• The korean journal of orthodontics
• /
• v.40 no.1
• /
• pp.40-49
• /
• 2010

Objective: The aim of this research was to evaluate the mechanical properties (MP) and degree of the phase transformation (PT) of martensitic (M-NiTi), austenitic (A-NiTi) and thermodynamic nickel-titanium wire (T-NiTi). Methods: The samples consisted of $0.016\;{\times}\;0.022$ inch M-NiTi (Nitinol Classic, NC), A-NiTi (Optimalloy, OPTI) and T-NiTi (Neo-Sentalloy, NEO). Differential scanning calorimetry (DSC), three-point bending test, X-ray diffraction (XRD), and microstructure examination were used. Statistical evaluation was undertaken using ANOVA test. Results: In DSC analysis, OPTI and NEO showed two peaks in the heating curves and one peak in the cooling curves. However, NC revealed one single broad and weak peak in the heating and cooling curves. Austenite finishing ($A_f$) temperatures were $19.7^{\circ}C$ for OPTI, $24.6^{\circ}C$ for NEO and $52.4^{\circ}C$ for NC. In the three-point bending test, residual deflection was observed for NC, OPTI and NEO. The load ranges of NC and OPTI were broader and higher than NEO. XRD and microstructure analyses showed that OPTI and NEO had a mixture of martensite and austenite at temperatures below Martensite finishing ($M_f$). NEO and OPTI showed improved MP and PT behavior than NC. Conclusions: The mechanical and thermal behaviors of NiTi wire cannot be completely explained by the expected degree of PT because of complicated martensite variants and independent PT induced by heat and stress.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.9
• /
• pp.502-507
• /
• 2016

Vanadium dioxide, $VO_2$, is a thermochromic material that exhibits a reversible metal-insulator phase transition at $68^{\circ}C$, which accompanies rapid changes in the optical and electronic properties. To decrease the transition temperature around room temperature, a number of studies have been performed. The phase transition temperature of 1D nanowire $VO_2$ with a 100 nm diameter was reported to be approximately $29^{\circ}C$. In this study, 1D or 2D nanostructured $VO_2$ was grown using the vapor transport method. Vanadium dioxide has a different morphology with the same growth conditions for different substrates. The 1D nanowires $VO_2$ were grown on a Si substrate ($Si{\setminus}SiO_2$(300 nm), whereas the 2D & 3D nanostructured $VO_2$ were grown on an exfoliated graphene nanosheet. The crystallographic properties of the 1D or 2D & 3D nanostructured $VO_2$, which were grown by thermal CVD, and exfoliated-transferred graphene nanosheets on a Si wafer which was used as substrate for the vanadium oxide nanostructures, were analyzed by Raman spectroscopy. The as-grown vanadium oxide nanostructures have a $VO_2$ phase, which are confirmed by Raman spectroscopy.

• Journal of the Mineralogical Society of Korea
• /
• v.32 no.2
• /
• pp.79-86
• /
• 2019

The white aluminum phases in acid mine drainage usually precipitates when mixed with stream waters with relatively high pH. The minerals in white precipitates play important roles in controlling the behavior of heavy metals by adsorbing and coprecipitation. By the phase transition of these minerals in white precipitates, dissolution and readsorption of heavy metals may occur. This study was conducted to obtain preliminary information on the phase transition of the mineral phases in white precipitates. In this study, the mineral phase changes in the white precipitates collected from the stream around Dogye Mining Site over time were investigated with different pH values and temperatures. White precipitates consist mainly of basaluminite, amorphous $Al(OH)_3$ and a small amount of $Al_{13}$-tridecamer. During aging, the incongruent dissolution of the basaluminite occurs first, increasing the content of the amorphous $Al(OH)_3$. After that, pseudoboehmite is finally precipitated following the precursor phase of pseudoboehmite. At $80^{\circ}C$, this series of processes was clearly observed, but at relatively low temperatures, no noticeable changes were observed from the initial condition with coexisting basaluminite and amorphous $Al(OH)_3$. At high pH, the desorption of $SO{_4}^{2-}$ group in basaluminite was initiated to promote phase transition to the pseudoboehmite precursor. Over time, the solution pH decreases due to the dissolution and phase transition of the minerals, and even after the precipitation of pseudoboehmite, only the particle size slightly increased but no clear cystal form was observed.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.24 no.6
• /
• pp.189-196
• /
• 2020

