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Raju, Kati,Kim, Seyoung,Seong, Young-Hoon,Yoon, Dang-Hyok The Korean Ceramic Society 2019 한국세라믹학회지 Vol.56 No.4
In this paper, the joining characteristics of GDC-LSM ceramics with Crofer 22 APU metal alloys was investigated at different brazing temperatures and holding times by reactive air brazing. Brazing was performed using Ag-10 wt% CuO filler, at three different temperatures (1000, 1050, and 1100℃ for 30 minutes) as well as for three different holding times (10, 30, and 60 minutes at 1050℃). The interfacial microstructures were examined by scanning electron microscopy and the joining strengths were assessed by measuring shear strengths at room temperature. The results show that with increasing brazing temperature and holding time, joint microstructure changed obviously and shear strength was decreased. Shear strength varied from a maximum of 100±6 MPa to a minimum of 18±5 MPa, depending on the brazing conditions. These changes were attributed to an increase in the thickness of the oxide layer at the filler/metal alloy interface.
Raju, K.,Muksin,Yoon, D.H. Ceramurgica ; Elsevier Science Ltd 2016 CERAMICS INTERNATIONAL Vol.42 No.14
This paper reports the effectiveness of a Ag-10wt% CuO braze filler for the joining of dense Ce<SUB>0.9</SUB>Gd<SUB>0.1</SUB>O<SUB>2-δ</SUB>-La<SUB>0.6</SUB>Sr<SUB>0.4</SUB>Co<SUB>0.2</SUB>Fe<SUB>0.8</SUB>O<SUB>3-δ</SUB> (GDC-LSCF) dual-phase ceramics for the oxygen transport membrane applications. Brazing was performed at 1050<SUP>o</SUP>C for 30min in air. The microstructure of the ceramic-filler-ceramic interfaces of the polished cross-sectional areas and the elemental distribution were examined. The results indicated that the Ag-10wt% CuO braze filler ensured reliable and compact joining without the formation of cracks and voids at the joining interface. The room temperature mechanical shear strengths were 59.3 and 40.2MPa for the as-brazed and isothermally aged joints at 800<SUP>o</SUP>C for 24h in air, respectively.
Joining of metal-ceramic using reactive air brazing for oxygen transport membrane applications
Raju, K.,Muksin,Kim, S.,Song, K.s.,Yu, J.H.,Yoon, D.H. Elsevier Ltd 2016 Materials & Design Vol.109 No.-
<P>This study examined the joining of dense Ce0.9Gd0.1O2 (-) (delta)-La0.6Sr0.4Co0.2Fe0.8O3 (-) (delta) (GDC-LSCF) ceramics to high temperature metal alloys for the fabrication of multilayered oxygen transport membrane (OTM) stacks. Reactive air brazing using a silver-based paste was performed at 1050 degrees C for 30 min in air to join GDC-LSCF/high temperature alloys, such as AISI 310S, Inconel 600 and Crofer 22 APU. The effects of the various filler materials, including CuO, GDC, LSCF, and GDC-LSCF mixture, in the Ag paste were also examined. The Ag-10 wt% CuO braze filler ensured in a reliable and compact joining without the formation of cracks and voids at the joining interface, while the addition of other ceramic fillers resulted in incomplete joining. Although none of the GDC-LSCF/metal alloy joints showed gas leakage at room temperature, the GDC-LSCF/Crofer joint only maintained the gas-tightness up to 800 degrees C under pressurized air up to 7 bars, which was explained by the microstructural rigidness of the oxide layer formed on the filler/alloy interface at high temperatures. This was supported by the minimal decrease in shear strength of the GDC-LSCF/Crofer joint, which was 91.1 and 88.3 MPa for the as-brazed and isothermally aged joint at 800 degrees C for 24 h in air, respectively. (C) 2016 Published by Elsevier Ltd.</P>
Raju, Kati,Kim, Seyoung,Yu, Ji Haeng,Kim, Soo-Hyun,Seong, Young-Hoon,Han, In-Sub Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.9
