Consideration of Diluents Selection and Input Amounts of the Hunter Process for Tantalum Production

Jae‑Jin Sim,Sang‑Hoon Choi,Yong‑Kwan Lee,Sung Gue Heo,Taek‑Soo Kim,Seok‑Jun Seo,Kyoung‑Tae Park 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7

Tantalum (Ta) is a heavy refractory metal with an atomic weight of 180.95 g/mol, a density of 16.6 g/cm3, and a high meltingpoint of 3017 °C. With its refractory characteristics, it shows excellent chemical and physical stability as well as corrosionand heat resistance at elevated temperatures. The demand for Ta metal and related compounds is increasing with the expansionof the electronics and chemical industries. The Hunter process was proven to be effective in producing Ta powder in1953. Hunter proposed a method in which potassium heptafluorotantalate (K2TaF7) was reduced by sodium (Na). Thus far,this process has been the primary commercial method to produce Ta powder. In this study, quantitative differences wereanalyzed for diluent selection. Additionally, consideration was given to changes in the caloric value depending on the inputamount of diluents. Finally, the optimum material input and the properties of the prepared Ta were analyzed. Stoichiometricratios of K2TaF7(1 mol), NaCl (6.2–6.7 mol), Na (5–7 mol) were weighed, to perform a metallothermic reduction reaction. After the reaction, the tantalum powder was recovered and the flush process was carried out. After that, it was dried in avacuum atmosphere. Physical properties such as oxygen concentration, PSA, ICP-OES, and XRD of powder were conductedto evaluate the characteristics of Ta powder that was finally manufactured.

초등학교 과학과 에너지영역의 STS 내용 변천

서승조,조태호,백남권,김성규,박강은,정인재 晋州敎育大學校 科學敎育硏究所 2001 科學敎育硏究 Vol.27 No.-

This research compared and analyzed the content ratio of the STS (Science-Technology-Society) Education and subjects and types of learning activities to determine the characteristics of STS education in science classes of elementary schools. In the 5th curriculum, the STS-related content on energy section took up 6.6% , in the 6th curriculum, compared with that of the 5th, the STS content ratio on the energy section increased 7.9% and the STS content on the energy section in the 7th curriculum showed an increased 20.8% proportion. Comparing the main subjects of the STS in the energy section for the science class according to curriculum in the 5th, they obviously have influenced technological development, energy, the development of space studies, and sociology of science, in that order. In the 6th curriculum. compared with that of the 5th, the energy section decreased and the sociology of science increased much. There were no significant changes in other subjects. In the 7th, the STS elements were distributed evenly but the extent of the STS main subjects reduced compared to that of the 6th. The STS education activities represented in science textbooks of elementary schools were mainly executed through discussion, research activities, and actual activities. Other activities such as role-playing, simulation tests, problem solving and decision making, data analysis, research design, case studies, etc. were hardly made.

폐콘크리트를 사용한 재생골재와 재생골재콘크리트의 공학적 특성 및 기준안 제시

서상구,박재성,허광희 建陽大學校 2000 建陽論叢 Vol.- No.8

The aim of this research is to characterize the waste concrete which is generated in large quantities in construction fields. In order to achieve this aim, htis research analyzes the engineering properties of recycled aggregate cnocrete classified by the factors such as aggregate composition and W/C. From the experimental results, it was found that the recycled aggregate concrete is rather good compared to general concrete in terms of workability and engineering properties. Besides, the reliable regression analysis equations between compressive strength and various experimental data for recycled aggregate concrete are presented. As a conclusion, this study shows that the recycled concrete is expected t4o be economically useful and also brings about positive result in aspect of environment.

