• Nuclear Engineering and Technology
• /
• v.43 no.6
• /
• pp.557-566
• /
• 2011

A cold spray coating (CSC) of copper was studied for its application to a high-level radioactive waste (HLW) disposal canister. Several copper coatings of 10 mm thick were fabricated using two kinds of copper powders with different oxygen contents, and SS 304 and nodular cast iron were used as their base metal substrates. The fabricated CSC coppers showed a high tensile strength but were brittle in comparison with conventional non-coating copper, hereinafter defined to as "commercial copper". The corrosion behavior of CSC coppers was evaluated by comparison with commercial coppers, such as extruded and forged coppers. The polarization test results showed that the corrosion potential of the CSC coppers was closely related to its purity; low-purity (i.e., high oxygen content) copper exhibited a lower corrosion potential, and high-purity copper exhibited a relatively high corrosion potential. The corrosion rate converted from the measured corrosion current was not, however, dependent on its purity: CSC copper showed a little higher rate than that of commercial copper. Immersion tests in aqueous HCl solution showed that CSC coppers were more susceptible to corrosion, i.e., they had a higher corrosion rate. However, the difference was not significant between commercial copper and high-purity CSC copper. The decrease of corrosion was observed in a humid air test presumably due to the formation of a protective passive film. In conclusion, the results of this study indicate that CSC application of copper could be a useful option for fabricating a copper HLW disposal canister.

• Journal of the Korean Electrochemical Society
• /
• v.25 no.1
• /
• pp.32-41
• /
• 2022

Various steps in the electrode production process, such as slurry mixing, slurry coating, drying, and calendaring, directly affect the quality and, consequently, mechanical properties and electrochemical performance of electrodes. Herein, a new method of slurry coating is developed: Double-coated electrode. Contrary to single-coated electrode, the cathode is prepared by double coating, wherein each coat is of half the total loading mass of the single-coated electrode. Each coat is dried and calendared. It is found that the double-coated electrode possesses more uniform pore distribution and higher electrode density and allows lesser extent of particle segregation than the single-coated electrode. Consequently, the double-coated electrode exhibits higher adhesion strength (74.7 N m^-1) than the single-coated electrode (57.8 N m^-1). Moreover, the double-coated electrode exhibits lower electric resistance (0.152 Ω cm^-2) than the single-coated electrode (0.177 Ω cm^-2). Compared to the single-coated electrode, the double-coated electrode displays higher electrochemical performance by exhibiting better rate capability, especially at higher C rates, and higher long-term cycling performance. Despite its simplicity, the proposed method allows effective electrode preparation by facilitating high electrochemical performance and is applicable for the large-scale production of high-energy-density electrodes.

• Proceedings of the KIEE Conference
• /
• 1998.07d
• /
• pp.1516-1518
• /
• 1998

$YBa_2Cu_3O_x$(Yl23) Superconducting thick films on $Y_2BaCuO_5$(Y211) substrate were Prepared by surface diffusion process between $BaCuO_2$+CuO composite coating powder and a Y2ll substrate. X-ray diffraction shows that the Yl23 layer onto Y2ll substrate is the orthorhombic crystal structure. The specimen heated at $940^{\circ}C$ for 2h showed the maximum $J_c$ fo 500A/$cm^2$. Based on optimal condition, the superconducting fault current limiter(FCL) having a current limiting area 1mm wide and 66mm long was fabricated on Y211 substrate. A typical current limiting waveform was measured. When a voltage of 3V was applied, the fault current with a peak of 15A was limited to about 0.11A.

• Transactions on Electrical and Electronic Materials
• /
• v.3 no.4
• /
• pp.16-20
• /
• 2002

The high bias voltage associated with the thick layer (typically 500-1000 ㎛) of selenium required to have an acceptable x-ray absorption in radiography and fluoroscopy applications may have some practical inconvenience. A hybrid x-ray detector with zinc sulfide-amorphous selenium structure has been developed to improve the x-ray sensitivity of a a-Se based flat-panel digital imaging detector. Photoluminescence(PL) characteristic of a ZnS:Ag phosphor layer showed a light emission peak centered at about 450 nm, which matches the sensitivity spectrum of selenium. The dark current of the hybrid detector showed similar characteristics with that of a a-Se detector. The x-ray sensitivity of hybrid and a-Se x-ray detector was 345 pC/㎠/mR and 295 pC/㎠/mR at an applied voltage of 10 V/㎛, respectively. The purpose of this study was to evaluate the pertinence of a solution using a thin selenium layer, as a photosensitive converter, with a thick coating of silver doped zinc sulfide phosphor.

• The Korean Journal of Ceramics
• /
• v.2 no.2
• /
• pp.95-101
• /
• 1996

Variations of the leakage current behaviors and interface potential barrier $({\Phi}_B)$ of rf-sputter deposited (Ba, Sr)$TiO_3$ (BST) thin films with thicknesses ranging from 20 nm to 150nm are investigated as a function of the thickness and bias voltages. The top and bottom electrodes are dc-sputter-deposited Pt films. ${\Phi}_B$ critically depends on the BST film deposition temperature, postannealing atmosphere and time after the annealing. The postannealing under $N_2$ atmosphere results in a high interface potential barrier height and low leakage current. Maintaining the BST capacitor in air for a long time reduces the ${\Phi}_B$ from about 2.4 eV to 1.6 eV due to the oxidation. ${\Phi}_B$ is not so dependent on the film thickness in this experimental range. The leakage conduction mechanism is very dependent on the BST film thickness; the 20 nm thick film shows tunneling current, 30 and 40 nm thick films show Shottky emission current.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.40 no.9
• /
• pp.631-637
• /
• 2003

