On the castable refractory composed of calcined flint clay aggregate below four millimeter and calcium aluminate cement, the effect of particle-size distribution on workability, packing properties, strength both green and fired and volume stability in firing were investigated as compared with the effect of cement content and additive plastic clay.
From the results, it was shown that (1) optimum flow value, denser density, stronger strength and better volume stability were obtained when q shifted 0.3 and δ shifted -0.2 on author's equation of particle-size grading, (2) the effects better than above mentioned effect were not obtained by increasing fineness of fine part of aggregate and by increasing cement content, (3) only better shape holding property in workability were obtained by addition of plastic clay.
These results suggested the importance of controlling particle-size grading to obtained satisfactory behavior of castable refractory.

View full abstract

Closely jointed couples made up of the sapphire single crystal and the periclase single crystal were heated at 1500°C, for 240h in air.
In order to reveal a topotaxy in the sapphire-grown spinel, a-, m- and d-planes of sapphire were chosen as joint surfaces with a cleavage plane of periclase.
The orientation in the sliced surface, parallel to the reaction surface, of the sapphire-grown spinel was estimated from the X-ray diffraction intensities. The relation between {110} plane of grown spinel and c-axis direction of sapphire was made clear from optical observation of etch pits.
Based on this observation, an illustration of the relation between grown spinel lattice and mother sapphire lattice was drawn.
The equations, 4H=2h-k-l, 4K=-h+2k-l and L=h+k+l were derived from the geometrical consideration, where (HKL) is a set of index for sapphire and (hkl) for spinel.
Calculated results from these equations agreed very well with the experimental results.

View full abstract

The purpose of the present work is to investigate the relation between chemical durability and composition of the vitrified part, which has formed during the firing process of heavy metal-containing sludges together with silicates. The glass forming regions of Na₂O-CaO-M_xO_y-SiO₂ systems (M_xO_y: Cr₂O₃, NiO and CuO) under firing at 1000°C for 2h were determined and the chemical durability of the glasses was examined by the determination of metal ions dissolved into acetic acid-ammonium acetate buffer solution of pH 4.5.
The maximum content of Cr₂O₃, NiO and CuO in the glasses formed at the present firing condition were 1.5, 5.0 and 23.0mol%, respectively. The ratio of the amount of the dissolved metal ions to the initial contents in the glass considerably increased when Na₂O content exceeded 30mol%. The addition of CaO reduced the dissolution ratio in each system. However, in the system of relatively lower content of silica and higher content of CaO, the soluble chromates of sodium and/or calcium were formed. Therefore, the care must be taken in the treatment process of the sludge of higher CaO content.

View full abstract

It was previously reported that a peak appeared in the internal friction curve of the chalcogenide glasses consisting of only network formers when strong and weak parts co-existed in the network structure. This investigation was performed for the purpose of clarifying whether the relaxation mechanism in the network-forming oxide glasses resembled that of the chalcogenide glasses. The glasses used in the measurement were the following binary systems; two network-forming oxides with different coordination numbers, or network-forming oxides and modifier oxides with divalent cations. A broad peak was observed in every system except the system of TeO₂-BO_1.5. It was suggested that a peak appeared when strong and weak parts co-existed in the network structure, and that the increase of the weak part raised the height of background as same as chalcogenide glasses.
The peak behaviour resembled that of chalcogenide glasses in the range where the weak part exceeded the strong part and was reverse to that of chalcogenide glasses in the range where the strong part exceeded the weak part. A peak was not observed in the system of TeO₂-BO_1.5 probably due to each aggregation of weak or strong parts in the network structure.

View full abstract

The electrical conductivity and dielectric relaxation of glasses in the system Ag₂O-P₂O₅ were studied in the temperature range 20-120°C. The silver phosphate glasses were found to be vitrified up to the amount 60mol% of Ag₂O content.
In the glasses containing Ag₂O, the conductivity increased with the increase of the amount of Ag₂O content. The values of logσ also increased with the increase of both the melting temperature and the melting time. The silver-containing phosphate glasses were shown to have higher values of logσ and their lower temperature coefficients than in sodium-containing glasses. The deviation of logσ value from the linearity showing the relationship between the conductivity and the Ag₂O content was considered to arise from the presence of colloidal silver metal.
The ε′ and ε″ increased rapidly with the increase of the amount of Ag₂O. The silver-containing phosphate glasses have larger dielectric constants and losses than those of the sodium phosphate glasses. The magnitude Δε of the dielectric relaxation showed the maximum at about 50mol% Ag₂O. The dielectric relaxation of glass containing less than 40mol% Ag₂O was considered to be attributed to migration loss and that of glasses containing above 50mol% Ag₂O be attributed to Maxwell-Wagner loss.
The similarity of the chain structure was observed by the comparison of the infrared spectra of silver- and sodium-containing phosphate glasses. However, the absorption bands of 1280cm^-1 and 1100cm^-1 were shifted toward its lower wave number by replacing Na₂O with Ag₂O. It is suggested that the Ag-O-P bond in the silver-containing phosphate glasses may have a partial covalent nature.

