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1.	Shen, Minhao, et al. (author) Effects of exposure time and printing angle on the curing characteristics and flexural strength of ceramic samples fabricated via digital light processing 2020 In: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 46:15, s. 24379-24384 Journal article (peer-reviewed)abstract The development of photosensitive slurries for additive manufacturing has attracted great interest due to their correlation with the final properties of the fabricated parts. This paper focus on the printing quality control in digital light processing (DLP) 3D printing of advanced ceramics. Systematic experiments were performed to assess the effects of the exposure time and printing angle on the three-point bending strength of the fabricated samples. The exposure time affected the bending strength of the printed zirconia ceramic dramatically. When the weak exposure time is 1 s and the strong exposure time is 13 s, the average bending strength can reach 580 MPa while Weibull modulus can reach 8.84. Meanwhile, the printing angle also affected the bending strength mechanical sample printed at 45 degrees exhibits the worst performance.
2.	Zhao, W., et al. (author) Bending Strength of 3D-Printed Zirconia Ceramic Cellular Structures 2019 In: IOP Conference Series. - : Institute of Physics Publishing. Conference paper (peer-reviewed)abstract Cellular structure has been applied in lightweight engineering application because of its high specific strength, high modulus and low relative density. Here we used 3Y-TZP ceramic to realize two typical cellular structures, Kelvin and Octet-truss, through a novel digital light processing (DLP) 3D printing method. The strut size was changed systematically to generate structures with porosities in the range of 10% ∼ 80% and the bending strength of these structures were investigated and analyzed by three-point bending test.
3.	Zhao, Weiming, et al. (author) Mechanical properties of zirconia octet truss structures fabricated by DLP 3D printing 2020 In: Materials Research Express. - : IOP PUBLISHING LTD. - 2053-1591. ; 7:8 Journal article (peer-reviewed)abstract Zirconia ceramic octet-truss structures with various strut size and unit cell numbers were successfully fabricated through a DLP-based 3D printing method. The mechanical properties and energy absorption capacity under compressive load were investigated systematically. The sides of all cubes are 10 mm, the strut size was changed from 0.25 mm to 2 mm, cells number was in the range of 1(1 x 1 x 1)-125(5 x 5 x 5). It has been seen that the relative density, compressive strength and energy absorption increases with the increase of strut size when cell numbers remain the same. It can be concluded that the strength and energy absorption were affected by the relative density, strut size and the stacking mode of the unit cells. So far, with this study, a high compressive strength of 75.3 MPa and a reasonably good energy absorption of 6.76 x 10(5)J m(-3)can be achieved at a relative density of 48.57%.
4.	Aimable, Anne, et al. (author) Synthesis and Sintering of ZnO Nanopowders 2017 In: TECHNOLOGIES. - : MDPI AG. - 2227-7080. ; 5:2 Journal article (peer-reviewed)abstract Nanopowders are continuously under investigation as they open new perspectives in numerous fields. There are two main challenges to stimulating their development: sufficient low-cost, high throughput synthesis methods which lead to a production with well-defined and reproducible properties; and for ceramics specifically, the conservation of the powders' nanostructure after sintering. In this context, this paper presents the synthesis of a pure nanosized powder of ZnO (dv(50)similar to 60 nm, easily redispersable) by using a continuous Segmented Flow Tubular Reactor (SFTR), which has previously shown its versatility and its robustness, ensuring a high powder quality and reproducibility over time. A higher scale of production can be achieved based on a "scale-out" concept by replicating the tubular reactors. The sinterability of ZnO nanopowders synthesized by the SFTR was studied, by natural sintering at 900 degrees C and 1100 degrees C, and Spark Plasma Sintering (SPS) at 900 degrees C. The performance of the synthesized nanopowder was compared to a commercial ZnO nanopowder of high quality. The samples obtained from the synthesized nanopowder could not be densified at low temperature by traditional sintering, whereas SPS led to a fully dense material after only 5 min at 900 degrees C, while also limiting the grain growth, thus leading to a nanostructured material.
5.	Bu, Junfu, et al. (author) Transport properties of BaZr0.5Ce0.3Y0.2O3-δ proton conductor prepared by spark plasma sintering 2016 In: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 42:3, s. 4393-4399 Journal article (peer-reviewed)abstract Dense BaZr0.5Ce0.3Y0.2O3-δ (BZCY532) proton conductors were prepared by a spark plasma sintering method. Their conductivities were determined in different atmospheres: dry air, wet N2 and wet H2. Moreover, the potential electronic conductivity contribution to the total conductivity was also identified by testing their total conductivities at different oxygen partial pressures (1-10-24 atm) in combination with an XPS analysis. It is found that the prepared dense BZCY532 ceramics are good proton conductors at 600 °C. In addition, the Ce3+ concentration in the dense BZCY532 ceramics is around 3.5 atm% of the total Ce element, and the electronic contribution to the total conductivity can be neglected after a postheat treatment.
