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Number of results: 5
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Abstract

The present study, aims to investigate the effect of minor Zr and Nb alloying on soft magnetic and electrical properties of Fe86(ZrxNb1-x)7B6Cu1 (x = 1, 0.75, 0.5, 0.25) alloys. The investigated alloys were prepared through the melt spinning process. Within the examined compositional range (Nb up to 5.25at%, respectively), the soft magnetic properties and electrical resistivity of the alloys continuously increase with increasing Nb content. However increasing the Nb content further decreases such properties. We could confirm the influence of ratio of Zr and Nb on grain growth and crystallization fraction during crystallization by using the soft magnetic properties and electrical properties.

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Authors and Affiliations

Junghyun Noh
Seungyeon Park
Haejin Hwang
Kyoungmook Lim
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Abstract

In this study, Ag-impregnated silica aerogel composites were fabricated via wet impregnation. In this approach, silver salt was reduced with ethylene glycol in the presence of polyvinylpyrrolidone (PVP) at reaction temperature 80°C. PVP was used as a capping agent to protect the Ag nanoparticles (NPs) from agglomeration. Wet impregnation was used to synthesize the Ag/SiO2 composite by combining the reduction of AgNO3 with a silica aerogel slurry. Experimental results showed that the AgNO3 concentration and PVP: AgNO3 ratio had an active influence on the growth of Ag NPs on silica surfaces. The X-ray diffraction (XRD) patterns of the composite material showed no imprints of impurities or parasitic materials except for Ag and SiO2. Scanning electron microscopy (SEM) images revealed that the Ag NPs were well impregnated into the porous silica aerogel structure. It was found that SiO2 aerogel surfaces were homogeneously surrounded by the Ag NPs.
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Authors and Affiliations

Pratik S. Kapadnis
1
Kyungsun Kim
1
Hyung-Ho Park
2
Haejin Hwang
1
ORCID: ORCID

  1. Inha university, Department of Materials Science and Engineering, Incheon 22212, Republic of Korea
  2. Yonsei University, Department of Materials Science and Engineering, Seoul 03722, Republic of Korea
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Abstract

Al and Nb-doped Li7La3Zr2O12 (LLZO) and W-doped LLZO lithium ion conducting electrolyte samples were prepared and their H2O stability was investigated. The LLZO samples were exposed to 50% humidified air for 48 h. After H2O exposure, a cubic to tetragonal transformation occurred and acquired SEM images exhibited the presence of reaction phases at the grain boundaries of Al and Nb-LLZO. As a result, the lithium ion conductivity significantly decreased after H2O exposure. On the contrary, W-LLZO showed good stability against H2O. Although the cubic to tetragonal transformation was also observed in H2O-exposed W-LLZO, the decrease in lithium ion conductivity was found to be modest. No morphological changes of the W-LLZO samples were confirmed in the H2O-exposed W-LLZO samples.

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Authors and Affiliations

Eun-Jeong Yi
Keun-Young Yoon
Hyun-Ah Jung
Haejin Hwang
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Abstract

In this study, agar-based nanocomposite films containing ultra-porous silica aerogel particles were fabricated by gel casting using an aqueous agar/silica aerogel slurry. The silica aerogel particles did not show significant agglomeration and were homogeneously distributed in the agar matrix. Transmission electron microscopy observations demonstrated that the silica aerogel particles had a mesoporous microstructure and their pores were not incorporated into the agar polymer molecules. The thermal conductivities of the agar and agar/5 wt.% silica aerogel nanocomposite films were 0.36 and 0.20 W·m–1·K–1, respectively. The transmittance of the agar films did not decrease upon the addition of silica aerogel particles into them. This can be attributed to the anti-reflection effect of silica aerogel particles.

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Authors and Affiliations

Min-Jin Lee
Hyun-Ah Jung
Kyong-Jin Lee
Haejin Hwang
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Abstract

In this study, lead-free bismuth sodium titanate (BNT; Bi0.5Na0.5TiO3) powder was synthesized using wet precipitation. The sintering behavior and dielectric properties of the BNT ceramics were investigated in terms of the sintering temperature. Titanium isopropoxide, sodium nitrate, and bismuth nitrate were used as starting materials. A titanium peroxo complex (TPC) solution was synthesized using titanium hydroxide, nitric acid, and hydrogen peroxide. A clear Bi-Na-Ti precursor solution was obtained by mixing the TPC, sodium, and bismuth nitrate solutions. The pH of the precursor solution was increased to 9 using NaOH and a white powder was precipitated. A spherical and pyrochlore phase-free BNT powders were obtained by calcining the white precipitate above 600°C for 3 h. Particle size analysis and SEM observations revealed that the BNT powder calcined at 700°C exhibited homogeneous distribution with particle size less than 300 nm. The sinterability of the BNT ceramic prepared through wet precipitation was significantly enhanced compared to that of the BNT powder prepared via the solid-state reaction of sodium carbonate, bismuth oxide, and titanium oxide powders.
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Authors and Affiliations

Islam Takiul
1
ORCID: ORCID
Sanghaw Lee
1
ORCID: ORCID
Haejin Hwang
1
ORCID: ORCID

  1. Inha University, Department of Materials Science and Engineering, 100 Inha-ro, Michuhol-gu, Incheon 22212, Korea

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