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Author''s personal copy
Journal of Alloys and Compounds 479 (2009) 803–806
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Characteristics of porous Al O –TiB ceramics fabricated
2 3 2
by the combustion synthesis
a a,? a b a
Junshou Li , Zongying Cai , Huansheng Guo , Bingshe Xu , Liang Li
a
Institute of Advanced Materials, Mechanical Engineering College, Shijiazhuang, Hebei, 050003, PR China
b
Taiyuan Institute of Technology, Taiyuan, Shanxi, 030024, PR China
article info abstract
Article history:
The porous Al O –TiB ceramics from stoichiometric mixtures of Al, TiO and B O has been prepared
2 3 2 2 2 3
Received 27 November 2008
by combustion synthesis technique. Products with high pore contents (86.3%) were obtained using the
Received in revised form 8 January 2009
startingmaterialscontaining10wt%pore-foamingagent(PFA).The?nerporesrangefrom300to500 m
Accepted 14 January 2009
and the larger ones are in the order of millimeters were obtained in the ceramics. Honeycomb structure
Available online 29 January 2009
micropores and acicular crystal TiB were formed at the ceramic pore when PFA added.
2
? 2009 Elsevier B.V. All rights reserved.
Keywords:
Porosity
SHS
Al O –TiB ceramics
2 3 2
1. Introduction of many investigators from the moment of its discovery. Combus-
tionsynthesisisoneofthemostprogressivemethodsforobtaining
Porousceramicsareincreasinglybecomingimportantincatalyst TiB and TiB -reinforced materials [11]. In this experiment, TiB
2 2 2
carriers, hot gas collectors, molten metal ?lters, separation mem- wasintroducedasareinforcingphasetoimprovemechanicalprop-
branesandparticulategas?ltration[1–3].Porousaluminaceramics erties of the porous ceramic. Porosity of Al O –TiB ceramics was
2 3 2
with the special property of high resistance and low in?ltration to formed and controlled to contain the required porosity and pore
hot gas, oil and molten are mainly used in ?ltering materials. The distributionduringthereactionbyintroducedtheorganicpolymer
propertiesofporousaluminaceramicsgreatlydependonporemor- as pore-foaming agent (PFA).
phology,sizeanddistribution.Therefore,thepreparationofporous In this paper, the complex phase porous Al O –TiB ceramics
2 3 2
ceramics with controlled microstructure (porosity, pore size and was prepared by combustion synthesis using pore-foaming agent,
pore space topology) has been a subject of constant interest during and the morphology and mechanical properties of the ceramics
the last decades. Porous ceramics are prepared by the poly-sponge were examined.
method, foaming method, extrusion method or by the gel casting
2. Experimental procedure
method [4–6].
Combustion synthesis or Self-propagating High Temperature
The starting powders used to prepare the porous Al O –TiB ceramics were Al
2 3 2
Synthesis (SHS) is a novel technique to produce high tempera-
(analysisreagent),TiO (analysisreagent),B O (analysisreagent)andorganicpore-
2 2 3
tureceramicandcompositematerials[7–10].Thisprocessishighly
foaming agent, all the particle size less 100 m. Combustion synthesis is conducted
by mixing the reactants in the desired reaction stoichiometry for 8h to ensure thor-
exothermic reaction within a mixture of reactive powders in a
ough mixing. The mixed powder was pressed into pellets having a cylindrical shape
few seconds and can allow for dif?cult intermetallics and porous
with a diameter of about 15mm by uniaxial pressing to densities from 30 to 60% of
materials to easily be manufactured. Due to the nature of the
the theoretical mixture density.
combustion synthesis technique, materials produced by this tech-
The materials of the current study were based on a composite of Al O –TiB
2 3 2
nique are porous typically containing about 50% porosity. Porosity produced by the following combustion synthesis reaction:
is the main cause for reduction in mechanical properties of alu-
10Al + 3B O + 3TiO = 5Al O + 3TiB + Q (1)
2 3 2 2 3 2 1
mina ceramic and brittle solids. As we all know, TiB ceramic is a
2
reinforcedmaterials,andtheTi–2Bsystemhasdrawntheattention In this reaction, ?ne powders of aluminium (Al), boron oxide (B O ), and tita-
2 3
nium dioxide (TiO ) were used, forming a composite of titanium boride (TiB ) and
2 2
aluminium oxide (Al O ). The samples were prepared according to the composition
2 3
shown in Table 1.
