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  • Temperature-Programmed Desorption Study of the Reaction of Water and Epitaxial Graphene

    on Silicon Carbide KAREN PORTER-DAVIS

    CHAMBLEE CHARTER HIGH SCHOOL

    STEP-UP PROGRAM 2013

    THE ORLANDO GROUP

    GEORGIA INSTITUTE OF TECHNOLOGY

  • Benefits of Nuclear Power   -­‐Much  less  greenhouse   gases  released     -­‐Produce  more  electric   power  for  less  cost     -­‐Technology  already   understood  

    However….  

    Plant  Vogtle  in   Waynesboro,  GA.   Two  new  reactors  will   start  producing   electricity  2016  and   2017.    First  new  reactor   built  in  US  in  30  years.   (NRC  approved  4  to  1  in   Feb.  2012)  AP1000   reactors  with  ZIRLO   cladding.  

  • Safety and Fuel-Cladding   Disaster  at  Fukushima  1  Nuclear  Power  Plant  in  March  of  2011  has  brought   concern  over  the  safety  of  nuclear  power.  

      The  tsunami  waves  destroyed  cooling  system  and  caused  the  reactors  to   overheat.  

      Zircaloy  fuel-­‐cladding  oxidized  and  produced  hydrogen  gas.     Hydrogen  gas  led  to  explosions  in  reactors.     Need  for  longer-­‐lasZng  materials  for  fuel-­‐cladding  that  are  able  to  hold  up  to   loss-­‐of-­‐cooling  accidents  (LOCA).  

  • Fuel-Cladding

    NUCLEAR  FUEL  ASSEMBLY  Zirconium  alloys  are  used  as   cladding  materialh?p://www.miningweekly.com/ arFcle/network-­‐advances-­‐beneficiaFon-­‐and-­‐ rd-­‐2012-­‐11-­‐02  

    h?p://crisasantos.com.br/com/nuclear-­‐rods-­‐melFng  

    cladding  

    Fuel-­‐cladding  is  used  to   separate  the  radioacZve   fuel  from  the  coolant  so  the   neutrons,  gamma  rays  and   alpha  and  beta  parZcles   that  are  created  during  the   fission  process  are  not   released  into  the   environment.    

  • Fuel-Cladding   There  are  several  factors  to  consider  when  deciding  on  the  type  of  Fuel-­‐ Cladding  material  but  most  notably:     1)    Transparency  to  neutrons     2)    High  Thermal  ConducZvity     3)    Low  Thermal  Expansion  Coefficient     4)    Chemical  CompaZbility     5)    Mechanical  Strength  

  • Current Materials for Fuel- Cladding   MeeZng  the  aforemenZoned  requirements  Zirconium  (Zr)  and  alloys  of  Zr  (Zircaloy  and  ZIRLO)   are  the  most  used  fuel-­‐cladding  materials.  

      However,  at  high  temperatures  and  high  energy  radiaZon  exposure  (like  LOCA)  exothermic   reacZons  of  Zr  with  water/steam  yield  hydrogen  in  great  amounts  which  could  lead  to    

      1)    Hydrogen  Embriblement  

      2)    ProducZon  of  hydrogen  gas  

    h?p://www.bing.com/ images/search? q=hydrogen+gas +explosion+nuclear +reactors&FORM=HDRSC 2#view=detail&id=14AB2 80C0A377C6DE79670777 5601E56B1935EC3&selec tedIndex=0  

    Hydrogen   Gas   explosion  at   Fukushima   Dai-­‐ishi    

    h?p:// www.machinerylubr icaFon.com/Read/ 573/moisture-­‐ contaminaFon-­‐ targets  

  • Additional Materials for Fuel- Cladding   Promising  research  into  Silicon  Carbide  (SiC)  as  a  replacement  for  fuel-­‐ cladding     Epitaxial  Graphene  (EG)  on  SiC  meets  the  thermal  and  mechanical  needs   for  fuel-­‐cladding  and  since  graphene  has  a  hydrophobic  nature  it  is   thought  to  be  less  reacZve  to  steam  and  therefore  less  likely  to  produce   hydrogen.     Single-­‐layered  graphene  has  not  been  fully  tested  under  extremely  high   temperatures  or  under  condiZons  that  mimic  LOCA.  

