A crystallization-type phosphorus removal agent was prepared by carbonating a composite consolidated body containing gypsum, calcia and calcium carbonate in the wet condition. We tried to give organic substances removal ability as well as phosphorus removal ability to the composite consolidated bodies by supporting useful microorganisms on the surface the bodies. Microorganisms were supported by immersing samples in a culture solution containing lactobacillus, bacillus natto and saccharomyces. In this study, the effect of water content during carbonation on the water purification property of the consolidated body supported with microorganisms was examined. For the samples immersed in the culture solution, adhesion of microorganisms was confirmed on the surfaces by SEM observation, and therefore, 85% organic substances in a model sewage could be removed efficiently. However, the ratio of phosphorus removal decreased by 30% by immersing in the culture solution, resulting from the collapse of calcium carbonate crystals on the surface as a crystallization site of calcium phosphate. So, the degree of decrease in phosphorus removal ability varied greatly depending on the state of calcium carbonate precipitated on the surface. When carbonation was performed at 30% water content, the large number of fine calcium carbonate crystals precipitated on the surface of the consolidated body. That is, the area of the crystallization site of calcium phosphate was probably large. Therefore, the degree of decrease in phosphorus removal ability was almost 0% in case of carbonation at 30% water content because the surface of calcium carbonate that acts as a crystallization site of calcium phosphate sufficiently remained even after immersing in the culture solution.
Nutrient salts such as phosphorus and nitrogen compounds contained in wastewater are the causative substances of eutrophication phenomena in lakes and rivers and cause water quality deterioration. Also, heavy metals such as lead and cadmium cause four major pollution diseases. In this study, we prepared composites of zeolite with cation exchange capacity and hydrotalcite with anion exchange capacity and examined the possibility of simultaneous removal of phosphorus and lead. Zeolite-hydrotalcite composite was prepared by geopolymer reaction using silica fume, sodium aluminate and commercial hydrotalcite as starting materials. The effects of aging temperature and water content of the precursor slurry on the formation of zeolite were investigated to determine the optimal solidification conditions. In addition, the effects of zeolite / hydrotalcite mixing ratio and particle size of on phosphorus and lead removal ability were investigated. Zeolite formation and solidification sufficiently proceeded by aging the precursor slurry with a moisture content of 35 mass% at 90 °C. The smaller particle size of composites, the higher both phosphorus and lead removal ratios. The lead removal ratio increased with increasing zeolite content. The phosphorus removal ratio also increased as the hydrotalcite content increased. However, the composite collapse easily as the hydrotalcite content increased. Therefore, the optimum mixing ratio of zeolite / hydrotalcite was probably 6/4 in this experiment.
Silica fume (SF) is a byproduct when purifying silicon materials used for semiconductors and so on. The development of effective utilization of SF has been paid attention to, accompanied by increase in production of SF due to increase in the demand for semiconductor. Zeolite is one of functional materials with ability toward to catalysts, ion exchange and reversible dehydration, because of a crystalline structure which has same size micropores of molecular and exchangeable cations. In general, zeolite is produced as the fine powders of several microns by a hydrothermal synthesis method. It is difficult to handle the fine powder of zeolite, therefore a binder is added to mold it. However, the addition of a binder causes the decrease of zeolite content and degradation of performance for micropores in zeolite, resulting in reduction of the function of zeolite. Our research group has reported that zeolite could be synthesized as a consolidated body by using a geopolymer reaction. In this study, the possibility of the usage of SF as a raw material for a functional material, especially consolidated zeolite, was investigated to suggest high-value application of SF. It was revealed that consolidated zeolite can be synthesized with SF as a raw material. It was also proved that foamed zeolite was obtained by adding Si powder and zinc stearate. The foamed zeolite exhibited better humidity conditioning characteristics than the unfoamed zeolite. Thus, the possibility of effective utilization of SF was suggested for a functional material.
The addition of B2O3 and GeO2 to ZnO-Al2O3-SiO2 glasses decreased the crystallization peak temperature measured by DTA and also decreased the temperature where nucleation rate becomes maximum. ZnAl2Si2O8, Al6Si2O13 and ZnAl2O4 precipitated when ZnO-Al2O3-SiO2 glass crystallizes, and Al6Si2O13 and ZnAl2O4 are transformed to ZnAl2O4. The addition of B2O3 and GeO2 suppressed the precipitation of ZnAl2Si2O8 and Al6Si2O13. The addition of of GeO2 promoted the nucleation of ZnAl2O4.
Effect of La2O3-Y2O3 additives on coating and thermal stability of alumina layer on FeCrAl-alloy substrate was investigated. The stable alumina catalytic coat layer is required and its processing parameters are important in practical technology to fabricate automotive honeycomb-type catalytic converters. The two-step modification in La2O3-Y2O3-modified Al2O3 induced better slurry regarding with surface charge as colloid dispersion and rheological properties with lower viscosity and low stress under moderate shear rate condition. Surface Y2O3 controls zeta potential to high pH region so that alkaline solution can be applied to metal and alloy substrates. The newly modified Al2O3 coat layer can react with alumina interlayer grown on FeCrAl alloy surface. In conclusion, the optimal coating stability was attained with present La2O3-Y2O3 co-doped Al2O3.
The environment in a reinforced concrete communications manhole is always very humid and exposed steel bar can easily become corroded. However, since the depth below ground of these manholes is relatively shallow and the annual temperature change is modest compared to that for above-ground structures, it is assumed that the factors controlling the progress of steel bar corrosion are different than those for other structures. Moreover, manholes basically represent an isolated environment and there are no additional substances such as sea salt present compared to the outside air. In this relatively static environment, it is thought that the amount of water vapor is the main cause of change in the corrosion rate. Therefore, in this study, in order to clarify the supply mechanism of water that promotes steel bar corrosion in manholes, the relationship among the actual manhole temperature, humidity, and the corrosion rate was investigated. The results show that in winter, the temperature of the manhole ceiling is lower than the dew point temperature, so condensation occurs and steel bar corrosion progresses. Based on repeated temporal experiments, we find that the increase in condensation due to the difference between the dew point temperature and the temperature of the ceiling must be considered in order to explain the steel bar corrosion rate in manholes.
Silicon is a promising anode material for lithium-ion battery applications because of its high specific capacity. When silicon is lithiated, it undergoes a volume expansion, which may lead to extensive damage. This is thought to be a primary cause of the rapid decay in the cell capacity. Amorphous silicon (a-Si) has been recently suggested to possess a higher resistance to the lithiation-induced cracking compared with crystalline silicon (c-Si). This paper presents some experimental results of charge-discharge tests conducted on a cell composed of a-Si negative electrode and Li metal. An acoustic emission (AE) technique was employed to carry out in-situ monitoring of the mechanical damage during the tests. A number of AE signals were detected on the first lithiation in the a-Si negative electrode and the AE activity decreased drastically on the subsequent cycles. Examination of frequency components of the AE signals obtained in the tests identified two types of events: one type from silicon cracking, and the other type from the gas generation. The AE results suggested that the mechanical damage due to the lithiation and delithiation took place primarily on the first cycle.
During tempering process of steel materials, a plastic strain occurs along loading direction even if the applied stress is less than yield stress. The authors name this phenomenon “tempering plasticity”. In the temperature raising process during tempering, volume change occurs in each temperature range, and it is known that the cause is the decomposition of retained austenite and the precipitation of carbide. The influence of these factors on tempering plasticity has not been considered so far. In this paper the plastic strain was experimentally investigated by tempering of quenched specimen with tensile stress under various conditions such as “subzero treatment”, “change of tempering heating rate”, “the case of extremely low carbon material”. And the effects of decomposition of retained austenite and precipitation of carbide on tempering plasticity were quantitatively evaluated. As a result, decomposition of retained austenite has little influence on tempering plasticity, while precipitation of carbide has a large influence on tempering plasticity. Furthermore, assuming the similarity with the transformation plasticity phenomenon, the tempered plastic strain was formulated based on the tensile test during tempering, and the tempered plastic coefficient was obtained. This coefficient was proportional to the volumetric strain difference before and after tempering and inversely proportional to the lower yield stress of the parent phase and the new phase during tempering. This shows the similarity to the mechanism of transformation plasticity proposed by Greenwood-Johnson.