Molybdenum, valued for its high melting point and exceptional physical and chemical properties, is studied in diverse fields such as electronics, petrochemicals, and aviation. Among molybdenum oxides, molybdenum dioxide stands out for its higher electrical conductivity than other transition metal oxides due to its structural characteristics, exhibiting metallic properties. It is applied as pellets to gas sensors, semiconductors, and secondary batteries for its properties. Thus, research on molybdenum dioxide compaction and pressureless sintering is necessary, yet research on pressureless sintering is currently insufficient. This study synthesized MoO₃ powder via solution combustion synthesis and reduced it using the 3% hydrogen/argon gas mixture to investigate the effect of reduction temperature on the powder. Additionally, the reduced powder was compacted and subjected to pressureless sintering with temperature as a variable. The density and the microstructure of brown parts were analyzed and discussed.

The structure and magnetic properties of composite powders prepared by ball milling a mixture of Fe2O3 ‧ (0.4-1.0)Fe were investigated. Hysteresis loops and differential scanning calorimetry (DSC) curves are used to characterize the materials and to examine the effect of the solid state reaction induced by ball milling. The results showed that a solid state reaction in Fe2O3 ‧ (0.4-1.0)Fe clearly proceeds after only 1 h of ball milling. The system is characterized by a positive reaction heat of +2.23 kcal/mole. The diffraction lines related to Fe2O3 and Fe disappeared after 1 h of ball milling and, instead, diffraction lines of the intermediate phase of Fe3O4 plus FeO formed. The magnetization and coercivity of the Fe2O3 ‧ 0.8Fe powders were changed by the solid state reaction process of Fe2O3 by Fe during ball milling. The coercivity of the Fe2O3 ‧ 0.8Fe powders increased with increasing milling time and reached a maximum value of 340 Oe after 5 h of ball milling. This indicates the grain size of Fe3O4 was clearly reduced during ball milling. The magnetic properties of the annealed powders depend on the amount of magnetic Fe and Fe3O4 phases.

We report the effect of plastic deformation on the thermoelectric properties of n-type Bi2Te2.5Se0.5 compounds. N-type Bi2Te2.5Se0.5 powders are synthesized by an oxide-reduction process and consolidated via sparkplasma sintering. To explore the effect of plastic deformation on the thermoelectric properties, the sintered bodies are subjected to uniaxial pressure to induce a controlled amount of compressive strains (-0.2, -0.3, and -0.4). The shaping temperature is set using a thermochemical analyzer, and the plastic deformation effect is assessed without altering the material composition through differential scanning calorimetry. This strategy is crucial because the conventional hotforging process can often lead to alterations in material composition due to the high volatility of chalcogen elements. With increasing compressive strain, the (00l) planes become aligned in the direction perpendicular to the pressure axis. Furthermore, an increase in the carrier concentration is observed upon compressive plastic deformation, i.e., the donorlike effect of the plastic deformation in n-type Bi2Te2.5Se0.5 compounds. Owing to the increased electrical conductivity through the preferred orientation and the donor-like effect, an improved ZT is achieved in n-type Bi2Te2.5Se0.5 through the compressive-forming process.

In this study, porous Mo-5 wt% Cu with unidirectionally aligned pores is prepared by freeze drying of camphene slurry with MoO3-CuO powders. Unidirectional freezing of camphene slurry with dispersion stability is conducted at -25℃, and pores in the frozen specimens are generated by sublimation of the camphene crystals. The green bodies are hydrogen-reduced at 750℃ and sintered at 1000℃ for 1 h. X-ray diffraction analysis reveals that MoO3- CuO composite powders are completely converted to a Mo-and-Cu phase without any reaction phases by hydrogen reduction. The sintered bodies with the Mo-Cu phase show large and aligned parallel pores to the camphene growth direction as well as small pores in the internal walls of large pores. The pore size and porosity decrease with increasing composite powder content from 5 to 10 vol%. The change of pore characteristics is explained by the degree of powder rearrangement in slurry and the accumulation behavior of powders in the interdendritic spaces of solidified camphene.

We investigate the reduction of SnO2 and the generation of syngas(H2, CO) using methane(CH4) and hydrogen(H2) or a mixed gas of methane and hydrogen as a reducing gas. When methane is used as a reducing gas, carbon is formed by the decomposition of methane on the reduced Sn surface, and the amount of generated carbon increases as the amount and time of the supply of methane increases. However, when hydrogen is used as a reducing gas, carbon is not generated. High purity Sn of 99.8 % and a high recovery rate of Sn of 93 % are obtained under all conditions. The effects of reducing gas species and the gas mixing ratio on the purity and recovery of Sn are not significantly different, but hydrogen is somewhat more effective in increasing the purity and recovery rate of Sn than methane. When 1 mole of methane and 1 mole of hydrogen are mixed, a product gas with an H2/CO value of 2, which is known to be most useful as syngas, is obtained.

