NEW LOW-COST MANUFACTIJRING METHODS TO PRODUCE SILICONCARBIDE (SIC) FOR LIGHTWEIGHT ARMOR SYSTEMS

James Campbell, Jeny LaSalvia, Walter Roy and Ernest ChinU.S. Army Research Laboratory

Aberdeen Proving Ground, MD. 21005-5069

Richard Palicka and Daniel AshkinBAE Systems-Advanced Ceramics Division

Vista, CA 92081

ABSTRACT

Ceramic-based armors, commonly used in personnelprotection, are actively being considered for platformvehicles due to their potential to dramatically reducesystem weight. Silicon carbide (SiC) has been shown tohold considerable promise as the ceramic component inan armor system, and comes in several grades withdiffering costs. Hot pressed silicon carbide has beenshown to provide excellent ballistic properties, but ismanufactured at high cost and in limited volumes througha batch process. The U.S. Army Research Laboratory(ARL), through the ManTech Armor program, hasdeveloped a program with BAE-Advanced CeramicsDivision, Vista, CA to dramatically reduce cost andincrease production volume of hot pressed silicon carbide.BAE has built a prototype manufacturing system andrecently conducted a one-ton manufacturing run todemonstrate cost and viability of the system. Thematerial will undergo ballistic evaluation to determine ifthe ceramic produced using these new manufacturingtechniques is equivalent to conventionally processedmaterial.

This paper provides an overview of ceramic hot pressing,changes made through the ManTech program, cost goalsand current status of the program.

1. INTRODUCTION

The ARL, through the Army's Armor ManTech program,is working with BAE-Advanced Ceramics Division toredesign their hot pressing process to dramatically reducecost to a level comparable to pressureless sintered SiC.Changes at all stages of the manufacturing process wereintroduced, including a semi-continuous furnace thatmanufactures near net-shape tiles and rapid computer­controlled fmal grinding machines. Thcse changes willnot only reduce cost, but will allow for increased

production volumes to the levels anticipated for futurearmor vehicle programs, smce the ManTechmanufacturing cell can be considered a simple unit cellthat can be easily duplicated. The goal of this effort is toproduce a SiC-N material with the same materialproperties and ballistic performance as that which isconventionally produced, but at a much lower cost in anautomated semi-continuous process.

2. BACKGROUND

Ceramic-based armor, with either a metallic or polymer­matrix fiber composite backing, has been demonstrated tobe a highly mass efficient armor design for commonground vehicle threats. Of the typical armor ceramics,aluminum oxide (AI,O,), boron carbide (B,C), siliconcarbide (SiC), titanium diboride (TiB,), SiC has beenshown to be the highest performing ceramic using currentarmor designs. These types of ceramics can bemanufactured by several different methods, including hotpressing, pressureless sintering and reaction bonding. Asis often the case, the fabrication route that is tbe highestcost (bot pressing) produces ceramics with the highestlevel of ballistic performance, and BAE Systems­Advanced Ceramic's SiC-N ceramic is considered to bethe industry benchmark. Historically, hot pressingrequires batch processing, consumable graphite toolingand the machining of densified billets into the desired tileshape, all of which contribute to the high cost and lowproduction volumes of hot pressed ceramics.

3. TRADITIONAL CERAMIC HOT PRESSING

Ceramics are commonly densified through sintering withthe concurrent application of pressure, and this process isknown as hot pressing. The application of pressurepromotes the closing of pores and allows for highdensities to be achieved. on-oxide ceramics, such assilicon carbide, silicon nitride and boron carbide are, arecommonly hot pressed. Other ceramics can be densifiedto full density without the application of pressure, and this

Report Documentation Page Form ApprovedOMB No. 0704-0188

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering andmaintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, ArlingtonVA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if itdoes not display a currently valid OMB control number.

1. REPORT DATE DEC 2008

2. REPORT TYPE N/A

3. DATES COVERED -

4. TITLE AND SUBTITLE New Low-Cost Manufacturing Methods To Produce Silicon Carbide (Sic)For Lightweight Armor Systems

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) US Army Research Laboratory, Aberdeen Proving Ground, MD 21005

8. PERFORMING ORGANIZATIONREPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)

11. SPONSOR/MONITOR’S REPORT NUMBER(S)

12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited

13. SUPPLEMENTARY NOTES See also ADM002187. Proceedings of the Army Science Conference (26th) Held in Orlando, Florida on 1-4December 2008, The original document contains color images.

