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Lab Network Colleagues,<br>
<br>
The thread about HCl corrosion comes at a timely time for the
Berkeley NanoLab as we are about to commission an epi system. <br>
<br>
As noted by others the issue with chlorine corrosion of ferrous
metals and nickel involves water vapor as a contaminant. The
combination results in incipient chlorine corrosion, an endless
cycle of corrosion because of the chemistry involved. Iron reacts
with chlorine to form a chloride which in turn reacts with water to
form an oxide thus releasing the Cl- to continue the corrosion of
new metal. Once this cycle begins the only way to stop it is to
remove the surfaces involved. I have heard some metallurgist use the
term "cancering" to describe this corrosion.<br>
<br>
At Berkeley we had good luck with our acid gas plumbing which was
typically done in 316 and 321 SS components and tubing. I attribute
our success to a policy of never intervening in an acid gas line
without a 24 hour N2 purge before when possible and a 24 hours purge
after intervention. We also took steps to flow N2 through pigtails
to our CGA and later our DISS cylinder connections when changing gas
cylinders. DISS crush gaskets were inspected at every cylinder
change. Perhaps a quirk, it was my policy to deliver the DISS crush
gaskets to the lab director for inspection, good third-party
verification; perhaps like a cat delivering the dead mouse. We also
coupon, i.e. saw open, fittings and valves when we modify a gas
delivery line to see if we have issues.<br>
<br>
Now, with more modern purge panels we've obviated the 24 hour
policy. It's worth the time and effort to do extensive purge cycles
when dealing with the acid gases. We currently use 50 pump/purges
which take about an hour to complete. Still, one cannot completely
replace time by purge.<br>
<br>
Some years ago I heard a presentation which noted the use of 317L SS
tubing for chlorine and HCl delivery. This is a
molybdenum-containing SS alloy. We experimented with oribtially
welding 317 to 316 and 321. A third-party verified weld integrity.
Regrettably, fittings for purge panels and connections are not made
in 317 so this has to be considered before using 317.<br>
<br>
I suspect there is some variance in experience with Cl2 and HCl
delivery because gas purity varies by grade and supplier. I have no
experience with using cartridge purifiers to clean up an acid gas
(we do use N2 and H2 purifiers in selected applications). One would
guess these would reduce corrosion and may prove cost effective by
permitting a slightly lower grade of gas. Perhaps someone on "the
list” can share experience about their experience with purifiers?<br>
<br>
Regards,<br>
Bob Hamilton<br>
<br>
<pre class="moz-signature" cols="72">--
Robert Hamilton
University of California at Berkeley
Marvell NanoLab
Equipment Eng. Mgr.
Room 520 Sutardja Dai Hall
Berkeley, CA 94720-1754
<a class="moz-txt-link-abbreviated" href="mailto:bob@eecs.berkeley.edu">bob@eecs.berkeley.edu</a>
Phone: 510-809-8600
Mobile: 510-325-7557 (Emergencies only)
e-mail preferred
</pre>
<br>
<br>
<div class="moz-cite-prefix">On 6/8/2014 1:35 PM, Tom Britton wrote:<br>
</div>
<blockquote
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type="cite">
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charset=us-ascii">
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<p class="MsoNormal"><span>Hi John,</span></p>
<p class="MsoNormal"><span> </span></p>
<p class="MsoNormal"><span>Based on what you wrote below, we
would recommend changing the pre and post purge cycles to 60
from a safety standpoint; 30 is not enough. 50 is
recommended on all HPM’s for safety reasons, and from a
quality standpoint on post cylinder change purge cycles you
want to make sure any residual atmosphere is gone, therefore
60 is the standard Troy used at ON Semi for the post purge
on all corrosives. He also recommend you look at the heel
weights (what's left in the cylinder) as sometimes running
the bottles too low can cause issues. If you're unsure of
what the heel weight should be, ask the gas supplier.
Typically 10% is a good number, so on a 60 lb cylinder most
manufacturers would recommend changing the cylinder at 6 lbs
remaining in the cylinder, but it's common to increase the
heel if contamination occurs at the pigtail connection. For
HCl, HBR and DCS it is not uncommon to increase the heel
from 10% to 15% just to alleviate contamination issues.</span></p>
<p class="MsoNormal"><span> </span></p>
<p class="MsoNormal"><span>Hope this helps. Feel free to call us
if you want to discuss this further in depth.