Metallic tantalum powder is manufactured by reducing tantalum oxide (Ta2O5) with magnesium gas at 1,073–1,223 K in a reactor under argon gas. The high thermodynamic stability of magnesium oxide makes the reduction reaction from tantalum oxide into tantalum powder possible. The microstructure after the reduction reaction has the form of a mixture of tantalum and magnesium oxide, and the latter could be entirely eliminated by dissolving in weak hydrochloric acid. The powder size in SEM microstructure for the tantalum powder increases after acid leaching in the range of 50–300 nm, and its internal crystallite sizes are observed to be 11.5 to 24.7 nm with increasing reduction temperatures. Moreover, the optimized reduction temperature is found to be 1,173 K as the minimum oxygen concentration is approximately 1.3 wt.%.

파이로 공정에서는 사용후핵연료 관리 공정 개발의 일환으로 산화 우라늄을 고온 용융염 전해질계에서 전기화학적 방법으로 환원시키기 위한 전해환원 공정이 개발되고 있다. 이에 따른 전해환원 공정의 반응기 설계를 위해서는 전기화학적 이론에 기초한 모델이 요구되고 있다. 본 연구에서는 상 분리를 설명하는 phase-field 이론에 기초하여 우라늄 산화물의 전해환원 모사를 위한 1차원 모델이 개발되었다. 모델은 우라늄 산화물 내 산소 원소의 확산과 펠렛 표면에서 전기화학 반응 속도를 나타내는 매개변수를 사용하여 외부로부터 내부로 진행되는 전해환원을 잘 모사하고 있으며 계산 결과 전체 전류는 산소 원소의 내부 확산에 크게 의존하는 것으로 나타났다. 전해환원 반응에 대한 모델은 대용량 장치 설계에 최적화된 조건 도출에 활용될 것으로 예상되며 장치 설계가 완료되면 공정 연계 모사에 직접 사용될 것으로 기대된다.

This study focuses on the fabrication of a WC/Co composite powder from the oxide of WC/Co hardmetal scrap using solid carbon in a hydrogen gas atmosphere for the recycling of WC/Co hardmetal. Mixed powders are manufactured by mechanically milling the oxide powder of WC-13 wt% Co hardmetal scrap and carbon black with varying powder/ball weight ratios. The oxide powder of WC-13 wt% Co hardmetal scrap consists of WO3 and CoWO4. The mixed powder mechanically milled at a lower powder/ball weight ratio (high mechanical milling energy) has a more rapid carbothermal reduction reaction in the formation of WC and Co phases compared with that mechanically milled at a higher powder/ball weight ratio (lower mechanical milling energy). The WC/Co composite powder is fabricated at 900℃ for 6 h from the oxide of WC/Co hardmetal scrap using solid carbon in a hydrogen gas atmosphere. The fabricated WC/Co composite powder has a particle size of approximately 0.25-0.5 μm.

Nitrogen (N)-doped protein-based carbon as platinum (Pt) catalyst supports from tofu for oxygen reduction reactions are synthesized using a carbonization and reduction method. We successfully prepare 5 wt% Pt@N-doped protein-based carbon, 10 wt% Pt@N-doped protein-based carbon, and 20 wt% Pt@N-doped protein-based carbon. The morphology and structure of the samples are characterized by field emission scanning electron microscopy and transmission electron micro scopy, and crystllinities and chemical bonding are identified using X-ray diffraction and X-ray photoelectron spectroscopy. The oxygen reduction reaction are measured using a linear sweep voltammogram and cyclic voltammetry. Among the samples, 10 wt% Pt@N-doped protein-based carbon exhibits exellent electrochemical performance with a high onset potential of 0.62 V, a high E1/2 of 0.55 V, and a low ΔE1/2= 0.32 mV. Specifically, as compared to the commercial Pt/C, the 10 wt% Pt@N-doped proteinbased carbon had a similar oxygen reduction reaction perfomance and improved electrochemical stability.