6.	Buscaglia, Maria Teresa, et al. (author) Fe2O3@BaTiO3 Core−Shell Particles as Reactive Precursors for the Preparation of Multifunctional Composites Containing Different Magnetic Phases 2010 In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 22:16, s. 4740-4748 Journal article (peer-reviewed)abstract Well-designed reactive precursors and templates allow for careful control of solid-state reactions at the nanoscale level, thus enabling the fabrication of materials with specific microstructures and properties. In this study, Fe2O3@BaTiO3 core−shell particles have been used as precursors for the in situ fabrication of multifunctional composites containing a dielectric/ferroelectric phase and two magnetic phases with contrasting coercivities (Fe2O3/Fe3O4, BaFe12O19/Ba12Fe28Ti15O84). The formation of new magnetic phases occurs during sintering or post-annealing via reaction between BaTiO3 and Fe2O3. The starting powders have been prepared using a multistep process that combines colloidal chemistry methods and a solid-state reaction. The nature and the amount of the magnetic phases and, consequently, the final magnetic properties of the composite can be controlled by varying the relative amount of Fe2O3 (30 or 50 vol %), the densification method (conventional or spark plasma sintering), and the processing temperature. The composites show constricted magnetic hysteresis loops with a coercivity of 0.1−2.5 kOe and a saturation magnetization of 5−16 emu/g. Composites obtained from powders containing 30 vol % Fe2O3 show, at temperatures of 20−80 °C and frequencies between 10 kHz and 1 MHz, a relative dielectric constant of 50 and dielectric losses of <10%.
7.	Buscaglia, M. T., et al. (author) Ferroelectric properties of dense nanocrystalline BaTiO3 ceramics 2004 In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 15:9, s. 1113-1117 Journal article (peer-reviewed)abstract Dense BaTiO3 ceramics with 50 nm average grain size obtained by spark plasma sintering were investigated. The dielectric data show a broad ferro-para phase transition with a maximum permittivity of approximate to1100 at 390 K and 1 kHz. The local ferroelectric switching behaviour was investigated by piezoresponse force microscopy. Typical piezoelectric hysteresis loops were recorded at different positions of the sample. The present results provide experimental evidence for polarization switching at the local scale, indicating that the critical grain size for the disappearance of ferroelectric behaviour in dense, bulk BaTiO3 nanocrystalline ceramics is below 50 nm.
8.	Buscaglia, M. T., et al. (author) High dielectric constant and frozen macroscopic polarization in dense nanocrystalline BaTiO3 ceramics 2006 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:6 Journal article (peer-reviewed)abstract Theoretical models for small ferroelectric particles predict a progressive decrease of the Curie temperature, spontaneous lattice strain, and polarization until the critical size corresponding to transition to the cubic phase and disappearance of ferroelectricity is reached. In contrast, the behavior of nanocrystalline BaTiO3 ceramics with a grain size of approximate to 30 nm is dominated by extrinsic effects related to the grain boundaries which mask the expected downscaling of properties. While the noncubic crystal structure, the high dielectric constant (approximate to 1600) and the variation of permittivity with temperature suggest a ferroelectric behavior, very slim, and nearly linear polarization hysteresis loops are observed. Evidence for the existence of a ferroelectric domain structure with domains extending over several grains and of polarization switching at local scale is given by piezoresponse force microscopy. The suppression of macroscopic ferroelectric hysteresis and switching originates from a frozen domain structure stable under an external field owing to the effects exerted by the grain boundaries, such as the clamping of the domain walls and the hindrance of polarization switching. Furthermore, the depolarization field originated by the low-permittivity nonferroelectric grain boundaries can cause a significant reduction of polarization. If the grain size is small enough, the ceramic is expected to undergo a "phase transition" to a polar phase with nonswitchable polarization. The BaTiO3 ceramics with grain size of 30 nm investigated in the present study are deemed to be close to this transition.
