Anisotropic sintering stress for sintering of particles arranged in orthotropic symmetry

Many sintering bodies shrink in an anisotropic manner when the particle packing is not isotropic. The thermodynamic driving force for the anisotropic shrinkage, i.e. the sintering stress tensor, is determined numerically for an open pore structure with orthotropic symmetry in three dimensions. The sintering stress tensor is calculated rigorously by the energy method, the force balance method and the volume averaging method. The deviatoric component of sintering stress is approximately proportional to the logarithm of the aspect ratio of the orthorhombic volume element, and acts so as to deform the elongated particles to be more isotropic in most cases.     

A generation of ultra-high pressure for phase transformation

A new method was devised to generate an ultra-high dynamic pressure for materials synthesis and phase transformation by using the cylindrical explosion. Unlike the ordinary cylindrical method, the specimen is not directly packed into the metal tube but sandwiched between the metal films that are rolled into a cylindrical geometry. For distinguishable point of view, we term it as ’rolled-film’ method. The numerical simulation demonstrates that this method can produce higher shock pressure than the ordinary cylindrical method. The practical experiment for boron nitride phase transformation also indicates thal a higher shock pressure is able to be achievable.     

Corrosion of ZrB2 Powder During Wet Processing – Analysis and Control

Corrosion behavior of ZrB₂ powder during wet processing in water or ethyl alcohol was studied both with and without an organic additive. Incorporation of oxygen and pH change did not intensively occur during static aging of aqueous slurries, but corrosion was enhanced when stirring the slurries. The oxygen content of the powder increased rather rapidly with milling time in ethyl alcohol. The molecular weight of polyethylenimine effected the pH change and oxygen content of ZrB₂ powder, after corrosion in water for 18 months. X-ray photoelectron spectroscopy analysis informed that the surface of both the pristine and corroded powders was mainly covered with ZrOH, but a certain amount of Zr–B bonding remained at the powder surface after the wet processing.     

Proposal and characteristics evaluation of a CO2-recovering hybrid power generation system utilizing solar thermal energy

A CO₂-recovering hybrid power generation system utilizing solar thermal energy is proposed. In the system, relatively low temperature saturated steam around 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine in which generated CO₂ is recovered based on the oxygen combustion method. Hence, solar thermal utilization efficiency is considerably higher as compared with that of conventional solar thermal power plants in which superheated steam near 400°C must be produced for use as the working fluid of steam turbines; the requirement for solar radiation in the location in which the system is constructed can be significantly relaxed. The proposed system is a hybrid energy system using both the fossil fuel and solar thermal energy, thus the capacity factor of the system becomes very high. The fuel can be used exergetically in the system; i.e., it can be utilized for raising the temperature of the steam heated by utilizing the turbine exhaust gas more than 1000°C. The generated CO₂ can be recovered by using an oxygen combustion method, so that a high CO₂ capturing ratio of near 100 percent as well as no thermal NO_x emission characteristics can be attained. It has been shown through simulation study that the proposed system has a net power generation efficiency of 63.4 percent, which is higher than 45.7 percent as compared with that of the conventional power plant with 43.5 percent efficiency, when the amount of utilized solar energy is neglected and the temperature of the saturated steam is 220°C.     

Distributed computing architecture for effective management of multimedia streams on DPE

We study a networking architecture model that is built on a distributed processing environment (DPE) for multimedia services suitable for high speed transport networks such as ATM networks. In this architecture, the applications are deployed as units of software building blocks. Each building block provides a layered view for the effective management and control of the multimedia network resources and services according to the concept of telecommunications management network (TMN) and telecommunications information networking architecture (TINA). For the purpose of flexible service provision to users and effective service introduction by service providers, this architecture proposes the adoption of ad hoc service building blocks such as a video on demand building block and a CSCW building block that have interactions with a general purpose building block. This paper also proposes a naming structure for the management of user profiles and session profiles using a directory service system, and an effective control model for multimedia logical device objects using a stream process approach. The proposed model is implemented on a DPE platform that provides various transparencies, ANSAware.     

