Wyniki wyszukiwania - BazTech

1

Effect of Milling Time Parameter on the Microstructure and the Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 Alloys

Sharief P., Madavali B., Koo J. M., Kim H. J., Hong S., Hong S.-J.

Archives of Metallurgy and Materials

|

2019

|

Vol. 64, iss. 2

585-590

EN

Nanostructured thermoelectric materials receiving great attention for its high thermoelectric performance. In this research, nanostructured n-type Bi2 Te2.7 Se0.3 alloys have prepared using high energy ball milling and followed by spark plasma sintering. Also, we have varied ball milling time to investigate milling time parameter on the thermoelectric properties of n-type Bi2 Te2.7 Se0.3 powder. The powders were discrete at 10 min milling and later particles tend to agglomerate at higher milling time due to cold welding. The bulk fracture surface display multi-scale grains where small grains intersperse in between large grains. The maximum Seebeck coefficient value was obtained at 20-min milling time due to their lower carrier density. The κ values were decreased with increasing milling time due to the decreasing trend observed in their κL values. The highest ZT of 0.7 at 350 K was observed for 30-min milling time which was ascribed to its lower thermal conductivity. The Vickers hardness values also greatly improved due to their fine microstructure.

2

Effect Of DyMn Alloy-Powder Addition On Microstructure And Magnetic Properties Of NdFeB Sintered Magnets

Lee M.-W., Dhakal D. R., Kim T. H., Lee S. R., Kim H. J., Jang T. S.

Archives of Metallurgy and Materials

|

2015

|

Vol. 60, iss. 2B

1407--1409

EN

Micostructural change and corresponding effect on coercivity of a NdFeB sintered magnet mixed with small amount of DyMn powder was investigated. In the sintered magnet mixed with the DyMn alloy-powder Dy-rich shell was formed at outer layer of the main grains, while Mn was mostly concentrated at Nd-rich triple junction phase (TJP), lowering melting temperature of the Nd-rich phase that eventually improved the microstructural characteristics of the gain boundary phase. The coercivity of a magnet increased more than 3.5 kOe by the mixing of the DyMn alloy-powder.

3

De-Lubrication Behavior Of Novel EBS Based Admixed Lubricant In Aluminum P/M Alloy

Oh M. C., Seok H., Kim H. J., Ahn B.

Archives of Metallurgy and Materials

|

2015

|

Vol. 60, iss. 2B

1427--1431

EN

The objective of the present research is to develop a novel lubricant for Al-Cu-Mg P/M alloy and to address the effects of the lubricant and compaction pressure on sintered properties. A lubricant mixture consisting of Ethylene Bis Stearamide, Zn-Stearate, and fatty acid was newly developed in this study, and the de-lubrication behavior was compared with that of other commercial lubricants, such as Ethylene Bis Stearamide, Zn-Stearate, and Al-Stearate. Density and transverse rupture strength of sintered materials with each lubricant were examined, respectively. The microstructural analysis was conducted using optical microscope.

4

User requirements supporting the safe navigation in Korean Coast

Jeong J.S., Jeong J., Kim H.J., Kim S. Y.

Annual of Navigation

|

2013

|

No. 20

37--48

EN

This research aims at investigating the user requirements at the service level for safe navigation system, following e-navigation strategy implementation plan. The user requirements is surveyed to collect real-time navigational information and then to find out services through the presentation of the collected information. To provide the information on user needs for the system developer, a questionnaire survey has been made. Based on this surveys, this research investigated which navigational information is with higher priority for the safe navigation during ship operation by bridge team in harbour and in coastal and confined.

PL

W artykule przedstawiono wyniki badań wymagań użytkownika związanych z poziomem bezpieczeństwa nawigacji, stosownie do strategii wprowadzania e-nawigacji. Badano oczekiwania użytkowników odnośnie informacji nawigacyjnej dostarczanej w czasie rzeczywistym oraz sposobu jej prezentacji metodą ankietową. Wykonano przegląd kwestionariuszy dla ustalenia informacji o potrzebach użytkownika z myślą o projektantach systemów. Na bazie opisywanych badań ustalono, jakie informacje nawigacyjne cechują się najwyższym priorytetem w opinii użytkowników, zarówno w warunkach żeglugi przybrzeżnej, jak i w porcie lub akwenie ograniczonym.

5

Collision Scenario-based Cognitive Performance Assessment for Marine Officers

Kim H., Kim H. J., Hong S.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

|

2010

|

Vol. 4, no. 1

73--77

EN

The overall aim of this paper is to determine a fatigue factor that can be applied to human performance data as a part of a software program that calculates total cognitive performance. This program enables us to establish the levels of cognitive performance in a group of marine pilots in order to test a decision-making task based on radar information. This paper addresses one of the factors that may contribute to the determination of various fatigue factors: the effects of different work patterns on the cognitive performance of a marine pilot.

