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Ceramics (ISSN 2571-6131) is an international peer-reviewed open access journal of ceramics science and engineering published quarterly online by MDPI.
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Latest Articles
Evidence of Phase Transitions and Their Role in the Transient Behavior of Mechanical Properties and Low Temperature Degradation of 3Y-TZP Made from Stabilizer-Coated Powder
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Ceramics 2019, 2(2), 271-285; https://doi.org/10.3390/ceramics2020022 - 3 April 2019
Abstract
The substance 3 mol% yttria stabilized zirconia (3Y-TZP) has become a commodity for the manufacture of components in biomedical and engineering applications. Materials made from stabilizer-coated rather than co-precipitated starting powders are known for their superior toughness and low temperature ageing resistance. The
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The substance 3 mol% yttria stabilized zirconia (3Y-TZP) has become a commodity for the manufacture of components in biomedical and engineering applications. Materials made from stabilizer-coated rather than co-precipitated starting powders are known for their superior toughness and low temperature ageing resistance. The reason for this phenomenon is however still not fully understood. In this study, 3Y-TZP materials hot pressed at 1300–1450 °C for 1 h were characterized. It was found that at a sintering temperature of 1375 °C, a transition from fine grain to coarse grain microstructure associated with a shift from tough and ageing resistant to brittle and prone to ageing was observed. The detailed analysis of the phase composition by X-ray diffraction revealed that TZPs consists of up to five crystallographically different phases of zirconia simultaneously whose contents dynamically change with sintering temperature. At low sintering temperature, the predominant phases are a tetragonal phase with low yttria content and large domain size and high tetragonality together with a cubic phase of high yttria content. At high temperature, a tetragonal phase of higher yttria content and lower tetragonality is formed together with a cubic phase of lower yttria content.
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Coatings Based on Organic/Non-Organic Composites on Bioinert Ceramics by Using Biomimetic Co-Precipitation
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Ceramics 2019, 2(2), 260-270; https://doi.org/10.3390/ceramics2020021 - 3 April 2019
Abstract
Bioinert ceramics have been commonly used in the field of orthopedic and dentistry due to their excellent mechanical properties, esthetic look, good biocompatibility and chemical inertness. However, an activation of its bioinert surface could bring additional advantages for better implant-integration in vivo. Therefore,
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Bioinert ceramics have been commonly used in the field of orthopedic and dentistry due to their excellent mechanical properties, esthetic look, good biocompatibility and chemical inertness. However, an activation of its bioinert surface could bring additional advantages for better implant-integration in vivo. Therefore, we introduce an innovative biomimetic co-precipitation technique by using modified simulated body fluid (SBF) to obtain a composite coating made of organic/non-organic components. The zirconia samples were soaked in SBF containing different concentrations of protein (0.01, 0.1, 1, 10 and 100 g/l). Bovine serum albumin (BSA) was applied as a standard protein. During the soaking time, a precipitation of calcium phosphate took place on the substrate surfaces. The proteins were incorporated into the coating during precipitation. Morphology changes of precipitated hydroxyapatite (HAp) due to the presence of proteins were observed on SEM-images. The presence of proteins within the coating was proven by using SEM/energy dispersive X-ray spectroscopy (EDX) and immunohistochemical analysis. We conclude that it is possible to co-precipitate the organic/non-organic composite on inert ceramic by using the wet-chemistry method. In future studies, BSA could be replaced by targeted proteins appropriate to the application area. This method could create new biomaterials, the surfaces of which could be tailored according to the desires and requirements of their use.
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Influence of a Bleaching Agent on the Color Stability of Indirect Composite Resins Immersed in Dyes
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Ceramics 2019, 2(2), 235-245; https://doi.org/10.3390/ceramics2020019 - 1 April 2019
Abstract
This study aimed to evaluate the effect of a bleaching agent on the color of extrinsically pigmented indirect composite resins. Samples of five resins (Adoro, Resilab, Cristobal, Sinfony, Epricord) were manufactured and divided into five groups: red wine, coffee, orange juice, Coca-Cola, and
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This study aimed to evaluate the effect of a bleaching agent on the color of extrinsically pigmented indirect composite resins. Samples of five resins (Adoro, Resilab, Cristobal, Sinfony, Epricord) were manufactured and divided into five groups: red wine, coffee, orange juice, Coca-Cola, and artificial saliva (control). The stained samples were immersed in a 38% hydrogen peroxide solution for 30 min per week, over three weeks. Color readings were performed at the initial state (L0), after 21 days of dye immersion (ΔE1, L1), and after 7 (ΔE2, L2), 14 (ΔE3, L3), and 21 days (ΔE4, L4) of bleach immersion. Data were subjected to ANOVA and Tukey’s honestly significant difference (HSD) test (α = 0.05). The color alteration was greater in ΔE1, regardless of color solution, indicating extrinsic pigmentation. The Resilab group exhibited greater ΔE1 values than the other resins. The bleaching agent promoted bleaching action on the surfaces of the materials studied, removing the previously impregnated pigments.
