• Korean Chemical Engineering Research
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• v.45 no.6
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• pp.611-618
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• 2007

We demonstrate the sol-gel coating technique of colloidal clusters for producing hollow micro-particles with complex morphologies. Cross-linked amidine polystyrene (PS) microspheres were synthesized by emulsifier-free emulsion copolymerization of styrene and divinylbenzene. The amidine PS particles were self-organized inside toluene-in-water emulsion droplets to produce large quantities of colloidally stable clusters. These clusters were coated with thin silica shell by sol-gel reaction of tetraethylorthosilicate (TEOS) and ammonia, and the organic polystyrene cores were removed by calcination at high temperature to generate nonspherical hollow micro-particles with complex morphologies. This process can be used to prepare hollow particles with shapes such as doublets, tetrahedra, icosahedra, and others.

• Computers and Concrete
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• v.17 no.6
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• pp.801-814
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• 2016

An alternative type of building system with masonry units is extensively used nowadays to reduce the emission of CO2 and embodied energy. Long-term performance of such structures has become essential for sustaining the building technology. This study aims to assess the strength and durability properties of concrete prepared with unprocessed bagasse ash (BA) and silica fume (SF). A mix proportion of 1:3:3 was used to cast concrete cubes of size $100mm{\times}100mm{\times}100mm$ with various replacement levels of cement and tested. The cubes were cast with zero slump normally adopted in the manufacturing of hollow blocks. The cubes were exposed to acid attack, alkaline attack and sulphate attack to evaluate their durability. The mass loss and damages to concrete for all cases of exposures were determined at 30, 60, and 90 days, respectively. Then, the residual compressive strength for all cases was determined at the end of 90 days of durability test. The results showed that there was slight difference in mass loss before and after exposure to chemical attack in all the cases. Though the appearance was slightly different than the normal concrete the residual weight was not affected. The compressive strength of 10% bagasse ash (BA) as a replacement for cement, with 10% SF as admixture resulted in better strength than the normal concrete. Hence concrete with 10% replacement with BA along with 10% SF as admixture was considered to be durable. Besides solid concrete cubes, hollow blocks using the same concrete were casted and tested simultaneously to explore the possibility of production of masonry units.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.467-467
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• 2011

Reflecting the growing importance of nanomaterials in science and technology, controlling the porosity combined with well-defined structural properties has been an ever-demanding pursuit in the related fields of frontier researches. A number of reports have focused on the synthesis of various nanoporous materials so far and, recently, the nanomaterials with multimodal porosity are getting an emerging importance due to their improved material properties compared with the mono porous materials. However, most of those materials are obtained in bulk phases while the spherical nanoparticles are one of the most practical platforms in a great number of applications. Here, we report on the synthesis of the core-shell silica nanoparticles with double mesoporous shells (DMSs). The DMS nsnoparticles are spherical and monodispersive and have two different mesoporous shells, i.e., the bimodal porosity. It is the first example of the core-shell silica nanoparticles with the different mesopores coexisting in the individual nanoparticles. Furthermore, the carbon and silica hollow capsules were also fabricated via a serial replication process.

• Journal of the Korea Institute of Building Construction
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• v.23 no.5
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• pp.547-558
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• 2023

This research delves into the fabrication of an ultra-high-strength concrete, enriched with oxidized graphene nanoplatelet(GO) and hollow glass powder(HGP), notably eschewing the conventional inclusion of silica fume(SF). The primary objective was to scrutinize the autogenous shrinkage characteristics of this innovative formulation. It was discerned that the NewMix specimen, which incorporated the cGO(sourced from Company C) and HGP, and intentionally bypassed SF, showcased a commendable 13% reduction in autogenous shrinkage relative to the benchmark(Ref) specimenthat incorporated SF. Moreover, the proclivity for crack formation owing to autogenous shrinkage in the NewMix was observed to manifested by NewMix at the juncture of cracking emerged as the apex value. Attributed to the expansive specific surface area and exemplary dispersibility of cGO, it was postulated that the concrete's pore structure benefitted from enhanced infill, leading to a reduction in autogenous shrinkage. Additionally, the cGO integration fortified the concrete's resistance to crack initiation. Consequently, such an enhancement is posied to be pivotal in mitigating crack propagation resulting from autogenous shrinkage in ultra-high-strength concrete.

