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Ceramics, Volume 1, Issue 1 (September 2018)

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Open AccessArticle Fracture Toughness Evaluation and Plastic Behavior Law of a Single Crystal Silicon Carbide by Nanoindentation
Ceramics 2018, 1(1), 198-210; https://doi.org/10.3390/ceramics1010017
Received: 10 July 2018 / Revised: 6 September 2018 / Accepted: 6 September 2018 / Published: 18 September 2018
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Abstract
Nanoindentation-based fracture toughness measurements of ceramic materials like silicon carbide (SiC) with pyramidal indenters are of significant interest in materials research. A majority of currently used fracture toughness models have been developed for Vickers indenters and are limited to specific crack geometries. The
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Nanoindentation-based fracture toughness measurements of ceramic materials like silicon carbide (SiC) with pyramidal indenters are of significant interest in materials research. A majority of currently used fracture toughness models have been developed for Vickers indenters and are limited to specific crack geometries. The validity of the indentation-cracking method for the fracture toughness measurement of single crystal SiC, the elastic-plastic anisotropy and orientation dependence around the c-axis when indented in the <0001> direction is examined using nanoindentation with different pyramidal indenters. The residual impressions are analyzed using scanning electron microscopy to measure the crack lengths and the validity of existing fracture toughness measurement methods and equations is analyzed. A combination of nanoindentation with different pyramidal indenters to produce a wide range of effective strains and finite element simulation is used to extract flow properties of single crystal SiC in the <0001> direction. It is observed that there is no orientation dependence around the c-axis when SiC-6H is indented in the <0001> direction with a Berkovich indenter, i.e., it is transversely isotropic. It is also found that for a Berkovich indenter, the Jang and Pharr model, which is based on the Lawn model for cone/halfpenny cracks, gives approximately constant values at low loads (<1 N), while at higher loads (>1 N), the Laugier model gives constant fracture toughness values. Finite element analysis using equivalent cones is used along with measured hardness values to estimate the yield strength, the work hardening exponents and the stress–strain curve for single crystal SiC-6H in the <0001> direction. Full article
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Open AccessArticle In-Situ Kinetic Investigation of Calcium Aluminate Formation
Ceramics 2018, 1(1), 175-197; https://doi.org/10.3390/ceramics1010016
Received: 3 August 2018 / Revised: 20 August 2018 / Accepted: 20 August 2018 / Published: 28 August 2018
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Abstract
Rapid in-situ non-ambient X-ray diffraction represents a powerful tool for characterizing the evolution of crystalline materials in real time. The calcium aluminate system and formation of Ca12Al14O33 (C12A7) is particularly sensitive to processing conditions. This report characterizes the
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Rapid in-situ non-ambient X-ray diffraction represents a powerful tool for characterizing the evolution of crystalline materials in real time. The calcium aluminate system and formation of Ca12Al14O33 (C12A7) is particularly sensitive to processing conditions. This report characterizes the kinetic pathways to thermodynamic equilibrium as a function of atmosphere (ambient, dry, and vacuum) and reactant heterogeneity (as-received, milled, and sol-gel reactants). When reactants are heterogenous (as-received and milled), intermediary phases of Ca3Al2O6 (C3A) and CaAl2O4 (CA) are observed as the route to C12A7 formation and Ca5Al6O14 (C5A3) is only observed as a decomposition product of C12A7. When reactants are heterogenous, C12A7 is only thermodynamically favorable under ambient conditions due to the stability provided by hydration. When reactants are homogenous (sol-gel), direct crystallization of C12A7 from an amorphous precursor is observed at low temperature regardless of atmosphere defining C12A7 as the kinetic equilibrium. These findings accurately define the heterogenous formation pathways and report for the first time the formation of C12A7 under a carbon-free vacuum environment. Full article
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Open AccessArticle High-Performance SiC-Polycrystalline Fiber with Smooth Surface