Each sample is placed in combustion chamber in an ambient atmosphere and
?
Corresponding author. Tel.: +86 311 87994092; fax: +86 311 87994091. ignited via a tungsten resistance coil at the top of the sample, with the propaga-
E-mail address: czy1106@sina.com (Z. Cai). tion wave traveling downwards. Samples are put into matrix and the combustion
0925-8388/$ – see front matter ? 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2009.01.055Author''s personal copy
804 J. Li et al. / Journal of Alloys and Compounds 479 (2009) 803–806
Table 1
Porosity of combustion products for different starting powders.
Sample Phase composition of starting powder (wt%) Character of combustion of products
Al TiO B O PFA Porosity Compressive strength
2 2 3
A 42.3 25.0 32.7 0 46.0–53.0% 7.2–15.1MPa
B 38.07 22.5 29.43 10 79.0–86.3% 4.7–6.2MPa
accomplished in several seconds. The product was cleaned by ultrasonic wave for
0.5h, after nature cooled from combustion.
To examine the relative density together with the amount of closed and open
pores, Archimedes’ method was employed. X-ray diffraction analysis XRD (D/max-
2200/PC,RigakuCorporation,Japan),wasusedtoexaminethephasesintheobtained
porous Al O –TiB ceramics. The morphologies of combustion products were stud-
2 3 2
ied by using scanning electron microscopy, SEM (Sirion200, Philips Corporation,
Netherlands).
3. Results and discussion
The combustion synthesis reaction represented by Eq. (1) had
characteristics of easy ignition, high combustion temperature, and
moderate combustion wave velocity. The sample was ignited at
room temperature and, once ignited, the combustion wave propa-
gated rapidly. Fig. 1 shows the X-ray diffraction pattern of obtained
porous Al O –TiB ceramics by combustion synthesis. The main
2 3 2
crystal phase was composed by Al O ,TiB and TiO , which indi-
2 3 2 2
Fig. 2. Optical micrograph of the porous Al O –TiB ceramics.
2 3 2
cated no side reaction occurred in this experiment. The unreacted
TiO was not detected in Sample B, which indicated the PFA pro-
2
motedthereaction.Thedifferenceofphaseproportionwascreated
Fig. 3. SEM of fracture surface of the porous Al O –TiB ceramics prepared by com-
2 3 2
Fig. 1. (a and b) XRD patterns of sintered porous Al O –TiB ceramics. bustion synthesis.
2 3 2
Author''s personal copy
J. Li et al. / Journal of Alloys and Compounds 479 (2009) 803–806 805
formation was from the mass change after the combustion syn-
thesis. Mass loss was partly due to the partial evaporation of boron
oxidedirectly,andpartlyduetotheprocessofvapourescapingthat
carried some mass away.
Typical distribution of open pores and closed pores was homo-
geneousincircleandellipseshape,the?nerporesrangefrom300to
500 mandthelargeronesareintheorderofmillimeters.Compar-
ison of the end products for two types of ceramic shows that large
amount of pore obtained in Sample B that increased the porosity
(79.0–86.3%) as shown in Table 1. Because of the pore and hollow
structure formed by the vapour in the combustion synthesis, more
vapour can lead to high porosity. The vapour of Sample A comes
from the water of starting materials in the combustion synthesis,
but more vapour was given off by PFA decomposition in Sample B
that made more pore formed. Increased additive content increases
the generation of bubble gas, which decreases the bubble size gen-
eratedduringfoamingandgavemoreopenporesthanclosed.After
the PFA burned out, presence of small pores give the connectivity
between the bigger pores. Hence, the PFA increases the intercon-
nectivityofthepores.Atthesametime,thecompressivestrengthof
such samples was decreased as the porosity increasing also shown
in Table 1.
