FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups 
 ProfileProfile   PreferencesPreferences   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Forum index » Science and Technology » Chem » Electrochem
Help with Pourbaix diagrams
Post new topic   Reply to topic Page 1 of 1 [10 Posts] View previous topic :: View next topic
Author Message
WAYNEL183
science forum beginner


Joined: 20 Aug 2005
Posts: 26

PostPosted: Fri Jun 02, 2006 8:08 pm    Post subject: Help with Pourbaix diagrams Reply with quote

I have a cell biased with 5v. Both electrodes are copper and the
cathode is at 0v and the anode is at +5v.
I am trying to read a Pourbaix diagram for copper on the following
paper from IBM
http://www.research.ibm.com/journal/rd/291/ibmrd2901E.pdf,

Can I disregard the -ve part of the diagram as my ref. point is zero
and should I only consider the anodic part of the diagram i.e. the +E?
If not then it implies that the -E(cathode??) is immune.


Cheers


WayneL
Back to top
guvenay@gmail.com
science forum beginner


Joined: 03 Jun 2006
Posts: 1

PostPosted: Sat Jun 03, 2006 2:13 pm    Post subject: Re: Help with Pourbaix diagrams Reply with quote

waynel
i am sorry but could you explain how can u polarize the anode and
cathode.
at 5v polarization at the anode means your electrode --copper-- will be
dissolved. but how can willbe zero at catode. can u explain your system
briefly. the pourbaix diagram at your referance is a true diagram for
cu-h20 system.
if you use a dc regulator for polarized the system u can use only the
cahtode or anode side of the diagram but they are related each other.
regards

WAYNEL wrote:
Quote:
I have a cell biased with 5v. Both electrodes are copper and the
cathode is at 0v and the anode is at +5v.
I am trying to read a Pourbaix diagram for copper on the following
paper from IBM
http://www.research.ibm.com/journal/rd/291/ibmrd2901E.pdf,

Can I disregard the -ve part of the diagram as my ref. point is zero
and should I only consider the anodic part of the diagram i.e. the +E?
If not then it implies that the -E(cathode??) is immune.


Cheers


WayneL
Back to top
Oscar Lanzi III
science forum Guru Wannabe


Joined: 30 Apr 2005
Posts: 176

PostPosted: Sun Jun 04, 2006 1:49 am    Post subject: Re: Help with Pourbaix diagrams Reply with quote

You can't call the anode +5v and the cxathode 0v on the Pourbaix
diagram. You CAN assume that they differ by 5 V (if there is no loss
due to ohmic resistance), but the cathode does not necesarily match
ground. The actal electrode potentials relative to the standard
hyydrogen electrode will be such that the anodic anc cathodic reaction
currents are in blanace. Thus electrochemical kinetics is involved, and
things ca nget a little tricky.

What would happen if you measured say the cathode potential against a
reference electrode?

--OL
Back to top
WayneL
science forum beginner


Joined: 03 May 2005
Posts: 33

PostPosted: Sun Jun 04, 2006 3:10 pm    Post subject: Re: Help with Pourbaix diagrams Reply with quote

I'm confused, have I misunderstood? Both electrodes are copper. One of
them is connected to ground (0V) and the other electrode to a more positive
(+5V), hence anode - in water.
My question is; on the Pourbaix diagram which part of the diagram
corresponds to the Cathode and which side corresponds to the Anode? On my
simple cell is the 0v electrode -E of the Pourbaix diagram and the +5v +E?
If so where is the 0v E point?

WayneL


"Oscar Lanzi III" <ol3@webtv.net> wrote in message
news:25601-44823C1C-56@storefull-3258.bay.webtv.net...
Quote:
You can't call the anode +5v and the cxathode 0v on the Pourbaix
diagram. You CAN assume that they differ by 5 V (if there is no loss
due to ohmic resistance), but the cathode does not necesarily match
ground. The actal electrode potentials relative to the standard
hyydrogen electrode will be such that the anodic anc cathodic reaction
currents are in blanace. Thus electrochemical kinetics is involved, and
things ca nget a little tricky.

What would happen if you measured say the cathode potential against a
reference electrode?

--OL
Back to top
Robert Copcutt
science forum beginner


Joined: 16 Jun 2005
Posts: 9

PostPosted: Sun Jun 04, 2006 5:31 pm    Post subject: Re: Help with Pourbaix diagrams Reply with quote

WayneL wrote:
Quote:
I'm confused, have I misunderstood? Both electrodes are copper. One of
them is connected to ground (0V) and the other electrode to a more positive
(+5V), hence anode - in water.
My question is; on the Pourbaix diagram which part of the diagram
corresponds to the Cathode and which side corresponds to the Anode? On my
simple cell is the 0v electrode -E of the Pourbaix diagram and the +5v +E?
If so where is the 0v E point?

