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Ceramics, Volume 3, Issue 4 (December 2020) – 8 articles

Cover Story (view full-size image): TiO2 ceramics were produced by the high-pressure SPS of an anatase nanopowder. When the pressure increased from 76 to 400 MPa, the anatase to rutile transition temperature decreased from 700 to 550 °C and the densification process occurred at lower temperatures. Under 400 MPa, the rate of the phase transition increased significantly, inducing an abrupt volume reduction of 8%, which generated strong stress leading to twinning and fracture of the rutile grains. In the final ceramic, the majority of the grains consisted of twinned crystals resulting in a reduction of the crystallite size, compare to ceramics sintered at lower pressure. View this paper
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Article
Dense MgB2 Ceramics by Ultrahigh Pressure Field-Assisted Sintering
Ceramics 2020, 3(4), 521-532; https://0-doi-org.brum.beds.ac.uk/10.3390/ceramics3040042 - 21 Dec 2020
Viewed by 837
Abstract
Magnesium diboride (MgB2) ceramics, due to their impressive transition temperature of 39 K for superconductivity, have been widely investigated. The possibility to obtain highly dense MgB2 ceramics with fine microstructure and grain boundaries acting as pinning sites by novel high-pressure-assisted [...] Read more.
Magnesium diboride (MgB2) ceramics, due to their impressive transition temperature of 39 K for superconductivity, have been widely investigated. The possibility to obtain highly dense MgB2 ceramics with fine microstructure and grain boundaries acting as pinning sites by novel high-pressure-assisted spark plasma sintering (HP-SPS) is reported in this article. HP-SPS was employed to reach 100% density in MgB2 ceramics, and high pressure was utilized in the consolidation of MgB2. An increase in pressure helped in stabilizing the MgB2 phase above thermal decomposition, thus avoiding the formation of non-superconducting phases such as MgO and MgB4. Pressure allowed strengthening of the covalent bond (condensation effect) to increase the thermal stability of MgB2. HP-SPS yielded high mechanical hardness in MgB2 (1488 HV). For better electrical connectivity, which leads to large magnetic moments in high density samples were obtained with the beneficial effect of high applied pressure (1.7–5 GPa) at high temperature (>1000 °C). The combination of the SPS process and high pressure ensured retention of the homogeneous fine microstructure required to obtain high current density and high hardness. Full article
(This article belongs to the Special Issue Spark Plasma Sintering Technology)
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Article
Effect of High Pressure Spark Plasma Sintering on the Densification of a Nb-Doped TiO2 Nanopowder
Ceramics 2020, 3(4), 507-520; https://0-doi-org.brum.beds.ac.uk/10.3390/ceramics3040041 - 04 Dec 2020
Viewed by 873
Abstract
Sintering under pressure by means of the spark plasma sintering (SPS) technique is a common route to reduce the sintering temperature and to achieve ceramics with a fine-grained microstructure. In this work, high-density bulk TiO2 was sintered by high pressure SPS. It [...] Read more.
Sintering under pressure by means of the spark plasma sintering (SPS) technique is a common route to reduce the sintering temperature and to achieve ceramics with a fine-grained microstructure. In this work, high-density bulk TiO2 was sintered by high pressure SPS. It is shown that by applying high pressure during the SPS process (76 to 400 MPa), densification and phase transition start at lower temperature and are accelerated. Thus, it is possible to dissociate the two densification steps (anatase then rutile) and the transition phase during the sintering cycle. Regardless of the applied pressure, grain growth occurs during the final stage of the sintering process. However, twinning of the grains induced by the phase transition is enhanced under high pressure resulting in a reduction in the crystallite size. Full article
(This article belongs to the Special Issue Spark Plasma Sintering Technology)
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Article
Production of Transparent Soda-Lime Glass from Rice Husk Containing Iron and Manganese Impurities
Ceramics 2020, 3(4), 494-506; https://0-doi-org.brum.beds.ac.uk/10.3390/ceramics3040040 - 25 Nov 2020
Viewed by 823
Abstract
Glass is a familiar material that requires abundant mineral sources, with devastating consequences for the environment. Rice husk ash (RHA) presents a very high silica content (>95%) and it can be a very promising alternative source for silica in silica-based glass. However, impurities [...] Read more.