14. ABSTRACT

15. SUBJECT TERMS

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT

UU

18. NUMBEROF PAGES

7

19a. NAME OFRESPONSIBLE PERSON

a. REPORT unclassified

b. ABSTRACT unclassified

c. THIS PAGE unclassified

Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

is known as pressureless sintering. Oxide ceramics arecommonly manufactured through this method, but somenon-oxide ceramics are doped with sintering aids topromote densification.

Sintering is a solid-state process whereby powdercompacts are densified at temperatures sufficient to allowfor diffusion but below the temperature for the material tomelt. Therefore, atoms of material are transported toareas of porosity and pores are transferred to the outside,and this requires sufficient time and temperature for thisall of this to occur. There are two main types ofdiffusion: (I) lattice diffusion and (2) surface diffusion.For surface diffusion, the driving force is the reduction ofsurface area of the particles and necks are formedbetween two contacting particles. Once the neck isformed and the driving force is reduced, the process slowsresulting in very little densification, which is not desired.For lattice diffusion, material is transported through theceramic particles and densification results. Since thecations and anions of each species have different diffusionrates for each type of diffusion, sintering is a verycomplex and scientifically rigorous process. Manyceramic systems can be densified without concurrentpressure (pressureless sintering) with the addition ofsintering aids, which affect the diffusion constants.Hexoloy, S1. Gobain, Niagara Falls, NY is a commercialsilicon carbide produced by pressureless sintering. Basedon the testing of a number of silicon carbide types, the hotpressed silicon carbides demonstrate superiorperformance.

Traditional hot pressing is a batch process, where the"green" (undensified) powder compacts are formedthrough some method with the ceramic powder andloaded into a hot pressing die. The die and powder arebrought up to the sintering temperature and a load isapplied to the die. Due to the very high temperaturerequired for sintering, graphite tooLing and specializedfurnaces are required. Many of these non-oxide ceramicsrequire sintering temperatures in excess of 20000C.Figure I shows a typical laboratory hot press with afurnace chamber, hydraulic system to apply load, and aload frame. As the size of the ceramic part increases, theload required for desired pressure becomes quite large toprovide the adequate pressure. This requires the hotpressing equipment to be very large, especially the loadframe, thus making hot pressing process typicallyassociated with small production volumes. Productionvolumes dictate that large billets be made instead ofindividual armor tiles, which are later sectioned into tiles.To increase throughput, commercial vendors typicallystack a number of plates together with spacers and applypressure to the entire stack. Another limitation to hotpressing is that the parts that can be produced are ratherlimited in shape, basically flat plates or plates with limited

curvature, such as a Small Arms Protective Insert (SAP!)plate.

After hot pressing, the stack of ceramic plates is allowedto cool to room temperature. Since the armor tiles sizestend to be rather small, the ceramic is typically hotpressed in large plates and tiles are machined from thesebillets. For companies that produce ceramics by sintering,they prefer to cut them in the "green" or undensified state,since the machining of ceramics tends to be expensiveand time consuming.

Figure 1. Laboratory hot press consisting of a furnacechamber and hydraulic system to apply load

With common armor ceramics being some of the hardestmaterials known, machining requires diamond tooling andslow grinding rates and cutting steps. The billets arepressed to be somewhat over in thickness and a diamondsurface grinder is used to grind the ceramic billet to exactthickness. The surface grinder usually makes a pass andthen the diamond wheel is indexed downward by severalthnusandths of on inch. Figure 2 shows a typical surfacegrinder. The machine has diamond wheel that is fixed inthe X and Y direction. The stage holding the billet ismoved back and forth and indexes left and right to coverthe whole billet is several passes. After the diamondwheel sweeps the entire billet, it is indexed downward inthe z direction and the process is repeated. With theseslow removal rates, it takes considerable time to grind thebillet down to a desired thickness. Grinding can alsointroduce damage and cracks onto the surface as well ascause sub-surface damage.

