Abnormal Swell and Shrinkage of Borosilicate Glass during Acid Leaching

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  • 高けい酸ガラスの製造と応用に関する研究　Ｖ　　酸処理時の分相性ほうけい酸ガラスの異常伸縮
  • コウ ケイサン ガラス ノ セイゾウ ト オウヨウ ニカンスルケンキュウ 5
  • 高ケイ酸ガラスの製造と応用に関する研究, 第5報

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Cause of swell or shrinkage of a phase-separated borosilicate glass during acid leaching has been investigated by the determination of leached amount of Na2O and B2O3, and by the measurement of the effects of temperature and concentration of leaching acid.<br>With high concentration or low temperature of acid, abrupt and abnormal swell and shrinkage was found at the early stage of leaching. These abnormal swell and shrinkage caused cracks.<br>At the early stage of leaching, Na2O was selectively leached out with concentrated acid or at low temperature and leaching out of B2O3 followed. After leaving a porous silica of a certain thickness, the ratio of leached out B2O3 and Na2O corresponded nearly to that of mother glass.<br>Cause of the abnormal swell and shrinkage can be explained as follows:<br>Since solubility of B2O3 in the low temperature acid is extremely low and that of Na2O is relatively high, exchange of Na+ ions in the glass with large H3O+ ions results in the strong swell. After that, B2O3, the glass former, leaches out to make shrinkage of ≡Si-O-Si≡ skeleton. Therefore, swell and shrinkage are considered to occur independently. In the case of concentrated acid, selective dissolution of Na2O can also be expected in the early stage. In addition, it is assumed that the porous silica layer developed to a certain thickness acts as a controller of the leaching of B2O3 and Na2O.

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