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.     

Ca-α SiAlON hollow spheres prepared by carbothermal reduction–nitridation from different SiO2 powders

The formation process of hollow spheres composed of nanosized Ca-α SiAlON particles was investigated using SiO₂ starting powders with different characteristics in particle size, shape and crystalline state. TEM observations showed Ca-α SiAlON hollow spheres composed of a large number of nanosized particles in the products prepared at 1450 °C for 120 min in nitrogen. In all systems, the Ca-α SiAlON hollow spheres were always produced through an intermediate Si–Al–Ca–O liquid phase in the same mechanism, regardless of the characteristics of SiO₂ starting powders used. Spherical solid particles consisted of amorphous phase containing Si, Al, Ca, O and a small amount of N were generated at the initial stage of carbothermal reduction–nitridation. These spherical solid particles changed into hollow particles with the progression of the reaction from the liquid phase to the crystalline Ca-α SiAlON with increasing temperature.     

Colorless polyimides derived from 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride,self-orientation behavior during solution casting,and their optoelectronic applications

A novel cycloaliphatic monomer for polyimides (PI), 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride (H′-PMDA) is proposed in this work. H′-PMDA shows high polymerizability with various diamines in contrast to its isomer, i.e., conventional hydrogenated pyromellitic dianhydride (H-PMDA) and leads to highly flexible and colorless PI films with very high T_g's. In particular, the combinations with rigid structures of diamines give rise to PIs with significantly decreased coefficients of thermal expansion (CTE) owing to high extents of in-plane chain orientation induced by thermal imidization, whereas the H-PMDA-based counterparts do not. The decreased CTE reflects structural rigidity/linearity of the H′-PMDA-based diimide units as supported by liquid crystallinity observed in the corresponding model compound. Solution casting of a chemically imidized PI derived from H′-PMDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) results in a lower CTE than that of the thermally imidized counterpart, suggesting the presence of a self-orientation phenomenon during solvent evaporation. The mechanism is proposed in this work. H′-PMDA/TFMB and its copolymer systems can be useful as plastic substrates in image display devices and/or novel coating-type optical compensation films.     

資源環境の保全をめざした二次副産材を導入するコンクリ一ト材料の発展的利用に関する研究

日本では,21世紀半ばに人工の固体物質の代表である解体コンクリート塊の排出量がピークを迎えると同時に,最終処分が困難になる状況が想定されていることから,コンクリート材料の完全資源型の利活用要求はより一層高まるといえる.本研究は,副産微粉,再生骨材などの二次副産材を積極的に混和し,同一産地*種類型の調合条件のもとで,コンクリートの物性改善,資源有効利活用を目的としたコンクリートを製造し,その基礎的物性の評価と環境影響評価を行い,環境保全に資するコンクリート材料の発展的利用のあり方を検討した.     

Optimization of magnesium hydroxide composite material mixed with expanded graphite and calcium chloride for chemical heat pumps

A composite chemical heat storage material (EMC) comprising a mixture of expanded graphite (EG), magnesium hydroxide (Mg(OH)₂), and calcium chloride (CaCl₂) was developed as a magnesium oxide/water chemical heat pump reactant. The optimization of a mixing weight ratio between the Mg(OH)₂ content of EMC and EMC itself was discussed from the viewpoints of both heat storage capacity and reactivity by considering the reaction rate constants from a kinetic analysis. It was confirmed that the dehydration reactivity of EMC increased as the mixing weight ratio decreased; however, the heat capacity of the EMC unit mass decreased. A multiplied factor consisting of the multiplied value dehydration rate constant and mixing weight ratio was introduced. It was suggested that a weight ratio of approximately 0.80 was the optimized value when the mixing molar ratio between CaCl₂ and Mg(OH)₂ was 0.10. Dehydration of EMC with an optimized mixing weight ratio and dehydration of pure Mg(OH)₂ were conducted under various temperatures to compare the reaction rate constants of each material. From this study, it was demonstrated that EMC performed better on dehydration than pure Mg(OH)₂.     

Effect of polyethyleneimine-fatty acid complex type dispersant structure on the overall processing chain of Si3N4 ceramics using multicomponent non-aqueous slurries

The effect of fatty acid structure of polyethyleneimine (PEI)-fatty acid complex, which was designed as a polymer dispersant for multi-component non-aqueous slurries, on the overall processing chain of Si₃N₄ ceramics involving slurry stabilization, spray drying, compaction, and liquid sintering was investigated using PEI-oleic acid (PEI-OA) and PEI-isostearic (PEI-ISA) complexes. Si₃N₄-Y₂O₃-Al₂O₃-AlN-TiO₂/toluene slurries were selected as a real model for Si₃N₄-based multicomponent slurries. It was observed that both PEI-OA and PEI-ISA can stabilize Si₃N₄-Y₂O₃-Al₂O₃-AlN-TiO₂/toluene slurries; however, the PEI-ISA system tended to have slightly higher slurry viscosity, which was suspected to be due to the interactions between protruded PEI segments among short ISA chains. The spray-dried granules from PEI-ISA-stabilized slurry were observed to have filled structures with higher surface roughness whereas those prepared from PEI-OA-stabilized slurry were observed to have hollow-structured granules. The granules prepared from PEI-OA slurry had improved flow and compaction properties with higher relative density of green compacts compared with those prepared from PEI-ISA-stabilized slurry, whereas the relative density and microstructural homogeneity of S₃N₄ ceramics sintered at 1600?°C for 2?h were observed to be higher for the PEI-ISA system. It is suspected that PEI-OA effectively improved the dispersion stability of multicomponent slurries and flow/compaction properties of granules; however, the inhomogeneous microstructures of green compacts induced by the hollow-structured granules had an adverse effect on the sintering of Si₃N₄ ceramics.     

用模态综合法对换气用小型马达进行振动解析

模态综合法是对复杂的机械进行振动解析的有效方法之一。本文将该法用于带换气扇马达的振动解析。整个马达系统分成四个子结构,用锤击试验法获得各子结构的传递函数。模态参数用曲线拟合法求得。然后用模态综合法进行综合,得到全系统的动特性。比较计算值和实验值,从而证明了这个方法的有效性。     

Behavior of Buried Flexible Pipe under High Fills and Design Implications

The existing design guidelines for buried flexible pipes are limited to depth up to 10?m. The increasing use of difficult terrains for infrastructure, landfills, and residential and industrial developments has prompted installation of drainage pipelines under 20–30?m high fills. This paper presents the behavior of an instrumented flexible pipe buried under a 47.1?m deep fill. For filling above 20?m, the measured vertical stress above the pipe exhibited a concave distribution, corresponding to 90 and 110% of the average vertical pressure at the center and edges of the pipe, respectively. The measured results suggest that a triangular lateral pressure distribution can lead to overly conservative and uneconomical results for high fills while Spangler’s analysis is unconservative. Based on the measured results, a revised vertical and lateral earth pressure diagram was proposed for the design of flexible pipe under high fills >20?m. This paper proposes closed-form analyses for estimating the moments and displacements of the pipe subjected to high fill earth pressures. These closed-form solutions agree well with the measured pipe displacements and strains.