• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.4
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• pp.321-336
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• 2012

The shear behavior at the particle/surface interface such as rock joint can determine the mechanical behavior of whole structure. Therefore, a fundamental understanding of the mechanisms governing its behavior and accurately estimation of the interface strength is essential. In this paper, PFC, a numerical analysis program of discrete element method was used to investigate the effects of the surface roughness crushing on interface strength. The surface roughness was characterized by smooth, intermediate, and rough surface, respectively. Particle shape was classified into one ball model of circular shape and 3 ball model of triangular shape. The surface shape was modelled by wall model of non-crushing surface and ball model of crushing surface. The results showed that as the bonding strength of ball model decreases, lower interface strength is induced. After the surface roughness crushing was occurred, the interface strength tended to converge and higher bonding strength induced lower surface roughness crushing. Higher friction angle was induced in wall model and higher surface roughness induced the higher friction angle. From these findings, it is verified that the surface roughness and surface roughness crushing effect on the particle/surface interface shear behavior.

• Korean Chemical Engineering Research
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• v.44 no.5
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• pp.513-519
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• 2006

We developed two kinds of the microchip for application to electrophoresis based on both glass and quartz employing the MEMS fabrications. The poly-Si layer deposited onto the bonding interface apart from channel regions can play a role as the optical slit cutting off the stray light in order to concentrate the UV ray, from which it is possible to improve the signal-to-noise (S/N) ratio of the detection on a chip. In the glass chip, the deposited poly-Si layer had an important function of the etch mask and provided the bonding surface properly enabling the anodic bonding. The glass wafer including more impurities than quartz one results in the higher surface roughness of the channel wall, which affects subsequently on the microflow behavior of the sample solutions. In order to solve this problem, we prepared here the mixed etchant consisting HF and $NH_4F$ solutions, by which the surface roughness was reduced. Both the shape and the dimension of each channel were observed, and the electroosmotic flow velocities were measured as 0.5 mm/s for quartz and 0.36 mm/s for glass channel by implementing the microchip electrophoresis. Applying the optical slit with poly-Si layer provides that the S/N ratio of the peak is increased as ca. 2 times for quartz chip and ca. 3 times for glass chip. The maximum UV absorbance is also enhanced with ca. 1.6 and 1.7 times, respectively.

• Restorative Dentistry and Endodontics
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• v.21 no.2
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• pp.602-618
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• 1996

The purpose of this study was to investigate the effect of acid treatment of fluoride applied dentin surface with various concentrations of phosphoric acid for various periods of time on dentin bonding. Dentin specimens prepared from freshly extracted bovine mandibular anterior teeth were divided into fluoridated and nonfluoridated groups. Specimens of nonfluoridated group were pretreated with 10% phosphoric acid for 15 seconds. Those of fluoridated groups were treated with 2% sodium fluoride or 2% stannous fluoride solution for 5 minutes and stored in $37^{\circ}C$ distilled water for 3 days, followed by phosphoric acid treatment. The concentrations of phosphoric acid were 10%, 32% or 50% and the treatment periods of time were 15, 30 or 60 seconds. All the specimens were bonded with All Bond$^{(R)}$ 2 and Bisfil$^{TM}$ composite resin. After bonded specimens were stored in $37^{\circ}C$ distilled water for 24 hours, tensile bond strengths of each specimens were measured and the pretreated dentin and the fractured dentin surfaces were examined under the scanning electron microscope. The results were as follows : The tensile bond strengths from the fluoridated groups were significantly lower than those from the nonfluoridated group when the concentrations of phosphoric acid and the treatment periods of time were equal in all the groups (p<0.05). In general, the higher the concentration of phosphoric acid and the longer the treatment period of time for acid etching on the fluoride applied dentin surface, the higher were the bond strength values. Recovery of bond strength of the dentin bonding agent was better in the NaF applied group than in the $SnF_2$ applied one. SEM findings of NaF applied and $SnF_2$ applied dentin surfaces demonstrated reaction product-covered and partially or completely obstructed dentinal tubules. SEM findings of dentin surfaces fluoridated for 5 minutes followed by etching showed wider tubular openings and more clean dentin surfaces when dentin was etched with higher concentration of phosphoric acid for longer period of time. On the SEM observations of the fractured dentin-resin interface, the etched specimens of fluoridated group showed an adhesive failure mode when the concentration of phosphoric acid and the treatment period of time were same as in the nonfluoridated group. As the concentration of phosphoric acid and the treatment period of time increase during acid etching, the cohesive failure area increased. However, excessive acid etching caused adhesive failure.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1061-1065
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• 1995

To improve dielectric and mechanical properties of insulating composite by plasma surface treatment, new plasma surface treatment process is designed with concentric and hemi-circle electrodes system, the plasma, which is generated between anode and cathode, is induced to the upper side of the electrode system and treats the surface of the insulators. The optimal surface treatment condition is that pressure : 0.5[torr], flux density 100[gauss], discharge current : 500[mA] and treatment time : 3 minutes. The composite filled with glass cloth surface-treated by plasma shows the improvement in electric and mechanical properties, comparing non- and coupling agent-treated samples.

