Synthesis of a high-performance citric acid-based polyester elastomer by a hot-pressing technique

Chon, Y.J.,Koo, J.M.,Park, Y.J.,Hwang, S.Y.,Jung, Y.M.,Im, S.S. IPC Science and Technology Press 2017 Polymer Vol.125 No.-

The high-performance bio-based elastomer, poly (1, 4-cyclohexanedimethanol succinate-co-citrate) (PCSC), was successfully synthesized through the combination of melt polymerization and hot pressing. Owing to the structural characteristics of citric acid (CA), an effective process of thermal- and pressure-integrated crosslinking was possible, revealing CA to be a progressive tetra-functional monomer. In the composition of PCSC, there can be four types of ester bonds amongst monomers, of which CA was used in three. Specifically, the stepwise hot-pressing method allowed β-carboxylic acid and hydroxyl group of CA to remain within the synthesized elastomer to enhance its crosslinking density via esterification. As a result, the synthesized PCSC possessed a wide range of mechanical properties along with good thermal resistance. The resulting characteristics were demonstrated by fourier-transform infrared spectroscopy (FT-IR), two-dimensional correlation spectroscopy (2D-COS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile and swelling tests. PCSC is a sustainable and versatile material that can be utilized in the field of engineering.

The effect of microstructural inhomogeneity on the growth paths of surface-cracks in copper processed by equal channel angular pressing

Goto, M.,Ando, Y.,Han, S.Z.,Kim, S.S.,Kawagoishi, N.,Euh, K. Pergamon Press ; Elsevier Science Ltd 2010 Engineering fracture mechanics Vol.77 No.11

The growth behavior of cracks is monitored on specimens of ultrafine grained copper produced by equal channel angular pressing. Temporary retardation of crack growth under low stress amplitudes occurs when the crack length reaches about 0.1mm, but there is no similar retardation at high stress amplitudes. Dependent on stress amplitude, different crack growth path morphologies develop. Analysis of the fracture surfaces is conducted by scanning electron microscopy, showing planer, granular and striated surfaces. The physical background of growth path and fracture surface formation is discussed by considering crack growth mechanism and microstructural inhomogeneity.

Effects of the degree of polymerization on the structure of sodium silicate and aluminosilicate glasses and melts: An ¹⁷O NMR study

Lee, S.K.,Stebbins, J.F. Pergamon Press ; Elsevier Science Ltd 2009 Geochimica et cosmochimica acta Vol.73 No.4

Revealing the atomic structure and disorder in oxide glasses, including sodium silicates and aluminosilicates, with varying degrees of polymerization, is a challenging problem in high-temperature geochemistry as well as glass science. Here, we report <SUP>17</SUP>O MAS and 3QMAS NMR spectra for binary sodium silicate and ternary sodium aluminosilicate glasses with varying degrees of polymerization (Na<SUB>2</SUB>O/SiO<SUB>2</SUB> ratio and Na<SUB>2</SUB>O/Al<SUB>2</SUB>O<SUB>3</SUB> ratio), revealing in detail the extent of disorder (network connectivity and topological disorder) and variations of NMR parameters with the glass composition. In binary sodium silicate glasses [Na<SUB>2</SUB>O-k(SiO<SUB>2</SUB>)], the fraction of non-bridging oxygens (NBOs, Na-O-Si) increases with the Na<SUB>2</SUB>O/SiO<SUB>2</SUB> ratio (k), as predicted from the composition. The <SUP>17</SUP>O isotropic chemical shifts (<SUP>17</SUP>O δ<SUB>iso</SUB>) for both bridging oxygen (BO) and NBO increase by about 10-15ppm with the SiO<SUB>2</SUB> content (for k=1-3). The quadrupolar coupling products of BOs and NBOs also increase with the SiO<SUB>2</SUB> content. These trends suggest that both NBOs and BOs strongly interact with Na; therefore, the Na distributions around BOs and NBOs are likely to be relatively homogenous for the glass compositions studied here, placing some qualitative limits on the extent of segregation of alkali channels from silica-enriched regions as suggested by modified random-network models. The peak width (in the isotropic dimension) and thus bond angle and length distributions of Si-O-Si and Na-O-Si increase with the SiO<SUB>2</SUB> content, indicating an increase in the topological disorder with the degree of polymerization. In the ternary aluminosilicate glasses [Na<SUB>2</SUB>O]<SUB>x</SUB>[Al<SUB>2</SUB>O<SUB>3</SUB>]<SUB>1-x</SUB>SiO<SUB>2</SUB>, the NBO fraction decreases while the Al-O-Si and Al-O-Al fractions apparently increase with increasing Al<SUB>2</SUB>O<SUB>3</SUB> content. The variation of oxygen cluster populations suggests that deviation from ''Al avoidance'' is more apparent near the charge-balanced join (Na/Al=1). The Si-O-Si fraction, which is closely related to the activity coefficient of silica, would decrease with increasing Al<SUB>2</SUB>O<SUB>3</SUB> content at a constant mole fraction of SiO<SUB>2</SUB>. Therefore, the activity of silica may decrease from depolymerized binary silicates to fully polymerized sodium aluminosilicate glasses at a constant mole fraction of SiO<SUB>2</SUB>.

