Thermite welding is an exceptional process that does not require additional energy supplies, resulting in welded joints that exhibit mechanical properties and conductivity equivalent to those of the parent materials. The global adoption of thermite welding is growing across various industries. However, in Korea, limited research is being conducted on the core technology of thermite welding. Currently, domestic production of thermite powder in Korea involves recycling copper oxide (CuO). Unfortunately, controlling the particle size of waste CuO poses challenges, leading to the unwanted formation of pores and cracks during thermite welding. In this study, we investigate the influence of powder particle size on thermite welding in the production of Cu-thermite powder using waste CuO. We conduct the ball milling process for 0.5–24 h using recycled CuO. The evolution of the powder shape and size is analyzed using particle size analysis and scanning electron microscopy (SEM). Furthermore, we examine the thermal reaction characteristics through differential scanning calorimetry. Additionally, the microstructures of the welded samples are observed using optical microscopy and SEM to evaluate the impact of powder particle size on weldability. Lastly, hardness measurements are performed to assess the strengths of the welded materials.

For the selective catalytic reduction of NOx with ammonia (NH3-SCR), a V2O5WO3/TiO2 (VW/nTi) catalyst was prepared using V2O5 and WO3 on a nanodispersed TiO2 (nTi) support by simple impregnation process. The nTi support was dispersed for 0~3 hrs under controlled bead-milling in ethanol. The average particle size (D50) of nTi was reduced from 582 nm to 93 nm depending on the milling time. The NOx activity of these catalysts with maximum temperature shift was influenced by the dispersion of the TiO2. For the V0.5W2/nTi-0h catalyst, prepared with 582 nm nTi-0h before milling, the decomposition temperature with over 94 % NOx conversion had a narrow temperature window, within the range of 365-391 °C. Similarly, the V0.5W2/nTi-2h catalyst, prepared with 107 nm nTi-2h bead-milled for 2hrs, showed a broad temperature window in the range of 358~450 °C. However, the V0.5W2/Ti catalyst (D50 = 2.4 μm, aqueous, without milling) was observed at 325-385 °C. Our results could pave the way for the production of effective NOx decomposition catalysts with a higher temperature range. This approach is also better at facilitating the dispersion on the support material. NH3-TPD, H2-TPR, FT-IR, and XPS were used to investigate the role of nTi in the DeNOx catalyst.

Conventionally, metal materials are produced by subtractive manufacturing followed by melting. However, there has been an increasing interest in additive manufacturing, especially metal 3D printing technology, which is relatively inexpensive because of the absence of complicated processing steps. In this study, we focus on the effect of varying powder size on the synthesis quality, and suggest optimum process conditions for the preparation of AlCrFeNi high-entropy alloy powder. The SEM image of the as-fabricated specimens show countless, fine, as-synthesized powders. Furthermore, we have examined the phase and microstructure before and after 3D printing, and found that there are no noticeable changes in the phase or microstructure. However, it was determined that the larger the powder size, the better the Vickers hardness of the material. This study sheds light on the optimization of process conditions in the metal 3D printing field.

PURPOSES : The purpose of this study is to identify a gradation control method that minimizes the volatility of recycled aggregates to maintain the quality of reclaimed asphalt mixtures. METHODS : In this study, two types (0~13 and 0~10 mm) of recycled aggregate stockpiles with an extraction viscosity of 40,000 poise and a 19 mm hot asphalt mixture with virgin aggregates are used. The test methods are evaluated for plastic deformation resistance using the Hamburg wheel-tracking test and for low-temperature crack resistance using the dynamic modulus test. In the field, the performance is evaluated via an accelerated pavement test. RESULTS : The Hamburg wheel-tracking test shows good water resistance as well as less than 5 mm of deformation. The result of a dynamic modulus test at -5 °C shows a 92.9% low-temperature crack resistance as compared with that of the 19 mm dense grade hot-mix asphalt mixture. The result of the accelerated pavement test confirms that the performances of the 19 mm dense grade hot-mix asphalt mixture and reclaimed asphalt mixture are equal owing a 1.2 cm plastic deformation. CONCLUSIONS : By evaluating the plastic deformation resistance and crack resistance of the reclaimed asphalt mixture based on a stockpile gradation controlled at 0~10 mm via an indoor test, it is discovered that the plastic deformation resistance increases partially, whereas the crack resistance remains almost unchanged. The accelerated pavement test confirms that a performance equivalent to that of a 19 mm dense grade hot-mix asphalt mixture is achieved.

