Degradation behaviours of Fe-doped La0.8Sr0.2CoO3-δ by thermal stress
Suyeon Kim, Jiseung Ryu and Heesoo Lee
School of Materials Science & Engineering, Pusan National University, Busan, South Korea
ABSTRACT
The improvement in durability by Fe doping to La0.8Sr0.2CoO3-δ (LSC) and its degradation mechanism were investigated in terms of structural and morphological analyses. Polarisation resistance of LSC was increased approximately by 65.7% after exposure to thermal stress at 900°C for 100 h because the oxygen reduction reaction was declined by particle coarsening and aggregation of LSC powders. The polarisation resistance of La0.8Sr0.2Co0.8Fe0.2O3-δ (LSCF) was increased from 0.269 to 0.328 Ωcm2 after the heat treatment. Increasing rate of polarisation resistance of LSCF was 21.9%, which was three times lower than that of LSC due
to reduced particle coarsening and aggregation by Fe doping. Particle size of LSCF powders was maintained about 0.5–3 μm, and morphologies were also similar before and after the heat treatment. Chemical reaction between the LSCF and Sm-doped Ceria electrolyte powders did not occur despite the thermal stress, indicating the interface between the cathode and electrolyte is chemically stable.
KEYWORD S
SOFCs; polarisation resistance; durability; degradation; thermal stress
Design of piezoelectric piston-like piezoelectric transducers based on a
phononic crystal
Silvia Ronda and Francisco Montero de Espinosa ITEFI-CSIC, Madrid, Spain
ABSTRACT
Many clinical surveys have evaluated the use of ultrasound in physiotherapy treatments, the question of its effectiveness still being under discussion possibly because of the randomized energy density applied, which depends on the acoustic pressure beam of the transducers. In this work, a phononic crystal made of holes in solid materials is the basis for the design of a transducer with a piston-like vibration pattern where the radial modes are stopped, thus favoring the thickness vibration and resulting in a better mechanical vibration amplitude and acoustic efficiency. Finite element simulations have been made of the standard transducer
and the proposed design; then demonstrator devices have been manufactured and tested so experimental results could be compared to the calculated ones. The transducers with this phononic structure show an efficient piston-like emission. The electrical impedance, the emitting surface vibration pattern and the acoustic diffraction field have been calculated and experimentally measured.
KEYWORD S
Ultrasound; piezoelectric transducers; phononic crystals; physiotherapy
Improving bulk Ca3Co4O9 thermoelectric materials through Zr doping
M. A. Madre , Sh. Rasekh, M. A. Torres , J. C. Diez and A. Sotelo
Dpto. de Ciencia y Tecnología de Materiales y Fluidos, ICMA (Universidad de Zaragoza-CSIC), Zaragoza, Spain
ABSTRACT
Ca3Co4 −xZrxOy polycrystalline ceramics with small Zr substitution have been prepared through the classical solid-state method. X-ray diffraction data have shown that all samples are composed only of Ca3Co4O9 and Ca3Co2O6 phases. Moreover, by increasing Zr substitution up to 0.07, Ca3Co2O6 phase content is decreased. Density measurements have revealed that all samples are very similar, with values around 74% of the theoretical density. Electrical resistivity is decreased in Zr-doped samples, with respect to the pure samples, while Seebeck coefficient is unchanged. Both factors lead to power factor values around 0.33 mW K−2 m −1 at 800°C in 0.07 Zr-doped samples, which are about 65% higher than those obtained for the undoped samples.
KEYWORD S
Ceramics; doping; electric properties; microstructure; power factor
Low-temperature catalytic synthesis of SiC nanopowder from liquid phenolic
resin and diatomite
Junkai Wanga, Yuanzhuo Zhanga, Haijun Zhang a, Lei Hana, Yubao Bia, Huifang Wanga, Shupeng Songa and Shaowei Zhangb
aThe State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan, People’s Republic of China; b College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
ABSTRACT
3C–SiC nanopowder was catalytically synthesised at 1400°C for 3 h in argon using industrial diatomite powder and phenolic resin as raw materials, and cobalt nitrate as a catalyst precursor. Phase composition and microstructure of product samples were characterised using X-ray diffraction analysis, scanning electronic microscopy and transmission electronic microscopy. The effects of temperature, catalyst content and reaction time on the formation of SiC were examined. The results indicated that (1) phase pure 3C–SiC can be synthesised at 1400°C for 3 h using 1.0 wt-% Co catalyst; (2) if no catalyst was used, only little 3C–SiC was formed under the identical firing condition; (3) as-prepared 3C–SiC nanoparticles had irregular shapes with overall sizes of 30–300 nm. Density functional theory calculations further reveal that the Co catalyst assisted Si–O bond breaking and thus the SiC formation.