An efficient decal transfer method using a roll-press to fabricate membrane electrode assemblies for direct methanol fuel cells

Mehmood, A.,Ha, H.Y. Pergamon Press ; Elsevier Science Ltd 2012 International journal of hydrogen energy Vol.37 No.23

This study has focused on the development of a roll-press based decal transfer method to fabricate membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs). This method exhibits an outstanding transfer rate of catalyst layers from substrates to the membrane, despite hot-pressing at a considerably lower pressure and for a much shorter duration than the flat-press based conventional decal method. The MEA produced by a roll-press (R-MEA) delivers an excellent single-cell performance with power densities more than 30% higher than that fabricated using a flat-press (F-MEA). The new method considerably improves catalyst active sites in both electrodes and renders a high cathode porosity. The superior pore structure of the cathode makes the R-MEA more efficient in terms of performance and operation stability under lower air stoichiometries. Moreover, MEAs can be prepared in a continuous mode using this new method due to the unique design of the roll-press. All these advantages demonstrate the superiority of this method over the conventional flat-press decal method and make it suitable for use in the commercial manufacturing of MEAs for direct methanol fuel cells.

The present status and analysis of Science & Technology Information (STI) service policy in Korea

Yun-Seok, L.,jae-sung, K. JAI Press ; Elsevier Science Ltd 2009 Government information quarterly Vol.26 No.3

National Science & Technology Information (STI) infrastructure of Korea has been independently developed as a decentralized system within the government ministry. In order to effectively establish the national STI infrastructure, it is essential to create a networked and integrated system in the domestic and foreign information infrastructure. This study aims to analyze current national STI infrastructure and to suggest specific ways in which domestic and foreign STI infrastructure may be utilized.

Design and performance test of a multi-channel diffusion charger for real-time measurements of submicron aerosol particles having a unimodal log-normal size distribution

Park, K.-T.,Park, D.,Lee, S.-G.,Hwang, J. Pergamon Press ; Elsevier Science Ltd 2009 Journal of aerosol science Vol.40 No.10

It is important to develop a simple and fast method for measuring the sizes of submicron particles in both laboratories and fields. In our previous studies, Park, An, and Hwang [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430] and Park, Kim, An, and Hwang [(2007). Real-time measurement of submicron aerosol particles having a log-normal size distribution by simultaneously using unipolar diffusion charger and unipolar field charger. Journal of Aerosol Science, 38, 1240-245], we introduced methodologies that our lab made unipolar charger could lead to detection times of under 5s in conjunction with an electrometer and a condensation particle counter (CPC), and under 3s with two electrometers. However, both methodologies require an appropriate assumption of the geometric standard deviation of particle sizes. In this paper, we introduce a methodology for determining the geometric standard deviation of particle sizes as well as the geometric mean diameter and the total number concentration of particles. For this purpose, a diffusion charger that consisted of discharge zone, mixing and charging zone, and three flow channels for obtaining three different residence times and average charges of particles in the channels, was designed and tested. For determining the average particle charge, various methods including theoretical calculations and the tandem differential mobility analyzer (TDMA) method were used. The results obtained from the different methods agreed well with each other. To compare the size distribution with the data that were measured through a scanning mobility particle sizer (SMPS), sodium chloride (NaCl) particles were used. The estimated results by using a data inversion algorithm were less than those measured by SMPS by around 22% for the total number concentration and 10% for both the geometric mean diameter and the geometric standard deviation. Furthermore, the detection time was under 3s.

Real-time measurement of submicron aerosol particles having a log-normal size distribution by simultaneously using unipolar diffusion charger and unipolar field charger

Park, D.,Kim, S.,An, M.,Hwang, J. Pergamon Press ; Elsevier Science Ltd 2007 Journal of aerosol science Vol.38 No.12

Recently, Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430] have introduced a methodology for performing simple and fast measurements of submicron aerosol particles having a log-normal size distribution, using a unipolar diffusion charger, an electrometer, and a condensation particle counter (CPC). The methodology can be applied to particles of 30-700nm and requires an assumption of their geometric standard deviation in size. In this paper we propose a much cheaper but faster method which involves substituting a unipolar field charger and another electrometer for the CPC. With the data obtained using this dual-charger system, we developed a data inversion algorithm and estimated the particle size distribution by minimizing the differences between the measured aerosol currents and the calculated values. To compare the size distribution with the data measured using a scanning mobility particle sizer (SMPS), sodium chloride (NaCl) particles smaller than 0.1μm in diameter, and dioctyl sebacate (DOS) particles with a diameter of 0.1-0.7μm, were used. The estimated results for the NaCl and DOS particles were within 10% of the data measured with the SMPS, while a 33% deviation from the SMPS results was obtained in Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430]. Furthermore, the detection time obtained with the use of our dual-charger system was faster (<3s) than the 5s obtained by Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430].

