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Ambient pressure dried tetrapropoxysilane-based silica aerogels with high specific surface area
Parale, Vinayak G.,Han, Wooje,Jung, Hae-Noo-Ree,Lee, Kyu-Yeon,Park, Hyung-Ho Elsevier 2018 Solid state sciences Vol.75 No.-
<P><B>Abstract</B></P> <P>In the present paper, we report the synthesis of tetrapropoxysilane (TPOS)-based silica aerogels with high surface area and large pore volume. The silica aerogels were prepared by a two-step sol-gel process followed by surface modification via a simple ambient pressure drying approach. In order to minimize drying shrinkage and obtain hydrophobic aerogels, the surface of the alcogels was modified using trichloromethylsilane as a silylating agent. The effect of the sol-gel compositional parameters on the polymerization of aerogels prepared by TPOS, one of the precursors belonging to the Si(OR)<SUB>4</SUB> family, was reported for the first time. The oxalic acid and NH<SUB>4</SUB>OH concentrations were adjusted to achieve good-quality aerogels with high surface area, low density, and high transparency. Controlling the hydrolysis and condensation reactions of the TPOS precursor turned out to be the most important factor to determine the pore characteristics of the aerogel. Highly transparent aerogels with high specific surface area (938 m<SUP>2</SUP>/g) and low density (0.047 g/cm<SUP>3</SUP>) could be obtained using an optimized TPOS/MeOH molar ratio with appropriate concentrations of oxalic acid and NH<SUB>4</SUB>OH.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Optically transparent and hydrophobic silica aerogel using TPOS was successfully synthesized. </LI> <LI> Sol-gel compositional effect using TPOS on the polymerization of aerogels was firstly reported. </LI> <LI> MeOH/TPOS and acid/base concentrations strongly influenced on the physical and textural properties. </LI> <LI> High surface area (938 m<SUP>2</SUP>/g) and low density (0.047 g/cm<SUP>3</SUP>) are obtained using TPOS as precursor. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Parale, Vinayak G.,Jung, Hae-Noo-Ree,Han, Wooje,Lee, Kyu-Yeon,Mahadik, Dinesh B.,Cho, Hyung Hee,Park, Hyung-Ho Elsevier 2017 Journal of Alloys and Compounds Vol.727 No.-
<P><B>Abstract</B></P> <P>To improve the high-temperature thermal insulation characteristics of silica aerogels, it is important to reduce the radiative heat transfer. This can be achieved by Y<SUB>2</SUB>O<SUB>3</SUB> doping in the silica sol to opacify the infrared radiation of silica aerogels. The purpose of the present work was to study the effect of Y<SUB>2</SUB>O<SUB>3</SUB> incorporation on the structural and physicochemical properties of opacified silica aerogels prepared by a simple ambient pressure drying method. The influence of Y<SUB>2</SUB>O<SUB>3</SUB> addition on specific extinction coefficient and high temperature thermal insulation of prepared aerogels were investigated. The synthesized aerogels were lightweight and crack-free, with a granular, nanoporous morphology. The specific surface area, pore diameter, and bulk density of the prepared samples were 917.5–937.6 m<SUP>2</SUP>/g, 5.64–6.58 nm, and 0.047–0.076 g/cm<SUP>3</SUP>, respectively. The thermal conductivity of opacified silica aerogel at 1000 K was 0.080 W/(m.K), which was lower than the unopacified silica aerogel and it was around 0.104 W/(m.K) at same temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Low density Y<SUB>2</SUB>O<SUB>3</SUB> opacified SiO<SUB>2</SUB> aerogels by APD for HT thermal insulation. </LI> <LI> Y<SUB>2</SUB>O<SUB>3</SUB> effect on structural, physicochemical and morphological properties of aerogels. </LI> <LI> Aerogels: 917.5 m<SUP>2</SUP>/g surface area, 3.422 cm<SUP>3</SUP>/g pore volume, 6.58 nm pore diameter. </LI> <LI> 0.080 W/(m.K) of thermal conductivity of Y<SUB>2</SUB>O<SUB>3</SUB> opacified aerogels at 1000 K. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Flexible and Transparent Silica Aerogels: An Overview
Parale, Vinayak G.,Lee, Kyu-Yeon,Park, Hyung-Ho The Korean Ceramic Society 2017 한국세라믹학회지 Vol.54 No.3
Silica aerogels are attracting attention due to certain outstanding properties such as low bulk density, low thermal conductivity, high surface area, high porosity, high transparency and flexibility. Due to these extraordinary properties of aerogels, they have become a promising candidate in thermal superinsulation. The silica-based aerogels are brittle in nature, which constrains their large scale-application. It is necessary to achieve transparency and flexibility of silica-based aerogels at the same time and with the same porous structure for optical field applications. Therefore, the present review focuses on the different sol-gel synthesis parameters and precursors in the synthesis of flexible as well as transparent silica aerogels. Also, a brief overview of reported flexible and transparent aerogels with some important properties and applications is provided.
