• Nuclear Engineering and Technology
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• 제28권5호
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• pp.458-466
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• 1996

The effects of dopants on the modification of microstructure of UO$_2$ and UO$_2$-4wt%CeO$_2$ sintered pellets have been studied in hydrogen and $CO_2$/CO mixture atmospheres by using $Ta_2O_5$, TiO$_2$ and $Nb_2O_5$ as sintering additives. The dopant were added as oxide powders and homogenized by attrition milling. The mixed powders were pressed, and then sintered in hydrogen at 1$700^{\circ}C$ , or in oxidizing atmosphere using Controlled $CO_2$/CO mixtures at 125$0^{\circ}C$. Both density and microstructure of UO$_2$ are modified by the addition of dopants in reducing atmosphere. The sintered density is increased with $Ta_2O_5$ addition up to 0.33wt% and subsequently decreased with higher content of the additive. The effect on the densification and the gain growth are apparent with the addition of 0.24wt% $Nb_2O_5$. With 0.lwt% titania and 0.6wt% $Ta_2O_5$, the sintered density is decreased, but the grain size is increased. In oxidizing atmosphere, the grain sizes for UO$_2$ doped with the above additives are smaller than that for pure UO$_2$. The grain size of Ta or Nb-doped UO$_2$ is decreased with increasing $CO_2$/CO ratio, but that of pure UO$_2$or T-doped UO$_2$ is increased. A large portion of second phases is observed in UO$_2$ doped with 0.lwt% TiO$_2$ sintered in hydrogen atmosphere, while, in $CO_2$/CO atmospheres, the second phases or dopant agglomerates are not observed. For UO$_2$-4wt%CeO$_2$ mixed oxide, the effect of additives on the gain growth is not so much as that for the pure UO$_2$. This is attributed to the formation of clusters by dopant cations and Ce ions, so that the additives contribute to a lesser exent to the grain growth for the mixed oxide.

• 한국환경농학회지
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• 제42권4호
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• pp.358-370
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• 2023

Composting has been proposed for the management of organic waste, and the resulting products can be used as soil amendments and fertilizer. However, the emissions of greenhouse gases (GHGs) such as CO₂, CH₄, and N₂O produced in composting are of considerable concern. Hence, various additives have been developed and adopted to control the emissions of GHGs. This review presents the different additives used during composting and summarizes the effects of additives on GHGs during composting. Thirty-four studies were reviewed, and their results showed that the additives can reduce cumulative CO₂, CH₄, and N₂O emission by 10.5%, 39.0%, and 28.6%, respectively, during composting. Especially, physical additives (e.g., biochar and zeolite) have a greater effect on mitigating N₂O emissions during composting than do chemical additives (e.g., phosphogypsum and dicyandiamide). In addition, superphosphate had a high CO₂ reduction effect, whereas biochar and dicyandiamide had a high N₂O reduction effect. This implies that the addition of superphosphate, biochar, and dicyandiamide during composting can contribute to mitigating GHG emissions. Further research is needed to find novel additives that can effectively reduce GHG emissions during composting.

• 한국수소및신에너지학회논문집
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• 제19권5호
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• pp.394-402
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• 2008

The Effects of Cu or Ni additives co-added with Ce/Zr mixed oxides to Fe-based oxide mediums were investigated for the purpose of the replacement of Rh, a precious metal additive, in terms of hydrogen storage(reduction by hydrogen) and release(water splitting). From the results of temperature programmed reduction(TPR), initial reduction rate of iron oxide in the mediums was greatly increased with the addition of Cu, similar to that of Rh. For isothermal redox reaction of 10 cycles, the total amounts of hydrogen evolved in water splitting steps for the mediums added with Cu or Ni were highly maintained at ca. 7 mmol/g-material, even though the oxidation rates were slightly lower than that for the medium added with Rh. This result suggests that the replacement of Rh to Cu or Ni is possible as a co-additive for Fe-based oxide mediums.

• 대한화학회지
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• 제61권3호
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• pp.97-103
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• 2017

In this study, the functional hydrogel ophthalmic lens containing tungsten oxide nanoparticles, 2,4-dihydroxy benzophenone and 2-hydroxy-4-(methacryloyloxy) benzophenone were manufactured. HEMA (2-hydroxyethyl methacrylate), MMA (methyl methacrylate), AA(acrylic acid), the cross-linker EGDMA (ethylene glycol dimethacrylate), the initiator AIBN (azobisisobutyronitrile) and the functional additives including tungsten oxide nanoparticles, 2,4-dihydroxy benzophenone, and 2-hydroxy-4-(methacryloyloxy) benzophenone were used respectively. The measurements of water content and refractive index of the sample was decreased and increased, respectively. And also, the UV transmittance of produced lens containing 2,4-dihydroxy benzophenone, 2-hydroxy-4-(methacryloyloxy) benzophenone and tungsten oxide nanoparticles was measured. Based on the results of this study, it is judged that the performance improvement increased over time when 2-hydroxy-4-(methacryloyloxy) benzophenone was used as an additive, while the use of tungsten oxide nanoparticles influenced on blue-ray-blocking effect of the hydrophilic lens.