Glass is a familiar material that requires abundant mineral sources, with devastating consequences for the environment. Rice husk ash (RHA) presents a very high silica content (>95%) and it can be a very promising alternative source for silica in silica-based glass. However, impurities like manganese and iron, which depend on the rice harvest, might limit RHA use, particularly in the production of optical transparent glasses. In this work, we discussed how Mn and Fe can affect the coloring of the produced glass, and how the effect of these impurities can be removed. First, the RHA was treated with acid solutions, leading to the production of a soda-lime glass with similar transparency to commercial glass (>70%). Secondly, another simpler approach was studied: a small amount of antimony oxide was added in the composition of the glass, obtaining a transparent glass (>80%, same thickness) with RHA. Full article
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Review
Spark Plasma Sintering of Ceramics: From Modeling to Practice
Ceramics 2020, 3(4), 476-493; https://0-doi-org.brum.beds.ac.uk/10.3390/ceramics3040039 - 17 Nov 2020
Cited by 1 | Viewed by 1236
Abstract
Summarizing the work of nearly a decade of research on spark plasma sintering (SPS), a review is given on the specificities and key factors to be considered in SPS of ceramic materials, based on the authors’ own research. Alumina is used primarily as [...] Read more.
Summarizing the work of nearly a decade of research on spark plasma sintering (SPS), a review is given on the specificities and key factors to be considered in SPS of ceramic materials, based on the authors’ own research. Alumina is used primarily as a model material throughout the review. Intrinsic inhomogeneities linked to SPS and operational parameters, which depend on the generation of atomistic scale defects, are discussed in detail to explain regularly observed inhomogeneities reported in literature. Adopting an engineering approach to overcome these inherent issues, a successful processing path is laid out towards the mastering of SPS in a wide range of research and industrial settings. Full article
(This article belongs to the Special Issue Spark Plasma Sintering Technology)
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Review
The Role of Sacrificial and/or Protective Layers to Improve the Sintering of Electroactive Ceramics: Application to Piezoelectric PZT-Printed Thick Films for MEMS
Ceramics 2020, 3(4), 453-475; https://0-doi-org.brum.beds.ac.uk/10.3390/ceramics3040038 - 16 Nov 2020
Viewed by 1049
Abstract
Piezoelectric thick films are of real interest for devices such as ceramic Micro-ElectroMechanical Systems (MEMS) because they bridge the gap between thin films and bulk ceramics. The basic design of MEMS includes electrodes, a functional material, and a substrate, and efforts are currently [...] Read more.
Piezoelectric thick films are of real interest for devices such as ceramic Micro-ElectroMechanical Systems (MEMS) because they bridge the gap between thin films and bulk ceramics. The basic design of MEMS includes electrodes, a functional material, and a substrate, and efforts are currently focused on simplified processes. In this respect, screen-printing combined with a sacrificial layer approach is attractive due to its low cost and the wide range of targeted materials. Both the role and the nature of the sacrificial layer, usually a carbon or mineral type, depend on the process and the final device. First, a sacrificial layer method dedicated to screen-printed thick-film ceramic and LTCC MEMS is presented. Second, the recent processing of piezoelectric thick-film ceramic MEMS using spark plasma sintering combined with a protective layer approach is introduced. Whatever the approach, the focus is on the interdependent effects of the microstructure, chemistry, and strain/stress, which need to be controlled to ensure reliable and performant properties of the multilayer electroceramics. Here the goal is to highlight the benefits and the large perspectives of using sacrificial/protective layers, with an emphasis on the pros and cons of such a strategy when targeting a complex piezoelectric MEMS design. Full article
(This article belongs to the Special Issue Innovative Processing Routes for Electroactive Materials)
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Article
Mechanical Properties of 2Y-TZP Fabricated from Detonation Synthesized Powder
Ceramics 2020, 3(4), 440-452; https://0-doi-org.brum.beds.ac.uk/10.3390/ceramics3040037 - 02 Nov 2020
Viewed by 992
Abstract
Yttria stabilized zirconia (Y-TZP) is frequently used in dental and engineering applications due to its high strength and fracture resistance. In this study, 2Y-TZP samples were manufactured from commercially available powder produced by detonation synthesis. Tests of the mechanical properties exhibited an unusual [...] Read more.
