Fused Quartz Used for SPI Supplies® Brand Quartz Slides and Cover Slips
Fused quartz vs. fused silica
SPI Supplies has offered the SPI Supplies® Brand Quartz Slides and
Cover Slips for some years for those requiring the ultimate in UV transparency, often
times for those doing UV microscopy. We have often found some amount of confusion as
to just what is the proper description for the quartz used in the fabrication of the SPI
Supplies slides and cover slips. Our intent is to make it more clear what is the meaning
of the different terms.
The most common starting material is sand, which is of course, SiO2
which is then heated, and melted, and after various processes to ensure its purity, it is
quenched to the amorphous state and formed into large ingots. This is what is called
"fused quartz" and is also the kind of quartz used for the fabrication of the SPI Supplies
quartz slides and cover slips. And typical trace element analyses by direct reading
spectrometer consistently shows any impurities to be in the low ppm range.
However, there another approach to the production of quartz products. In this case, the
starting material is a synthetic quartz (as opposed to natural quartz) that is produced by
way of reaction of silicon tetrachloride. The quartz produced this way is called "fused silica"
and is a separately definable material from "fused quartz". While the difference might seem
subtle, and bordering on being unimportant, in many instances this difference can be extremely
important. First, the purity is better, but not by very much, roughly the improvement is a
few ppm better. For applications to microscope slides and cover slips, such an impurity
improvement is meaningless and not important. But for certain applications in lens making,
especially for high end electronics industry application, this improvement in impurity can
make a large difference in the performance of the final system.
One should appreciate however that the cost of the higher purity fused silica product is about
5 or 6 times higher than for an equivalent amount of the fused quartz product. When used to
produce quartz slides, because the amount of raw material being purchased is much lower, the
final differential between a slide in fused silica vs. fused quartz could be a factor of ten.
We hope this discussion has been helpful to you. Because of these different kinds of quartz
products, it is always considered good scientific practice to reference the kind of quartz
being used so that others attempting to reproduce results will be using the same identical
quartz. We willingly pay more for the use of GE 124 quartz but cheaper grades of quartz
are available, and with an even higher level of impurities. Beware of a supplier that
does not disclose the properties and characteristics of the quartz being used in the
production of their quartz products. There is often times a reason!
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Monday December 01, 2008
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