Ceramics 2018, 1(1), 165-174; https://doi.org/10.3390/ceramics1010015
Received: 28 June 2018 / Revised: 7 August 2018 / Accepted: 22 August 2018 / Published: 23 August 2018
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Abstract
Polymer-derived SiC-polycrystalline fibers show excellent heat-resistance up to 2000 °C, and relatively high strength. Up to now, through our research, the relationship between the strength and residual defects of the fiber, which were formed during the production processes (degradation and sintering), has been
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Polymer-derived SiC-polycrystalline fibers show excellent heat-resistance up to 2000 °C, and relatively high strength. Up to now, through our research, the relationship between the strength and residual defects of the fiber, which were formed during the production processes (degradation and sintering), has been clarified. In this paper, we addressed the relationship between the production conditions and the surface smoothness of the obtained SiC-polycrystalline fiber, using three different raw fibers (Elementary ratio: Si1Al0.01C1.5O0.4~0.5) and three different types of reactors. With increase in the oxygen content in the raw fiber, the degradation during the production process easily proceeded. In this case, the degradation reactions (SiO + 2C = SiC + CO and SiO2 + 3C = SiC + 2CO) in the inside of each filament become faster, and then the CO partial pressure on the surface of each filament was considered to be increased. As a result, according to Le Chatelier’s principle, the surface degradation reaction and grain growth of formed SiC crystals would be considered to become slower. That is to say, using the raw fiber with higher oxygen content and closed system (highest CO content in the reactor), a much smoother surface of the SiC-polycrystalline fiber could be achieved. Furthermore, the similar effect obtained by simple oxidation of the SiC-polycrystalline fiber was confirmed, and the advantageous points of the aforementioned process were also considered. Full article
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Open AccessArticle Spark Plasma Sintered Zirconia Ceramic Composites with Graphene-Based Nanostructures
Ceramics 2018, 1(1), 153-164; https://doi.org/10.3390/ceramics1010014
Received: 27 June 2018 / Revised: 12 August 2018 / Accepted: 15 August 2018 / Published: 22 August 2018
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Abstract
The addition of graphene-based nanostructures (GBNs) can improve the inherent fragility of ceramics and provide them with improved electrical and thermal conductivities. However, both the starting material (ceramic matrix and GBNs) and the processing/sintering approach are crucial for the final composite microstructure and
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The addition of graphene-based nanostructures (GBNs) can improve the inherent fragility of ceramics and provide them with improved electrical and thermal conductivities. However, both the starting material (ceramic matrix and GBNs) and the processing/sintering approach are crucial for the final composite microstructure and properties. This work focuses on the influence of the content and dimensions of the GBN filler (10 and 20 vol%; 3 and ~150 layers), the powder-processing conditions (dry versus wet), and the homogenization method (ultrasound sonication versus high-energy planetary ball milling) on GBN/tetragonal zirconia (3YTZP) composites. The microstructure and electrical properties of the spark plasma sintered (SPS) composites were quantified and analyzed. The highest microstructural homogeneity with an isotropic microstructure was achieved by composites prepared with thicker GBNs milled in dry conditions. A high content (20 vol%) of few-layered graphene as a filler maximizes the electrical conductivity of the composites, although it hinders their densification. Full article
(This article belongs to the Special Issue Advances in the Field of Nanostructured Ceramic Composites)
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Open AccessArticle Bacterial Adhesion on Lithium Disilicate Ceramic Surface Exposed to Different Hydrofluoric Solutions
Ceramics 2018, 1(1), 145-152; https://doi.org/10.3390/ceramics1010013
Received: 18 July 2018 / Revised: 7 August 2018 / Accepted: 15 August 2018 / Published: 19 August 2018
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Abstract
The effect of Fluorine solutions on the surface and bacterial adhesion of lithium disilicate is a concern. The aim was to evaluate the surface roughness and the adhesion of Streptococcus sanguinis on lithium disilicate ceramic, under the influence of different solutions containing Fluorine.
