Key Engineering Materials Vols. 321-323

Abstract: Dynamic stability of axially accelerated beams is investigated in this paper. The equations of motion of a fixed-free beam undergoing axially accelerated motion are derived. Unstable regions due to the acceleration are obtained by using the Floquet’s theory. Stability diagrams are presented to illustrate the influence of the acceleration characteristics. Large unstable regions of flutter type instability exist around the first, twice the first, and twice the second bending natural frequencies. Divergence type instability also occurs when the acceleration exceeds a certain value. The validity of the stability diagram is confirmed by direct numerical integration of the equations of motion.

Abstract: This paper presents experimental and simulation results of discharge in spherically convergent beam fusion device. The deuterium-deuterium (D-D) fusion reaction in that device will generate neutron. The experimental device is consists of a vacuum chamber made of stainless steel, spherical mesh type anode and concentric grid cathode of 5cm diameter. The pressure of chamber maintained constant by injecting gas and pulsed voltage applied to grid cathode. A star mode discharge which has possibility of neutron generation was observed.

Abstract: Neutron imaging using a pulsed neutron time-of-flight method can give an energy dependent transmission image, namely, spectroscopic image. This image includes the structure information if the sample is coherent scatterer. Here, two examples are introduced. First, we obtained the transmission image of a welded sample of SS304 and 308. Change of the crystal structure depending on the position was observed. Furthermore, we measured spatial dependent transmission of SS samples treated in different ways, surface treatment and whole body treatment. There were almost no spatial dependent change, but the cross section change was found between surface and whole body treatment samples. It was suggested that this might be due to the difference of a grain size. These results demonstrated that the spectroscopic imaging using a pulsed neutron source is a useful tool for material characterization.

Abstract: The irradiation induced defects of irradiated reactor pressure vessel(RPV) steel were investigated by a small angle neutron scattering. The degradation of the mechanical properties of RPV steels during an irradiation in a nuclear power plant is closely related to the irradiation induced defects. The size of these defects is known to be a few nanometers, and the small angle neutron scattering technique is regarded as the best non destructive technique to characterize the nano sized inhomogeneities in bulk samples. The RPV steel was irradiated in the HANARO reactor in KAERI. The small angle neutron scattering experiments were performed at SANS instrument in the HANARO reactor. Both unirradiated and irradiated RPV steels were measured and the SANS data of both steels were compared. The nano sized irradiation induced defects were quantitatively analyzed by SANS. The type of defects was also analyzed based on the SANS results, and the effect of the chemical composition of the RPV steel on the irradiation induced defects was discussed.

Abstract: In this paper, we propose a dynamic Electrical Capacitance Tomography (ECT) image reconstruction algorithm based on the extended Kalman filter (EKF) to estimate the rapidly time-varying changes in the permittivity within the time taken to acquire a full set of independent measurement data. The ECT inverse problem is formulated as a state estimation problem in which the system is modeled with the state equation and the observation equation. Computer simulation with synthetic data is provided and comparison is done with existing modified Newton Raphson (mNR) method to illustrate the reconstruction performance of the proposed algorithm.

Abstract: Adhesion of flexible copper clad laminates (FCCL) on two different types of polyimide (PI), sputtering raw polyimide (SRPI) and casting raw polyimide (CRPI), were studied. Chromium (Cr), strongly reacts with dangling O bonds, was used as tie-coating layer in order to improve low adhesion between copper (Cu) and polyimide (PI). Polyimide surfaces were pretreated with gas plasma that was generated with a mixture of argon and oxygen before sputtering process. Adhesion measurement was performed on these samples according to IPC specification. The results show that the peel strength of the FCCL on SRPI was higher than on CRPI. This is considered to be due to the formation of Cu-Cr-O solid solution at the metal- PI interface.

Abstract: As the TFT-LCDs are getting more attention for the next generation display device, specifications of the mechanical functionalities of the device is to be more tighter as well as the electrical user specifications. Due to its brittle characteristics of TFT-LCD panels, maintaining mechanical integrity under an impact loading situation is the one of the key design concerns. Furthermore, as the TFT-LCDs are popularly adopted for various mobile equipments such as cellular phones and digital cameras, shock failure of the display should be prohibitive for the design engineers. A major incident being monitored during the shock loading is of course the local material failure of the TFT-LCD panel that might happen at its maximum deformation. The present work delivers a systematic approach for the shockproof design of mobile TFT-LCD. A specially designed shock test setup evaluated by a set of rigorous FEM analyses is shown and comments for the shockproof method is to be also delineated.

Abstract: In this paper, nano-sized Al2O3 powders are synthesized by a thermal MOCVD (Metal Organic Chemical Vapor Deposition) combined with plasma. The effect of reaction temperature on the characteristics of the synthesized Al2O3 powders is investigated. The experimental results demonstrate that while the temperature is increased from 200oC to 1000oC, the mean diameter of Al2O3 powders reaches from 400nm to 10nm. Hence, the increment of temperature can promote the synthesis of fine Al2O3 particle. Furthermore, the powder morphologies and crystallite size are also examined by the transmission electron microscopy (TEM) and XRD. Based on TEM observation, it is found that the particles are sphere shape. The XRD analysis shows that the particles are typical γ-Al2O3 crystalline phase over 400oC. Lastly, the effect of plasma on the characteristic of Al2O3 synthesized by thermal MOCVD is also considered.

Abstract: In the paper, zinc oxide (ZnO) thin films are deposited by plasma enhanced chemical vapor deposition (PECVD) at different substrate temperatures. The ZnO films are characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The analysis results indicate that highly crystalline films with high orientation can be obtained at a substrate temperature of 300 oC with 50 ml/min flow rate from Diethylzinc (DEZ). Furthermore, the investigation of optical property shows that ZnO films are transparent, and the peak transmittance in the visible region is as high as 85%.

Abstract: Optical emission spectra from plasma during deposition of diamond film were investigated by an optic multi-channel spectrometer using a CCD array sensor. The diamond film was deposited by DC plasma enhanced (PE) chemical vapor deposition (CVD) using hydrogen and methane gas mixture, where substrate was located at near the plasma and the discharge was performed by intermittent discharge. When Pg during the deposition was increased from 50 to 250 Torr, the optical emissions of hydrogen (Hα and Hβ) and C2 were increased, and corresponding to these increases, deposition rate of the diamond film was increased and crystalline quality became superior. When Cm was changed from 1 to 3 %, the emission from C2 was increased, and whereas, the emission from hydrogen was decreased. Corresponding to these changes of the emission, the deposition rate of the film was increased and amorphous component in the deposited film was also increased. These results show that the increase of C2 results in the increase of the deposition rate, and increase of hydrogen is effective to eliminate amorphous component, and therefore, monitoring of the optical emission from hydrogen and C2 is useful for the deposition process of the diamond film.