We’ve discussed tempered glass before, but so far we’ve only discussed the process of thermal tempering, or tempering using heat. This is not the only type of tempering available in the glass industry, however. Recently, chemical tempering has been on the rise in the smartphone market and may soon be included in the mix of architectural glass. So what exactly is chemical tempering and how does it work?

The Process

Chemically tempered glass starts as a sheet of float glass that is submerged in a molten potassium salt bath. Now, the chemistry behind the process is a little complex, but the result is simply that the potassium ions in the bath replace some of the salt ions in the glass. The potassium ions are stronger than the salt that was already in the glass, which creates an overall stronger sheet.

ion bath diagram chemical

Ion bath credit to Trend Marine

The Advantages

Chemical tempering can be used on glass that is much thinner than glass used in the thermal process. The current uses for this glass have taken advantage of this property as they’ve been used in semiconductors, smartphones, and other small technical applications. Glass that has gone through the chemical process is much stronger than a standard sheet of float glass, though it lags slightly behind the strength of a thermally treated sheet.

The Disadvantages

So far, no chemical bath has been able to create a sheet of glass that passes the requirements to be labeled as a safety glass. Coupled with the added expense of a molten potassium bath, chemically tempered glass has not found its way into the construction/architectural world as of yet. This is not to say that it won’t, though. Scientists are constantly tweaking the chemical makeup of the bath to create stronger and stronger recipes. It’s likely that in the near future we will see a mixture that is strong and cheap enough to replace some of the thermally tempered glass that we use today.

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