When concrete member become large like in high rise buildings, hydration heat makes temperature difference inside and outside and cause cracks. The method of using latent heat material as heat reducer could be more accessible, usable and efficient than other methods. Therefore, many studies using PCM as heat reducer are being conducted. Since heat reducer have different reacting temperature, they may be affected by environmental factors like ambient and concrete mixing temperature but studies issuing this are insignificant. Therefore, this paper attempt to evaluate the hydration heat characteristics and quality of concrete using strontium-based PCM under hot weather conditions. As a result, when the strontium-based hydration heat reducer was mixed 3wt.% and 5wt.% in hot weather condition, hydration heat speed and heating rate could be reduced by 8%, 21%, and 75, 85 minutes compared to OPC, respectively. This is considered to be the phase change reaction is relatively promoted when the temperature is high and cause improve performance than room condition result. Later, comparing the efficiency of other types of P.C.M in hot weather condition, and conduct detailed reviews on the strength development in long-term age.

• Economic and Environmental Geology
• /
• v.56 no.1
• /
• pp.13-21
• /
• 2023

X-ray powder diffraction study was conducted on the bulk modulus and phase transition behavior of synthetic zeolite X under high temperature and high pressure. Water and HCO₃^- solution were used as a PTM. Sample was heated and pressurized up to 250 ℃ and 5.18 GPa. The change of unit cell volume and phase transition were observed by X-ray diffraction. The lattice constants and unit cell volume of zeolite X, gmelinite, natrolite, and smectite were calculated using the GSAS2 program to which Le Bail's whole powder pattern decomposition (WPPD) method was applied. The bulk modulus of each zeolite X and smectite were calculated using the EosFit program to which the Birch-Murnaghan equation was applied. The bulk modulus of zeolite X is 89(3) GPa in water run, and zeolite X is 92(3) GPa in HCO₃^- solution run. In both run, pressure induced hydration (PIH) occurred due to the inflow of PTM into the zeolite X framework at initial pressure. Zeolite X transited to gmelinite, natrolite, and smectite in water run. Zeolite X, however, transited to smectite in HCO₃^- solution run. Interzeolite transformation occurred in water run, and did not occur in HCO₃^- solution run, which is assumed that conflict between the environment to form zeolite and the pH of the HCO₃^- solution.

• 전기의세계
• /
• v.18 no.4
• /
• pp.16-21
• /
• 1969

3상유도전동기에 정현파형의 불평형 3상전압 혹은 고주파성분을 포함한 동일파형의 3상전압을 인가했을때의 전동기의 특성에 대ㅏㄴ 것은 발표되어 있지만, 고주파성분을 포함하고, 동시에 동일파형이 아닌 3상전압을 인가했을때의 특성에 대한것은 별로없는 것 같다. 수전단에서는 이러한 전압이 실제 인가되므로, 본논문은 고주파성분을 포함한 동일파형이 아닌 3상전압을 중성점이 접지되어 있지않은 3상유도전동기에 인가할때의 전동기의 특성을 몇가지 가정하에 작성한 등가회로에 의하여 수식적으로 해석하고 이를 실험에 의하여 확인하였다.

• Proceedings of the Korean Fiber Society Conference
• /
• 2002.04a
• /
• pp.285-288
• /
• 2002

옥타데칸[$CH_3$[C $H_2$]$_{l6}$$CH_3$]은 상전이 물질(phase change material)이며, 상전이 물질은 상변화를 통해 주변의 온도가 상승하면 녹으면서 열을 흡수하고, 주변의 온도가 낮아지면 결정화(crystallization)하면서 열을 방출하는 축열ㆍ방열성을 반복적으로 나타내는 에너지 물질(enthalpic substance)이다[1, 2]. 옥타데칸은 메탄계열 탄화수소로서 파라핀류(paraffins)에 해당된다. (중략)략)

• Korean Journal of Optics and Photonics
• /
• v.8 no.6
• /
• pp.461-465
• /
• 1997

The 3rd order nonlinear optical susceptibility was measured through the self-induced ellipse rotation. The phase separation temperature increases with the increase of salt and it decreases with the increase of glycerol.

• Ceramist
• /
• v.12 no.5
• /
• pp.33-38
• /
• 2009

• Bulletin of Food Technology
• /
• v.12 no.3
• /
• pp.47-53
• /
• 1999