Papers by Author: Whan Gi Kim

Abstract: Sulfonated poly (ethersulfone) s (S-PDHTPEs) were prepared from 4,4-(2,2-diphenylethenylidene) bisphenol (DHTPE), 4,4-sulfonyldiphenol, 4-fluorophenylsulfone using potassium carbonate, and followed sulfonation reaction with conc. sulfuric acid. DHTPE is a conjugated structure, which enables to form planar conformation between aromatic rings, and selectively sufonated on phenyl rings of polymer side chain. Composite membranes were prepared with copolymers and SiO₂ nanoparticles (20 nm, 4~10%wt). The composite membranes were cast from DMSO. A series of composite membranes structures and characteristic were evaluated by the ¹H-NMR spectroscopy, and thermal stabilities. The membranes were performed by ion exchange capacity (IEC), water uptake and proton conductivity as a function of degree of sulfonation.

Abstract: Sulfonated poly (diphenyl ether ketone sulfone) s, SPDPEKSs were successfully synthesized for proton exchange membranes (PEMs). Poly (diphenyl ether ketone sulfone) s, PDPEKSs were prepared by the polycondensation of 4,4'-sulfonyldiphenol with 1,2-bis (4-fluorobenzoyl)-3,6-diphenylbenzene (BFBDPB) and 4-fluorophenylsulfone respectively, at 210 °C using anhydrous potassium carbonate as catalyst in sulfolane. PDPEKSs were followed by sulfonation using chlorosulfonic acid and concentrated sulfuric acid at two step reactions. Different contents of sulfonated unit of SPDPEKS (25, 35, 45 mol% of BFBDPB) were studied by FT-IR, ¹H NMR spectroscopy, and thermogravimetric analysis (TGA). The ion exchange capacity (IEC), water uptake and proton conductivity of SPDPEKS were evaluated with increase of degree of sulfonation.

Abstract: Half-Heusler alloys are one of the potential thermoelectric materials for medium to high temperature range application. As a part of fundamental study to establish processing route and to observe thermoelectric properties in undoped state, ZrCoSb was selected, processed and evaluated. In an attempt to produce a half-Heusler thermoelectric materials having ultra fine grain structures, ZrCoSb was synthesized by mechanical alloying of stoichiometric elemental powder compositions, and consolidated by vacuum hot pressing. Phase transformations during mechanical alloying and hot consolidation were investigated using XRD, SEM and EDS. Single-phase, half-Heusler was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. Thermoelectric properties as functions of temperature were evaluated in terms of Seebeek coefficient, electrical conductivity, thermal conductivity and the figure of merit for the hot pressed specimens. Mechanically alloyed half-Heusler phase, ZrCoSb, appeared to have a great potential as a thermoelectric materials in this study.

Abstract: Poly(ethersulfone)s carrying pendant sulfonated imide side group. The first step in the preparation involved nitration of poly(ethersulfone) (ultrason^®-S6010), with ammonium nitrate and trifluoroacetic anhydride resulting in the nitrated poly(ethersulfone) (NO₂-PES). In the second step, the nitro groups on polymer were reacted with tin(II)chloride and sodium iodide as reducing agents for creating the amino poly(ethersulfone) (NH₂-PES). The imide-poly(ethersulfone)s (IPES) were obtained by reaction of phthalic anhydride and the amino-poly(ethersulfone) with triethyl amine. The sulfonated imide-poly(ethersulfone)s (SIPES) were prepared by chlorosulfonic acid. The different degrees of sulfonated imide units of poly(ethersulfone) were successfully synthesized by an optimized condition. The Sulfonated imide-poly(ethersulfone)s (SIPES) were studied by FT-IR, ¹H-NMR spectroscopy and thermo gravimetric analysis(TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water. The ion exchange capacity (IEC) and proton conductivity of SIPES membranes were evaluated with increase of degree of sulfonation. The water uptake of synthesized SIPES membranes exhibit 30 ~ 65 % compared with 28 % of Nafion 211^®. The SIPES membranes exhibit proton conductivities (25 °C) of 1.21 ~ 2.62´10^-3 S/cm compared with 3.37´10^-3 S/cm of Nafion 211^®.

Abstract: Poly(ether sulfone)s (PES) containing 25-75 mol % valeric acid were prepared with bisphenol A, bis(4-chlorophenyl)sulfone and 4,4-Bis(4-hydroxylphenyl)valeric acid using potassium carbonate in DMAc (dimethylacetamide) at 160 °C. Copolymers containing carboxylacid group were reduced to hydroxy group by BH₃ solution 1M in THF and NaBH4 co-catalyst. Sulfonated poly(ether sulfone)s (S-PES) were obtained by reaction of 1,3-propanesultone and the reduced copolymer (PES-OH) with potassium t-butoxide. Composite membranes were prepared with copolymers and SiO₂ nanoparticles(20 nm, 4-10 wt%). The composite membranes were cast from DMSO.A series of composite membranes were studied by ¹H-NMR spectroscopy, differential scanning calorimetry (DSC), and thermo gravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol.

