• Journal of Powder Materials
• /
• v.4 no.3
• /
• pp.196-204
• /
• 1997

Joining of AIN ceramics to W and Cu by active-metal brazing method was tried with use of (Ag-Cu)-Ti alloy as insert-metal. Joints were produced under various conditions of temperature, holding time and Ti-content in (Ag-Cu) alloy Reaction and microstructural development in bonded interface were investigated through observation and analysis by SEM/EDS, EPMA and XRD. Joint strengths were measured by shear test. Bonded interface consists of two layers: an insert-metal layer of eutectic Ag- and Cu-rich phases and a reaction layer of TiN. Thickness of reaction layer increases with bonding temperature, holding time and Ti-content of insert-metal. It was confirmed that the growth of reaction layer is a diffusion-controlled process. Activation energy for this process was 260 KJ/mol which is lower than that for N diffusion in TiN. Maximum shear strength of 108 MPa and 72 MPa were obtained for AIN/W and AIN/Cu joints, respectively. Relationship between processing variables, joint strength and thickness of reaction layer was also explained.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.7
• /
• pp.679-688
• /
• 2010

The major objective of the present study is to extend the applications of inverse analysis to more realistic engineering fields with a complex combustion process rather than the traditional simple heat-transfer problems. In order to do this, the unknown initial mass fractions of $CH_4/O_2$ are estimated from the temperature measurement data by inverse analysis in the practical diffusion-controlled turbulent combustion problem. In order to ensure efficient inverse analysis, the repulsive particle swarm optimization (RPSO) method, which belongs to the class of stochastic evolutionary global optimization methods, is implemented as an inverse solver. Based on this study, it is expected that useful information can be obtained when inverse analysis is used in the diagnosis, design, or optimization of real combustion systems involving unknown parameters.

• Macromolecular Research
• /
• v.10 no.5
• /
• pp.259-265
• /
• 2002

The cure kinetics of blends of epoxy (DGEBA, diglycidyl ether of bisphenol A)/anhydride resin with polyamide copolymer, poly(dimmer acid-co-alkyl polyamine), were studied using differential scanning calorimetry (DSC) under isothermal condition. On increasing the amount of polyamide copolymer in the blends, the reaction rate was increased and the final cure conversion was decreased. Lower values of final cure conversions in the epoxy/(polyamide copolymer) blends indicate that polyamide hinders the cure reaction between the epoxy and the curing agent. The value of the reaction order, m, for the initial autocatalytic reaction was not affected by blending polyamide copolymer with epoxy resin, and the value was approximately 1.3, whereas the reaction order, n, for the general n-th order of reaction was increased by increasing the amount of polyamide copolymer in the blends, and the value increased from 1.6 to 4.0. A diffusion-controlled reaction was observed as the cure conversion increased and the rate equation was successfully analyzed by incorporating the diffusion control term for the epoxy/anhydride/(polyamide copolymer) blends. Complete miscibility was observed in the uncured blends of epoxy/(polyamide copolymer) up to 120 $^{\circ}C$, but phase separations occurred in the early stages of the curing process at higher temperatures than 120 "C. During the curing process, the cure reaction involving the functional group in polyamide copolymer was detected on a DSC thermogram.gram.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.831-832
• /
• 2006

Solid-state processing via the bulk mechanical alloying enables us to directly fabricate $Mg_2X$ semi-conductive material performs. Precise control of chemical composition leads to investigation on the dilution and enrichment of X in $Mg_2X$. Two types of solid-state reactivity are introduced: e.g. synthesis of $Mg_2Si$ from elemental mixture Mg-Si is nucleation-controlled process while synthesis of $Mg_2Sn$ from Mg-Sn, diffusion-controlled process. Thermoelectricity of these $Mg_2X$ is evaluated for discussion on the validity and effectiveness of this new PM route as a reliable tool for fabrication of thermoelectric compounds.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.20 no.2
• /
• pp.51-57
• /
• 2021

The quality of the ceramic sintered coating on a metal surface through laser surface treatment is affected by the laser irradiation pattern. Depending on the laser irradiation pattern, the amount of residual stress and heat applied or accumulated on the surface increases or decreases, affecting the thickness attained in the ceramic sintering area. When the heat energy accumulated in the sintering area is high, the ceramic and the metal alloy melt and sufficiently mix to form a homogeneous and thick bonding interface. In this study, the thermal energy accumulation in the region sintered with zirconia was controlled using four types of laser processing patterns. The thickness of the diffusion region is analyzed by laser-induced breakdown spectroscopy of Mg-ZrO2 generated by laser sintering zirconia powder on the magnesium alloy surface. On the basis of the analysis of the Mg and Zr present in the sintered region through LIBS, the effect of the irradiation pattern on the sintering quality is confirmed by comparing and analyzing the heat and mass transfer tendency of the diffusion layer and the degree of diffusion according to the irradiation pattern. The derived diffusion coefficients differed by up to 9.8 times for each laser scanning pattern.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.20 no.3
• /
• pp.207-212
• /
• 2007