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External Field Assisted Freeze Casting
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Ceramics 2019, 2(1), 208-234; https://doi.org/10.3390/ceramics2010018 - 24 March 2019
Abstract
Freeze casting under external fields (magnetic, electric, or acoustic) produces porous materials having local, regional, and global microstructural order in specific directions. In freeze casting, porosity is typically formed by the directional solidification of a liquid colloidal suspension. Adding external fields to the
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Freeze casting under external fields (magnetic, electric, or acoustic) produces porous materials having local, regional, and global microstructural order in specific directions. In freeze casting, porosity is typically formed by the directional solidification of a liquid colloidal suspension. Adding external fields to the process allows for structured nucleation of ice and manipulation of particles during solidification. External control over the distribution of particles is governed by a competition of forces between constitutional supercooling and electromagnetism or acoustic radiation. Here, we review studies that apply external fields to create porous ceramics with different microstructural patterns, gradients, and anisotropic alignments. The resulting materials possess distinct gradient, core–shell, ring, helical, or long-range alignment and enhanced anisotropic mechanical properties.
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Sintering of Cermets: A Case Study of Sintering Ni–Co Ferrite with Ag-, Cu- and Ni-Dispersed Alloy Particles
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Ceramics 2019, 2(1), 190-207; https://doi.org/10.3390/ceramics2010017 - 20 March 2019
Abstract
Literature has shown that the development of ferrite cermets makes possible the enhancement of the mechanical properties of these ceramics for applications in electronics, magnetomechanical sensors, and inert anodes. In this work, a Ni–Co ferrite powder was mixed with metallic powders, compacted, and
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Literature has shown that the development of ferrite cermets makes possible the enhancement of the mechanical properties of these ceramics for applications in electronics, magnetomechanical sensors, and inert anodes. In this work, a Ni–Co ferrite powder was mixed with metallic powders, compacted, and sintered. The metallic powders used were Ag–Ni and Cu–Ni, prepared by mechanical alloying, and commercial Ag and Ag–Cu powders. The microstructures, crystal structures, and chemical compositions of the sintered samples were analyzed. The Cu–Ni cermet did not present traces of second phases in its XRD pattern, and the experimental results indicate a high reactivity between the ferrite and the Cu–Ni alloy. In the Ag–Cu and Ag–Ni cermets, the composition of the metallic particles was nearly 100% Ag after sintering. It was observed that, for the production of ferrite particulate cermets, the composition, particle size, and melting point of the metallic phase must be carefully adjusted in order to obtain a material with proper chemical composition and microstructure (uniform distribution of the metallic phase and no cracks in the metal–ceramic interfaces).
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Ammonium Hydroxide Mediated Hydrothermal Crystallization of Hydroxyapatite Coatings on Titanium Substrate
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Ceramics 2019, 2(1), 180-189; https://doi.org/10.3390/ceramics2010016 - 19 March 2019
Abstract
Controlled growth of hydroxyapatite (HAp) coatings on titanium substrate plays an important role in the fabrication of the composites for bone tissue engineering. We describe the synthesis of the crystalline hydroxyapatite coatings on the Ti/TiO2 substrate through a hydrothermal method by using
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Controlled growth of hydroxyapatite (HAp) coatings on titanium substrate plays an important role in the fabrication of the composites for bone tissue engineering. We describe the synthesis of the crystalline hydroxyapatite coatings on the Ti/TiO2 substrate through a hydrothermal method by using ethylenediamine tetraacetic acid disodium salt (Na2EDTA) and varying concentrations of ammonium hydroxide (NH4OH) in calcium-phosphate precursor solution. Na2EDTA serves as a chelating agent, while NH4OH is used as an alkaline source and crystal growth modifier. We characterized the HAp coatings using x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. We also performed the elemental chemical analysis by means of a particle induced x–ray emission method. Our results show that there is a pH limit for which the hydrothermal deposition of HAp on titanium occurs. Moreover, we observed that NH4OH had a measurable influence on the coating thickness as well as on the size and shape of the HAp crystals. We found that with the increase of NH4OH concentration, the thickness of the Hap layer increases and its morphology changes from irregular flakes to well-defined hexagonal rods.
