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Name: Chuck
Status: educator
Grade: post 12
Location: MS



Question:
I teach Analytical Chemistry and Instrumental Analysis at a small university in Mississippi. My colleagues and I were discussing the differences between quartz and amorphous glass recently and the topic of UV transmission came up. We are all aware that amorphous glass does not transmit UV well, but we could not arrive at a satisfactory reason why. Can you explain why?


Replies:
Chuck,

While both standard glass and quartz glass use SiO2 as its main ingredient, the difference between standard glass or "soda-lime glass" from quartz glass (may be fused quartz or synthetic fused silica) is in the manufacturing process.

Soda-lime glass uses SiO2 and adds sodium carbonate to lower the melting point (think freezing point depression) and allow working the material at lower temperatures. Since the addition of soda makes the material somewhat water soluble, calcium oxide is added to have better chemical durability. Depending on the use, other substances may also be added (lead for luster, boron to have Pyrex, iron for heat filtering, etc.)

Quartz glass, on the other hand, is usually made from pure silica (either by fusing SiO2 or from other sources of Si and O).

Thus, the purity of quartz minimizes interaction with UV, whereas standard glass have additives that can absorb or disperse UV.

Greg (Roberto Gregorius)


Glass is a mixture of various metal oxides, boron oxides in particular. The composition of this, or any of numerous other glasses, depends upon the composition of the particular glass. Quartz on the other hand is usually reserved to pure SiO2, which may be amorphous or crystalline. The composition and structure of the quartz determines its UV transmission.

Vince Calder



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