Ride thhe h igh- temperature mlcro-

wave processing of materials is

becoming an industrial realitY

with the avaiiability of commer-

cial microwave furnaces and the successfui

efforts to develop process know-how by

several advanced technology development

groups worldwide. The impetus for this

development is the realization that high-

temperature microwave processing can be

a faster, greener and cheaper alternative to

conventional electric- and gas-based heat-

ing technologies. Microwave processing is

often preferred over conventional meth-

ods due to substantial economic advan-

tages and comparable or better properties

of the finished product.Historicaliy in the U.S., low-temper-

ature microwave processing has been

used extensively in appl icat ions such as

food and wood processing and drying.

However, to date there are few domestic

h igh- temperal ure com merc ia l microwave

applications. A primary challenge has been

the lack of sophisticated high-temperature

rnicrowave furnaces.This obstacle is being overcome through

the availability of new high-temperature

automated microwave furnaces, including

the la test cont inuous microwave pusher

system.- Wi th a footpr i r r t in the range o l

2 x 6 to 2 x 18 m, the sYstem's maximum

output power is 9-36 kW. The maximum

temperature is 1500'C, and processing

atmospheres can be air, nitrogen' inert

gases and mixtures. This industrial micro-

wave system offers advanced industrial

direct energy transfer technology and high

efficiency that enables ceramic and metal

parts to be processed at a fraction of the

time and cost of conventional kilns.

6nl n g 6 r#en, i ilipl r.,rr*rliil g {}lal'i'y

A major advantage of high-temperature

microwave systems is their "green' nature.

Microwave furnaces generally heat oniy

the objects to be processed, not the fur-

nace walls or atmosphere. Energy-efficient

microwave furnaces produce a substan-

tially smaller carbon footprint, less poliut-

ants, and lower operating and end-prod-

uct costs. In addi t ion, microwave Process-ing can involve up to 90olo shorter process-

ing times and a corresponding decrease of

up to 80o/o in energy consumption when

compared with conventional methods for

many commercial Products.Microwaving can also yield improved

product quality with finer grain size,

higher sintered density, increased corro-

sion resistance, and greater strength of

finished parts. These advantages can be

obtained with ceramics, a range of pow-

dered metals (such as titanium, tungsten,

molybdenum and steels), and "hardmet-

als" like tungsten carbide.

> High-temperaturemicrowave processingcan be a faster, greenerand cheaper alternativeto conventiona[ electric-and gas-based heatingtechnologies.

by K. Cherian,l M.KirkseY,lP.Hu,2 L. Hurtt,2 J. Cheng,3D. Agrawal3 and R. RoY3

With the realization of not only the

technical but also the substantial economic

advantages h igh- temperal .ure microwave

processing offers, the implementation of

this new processing method began mostly

in ceramics and related industries, includ-

ing advanced ceramic/carbide wear parts,

electro-ceramics and bio-ceramics. Subse-

quently, microwave processing has begun

to migrate to other industries' such as

powder metallurgy, waste remediation,

and mater ia ls symthesis/microwave chem-

istry applications.

. . 1 | : ! ' ; ' i . '

In Iune 2006, Pennsylvania State Univer-

sity hosted the National Academy. of Engi-

neering Regional Meeting on "Immediate

Energy Savings via Microwave Usage in

Maior Materials Technologies." Several

leading microwave research, development

and application groups from Asia' Europe

and the U.S. presented reports detail ing

the technical and economic advantages

and energy savings achieved through their

implementat ion of m icrowave processing

technologies in industrial applications.For t radi t ional ceramic s inter ing,

Japan's National Institute of Fusion Sci-

ence reported that microwave use enabled

the reduction of processing time from

8 to 2 hours, energy consumpt ion reduc-

tion from 335 to 63 KWh, and reduction

I1.Spher icTechnotog ies ,Phoen ix ,Ar iz .2 .Syno-ThermCo.L td ' ,Changsha,Hunan,PR Ch ina '

3. Microwave Processing & Engineering Center, Pennsytvania State University' Pa'

16 Sep tember 2008 L www.CERAMIC INDUSTRY 'COM

ofenergy cost from $14 to $7 per batch. In the case oflarge-partalumina (up to 60 cm diameter), the sintering time was reducedfrom 96 to 20 hours, energy consumption from 5000 to 484 k\,Vhand energy cost from $420 to $70 per batch.