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Radial-Concentric Freeze Casting Inspired by Porcupine Fish Spines
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Ceramics 2019, 2(1), 161-179; https://doi.org/10.3390/ceramics2010015 - 6 March 2019
Abstract
Freeze casting is a technique used to manufacture porous ceramics with aligned microstructures. In conventional freeze casting, these microstructures are aligned along a single direction of freezing. However, a caveat to these ceramics has been their ensuing lack of strength and toughness due
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Freeze casting is a technique used to manufacture porous ceramics with aligned microstructures. In conventional freeze casting, these microstructures are aligned along a single direction of freezing. However, a caveat to these ceramics has been their ensuing lack of strength and toughness due to their high porosity, especially in the direction orthogonal to the direction of alignment. In this work, a novel freezing casting method referred to as “radial-concentric freeze casting” is presented, which takes its inspiration from the radially and concentrically aligned structure of the defensive spines of the porcupine fish. The method builds off the radial freeze casting method, in which the microstructure is aligned radially, and imposes a concentric alignment. Axial compression and Brazilian tests were performed to obtain axial compressive strengths, axial compressive moduli, and splitting tensile strengths of freeze cast samples with and without epoxy infiltration. Notably, radial-concentric freeze cast samples had the greatest improvements in axial compressive modulus and splitting tensile strength with infiltration, when compared against the changes in mechanical properties of conventional and radial freeze cast ceramics with infiltration. These results provide further evidence for the importance of structure in multiphase materials and the possibility of enhancing mechanical properties through the controlled alignment of microstructures.
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Ice-Templated Geopolymer—Fe/Mn Oxide Composites Conceived as Oxygen Carriers
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Ceramics 2019, 2(1), 148-160; https://doi.org/10.3390/ceramics2010014 - 1 March 2019
Abstract
Ice-templating (freeze-casting) technique was applied to a novel class of geopolymer composites containing Fe/Mn oxides, previously tested and reported in others works as synthetic oxygen carriers for chemical looping combustion (CLC), in order to obtain composite monoliths with lamellar macro-porosities by unidirectional freezing
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Ice-templating (freeze-casting) technique was applied to a novel class of geopolymer composites containing Fe/Mn oxides, previously tested and reported in others works as synthetic oxygen carriers for chemical looping combustion (CLC), in order to obtain composite monoliths with lamellar macro-porosities by unidirectional freezing of water-based sol-gel systems. Geopolymer-Fe/Mn oxides composites carriers were also produced as beads, suitable for fixed bed reactors, by an injection-solidification method in liquid nitrogen. After conditioning at 900 °C, the temperature needed for CLC applications, the composite beads and monoliths possess similar total porosity % and total pore volume, being ≈65% and 570 mm3 g−1, respectively, as well as a specific surface area of around 2.4–2.9 m2/g.
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Roughness Effect in Micropitting and Rolling Contact Fatigue of Silicon Nitride
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Ceramics 2019, 2(1), 135-147; https://doi.org/10.3390/ceramics2010013 - 18 February 2019
Abstract
An experimental analysis of the role of surface roughness parameters on micropitting and the succeeding rolling contact fatigue (RCF) of silicon nitride against AISI 52100 steel under lubricated conditions was performed. In accelerated fatigue tests using a four-ball tester, the arithmetic mean, root
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An experimental analysis of the role of surface roughness parameters on micropitting and the succeeding rolling contact fatigue (RCF) of silicon nitride against AISI 52100 steel under lubricated conditions was performed. In accelerated fatigue tests using a four-ball tester, the arithmetic mean, root mean square, and peak-to-valley roughnesses of silicon nitride surfaces varied, while the roughness of the steel surface was unchanged. The correlation between the fatigue life and roughness parameters for silicon nitride was obtained. The peak-to-valley roughness was the roughness parameter that dominantly affected the RCF life of silicon nitride. The micropitting of surfaces leading to fatigue intensified as the roughness was increased. Extensive micropitting was observed on the rolling track beyond the trailing edge of the spall region in the circumferential direction.