View full abstract

The effects of history of preparation on the sinterability of compact of alumina powders prepared in different processes from a hydrated aluminium sulfate were studied. By calcination, the sinterability increases with transition to α-alumina and is lowered with strengthening aggregates in the powder. Laminated plate-like particles of anhydrous aluminium sulfate are prepared by heating under reduced pressure, from which a highly sinterable powder consisted of two-dimensional chained aggregates is produced by calcination. In contrast, cubic shaped ones are prepared by heating with conc. H₂SO₄, from which an almost no sinterable powder consisted of three-dimensional chained, cubic shaped aggregates is produced. The calcined powders from the ordinary dehydrates are of middle characteristics in the above two. Dehydrations or decompositions at relatively low temperature and long duration result in decrease of the sinterability with increase of three-dimensional bonding in the aggregates after calcination. By contraries, dry milling at the stage of anhydrous sulfate results in remarkable increase of the sinterability of the calcined powders with increase of discrete particles. Dehydrations after dry milling of the starting hydrate or after dissolving it in added free water also increase the sinterability of the calcined powder. It seems likely that two-dimensional bonding configuration of Al atoms in a layer structure of the hydrate is not broken up with dissolving in its water of crystallization but persist in the structure of anhydrate to affect directly the structure of aggregates after calcination.

View full abstract

The thermal diffusivity, the heat capacity, and the thermal conductivity of borosilicate glasses suitable for the storage of high level radioactive wastes have been measured by means of laser flash technique at room temperature. In the course of a search of the absorbing film for laser-beam, it was found that the silver-gold double film which was succesively vacuum deposited on the surface of sample was more useful than colloidal carbon film.
The thermal diffusivity and the thermal conductivity of this glass system increased with increasing silica contents, while the heat capacity decreased slightly with increasing silica contents. The phonon mean-free path was calculated from the thermal conductivity and the wave velocity obtained from Young's modulus. The resultant phonon mean-free path decreased pronouncedly with the addition of alkali oxides. It is obvious, therefore, that the decrease of the thermal diffusivity and conductivity with increasing alkali contents mainly depend upon the decrease of phonon mean-free path.

View full abstract

Compacts of Li_0.45Ni_0.10Fe_2.45O₄ square-loop ferrite added with 0-4wt% rare earth oxides were sintered in oxygen from 1100 to 1200°C, and the effects of addition on the sintering and magnetic properties were studied. Additives reduce the grain size and the bulk density of the sintered ferrite bodies. Grain growth in ferrite is proportional to 1/3 power of sintering time independent of added amount of rare earth oxides, and the activation energy is 115±10kcal/mol. Densification is proportional to logarithm of sintering time in the initial stage of sintering.
Additives reduce the switching time of magnetic flux, whose reduction is attributed to the reduction of grain size, and deteriorate slightly the squareness of magnetic hysteresis loop.

View full abstract

The changes of transparent Y₂O₃ and Y₂O₃-ThO₂ sintered piece heated in a saturated Na vapor were investigated in order to know if these materials were available for an envelope of a high pressure sodium discharge lamp.
These pieces were sealed with a Na block in a Nb pipe. The Nb pipe was heated for 6h at 1, 200°C.
Transparency, weight and crystal structure of a Y₂O₃ piece remained unchanged. However, a slight discoloration took place partially resulting in a light brown color or light blue tint. It was found that these colors were not due to the reaction of Na on Y₂O₃, but due to the Cu in the Na block and Fe in the Nb pipe, respectively.
A Y₂O₃-ThO₂ piece became extremely black. The black color does not appear to be due to the reduction of Y₂O₃ but to some reactions related to Y₂O₃-ThO₂ or ThO₂. A Y₂O₃-ThO₂ sintered body is not available for the envelope.

View full abstract