Advanced Materials Research Vols. 26-28

Abstract: Silicon nitride (Si3N4) ceramics have been considered for various components of nuclear power plants such as mechanical seal of reactor coolant pump (RCP), guide roller for control rod drive mechanism (CRDM), and seal support, etc. Corrosion behavior of Si3N4 ceramics in high-temperature and high-pressure water must be elucidated before they can be considered for components of nuclear power plants. In this study, the corrosion behaviors of Si3N4 ceramics at hydrothermal condition (300°C, 9.0 MPa) were investigated in pure water. The grain-boundary phase was preferentially corroded and the corrosion reaction was controlled by the diffusion of the reactive species and/or products through the corroded layer. Results of this study imply that the variation of sintering aids and/or the control (e.g., crystallization) of the grain-boundary phase are necessary to increase the corrosion resistance of Si3N4 ceramics in high-temperature water.

Abstract: Li2O excess 0.95(Na0.5K0.5)NbO3-0.05LiTaO3 (NKN-5LT) ceramics were developed by conventional sintering method. Abnormal grain growth in NKN-5LT ceramics was observed with varying Li2O content during sintering. In the 1 mol% Li2O excess NKN-5LT samples sintered at 1000 oC for 4h in air, electromechanical coupling factor and piezoelectric constant of NKN-5LT ceramics were found to reach the highest values of 0.37 and 250 pC/N, respectively. Lead-free piezoelectric of the composition 1 mol% Li2O excess NKN-5LT were fabricated. 10×10×3 mm3 size multilayer ceramic actuators (MLCA) were fabricated by conventional tape casting method. The displacement of the MLCA was ~ 1 μm at 150 V. These results show that the NKN-5LT ceramics with reasonable good piezoelectric properties have the potential to become the next generation material for a wide range of electro-mechanical transducer applications.

Abstract: Due to the need for CO2 sequestration associated with H2 production from fossil fuels, zeolite membrane are very promising due to their low cost, high stability and high permeance. Recently, the faujasite(FAU), the silica/aluminophophate(SAPO-4) framework family of zeolite have been studied for CO2 gas separation. In our study, ZSM-5 membrane was prepared on the porous alumina support using a hydrothermal technique. The thickness of zeolite membrane was controlled by the hydrothermal reaction time and temperature. The prepared zeolite membranes were characterized with SEM and thin film XRD. The hydrogen permeability and selectivity toward carbon dioxide gas were 0.6x 10-6 mole/m2.s.pa and 3.16, respectively. The hydrogen selective zeolite membranes show promising application in hydrogen separation from coal gasification such as Integrated Gasification Combined Cycle (IGCC).

Abstract: Ceramic membranes having less than 1nm size pores have great potential for gas separation at high temperature due to their good thermal stability. Moreover, nanoporous silicon carbide membrane has potential application under hydrothermal condition at high temperature since it is highly stable at high temperature. In this research, nanoporous SiC membrane has been developed on porous alumina support using preceramic polymer. Pore size of the SiC membrane was controlled using polystylene(PS) as the pore forming agent. The SiC membrane having controlled pore size was characterized with SEM, EDS, FT-IR, XRD and pore size measurement. The hydrogen permeability and selectivity toward nitrogen gas of the developed membrane were 0.3 x 10-6 mole/m2.s.pa and 4.1, respectively. The nanoporous hydrogen selective SiC membrane shows promising application in membrane reactor for steam reforming reacti on of natural gas, water gas shift reactions and hydrogen separation from coal gasification such as Integrated Gasification Combined Cycle (IGCC).

Abstract: Electrochemical properties (terminal voltage, ohmic resistance and overpotential) were measured for the cells of indium tin oxide (ITO, 90 mass% In2O3-10 mass% SnO2), perovskite-type oxide La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) or SrRuO3 cathode / Gd-doped ceria electrolyte (Ce0.8Gd0.2O1.9, GDC, 600-700 μm thick) / Ni-GDC anode using 3 vol% H2O-containing H2 fuel at 873 and 1073 K. The highest power density was obtained for the cell with SrRuO3 cathode, and was 36 and 328 mW/cm2 at 873 and 1073 K, respectively. The voltage drop was larger for the cathode than for the anode. Both of the ohmic resistance and overpotential were lowest for the SrRuO3 cathode among the investigated cathodes.

