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3 2021

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Characterizing the bacterial community during aerobic stabilization of livestock manure. Why should feedstock not be aged before composting?

Byun Seokjong, Lee Chang-Jun, Kim Sungpyo, Kim Jun-Young, Kang Soo-Mee, Cha Shang-Wha, Kim Hyun-Chul

Environment Protection Engineering

2021

Vol. 47, nr 1

41--51

The compositions of bacterial communities and populations during aerobic stabilization of livestock manure have been investigated, focusing on how the aging of feedstock affected the bacterial diversity of the composting mass. The livestock manure was divided into two groups – aged and fresh, and then used to prepare the feedstock with additives. Composting experiments were carried out for 15 days using a pilot-scale batch reactor with vacuum-induced aeration. Two different aeration rates were applied to the batch reactor, and their effectiveness was evaluated. Changes in total heterotrophic bacteria count and moisture content were monitored. The associated changes in bacterial community compositions were characterized using 16S ribosomal ribonucleic acid (rRNA) gene sequencing. The Firmicutes in the fresh manure decreased from 48 to 13% for the first ten days, and the dominant phylum shifted to the Proteobacteria (29%), Bacteroidetes (23%), Actinobacteria (20%), and others(15%). Under the given conditions, the use of relatively fresh manure was essential to preserve thediverse bacterial populations in the feedstock and enhance the bacterial diversity during aerobic stabilization.More research should be performed to investigate the degradability of emerging contaminants (e.g., antibiotics) in livestock manure using an engineered composting system providing well-controlled environmental conditions.

Production of High-Purity Tantalum Metal Powder for Capacitors Using Self-Propagating High-Temperature Synthesis

Lee Yong-Kwan, Sim Jae-Jin, Byeon Jong-Soo, Lee Yong-Tak, Cho Yeong-Woo, Kim Hyun-Chul, Heo Sung-Gue, Lee Kee-Ahn, Seo Seok-Jun, Park Kyoung-Tae

Archives of Metallurgy and Materials

2021

Vol. 66, iss. 4

935--939

In this study, high-purity tantalum metal powder was manufactured via self-propagating high-temperature synthesis. During the process, Ta2O5 and Mg were used as the raw material powder and the reducing agent, respectively, and given that combustion rate and reaction temperature are important factors that influence the success of this process, these factors were controlled by adding an excessive mass of the reducing agent (Mg) i.e., above the chemical equivalent, rather than by using a separate diluent. It was confirmed that Ta metal powder manufactured after the process was ultimately manufactured 99.98% high purity Ta metal powder with 0.5 μm particle size. Thus, it was observed that adding the reducing reagent in excess favored the manufacture of high-purity Ta powder that can be applied in capacitors.

Effects of ZrO2 and Al2O3 Addition on the Physical Properties of Cu-Mo-Cr Alloy by Liquid Phase Sintering

Cho Yeong-Woo, Sim Jae-Jin, Heo Sung-Gue, Kim Hyun-Chul, Lee Yong-Kwan, Byeon Jong-Soo, Lee Yong-Tak, Lee Kee-Ahn, Seo Seok-Jun, Park Kyoung-Tae

Archives of Metallurgy and Materials

2021

Vol. 66, iss. 3

683--687

In this study, the effect of the addition of ZrO2 and Al2O3 ceramic powders to Cu-Mo-Cr alloy was studied by examining the physical properties of the composite material. The ceramic additives were selected based on the thermodynamic stability calculation of the Cu-Mo-Cr alloys. Elemental powders, in the ratio Cu:Mo:Cr = 60:30:10 (wt.%), and approximately 0-1.2 wt.% of ZrO2 and Al2O3 were mixed, and a green compact was formed by pressing the mixture under 186 MPa pressure and sintering at 1250°C for 5 h. The raw powders were evenly dispersed in the mixed powder, as observed by scanning electron microscopy. After sintering, the microstructures, densities, electrical conductivities, and hardness of the composites were evaluated. We found that the addition of ZrO2 and Al2O3 increased the hardness and decreased the electrical conductivity and density of the composites.