• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.791-797
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• 1998

As organosilicon based preceramic polymer, new zirconium hybridized polycarbosilane having a good thermal stability and forming stage was synthesized. Oxidative stability(infusibility) and mechanical property of this polymer during the thermal curing process and heat treatment were examined. Prepared zirconium hybridized polycarbisilane (PZC) was spun into fiber at $250{\sim}270^{\circ}C$. Spinnability of PZC polymer having a molecular weight of 1000 to 1400 and having a dispersity<2 was good. The thermal curing process of the PZC fiber was done at 140 to $200^{\circ}C$. The mechanical properties of PZC ceramic fiber depend on curing temperature of PZC as precursor of PZC ceramic fiber. It was found that the optimum curing temperature was variable with the molecular weight of PZC. The cured PZC fiber need constant gel fraction to have good tensile strength.

• Resources Recycling
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• v.14 no.6 s.68
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• pp.60-63
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• 2005

It was possible to understand the adsorption characteristics of ions in aqueous environment based on the variations of PZC and IEP of particles when adsorption of ions on particle surface occurred. The specific adsorption of $Cu^{2+}$ ion upon chalcopyrite surface provoked a lowered PZC, which was considered to be due to increased adsorption of OH- ion via the electrostatic attraction between the two ions. On the contrary, IEP of chalcopyrite was observed to rise when Cu2+ was specifically adsorbed on its surface. The reason for this could be explained by the necessity of the increase of pH to offset the positively increased surface potential of chalcopyrite for the reestablishment of IEP. Neither PZC or IEP of chalcopyrite was observed to change when non-specific adsorption occurred since no change in the surface potential of chalcopyrite was invoked under this condition.

• Journal of Radiation Industry
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• v.4 no.3
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• pp.265-269
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• 2010

Silicon-based non-oxide ceramic carbide fiber is one of the leading candidate ceramic materials for engineering applications because of its excellent mechanical properties at high temperature and good chemical resistance. In this study, polycarbosilane(PCS) and zirconium butoxide were used as a precursor to prepare polyzirconocarbosilane (PZC) fibers. A polymer solution was prepared by dissolving PCS in zirconium butoxide (50/50 wt%). This solution was heated at $250^{\circ}C$ in a nitrogen atmosphere for 2 hour with stirring, and then dried in a vacuum oven for 48 hour. PZC fibers were fabricated using an electrospinning technique. The fibers were irradiated with an electron beam to induce structural crosslinking. Crosslinked PZC fibers were heat treated at $1,300^{\circ}C$ in a nitrogen atmosphere. The microstructures of PZC fibers were examined by SEM. Chemical structures of PZC fibers were examined by FT-IR and XRD. Thermal stability of PZC fibers was investigated by TGA.

• Korean Journal of Ecology and Environment
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• v.49 no.4
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• pp.289-295
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• 2016

The purpose of this study is to find out the effect of particle size of sediment on adsorption of fluoride. Particle size is classified as sand, silt and clay. Adsorption equilibrium time, adsorption isotherms and the effect of pH were investigated through batch tests. The $pH_{pzc}$ of sand, silt, clay was respectively 6, 8, 4.5 and AEC (anion exchange capacity) was highest in silt, respectively 0.0095, 0.0224, $0.014meq\;g^{-1}$. Adsorption of fluoride on the sediment was in equilibrium within 300 minutes from all particle size. The experimental data of isotherms at various pH were well explained by Freundlich equation. As the experimental results of the effect of pH, the adsorption efficiency of sand and silt were reduced after the $pH_{pzc}$. However, the adsorption efficiency of clay was maintained after the $pH_{pzc}$, and decreased rapidly higher than pH 12.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1099-1103
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• 1999

The surface of an ${\alpha}$-alumina tube was coated with zirconium modified polycarbosilane(PZC) by dip-coating method. Then the tube was pyrolyzed at 573~823 K. The prepared inorganic composite membrane was in $1{\mu}m$ thickness and had no pinholes larger than several nm. For the pyrolyzed inorganic composite membrane, the permeation test of He, $N_2$, $CO_2$, and $O_2$ was performed at 303~423 K. The gas permeation and separation factor were increased with increasing permeation temperature. The permeation for gases was controlled by the activated diffusion mechanism. The separation factor of $CO_2$, to $N_2$was 4.9 at 363 K on the composite membrane pyrolyzed at 823 K and its value was higher than that of He and $O_2$.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.3
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• pp.407-414
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• 2015

The effect of activated carbon particle diameter (i.e. US sieve No. $8{\times}10$ ($d_p{\approx}2.19mm$), $18{\times}20$ ($d_p{\approx}0.92mm$), $50{\times}60$ ($d_p{\approx}0.27mm$) and $170{\times}200$ ($d_p{\approx}0.081mm$) on caffeine adsorption is investigated. BET surface area was increased with decreasing particle diameter ($d_p$), and caffeine adsorption rates increased with decreasing $d_p$. Moreover, pseudo-second order model is predicted the experimental data more accurately than pseudo-first order model, and the fastest rate constant ($k_2$) was $1.7g\;mg^{-1}min^{-1}$ when $d_p$ was 0.081 mm. Surface diffusion coefficient (Ds) was decreased with decreasing $d_p$ based on the minimum sum of square error (SSE). Practically, certain ranges of Ds are acceptable with high reliability ($R^2$) and it is determined that the effect of $d_p$ on Ds is unclear. The effect of pH on caffeine adsorption indicated the dependency of m/L ratio (mass liquid ratio) and $pH_{pzc}$. The $pH_{pzc}$ (i.e. $7.9{\pm}0.2$) was not affected by $d_p$. The higher caffeine adsorption at pH 4 and pH 7 than at pH 10 is due to $pH_{pzc}$, not $pk_a$ of caffeine.

