Autor/a:
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Rayón Encinas, Emilio; Moreno, R.; Alcázar, C.; Salvador Moya, Maria Dolores; Manjon Herrera, Francisco Javier; Jiménez Piqué, Emilio; Llanes Pitarch, Luis Miguel
|
Abstract:
|
Two commercial zirconia powders with 3 mol% of yttria
(TZ3YE and TZ3YS, labeled as ZE and ZS, respectively) sup-
plied by Tosoh (Japan) were used for this study. Maximum
colloidal stability for ZE was achieved by dispersing the pow-
ders in a mixture of water/ethanol of 90:10 (wt/wt) using a
sonication probe. The rheological behavior of the suspensions
was optimized in terms of solids content ranging from 20 to
33 vol% and sonication time (0
–
6 min), the best results being
obtained after 2 min. ZS samples were prepared to a solids
loading of 30 vol% in water dispersing with 2 min-sonication.
Samples obtained by slip casting in plaster molds were used for
dynamic sintering studies, and fully dense and nanostructured
specimens were obtained at temperatures of 1300
°
C
–
1350
°
C
(ZE samples) and 1400
°
C per 2 h (ZS samples). The Hardness
(
H
) and Young’s Modulus (
E
) properties of the specimens were
studied by nanoindentation technique giving 17 and 250 GPa
mean values for
H
and
E
, respectively. The specimens were
then forced to a low-temperature degradation (LTD) treatment
at 130
°
C for 240 h in steps of 60 h. Raman spectroscopy and
nanoindentation results of hydrothermally treated samples
showed the absence of transformation from tetragonal to
monoclinic phase until 180 h whereas the mechanical properties
maintained constant even at the sample surface. After 240 h of
LTD, the monoclinic phase was detected on all specimens by
Raman peaks centered at 180, 191, and 383 cm
1
. The nanoin-
dentation study revealed an important loss of mechanical fea-
tures reaching 10 and 175 GPa for
H
and
E
, respectively. In
the case of the ZS specimens, no monoclinic phase is detected
after 240 h of LTD treatment and no decay of
E
or
H
is
detected. The free defect microstructure reached for the ZS
specimen revealed a higher hydrothermal resistance so that it is
concluded that the excellent behavior against thermal degrada-
tion is possible due to the large uniformity obtained by colloi-
dal processing rather than the particle size of the starting
powders |