I would say the surrounding alumina is the seal that is important, and I do not
think it is an hermetic seal. Its porosity allows some leakage, particularly
at the temperatures of 1000 degrees C. Thermal stresses in non-ductile
materials are bad when it comes to hermetic sealing. Glass which flows is
somewhat better. If one wants real hermetic sealing, he should test it at
temperature with He for leakage.
Bob
----- Original Message -----
From: Jack Cole
To: vortex-l@eskimo.com
Sent: Thursday, January 01, 2015 5:33 PM
Subject: Re: [Vo]:Lithium aluminum thin film and the Kretschmann geometry
According to the specs, it requires 24 hours to cure at room temperature. Do
you think it is not hermetic because it's not capable of that, or because it
wasn't cured?
On Thu, Jan 1, 2015 at 2:23 PM, Bob Higgins <rj.bob.higg...@gmail.com> wrote:
The first attempt did use a Cotronics Resbond 919, I think. These alumina
cements are not hermetic. That's why glass frit seals are being examined -
they are hermetic.
On Thu, Jan 1, 2015 at 1:15 PM, Jack Cole <jcol...@gmail.com> wrote:
Hi Bob,
I wonder about this Thermeez Ceramic putty.
http://www.cotronics.com/catalog/51%20%20%207020%20%20901.pdf
It cures at room temperature, so that removes the issue of hydrogen off
gassing during curing. What I don't know is if it will be effective against
holding in the hydrogen. I emailed the company and hopefully they can provide
some guidance.
On Thu, Jan 1, 2015 at 1:41 PM, Bob Higgins <rj.bob.higg...@gmail.com>
wrote:
Parkhomov starts with a 10mm OD alumina tube with a 5mm ID bore (so the
wall of the tube is 2.5mm thick). He plugs both ends with an alumina rod and
"cement" with the fuel inside. He hasn't said what "cement" he uses to
hermetically seal the plugs in the tubing, but he does say that it is a hard
3-day process. After the hermetic plugged tube assembly is made he winds this
tube directly with a nichrome wire coil and paints it all over with a thick
alumina cement. MFMP has asked Parkhomov what he used for cement and what his
hermetic sealing process was and he has not yet responded.
In the mean time MFMP is discussing using a high temperature glass frit
seal for the plug. One end is already molded and fired closed - the tube was
purchased that way. So the fuel will be added, then an alumina wool plug near
the seal end, then the alumina plug painted with a glass frit paste having a
resulting thermal expansion matched to alumina. Then the fuel end will be
cooled while the seal end is heated with a torch to melt the seal glass and
form a hermetic seal. This is the MFMP "reaction tube", about 0.25" OD.
The dogbone heater coil is wrapped around another alumina tube into
which the reaction tube can be inserted (slightly larger than 0.25" ID). This
allows the reaction tube to be replaced without having to wind a new heater
coil and overmold it for every experiment. In MFMP testing, the previously
fueled and sealed reactor tube is inserted into a dogbone heater tube that has
the coil wrapped and enclosed in molded alumina cement. Power is applied to
the dogbone heater coil which heats the reactor tube that was slipped inside.
Bob
On Thu, Jan 1, 2015 at 12:24 PM, Bob Cook <frobertc...@hotmail.com>
wrote:
Bob--
How does Parkhomov get a uniform thickness of alumina cement,
whatever that is, between the 2.5mm alumina tube (reactor tube in previous
correspondence) and the alumina dogbone with the electrical heater wires? It
may be that I do not understand the physical arrangement of the various alumina
components of the Parkhomov experiment.
Bob