섬이 있는 포켓의 가공을 위한 최적공구경로의 결정에 관한 연구

서만승,송재성,김혜령 동명정보대학교 2000 東明情報大學校論文集 Vol.3 No.-

In area milling such as pocket machining with islands, optimal tool path planning is very difficult problem. In this paper, new algorithm is presented, which determine it. Our algorithm is consisting of three modules; (1)generating the offset curves, (2)constructing and removing the offset loop and between loops, (3)finding the shortest path for minimal tool movement, and the uncut areas. For optimal tool path planning, we make use of the concepts of loop entity, which is chain of offset curves of contour curves. It is an entity that treat systematically both the intersection of offset curves and detection of an unuseful offset curves. And our algorithm is also applied to path planning for uncut area without the modification of our algorithm. Emprical tests show that the proposed algorithm fulfils its requirements.

Al₂O₃-ZrO₂/Al₂O₃-TZP 세라믹스의 기계적 특성 및 열충격 거동

서정철,박재성,남효덕 영남대학교 공업기술연구소 1999 工業技術硏究所論文集 Vol.27 No.2

The effects of the addition of either monoclinic ZrO2(pure) or tetragonal ZrO2 containing 5.35wt% Y2O3 (Y-TZP) on the mechanical properties and thermal shock resistance of Al2O3 ceramics were investigated. The addition of ZrO2(m) and Y-TZP increased sintered density of Al2O3. The Vickers hardness also increased as the volume fraction of Y-TZP increased going through a maximum at 20wt%. The hardness of the specimens was found to be dependent on the sintered density. The higher volume fraction of either ZrO2(m) or Y-TZP resulted in the higher fracture toughness of the composite was. This result may be taken as evidence that toughening of Al2O3 can be achieved by not only the transformation toughening but microcrack toughening of ZrO2. The thermal shock property for Al2O3-ZrO2 composites was improved by increasing the volume fraction of monoclinic ZrO2(pure). The grain size increased as the volume fraction of ZrO2 did.

Chlorhexidine과 fluoride 성분의 varnish가 타액 내 mutans streptococci 수에 미치는 효과

서정아,김재곤,백병주,양연미,이용희,김상훈 大韓小兒齒科學會 2004 大韓小兒齒科學會誌 Vol.31 No.4

본 연구의 목적은 chlorhexidine(Cervitec)과 fluoride(Fluor-protector) 성분을 각각 포함한 varnish를 치아에 적용하였을 때 타액내의 mutans streptococci의 수의 감소에 미치는 효과를 알아보기 위한 것이다. 전북대학교 치과대학생 40명을 대상으로 하여 mutans streptococci 균종 수를 평가하였으며, 이들을 무작위로 네 군으로 나누어 다음과 같이 varnish를 적용하였다; A) varnish를 적용하지 않은 군(n=10), B) chlorhexidine varnish 적용군(n=10), C) fluoride varnish 적용군(n=10), D) chlorhexidine과 fluoride varnish를 모두 적용한 군(n=10), Mutans streptococci 수 측정에는 Orion diagnostica 사의 Dentocult SM을 사용하였다. Varnish를 적용하지 않은 상태에서 1차로 Mutans streptococci 수를 측정한 후 각각의 varnish를 적용하였으며, varnish 적용 12주 후 다시 측정하여 기록하였다. 모든 실험군(group B, C, D)에서 12주 후에 측정한 Mutans streptococci 수가 감소한 개체가 증가한 개체보다 많았으나 통계적으로 유의한 차이는 보이지 않았다(p>0.05). 실험에 사용된 어떠한 varnish도 적용 12주 후에 타액 내 mutans streptococci 수에 통계적으로 유의할 만한 변화를 주지는 못하는 것으로 나타났다(p>0.05). The objective of the present prospective trial was to compare the efficacy of chlorhexidine(Cervitec), Fluoride(Fluorprotector) and combination of chlorhexdine and fluoride varnishes in decreasing the level of salivary mutans streptococci. Forty healthy students of school of dentistry, Chonbuk national university were investigated to evaluate mutans streptococci(MS) counts and randomized into four groups to treat with the experimental varnishes: A) untreated group(n=10), B) chlorhexidine group(n=10), C) fluoride group(n=10), D) chlorhexidine and fluoride group(n=10). Dentocult SM^(�)(Orion Diagnostica) strip method was used for measurement of the level of mutans streptococci in saliva. Stimulated saliva were collected at baseline for mutans streptococci counts evaluation(ms1), 12 weeks later the completion of each varnish treatment, mutans streptococci counts were re-evaluated. In varnish group with chlorhexidine, fluoride and combination of chlorhexidine and fluoride, the level of mutans streptococci was lower after 12 weeks than at baseline, but there were no significant differences in saliva(p>0.05), when compared with baseline. After 12 weeks, a remarkable reduction was still found in the subjects with high level of mutans streptococci at baseline, but not different in the low and moderate level of mutans streptococci(p>0.05).