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The effect of Fluorine solutions on the surface and bacterial adhesion of lithium disilicate is a concern. The aim was to evaluate the surface roughness and the adhesion of Streptococcus sanguinis on lithium disilicate ceramic, under the influence of different solutions containing Fluorine. Forty lithium disilicate (IPS e.max Press Impulse) discs (2.5 × 5 mm) was divided into 4 groups (n = 10): artificial saliva (Group AS), 0.2% sodium fluoride (Group NaF), 1.23% acidulated phosphate fluoride gel (Group APF), and mouthwash (Group MW). Roughness analyses were performed before and after the immersion. The surface aspect was evaluated by scanning electron microscopy (SEM) and the adhesion of Streptococcus sanguinis were evaluated after immersion in the solutions. The data obtained were submitted to the analysis of variance (ANOVA) and the Tukey test (α = 0.05). The Group APF presented a bigger roughness (3.263), statistically different to the other solutions. The bacterial adhesion in the Group APF (5.85) presented statistical difference to the other solutions. The SEM micrographs showed a rougher surface in Group APF. The 1.23% APF gel promoted major surface roughness and bacterial adhesion and could be inadequate for the use of patients with lithium disilicate ceramic restorations. Clinical significance: The Fluorine solution can affect the lithium disilicate ceramics, generating a rough and non-esthetic surface. This altered surface could be susceptible to bacterial adhesion, being directly related with periodontal health, the longevity of the restoration and the success of the rehabilitation. Full article
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Open AccessArticle Tantalum Arsenide-Based One-Dimensional Photonic Structures
Ceramics 2018, 1(1), 139-144; https://doi.org/10.3390/ceramics1010012
Received: 11 July 2018 / Revised: 4 August 2018 / Accepted: 10 August 2018 / Published: 13 August 2018
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Abstract
Weyl semimetals can be described as the three-dimensional analogue of graphene, showing linear dispersion around nodes (Weyl points). Tantalum arsenide is among the most studied Weyl semimetals. It has been demonstrated that TaAs has a very high value of the real part of
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Weyl semimetals can be described as the three-dimensional analogue of graphene, showing linear dispersion around nodes (Weyl points). Tantalum arsenide is among the most studied Weyl semimetals. It has been demonstrated that TaAs has a very high value of the real part of the complex refractive index in the infrared region. In this work we show one-dimensional photonic crystals alternating TaAs with SiO2 or TiO2 and a microcavity where a layer of TaAs is embedded between two SiO2-TiO2 multilayers. Full article
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Open AccessArticle Siloxane Precursor-Based Protective Coatings for High Modulus Carbon Fibers in Ceramic Matrix Composites
Ceramics 2018, 1(1), 128-138; https://doi.org/10.3390/ceramics1010011
Received: 15 May 2018 / Revised: 20 July 2018 / Accepted: 24 July 2018 / Published: 26 July 2018
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Abstract
Carbon fibers are outstanding reinforcements for ceramic components due to their excellent creep and long-term thermochemical and thermomechanical stability. Nevertheless, these properties are dramatically downgraded if the unprotected fibers are exposed to an oxidative or corrosive environment. Thin ceramic coatings can improve the
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Carbon fibers are outstanding reinforcements for ceramic components due to their excellent creep and long-term thermochemical and thermomechanical stability. Nevertheless, these properties are dramatically downgraded if the unprotected fibers are exposed to an oxidative or corrosive environment. Thin ceramic coatings can improve the corrosion resistance and tailor the fiber/matrix interface in order to achieve optimized stress transfer and damage tolerance. The continuous liquid phase coating (CLPC) technique with subsequent pyrolysis is a promising alternative to chemical vapor deposition (CVD) processes. The possibility to deposit homogenous thin flaw-free coating layers on every filament of high tenacity carbon fiber bundles has been successfully proven in previous studies. In this work, high modulus carbon fibers were coated with different polysiloxane-based resins, and the obtained rovings were implemented in SiOC matrices by the precursor impregnation and pyrolysis (PIP) route. Thermogravimetric analysis shows an increased oxidation resistance of the coated fibers compared with reference samples. Enhanced fiber/matrix interface strength further improved the mechanical performance of the fabricated composites. Full article
(This article belongs to the Special Issue Advances in the Field of Nanostructured Ceramic Composites)
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Open AccessArticle Synthesis and Characterization of Nano-Tungsten Oxide Precipitated onto Natural Inorganic Clay for Humidity-Sensing Applications
Ceramics 2018, 1(1), 120-127; https://doi.org/10.3390/ceramics1010010
Received: 28 May 2018 / Revised: 27 June 2018 / Accepted: 10 July 2018 / Published: 12 July 2018
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Abstract