In this study, quantum dot-sensitized solar cells (QDSSC) using CdSe/ZnS quantum dots (QD) of various sizes with green, yellow, and red colors are developed. Quantum dots, depending their different sizes, have advantages of absorbing light of various wavelengths. This absorption of light of various wavelengths increases the photocurrent production of solar cells. The absorption and emission peaks and excellent photochemical properties of the synthesized quantum dots are confirmed through UV-visible and photoluminescence (PL) analysis. In TEM analysis, the average sizes of individual green, yellow, and red quantum dots are shown to be 5 nm, 6 nm, and 8 nm. The J-V curves of QDSSC for one type of QD show a current density of 1.7 mA/cm2 and an open-circuit voltage of 0.49 V, while QDSSC using three type of QDs shows improved electrical characteristics of 5.52 mA/cm2 and 0.52 V. As a result, the photoelectric conversion efficiency of QDSSC using one type of QD is as low as 0.53 %, but QDSSC using three type of QDs has a measured efficiency of 1.4 %.

노란잔산잠자리(멸종위기야생생물 II급) 약충은 내성천 일대 서식하는 것으로 알려져 있다. 2019년 3월 서식이 확인된 37개 지점의 하상 0.2㎡ 면적에서 채취한 퇴적물 입도 분석 및 개체수와의 상관관계를 분석하였다. 입도 분석 결과 ‘조립사’(500 ~ 1,000 ㎛) 52.5%, ‘극조립 사’(1,000 ~ 2,000 ㎛) 25.6%, ‘중립사’ (250 ~ 500 ㎛) 17.2%, ‘세립사’(125 ~ 250 ㎛) 3.1%, ‘극세립사’(63 ~ 125 ㎛) 1.0%, ‘실트’(63 ㎛미 만) 0.7% 순으로 나타났다. 노란잔산잠자리 약충의 개체수는 ‘극세립사’(63 ~ 125 ㎛), ‘세립사’(125 ~ 250 ㎛)와는 양의 상관관계를, ‘조립사’ (500 ~ 1.000 ㎛)와는 음의 상관관계를 나타내었다. 본 연구 결과를 통해 노란잔산잠자리 약충이 고운 모래를 서식처로 활용하고 있는 것을 확인 하였으며, 이러한 연구결과는 이후 내성천 일대 하상 환경변화 모니터링에 활용 할 수 있을 것이다.

Powder characteristics, such as density, size, shape, thermal properties, and surface area, are of significant importance in the powder bed fusion (PBF) process. The powder required is exclusive for an efficient PBF process. In this study, the particle size distribution suitable for the powder bed fusion process was derived by modeling the PBF product using simulation software (GeoDict). The modeling was carried out by layering sintered powder with a large particle size distribution, with 50 μm being the largest particle size. The results of the simulation showed that the porosity decreased when the mean particle size of the powder was reduced or the standard deviation increased. The particle size distribution of prepared titanium powder by the atomization process was also studied. This study is expected to offer direction for studies related to powder production for additive manufacturing.

A composite material was prepared for the bipolar plates of phosphoric acid fuel cells(PAFC) by hot pressing a flake type natural graphite powder as a filler material and a fluorine resin as a binder. Average particle sizes of the powders were 610.3, 401.6, 99.5, and 37.7 μm. The density of the composite increased from 2.25 to 2.72 g/cm3 as the graphite size increased from 37.7 to 610.3 μm. The anisotropy ratio of the composite increased from 1.8 to 490.9 as the graphite size increased. The flexural strength of the composite decreased from 15.60 to 8.94MPa as the graphite size increased. The porosity and the resistivity of the composite showed the same tendencies, and decreased as the graphite size increased. The lowest resistivity and porosity of the composite were 1.99 × 10−3 Ωcm and 2.02 %, respectively, when the graphite size was 401.6 μm. The flexural strength of the composite was 10.3MPa when the graphite size was 401.6 μm. The lowest resistance to electron mobility was well correlated with the composite with lowest porosity. It was possible the flaky large graphite particles survive after the hot pressing process.

