Key Engineering Materials Vols. 368-372 (2008) pp 1526-1528
online at
http://www.scientific.net
? (2008) Trans Tech Publications, Swit
zerland
Online available since 2008/Feb/11
Combustion Synthesis o
f Alumina-Based Multiphase Foam Ceramic
1,2,a 1 1 2 1
Junshou
Li , Liang Li , Jiangjiang Wang , Bingshe Xu and Yujun Yin
1
In
stitute of Advanced Materials, Shijiazhuang Mechanical Engineerin
g College, Shijiazhuang
050003, China
2
Taiyuan Institute of T
echnology, Taiyuan 030024, China
a
lijs258@sina.com
Keywords:
Alumina; Foam ceramics; Combustion synthesis
Abstract.Al O TiOT
iO multiphasefoamceramicwaspreparedwithAlpowdersandTi O powdersby
2 3 2 2
combustionsynthesis,Directobservationandmetallographicmi
c roscopeindicatedthattheporediameter
is00~6000m,ndrchimedeanetho
dhowedhatheporositys5~50%.henfluencingactors
ofheporeiameterndpor
ositynd,heffectsfddingiO nompressiontrengthfhel O
2 2 3
TiOTiO mu
ltiphasefoamceramicwerediscussed.Itwasshownthatthe additionofprop
erhightempe
2
ratureoaminggentanncreaseporosityndddingiO anecreas
eporosity.hel O TiOTiO
2 2 3 2
multiphaseoameramicasoodechanicalp
ropertiesndightempera tureesistance.
Introduction
Combustionsynt
hesis[14]hasbecomeafastdevelopingmethodforp reparingfoamceramicsd
uring
thelast20ears.singombustionynthesisoprepareoameramicas anyd
vantages,uchs
highporosity,argeporeize,ownergyonsumptiontc.
Inthi
sstudy,Al O TiOTiO multiphasefoamceramicwaspreparedwithAlpowdersa
ndTi O
2 3 2 2
powdersbycombustionsynthesis.Theinfluencesofthehig
htemperat urefoamingagentandSiO on
2
porositiesereiscussed.
Exper
imental
ThestartmaterialswereAl,TiO ,SiO (allofthemareanalytical
reagent,particlesizeisl essthan
2 2
100m)andhightemperaturefoamin
gagent.Alltheexperimentala gentsweredriedfor1h.The
chemicaleactio
nquations:
2Al3TiO l O TiO
2 2 3
Theollowing fourroupsfawaterials
ereprepared:
a. 2mollmoliO .5molighemperatureoaminggent;
2
b. 2m
ollmoliO molighemperatureoaminggent;
2
c. 2mollmoliO .5molighempe
ratureoaminggent;
2
d. 2mollmoliO molighemperatureoaminggentmoliO
.
2 2
Therawmaterialswereputintothefouropenreactiontanksre spect
ivelyandignited.Thegas
decomposedfromthehightemperaturefoamingage
ntwouldpassthrough themeltingreactantsand
release to the open air
. After combustion synthesis finished and t he crystallization co
mpleted,
Al O based multiphase foam ceramic were obtained and mar
ked as sa mple A, B, C and D
2 3
correspondedithroup,b,ndespectiv
ely.
Crystal structure was analyzed by Xray diffraction (XRD); mo
rphology was observed and
characterizedbyopticalmicroscope,scanni
ngelectronmicros copy(SEM),energydispersiveXray
spectroscope(EDS)
attachedtotheSEM;compressionstrength wastestedbymaterialexperimen
t
machine;porosityaseasuredbyrchimedesethod.
Results and Discussi
on
Effects of the high temperature foaming agent on porosity. Fi
g.1istheXRDpatternofsampleA.
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publisher: T
rans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 218.12
.12.180-20/05/08,18:25:52)
Key Engineering Materials Vols. 368-37
2 1527
ItshowsthatthefoamceramiciscomposedofAl O ,TiOand
2 3
TiO
.Thereactiontankwasopentotheair,sopartofAl O was
2 2 3
synthesize
d from Al and O at high temperature. That’s the
2
reasonwhystoich
iometryratiodeviatedthechemicalreaction
equationndomeiO ereeft.
2
Fig.2showsthemacrographsofsamplesA,B,CandD.A
great deal number o
f pores distribute homogeneouslyand the
porediameterisabout~6mm.h
ebiggestporenheenters
theombustionarkfadiationiring.