We have evaluated structural and electric, ferroelectric properties of PZT(30/70) thick film prepared by using 1,3-propanediol based sol-gel method on Pt/Ti/SiO$_2$/Si substrates. Rapid thermal annealing (RTA) is used to reduce the thermal stress and final furnace annealing is processed at $650^{\circ}C$. As the results of SEM analysis, we find that we get 350 nm in thickness for one coating and 1 $\mu$m for three times of coating. In the results of C-D analysis at 1 kHz, dielectric constant ($\varepsilon$$_{r}$) and dissipation factor were 886 and 0.03, respectively. C-V curve is shaped as a symmetrical butterfly. Leakage current density at 200 kV/cm is 1.23${\times}$10$^{-5}$ A/cm$^2$ and in the results of hysteresis loops measured at 150 kV/cm, the remnant polarization (P$_{r}$) and the coercive field (E$_{c}$) are 33.8 $\mu$C/cm$^2$ and 56.9 kV/cm, respectively. PZT(30/70) thick film exhibits relatively good ferroelectric, electric properties.s..

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.7
• /
• pp.673-677
• /
• 2016

Recently, engineering applications have started to adopt solutions inspired by nature. The peculiar adhesive properties of gecko skin are an example, as they allow the animal to move freely on vertical walls and even on ceilings. The high adhesive forces between gecko feet and walls are due to the hierarchical microscopical structure of the skin. In this study, the effect of metal coatings on the adhesive strength of synthetic, hierarchically structured, dry adhesives was investigated. Synthetic dry adhesives were fabricated using PDMS micro-molds prepared by photolithography. Metal coatings on synthetic dry adhesives were formed by plasma sputtering. Adhesive strength was measured by pure shear tests. The highest adhesion strengths were found with coatings composed of 4 nm thick layers of Indium, 8 nm thick layers of Zinc and 6 nm thick layers of Gold, respectively.

• Korean Journal of Materials Research
• /
• v.16 no.4
• /
• pp.225-230
• /
• 2006

Nanoimprint lithography (NIL) is a novel method of fabricating nanometer scale patterns. It is a simple process with low cost, high throughput and resolution. NIL creates patterns by mechanical deformation of an imprint resist and physical contact process. The imprint resist is typically a monomer or polymer formulation that is cured by heat or UV light during the imprinting process. Stiction between the resist and the stamp is resulted from this physical contact process. Stiction issue is more important in the stamps including narrow pattern size and wide area. Therefore, the antistiction layer coating is very effective to prevent this problem and ensure successful NIL. In this paper, an antistiction layer was deposited and characterized by PECVD (plasma enhanced chemical vapor deposition) method for metal stamps. Deposition rates of an antistiction layer on Si and Ni substrates were in proportion to deposited time and 3.4 nm/min and 2.5 nm/min, respectively. A 50 nm thick antistiction layer showed 90% relative transmittance at 365 nm wavelength. Contact angle result showed good hydrophobicity over 105 degree. $CF_2$ and $CF_3$ peaks were founded in ATR-FTIR analysis. The thicknesses and the contact angle of a 50 nm thick antistiction film were slightly changed during chemical resistance test using acetone and sulfuric acid. To evaluate the deposited antistiction layer, a 50 nm thick film was coated on a stainless steel stamp made by wet etching process. A PMMA substrate was successfully imprinting without pattern degradations by the stainless steel stamp with an antistiction layer. The test result shows that antistiction layer coating is very effective for NIL.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.2
• /
• pp.670-674
• /
• 2012

The photovoltaic performance of solid-state dye-sensitized solar cells employing hole transport material (HTM), 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), has been investigated in terms of HTM overlayer thickness. Two important parameters, soak time and spin-coating rate, are varied to control the HTM thickness. Decrease in the period of loading the spiro-MeOTAD solution on $TiO_2$ layer (soak time) leads to decrease in the HTM overlayer thickness, whereas decrease in spin-coating rate increases the HTM overlayer thickness. Photocurrent density and fill factor increase with decreasing the overlayer thickness, whereas open-circuit voltage remains almost unchanged. The improved photocurrent density is mainly ascribed to the enhanced charge transport rate, associated with the improved charge collection efficiency. Among the studied HTM overlayer thicknesses, ca. 230 nm-thick HTM overlayer demonstrates best efficiency of 4.5% at AM 1.5G one sun light intensity.

• Korean Journal of Materials Research
• /
• v.26 no.8
• /
• pp.417-421
• /
• 2016

We improve the energy conversion efficiency (ECE) of a dye sensitized solar cell (DSSC) by preparing a working electrode (WE) with localized surface plasmon resonance (LSPR) by inducing Au thin films with thickness of 0.0 to 5.0 nm, deposited via sputtering. Field emission scanning electron microscopy and atomic force microscopy were used to characterize the microstructure of the blocking layer (BL) of the Au thin films. Micro-Raman measurement was employed to confirm the LSPR effect, and a solar simulator and potentiostat were used to evaluate the photovoltaic properties, including the impedance and the I-V of the DSSC of the Au thin films. The results of the microstructural analysis confirmed that nano-sized Au agglomerates were present at certain thicknesses. The photovoltaic results show that the ECE reached a value of 5.34% with a 1-nm thick-Au thin film compared to the value of 5.15 % without the Au thin film. This improvement was a result of the increase in the LSPR of the $TiO_2$ layer that resulted from the Au thin film coating. Our results imply that the ECE of a DSSC may be improved by coating with a proper thickness of Au thin film on the BL.