• Journal of Soil and Groundwater Environment
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• v.10 no.4
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• pp.62-69
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• 2005

Removal of 4-chlorophenol (4CP) by natural manganese dioxide (NMD) catalyzed reaction was investigated in this study. Tests were also carried out to evaluate the effects of pH and natural organic matter (NOM) on the degradative oxidation of 4CP. Experimental results proved that NMD was effective for the removal of 4CP. Extensive kinetic analysis suggests that overall oxidation of 4CP by NMD is second-order reaction, the first-order with respect to 4CP, and the first-order with respect to NMD, respectively. Also, 4CP oxidation rates on the Mn-oxide surfaces were highly dependent upon experimental conditions such as pH, initial concentration of 4CP or NMD, and existence of humic acid. As pH increased above PZC of NMD, the reaction rate of 4CP was decreased, due to the low affinity of 4CP on NMD at high pH. At pH lower than PZC of NMD, reaction rate of 4CP was also decreased. It was considered that humic acid was involved in the oxidative coupling reaction of 4CP by NMD, resulting in the enhanced degradation rate of 4CP. This study proved that natural manganese oxide can be effectively applied for the removal of chlorophenols in aqueous phase.

• Journal of Soil and Groundwater Environment
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• v.7 no.3
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• pp.85-94
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• 2002

Overall objective of this study was to evaluate the electrochemical characteristics of fine soils during the electrokinetic(EK) remediation. Zeta potential of kaolinite as a function of solution pH and surfactant concentration was investigated to make a relationship with electroosmotic flow direction and rate. During the EK experiments, pH of pore solution, electroosmotic permeability($k_e$), electric conductivity($\delta_e$) and voltage distribution was measured, respectively, The point of zero charge(PZC) of kaolinite was estimated to be about 4.2 and the zeta potential of kaolinite above PZC was more negative as solution pH increased. Sorption of surfactants on the kaolinite altered the zeta potential of kaolinite. resulting from the variation of electrochemical characteristics of kaolinite surface. hs the EK experiment progressed, low pH was predominant over most of the kaolinite specimen and thus resulted in very low mass and charge flow. The $k_e$ and $\delta_e$ was also affected by the variation of voltage drop across the EK column with time. Results from this study implied that zeta potential of kaolinite affected by the pH variation of pore solution and voltage distribution in soil column played important role in the determination of mass and charge flow during EK process. It was also suggested that pH adjustment or addition of suitable sorbates could alter the electrochemical characteristics of soil surface and thus maintain high mass and charge flow rate with time.

• Korean Journal of Soil Science and Fertilizer
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• v.31 no.4
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• pp.407-413
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• 1998

The influence of the anion composition of simulated acid rain on cation leaching of two soils with different surface charge properties was examined. Four mixtures of mole ratio of $SO_4:NO_3$(1:0, 2:1, 1:1, 0:1) with pH 2.0 simulated acid rain were applied to an Inceptisols(Gyuam series) and Andisols(Pyeongdae series). The Andisols had higher $SO_4{^{2-}}$ adsorption capacity than the Inceptisols because of its higher point of zero charge(PZC, pH 6.5) than Inceptisols(PZC pH 3.1). Cation leaching in Andisols varied directly with the $NO_3$ content of the leaching input due to higher mobility of $NO_3$ compared with $SO_4$ that was absorbed. The pH of the Andisols was higher with the addition of $Na_2SO_4$ than the addition of $NaNO_3$ indicating that this soil behaves as a base and has a high $SO_4$ adsorption capacity. The relative $NO_3{^-}/SO_4{^{2-}}$ content input had no effect on cation leaching of the Inceptisols. Amounts of leaching on the Andisols by simulated acid rain were higher than Inceptisols. This experiment explained that anion composition of acid rain plays a significant role in the cation leaching of soils which are able to adsorb $SO_4$.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.12
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• pp.2227-2238
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• 2000

The interfacial features of suspension system made of $CaCO_3$ particles have been investigated for the purpose of designing its effective treatment process. For the examination of variation of electrokinetic potential as a function of pH. the value of potential was observed to shift in the negative direction, which was thought to be due to the adsorption of hydroxide ion on the particle surface. Adsorption of surfactant on suspended particles resulted in the change of surface charge and shift in electrokinetic potential, which was dependent upon the sign of head charge and concentration of surfactant. Addition of inorganic salts affected stability of suspension greatly and sedimentation rate of suspension was influenced by the electric valence and amount of ions produced by dissolution of inorganic coagulants. DLVO theory made it possible to construct a energy profile diagram and a close correlation was found between experimental result and theoretically derived consequences. Non-specific adsorption of indifferent electrolyte resulted in the compression of electrical double layer and specific adsorption induced the shift of IEP and PZC in the opposite direction.