• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.84-87
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• 2003

Microstructural evolution and dry sliding wear behavior of ultra-fine grained 5052 Al alloy obtained by an accumulative roll-bonding process have been investigated. After 7 ARB cycles, ultra-fine grains with large misorientations between neighboring grains were obtained. The grain size was about 0.2$\mu\textrm{m}$. The hardness, tensile and yield strengths of the ultra-fine grained alloy increased as the amount of accumulated strain increased with the ARB cycles. Sliding wear teats of the ultra-fine grained 5052 Al alloy were conducted at room temperature. Wear rate of the ultra-fine grained alloy increased in spite of the increase of hardness. Surfaces of the worn specimens were examined with SEM to investigate wear mechanism of the ultra-fine grained alloy.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.21-24
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• 2000

Ultra-fine grains were produced in pure Al using an Accumulative Rolling-Bonding (ARB) process. After several cycles of the ARB process, pure Al sheets were filled with the ultra-fine grains whose diameters were several hundred nano-meters. With ARB cycles, the nature of grain boundaries of the ultra-fine grains changed from diffusive sub-boundaries to well-defined high angle boundaries. After 7 cycles, ultra-fine polycrystals with large misorientations between neighboring grains were obtained. Sliding wear tests using a pin-on-disk type wear tester were co ducted on the ultra-fine grained pure Al. Wear rates of pure Al increased with the increase of ARB cycle numbers in spite of the increase in hardness. Worn surfaces and cross-sections were examined with optical microscopy (OM) and scanning electron microscopy (SEM) In investigate the wear mechanism of the ultra-fine grained pure Al.

• Macromolecular Research
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• 제17권9호
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• pp.631-637
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• 2009

This study examined the unique self-doping behavior of carboxylated polyaniline (PCA). The self-doped PCA was synthesized using an environmentally benign enzymatic polymerization method with cationic surfactants. XPS showed that HCl-doped PCA contained approximately 34% of protonated amines but self-doped PCA contained 9.6% of the doped form of nitrogen at pH 4. FTIR and elemental analysis showed that although the PCA was doped with the proton of strong acids at low pH via the protonation of amines, the self-doping mechanism of PCA at pH > 4 was mainly due to hydrogen bonding between the carboxylic acid group and amine group.

• 소성∙가공
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• 제12권4호
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• pp.376-381
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• 2003

Microstructural evolution and dry sliding wear behavior of ultra-fine grained 5052 Al alloy obtained by an accumulative roll-bonding process have been investigated. After 7 ARB cycles, ultra-fine grains with a large misorientation between neighboring grains were obtained. The grain size was about 0.2 $\mu$m. The hardness, tensile and yield strengths of the ultra-fine grained alloy increased as the amount of accumulated strain increased with the ARB cycles. Sliding wear tests of the ultra-fine grained 5052 Al alloy were conducted at room temperature. Wear rate of the ultra-fine grained alloy increased in spite of the increase of hardness. Surface of the worn specimens were examined with SEM to investigate wear mechanism of the ultra-fine grained alloy.

• Steel and Composite Structures
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• 제20권3호
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• pp.671-692
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• 2016

FRP stay-in-place (SIP) formworks are designed as a support for casting concrete and as a tension reinforcement when concrete is cured. Bond development between SIP formwork and concrete is critical for FRP tension element to be effective. This paper reports the bond strength between FRP formwork and concrete for different interfacial treatments. A novel experimental setup is prepared for observing the bond behaviour. Three different adhesives with varying workability have been investigated. Along with the load-deformation characteristics, bond slip and strains in the formwork have been measured. A finite element numerical simulation was conducted for the experiments to understand the underlying mechanism. The results show that the adhesive bonding has the best bond strength.

• 한국세라믹학회지
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• 제31권4호
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• pp.381-388
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• 1994

A new process which co-fires the low-firing-substrate and copper conductor was studied to achieve good bond strength and low sheet resistance of conductor. Cupric oxide is used as the precursor of conductive material in the new method and the firing atmosphere of the new process is changed sequently in air H2N2. The addition of cupric oxide and variations of firing atmosphere permited complete binder-burnout in comparison with the conventional method and contributed to the improvement of resistance and bonding behaviors. The potimum conditions of this experiment to obtain the satisfactory resistance and bond strength are as follows (binder-burnout temperature in air; 55$0^{\circ}C$, reducing temperature in H2; 40$0^{\circ}C$ for 30 min, ratio of copper and cupric oxide; 60:40~30:70 wt%). The bonding mechanism between the substrate and metal was explained by metal diffusion layer in the interface and the bond strength mainly depended on the stress caused by the difference of shrinkage and thermal expansion coefficient between the substrate and metal.