<P><B>Abstract</B></P> <P>The phase purity and crystal structure of dual-phase Ce<SUB>.9</SUB>Gd<SUB>.1</SUB>O<SUB>2–δ</SUB>–La<SUB>.6</SUB>Sr<SUB>.4</SUB>Co<SUB>.2</SUB>Fe<SUB>.8</SUB>O<SUB>3–δ</SUB> (GDC–LSCF) composites were refined using data obtained from X-ray diffraction (XRD) by employing the Rietveld method. Rietveld analysis indicated that the structures of GDC and LSCF phases are well crystallized as cubic <I>Fm</I> 3 ̅ <I>m</I> and rhombohedral <I>R</I> 3 ̅ <I>c</I> space groups, respectively. Scanning electron microscopy images showed smooth and dense structures, depicting a homogeneous crystalline structure of the samples. When the composites were cooled from their sintering temperature (1250 °C), compressive stresses were generated in the GDC and corresponding tensile stresses were generated in the LSCF due to differences in thermal expansion coefficients. The compressive residual stresses of the composites were investigated by high-angle XRD measurements using the well-known sin<SUP>2</SUP>ψ method. The average compressive residual stresses in GDC phase are estimated to be − 312 and − 290 MPa for 80 GDC–20 LSCF and 50 GDC–50 LSCF, respectively. The aim of this study is to provide a better understanding of the crystal structures and residual stresses in GDC–LSCF composites through XRD and the suitability of these composites for oxygen transport membranes.</P>
Raju, G. Seeta Rama,Pavitra, E.,Ko, Yeong Hwan,Yu, Jae Su The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.31
<P>Stable CaMoO<SUB>4</SUB> spherulites were synthesized by a facile hydrothermal method using (NH<SUB>4</SUB>)<SUB>6</SUB>Mo<SUB>7</SUB>O<SUB>24</SUB>·4H<SUB>2</SUB>O as a Mo source and these spherulites were formed according to the theoretical predictions of the crystal splitting theory. Rietveld refinement and photoluminescence studies confirmed that the CaMoO<SUB>4</SUB> spherulites are defect-free. The CaMoO<SUB>4</SUB> spherulites showed greenish-blue emission and the single emitting component of CaMoO<SUB>4</SUB>:Eu<SUP>3+</SUP> spherulites led to a novel excitation induced efficient emission property like organic light emitting diodes. Cathodoluminescent properties of the CaMoO<SUB>4</SUB>:Eu<SUP>3+</SUP> exhibited individual emissions from MoO<SUB>4</SUB><SUP>2−</SUP> clusters and Eu<SUP>3+</SUP> ions. The white color emissions were clearly explained using Gaussian fitting curves. The corresponding CIE chromaticity coordinates provided their emission potentiality in the green, red and white regions for optical and biological applications.</P> <P>Graphic Abstract</P><P>Stable CaMoO<SUB>4</SUB> spherulites with tunable luminescent properties have been synthesized and the growth mechanism is in well agreement with the theoretical predictions of the crystal splitting theory. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm32049e'> </P>
Raju Bandu,오재원,김광표 생화학분자생물학회 2019 Experimental and molecular medicine Vol.51 No.-
Over the past three decades, extracellular vesicles (EVs) have arisen as important mediators of intercellular communication that are involved in the transmission of biological signals between cells to regulate various biological processes. EVs are largely responsible for intercellular communication through the delivery of bioactive molecules, such as proteins, messenger RNAs (mRNAs), microRNAs (miRNAs), DNAs, lipids, and metabolites. EVs released from cancer cells play a significant role in signal transduction between cancer cells and the surrounding cells, which contributes to the formation of tumors and metastasis in the tumor microenvironment. In addition, EVs released from cancer cells migrate to blood vessels and flow into various biological fluids, including blood and urine. EVs and EVloaded functional cargoes, including proteins and miRNAs, found in these biological fluids are important biomarkers for cancer diagnosis. Therefore, EV proteomics greatly contributes to the understanding of carcinogenesis and tumor progression and is critical for the development of biomarkers for the early diagnosis of cancer. To explore the potential use of EVs as a gateway to understanding cancer biology and to develop cancer biomarkers, we discuss the mass spectrometric identification and characterization of EV proteins from different cancers. Information provided in this review may help in understanding recent progress regarding EV biology and the potential roles of EVs as new noninvasive biomarkers and therapeutic targets.