화학환원법을 이용한 Ag 나노분말의 합성

서원식,김태환,성재석,송기창 한국화학공학회 2004 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.42 No.1

화학환원법을 이용하여 AgNO_(3) 수용액에 환원제를 첨가시키는 방법으로 Ag분말을 제조하였으며, 이 과정 중 환원제의 종류 변화(N_(2)H_(4), NaBH_(4))가 얻어진 분말의 특성 변화에 미치는 영향을 살펴보았다. 또한 분말합성 과정 중 계면활성제(Tween20)를 수용액에 첨가하여 계면활성제가 분말의 특성에 미치는 영향도 살펴보았다. 제조된 분말의 SEM 측정결과 환원제로 sodium borohydride(NaBH_(4))를 사용하면서 제조된 Ag 분말의 크기는 약 0.3㎛인 반면 hydrazine(N_(2)H_(4))을 사용하여 제조된 분말의 크기는 약 1㎛로 sodium borohydride를 사용해 제조한 분말의 크기가 더 작고 고른 크기 분포를 보였다. 또 환원제로써 hydrazine을 사용시 계면활성제를 첨가하여 제조된 Ag 나노분말의 크기는 50nm정도로 계면활성제를 첨가하지 않고 제조된 분말보다(1㎛) 입자의 크기가 더 작고 균일한 입도 분포를 나타내었다. Silver powders were prepared by chemical reduction method using reductants in AgNO_(3) aqueous solution. The effect of the type of reductants(N_(2)H_(4), NaBH_(4)) was investigated on the properties of the obtained powders. In addition, the effect of the addition of asurfactant(Tween 20) during particle synthesis was studied. The Ag powders prepared using the sodium borohydride as a reductant were found to be 0.3㎛ in particle diameter, while those using the hydrazine showed 1㎛ in particle diameter. The mean particle size of Ag nanopowders, prepared by the addition of Tween 20 as a surfactant, was 50㎚, which is smaller than 1㎛ powders formed without the surfactant.

전립선암과 전립선비대증 환자에서 혈청 유리 및 총전립선특이항원 측정의 의의

서혁준,박형민,권태균,정성광,김법완,이재태 경북대학교 의학연구소 2000 경북대학교병원의학연구소논문집 Vol.4 No.1

Purpose: This study was peformed to investigate whether the free to total PSA ratio(F/T PSA ratio) offers a better discriminant for the detection of patient with prostatic cancer(CaP) and those with benign prostatic hyperplasia(BPH) than serum total PSA alone. Materials and Methods: From September 1996 to February 1999, free and total PSA levels were measured on frozen sera samples of 154 men with BPH and 46 with CaP using immunoradiometric assay. Results: In all subjects, the mean total PSA was significantly higher in CaP group(72.57±66.58ng/ml) than BPH group(3.12±4.10ng/ml). The mean PSAD was significantly higher in CaP group(1.64± 1.86) than BPH group(0.08±0.01). The mean F/T PSA ratio was significantly lower in CaP group(0.19± 0.07) than BPH group(0.30±0.13). Among 41 subjects whose total PSA were between 4-20ng/ml, the mean PSAD was significantly higher in CaP group(0.37±7.16) than BPH group(0.17± 0.07), but the mean F/T PSA ratio was not significantly different between CaP(0.19± 0.10) and BPH group(0.25±7.13). By comparing the sensitivity and specificity of total PSA alone, PSAD and F/T PSA ratio on receiver operating characterislic (ROC) Cutie in all subiects and subiects with total PSA between 4-20ng/ml, F/T PSA ratio had no superiority than total PSA alone and PSAD for discrimination between CaP and BPH. Conclusions: We suggest that the F/T PSA ratio is not superior to total PSA alone and FSAD in the detection of prostatic cancer, and further evaluation of the usefulness of F/T PSA ratio should be required.