WayneL

You sound very confused and need to read up on reference electrodes. The

hydrogen reference electrode has been assigned a chemical potential of
zero volts and Pourbaix diagrams measure all potentials against this
standard. Do not get chemical and electrical potentials confused. Just
because you have decided to ground the negative terminal does not mean
that it is anywhere near 0V as used in the diagram. In order to measure
chemical potentials you need at least 3 electrodes - the 2 electrodes
that carry the current and a reference electrode that carries negligible
current and which is built to have a well defined electrochemical
reaction occur on it. You also need to compensate for IR losses in all
parts of your system that carry current (think ohms law).

Look at figure 7 of the pdf you referenced. The working electrode is the
copper plate bottom left. The counter electrode is the dotted bar top
left. These 2 electrodes carry the current. They then have a salt bridge
to a beaker and top right they have clearly drawn a reference electrode.
Back to top
nagy@anl.gov
science forum beginner


Joined: 18 Jul 2005
Posts: 16

PostPosted: Mon Jun 05, 2006 3:52 pm    Post subject: Re: Help with Pourbaix diagrams Reply with quote

Wayne,

Read about reference electrodes, etc in Electrochemistry Dictionary

http://electrochem.cwru.edu/ed/dict.htm

Good luck :ZN

Robert Copcutt wrote:
Quote:
WayneL wrote:
I'm confused, have I misunderstood? Both electrodes are copper. One of
them is connected to ground (0V) and the other electrode to a more positive
(+5V), hence anode - in water.
My question is; on the Pourbaix diagram which part of the diagram
corresponds to the Cathode and which side corresponds to the Anode? On my
simple cell is the 0v electrode -E of the Pourbaix diagram and the +5v +E?
If so where is the 0v E point?

WayneL

You sound very confused and need to read up on reference electrodes. The
hydrogen reference electrode has been assigned a chemical potential of
zero volts and Pourbaix diagrams measure all potentials against this
standard. Do not get chemical and electrical potentials confused. Just
because you have decided to ground the negative terminal does not mean
that it is anywhere near 0V as used in the diagram. In order to measure
chemical potentials you need at least 3 electrodes - the 2 electrodes
that carry the current and a reference electrode that carries negligible
current and which is built to have a well defined electrochemical
reaction occur on it. You also need to compensate for IR losses in all
parts of your system that carry current (think ohms law).

Look at figure 7 of the pdf you referenced. The working electrode is the
copper plate bottom left. The counter electrode is the dotted bar top
left. These 2 electrodes carry the current. They then have a salt bridge
to a beaker and top right they have clearly drawn a reference electrode.
Back to top
WayneL
science forum beginner


Joined: 03 May 2005
Posts: 33

PostPosted: Mon Jun 05, 2006 8:48 pm    Post subject: Re: Help with Pourbaix diagrams Reply with quote

Thanks, not so confused now. Get warm in here in the summer.
Is there a way of using Pourbaix diagrams with only two electrodes as I an
investigating electrochemical corrosion on two electrode systems?
Thanks for your patience.


WayneL

<nagy@anl.gov> wrote in message
news:1149522756.570190.230120@c74g2000cwc.googlegroups.com...
Quote:

Wayne,

Read about reference electrodes, etc in Electrochemistry Dictionary

http://electrochem.cwru.edu/ed/dict.htm

Good luck :ZN

Robert Copcutt wrote:
WayneL wrote:
I'm confused, have I misunderstood? Both electrodes are copper. One
of
them is connected to ground (0V) and the other electrode to a more
positive
(+5V), hence anode - in water.
My question is; on the Pourbaix diagram which part of the diagram
corresponds to the Cathode and which side corresponds to the Anode? On
my
simple cell is the 0v electrode -E of the Pourbaix diagram and the +5v
+E?
If so where is the 0v E point?

WayneL

You sound very confused and need to read up on reference electrodes. The
hydrogen reference electrode has been assigned a chemical potential of
zero volts and Pourbaix diagrams measure all potentials against this
standard. Do not get chemical and electrical potentials confused. Just
because you have decided to ground the negative terminal does not mean
that it is anywhere near 0V as used in the diagram. In order to measure
chemical potentials you need at least 3 electrodes - the 2 electrodes
that carry the current and a reference electrode that carries negligible
current and which is built to have a well defined electrochemical
reaction occur on it. You also need to compensate for IR losses in all
parts of your system that carry current (think ohms law).