9.	Buscaglia, M. T., et al. (author) Synthesis of BaTiO3 core-shell particles and fabrication of dielectric ceramics with local graded structure 2006 In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 18:17, s. 4002-4010 Journal article (peer-reviewed)abstract The coating of BaTiO3 particles with a different perovskite and the subsequent consolidation to dense ceramics retaining a radial composition gradient within the single grains are presented and discussed. A shell of SrTiO3 or BaZrO3 was directly grown on the surface of BaTiO3 spherical templates suspended in aqueous solution by means of a precipitation process making use of inorganic precursors. The overall composition and the particle size can be tailored over a wide range. Densification of the resulting core-shell particles was realized using spark plasma sintering or conventional sintering. Dense ceramics with locally graded structure can be only obtained by a careful choice of the sintering conditions, that is, controlling the interdiffusion between core and shell. The final materials show strongly modified dielectric properties in comparison to both the parent compounds and the homogeneous solid solutions. The proposed approach is generic and suggests a new avenue to create functional and structural polycrystalline materials with locally graded structure by the controlled sintering of core-shell particles.
10.	Buscaglia, V., et al. (author) Nanostructured barium titanate ceramics 2004 In: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 148:1, s. 24-27 Journal article (peer-reviewed)abstract Dense nanocrystalline ceramics can be obtained starting from non-agglomerated nanopowders and using low-temperature sintering processes. The preparation and the properties of Barium Titanate (BaTiO3) ceramics and thick films are reported: ceramics were prepared by Spark Plasma Sintering (SPS) at 800 degreesC of nanopowders produced by a wet chemical process, while films were fabricated by airflow deposition (AD) of mixed fine and coarse powders at room temperature followed by isothermal firing. Ferroelectric ordering was found in both the ceramics and the sintered films by a.c. impedance. The transition from ferroelectric to paraelectric state was broadened over a wide temperature range with Curie-Weiss parameters strongly depressed in comparison to coarse-grained ceramics.
11.	Buscaglia, V., et al. (author) Raman and AFM piezoresponse study of dense BaTiO3 nanocrystalline ceramics 2005 In: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 25:12, s. 3059-3062 Journal article (peer-reviewed)abstract Dense nanocrystalline BaTiO3 (BT) ceramics with grain sizes (GSs) below 100 nm obtained by spark plasma sintering (SPS), were investigated by micro-Raman spectroscopy in order to obtain information about the changes in the local order induced by size effects. The obtained spectra in the range 80-700 K showed the presence of all the crystalline phases of BaTiO3, even in the finest structure (50 nm grain size ceramic), with particularities attributed to the high density of non-ferroelectric grain boundaries. The AFM piezoresponse study incontestably proved the ferroelectric switching at local scale in nanocrystalline BaTiO3 ceramics at room temperature.
12.	Cao, C., et al. (author) Optimization of Curing Behavior of Si3N4 UV Resin for Photopolymerization 3D Printing 2019 In: IOP Conference Series. - : Institute of Physics Publishing. Conference paper (peer-reviewed)abstract Silicon nitride (Si3N4) ceramics are widely used in mechanical and thermal management applications due to their excellent properties. To overcome the difficulties in traditional Si3N4 ceramic forming techniques, it is interesting to see the possibility of making complex-shaped silicon nitride ceramic component with novel 3D printing methods. In this study, we aim to study the effect of photo-initiators on the curing behavior of pre-formulated Si3N4 ceramic UV resin suspension. To elucidate the potential multi-factor interactions, a statistic experiment design was implemented in a sequence of screening and optimization by using Modde software. It was found that the kinds of photo-initiators, total amount of initiators and the mixture ratio between initiators have a great influence on the curing properties of silicon nitride UV ceramic resin. Based on these results, a formula was selected based on the criterion of using least amount photo-initiator while reaching the highest curing thickness.
13.	Cheng, Z., et al. (author) Ink-jet printed BNT thin films with improved ferroelectric properties via annealing in wet air 2018 In: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 44:9, s. 10700-10707 Journal article (peer-reviewed)abstract In this work, an ink-jet printing process based on the sol-gel route was applied to prepare lead-free ferroelectric Na0.5Bi0.5TiO3(BNT) thin films for the first time. Dense and crack-free films with perovskite structure were obtained from a modified precursor solution through multiple printing and pyrolysis processes. The ferroelectric, dielectric and electrical properties were significantly affected by the annealing temperature and atmosphere. The film annealed at 670 °C in wet air showed a high remnant polarization of 24.7 μC/cm2 with a low coercive field of 263 kV/cm, the dielectric constant and loss were 185 and 0.1 at 10 kHz, respectively. It was found that wet air was an alternative to reduce oxygen vacancies and enhance properties of ferroelectric films, which can be explained by the defect chemical reaction between water and oxygen vacancies. X-ray photoelectron spectroscopy(XPS) confirmed the decrease of oxygen vacancies after annealing with water presence, with a formation of Ohmic conduction mechanism dominated by charged hydroxyl groups.
