• 한국분말재료학회지
• /
• 제12권1호
• /
• pp.56-63
• /
• 2005

Ag powder was prepared from $AgNO_3$ by wet chemical reduction method using various reduction agent system involving $AgNO_3$, $AgNO_2$(AgCl) and Ag complex ion aqueous solution. The pure Ag powder could be prepared regardless of reaction system but the particle shape and distribution were affected very much according to the kind of reduction agents and reaction systems. The optimum reaction system for the preparation of the silver powder having the uniform particle shape and size distribution was Ag complex ion aqueous solution-reduction agent system and in particular, $H_2O_2$ and $C_6H_8O_6$as a reduction agent leaded the more uniform particle shape and size distribution.

• 한국분말재료학회지
• /
• 제13권4호
• /
• pp.278-284
• /
• 2006

Spherical Ag powder was prepared in the system of $AgNO_3\;and\;NaBH_4$ by wet chemical reduction method. The size of Ag powder was increased as the reaction temperature and the concentration of reducing agent was decreased in the constant concentration of dispersion agent. Optimum conditions of producing Ag powder having $1.39{\mu}m$ of D50 was 1M of $AgNO_3$, 0.5M of $NaBH_4$, 1.5g of Gelatine in the room temperature.

• 한국분말재료학회지
• /
• 제21권2호
• /
• pp.93-96
• /
• 2014

Cobalt coated tungsten carbide-cobalt composite powder has been prepared through wet chemical reduction method. The cobalt sulfate solution was converted to the cobalt chloride then the cobalt hydroxide. The tungsten carbide powders were added in to the cobalt hydroxide, the cobalt hydroxide was reduced and coated over tungsten carbide powder using hypo-phosphorous acid. Both the cobalt and the tungsten carbide phase peaks were evident in the tungsten carbide-cobalt composite powder by X-ray diffraction. The average particle size measured via scanning electron microscope, particle size analysis was around 380 nm and the thickness of coated cobalt was determined to be 30~40 nm by transmission electron microscopy.

• Bulletin of the Korean Chemical Society
• /
• 제31권10호
• /
• pp.2961-2966
• /
• 2010

Reduction of carbonyl compounds such as aldehydes, ketones, $\alpha,\beta$-unsaturated enals and enones, $\alpha$-diketones and acyloins was carried out readily with $NaBH_3CN$ in the presence of wet $SiO_2$ as a neutral media. The reactions were performed at solvent-free conditions in oil bath (70 - $80^{\circ}C$) or under microwave irradiation (240 W) to give the product alcohols in high to excellent yields. Regioselective 1,2-reduction of conjugated carbonyl compounds took place in a perfect selectivity without any side product formation.

• 한국분말재료학회지
• /
• 제18권3호
• /
• pp.244-249
• /
• 2011

Spherical nanosized cobalt powder with an average size of 150-400 nm was successfully prepared at room temperature from cobalt sulfate heptahydrate ($CoSO_4{\cdot}7H_2O$). Wet chemical reduction method was adopted to synthesize nano cobalt powder and hypophosphorous acid ($H_3PO_2$) was used as reduction agent. Both the HCP and the FCC Co phase were developed while $CoSO_4{\cdot}7H_2O$ concentration ranged from 0.7 M to 1.1 M. Secondary phase such as $Co(OH)_2$ and $CO_3O_4$ were also observed. Peaks for the crystalline Co phase having HCP and FCC structure crystallized as increasing the concentration of $H_3PO_2$, indicating that the amount of reduction agent was enough to reduce $Co(OH)_2$. Consequently, a homogeneous Co phase could be developed without second phase when the $H_3PO_2/CoSO_4{\cdot}7H_2O$ ratio exceeded 7.