Yttria stabilized zirconia (Y-TZP) is frequently used in dental and engineering applications due to its high strength and fracture resistance. In this study, 2Y-TZP samples were manufactured from commercially available powder produced by detonation synthesis. Tests of the mechanical properties exhibited an unusual combination of both very high strength and toughness. The materials show a very weak correlation between toughness and grain size. The transformability, measurable by XRD, cannot explain the high toughness. Fractographic analysis revealed a broad transformation affected zone with secondary cracks and shear bands on the tensile side of bending bars which can be made responsible for the high toughness and non-linear stress–strain curves. Full article
(This article belongs to the Special Issue Biomedical Ceramics and Glasses)
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Article
Grain-Size Effects on Multi-Wire Slurry Sawing of Translucent Alumina Ceramics
Ceramics 2020, 3(4), 428-439; https://0-doi-org.brum.beds.ac.uk/10.3390/ceramics3040036 - 13 Oct 2020
Viewed by 853
Abstract
The technology of multi-wire sawing is well established in the production of silicon wafers but can also be applied in the production of ceramic substrates. In this study, the influence of the Al2O3-grain size of the alumina ceramic on [...] Read more.
The technology of multi-wire sawing is well established in the production of silicon wafers but can also be applied in the production of ceramic substrates. In this study, the influence of the Al2O3-grain size of the alumina ceramic on the efficiency of the multi-wire slurry process was investigated. The grain size of HIPed alumina ceramics was changed by heat treatment processes at 1350 °C and 1400 °C. A B4C slurry was used for the investigation of the cutting of high purity alumina ceramic. With increasing grain size of the ceramic, the efficiency of the sawing process increases. The analysis of the as-cut surface morphology of the substrates shows a change in material removal from trans- to intergranular micro-fracture with increasing grain size. Furthermore, grain coarsening leads to substrates with increased roughness values and reduced biaxial strength. Full article
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Article
Transmission Electron Microscopy Investigations on a Polysiloxane Preceramic Polymer Pyrolyzed at High Temperature in Argon
Ceramics 2020, 3(4), 421-427; https://0-doi-org.brum.beds.ac.uk/10.3390/ceramics3040035 - 03 Oct 2020
Viewed by 939
Abstract
A commercially available methylphenylvinylhydrogen polysiloxane preceramic polymer was cross-linked and pyrolyzed in argon in order to study if this compound could be used as an organic precursor for the manufacture of silicon carbide parts by photopolymerisation-based three-dimensional printing. X-Ray diffraction experiments and transmission [...] Read more.
A commercially available methylphenylvinylhydrogen polysiloxane preceramic polymer was cross-linked and pyrolyzed in argon in order to study if this compound could be used as an organic precursor for the manufacture of silicon carbide parts by photopolymerisation-based three-dimensional printing. X-Ray diffraction experiments and transmission electron microscopy observations showed that the pyrolyzed material was constituted by an interconnected polycrystalline network made of faulted/twinned β-SiC grains surrounded by an amorphous and porous second phase mainly constituted (at least 80 at%) of carbon. The free carbon residual content was estimated to be around 17.2 wt%. Additional efforts are then required to be able to use such a preceramic polymer to manufacture SiC parts by photopolymerisation-based three-dimensional printing. Full article
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