The process of chemically strengthening glass replaces sodium ions in the glass's surface with potassium ions through a process that uses a potassium nitrate bath solution. These potassium ions are larger than the sodium ions and therefore wedge into the gaps and create pressure on the surface of the glass which can make it 6-8 times stronger than glass that is untreated. My question is whether this process would be expected to cause the glass to swell or change volume.

I have conducted experiments with chemically strengthening blown glass globes and have measured a consistent volumetric increase in the diameter of the globes post process. I am trying to determine how to predict and estimate this change. I can't determine if this is the result of the added mass from the potassium ions or if the surface pressures themselves are stretching the material.

I have talked to a few chemical engineers and looked through textbooks and online journals but much of the research done on this topic seems to be proprietary. I am posting my question here in hopes of finding someone who can point me in the right direction with my research.

This is my first question asked in this Stack Exchange Chemistry Site. Please let me know if there is anyway I can improve my question.

  • $\begingroup$ So you know that there is a volume change in the near-surface region that leads to compressive stress. Knowing the volume change in unstressed material, and an estimate of the Youngs modulus, you can come up with the expected near-surface volume expansion. $\endgroup$
    – Jon Custer
    Commented Dec 1, 2020 at 16:37
  • $\begingroup$ related chemistry.stackexchange.com/questions/77249/… $\endgroup$
    – Mithoron
    Commented Dec 1, 2020 at 20:59
  • $\begingroup$ If I remember correctly, the technique of strengthening glass by ion exchange was discovered accidentally, when a glass maker noticed that preforms had shrunk noticeably after tempering... but I have not been able to verify that on the Web. $\endgroup$ Commented Dec 1, 2020 at 21:10


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