Crystallization behavior of poly(l-lactic acid)

The crystallization behavior of poly(l-lactic acid) was studied in the range of 80-160 °C. The peak crystallization time (τ_p) was defined and obtained from the crystallization isotherm measured with a differential scanning calorimeter (DSC). Isothermal crystallization temperature (T_c) dependence of log(τ_p) discretely changed at 113 °C (= T_b). The linear growth rate of spherulite, G, was measured with a polarizing microscope. The T_c dependence of G and the size of the spherulite also discretely changed at T_b. Crystal structures for samples isothermally crystallized at temperatures which were higher and lower than T_b were orthorhombic (α-form) and trigonal (β-form), respectively. The discrete change of the crystallization behavior was explained by the formation of different crystal.     

Formation Mechanism of Hydrous-Zirconia Particles Produced by Hydrolysis of ZrOCl2 Solutions: II

The primary and secondary particle sizes of monoclinic hydrous-ZrO₂ particles produced by the hydrolysis of various ZrOCl₂ solutions, with and without the addition of NaCl, CaCl₂, or AlCl₃, were measured using X-ray diffraction and transmission electron microscopy in order to clarify the formation mechanisms of primary and secondary particles. The primary particle size of hydrous ZrO₂, under a constant ZrOCl₂ concentration, decreased monotonously with increasing Cl⁻-ion concentration. On the contrary, the secondary particle size increased monotonously with increasing Cl⁻-ion concentration. The present experimental results revealed that the primary and secondary particle sizes of hydrous ZrO₂ are controlled primarily by the concentrations of H⁺ and Cl⁻ ions produced during hydrolysis, and are independent of the type of added metal ions. The formation mechanisms of the primary and secondary particles of hydrous ZrO₂ were determined on the basis of the present experimental results.     

Densification and Thermal Conductivity of AIN Doped with Y2O3, CaO, and Li2O

Small amounts of Li₂O result in sintering in the AIN-Y₂O₃-CaO and AIN-CaO systems at firing temperatures <1600°C. The effect is ascribed to reduction of the liquidus temperature. Furthermore, Li₂O is removed by volatization at temperatures from 1300° to 1600°C, and its content decreases several ppm from the initial 0.3 wt%. Li₂O-doped AIN specimens containing Y₂O₃ and CaO additives are well densified by firing at 1600°C for 6 h, and their thermal conductivity is 135 W^.m^−1.K⁻¹.The effect of Li₂O addition on sintering and thermal conductivity also is discussed through thermo-dynamic considerations.     

High Thermal Conductivity in Silicon Nitride with Anisotropie Microstructure

Silicon nitride was fabricated by tape casting of α-Si₃N₄ powder with 5 wt% Y₂O₃ and 5 vol% rodlike β-Si₃N₄ seed particles, followed by tape stacking, hot pressing under 40 MPa, and annealing at 1850°C for 2-66 h under a nitrogen pressure of 0.9 MPa. Silicon nitrides fabricated by this procedure exhibited a highly anisotropic microstructure with large elongated grains (developed from seed particles) uniaxially oriented parallel to the casting direction. Thermal conductivities parallel to the grain alignment were much higher than those measured in other directions and exhibited high values of up to 120 W/(m.K). The anisotropic thermal conductivity of the specimen could be explained by the rule of mixture, considering that large elongated grains developed from seeds have higher thermal conductivity than a small-grained matrix.     

Numerical analysis of coupled transport and reaction phenomena in an anode-supported flat-tube solid oxide fuel cell

Heat and mass transfer with electrochemical reaction in an anode-supported flat-tube solid oxide fuel cell (FT-SOFC) is studied by means of three-dimensional numerical simulation. The distributions of the reaction fields in the anode-supported FT-SOFC are found to be similar to those in the planar SOFC with co-flow arrangement. However, in comparison with the latter, the concentration and activation overpotentials of the former can be reduced by additional reactant diffusion through the porous rib of the fuel channel. Parametric survey reveals that, for a fixed activation overpotential model, the output voltage can be improved by increasing the pore size of anode, while the cross-sectional geometry has smaller effect on the cell performance. Based on the results of three-dimensional simulation, we also develop a simplified numerical model of anode-supported FT-SOFC, which takes into account the concentration gradients in the thick anode of complex cross-sectional geometry. The simplified model can sufficiently predict the output voltage as well as the distributions of temperature and current density with very low computational cost. Thus, it can be used as a powerful tool for surveying wide range of anode-supported FT-SOFC design parameters.     