KEYWORD S
Diatomite; 3C–SiC; catalytic reaction; low-temperature synthesis; DFT
Microstructure and suppressed thermal depolarisation behaviours of lead-free
Na0.5Bi0.5TiO3:ZnO ferroelectric composite ceramics
Ling Li, Mankang Zhu, Qiumei Wei, Zhihua Guo, Mupeng Zheng and Yudong Hou
College of Materials, Beijing University of Technology, Beijing, China
ABSTRACT
A 0–3 type 0.8Na0.5Bi0.5TiO3(BNT):0.2ZnO lead-free ferroelectric composite ceramic structure was prepared by a solid-state oxide route. The X-ray diffraction analysis and scanning electron microscopy observation indicate that ZnO grains were scattered in the matrix consisting of BNT grains to form a (0–3) type composite structure, and a third phase Zn2TiO4 was formed due to the reaction ability of nano-sized ZnO with NBT compositions. The temperature-dependent electrical responses show that the dielectric anomaly at around 200° C inherited from NBT itself was suppressed as ZnO is composited, and the Pr of the specimen
sintered at 1000°C keeps almost unchanged as the poling temperature is 175°C, while its retained piezoelectric strain d33 value maintains 77% of the initial as exposed to 125°C annealing. These results suggest that the thermal depolarisation of BNT is suppressed due to the introduction of ZnO, even though the third phase Zn2TiO4 exists.
KEYWORD S
Sodium bismuth titanate; thermal depolarisation; ferroelectrics; composite ceramics
Preparation and characterisation of closed-pore Al2O3-MgAl2O4 refractory
aggregate utilising superplasticity
Lei Yuana, Xiaodong Zhanga, Qiang Zhub, Guo Weia, Jingkun Yua and Shaowei Zhangc
aSchool of Metallurgy, Northeastern University, Shenyang, People’s Republic of China; bSchool of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, Australia; cCollege of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
ABSTRACT
A novel high closed porosity Al2O3-MgAl2O4 refractory aggregate has been successfully fabricated by utilising superplasticity with Al2O3 and MgO as raw materials, SiC as high temperature pore-forming agent. The effects of the addition amounts of MgO and SiC on porosity, sintering behaviours, phase composition, pore size distribution and microstructure of the refractory aggregate have been investigated. The formation mechanism of the closed pore in the refractory aggregate has been discussed. The results showed that the MgO can improve the superplastic deformation ability of Al2O3-based ceramic at high temperature.
With the content of MgO and SiC increased, the closed porosity and the pore size increased. The oxidation of SiC improved the sinterability of materials at the initial stage of sintering, and then the released gases due to the further oxidation of SiC promoted the formation of closed pores by motivating the superplastic deformation ability of Al2O3-based materials.
KEYWORD S
Refractory aggregate; closed pore; Al2O3-MgAl2O4; SiC; superplasticity
The influence of microstructure on the mechanical properties of polycrystalline
diamond: a literature review*
Thomas A. Scotta,b
aDepartment of Materials, University of Oxford, Parks Road, Oxford, UK; bCentre for Doctoral Training in Diamond Science and Technology, Warwick, UK
ABSTRACT
Polycrystalline diamond (PCD) is an extremely high-performance cutting tool material used in the machining of rock, high-strength, non-ferrous metal alloys and carbon-fibre-reinforced composites. It is favoured for its exceptional hardness and wear resistance which results in at least an order of magnitude improvement in performance over previous technologies in almost all metrics. However, PCD suffers from unpredictable brittle fracture and degradation at high temperature during service which limits its capabilities in cutting applications. The literature on the link between its microstructure and its mechanical properties, including strength, toughness and flaw size distribution as measured by pseudo-static tests, is investigated. The conclusions of the seminal paper on this topic are re-examined in the light of modern ceramics research and an alternative explanation is put forth for the strength–grain size relationship published in this paper. All known literature values for strength and toughness vs. grain size and binder content are collated showing no overall trend in strength with binder content but moderate trends in all other combinations. The common claim of weak grain boundaries is brought into question in the light of the lack of any evidence of
this fracture mode being evident in pseudo-static tests. The industrial literature on wear testing and failure modes of PCD in service and service-like tests is examined to bridge the gap between pseudo-static and dynamic, application-based experiments. Six main failure modes are recorded and summarised with intergranular fracture being the most conspicuously absent from the pseudo-static tests. It is suggested that the temperature generated by friction in dynamic tests causes the weakening of grain boundaries, resulting in a transition from transgranular to intergranular fracture and a call for further research in this area is made.
KEYWORD S
Polycrystalline diamond; PCD; microstructure; mechanical properties; fracture toughness; strength; flaw size distribution; thermal degradation