혈관신경성부종의 문헌적 고찰 및 증례 보고

서보영,임재석,김 온,김성문 大韓顎顔面成形外科學會 1989 Maxillofacial Plastic Reconstructive Surgery Vol.11 No.1

Angioneurotic edema is rarely seen in dental practice and manifested by acute attacks of swelling of the extremities, face, airway, or abdominal visera, occuring spontaneously and suddenly or secondary to trauma. Two types are recognized : hereditary and nonhereditary. Prophylatic therapy may be used by fresh frozen plasma or antifibrinolytic agents in hereditary type. Good supportive care for acute attacks, together with a knowledge of course of the disease, can prevent asphyxiation from airway obstruction. A case of acute angioneurotic edema of the facial area in a 19-year-old man is presented in conjunction with a review of the literature. Angioneurotic edema attacks him acutely after the extraction of the lower, right 3rd molar.

기업ㆍ민간 스포츠센터 소비자의 이용만족도 비교 분석

서봉한,노영태,이상봉,이영덕,정용제,박병주 부산대학교 체육과학연구소 2000 體育科學硏究所 論文集 Vol.16 No.-

The purpose of this study was to analyze differences between satisfaction of members who attend sports center managed by enterprise and those of members who attend sports center managed by private. We hoped through these analysis, consumer could get useful date for choosing sports center and managers could gets data for establishing effective marketing strategy. The objective of this study was 500 members of sports center managed by enterprise and by private in city of Ulsan. Questionnaires were completed through self-administration. We used SPSSWIN 8.0 to analyze gathered data Chi-square test was used for analyzing conditions of members. All statistical data were tested with p〈.05. The result were as follows. 1.Satisfaction of facility and service 1) According to sex, men showed higher satisfaction with enterprise center. In detail, men showed higher satisfaction with enterprise center in exercise facility, dressing room, shower room and sanitation. 2) According to age, 30's show the highest satisfaction with enterprise center in all items but in parking lot. In the comparison of whole mean, 50's showed the highest satisfaction with both enterprise and private center. 3) According to education level, more than college graduation, college student or dropout and high school graduation showed their satisfaction in turn in enterprise center and college student or dropout, more than college graduation and high school graduation showed their satisfaction in turn in private center. In the comparison of whole mean, the satisfaction of enterprise center was higher than that of private center. 4) According to income, all groups but group(100-149 million won) showed higher satisfaction with enterprise center in the comparison of whole mean. 5) According to the type of job, salary worker and functional occupation showed higher satisfaction with enterprise center and educational occupation and owner of small business or store showed higher satisfaction with private center. 2.Satisfaction of offered service 1) According to sex, men showed higher satisfaction with both centers. 2) According to age, in the comparison of whole mean, 50's showed the highest satisfaction with both enterprise and private center. 3) According to education level, more than college graduation, college student and high school graduation showed their satisfaction in turn with both centers. In the comparison of whole mean highschool graduation and college graduation showed the highest satisfaction with enterprise center and college student or dropout showed the highest satisfaction with private center. 4) According to income, all groups but the group(250-299 million wons) showed higher satisfaction with enterprise center in the comparison of whole mean. 5) According to the type of job, salary worker and functional occupation showed higher satisfaction with enterprise center and worker in special jobs and owner of small business or store showed higher satisfaction with private center.