The authors have studied the reaction in the system
KOH-CaO-Silica gel-H₂O
at 20±1°C and the solid phase formed by the reaction.
The mixture of CaO and SiO₂ gel of the mol ratio CaO/SiO₂=2.5 was added to KOH solution whose concentration was changed up to 50g/l. After keeping 95 days with occasional agitation the reaction products were subjected to chemical and X-ray analyses and to the observation under electron microscope.
The results obtained are summarized as follows:
(1) The solid reaction product came into sight was identified as tobermorite phase which appeared under electron microscope as films or crumpled foils. In general, the individual crystals were smaller than 5μ, which grow comparatively well in the direction of thickness with increasing concentration of K₂O, although this effect was not so pronounced as that of Na₂O, which had been reported elsewhere.
(2) With increasing concentration of K₂O the concentration of CaO found in the liquid phase decreased, whereas that of SiO₂ increased. The change of CaO was by far larger especially up to about K₂O≤5.86g/l. From this point the decrease became slow and the concentration dropped below 0.1gCaO/l. The amount of CaO entered into the reaction to form solid phase was therefore, increased with increasing K₂O concentration up to about the same limit.
(3) A part of Ca²⁺ in tobermorite is very likely to be replaced by K⁺ whose amount seems to be governed by the concentration of K₂O in the liquid phase.
In the case of 13.78gK₂O/l or more in the final concentration the mol ratio K₂O/SiO₂ of the solid reaction product came up to 0.22. It was also found that there exist a relation
(CaO/SiO₂ mol. ratio)+(K₂O/SiO₂ mol. ratio)=1.2-1.3
in the solid reaction product.
(4) Like NaOH the KOH-solution acts as an accelerator in the formation of tobemorite phase from Ca(OH)₂ and silica gel.
In the first place there would be the combination of KOH with silica gel to form K₂O-SiO₂-nH₂O, which then acts upon Ca(OH)₂ to precipitate tobermorite phase liberating K₂O passing again into the liquid phase, so that the reactions are repeating round on the same way. In the mean time the replacement of Ca²⁺ and K⁺ would take place.
The chemical equation may be written as follows;
Si(OH)₄+2KOH=K₂O⋅SiO₂+3H₂O SiO₂+2KOH=K₂O⋅SiO₂+H₂O}…(1)
K₂O⋅SiO₂+xCa(OH)₂+mH₂O=zK₂O⋅xCaO⋅SiO₂⋅yH₂O/solid reaction product (tobermorite)+2(1-z)KOH+(x+z+m-y-1)H₂O…(2)
where, z was estimated to≤0.22 in the present experiment.

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Samples prepared by adding the small amounts of polyvalent elements, Sn, Fe, Ce, Cr, Sb, Sb to the base glass of the composition, Na₂O 18.0, CaO 8.0, Al₂O₃ 1.5, SiO₂ 72.0; Ag₂O 0.025 (parts) were applied to the irradiation of ultra violet ray, X-ray and γ-ray.
The specimens so obtained were subjected to the heat treatment at constant temperatures of 400°-600°C, and the progress of color development was followed up by means of the change of the absorption at 410μ, the characteristic absorption peak of silver yellow glass in the spectral transmission curves.
It was confirmed that the reduction of Ag⁺-ion, the initial stage of color development, proceeds through three different ways, i.e.
(1) equilibrium Ag⁺_??_Ag°
(2) photochemical reduction
(3) thermal reduction.
At higher temperatures the coagulation of atomic silver takes place to produce the yellow stain of silver. Furthermore, the relation of the amount of separated silver C to the holding time t may be represented by
C=(C₁+C₂)(1-e^-jt)+C₃(1-e^-kt),
where C₁ is the amount of atomic silver existing under equilibrium, C₂ and C₃ are those produced, respectively, by photochemical and thermal reduction, and j, k are constants.
For extremely small amount of separation the value C is approximately proportional to the hight of the peak at 410μ.

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An approach to the structure was made from the comparative study of X-ray diffraction patterns of the glasses composed of Na₂O, K₂O, Li₂O, CaO, MgO, BaO, PbO and SiO₂, GeO₂, P₂O₅, Al₂O₃, B₂O₃.
All glass specimens gave single diffraction peak. The diffraction angle of the center of the peak was found to be determined principally by the ratio of the number of cations coordinated, respectively, by six and four oxygen ions.
Lead silicate glass in which lead ions are coordinated with oxygen ions in peculiar manner gave a distinct pattern.

