Applied Sciences

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17 pages, 5756 KiB

Open AccessArticle

The Effect of Noble Metals on Co Gas Sensing Properties of In₂O₃ Nanoparticles

by JinAh Hwang, Hyunsung Jung, Hyo-Soon Shin, Dae-Sung Kim, Dong Soo Kim, Byeong-Kwon Ju and MyoungPyo Chun

Appl. Sci. 2021, 11(11), 4903; https://doi.org/10.3390/app11114903 - 26 May 2021

Cited by 15 | Viewed by 2873

Abstract

Three types of In₂O₃ nanoparticles decorated with Au, Pd and Pt nanoparticles, respectively, were synthesized by thermal decomposition method, and the effects of metal nanoparticles on their phase, microstructure, chemical state, carrier types were investigated with XRD, SEM/TEM, and XPS. [...] Read more.

Three types of In₂O₃ nanoparticles decorated with Au, Pd and Pt nanoparticles, respectively, were synthesized by thermal decomposition method, and the effects of metal nanoparticles on their phase, microstructure, chemical state, carrier types were investigated with XRD, SEM/TEM, and XPS. Additionally, sensing properties to CO gas, such as sensitivity, etc., were examined with sensing apparatus. Au-decorated In₂O₃ nanoparticles exhibited the highest sensitivity to CO gas, with S = 5.59 at a 10 ppm CO gas concentration at 50 °C compared to Pd or Pt-decorated In₂O₃ nanoparticles. This can be interpreted as a much higher adsorption of oxygen molecules on the In₂O₃ surface due to the high oxygen vacancies in the In₂O₃ lattice, which generates an electron depletion region in the outer layer of In₂O₃ to sharply increase the resistance or the spill-over effect due to Au nanoparticles on In₂O₃. Au nanoparticles were observed in the TEM images and confirmed by XPS analysis. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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8 pages, 3170 KiB

Open AccessArticle

Segregation of NiTe₂ and NbTe₂ in p-Type Thermoelectric Bi_0.5Sb_1.5Te₃ Alloys for Carrier Energy Filtering Effect by Melt Spinning

by Hyun-Sik Kim, TaeWan Kim, Jiwoo An, Dongho Kim, Ji Hoon Jeon and Sang-il Kim

Appl. Sci. 2021, 11(3), 910; https://doi.org/10.3390/app11030910 - 20 Jan 2021

Cited by 9 | Viewed by 2982

Abstract

The formation of secondary phases of NiTe₂ and NbTe₂ in p-type Bi_0.5Sb_1.5Te₃ thermoelectric alloys was investigated through in situ phase separation by using the melt spinning process. Adding stoichiometric Ni, Nb, and Te in a [...] Read more.

The formation of secondary phases of NiTe₂ and NbTe₂ in p-type Bi_0.5Sb_1.5Te₃ thermoelectric alloys was investigated through in situ phase separation by using the melt spinning process. Adding stoichiometric Ni, Nb, and Te in a solid-state synthesis process of Bi_0.5Sb_1.5Te₃, followed by rapid solidification by melt spinning, successfully segregated NiTe₂ and NbTe₂ in the Bi_0.5Sb_1.5Te₃ matrix. Since heterointerfaces of Bi_0.5Sb_1.5Te₃ with NiTe₂ and NbTe₂ form potential barriers of 0.26 and 0.08 eV, respectively, a low energy carrier filtering effect can be expected; higher Seebeck coefficients and power factors were achieved for Bi_0.5Sb_1.5Te₃(NiTe₂)_0.01 (250 μV/K and 3.15 mW/mK²), compared to those of Bi_0.5Sb_1.5Te₃ (240 μV/K and 2.69 mW/mK²). However, there was no power factor increase for NbTe₂ segregated samples. The decrease in thermal conductivity was seen due to the possible additional phonon scattering by the phase segregations. Consequently, zT at room temperature was enhanced to 0.98 and 0.94 for Bi_0.5Sb_1.5Te₃(NiTe₂)_0.01 and Bi_0.5Sb_1.5Te₃(NbTe₂)_0.01, respectively, compared to 0.79 for Bi_0.5Sb_1.5Te₃. The carrier filtering effect induced by NiTe₂ segregations with an interface potential barrier of 0.26 eV effectively increased the Seebeck coefficient and power factor, thus improving the zT of p-type Bi_0.5Sb_1.5Te₃, while the interface potential barrier of 0.08 eV of NbTe₂ segregation appeared to be too small to induce an effective carrier filtering effect. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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9 pages, 1002 KiB

Open AccessArticle

CNT-Coated Quartz Woven Fabric Electrodes for Robust Lithium-ion Structural Batteries

by Mi-Young Park, Chun-Gon Kim and Joo-Hyung Kim

Appl. Sci. 2020, 10(23), 8622; https://doi.org/10.3390/app10238622 - 2 Dec 2020

Cited by 2 | Viewed by 1987

Abstract

Reliability in various conditions for Li-ion batteries has been considered one of the most important factors when determining usability. Silica-based fabric has great potential to be an alternative material for electrode support, providing mechanical and physical stability in lithium-ion batteries. In this study, [...] Read more.

