YooJin Kim

One-dimensional copper–pyridinedicarboxylate polymer containing square-planar Cu(II) centers exhibiting antiferromagnetic coupling

Abstract The hydrothermal reaction of Cu(NO 3 ) 2 ·2.5H 2 O with 2,5-pyridinedicarboxylic acid (2,5-PDCH 2 ) led to the formation of aone-dimensional coordination polymer with the empirical formula of Cu(2,5-PDC)(H 2 O) ( 1 ). On the other hand, the hydrothermalreaction of Cu(NO 3 ) 2 ·2.5H 2 O with 2,4-pyridinedicarboxylic acid (2,4-PDCH 2 ) gave a mononuclear Cu(II) compound Cu(2,4-PDC) 2 ( 2 ). The structures of both compounds have been determined by X-ray diffraction. In both compounds, the coordinationsphere of the Cu metal is square-planar. The polymer 1 exhibits strong antiferromagnetic coupling between the paramagneticCu(II) metals in the adjacent layers even in the absence of intervening groups.

Conformation change of the cyclohexanedicarboxylate ligand toward 2D and 3D La(III)-organic coordination networks

2D and 3D structures of La-1,4-cyclohexanedicarboxylates (chdc) coordination networks, have been constructed using flexible chdc ligands which can have cis and trans conformations of two dicarboxylate groups, controlled by the solution pH in hydrothermal reaction conditions.

Decomposition Mechanism of Waste Hard Metals using by ZDP (Zinc Decomposition Process)

Decomposition promoting factors and decomposition mechanism in the zinc decomposition process of waste hard metals which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility amount was suppressed and zinc valatilization pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP. Reaction was done for 2 h at 650℃, which 100 % decomposed the waste hard metals that were over 30 ㎜ thick. As for the separation-decomposition of waste hard metals, zinc melted alloy formed a liquid composed of a mixture of γ-β₁ phase from the cobalt binder layer (reaction interface). The volume of reacted zone was expanded and the waste hard metal layer was decomposed-separated horizontally from the hard metal. Zinc used in the ZDP process was almost completely removed-collected by decantation and volatilization-collection process at 1000℃.

Effect of Mullite Generation on the Strength Improvement of Porcelain

Alumina powder was added in a general porcelain (Backja) with clay, feldspar and quartz contents to promote the mullite (3Al₂O₃ㆍ2SiO₂) generation in the porcelain. Low melting materials (B₂O₃(450℃), MnO₃(940℃), CuO(1080℃)) were doped at ~3 wt% to modify the sinterability of porcelain with a high alumina contents and promote the mullite generation. Green body was made by slip casting method with blended slurry and then, they were fired at 1280°C for 1hr by a 2℃/min. Densifications of samples with high alumina contents (20~30 wt%) were impeded. As the doping contents of low melting materilas increased, the sinterability of samples was improved. The shrinkage rate and bulk density of samples were improved by doping with low melting materials. Mullite phase increased with increasing the low melting contents in the phase analyses. This means lots of alumina and quartz were transformed into mullite phase by low melting contents doping. In the results, high bending strength of samples with high alumina contents was accomplished by improving the densification and mullite generation in the porcelain.

Two-dimensional carboxylate bridged network of europium(III)–transition metal(II) glutarate compounds

Four new heterometallic glutarate coordination polymers, [Eu2M(H2O)4][O2C(CH2)3CO2]4.2H2O (M = Mn (1), Fe (2), Co (3) and Ni (4)) have been obtained under hydrothermal synthesis. The single-crystal X-ray diffraction analyses showed that they have two-dimensional frameworks based on the linear polyhedral chains consisting of two nine-coordinated Eu(III)O9 and a six-coordinated M(II)O6. These 1-D MO6-Eu2O16 chains are cross-linked by glutarate ligands as an interchain pillared architecture, whose conformations vary depending upon the transition metals. The magnetic behavior of the compounds show a weak antiferromagnetic interaction, in which shielding of the 4f electrons by the outer shell electrons effectively precludes significant coupling interactions between the Eu-4f electrons and transition metal (M)-3d electrons.

Structure evolution and coordination modes of metal-carboxylate frameworks with robust linear trinuclear complexes as building units

Five metal organic frameworks of trinuclear metal-dicarboxylate networks provide metal–oxygen coordination modes in robust trinuclear secondary building units.

Synthesis and characterization of Zn2SiO4:Mn2+ nanocrystals and tuning of phase by controlling of silica shell thickness

AbstractIn this paper is reported the synthesis and characterization of ZnO@Zn2SiO4:Mn2+ and Zn2SiO4:Mn2+ using ZnO@SiO2 nano spheres. The SiO2-shell thickness of the nano sphere was controlled 20 to 60 nm, and was controlled by selecting the reaction time of the Stöber method. The Zn2SiO4:Mn2+ as a glaze was prepared by addition of Mn2+ precursor the ZnO@SiO2 core-shell and then reacted in aqueous solution. Finally, the reactant was annealed at 1000°C so that Zn2SiO4:Mn2+ particles were obtained. The influences of the Zn/Si volume ratio on the PL (photoluminescence) properties of Zn2SiO4:Mn2+ were tunable by control the silica thickness of the ZnO core. The structure, morphology and luminescent property of the synthesized samples were determined by XRD (x-ray diffraction), TEM (transmission electron microscopy) and PL (photoluminescence).

Synthesis of porous nano-sized AlN by chemical vapor synthesis

We report the synthesis of AlN powders by the chemical vapor synthesis of an AlCl3–NH3–N2–H2 system. The starting material was gasified AlCl3, generated using a preheating system. AlCl3 gas was transported to a tube furnace in NH3–N2–H2 atmosphere. We synthesized highly crystalline AlN at over 900  °C. The average size of the spherical AlN particles decreased from 250 to 40 nm with increasing reaction temperature in the tube furnace. Porous nano-sized particles synthesized at high reaction temperatures have low oxygen contents and high thermal stability.

Synthesis of Nano-size Aluminum Nitride Powders by Chemical Vapor Process

Aluminum nitride (AlN) powders were prepared by the chemical vapor synthesis (CVS) process in the system. Aluminum chloride () as the starting material was gasified in the heating chamber of . Aluminum chloride gas transported to the furnace in atmosphere at the gas flow rate of 200-400ml/min. For samples synthesized between 700 and , the XRD peaks corresponding to AlN were comparatively sharp and also showed an improvement of crystallinity with increasing the reaction temperature. In additions, the average particle size of the AlN powders decreased from 250 to 40 nm, as the reaction temperature increased.

Synthesis of LiCoO 2 Powders using Recycled Cobalt Precursors from Waste WC-Co Hard Metal

[ ] a cathode material for lithium rechargeable batteries, was prepared using recycled . First, the cobalt hydroxide powders were separated from waste WC-Co hard metal with acid-base chemical treatment, and then the impurities were eliminated by centrifuge method. Subsequently, powders were prepared by thermal treatment of resulting . By adding a certain amount of and , the was obtained by sintering for 10 h in air at . The synthesized particles were characterized by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analysis.