Figure 2. Typical surface grinder with a diamond wheel

After the billet is ground to the correct thickness, thebillet is sectioned to armor tiles of the desired shape andsize. Surface grinding takes considerable time and effortto produce ceramic tiles; therefore, machining is asignificant portion of the total cost of producing tile. Forsquare tiles, the entire billet can be sectioned into tile,thereby giving a high yield. But for hexagonal tiles,rectangles of ceramic are sectioned from the billet and thecomers are then removed to produce a hexagonal shape.Therefore, a significant portion of billet is not utilized,which results in a 50% price premium for these tiles. Onebenefit of diamond machining is that the dimensionaltolerances are very good and superior when compared totiles produced by pressureless sintering. Depending onthe ceramic dimensional tiles required for future vehicleprograms. tiles may need to be diamond machinedregardless of how they are manufactured. Tile gapspacing is critical when a large array of tiles is puttogether, and this can quickly become a problem whentiles don't have a high degree of dimensional uniformity.This is more severe when tiles are hexagonal in shape.Ceramic tiles made by sintering alone are inherently lessexpensive to manufacture, but if they need to be machinedfor higher dimensional uniformity, than any cost savingwill would be greatly diminished.

4. MANTECH HOT PRESSING SYSTEM

The ManTech low-cost tile program was formulated in2002 to look at greatly reducing the cost associated withhot pressing tiles, and to build a system that could bemore easily duplicated to meet the needs of much largeproduction volumes anticipated for future vehicleprograms. The major elements of this transformationwere (I) the use of high speed computer-controlledmachining. (2) a semi-continuous furnace that producesnear net-shaped tiles. The most significant change isfocusing on manufacturing tiles from start-to-finish tonear net-shape, instead of large billets that are sectionedinto tiles. Either a 4" square or a 4" flat-to-flat hexagonalshape were the tiles sizes the system was designed andoptimized to efficiently manufacture. Producing justthese small tiles allowed for the large load frame and

large hydrauHc system used in a conventional commercialhot press, Figure 3, to be replaced by a much smallersystem. So the hot pressing chamber became rather smalland not much larger than the laboratory-scale systemshown in Figure I. Since only small tiles need to beground, the surface grinders were replaced by double-diskgrinders, and these can grind a small areas (such as tiles)at a much faster rate and can grind two surfaces at onetime. This allowed from machining times to dropsignificantly.

Figure 3. Commercial traditional hot press at BAESystems

Since the ManTech processing produces near net-shapedtiles. some changes in the powder processing and fonningwere necessary. The most significant change was usingdry pressing to form the "green" (undensified) ceramicprefonns, this entailed mixing the ceramic powder with abinder and compacting the part in a die. To aid in thefilling of the die. the powder was granulated to improvepowder flow. Several other changes were made topowder processing with the goal of developing a processthat could be scaled to much larger production volumes.Figure 4 shows the green compacts for hexagonal tiles atseveral thicknesses. The tiles maintained the same cross­sectional area, but were reduced in thickness whendensified.

Figure 4 Hexagonal shaped preforms dry pressed to shape

5. PRICING GOALS

Cost reductions and a processing system amendable torapid scale at the two major goals of the program. Hotpressed silicon carbide is an expensive ceramic comparedto sintered aluminum oxide and sintered silicon carbide.The conventionally produced SiC-N from BAE has a costof $ J35/1b for a square tile, while a hexagonal tile (a 50%premium) is $200/lb. As of October 2006 withdemonstration of the ManTech machining methods onbillets conventionally manufactured and sectioned intotiles, the current cost of the material is $85/1b. The goalof the ManTech program, with the current ManTechcurrent is a cost of $50 Ib for both hexagonal and squaretiles. Since the tiles are manufactured to near net-shape,there is no additional waste associated with the hexagonaltiles, which keeps the costs the same. There may be anadditional cost associated with the hexagonal tiles, if thereare issues of yield due to the grinding a more complexshaped part. This is a first-generation furnace, it isanticipated that the cost can be reduced further byreducing the amount of grind stock on the part and addingadditional efficiencies in the furnace to increasethroughput. The final goal would be to produce hotpressed SiC-N at $35/lb, which is a cost comparable to asintered (unmachined) silicon carbide. Optimizing thefurnace design to meet these goals may require a newfurnace to be built.

grinders implemented under theThey are fully automated and

Figure 6 Double-discManTech program.computer controlled.

