has anyone ever used a glass condenser in a stainless steel
reaction vessel . and is there a problem with the stainless expanding greater than glass and then the glass getting stuck ,or will using the right
grease stop this
b 34 fittingskilowatt - 18-3-2008 at 01:22
You should look up the thermal expansion coefficients. For example teflon stoppers in labware can be extremely annoying and inconvenient as they
expand a great deal more than glass and get stuck easily. That's an extreme example being a plastic with high thermal expansion, but you get the
idea. I'm not sure about stainless steel, but I can gurantee that an invar (FeNi) alloy can be made with exactly the same coefficient of expansion as
borosilicate glass, since the 36% Fe has a thermal coefficient approaching that of fused silica. I don't know if any labwares are made of just such
an alloy, but if not it should be weldable and you may be able to fabricate an adapter of some sort if you happen to be into that sort of thing.not_important - 18-3-2008 at 01:47
I've seen setups such as you are taliking about, and in at least some of those there was a straight SS extension tube between the SS flask and the
condenser. I'm assuming that the upper end of the extension would be kept relatively cool, avoiding too much grabbing of the glass; also it seems you
could remove the condenser shortly after turning off heating, or pull the condenser upwards several times early in cool down.evil_lurker - 18-3-2008 at 01:49
Use threaded glassware with PTFE bushings.
I've adapted stainless steel 1" OD pipe to 24/40 joint using a custom built #25 adapter made by Chemglass.
If your need anything fabricated let me know.kilowatt - 18-3-2008 at 01:55
They also have glass reaction vessel tops that can be clamped onto a stainless or whatever vessel to connect it to glass columns and the like.unionised - 18-3-2008 at 12:00
I'm not sure about stainless steel, but I can gurantee that an invar (FeNi) alloy can be made with exactly the same coefficient of expansion as
borosilicate glass, since the 36% Fe has a thermal coefficient approaching that of fused silica.
Yes, there exist several alloys such as Kovar, Sealmet, and Dumet metal which have been specifically designed
to have coefficients of expansion which agree with those of various types of glass. Like stainless steel and invar,
these are nickel-iron alloys with other elements perhaps present. The primary use for them is in making electrode
wires to be sealed in glass, such as the wires in light bulbs. While matching expansions is crucial when attaching
hot glass to a piece of metal thicker than foil, in your case I think the use of this would be overkill.
First, the range of temperatures involved is more like 100 degrees than 1000 degrees in your application.
For a typical pipe, this mismatch amounts to a few microns of expansion. To be sure, if you shove
the metal firmly into the glass, that may be enough to make the glass crack, but it would also be quite easy
to take up this slack with a flexible material like plastic or rubber.
Another trick would be to make the metal pipe which actually touches the glass thin enough that it can bend
upon expanding without exerting enough pressure to damage the glass. In fact, this is the basis for the
Householder seal between glass and copper tubing. To make one of those, one first files, reams, or turns
the inside of the metal pipe so that it slopes to a knife edge at an angle of ten degrees before attaching it
to the glass. Something like this might work for you if you prefer not to use a flexible material.
Second, the alloys are specialty metals which, AFAIK, are usually only made as wires ready for sealing to
glass. Thus, I think that unless you or somebody you know is going to melt down sealing wire or mix the alloy,
it would be hard to locate a piece suitable for making an adapter; I doubt a steel mill is going to bother to make
some Kovar pipe or rod just for a few people or even sell individual ingots.
As it turns out, there are also special composition glasses whose coefficients of expansion are adjusted
to match various metals. One or more of these can be used to join a piece of metal to ordinary glass
by easing the transition between coefficients of expansion, so spreading out the stress so that nothing
cracks or comes loose. Quite likely, this was how evil_lurker's adapter was made.
So there you have what I know about the subject; hopefully, it will give you an idea which is practical
for your situation.
[Edited on 18-3-2008 by microcosmicus]bio2 - 18-3-2008 at 17:56
These adapters are called graded seals. Kontes makes a 304SS to borosilicate
in many sizes designated 65930-XXXX.
Several other types are also available.
Adapting Metal Tubes to Glassware
leu - 24-3-2008 at 18:22
This method of joining metal to glass devised by Ralph Nester of the Experimental Station of Dupont could be useful to a well equipped craftsperson
Attachment: metaltoglass.djvu (17kB) This file has been downloaded 550 times
GLASS TO STAINLESS
azo - 25-3-2008 at 01:03
THANKS ALL FOR THE TIME YOU TOOK OUT TO PROVIDE A GREAT LOT OF INFORMATION THIS REALY HELPS
