Maybe someone who's used graphite anodes in a chlorate or perchlorate cell can tell me:
Do they appear to only erode, or do they seem to undergo a chemical reaction?
And a related question:
Does the volume of material lost from the anode seem to correlate well with the amount of powder filtered out from the product?12AX7 - 22-12-2005 at 21:01
I've never weighed the difference but I imagine it's *only* eroded.
TimNERV - 22-12-2005 at 23:40
Whenever I used graphite it always appeared to erode away not chemically react. Graphite is fairly chemically stable in electrolysis reactions
that’s why it’s generally used as an inert electrode IIRC (I am no electro chem specialist). I am sure there are special circumstances where it
would react, but if your just running a chlorate cell than no it shouldn’t be reacting at all. It’s a whole different story though if your
graphite electrodes contain something other than graphite in that case that material might react in your electrolysis.Fleaker - 23-12-2005 at 10:56
Don't they usually contain some clay (kaolin) to serve as a binder?
I know graphite will sometimes react (as will platinum even) when doing reactions, particularly with the halogens. Carbon tetrachloride can even be
formed during some high temperature reactions!NERV - 23-12-2005 at 13:03
Quote:
Originally posted by Fleaker
Don't they usually contain some clay (kaolin) to serve as a binder?
Yeah I think that most graphite pencil leads use Kaolin or some other clay as a binder. I am not sure about graphite welding rods although I imagine
that they would contain a similar if not the same clay binder. Does anyone know how the clay binder would behave in an electrolysis reaction? I
imagine that it really wouldn’t do much unless in an extremely reactive process like Fleaker described.12AX7 - 23-12-2005 at 14:01
Kaolin is inert, and you're using the shitty wrong kind of electrodes if they contain any, anyway. The proper kind is sintered, the only binder is
carbon.
Timjpsmith123 - 25-12-2005 at 15:13
I wonder if it's possible to "bag" the anode; IOW, enclose the graphite in some kind of fine plastic mesh, for example, that would keep the eroded
powder from contaminating the cell?
Regards,
Joe12AX7 - 25-12-2005 at 15:34
I don't see how you could, the product is often colloidial so you would need a very fine membrane, the very sort of thing that would prevent the
anolyte and catholyte from mixing and producing the necessary reaction. Unless you intentionally set it up so the anode's chlorine gas is bubbled
into the catholyte.
Timjpsmith123 - 25-12-2005 at 16:18
Hello Tim,
What kind of filter media have you used to filter it out of the cell liquor?
Regards,
JoeThe_Davster - 25-12-2005 at 16:50
Regular lab filters work fine for removing carbon particles after running a chlorate cell.
I have done the electrode bagging in other electrolytic cells, not chlorate, but in some other experiments of mine, and even when they are simply
filter paper, you do have increased cell resistance.jpsmith123 - 27-12-2005 at 02:41
I found a journal article which may shed some light on what happens to graphite in a chlorate cell at least.
Carbon Volume 29, Issue 2 , 1991, Pages 165-171:
Electrochemical wear of graphite anodes during electrolysis of brine
M. A. Rabah, Nabil Nassif and A. A. Abdul Azim
Central Metallurgical Research and Development Institute (CMRDI), P.O. Box 87, Helwan, Cairo, Egypt
Received 13 July 1989; accepted 3 April 1990. ; Available online 9 May 2003.
Abstract
Graphite electrode samples measuring 30 × 30 × 6 mm were machined from an industrial synthetic graphite plate. These were anodically polarized in
sodium chloride solution under galvanostatic and potentiostatic conditions. Electolyses experiments were performed within the current density of
25–50 mA/cm−2 for periods ranging from 20–160 hours. The effects of chloride ion concentration, bath temperature, brine pH value and current
density on the wear rate of the graphite anodes were investigated. The results obtained reveal that corrosion rate of the graphite anodes during
electrolysis of brine takes place
1. (1) due to the neucleophilic attack of water, and
2. (2) via the formation of a chloride-graphite compound having the chemical formula:
The compound was isolated and identified. It decomposes to carbon slimes, carbon monoxide, carbon dioxide, chlorine gases, and water. A model for
corrosion of graphite anodes has been suggested which assumes that chloride ions are adsorbed on the anode blanketing its surface from the brine
attack, and hence inhibit corrosion rate. The overall formation and decomposition reactions of the isolated compound are an endothermic process
whereby wear rate is enhanced with rise in temperature. Increasing the current density imparts a corresponding increase in positively charged carbon
atoms maintained on the anode surface leading to an increase in wear rate. The latter attains its maximum at neutral rather than in acidic or alkaline
solutions. Dense electrode material having mesopores is less corroded than electrodes having pores with pore diameter 5,000 nm.
If the following link works you can see the proposed compound. Unfortunately I don't have access to the full text as that requires either a
subscription or the payment of a $15.00 fee.
"I wonder if it's possible to "bag" the anode; IOW, enclose the graphite in some kind of fine plastic mesh, for example, that would keep the eroded
powder from contaminating the cell?"
Like whats in a car battery, a one way membrane, that will pass current, but stops lead passing.neutrino - 16-1-2006 at 06:53
