• Journal of the Korean Ceramic Society
• /
• v.42 no.10 s.281
• /
• pp.649-653
• /
• 2005

A mono-disperse Ni powders for multilayer ceramic capacitors were prepared in a large scale by solution reduction method using $NiSO_{4}$ $N_{2}$$H_{4}$and NaOH. The exothermic reactions such as Ni-complex formation between highly concentrated $NiSO_{4}$ and $N_{2}$$H_{4}$ and the reduction of $Ni^{2+}$ into Ni provided thermal energy sufficient for spontaneous solution-reduction reaction. Because well-defined Ni particles could be prepared without external heating, the present method was named as 'auto-thermal method'. The formation of Ni­complex, the precipitation of $Ni(OH)_{2}$ gel triggered by NaOH addition, and its reduction into Ni by dissolution-recrystallization route were the reaction mechanism. The preparation of mono-disperse and spherical Ni powder was attributed to uniform distribution of reducing agent $N_{2}$$H_{2}$ within $Ni(OH)_{2}$ gel due to the decomposition of$NiSO_{4}$-$N_{2}$ $H_{4}$ complex.

• Journal of Powder Materials
• /
• v.17 no.5
• /
• pp.390-398
• /
• 2010

Aqueous gold nanoparticle dispersion was synthesized by chemical reduction method using diethanolamine as reducing agent and polyethyleneimine as dispersion stabilizer. The synthesis conditions for the stable dispersion of the gold nanoparticle suspension were determined by changing the amount of the reducing agent and dispersant during the wet chemical synthesis procedures. The face centered cubic lattice structure of the gold nanoparticles was confirmed by using X-ray diffraction and the morphologies of the nanoparticles were observed by transmission electron microscope. The synthesized gold nanoparticle dispersion was concentrated by evaporating the dispersion medium at room temperature followed by the addition of ethyleneglycol as humectant for the increase of the elastic properties to obtain gold nanoparticle inks for direct ink writing process. The line patterns were obtained with the gold nanoparticle inks during the writing procedures and the morphologies of the fine patterns were observed by scanning electron microscope.

• Korean Journal of Materials Research
• /
• v.3 no.2
• /
• pp.103-110
• /
• 1993

Abstract It has been attempted to make the copper-graphite composites by deposition of copper on the surface of graphite through the hydrogen reduction of copper chlorides. Both KISH and natural graphites of less than 325 mesh were used as substrates and the hydrogen reduction also was conducted in the range of 350-50$0^{\circ}C$. The distribution of copper on the surface of graphite was found to increase with the decrease of reduction temperature. In addition. the partial pressure of hydrogen played an important role in the overall rate of reduction which was substantially dominated by the chemical reaction on the surface of each particle. It was concluded that the reduction temperature should be maintained as low as possible to accomplish the well distribution of copper in the composites.

• Korean Journal of Materials Research
• /
• v.33 no.2
• /
• pp.29-46
• /
• 2023

The electrochemical reduction of carbon dioxide (CO₂) to value-added products is a remarkable approach for mitigating CO₂ emissions caused by the excessive consumption of fossil fuels. However, achieving the electrocatalytic reduction of CO₂ still faces some bottlenecks, including the large overpotential, undesirable selectivity, and slow electron transfer kinetics. Various electrocatalysts including metals, metals oxides, alloys, and single-atom catalysts have been widely researched to suppress HER performance, reduce overpotential and enhance the selectivity of CO₂RR over the last few decades. Among them, single-atom catalysts (SACs) have attracted a great deal of interest because of their advantages over traditional electrocatalysts such as maximized atomic utilization, tunable coordination environments and unique electronic structures. Herein, we discuss the mechanisms involved in the electroreduction of CO₂ to carbon monoxide (CO) and the fundamental concepts related to electrocatalysis. Then, we present an overview of recent advances in the design of high-performance noble and non-noble singleatom catalysts for the CO₂ reduction reaction.

• Korean Journal of Materials Research
• /
• v.13 no.9
• /
• pp.631-634
• /
• 2003

To fabricate W-Cu nanocomposite powder, $WO_3$-CuO powder mixture was high-energetically ball-milled and subsequently hydrogen-reduced. The effect of ball-milling on the hydrogen-reduction behavior of$ WO_3$-CuO was investigated with non-isothermal hygrometric analysis during hydrogen-reduction. Increasing the ball-milling time, the reduction peak temperatures of humidity curves were shifted to low temperature. It was considered that the reduction temperature should be decreased because the specific surface area of each oxide considerably increased with increasing the ball-milling time. In case of ball-milling for 0 h, $WO_3$and CuO were independently hydrogen-reduced and W particles were nucleated on the surface of Cu adjacent to W by CVT. However, in case of ball-milling for 50 h, the aggregates of about 200-300 nm were observed. W particles of size below 30-50 nm were homogeneously distributed with Cu in the aggregates.

