• Journal of Welding and Joining
• /
• 제13권3호
• /
• pp.106-115
• /
• 1995

To know the bonding phenomena of Ti/Cu brazed joint, a characteristic of microstructures in bonding interlayer of vacuum brazed pure Ti to Cu has been studied in the temperature range from 1088 to 1133K for various bonding times using Ag-28wt%Cu filler metal. Also intermediate phases formed in bonded interlayer and behavior of layer growth have been investigated. The obtained results in this study are as follows: 1) Liquid insert metal width at the each brazing temperature was proportional to the square root of brazing time, and it was considered that the liquid insert metal width was controlled by the diffusion rate process of primary .alpha.-Cu formed at the Ti side. 2) Intermediate phases formed near the Ti interface were .betha.-Ti and intermetallic compounds TiCu, Ti$_{2}$Cu, Ti$_{3}$Cu, and TiCu. 3) .betha.-Ti formed in Ti base metal durig brazing transformed to lamellar structure, .alpha.-Ti + Ti$_{2}$Cu. The structure came from the eutectoil decomposition reaction in cooling. And the width of .betha.-Ti layer was proportional to the square root of brazing time, and it was considered that the growth of .betha.-Ti layer was controlled by interdiffusion rate process in .betha.-Ti. 4) The layer growth of TiCu, Ti$_{3}$Cu$_{4}$ and TiCu, phases formed near the Ti interface was linerface was linearly proportional to the brazing time, and it was considered that the layer growth of these phases was controlled by the chemical reaction rate at the interface.

• Bulletin of the Korean Chemical Society
• /
• 제33권8호
• /
• pp.2719-2723
• /
• 2012

A kinetic study is reported for nucleophilic substitution reactions of benzyl 4-pyridyl carbonate 6 with a series of alicyclic secondary amines in MeCN. The plot of pseudo-first-order rate constant ($k_{obsd}$) vs. [amine] curves upward, which is typical for reactions reported previously to proceed through a stepwise mechanism with two intermediates (i.e., a zwitterionic tetrahedral intermediate $T^{\pm}$ and its deprotonated form $T^-$). Dissection of $k_{obsd}$ into the second- and third-order rate constants (i.e., $Kk_2$ and $Kk_3$, respectively) reveals that $Kk_3$ is significantly larger than $Kk_2$, indicating that the reactions proceed mainly through the deprotonation pathway (i.e., the $k_3$ process) in a high [amine] region. This contrasts to the recent report that the corresponding aminolysis of benzyl 2-pyridyl carbonate 5 proceeds through a forced concerted mechanism. An intramolecular H-bonding interaction was suggested to force the reactions of 5 to proceed through a concerted mechanism, since it could accelerate the rate of leaving-group expulsion (i.e., an increase in $k_2$). However, such H-bonding interaction, which could increase $k_2$, is structurally impossible for the reactions of 6. Thus, presence or absence of an intramolecular H-bonding interaction has been suggested to be responsible for the contrasting reaction mechanisms (i.e., a forced concerted mechanism for the reaction of 5 vs. a stepwise mechanism with $T^{\pm}$ and $T^-$ as intermediates for that of 6).

• Journal of Welding and Joining
• /
• 제32권1호
• /
• pp.66-70
• /
• 2014

In Ti active brazing of YSZ to STS 430 using Ag-Cu Filler Metal, the effect of Ti contents on the shear bonding strength were investigated together with the effect of brazing temperature and holding time. The addition of Ti in Ag-Cu Filler Metal increased the bonding strength up to 4.68% Ti, followed by the decrease with further addition. This seems to be caused by formation of TixOy at the reaction layer. Brazing temperature was optimized at $960^{\circ}C$ among a given temperature ranges. The addion of Sn to Ag-Cu filler metal brought the decrease of its melting temperature its melting temperature without a significant decrease of bonging strength.

• 한국분말재료학회지
• /
• 제20권2호
• /
• pp.114-119
• /
• 2013

In the DBC (direct bonding of copper) process the oxygen partial pressure surrounding the AlN/Cu bonding pairs has been controlled by Ar gas mixed with oxygen. However, the direct bonding of Cu with sound interface and good adhesion strength is complicated process due to the difficulty in the exact control of oxygen partial pressure by using Ar gas. In this study, we have utilized the in-situ equilibrium established during the reaction of $2CuO{\rightarrow}Cu_2O$ + 1/2 $O_2$ by placing powder bed of CuO or $Cu_2O$ around the Cu/AlN bonding pair at $1065{\sim}1085^{\circ}C$. The adhesion strength was relatively better in case of using CuO powder than when $Cu_2O$ powder was used. Microstructural analysis by optical microscopy and XRD revealed that the interface of bonding pair was composed of $Cu_2O$, Cu and small amount of CuO phase. Thus, it is explained that the good adhesion between Cu and AlN is attributed to the wetting of eutectic liquid formed by reaction of Cu and $Cu_2O$.