Reliability in various conditions for Li-ion batteries has been considered one of the most important factors when determining usability. Silica-based fabric has great potential to be an alternative material for electrode support, providing mechanical and physical stability in lithium-ion batteries. In this study, a carbon nanotube (CNT)-coated quartz woven fabric electrode (C-QWF) with impressive electrochemical characteristics was synthesized via a sequential two-step deposition process using Al and Fe as metal catalyst and CH₄ as a carbon source. The C-QWF electrode exhibited a considerable specific discharge capacity of 369 mAh g⁻¹ at a rate of 0.1 C-rate after cycling. The battery cell showed self-recovering ability during the cycling test at 1 C-rate, although the silica fabric has sluggish electrical conductivity. The C-QWF electrode has a superior electrochemical performance, providing new perspectives on textile fabric electrodes for robust Li-ion batteries, especially load-bearing structural batteries. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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8 pages, 2993 KiB

Open AccessArticle

Charge Transport Behavior of Al-Doped ZnO Incorporated with Reduced Graphene Oxide Nanocomposite Thin Film

by Woo Hyun Nam, Hyung Mo Jeong, Jong-Hyeong Lim, Jong-Min Oh, Hiesang Sohn, Won-Seon Seo, Jung Young Cho and Weon Ho Shin

Appl. Sci. 2020, 10(21), 7703; https://doi.org/10.3390/app10217703 - 30 Oct 2020

Cited by 1 | Viewed by 1874

Abstract

ZnO is utilized as a promising material for various electronic and energy areas due to its outstanding chemical stability, abundance, non-toxicity, and low cost. However, controlling electronic transport properties of ZnO by facile strategy is still necessary for wider applications. Here, we synthesized [...] Read more.

ZnO is utilized as a promising material for various electronic and energy areas due to its outstanding chemical stability, abundance, non-toxicity, and low cost. However, controlling electronic transport properties of ZnO by facile strategy is still necessary for wider applications. Here, we synthesized reduced graphene oxide incorporated Al-doped ZnO nanocomposite thin film prepared by the electrospray deposition method and investigated the electronic transport behavior. The electron transport in pristine Al-doped ZnO thin film is strongly affected by grain boundary scattering, but significant enhancement of carrier mobility is observed in reduced graphene oxide-incorporated Al-doped ZnO nanocomposite thin film. The results demonstrate that this hybrid strategy with graphene has an important effect on the charge transport behavior in ZnO polycrystalline materials. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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11 pages, 28078 KiB

Open AccessArticle

Microstructure and Magnetic Properties of La-Ca-Co Substituted M-Type Sr-Hexaferrites with Controlled Si Diffusion

by Kyoung-Seok Moon, Pyeong-yeol Yu and Young-Min Kang

Appl. Sci. 2020, 10(21), 7570; https://doi.org/10.3390/app10217570 - 27 Oct 2020

Cited by 10 | Viewed by 1941

Abstract

La-Ca-Co substituted M-type Sr-hexaferrites (Sr_0.3Ca_0.4La_0.3Fe_9.8Co_0.2O_19-δ) were prepared by a solid-state reaction using two different procedures, where the SiO₂ additive was mixed either before calcination (pre-Si) or after calcination (post-Si). At [...] Read more.

La-Ca-Co substituted M-type Sr-hexaferrites (Sr_0.3Ca_0.4La_0.3Fe_9.8Co_0.2O_19-δ) were prepared by a solid-state reaction using two different procedures, where the SiO₂ additive was mixed either before calcination (pre-Si) or after calcination (post-Si). At the same sintering temperature, smaller cell volumes and reduced saturation magnetization (M_s) values were obtained for samples processed with the pre-Si method than those with the post-Si method. This implied that the pre-Si method resulted in a greater degree of Si substitution into the M-type lattice and increased Fe extrusion out of the lattice. The grain growth behavior was controlled by the SiO₂ amount and sintering temperature. It was found that abnormal grains occur with a bimodal distribution in the 0.5 wt% SiO₂ samples sintered at 1240 °C, due to the increased critical driving force for growth caused by an increased amount of SiO₂ addition. The M_s and coercivity values were altered with the control of Si diffusion and abnormal grain growth. The control of the additive diffusion behavior is one of the important keys in the material design under same materials compositions. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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11 pages, 3701 KiB

