In the present paper effects of the composition consisting of graphte, silicon carbide, ferrosilicon, borosilicate glass and fluoride upon the quality of graphite crucibles were studied.
In order to confirm these effects, L₁₆(2¹⁵) type orthogonal array experiment was carried out, in which 5 factors with 2 levels were examined, A: type of borosilicate glass (T-20, T-51), B: borosilicate glass content (10 parts, 15 parts), C: type of fluoride (cryolite, fluorite), D: fluoride content (little, much), E:SiC:FeSi (20:25, 25:20), F: type of graphite (Amo, Cylon), and the water absorption of newlyfired test pieces and both the water absorption and the weight change of above pieces after the oxidation test were measured as characteristic values with results as follows.
1) Amo crystalline graphite produced in Japan showed better quality than that from Ceylon.
2) The lower silicon carbide composition (SiC:FeSi=20:25) showed better quality than that of the richer (25:20).
3) The graphite crucible of the lower borosilicate glass content (10 parts, total being 84 parts) showed better result than that of the higher one (15 parts), and borosilicate glass of the lower alkali content (Na₂O+K₂O, 4.1%) showed better result than that of the higher one (6.5%).
4) Cryolite gave better effect upon the quality of graphites crucibles than fluorite, and the graphite crucible of the 3 parts cryolite content (total being 84 parts) showed better result than that of the 1.5 parts content.
5) Finally, cryolite flux containing borosilicate glass showed the best quality of those in the present studies.
In this studies it was found that the positive correlation exists among above three characteristic values, so that the quality of graphite crucibles can be judged by any one of these characteristic values.

View full abstract

Glass transition is observed on almost all materials in glassy state. Some properties change abruptly at glass transition temperature, T_g, which itself changes with experimental conditions, and in glass transition region properties or structure of glasses change with time to approach to their own equilibrium states respectively. It has been an unsolved problem whether glass transition is a thermodynamical one such as second order transition or is originated from relaxation phenomenon in freezing-in of glass structure.
Results of many investigators on glass transition characteristics of various kinds of glasses (organic high polymer, chalcogenide or inorganic oxide glasses) are examined and compared. Similarities are found in the following situations, namely; 1. Glass transition is related to several mechanisms with different relaxation times and activation energies, 2. T_g changes with experimental condition in a similar fashion, 3. Many thermodynamical functions show similar behaviors in transition region and 4. “Cooperativeness” is recognized in a resembled form. On the other hand, there are some differences, namely; 1. Change of T_g with experimental condition is far more distinct in inorganic glasses, 2. Change of viscosity or relaxation time with temperature is more striking in organic glasses, 3. Cooperativeness is better distinguished in organic glasses and 4. Linear relations between temperature and log viscosity or equilibrium specific volume are realized in larger temperature range by inorganic glasses.
As a result, glass transition characteristics of organic glasses are resembled to those of thermodynamical transition, and in inorganic oxide glasses transition seems to be a mere consequence of relaxation phenomenon.
Following the author's opinion, these differences are originated from 1. Difference of flow-units which take part in transition, 2, Distinction in bonding forces and interference between flow-units and 3. Different degree in tendency of glass structure to freeze-in at relatively low temperatures.

View full abstract

Generation of stresses was found by the authors at surface layers of a soda-borosilicate and 96% silica glasses severely irradiated by ultra-violet ray (J. Ceram. Assoc. Japan, 72 [11] 193-96 (1964).). As the first step to elucidate mechanisms of the phenomenon, experimental studies were carried out on some kinds of alkali borosilicate test glasses. Six series of glasses in the system R₂O-B₂O₃-SiO₂, all containing 15mol% B₂O₃, were prepared, namely; 1. glasses containing 4-13mol% Na₂O, 2. Glasses containing 4-14 mol% K₂O, 3. The same as series 1 but melted in reducing condition, 4. glasses containing 4-13mol% Na₂O with addition of 0.2wt% Li₂O, 5. glasses containing 6.5mol% Na₂O with addition of 0.05-0.2wt% As₂O₃ and 6. glasses containing 6.5mol% Na₂O with addition of 0.3-0.8wt% Ce₂O₃. The glasses were melted from powder of rock crystal and reagent grade raw materials in silica glass crucibles in a gas-fired furnace. After irradiation by mercury lamp under fixed condition, tension at surfaces and thickness of stressed layers were measured photo-elastically. Density increase by irradiation was measured on thin plates of test glasses by sink-float method. Surfaces of some test glasses were examined before and after irradiation by electron microscope.
Results were as follows: 1. Usually, tension decreased with increasing Na₂O or K₂O contents, 2. In glasses melted in reducing condition, however, tension was nearly constant regardless of their Na₂O contents, 3. In glasses containing As₂O₃ or Ce₂O₃, stressed layers were thin, but tensions were considerably severe, 4. In glasses containing 0.2% Li₂O, tensions were less than those without Li₂O, 5. These stresses originated from compaction of irradiated surface layers, 6. When heated, these stresses began to release themselves at about 250°C, faded away perfectly at 480°C and did not appear again on cooling and 7. In some cases, enlargement of inhomogeneous structure of surfaces was recognized by electron microscope.
On the assumption that these stresses were due to compaction of network structure of borosiilicate glasses, effects of quantities and kinds of alkali ions in glasses or of presence of As or Ce ions and their ultra-violet absorbing action were discussed.

View full abstract

It's well known that heat transfer to the reacting surface is the rate controlling step for some reactions such as the calcination of lime or dolomite in shaft kiln.
Therefore to know the behaviours of particles flow in shaft kiln is of the most importance. In this paper, determination was made on the velocity distributions of particle flow in shaft kiln, using the apparatus showed in Fig. I. Tracer particles were added on the top of the apparatus and velocity distributions in vertical semi-cylinder were observed and measured. The next equation was obtained for the radial velocity distribution.
(u₀-u)/(u₀-u_w)=(r/D_T)^2+m
In the boundary layer having velocity gradient the bulk density of particle layer shows great difference, and there are some important relations between velocity distribution and bulk density. The value m above mentioned well accounts for this reason.

View full abstract