Distribution of pore size also changes with the nature of pore
generation of PFA added. When the pores microstructure of the
Sample B was examined as shown in Fig. 4, the matrix which were
constituted with honeycomb structure of Al O and pore walls
2 3
whereacicularcrystalTiB wereaccumulatedareshowninFig.4(b)
2
and (c), respectively. It can also be seen that the alumina matrix is
in?ltrated not only into the large pores but also in the micropores
among the particles. It can be concluded that the formation of TiB
2
belonging to the local reaction. The combustion synthesis reaction
started at the melting point of Al (933K), which reduced molten
B O (melts at 723K) at the combustion front forming Al O and
2 3 2 3
free boron (B). At the same time, TiO was reduced by aluminium
2
(Al) to free titanium (Ti) at a higher temperature. Then the free
boron and titanium reacted and TiB formed as follows:
2
2Al + B O → Al O +2B (2)
2 3 2 3
4Al + 3TiO → 2Al O +3Ti (3)
2 2 3
Ti + 2B → TiB (4)
2
In this local reaction, with the increase of PFA content, the com-
bustiontemperatureincreasesandlocalreactionformedeasily.This
proves that pore sizes can be in?ltrated that gives the ?exibility to
change the starting materials/PFA ratio.
4. Conclusions
High porosity porous Al O –TiB ceramics was successfully
2 3 2
preparedbycombustionsynthesisaddedPFA.Thephasewasdeter-
Fig. 4. (a–c) SEM of wall of hole of the porous Al O –TiB ceramics prepared by mined by XRD and no impurity detected except the main phase
2 3 2
combustion synthesis added 10% PFA.
of Al O and TiB . The ?ner pores range from 300 to 500 m and
2 3 2
the larger ones are in the order of millimeters were obtained in
the ceramics. Honeycomb structure micropores and acicular crys-
by the starting materials PFA, which made the starting materials
tal TiB were formed at the ceramic pore when PFA added. The
2
and product loss accompanied gas release.
compressive strength of the composite decreased as the porosity
As shown in Figs. 2 and 3, the optical micrograph and scanning
increasing.
electron microscope (SEM) photomicrograph exhibits the highly
porous morphology of the combustion synthesis produced. Since
both Al and B O had a relatively low melting point 933 and 723K, Acknowledgement
2 3
resultinginformationpartliquidphasebeforethereactionstarted,
which leads to a porous structure of the product. Residual vapour The authors would like to express their thanks for ?nancial
and the PFA may also have generated since the sample was pre- support of the national Natural Science Foundation of China No.
pared in the ambient atmosphere. Further evidence of the vapour 50572122.Author''s personal copy
806 J. Li et al. / Journal of Alloys and Compounds 479 (2009) 803–806
References [6] Y. Han, J. Li, Y. Chen, Mater. Res. Bull. 38 (2003) 373–379.
[7] N.P. Tubalov, O.A. Lebedeva, V.I. Vereshchagin, Refract. Ind. Ceram. 44 (2003)
343–345.
[1] T.D. Senguttuvan, H.S. Kalsi, S.K. Sharda, B.K. Das, Mater. Chem. Phys. 67 (2001)
[8] A. Morancais, F. Louvet, D.S. Smith, J.P. Bonnet, J. Eur. Ceram. Soc. 23 (2003)
146–150.
1949–1956.
[2] J. Song, L. Zeng, A. Shui, X. Ren, Y. Liu, J. Wu, Bull. Chin. Ceram. Soc. 26 (2007)
[9] Douglas E. Burkes, G. Gottoli, John J. Moore, Compos. Sci. Technol. 66 (2006)
173–176.
1931–1940.
[3] Z. Deng, J.M.F. Ferreira, Y. Tanaka, Acta Mater. 2 (2007) 1–7.
[10] H.C. Yi, J.Y. Guigne, ′ L.A. Robinson, A.R. Manerbino, J.J. Moore, J. Porous Mater. 11
[4] I. Toshihiro, T. Takahiro, K. Yoshikazu, N. Akira, O. Kiyoshi, J. Eur. Ceram. Soc. 26
(2004) 5–14.
(2006) 957–960.
[11] O.K. Lepakova, L.G. Raskolenko, Y.M. Maksimov, J. Mater. Sci. 39 (2004)
[5] D.U. Tulyaganov, M.E. Tukhtaev, J.I. Escalante, M.J. Ribeiro, J.A. Labrincha, J. Eur.
3723–3732.
Ceram. Soc. 22 (2002) 1775–1782. |
|