Successful pilot-scale investigations have been completed in

fapan for using microwaves in steel production. The U.S. Depart-ment of Energy estimates that conversion of domestic steelmak-ing from conventional to microwave-assisted processing wouldsave up to 14 million tons of coal burned for energy, thus reduc-ing pollutant emissions by over 30 million tons of carbon mon-oxide and carbon dioxide annualh

Total processing timewas decreased from 1-500hours using corrventionalprocessing to around 50hours with a microwave-

assisted route.

Britain's Loughborough University investigated microwave-assisted hybrid processes for the sintering and chemical vaporinfiltration (CVI) of ceramic matrix composites (CMCs). Fora 13-mm-thick woven fabric preform, the total processing timewas decreased from 1500 hours using conventional processing toaround 50 hours with a microwave-assisted route.

Canada's Ontario Energy Agency estimated that if the ceramicindustry started using microwave instead of conventional processesfor various ceramic products, the industry would save 412 millionKWh per year, or the equivalent of one 350 MW coal-fired powerplant. When extrapolated to all applications in North America,annual energy savings could be measured in Gigawatt hours.

The Penn State Microwave Processing and Engineering Cen-ter cut the sintering cycle time for cemented carbides from 2.5hours to 15 minutes, producing parts with improved abrasionand corrosion resistance. This has now developed into a frrll-scalecommercial technolo gy.

Additional studies comparing high-temperature microwaveprocessing with traditional methods have been carried out for anumber of applications and are summarized below.

PTC Electronic Ceramic Heating Parts

ConventionalFootprint (square meters) 50Furnace hotding power (kW) 35Power consumption (kWh/10,000 pieces) 300Productivity (pieces/year) 24 mittionEnergy costs per 10,000 pieces (@ $0.1/kwh) $lOAnnuaI maintenance costs $3750Total savi n gs/ y ear (24 m illion pieces) : 548,000

MicrowaveI O

1,2100

24 milt ion$ro

$3750

Footprint (sq uare meters)Furnace input power (kW)Power consumption (kWh/ton of product)Productivity (tons/year)Energy costs per ton of product ($0.1/kwh)

Total savings/year (100 tons): S70,000

Footprint (sq uare meters)Furnace input power (kW)Power consumption (kWh/ton of product)Productivity (tons/year)Energy costs per ton of product ($0.1/kwh)

Total savings/year (200 tons): 596,000

120180

9000100

$9oo

100100

6000200

$ooo

4050

2000100

$200

4024

1200200

$120

Footprint (square meters) 200Furnace input power (kW) 550Productivity (tons/yeaO 2ooPower consumption (kWh/ton of product) 13,500Nitrogen gas consumption (m3/hr) 240Annual maintenance costs $150,000Energy costs per ton of product ($0.1/kWh) $fffOAnnual maintenance costs per ton of products $750Nitrogen gas use per ton of products $tOll

Total savings/year (200 tons): 5358,800

6080

1004500

60$37,500

$4sb$tts$sre

The debinding and sintering of positive temperature coeffi- AluminaGrindingSandscient (PTC) electronic ceramic heating parts was carried out in For alumina grinding sand processing with microwaves, thea continuous tunnel microwave furnace. Each PTC ceramic part required microwave sintering temperature was lower (by approx-weighed 7 g and the maximum temperature used was 1240'C. imately 100"C) and the hold time significantly shorter (by about*SPHERIC/SYNO-THERMTM computer-controlled microwave furnace with the AMPS pusher system,marketed in the U.S. by Spheric Technologies, Phoenix, Ariz..

