Considering the situation of energy demand in Japan, nuclear power generation might be growing up from now on. Nuclear power plants, however, produce radioactive wastes. The wastes must be disposed safely for long term. In this paper, the present plans of the waste disposal of several radioactive levels in Japan are summarized. First of all, the radioactive wastes are categorized into low and high levels in accordance of their radioactivities.Since the low level wastes also have several classes depending on their activities, we have to select a different disposal design. Of these disposal designs, the projects for low levels are explained in detail. Moreover, it is noteworthy to dispose the relatively high low-level radioactive wastes. Its disposal design is called as “subsurface disposal” and its facilities are being planned to be constructed more deeply than the facilities for the other low level wastes. A fundamental concept for the subsurface disposal design is discussed on the view of assuring safety against the radioactive pollution. Scientific knowledge and engineering technologies for the study on the subsurface disposal design are discussed. In particular, the following items; the 3D seismic survey for searching faults, 3D groundwater flow analysis by considering long-term changes in topography and climate,and evaluation of the changes in geochemical conditions and rock characteristics around a spacious cavern.
Waste H3PO4 solution containing Al and Mo is discharged from a liquid crystal display production process. The discharged amount of waste acid solution, for example, reaches about 3,000 ton/year at one factory. Neutralization and activated sludge methods have been used for the waste acid solution. From the viewpoint of environment and resources recycling, it is important to recover and recycle H3PO4 from the waste acid solution. Separation technologies such as solvent extraction, electrodialysis and ion exchange resin methods, may be used to remove metal ions from the waste acid solution and regenerate H3PO4. In this study, the removal of Al and Mo in the waste H3PO4 solution by ion exchange resin was investigated. It was found that the ion exchange resin method is useful to remove Al and Mo in the H3PO4 solution. The waste H3PO4 solution was diluted by 5 times and then, Al ions were captured by H+ type cation exchange resin in the cation exchange step and next Mo ions were captured by OH- type anion exchange resin in the anion exchange step. These experiments were carried out using an ion exchange resin column of φ 20mm and 410mm height. From the breakthrough curve of Al ions, it is possible to feed the H3PO4 solution by 14.4 times as large as the bed volume of cation exchange resin before reaching the breakthrough point if the flow rate represented by SV is set to be 5. For Mo removal, the H3PO4 solution can be fed by 6 times as large as the bed volume of anion exchange resin.
Water pollution and salt damage are caused by seawater intrusion into coast area. Salt and fresh water boundary fluctuation is a one of an index to detect seawater intrusion. In this research, electrical survey was applied to grasp the salt and fresh water boundary fluctuation. The measurement line was set at southeastern J-PARK in Tokai village, Ibaraki prefecture where is on coast area. The survey was carried out every one to three months during one year. Electrical survey machine was used in this survey so that enough current can flow coast area where is covered by sand layer. As a result, high resistivity zone fluctuates at the 35 m point of east to south in the depth of 12 to 15 m. This fluctuation is clear on dry and rainy seasons. Hence, seasonal resistivity fluctuation is clarified in the coast area. Comparing this fluctuation with precipitation, underground temperature and conductivity, salt and fresh water boundary is extracted from resistivity distributions. From this, underground structure and salt and water boundary model in rainy and dry seasons can be estimated in this site.
M. Pourbaix in Belgium proposed the Eh—pH diagram to examine the thermodynamic aspects of corrosion in 1940s. Thereafter, this potential—phase diagram was applied to the fields of, hydrometallurgy and fused salt chemistry as well as analytical chemistry, and it has been extended to the systems containing complex formation or sulfide formation reactions. It is because the diagram is quite useful to understand the thermodynamic aspects of reactions involved in the various processes from a bird’s eye view. In this paper, I briefly reviewed the applications of the diagram by exemplifying the electroless plating of nickel, the formation of ZnO thin films and the electrodeposition of CdTe films to contribute to understanding aqueous processing of material surfaces.