• Journal of Industrial and Engineering Chemistry
• /
• 제67권
• /
• pp.448-460
• /
• 2018

Copper nanoparticle-doped and graphitic carbon nanofibers-covered porous carbon beads were used as an efficient catalyst for treating synthetic phenolic water by catalytic wet air oxidation (CWAO) in a packed bed reactor over 10-30 bar and $180-230^{\circ}C$, with air and water flowing co-currently. A mathematical model based on reaction kinetics assuming degradation in both heterogeneous and homogeneous phases was developed to predict reduction in chemical oxygen demand (COD) under a continuous operation with recycle. The catalyst and process also showed complete COD reduction (>99%) without leaching of Cu against a high COD (~120,000 mg/L) containing industrial wastewater.

• 펄프종이기술
• /
• 제35권5호
• /
• pp.26-36
• /
• 2003

The wet-end dynamics of a paper mill was analyzed to characterize its dynamic behavior during the grade change of paper. The model representing the wet-end section is developed based on the mass balance relationships written for the simplified wet-end white water network. From the linearization of dynamic model, higher-order Laplace transfer functions were obtained followed by the reduction procedure to give simple lower-order models in the form of 1$^{st}$-order or 2$^{nd}$ -order plus dead times. The dynamic response of the wet-end is influenced both by the white water volume and by the level of wire retention. Effects of key manipulated variables such as the thick stock flow rate, the ash flow rate and the retention aid flow rate on the major controlled variables were analyzed by numerical simulations. The simple dynamic model developed in the present study can be effectively used in the operation and control of paper mills.s.

• 한국분말재료학회지
• /
• 제20권3호
• /
• pp.191-196
• /
• 2013

Nano-sized cobalt powder was fabricated by wet chemical reduction method at room temperature. The effects of various experimental variables on the overall properties of fabricated nano-sized cobalt powders have been investigated in detail, and amount of NaOH and reducing agent and dropping speed of reducing agent have been properly selected as experimental variables in the present research. Minitab program which could find optimized conditions was adopted as a statistic analysis. 3D Scatter-Plot and DOE (Design of Experiments) conditions for synthesis of nano-sized cobalt powder were well developed using Box-Behnken DOE method. Based on the results of the DOE process, reproducibility test were performed for nano-sized cobalt powder. Spherical nano-sized cobalt powders with an average size of 70-100 nm were successfully developed and crystalline peaks for the HCP and FCC structure were observed without second phase such as $Co(OH)_2$.

• 한국분말재료학회지
• /
• 제24권2호
• /
• pp.141-146
• /
• 2017

$Bi_2Te_3$ powders are recovered by wet chemical reduction for waste n-type thermoelectric chips, and the recovered particles with different morphologies are prepared using various surfactants such as cetyltrimethylammonium bromide (CTAB), sodium dodecylbenzenesulfonate (SDBS), and ethylenediaminetetraacetic acid (EDTA). When citric acid is added as the surfactant, the shape of the aggregated particles shows no distinctive features. On the other hand, rod-shaped particles are formed in the sample with CTAB, and sheet-like particles are synthesized with the addition of SDBS. Further, particles with a tripod shape are observed when EDTA is added as the surfactant. The growth mechanism of the particle shapes depending on the surfactant is investigated, with a focus on the nucleation and growth phenomena. These results help to elucidate the intrinsic formation mechanism of the rod, plate, and tripod structures of the $Bi_2Te_3$ recovered by the wet reduction process.

• 펄프종이기술
• /
• 제39권3호
• /
• pp.12-23
• /
• 2007

Frequently spraying of natural starch slurry onto the formed wet web has been adopted to improve properties of paperboards. This conventional starch spraying technique, however, becomes less effective in strength improvement. In this study the effects of various factors including wet web dryness, quantity of starch slurry sprayed, and drying temperature on paperboard properties were investigated. Migration of starch granules into the webs appeared to cause a reduction in plybond strength when the web dryness was lower than this level. Wet webs should contain enough water to swell the starch granules, and at the same time they should be heated to a temperature high enough for complete cooking of the sprayed starches to occur. This suggested that preheating of the wet web can be employed to improve the plybond strength.