An optimum route to fabricate a hybrid-structured W powder composed of nano and micro size powders was investigated. The mixture of nano and micro W powders was prepared by a ball milling and hydrogen reduction process for WO3 and W powders. Microstructural observation for the ball-milled powder mixtures revealed that the nano-sized WO3 particles were homogeneously distributed on the surface of large W powders. The reduction behavior of WO3 powder was analyzed by a temperature programmed reduction method with different heating rates in Ar-10% H2 atmosphere. The activation energies for the reduction of WO3, estimated by the slope of the Kissinger plot from the amount of reaction peak shift with heating rates, were measured as 117.4 kJ/mol and 94.6 kJ/mol depending on reduction steps from WO3 to WO2 and from WO2 to W, respectively. SEM and XRD analysis for the hydrogen-reduced powder mixture showed that the nano-sized W particles were well distributed on the surface of the micro-sized W powders.

바나듐 산화환원 흐름 전지에 핵심적으로 사용되는 이온교환막은 일반적으로 양이온교환막을 사용하고 있으나 co-ion인 바나듐 이온의 투과에 의한 장기적 성능 저하 문제를 해결하기 어렵다. 따라서 본 연구에서는 바나듐 투과도 및 장 기 운전 안정성의 특성을 파악하기 위해 세 가지 다른 관능기를 보유한 음이온교환막을 제조하였다. 기저막으로는 다공성 폴 리에틸렌 필름에 benzyl chloride (VBC)과 divinylbenzene (DVB)을 충진 및 가교 중합하여 제조한 후, 세 가지 다른 아민 관 능기를 각각 도입하였다. 제조된 음이온교환막들에 대해 바나듐 이온 투과 정도 및 장기 운전 안정성을 관찰한 결과 triethylamine을 관능기로 적용한 음이온교환막에서 높은 에너지효율을 유지하면서도 가장 장기적 운전 안정성을 확보할 수 있었다.

질산성 질소는 수용액에서 상당히 안정하게 존재하기 때문에 제거하는 데에 있어 상당한 기술 이 요구된다. 또한 저 농도의 질산성 질소는 쉽게 제거되는 반면 고농도 질산성 질소는 제거하기가 힘들 다. 따라서 본 연구에서는 직경 3mm 정도의 아연 ball을 이용하여 고농도의 질산성 질소를 기체 질소의 형태로 제거하는 것을 목적으로 하였고, 다양한 반응조건에서 질산성 질소의 제거 특성을 실험하였다. 본 연구의 결과로 아연 ball을 사용하여 연속식 처리를 통한 질산성 질소의 처리효율은 약 80%정도 되었다. 하지만 폐수를 수소이온농도 2 정도의 산성 분위기로 유지시켜야하고 처리된 폐수를 중화 처리하여 방류 시켜야하는 등의 문제점은 상존하고 있다.

본 연구는 강산 분위기에서 아연의 산화 환원 반응을 통한 폐수 중 질산성 질소 제거에 관한 연구이다. 폐수에 황산(H2SO4)을 첨가하여 강산 분위기를 조성한 다음, 아연과 설파믹산을 넣어주게 되면 금속 아연이 산화되고, 이온화된 질산성 질소가 환원 처리되어 제거되는 연구이다. 산화 반응은 강산 분 위기일수록 반응이 잘 일어나기 때문에 pH 2.0~4.0 범위 중 pH 2.0에서 제거효율이 높았다. 설파믹산을 첨가함으로써 질산 이온을 최종 질소가스로 환원시켜 제거하는 것이 설파믹산이 존재하지 않을 때보다 H+ 이온 소모량이 적기 때문에 설파믹산을 투입하는 것이 유리하였다. 같은 아연 양에 따라 설파믹산을 넣지 않은 것은 질산성 질소가 46.0% 제거되는 반면, 설파믹산을 넣게 되면 질산성 질소가 93.0% 제거 된다. 본 실험에서 아연은 입자가 분말 형태로 제조되어 반응성이 다른 일반 아연 금속보다 크기 때문에 반응 후 1분 만에 제거 효율이 약 80.0% 로 매우 높게 나타났다.

This study is carried out to obtain basic data regarding oxidation and reduction reactions, originated on the recycling of waste tungsten hard scraps by oxidation and reduction processes. First, it is estimated that the theoretical Gibbs free energy for the formation reaction of WO2 and WO3 are calculated as ΔG1,000K= -407.335 kJ/mol and ΔG1,000K = -585.679 kJ/mol, from the thermodynamics data reported by Ihsan Barin. In the experiments, the oxidation of pure tungsten rod by oxygen is carried out over a temperature range of 700-1,000oC for 1 h, and it is possible to conclude that the oxidation reaction can be represented by a relatively linear relationship. Second, the reduction of WO2 and WO3 powder by hydrogen is also calculated from the same thermodynamics data, and it can be found that it was difficult for the reduction reaction to occur at 1,027oC, in the case of WO2, but it can happen for temperatures higher than 1127oC. On the other hand, WO3 reduction reaction occurs at the relatively low temperature of 827oC. Based on these results, the reduction experiments are carried out at a temperature range of 500-1,000oC for 15 min to 4 h, in the case of WO3 powder, and it is possible to conclude that the reduction at 900oC for 2h is needed for a perfect reduction reaction.