한국쌀가공식품협회에 의하면 쌀가루 시장은 2008년 만톤, 2012년 5만톤으로 5배 성장하였으며, 2017년은 10만톤 2500억 규모로 쌀가루 시장은 급속히 성장하여 쌀 가공제품 생산에 이용하고 있다. 또한 쌀 사용량 현황은 55,794톤이며, 총매출액은 12,380억원에 이르고 있으나 현재 대부분의 떡 제조업체에서는 쌀을 물에 불려 빻아서 쓰는 습식제분법을 여전히 사용하고 있어서 시간과 노력이 많이 투입되고 있는 실정이다. 현재 건식 쌀가루를 이용하여 각종 가공품 제조를 위한 연구를 시도하고 있으나 아직까지 떡 종류별 사용기준이 명확히 없어 이의 기준설정이 필요하여 본 연구는 건식제분한 쌀가루를 이용하여 발효떡인 증편을 만들기 위한 조건설정의 기초자료로 활용하고자 시험을 실시하였다. 공시품종으로는 2016년에 재배된 한가루, 삼광, 다산1호, 한아름2호, 보람찬 등 5품종을 사용하였고, 제분기 Air mill(AM, Nara Machinery Co., LTD, Japan)을 사용하여 쌀가루 입도를 50, 100, 150㎛ 수준으로 각각 제조하였고, 대조구로는 관행의 습식제분한 쌀가루를 사용하였다. 시험결과 색도는 대조구 대비 품종별로는 명도(L)가 낮고 황색도(b)가 높았으며, 입도별로는 입도가 작을수록 명도가 높아지고 황색도가 낮아져서 대조구에 가까운 색도를 나타내었다. 호화특성으로는 대조구 대비 건식쌀가루 품종에서 호화온도에 이르는 시간이 짧았으며, setback(노화도)이 낮은 경향이었고, 품종별로는 한가루> 보람찬> 삼광> 다산1호, 한아름 1호의 순으로 노화가 덜 되는 경향이었으며, 입도별로는 큰 차이가 없었다. 대조구 대비 pH는 높고 산도는 비슷하였으며, 당도가 낮은 경향이었다. 당도는 입도가 작을수록 높았는데, 이는 발효과정 중 당화에 의한 영향으로 판단되었다. 색도는 대조구보다 명도는 낮고 황색도는 증가하는 경향이었으며, 물성은 대조구 대비 경도, 응집성, 점착성이 입도 50~100㎛간에는 비슷한 경향이었고, 입도 150㎛에서 경도와 점착성이 높아서 떡이 딱딱하게 굳는 경향이었다. 품종별로는 보람찬과 다산 1호가 부착성이 커서 달라붙는 정도가 컸다.

