• 대한기계학회논문집B
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• 제32권3호
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• pp.224-230
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• 2008

In this article, $TiO_2$ nanoparticles were synthesized by using $O_2$-enriched coflow, hydrogen, diffusion flames. We investigated the thermal stability of the flame-synthesized $TiO_2$ nanoparticles by examining the crystalline structures of the nanoparticles. Also, the results were compared with those of commercial P-25 nanoparticles. $TiO_2$ nanoparticles, which were spherical with diameters approximately ranging from 30 to 60nm, were synthesized. From the XRD analyses, about 96wt% of the synthesized nanoparticles were anatase-phase. After the heat-treatment at $800^{\circ}C$ for 30 minutes, the synthesized $TiO_2$ nanoparticles showed no significant changes of their shapes and crystalline phases. On the other hand, most of the commercial particles sintered with each other and changed to the rutile-phase. Based on the result of XRD analysis it is believed that the flame-synthesized $TiO_2$ nanoparticles have higher thermal stability at $800^{\circ}C$ than the commercial particles.

• 대한화학회지
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• 제63권2호
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• pp.94-101
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• 2019

Nb, Mo-doped and Nb/Mo-codoped $VO_2(M)$ nanocrystallites with various doping levels were synthesized for the first time by a hydrothermal and post thermal transformation method. The reversible phase transition characteristics of those doped $VO_2(M)$ was comparatively investigated. Nb-doping of $VO_2(M)$ by this method resulted in a very efficient lowering of the transition temperature ($T_c$) with a rate of $-16.7^{\circ}C/at.%$ that is comparable to W-doping, while Mo-doping did not give a serious reduction of $T_c$ with only a rate of $-5.1^{\circ}C/at.%$. Nb/Mo-codoping gave a similar result to Nb-doping without a noticeable difference. The thin films of Nb-doped and Nb/Mo-codoped $VO_2(M)$ with a thickness of ca. 120 nm were prepared by a wet-coating of the nanoparticle-dispersed solutions. Those films showed a good thermochromic modulation of near infrared radiation with 30-35% for Nb-doped $VO_2(M)$ and 37-40% for Nb/Mo-codoped ones. Nb/Mo-codoped $VO_2(M)$ film showed slightly enhanced thermochromic performance compared with Nb-doped $VO_2(M)$ film.

• 열처리공학회지
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• 제5권3호
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• pp.179-185
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• 1992

The shape memory effect results from the martensite transfomation of each individual grain. Thus it is necessary to study the texture and its variation. In this study the change of texture during thermal cycling and it's effect on shape memory ability are investigated. The major component of the rolling texture in the parent phase is identified (001) [110], and minor components are (112) [110], (111) [112], {hkl}<100> fiber texture is developed at $45^{\circ}$ from rolling direction. In the case of martensite phase, it is estimated that the major component is (011) [100] and the minor components are (105) [501], (010) [101] and (100) [001]. According to thermal cycling. severity of texture, especially (001) [110] component in parent phase and (011) [100] component in martensite phase are increased. The shape memory ability is increased with increase of thermal cycles and also increased as the direction of specimen approach to $45^{\circ}$ from rolling direction. After first thermal cycling the temperature of transformation can be define clearly and Ms and As are raised by thermal cycling.

• 소성∙가공
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• 제26권1호
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• pp.5-10
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• 2017

Fluid cooling is one of the manufacturing processes used to control mechanical properties, and is recently used for hot stamping of automobile parts. The formed part at room temperature is heated and then cooled rapidly using various fluids in order to obtain better mechanical properties. The formed part may undergo excessive thermal deformation during rapid cooling. In order to predict the thermal deformation during fluid cooling, a coupled simulation of different fields is needed. In this study, cooling simulation of boron steel square sheet was performed. Material properties for the simulation were calculated from JMatPro, and three convection heat transfer coefficients such as water, oil and air were obtained from the experiments. It was found that the thermal deformation increased when the difference of cooling rate of sheet face increased, and the thermal deformation increased when the thickness of sheet decreased.

• 한국세라믹학회지
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• 제46권5호
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• pp.493-496
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• 2009

Phase stabilized leucite, which has high coefficient of thermal expansion, was synthesized, and its thermal expansion behavior was investigated. The homogeneous leucite phase was synthesized by solid state reaction from the mixture of $K_2CO_3-Al_2O_3-SiO_2$. and its stabilization from tetragonal to cubic phase was attempted by adding $Cs_2CO_3$ into starting materials. And fine powder with an average particle size of a few hundreds ${\mu}m$ were fabricated by planetary milling. During milling, amorphization of leucite was observed and recrystallized after heat treatment. The thermal expansion behavior of tetragonal and cubic leucite has measured and discussed. The average coefficient of thermal expansion of tetragonal and cubic phase leucite from room temperature to $750^{\circ}C$ was $21.4{\times}10^{-6}/^{\circ}C$ and $14.5{\times}10^{-6}/^{\circ}C$, respectively.

