• The Journal of Korean Academy of Prosthodontics
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• v.36 no.5
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• pp.772-785
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• 1998

This study was undertaken to clarify the microstructure of the different IPS Empress ingots by etching and to observe the change of leucite crystal structure according to subsequent heat treatment and the crystal distribution according to sprue types(${\phi}2.8mm$, single sprue; ${\phi}1.8mm$, double sprue) by scanning electron microscopy. IPS Empress T1, O1 ingots used for staining technique, and Dentin(A2) ingots used for layering technique were selected for this study. To observe the microstructures of these ingots before pressing, the specimens were prepared in splinters($3{\times}3{\times}3mm$) taken from the original ingots. And to estimate crystal distribution and microstructural change by sprue type and subsequent heat treatment. the specimens($3{\times}3{\times}3mm$) were heat-pressed through the two types of sprues with different diameters and numbers, and all specimens were fired according to the recommended firing schedule. The observed surface was ground with waterproof papers($#800{\sim}#1800$) on the grind polisher and was cleaned ultrasonically. All specimen were etched with 0.5% hydrofluoric acid. After etching, the surface was treated by ion sputter coating for SEM observation at an accelerating voltage of 20kV. In all specimens, the central area of ground surface was observed because there was less difference in microstructure between the peripheral area and the central area. The results were as follows ; 1. In the microstructure according to the ingot type, there was a wide difference between the staining (T1,O1) and layering(Dentin A2) ingots, but there was not a considerable difference between the T1 ingot and the O1 ingot for staining technique. 2. In all specimens, the crystal dispersion of IPS Empress ceramic using double sprue was significantly more scattered than that of IPS Empress ceramic using single sprue. The degree of scattering was strongest in the Dentin(A2) specimen and weakest in the O1 ingot. 3. In the microstructural change according to the subsequent heat treatment, all of ingots had some microcracks in the inside of the leucite crystal and the glass matrix after pressing. The inner splinters of the leucite crystal became smaller, and more microcracks occurred in the glass matrix due to increasing heat treatment times. 4. The size of leucite crystals varied from $1{\mu}m\;to\;5{\mu}m$. The mean size of mature crystals was about $5{\mu}m$. The form of the crystal was similar to a circle when it was smaller and similar to an ellipse when it was larger.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.5
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• pp.212-223
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• 2019

This study is to investigate the relationship between microstructural factors and tensile properties after aging heat treatment of the 15-5PH stainless steel at the temperature range of $450^{\circ}C$, $500^{\circ}C$ and $550^{\circ}C$ for various time. For the aging time of 2 hours, hardness showed maximum at $450^{\circ}C$ and then decreased with increasing aging temperature. While, hardness decreased gradually during aging $450^{\circ}C$, $500^{\circ}C$ and $550^{\circ}C$ from 1 hour to 5 hours but the hardness nearly unchanged until the 100 hours after 5 hours aging. When aging at $450^{\circ}C$, Cu atoms preferentially aggregated at the prior austenite grain boundaries and martensite lath boundaries, and Cu concentration at those boundaries was nearly unchanged even after aging for 100 hours. Therefore it was suggested that the coherency is still maintained after 100 hours aging at $450^{\circ}C$. Aging at $500^{\circ}C$ and $550^{\circ}C$ results in an increase in the concentration of Ni at the martensite lath boundaries and prior austenite grain boundaries, resulting in the formation of reversed austenite. Especially, when aged at $550^{\circ}C$ for 100 hours, the concentration of Ni remarkably increased at those boundaries, and thus the microstructure of herring bone shape was appeared. Considering the migration of Ni atom to the lath boundaries and prior austenite grain boundaries, Ni atoms contributed greatly to the formation of reversed austenite. On the other hand, it was found that Cu atoms hardly moving to those boundaries may not be contributed to the formation of reversed austenite. When aging at $450^{\circ}C$, the coarsening of the precipitated Cu atoms proceeded very slowly with increasing aging time, therefore the decrease in strengths were small but the reduction area was considerably increased due to the softening of the matrix. At the aging temperature of $500^{\circ}C$ and $550^{\circ}C$, the strengths decreased and the elongation and reduction area increased due to the appearance of the reversed austenite. Especially, the increase of reduction area was remarkable.

• Korean Journal of Acupuncture
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• v.20 no.2
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• pp.101-120
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• 2003

This study is performed to investigate the cause, symptom and acupuncture on Dudurugi through the literature of oriental medicine. The findings of this study are as follows: 1. Dudurugi is caused by exogenous pathogenic factors(wind, heat, cold, damp), sthenic inter damage factors(heat accumulated in the intestine and stomach, blood-heat, blood-stasia) and asthenia inter damage factors(asthenia of the spleen and stomach, blood-asthenia, asthenia of energy-blood, yin-asthenia and blood-dryness, yan-asthenia and energy-asthenia). 2. The symptom of Dudurugi is appeared in the skin and its surface is processed apparently or itch. 3. The treatment of Dudurugi was used by expelling the wind with removing pathogen. 4. In the treatment of Dudurugi, The su-yangmyong taejang-kyong of 12 merdians was mainly used and, the kokchi(LI11) of acupoints was most used in the acupuncture and moxibustion. 5. In the treatment of Dudurugi, acupoints of tok-maek and chok-t'aeyangkyong were mainly used in the case of showing symptoms caused by exogenous pathogenic factors and, acupoints of chok-t'aemkyong were mainly used in the case of showing symptoms caused by damp-heat accumulated in the intestine and stomach. When there were any other symptoms accompanied, other acupoints were more used.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.619-628
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• 2010