Fig.RDpatter
nfample
Fig.3displaysthemetallographicstructureofthesampleB.
Besi
destheporesobservedinFig.2,therearesomeporeswitha
regularshapewho
sediameterismorethan100m.Thethicknessofpor ewallincreasesfrom30mt
o
400mithheecreasefheporeiameter.
Fig.4istheSEMimageofsampleB,thr
eephasesarefoundint heporewall.ComparedwithEDS
analysis,itconform
sthatthecharcoalgrayphaseisAl O ,depositedatfirstbecauseofthehigh
est
2 3
meltingpoint(2054oC).ThegrayishphaseisTiO,depositedsecond
ly becauseoflowermeltingpoint
(1843oC).ThegrayphaseisTiO ,deposit
edatlastbecauseofthelowestmeltingpoint(1750oC).T he
2
graypointph
asenherayishphasesiOparticleistributedn iO rystals.
2
Fig.acrogra
phsfheamplesD:a)ample;b)ample;c) ample;d)ample.
Fig.etallographic
tructurefample Fig.EMmagefample
Thealculationormulafporositys:
W
W
2 0
P= ×100%
(1)
W W
2 1
where Pistheporosityoffoamceramic; W i
sthemassofintensivedryingfoamceramicintheair;
0
W istheapparentma
ssoffoamceramicinwater,whichhasabs orbedwatersufficiently; W isth
e
1 2
massfoameramicnheir,hichasbeenbsorbedaterufficiently .
Thec
alculationresultsare35.9%,48.0%,44.5%and23.1%,whicharerespectivel
ycorresponding
totheporosityofsampleA,B,CandD.Theseresultsconfir
mtha taddinghightemperaturefoaming
agentintotherawmaterialscaninc
reasetheporosityofAl O TiOTiO multiphasefoamceramic,
2 3 2
buthep
orositywillbelittlechangedwhenthehightemperature foamingagentisad
dedtoacertain
quantity.Becausethegasdecomposedfromthehightemperat
urefoam ingagentcanpassthroughthe
1528 High-Performance Ceramics
V
pores quicklyand freelywhen the diameter reaches millimeter ord
er, and no more pores will be
producednhel O TiOTiO ultiphaseoame
ramic.
2 3 2
Effects of SiO2 on compression strength and porosity
MakesampleBandDintocylinderform
(boththebasaliameterndeightre0mm)
ndestheirompressiontre ngth.heompression
strengthfoameramicanbeal
culateds
P
R =
(2)
c
S
where R sompressiontrength; Psbreakingoad;
Ssffectivereaherehepressurectsn.
c
ThetestresultshowsthatSiO can
increasethecompressionstrengthfrom9.74MPato13.16MPa
2
asfromsampl
eoample,butheporosityecreasesrom8.0%o3.1%.iO aneducehe
2
porosity
remarkably,sothecompressionstrengthwillbeincrea sedaccordingtothe
densificationof
Al O TiOTiO multiphase foam ceramic. Because both
the melting point (1670oC) and density
2 3 2
3 3
(2.65g/cm )ofSi
O arethelowest(densitiesofAl O ,TiOandTiO are3.97,4.95and4.23g/cm
),
2 2 3 2
SiO willnotonlycovertherawmaterials’surfaceeasilywhen
a llofthemareatmeltingstate,but
2
alsodelaytheheatexchangeofAl O
,TiOandTiO withair.Thus,duringthetimeofthehigh
2 3 2
temperature
foaming agent decomposes to gas, the noncrystalline part of raw m
aterials will be
increased, crystallization time will be extended
and porosity w ill be reduced. As a result the
compressiontrengt
hfl O TiOTiO ultiphaseoameramicillbencreased.
2 3 2
Conclusions
High temperature foaming agent was imported to combustion synthes
is and Al O TiOTiO
2 3 2
multiphasefoamceramicwasprepared.Thepor
osityisabout35 ~50%,theporediameterisabout
100~6000m and the pore
wall thickness is about 30~400m. The porositycan be increased by
adding high temperature foaming agent in the raw materials, but
little changed when the high
temperaturefoamingagent’scontentisab
ovethepropermolep ercent.AdditionofSiO particlesin
2
therawmaterialscanreducetheporosityofAl O TiOTiO multiphasefoamceramicandincrease
2 3 2
theompressiontrengthonsequently.
Acknowledgements
ThistudyasupportedbyNationalNaturalcienceoundationfhinaNo.0572122).
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