A new method for testing the interface toughness of ceramic environmental barrier coatings (EBCs) on ceramic matrix composites (CMCs) J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-21 Hideki Kakisawa, Toshiyuki Nishimura
A simple interface fracture test for ceramic environmental barrier coatings (EBCs) on ceramic matrix composites (CMCs) was developed. A variation on the asymmetric double cantilever beam (ADCB) test was proposed so that the interface toughness could be measured in a small specimen of simple shape without applying interlaminar loading to the CMC substrate. The proposed test was applied to an EBC consisting of a mullite layer and Si bond coat on a monolithic SiC substrate. A pre-crack was introduced by pop-in cracking, and then a notch overlapping the pre-crack was machined. The pre-crack was opened by inserting a wedge into the notch. From the critical notch opening displacement the crack starts to propagate, interface toughness is calculated. The measured interface toughness was 4.1 J/m2. Finally, the application range of the test was discussed and suggestions were made for introduction of the notch and pre-crack.
Protecting nuclear graphite from liquid fluoride salt and oxidation by SiC coating derived from polycarbosilane J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-21 Zhao He, Pengfei Lian, Yan Song, Zhanjun Liu, Jinliang Song, Junpeng Zhang, Xiaobo Ren, Jing Feng, Xi Yan, Quangui Guo, Wenhong Liu
Dissolution of MgO Based Refractories in CaO-Al2O3-MgO-SiO2 Slag J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-20 Huijun Wang, Roberto Caballero, Du Sichen
Dissolution of different types of MgO based refractories into molten CaO-Al2O3-MgO-SiO2 slag was studied. Formation of micro spinel particles by addition of either colloidal alumina or micro alumina powder in the MgO matrix efficiently reduced the dissolution. The dissolution of MgO was found to be controlled by the slag penetration into the MgO matrix. In the case of stagnant slag, the slag-penetration would lead to the final dissociation of the decarbonized commercial MgO-carbon cube in less than 6 minutes. The major dissolution took place between the MgO grains and the liquid in this penetrated layer. The increase of the thickness slowed down the dissolution. In the case of stagnant slag and slag stirred at low speed, the internal mass transfer in the slag penetrated layer is the controlling step. At higher stirring speeds, the slag penetrated layer was removed. The removal of the penetrated layer would enhance the dissolution process.
Densification, mechanical and thermal properties of ZrC1−x ceramics fabricated by two-step reactive hot pressing of ZrC and ZrH2 powders J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-19 Boxin Wei, Lei Chen, Yujin Wang, Haibin Zhang, Shuming Peng, Jiahu Ouyang, Dong Wang, Yu Zhou
Densification behavior, mechanical and thermal properties of ZrC1−x ceramics with various C/Zr ratios of 0.6 ∼ 1.0 have been investigated by two-step reactive hot pressing of ZrC and ZrH2 powders at 30 MPa and 1500–2100 °C. The two-step reactive hot pressed ZrC1−x ceramic has a higher relative density (>95.3%) than that (91.9%) of stoichiometric ZrC sintered at 2100 °C. A cubic Zr2C-type ordered phase forms in the ZrC1−x sample obtained at a ZrC/ZrH2 molar ratio of 0.6 at a relatively low temperature of 1100 °C. The decrease in C/Zr ratio is beneficial to densification of ZrC1−x ceramic, however, excess grain growth occurs after sintering above densification temperature. The elastic modulus and Vickers hardness decrease with decreasing the C/Zr ratio. With decreasing the C/Zr ratio, both thermal conductivity and specific heat decrease due to the enhanced scattering of conducting phonons and electrons by carbon vacancies.
Repeated nanoscratch and double nanoscratch tests of Lu2O3 transparent ceramics: Material removal and deformation mechanism, and theoretical model of penetration depth J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-19 Chen Li, Feihu Zhang, Xin Wang, Xiaoshuang Rao
The single nanoscratch, repeated nanoscratch and double nanoscratch tests of Lu2O3 transparent ceramics are carried out on a nanoindenter. Theoretical models of the penetration depth in single scratch, repeated nanoscratch and double nanoscratch tests are established by taking the elastic recovery into account. The surface morphology, friction characteristics of repeated nanoscratch and elastic recovery of double nanoscratch are researched. Ductile surface with hardly cracks and burrs, and obvious pile-up at the leading edge and both sides of the scratch path are obtained. TEM results indicate that the ductile deformation mechanism of Lu2O3 transparent ceramics is a combination of poly-crystalline nano-crystallites in the inner grain and amorphous transformation. Many defects including dislocations, stacking faults, nano twins, torsion of atomic plane, fracture of atomic plane and wrong arrangement of atomic plane are induced in nano grains generated during the ductile removal process. The dominant way of subsurface crack propagation is intergranular fracture.
Comparative study of surface properties of Mg-substituted hydroxyapatite bioceramic microspheres J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-19 Liga Stipniece, Valentina Stepanova, Inga Narkevica, Kristine Salma-Ancane, Adrian Boyd
Mg-substituted hydroxyapatite (HAp) bioceramic microspheres were prepared by spray drying and subsequent processing at 1173, 1273 and 1372 K. Influence of various Mg substitution levels (up to 0.84 ± 0.10 wt%) on physicochemical properties of the HAp bioceramic microspheres was evaluated. Obtained results were used for the elucidation of the compositional and structural characteristics of the microspheres in conjunction with adsorption of protein, namely, bovine serum albumin (BSA). The primary difference among the microspheres processed at various temperature was the presence or absence of the micropores (<2 nm in diameter) and mesopores (between 2 and 50 nm). Presence of the micro- and mesopores resulted in higher specific surface area (SSA), enhanced solubility, i.e., ion release, and, accordingly, increase in the amount of BSA adsorbed on the microspheres. Furthermore, the BSA adsorption capacity of the microspheres decreased with increasing Mg content despite of higher SSA.
Centrifuge-aided micromolding of micron- and submicron-sized patterns J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-18 Hong-Fei Ju, Kaijie Ning, Kathy Lu
Developed from soft lithography, replica molding has been proven to be a good method to prepare micron- and submicron-sized features. However, the fidelity of the features can be compromised by incomplete feature cavity filling and feature shrinkage during the forming process. In this study, centrifuge-aided micromolding is developed to prepare micro- and submicron-sized ZnO features. By introducing a centrifugal force, the shear-thinning behavior of the suspensions is utilized, and the cavity filling process and the diffusion of trapped air out of the features are accelerated. The drying shrinkage is decreased by increasing the density of the wet nanoparticle packing from the centrifugal process. The centrifugal force improves the fidelity of all the designed features. ZnO ridges from 0.4 μm to 2 μm size and rods of 1.6 μm size are prepared successfully. The wide applicability of this strategy has been demonstrated by preparing ZrO2 features via the same method.
Mechanical behaviour of porous lanthanide oxide microspheres: experimental investigation and numerical simulations J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-18 P. Parant, E. Remy, S. Picart, J.P. Bayle, E. Brackx, A. Ayral, T. Delahaye, C.L. Martin
Actinide oxide microspheres are considered as promising substituents to powder precursors for the production of ceramic pellets of nuclear fuel or targets. Porous microspheres of sub-millimetric size are synthesised using the Weak Acid Resin process. Controlling their microstructure and their mechanical properties is essential to predict the microstructure of green compacts and sintered pellets. Here, cerium and gadolinium are used to mimic actinides as metal cation. Single microspheres are crushed experimentally using a micropress in a Scanning Electron Microscope (SEM) to investigate their mechanical properties and visualise their fracture behaviour. The results are compared to numerical simulations based on the Discrete Element Method (DEM). In DEM, a microsphere is modelled as an assembly of bonded spheres representing aggregates. Bonds may fracture in tension or shear. A limited number of material parameters (aggregate elastic modulus, bond strength) are sufficient for the accurate simulation of the fracture behaviour of a microsphere.