Abstract: Hydrogen energy had recognized clean systems and high energy carrier. Mg and Mg-based materials have been lightweight and low cost materials which had been 7.6wt.% hydrogen capacity. However, Mg and Mg-alloys were currently hinder by its high absorption/desorption temperature, and very slow reaction kinetics. Therefore, one of the most methods to improve kinetics focused on addition transition metal oxide. Addition to transition metal oxide in MgH_x powder produce MgH_x-metal oxide composition by mechanical alloy and it analyze XRD, EDS, TG/DSC, SEM, and PCI. This report considers kinetics by transition metal oxide rate and hydrogen pressure. In this research, we can see behavior of hydriding/dehydriding profiles by addition catalyst (transition metal oxide). MgH_x-5wt.%Fe₂O₃ composite was measured most high hydrogen capacity and fast kinetics.

Abstract: Poly(ether ketone)s (PEK) containing 25-75 mol % valeric acid were prepared with bisphenol A, 4,4-dichlorobenzophenone and 4,4-Bis(4-hydroxylphenyl)valeric acid using potassium carbonate in DMAc (dimethyl acetami de) at 165 °C. Copolymers containing carboxylacid group were reduced to hydroxy group by BH3 solution 1M in THF and NaBH4 co-catalyst. Sulfonated poly(ether ketone)s (S-PEK) were obtained by reaction of 1,3-propanesultone and the reduced copolymer (PEK-OH) with sodium methoxide. A series of copolymers were studied by 1H-NMR spectroscopy, differential scanning calorimeter (DSC), and thermo gravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The S-PEK membranes exhibited proton conductivities from 1.31  10-3 to 3.52  10-3 S/cm, water swell from 12.70 to 35.50 %, IEC from 0.45 to 0.75 meq/g and methanol diffusion coefficients from 3.65  10-7 to 5.10  10-7 cm2/S at 25 °C.

Abstract: Recent search for novel thermoelectric materials has revealed a new class of compounds with half-Heusler structure as good candidates for higher performance thermoelectric conversion [1-2], since the structure was first found [3]. The unit cell of the half-Heusler with a space group F4¯ 3m consists of 4 interpenetrating cubic lattices. The crystallographic sites (0,0,0) and (1/4, 1/4, 1/4) are occupied by two different transition metals, the (1/2, 1/2, 1/2) site is occupied by Sn, Sb, or Bi, and the site (3/4, 3/4, 3/4) is empty [4,5]. Candidates with this structure for the investigation would be categorized into the combination of (Ti/Zr/Hf)(Co/Ni/Pt)(Sb/Sn/Bi) [4-6].

Abstract: Sn-doped CoSb3 skutterudites were prepared by encapsulated induction melting and their electronic transport properties were examined. The Sn dopant generated excess charge carriers, which increased in concentration with increasing Sn doping content. However, the carrier mobility decreased with increasing doping content, indicating a decrease in the hole mean free path by impurity scattering. The Seebeck coefficient decreased and the electrical resistivity decreased slightly with increasing the carrier concentration due to the reduced carrier mobility by impurity scattering. The lattice thermal conductivity was dominant in the Sn-doped CoSb3 skutterudites.

Abstract: Organic-inorganic Nano composite membranes were prepared by Sulfonated amine-poly(ether sulfone)s (S-APES)s and SiO2. S-APESs were prepared by nitration, reduction and sulfonation of poly(ether sulfone) (ultrason®-S6010). Poly(ether sulfone) was reacted with ammonium nitrate and trifluoroacetic anhydride to produce the nitrated poly(ether sulfone), and was followed by reduction using tin(Ⅱ)chloride and sodium iodide as reducing agents to give the amino-poly(ether sulfone). The S-APES was obtained by reaction of 1,3-propanesultone and the amino-poly(ether sulfone) (NH2-PES) with sodium methoxide. The different degrees of nitration and reduction of poly(ether sulfone) were successfully synthesized by an optimized process. Organic-inorganic nano composite membranes were obtained by mixing S-APES (45 %) with hydrophilic SiO2 (20 nm, 4-10 %) obtained by sol-gel process. Different contents of SiO2 of the S-APES were studied by FT-IR, 1H-NMR spectroscopy, differential scanning calorimetry (DSC), and thermo gravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion exchange capacity (IEC), a measure of proton conductivity, was evaluated. The nano composite membranes exhibit conductivities (25 °C) from 3.51 x 10-3 to 4.10 x 10-3 S/cm, water swell from 57.25 to 60.50 %, IEC from 0.68 to 0.73 meq/g, and methanol diffusion coefficients from 2.81 x 10-7 to 3.33 x 10-7 cm2/S at 25 °C.