The group III-V compound semiconductors and their solid solutions are important materials used in high speed electronic and optical electronic devices. Crystal growth of these semiconductor materials involves processes between the solid and liquid phases or solid and gas phase at near equilibrium conditions. Therefore, knowledge of thermodynamic and thermochemical properties for the semiconductor systems is important for providing optimum conditions in the analysis of processes for the crystal growth. In this report, some thermodynamic and thermochemical data such as heat capacity, standard entropy, heat and free energy of formation of compounds and heat of mixing of solid solutions on calorimetry are summarized. Base on these data, the vapor epitaxial growth of the III-V solid solution crystal are analyzed thermodynamically. The calculated compositions of the alloys have been compared with experiment, showing remarkably good agreement.
Based upon thermodynamic considerations for various materials processing, solution processings appear to be the most energetically (environmentally) benign techniques. Various solution procesings for ceramics are critically reviewed with emphasis on their merits and demerits. Existing confusions and contradictions are pointed out in the definitions and concepts of various methods: i.e. precipitation, colloid, sol-gel, polymer-gel, complexed-gel (polymerized complex), soft process (soft solution process) and/or more widely, solution deposition, chemical solution deposition, bio-mimetic, bio-inspired, ink-jet, spray, etc. In particular, for ceramic films and patterns, the conventional methods where firing is essential after coating of powders from their suspensions or their solution precursors might be rather close to solid (powder) processes. This is especially true when significant chemical reactions are not involved during the coating processes, thus most reactions such as pyrolysis, compound formation (synthesis), crystallization, consolidation, substrate adhesion, etc., occur in the solid states by heat. In those solid state processes using firing of powders after shape-forming, the cracking/peeling of the film and/or the bulk is serious problems because volume shrinkage during firing is inevitable for packed powders. Those shrinkages practically limit the application of those powder processes. In order to overcome those limitations, alternative methods where chemical reactions at the interface between a solution and a substrate solid and/or a reactant are described here as typical Soft Processing Methods. They may lower the difficulties in powder processes by forming shaped materials in a single step at lower temperatures. In addition to the production of nano-crystals such as SrTiO3, Zr0.6Ce0.4O2, etc., direct fabrication of LiCoO2 and PbS films in solutions at room temperature to 150°C without post firing are described. “Direct Patterning of Ceramics” using ink-jet reaction or ink-jet deposition method has also been proposed.
The proton transport properties of a single crystal of acceptor (Mg, Ca, Sr, Ba) doped α-alumina was surveyed by reviewing our recent works. Here, the dissolution mechanism of hydrogen, the site of proton in the crystal, the value of conductivity, the mobility, and the concentration of defect for α-alumina are discussed. It was clarified that proton is incorporated into acceptor-doped α-alumina and it become the dominant charge carrier under the reducing atmosphere containing hydrogen at 1073-1673 K. Although the proton conductivity was very low, the transport number of proton for α-alumina was larger than the other defect structure-type proton conducting oxide at high temperature region.
Oxygen diffusivity in perovskite oxide was introduced based on oxygen tracer diffusion constant. The high oxide ion conductivity in LaGaO3 based oxide was explained by high mobility of vacancy. Although electrical conductivity increased with increasing dopant amount, mobility of vacancy estimated by oxygen self diffusion decreases with increasing dopant amount, which could be explained by the formation of dopant and vacancy cluster. Difference in oxygen diffusion in fluoride and perovskite oxide was also introduced.
Metal powders were prepared by precursor—thermal decomposition method and chemical reduction method in aqueous solutions. In precursor—thermal decomposition method, the morphology and size of nickel powder were controlled via the thermal decomposition of nickel oxalate powder, that was prepared by mixing a solution containing oxalic acid ion with some kinds of nickel sources such as nickel ion, ammoniacal nickel complex ion, and nickel hydroxide. Needle-like nickel oxalate powder with high aspect ratio, [Ni(NH3)2]C2O4 2H2O, was synthesized by using ammoniacal nickel complex ion, and rectangular parallelepiped shape of nickel oxalate powder, NiC2O4 2H2O, was by nickel hydroxide. As for the chemical reduction method in aqueous solution, ascorbic acid (vitamin C) at pH 3 reacts with copper ion as a reducing agent, and copper metal particle in size of 100 nm was obtained. Under the condition of pH > 3, reduction property is weakened, and precipitates consisted of copper powder with cuprous oxide. Ti3+ ion (Ti2(SO4)3 solution) also has a reducing property for copper ion and acts as a new reducing agent in liquid phase reduction process.