New bio-aerosol collector using a micromachined virtual impactor

Park, D.,Kim, Y.H.,Woo Park, C.,Hwang, J.,Kim, Y.J. Pergamon Press ; Elsevier Science Ltd 2009 Journal of aerosol science Vol.40 No.5

For collection and concentration of bioaerosols, we designed and evaluated a single stage virtual impactor, which was fabricated by micro-electro-mechanical systems (MEMS) process. The cut-off diameter of 1μm was selected, since 1μm is the lowest size as used in the US Government Joint Biological Point Detection System [Haglund, J. S., & McFarland, A. R. (2004). A circumferential slot virtual impactor. Aerosol Science and Technology, 38, 664-674; Moshier, T., & Buonaugurio, T. (2000). Joint Biological Point Detection System (JBPDS) requirements and design interplay. Proceedings of the First Joint Conference on Point Detection for Chemical and Biological Defense, October 23-27, 2000, Williamsburg, VA.] The design value of a 1μm cut-off diameter required a nozzle width and thickness of 880 and 200μm, respectively. The virtual impactor was evaluated for physical and biological collection efficiencies. For the performance evaluation of physical collection efficiency and wall loss, polystyrene latex (PSL) particles were generated from an atomizer and their size distribution was measured using an aerodynamic particle sizer (APS, TSI model 3321) and a scanning mobility particle sizer (SMPS, TSI model 3936). The measured cut-off diameter was 0.95μm, which agreed with the calculated results (=0.94μm) determined with a commercial computational fluid dynamics (CFD) package, FLUENT, and the measured wall loss was below 33.5%. For the performance evaluation of biological collection efficiency, Staphylococcus epidermidis bioaerosols were dispersed into air by a nebulizer. The bioaerosols were measured using APS and sampled with a bioaerosol sampler. The overall physical collection efficiency based on the number concentration was 73.8+/-3%, which was similar to the one based on the number of colonies (=76.7+/-7%). We found that most of the bioaerosols collected and concentrated by our virtual impactor were viable.

Fabrications and evaluations of hydrogen permeation on Al₂O₃/CeO₂/graphene (ACG) composites membrane by Hot Press Sintering (HPS)

Lee, N.R.,Lee, S.S.,Kim, K.I.,Kim, W.G.,Ju, H.,Kim, D.M.,Hong, T.W. Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.18

Ceramic membrane has high permeation rate of hydrogen and chemical stability. Al<SUB>2</SUB>O<SUB>3</SUB> indicates stable at high temperature and a relatively large surface area. In addition, Al<SUB>2</SUB>O<SUB>3</SUB> of porous is used as hydrogen separation membranes support, because of the high hydrogen permeability based on Knudsen diffusion mechanism. In this work, metal alkoxides as starting materials was used Aluminum isopropoxide powder. Then CeO<SUB>2</SUB> as catalyst at the partial oxidation and Graphene Oxide as electrical conductivity are added, Al<SUB>2</SUB>O<SUB>3</SUB>-CeO<SUB>2</SUB>-Graphene oxide (ACG) composites are synthesized by sol-gel process. ACG membrane was fabricated type of disk by Hot Press Sintering. A synthesized ACG composite material was characterized by EDS, SEM, TG/DTA, XRD, BET. The hydrogen permeation property of ACG membrane was measured by Sievert's type hydrogen permeation membrane equipment. The hydrogen permeability of ACG membranes was examined at RT-673 K under increasing pressure. Results, hydrogen permeability was obtained to 2.62 x 10<SUP>-7</SUP> mol/ms Pa<SUP>½</SUP> at 673 K under 0.3 MPa.

Properties of solid wood and laminated wood lumber manufactured by cold pressing and heat treatment

Kwon, J.H.,Shin, R.H.,Ayrilmis, N.,Han, T.H. Scientific and Technical Press ; Elsevier Science 2014 Materials & design Vol.62 No.-

Physical, mechanical, and morphological properties of solid wood lumbers which were cold pressed in a press and then heat treated in a kiln. Two different kinds of domestic thinning small-diameter softwood (Ginko biloba L.) and hardwood (Tilia amurensis Rupr.) were used in this study. First 50mm thick lumbers were cold pressed until 35mm (30% of control lumber) using a stopper for 5min. Then the cold pressed lumbers were heat treated in an electric kiln at 180<SUP>o</SUP>C for 6, 12, 24, or 48h. To increase the utilizability of woods, the LVLs were produced from 4mm thick veneers prepared from the heat treated lumbers using a veneer saw. Each LVL sample consisted of 5 layers which were subsequently 48h-, 24h-, 12h-, and 6h-treated veneers and untreated veneer (from top layer to bottom layer). The shrinkage rates of softwood and hardwood were considerably decreased with increasing temperature. The mechanical properties of heat treated samples were better than those of unpressed control samples. The bending strength and modulus of elasticity of the LVLs manufactured from cold pressed and then heat treated lumbers were slightly lower than those of untreated woods. The colour values obtained from the heat treated wood samples showed a clear effect of the temperature on the colour changes.