Synthesis and electrical properties of lead-free piezoelectric Bi0.5Na0.5TiO3 thin films prepared by Sol-Gel method J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-18 S. Abou Dargham, F. Ponchel, N. Abboud, M. Soueidan, A. Ferry, R. Desfeux, J. Assaad, D. Remiens, D. Zaouk
Lead-free Bi0.5Na0.5TiO3 (BNT) piezoelectric thin films were deposited on Pt/TiOx/SiO2/Si substrates by Sol-Gel method. A dense and well crystallized thin film with a perovskite phase was obtained by annealing the film at 700 °C in a rapid thermal processing system. The relative dielectric constant and loss tangent at 12 kHz, of BNT thin film with 350 nm thickness, were 425 and 0.07, respectively. Ferroelectric hysteresis measurements indicated a remnant polarization value of 9 μC/cm2 and a coercive field of 90 kV/cm. Piezoelectric measurements at the macroscopic level were also performed: a piezoelectric coefficient (d33effmax) of 47 pm/V at E = 190 kV/cm was obtained. The piezoresponse force microscopy data confirmed that BNT thin films present ferroelectric and piezoelectric behavior at the nanoscale level.
Microscopic Scale Evidence of Phase Transformation Process in Barium Aluminosilicate Glass-Ceramic J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-18 Songsong Wu, Long Xia, Bin Shi, Guangwu Wen
The hexacelsian-celsian (H-M) phase transformation in barium aluminosilicate glass-ceramics (BAS) is sluggish. It is reported that Li+ dopants can promote this conversion effectively, but the detail reasons are still unclear. In this work, BAS glass-ceramics doped with different content of Li+ were synthesized by sol-gel method. Results suggest that Li+ dopant can accelerate the formation of hexacelsian at ∼800 °C and promote the phase separation between virgilite and BAS. Then the obtained hexacelsian phase starts to transform into celsian at 1300 °C and approximately completes at 1400 °C. During phase transformation process, the microstructure of hexacelsian-paracelsian, paracelsian-celsian and celsian coherent-phase were observed. It indicates that paracelsian serves as transient phase to reduce the difficulty of H-M phase conversion. This mechanism of hexacelsian-paracelsian-celsian (H-P-M) phase transformation gives the novel explanation of the effects of Li+ dopants on H-M phase transformation at microscopic scale.
Coexistence of three ferroelectric phases and enhanced piezoelectric properties in BaTiO3–CaHfO3 lead-free ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-17 Yang Yang, Yibei Zhou, Juan Ren, Qiaoji Zheng, Kwok Ho Lam, Dunmin Lin
Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO3-xCaHfO3 was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO3 (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06 ≤ x ≤ 0.08. Both large piezoelectric coefficient (d33∼400 pC/N), inverse piezoelectric coefficient (d33*∼547 pm/V) and planar electromechanical coupling factor (kp∼58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response.
Direct Preparation of La-doped SrTiO3 Thermoelectric Materials by Mechanical Alloying with Carbon Burial Sintering J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-17 Daquan Liu, Yuwei Zhang, Huijun Kang, Jinling Li, Zongning Chen, Tongmin Wang
Thermoelectric Sr1-xLaxTiO3 (x = 0, 0.02, 0.05, 0.08) nanoparticles were directly prepared by mechanical alloying, followed by carbon burial sintering to produce the bulk counterparts, for the purpose of obtaining pure phase and fine microstructures in a facile process. Electrical and thermal transport properties have been measured over the temperature range from 300 K to 1100 K. La was successfully doped into the SrTiO3 during the milling process and acted as an n-type dopant. Core structure and superstructure in bulk samples, leads to a relatively high absolute Seebeck coefficient. The dimensionless figure-of-merit ZT changes with the increasing of La content and temperature, and the maximum ZT value can reach 0.06 at 300 K for x = 0.02 and 0.20 at 1000 K for x = 0.08. This strategy for bulk thermoelectric materials is simple, cost-effective and has great potential in large-scale industrial applications.
Porosity, mechanical and insulating properties of geopolymer foams using vegetable oil as the stabilizing agent J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-15 Chengying Bai, Tao Ni, Qiaoling Wang, Hongqiang Li, Paolo Colombo
Geopolymer foams, as a potential eco-friendly building materials, are increasingly being discussed in the literature. This study reports the synthesis and characterization of geopolymer foams using hydrogen peroxide (H2O2) solution as pore-forming agent and oil as the stabilizing agent. The geopolymer foams with low bulk densities (0.37 < ρb < 0.74 g/cm3), low thermal conductivities (0.11 < λ < 0.17 W/(m.K)), high porosity (66 < p < 83 vol%), and acceptable compressive strength (0.3 < σ < 11.6 MPa) were successfully fabricated at appropriate conditions. Factors that influence the insulating, mechanical, porous, and microstructural properties were investigated. It was found that the content of the stabilizing agent and the blowing agent had a significant influence on the porous structure and associated foam performance.
Effect of Y-doping on the phase relation and electrical properties of Fe-doped BaZrO3 J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-14 Dongyoung Kim, Daae Lee, Jong Hoon Joo
The effects of the co-doping of Y in Fe-doped BaZrO3 (BaZr0.7-yFe0.3YyO3-δ) on the phase relation and electrical properties are investigated in this study. While a single phase is formed up to y = 0.1 by the substitution of Y for Zr-sites (phase-1), the amphoteric substitution of Y for both Zr-sites and Ba-site (phase-2) is observed above y = 0.1. Electrical conductivity measurements suggest that p-type conduction prevails under an oxidizing atmosphere. The hole conductivity increases with an increase of Y concentration up to y = 0.1, but a further increase of Y concentration causes a decrease in the conductivity. The maximum conductivities of both bulk and grain boundary are obtained at y = 0.1, and a further increase of Y concentration leads to a decrease of the conductivity due to the possible formation of phase-2 with the partial replacement of Y for Ba-sites ( Y Ba • ). Partial proton conductivity is also improved by Y-doping up to y = 0.1, but a further doping cannot contribute to an increase in the proton conductivity. The results indicate that the mixed proton and hole conductivity of Fe-doped BaZrO3 can be improved by the co-doping of a rare-earth acceptor (Y3+), but the doping level is limited to y = 0.1 to avoid the formation of phase-2.
Biaxial strength and slow crack growth in porous alumina with silica sintering aid J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-14 Astrid Bakken, Susanne Wagner, Michael J. Hoffmann, Bernt Thorstensen, Mari-Ann Einarsrud, Tor Grande
Biaxial strength, fracture toughness and subcritical crack growth are reported for coarse grained porous alumina ceramics. The materials were prepared with a varying amount of a silica sintering aid, which resulted in the formation of a glassy secondary phase at the grain boundaries. Crystalline mullite was additionally found in the material with the highest silica content. The biaxial strength, measured by Ball-on-Ring and Ball-on-3-Balls, was highest for the material without mullite at the grain boundaries, and the biaxial strength decreased with increasing porosity. The fracture toughness of the materials was in the range of 1.7–1.9 MPa m0.5. Measurements of subcritical crack growth by a modified lifetime method in air and aqueous environments demonstrated a higher crack growth rate in water and acid relative to in air. The effect of porosity and grain boundary phase were discussed in relation to subcritical crack growth and fracture mode in the coarse grained alumina ceramics.
Long Term Stability of Electrocaloric Response in Barium Zirconate Titanate J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-14 Florian Weyland, Thorsten Eisele, Sebastian Steiner, Till Frömling, George A. Rossetti Jr., Jürgen Rödel, Nikola Novak
The stability of the electrocaloric effect under electric field cycling is an important consideration in the development of solid-state cooling devices. Here we report measurements carried out on Ba(Zr0.2Ti0.8)O3 ceramics which reveal that the adiabatic temperature change, polarization-electric field hysteresis loops and dielectric permittivity/loss show stable behavior up to 105 cycles. We further demonstrate that the loss in electrocaloric response observed after 105 cycles is associated with the migration of oxygen vacancies. As a result, the electrical properties of the material are changed leading to an increase in leakage current and Joule heating. Reversing the polarity of the electric field after every 105 cycles changes the migration direction of oxygen vacancies, thereby preventing charge accumulation at grain boundaries and electrodes. By doing so, the electrocaloric stability is improved and the adiabatic temperature remains constant even after 106 cycles, much higher than achieved in commercially available barium titanate ceramics.