• Journal of Environmental Health Sciences
• /
• v.40 no.6
• /
• pp.484-491
• /
• 2014

Objectives: A radon emission reducing agent was prepared using charcoal and zeolite, and the amount was measured after coating construction materials with the agent. The availability of the radon emission reducing agent was evaluated. Methods: Construction materials (red brick, cement brick, and gypsum board) coated with reducing agent were placed in a chamber to measure radon emissions. The construction materials were coated one through three times. The spread volume for brick and gypsum board was 50 mL and 75 mL per application, respectively. The amount of radon emitted was measured by RAD-7 after 48 hours. Results: The reduction ratio increased with the number of coatings, and the reduction ratios for red brick, cement brick, and gypsum board were 63.3, 73.6, and 58%, respectively, in the case of three coatings of RA-1. The reduction ratios for red brick, cement brick, and gypsum board were 42.8, 58.1, and 26.2%, respectively in the case of three coatings with RA-2. RA-1 was slightly better than RA-2 in radon emission reduction. Conclusions: Radon emissions from construction materials decreased according to the concentration of reducing agent coating, and it was more effective than existing methods.

• Transactions of the Korean hydrogen and new energy society
• /
• v.17 no.3
• /
• pp.324-330
• /
• 2006

In this study, carbothermal reduction method was employed to synthesis Sn-Sb alloy powders from chief metal oxides with ultrafine sizes. The Sn-Sb powders consisting of ultrafine particles were formed at $800{\sim}900^{\circ}C$ by reduction of oxides. Those powders have high initial discharge capacities ($570{\sim}637\;mAh/g$) and discharge capacities of those powders maintain initial capacity after 20 cycle due to existence of ultrafine particles in powders and alloying effect of Sn-Sb.

• Korean Journal of Materials Research
• /
• v.11 no.12
• /
• pp.1052-1056
• /
• 2001

Pure tantalum powder has been produced by sodium as a reluctant, $K_2TaF_7$as a feed material and KCl/KF as a diluent in an inconel stainless steel bomb by the metallothermic reduction. The influence of experimental variable, such as temperature of reduction on the yield and characteristics of the Ta powder has been studied. As the temperature of the reduction was varied from$ 800{\circ}C~980{\circ}C$, the yield of tantalum powder increased from 41% to 56%. However no appreciable improvement was observed above$920{\circ}C$. The fraction of fine Ta Powder decreased appreciably with the increase of temperature, and particle size was$2~3{\mu}m$at reduction temperature of$920{\circ}C$.Therefore a reduction temperature of$920{\circ}C$was optimally fixed for subsequent runs.

• Journal of Magnetics
• /
• v.16 no.2
• /
• pp.104-107
• /
• 2011

In the present study, we systematically investigated the effect of mechanical milling on the magnetic properties of $Sm_2Fe_{17}N_x$ powders produced by the reduction-diffusion process. The Sm-Fe powders obtained by the reduction-diffusion process were composed of an $Sm_2Fe_{17}N_x$ single phase. After nitrogenation, the coercivity and saturation magnetization of the powders were 0.48 kOe and 13.32 kG, respectively. The particle size largely decreased down to less than $2\;{\mu}m$ in diameter after ball milling for 30 hours. However, there is no evidence that the $Sm_2Fe_{17}N_x$ was decomposed to Sm-N and ${\alpha}$-Fe even after ball milling for 30 hours. The coercivity was significantly improved up to 8.82 kOe after milling for 60 hours. However, the magnetization decreased linearly with the ball milling time.

• Journal of the Korean Ceramic Society
• /
• v.44 no.10
• /
• pp.542-547
• /
• 2007

We have determined an optimal reduction condition for NiO-based anode in single chamber solid oxide fuel cells that involve samaria-doped ceria (SDC) as an electrolyte. Optimal condition should not only induce sufficient reduction of NiO to Ni, but also prevent the reduction of SDC electrolyte in order to achieve high open circuit voltage (OCV) and power output. Thermodynamic consideration allowed us to determine the optimal anode reduction condition as $96%H_2-4%H_2O$ atmosphere at $250^{\circ}C$. This finding was in a good agreement with the experimental verifications by monitoring the conductivities of SDC and NiO under different reducing conditions.