A wet chemical method was used to obtain tungsten oxide nanoparticles from tungsten tetrachloride and natural microfibrous inorganic clay (sepiolite) as a starting material. Precipitation of tungsten oxide species onto sepiolite under basic conditions and subsequent thermal treatment was investigated, prompted by the
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A wet chemical method was used to obtain tungsten oxide nanoparticles from tungsten tetrachloride and natural microfibrous inorganic clay (sepiolite) as a starting material. Precipitation of tungsten oxide species onto sepiolite under basic conditions and subsequent thermal treatment was investigated, prompted by the abundance of sepiolite in nature and the useful environmental applications that could be attained. Laser granulometry, X-ray diffraction, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), and high-resolution transmission electron microscopy (HR-TEM) techniques were used to study the particle-size distribution, the morphology, and the composition of the prepared sample. Our findings show the presence of tungsten oxide nanoparticles, which are less than 50 nm, on the needles of the modified sepiolite. Full article
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Open AccessReview Semiconducting Metal Oxides Nanocomposites for Enhanced Detection of Explosive Vapors
Ceramics 2018, 1(1), 98-119; https://doi.org/10.3390/ceramics1010009
Received: 15 May 2018 / Revised: 11 June 2018 / Accepted: 21 June 2018 / Published: 25 June 2018
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Abstract
In recent years, the detection of ultratraces of nitroaromatic compounds (NACs), such as 2,4,6-trinitrotoluene (TNT), has gained considerable attention due to associated problems related to environment, security against terrorists and health. The principle of NACs detection is simple since any explosive emits a
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In recent years, the detection of ultratraces of nitroaromatic compounds (NACs), such as 2,4,6-trinitrotoluene (TNT), has gained considerable attention due to associated problems related to environment, security against terrorists and health. The principle of NACs detection is simple since any explosive emits a rather small, but detectable number of molecules. Thus, numerous detection techniques have been developed throughout the years, but their common limitations are rather large sizes and weights, high power consumption, unreliable detection with false alarms, insufficient sensitivity and/or chemical selectivity, and hyper-sensitivity to mechanical influences associated with very high price. Thus, there is a strong need of cheap, rapid, sensitive, and simple analytical methods for the detection and monitoring of these explosives in air. Semiconducting metal oxides (SMOs) allow the preparation of gas sensors able to partially or totally overcome these drawbacks, and this paper aims to shortly review the most recent SMOs nanocomposites able to sense explosives. Full article
(This article belongs to the Special Issue Advances in the Field of Nanostructured Ceramic Composites)
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Open AccessArticle Alumina Porous Ceramics Obtained by Freeze Casting: Structure and Mechanical Behaviour under Compression
Ceramics 2018, 1(1), 83-97; https://doi.org/10.3390/ceramics1010008
Received: 18 April 2018 / Revised: 13 June 2018 / Accepted: 14 June 2018 / Published: 20 June 2018
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Abstract
The aim of the work is to analyse the mechanical behaviour of anisotropic porous alumina ceramics processed by freeze casting (ice templating). The freeze cast specimens were characterised by a lamellar structure with ellipsoidal pore shape, with a size ranging from 6 to
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The aim of the work is to analyse the mechanical behaviour of anisotropic porous alumina ceramics processed by freeze casting (ice templating). The freeze cast specimens were characterised by a lamellar structure with ellipsoidal pore shape, with a size ranging from 6 to 42 µm and 13 to 300 µm for the minor and major axes, respectively, as a function of the freezing rate and the powder and binder contents. The pore volume fraction ranged from 40 to 57%. SEM analysis of the porous structures after the compression test showed a typical deformation pattern caused by the porosity gradient through the specimen, as determined by X-ray radiography. The apparent elastic modulus of the anisotropic porous alumina ranged from 0.2 to 14 GPa and the compressive strength from 6 to 111 MPa, varying as a function of the process parameters which determine the pore network characteristics. The relationships between stress-strain behaviour in compression and the microstructure and texture were established. An analytical model based on a Gibson and Ashby relationship was used and adapted from SEM microstructural analysis after a mechanical test in order to predict the compressive strength of processed anisotropic alumina. Full article
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Open AccessArticle Deriving Principles of the Freeze-Foaming Process by Nondestructive CT Macrostructure Analyses on Hydroxyapatite Foams
Ceramics 2018, 1(1), 65-82; https://doi.org/10.3390/ceramics1010007
Received: 2 May 2018 / Revised: 8 June 2018 / Accepted: 8 June 2018 / Published: 17 June 2018
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Abstract