최근 두부시장은 화학응고제 무사용, 영양성분 강화, 간편화 등의 새로운 두부 형태 제품이 출시되었으며, 기류분쇄기 보급에 따라 초미세분말 제조가 가능하게 되면서 전두부 제조가 가능하여 졌다. 전두부는 콩가루를 이용하여 만들기 때문에 콩에 포함된 단백질, 식이섬유, 이소플라본 등의 전체적인 영양성분 섭취가 가능하여 영양이 우수하며, 부산물인 비지가 생산되지 않아 생산 편리성 및 환경오염 방지 효과가 있는 제조방식이다. 본 연구에서는 건식 콩가루를 이용하여 전두부 제조를 위한 조건설정의 기초자료로 활용하고자 시험을 실시하였다. ’16년에 재배된 대원콩 품종을 사용하였고, 제분기는 Air mill을 사용하여 콩가루 입도를 50, 100, 150㎛ 수준으로 각각 제조하였으며, 두유온도를 60, 80, 90, 100°C까지 끓인 후 두유의 적정 응고조건을 설정하고자 품질특성을 조사하였다. 전두부는 유미원 전두부제조기(HTM-100A)를 이용하여 5배의 물을 넣고 제조하였고, 대조구로는 압착두부를 사용하였다. 콩분말 입도에 따른 전두부 품질분석 결과 pH, 산도, 수분활성도는 거의 차이가 없었으며, 입도가 클수록 수분이 낮아지는 경향이었다. 7점척도법에 의한 관능조사 결과 대조구인 압착두부 대비 전반적인 기호도는 낮았지만 입도별로는 향이나 맛, 씹힘성에서 콩분말 입도 50㎛에서 가장 높았으며 전반적인 기호도는 50㎛ > 100㎛ ≥ 150㎛ 순이었고, 전자현미경 관찰결과 입도가 작을수록 두부구조가 치밀하였다. 두유 온도에 따른 전두부의 품질 비교 결과 전두부는 대조구 대비 수분함량, 산도, 당도, 염도가 전반적으로 높았으며, 두유 온도 60°C에서는 두부의 응고반응이 일어나지 않았으며, 80°C 이상에서 응고되기 시작하여, 90°C에서 가장 양호하였다. 100°C 이상에서는 단시간에 응고가 되어 두부의 모양이 고르지 않았다. 전두부의 일반세균수는 모두 규격기준(106cfu/㎖) 이하로, 90°C 이상에서는 거의 발생되지 않았다.

Recycled cenosphere, which is a hollow shaped particle from fly ash, has become attractive as a building material due to its light weight and excellent heat insulation and soundproof properties. In this paper, we investigated the effect of cenosphere size on the physical and optical properties. High brightness of cenosphere as raw material is required for a wide range of ceramics applications, particularly in fields of building materials and industrial ceramic tiles. Cenospheres were sorted by particle size; the microstructure was analyzed according to the cenosphere size distribution. Cenospheres were generally composed of quartz, mullite, and amorphous phase. Colour measurement corresponding to chemical composition revealed that the contents of iron oxide and carbon in the cenospheres were the major factors determining the brightness of the cenospheres.

본 연구에서는 입도에 따른 조미료 원료의 항산화 활성을 분석하여 원료에 따른 차이를 비교하고, 건강기능성이 우수한 천연조미료 원료로서 적합한 입도를 선정하고자 하였다. 8종(다시마, 멸치, 새우, 표고버섯, 양배추, 무, 마늘, 양파)의 조미료 원료를 일반분쇄를 통해 평균 300 μm 입도의 분말과 초미세분쇄를 통해 평균 23 μm 입도의 분말을 준비하여 DPPH와 ABTS 라디칼 소거능을 분석하였다. 모든 원료에서 항산화 활성은 농도에 비례하여 증가하였으며, DPPH 라디칼 소거능은 표고버섯이 가장 높게 나타났으며, ABTS 라디칼 소거능은 무가 가장 높게 나타났다. 입도에 따른 항산화 활성은 양배추와 표고버섯은 입도가 큰 일반분쇄 분말이 더 높게 나타난 반면, 나머지 원료는 입도가 작은 초미세분쇄 분말에서 더 높게 나타났다. 본 연구결과를 바탕으로 선정된 항산화 활성이 우수한 조미료 원료의 종류와 입도는 건강기능성 천연조미료 배합에 기초 자료로 활용될 수 있을 것으로 기대된다.

Neodymium-iron-boron (Nd-Fe-B) sintered magnets have excellent magnetic properties such as the remanence, coercive force, and the maximum energy product compared to other hard magnetic materials. The coercive force of Nd-Fe-B sintered magnets is improved by the addition of heavy rare earth elements such as dysprosium and terbium instead of neodymium. Then, the magnetocrystalline anisotropy of Nd-Fe-B sintered magnets increases. However, additional elements have increased the production cost of Nd-Fe-B sintered magnets. Hence, a study on the control of the microstructure of Nd-Fe-B magnets is being conducted. As the coercive force of magnets improves, the grain size of the Nd2Fe14B grain is close to 300 nm because they are nucleation-type magnets. In this study, fine particles of Nd-Fe-B are prepared with various grinding energies in the pulverization process used for preparing sintered magnets, and the microstructure and magnetic properties of the magnets are investigated.