Design of polymer-derived SiC for nuclear applications from the perspective of heterogeneous interfaces J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-13 Wen Liu, Yejie Cao, Laifei Cheng, Yiguang Wang
Polymer-derived SiC ceramics have been increasingly used in the field of nuclear energy. Herein, we synthetized polymer-derived SiCs with varying SiC/C heterogeneous interfacial properties by pyrolyzing the ceramics at different temperatures. Subsequently, we studied the effect of these interfacial properties on the irradiation behavior (i.e., volume swelling, amorphization, and mechanical properties) of the SiC ceramics. In the case of crystalline ceramics (pyrolyzed at 1150–1500 °C), the presence of a nano-crystalline graphite (NC-G) phase with sp3/sp2 hybridization ratios of 0.40–1.27 further enhanced the swelling resistance of nano-SiC by increasing the defect trapping capability of the interfaces. In contrast, amorphous ceramics (pyrolyzed at 900–1100 °C) showed low penetration depths and superior stabilities upon irradiation. These strong ion cascade blocking characteristics may result from the atomic short-range order of these materials. This approach allows optimum design of polymer-derived SiC with superior swelling resistance and stability under room-temperature irradiation.
MgO assisted densification of highly transparent YAG ceramics and their microstructural evolution J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-12 Tianyuan Zhou, Le Zhang, Shuai Wei, Lixi Wang, Hao Yang, Zhenxiao Fu, Hao Chen, Farida A Selim, Qitu Zhang
In current study, various amounts of MgO single dopant was adopted to fabricated high quality transparent YAG ceramics, by utilizing a simple one-step solid state reaction sintering method in vacuum. At a MgO doping amount of only 0.03 wt.%, YAG transparent ceramics with a transmittance of 84.5% at 1064 nm could be obtained, after sintering at 1820 °C for 8 h. The microstructure evolution and optical property of as-fabricated YAG ceramics as a function of MgO doping concentration were systematically investigated. MgO dopant could effectively promote densification of YAG ceramics when the sintering temperature was lower than 1660 °C, and dramatically accelerate its grain growth between 1540 °C and 1660 °C. Further increase the doping amount of MgO would not benefit to the optical quality of YAG ceramics, and the intragranular pores as well as the Mg-riched secondary phase were observed from the MgO heavily doped ceramics.
Exposure of refractory materials during high-temperature gasification of a woody biomass and peat mixture J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-12 Markus Carlborg, Fredrik Weiland, Charlie Ma, Rainer Backman, Ingvar Landälv, Henrik Wiinikka
Finding resilient refractory materials for slagging gasification systems have the potential to reduce costs and improve the overall plant availability by extending the service life. In this study, different refractory materials were evaluated under slagging gasification conditions. Refractory probes were continuously exposed for up to 27 hours in an atmospheric, oxygen blown, entrained flow gasifier fired with a mixture of bark and peat powder. Slag infiltration depth and microstructure were studied using SEM EDS. Crystalline phases were identified with powder XRD. Increased levels of Al, originating from refractory materials, were seen in all slags. The fused cast materials were least affected, even though dissolution and slag penetration could still be observed. Thermodynamic equilibrium calculations were done for mixtures of refractory and slag, from which phase assemblages were predicted and viscosities for the liquid parts were estimated.
Oxidation mechanisms under water vapour conditions of ZrB2-SiC and HfB2-SiC based materials up to 2400 °C J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-12 V. Guérineau, A. Julian-Jankowiak
This study aims at observing and understanding the oxidation mechanisms of ZrB2-20 vol%SiC (ZS), HfB2-20 vol%SiC (HS) and HfB2-20 vol%SiC- 3 vol%Y2O3 (HSY) materials up to 2400 °C under water vapour conditions. After SPS sintering, fully densified samples were oxidized at several temperatures with 30 vol% H2O/70 vol% Ar during 20 s. Weight variations as well as post-test microstructural and XRD analyses allowed understanding the influence of the composition on the oxidation behavior and the evolution of each oxide sublayer. Below 1550 °C, oxidation is limited, and thin oxide layers are observed. At 1900 and 2200 °C, ZS and HS show mechanical damage (cracks, spallation), while HSY keeps its structural integrity and interlayer adherence. The addition of Y2O3 reduces the damages due to thermal stresses in the material due to the stabilization of the cubic phase of HfO2, and the formation of a Y2Si2O7 interphase that mitigates thermal expansion mismatch between the SiC-depleted layer and the HfO2 layer.
Formation of different calcium phosphate phases on the surface of porous Al2O3-ZrO2 nanocomposites J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-12 Thauane Aparecida Inácio da Costa Sartori, Julieta Adriana Ferreira, Denise Osiro, Luiz Alberto Colnago, Eliria Maria de Jesus Agnolon Pallone
Biomimetic deposition of calcium phosphates onto Al2O3-ZrO2 nanocomposites provides greater surface bioactivity, leading to the formation of biomaterials that can potentially replace and restore bone tissues. This study is aimed at evaluating the formation of different calcium phosphate phases using biomimetic coating on chemically treated and untreated surfaces of porous Al2O3-ZrO2 (5 vol%) nanocomposites at different incubation times. To this end, the porous materials fabricated by gelcasting were calcined, sintered, chemically treated or left untreated, and biomimetically coated during a period of 14–21 days. The results indicated high porosity of the nanocomposite surfaces as well as high pore interconnectivity, which favours osseointegration. Additionally, it was observed that chemical treatment may influence the amount of calcium phosphates formed on the nanocomposite surfaces as well as the minimum incubation time, favouring the formation of a particular calcium phosphate phase over the nanocomposite surface.
Inherent anisotropy in transition metal diborides and microstructure/property tailoring in ultra-high temperature ceramics—a review J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-12 Guo-Jun Zhang, De-Wei Ni, Ji Zou, Hai-Tao Liu, Wen-Wen Wu, Ji-Xuan Liu, Tohru S. Suzuki, Yoshio Sakka
This is the first comprehensive review on inherent anisotropic features of transition metal diboride (MB2) and their implementation for tailoring the microstructure and properties of MB2-based Ultra-high temperature Ceramics (UHTCs). The emphasis is on the processing approaches, microstructures, and properties of self-reinforced and/or textured MB2-based composites with elongated MB2 grains. The crystal structure characteristics and grain growth behaviour of MB2 are also critically reviewed. Benefiting from the tailored microstructure, the MB2-based ceramics exhibit some improved properties. Considering the success of Si3N4 ceramics in the field of structural ceramics, it is expected that the potential MB2-based ceramic composites with abundant elongated MB2 grains, textured structures, and controlled grain boundaries would possess improved fracture toughness, thermal shock resistance, and reliable high-temperature properties, which are desired for their practical applications. Accordingly, microstructure designing and tailoring provide an important perspective for the future development of UHTCs.
Mechanical properties and grain orientation evolution of zirconium diboride-zirconium carbide ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-12 A. D’Angio’, J. Zou, J. Binner, Hai-Bin Ma, G.E. Hilmas, W.G. Fahrenholtz
The effect of ZrC on the mechanical response of ZrB2 ceramics has been evaluated from room temperature to 2000 °C. Zirconium diboride ceramics containing 10 vol% ZrC had higher strengths at all temperatures compared to previous reports for nominally pure ZrB2. The addition of ZrC also increased fracture toughness from <img height="60" border="0" style="vertical-align:bottom" width="165" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0955221917306015-si2.gif">∼3.5MPam for nominally pure ZrB2 to <img height="60" border="0" style="vertical-align:bottom" width="166" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0955221917306015-si3.gif">∼4.3MPam due to residual thermal stresses. The toughness was comparable with ZrB2 up to 1600 °C, but increased to <img height="60" border="0" style="vertical-align:bottom" width="145" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0955221917306015-si4.gif">4.6MPam at 1800 °C and 2000 °C. The increased toughness above 1600 °C was attributed to plasticity in the ZrC at elevated temperatures. Electron back-scattered diffraction analysis showed strong orientation of the ZrC grains along the  direction in the tensile region of specimens tested at 2000 °C, a phenomenon that has not been observed previously for fast fracture (crosshead displacement rate = 4.0 mm min−1) in four point bending. It is believed that microstructural changes and plasticity at elevated temperature were the mechanisms behind the ultrafast reorientation of ZrC.
