387 replies to this topic

[Pretty green flames]

so what is your anode material?

Magnetite (Fe3O4)

[Old1953]

so what is your anode material?

Magnetite (Fe3O4)

Sintered platinum over tantalum. The binder has adhered properly to the wire, if the platinum sticks after the heat treatment it will be a winner. It should, similar products stick to silver and gold without problems, not to mention ceramics.

Google up "Hanovia Bright Platinum" and take a look. Englehard's product is used quite a bit in labs to avoid the expense and mess of electroplating platinum.

2 grams of the HBP cost me $15.50 at a local potters shop, and there is enough to do at least three or four of these anodes, at about 5sqcm per anode. Likely more than that, this paint is tricky to use on something this small and I probably covered the wire much too thickly, and left quite a bit on the brush. I got the tantalum as surplus off ebay, it didn't cost enough per meter to bother adding it up - probably half a dollar per meter or less.

So today I'll heat it up to a nice cherry red for about ten minutes and burn off all the binders and let the platinum bond itself to the tantalum wire (I hope). That's how you do it when bonding to a small piece of metal. It needs about 1400F to bond properly. When using a kiln, they recommend opening all the air ports and vent holes, it really wants a lot of oxygen to burn off the binders and flux.

Like I said, wish me luck!

Edited by Old1953, 10 March 2005 - 04:15 PM.

[Pretty green flames]

Like I said, wish me luck!

Good luck!

[Old1953]

Good luck!

Thanks!

[alany]

I was thinking of trying something similar to bond Manganese Dioxide or Magnetite to Titanium. I don't have a kiln unfortunately, but I am working on building one slowly, it would be a very useful tool at times.

The one concern I have is the Titanium/Oxide layer, I am unsure if the sintered material burns through the oxide layer and bonds to the metal itself, I'd imagine a suitable flux would help? I don't want to get into exotic pickling if I can avoid it. That is probably why Lead Dioxide is never plated on Titanium, it is probably too difficult as the Lead Dioxide plating is an anodizing process which would passivate the titanium pretty quickly at low voltages and just erode it at higher ones.

I can get 5 mm Ti rod glowing orange in my gas torch flame (that's how I softened it a bit so I could cut it at the cost of only one HSS hacksaw blade for my latest cell - Pt/Ir||NaCl||Ti), so maybe with a bit of research into fluxes it might be something I can achieve with what I've got.

Edited by alany, 10 March 2005 - 05:09 PM.

[Old1953]

I was thinking of trying something similar to bond Manganese Dioxide or Magnetite to Titanium.  I don't have a kiln unfortunately, but I am working on building one slowly, it would be a very useful tool at times.

The one concern I have is the Titanium/Oxide layer, I am unsure if the sintered material burns through the oxide layer and bonds to the metal itself, I'd imagine a suitable flux would help?  I don't want to get into exotic pickling if I can avoid it.  That is probably why Lead Dioxide is never plated on Titanium, it is probably too difficult as the Lead Dioxide plating is an anodizing process which would passivate the titanium pretty quickly at low voltages and just erode it at higher ones.

I can get 5 mm Ti rod glowing orange in my gas torch flame (that's how I softened it a bit so I could cut it at the cost of only one HSS hacksaw blade for my latest cell - Pt/Ir||NaCl||Ti), so maybe with a bit of research into fluxes it might be something I can achieve with what I've got.

There is supposed to be a method for growing manganese dioxide crystals (pryolusite) on an anode by electrolyzing a solution of manganese sulfate and sulfuric acid. It works better if the solution is heated.

Unfortunatly, that's all I know about it. I may experiment with it sometime though, and see if I can manage to grow an anode for chlorate solutions.

I suppose if you could get a big enough piece of natural pyrolusite it would do as an anode. And I've suspected some of the more perfect chunks that have turned up on ebay were grown somehow - they just don't look natural to me.

Magnetite will melt, and cast, however it is a bit fragile. It won't make perchlorate though. Manganese dioxide will (I think). But MnO2 heated past about 500C will change to MnO.

I've wondered about binding MnO2 powder together somehow. There are a few references to "silica supported Manganese Dioxide" this and that, but I'm not sure exactly how they mean it. Do they mean MnO2 bonded to glass, which sounds feasible, or something else? I'm sure not going to pay their fees to read the papers on the web, I'll make a trip to the local college and read the references in the science library for a lot less than these guys want.

