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Ceramics, Volume 2, Issue 4 (December 2019) – 7 articles

Cover Story (view full-size image): The clinical safety of zirconia dental implants by means of long-term stability is being addressed by two international ISO standards. These standards impose different experimental setups concerning the dynamic fatigue resistance of the final product (ISO 14801) or the aging behavior of a standardized sample (ISO 13356) separately. This communication is a contribution to the current discussion on how to optimize the aforementioned standards in order to guarantee clinical safety for patients. View this paper
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Article
Mechanism of Carbon Contamination in Transparent MgAl2O4 and Y3Al5O12 Ceramics Sintered by Spark Plasma Sintering
Ceramics 2019, 2(4), 612-619; https://doi.org/10.3390/ceramics2040048 - 13 Dec 2019
Cited by 6 | Viewed by 1224
Abstract
An investigation of MgAl2O4 spinel and Y3Al2O5 (YAG) materials sintered by spark plasma sintering (SPS) was performed. The optical properties of the materials are modified depending on the powder source and the SPS sintering conditions. [...] Read more.
An investigation of MgAl2O4 spinel and Y3Al2O5 (YAG) materials sintered by spark plasma sintering (SPS) was performed. The optical properties of the materials are modified depending on the powder source and the SPS sintering conditions. Spectrophotometer and Raman analysis are presented in this work, along with optical and scanning electron microscope (SEM) observations and cathodoluminescence analysis. The results show a correlation between carbon contamination and the optical properties of the materials. Herein, the source of the contamination is explained, along with its genesis and diffusion. The carbon contamination originates from the powder itself (carbonates), as well as the SPS environment (papiex® graphite foil, graphite die, graphite felt) to form carbon clusters. During the high-temperature SPS process, carbon from those carbon clusters diffuses, resulting in an increase in the contamination volume, thereby increasing the light absorption. Full article
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Article
Hydrothermal Corrosion Behaviors of Constituent Materials of SiC/SiC Composites for LWR Applications
Ceramics 2019, 2(4), 602-611; https://doi.org/10.3390/ceramics2040047 - 09 Dec 2019
Cited by 2 | Viewed by 822
Abstract
The corrosion behaviors of SiC/SiC composite constituent materials in pure water at operating conditions, such as 300 °C and 8.5 MPa, were studied for potential application in accident-tolerant light water reactor (LWR) fuel cladding and core structures. Five kinds of SiC fibers, four [...] Read more.
The corrosion behaviors of SiC/SiC composite constituent materials in pure water at operating conditions, such as 300 °C and 8.5 MPa, were studied for potential application in accident-tolerant light water reactor (LWR) fuel cladding and core structures. Five kinds of SiC fibers, four kinds of SiC matrices, and three kinds of fiber/matrix interphase materials were examined in autoclaves. The potential constituent materials for future use in SiC/SiC composites were selected by considering corrosion rates and residual strength characteristics. The mass changes and the residual strength of each specimen were measured. SEM images of the surface layers were also inspected. The SiC fibers, regardless of their purity, crystallinity or stoichiometric ratio, decreased in strength due to the hydrothermal corrosion. For its part, the hydrothermal corrosion resistance of CVD-SiC, as a SiC matrix, was found to be affected by manufacturing conditions such as raw material gas type and synthesis temperature, as well as post-machining morphology. The CVD-carbon (CVD-C), as a fiber/matrix interphase material, showed good hydrothermal corrosion resistance. In order to protect the SiC fibers and the SiC matrices from hydrothermal corrosion, it would appear to be necessary to apply a dense CVD-C coating to both every fiber and the entire surface of the SiC matrices. Full article
(This article belongs to the Special Issue Physical Properties of Metals/Metal-Base Materials)
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Article
Thermomechanical Characterisation of Mullite Zirconia Composites Sintered from Andalusite for High Temperature Applications
Ceramics 2019, 2(4), 587-601; https://doi.org/10.3390/ceramics2040046 - 06 Dec 2019
Cited by 4 | Viewed by 1101
Abstract
Mullite-Zirconia refractories are well known for their good resistance to corrosion and thermal shock. In this study, several mullite-zirconia composites were developed from andalusite, alumina and zircon sintered at 1600 °C for 10 hours. The samples were subjected to thermal shock carried out [...] Read more.
Mullite-Zirconia refractories are well known for their good resistance to corrosion and thermal shock. In this study, several mullite-zirconia composites were developed from andalusite, alumina and zircon sintered at 1600 °C for 10 hours. The samples were subjected to thermal shock carried out after heating at 1200 °C, in order to study the mechanical and thermomechanical behaviour as a function of the amount of zirconia dispersed in the mullite matrix. It appears that that the amorphous phase (SiO2), determined by X-ray diffraction, produced by the decomposition of andalusite, increases considerably with the amount of final zirconia in the composite and has a very important influence on the porosity. This amorphous phase seems also to have an important influence on the mechanical properties of the material. The characterisation of the thermomechanical behaviour (elastic properties and damage monitoring) was carried out thanks to ultrasonic techniques (US echography and Acoustic Emission). The “surprising” evolution (increase) of the Young’s modulus E of the material after being submitted to repeated thermal shocks is highlighted and explained. The acoustic emission technique carried out at high temperature and also coupled to 4-points bending tests (at room temperature) demonstrates its effectiveness for providing a better understanding of the chronology of the involved mechanisms involved at microstructural scale. Full article
(This article belongs to the Special Issue Design, Properties, Damage and Lifetime of Refractory Ceramics)
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Review
Direct Laser Interference Patterning of Bioceramics: A Short Review
Ceramics 2019, 2(4), 578-586; https://doi.org/10.3390/ceramics2040045 - 28 Oct 2019
Cited by 11 | Viewed by 1549
Abstract
Bioceramics are a great alternative to use in implants due to their excellent biocompatibility and good mechanical properties. Depending on their composition, bioceramics can be classified into bioinert and bioactive, which relate to their interaction with the surrounding living tissue. Surface morphology also [...] Read more.