Process-tolerant pressureless-sintered silicon carbide ceramics with alumina-yttria-calcia-strontia J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-11 Yu-Kwang Seo, Jung-Hye Eom, Young-Wook Kim
Process-tolerant SiC ceramics were prepared by pressureless sintering at 1850–1950 °C for 2 h in an argon atmosphere with a new quaternary additive (Al2O3-Y2O3-CaO-SrO). The SiC ceramics can be sintered to a >94% theoretical density at 1800–1950 °C by pressureless sintering. Toughened microstructures consisting of relatively large platelet grains and small equiaxed grains were obtained when SiC ceramics were sintered at 1850–1950 °C. The presently fabricated SiC ceramics showed little variability of the microstructure and mechanical properties with sintering within the temperature range of 1850–1950 °C, demonstrating process-tolerant behavior. The thermal conductivity of the SiC ceramics increased with increasing sintering temperature from 1800 °C to 1900 °C due to decreases of the lattice oxygen content of the SiC grains and residual porosity. The flexural strength, fracture toughness, and thermal conductivity of the SiC ceramics sintered at 1850–1950 °C were in the ranges of 444–457 MPa, 4.9-5.0 MPa ∙ m1/2, and 76-82 Wm−1K−1, respectively.
Effect of oxygen partial pressure on temperature for onset of flash sintering 3YSZ J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-07 Dianguang Liu, Yejie Cao, Jinling Liu, Yan Gao, Yiguang Wang
In this paper, it is demonstrated that in an oxygen-enriched environment, the oxygen partial pressure affects the onset temperature of flash sintering of 3 mol% yttria-stabilized zirconia (3YSZ). Flash sintering experiments were performed with oxygen partial pressures in the range of 0.25 to 1 atm. The results indicate that the onset temperature increased by increasing oxygen partial pressure. According to the plots of the conductivity as a function of temperature, the oxygen partial pressure might affect the onset temperature, by changing the conductivity in the pre-flash stage. Combined to the analysis of the law of mass action, it was established that electron conduction might also represent a critical parameter during the pre-flash stage of flash sintering, excluding the oxygen vacancy conduction.
Micro-structure of ITO ceramics sintered at different temperatures and its effect on the properties of deposited ITO films J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-07 Fangsheng Mei, Tiechui Yuan, Ruidi Li, Kai Qin, Libo Zhou, Wenjun Wang
Structural characterizations of two ITO ceramics that were respectively sintered at 1560 °C and 1600 °C were focused on and the results indicate that the lower sintering temperature is good for ITO ceramics to have the triangle fine grains, larger elemental concentration gradients of indium and tin and more content of In4Sn3O12 phase which displays the stronger grain orientation growth along the crystallographic direction of [0-11]. ITO films with 100 nm thickness deposited at 25 °C ∼ 230 °C were used to investigate the effect of micro-structure on the film properties. Grain orientation growth of In4Sn3O12 phase is conductive to form ITO films of columnar structure. Otherwise, uniform micro-structure and higher solubility of SnO2 in In2O3 main phase contribute to deposit ITO films of higher sheet resistance, less thickness uniformity and higher transmittance at 25 °C, smaller etching angle and lower etching rate at 230 °C.
(Al3+, Nb5+) co–doped CaCu3Ti4O12: An extended approach for acceptor–donor heteroatomic substitutions to achieve high–performance giant–dielectric permittivity J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-07 Jakkree Boonlakhorn, Pinit Kidkhunthod, Narong Chanlek, Prasit Thongbai
Substitution of (Al3+, Nb5+) co–dopants into TiO6 octahedral sites of CaCu3Ti4O12 ceramics, which were prepared by a solid state reaction method and sintered at 1090 °C for 18 h, can cause a great reduction in a low–frequency loss tangent (tanδ≈0.045–0.058) compared to those of Al3+ or Nb5+ single–doped CaCu3Ti4O12. Notably, very high dielectric permittivities of 2.9 − 4.1 × 104 with good dielectric–temperature stability are achieved. The room–temperature grain boundary resistance (Rgb≈0.37–1.17 × 109 Ω.cm) and related conduction activation energy (Egb≈0.781–0.817 eV), as well as the non–Ohmic properties of the co–doped ceramics are greatly enhanced compared to single–doped ceramics (Rgb≈104–106 Ω cm and Egb≈0.353–0.619 eV). The results show the importance of grain boundary properties for controlling the nonlinear–electrical and giant–dielectric properties of CaCu3Ti4O12 ceramics, supporting the internal barrier layer capacitor model of Schottky barriers at grain boundaries.
Polymer-derived Ceramic Tapes with small and negative Thermal Expansion Coefficients J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-06 A. Fedorova, L. Michelsen, M. Scheffler
A polysiloxane filled with ß-eucryptite and/or SiC was used for the processing of polymer derived ceramic tapes. The combination of both fillers in varying proportions allowed to tailor the overall bulk thermal expansion and the flexural strength of the resulting composite materials simultaneously. Incorporation of SiC increased noticeably the flexural strength of the samples and influenced the phase changes resulting from the interactions between the β-eucryptite filler and the polymer derived ceramic matrix. Changes in the phase composition and changes of the unit cell parameters of β-eucryptite because of the formation of solid-solutions with silica originating from the SiO2 constituent of the polymer derived ceramic matrix were observed by Rietveld refinement. Tapes resulting from this process possess a sufficient mechanical stability and their coefficient of thermal expansion can be adjusted from slightly positive to moderate negative values.
Enhancement of the dielectric permittivity and magnetic properties of Dy substituted strontium titanate ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-06 Alexander Tkach, João S. Amaral, Sebastian Zlotnik, Vítor S. Amaral, Paula M. Vilarinho
Structural, dielectric and magnetic properties of dense Dy-substituted strontium titanate ceramics prepared by the conventional mixed oxide method are investigated. In the Sr1-1.5xDyxTiO3 system, the incorporation of Dy onto the Sr site of the perovskite lattice of strontium titanate is confirmed by a linear decrease of the lattice parameter up to x = 0.05. Dielectric spectroscopy analysis of Sr1-1.5xDyxTiO3 ceramics reveals four relaxations. Two relaxations observed below 55 K are attributed to individual dipoles formed by off-centre displacement of Dy3+ ions on the Sr sites in a highly polarizable lattice of strontium titanate. Other two dielectric relaxations observed at higher temperatures are attributed to the vacancy related interfacial polarization mechanisms. As result, very high dielectric permittivity of ∼33500 at 28 K and of ∼9600 around room temperature are obtained for Sr0.985Dy0.01TiO3 ceramics at moderate dissipation factor of ∼0.02, making it a promising material for capacitor electronic applications. Paramagnetic behaviour is observed for both Sr1-1.5xDyxTiO3 and Sr1-xDy2xTi1-xO3 ceramics, indicating impossibility to induce a magnetic order and hence magnetoelectric coupling in strontium titanate by Dy substitution on either Sr or both Sr and Ti sites.
Effect of Na-doping on thermoelectric and magnetic performances of textured Bi2Sr2Co2Oy ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-06 G. Çetin Karakaya, B. Özçelik, M.A. Torres, M.A. Madre, A. Sotelo
Bi2Sr2-xNaxCo2Ox (x = 0.0, 0.025, 0.050, 0.075, 0.100, and 0.125) samples were prepared through the solid-state route and textured using the laser floating zone technique. Microstructural analysis of as-grown samples showed well oriented grains and a relatively high amount of secondary phases due to their incongruent melting. Annealing procedure has drastically decreased the number and amount of secondary phases. Moreover, Na-doping has further decreased the secondary phases content and improved grain alignment. These modifications have been reflected in a large decrease of electrical resistivity with the annealing procedure. The maximum power factor values have been obtained in 0.075 Na-doped annealed samples, 0.20 mW/K2m, which are much higher than the best values obtained in textured materials through hot uniaxial pressing. Magnetic properties were very similar for all samples, with paramagnetic Curie temperature and effective magnetic moment values of − 48.6 K and ≈2 μB, respectively.
