(1) The phase diagram of the system BaTiO₃-BaB₂O₄ has been determined by analyzing the quenched meterial by X-ray and polarizing microscope. Differential thermal analysis has been also used to determine the eutectic temperature in this system. The system makes a simple eutectic type diagram which has no intermediate compound. The eutectic point has been found at the composition of 32 mole% BaTiO₃ and the temperature 942°C.
(2) The diagram shows possibility of growing pure BaTiO₃ by using BaB₂O₄ as flux material. Actually, pale lumpish crystals of about 5mm on edge were produced by simple cooling a mixture of 45 mole% BaTiO₃ in platinum crucible from 1150° down to 955°C at the rate of 1°-5°C/hr. But a seed rotating technique seems to be more preferable to get good crystals, since the crystals grown by simple cooling method often encompass large flux inclusions.
(3) Crystals thus obtained have Curie temperature at 132.5°C in heating process and 130.3°C in cooling process.
The authors thank Dr. F. W. Perry for his valuable discussions in growing crystals by seed rotating technique.

View full abstract

Processes of corrosion of mullite by vapors of different potassium salts were investigated. Small size test pieces or powders taken from mullie refractories were exposed to the vapors of potassium carbonate, potassium sulfate and potassium chloride at temperatures ranged from 1000° to 1300°C. Phase assemblies of the samples were determined petrographically after each run.
Although potassium chloride was found to evaporate faster than potassium carbonate and potassium sulfate, K₂CO₃ vapor was the most corrosive against mullite.
The corrosion products of mullite differed from each other depending on the kinds of vapors. With K₂CO₃ vapor, a small amount of leucite and kalsilite were formed at the initial stage of the corrosion process, but gradually they were replaced by the final products, i.e, potassium aluminate and glassy phase. Leucite, kalsilite, corundum and β-alumina were the common products of the corrosion by vapors of K₂SO₄ and KCI, and additional phase in the case with K₂SO₄ was solid solution potassium and sodium sulfate.

View full abstract

Crystallization process of the BaO⋅TiO₂ 60, Al₂O₃ 14, SiO₂ 26 mole% glass was examined in detail, for near its surface as well as in the interior. It was found that near the surface of the glass, a metastable benitoite-type crystal formed firstly and then transformed progressively to the stable barium titanate and hexacelsian whereas in the interior the barium titanate and hexacelsian formed from the first.
The cause of the preferred orientation of hexacelsian in the crystallized products was attributed to the preferred orientaion of the metastable benitoite-type crystal and the resemblance of the structure between the benitoite-type crystal and hexacelsian.

View full abstract

The investigation was made concerning the dependence of transformation temperatures, softening temperatures and thermal expansion coefficients of Si-As-Te glasses on composition. Transformation temperatures, T_g, are in the range from about 110 to 368°C, and increase with increasing silicon content and decrease with increasing tellurium content. Temperatures of initial deformation under load, i.e., softening temperatures, T_s, are within about 125 to 425°C and exhibit the same dependence on composition as in the case of T_g. Average linear thermal expansion coefficients at temperatures from room temperature to T_g, α_l and from T_g to T_s, α_h, are in the range (0.8-2.1)×10^-5cm/cm/°C and (1.3-6.2) 10^-5cm/cm/°C, respectively. In contrast to the dependence of T_g and T_s on composition, α_l and α_h decrease with increasing silicon content and increase with increasing tellurium content. For the glasses of a given atomic ratio of silicon to arsenic, both T_g and T_s increase linealy with increasing the concentration of covalent bonds per unit volume, [v], and the following relations are obtained:
When the (Si/As) atomic ration is 1.50,
T_g=97.19[v]×10²-441.4, T_s=112.06[v]×10²-506.3.
When the (Si/As) atomic ratio is 0.67,
T_g=78.49[v]×10²-350.6, T_s=84.85[v]×10²-368.6.
When the (Si/As) atomic ratio is 0.25,
T_g=51.61[v]×10²-201.1, T_s=60.14[v]×10²-237.8.
The values of [v] in this investigation are in the range from 5.79×10^-2 to 8.32×10^-2 mole/cm³. Thermal expansion coefficients, α_l and α_h, decrease linearly with increasing the concentration of covalent bonds, regardless of the (Si/As) atomic ratio α_l×10⁵=-0.4725[v]×10²+4.826,
α_h×10⁵=-1.4976[v]×10²+14.616.
From the above relations, the following values are estimated for amorphous tellurium:
T_g=35±4°C, T_s=43±3°C,
α_l=(2.54±0.13)×10^-5cm/cm/°C and α_h=(7.38±0.28)×10^-5cm/cm/°C.

View full abstract

The effect of application of high pressure with an opposed-anvil type apparatus on the formation of silver colloids in silicate glass has been studied mainly by optical absorption measurements, and the following results were obtained.
1) Application of pressure at room temperature promotes the formation of silver colloids in glass due to subsequent heating at high temperatures ranging from 250°C to 500°C. This is attributed to the effect of high pressure in enhancing nucleation of silver colloids by producing defect sites in glass.
2) Application of pressure at high temperatures where silver colloids form under the pressure also promotes the precipitation of silver colloids. In this case, however, the size of the particles precipitated are smaller than in the case where the glass is compressed at room temperature and subsequently heated, possibly because the application of pressure decreases the ratio of growth to nucleation rate.
3) Application of pressure to glass at room temperature after heating at high temperatures, for example, at 500°C, under atmospheric pressure has pronounced effects on the absorption spectra of silver colloids in glass: shift of absorption peaks to longer wavelengths and broadening of absorption bands. These effects are attributed to the size distribution of enlarged silver particles and/or deformed, large silver particles.

View full abstract

Soda-borosilicate glasses doped with oxides of the tratsition metals, respectively, were irradiated by Ultra-violet Light and the stresses thus caused in the lasses were measured. The effects of the oxides were elassified as follows: (A) The stress increased by small addition and then decreased to zero with increase of the concentration (B) The stress decreased by small addition and then kept low value in considerably wide concentration range, (C) The stress decreased monotonically with increase of the concentration. Threshold photon energies for the stress build-up were 5.5eV (220mμ in wavelength) or more and were the same as those of the undoped glasses. For the A group cases, the effects of the assuming excitation of the added ions additives were explained by assuming excitation of the added ions which causes rearrangement of the electrons and chemical bonds in the glass network. For the other cases, no conclusions were obtained.

View full abstract