Look at figure 7 of the pdf you referenced. The working electrode is the
copper plate bottom left. The counter electrode is the dotted bar top
left. These 2 electrodes carry the current. They then have a salt bridge
to a beaker and top right they have clearly drawn a reference electrode.
Back to top
Robert Copcutt
science forum beginner


Joined: 16 Jun 2005
Posts: 9

PostPosted: Mon Jun 05, 2006 9:57 pm    Post subject: Re: Help with Pourbaix diagrams Reply with quote

WayneL wrote:
Quote:
Thanks, not so confused now. Get warm in here in the summer.
Is there a way of using Pourbaix diagrams with only two electrodes as I an
investigating electrochemical corrosion on two electrode systems?
Thanks for your patience.


WayneL


Without a reference electrode you can only make intelligent guesses
about the chemical potentials of your 2 electrodes. You could do quick
and rough comparisons of coatings using 2 electrodes but to do work
worth publishing a third electrode is essential.
Back to top
Dieter Britz
science forum beginner


Joined: 04 May 2005
Posts: 45

PostPosted: Tue Jun 06, 2006 7:53 am    Post subject: Re: Help with Pourbaix diagrams Reply with quote

WAYNEL wrote:

Quote:
I have a cell biased with 5v. Both electrodes are copper and the
cathode is at 0v and the anode is at +5v.
I am trying to read a Pourbaix diagram for copper on the following
paper from IBM
http://www.research.ibm.com/journal/rd/291/ibmrd2901E.pdf,

Can I disregard the -ve part of the diagram as my ref. point is zero
and should I only consider the anodic part of the diagram i.e. the +E?
If not then it implies that the -E(cathode??) is immune.

I suspect there is something here you have not mentioned,
that the two electrodes are probaby sitting in pure water (?).
People have wondered how you can polarise the anode at
+5V; well, most of that is probably iR drop. Am I right?
--
Dieter Britz, Kemisk Institut, Aarhus Universitet
Back to top
WAYNEL183
science forum beginner


Joined: 20 Aug 2005
Posts: 26

PostPosted: Tue Jun 06, 2006 6:25 pm    Post subject: Re: Help with Pourbaix diagrams Reply with quote

You are correct, I forgot to mention that the electrodes are in pure
water. I has assumed, correctly or incorrectly that because it is
biased as a "convential" anode that it is an anode.
I am not a true electrochemist rather an electronic engineer. This may
explain some of the confusion.

WayneL

Dieter Britz wrote:
Quote:
WAYNEL wrote:

I have a cell biased with 5v. Both electrodes are copper and the
cathode is at 0v and the anode is at +5v.
I am trying to read a Pourbaix diagram for copper on the following
paper from IBM
http://www.research.ibm.com/journal/rd/291/ibmrd2901E.pdf,

Can I disregard the -ve part of the diagram as my ref. point is zero
and should I only consider the anodic part of the diagram i.e. the +E?
If not then it implies that the -E(cathode??) is immune.

I suspect there is something here you have not mentioned,
that the two electrodes are probaby sitting in pure water (?).
People have wondered how you can polarise the anode at
+5V; well, most of that is probably iR drop. Am I right?
--
Dieter Britz, Kemisk Institut, Aarhus Universitet
Back to top
Google

Back to top
Display posts from previous:   
Post new topic   Reply to topic Page 1 of 1 [10 Posts] View previous topic :: View next topic
The time now is Wed Jun 28, 2017 5:26 am | All times are GMT
Forum index » Science and Technology » Chem » Electrochem
Jump to:  

Similar Topics
Topic Author Forum Replies Last Post
No new posts Name of chapter dependency diagrams sought google03@sigfpe.com Math 2 Wed Jul 12, 2006 10:35 pm
No new posts S/W Eng Asks For Intuitive Explanation Of Logic Diagrams ... clusardi2k@aol.com Control 6 Fri Jul 07, 2006 12:23 pm
No new posts Finding data visualization graphs, charts, diagrams etc.. gnh888@gmail.com Recreational 0 Thu Feb 02, 2006 6:16 am
No new posts Where do I find Data Visualization graphs, charts, diagr... gnh888@gmail.com Math 1 Thu Feb 02, 2006 6:13 am
No new posts [OT] favorite vector-based gaphics tool for mathematical ... Alex Hunsley Math 8 Tue Nov 22, 2005 3:17 pm

Copyright © 2004-2005 DeniX Solutions SRL
Other DeniX Solutions sites: Electronics forum |  Medicine forum |  Unix/Linux blog |  Unix/Linux documentation |  Unix/Linux forums  |  send newsletters
 


Powered by phpBB © 2001, 2005 phpBB Group
[ Time: 0.0232s ][ Queries: 16 (0.0030s) ][ GZIP on - Debug on ]