Effects of surface treatment of field emitter arrays on electrical characteristics of active matrix cathode

The effects of a wet chemical surface treatment of molybdenum-tip (Mo-tip) emitters on the electrical characteristics of an active matrix cathode composed of hydrogenated amorphous silicon thin film transistors and Mo-tip emitters are described. X-Ray photoelectron spectroscopy measurements showed that the surface treatment removed MoO₃ from the surface of the e-beam evaporated Mo film. In addition, the surface roughness of the Mo film was increased as the result of the surface treatment. The surface-treated active matrix cathode showed stable emission characteristics and immunity from emitter failures during its operation. The response time of the active matrix cathode was decreased by the surface treatment of the Mo-tip emitters. A change in surface composition and surface roughness appear to be responsible for the enhancement of the active matrix cathode.     

Influence of calcination temperature on structural and optical properties of TiO2-SiO2 thin films prepared by sol-gel dip coating

We prepared TiO₂-SiO₂ thin films with various TiO₂/SiO₂ ratios by sol-gel dip coating method and explored the dependence of their structural and optical properties on calcination temperature. The absorption peaks relevant to Si—O, Si—O—Ti and Ti—O bonds appeared in the FTIR spectra. With increasing TiO₂ content, the intensity of Si—O bond peaks decreases and that of Ti—O bond peaks increases. The XRD results show that the temperature of transformation from amorphous to anatase phase is lowered as TiO₂ content increases. The crystallite size of anatase phase in composite thin films increases with increasing TiO₂ content and calcination temperature. At 1000°C, the mixed phase of anatase and rutile appears in the pure TiO₂ thin films. The rutile films are denser than the anatase films. The increase in refractive index of composite thin films with calcination temperature is related to the decreased thickness and increased density as a result of evaporation of water and organic matters below 400°C. On the other hand, it is related to the change in the crystal phase and crystallite size of the films over 400°C.     

Influence of Powder Morphology and Chemical Composition on Metallic Foams produced by SlipReactionFoamSintering (SRFS)‐ Process

The SlipReactionFoamSintering (SRFS)‐ process is a metallurgical method to produce open‐cell metallic foams of iron based materials, steels and nickel based materials. In this process several chemical reactions take place. Through the most influential parameter, the morphology of the metallic powder, different properties of the foam can be adjusted, such as the viscosity of the slip, the cell structure and the mechanical properties. Several examples are presented in this paper. Moreover, the thermal conductivity of three foams is measured with the transient‐heat‐source‐technique.     

Semi‐Solid Processing of Metal Alloys

Semi‐solid metal casting is an innovative technology for the production of near‐net‐shape parts with demanding mechanical properties. The paper describes different processing routes and materials for semi‐solid‐metal casting (SSM), which have been investigated and also partially developed at the Foundry‐Institute of Aachen University. The standard thixocasting process for aluminium, highly reactive magnesium alloys and steel alloys with high melting points was investigated under variation of a wide range of process parameters. Specially adapted pre‐material production and reheating methods were developed for different materials and their application and future potential is pointed out. The thixocasting experiments were executed on a modified high pressure die‐casting machine with a specially designed “step‐die” providing wall thicknesses from 0.5 to 25 mm. The mechanical properties were tested in dependence of the wall thickness and the metal velocity. The results of these examination show high tensile strength values in combination with very good elongations. The rheocasting process is a new SSM‐forming method with liquid melt as feed‐stock and a high recycling potential. The research results of RCP‐technology (Rheo‐Container‐Process) invented at the Foundry‐Institute and of the Cooling‐Channel‐Process for aluminium and magnesium alloys are promising and are presented in this paper. Studies on semi‐solid processing of magnesium alloys and mixtures of them were conducted by Thixomolding^TM. To establish the most adequate process parameters, the temperature and the mixture relations were varied. Using a mould for tensile test specimens, the mechanical properties and the microstructure evolution could be evaluated. The chemical composition of the different phases was determined using SEM and EDX technologies. Evaluations of the flowing properties were conducted using a spiral mould with a total length of 2m and a cross section of 20mm x 1.5mm.     

Assuring Microstructural Homegeniety in Dual Phase and Trip Steels

The presence of ferrite/pearlite bands in dual phase and TRIP assisted steels is a consequence of microchemical segregation which causes mechanical properties anisotropy. Such inhomogeneous phase distribution produces a lowering of the mechanical properties such as fracture behaviour. This anisotropy is commonly not accounted in micromechanics computations which often assume a random distribution of phases in the solid. The present paper deals with an integral model for this undesirable band formation accounting for the solute segregation caused by solidification, microcomponent diffusion present in the austenitisation process, and the nucleation of the transformed phase in segregated regions. In the present work, the model was applied to two industrial grade dual phase steels and two TRIP assisted steels. The influence of such parameters on band formation is summarised in a number of “band prevention plots”, which are aimed at providing the optimum processing conditions for ferrite/pearlite band prevention.     

