Ceramics

27 pages, 13395 KiB

Open AccessReview

by Pooya Niksiar, Frances Y. Su, Michael B. Frank, Taylor A. Ogden, Steven E. Naleway, Marc A. Meyers, Joanna McKittrick and Michael M. Porter

Ceramics 2019, 2(1), 208-234; https://doi.org/10.3390/ceramics2010018 - 24 Mar 2019

Cited by 36 | Viewed by 7597

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ice-Templated and Freeze-Cast Ceramics)

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18 pages, 18671 KiB

Open AccessArticle

Sintering of Cermets: A Case Study of Sintering Ni–Co Ferrite with Ag-, Cu- and Ni-Dispersed Alloy Particles

by Vera Lúcia Othéro de Brito, Mônica Sumie Hieda, Eduardo de Oliveira Silva , Júnior, Jessica Aparecida Nascimento Ferreira and João Paulo Barros Machado

Ceramics 2019, 2(1), 190-207; https://doi.org/10.3390/ceramics2010017 - 20 Mar 2019

Cited by 2 | Viewed by 3506

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 [...] Read more.

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). Full article

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10 pages, 1545 KiB

Open AccessArticle

Ammonium Hydroxide Mediated Hydrothermal Crystallization of Hydroxyapatite Coatings on Titanium Substrate

by Katarzyna Suchanek, Marcin Perzanowski, Janusz Lekki, Martyna Strąg and Marta Marszałek

Ceramics 2019, 2(1), 180-189; https://doi.org/10.3390/ceramics2010016 - 19 Mar 2019

Cited by 10 | Viewed by 4407

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ceramics for Biomedical Applications)

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19 pages, 4538 KiB

Open AccessArticle

Radial-Concentric Freeze Casting Inspired by Porcupine Fish Spines

by Frances Y. Su, Joyce R. Mok and Joanna McKittrick

Ceramics 2019, 2(1), 161-179; https://doi.org/10.3390/ceramics2010015 - 6 Mar 2019

Cited by 27 | Viewed by 6684

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ice-Templated and Freeze-Cast Ceramics)

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13 pages, 5926 KiB

Open AccessCommunication

Ice-Templated Geopolymer—Fe/Mn Oxide Composites Conceived as Oxygen Carriers

by Elettra Papa, Valentina Medri, Annalisa Natali Murri, Francesco Miccio and Elena Landi

Ceramics 2019, 2(1), 148-160; https://doi.org/10.3390/ceramics2010014 - 1 Mar 2019

Cited by 13 | Viewed by 3154

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ice-Templated and Freeze-Cast Ceramics)

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13 pages, 9356 KiB

Open AccessArticle

Roughness Effect in Micropitting and Rolling Contact Fatigue of Silicon Nitride

by Mohsen Mosleh, Keron K. Bradshaw, Sonya T. Smith, John H. Belk and Khosro A. Shirvani

Ceramics 2019, 2(1), 135-147; https://doi.org/10.3390/ceramics2010013 - 18 Feb 2019

Cited by 3 | Viewed by 3636

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 [...] Read more.

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. Full article

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9 pages, 7455 KiB

Open AccessArticle

Structural and Mechanical Properties of Amorphous Si₃N₄ Nanoparticles Reinforced Al Matrix Composites Prepared by Microwave Sintering

by Manohar Reddy Mattli, Penchal Reddy Matli, Abdul Shakoor and Adel Mohamed Amer Mohamed

Ceramics 2019, 2(1), 126-134; https://doi.org/10.3390/ceramics2010012 - 14 Feb 2019

Cited by 24 | Viewed by 3852

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 [...] Read more.

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%. Full article

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14 pages, 9086 KiB

Open AccessArticle

Near-Zero Thermal Expansion in Freeze-Cast Composite Materials

by Sarah N. Ellis, Carl P. Romao and Mary Anne White

Ceramics 2019, 2(1), 112-125; https://doi.org/10.3390/ceramics2010011 - 13 Feb 2019

Cited by 8 | Viewed by 4961

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ice-Templated and Freeze-Cast Ceramics)

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12 pages, 6625 KiB

Open AccessArticle

Exchange-Coupling Behavior in SrFe₁₂O₁₉/La_0.7Sr_0.3MnO₃ Nanocomposites

by Jiba Nath Dahal, Dipesh Neupane and Sanjay R. Mishra

Ceramics 2019, 2(1), 100-111; https://doi.org/10.3390/ceramics2010010 - 8 Feb 2019

Cited by 29 | Viewed by 3840

Abstract

Magnetically hard-soft (100-x) SrFe₁₂O₁₉-x wt % La_0.7Sr_0.3MnO₃ 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 [...] Read more.

