The mechanism for producing the white stain on the surface of some optical glasses possessing low chemical durability was investigated.
The compositions of the optical glasses used are given in Table 1. All the glasses were ground and polished in the same manner so as to present a similar type of surface. The samples were kept in the humidity cell (Fig. 1) with varying relative humidity from 100, 80.2 to 68.6%, and atmospheres were controlled by adding small content of CO₂, H₂S or other acidic gases. Weathering was once a time stopped afer 5hrs, the grade of deterioration of glass surface was measured and then the samples were provided for the repeated exposures under 5hrs, cycle.
The surface deterioration was observed by optical microscope, ellipsometer (Figs. 3 and 4), electron diffractometer and electron microprobe X-ray analyzer (EMX). The refractive index and the thickness of anomalous surface film on the glass were measured by means of ellipsometry. The quality and quantity of anomalous surface film were determined by means of electron diffraction and EMX.
The relations between the relative humidity and the thickness of anomalous film on the glass SK-16, exposed to the atmosphere containing 50% CO₂ gas at 50°C during the period of 10 and 20hrs, are shown in Fig. 7. It can be found that the growth of anomalous film increases rapidly with increasing relative humidity and water vapor plays a most important role in these reactions. The changes of film thickness in the case of air atmosphere are shown in Fig. 8. HCI and SO₂ show very violent attack, so the film thickness can not be measured.
When acidic gas was added to the atmosphere, the water adsorbed on the surface of glass becomes acidic. Then the exchange reaction takes place between Na⁺, Ba²⁺ in glass and H⁺ in adsorbed acid solution. In the case of CO₂ gas attacking on the glass SK-16, the growth of stain increases straightly with increasing ionic concentration of H⁺ (Fig. 19). In the case of glass BaF-10, the curves are shown in Fig. 20. Clearly the diffusion of Ba²⁺ will carry out the important role in this exchange reaction.
The changes of refractive index of the films produced on the glass samples under various conditions are shown in Table 2. It can be found from Table 2 that in the first stage of attacking, the refractive index of anomalous films are 1.45-1.47 in spite of different glasses and different conditions. But in severe attackng by strong acidic vapor, the values of refractive index become large. From these results, the following model (Fig. 21) may be figured for the mechanism of growth of stain. The Na⁺ and Ba²⁺ are diffused out to the surface of glass and these salts are produced to form spotty stain, and SiO₂ rich films are formed underneath (model 1). Corresponding to the increase of anomalous film thickness, the quantity of the salts taking the form of spotty stain increases, and SiO₂ rich films are spread out as shown in model 2. Then the formation of the salts grows large and all of the glass surface will be covered (model 3).
The concentrations of Ba and Si in the spot of stain are measured by using EMX. As shown in Fig. 14 the concentration of Ba increases and that of Si decreases in the same place of spot and it may be proved that the present considerations are reasonable.
The anomalous films formed on the glass surface are determined by using electron diffraction method and the results are shown in Table 3. It is clear that large parts of crystallites on the glass surface belong to Ba-salts and this also supports the structural pictures figured for reaction mechanism.

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An extremely pure MgO as one of the starting materials was prepared by decomposing magnesium nitrate solution of 99.9% magnesium. No boric compound in magnesia obtained was recognized by the emission spectral analysis. Many mixtures of magnesium nitrate solution and boric acid corresponding to the various mixing ratio of MgO and B₂O₃ were preheated at around 600°C for 10hrs and then heat-treated at 910°, 1050°, 1300° 1500°, 1600°, 1700° and 1750°±5°C for 24 to 72hrs.
The lattice constant of MgO and the crystallite size of MgO were measured with the internal standard of 99.999% Si and phases presented in the heat-treated specimens were identified with a X-ray diffractometer using the radiation of Cu K_α.
Particle size of periclase was observed with a scanning electron microscope. The shrinkage, apparent porosity of magnesia body after heat-treatment and evaporation of B₂O₃ were also measured for evaluating the effects of the addition of B₂O₃ on the physical properties of sintered magnesia.
The compound MgO⋅B₂O₃ was not detected, but the compounds 3MgO⋅B₂O₃, 2MgO⋅B₂O₃ and MgO⋅2B₂O₃ were recognized. It was confirmed that there was no solid solubility of B₂O₃ in MgO up to the temperature of 1750°C, and the grain growth of periclase was extremely accelerated by the addition of B₂O₃ particularly at the heat treatments of 1500°C. The shrinkage of magnesia body was maximum with the addition of B₂O₃, 2 to 3%, and decreased rapidly with the associate of bubbling of B₂O₃ when the temperature was higher than 1500°C in specimens containing more than 5wt% B₂O₃. Apparent porosity of magnesia body after heat-treatment at 1750°C for 24hrs was minimum with the addition of 0.1wt% B₂O₃ to be about 8%. The porosity increased with the increase in the addition of B₂O₃ for the sintered bodies containing higher than 0.1wt% B₂O₃.