A case study of mechanical properties of perovskite-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxygen transport membrane J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-06 Li Wang, Rui Dou, Gong Wang, Yizhe Li, Mingwen Bai, David Hall, Ying Chen
This study has investigated mechanical properties of perovskite-structured Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) oxygen transport membrane. The Young’s modulus and fracture toughness are determined by both macroscopic-scale and microscopic-scale methods Both three-point and ring-on-ring bending tests as macroscopic-scale methods produce broadly similar results with a Young’s modulus, which is lower than that measured from micro-indentation method under a 10 N load. Young’s modulus and fracture toughness of BSCF show strongly dependent of the porosity. However, the fracture toughness of BSCF is independent of grain size. The fracture toughness determined by macroscopic-scale method is similar with that measured by microscopic-scale method. The crack shape of BSCF under a 10 N load is determined to be a median-radial mode. The intrinsic Young’s modulus and fracture toughness are determined to be 105.6 GPa and 1.49 MPa m0.5, respectively, according the Minimum Solid Area (MSA) model. Annealing decreases the fracture toughness of BSCF between RT and 800 °C.
Structural evolution, grain growth kinetics and microwave dielectric properties of Li2Ti1-x(Mg1/3Nb2/3)xO3 J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-05 J.J. Bian, X.H. Zhang
Li2Ti1-x(Mg1/3Nb2/3)xO3 ceramics were prepared by conventional solid state process. Their structural evolution, grain growth kinetics and microwave dielectric properties have been studied in this paper. The results show that continuous solid solution could be formed within the experiment compositional range. The structure changed from long range ordered monoclinic into short range ordered cubic phase as the increase in x. Small levels of substitution for Ti4+by (Mg1/3Nb2/3)4+ slightly decreased the dielectric permittivity, while considerably improved the Q×f value. The temperature coefficient of resonant frequency changed from positive into negative value. The grain growth kinetics during sintering process and Q × f value of the sintered body were affected by different calcining temperature of mixed powders. Excellent combined microwave dielectric properties with εr ∼21.0, Q × f ∼ 200 000 GHz and τf value of −1 ppm/ °C could be obtained after optimizing calcining temperature for the x = 0.24 composition after sintering at 1250 °C/2 h.
Oxidation resistance of SiC/SiC composites containing SiBC matrix fabricated by liquid silicon infiltration J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-05 Xinnan Sun, Xiaowei Yin, Xiaomen Fan, Xiaokang Ma, Xiaoyu Cao, Laifei Cheng, Litong Zhang
The mechanical behavior and oxidation resistance of SiC/SiC-SiBC composites were studied in this work. According to the debonding criterion of He and Hutchinson, the debonding could occur at the BN interphase, which insures that the fibers can well play the strengthening and toughening performance. The oxidation resistance of SiC/SiC-SiBC composites consisting of SiC fibers with thermal expansion coefficients (CTE) of 5.1 × 10−6 K−1 and 4.0 × 10−6 K−1 was compared. The composites consisting of SiC fibers with higher CTE show slight weight changes at 800, 1000, and 1200 °C, and the corresponding strength retention ratios are 109.6%, 103.2% and 102.9%, exhibiting excellent oxidation resistance. The CTE of composites consisting of SiC fibers with higher CTE matches well with the CTE of SiC coating, so rarely no cracks can be formed in the coating, which inhibits the inward diffusion of oxidizing medium and leads to high strength retention ratios after oxidation tests.
Effect of spherical porosity on co-fired dense/porous zirconia bi-layers cambering J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-05 Francesca Teocoli, Debora Marani, Ragnar Kiebach, Vincenzo Esposito
Geometrical instability leading to cambering is recorded during co-sintering of zirconia dense/porous bi-layered planar structures. Sintering strain in the bi-layers rises mainly from mismatch between the different porosity volume fractions at the layers and their interface. In this paper, we analyze the model case of dense taped of 8 mol% Y2O3-stabilized ZrO2 laminated on ca. 400 μ thick 3 mol% Y2O3 doped zirconia porous tapes, with homogenous spherical porosity of 13 vol%, 46 vol%, and 54 vol%. Sintering stress during densification is evaluated from the shrinkage rates and viscoelastic behavior during sintering by thermo-mechanical analysis, using cyclic loading dilatometry. The camber development of the bi-layers is measured by in-situ optical dilatometry. In accordance with the model prediction, cambering can be controlled tuning the porosity while achieving a synergetic effect between densification and formation of open porosity at the bilayers.
Characterization of nickel manganite NTC thermistor films prepared by aerosol deposition at room temperature J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-05 Michaela Schubert, Christian Münch, Sophie Schuurman, Véronique Poulain, Jaroslaw Kita, Ralf Moos
NiMn2O4+δ thermistor thick films have been successfully deposited by the so-called Aerosol Deposition Method (ADM) at room temperature on alumina substrates, Si-wafers, as well as on special planar four-wire interdigital electrode structures for high-precision electrical characterization. The NTCR films are homogeneous, completely dense and scratch resistant. Both as-deposited and tempered, the NTCR films exhibit a cubic spinel structure. Between 25 °C to 90 °C, the NTCR film resistance behaves as it is typical for variable range hopping (VRH) with parabolic density of states. As a result of moderate film tempering, the thermistor constant B and the specific resistance at 25 °C (ρ25) decrease from 4250 K to 4020 K and 65 Ω·m to 40 Ω·m respectively, and are close to bulk values. In combination with the excellent reproducibility of the ρ25 and B values, AD processing of films appears to be a promising alternative for classical ceramic bulk processes.
Effects of Al2O3 crystal types on morphologies, formation mechanisms of mullite and properties of porous mullite ceramics based on kyanite J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-04 Huishi Guo, Wenfeng Li
Porous mullite ceramics with different crystal shapes of mullite are fabricated by in-situ reaction with middle-grade kyanite as raw material, Al(OH)3, γ-Al2O3, ρ-Al2O3 and α-Al2O3 as alumina sources. Effects of Al2O3 crystal types on morphology evolution and formation mechanisms of mullite, and properties of porous ceramics are investigated. Results show that mullite in the sample with Al(OH)3 mainly shows acicular morphology, because its (001) plane has the minimum interplanar crystal spacing and maximal attachment energy, it grows fast along  direction by screw dislocation mechanism. With a successive slowdown in reactivities of Al(OH)3, γ-Al2O3, ρ-Al2O3 and α-Al2O3, the amount and aspect ratio of mullite reduce, its growth mechanism gradually transforms into two-dimensional nucleation. Acicular mullite not only reinforces samples, but makes effective pore sizes smaller, which enable the sample with Al(OH)3 to present low bulk density, high apparent porosity and linear changes, small average pore size and good mechanical strength.
The Structural Origin of Enhanced Energy Harvesting Performance in Piezoelectric Perovskite J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-04 Mupeng Zheng, Yudong Hou, Xiaodong Yan, Mankang Zhu
Energy harvesting, which can translate the wasted vibration energy into electric energy, is now a hot topic in the field of new energy, and the key point is to design high power piezoelectric ceramic according with the requirements of low-frequency vibration energy harvesting. In this study, high quality Co-modified 0.2Pb(Zn1/3Nb2/3)O3–0.8Pb(Zr0.50Ti0.50)O3 (PZN–PZT ± Co) ceramics have been prepared by the two-stage method, and the energy harvesting characteristics were investigated. The results showed that the hierarchical nanodomain structure boosts the strong piezoelectric activity, leading to the high energy harvesting performance. The PZN–PZT ± Co ceramic sintered at 1000 °C exhibits an excellent d33 × g33 value of 14080 × 10−15 m2/N, which are much larger than that of commercial PZT-based ceramics. In the mode of the cantilever-type energy harvester, the output voltage and energy density of 33 V, 4.4 μW/mm3 were obtained at a low resonance frequency of 85 Hz and acceleration of 10 m/s2, showing potential application in piezoelectric energy harvester.