14.	Curecheriu, Lavinia, et al. (author) Grain size effect on the nonlinear dielectric properties of barium titanate ceramics 2010 In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 97:24 Journal article (peer-reviewed)abstract The nonlinear dielectric properties of dense BaTiO(3) ceramics with grain size of 1 mu m-90 nm were investigated. In the finest ceramics, the permittivity reduces below 1000 and a remarkable nonhysteretic linear dc-tunability [epsilon(E)] is obtained at high field, above 40 kV/cm. The observed behavior was explained by considering the nanostructured ceramic as a composite formed by ferroelectric grains, whose nonlinearity is reducing, and by low-permittivity nonferroelectric grain boundaries, whose volume fraction increases when decreasing the grain size. Reducing the grain size in ferroelectric dense materials is an alternative route to accomplish the application requirements: nonhysteretic tunability and permittivity below 1000.
15.	Dahl, P., et al. (author) Densification and properties of zirconia prepared by three different sintering techniques 2007 In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 33:8, s. 1603-1610 Journal article (peer-reviewed)abstract Densification of nanocrystalline yttria stabilized zirconia (YSZ) powder with 8 mol% Y2O3, prepared by a glycine/nitrate smoldering combustion method, was investigated by spark plasma sintering, hot pressing and conventional sintering. The spark plasma sintering technique was shown to be superior to the other methods giving dense materials (>= 96%) with uniform morphology at lower temperatures and shorter sintering time. The grain size of the materials was 0.21, 0.37 and 12 mu m after spark plasma sintering, hot pressing and conventional sintering, respectively. Total electrical conductivity of the materials showed no clear correlation with the grain size, but the activation energy for spark plasma sintered materials was slightly higher than for materials prepared by the two other densification methods. The hardness, measured by the Vickers indentation method, was found to be independent on grain size while fracture toughness, derived by the indentation method, was slightly decreasing with increasing grain size.
16.	Dong, H., et al. (author) Effect of powder characteristics on the thermal conductivity and mechanical properties of Si 3 N 4 ceramics sintered by Spark plasma sintering 2019 In: Journal of materials science. Materials in electronics. - : Springer-Verlag New York. - 0957-4522 .- 1573-482X. ; 30:8, s. 7590-7599 Journal article (peer-reviewed)abstract The effect of powder characteristics on the thermal conductivity and mechanical properties of silicon nitride (Si 3 N 4 ) ceramics were investigated systematically by using two α-Si 3 N 4 powders as raw materials and using MgSiN 2 or MgO + Y 2 O 3 as sintering additives. The Si 3 N 4 ceramics with a higher density were obtained by α-Si 3 N 4 powders with lower oxygen content and impurities and using none-oxide sintering additive MgSiN 2 . The α–β phase transformation completely taken place in all the specimen at 1750 °C. The specimens sintered by powders with lower levels of oxygen and impurities show higher mechanical properties than other specimens. The Y 2 O 3 and MgO sintering additives lead to higher flexural strength and fracture toughness than MgSiN 2 . The Vickers’ hardness is just the opposite. The thermal conductivity value of powders with lower oxygen content is higher than that of the materials prepared by the other type of powder at the same conditions. The effects of the Si 3 N 4 particle size, native oxygen and impurities on the thermal conductivity of resultant materials were discussed in detail. This work demonstrates that the improvement in thermal conductivity of Si 3 N 4 can be obtained by using none-oxide sintering additive MgSiN 2 and the Si 3 N 4 powder with lower oxygen content, and impurities.
17.	Gao, S., et al. (author) Mechanical Properties of ZrO2 Honeycomb Sandwich Structures by 3D Printing 2019 In: IOP Conference Series. - : Institute of Physics Publishing. Conference paper (peer-reviewed)abstract Honeycomb sandwich structures were widely used in lightweight design. However, the difficulties with the fabrication process actually highly limit their practical usage, especially for ceramic materials. In this paper, 3 mol% yttria-stabilized ZrO2 (3Y-TZP) honeycomb sandwich structures with square and hexagonal cell were prepared successfully by using digital light processing (DLP) printing method. With a base material density of >6.02g/cm3, square/hexagonal honeycomb sandwich structures with structural density of 42.89%-66.24% were achieved by modifying unit cell wall thickness. It can be concluded that square honeycomb cell is preferred for getting higher bending strength at the same structural density.