• Membrane Journal
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• v.19 no.1
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• pp.47-53
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• 2009

The aim of this paper is to prepare metal/ceramic composite ultrafiltration membranes by coating inorganic particles on a metallic hollow fiber filter. The diameter and the pore size of the filter was 2.0 mm and $2{\sim}8{\mu}m$. The metal/ceramic composite ultrafiltration membranes were obtained by a coating process of silica and titania sols on top of the metallic filter. For this purpose the method of fast freeze drying and dip-coating were used. It was found that the pore size of the membrane was about 50 nm from SEM and PMI characterization. The pore size was controlled by changing the size of the particles, sintering period and temperature.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.377-382
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• 2014

Micro-/macroporous carbons (MMCs) were prepared using a hollow mesoporous silica capsule (HMSC) as a sacrificial hard template. The carbonization process after the infiltration of furfuryl alcohol into the template-free HMSC material afforded MMC materials in high yield. The hard template HMSC could be removed by HF etching without deteriorating the structure of MMC. The MMC materials were fully characterized by SEM, TEM, PXRD, XPS, and Raman spectroscopy. The replication processes were so successful that MMCs exhibited a hollow capsular structure with multimodal microporosity. Detailed textural properties of MMC materials were investigated by volumetric $N_2$ adsorption-desorption analysis at 77 K. To explore the gas sorption abilities of MMCs for other gases, $H_2$ and $CO_2$ sorption analyses were also performed at various temperatures. The multimodal MMC materials were found to be good sorbents for both $H_2$ and $CO_2$ at low pressure.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.67-75
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• 2005

For th aim of lightweight microwave absorbers, conductive and magnetic microspheres are fabricated by plating of Co films on hollow ceramic microspheres of low density. Metal plating was carried out in a two-step electroless plating process (pre-treatment of activation and plating). Uniform coating of the film with about $2{\~}3{\cal}um$ thickness was identified by SEM. High-frequency magnetic and microwave absorbing properties were determined in the rubber composites containing the Co-coated microspheres. Due to conductive and ferromagnetic behavior of the Co thin films, high dielectric constant and magnetic loss can be obtained in the microwave frequencies. Due to those electromagnetic properties, high absorption rate (25 dB) and thin matching thickness ($2.0{\~}2.5{\cal}mm$) are predicted in the composite layers containing the metal-coated microspheres of low density (about 0.84 g/cc) for the electromagnetic radiation in microwave frequencies.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.621-626
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• 2012

In this study, the composite coating materials with improved thermal insulation property were prepared by incorporating the hollow micro-spheres with high heat transfer resistance. The UV curable resin system consisting of hexa aliphatic urethane acrylate (UP118), trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDDA), and photoinitiator (Irgacure184) was employed as an organic binder. The glass substrates were coated by the prepared composites via bar coating method and cured under UV radiation. The optical transparency, thermal insulation property, adhesion, and surface hardness of the glass coated with composites containing different type of micro-spheres were investigated. The incorporation of micro-spheres with only 20 vol% of content resulted in remarkable improvement in the thermal insulation property of the coated glass. In addition, the transparent coated glass with light transmittance of about 80% could be obtained when silica micro-sphere (SP) was used as a thermal barrier.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.30 no.3 s.47
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• pp.321-328
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• 2004

Nano silica ball and nano carbon ball are developed commercially by template synthesis method. Adsorption of unpleasant smelling substances such as ammonia, trimethylamine, acetaldehyde and methyl mercaptane onto nano carbon ball with hollow macroporous core/mesoporous shell structures, nano carbon ball, was investigated and compared with that onto odor adsorbent materials, activated carbon, commercially available. The adsorption and decomposition of malodor at nano carbon ball exhibited superior than those onto activated carbon. The physicochemical properties such as mesopore size distributions, large nitrogen BET specific surface area and large pore volume and decomposition of malodor were studied to interpret the predominant adsorption performance. The nano carbon ball is expected to be useful in many applications such as deodorizers, adsorbent of pollutants.

• Journal of Power System Engineering
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• v.19 no.3
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• pp.5-10
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• 2015

Femtosecond laser machining has been applied for creating a sensor function in silica glass optical fibers. Femtosecond laser pulses make it possible to fabricate micro structures in processed regions of a very thin glass fiber line because femtosecond laser pulses can extremely minimize thermal effects. With the laser machining to optical fiber using a single shot of 210-fs laser at a wavelength of 800 nm, it was observed that a processed region surrounded a thin layer which seemed to be a hollow cavity monitored by scanning electron microscopy (SEM). This study aims at a theoretical investigation for the processed region by using a numerical analysis in order to embed sensing function to optical fibers. Numerical methods based finite element method (FEM) has been used for an optical waveguide modeling. This report suggests two types modeling and describes a comparative study on optical losses obtained by the experiment and the numerical analysis.