• Bulletin of the Korean Chemical Society
• /
• 제31권7호
• /
• pp.1837-1838
• /
• 2010

• Bulletin of the Korean Chemical Society
• /
• 제35권8호
• /
• pp.2371-2374
• /
• 2014

A kinetic study is reported on SNAr reaction of 1-fluoro-2,4-dinitrobenzene with a series of primary amines including hydrazine in $H_2O$ at $25.0^{\circ}C$. The plots of $k_{obsd}$ vs. [amine] are linear and pass through the origin, indicating that general-base catalysis by a second amine molecule is absent. The Br${\o}$nsted-type plot exhibits an excellent linear correlation with ${\beta}_{nuc}$ = 0.46 when hydrazine is excluded from the correlation. The reaction has been suggested to proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the rate-determining step (RDS). Hydrazine is ca. 10 times more reactive than similarly basic glycylglycine (i.e., the ${\alpha}$-effect). A five-membered cyclic intermediate has been suggested for the reaction with hydrazine, in which intramolecular H-bonding interactions would facilitate expulsion of the leaving group. However, the enhanced leaving-group ability is not responsible for the ${\alpha}$-effect shown by hydrazine because expulsion of the leaving group occurs after RDS. Destabilization of the ground-state of hydrazine through the electronic repulsion between the nonbonding electron pairs is responsible for the ${\alpha}$-effect found in the current $S_NAr$ reaction.

• 한국재료학회지
• /
• 제6권2호
• /
• pp.210-220
• /
• 1996

The purpose of this study is to develop the processing techniques of Fiber Reinforced Metal by Liquid Phase Diffusion Bonding method with SiC fiber as a reinforcing material and CP Ti(Commercial Pure) as a matrix. The microstructure and the distribution of elements in reaction and CP Ti(Commercial Pure) as a matrix. The microstructure and the distribution of elements is reaction zone among CP Ti/Ti-15wt%Cu-20wt%Ni(TCN20)/SiC long fiber were investigated by Optical Microscope, SEM/EDX, EPMA, X-ray and AES. The results obtained in this study are as follows. 1) When Ti matrix composite materials are fabricated under the bonding condition of 1273Kx1200sec, the SiC long fiber was the most suitable reinforcing material for Ti matrix composite materials. 2) With SiC long fiber under same condition, a TiC layer(1.0-1.6$\mu\textrm{m}$) was observed on the surface of SiC long fiber. 3) Liquid Phase Diffusion Bonding has shown the feasibility of production of Ti matrix composite materials.

• 대한치과기공학회지
• /
• 제29권2호
• /
• pp.213-223
• /
• 2007

The success of a porcelain fused to metal (PFM) restoration depends upon the quality of the porcelain-metal bond. The adhesion between metal substructure and dental porcelain is related to the diffusion of oxygen to the reaction layer formed on cast-metal surface during firing. The purposed of this investigation was to study the effects of gold based bonding agent on Ni-Cr alloy-ceramic adhesion between porcelain matrix, gold based bonding agent and metal substructure interface. gold based bonding agent have been applied as an intermediate layer between a metal substructure and a ceramic coating. gold based bonding agent(Aurofilm NP, Metalor, Swiss) was applied on Ni-Cr alloy surface by four method. Surfaces only air abraded with 110${\beta}\neq$ Al2O3 particles were used as control. metal ceramic adhesion was evaluated by a biaxial flexure test(N=5) and volume fraction of adherent porcelain was determined by SEM/EDS analysis. Result of this study suggest that the layering sequence of gold based bonding agent is very important and can improve porcelain adherence to PFM.

• Bulletin of the Korean Chemical Society
• /
• 제35권7호
• /
• pp.2081-2085
• /
• 2014

Second-order rate constants ($k_N$) have been measured spectrophotometrically for the reactions of phenyl 2- pyridyl carbonate (6) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plot for the reaction of 6 is linear with ${\beta}_{nuc}$ = 0.54, which is typical for reactions reported previously to proceed through a concerted mechanism. Substrate 6 is over $10^3$ times more reactive than 2-pyridyl benzoate (5), although the reactions of 6 and 5 proceed through the same mechanism. A combination of steric hindrance, inductive effect and resonance contribution is responsible for the kinetic results. The reactions of 6 and 5 proceed through a cyclic transition state (TS) in which H-bonding interactions increase the nucleofugality of the leaving group (i.e., 2-pyridiniumoxide). The enhanced nucleofugality forces the reactions of 6 and 5 to proceed through a concerted mechanism. In contrast, the corresponding reaction of 4-nitrophenyl 2-pyridyl carbonate (7) proceeds through a stepwise mechanism with quantitative liberation of 4-nitrophenoxide ion as the leaving group, indicating that replacement of the 4-nitrophenoxy group in 7 by the PhO group in 6 changes the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway) as well as the leaving group (i.e., from 4-nitrophenoxide to 2-pyridiniumoxide). The strong electron-withdrawing ability of the 4-nitrophenoxy group in 7 inhibits formation of a H-bonded cyclic TS. The presence or absence of a H-bonded cyclic TS governs the reaction mechanism (i.e., a concerted or stepwise mechanism) as well as the leaving group (i.e., 2-pyridiniumoxide or 4-nitrophenoxide).

• 한국자동차공학회논문집
• /
• 제21권4호
• /
• pp.113-119
• /
• 2013

The transient liquid phase (TLP) bonding was used to fabricate autogenous joints in a magnesium alloy AZ31 with the aid of a pure Ni interlayer. A $13{\mu}m$ thick pure Ni foil was used in order to form a Mg-Ni eutectic liquid at the joint interface. The interface of reaction and composition profiles were investigated as a function of bonding time using a pressure of 0.16 MPa and a bonding temperature of $515^{\circ}C$. The quality of the joints produced was examined by metallurgical characterization and the joint microstructure developed across the diffusion bonds was related to changes in mechanical properties as a function of the bonding time.