Freeze Foaming is a direct foaming method that aims at manufacturing ceramic cellular scaffolds for diverse applications. Next to porous structures for a potential use as refractories, the focus lies on potential bone replacement material. The main challenge of this foaming method is
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Freeze Foaming is a direct foaming method that aims at manufacturing ceramic cellular scaffolds for diverse applications. Next to porous structures for a potential use as refractories, the focus lies on potential bone replacement material. The main challenge of this foaming method is to achieve a homogeneous and predictable pore morphology. That is why, in a current project, the authors report on the pore morphology formation and evolution of the foaming process by means of nondestructive testing. This contribution primarily compares the effect of the suspension’s temperature on the resulting foam structure (foaming at 5 and 40 °C). As a basis for computed tomographic analysis, a stable and reproducible model suspension was developed that resulted in reproducible foam structures. Characterized by viscosity, foam structure analyses and foaming rate, the resulting Freeze Foams became adjustable with regards to their porosity and pore shape/size. Under certain conditions, we succeeded in achieving a relatively homogeneous pore structure, as proven by computed tomography-derived quantitative analysis. Full article
(This article belongs to the Special Issue Novel Processing Routes of Ceramics for Functional Applications)
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Open AccessArticle On the Synthesis and Characterization of Lanthanide Metal-Organic Frameworks
Ceramics 2018, 1(1), 54-64; https://doi.org/10.3390/ceramics1010006
Received: 28 March 2018 / Revised: 2 June 2018 / Accepted: 11 June 2018 / Published: 12 June 2018
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Abstract
In this study, lanthanide metal-organic frameworks Ln(BTC)(DMF)2(H2O) (LnMOFs) are synthesized using the metal nitrates as lanthanide (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu) source and 1,3,5-benzenetricarboxylic acid (BTC) as a
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In this study, lanthanide metal-organic frameworks Ln(BTC)(DMF)2(H2O) (LnMOFs) are synthesized using the metal nitrates as lanthanide (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu) source and 1,3,5-benzenetricarboxylic acid (BTC) as a coordination ligand. X-ray diffraction (XRD) analysis, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TG/DTG) analysis fluorescence spectroscopy (FLS), and scanning electron microscopy (SEM) are employed to characterize the newly synthesized LnMOFs. Full article
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Open AccessArticle A Facile Method Using a Flux to Improve Quantum Efficiency of Submicron Particle Sized Phosphors for Solid-State Lighting Applications
Ceramics 2018, 1(1), 38-53; https://doi.org/10.3390/ceramics1010005
Received: 17 May 2018 / Revised: 2 June 2018 / Accepted: 6 June 2018 / Published: 8 June 2018
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Abstract
This work successfully verified that the addition of a flux (NH4F, NH4Cl, and H3BO3) during synthesis has an impact on the crystallite size and quantum efficiency of submicron-sized particles of CaMgSi2O6:Eu
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This work successfully verified that the addition of a flux (NH4F, NH4Cl, and H3BO3) during synthesis has an impact on the crystallite size and quantum efficiency of submicron-sized particles of CaMgSi2O6:Eu2+ phosphors. The addition of NH4F or NH4Cl increased the crystallite size in the submicron-sized particles, yielding an increase in emission intensity and quantum efficiency. On the other hand, the use of the H3BO3 flux crystallized a secondary phase, SiO2, and changed the lattice parameters, which degraded the luminescent properties. In addition, an excessive amount of NH4Cl was examined, resulting in nucleation of a secondary phase, CaSiO3, which changed the lattice parameters with no improvement in luminescent properties. These results demonstrate that the addition of a flux could be a method to improve the quantum efficiency of submicron-sized particles composed of nanocrystallites; however, a judicious choice of the flux composition and amount has to be carefully considered. Full article
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Open AccessArticle Enhanced Mechanical Properties in ED-Machinable Zirconia-Tungsten Carbide Composites with Yttria-Neodymia Co-Stabilized Zirconia Matrix
Ceramics 2018, 1(1), 26-37; https://doi.org/10.3390/ceramics1010004
Received: 15 May 2018 / Revised: 29 May 2018 / Accepted: 30 May 2018 / Published: 5 June 2018
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Abstract
The electrical discharge machining-process (EDM) is a smart solution to optimize the manufacturing chain of customized and complex shaped ceramic components. To comply with the high requirements for the machine and mold design, it is necessary to improve the mechanical properties of ED-machinable
