Dear Pier,

Vycor is a 96% SiO2-glass.

High-purity quartz glass is difficult to melt and to bring into shape
even
at high temperatures because of it's high viscosity. Another problem are

bubbles which can't rise and leave the high-viscosity melt.

Vycor is made by melting a borocilicate glass (containing 65% SiO2,
26% B2O3, and 9% Na2O). The melt is brought into shape by blowing or
pressing processes. During heat treatment, there is a spinodal phase
decomposition. The glass ends up with a closely intermingled
microstructure
of a Na2O-B2O3 phase and a silica-rich phase. A leaching process in hot
dilute HCl, H2SO4, or HNO3 leaves behind a silica-rich skeleton. The
shapes are then sintered to high density.

In the end Vycor-glass  has a composition of 96% SiO2, 4% B2O3, 0.1%
Na2O.

That unique way of processing high-silica glass was dicovered by
Hood and Nordberg in 1938.

I don't know, whether "Vycor" is also used as a brand name. For more
detailed
information try to contact Corning (THE glass company in the US) or
Dr. Alix Clare/Dr. Pye, Glass Department,
New York State College of Ceramics at Alfred University, Alfred, NY.

Regards

Maike

----------------------------------------------------------
Dipl.-Ing. Maike Eitschberger

Metals Department
Institute for Materials Science
University of Erlangen-Nuernberg

Martensstrasse 5
D - 91058 Erlangen
Tel. 09131 / 85 28748
Fax 09131 / 85 27515
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