• Natural Product Sciences
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• 제27권1호
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• pp.10-17
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• 2021

The purpose of this study is to develop a new method of producing tienchi seng (notoginseng, Panax notoginseng) extracts featuring high concentrations of the ginsenoside Rg3, Rg5, and Rg6, special components of Korean red ginseng. The chemical transformation from ginseng saponin glycosides to prosapogenin was analyzed by HPLC. Tienchi seng was heat-processed at 100℃ and the optimum conditions were identified. The highest concentrations of total saponin (29.723%) and the ginsenoside Rg3 (1.769%), Rg5 (5.979%), and Rg6 (13.473%) were produced at 48 hours. Also, when tienchi seng was subjected to the ultrasonic thermal fusion (100℃) process, the concentrations of total saponin (30.578%), ginsenoside Rg3 (2.392%), Rg5 (6.614%), and Rg6 (13.017%) were highest at 36 hours. On the other hand, the 2-hour heat-processed extract and 2-hour ultrasonic thermal fusion-processed extract did not contain ginsenoside Rg3, Rg5, and Rg6. The ultrasonic thermal fusion process had an extraction yield that was approximately 1.26 times greater than that of the heat process. These results indicate that the highly functional tienchi seng extracts created through the ultrasonic thermal fusion process are more industrially useful than those produced using the heat process.

• Journal of Welding and Joining
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• 제35권1호
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• pp.89-94
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• 2017

The microstructure and dilatation for 0.15C steels were investigated to define the phase transformation during the quenching and partitioning (Q&P) process. For the one step Q&P dilatation, the isothermal martensite/bainite transformation occurred because the holding temperature was between $M_s$ and $M_f$. The isothermally transformed martensite/bainite and the athermally transformed martensite were produced by a loss of retained austenite. As the holding time increased, new martensite-start ($M_s$) temperature produced from the final quenching process decreased due to the carbon partitioning from the martensite to the retained austenite. This was the direct evidence of increment for the retained austenite stability. For the two step Q&P dilatation, the isothermal bainitic transformation occurred because the partitioning temperature was larger than the $M_s$ and new $M_s$. The partitioning at $400^{\circ}C$ indicated the short incubation period for the bainite transformation than the $350^{\circ}C$ partitioning because the partitioning at $400^{\circ}C$ should acquire the larger thermal driving force for carbon partitioning than the $350^{\circ}C$ partitioning. A quick drop of $M_s$ and short period of bainite incubation for the $400^{\circ}C$ partitioning steel were also the direct evidence of significant effects of carbon partitioning on the stability of retained austenite.

• Transactions on Electrical and Electronic Materials
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• 제12권1호
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• pp.28-31
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• 2011

Transformation behavior and shape memory characteristics of Ti-(45-x)Ni-5Cu-xCr (x=0.5-2.0) alloys have been investigated by means of electrical resistivity measurements, differential scanning calorimetry, X-ray diffraction and thermal cycling tests under constant load. Two-stage B2-B19-B19' transformation occurred in Ti-(45-x)Ni-5Cu-xCr alloys. The B2-B19 transformation was separated clearly from the B19-B19' transformation in Ti-44.0Ni-5Cu-1.0Cr and Ti-43.5Ni-5Cu-1.5Cr alloys. A temperature range where the B19 martensite exists was expanded with increasing Cr content because decreasing rate of Ms (85 K / % Cr) was larger than that of Ms' (17 K / % Cr). Ti-(45-x)Ni-5Cu-xCr alloys were deformed in plastic manner with a fracture strain of 68% ~ 43% depending on Cr content. Substitution of Cr for Ni improves the critical stress for slip deformation in a Ti-45Ni-5Cu alloy due to solid solution hardening.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기물성,응용부문
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• pp.128-130
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• 2001

In this study, we investigate the deposition characteristics of merocyanine dye(MD) Langmuir-Blodgett(LB) film using quartz crystal microbalance (QCM). The MD optical system mixed with fatty acid was fabricated using LB method. And their optical characteristics were investigated using UV spectroscopy. The optical behavior of MD LB film was investigated asto thermal treatment. The resonant frequency and admittance was measured during dissociation of J-aggregate of MD LB film. As a result, it has been suggested that the J-aggregate dissociation in MD LB film by thermal treatment give rise to transformation of oscillation characteristics of quartz crystal.

• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.355-355
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• 2006

In this study, we have applied principal component analysis-based 2D (PCA2D) correlation spectroscopy to the temperature-dependent IR spectra of biodegradable poly(hydroxyalkanoate). PCA2D analysis reveals clearly that there are two components in crystalline band of C=O stretching mode without being hampered by noise. To better understand the thermal behavior of biodegradable poly(hydroxyalkanoate), eigenvalue manipulating transformation (EMT) technique was also employed. By uniformly lowering the power of a set of eigenvalues associated with the original data, the subtle contributions from minor eigenvectors are highlighted. Details of thermal behavior of biodegradable poly(hydroxyalkanoate) studied by PCA2D correlation spectroscopy with EMT will be discussed.