6

A study of the gas specificity of porous silicon sensors for organic vapours

Choi S. H., Cheng H., Park S. H., Kim H. J., Kim Y. Y., Lee K. W.

Materials Science Poland

|

2009

|

Vol. 27, No. 2

603--610

EN

A porous silicon sensor was investigated as a means to determine the response specificity for organic vapours. Porous silicon layers were fabricated by electrochemical anodization of p-type crystalline silicon in an HF ethanol solution under various conditions. The porous silicon sensors were placed in a gas chamber with various organic vapours, and the changes in electrical resistance under constant voltage of each sensor were used as detection signals. The sensors recorded various changes in resistivity for various organic vapours.

7

Quality control for the continuous casting process using electromagnetic transducers

Kim I. S., Son J. S., Kim H. J., Sung B. S.

Journal of Achievements in Materials and Manufacturing Engineering

|

2008

|

Vol. 31, nr 2

683-689

EN

Purpose: The continuous casting process is controlled automatically because various sensors and control units are connected to the mold and lower tundish roll. The solidification point in the process has a major factor on the quality of products, but the point has been predicted depending on the inaccurate calculated results from a computer simulation until now. Therefore, the objective of this paper is to develop the EMAT sensors for the measurement of the solidification point made by a through transmission technique based on the relationship between ultrasonic speed and measured temperature. Design/methodology/approach: The EMAT sensor is composed of an Elongated Spiral (ES) forming an eddy current and a permanent magnetic core generating a static magnetic field. ES coils of the sensor to measure 0.08mm, 0.2mm and 0.45mm as solidification points were employed respectively. Probes for receiving and transmitting which included 4 permanent magnets measuring 5 x 5 x 10mm, were placed together in one unit. Each coil was used to magnetic cores measuring 0.08mm and 0.45mm wound around it forty three times. The AI 75 x 75mm and 75 x 100mm simulators to identify whether the solidification point can be detected using an EMAT sensor, were machined with 2mm, 4mm, 8mm, 16mm and 32mm holes in diameter respectively. Findings: The electromagnetic interaction decreases in a high sphere of lift-off. Solidification point in a continuous casting processing could be detected through a series of tests with the use of a fabricated probe and the amplitude extent of ultrasonic wave decreases as the hole diameter of the simulators increases, Furthermore, the sensor developed is useful for measuring things such as lift-off. Research limitations/implications: A considerable amount of time and energy for miniaturization of the sensor and construction of an on-line system for a field installation should be saved by reducing mistake ratio and curtailing unnecessary processes. Originality/value: The solidification point in a continuous casting processing could be detected through a series of tests with the use of the developed EMAT sensor.

8

Microstructural parameter controlling weld metal cold cracking

Seo J. S., Kim H. J., Ryoo H. S.

Journal of Achievements in Materials and Manufacturing Engineering

|

2008

|

Vol. 27, nr 2

199-202

EN

Purpose: Facing with the practical limitation in lowering diffusible hydrogen content, the possible modification of weld microstructure would alleviate the flux cored arc (FACW) weld deposits from the risk of weld metal cold cracking. Therefore, it was aimed to identify and evaluate the effect of weld microstructure on cold cracking susceptibility of FCAW weld metals, and then to give a basic guideline for designing new welding consumables from the microstructural point of view. Design/methodology/approach: In order to figure out the parameter(s) that can quantify the microstructural susceptibility of multi-pass weld deposit, two sets of FCAW deposits having tensile strength of about 600MPa were prepared by controlling the Ni content to allow a sufficient variation in weld microstructure but with little change in weld metal strength. Cold crack susceptibility of those two chemistries was evaluated by' multi-pass weld metal cracking test' at various levels of diffusible hydrogen content. Findings: All of the cold cracks developed were Chevron-type cracks and the occurrence of such cracks was depending on the proportion of grain boundary ferrite as well as the diffusible hydrogen content. In fact, at the same level of diffusible hydrogen, 1.5%Ni wire showed better resistance to cold cracking than the 0%Ni even though that was higher in strength and carbon equivalent. This result could be explained by the difference in grain boundary ferrite content between those two welds based on the microstructural characteristics of Chevron cracking that preferentially propagates along grain boundary ferrite. Research limitations/implications: Detrimental effect of grain boundary ferrite against cold cracking has been addressed for Chevron-type cracks that is commonly developed in the ferritic weld metals having 600MPa strength level so that present result may not be valid for higher strength welds over 700MPa which shows vertical-type cracks. Practical implications: In addition to hydrogen control approach, microstructural modification in a way to reduce the proportion of grain boundary ferrite can be pursued for developing welding consumables with improved resistance to cold cracking. Originality/value: Proportion of grain boundary ferrite was proposed as a parameter that can quantify the microstructural susceptibility of multi-pass weld deposit. This fact can be used for users and manufacturers in selecting and designing welding consumables with better resistance to cold cracking.