Magnetically hard-soft (100-x) SrFe₁₂O₁₉-x wt % La_0.7Sr_0.3MnO₃ 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. Full article

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2 pages, 177 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Ceramics in 2018

by Ceramics Editorial Office

Ceramics 2019, 2(1), 98-99; https://doi.org/10.3390/ceramics2010009 - 2 Feb 2019

Viewed by 2022

Abstract

Rigorous peer-review is the cornerstone of high-quality academic publishing [...] Full article

12 pages, 8320 KiB

Open AccessArticle

Structure and Properties of Piezoelectric Strontium Fresnoite Glass-Ceramics Belonging to the Sr–Ti–Si–Al–K–O System

by Marie-Sophie Renoirt, Nathalie Maury, Florian Dupla and Maurice Gonon

Ceramics 2019, 2(1), 86-97; https://doi.org/10.3390/ceramics2010008 - 26 Jan 2019

Cited by 14 | Viewed by 3512

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Novel Processing Routes of Ceramics for Functional Applications)

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12 pages, 2557 KiB

Open AccessArticle

Low-Threshold Coherent Emission at 1.5 µm from Fully Er³⁺ Doped Monolithic 1D Dielectric Microcavity Fabricated Using Radio Frequency Sputtering

by Cesare Meroni, Francesco Scotognella, Yann Boucher, Anna Lukowiak, Davor Ristic, Giorgio Speranza, Stefano Varas, Lidia Zur, Mile Ivanda, Stefano Taccheo, Roberta Ramponi, Giancarlo C. Righini, Maurizio Ferrari and Alessandro Chiasera

Ceramics 2019, 2(1), 74-85; https://doi.org/10.3390/ceramics2010007 - 21 Jan 2019

Cited by 4 | Viewed by 3258

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Design, Fabrication and Assessment of Nanostructured Materials and Systems for Advanced Optical Applications)

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10 pages, 2436 KiB

Open AccessArticle

Flash Sintering Samaria-Doped Ceria–Carbon Nanotube Composites

by Reginaldo Muccillo, André S. Ferlauto and Eliana N.S. Muccillo

Ceramics 2019, 2(1), 64-73; https://doi.org/10.3390/ceramics2010006 - 18 Jan 2019

Cited by 20 | Viewed by 4641

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Novel Processing Routes of Ceramics for Functional Applications)

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8 pages, 1926 KiB

Open AccessArticle

Hydrothermal Synthesis of Pseudocubic Rutile-Type Titania Particles

by Makoto Kobayashi, Hideki Kato, Takamichi Miyazaki and Masato Kakihana

Ceramics 2019, 2(1), 56-63; https://doi.org/10.3390/ceramics2010005 - 18 Jan 2019

Cited by 7 | Viewed by 4066

Abstract

The functional properties of materials depend strongly on their morphologies. Here, the hydrothermal synthesis of rutile-type titania crystals with pseudocubic shapes using a water-soluble titanium complex is reported. This approach does not require extra additives or doping. Transmission electron microscopy and selected-area electron [...] Read more.

The functional properties of materials depend strongly on their morphologies. Here, the hydrothermal synthesis of rutile-type titania crystals with pseudocubic shapes using a water-soluble titanium complex is reported. This approach does not require extra additives or doping. Transmission electron microscopy and selected-area electron diffraction analysis revealed that they exposed high-index facets, such as {121}, and high-energy facets, such as {001}, which do not usually appear in rutile crystal. In terms of the formation of steps and kinks on pseudocubic rutile and coexisting anatase and brookite nanoparticles, the adsorption of nanoparticles might inhibit crystal growth, resulting in the formation of crystals with uncommon shapes exposing high-index and high-energy facets. Full article

(This article belongs to the Special Issue Novel Processing Routes of Ceramics for Functional Applications)

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22 pages, 5224 KiB

Open AccessArticle

Coupled Photonic Crystal Nanocavities as a Tool to Tailor and Control Photon Emission

by Annamaria Gerardino, Giorgio Pettinari, Niccolò Caselli, Silvia Vignolini, Francesco Riboli, Francesco Biccari, Marco Felici, Antonio Polimeni, Andrea Fiore, Massimo Gurioli and Francesca Intonti

Ceramics 2019, 2(1), 34-55; https://doi.org/10.3390/ceramics2010004 - 14 Jan 2019

Cited by 2 | Viewed by 3735

Abstract

In this review, we report on the design, fabrication, and characterization of photonic crystal arrays, made of two and three coupled nanocavities. The properties of the cavity modes depend directly on the shape of the nanocavities and on their geometrical arrangement. A non-negligible [...] Read more.

In this review, we report on the design, fabrication, and characterization of photonic crystal arrays, made of two and three coupled nanocavities. The properties of the cavity modes depend directly on the shape of the nanocavities and on their geometrical arrangement. A non-negligible role is also played by the possible disorder because of the fabrication processes. The experimental results on the spatial distribution of the cavity modes and their physical characteristics, like polarization and parity, are described and compared with the numerical simulations. Moreover, an innovative approach to deterministically couple the single emitters to the cavity modes is described. The possibility to image the mode spatial distribution, in single and coupled nanocavities, combined with the control of the emitter spatial position allows for a deterministic approach for the study of cavity quantum electrodynamics phenomena and for the development of new photonic-based applications. Full article

(This article belongs to the Special Issue Design, Fabrication and Assessment of Nanostructured Materials and Systems for Advanced Optical Applications)