Shape Memory Alloy (SMA) has recently received attention in developing implantable surgical equipments and it is expected to lead the future medical device market by adequately imitating surgeons' flexible and delicate hand movement. However, SMA actuators have not been used widely because of their nonlinear behavior called hysteresis, which makes their control difficult. Hence, we propose a parameter, $t_1$, which is necessary for temperature control, by analyzing the open-loop step response between current and temperature and by comparing it with the values of linear differential equations. $t_1$ is a pole of the transfer function in the invariant linear model in which the input and output are current and temperature, respectively; hence, $t_1$ is found to be related to the state variable used for temperature control. When considering the parameter under heat treatment conditions, $T_{max}$ was found to assume the lowest value, and $t_1$ was irrelevant to the heat treatment.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.5
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• pp.275-280
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• 2003

• Journal of Welding and Joining
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• v.5 no.2
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• pp.9-16
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• 1987

Post weld heat treatment (PWHT) is carried out to increase the fracture toughness in heat affected zone(HAZ) and remove the residual stress. There occur some problems such as toughness decreement and stress relief cracking(SRC) in the coarse grained HAZ subjected to the effect of tempering treatment. Especially, embitterment of structure directly relates to the mode of fracture and is appeared as the difference of fracture surface, that is, grain boundary failure. Therefore, in this paper, PWHT was carried out under the stress of 0, 10, 20 and $30kg/cm^2$ to simulate residual stress in HAZ welded by heat input of 10, 30 and 40KJ/cm. Applied stress in weld HAZ during PWHT assisted precipitin of over saturated alloying element in the structure, and grain boundary failure according to welding heat input didn't almost appear at the heat input of 10 KJ/cm, but it appeared from being the applied stress of $30kg/cm^2$ at $30KJ/cm and 20kg/mm^2$ at 40KJ/cm.

• Journal of Powder Materials
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• v.17 no.5
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• pp.359-364
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• 2010

In an attempt to optimize the magnetic properties of (Nd, Dy)-Fe-B sintered magnets, hydrogenation and post-sintering heat treatment processes were investigated at various hydrogenation temperatures and heat treatment temperatures. The coercivity of (Nd, Dy)-Fe-B sintered magnets hydrogenated at $400^{\circ}C$ increased to about 1.2 kOe without any detrimental effect on the remanence. Moreover, the coercivity of the magnets was enhanced further by a consecutive $2^{nd}$ and $3^{rd}$ step heat treatment. These results eventually leaded to the reduction of the Dy content in a high coercive (> 30 kOe) (Nd, Dy)-Fe-B sintered magnets, as much as 10%.

• Journal of Animal Environmental Science
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• v.5 no.3
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• pp.181-188
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• 1999

This study was carried out to investigate the effect of blowing fan for reducing heat stress in lactating dairy cows in summer. Treatment conditions were divided into 3 types ; No blow(T1), blow to oblique angle(T2) and blow to right angle(T3). Feed intake milk yield, respiration rate, rectal temperature and plasma cortisol concenration were measured to investigate the effect of hot environment on the physiological, productive responses in lactating dairy cows. The results obtained are summarized as follows: The daily milk yields were 20.47, 22.82 and 24.31kg per head in T1, T2 and T3 during experimental period, respectively. The respiration rate was significantly (p<0.05) higher in T1 than those of T2 and T3. The rectal temperature in T1(39.4$^{\circ}C$) was higher than those of T2(39.1$^{\circ}C$), (P<0.05). The plasma cortisol concentration was higher in T1 than those of T2 and T3(P<0.05). It was suggested that blowing fan installed in the pen was effective means to reduce heat stress.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.6
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• pp.475-480
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• 2001

Glasses in he system CuO-P$_2$O$_{5}$ -Nb$_2$O$_{5}$ -Nb$_2$O$_{5}$ -V$_2$O$_{5}$ were prepared by a press-quenching method on the copper plate. the glass-ceramics from these glasses were obtained by post-heat treatment, and the crystallization behavior and DC conductivities were determined. The conductivities of the glasses were range from 10$^{-6}$ s.$cm^{-1}$ / at room temperature ,but the conductivities of the glass-ceramics were 10$^{-3}$ s.$cm^{-1}$ / increased by 10$^3$ order. The crystalline product in the glass-ceramics was CuV$_2$O$_{6}$ . the crystal growth of CuV$_2$O$_{6}$ phase increased with heat-treatment conditions. The linear relationship between il($\sigma$T) and T$^{-1}$ suggested that the electrical conduction in the present glass-ceramics would be due to a small polaron hopping(SPH) mechanism.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.1018-1021
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• 2001

1018-1021 The CuO-P$_2$O$_{5}$ containing P$_2$O$_{5}$ as glass-former were prepared by press-quenching method on the copper plate. By post-heat treatment of these glasses, the CuO-P$_2$O$_{5}$ -V$_2$O$_{5}$ -g1ass ceramics was obtained and the crystallization behavior and dc conductivities were investigovted. The heat-treated glass-ceramics decreased in electrical conductivity by the order of 10$^1$ compared to amorphous glass. The linear relationship between In($\sigma$T) and T$^{-1}$ indicated that electrical conduction in CuO-P$_2$O$_{5}$ -V$_2$O$_{5}$ -gass occurred by a small polaron hopping.