• Tribology and Lubricants
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• v.16 no.6
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• pp.415-424
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• 2000

The use of magnetoresistive (MR) head requires much tighter control of particle contamination in a drive since loose particles on the disk surface will generate thermal asperities (TA). In this study, a spinoff test was performed to investigate the adhesion and removal capability of a particle to disk surface. Numerical simulation was also performed to investigate dominant factor of particle detachment and to support experimental results. It was shown that particles are detached from the disk surface by the moment derived from the centrifugal force and the drag force and that the centrifugal force and capillary force are the dominant force, which determines spin-off of a particle on the disk surface. Removal of particles smaller than several micrometers, which are the main source of TA generation, is extremely difficult since the adhesion forces exceed the centrifugal force. Lubricant types and manufacturing process also influence the particle removal. Lower bonding ratio and lower viscosity of the lubricant will help to increase the removal rate of the particles from the disk surface.

• Textile Coloration and Finishing
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• v.19 no.1 s.92
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• pp.45-52
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• 2007

Polyacrylonitrile(PAN) fiber was treated with low-temperature plasmas of argon and oxygen for surface modification, and its surface chemical structure and morphology were examined by a field emission scanning electron microscope(FESEM) and a Fourier-transform infrared microspectroscopy(IMS). The argon-plasma treatment caused the only mechanical effect by sputtering of ion bombardment, whereas the oxygen plasma brought about a chemical effect on the PAN fiber surface. The experimental evidences strongly suggested that cyclization of nitrile group and crosslinking were likely to occur in the oxygen-plasma treatment. On the other hand, with the argon-plasma treatment, numerous my pits resulted in ranging from several tens to hundreds nanometers in radius. The plasma sensitivity of functional groups such as C-H, $C{\equiv}N$, and O-C=O groups in the PAN fiber was dependent on their chemical nature of bonding in the oxygen-plasma, in which the ester group was the most sensitive to the plasma. Vacuum-ultraviolet(VUV) radiation emitted during plasma treatment played no substantial role to alter the surface morphology.

• Electrical & Electronic Materials
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• v.8 no.4
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• pp.434-442
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• 1995

To improve dielectric and mechanical properties of insulating composite by plasma surface treatment, new plasma surface treatment process is designed with concentric and hemi-circle electrodes system. the plasma, which is generated between anode and cathode, is induced to the upper side of the electrode system and treats the surface of the insulators. The optimal surface treatment condition is that pressure : 0.5[torr], flux density : 100[gauss], discharge current : 500[mA] and treatment time : 3 minutes. The composite filled with glass cloth surface-treated by plasma shows the improvement in electric and mechanical properties, comparing non- and coupling agent treated samples.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.632-637
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• 2003

In this study, the effect of surface treatment of CFRP and aluminum on the fracture toughness of CFRP/aluminum composites was investigated. CFRP was surface-treated by Ar$^{+}$ ion beam under oxygen environment, and the aluminum was surface-treated by DC plasma. CFRP was adhesively bonded to aluminum using the secondary bonding procedure. Cracked lap shear specimens were used to determine fracture toughness. Three cases of cracked lap shear specimens were made depending on the surface treatment. The values of fracture toughness of three cases were compared to each other It was found that the fracture toughness of ion beam-treated CFRP/aluminum composites was almost 72 % higher than that of unrented CFRP/aluminum composites. The fracture toughness of CFRP/plasma-treated aluminum composites was 50 % higher than that of untreated CFRP/aluminum composites.s.

• Journal of Surface Science and Engineering
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• v.26 no.2
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• pp.71-81
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• 1993

Thed effects of Ar or Oxygen RF plasma treatment on the adhesion behavior of Cr films to polyimide sub-strates have been investigated by using SEM, XRD, AES, and $90^{\circ}$peel test. By applying RF plasma treatment of the polyimide surface prior to metal deposition, the peel adhesion strength of Cu/Cr films sputtered onto the fully cured BPDA-PDA polyimide was highly increased from about 3g/mm to 90 ~ 100g/mm. Improved peel adhesion strength of Cr/polyimide interfaces due to RF plasma treatment was attributed to the contributions from surface cleaning, Cr-polyimide bonding at the interface, and force required for plastic deformation of the film. While the surface topology change of the polyimide caused by RF plasma treatment makes a little contri-bution to the improved adhesion.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.155-155
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• 2000

Adsorption of alkali metals on a silicon surface has attracted much attention due to its importance in metal-semiconductor interface technology, In particular, the bonding nature of alkali metal to silicon substrate has been a focus of fundamental research efforts. We examined the adsorbed layer of Cs on a Si(111)-(7$\times$) surface by reactive ion scattering (RIS) of hyperthermal Cs+ beams. RIS from a Cs-adsorbed surface gives rise to Cs, representing pickup of surface Cs by Cs projectile. The Cs intensity is proportional to surface coverage of Cs at a high substrate temperature (473 K), while it varies anomalously with Cs coverage at low temperatures (130-170 K). This observation indicates that RIS selectively detects metallic Cs on surface, but discriminates ionic Cs. Transition from ionic to metallic Cs adlayer is driven by thermal diffusion of Cs and their clustering process.