Bioceramics are a great alternative to use in implants due to their excellent biocompatibility and good mechanical properties. Depending on their composition, bioceramics can be classified into bioinert and bioactive, which relate to their interaction with the surrounding living tissue. Surface morphology also has great influence on the implant biological behavior. Controlled texturing can improve osseointegration and reduce biofilm formation. Among the techniques to produce nano- and micropatterns, laser texturing has shown promising results due to its excellent accuracy and reproducibility. In this work, the use of laser techniques to improve surface morphology of biomaterials is reviewed, focusing on the application of direct laser interference patterning (DLIP) technique in bioceramics. Full article
(This article belongs to the Special Issue Ceramics for Biomedical Applications)
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Communication
Is a Zirconia Dental Implant Safe When It Is Available on the Market?
Ceramics 2019, 2(4), 568-577; https://doi.org/10.3390/ceramics2040044 - 12 Oct 2019
Cited by 4 | Viewed by 1585
Abstract
The market share of zirconia (ZrO2) dental implants is steadily increasing. This material comprises a polymorphous character with three temperature-dependent crystalline structures, namely monoclinic (m), tetragonal (t) and cubic (c) phases. Special attention is given to the tetragonal phase when maintained [...] Read more.
The market share of zirconia (ZrO2) dental implants is steadily increasing. This material comprises a polymorphous character with three temperature-dependent crystalline structures, namely monoclinic (m), tetragonal (t) and cubic (c) phases. Special attention is given to the tetragonal phase when maintained in a metastable state at room temperature. Metastable tetragonal grains allow for the beneficial phenomenon of Phase Transformation Toughening (PTT), resulting in a high fracture resistance, but may lead to an undesired surface transformation to the monoclinic phase in a humid environment (low-temperature degradation, LTD, often referred to as ‘ageing’). Today, the clinical safety of zirconia dental implants by means of long-term stability is being addressed by two international ISO standards. These standards impose different experimental setups concerning the dynamic fatigue resistance of the final product (ISO 14801) or the ageing behavior of a standardized sample (ISO 13356) separately. However, when evaluating zirconia dental implants pre-clinically, oral environmental conditions should be simulated to the extent possible by combining a hydrothermal treatment and dynamic fatigue. For failure analysis, phase transformation might be quantified by non-destructive techniques, such as X-Ray Diffraction (XRD) or Raman spectroscopy, whereas Scanning Electron Microscopy (SEM) of cross-sections or Focused Ion Beam (FIB) sections might be used for visualization of the monoclinic layer growth in depth. Finally, a minimum load should be defined for static loading to fracture. The purpose of this communication is to contribute to the current discussion on how to optimize the aforementioned standards in order to guarantee clinical safety for the patients. Full article
(This article belongs to the Special Issue Ceramics for Biomedical Applications)
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Article
Osteogenic Enhancement of Zirconia-Toughened Alumina with Silicon Nitride and Bioglass®
Ceramics 2019, 2(4), 554-567; https://doi.org/10.3390/ceramics2040043 - 04 Oct 2019
Cited by 4 | Viewed by 1438
Abstract
Alumina (Al2O3) ceramic implants do not stimulate osteoblasts in vivo. Surface alterations targeted at changing the chemistry or topography have been proposed to enhance the bioactivity of alumina. This surface modification is intended to improve oxide bioceramic’s ability to [...] Read more.
Alumina (Al2O3) ceramic implants do not stimulate osteoblasts in vivo. Surface alterations targeted at changing the chemistry or topography have been proposed to enhance the bioactivity of alumina. This surface modification is intended to improve oxide bioceramic’s ability to integrate with the biological environment and, in particular, to rapidly osteointegrate. In this study, the surface of zirconia-toughened alumina (ZTA) was functionalized using two methods: (i) Surface laser-patterning and successive filling of patterned wells with powder mixtures of bioglass and Si3N4; and, (ii) Si3N4 coating by pulse-laser sintering. Functionalized ZTA surfaces were characterized with vibrational spectroscopy, biological testing, and laser microscopy. Both enhancements resulted in osteoblast activation, a property that is relevant to osteosynthesis. Full article
(This article belongs to the Special Issue Ceramics for Biomedical Applications)
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Editorial
Advances in Ice-Templated and Freeze-Casted Ceramics
Ceramics 2019, 2(4), 551-553; https://doi.org/10.3390/ceramics2040042 - 26 Sep 2019
Cited by 2 | Viewed by 1160
Abstract
Ice-templating, also known as freeze-casting, has become over the past 15 years a well-established materials processing route [...] Full article
(This article belongs to the Special Issue Ice-Templated and Freeze-Cast Ceramics)
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