18.	Lapina, Alberto, et al. (author) Synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 powder by gel combustion route with two-step doping strategy 2012 In: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 32:10, s. 2325-2331 Journal article (peer-reviewed)abstract A two-step doping strategy was applied to the synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 (LSGM1020) powder by a gel combustion method. The Mg-doped LaGaO 3 powder was prepared in the first step, and Sr incorporation in the Mg-doped LaGaO 3 powder was done in the second step to obtain the final LSGM1020 powder. The two-step procedure is effective in preparing higher purity powders than the traditional one-step procedure. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that incorporation of Mg in LaGaO 3 in the first step enlarges the LaGaO 3 lattice: this facilitates the incorporation of Sr in the second doping step and thus high purity powder is obtained. Relatively phase pure LSGM1020 powder with only 3.1% of LaSrGaO 4 was obtained after calcination at 1300°C for 5h. Therefore, the two-step doping strategy is an effective procedure for the preparation of LSGM powders with high Sr- and Mg-doping levels.
19.	Mitoseriu, L., et al. (author) Local switching properties of dense nanocrystalline BaTiO3 ceramics 2004 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 84:13, s. 2418-2420 Journal article (peer-reviewed)abstract The switching properties of dense BaTiO3 ceramics with 50 nm average grain size were investigated at local scale by piezoresponse force microscopy. Large areas with low piezoelectrical activity beside islands with strong piezoresponse were found. The application of electric fields induces stable domain structures and changes in the polarization state far away from the probing area, probably via trans-granular dipole interactions. Piezoelectric hysteresis loops were recorded on various positions, even in regions with initial zero piezoresponse, which possibly showed a superparaelectric behavior. The results are incontestable proof that 50 nm BaTiO3 ceramics retain ferroelectricity at a local scale.
20.	Ren, Yanan, et al. (author) 3DOM-NiFe2O4 as an effective catalyst for turning CO2 and H2O into fuel (CH4) 2018 In: Journal of Sol-Gel Science and Technology. - : SPRINGER. - 0928-0707 .- 1573-4846. ; 88:3, s. 489-496 Research review (peer-reviewed)abstract Three-dimensional ordered macroporous NiFe2O4 (3DOM-NFO) powder was synthesized through the direct templating method combined with the sol-gel combustion technique. Polymethyl methacrylate (PMMA) spheres with different sizes were used as the hard templates. In order to understand the effect of PMMA spheres mean size on the structure and catalytic activity of synthesized 3DOM-NFO, the detailed characterization of the material was carried out by XRD, SEM, BET, XPS, UV-VIS, and DRS techniques. Direct hydrogeneration production of CH4 from CO2 and H2O was used to evaluate the catalysis performance of 3DOM-NFOs. The production of CH4 evolution can reach 1040.8mol/g at 350 degrees C and ambient pressure when 300nm template was used. It was concluded that the specific surface area and moderate concentration of oxygen vacancies are the crucial factors affecting the catalysis properties. Reasonably high turnover number of 0.244 and high CH4 conversion efficiency of 0.897% were obtained in this study. 3DOM-NFO can be a promising catalyst for hydrocarbon fuel production by directly using CO2 and H2O as the safe and cheap feedstocks. [GRAPHICS] .
21.	Shen, M., et al. (author) Mechanical Properties of ZrO2 TPMS Structures Prepared by DLP 3D Printing 2019 In: IOP Conference Series. - : Institute of Physics Publishing. Conference paper (peer-reviewed)abstract Compressive strength is one of the most important mechanical properties for cellular ceramics. But the dependence of compressive strength of highly porous cellular ceramic structures on porosity remains unclear due to the limit of available methods for making such strong structures based on specific structural designs. In this paper, the TPMS structures, namely P-cell, and neovius structure, were prepared based on the DLP 3D printing technology. Samples with various unit cells were fabricated with zirconia. The relative density of the sintered samples exceeds 99%. The effects of cell number on the compressive strength and deformation of the model were investigated. Samples with similar relative densities exhibited comparable mechanical property in aspect of compressive strength. It is very interesting that the cell number eventually only influence the total strain.
22.	Sheng, Xiaofei, et al. (author) Controllable Fabrication of Large-Size Defect-Free Domains of 2D Colloidal Crystal Masks Guided by Statistical Experimental Design 2021 In: Coatings. - : MDPI. - 2079-6412. ; 11:1 Journal article (peer-reviewed)abstract Large defect-free domains of a hexagonal packed monolayer of silica spheres with the size of 4000 mu m(2) were successfully prepared by dual-speed spin coating. Experimental design and statistical analysis instead of the traditional 'changing one separate factor at a time' (COST) approach were employed to guide the implementation of the experiments. With its assistance, the hexagonal-close-packed (HCP) percentage was elevated to 84% in this study. Furthermore, almost all the samples with parameters in the selected ranges possessed more than a 60% HCP percentage. In addition, the optimal values for parameters of the suspension concentration, the first rotation speed, and the spinning time to obtain well-ordered silica spheres arrays were also identified as 30 wt.%, 1000 rpm and 20 s, respectively.
