In this study, ferric phosphate precursors were prepared by controlling precipitation time, and the resulting LiFe PO4 active materials were thoroughly investigated. Microscale LiFePO4 cathode materials, designed for high energy density at the cell level, were successfully synthesized through a 10 h co-precipitation. As the reaction time increased, smaller primary particles were aggregated more tightly, and the secondary particles exhibited a more spherical shape. Meanwhile, ammonia did not work effectively as a complexing agent. The carbon coated LiFePO4 (LiFePO4/C) synthesized from the 10 h ferric phosphate precursor exhibited larger primary and secondary particle sizes, a lower specific surface area, and higher crystallinity due to the sintering of the primary particles. Enhanced battery performance was achieved with the LiFePO4/C that was synthesized from the precursor with the smaller size, which exhibited the discharge capacity of 132.25 mAh ‧ g-1 at 0.1 C, 70 % capacity retention at 5 C compared with 0.1 C, and 99.9 % capacity retention after the 50th cycle. The better battery performance is attributed to the lower charge transfer resistance and higher ionic conductivity, resulting from smaller primary particle sizes and a shorter Li+ diffusion path.

Cs-137, a radioactive isotope of caesium, is a commonly occurring fission product that is generated during the nuclear fission of U-235 and other fissionable isotopes in both nuclear reactors and weapons. Due to its long half-life of about 30 years and propensity to accumulate in sediments and marine organisms, Cs-137 is considered a major radionuclide for environmental radioactivity monitoring. In April 2021, as the Japanese government decided to discharge Fukushima contaminated water into the sea, the monitoring of marine radioactivity in South Korea has become increasingly significant. In this study, as an initial step towards establishing a standardized procedure for analyzing radioactive caesium in seawater, the radioactivity of Cs-137 was analyzed on a 2 L of seawater spiked with 10 Bq of Cs-137 standard solution supplied by KRISS. The seawater was collected from Im-nang Beach, situated at a distance of approximately 2 kilometers from DIRAMS. The radioactivity of Cs-137 in seawater was determined according to the improved AMP procedure presented by M.Aoyama in 2000. The seawater was pretreated using Ammonium Phosphomolybdate (AMP) coprecipitation, which has a high selectivity for caesium (Kd = ~5500), and the activity of Cs-137 was determined by gammaspectroscopy and subsequently corrected via the weight yield. The weight yield of the dried AMP/Cs compound was more than 93%. For the gamma-spectroscopy analysis, the AMP/Cs compound was dissolved in a cylindrical U8 beaker with NaOH to ensure that its shape and volume were consistent with the CRM (KRISS, 221U890-1) used to calibrate the detector. The dissolved compound was then positioned directly onto the detector housing and subjected to a measurement duration of 80,000 seconds utilizing a p-type HPGe (Ortec, GEM60) with a relative efficiency of 54%. The activity of Cs-137 was determined to be 10.81 Bq, confirming the reproducibility of the AMP coprecipitation and weight yield methods. The present experiment was carried out using a 2 L sample, but a large volume of seawater would be required to achieve a sufficient minimum detectable activity (MDA) for Cs-137 in natural seawater. Thus, a standardized procedure for analysis of radioactive caesium in natural seawater will be established through the analysis of a large volume of seawater in future studies.

공침법을 이용하여 In2O3가 0-10 wt.% 첨가된 SnO2 계 미세 분말을 합성한 후, 스크린 인쇄법(screen printing)으로 후막형 가스센서를 제조하고 탄화수소(C3h8, C4h10) 가스에 대하여 가스 감응 특성을 조사하였다. In2O3는 SnO2의 입자 성장을 억제시키기 위하여 첨가해 주었는데, 600˚C에서 하소한 후에도 수 nm 크기의 미세한 입자를 얻을 수 있었다. 공침시 pH 값은 SnO2 의 입자 크기에 영향을 거의 미치지 않은 반면, In2O3 첨가량은 입자 크기와 미세 구조에 큰 영향을 주었다. In2O3 첨가량이 증가할수록 입자 크기는 감소하고 비표면적은 증가하였으며, 센세의 동작 온도를 약 500˚C로 하여 측정한 가스 감응 특성은 3wt.% 첨가했을 때 최대 감도를 나타내고 그 이상의 첨가량에서는 오히려 저하되었다. 3wt.%의 In2O3첨가시 SnO2의 입자 크기와 비표면적은 각각 9.5nm, 38m2/g이었다. 임피던스 측정으로부터 얻은 단일 반원의 Nyquist curve와 선형의 전류-전압(1-V)특성 곡선으로부터, In2O3를 첨가하여 수nm로 입자 크기를 억제한 SnO2 계 가스센서는 미세 입자들끼리 형성한 치밀한 응집체와 이들 간의 계면(boundary)에 의해서 가스 감응 특성이 영향을 받음을 알 수 있었다.

[ ZrO2+Y2O3 ] 계 분말결정을 ZrOCl2·8HO-YCl33·6H2O를 출발물질로 하여 공침법으로 합성하였다. 출발물질의 농도, 용액의 pH, 부분안정화제로 사용된 Y2O3의 양, 합성 후 소결온도 등 합성에 요구되는 실험변수에 따른 상 변이에 대한 연구결과를 바탕으로 실험조건을 고정시켜 3 mole% Y2O3를 포함하는 부분안정화 지르코니아 3YSZ를 합성할 수 있었다. 합성된 3YSZ의 소결특성에 따른 ZrO2 상전이에 대한 연구를 위하여 XRD, Raman, DTA 및 SEM을 사용하였다. 순수한 ZrO2에 비하여 합성된 3YSZ는 ZrO2+Y2O3 계에서 Y2O3의 함량 면화에 따라 순수한 ZrO2고온상의 단사정상에서 정방정상으로 상전이가 일어나게 되고 이때 Raman 스팩트럼이 낮은 파수쪽에서 현저하게 나타나는 것으로 쉽게 구분이 되었다.