본 연구는 구리 아연 금속합금의 산화 환원 반응과 합성 알루미늄 실리케이트의 흡착 반응을 이용한 폐수 중 중금속 처리에 관한 연구이다. 극세사 형태로 제조된 구리 아연 금속합금이 수용액 중에 서 산화 환원반응에 의해 아연보다 이온화 경향이 작은 중금속은 환원 처리되고, 이온화 된 아연 및 미 반응 중금속은 흡착 처리하여 제거하는 연구이다. 극세사 형태로 제조된 금속합금 물질은 표면적이 커서 1회 처리만으로도 반응 평형에 도달하게 하여 효율이 높은 것으로 나타났다. 크롬(Cr+3)은 redox 반응 1 회 처리만으로도 100.0 % 제거 되었으며, 수은은 98.0 %, 주석 92.0 %, 구리는 91.4 % 정도 제거되었 다. 카드뮴, 니켈, 납도 각각 40.0 %, 50.0 %, 58.0 %가 제거 되었다. 크롬(Cr+3)은 아연과 이온화 경향 차이가 거의 없지만 제거 효율이 높은 것으로 나타났는데 이는 3가 크롬은 이온 상태로 존재하면 redox 반응에서 발생한 OH- 이온과 결합하여 수산화물 침전을 형성하는 것으로 판단된다. Redox 반응 후 증 가한 아연 및 미반응 중금속 농도를 알루미늄실리케이트를 1회 통과하여 거의 100.0 % 제거할 수 있었 다. 이는 합성 알루미늄 실리케이트의 비표면적이 크고 금속 이온의 흡착능력이 우수한 것으로 나타났으 며, 반응 후 알루미늄 이온은 증가하지 않는 것으로 보아 이온 교환이 아닌 흡착으로 아연 및 중금속 이 온들을 제거할 수 있는 것으로 나타났다.

본 연구는 통상 muntz metal로 불리는 구리와 아연의 합금 금속의 산화 환원 반응을 이용한 폐수 중 탈인 처리에 관한 연구이다. 연구를 위하여 200 ㎛ 두께의 극세사 형태로 제조된 구리 아연 금 속합금이 수용액 중에서 산화 환원 반응 작용으로 인하여 발생하는 OH radical을 이용하여 금속과 phosphate의 공침 반응에 의해 탈인 처리되는 원리를 이용한 인 처리법에 관한 연구이다. 인 제거 효율은 장시간의 순환 처리보다는 1회 처리에서 가장 제거 효율이 높았으며, 1시간 이후의 순환처리에서는 더 이 상의 제거효율을 보이지 않았다. 이는 금속합금 물질은 표면적이 넓어서 1회 처리만으로도 수용액의 pH 를 평형에 도달하게 하여 반응 효율이 높은 것으로 나타났다. 제조한 합성폐수의 pH 조건은 pH 5 에서 pH 9 사이이며, pH 8일 때 제거 효율이 가장 높았으며 pH 8 이상에서는 효율 증가를 보이지 않았다. 이때 인산염은 H2PO4 -, HPO4 2-의 형태로 가장 많이 존재하는 것으로 조사되었으며, 온도에 따른 인 제 거는 온도만의 영향이 아닌 타 영향인자와의 관계를 고려해야 하며 본 연구에서는 온도가 낮을수록 높은 인 제거 효율을 보였다.

In this study, the reduction kinetics and behaviors of oxides in the water-atomized iron powder have been evaluated as a function of temperature ranging 850-1000˚C in hydrogen environment, and compared to the reduction behaviors of individual iron oxides including Fe2O3, Fe3O4 and FeO. The water-atomized iron powder contained a significant amount of iron oxides, mainly Fe3O4 and FeO, which were formed as a partially-continuous surface layer and an inner inclusion. During hydrogen reduction, a significant weight loss in the iron powder occurred in the initial stage of 10 min by the reduction of surface oxides, and then further reduction underwent slowly with increasing time. A higher temperature in the hydrogen reduction promoted a high purity of iron powder, but no significant change in the reduction occurred above 950˚C. Sequence reduction process by an alternating environment of hydrogen and inert gases effectively removed the oxide scale in the iron powder, which lowered reduction temperature and/or shortened reduction time.