Parale, Vinayak G.,Lee, Kyu-Yeon,Jung, Hae-Noo-Ree,Nah, Ha-Yoon,Choi, Haryeong,Kim, Tae-Hee,Phadtare, Varsha D.,Park, Hyung-Ho Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.4
<P><B>Abstract</B></P> <P>Silica aerogels have low density and high specific surface area, but there are restrictions regarding their durability and commercialization owing to their fragile nature and the strong moisture absorbing behavior of the siloxane network. To overcome these restrictions, this study evaluated hybrid organically modified silica (ORMOSIL) aerogels by employing 3-(trimethoxysilylpropyl) methacrylate (TMSPM) in tetraethyl orthosilicate (TEOS) through a two-step sol-gel co-precursor method. The methacrylate organic groups were incorporated into the silica networks via reactions between the Si-OH moieties in silica aerogels, resulting in ORMOSIL aerogels. The properties of the ORMOSIL aerogels were strongly affected by the amount of TMSPM co-precursor. The highest concentration of TMSPM (30wt%) resulted in ORMOSIL aerogels with improved characteristics when compared with the pristine TEOS-based silica aerogels, such as hardness (0.15GPa), Young's modulus (1.26GPa), low thermal conductivity (0.038W/mK), high water contact angle (140°), and high thermal stability (350°C).</P>
Rushikesh P. Dhavale,Vinayak G. Parale,김태희,최해령,김용헌,이규연,정해누리,박형호 한국마이크로전자및패키징학회 2020 마이크로전자 및 패키징학회지 Vol.27 No.2
Robust and hydrophobic tetraethoxysilane (TEOS) based silica aerogel was synthesized by supercritical alcohol drying with surface modification using the phenyl based silica co-precursor (PTMS). The aerogels were synthesized by hydrolysis and polycondensation reaction in which TEOS and PTMS in methanol were reacted together in presence of oxalic acid and ammonium hydroxide as the catalysts. Supercritical alcohol dried PTMS/TEOS composite silica aerogel were examined for the hydrophobicity, chemical interaction, surface morphology, and textural characteristics. The hydrophobic silica-based aerogels were characterized by Fourier transform infrared spectroscopy to investigate the presence of functional groups and chemical bonds. The prepared silica demonstrates hydrophobicity (76o-149o), a high specific surface area (398 m2/g to 739 m2/g). The present investigation provides a simple approach to synthesize hydrophobic and thermally stable silica aerogels.