23.	Sheng, Xiaofei, et al. (author) Optimization of Synthesizing Upright ZnO Rod Arrays with Large Diameters through Response Surface Methodology 2020 In: Processes. - : MDPI. - 2227-9717. ; 8:6 Journal article (peer-reviewed)abstract The deposition parameters involved in chemical bath deposition were optimized by a response surface methodology to synthesize upright ZnO rod arrays with large diameters. The effects of the factors on the preferential orientation, aspect ratio, and diameter were determined systematically and efficiently. The results demonstrated that an increased concentration, elevated reaction temperature, prolonged reaction time, and reduced molar ratio of Zn(2+)to tri-sodium citrate could increase the diameter and promote the preferential oriented growth along the [002] direction. With the optimized parameters, the ZnO rods were grown almost perfectly vertically with the texture coefficient of 99.62. In the meanwhile, the largest diameter could reach 1.77 mu m. The obtained rods were merged together on this condition, and a dense ZnO thin film was formed.
24.	Stuer, Michael, et al. (author) Comparison of apparent activation energies for densification of alumina powders by pulsed electric current sintering (spark plasma sintering) and conventional sintering-toward applications for transparent polycrystalline alumina 2017 In: Journal of Materials Research. - : CAMBRIDGE UNIV PRESS. - 0884-2914 .- 2044-5326. ; 32:17, s. 3309-3318 Journal article (peer-reviewed)abstract In the quest for high real in-line transmittances for transparent polycrystalline alumina (PCA), we need defect free processing. One of the biggest advances in producing high density defect free ceramics over recent years has been the advent of spark plasma sintering (SPS) or pulsed electric current sintering. The production of PCA with high transmittances >60% has been demonstrated, but the mechanisms behind this fast, pressure aided sintering method are still much debated. Here, we investigate the sintering of doped a-alumina powders using traditional and pulsed electric current dilatometry. We demonstrate that at the final sintering stage, there is no major difference in the sintering mechanisms between conventional sintering and SPS sintering. High densification rates occurring in SPS are shown to be related to powder reorientation at the very early sintering stage and viscous-flow dominated densification in the intermediate sintering cycle. This paper clarifies what parameters in the processing-sintering domain have to be improved for even higher real in-line transmittances for PCA.
25.	Stuer, Michael, et al. (author) Editorial - “From powder to microstructure of ceramics” 2022 In: Open Ceramics. - : Elsevier BV. - 2666-5395. ; 10 Journal article (other academic/artistic)
26.	Suarez, M., et al. (author) Hot isostatic pressing of optically active Nd:YAG powders doped by a colloidal processing route 2010 In: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 30:6, s. 1489-1494 Journal article (peer-reviewed)abstract In this work, 1 at.% Nd doped Yttrium Aluminum Garnet Y(3)Al(5)O(12) (YAG) nano-sized powder prepared by colloidal route was investigated thoroughly concerning agglomeration control and preparation of transparent ceramic by post-HIP. Electrostatic and mechanical deagglomeration process followed by freeze-drying turned out to be an effective method to alleviate agglomeration, yielding a powder with a homogeneous particle size distribution around 100 nm. Transparent Nd:YAG ceramic samples have been successfully prepared by post-HIP without the aid of sintering additives. The optical properties varied markedly with the sintering and hot isostatic pressing conditions used. In-fine transmittance values of 56% at 680 nm and close to 80% in the infrared region were recorded.
27.	Sun, Y., et al. (author) ZTA Ceramic Materials for DLP 3D Printing 2019 In: IOP Conference Series. - : Institute of Physics Publishing. Conference paper (peer-reviewed)abstract As a new additive manufacturing method, DLP has the advantages of high precision, fast speed and low cost. ZTA ceramic is anticipated to be used in more applications due to its superior bending strength, fracture toughness and thermal conductivity. But the detailed study with ZTA printing material for DLP is still rarely reported. In this experiment, ZTA ceramic UV resin with various ZrO2 concentration (5-15wt.%) were investigated and tested for their 3D printing performance. ZTA ceramic UV resin with low viscosity (<3Pa•s at shear rate of 10s-1) and high solid load (55vol.%) were successfully developed. After sintering at a temperature of 1600°C, a relative density of >96% can be always promised. For the optimized doping level of ZrO2 at 11wt%, a density of 99% can be achieved.