Figure 5. ManTech hot pressing furnaces with multipleheating and cooling chambers, and a central hot pressingchamber

The surface grinders (used to grind billets down to desiredthickness) were replaced by high-speed double-sidesgrinders that can rapidly removed grind stock, Figure 6.The tiles are pressed to dimensions slightly larger than the4" desired size, and then they are ground to the desiredthickness. The edges are ground to thickness, two sides ata time. Therefore, the tiles are never diamond sectionedto the appropriate size, only ground to size. Since theyare ground to fmal size, the tiles can be measured forthickness during grinding to reduce the potential ofproducing out-of-spec parts. The grinding system isautomated and computer-controlled, and includes anoptical gaging system to accurately measure tile sizeduring then grinding operations. These additionalmachining features should increase tile yield. Also, byreducing the amount of grind stock removed duringgrinding is another potential way to further reduce cost.

The ManTech furnace was designed so that the. hotpressing chamber is always at the bot pressingtemperature and die sets containing the green compactsare automatically ramped up to temperature by steppingthe die through a series of furnace chambers of varyingtemperature. The die is then stepped into the hot pressingchamber and the compact is densified under pressure andtemperature. The system was designed to press four partsin each die. After the part has been densified, it is rampeddown in temperature through a series of furnace chambersuntil the die is able to be handled. Figure 5 shows theManTech furnace with a number of ramp-up and ramp­down chambers, as well as the hot pressing chamber inthe center. Since the loads only need to be supplied to asmall area, the load frame and hydraulic system is quitesmall compared to a commercial hot pressing operation.When the system is running, multiple dies sets (one ineach chamber) are in the furnace; some are being rampingup in temperature, ODC set is being hot pressed, whileothers are cooling. The time it takes for the die set in thehot pressing chamber to be densified is the rate-limitingstep.

Table I Cost goals for the ManTech process compared tothe conventionally processed SiC-N for two tile shapes.

4"X 4" 135 85 50 35tile

4" flat-to- 200 125 50 35flat hex

After several years ofredesigning the hot pressing processand ordering new equipment, the start-up operation of theManTech furnace was a major milestone in July 2007.Initial tiles manufactured with the furnace containedundesirable features that resulted from ceramic processingissues inherent in the SiC-N formulation. These tilescontained regions of low density, or "white edge," Figure7, on and near the surface. This is due to chemicalreactions in the material at the high temperatures seenduring sintering. At these temperatures, the loss ofsintering aid in the near-surface regions of the tileretarded the densification process. While some whiteedge is acceptable on the near net-shaped tiles, it shouldbe completely ground away during final machining, sincethe white edge material has been shown to have degradedballistic properties.

9. SUMMARY

8. Future Efforts

If the ballistic properties of the ManTech SiC are shownto the equivalent to conventionally processed SiC-N, thenit is planned that BAE will conduct another one-ton runon a different composition of hot pressed SiC. They willalso investigate the possibility of manufacturing a numberof individual small tiles in the same die used for thecurrent tiles. This would allow the same system toefficiently produce tiles of different sizes. Currently, thesystem is optimized to produce only 4" square andhexagonal tiles, while other sizes would reduceproduction yield. Also, the system designed here is afirst-generation system and overall efficiency would beimproved if the lessons learned with this system wereincorporated into a second-generation furnace

back in operation in June 2008 and producing ceramic ofgood quality, the one-ton campaign run was commencedto determine actual productions costs to compare to thecost estimates. The production run occurred in July andAugust 2008. Approximately 1500 tiles were producedunder this run and all of the tiles were tracked frompowder compacts, to binder burnout, and finally positionin the run. Density of the tiles was measured before andafter machining along with several other parameters, andcompared to previously detennined yield criteria. Astatistical analysis is being conducted to look at trends inthe processing conditions to determine subtle changes inprocessing that affect quality and final yield. A costanalysis for the run will be conducted to compare againstthe cost estimates (Table I). In the fall of 2008, asignificant number of tiles will be selected for ballisticqualification testing. The goal is to provide equivalentballistic performance compared to conventionallyprocessed material, but at a much lower price.