Phadtare, Varsha D.,Parale, Vinayak G.,Kulkarni, Gopal K.,Park, Hyung-Ho,Puri, Vijaya R. Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.765 No.-
<P><B>Abstract</B></P> <P>Multiwalled carbon nanotube (MWCNT)/Ca<SUB>1−x</SUB>Ba<SUB>x</SUB>Bi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (0 ≤ x ≤ 1)-layered thick film microwave-absorbing composites were prepared through the screen-printing method. The multilayered thick film composites were designed to improve their microwave absorption capabilities and the thickness of prepared thick films is around 115 μm. The layered thick film composites were synthesized with functionalized MWCNTs and co-precipitated Ca<SUB>1−x</SUB>Ba<SUB>x</SUB>Bi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (0 ≤ x ≤ 1) (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) Aurivillius-type ceramics. The microwave absorption, transmission and reflection properties were investigated in the J, X, and Ku-bands with a frequency range of 6–18 GHz. The multilayered thick film composites showed enhanced microwave absorption properties in the broadband frequency region. The multilayered composite with x = 0.8 had 1.5 times better microwave absorption than the only MWCNT thick film. This work presents a new approach to the fabrication of multilayered composites with enhanced microwave absorbance via simple screen-printing method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> MWCNT/Ca<SUB>1−x</SUB>Ba<SUB>x</SUB>Bi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (0 ≤ x ≤ 1) layered thick film composites have been prepared via screen-printing method. </LI> <LI> Enhanced microwave absorption up to 88% was obtained due to the multilayered structure with thickness 115 μm. </LI> <LI> MWCNT/Ca<SUB>1−x</SUB>Ba<SUB>x</SUB>Bi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (0 ≤ x ≤ 1) layered thick film composite shows broadband (6–18 GHz) microwave absorption characteristic. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Phadtare, Varsha D.,Parale, Vinayak G.,Lee, Kyu-Yeon,Kim, Taehee,Puri, Vijaya R.,Park, Hyung-Ho Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.805 No.-
<P><B>Abstract</B></P> <P>Lightweight and highly porous magnetic polymer foam (MPF) composites were synthesized using a simple, efficient, and environmentally friendly strategy. Their scaffold structure was well controlled using a surfactant and by varying the amount of Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles (NPs) added to the emulsion solution used in their preparation. The three-dimensional (3D) sponge-like MPFs are microwave-absorbing materials, and their structural and microstructural characteristics were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The magnetic properties of the MPF composites were also characterized. The polymer matrix of the composites exhibited excellent thermal stability. The microwave-absorbing properties of the MPF composites with increasing amounts of Fe<SUB>3</SUB>O<SUB>4</SUB> NPs (5 wt%, 10 wt%, and 15 wt%) were systematically studied. The microwave absorption of the polymer foam was enhanced to as high as 82% with the addition of Fe<SUB>3</SUB>O<SUB>4</SUB> NPs. Our results demonstrate that the prepared MPF composites have the potential to be used as lightweight, microwave-absorbing materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Magnetic polymer foam was fabricated by high internal phase emulsion method. </LI> <LI> Fe<SUB>3</SUB>O<SUB>4</SUB> NPs provide magnetic properties without disturbing porous structure. </LI> <LI> The foam exhibited magnetic properties and compressibility. </LI> <LI> Microwave absorption was enhanced with macroporous polymer foam/Fe<SUB>3</SUB>O<SUB>4</SUB> composite. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Phadtare, Varsha D.,Parale, Vinayak G.,Kulkarni, Gopal K.,Park, Hyung-Ho,Puri, Vijaya R. Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.7
<P><B>Abstract</B></P> <P>In the present study, Aurivillius-structured Ba<SUP>2+</SUP> substituted CaBi<SUB>2</SUB>Nb<SUB>2</SUB>O<SUB>9</SUB> (CBNO) ceramic powder was synthesized by co-precipitation method. The CBNO thick films were delineated by screen printing method on alumina substrates using co-precipitated ceramic powder. The overlay method was adopted to measure the microwave dielectric properties of prepared thick films. Single phase layered perovskite structure of the prepared thick films was confirmed by X-ray Diffraction. The effects of Ba<SUP>2+</SUP> substitution on the surface morphology, bonding, and microwave dielectric properties of thick films were systematically presented. The maximum value of microwave dielectric constant for the CBNO thick films at 11.8GHz is 15.6 for Ba<SUP>2+</SUP>=0.8 substitution. The shift in the stretching vibration modes of the Nb-O bond of NbO<SUB>6</SUB> octahedron in the Raman spectra with a substitution of Ba<SUP>2+</SUP> in CBNO was observed. The substitution of Ba<SUP>2+</SUP> on A-site of CBNO improves the microwave dielectric properties of prepared thick films. This work may provide a new approach to enhance the microwave dielectric performance of Aurivillius-structured ceramic thick films.</P>