[labnetwork] Anhydrous HCl
Bob Hamilton
roberthamilton at berkeley.edu
Tue Jun 10 11:49:42 EDT 2014
Lab Network Colleagues,
The thread about HCl corrosion comes at a timely time for the Berkeley
NanoLab as we are about to commission an epi system.
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.
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.
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.
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.
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?
Regards,
Bob Hamilton
--
Robert Hamilton
University of California at Berkeley
Marvell NanoLab
Equipment Eng. Mgr.
Room 520 Sutardja Dai Hall
Berkeley, CA 94720-1754
bob at eecs.berkeley.edu
Phone: 510-809-8600
Mobile: 510-325-7557 (Emergencies only)
e-mail preferred
On 6/8/2014 1:35 PM, Tom Britton wrote:
>
> Hi John,
>
> 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.
>
> Hope this helps. Feel free to call us if you want to discuss this
> further in depth.
>
>
> Enjoy the day.
>
> Thank you!
>
> Tom Britton
>
> Director of Sales
>
> /Critical Systems, Inc./
>
> Direct: 208-890-1417
>
> Office: 877-572-5515
>
> /www.CriticalSystemsInc.com/ <http://www.criticalsystemsinc.com/>/__/
>
> /__/
>
> logo for email signature png
>
> *From:*John Shott [mailto:shott at stanford.edu]
> *Sent:* Friday, June 06, 2014 2:55 PM
> *To:* Tom Britton; labnetwork at mtl.mit.edu
> *Subject:* Re: [labnetwork] Anhydrous HCl after it escapes ...
>
> Tom, Craig, and Dennis:
>
> Thanks for each of your comments. I should have thought to mention
> more about the details of our gases:
>
> 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 ...
> Note: this is also set up with a DISS fitting (CGA 634 for HCl).
>
> 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:
>
> Nitrogen:
>
> 02 < 1ppm
> H20 < 3ppm
> THC < 0.5ppm
>
> Helium:
>
> 02 < 1ppm
> H20 < 2ppm
> THC < 0.5ppm
>
> 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
>
> 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.
>
> Thanks again for all of your input,
>
> John
>
> On 6/6/2014 1:07 PM, Tom Britton wrote:
>
> Hi John,
>
> 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.
>
> To solve the problem of how to prevent leaks with HCl and other
> corrosives these are the questions I would start with.
>
> ·What is the quality of the purge gas?
>
> ·Are you using a purifier on the purge gas?
>
> ·Is H2O or O2 analysis done on the gas system prior to gas
> introduction?
>
> ·How many purge cycles on gas line prior to gas introduction?
>
> ·How many purge cycles post cylinder change are being done?
>
> 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.
>
> See you at Harvard.
>
> Thank you!
>
> Tom Britton
>
> Director of Sales
>
> /Critical Systems, Inc./
>
> Direct: 208-890-1417
>
> Office: 877-572-5515
>
> /www.CriticalSystemsInc.com/ <http://www.criticalsystemsinc.com/>
>
> //
>
> logo for email signature png
>
> -----Original Message-----
> From: labnetwork-bounces at mtl.mit.edu
> <mailto:labnetwork-bounces at mtl.mit.edu>
> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of John Shott
> Sent: Thursday, June 05, 2014 1:09 PM
> To: labnetwork at mtl.mit.edu <mailto:labnetwork at mtl.mit.edu>
> Subject: [labnetwork] Anhydrous HCl after it escapes ...
>
> Labnetwork Community:
>
> 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.
>
> 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?
>
> Thanks for sharing your experience and insights,
>
> John
>
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