Phase equilibria modelling in Bi–Sr–Co–O system—Towards crystal growth and melt-assisted material processing J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-01 Ondřej Jankovský, David Sedmidubský
In this contribution, high-temperature phase equilibria of the partly open Bi–Sr–Co–(O) system with oxygen content given by its activity in the surrounding atmosphere, were modelled based on the experimental phase diagram determined previously. For the assessment, we also used the previously reported thermodynamic data and phase equilibria for the quasibinary Bi–Co–(O), Sr–Co–(O) and Bi–Sr–(O) subsystems as well as the thermodynamic data of quaternary phases obtained from calorimetry and simultaneous thermal analysis. Namely, the oxide melt was described based on the Redlich-Kister parameters of the corresponding quasibinary systems and the solid oxides were considered as stoichiometric. Their heat capacity and entropy were determined from calorimetry and the enthalpy of formation was refined to reproduce their melting behaviour. The constructed phase diagram focused on solid-liquid equilibria is particularly important for designing the experiments of single crystal growth and melt assisted material processing of these highly significant cobaltites.
Controlled precipitation of lithium disilicate (Li2Si2O5) and lithium niobate (LiNbO3) or lithium tantalate (LiTaO3) in glass-ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-01 Marc Dittmer, Christian Ritzberger, Wolfram Höland, Markus Rampf
In the present study, the crystallization principles and phenomena of base glasses from the system of SiO2-Li2O-P2O5-Al2O3-K2O-Nb2O5 or Ta2O5 were investigated. Annealing parameters such as temperature and time were varied. Annealing the base glasses 10 min at temperatures <850 °C for for Nb2O5 or Ta2O5 containing samples lead to the crystallization of Li2SiO3. At higher annealing temperatures or longer annealing times, Li2SiO3 disappeared and Li2Si2O5 was the main crystal phase in all glass-ceramics. After the dissolution of Li2SiO3, the minor crystal phases of LiNbO3 or LiTaO3 were precipitated. Increasing the annealing temperatures as well as the annealing times lead to higher bending strengths up to about 676 MPa and CR-values of up to 100. Increasing the contents of Nb2O5 or Ta2O5 lead to higher CR-values. The radiopacities increased up to 355% compared to aluminum.
A heat-resistant preceramic polymer with broad working temperature range for silicon carbide joining J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-01 Bo Tang, Mingchao Wang, Ruiming Liu, Jiachen Liu, Haiyan Du, Anran Guo
A room temperature curable heat-resistant adhesive with broad working temperature range was prepared through organic and inorganic modification. The preceramic polymethylsiloxane showed low bonding strength for silicon carbide from 400 °C to 600 °C because of the decomposition of polymer network. So the modification with epoxy resin was used to generate strong blending and copolymerization network which decomposed at higher temperature over 500 °C. The ceramization of active fillers and preceramic polymer compensated the bonding strength with rising temperature, thus eliminating the weak stage from 400 °C to 600 °C. The modification with fillers greatly improved its bonding strength at high temperature over 1000 °C. Consequently, the modified adhesive exhibited outstanding bonding strength tested at room temperature between 9.29 ± 0.56 MPa and 37.28 ± 1.33 MPa after heat-treatment from 25 °C to 1500 °C and the bonding strength directly tested at the temperature from 25 °C to 800 °C over 8.21 ± 0.40 MPa. The adhesive shows the potential to extend the application for engineering ceramic joining.
Fast re-oxidation kinetics and conduction pathway in Spark Plasma Sintered ferroelectric ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-01 M. Legallais, S. Fourcade, U.-C. Chung, D. Michau, M. Maglione, F. Mauvy, C. Elissalde
The re-oxidation kinetics of BaTiO3 ceramics sintered by Spark Plasma Sintering (SPS) was investigated using in-situ impedance spectroscopy. Thanks to the flexibility of the SPS process, the grain size of the dense ceramics was tuned from 0.5 μm to 10 μm. The re-oxidation kinetics are found to be very fast regardless of the grain size and a full re-oxidation of the ceramics are achieved after 20 hours of exposure to an ambient environment at only 600 °C. The residual density of charge carriers is reduced when using finer starting powders. SPS ceramics made with micrometer size grains demonstrate a residual charge-carrier density that is one tenth that of ceramics made from 10 μm particles. Grain-boundary conduction is dominant through fine-grain SPS ceramics. This latter feature is similar to BaTiO3 sintered using the conventional route with 10 μm size grain. Finally, the critical grain size for optimal dielectric permittivity is found to shift from 0.7 μm in standard ceramics to 1.5 μm in SPS ceramics.
Ordering of fluorite-type phases in erbium-doped oxyfluoride glass ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-09-01 Guna Krieke, Anatolijs Sarakovskis, Maris Springis
In this study, novel transparent Er3+ doped glass ceramics were prepared from melt-quenched oxyfluoride glasses with general composition of Na2O-NaF-BaF2-YbF3-Al2O3-SiO2. The crystallization of fluorite (BaF2, BaF2-YbF3, NaF-BaF2-YbF3 and Na0.5-xYb0.5+xF2+2x) and distorted fluorite (rhombohedral Ba4Yb3F17 and tetragonal NaF-BaF2-YbF3) phases was analysed in glass ceramics with different BaF2 and YbF3 ratio. The phase composition and microstructure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Intense red upconversion luminescence (UCL) was detected under near-infrared excitation resulting from three photon upconversion followed by cross-relaxation between Er3+ and Yb3+ ions.The local environment of Er3+ ions in fluorite and distorted phases was analysed using site-selective spectroscopy. The Er3+ ions were found to act as nucleation centres in the glass ceramics containing BaF2. The phase transition from metastable fluorite to rhombohedrally and tetragonally distorted fluorite phases was detected using Er3+ ions as a probe.
Electronic states and cation distributions of MgAl2O4 and Mg0.4Al2.4O4 microwave dielectric ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-31 Susumu Takahashi, Hirotaka Ogawa, Akinori Kan
The electronic state and microwave dielectric properties of MgAl2O4 prepared using solid-state (MA-S) and molten salt (MA-M) methods and those of Mg0.4Al2.4O4 (M04A24) were investigated. The λ values, which correspond to the fraction of Al3+ cations in tetrahedral sites, for MA-S, MA-M, and M04A24 were 0.23, 0.41, and 0.60, respectively. In molecular orbital calculations, a larger overlap was observed between Al-3 s or Al-3p in tetrahedral sites and O-2p orbitals for M04A24, and the bond order for Al O at tetrahedral sites of M04A24 (0.241) was higher than those for MA-S (0.178) and MA-M (0.205). The dielectric constant, εr, for M04A24 (7.6) was lower than those for MA-S and MA-M (both 7.9), and the highest quality factor, Q·f, was obtained for M04A24 (235, 800 GHz). It was found that the covalency of the Al O bonds in the MO4 tetrahedra is closely related to the Q･f values of the present ceramics.
Crystallization kinetics of PbTiO3 ferroelectric films: Comparison of microwave irradiation with conventional heating J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-31 Ya-Ju Zhang, Zhan Jie Wang, Yan Na Chen, Zhi Dong Zhang
Lead titanate (PTO) films were deposited onto Pt/Ti/SiO2/Si substrates by a sol-gel method and annealed by microwave irradiation and conventional heating. In contrast to conventional heating, microwave irradiation can crystallize the PTO films at a low temperature of 450 °C or at 550 °C for only 5 min. The XRD and TEM studies reveal that microwave radiation can reduce the nucleation time, and increase the growth rate of perovskite grains in the crystallization process. Moreover, the results using the Avrami’s model show that the effective activation energy for crystallization process by microwave irradiation is 131 kJ/mol, much lower than that for the PTO films by conventional heating (216 kJ/mol). Therefore, microwave irradiation can reduce the effective activation energy for the nucleation and grain growth of the perovskite phase during the crystallization process, contributing to a low-temperature or a short-time preparation process of ferroelectric films.