Recrystallization of TiC dispersion Mo-alloy

The recrystallization of Mo sheet which was mechanically alloyed with 1.0 TiC and 0.2 C (weight %) was investigated in H₂ atmosphere. The change in hardness (Hv) was measured as a function of annealing temperature and the microstructure was observed using scanning, transmission and Auger electron microscopy. Hv decreased slowly below 1800 °C and steeply above 1800 °C. Dislocations and grain boundaries were still pinned by small Ti-oxy-carbide and/or Ti-oxide particles even at 1800 °C, while the grain size increased. Above 1800 °C, however, such particles were coarsened with the formation of pores and also the grain size increased further. As a result, the slow drop phenomena of Hv below 1800 °C should be interpreted in terms of a retarding effect of fine particles on the recrystallization. The prominent drop phenomena of Hv over 1800 °C can be understood by the grain growth and particle coarsening accompanying an evolution of pores.     

Influence of heating in vacuum on low-temperature fracture behavior of carburized Mo-Ti alloys

In order to deduce the state of carbon and its interaction with titanium in the carburized molybdenum-titanium alloys (target titanium content: 0.1, 0.2, 0.5 and 1.0 mass%), changes of low-temperature fracture strength and ductility after heating in vacuum at 1773 K were investigated.

Bend tests were performed at temperatures from liquid nitrogen temperature to room temperature and yield strength, maximum strength and bend angle were calculated in each temperature. In this study the low-temperature fracture strength and ductility of a material were represented by the critical stress and the critical temperature, respectively. Fracture surfaces of the specimens failed at low temperatures were examined by using a scanning electron microscope and crack initiation and propagation characteristics were investigated. The results are summarized as follows.

1. (1) For the alloy with lower titanium content (e.g. Mo-0.1 mass%Ti alloy): the critical stress, the critical temperature and the fracture mode were almost unchanged after heating in vacuum. In this case it is deduced that carbon exists as free carbon and carbides at the grain boundaries. During heating, reduction of free carbon occurred by decarburizing, but it was compensated by the carbon produced by the resolution of carbides in a manner similar to pure molybdenum. Consequently there still remained enough carbon to strengthen the grain boundaries.

2. (2) For the alloy with higher titanium content (e.g. Mo-1.0 mass%Ti alloy): the critical stress remarkably decreased and the critical temperature increased after heating in vacuum. The fracture mode also changed from transgranular to intergranular. In this case it is deduced that carbon exists as free carbon both at the grain boundaries and at the interfaces between titanium-oxides and matrix. During heating, only the reduction of free carbon proceeded and consequently the grain boundaries became short of carbon.

     

Chemical Fixation of Carbon Dioxide to Propylene Carbonate Using Smectite Catalysts with High Activity and Selectivity

The reaction of propylene oxide and carbon dioxide to propylene carbonate was carried out using Mg-, Ni- and Mg-Ni-containing smectite catalysts which contain different amounts of alkali atoms such as sodium, potassium and lithium. These catalysts are highly active and selective for this reaction. The catalytic activity strongly depends on the elemental composition of the catalyst used. Particularly the amount of alkali atoms incorporated in the catalyst is the most important factor governing the catalytic performance. The most active catalyst among those prepared in the present study shows a turnover number of 105 mmol/g for the propylene carbonate formation, which is the highest turnover number compared with those reported so far (10 mmol/g) for the title reaction.     

Cellulosic solid films exhibiting cholesteric liquid crystalline order

Ethyl cellulose (EC) and hydroxypropyl cellulose (HPC) films were cast under different conditions and were observed optically. The creep behaviour of those films was determinedin vacuo as a function of applied stress or temperature and was analysed on the basis of the Eyring thermally activated process.EC and HPC films cast from liquid crystal-forming systems remained cholesteric liquid crystalline order (the cholesteric sense was different in each case), whereas EC film cast from non-liquid crystal system (benzene) had no liquid crystalline order and was amorphous. The Eyring activated process could be applied to the creep behaviour of our films and activated parameters could be evaluated. The activated volumeV was of the order of 1 nm³ and greatly depended on the casting conditions and testing temperature. The value ofV tended to decrease as the liquid crystalline order increased. The value ofV was smaller than the size of liquid crystalline domain.