?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=http%3A%2F%2Fmiis.maths.ox.ac.uk%2Fmiis%2F720%2F&rft.title=A+Model+for+the+Reduction+of+Specific+Surface+Area+of+Powders+with+Age&rft.creator=Curtis%2C+John+P.&rft.creator=Black%2C+Jonathan&rft.creator=Chapman%2C+Lloyd&rft.creator=Connaughton%2C+Colm&rft.creator=Cooker%2C+Mark+J.&rft.creator=Coskun%2C+Erhan&rft.creator=Davies%2C+Russell&rft.creator=Fernandez%2C+Andrea&rft.creator=Hall%2C+Cameron&rft.creator=Lacey%2C+A.A.&rft.creator=Ockendon%2C+J.R.&rft.creator=Please%2C+C.P.&rft.creator=Ranner%2C+Tom&rft.creator=Skorski%2C+Maciej&rft.creator=Wang%2C+Chang&rft.subject=Materials&rft.description=PETN+is+a+high+explosive%2C+sometimes+stored+for+periods+of+up+to+many+years%2C+in+powdered+form.+In+storage%2C+the+explosive+particles+change+size+and+shape+owing+to+sublimation%2C+condensation+and+surface+di+usion.+AWE+measurements+are+available+on+the+changing+particle+size+distri-+bution+(PSD)%2C+and+the+speci+c+surface+area+(SSA)+of+the+powder%2C+taken+from+experiments+on+accelerated+ageing.+But+a+mathematical+model+of+the+ageing+process+is+wanted+in+order+to+interpret+the+processes+at+work.+Various+modelling+issues+and+unusual+features+of+the+measure-+ment+data+were+discussed.+Four+models+of+important+processes+were+developed%2C+and+are+reported+here.+Model+(i)+addresses+the+fundamental+physics+associated+with+the+transport+of+mass+by+sublimation%2C+di+usion+and+condensation.+Model+(ii)+uses+chemical+kinetics+to+develop+a+system+of+ordinary+di+erential+equations+(ODEs)+for+the+time-evolution+of+the+frequencies+of+particle+sizes.+Model+(iii)+extends+Model+(ii)+to+a+contin-+uum+particle+size+distribution.+Lastly%2C+Model+(iv)+considers+the+growth+of+particles+as+described+by+Cahn-Hilliard+equations+for+the+inter-particle+transport+of+matter+in+Ostwald+Ripening.+Models+(i)+and+(iv)+include+the+complex+geometry+and+thermodynamics+of+the+problem.+By+con-+trast%2C+Models+(ii)+and+(iii)+focus+on+the+time+evolution+of+the+PSD%2C+but+they+are+more+di+cult+to+associate+with+controllable+variables%2C+such+as+ambient+temperature.+Our+discussions+of+models+(ii)+and+(iii)+suggest+we+can+choose+mass-transfer+rate+constants+that+reproduce+the+kind+of+ob-+served+evolution+to+a+bimodal+PSD.+But+more+investigation+is+needed+to+determine+how+the+rate+constants+may+be+associated+with+the+particles'+geometry+and+the+thermodynamics+of+the+mass+transport+processes.&rft.date=2012&rft.type=Study+Group+Report&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=http%3A%2F%2Fmiis.maths.ox.ac.uk%2Fmiis%2F720%2F1%2FESGI85-AWE_CaseStudy.pdf&rft.identifier=++Curtis%2C+John+P.+and+Black%2C+Jonathan+and+Chapman%2C+Lloyd+and+Connaughton%2C+Colm+and+Cooker%2C+Mark+J.+and+Coskun%2C+Erhan+and+Davies%2C+Russell+and+Fernandez%2C+Andrea+and+Hall%2C+Cameron+and+Lacey%2C+A.A.+and+Ockendon%2C+J.R.+and+Please%2C+C.P.+and+Ranner%2C+Tom+and+Skorski%2C+Maciej+and+Wang%2C+Chang++(2012)+A+Model+for+the+Reduction+of+Specific+Surface+Area+of+Powders+with+Age.++%5BStudy+Group+Report%5D+++++