</span></p>
<p class="MsoNormal"><span><br>
Enjoy the day.</span></p>
<p class="MsoNormal"><span> </span></p>
<p class="MsoNormal"><span>Thank you!</span></p>
<p class="MsoNormal"><span> </span></p>
<p class="MsoNormal"><span>Tom Britton</span><span></span></p>
<p class="MsoNormal"><span>Director of Sales</span><span></span></p>
<p class="MsoNormal"><i><span>Critical Systems, Inc.</span></i><span></span></p>
<p class="MsoNormal"><span>Direct: 208-890-1417</span></p>
<p class="MsoNormal"><span>Office: 877-572-5515</span></p>
<p class="MsoNormal"><span><a moz-do-not-send="true"
href="http://www.criticalsystemsinc.com/"><i><span>www.CriticalSystemsInc.com</span></i></a></span><i><u><span></span></u></i></p>
<p class="MsoNormal"><i><u><span><span> </span></span></u></i></p>
<p class="MsoNormal"><span><img moz-do-not-send="true"
id="_x0000_i1026"
src="imap://roberthamilton%40berkeley%2Eedu@imap.gmail.com:993/fetch%3EUID%3E/INBOX%3E34335?header=quotebody/;section=1.2?part=1.1.2&filename=image001.png"
alt="logo for email signature png" height="38" width="196"></span><span></span></p>
<p class="MsoNormal"><span> </span></p>
<p class="MsoNormal"><span> </span></p>
<p class="MsoNormal"><span> </span></p>
<div>
<div>
<p class="MsoNormal"><b><span>From:</span></b><span> John
Shott [<a class="moz-txt-link-freetext" href="mailto:shott@stanford.edu">mailto:shott@stanford.edu</a>]
<br>
<b>Sent:</b> Friday, June 06, 2014 2:55 PM<br>
<b>To:</b> Tom Britton; <a class="moz-txt-link-abbreviated" href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a><br>
<b>Subject:</b> Re: [labnetwork] Anhydrous HCl after it
escapes ...</span></p>
</div>
</div>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Tom, Craig, and Dennis:<br>
<br>
Thanks for each of your comments. I should have thought to
mention more about the details of our gases:<br>
<br>
We are using electronic grade HCl specified to be 99.995%
pure. While I think that there is one grade higher, at $1200
a cylinder it should be pretty good ...<br>
Note: this is also set up with a DISS fitting (CGA 634 for
HCl).<br>
<br>
For our purge gas we use 10% He in a balance of nitrogen,
again with a DISS fitting. Each of the component gases is of
UH grade that, I believe translates in to:<br>
<br>
<span>Nitrogen:</span> <br>
<br>
<span>02 < 1ppm</span>
<br>
<span>H20 < 3ppm</span>
<br>
<span>THC < 0.5ppm</span>
<br>
<br>
<span>Helium</span>:<br>
<br>
<span>02 < 1ppm</span>
<br>
<span>H20 < 2ppm</span>
<br>
<span>THC < 0.5ppm</span>
<br>
<br>
<span>After a cylinder change, we do a He leak check of the
purge gas following each cylinder change. I think that we
are currently using 30 purge cycles both pre- and post-purge
... it sounds as if that should be bumped up. While I
believe that we have hastelloy running between cabinet and
tool, I believe that the components in the panel are all SS
... but I believe are electopolished to
<br>
<br>
We have a manifolded two-cylinder (plus purge) cabinet that
supplies an epi reactor. It is not uncommon to use a 60
pound cylinder of HCl in a period of 1-2 weeks ... so, we
unfortunately, have a number of chances for problems each
year.<br>
<br>
Thanks again for all of your input,<br>
<br>
John<br>
<br>
</span></p>
<div>
<p class="MsoNormal">On 6/6/2014 1:07 PM, Tom Britton wrote:</p>
</div>
<blockquote>
<p class="MsoPlainText">Hi John,</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">Sorry to hear about your HCl issue. As
we all know, HCl is very difficult to manage once it
escapes. Neutralizing is seldom effective in a clean room
environment, and replacement of metal components that have
come in contact with the HCL is the proper way to keep it
from spreading. If the proper leak test procedures are in
place, one thing that could be causing the leaks is residual
moisture that may be present due to either low quality
purge gas or inadequate purging.
