Ce1−x Sm x O2−x/2—A novel type of ceramic material for thermal barrier coatings
Journal of Advanced Ceramics
2226-4108
Ce1xSmxO2x/2-A novel type of ceramic material for thermal barrier coatings
Xiao-ge CHEN
Haoming ZHANG
Hong-song ZHANG 0 1
a b Yong-de ZHAO
Gang LI 0
c
0 Department of Mechanical Engineering, Henan Institute of Engineering , Zhengzhou 450007 , China
1 Institute of Chemistry Henan Academy Sciences , Zhengzhou 450052 , China
2 Department of Construction Engineering, Henan Institute of Engineering , Zhengzhou 450007 , China
In this study, Ce1xSmxO2x/2 ceramics were synthesized by sol-gel route and solid state sintering method. The phase structure was analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. The morphologies of the synthesized powders and the corresponding bulk samples were observed using scanning electron microscopy (SEM). Their thermal diffusivities and thermal expansion coefficients were measured by the laser-flash method and the pushing-rod method, respectively. Results show that pure Ce1xSmxO2x/2 powders with single fluorite structure are synthesized successfully, and their microstructures of the corresponding bulk samples are very dense. With the increase of Sm2O3 content, their thermal expansion coefficients decrease due to the higher electro-negativity of Sm3+ ions as compared with that of Ce4+ ions. Their thermal conductivities at 1000 ℃ lie in the range of 1.62-2.02 W/(m·K) due to the phonon scattering caused by the substituted atoms and oxygen vacancies. The Ce1xSmxO2x/2 ceramics can be used as ceramic candidates for novel thermal barrier coatings (TBCs).
thermal barrier coatings (TBCs); CeO2 oxides; doping; thermophyscial properties
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properties, 7–8 wt% yttria-stabilized zirconia (YSZ)
ceramic has been widely employed as the top coat
material by the current commercial thermal barrier
coatings in high temperature turbine components.
However, the thermal insulation ability and working
lifetime of the YSZ thermal barrier coating can be
injured severely for long-term application above
1200 ℃ due to its inherent phase transformation and
enhanced sintering [5,6]. Therefore, it is very urgent to
develop alternatives to YSZ for advanced TBC
applications.
The excellent ceramic candidates for TBCs must
possess a few important performances, such as low
thermal conductivity, appropriate thermal expansion,
good phase stability at high temperature, low sintering
rate, high melting point, chemical inertness, and good
adherence to the metal substrate [7]. However, ceramic
materials matching all the requirements are still very
rare in light of the current standard. Now, low thermal
conductivity and appropriate thermal expansion
coefficient have been regarded as the primary selection
criterions of the ceramic materials for TBC applications.
In recent years, ceramic oxides with pyrochlore
structure or defect fluorite structure have been widely
studied [8–11]. Except for the A2B2O7-type (A = rare
earth element, B = Zr, Ce, Hf, Sn) oxides [1–10], the
cerium oxides with fluorite structure have recently
attracted extensive attention due to a diversity of
applications, such as conversion catalysts for selective
hydrogenation of unsatured compounds, catalysts for
three-way automobile exhaust systems, abrasives for
chemical polishing slurries, gates for metal-oxide
semiconductor devices, and luminescent materials for
violet/blue fluorescence [12–14]. Now, the rare earth
doped CeO2 (RE2O3–CeO2) have also been considered
to be new materials for TBCs and solid oxide fuel cells
due to the excellent electrical, mechanical, and
thermophysical properties [15–17]. For example, Cao et
al. [18] studied the thermal conductivity and thermal
expansion coefficient of La2Ce2O7. Patwe et al. [19]
reported the lattice thermal expansion of Gd2CexZr2xO7.
Zhang et al. investigated the thermophysical properties
of (Sm1xGdx)2Ce2O7 [20] and (Sm1xDyx)2Ce2O7 [21].
Zha et al. [22] found that the electrical conductivities of
Ce1xGdxO2x/2 (GDC) and Ce1xSmxO2x/2 (SDC) at
700 ℃ are almost equal to the value of YSZ at 1000 ℃.
Compared with pure doped ceria oxide (DCO)
electrolyte, the DCO–chloride or DCO–carbonate
composite electrolyte not only has much higher ionic
conductivity, but also shows higher ionic transference
number at intermediate temperature range [23,24], and
these electrolytes also have good chemical stability
[25].
Although thermophysical properties of a few
rare earth stabilized CeO2 have been reported by
some researchers, the present reports about rare
earth stabilized CeO2 applications for TBCs are still
not systemic. Therefore, investigation of the
thermophysical properties of rare earth stabilized CeO2
is still of notable significance. Previous works have
discussed the electrical conductivity of Ce1xSmxO2x/2
system, but did not deal with thermophysical properties
of Ce1xSmxO2x/2 oxides. In the present study,
Ce1xSmxO2x/2 oxides were synthesized by sol–gel
method and pressureless sintering technology (...truncated)