[Old1953]

So far so good, there is a coating of metal over the tantalum. Rather dull though, I expect I didn't heat it quite long enough. Not that the appearance matters at all, for this application.

It is a silver gray metallic coating, not at all like the tantalum where it has heated without the paint over it. It almost looks like aluminum. I suppose a jeweler would give it a bit of a polish about now.

Where the tantalum has heated enough to get a slight coating of oxide, it appears bluish purple. The oxide layer is quite thin. The bluish color is nowhere present on the part coated with the platinum paint.

I tried to scrape it off with my fingernail, it appears to be on there to stay.

I'll set up a test cell in a day or so, see what kind of results I get.

[Old1953]

I was thinking of trying something similar to bond Manganese Dioxide or Magnetite to Titanium.  I don't have a kiln unfortunately, but I am working on building one slowly, it would be a very useful tool at times.

The one concern I have is the Titanium/Oxide layer, I am unsure if the sintered material burns through the oxide layer and bonds to the metal itself, I'd imagine a suitable flux would help?  I don't want to get into exotic pickling if I can avoid it.  That is probably why Lead Dioxide is never plated on Titanium, it is probably too difficult as the Lead Dioxide plating is an anodizing process which would passivate the titanium pretty quickly at low voltages and just erode it at higher ones.

I can get 5 mm Ti rod glowing orange in my gas torch flame (that's how I softened it a bit so I could cut it at the cost of only one HSS hacksaw blade for my latest cell - Pt/Ir||NaCl||Ti), so maybe with a bit of research into fluxes it might be something I can achieve with what I've got.

Ok, I found what you are looking for in a US patent search. Gotta say, I think it would be easier to sinter the platinum and then coat with MnO2, unless you just happened to have the chemical to plate tin over it on hand.

http://164.195.100.1...RS=PN/4,265,728

(Patents are public domain)

EXAMPLE 1

A solution for the semiconductive intermediate coating was prepared by mixing 30 ml of butyl alcohol, 6 ml of concentrated sulphuric acid (H.sub.2 SO.sub.4), 1.1 grams of antimony trichloride (SbCl.sub.3), and 9.7 grams of stannic chloride pentahydrate (SnCl.sub.4 .multidot.5H.sub.2 O). A strip of titanium (Ti) mesh with an approximately 0.033 cm layer of porous titanium on both sides was coated by brush with the Sn and Sb sulphate solution, dried at 120.degree. C. for 30 minutes and then baked at 600.degree. C. for 30 minutes. This procedure was repeated three times to yield a surface layer of SnO.sub.2 and Sb.sub.2 O.sub.3 (85.6%:14.4% by weight). Twelve coats of a 50% aqueous solution of Mn(NO.sub.3).sub.2 were applied by brush to the titanium followed by heating at 235.degree. C. for 30 minutes after each coating application. A total weight gain of MnO.sub.2 of 386 g/m.sup.2 was obtained. The anode potential in 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. was 1.48 V vs. SCE at 0.15 A/cm.sup.2 and 1.57 V at 0.45 A/cm.sup.2. The anode lifetime (measured as the time for the total cell voltage to reach 8 volts) in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. operating at a current density of 0.45 A/cm.sup.2 was 224 hours.

EXAMPLE 2

A strip of titanium mesh with an approximately 0.033 cm layer of porous titanium on both sides was coated with SnO.sub.2 and Sb.sub.2 O.sub.3 as described in Example 1. Twelve coats of a 50% aqueous solution of Mn(NO.sub.3).sub.2 were then applied by brush to the titanium sheet followed by heating at 315.degree. C. for 30 minutes after each coating application. A total weight gain of MnO.sub.2 of 463 g/m.sup.2 was obtained. The anode lifetime in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. operating at a current density of 0.45 A/cm.sup.2 was 540 hours.

EXAMPLE 3

A strip of titanium mesh with an approximately 0.033 cm layer of porous titanium on both sides was coated with SnO.sub.2 and Sb.sub.2 O.sub.3 as described in Example 1. Twelve coats of a 50% aqueous solution of Mn(NO.sub.3).sub.2 were then applied by brush to the titanium sheet followed by heating at 400.degree. C. for 30 minutes after each coating application. A total weight gain of MnO.sub.2 of 643 g/m.sup.2 was obtained. The anode is still running after 900 hours in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. operating at a current density of 0.45 A/cm.sup.2. Table 1 below more clearly shows the effect of bake temperature on the anode performance.

