What the Workshop 
can do for you.

Custom Built Apparatus 
in Pyrex, 
Quartz, Soda or Lead.
Vacuum Lines-
Solvent Still Heads-
Schlenk Tubes & Flasks
-Glass to Metal Seals
-Quartz to Pyrex Seals-
or any idea you come up with.

WebPage By


Silicon greases have one major wonderful noteworthy feature--they are cheap! Secondly, they are mostly impervious to hydrocarbon solvents. Unfortunately, they are not perfect. The biggest problem is that they are composed of two materials, a volatile and a non-volatile component, and the volatile is very volatile. In fact, once purchased, silicon grease should not be kept in the lab over 18 months as it ages in the tube. Once applied on a joint or stopcock, it should be completely removed and replaced every month or two. Even if you do not rotate the plug, a stopcock or joint may leak if left alone for several months. In addition, although silicon grease has a low vapor pressure (<10-5), it does creep under vacuum and will spread from a joint into the apparatus itself laying a film throughout. While silicon grease is very inert and not likely to cause any problems, complications do arise if you want the items repaired and/or altered. The problem is that it is not easy to remove the non-volatile component of silicon grease: the silicon. Under high heat (>400°C), the silicon component will fuse onto the surface of the glass and if a torch is applied to the glass, the silicon will burn into the glass destroying the glass that was heated. The best way to remove silicon grease is to remove the bulk of it with methalene chloride followed by a soaking for about 20-30 minutes in a base bath.
Also items that will be used for long term storage, e.g., desiccator jars for long term storage, should also never use silicon grease because of all of the aforementioned issues.
 Full Article

Gary Coyne is the author of 
"The Laboratory Companion,"
from Wiley Scientific

This book can be obtained by such vendors as Amazon.com

Glassblowing Workshop, School of Chemistry, North Haugh, St Andrews, KY16 9ST 

Colin F. M. Smith
Tel: 01334 463890 

Fax: 01334 463890

Email:  cfms@st-and.ac.uk

The workshop is always open 
for anyone to come and discuss 
or design work projects.
Please let me know as early 
as possible any projects you 
have planned for the future as 
soon as possible as the 
materials needed may have to 
be ordered and deliveries can 
take a long time.