Finalgoal

($l1b)

FullManTechProcess($l1b)

Current(Conv.

wIManTechMachining)

($l1b)

6. PROCESSING ISSUES

Conven­tional($l1b)

Figure 7. White edge region shown in initial group ofManTech tiles ground to final size

In the fall of 2007, a series of design-of-experiments wereconducted to reduce and eliminate this white edgeproblem by better controlling the atmosphere and slowingthe loss of sintering aid in the near surface regions. Bythe spring of 2008, several of these modifications allowedfor the fabrication of tiles with no or very minimalamount of white edge on tiles after final machining.

7. CURRENT STATUS

After the white edge problem was solved on the ManTechtiles and furnace conditions for a large production runwere determined, an important component of the furnacebroke and it took several months to fix. With the furnace

Silicon carbide is an important ceramic material that maybe used for future ceramic-based armor systems. Basedon performance, hot pressed silicon carbide is of greatinterest, but high production costs and limited productionvolumes may limit the use of this material. Therefore, aManTech program was initiated to explore ways todramatically reduced cost and provide a manufacturingsystem that could be easily duplicated to meet anticipatedneeds. A first-generation ManTech line has been builtand recently produced one ton of silicon carbide tiles.The cost estimates of the process are being verified onthis run, and the material will be ballistically evaluated inthe fall of 2008 to compare against conventionallyprocessed material. The goal is to produce a siliconcarbide with equivalent performance to the industry­standard SiC-N, but at a much lower cost.

Quality Assurance and OPSEC Review

This form is an approvall'elXlrd for ARl generated information to be presented or disseminated extemallo ARL Note: Submit all manusClipls ineledronic format or camera ready copy. see attadled instructions. If more space is needed, use reverse of form (indude block numbers).

A. Generallnfonnation 1. Present Dale 2. Undassified Trtle

09-19-2008 New Low-Cost Manufacturing Methods to Produce Silicon Carbide (SiC) for Lig

3. Authof(s) 4. Office Symbol(s) 5. Telephone Nr(s)

James Campbell, Jerry LaSalvia, Ernest Chin, AMSRD-ARL-WM-MD 4-0896Richard Palicka and DanAshkin

6. Contrador generated ON, DYes 7. Type: 0 Report 0 Abstract 1iI Publication 0 Presentation (speecfl. briefing, video dip,

If yes. enter Contract No. and ARL COR poster, etc) o Book o Book Chapter o Web

8. Key words

Silicon carbide, ceramic processing, armor, manufacturing

9. Distribution Statement (required) Is manuscript CirCle appropriate letter and number. (see instructions for statement text) 10. Seo..uitysubject to export CtIntrol? Classification

ON, DYes ,. BCD E F X \ 2 3 4 5 67891011unclasified

B. Reports 11. Series 12. Type 13. No. of pages 14. Project No. 15. Period Covered 16. Sponsor

C. Publications

17. Is MS an invited paper? D No DYes 19. Material will be submitted for pUblication in

18. Publication is a refereed journal?Proceeding of the 2008 Anny Science Conf USA

Ii<IN, DYesJournal Country

D. Presentations 20. Coflference NameJLocation 21. Sponsor

Army Science ConferenceJ D,..{~o,rL USAnny

~;:T7~y23. Due Date 24. Confellmce is ~ Open 10 general public D UndassifiedlCtlntrolled access

09-22·2008 o Classified

25. For nonpLblic meetings: Will foreign nationals be attending? 26. Material will be

ON' DYes (ff yes. Jist COU'Itries and identify Inrematiooal Agreemenl(:s)) o Oral presented only rtJ....Oral presented ancl published inD Don't know

Procccdinis of the 2008 Army Science Conference

(If pUblished, complete block 18 and 19, Section G.)

E. Authors Statement: 27. All authors have concurred in the technical content and the sequence of authors. All authors have made a

substantial contribution to the manuscript and an authors who have made a substantial contribution are identified in BloCk 3.