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The electrical discharge machining-process (EDM) is a smart solution to optimize the manufacturing chain of customized and complex shaped ceramic components. To comply with the high requirements for the machine and mold design, it is necessary to improve the mechanical properties of ED-machinable ceramics. In this study, ceramic composites with a tetragonal zirconia matrix and tungsten carbide as electrically conductive dispersion were investigated. To improve the toughness of this high strength material, co-stabilized zirconia coated with yttria and neodymia as dopants were used in the compositions with 1.5/1.5 and 1.75/1.25 mol %. These recipes were compared to commercial 3Y-TZP as a reference matrix material combined with the same WC raw powder. The electrically conductive phase content was varied from 20 to 28 vol %. For all compositions, the ceramic blanks were hot pressed at identical dwell and pressure, but with various sintering temperatures (1300 °C to 1450 °C) and then tested with respect to the mechanical and electrical properties. By variation of the stabilizer system, a significantly higher toughness of up to 11.3 MPa√m compared to 5.3 MPa√m for 3Y-TZP-20WC is achieved while the bending strength stays at a comparable high level of >1500 MPa. Full article
(This article belongs to the Special Issue Advances in the Field of Nanostructured Ceramic Composites)
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Open AccessArticle Preparation and Characterization of Pressureless Sintered Alumina/5 vol % SiC Micro-Nanocomposites
Ceramics 2018, 1(1), 13-25; https://doi.org/10.3390/ceramics1010003
Received: 11 April 2018 / Revised: 17 May 2018 / Accepted: 22 May 2018 / Published: 24 May 2018
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Abstract
Alumina/5 vol % SiC micro-nanocomposites were produced by slip-casting and pressureless sintering. The dispersion of alumina and SiC particles in water using an electrosteric dispersant was studied for different solid contents. Although the rheological and granulometry measurements showed that the optimum amount of
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Alumina/5 vol % SiC micro-nanocomposites were produced by slip-casting and pressureless sintering. The dispersion of alumina and SiC particles in water using an electrosteric dispersant was studied for different solid contents. Although the rheological and granulometry measurements showed that the optimum amount of Darvan C for well-dispersing 50 wt % dry matter slurries was 0.20 vol %, this content was increased to 1.00 vol % in order to avoid the demixing of SiC nanoparticles during shaping. Well densified (>99%) alumina–SiC pressureless sintered materials were obtained at 1800 °C-2 h in which SiC nanoparticles occupied inter/intragranular positions. The creep behaviour of these materials was examined at 1200 °C under stresses ranging from 70 to 140 MPa. A good creep resistance in alumina-SiC materials was obtained demonstrating that the use of less expensive conventional sintering methods is possible and highlighting the importance of the dispersion step. Full article
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Open AccessArticle Electrical Behavior and Microstructural Features of Electric Field-Assisted and Conventionally Sintered 3 mol% Yttria-Stabilized Zirconia
Ceramics 2018, 1(1), 3-12; https://doi.org/10.3390/ceramics1010002
Received: 28 December 2017 / Revised: 10 February 2018 / Accepted: 18 February 2018 / Published: 21 February 2018
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Abstract
ZrO2: 3 mol% Y2O3 (3YSZ) polycrystalline pellets were sintered at 1400 °C and by applying an alternating current (AC) electric field at 1000 °C. An alumina sample holder with platinum wires for connecting the sample to a power
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ZrO2: 3 mol% Y2O3 (3YSZ) polycrystalline pellets were sintered at 1400 °C and by applying an alternating current (AC) electric field at 1000 °C. An alumina sample holder with platinum wires for connecting the sample to a power supply was designed for the electric field-assisted sintering experiments. The apparent density was evaluated with the Archimedes technique, the grain size distribution by analysis of scanning electron microscopy images, and the electrical behavior by the impedance spectroscopy technique. Sintering with the application of AC electric fields to 3YSZ enhances its ionic conductivity. An explanation is proposed, based on the dissolution back to the bulk of chemical species, which are depleted at the grain boundaries, leading to an increase in the oxygen vacancy concentration. For the enhancement of the grain boundary conductivity, an explanation is given based on the diminution of the concentration of depleted chemical species, which migrate to the bulk. This migration leads to a decrease of the potential barrier of the space charge region, known to be responsible for blocking the oxide ions through the intergranular region. Moreover, the heterogeneity of the distribution of the grain sizes is ascribed to the skin effect, the tendency of the AC current density to be largest near the surface, decreasing towards the bulk. Full article
(This article belongs to the Special Issue Novel Processing Routes of Ceramics for Functional Applications)
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Open AccessEditorial Welcome to Ceramics: A New Open Access Scientific Journal on Ceramics Science and Engineering
Ceramics 2018, 1(1), 1-2; https://doi.org/10.3390/ceramics1010001
Received: 16 October 2017 / Accepted: 16 October 2017 / Published: 20 October 2017
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Abstract
The word ceramics comes from the Greek word keramikos, which means pottery and corresponds to a very old human activity. Indeed, one of the oldest materials fabricated in the world is ceramic pottery [...]
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