28.	Wang, Cao, et al. (author) FEM analysis of the temperature and stress distribution in spark plasma sintering : Modelling and experimental validation 2010 In: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 49:2, s. 351-362 Journal article (peer-reviewed)abstract A fully thermal-electrical-mechanical coupled and dynamic finite element model (FEM) is implemented to analyze of the temperature and stress distribution in spark plasma sintering (SPS) process. The real densification behaviour is also integrated by the moving mesh technique. The simulation studies were conducted using COMSOL and a range of die sizes, heating rates and uniaxial stresses were considered. The further validation experiments are implemented to validate the simulation results. The detailed microstructure investigations generally demonstrate that the temperature and stress profile obtained in present model are correct. But further development of complicated models is still needed for more precise prediction of sintering condition and microstructure development in SPS.
29.	Wei, Guohui, et al. (author) Photothermal catalytic activity and mechanism of LaNixCo1-xO3(0 <= x <= 1) perovskites for CO2 reduction to CH4 and CH3OH with H2O 2019 In: Materials Research Express. - : IOP Publishing. - 2053-1591. ; 6:8 Journal article (peer-reviewed)abstract A series of LaNixCo1-xO3 perovskites were synthesized by sol-gel combustion method, the photothermal catalysis of CO2 and H2O into CH4 and CH3OH was investigated systematically. The crystal structure, surface area, oxygen vacancies, band structures and catalytic performance of LaNixCo1-xO3 perovskites were characterized thoroughly in order to understand the design principle of the material for such a photothermal catalysis of CO2 and H2O. With the change of x value, the best catalytic performance was achieved at x = 0.4 and the accumulated yield of CH4 and CH3OH can reach 678.57, 20.83 mu molg(-1) in 6 h, which were 3.4 and 3.8, 1.9 and 2.2 times of that of two end composition, LaCoO3 and LaNiO3 under the same condition. For LaNi0.4Co0.6O3, the surface area reached a maximum concentration of oxygen vacancy while the band gap reached a minimum of 1.42 eV. It is evident that the formation of solid solution between LaMO3 (M = transition metals) compounds can be a general strategy for the new catalyst design.
30.	Yao, Y., et al. (author) Highly Concentrated Hydroxyapatite Suspension for DLP Printing 2019 In: IOP Conference Series. - : Institute of Physics Publishing. Conference paper (peer-reviewed)abstract Due to the lack of commercially available high-quality hydroxyapatite (HA) powder, it is still rarely reported by the literature concerning the development of UV resin for digital light processing 3D printing. The previous studies still had the problem of delamination and also poor sintering performance led by low solid-load slurry. Here low viscosity and high solid-load hydroxyapatite (HA) UV resin suspensions were developed for digital light processing 3D printing. In this study, the effect of the type of dispersant, the dose levels of dispersant and the solid load of HA powder on the rheology properties were thoroughly investigated to obtain a flowable highly-concentrated HA UV resin suspension. Finally, a 40vol% slurry with viscosity of 3.7Pa•s at a shear rate of 10 s-1 was successfully developed. After 3D printing and sintering, a dense ceramic with relative density of 95.85% can be obtained at a sintering temperature of 1300°C.
31.	Zhao, Zhe, 1973-, et al. (author) Grain-size effects on the ferroelectric behavior of dense nanocrystalline BaTiO3 ceramics 2004 In: Physical Review B. Condensed Matter and Materials Physics. - : American Institute of Physics (AIP). - 1098-0121 .- 1550-235X. ; 70:2 Journal article (peer-reviewed)abstract A progressive reduction of tetragonal distortion, heat of transition, Curie temperature, and relative dielectric constant has been observed on dense BaTiO3 ceramics with grain size decreasing from 1200 to 50 nm. The correlations between grain size, extent of tetragonal distortion, and ferroelectric properties strongly support the existence of an intrinsic size effect. From the experimental trends the critical size for disappearance of ferroelectricity has been evaluated to be 10-30 nm. The strong depression of the relative permittivity observed for the nanocrystalline ceramics can be ascribed to the combination of the intrinsic size effect and of the size-dependent "dilution" effect of a grain boundary "dead" layer.