Robocast zirconia-toughened alumina scaffolds: processing, structural characterisation and interaction with human primary osteoblasts J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-31 Ana-Maria Stanciuc, Christoph Martin Sprecher, Jérôme Adrien, Lucian Ioan Roiban, Mauro Alini, Laurent Gremillard, Marianna Peroglio
Zirconia-toughened alumina (ZTA) is the gold-standard ceramic in hip arthroplasty, but still lacks direct osseointegration and a metal shell, often coated with a bioactive layer, is currently required. The latter could potentially be replaced by a thinner, architectured ZTA layer, thereby allowing for larger acetabular components, with larger range of motion and lower dislocation risk. Robocasting may be an adequate technique to fabricate the architectured layer. Therefore, as a first step, this study aimed to produce ZTA scaffolds (3D-ZTA) by robocasting and assess their in vitro response. Shape retention was achieved by using a stable, well-dispersed, high solid loading ink injected in acid pH waterbath. 3D-ZTA exhibit regularly spaced microporous, rough struts and fully interconnected macroporosity. Human primary osteoblasts were homogenously distributed inside 3D-ZTA and showed increased osteogenic marker expression compared to 2D-ZTA control. Further work will focus on optimizing scaffold design to improve cell retention and extracellular matrix maturation.
Enhancement of Seebeck coefficient of mesoporous SrTiO3 with V-group elements V, Nb, and Ta substituted for Ti J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-30 Chang-Sun Park, Min-Hee Hong, Hyung Hee Cho, Hyung-Ho Park
The carrier concentration and effective mass of mesoporous SrTiO3 films were controlled by the substitution of Ti with V-group elements (V, Nb, and Ta) to enhance the thermoelectric properties. We calculated the effect of the substitution on the effective mass of SrTiO3 by analyzing its structural and electrical properties. When V was used as a substitute, the effective mass increased slightly due to a small change in the V O bond distance. Moreover, when Nb and Ta were used as substitutes, the effective mass increased owing to an increase in the electronic density of states near the fermi level due to the increased bond length of Nb(or Ta) O. Consequently, the use of Nb and Ta as substitutes in the SrTiO3 film induced an increase in the figure of merit value, which was due to increases in both the effective mass and carrier concentration.
Performance and stability in H2S of SrFe0.75Mo0.25O3-δ as electrode in proton ceramic fuel cells J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-26 S. Wachowski, Z. Li, J.M. Polfus, T. Norby
The H2S-tolerance of SrFe0.75Mo0.25O3-δ (SFM) electrodes has been investigated in symmetric proton ceramic fuel cells (PCFC) with BaZr0.8Ce0.1Y0.1O3-δ (BZCY81) electrolyte. The ionic conductivity of the electrolyte under wet reducing conditions was found to be insignificantly affected in the presence of up to 5000 ppm H2S. The fuel cell exhibited an OCV of about 0.9 V at 700 °C, which dropped to about 0.6 V and 0.4 V upon exposure to 500 and 5000 ppm H2S, respectively, on the fuel side. Post characterization of the fuel cell revealed significant degradation of the anode in terms of microstructure and chemical composition due to formation of sulfides such as SrS, MoS2 and Fe3S4. Nevertheless, the fuel cell was still functional due to the sufficient electronic conductivity of some of these sulfides.
A novel low-temperature firable La2Zr3(MoO4)9 microwave dielectric ceramic J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-25 Weiqiong Liu, Ruzhong Zuo
A novel low-temperature fired La2Zr3(MoO4)9 microwave dielectric ceramic was successfully fabricated by a conventional solid-state reaction method. The powder compact was densified in air in the temperature range of 700–800 °C for 4 h. X-ray diffraction analysis indicated that all studied samples presented a single phase structure. Rietveld refinement results further confirmed that La2Zr3(MoO4)9 belonged to a trigonal system with space group R 3 ¯ c. Scanning electron microscopy results revealed dense and homogeneous microstructure of La2Zr3(MoO4)9 ceramics as sintered in the temperature range of 725–800 °C. The La2Zr3(MoO4)9 ceramic sintered at 775 °C for 4 h possessed excellent microwave dielectric properties of relative permittivity εr ∼ 10.8, quality factor Qxf ∼ 50,628 GHz (at 10.45 GHz), and temperature coefficient of the resonant frequency τf ∼ −38.8 ppm/°C, showing great potentials for applications of low temperature co-fired ceramic technology.
Thermodynamic evaluation of the BaO-CaO-YO1.5 system J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-24 Zhu Li, Jing Wang, Baotong Li, Shusen Wang, Ali Wajid, Shihua Wang, Xueguang Wang, Xionggang Lu, Chonghe Li, Kun Wang
A series of experiments were performed to study the solid solubility of CaO in BaY2O4, and the observed results were then adopted to the present thermodynamic evaluation to derive a set of thermodynamic database for the BaO-CaO-YO1.5 system. The database was constructed by the CALPHAD method where the binary parameters from the BaO-CaO and CaO-YO1.5 systems were presently optimized, those from the BaO-YO1.5 system were simulated by our previous assessments, and only limited amount of ternary parameters were introduced. All the model parameters were emanated from the Bragg-Williams approximation where the liquid and terminal solid-solution phases were treated by the one-sublattice model, and two ternary intermediate phases, named BCY (BaCa2Y6O12) and BaY2O4, were described by the three-sublattice and two-sublattice models, respectively. Good agreement between the experimental data and the calculated results demonstrates that the present thermodynamic database is self-consistent and credible and able to be used to design novel refractory.
Persistent Luminescent Particles Containing Bioactive Glasses: Prospect Toward Tracking in-vivo Implant Mineralization using Biophotonic ceramics J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-24 M. Saarinen, A. Nommeots-Nomm, M. Hokka, J. Laurila, I. Norrbo, M. Lastusaari, J. Massera, L. Petit
In this paper, we demonstrate that persistent luminescent bodies can be obtained by carefully choosing the sintering temperatures and duration. A borosilicate and a phosphate glasses were sintered into bodies with persistent luminescent (PeL) SrAl2O4:Eu2+, Dy3+ microparticles which have a green emission up to tens of hours after ceasing irradiation. When sintered at high temperature for a short time or at lower temperature for a longer time, a decrease in the PeL from the bodies was observed and was related to the glasses crystallization. A decrease in the PeL from the bodies was also observed after immersion in simulated body fluid and was related to the mineralization of the sintered bodies. Therefore, we clearly show that by tracking the changes in the PeL overtime, these PeL bodies have a real potential application as biophotonic sensors to track dissolution and mineralization of the implant in the body.
Controlling microstructure and film growth of relaxor-ferroelectric thin films for high break-down strength and energy-storage performance J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-24 Minh D. Nguyen, Chi T.Q. Nguyen, Hung N. Vu, Guus Rijnders
The relaxor ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin films were deposited using pulsed laser deposition, and their microstructures, break-down field strengths and energy storage performances were investigated as a function of the buffer layer and electrode. A large recoverable energy-storage density (Ureco) of 23.2 J/cm3 and high energy-storage efficiency (η) of 91.6% obtained in the epitaxial PLZT film grown on SrRuO3/SrTiO3/Si are much higher than those in the textured PLZT film (Ureco = 21.9 J/cm3, η = 87.8%) on SrRuO3/Ca2Nb3O10-nanosheet/Si and the polycrystalline PLZT film (Ureco = 17.6 J/cm3, η = 82.6%) on Pt/Ti/SiO2/Si, under the same condition of 1500 kV/cm and 1 kHz, due to the slim polarization loop and significant antiferroelectric-like behavior. Owing to the high break-down strength (BDS) of 2500 kV/cm, a giant Ureco value of 40.2 J/cm3 was obtained for the epitaxial PLZT film, in which Ureco values of 28.4 J/cm3 (at BDS of 2000 kV/cm) and 20.2 J/cm3 (at BDS of 1700 kV/cm), respectively, were obtained in the textured and polycrystalline PLZT films. The excellent fatigue-free properties and high thermal stability were also observed in these films.