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9 pages, 2320 KiB

Open AccessArticle

Hybrid Carbon Nano-Fibers with Improved Oxidation Resistance

by Saja M. Nabat Al-Ajrash and Khalid Lafdi

Ceramics 2019, 2(1), 25-33; https://doi.org/10.3390/ceramics2010003 - 10 Jan 2019

Cited by 1 | Viewed by 2950

Abstract

Hybrid Carbon-Silicon Carbide (C-SiC) nano-fibers were fabricated while using a mixture of polyacrylonitrile (PAN) and silicon (Si) nanoparticles as precursors. The microstructure of the material was examined using X-ray diffraction and Raman spectroscopy as a function of processing temperature and holding time. A [...] Read more.

Hybrid Carbon-Silicon Carbide (C-SiC) nano-fibers were fabricated while using a mixture of polyacrylonitrile (PAN) and silicon (Si) nanoparticles as precursors. The microstructure of the material was examined using X-ray diffraction and Raman spectroscopy as a function of processing temperature and holding time. A complete transformation of Si to SiC occurred at 1250 °C. However, for heat treatments below 1000 °C, three distinct phases, including Si, C, and SiC were present. The effect of microstructural changes, due to the heat treatment, on oxidation resistance was determined using thermogravimetric analysis (TGA). Furthermore, the char yield showed exponential growth with increasing the carbonization temperature from 850 °C to 1250 °C. The holding times at higher temperatures showed a significant increase in thermal properties because of SiC grain growth. At longer holding times, the SiC phase has the function of bothcoating and reinforcing phase. Such structural changes were related to fibers mechanical properties. The tensile strength was the highest for fiber carbonized fibers at 850 °C, while the modulus increased monotonically with increasing carbonization temperature. Full article

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12 pages, 2261 KiB

Open AccessArticle

Dielectric and Ferroelectric Studies on High Dense Pb(Zr_0.52Ti_0.48)O₃ Nanocrystalline Ceramics by High Energy Ball Milling and Spark Plasma Sintering

by Venkata Ramana Mudinepalli and Feng Leng

Ceramics 2019, 2(1), 13-24; https://doi.org/10.3390/ceramics2010002 - 7 Jan 2019

Cited by 16 | Viewed by 4174

Abstract

In our previous work, we synthesized Pb(Zr_0.52Ti_0.48)O₃ (PZT) ceramics by conventional and microwave sintering methods and studied their structural and electrical properties. We observed that the microwave sintered PZT ceramics show higher densification, fine and uniform grain size, [...] Read more.

In our previous work, we synthesized Pb(Zr_0.52Ti_0.48)O₃ (PZT) ceramics by conventional and microwave sintering methods and studied their structural and electrical properties. We observed that the microwave sintered PZT ceramics show higher densification, fine and uniform grain size, higher dielectric constant, remnant polarization (P_r), and spontaneous polarization (P_s) in comparison to conventional sintered ones. In the present work, we studied the microstructure, phase formation, dielectric, ferroelectric and piezoelectric properties of the PZT ceramics synthesized by using Spark plasma Sintering (SPS) method. The SPS sintering temperature is lower (300 to 400 °C) than both conventional and microwave sintering methods. The dielectric constant at room temperature and at transition temperature shows higher values compared to the microwave and conventional sintering methods. This SPS sintering technique is currently attracting growing attention among productions engineers and materials researchers. Full article

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12 pages, 6828 KiB

Open AccessArticle

Optical, Dielectric and Magnetic Properties of La_1−xNd_xFeO₃ Powders and Ceramics

by Paweł Głuchowski, Karen Oganisian, Robert Tomala, Anna Łukowiak, Dmitry Karpinsky, Denis Alikin, Andrei Kholkin and Wiesław Stręk

Ceramics 2019, 2(1), 1-12; https://doi.org/10.3390/ceramics2010001 - 21 Dec 2018

Cited by 5 | Viewed by 3658

Abstract

Nanocrystalline La_1−xNd_xFeO₃ powders with different concentrations of Nd³⁺ have been synthesized using a modified Pechini method. Their structures were studied by X-ray powder diffraction (XRD). Furthermore, La_1−xNd_xFeO₃ nanoceramics were prepared using a [...] Read more.

Nanocrystalline La_1−xNd_xFeO₃ powders with different concentrations of Nd³⁺ have been synthesized using a modified Pechini method. Their structures were studied by X-ray powder diffraction (XRD). Furthermore, La_1−xNd_xFeO₃ nanoceramics were prepared using a high pressure sintering technique. The luminescence spectra of the powders were investigated as a function of concentration of active dopant to check the possible energy transfers observed due to Nd³⁺ concentration changes. The electrical and magnetic properties of the powders and ceramics were investigated to determine the effect of Nd³⁺ doping on the dielectric permittivity and magnetization in the wide frequency range. Full article

(This article belongs to the Special Issue Design, Fabrication and Assessment of Nanostructured Materials and Systems for Advanced Optical Applications)

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