母体ガラスの組成, 熱処理, 酸処理とできた高ケイ酸ガラスのケイ酸含有量との関係を検討するとともにケイ酸含有量を98%以上に高めることを目的として新しく水蒸気処理法を考案し, その処理条件を検討した.
500°-560℃の各温度とも母体ガラスの熱処理時間 (t) が増すにつれて, できた高ケイ酸ガラスのケイ酸含有量が減少し, ケイ酸含有量とlogtとは直線関係が成り立つ. そして平衡値に達する. ケイ酸含有量の平衡値はI, III-シリーズともNa₂O/B₂O₃比が小さくなるにつれて減少する.
普通法で作った多孔性ガラスを700°-900℃で水蒸気処理し, 高ケイ酸ガラスのケイ酸含有量を99%程度まで増大できることを見いだした. また, 元の多孔性ガラスを作る時の母体ガラスの熱処理時間の短いものの方がケイ酸含有量が増大しやすい.
水蒸気処理によるケイ酸含有量の増大機構としては多孔性ガラスのケイ酸骨格中に残留しているB₂O₃と細孔を通って浸入した水蒸気とが反応して水和物となり, これが揮発すると考えた. したがって, 元の多孔性ガラスを作るための熱処理時間の短いものの方が, ケイ酸骨格が発達していないのでB₂O₃が揮発しやすい.

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分相したホウケイ酸ガラスの酸処理中の伸縮の原因をNa₂OとB₂O₃の溶出量の測定及び酸の温度, 濃度の影響について測定することによって検討した.
濃い酸又は低温の酸で処理すると, その初期に異常な膨張と収縮が起こることを見いだした. この異常な膨張と収縮は割れの原因になる.
濃い酸又は低温の酸では溶出の初期にNa₂Oが選択的に溶出され, 続いてB₂O₃が溶出する. ある厚さの多孔性のケイ酸層が生成すると酸に溶出したNa₂O/B₂O₃比は大略母体ガラス中のNa₂O/B₂O₃比と同じになる.
異常な膨張と収縮の原因は次のように説明することができる. 酸の温度が低いとB₂O₃の溶解度が極端に低くなり, そのためにNa₂Oの溶出量が相対的に多くなるため, Na⁺と大きいH₃O⁺の交換によう膨潤が強く起こり, これに続いて, ガラス構成酸化物のB₂O₃が溶出して≡Si-O-Si≡骨格の収縮が起こる. このように膨潤と収縮が分離して起こると推定される. また, 酸濃度が高いときの異常な伸縮の原因も同様に酸の濃度が高くNa₂Oが選択的に溶出すると考えて説明できる. 更に, ある厚さの多孔性のケイ酸層が生ずるとこれらがB₂O₃とNa₂Oの溶出をコントロールするものと推定される.

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Some borosilicate glasses having limited compositions will be separated, by the heat treatment in the transformation range, into two glass-phases. One of them is acid-soluble B₂O₃⋅Na₂O phase and the other is acid-insoluble SiO₂ phase. When the segregated glass is acid treated, B₂O₃⋅Na₂O phase is leached out leaving SiO₂ rich porous glass without any destruction of original shape. This porous glass shrinks about 30% in volume by firing between 900°C and 1200°C, turning into 94-98% SiO₂ glass having quartz glass-like properties.
Object of this study is to clarify the relation between glass compositions and treatments of original borosilicate glass to make the above-mentioned porous glass.
Experimental results were summarized as follows:
(1) Minimum time required for phase-separation, t, were measured for various glasses at various temperatures. For every glasses, liner relation exists between log t and the reciprocal of the absolute temperature of heat treatment.
The required time for phase-separation change with glass composition about ten times, however log t-1/T relation for various compositions showed identical gradients, and the apparent activation energy of phase-separation calculated from these results was 62kcal/mol. These values correspond to activation energy of oxygen diffusion in glasses.
Linearity was found between log t (at 500°C) and Na₂O/B₂O₃ mole ratio of these glasses.
(2) The leaching rate by 1 N-H₂SO₄ of B₂O₃⋅Na₂O phase of sufficiently segregated glasses were measured at 100°C, 80°C and 60°C. It was found that the rate changes about ten times depending on SiO₂ content and Na₂O/B₂O₃ mole ratio, and this will be explained in terms of difference of diameter of pores in SiO₂ membrane for each glass.
Linear relation between the thickness of leached layer, δ_M*, and square root of leaching time, √t, was found for every glass examined. Plotting of log δ_M* √t versus 1/T for various compositions gave straight lines of nearly same slopes, from which activation energies of leaching in the range 6.5-6.8kcal/mol were obtained.
From these results, it is concluded that, as far as sufficiently segregated glass is concerned, the rate controlling process of leaching may arise from the diffusion of B₂O₃⋅Na₂O through porous SiO₂ membrane filled by the acid.
Anothr linear relation was found between log δ_M*/√t-SiO₂ content as well as between log δ_M*√t-Na₂O₂/B₂O₃ mole ratio.

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