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The author's papers (J. Ceram. Assn. Japan, 63 [715] 566 (1955); J. Ceram. Assn. Japan, 64 [723] 110 (1956); 65 [733] 45 (1957); 65 [737] 104 (1957)) concerned the effects of the body composition etc. on the physical properties of the pot for melting optical glass which, however, did not cover the problems of the effects of firing temperatures of grog and green body.
In order to summarize and reexamine the data a series of investigations on the spalling and load deformation properties of the pot materials containing the grog fired at the temperatures 1280°-1525°C and matured at the temperatures ranging from 1290° to 1545°C, have been carried out.
The important results are as follows:
(a) As far as the present test is concerned the strength of clay-grog bodies showed an increase with increasing firing temperature, while the elevation of the firing temperature of grog did not necessary show the same effect.
(b) The total linear shrinkage from greeen to fired specimen increased with increasing firing temperature, but the same result could not always be expected with the grog.
(c) The increase of bulk density with the firing temperature was observed with the body, but the same trend did not hold with the grog.
(d) The strength of the body decreased with raising quenching temperature.
(e) The quenched specimen subjected to the firing at higher temperature proved to be stronger so long as the quenching temperature was low, but when it was raised the difference became neglible.
(f) The resistance to spalling decreased with the raise of quenching temperature.
(g) Irrespective of the firing temperature of grog the body fired at higher temperature showed positively the poorer spalling resistance when it was quenched from higher temperature, but for lower quenching temperature this relation did not hold so that it is highly probable that the specimen fired at some intermediate temperature would show the lowest spalling resistance.
(h) In the specimen fired at a higher temperature cracks in the intermediate layer between the grog and the bonding clay were observed, while it was impossible to locate such cracks in the body fired at lower temperature.
(i) By quenching, cracks came into existence in the intermediate layer, and also the grow up of the existing cracks was observed. This phenomenon was most remarkable with the bodies composed of the grogs fired at higher temperature, as long as the green was fired at comparatively lower temperature.
(j) The adhesion between the grog and the bonding clay seems to play the most important roll to the resistance to spalling of fire-clay pots.
(k) The firing temperature of the body was found to be the most influential, whereas the influence of the firing temperature of grog seemed to be not so remarkable as the former.
(l) Comparing the specimens prepared by high temperature with those by low temperature firing a marked difference was seen in the initial stage of load test, the latter being deformed much slower than the former. And up to 20% deformation, these values came closer more and more with the elevation of temperature.
(m) It was found thatthe body containing the grog fired at higher temperatures did not always give a higher softening temperature.

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In the previous paper (J. Ceram. Assoc. Japan, 68 [10] 223 1960)) the authors have given the method of converting the glasses of the system Li₂O-MgO-Al₂O₃-SiO₂ into a polycrystalline material with or without the addition of platinum nucleus, the amount of which was limited to a very small value. The results of the measurement of the mechanical and thermal properties of the material produced were also published (J. Ceram. Assoc., Japan, 69 [2] 35 (1961)). The present paper concerns the dielectric loss of the same material which was expected to show the effect of chemical composition and heat treatment.
(1) Effect of heat treatment
The glass of the composition, MgO 15, Al₂O₃ 23, SiO₂ 62, Li₂Ox, where x=4, 6, 8, 12 by weight ratio, were melted, and reheated with the constant rate of 5°C/min. to a temperature from 750° to 1200°C.
The tan δ at 1 Mc of the crystallized specimens (cf. Fig. 1) showed that, in general, it became higher than the base glass by the heat treatment at a temperature between 750° and 950°C, whereas the heating at a temperature higher than 1000°C brought about a great decrease in tan δ.
The increase of tan δ may be attributed to the formation of β-eucriptite which usually occurs in the low temperature range, while the sudden decrease in tan δ may be attributed to the formation of β-spodumen which appears with the cost of vanishing β-eucryptite.
(2) Effect of the chemical composition of the base glass
It is likely that the amount of platinum, 0.01%, was too small to have an effect on tan δ, and also the cardinal component of base glass, such as MgO, Al₂O₃ and SiO₂ behaved themselves rather indifferent. On the contrary, Li₂O showed a strong influence, and the decrease of Li₂O content seemed to be especially fovourable for the formation of β-spodumen and consequently the lowering of tan δ.
(3) Effect of additional components
The glasses of the base composition, Li₂O 4, MgO 15, Al₂O₃ 15, and SiO₂ 62 by weight, and added by a small amount of any of the components, Na₂O, K₂O, BeO, CaO, SrO, ZnO, CdO or PbO were melted and reheated at above 950°C. Among such second components PhO was the most effective, giving tan δ of 3-4×10^-4 at 1 Mc at room temperaure with the addition of PbO: 0.045mols to 104g of the base glass (cf. Fig. 4).

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