• 대한치과의사협회지
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• 제53권3호
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• pp.195-200
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• 2015

Cementation is the last procedure and an important factor to access successful fixed prosthodontic treatment. Even though there are many kinds of luting materials in dental field, the resin cements are popularly used in now. Metals, polymers and ceramics are used as a material of fixed dental prosthesis. The bonding mechanisms between teeth and fixed restorations are composed of mechanical and chemical mechanism. In dentistry, we are relying on mechanical bonding, but we tried to get chemical bonding and many ways are introduced. So, we have to approach luting procedure differently by the materials of prosthesis for clinical success. In this article, let us think the proper cementation ways according to each prosthesis material.

• Journal of the Korean Wood Science and Technology
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• 제43권5호
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• pp.682-690
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• 2015

The bonding performance of two types of wood adhesives, namely phenol-resorcinol-formaldehyde (PRF) resin and melamine-urea-formaldehyde (MUF) resin for glued laminated timber manufactured by high frequency (HF) heating was evaluated. The HF heating system consists of HF oscillator with dielectric heating system for curing adhesives, and hydraulic press system for clamping glued laminated timber. The designed frequency and output power of the HF system was as 5 MHz and 60 kW, respectively. To verify dielectric heating mechanism under HF oscillation, the heat loss factors of laminae and adhesives were measured. The results show that it is possible to selectively heat adhesives for their curing due to the remarkably higher loss factor of the adhesives than those of wood laminae. The temperature of adhesive in the bonding line reached up to the set temperature within a few seconds by high frequency oscillating, which advanced the curing of adhesive afterwards. The bonding performance, such as shear strength of bonding line, water soaking delamination, and boiling water soaking delamination of PRF resin met the requirement of Korean Standard (KS), however the MUF resin did not meet the KS requirement of boiling water soaking delamination. These results indicate that the HF heating system is successful to manufacture glued laminated timbers with PRF resins to meet the bonding requirements.

• Bulletin of the Korean Chemical Society
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• 제33권9호
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• pp.2971-2975
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• 2012

Second-order rate constants $k_N$ have been measured spectrophotometrically for nucleophilic substitution reactions of t-butyl 4-pyridyl carbonate 8 with a series of alicyclic secondary amines in $H_2O$ at $25.0{\pm}0.1^{\circ}C$. The Br${\emptyset}$nsted-type plot for the reactions of 8 is linear with ${\beta}_{nuc}$ = 0.84. The ${\beta}_{nuc}$ value obtained for the reactions of 8 is much larger than that reported for the corresponding reactions of t-butyl 2-pyridyl carbonate 6 (i.e., ${\beta}_{nuc}$ = 0.44), which was proposed to proceed through a forced concerted mechanism. Thus, the aminolysis of 8 has been concluded to proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate $T^{\pm}$, in which expulsion of the leaving-group from $T^{\pm}$ occurs at the rate-determining step (RDS). In contrast, aminolysis of benzyl 4-pyridyl carbonate 7 has been reported to proceed through two intermediates, $T^{\pm}$ and its deprotonated form $T^-$ on the basis of the fact that the plots of pseudo-first-order rate constant $k_{obsd}$ vs. amine concentration curve upward. The current study has demonstrated convincingly that the nature of the leaving and nonleaving groups governs the reaction mechanism. The contrasting reaction mechanisms have been rationalized in terms of an intramolecular H-bonding interaction, steric acceleration, and steric inhibition.

• Bulletin of the Korean Chemical Society
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• 제32권spc8호
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• pp.3090-3093
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• 2011

Curcumin is a natural product with antioxidant, anti-inflammatory, antiviral and antifungal functions. As it is known that the excited state intramolecular hydrogen transfer of curcumin are related to its medicinal antioxidant mechanism, we investigated its excited state dynamics by using femtosecond transient absorption spectroscopy in an effort to understand the molecule's therapeutic effect in terms of its photophysics and photochemistry. We found that stronger intermolecular hydrogen bonding with solvents weakens the intramolecular hydrogen bonding and decelerates the dynamical process of the enolic hydrogen. Exceptions are found in methanol and ethylene glycol due to their nature as simultaneous hydrogen bonding donor-acceptor and high viscosity solvent, respectively.