Open AccessArticle

Structural and Magnetic Properties of NiZn Ferrite Nanoparticles Synthesized by a Thermal Decomposition Method

by JinAh Hwang, Moonhee Choi, Hyo-Soon Shin, Byeong-Kwon Ju and MyoungPyo Chun

Appl. Sci. 2020, 10(18), 6279; https://doi.org/10.3390/app10186279 - 9 Sep 2020

Cited by 36 | Viewed by 9424

Abstract

Ni_1−xZn_xFe₂O₄ (x = 0.5, 0.6, 0.7) nanoparticles were synthesized by a thermal decomposition method. The synthesized particles were identified as pure spinel ferrite structures by X-ray diffraction analysis, and they were calculated to be 46–51 nm [...] Read more.

Ni_1−xZn_xFe₂O₄ (x = 0.5, 0.6, 0.7) nanoparticles were synthesized by a thermal decomposition method. The synthesized particles were identified as pure spinel ferrite structures by X-ray diffraction analysis, and they were calculated to be 46–51 nm in diameter by the Scherrer equation, depending on the composition. In the FE-SEM image, the ferrite nanoparticles have spherical shapes with slight agglomeration, and the particle size is about 50 nm, which was consistent with the value obtained by the Scherrer equation. The lattice parameter of the ferrite nanoparticles monotonically increased from 8.34 to 8.358 Å as the Zn concentration increased from 0.5 to 0.7. Initially, the saturation magnetization value slowly decreases from 81.44 to 83.97 emu/g, then quickly decreases to 71.84 emu/g as the zinc content increases from x = 0.5, through 0.6, to 0.7. Ni_1−xZn_xFe₂O₄ toroidal samples were prepared by sintering ferrite nanoparticles at 1250 °C and exhibited faceted grain morphologies in the FE-SEM images with their grain sizes being around 5 µm regardless of the Zinc content. The real magnetic permeability (μ′) of the toroidal samples measured at 5 MHz was monotonically increased from 106, through 150, to 217 with increasing the Zinc content from x = 0.5, through 0.6, to 0.7. The cutoff frequency of the ferrite toroidal samples was estimated to be about 20 MHz from the broad maximum point in the plot of imaginary magnetic permeability (μ″) vs. frequencies, which seemed to be associated with domain wall resonance. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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10 pages, 4741 KiB

Open AccessArticle

Development of a Highly Densified Magnetic Sheet for Inductors and Advanced Processes through Silane Surface Treatment of Fe Nanopowder

by Taegyu Lee, Hyeonjin Jung, Yeonghwan Song, Seungchan Cho, Dong-Hyun Kim, Yangdo Kim, Yoon-Seok Lee, Yongho Park and Moonhee Choi

Appl. Sci. 2020, 10(14), 4770; https://doi.org/10.3390/app10144770 - 10 Jul 2020

Cited by 1 | Viewed by 2605

Abstract

For developing subminiature and highly integrated multilayer inductors, soft magnetic powder was used; however, its ferrite magnetic component is characterized by high resistivity and reduced direct current saturation, leading to the deterioration of the inductor under high currents. Therefore, herein, to improve the [...] Read more.

For developing subminiature and highly integrated multilayer inductors, soft magnetic powder was used; however, its ferrite magnetic component is characterized by high resistivity and reduced direct current saturation, leading to the deterioration of the inductor under high currents. Therefore, herein, to improve the electromagnetic properties of thin-film inductors, Fe nanopowder was used to increase the volume fraction of magnetic sheets. Surface treatment was performed by using silane coupling agents, which improved the bonding strength and dispersibility of the Fe nanopowder with a heterogeneous epoxy binder. For uniform surface treatment on the nanopowder, the silane-treated powder was aged for 24 h, at a temperature of 3 °C. The surface-treated Fe nanopowder was used with a mixing ratio of the soft magnetic powder (coarse:fine:nano) of 7:2.5:0.5 wt.%; this was successful in producing a flexible and highly densified magnetic sheet. As a result, the volume fraction of the magnetic sheet for thin-film inductors to which a low-temperature aging-treated nanopowder was applied was significantly improved. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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9 pages, 2512 KiB

Open AccessArticle

Composition-Dependent Structural Integrity of Hf₆Ta₂O₁₇ Superstructure during Sintering in a Reducing Atmosphere

by Sang-chae Jeon

Appl. Sci. 2020, 10(11), 3871; https://doi.org/10.3390/app10113871 - 2 Jun 2020

Cited by 7 | Viewed by 2043

Abstract

The applicability of a Hf₆Ta₂O₁₇ superstructure to a sintering crucible in pyroprocessing was evaluated herein. Samples were prepared by simple oxidation of casted Hf-Ta alloys containing different Ta contents (20.2, 27.2, and 35.2 in at. %). The physical [...] Read more.