James Campbell 09-19-2008

ARllead Author or COR ""e

F.Approvals'3f:) 'ne S"p.""',.,, ,fSeoio, ARL Aulho< '" 29. Reviewe,(s) ~VEditori.lINA)CO

I I ~~ ,1\,0 L /207.; V r ' Yll\ Cho 09-19-2008

((/1/ «T ~ Name(s)/ Name / Cite Date

30. limited distribution information for release 10 31. Classified Informationforeign nationals

Classified by

Declassified on

Foreign Disclosure "'Ie Command SeaJrity Manager "'Ie

ARLForm 1Odober2003

OPSEC REVIEW CHECKLISTOPSEC poc: Complete and explain any positive responses in block 9.

Note: ARl must be too proponent of the proposed inf~mationfor release.

,. Does Ulis material c:orQin Sensi~ Information? 0 YES ~ 8. Does !his malcrial c:oota....;

2. Does this irlOfITI3lion CClnUIio stale-<lf-~rt.3. AIry oooll'acI proposals, bids. <IndiOI' pmprietary

&0breaktfYough lectmoloW? DYES ~NOinformation? DVES

3. Oocs the United Stales hold a signilicantlcad

~NOb. Any iofOfm3tion on lnventioosJpatcot application

~Otime in Ulis technology? DYESrOf which palen! seo'"eq orders have been issued? DYES

.c. Docs this iofonnalion reveal aspects of reverse

~NOc. A1rt weapoo systems/component test resdts? DYES ~NO

engineering? DYES d. A1rt ARt-originated slud"lC$ or after adioo reports

(l(NOcontairiog a<Mce and recomrncndalions? DYES5. Docs Ihi$ malerial reveal any 5eO.Irity practices- 'tNOor procedufes? DYES e. Wealtoes.s and/or VlJtnetability Woonation? DYES It""6. Does this QOITl'I3tion reveal any s.ea.rity 1. Arry inIotTn3tioo on COUfItcrmeaslKt'S? DYES ~""pradk:es or procedures? DYES ~NO g.Arry~$dledule information? DYES j!tNO7. Woufd release ollhis infocmalioo be of. ecooomic h.Hrj Force Protc<:tion, Homeland oeronse

~NObcocfit to a beign entity, adversafy, Of.aIIow for the (secuity) nOlTl\3tion? DYESdcYelopmCClI of COU'ltenne:asures to the system or

~NO llnfonmtion 00 subjects 01 potential mnttoversy"""'-' DYESamong rrRtaty semccs or ottlcI' federal agencies? DYES rptNO

J,. IrIommioo on nVitary app6c:atioos .... spare,nude3r chetrical or biobgical efforts: high eoergy

twoIaser .....~ patijdc beam led'lnology; etc? DYES

~ Contain ilforma6on with fol'eign poCiq or Joreign

~NOrelations~? DYES

O~SECApproval· StatementI,the~, am aware of !he advefSal')"s interesl in DOD pobrlC3lioos and in lhe wbjcct matter 0( this material and tMllo the best of my~, the net benefil of this release oul weighls the pot.cotial damage 10 !he essen6al $CCUI'ity of all ARL AMC, AArry, or oIr\Cf DOD programs,

"7~ ~/Jfa . o1J:0h~o~OPSEC . ed namelU}natt.n!) I ",of,

9.\.~~ fnc Pl'nlarutionslcnntjnuationodOP~F·r.: r",yiPw,

/1~~~r-tJ~ J'~ ~ -No ~Co. .

Final Retease Clearances32. Publia'I..mted Idea$e·Wotmaliona Malcrial has been reWlwed for OPSC-c poIiey.

ARt:. QPSEC OfIiccr "'tob. l'tte InrOl'll'\ation contained inlt1is matcricll is o lisncM D approved for public relcascl has received approprole lecNeditorl3l review.

$tevCll H. McKnight, Chief, Malerials Division

OiYision Olie! Dale

e. This ""ormation is acoepWd for public release.

P\.OlK; AIJ.aifs OffICe "'IeARlForm 1

Oc.lobcf 2003Page 2 of 4