The concentration profiles of deep energy levels($E_c$ -0.23e V, $E_v$+0.36e V and $E_c$ -0.23e V) in platinum-diffused silicon have generally a sharp gradient in the vicinity of the surface of the silicon wafer. In this work two efficient methods are proposed to obtain the uniform concentration profiles throughout the silicon wafer. One is that the platinum diffusion is carried out at $1000^{\circ}C$ for 1h in oxygen atmosphere. In this case the values of obtained uniform concentration, $1{\times}10^{15}cm^{-3}$ for the $E_c$ -0.23e V level, and 1{\times}10^{14}cm^{-3}$ for the $E_c$ -0.52e V level, are very restricted, respectively. The other is two-step annealing process. The platinum diffusion is carried out at $850{\sim}1100^{\circ}C$ in a nitrogen ambient for 1h and then the annealing is performed at $1000^{\circ}C$ in oxygen ambient after removing platinum-source from the platinum diffused samples. The advantage of this method is that the uniform concentration of these levels required power devices can be controlled by setting the desired temperatures when the platinum diffusion is carried out in nitrogen ambient.

• Korean Journal of Acupuncture
• /
• v.24 no.2
• /
• pp.1-17
• /
• 2007

Objectives : Extra Meridians are important conception for the proper comprehension of the defensive Gi & the defensive Gi, and the principle of the Gi (氣)‘s flow or diffusion. Methods : Extra Meridians could be explained by an anatomical feature and a functional stage. We should analyze the principle of samhap (三合) to have application to meridians. The study of the relationship between Extra Meridians and regular meridians (12正經) is useful to understand origination of the defensive Gi & the nutritive Gi. Results : The origination of the nutritive Gi & the defensive Gi could be interpreted by the principle of samhap correctly. The energic patterns in the flow of Gi (氣) are changed by cooperation with Extra Meridians and regular meridians (12正經). Conclusions : We could inferred that growth, disease, health, etc are controlled in cooperation with Extra Meridians (寄經脈) and the nutritive Gi & the defensive Gi (營衛). Extra Meridians take many parts in origination of the nutritive Gi & the defensive Gi, in the flow or diffusion of them but various energies are controlled basically by regular meridians (12正經). The defensive Gi is originated by Penetration Vessel (衝脈)) and it seems to be made by the principle of samhap (三合) in the process of the nutritive Gi flow (瀯氣流注).

• Journal of Welding and Joining
• /
• v.21 no.2
• /
• pp.82-88
• /
• 2003

The bonding phenomenon and mechanism in the transient liquid phase bonding(TLP Bonding) of directionally solidified Ni base superalloy, GTD-111 was investigated. At the bonding temperature of 1403K, liquid insert metal was eliminated by isothermal solidification which was controlled by the diffusion of B and Si into the base metal and solids in the bonded interlayer grew epitaxially from mating base metal inward the insert metal. The number of grain boundaries formed at the bonded interlayer was corresponded with those of base metal. The liquation of grain boundary and dendrite boundary occurred at 1433K. At the bonding temperature of 1453K which is higher than liquation temperature of grain boundary, liquids of the Insert metal were connected with liquated grain boundaries and compositions in each region mixed mutually. In Joints held for various time at 1453t phases formed at liquated grain boundary far from the interface were similar to those of bonded interlayer. With prolonged holding time, liquid phases decreased gradually and liquids of continuous band shape divided many island shape. But liquid phases did not disappeared after holding for 7.2ks at 1453k. Isothermal solidification process at the bonding temperature which is higher than the liquation temperature of the grain boundary was controlled by diffusion of Ti to be result in liquation than B or Si. in insert metal. (Received January 15, 2003)

• Journal of the Korean Chemical Society
• /
• v.37 no.8
• /
• pp.730-734
• /
• 1993

The electrochemical reduction behavior or Biliverdin (BV) in N,N-dimethylformamide solvent was studied by DC polarography, cyclic voltammetry and the controlled potential coulometry. The reduced product was indentified by UV-Vis spectroscopy. In DC polarogram, two reduction waves of BV were founded. The half wave potentials of two reduction waves were -0.71 and -0.91 V vs. Ag/Ag$^+$ respectively. The current type of the 1st reduction wave was diffusion-controlled and the 2nd was diffusion current containing a little kinetic current. The 1st electrochemical reduction process was irreversible and BV reduced to Bilirubin.

• Analytical Science and Technology
• /
• v.15 no.2
• /
• pp.97-101
• /
• 2002

Co(II) complexes with tridentate Schiff base-NOIPH and tetradentate Schiff base-$NOTDH_2$ and $TNBPH_4$ were synthesized. The redox process of the complexes in DMF solution containing 0.1M TBAP was investigated at glassy carbon electrode by cyclic voltammetry and differential pulse voltammetry techniques. Reduction step of [Co(II)$(NOIP)_2$] and [Co(II)$(H_2O)_2$] complexes were observed in two step as one electron process of irreversible or quasi-reversible and diffusion-controlled reaction. [$Co(II)_2$(TNBP)] complex was observed in one step as one electron process of quasi-reversible and diffusion-controlled reaction.