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Structural and Mechanical Properties of Amorphous Si3N4 Nanoparticles Reinforced Al Matrix Composites Prepared by Microwave Sintering
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Ceramics 2019, 2(1), 126-134; https://doi.org/10.3390/ceramics2010012 - 14 February 2019
Abstract
The present study focuses on the synthesis and characterization of amorphous silicon nitride (Si3N4) reinforced aluminum matrix nanocomposites through the microwave sintering process. The effect of Si3N4 (0, 1, 2 and 3 wt.%) nanoparticles addition to
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The present study focuses on the synthesis and characterization of amorphous silicon nitride (Si3N4) reinforced aluminum matrix nanocomposites through the microwave sintering process. The effect of Si3N4 (0, 1, 2 and 3 wt.%) nanoparticles addition to the microstructure and mechanical properties of the Al-Si3N4 nanocomposites were investigated. The density of Al-Si3N4 nanocomposites increased with increased Si3N4 content, while porosity decreased. X-ray diffraction (XRD) analysis reveals the presence of Si3N4 nanoparticles in Al matrix. Microstructural investigation of the nanocomposites shows the uniform distribution of Si3N4 nanoparticles in the aluminum matrix. Mechanical properties of the composites were found to increase with an increasing volume fraction of amorphous Si3N4 reinforcement particles. Al-Si3N4 nanocomposites exhibits higher hardness, yield strength and enhanced compressive performance than the pure Al matrix. A maximum increase of approximately 72% and 37% in ultimate compressive strength and 0.2% yield strength are achieved. Among the synthesized nanocomposites, Al-3wt.% Si3N4 nanocomposites displayed the maximum hardness (77 ± 2 Hv) and compressive strength (364 ± 2 MPa) with minimum porosity level of 1.1%.
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Near-Zero Thermal Expansion in Freeze-Cast Composite Materials
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Ceramics 2019, 2(1), 112-125; https://doi.org/10.3390/ceramics2010011 - 13 February 2019
Abstract
Most materials expand when heated, which can lead to thermal stress and even failure. Whereas thermomiotic materials exhibit negative thermal expansion, the creation of materials with near-zero thermal expansion presents an ongoing challenge due to the need to optimize thermal and mechanical properties
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Most materials expand when heated, which can lead to thermal stress and even failure. Whereas thermomiotic materials exhibit negative thermal expansion, the creation of materials with near-zero thermal expansion presents an ongoing challenge due to the need to optimize thermal and mechanical properties simultaneously. The present work describes the preparation and properties of polymer–ceramic composites with low thermal expansion. Ceramic scaffolds, prepared by freeze-casting of low-thermal-expansion Al2W3O12, were impregnated with poly(methylmethacrylate) (PMMA). The resulting composites can have a coefficient of thermal expansion as low as 2 × 10−6 K−1, and hardness values of 4.0 ± 0.3 HV/5 (39 ± 3 MPa) and 16 ± 3 HV/5 (160 ± 30 MPa) parallel and perpendicular to the ice growth, respectively. The higher hardness perpendicular to the ice growth direction indicates that the PMMA is acting to improve the mechanical properties of the composite.
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Exchange-Coupling Behavior in SrFe12O19/La0.7Sr0.3MnO3 Nanocomposites
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Ceramics 2019, 2(1), 100-111; https://doi.org/10.3390/ceramics2010010 - 8 February 2019
Abstract
Magnetically hard-soft (100-x) SrFe12O19-x wt % La0.7Sr0.3MnO3 nanocomposites were synthesized via a one-pot auto-combustion technique using nitrate salts followed by heat treatment in air at 950 °C. X-ray diffraction (XRD), transmission
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Magnetically hard-soft (100-x) SrFe12O19-x wt % La0.7Sr0.3MnO3 nanocomposites were synthesized via a one-pot auto-combustion technique using nitrate salts followed by heat treatment in air at 950 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM) were used to characterize the structural and magnetic properties of the samples. XRD spectra revealed the formation of a mixture of ferrite and magnetite phases without any trace of secondary phases in the composite. Microstructural images show the proximity grain growth of both phases. The room temperature hysteresis loops of the samples showed the presence of exchange-coupling between the hard and soft phases of the composite. Although saturation magnetization reduced by 41%, the squareness ratio and coercivity of the nanocomposite improved significantly up to 6.6% and 81.7%, respectively, at x = 40 wt % soft phase content in the nanocomposite. The enhancement in squareness ratio and coercivity could be attributed to the effective exchange-coupling interaction, while the reduction in saturation magnetization could be explained on the basis of atomic intermixing between phases in the system. Overall, these composite particles exhibited magnetically single-phase behavior. The adopted synthesis method is low cost and rapid and results in pure crystalline nanocomposite powder. This simple method is a promising way to tailor and enhance the magnetic properties of oxide-based hard-soft magnetic nanocomposites.