Preparation of AZ91D Slurries for Semi-Solid Forming Using Al8 ( Mn, Fe) 5 Precipitates

During the solidification of the AZ91D-alloys, the Al8(Mn, Fe)5 phase is generally precipitated in the melt in advance of the precipitation of the primary α-Mg. The basic principle for manufacturing AZ91D-alloy slurries for semi solid forming is to use the Al8(Mn, Fe)5 precipitates as the heterogeneous nucleation sites for primary α-Mg phases. Microscopic analysis for the location of the Al8(Mn, Fe)5 precipitate explains that the Al8(Mn, Fe)5 precipitate is the effective heterogeneous nucleation site for the primary α-Mg phase. It was also observed that increase of the Mn content in the melt and the cooling rate below to the solid/liquid two-phase region resulted in smaller and more globular primary α-Mg due to the increase of heterogeneous nucleation sites. It was found that the average α-Mg diameter grew as a function of t0.278, where t is the holding time at the solid/liquid two-phase region. This would be attributed to the Ostwald type ripening and coalescence between primary α-Mg phases. The cooling rate below to the solid/liquid two-phase region, Mn content in AZ91D alloy, and the holding time and temperature affected on the quality of slurry.     

Numerical investigation on the heat transfer characteristics of a liquid-metal pool subjected to a partial solidification process

The main purpose of this paper is to investigate numerically the effects of solidification on the heat transfer characteristics of the liquid metal layer, for use in accident analyses. The situation is very similar to an overlying liquid melt pool that could be fooned in the reactor lower head during the late phase of a severe nuclear accident. Based on a computational model, MPCOOL, the numerical predictions were then assessed through a comparison with the experimental data that was obtained with various boundary temperature conditions and geometrical aspect ratios, especially for the Ra-Nu relationship. For the cases with solidification, the results of the comparison show that(a) the computational model does show a good agreement with heat transter rates inferred from the experimental data, with a few exceptions at the Ra numbers which suggest a turbulent transport; and also (b) the computational model underpredicts the heat transfer rates by about 6% than that inferred from the experimental data when it is integrally evaluated with the Ra-Nu correlation. The foregoing results are mainly due to the currently limited applicability of the computational model up to the laminar-to-turbulence transition flows and its application to the turbulence flows because it is always subjected to a model uncertainty between the laminar and turbulence. Next, an additional comparison for the cases with and without solidification was made to examine the effects of the solidification on the energy partition within the liquid metal layer and its effects on the directional heat transfer rates. The results of the comparison show that the computational model for the case without solidification predicts higher heat transfer rates by about 15% than when solidification is included, but there isn't any experimental data that directly supports this trend.     

Influences of the dynamic strain aging on the J–R fracture characteristics of the ferritic steels for reactor coolant piping system

The leak-before-break (LBB) design of the piping system for nuclear power plants has been based on the premise that the leakage due to the through-wall crack can be detected by using leak detection systems before a catastrophic break. The piping materials are required to have excellent J–R fracture characteristics. However, where ferritic steels for reactor coolant piping systems operate at the temperatures where dynamic strain aging (DSA) could occur, the fracture resistance could be reduced with the influence of DSA under dynamic loading. Therefore, in order to apply the LBB design concept to the piping system under seismic loading, both static and dynamic J–R characteristics must be evaluated.Materials used in this study are SA516 Gr.70 for the elbow pipe and SA508 Cl.1a for the main pipe and their welding joints. The crack extension during the dynamic and the static J–R tests was measured by the direct current potential drop (DCPD) and the compliance method, respectively. This paper describes the influences of the dynamic strain aging on the J–R fracture characteristics with the loading rate of the pipe materials and their welding joints.     

Effect of irradiation on the impact and seismic response of a spent fuel storage and transport cask

The spent fuel storage and transport cask must withstand various accident conditions such as fire, free drop and puncture in accordance with the requirement of the IAEA and domestic regulations. The spent fuel storage and transport cask should maintain the structural safety not to release radioactive material in any condition. And also the effects of the irradiation should be considered because the spent fuels stored in the cask for a long time and be possible to change the mechanical properties of the cask.In this study, the changed mechanical properties of the cask after irradiation for the 30 years storage periods are assumed and applied to the impact analysis using ABAQUS/Explicit code and seismic analysis using ANSYS code. The stress intensity on each part of the cask is calculated and the effects of irradiation are studied and structural integrity of the package is evaluated.