The product quality was found to be as good as that in parts sin-tered by a conventional furnace.

For an annual production level of 24 million pieces of theproduct, lab/field trials demonstrated potential yearly savings ofapproximately $48,000 by using a microwave processing routerather than a conventional processing route. Additional compar-ative data is detailed in Thble 1.

Conventional Microwave

ConventionaI Microwave

Conventiona[ Microwave

CERAMIC INDUSTRY ) Seotember 2005 17

RIDE THE WAVE

ffi suNRocK cERAMtcsSpecia/ists in hish alumina kiln furniture

Saggers, setters, tile, rings/disks& pusher plates

-MW -Conv

Sunrock Geramlcs ComPanY, LLC2625 S. 21-st Ave. Broadview, lL 60155PH: 708.3 44.7 600, FX: 708.34 4.7 636

Time {Hrsl

Figure 1. Alumina gr inding sand processing.

-MW -Conv

1400

1200

1000

800

600

400

200

0

Tim€ {Hrs}

Figure 2. Ni-Zn ferrite parts sintering.

-MW -Cony

part

L8001600

O 1400

; 1200

E 1000

$ sooE U U U

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0

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o

o

Eo

€

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F

1600

14001200

1000800

600

40c

200

T ime lHrs ) : : i : .

Figure 3. Vanadium nitride synthesis and sintering.

one-sixth) in comparison to a conventional continuous sinter-

ing furnace for a similar product. The overall process time' from

room temperature to room temperature' was reduced by more

than660/o (see Figure l). Table 2lists additionalbenefits..)

Ni-Zn Ferrite PartsIt was found that the required microwave sintering temperature forr

Ni-Zn ferrite parts was lower (by about 100oC), and the hold time

was significantly shorter (by approximately one-third) in compari-

son to a conventional continuous sintering furnace for a similar

product. Figure 2 illustrates the 50% reduction in overall process

time that resulted with microwave processing. For an annual pro-

duction of 200 tons of Ni-Zn ferrite parts, lab/field trials demon-

strated that a potential savings of $96,000 could be achieved by uti-

lizing microwave vs. conventional processing (see Table 3).

4 to 6 week standard lead time

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Vanadium NitrideVanadium nitride (VN) synthesis andsintering through microwave process-ing was also investigated. The requiredmicrowave sintering temperature waslower (by - 50 'C) and the hold t imewas s igni f icant ly shor ter (about one-s ix th) compared to a convent ionalp rocess ( l i ke a tmosphe r i c p ressu recarbothermic reduction) for a similarproduct. Microwave processing reducedthe overall process time by at least 50olo(see Figure 3) , and potent ia l savingscould reach $358,000 per year for anannual production of 200 tons. Table 4lists additional details.

A Hot FutureHigh-temperature microwave process-ing can provide substantial economicand envi ronmental advantages overt radi t ional processes as a resul t o f acombination of several factors, includ-ing reduced processing t imes, lower

processing temperatures, reduced con-sumable costs in cer ta in cases, fewerp o l l u t a n t s , a n d e n e r g y s a v i n g s - i naddi t ion to improvements in prod-uct propert ies. Also, the appl icat ionof microwaves involves substantiallyreduced or near-zero product ion ofenvi ronmental ly harmful emiss ions,the reby mak ing th i s an env i ronmen-tally friendlier-or "greener"-tech-

nology as well.With a smaller physical footprint and

a substantially smaller carbon footprint,microwave furnaces offer lower operat-ing and end-product costs. Thus, micro-wave processing technology is a faster,greener and more energy-efficient alter-native for industry. @

For more information regarding microwayeprocessing contact Spheric Technologies, Inc.at 4708 E. Van Buren St., Phoenix AZ 85008;(602) 2 1 S-9292; e-mail info@SphericTbch.com;or visit www. SohericTbch. mm.

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CERAMIC INDUSTRY l September 2008 t9