32.	Zhao, Zhe, 1973-, et al. (author) Spark plasma sintering of nano-crystalline ceramics 2004 In: EURO CERAMICS VIII, PTS 1-3. - : Trans Tech Publications Inc.. ; , s. 2297-2300 Conference paper (peer-reviewed)abstract Spark Plasma Sintering (SPS) has been successfully applied in the sintering of nanocrystalline BaTiO3 and gamma-Al2O3 in order to reach fully dense nanostructured ceramics at moderate pressure and temperature. BaTiO3 compacts with densities exceeding 97% and gain size of 50 nm have thus been prepared at temperatures not exceeding 850degreesC using a uniaxial pressure of 100MPa. The selection of sintering temperature is critical for the purpose of minimizing grain growth and there is a demarcation temperature (820degreesC) between normal and abnormal grain growth for the nanocrystalline BaTiO3 powder used in this study. Fully dense alpha-Al2O3 compacts containing grains of the size 300nm or less were consolidated from high-purity gamma-Al2O3 powders without the use of additives or seeds. The transition temperature of gamma-Al2O3 to alpha-Al2O3 can be lowered to 960degreesC when gamma-Al2O3 powder is compacted in the SPS apparatus. The possible mechanisms related to this low transition temperature and to the sintering of both BaTiO3 and gamma-Al2O3 are discussed with special reference to the effect of the pulsed electric field generated by the pulsed electrical current used to heat the sample.
33.	Zheng, D., et al. (author) LaNi x Fe 1- x O 3 (0 ≤ x ≤1) as photothermal catalysts for hydrocarbon fuels production from CO 2 and H 2 O 2019 In: Journal of Photochemistry and Photobiology A. - : Elsevier B.V.. - 1010-6030 .- 1873-2666. ; 377, s. 182-189 Journal article (peer-reviewed)abstract LaNi x Fe 1- x O 3 perovskite compounds (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were successfully synthesized by a sol-gel combustion method. The crystal structure, morphology, BET surface area, oxygen vacancies, band gap and catalytic properties of the catalyst were characterized in detail. The results showed that LaNi 0.4 Fe 0.6 O 3 compound exhibits the best photothermal catalytic performance. Under the same catalytic conditions (350 ℃ + Vis-light), CH 4 and CH 3 OH yields are about 3.5 and 4.0 times, 1.8 and 2.1 times of that of LaFeO 3 and LaNiO 3 . It was found that all the solid solutions possesses better catalytic properties than the pure end compounds. The doping of Ni lead to a significant modification with the quantity of oxygen vacancies and band gaps. These findings may further broaden the materials scope for photothermal conversion of CO 2 and H 2 O.
34.	Zhou, L. J., et al. (author) Electric fatigue in antiferroelectric lead zirconate stannate titanate ceramics prepared by spark plasma sintering 2005 In: Journal of The American Ceramic Society. - : American Ceramic Society. - 0002-7820 .- 1551-2916. ; 88:10, s. 2952-2954 Journal article (peer-reviewed)abstract The fatigue behavior of lead zirconate stannate titanate (PZST) ceramics prepared by spark plasma sintering (SPS) was investigated. Polarization and strain hysteresis loops were monitored. The material shows a high resistance to fatigue because of bipolar electric cycling. Both maximum strain and switchable polarization first show a fatigue stage 0 to 10(5) cycles and then a fatigue-free period up to 10(8) cycles. The maximum losses of maximum strain and switchable polarization are 18% and 10% of their initial values, respectively. The dominant fatigue mechanism is assigned to the pinning of domain walls by charged defects.
35.	Zhou, L. J., et al. (author) Electric fatigue in ferroelectric lead zirconate stannate titanate ceramics prepared by spark plasma sintering 2006 In: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 89:12, s. 3868-3870 Journal article (peer-reviewed)abstract Ferroelectric lead zirconate stannate titanate ceramics were prepared by spark plasma sintering (SPS). Compared with its counterpart densified by conventional sintering (CS), the SPS material shows a smaller remanent polarization and maximum strain as well as a higher coercive field. Electric fatigue in both materials was investigated. In contrast to CS samples, the SPS specimens show a lower resistance to bipolar electric cycling, characterized by a faster decrease in remanent polarization and maximum strain at cycle number below 10(6.5) and a subsequent slower reduction of the properties at high cycle numbers up to 10(8).
36.	Zhou, L. J., et al. (author) Preparation and properties of lead zirconate stannate titanate sintered by spark plasma sintering 2004 In: Journal of The American Ceramic Society. - : American Ceramic Society. - 0002-7820 .- 1551-2916. ; 87:4, s. 606-611 Journal article (peer-reviewed)abstract Lanthanum-doped lead zirconate stannate titanate ceramics were successfully compacted to full density by spark plasma sintering (SPS). SPS samples densified at 900degrees or 950degreesC exhibit nearly full density and fine grain size (about 300 nm). Compared with samples from conventional sintering (CS), SPS samples show larger permittivity accompanied by a deterioration in dielectric loss and special strain hysteresis loops similar to those of ferroelectric relaxors, with a diffuse AFE-FE phase transition and less field-induced longitudinal strain. The differences in the properties of SPS and CS materials are attributed to the variations of the resultant microstructures, especially the grain size, of the ceramics.

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