High temperature creep of 20 vol%. SiC-HfB2 UHTCs up to 2000 °C and the effect of La2O3 addition J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-24 E. Zapata-Solvas, D. Gómez-García, A. Domínguez-Rodríguez, W.E. Lee
High temperature compressive creep of SiC-HfB2 UHTCs up to 2000 °C has been studied. Microstructural analysis after deformation reveal the formation of new phases in the Hf-B-Si and Hf-B-Si-C systems, which are responsible of the poor creep oxidation resistance shown. The RE oxide additions have a negative effect reducing the creep resistance of SiC-HfB2 UHTCs. A simplistic analysis for the required creep resistance is described, indicating that only SiC-HfB2 UHTCs could withstand re-entry conditions during 5 minutes for a single use. However, RE oxide addition to SiC-HfB2 UHTCs does not provide the required creep resistance to be a candidate for hypersonic applications from a structural point of view.
A New Method to Extract Elastic Modulus of Brittle Materials from Berkovich Indentation J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-24 Yan Chen, MariAnne Sullivan, Anqi Zhang, Barton C. Prorok
This work describes a method to reliably measure the elastic modulus of brittle materials from Berkovich indents under the continuous stiffness mode. It involves depositing a metallic film at the surface of the tested material to absorb the inelastic damage caused by the penetrating indenter. The Zhou-Prorok model was employed and rearranged to decouple the film and substrate contributions. This converted it into a hyperbolic form that approached an asymptote as the indenter approaches the film/substrate interface. This asymptote was described by a simple linear approximation whose slope directly revealed the substrate’s elastic modulus. The method enabled the elastic behavior of the brittle ceramic to be assessed without the indenter penetrating it. In fact, this method can assess properties of an unknown film/substrate composite as long as one has an estimate of the film thickness and the film can appreciably plastically deform.
Femtosecond laser multi-patterning of zirconia for screening of cell-surface interactions J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-19 Ana-Maria Stanciuc, Quentin Flamant, Christoph Martin Sprecher, Mauro Alini, Marc Anglada, Marianna Peroglio
Yttria-stabilised tetragonal zirconia polycrystals (3Y-TZP) bioinert ceramics combine excellent strength and toughness, good aesthetics, high resistance to corrosion and absence of allergic reaction. However, improved osseointegration is needed as higher marginal bone loss was sometimes reported. In the present work, 3Y-TZP multi-patterned samples for rapid screening of cell-surface interactions were fabricated by femtosecond laser micromachining. Pits with well-defined edges and micrometric precision in pit diameter, depth and spacing were produced, as determined by white light interferometry. Pits showed a nanometric granular texture on the sidewalls and ripples at pit bottom, as attested by scanning electron microscopy. Focused ion beam analyses indicated limited laser-induced damage. Micropatterns impacted human mesenchymal stem cell (hMSC) size and morphology. Cell area and aspect ratio were mainly influenced by pit diameter, while solidity and circularity were affected by both pit diameter and depth. The pattern 30 μm diameter/10 μm depth induced the strongest osteoblastic hMSC commitment.
A fast, stepwise procedure to assess time-temperature equivalence for hydrothermal ageing of zirconia-based materials J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-18 L. Gremillard, C. Wei, J. Chevalier, K. Hans, T. Oberbach
Hydrothermal ageing is one lifetime-limiting phenomenon of zirconia-based ceramics and composites for many applications, from biomedical implants to ferrules and watches. Predicting hydrothermal ageing at use-temperature implies a set of accelerated ageing experiments conducted under water vapour at several, high temperatures (usually between 100 °C and 140 °C). From these data, the activation energy of ageing can be determined, and thus ageing can be predicted at any temperature. However, obtaining precise extrapolations with this procedure requires the use of lower temperatures (70 or 80 °C), leading to a rather long procedure (up to a few thousand hours), and should involve at least one specimen for each test temperature. This article presents a new procedure that allows the determination of all ageing parameters and the estimation of kinetics at use-temperatures with the use of a single specimen within a shorter time, accurate enough for fast screening of new materials.
Influence of carbonaceous materials on the interactions among (Al2O3-C)/Fe system with temperature and soaking time J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-18 Yaowu Wei, Yong Shao, Junfeng Chen, Nan Li
It has practical significance for improving the service life of Al2O3-C refractories and reducing its influence on steel quality to reveal the reaction mechanism among (Al2O3-C)/Fe system under high temperature. The influence of carbonaceous materials on the interactions among (Al2O3-C)/Fe system with temperature and soaking time were studied using thermalgravity method in this paper in order to get a better understanding on the reaction mechanism among (Al2O3-C)/Fe system. The weight loss of (Al2O3-C)/Fe samples and the formation of Al2O3 crystal whiskers along with the change of aluminium and carbon content in iron indicates the mechanism of the effects of carbonaceous materials on the reactions among (Al2O3-C)/Fe system under high temperature. The result showed that the aluminium pickup of iron was not only due to the dissolution of Al2O3 in molten iron but mostly due to the carbothermic reduction of Al2O3 and carbonaceous materials in the presence of molten iron.
A New Method to Improve the Electrical Properties of KNN-based Ceramics: Tailoring Phase Fraction J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-18 Xiang Lv, Jiagang Wu, Jianguo Zhu, Dingquan Xiao, Xixiang Zhangb
Although both the phase type and fraction of multi-phase coexistence can affect the electrical properties of (K,Na)NbO3 (KNN)-based ceramics, effects of phase fraction on their electrical properties were few concerned. In this work, through changing the calcination temperature of CaZrO3 powders, we successfully developed the 0.96 K0.5Na0.5Nb0.96Sb0.04O3-0.01CaZrO3-0.03Bi0.5Na0.5HfO3 ceramics containing a wide rhombohedral-tetragonal (R-T) phase coexistence with the variations of T (or R) phase fractions. It was found that higher T phase fraction can warrant a larger piezoelectric constant (d33) and d33 also showed a linear variation with respect to tetragonality ratio (c/a). More importantly, a number of domain patterns were observed due to high T phase fraction and large c/a ratio, greatly benefiting the piezoelectricity. In addition, the improved ferroelectric fatigue behavior and thermal stability were also shown in the ceramics containing high T phase fraction. Therefore, this work can bring a new viewpoint into the physical mechanism of KNN-based ceramics behind R-T phase coexistence.
Advances in oxidation and ablation resistance of high and ultra-high temperature ceramics modified or coated carbon/carbon composites J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-12 Xiaochao Jin, Xueling Fan, Chunsheng Lu, Tiejun Wang
Carbon/carbon (C/C) composites are considered as one of the most promising materials in structural applications owing to their excellent mechanical properties at high temperature. However, C/C composites are susceptible to high-temperature oxidation. Matrix modification and coating technology with ultra-high temperature ceramics (UHTCs) have proved to be highly effective to improve the oxidation and ablation resistance of C/C composites. In this paper, recent advances in oxidation and ablation resistance of C/C composites were firstly reviewed, with attention to oxidation and ablation properties of C/C composites coated or modified with UHTCs. Then, several new methods in improving oxidation and ablation resistance were discussed, such as by using nanostructures to toughen UHTCs coatings or carbon matrix and the combination of matrix modification and coating technology. In addition, relevant ablation tests with scaled models were also briefly introduced. Finally, some open problems and future challenges were highlighted in the development and application of these materials.
Self-Propagating High-Temperature Synthesis of Nanocomposite Ceramics TaSi2-SiC with Hierarchical Structure and Superior Properties J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-15 S. Vorotilo, E.A. Levashov, V.V. Kurbatkina, D.Yu. Kovalev, N.A. Kochetov
Fabrication of practically pure Si2N2O ceramic with high performance from amorphous BN surface modified nano-sized Si3N4 powders J. Eur. Ceram. Soc. (IF 3.411) Pub Date : 2017-08-16 Liu Qiang, Zhao Bo, Yang Chunping, Zhang Haoqian, Zhang Haijiao, Zhang Biao, Ye Feng, Zhou Yu
In this study, amorphous nano-sized Si3N4 powders were surface modified by BN. Then a stable and dense Si2N2O ceramic was fabricated using the BN surface modified powders, rather than Si2N2O-Si3N4 composites usually prepared from nano-sized Si3N4 powders without surface modification. The effect of BN surface modification on phase transformation, microstructure and mechanical properties were also investigated. Si2N2O ceramics obtained by means of the present method have no residual Si, crystal SiO2 and other oxide additives, which are usually produced by other methods and may seriously influence high-temperature structural and functional applications of Si2N2O ceramics.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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