Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Production of Ceramic Nanofibers with Negative Coefficient of Thermal Expansion
Nasser Khazeni* ,1 , Irem Vural 1 , Bora Mavis 2 , Güngör Gündüz 1 and Üner Çolak 3
1 Department of Chemical Engineering, Middle East Technical University, Ankara 06531, Turkey
2 Department of Mechanical Engineering, Hacettepe University, Ankara 06800, Turkey
3 Department of Nuclear Engineering, Hacettepe University, Ankara 06800, Turkey
Abstract—Zirconium tungstate (ZrW 2 O 8 ) is a ceramic that shows negative coefficient of thermal expansion (NCTE) over a
wide range of temperature from 0.3 to 1443K. In this study, by adopting new low temperature synthesis and micro-emulsion
synthesis approaches, phase pure nano particles of ZrW 2 O 8 were prepared. After a series of size distribution homogenization
and filtering processes, recovered nanoparticles were used in an electrospinning process for production of nanofibers with
diameters around 300nm.
Thermal mismatch between different components of a
system can often be sources of problems like residual stress
induced cracking, thermal fatigue or even optical
misalignment in certain high technology applications. Use of
materials with tailored thermal expansion coefficient is a
counter-measure to overcome such problems. With its
negative thermal expansion coefficient (NCTE), ZrW 2 O 8 is a
candidate component to be used in synthesis of composites
with controlled coefficient of thermal expansion (CTE).
Tuning of the thermal expansion property is expected to
compensate such thermal mismatch problems.
Production of composites could be achieved by blending
negatively and positively expanding materials in different
forms. While blending the respective components in particle
form is the first obvious choice, different process or
application constraints can dictate the production of
components in core-shell structures or in the form of fibers.
The aims of this study are; i) synthesis of zirconium tungstate
nanoparticles by a new low temperature approach using
shorter aging times and, ii) applying an electrospinning
process to produce ZrW 2 O 8 nanofibers.
Cubic ZrW 2 O 8 can be synthesized by a variety of
methods. Solid state methods have been traditionally used to
produce ZrW 2 O 8 [1]. Other strategies involve sol-gel, non
hydrolytic sol-gel [2], hydrothermal [2], co-precipitation [3],
combustion synthesis [2] and low temperature synthesis [4]. In
sol-gel technique, long aging times (1-3 weeks) are used to
produce ZrW 2 O 8 . To shorten aging times, hydrothermal
ageing can be applied. Although different compounds have
been used as tungsten sources in the reported sol-gel and
hydrothermal methods, the low cost tungstic acid (TA) that
can readily be produced in Turkey has never been considered
as a possible source. A modified low temperature method by
using TA and ZrOCl 2 as starting materials was chosen to
synthesize the ZrW 2 O 8 precursor. The production technique is
given in Figure 1. By using this procedure, ZrW 2 O 8 is
produced in shorter aging times and without the use of a
hydrothermal ageing condition over 100 o C.
After obtaining ZrW 2 O 8 precursor, the product was
calcined at 600 o C for 10 hours. Obtained particles had sizes in
the range of 300nm-1μm. It was determined that, for the
preservation of integrity of nanofibers, particle sizes should be
smaller than 100nm. In order to decrease the particle sizes
further, a microemulsion (ME) technique was developed
taking the baseline recipe from the procedure given in figure1.
For ME, oleylamine (OAm) and hexane system was used.
XRD patterns of produced particles can be seen in figure 2.
Figure 1. Experimental flowchart
Figure 2. XRD pattern of produced ZrW 2 O 8 .
In order to produce nanofibers, produced particles were
dispersed in isopropyl alcohol (IPA) and, simple decantation
and filtering processes were applied to obtain 10-100 nm
diameter particles. Then spin dope containing PVP, IPA and
nanoparticles were prepared. The dope was spun by a syringe
pump at a rate of 2ml/hr. Typically applied voltage was 10kV
to the tip-target distance of 10cm. The spun mat was burnt for
8hr at 325 o C and then for 10hr at 600 o C. Produced fibers have
diameters around 300nm. SEM image of burnt fibers has been
depicted in figure 3. This work is supported by
TÜBTAK under Grant No. MAG–107M006.
Figure 3. SEM images of fibers.
*Corresponding author: khazeni.n@gmail.com
[1] Graham, J., Wadsley, A. D., Weymouth, J. H. and Williams, L. S.
Journal of American Ceramic Society 42, 570 (1959).
[2] Kameswari, U., Sleight, A. W. and Evans, J. S. O. International
Journal of Inorganic Materials 2, 333-337 (2000).
[3] Sun, X. J., Yang, J., Liu, Q. and Cheng, X. N. Wuji Huaxue
Xuebao 21, 1412-1416 (2005).
[4] Closmann, C., Sleight, A. W. and Haygarth, J. C. Journal of Solid
State Chemistry 139, 424 (1998).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 415