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In order to study the rheological preperties of plastic clay body, cyclic tortion test method by Astbury was examined on a plastic mass for electrical insulators. Thin hollow cylindrical tubes, 10φ-20φ×100, were formed by extruding. One end of specimen was fixed, and the other free end was oscillated torsionally, while the rotating angle was changed in a sinusoidal way. By analyzing the hysteresis loops of the stress-strain curves, the following results were obtained. (1) By the sinusoidal torsional motion, S-S curve was constricted in a steady hysteresis loop, showing that the phenomenon of the “Memory” was lost. (2) The remanent sterin depended markedly on the maximum strain (torsional strain amplitude). (3) The coercive force and the maximum stress much decreased on the increase of the moisture content. (4) The ratio of the coercive force to the maximum stress was constant regardless of experimental conditions. (5) The energy absorbed during one cycle was directly proportional to the maximum strain, and was reduced with increasing moisture content. (6) If the torsional strain amplitude and the frequency of sinusoidal oscillation were taken as the same condition, the ratio of energy lost during one cycle to the one for the perfectly plastic body was equal to the ratio of the coercive force to the maximum stress, which was constant, irrespective of experimental conditions. (7) The critical value of the strainen ergy, which determines the ratio of the number of the elastic elements to the that of viscous elements was not constant.
The writers, on the basis of the results, pointed out, (1) the plastic property should be added to the Astbury's model as one of the mechanical components, (2) the assumption that the elastic elements would be changed to the same number of the viscous elements due to the increase of strain energy, shoud be modified, (3) the term which gives the effect of moisture content on the behaviour of plastic clay body must be added in the fundamental rheological equation, (5) the model by Astbury should be revaluated after determining more precisely the model parameters.

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Electric conductivities of molten oxide system PbO-SiO₂-Fe₂O₃ were measured over the temperature range from liquidus to 1200°C (Fig. 3-6). The mechanism of conduction was discussed and compared with that of system PbO-B₂O₃-Fe₂O₃ from the view point of the behaviour of ferric ion in the melt.
The samples, containing Fe₂O₃ 0-25mol%, were quenched from 1200°C, and most of them were glass. Some glasses were crystallized by heat-treatment. Measurements of Infra-red absorption spectra and X-ray diffraction were carried out of the samples quenched and then crystallized (Fig. 9, 10), and the structure of complex silicates in these samples was discussed.
Based upon these measrements, the behaviou of ferric ions and structure of complex silicate ions in molten oxide were discussed, and the following results were obtained.
(1) Specific conductivity increases with temperature, and obeys the Arrhenius equation (e.g. Fig. 2). The values of the apparent activation energy for conduction are about 10-25kcal/mol, and are nearly the same values as in the system PbO-SiO₂. Specific conductivity increases when the SiO₂ content decreases (Fig. 6), and increases with the Fe₂O₃ content when the ratio (PbO)/(SiO₂) is constant (Fig. 4, 5). From these results, it is considered that the electric conduction in this system is ionic and that the electric charge is mainly carried by Pb²⁺ and Fe³⁺ ions.
(2) The activation energy for conduction increases with the increase of effect of Fe³⁺ ion, because it seems to have larger interaction with silicate anion than Pb²⁺ ion. However, the activation energy decreases when the dissociation of chain or sheet (or ring) silicate ions occurs in the melts containing more Fe₂O₃, 10-20mol% (Fig. 8). The dissociation of silicate ions is caused by the dissociation of Fe₂O₃ into Fe³⁺ and O^2- ions.
(3) The complex anion, corresponding to the unknown ternary compound PbO-Fe₂O₃ SiO₂, seems to exist in the molten oxide of this system which contains more than 20mol% of Fe₂O₃. The activation energy for conduction increases with the presence of this complex anion.

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In view of good properties of hollow glass micro-sphere such as lightness, thermal insulating and sound arresting properties, high melting point and incombustibility and ability to increase quantity, some new composites of unparalleled characteristics are being developed by mixing them into plastics, carbon, cement, lime and its kind and metals.
For instance they are now being used in diverse fields for making synthetic wood, master model, electric accessories, materials of low thermal conductivity ceramics, including aircraft materials and submarine diver-ship materials, and their demand is rapidly increasing.
So, Some methods to produce them have been invented already, but as the processes of them are rather complicated and the materials are expensive, the production become very expensive, too.
Hereon, we authors discovered that hollow glass micro-sphere can be produced from the “Shirasu”, which is acidic volcanic ejecta and one of the unutilized mineral resources distributes widely in southern Kyushu and other districts in Japan, through simple and inexpensive method. Incidentally, we will call it as “Silas Balloons”.
We made up an apparatus for calcining of raw material, and investigated the conditions for production of Silas Balloons, bubbling and expansive mineral component in Shirasu, the effectiveness of processing of raw material and producibility of Silas Balloons from some Shirasu produced in various districts, and measured general characteristics of Silas Balloons.
And following results have been obtained.
1) Using the Shirasu as the material, it is optimum to calcine it at a temperature about 1000°C shortly within 60 seconds.
2) Maximum size of calcining material is 300μ to obtain hollow glass microsphere.
3) It has been found that bubbling and expansive mineral component in the Shirasu is volcanic glass, and more accurately, the effective H₂O contained in it is estimated the bubbling agent.
4) Enriching the volcanic glass in the material through processing of raw material, especially through classification and magnetic separation, yield of Silas Balloons has considerably increased.
5) Some Shirasu produced in various districts would be able to be used as materials of Silas Balloons.
6) Compared with the known micro-sphere heretofore such as Microballoons of Emerson and Cuming Inc., Silas Balloons is superior to the former in its strength, melting point and hygroscopic property, though inferior to the former in its appearance.

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