EXAMPLE 4

A strip of titanium mesh was coated with the Sn and Sb sulphate solution described in Example 1, dried at 120.degree. C. for 15 minutes and then baked at 600.degree. C. for 15 minutes. This procedure was repeated three times to yield a surface layer of SnO.sub.2 and Sb.sub.2 O.sub.3 (85.6%:14.4% by weight). Twelve coats of a 50% aqueous solution of Mn(NO.sub.3).sub.2 were applied by brush to the titanium followed by heating at 235.degree. C. for 15 minutes after each coating application. A total weight gain of MnO.sub.2 of 171 g/m.sup.2 was obtained. The anode lifetime in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. operating at a current density of 0.45 a/cm.sup.2 was 28 hours.

EXAMPLE 5

A strip of titanium mesh was coated with the Sn and Sb sulphate solution as described in Example 4. Sixteen coats of a 50% aqueous solution of Mn(NO.sub.3).sub.2 were applied by brush to the titanium followed by heating at 400.degree. C. for 15 minutes after each coating application. A total weight gain of 909 grams MnO.sub.2 /m.sup.2 was obtained. The anode lifetime in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. operating at a current density of 0.45 A/cm.sup.2 was 1512 hours.

EXAMPLE 6

A strip of titanium mesh was coated with the Sn and Sb sulfate as described in Example 4. Fifteen coats of a 50% aqueous solution of Mn(NO.sub.3).sub.2 were applied by brush to the titanium followed by heating at 400.degree. C. for 15 minutes aftereach coating application. A total weight gain of 742 g MnO.sub.2 /m.sup.2 was obtained. The anode has maintained a stable half cell potential for 4000 hours in a solution of 150 gpl H.sub.2 SO.sub.4, 50.degree. C. at a current density of 0.075 A/cm.sup.2.

EXAMPLES 7-24

Several strips of titanium mesh were coated with the Sn and Sb sulphate solution as described in Example 4. These were then coated with a 50% aqueous solution of Mn(NO.sub.3) by brush application and baked at various temperatures according to Table 1 below to attain MnO.sub.2 catalyst loadings as shown. The results of life testing are shown in Table 1 below.


TABLE 1
______________________________________
Comparison of MnO.sub.2 Anode Lifetime
as a Function of the Bake Temperature
Bake
Temperature of
Catalyst Lifetime, 0.45 A/cm.sup.2
Example
the MnO.sub.2
Loading 150 gpl H.sub.2 SO.sub.4, 50.degree. C.
No. Topcoat (.degree.C.)
(g Mn/m.sup.2)
(hours)
______________________________________
7 235 276 182
8 245 304 272
9 255 260 264
10 265 285 357
11 275 277 327
12 285 296 405
13 295 296 488
14 305 355 625
15 315 292 540
16 340 305 514
17 360 306 619
18 380 256 852
19 400 405 1355
20 420 354 1231
21 440 256 442
22 460 417 244
23 480 362 217
24 500 313 0
______________________________________



EXAMPLE 25

A 20 mil thick Ti sheet (5 cm.times.12 cm) was etched in a mixture of distilled H.sub.2 O and HCl (50:50) and then coated with a semiconductive intermediate coating of Sb doped SnO.sub.2. This was accomplished by painting a solution consisting of 30 ml n-butyl alcohol, 6 ml of concentrated sulfuric acid (H.sub.2 SO.sub.4), 1.1 g of antimony trichloride (SbCl.sub.3) and 9.7 g of stannic chloride pentahydrate (SnCl.sub.4 .multidot.5H.sub.2 O) onto the Ti sheet, drying the sheet at 120.degree. C. for 15 minutes and then baking it at 600.degree. C. for 15 minutes. This procedure was repeated three times. The Ti sheet was centered between two Ti rod cathodes (3/8" diameter) in a plating bath consisting of 300 ml of 50% aqueous Mn(NO.sub.3).sub.2 and 10 g of a surfactant available commercially from Rohn & Haas Co. under the trademark TRITON X100. The electrolyte was heated to 95.degree. C. and electrolyte agitation was maintained by means of a magnetic stirring motor. A total current of 0.45 amps (3.75 mA/cm.sup.2) was applied to the cell for 18 hours after which time the anode was removed from the cell, rinsed in distilled water and dried at 100.degree. C. The anode was then baked for 1 hour at 400.degree. C. to convert the electrolytic MnO.sub.2 to the MnO.sub.2 structure. A very adherent, metallic, gray deposit with a total weight gain of 1.8 g of MnO.sub.2 (150 g/m.sup.2 MnO.sub.2) was obtained by this method. The anode potential in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. was 1.49 volts vs. SCE at 0.15 A/cm.sup.2 and 1.54 volts vs. SCE at 0.45 A/cm.sup.2.