9

A study on variation of shielding gas in GTA welding using finite element method

Kim I. S., Son J. S., Kim H. J., Chin B. A.

Journal of Achievements in Materials and Manufacturing Engineering

|

2006

|

Vol. 17, nr 1-2

249--252

EN

Purpose: Generally discrete alternate supply of shielding gas is a new technology which alternately supplies the different kinds of shielding gases in weld zone. In this study, welding characteristics under variation of alternate supply method of shielding gases in austenite stainless steel using a GTA welding process have been investigated and found the relationship between welding distortions and welding speed and different types of shielding gas and shielding gas supply. Design/methodology/approach: 2-D axisymmetric heat and fluid mathematical model about welding arc and weld pool has been developed for verifying the effect of alternate supply of shielding gas. The developed models were solved using a general thermofluid-mechanics computer program, PHOEINCS code, which is based on SIMPLE algorithm. Findings: The computed results showed that the developed computational models are very adequate to predict in the weld pool and bead geometry, and the technique of alternate supply of shielding gas should be useful to increase higher productivity, cost savings and better quality in arc welding. Research limitations/implications: The effect of alternate supply of shielding gas should be useful to apply for a narrow-gap welding process. Originality/value: The range of molten metal at the top of weld pool for supply of He shielding gas became wider than that for supply of Ar shielding gas. The developed computational models are very adequate to predict in the weld pool and bead geometry.

10

A study on electromagnetic transducers for the continuous casting process

Kim I. S., Son J. S., Kim H. J., Chin B. A.

Journal of Achievements in Materials and Manufacturing Engineering

|

2006

|

Vol. 17, nr 1-2

357--360

EN

Purpose: One of the areas in the continuous casting process that has not been definitively instrumented is a method for reliably locating the part of a continuously cast strand that remains liquid for a period after the outer portion has solidified. Therefore, this paper is focused on the measurement of the solidification point made by a through transmission technique based on the relationship between ultrasonic speed and measured temperature using an EMAT sensor. Design/methodology/approach: An EMAT (Electro Magnetic Acoustic Transducer) has been designed and fabricated with an elongated spiral coil and a permanent magnetic core. Al75×75mm and 75×100mm simulators with 2, 4, 8, 16 and 32 mm holes were produced and demonstrated that the location of the final solidification point during the continuous casting process can be monitored using a 1.0 MHz frequency. Findings: The solidification point in a continuous casting bloom could be detected through a series of tests with the use of a fabricated probe and the amplitude extent of ultrasonic wave decreases as the hole diameter of the simulators increases. Furthermore, through a test of lift-off effect it was found that the extent of amplitude decreases as lift-off increases, thus one of the most important factors for a field application. Research limitations/implications: As cutting speed and cutting length can be predicted from a miniaturization of the sensor and construction of an on-line system for a field installation, a considerable amount of time and energy can be saved by reducing mistake ratio and curtailing unnecessary processes. Originality/value: The measured ultrasonic waves allow for prediction of the casting speed necessary to correctly locate the liquid core and thereby maximize the benefits of soft reduction and the productivity of the machine.

11

Surface passivation of Hg0.8Cd0.2Te grown by MBE

Jeon H. C., Leem J. H., Ryu Y. S., Kang C. K., Kim N. H., Kang T. W., Kim H. J., Kim D. Y., Han M. S.

Opto-Electronics Review

|

1999

|

Vol. 7, No. 4

357-360

EN

We have investigated on the surface passivation of HgCdTe with various surface treatment method; chemical oxidation, photochemical oxidation, and sulfur treatment. The density of fast state, slow state and fixed charge are analyzed by C-V method. We confirm that the sulfur treatment is the best surface passivation condition showing low density of the fast states and the fixed charge.

12

Structural and magnetic properties of the Co-sputtered Fe-ceramic thin film

Yu S. C., Kim W. T, Han S. H., Kim H. J.

Electron Technology

|

1998

|

Vol. 31, No. 1

102-107

EN

The structure and magnetic properties of Fe-ceramics (Si₃N₄, Al₂O₃) thin films fabricated gy an rf magnetron co-sputtering technique were studied by X-ray diffractometry, magnetometry and electrical resustivity measurement. The concentration of Fe in the film decreases linearly with the area fraction of ceramic pieces on the target. As the area fraction of the ceramic pieses increases, the phase of thin film changes from bcc crystaline phase to amorphous phase, and the magnetization of the film decreased due to the decrease of Fe content and also due to the decreased of grain size. The electrical resistivity of thin films increases significantly with decreasing Fe content. Saturation magnetization of co-sputtered thin films could be explained by a mixture of two types of particles showing paramagnetism and ferromagnetism.