</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">To solve the problem of how to prevent
leaks with HCl and other corrosives these are the questions
I would start with.
</p>
<p class="MsoPlainText">
<span><span>·<span>
</span></span></span>What is the quality of the purge
gas? </p>
<p class="MsoPlainText">
<span><span>·<span>
</span></span></span>Are you using a purifier on the
purge gas? </p>
<p class="MsoPlainText">
<span><span>·<span>
</span></span></span>Is H2O or O2 analysis done on the
gas system prior to gas introduction?
</p>
<p class="MsoPlainText">
<span><span>·<span>
</span></span></span>How many purge cycles on gas line
prior to gas introduction?
</p>
<p class="MsoPlainText">
<span><span>·<span>
</span></span></span>How many purge cycles post cylinder
change are being done?
</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">If you want, I can set up a conference
call with Troy Reese, who was the gas systems manager at ON
Semi before he came to us, and we can go over these
questions. Troy is very knowledgeable in these situations
and we would be happy to help wherever possible. He is also
presenting with you at the Bootie Camp coming up at the UGIM
conference, so we can talk about it there as well if
necessary.</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">See you at Harvard.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Thank you!</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Tom Britton</p>
<p class="MsoNormal">Director of Sales</p>
<p class="MsoNormal"><i><span>Critical Systems, Inc.</span></i></p>
<p class="MsoNormal">Direct: 208-890-1417</p>
<p class="MsoNormal">Office: 877-572-5515</p>
<p class="MsoNormal"><span><a moz-do-not-send="true"
href="http://www.criticalsystemsinc.com/"><i>www.CriticalSystemsInc.com</i></a></span></p>
<p class="MsoNormal"><i><span> </span></i></p>
<p class="MsoNormal"><span><img moz-do-not-send="true"
id="Picture_x0020_1"
src="imap://roberthamilton%40berkeley%2Eedu@imap.gmail.com:993/fetch%3EUID%3E/INBOX%3E34335?header=quotebody/;section=1.2?part=1.1.2&filename=image001.png"
alt="logo for email signature png" height="38"
width="196"></span></p>
<p class="MsoNormal"> </p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">-----Original Message-----<br>
From: <a moz-do-not-send="true"
href="mailto:labnetwork-bounces@mtl.mit.edu">labnetwork-bounces@mtl.mit.edu</a>
[<a moz-do-not-send="true"
href="mailto:labnetwork-bounces@mtl.mit.edu">mailto:labnetwork-bounces@mtl.mit.edu</a>]
On Behalf Of John Shott<br>
Sent: Thursday, June 05, 2014 1:09 PM<br>
To: <a moz-do-not-send="true"
href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a><br>
Subject: [labnetwork] Anhydrous HCl after it escapes ...</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">Labnetwork Community:</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">Sooner or later, it seems, anhydrous
hydrogen chloride (or a number of equally corrosive
materials) is going to escape. At least that is our
experience at the Stanford Nanofabrication Facility.
Despite our best efforts to use quality components, do
proper leak checking, etc., it seems as if we end up with a
leak either in a gas cabinet or in a tool near a mass flow
controller. At that point, anything near the site of the
original leak has been covered with now moisture-laden
hydrogen chloride ... which, I believe, is far more
corrosive than the original anhydrous material.</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">For those of you who have encountered
similar situations, how do you recover or what to you
replace? Do you have effective means of neutralizing those
metal surfaces? Do your replace VCR gaskets with
thicker-than-normal or grooved "super gaskets"? Do you
replace the entire assembly? Do you leak check, put back in
service, and pray?</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">Thanks for sharing your experience and
insights,</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">John</p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText"> </p>
<p class="MsoPlainText">_______________________________________________</p>
<p class="MsoPlainText">labnetwork mailing list</p>
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href="https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork"><span>https://www-mtl.mit.edu/mailman/listinfo.cgi/labnetwork</span></a></p>
</blockquote>
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