  • Epitaxial Graphene   Mono-­‐layered  graphene  in  a  2-­‐D  honeycomb  arrangement  of   carbon  atoms     Studied  for  its  electrical,  chemical,  thermal  and  mechanical   properZes.     Epitaxial  means  that  the  graphene  is  grown  on  a  surface  of  a  crystal   material  and  mimics  the  arrangement  of  that  substrate.     Sample  from  Dr.  de  Heer’s  group  using  a  “Confinement  Controlled   SublimaZon”  to  grow  high  quality  layers  of  EG  on  SiC.  

    Epitaxial  Graphene   on  Silicon  Carbide   h?p://cnx.org/content/ m29187/latest/    

  • Raman Spectroscopy

    J.  Phys.  Chem.  C  2008,   112,  10637–10640.  Copyright  2008  American  Chemical  Society;  h?p://www3.ntu.edu.sg/home/yuFng/papers/nano %20research-­‐review%20graphene.pdf  

    Used  to  detect  low  frequency  modes  in  a  sample.   InelasZc  scabering  (KE  is  not  conserved)  

    h?p://www-­‐che.engr.ccny.cuny.edu/courses/che5535/lecture5/ sld002.htm  

  • Raman Data of EG on SiC The  sample  of  EG   on  SiC  showed  the   characterisZc  G   (1500  –  1620  cm¯ˉ¹)   and  2D  (2700-­‐2750   cm¯ˉ¹).    SiC  was   subtracted.  

    Wavenumber  (cm¯ˉ¹)  

    In te ns ity

     (a rb itr ar y   un

    its )   2  D  peak  

    G  peak  

  • Monitoring Desorbed molecules of EG on SiC

      To  test  the  thermal  stability  of  the  sample  the  desorpZon  defects   were  measured  with  a  special  interest  in  hydrogen  gas.  

      Temperature  Programmed  DesorpZon  (TPD):    the  technique  of   observing  desorbed  molecules  from  a  surface  as  the  surface   temperature  is  increased  via  a  mass  analyzer.    

      Quadrupole  analyzer  commonly  used.     As  desorpZon  occurs  ions  are  released  into  the  chamber  and   guided  to  the  quadrupole.  

      The  ions  move  through  the  electric  field  formed  by  the  rods.    The   strength  and  frequency  of  the  field  dictates  if  an  ion  of  a  parZcular   mass  will  pass  through  the  rods  and  therefore  counted  by  the   detector  or  collides  into  a  nearby  surface.  

  • TPD   Designed  and  created  by  Orlando  Group     Ultra  High  Vacuum  chamber  (1.4  E-­‐8  Torr)     Sample  stage  with  thermocouple  abached  to  a  thin  tantalum  wire  acZng  as  a  spring  clip,   allowing  direct  contact  with  the  sample.  

      Nitrogen  chamber  to  keep  out  pump  oil  and  other  impuriZes.     Temperature  range  500°C  to  1000°C  (5  minute  intervals)     Temperature  controlled  by  adjusZng  current  7  A  –  19/20  A     Empty  chamber,  SiC  ,  EG  on  SiC    (with  and  without  water  –  dose  set  for  2.5  E  -­‐10  A.     Quadrupole  analyzer     Quadera  sooware  

  • Thermal Programmed Desorption Sample   stage  

    Vacuum   Chamber  

    Quadrupole  

    Water  Source  

    O rla

    nd o   Gr ou

    p   Ge

    or gi a   In sF tu te  o f  T

    ec hn

    ol og y  

  • TPD Data of H2

    0  

    0.2  

    0.4  

    0.6  

    0.8  

    1  

    1.2  

    0   0.2   0.4   0.6   0.8   1   1.2  

    Time  (s)  

    Io n   Cu

    rr en

    t  I nt en

    si ty  (A

    )  

    0.00E+00  

    2.00E-­‐11  

    4.00E-­‐11  

    6.00E-­‐11  

    8.00E-­‐11  

    1.00E-­‐10  

    1.20E-­‐10  

    0   500   1000   1500   2000   2500   3000   3500   4000   4500   5000  

    Run  1  Empty  Chamber_H2O  

    Run  1  SiC_H2O  

    Run  1  EG  

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