Abstract: In this work, porous alumina ceramics were obtained by controlled sintering of alumina-carbon black powder mixtures. In order to develop the porous alumina ceramics with high strength, as the amount of carbon black increased, the number of small pores increased because the pore characteristics and relative density the influence of SPS condition and carbon black content on was studied.

Abstract: The dynamic thermo-mechanical properties of two types of chemically surface modified (Carboxylated and Octadecylated) multi-walled carbon nanotubes (MWCNTs) and As produced MWCNTs reinforced epoxy matrix composites are investigated by Dynamic Mechanical Thermal Analyzer at 1.0 wt% concentration. Moreover, influence of MWCNTs concentration variations to the dynamic thermo-mechanical properties are evaluated at Carboxylated MWCNT reinforced polymeric composites (from 0.1 to 5.0 wt %). Higher interfacial bonding strength is achieved by introducing the chemical surface modification. Also MWCNTs reinforced polymer shows higher storage modulus (from 30°C to 70°C) than pure polymer. Moreover, the storage modulus of composites increases linearly by increasing MWCNTs concentration. However, glass transition temperature (Tg) of composites decreases linearly by increasing MWCNTs concentration.

Abstract: Optimization process for fabrication of Carbon nanotubes (CNTs) reinforced Polyethylene (PE) fibers by melt spinning has been studied. Three main melt spinning process parameters (spinning temperature, spinning distance, and spinning revolution) are evaluated by the Taguchi’s method to decrease the diameter of fibers. Decreasing diameter of fibers is greater influenced by spinning revolution and distance than spinning temperature. Moreover, fibers in diameter 22 μm (average) are successfully fabricated. Mechanical properties are measured by tensile test machine based on ASTM D3822 for single fibers which were fabricated at optimized melt spinning process parameters. Pure PE polymer fibers and chemically surface modified CNTs reinforced fibers also fabricated for comparison purpose. The interfacial bonding of CNTs with PE matrix is investigated through fracture surfaces image analysis by Scanning Electron Microscopy (SEM).

Abstract: To improve the wear resistance of high chromium white cast iron under severe abrasive conditions, a composites layer was designed for wear surface, which were locally reinforced with WC particles. And the local composites were successfully fabricated by optimized centrifugal casting process. Then the interface between WC and iron matrix was analyzed with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). And three body wear tests were carried out on a self-made rig to investigate the wear resistance of the composites. For comparison, the wear tests of high chromium white cast iron were also carried out under the same conditions. The results show that: There are no defects such as inclusion, crack, gas pore and so on in the obtained composites layer, which with a uniform thickness of 10 mm. WC particles are homogeneously distributed in the composites layer and tightly bonded with the iron matrix. The WC particles are partially dissolved in the iron matrix during centrifugal casting. The elements W, C and Fe react to form new carbides such as Fe3W3C or M23C6, which precipitate around former WC particles during subsequent solidification. So the interface between WC particles and the iron matrix is a strong metallurgical bonding. WC particles in the composites layer can effectively resist cutting by the abrasive, and then protect the matrix. The wear resistance of the composites layer is 7.23 times of that of high chromium cast iron.

Abstract: This paper develops a spectral element model for elastic-elastic two-layered beams. First, the axial-bending coupled equations of motion for an elastic two-layer laminated beam are derived. The spectral element model is then formulated by using the wave solutions satisfying governing equations in frequency-domain as the frequency-dependent shape functions. The spectral element model is finally applied to a cantilevered elastic-elastic two-layered beam as an illustrative problem. The high accuracy of the present spectral element model is verified by comparing the SEM results with those obtained by conventional FEM.