Sintering Kinetics at Constant Rates of Heating: Effect of Al2O3 on the Initial Sintering Stage of Fine Zirconia Powder

The sinterabilities of fine zirconia powders including 5 mass% Y₂O₃ were investigated, with emphasis on the effect of Al₂O₃ at the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The powder compact including a small amount of Al₂O₃ increased the densification rate with elevating temperature. The activation energies at the initial stage of sintering were determined by analyzing the densification curves. The activation energy of powder compact including Al₂O₃ was lower than that of a powder compact without Al₂O₃. The diffusion mechanisms at the initial sintering stage were determined using the new analytical equation applied for CRH techniques. This analysis exhibited that Al₂O₃ included in a powder compact changed the diffusion mechanism from grain boundary to volume diffusions (VD). Therefore, it is concluded that the effect of Al₂O₃ enhanced the densification rate because of decrease in the activation energy of VD at the initial sintering stage.     

Mechano-electrochemistry of a passive surface using an in situ micro-indentation test

Depassivation–repassivation of iron surfaces in boric–borate solutions were investigated by using the micro-indentation test. A pair of current peaks due to repair of the passive film following rupture of the film were observed during a series of indenter drives, i.e., loading and unloading of the indenter. The shape of the current peak depended on environmental conditions (conductivity and pH of the solution) and substrate conditions (mechanical processing history, alloyed element) as well as indentation conditions (repetition, maximum depth, and maximum load). Plastic deformation of the surface was accompanied by surface depassivation, while no depassivation occurred during the elastic deformation, indicating that the passive film on iron has a ductile property. The solution conditions did not affect the scale of depassivation but affected the rate of repassivation. Dislocations in the substrate made surface depassivation difficult but enhanced reactivity during the repassivation. The test also revealed that type-312L stainless steel has high corrosion resistance in a concentrated NaCl solution.     

Leak detection in pipe using transient flow and genetic algorithm

An inverse transient method with genetic algorithm (GA) was applied to leak detection in pipeline. Transient flow caused by valve operation was calculated using the characteristics method. The location and discharge of leak were determined so that the difference of the calculated pressure may be minimized from the reference pressure calculated under a given leak condition. Calculations were done for the leak at one and two locations in pipeline. Furthermore, the effect of noise in pressure data was discussed, and the leak locations and leak discharges can be predicted precisely even in the case of noisy data. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju Korea, October 16–19, 2007.     

Low cycle fatigue behaviors of elbow pipe with local wall thinning

Low cycle fatigue tests were conducted using 100A elbow specimens made of STPT410 carbon steel with local wall thinning. Local wall thinning by erosion/corrosion was simulated by machined pipe wall thinning. The local wall thinning areas were located at three different areas, called extrados, crown and intrados. The elbow specimens were subjected to cyclic in-plane bending under displacement control without internal pressure. The effects of eroded conditions, such as eroded ratio, eroded angle and position, on the low cycle fatigue behavior and fatigue life were discussed by using experimental results and finite element analyses. Also the location of crack initiation and the crack growth direction could be predicted by three dimensional elasto-plastic finite element analyses. In addition, the safety margin of eroded elbows against seismic loading was discussed by comparing the fictitious stress of elbows with the allowable stress limit demanded by the design code.     

纳米Pt膜的晶粒尺寸及其对热导率的影响

采用电子束-物理气相沉积法（EB-PVD）制备了6个厚度为15-62nm的铂薄膜,研究了纳米薄膜的晶粒尺寸及其对热导率的影响规律．当薄膜厚度小于30nm时,晶粒平均尺寸接近于薄膜的厚度;晶粒尺寸随着薄膜厚度的增加而增大并趋于定值;当薄膜厚度大于30nm时,晶粒尺寸约为20nm．受薄膜的表面和内部晶界的综合影响,铂纳米薄膜的热导率大大低于体材料的值,并且纳米薄膜的热导率随着薄膜厚度的增加而增大并趋于一个低于体材料热导率的值．