• 한국환경보건학회지
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• 제14권1호
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• pp.11-22
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• 1988

Calcium oxide, lithium oxide and titanium oxide were investigated as additives of zinc oxide for the removal of hydrogen sulfide at high temperature. This experiment was performed in the range of 1.0-2.0 vol.% H$_2$S concentration at 623-873 K reaction temperature, using a thermogravimetric analyzer. A pore blocking model was found to fit the reaction rate and the kinetics data were sucessfully expressed by this model. The reactions between additive sorbents and hydrogen sulfide were first order with respect to hydrogen sulfide concentration in a gaseous mixture with nitrogen. Among the used sorbents, ZnO-CaO 0.5 at.% and ZnO-TiO$_2$ 2.0 at.% sorbents had the best additive effects on the sulfidation reaction between additive sorbents and hydrogen sulfide, whereas the ZnO-Li$_2$O sorbents were ineffective.

• 센서학회지
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• 제26권4호
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• pp.228-234
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• 2017

Gas sensors based on metal-oxide-semiconductors are predominantly used in numerous applications including monitoring indoor air quality and detecting harmful substances such as volatile organic compounds. Nanostructures, e.g., nanoparticles, nanotubes, nanodomes, or nanofibers, have been widely utilized to improve the gas sensing properties of metal-oxide-semiconductors by increasing the effective surface area participating in the surface reaction with target gas molecules. Recently, 1-dimensional (1D) metal oxide nanostructures fabricated using glancing angle deposition (GAD) method with e-beam evaporation have been widely employed to increase the surface-to-volume ratio significantly with large-area uniformity and reproducibility, leading to promising gas sensing properties. Herein, we provide a brief overview of 1D metal oxide nanostructures fabricated using GAD and their gas sensing properties in terms of fabrication methods, morphologies, and additives. Moreover, the gas sensing mechanisms and perspectives are presented.

• Carbon letters
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• 제1권2호
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• pp.64-68
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• 2000

This paper describes the mechanical properties and oxidation resistance of carbon fibers with and without additions of boron oxide additives, and describes the changes in the properties resulting from increased heat treatment temperature (HTT) of the fibers. Carbon fibers in this experiment were heat treated up to $2800^{\circ}C$ each with and without boron oxide treated on the surface of fibers. In the case of boron oxide added carbon fibers, they do not show the improvement of tensile strength and modulus compared to those of no treated carbon fibers below $2200^{\circ}C$ since they are doped substitutionally with boron above $2600^{\circ}C$, which accelerate the graphitization of carbon fibers. Boron oxide implanted carbon fibers showed high resistance to oxidation, however, when carbon fibers were heat treated below $2200^{\circ}C$, they showed almost the same trend of air oxidation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.900-903
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• 2003

Using $DV-X{\alpha}$ method, it is calculated that nickel reduces the energy band gap of manganese oxide in 3 additives of titanium, nickel and tin. Therefore, it is estimated that the electrical conductivity of manganese-nickel oxide has the lowest value in 3 kinds of manganese oxide. The manganese oxide and manganese-nickel oxide which were produced by anodic deposition under $30mA/cm^2$ at room temperature in manganese sulfate and manganese-nickel sulfate solution were thermal-analyzed by DTA and TGA. The weight change of manganese oxide continuously decreased below $508^{\circ}C$ and kept constant at $518{\sim}600^{\circ}C$. However, the manganeses-nickel oxide transformed at the temperature range of $510{\sim}537^{\circ}C$. It is observed that the nickel addition to manganese oxide increases transformation temperature and its range.

• 한국세라믹학회지
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• 제19권2호
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• pp.127-132
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• 1982

This experiment has been carried out for the purpose of investigating the effect of additives on densification and grain growth in magnesium oxide by a two-step process; hot pressing and heat treating. MgO powder has been obtained by calcining extra reagent grade MgCO3 at 90$0^{\circ}C$ for 30 minutes, and additives have been added to $MgCO_3$ in the form of soluble salts-Al$(NO_3)_3$$. $9H_2O$ and $Cr(NO_3)_3$.9H_2O$. The hot pressing has been carried out with changes of soaking time at 125$0^{\circ}C$ under the pressure of 250kg/$\textrm{cm}^2$, and the heat treating also at same temperature. The initial particle size of MgO measured by particle size analyzer was 0.86 microns. Densification rate obeyed the equation D=K lnt + C, and grain growth rate obeyed the equation G-G0=kt1/2. It was vaporization of some $Cr_2O_3$ and formation of solid solution that had an influence on desification of MgO containing $Cr_2O_3$. Activation energy for grain growth of pure MgO was 62.4 kcal/mole, therefore grain growth was supposed to be diffusioncontrolled process. But after heat treatmeat, excess additives were expected to slow down the grain growth by the formation of second phase or the solute atoms at grainboundary.

• 태양에너지
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• 제19권2호
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• pp.37-44
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• 1999

Experimental investigation has been carried out to determine drag reducing effects of polymer additives for a plate type heat exchanger(evaporator or condenser) in OTEC power plant applications, where the pressure drop in the heat exchangers takes up $70{\sim}80%$ of the total pumping power in the existing system. The rate of drag reduction was investigated with various polymer concentrations and mass flow rates. Experiments were undertaken for a test section in Alfa-Laval plate heat exchanger utilizing Poly Ethylene Oxide(Mw $5{\times}10^6$) as polymer additives. Concentrations of polymer additives were 5, 10, 20, 30, 40, 50, 100, 200, 400 wppm at $25^{\circ}C$ and mass flow rates were 0.6kg/s, 0.7kg/s, 0.8kg/s and 0.9kg/s in normal operating ranges for a 15kW Alfa-Laval plate heat exchanger. The maximum effects of drag reductions were found at approximately 0.7kg/s of mass flow rate. The results show that there exists the optimum mass flow rate for the plate heat exchanger to obtain maximum drag reductions. Drag reduction of 20% means considerable savings in pumping power for a large size of OTEC plant.