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Q & A with Schott Glass India

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What is the shelf-life of glass?

Glass is in use for centuries already. The earliest finding of a glass recipe comes from Syria (700 BC) stating to take 60 parts of sand, 180 of ash from seaweed and 5 parts of chalk, mix it together and you receive glass. Since that time glass vessels are in use and the oldest existing glass vessel is a cup from the Egyptian king from 1450 BC. Clearly from that glass is not decomposing or degrading with uv light. It keeps its properties over the time. As this is also known from church windows such studies to prove this were never really made. The shelf life of glass is generally considered to be infinite.

What is the chemical resistance of glass?

The chemical resistance describes the resistance against chemical attack by defined agents. As glass does not react with organic solutions this can be neglected. The reaction of glass with an aqueous and acidic solution is basically the same. A Hydrogen ion from the solution exchanges with a Sodium ion from the glass. So in the end there is an accumulation of Sodium in the solution which can be measured by titration or flame spectroscopy. This reaction is provoked in the test for hydrolytic resistance according to USP and Ph. Eur. The lower the accumulation of Sodium in the solution the better is the quality of the glass. The reaction with alkaline solutions is completely different. Here the Hydroxide ions directly attack the silicon in the glass structure and erode the surface. This happens more intense at higher pH values, around pH 10 and higher.

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