The applicability of a Hf₆Ta₂O₁₇ superstructure to a sintering crucible in pyroprocessing was evaluated herein. Samples were prepared by simple oxidation of casted Hf-Ta alloys containing different Ta contents (20.2, 27.2, and 35.2 in at. %). The physical integrity of the oxidized samples was tested after passivation, which resulted in the formation of a Hf₆Ta₂O₁₇ superstructure. As a result, only the sample with the lowest Ta content (20.2 at. %) was intact while others were destroyed by peeling off. Based on the XRD analysis, this originates from reduction of the Ta oxide phase from Ta₂O₅ to Ta2O_2.2, which may lead to severe stresses due to changes in the crystal structure and lattice constant. It is therefore concluded that the Ta content should be lowered within a range permitting the formation of Hf₆Ta₂O₁₇. This provides practical data for a beneficial composition design that can be extended to other applications prepared under reducing atmospheres. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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16 pages, 19098 KiB

Open AccessFeature PaperArticle

Controlled-Atmosphere Sintering of KNbO₃

by Doan Thanh Trung and John G. Fisher

Appl. Sci. 2020, 10(6), 2131; https://doi.org/10.3390/app10062131 - 20 Mar 2020

Cited by 5 | Viewed by 2633

Abstract

The effect of sintering atmosphere (O₂, air, N₂, N₂-5% H₂, and H₂) on the densification, grain growth, and structure of KNbO₃ was studied. KNbO₃ powder was prepared by solid state reaction, [...] Read more.

The effect of sintering atmosphere (O₂, air, N₂, N₂-5% H₂, and H₂) on the densification, grain growth, and structure of KNbO₃ was studied. KNbO₃ powder was prepared by solid state reaction, and samples were sintered at 1040 °C for 1–10 h. The sample microstructure was studied using Scanning Electron Microscopy (SEM). The sample structure was studied using X-Ray Diffraction (XRD). H₂-sintered samples showed reduced density, whereas other sintering atmospheres did not affect density much. Samples sintered in N₂-5% H₂ showed abnormal grain growth, whereas sintering in other atmospheres caused stagnant (O₂, air, N₂) or pseudo-normal (H₂) grain growth behavior. Samples sintered in reducing atmospheres showed decreased orthorhombic unit cell distortion. The grain growth behavior was explained by the mixed control theory. An increase in vacancy concentration caused by sintering in reducing atmospheres led to a decrease in the step free energy and the critical driving force for appreciable grain growth. This caused grain growth behavior to change from stagnant to abnormal and eventually pseudo-normal. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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15 pages, 4875 KiB

Open AccessArticle

Preparation and Characterization of a Low-Cost and Natural Material-Based Reticulated Porous Diatomite-Kaolin Composite

by Sujin Lee, Jang-Hoon Ha, Jongman Lee, In-Hyuck Song and Se-Hun Kwon

Appl. Sci. 2020, 10(6), 2125; https://doi.org/10.3390/app10062125 - 20 Mar 2020

Cited by 7 | Viewed by 2672

Abstract

In recent years, porous ceramics have been increasingly developed owing to their high levels of high-temperature stability and chemical stability. These properties are far superior to porous polymers and porous metals. As a representative porous ceramic, reticulated porous ceramics have been fabricated for [...] Read more.

In recent years, porous ceramics have been increasingly developed owing to their high levels of high-temperature stability and chemical stability. These properties are far superior to porous polymers and porous metals. As a representative porous ceramic, reticulated porous ceramics have been fabricated for several decades owing to their overwhelmingly high porosity, which is usually above 90%. There are growing concerns about the environmental problems. However, the data on the preparation of low-cost and natural material-based reticulated porous ceramics are not enough. Therefore, the authors studied the preparations and characterizations of reticulated porous ceramics prepared using diatomite and kaolin, and compared them to typical reticulated porous alumina. The obtained data were used to determine whether the reticulated porous diatomite-kaolin composite can be practically used in non-hard loading conditions. The structural properties and dielectric breakdown strength of the reticulated porous ceramics were examined using scanning electron microscopy, mercury porosimetry, μ-computed tomography (CT), and standard test apparatus of dielectric breakdown voltage. Full article

(This article belongs to the Special Issue Sintering Phenomena and Microstructural Control)

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