EXAMPLE 26

An 80 mil thick Ti mesh was sandblasted and etched in a mixture of distilled H.sub.2 O and HCl (50:50) and then coated with an intermediate layer of Sb doped SnO.sub.2 according to the procedure in Example 1. The Ti mesh was then centered between two Ti rod cathodes (3/8" diameter) in a plating bath consisting of 800 ml of 2 M Mn (NO.sub.3).sub.2 and 0.5 g of a surfactant available from Rohn & Haas Co. and the trademark TRITON X100. The electrolyte was heated to 95.degree. C. and stirred by means of a magnetic stirring motor. A total current of 0.085 amps (3.4 mA/cm.sup.2) was applied to the cell for 17 hours after which time the anode was removed from the cell, rinsed in distilled water and dried at 100.degree. C. A very adherent, metallic, gray deposit (341 g/m.sup.2 MnO.sub.2) was obtained by this method. After baking the anode for 1 hour at 400.degree. C., the electrode was polarized anodically at a current density of 0.75 A/cm.sup.2 in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. The anode lifetime (measured as the time for the total cell voltage to reach 8.0 volts) was 312+ hours. It can be seen from the weight gain that Ti mesh yields superior lifetimes.

EXAMPLES 27-37

Pieces of 060 Ti mesh were etched in a mixture of distilled H.sub.2 O and HCl (50:50) and then coated with an intermediate layer of Sb doped SnO.sub.2 according to the procedure in Example 1. The Ti mesh was then centered between two It rod cathodes (3/8" diameter) in a plating bath consisting of MnSO.sub.4 for Examples 27 through 29 and Mn(NO.sub.3).sub.2 for Examples 30 through 37. The anodes were plated with MnO.sub.2 according to the data of Table 2 below. Following the electroplating the anode was baked. This procedure yielded a surface coverage as stipulated MnO.sub.2. The electrode was polarized anodically at a current density of 0.75 A/cm.sup.2 in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. to derive the lifetime data shown in Table 2 below.

[alany]

You are right, it sounds like a lot of work. Although the Antimony and Tin chlorides would be easy enough to prepare from the metals. Manganese Sulfate is pretty cheap commercially.

I can't see how silica will bind manganese dioxide, silica's melting point is *way* too high. Maybe you could bind it with waterglass and fuse it at a relatively low temperature.

Magnetite sounds like it lasts longer, although I am not quite sure how I could fasion it into a usable shape, it isn't very conductive, so a hollow rod that I could fill with a fairly conductive metal would be best. To do that you'd need graphite molds and a very hot furnace.

[Old1953]

You are right, it sounds like a lot of work.  Although the Antimony and Tin chlorides would be easy enough to prepare from the metals.  Manganese Sulfate is pretty cheap commercially.

I can't see how silica will bind manganese dioxide, silica's melting point is *way* too high.  Maybe you could bind it with waterglass and fuse it at a relatively low temperature.

Magnetite sounds like it lasts longer, although I am not quite sure how I could fasion it into a usable shape, it isn't very conductive, so a hollow rod that I could fill with a fairly conductive metal would be best.  To do that you'd need graphite molds and a very hot furnace.

I was thinking perhaps they meant bonding to a sheet or rod of regular soda glass, the low melting point type of glass. Or maybe they do mean water glass. It's hard to tell from the abstracts, which are all you get without subscribing.

A sad day, when the tech journals decide they must profit instead of spreading knowledge.

[alany]

A sad day, when the tech journals decide they must profit instead of spreading knowledge.

I agree.

I understand that IP is important, but the prices they ask are just plain profiteering. I guess the market is pretty small, but it is a bad trend. The internet and its wonderful level playing field for information was not built on that kind of crap.