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Structure and Properties of Piezoelectric Strontium Fresnoite Glass-Ceramics Belonging to the Sr–Ti–Si–Al–K–O System
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Ceramics 2019, 2(1), 86-97; https://doi.org/10.3390/ceramics2010008 - 26 January 2019
Abstract
Crystallization of strontium fresnoite Sr2TiSi2O8 piezoelectric crystals in Sr–Ti–Si–K–Al–O parent glasses is investigated with the aim of showing the influence of composition and crystallization conditions on the microstructure and piezoelectric properties of the resulting glass-ceramic. All the investigated
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Crystallization of strontium fresnoite Sr2TiSi2O8 piezoelectric crystals in Sr–Ti–Si–K–Al–O parent glasses is investigated with the aim of showing the influence of composition and crystallization conditions on the microstructure and piezoelectric properties of the resulting glass-ceramic. All the investigated conditions lead to a surface crystallization mechanism that induces a preferential orientation of crystal growth in the glasses. Near the surface, all the glass-ceramics obtained exhibit (002) planes preferentially oriented parallel to their faces. Deeper in the specimens, this preferential orientation is either kept or tilted to (201) after a depth of about 300 µm. The measurement of the charge coefficient d33 of the glass-ceramic highlights that surface crystallization induces mirror symmetry in the polarization. It reaches 11 to 12 pC/N and is not significantly influenced by the preferential orientation (002) or (201). High temperature XRD shows the stability of the fresnoite phase in the glass-ceramics up to 1000 °C. Mechanical characterization of the glass-ceramics by impulse excitation technique (IET) highlights that the softening of the residual glass leads to a progressive decrease of Young’s modulus in the temperature range 600–800 °C. Damping associated to the viscoplastic transition become severe only over 800 °C.
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Low-Threshold Coherent Emission at 1.5 µm from Fully Er3+ Doped Monolithic 1D Dielectric Microcavity Fabricated Using Radio Frequency Sputtering
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Ceramics 2019, 2(1), 74-85; https://doi.org/10.3390/ceramics2010007 - 21 January 2019
Abstract
Low threshold coherent emission at 1.5 µm is achieved using Er3+-doped dielectric 1D microcavities fabricated with a Radio Frequency-sputtering technique. The microcavities are composed of a half-wavelength Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of
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Low threshold coherent emission at 1.5 µm is achieved using Er3+-doped dielectric 1D microcavities fabricated with a Radio Frequency-sputtering technique. The microcavities are composed of a half-wavelength Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of ten, five, and seven pairs of SiO2/TiO2 layers, also doped with Er3+ ions. The morphology of the structure is inspected using scanning electron microscopy. Transmission measurements show the third and first order cavity resonance at 530 nm and 1.5 µm, respectively. The photoluminescence measurements are obtained using the optical excitation at the third order cavity resonance using a 514.5 nm Ar+ laser or Xe excitation lamp at 514.5 nm, with an excitation angle of 30°. The full width at half maximum of the emission peak at 1535 nm decreased with the pump power until the spectral resolution of the detection system was 2.7 nm. Moreover, the emission intensity presents a non-linear behavior with the pump power and a threshold at about 4 µW.
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Flash Sintering Samaria-Doped Ceria–Carbon Nanotube Composites
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Ceramics 2019, 2(1), 64-73; https://doi.org/10.3390/ceramics2010006 - 18 January 2019
Abstract
Composite ceramic green pellets were prepared by attrition milling a mixture of (CeO2)0.8(Sm2O3)0.2 (samaria-doped ceria, SDC) ceramic powder and carbon nanotubes (CNTs), followed by uniaxial and isostatic pressing. The pellets were sintered inside a
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Composite ceramic green pellets were prepared by attrition milling a mixture of (CeO2)0.8(Sm2O3)0.2 (samaria-doped ceria, SDC) ceramic powder and carbon nanotubes (CNTs), followed by uniaxial and isostatic pressing. The pellets were sintered inside a dilatometer by applying AC electric fields at 850 °C and limiting the electric current to 1 A, achieving 20.2% final shrinkage. The SDC samples reached 13.3% shrinkage under the same conditions. Higher average grain sizes were measured in specimens flash sintered with CNTs. Impedance spectroscopy analyses show that the specimens flash sintered with addition of CNTs have higher electrical conductivity. Higher delivered Joule heating at the interfaces due to the presence of the electronic conductors (CNTs) are proposed as the main reason for that improvement of the electrical behavior.
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