WFC Tubes conditioning

[Farrah Day]

My test cell is now starting to get the white compound build up on the cathodes.

Originally I had assumed that the protective oxide layer on the ss was the source of the dielectric, but it would appear that it is the cathode that is creating the dielectric, not the anode.  We know from Ravi's tests that the white coating is an insulator, but as it's on the cathode which is oxygen defficient during electrolysis, it surely can't be an oxide.

Clearly the protective oxide layer on the ss cathode is removed, allowing corrosion of the metal beneath, but what is it that we then produce. What reaction is taking place?

It must be a reduction reaction, but what exactly is reacting? Any chemist out there know, or want to hazard an educated guess as to what this white coating is?

Initially I'd compared our wfc to a 'wet electrolytic capacitor', but know I see that this is not a correct analogy, in that it is the anode that has the dielectric oxide layer in a 'wet electrolytic capacitor', not the cathode.  That said, current is not designed to flow through a wet electrolytic capacitor as in our wfcs, and apart from inherent leakage current, only does so in the case of dielectric breakdown.

Time to regroup and rethink things then.

[Farrah Day]

Here's something interesting that I found.

I believe this emphasises the conditioning process our wfc's need to go through before they become efficient capacitors. It also confirms Ravi's description of the time-consuming process

Electrolytic:  Electrolytic caps are named for the chemicals that cause the dielectric to exist. Electrolytic caps have plates wound from a long, thin strip of aluminum foil. The dielectric is a thin (several atoms thick) coating of aluminum oxide (an excellent insulator). The aluminum oxide is formed by a chemical reaction between the electrolyte and the aluminum, in the presence of an electric field. This formed dielectric gives the capacitors some unique advantages and disadvantages. Electrolytic caps have very large capacitances per unit space, since the dielectric is so thin. The dielectric can tailored to allow voltages up to about 450 VDC, the upper limit for electrolytic caps. The disadvantages of the electrolytic come from the electrolyte, and how the dielectric is formed. The electrolyte will dry up in time, causing the capacitors to gradually decrease in capacitance. Pushing the capacitor beyond its ratings (either voltage, polarity, or ripple current) will increase the pressure in the cap until it either vents (and loses electrolyte) or explodes. The other problem is that if the electrolytic cap is not used for a long time, the dielectric becomes thinner, decreasing the voltage it can withstand. The dielectric needs an electric field (charge) in order to maintain its strength.

Electrolytics that have been unused (either in storage or in unused equipment) can have their dielectric layers restored by slowly applying increasing levels of DC voltage. The procedure can take days. Electrolytics suffer from accelerated aging at elevated temperatures. A rule of thumb is that their life is cut in half for each 10 degree Celsius rise above ambient (25C). For all these reasons, electrolytics have a limited life and the user may expect to replace them at some time in the future. Excess hum on a power supply, unstable rolling picture on a monitor are often signs of an electrolytic nearing the end of its useful life. Electrolytic capacitors have a substantial amount of leakage and Dielectric Absorption. This can be a problem in timing circuits, and often limits their use. Some designs (like the 555 timer) minimize these faults by operating the capacitor at voltages where this is less of a problem. The temperature stability of electrolytics is poor and seldom specified

[dutchy1966]

Hi Farrah Day,

First of all I's like to say I'm following your tests with great interest. I like the way you aproach things, scientific but with an open mind. I think I'm gonna pick up again where i left off a while ago (lack of time). I've got most of it ready to follow you in your tests. I've got my tubes ready (20mm/25mm 1mm spacing). I have 6 tubes of 20 cm, SS 316L. The pulser as per D14 is build but still needs testing.
What I'd like to know from you is how you have assembled the tubes in the acrylic tube. I have had them in there already but there is hardly any space left to prevent shorting when I was using jubilee clips (hose clamps). What is your view on this? I have 110 mm acrylic tube. I'd like to have a setup which is easy to disassemble, so I can change the tubes or inspect them.
Therefore I'm debating to use another type of container for the tubes. Maybe some sort of square container with more space.
How are you going about this?

Regards Robert

[AhuraMazda]

One idea leads to another and...
First I thought of anodizing aluminium and then I ended up with this:

http://www.midwesternanodizing.com/stainlesspassivate.html

[Farrah Day]

With Dogs' current and promising work on the electronics side of the wfc subject, and in light of the fact that it again appears that conditioning maybe crucial to success I thought I'd bring this thread back up.

I'm going to try to speed up the conditioning of my electrodes by getting hold of some calcium carbonate to add to my tap water.