondioxideannualh
Totalprocessingtime
was decreasedfrom 1-500
hours using corrventional
processingto around50
hourswith a microwave-
assistedroute.
Britain's Loughborough University investigatedmicrowave-
assistedhybrid processesfor the sinteringand chemicalvapor
infiltration (CVI) of ceramicmatrix composites(CMCs). For
a 13-mm-thickwovenfabricpreform,the total processingtime
wasdecreasedfrom 1500hours usingconventionalprocessingto
around 50hourswith a microwave-assistedroute.
Canada'sOntario EnergyAgencyestimatedthat if the ceramic
industrystartedusingmicrowaveinsteadof conventionalprocesses
for variousceramicproducts,the industry would save412million
KWh per year,or the equivalentof one350MW coal-firedpower
plant. When extrapolatedto all applicationsin North America,
annualenergysavingscouldbemeasuredin Gigawatthours.
The PennStateMicrowaveProcessingand EngineeringCen-
ter cut the sinteringcycletime for cementedcarbidesfrom 2.5
hours to 15minutes,producingpartswith improvedabrasion
andcorrosionresistance.This hasnow developedinto a frrll-scale
commercialtechnology.
Additional studiescomparinghigh-temperaturemicrowave
processingwith traditional methodshavebeencarriedout for a
number of applicationsand aresummarizedbelow.
PTCElectronicCeramicHeatingParts
Conventional
Footprint(squaremeters) 50
Furnacehotdingpower(kW) 35
Powerconsumption(kWh/10,000pieces) 300
Productivity(pieces/year) 24mittion
Energycostsper10,000pieces(@$0.1/kwh) $lO
AnnuaImaintenancecosts $3750
Totalsavings/year(24million pieces): 548,000
Microwave
I O
1,2
100
24miltion
$ro
$3750
Footprint(squaremeters)
Furnaceinputpower(kW)
Powerconsumption(kWh/tonofproduct)
Productivity(tons/year)
Energycostspertonofproduct($0.1/kwh)
Totalsavings/year(100tons):S70,000
Footprint(squaremeters)
Furnaceinputpower(kW)
Powerconsumption(kWh/tonofproduct)
Productivity(tons/year)
Energycostspertonofproduct($0.1/kwh)
Totalsavings/year(200tons):596,000
120
180
9000
100
$9oo
100
100
6000
200
$ooo
40
50
2000
100
$200
40
24
1200
200
$120
Footprint(squaremeters) 200
Furnaceinputpower(kW) 550
Productivity(tons/yeaO 2oo
Powerconsumption(kWh/tonofproduct) 13,500
Nitrogengasconsumption(m3/hr) 240
Annualmaintenancecosts $150,000
Energycostspertonofproduct($0.1/kWh) $fffO
Annualmaintenancecostspertonofproducts$750
Nitrogengasusepertonofproducts $tOll
Totalsavings/year(200tons):5358,800
60
80
100
4500
60
$37,500
$4sb
$tts
$sre
The debinding and sintering of positivetemperaturecoeffi- AluminaGrindingSands
cient (PTC)electronicceramicheatingpartswascarriedout in For alumina grinding sand processingwith microwaves,the
a continuoustunnel microwavefurnace.EachPTC ceramicpart requiredmicrowavesinteringtemperaturewaslower (by approx-
weighed7 g andthe maximum temperatureusedwas 1240'C. imately100"C)andthehold time significantlyshorter(by about
*SPHERIC/SYNO-THERMTMcomputer-controlledmicrowavefurnacewiththeAMPSpushersystem,
marketedintheU.S.bySphericTechnologies,Phoenix,Ariz..
The product qualitywasfound to be asgoodasthat in partssin-
teredby a conventionalfurnace.
For an annualproduction levelof 24 million piecesof the
product,lab/field trials demonstratedpotentialyearlysavingsof
approximately$48,000by usinga microwaveprocessingroute
rather than a conventionalprocessingroute.Additional compar-
ativedatais detailedin Thble1.
Conventional Microwave
ConventionaI Microwave
Conventiona[ Microwave
CERAMIC INDUSTRY ) Seotember 2005 17

3. RIDETHEWAVE
ffi suNRocKcERAMtcs
Specia/istsin hishaluminakiln furniture
Saggers,setters,tile,rings/disks
& pusherplates
-MW -Conv
SunrockGeramlcsComPanY,LLC
2625 S. 21-stAve. Broadview,lL 60155
PH:708.344.7600, FX:708.344.7636
Time{Hrsl
Figure1. Aluminagrindingsand processing.
-MW -Conv
1400
1200
1000
800
600
400
200
0
Tim€{Hrs}
Figure2. Ni-Znferrite parts sintering.
-MW -Cony
part
L800
1600
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Figure3.Vanadiumnitridesynthesisandsintering.
one-sixth) in comparisonto a conventionalcontinuous sinter-
ing furnacefor a similar product.The overallprocesstime' from
room temperatureto room temperature'wasreducedby more
than660/o(seeFigurel). Table2lists additionalbenefits.
.)
Ni-Zn FerriteParts
It wasfound that the requiredmicrowavesinteringtemperatureforr
Ni-Zn ferritepartswaslower (by about100oC),andthe hold time
wassignificantlyshorter (by approximatelyone-third) in compari-
sonto a conventionalcontinuoussinteringfurnacefor a similar
product.Figure2 illustratesthe 50% reduction in overallprocess
time that resultedwith microwaveprocessing.For an annualpro-
duction of 200tonsof Ni-Zn ferriteparts,lab/field trials demon-
stratedthatapotentialsavingsof $96,000couldbeachievedby uti-
lizingmicrowavevs.conventionalprocessing(seeTable3).
4 to 6 weekstandardleadtime
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4. VanadiumNitride
Vanadium nitride (VN) synthesisand
sintering through microwaveprocess-
ing wasalsoinvestigated.The required
microwavesintering temperaturewas
lower (by - 50'C) and the hold time
was significantlyshorter (about one-
sixth) compared to a conventional
process(like atmosphericpressure
carbothermic reduction) for a similar
product. Microwaveprocessingreduced
the overallprocesstime by at least50olo
(seeFigure 3), and potential savings
could reach$358,000per year for an
annualproduction of 200tons.Table4
listsadditionaldetails.
A HotFuture
High-temperaturemicrowaveprocess-
ing can provide substantialeconomic
and environmental advantagesover
traditional processesas a result of a
combinationof severalfactors,includ-
ing reducedprocessingtimes, lower
processingtemperatures,reducedcon-
sumablecostsin certain cases,fewer
p o l l u t a n t s ,a n d e n e r g ys a v i n g s - i n
addition to improvements in prod-
uct properties.Also, the application
of microwavesinvolves substantially
reducedor near-zeroproduction of
environmentallyharmful emissions,
therebymakingthis an environmen-
tally friendlier-or "greener"-tech-
nology aswell.
With a smallerphysicalfootprint and
a substantiallysmallercarbonfootprint,
microwavefurnacesoffer lower operat-
ing and end-productcosts.Thus,micro-
waveprocessingtechnology is a faster,
greenerand more energy-efficientalter-
nativefor industry. @
For moreinformationregardingmicrowaye
processingcontactSphericTechnologies,Inc.
at 4708E.VanBurenSt.,PhoenixAZ 85008;
(602)21S-9292;e-mailinfo@SphericTbch.com;
or visitwww.SohericTbch.mm.
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TOKUYAMAAluminumNitride
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