![]() ![]() butassignedthecompositionFeBe 7,yetthecompoundisstillpresentedwithacompositionof8at. AldingerandPetzow usedthestructureofJohnsonet al. reportanewhexagonalphasewithunknowncompositionFeBe x,butassignthespacegroup P ¯ 6 m 2andabasisconsistingof19symmetricallyuniquesites,thoughpotentiallywithpartialoccupancy.X-raydiffractionrevealsmanysimilaritieswiththeFeBe 11phaseofTetiel TeitelandCohen ,butaccuratedensitymeasurementsexcludethepossibilityofaAB 11composition.Aldingeret al. 1 \sfrac 1 2formulaunits),whichremainsapeculiarandunexplainedresult.Insubsequentpublications,thishexagonalphaseisthemostcommonlyreported OkamotoandTanner ,howeverthereisconflictinginformation.Forexample,VonBatchelderandRaeuchle vonBatchelderandRaeuchle proposedabodycentredtetragonalMn 12Th-typestructure.HindleandSlattery HindleandSlattery reportsabody-centredtetragonalBe-richcompound.Johnsonet al. ?).Bymeansofdensitymeasurements,theirworkshowsthataunitcellofFeBe 11shouldcontain18atoms(i.e. ![]() ![]() Regardingthe εphase,TeitelandCohen TeitelandCohen firstreportitashexagonalwithcompositionFeBe 11(orpotentiallyFeBe 12),whichformsonlyattemperaturesbelow 1065 ° Candexhibitslimitedsolubility(7.8–8.2at. Figure 1: Be-Fephasediagramreproducedfrom OkamotoandTanner ,withintermetallicphaseshighlightedincolour. expandedtheunderstandingofBesolutionin α-Fe,byincludingtheeffectofmagnetictransitionandorder-disordertransitions.Theyalsoproposethatthe δphaseundergoesafirstordertransitionat ∼ 1150K,decomposinginto εand ζbelowsaidtemperature.Thiswasnotcapturedinearliercomputationalwork KaufmanandTanner ,andexperimentalinvestigationwaschieflyconcernedwithtemperaturesabove ∼ 1200K OkamotoandTanner. Thissystemexhibitssolidsolutionsateitherendofthecompositionrange,ametastableBeFe 3phaseandthreestableintermetalliccompounds:FeBe 2( ζ),FeBe 5( δ)andaBe-richintermetallicphase( ε)ofunknownstructureanduncertaincomposition.Arecent claphadstudy Ohtaniet al. 1.However,‘moredataonthethermodynamicpropertiesandphasediagramofthissystemareneededtoimprovethemodel’ OkamotoandTanner. InareviewofthebinaryBe-Fesystem,TannerandOkamoto OkamotoandTanner highlightthat,despitethemanyconflictingreports,muchofthephasediagramisnowwellcharacterised,seefig. andhasbeenselectedforuseintheInternationalThermonuclearExperimentalReactor(ITER) Thompsonet al.However,Beisalsohighlytoxic Kriebel1988 ,whichmakesexperimentalresearchanddevelopmentofBealloysadifficultandexpensivetask.Intheextremeenvironmentassociatedwiththefusionplasma,thepresenceofimpuritiesandalloyingadditionsmayplayacrucialroleintheageinganddegradationprocesses.IftheimpurityelementsarenotretainedinsolutionwithintheBephase,theywillformsecondphaseparticlesembeddedwithinthegrainsorformatgrainboundariesandsurfaces,wheretheirpresencecanbedeleterioustothemechanicalandchemicalpropertiesofthealloy.Herewewillbeconcernedwiththeiron(Fe)andaluminium(Al)containingintermetallicphasesofBe,asFeandAlarecommonadditions/impuritiesinBealloys RooksbyandGreen. Beryllium(Be)isalightelementwithexcellentneutrontransparency,andforthisreasonitiscurrentlyusedasaplasmafacingmaterialintheJointEuropeanTorus(JET)fusionreactor Deksniset al. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |