Tadato Mizota

Cation distribution and bond lengths in CoAl2O4 spinel

Abstract It is widely known that CoAl2O4, IV(Co1−xAlx) VI[CoxAl2−x]O4, is a largely normal spinel (0

Hydration enthalpies of synthetic Na-A, cation-exchanged-A and some natural zeolites for evaluating as heat exchange absorbents

Abstract Hydration enthalpies of synthetic A-type and some natural zeolites have been measured by an adiabatic gas-absorption calorimeter to evaluate zeolite as a heat exchange absorbent for a solar-powered system. The Mg-exchanged A-zeolite is a suitable absorbent, if it is dehydrated at 100°C. The total hydration heat is the highest (531 kJ kg −1 ) of the A-type zeolites treated in the present work and is twice that of natural mordenite or clinoptilolite. An empirical equation is proposed to simulate the relation between differential enthalpies and hydration amounts.

Hydration heats of zeolites for evaluation of heat exchangers

The enthalpy of hydration of purified clinoptilolite from Beli Plast, Bulgaria, and various cation-exchanged types such as Na-, K-, Ca- and Mg-clinoptilolite was determined by the adiabatic water-vapor absorption calorimeter. The hydration enthalpy becomes more exothermic in the sequence K, Na, Ca, Mg depending on hydration energy values of exchanged cations. Na-clinoptilolite would be an efficient heat exchanger in a wide temperature range of dehydration, 180–300°C, while Mg-clinoptilolite in higher temperatures, 300–350°C.

Cubic phase of single-crystal LaAlO3 perovskite synthesized at 4.5 GPa and 1273 K

Single crystals of LaAlO3 (lanthanum aluminium trioxide) have been synthesized at 4.5 GPa and 1273 K, in the presence of an NaCl + KCl flux. The compound crystallizes with the cubic perovskite structure (space group Pm\overline{3}m). The thermal vibration of the O atom is remarkably suppressed in the directions of the Al—O bonds, and this anisotropy ranks among the largest observed in stoichiometric cubic perovskites.

Oxygen-deficient strontium cobaltate, SrCoO2.64.

Single crystals of strontium cobaltate, SrCoO(3-x), have been grown by the floating-zone method in an oxygen flow. The compound crystallizes with the cubic perovskite structure, with Pm-3m symmetry, as determined by X-ray diffraction. Refinement of the O-atom site occupancy yields the chemical composition SrCoO(2.64) [x = 0.36 (3)]. The anisotropic displacement ellipsoids of the O atoms suggest that their positional disorder occurs in a direction perpendicular to that of the Co-O bonds.

Entropy of Zeolitic Water

Zeolite-water heat-pump system is suitable for effective use of low temperature heat sources such as solar energy and waste heats from factories, that is,for energy saving. The heat exchange function of zeolite owes obviously to the nature of the zeolitic water, the state of which can be described in terms of the entropy value as an independent component of H2O. Most entropy values of zeolitic water have been given so far to be intermediate between those of liquid water (69.9 J mol-1 K-1 at 298 K) and ice (41.5 J mol-1 K-1 at 273 K).The present calorimetric measurements proved, however, that the entropy value for Mg-exchanged A-type zeolite is so small, even at the ambient temperature, as to be compared with the residual entropy of ice at 0 K.

Effective Use of Low Temperature Heat Sources by Using Confined State of Water in Various Microporous Absorbents

Energy saving is the most serious issue to sustain our life on the earth. Despite the limiting energy resources, we have been wasting enormous amount of heat from various places, such as factories, transportation systems and even houses, private or public. The exposed heat is difficult to use due to the nature of low temperature and low energy density, although the total amount is very large. We therefore lose much electric energy only to fell room temperatures by few degrees in summer, although electricity should be used for any other higher‐grade objects. Zeolite heat pump was proposed initially for effective use of low grade‐energy for cooling, such as air‐conditioning and refrigeration, but few practical application have been developed so far. Here, I emphasize that we have no other way except for using absorbing states of vapor in micro‐porous materials for effective energy‐conversion from the low grade‐energy. The zeolite‐water combination may be one of the most prospective pair for the object, beca...

Leaching Characterization of Red Mud

Red mud produced in the Bayer process is usually disposed of as a slurry. In spite of the great amount ofit, economically worthwhile utilization has not yet been realized. The main purpose of this study is to recover valuable components, especially titanium in red mud. The difficulty of applying flotation to red mud for recovering titanium, iron and aluminum compounds is based on the fact that red mud is composed of very fine particles in which the individual components become associated with the others prevailing in the slurry. Therefore, the leaching of valuable components from red mud was investigated by means of a few inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid as a function of leaching time, acid concentrations, and solution temperatures. Leaching of Si and Al in red mud is little affected by the kinds of acids and the solution temperatures. The extraction of both elements amounts in equilibrium to 70 percentages after about ten minutes. On the other hand, leaching of Fe and Ti in red mud is much affected by both of the leaching temperatures and the acid concentrations, especially by hydrochloric acid concentrations.