|
31.Zirconium Aluminum Carbides: New Precursors
for Synthesizing ZrO2–Al2O3
Composites
L.F.
He, Y.W. Bao, Y.C. Zhou,
J. Am. Ceram. Soc., 92 [11] 2751–2758
(2009)
|
Abstract
ZrO2–Al2O3
nanocrystalline powders have been synthesized by oxidizing
ternary Zr2Al3C4 powders.
The simultaneous oxidation of Al and Zr in Zr2Al3C4
results in homogeneous mixture of ZrO2 and
Al2O3 at nanoscale. Bulk nano- and
submicrocomposites were prepared by hot-pressing as-oxidized
powders at 1100oC–1500oC. The composition
and microstructure evolution during sintering was investigated
by XRD, Raman spectroscopy, SEM, and TEM. The crystallite
size of ZrO2 in the composites increased from
7.5 nm for as-oxidized powders to about 0.5 lm at 1500
oC, while the tetragonal polymorph gradually
converted to monolithic one with increasing crystallite
size. The Al2O3 in the composites
transformed from an amorphous phase in as oxidized powders
to h phase at 1100 oC and a phase at higher
temperatures. The hardness of the composite increased
from 2.0 GPa at 1100 oC to 13.5 GPa at 1400
oC due to the increase of density. |
32. High-temperature
powder x-ray diffraction experiments and ab initio calculation
of Ti3AlC2
H.
B. Zhang, X. Wu, Klaus Georg Nickel, J. X. Chen, Volker Presser1,
J.
Appl. Phys.,
106(2009):013519
|
Abstract
The structural
stability of the layered ternary carbide Ti3AlC2
was studied up to 35 GPa using x-ray diffraction with
a Merrill–Basset-type diamond anvil cell and ab initio
calculations. The structure P63 /mmc
was stable in the present pressure range without any phase
transition. The Birch–Murnaghan equation of state was
employed to fit the experimental pressure-volume date,
from which the isothermal bulk modulus of Ti3AlC2
was determined as 156±5 GPa, which was also supported
by theoretical results. In addition, theoretical calculations
described anisotropic pressure dependences of the lattice
parameters, electronic structure, and bonding properties
of Ti3AlC2. |
previous
page
|
Papers
published during 2009: part Ⅲ