[Old1953]

You are right, it sounds like a lot of work.  Although the Antimony and Tin chlorides would be easy enough to prepare from the metals.  Manganese Sulfate is pretty cheap commercially.

I can't see how silica will bind manganese dioxide, silica's melting point is *way* too high.  Maybe you could bind it with waterglass and fuse it at a relatively low temperature.

Magnetite sounds like it lasts longer, although I am not quite sure how I could fasion it into a usable shape, it isn't very conductive, so a hollow rod that I could fill with a fairly conductive metal would be best.  To do that you'd need graphite molds and a very hot furnace.

Looks to me like #5 or #6 would be the way to go. If you have an oven that does that self cleaning cycle, they get really hot during that cycle, so it might be hot enough to bake on the coatings. Don't know how repeated baking would be on the elements though!

You CAN get metal really hot in a microwave, and this would work for small items, but temp control is a problem. Experiments have shown that you can melt up to a half kilogram of silver in a big old microwave, if you surround the crucible with a few of those light ceramic kiln bricks to keep the heat in. But how to control the level of the heat, that's the question.

[Old1953]

It just came to me that the major reason for the conductive oxide plating might be avoided if graphite was used for the substrate!

If graphite was electroplated in this fashion, it would stop the shredding and damage done by the anodic attack from the chlorine. The chlorine would be sealed away from the graphite by the MnO2 coating.

Given the amperage in this procedure:

The Ti mesh was then centered between two It rod cathodes (3/8" diameter) in a plating bath consisting of MnSO.sub.4 for Examples 27 through 29 and Mn(NO.sub.3).sub.2 for Examples 30 through 37. The anodes were plated with MnO.sub.2 according to the data of Table 2 below. Following the electroplating the anode was baked. This procedure yielded a surface coverage as stipulated MnO.sub.2. The electrode was polarized anodically at a current density of 0.75 A/cm.sup.2 in a solution of 150 gpl H.sub.2 SO.sub.4 at 50.degree. C. to derive the lifetime data shown in Table 2 below. (drat, wrong example, I meant the current in #25)

I'd think the manganese dioxide would cover the graphite rapidly enough to prevent damage sufficient to shred away the manganese coating.

IOW, if the pyrolusite crystals grow rapidly enough to cover the graphite and protect it, we could manufacture anodes for almost nothing! Plate them for a couple of days, then flip and plate some more, then on to the baking. I don't think graphite ignites at 400C, even if it does there is a potters trick that will protect it from being oxidized.

This is most certainly worth a try, we'll never know if we don't try.

Manganese sulfate is cheap and easy to get, graphite is pretty easy too. I've got to know if this will work.

Edited by Old1953, 15 March 2005 - 02:46 AM.

[sasman]

Alany i only just noticed that you made an addition to your webpage ..The last time i looked you were using the Graphite electrodes..i did not think of looking to see if you had added further info on your Pt electrode...

Very nice.page on Platinium electrode.. i like the fact that you bothered to work out your cell efficiency ..I am not surprised at how low it was.. if you read other webpages you would expect near 50%..But thats what i like to read.. real life experiments ...You did a good job with your cell.. many will be running more inefficient cell's thinking there getting good efficiency..when in real life conditions you get much less...You are the first person i have found who has given me some "real life info"...on chlorate production

I asked a question a few months back about making Perc and BigG relplied...

.
second ? out of the two ?commonly used option?, platinum is the safest and produces the best quality perchlorate. However, the only inexpensive sort (usually very thin wire), will produce perchlorate at an extremely slow rate. Think about 15%-20% efficiency.

Now when i first read that, the only iformation i had was from webpages stating much higher efficiency...and so i assumed that BigG was way off with 15% to 20%
..But now that i just read your Detailed experiment i can see BigG is right!!..Its one thing reading about it but often when in practice things dont always go according to plan....

Hope you update your page when you manage to make some Perc... ..

[alany]

The low efficiency isn't too suprising I guess, using KCl is less efficient than NaCl.

I am running a NaCl cell now with Ti and Pt/Ir electrodes. I think it is pretty much done, at least chlorate wise, the chloride is very low with a quick Silver Nitrate test. I am waiting for some Methylene Blue and Indigo Carmine to arrive so I can see how much perchlorate I've got and process the electrolyte.