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Ceramics, Volume 1, Issue 1 (September 2018)

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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), 7; https://doi.org/10.3390/ceramics1010007 (registering DOI)
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
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
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
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
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
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
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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