Another CS setup

[Silvio]

Hi all. I thought I would post my new CS setup, which is based on what I have learned here at cgcsforum.
The generator is a modified version of the one Heino_R posted. I added a full wave rectifier and an
additional power supply for a digital amp. meter.

I picked one of the recipes constructed by Kephra, which uses salt and maltodextrin, and I doubled all the
ingredients and times from the original 250ml process for a larger batch. I am hoping it is scalable like that.

The specifics of the recipe are:

500ml water (Boiling)
10mg salt
18min electrolysis @ 8,3mA
Cut power, removed electrodes 
Added 240mg maltodextrin
Boiled an additional 15min

Regards
Silvio

[Kephra]

Silvio,

That's perfect!  Yes, it is scalable to a degree.  If you were to try to make 5 gallons at a time though, you would be faced with a pretty long process time unless you also scaled up the current and the surface area of the electrodes.  But for home use, your system is great.

[Silvio]

Thank you for the reply.

This was my very first batch, so I'm not really sure what to expect. One minor question that still remains
for me is what (if any) amount of residual conductivity is acceptable before one starts to look for contamination.
Currently the batch measures ~40'S/cm using the old Hanna PWT.

Sorry if this has already been covered elsewhere on the forum.

Regards


Edited to fix display problem

[Kephra]

There will always be high conductivity because of the sodium ions that are present.  Therefore, the conductivity meter does not provide meaningful information.

There are two kinds of contaminants, harmful and benign.

Starting with food grade ingredients, you can be pretty sure that they contain no harmful contaminants.  There are things that we do not necessarily want, but we can't really get rid of anyway.  For instance, in the US, there is a tiny amount of iodine added to the salt.  This is a contaminant, but is not harmful either to the process or to us.  Salt also contains anti-caking agents which again are not harmful.

The important thing is to start with the purest water possible because that will be the biggest source of unknown contaminants. 

[Silvio]

It never occurred to me that sodium ions could be responsible, for some reason I assumed that those would be stabilized
by the maltodextrin as well, if I'm using the term correctly.

The additives you mentioned are very common in salt products in Sweden as well, but I generally try to avoid that stuff
for other reasons. Instead I found a purified salt (99,99% sodium chloride) in my local health food store, which is apparently
used to produce saline solutions for nasal irrigation and so on.

Thanks again.

[Kephra]

It never occurred to me that sodium ions could be responsible, for some reason I assumed that those would be stabilized
by the maltodextrin as well, if I'm using the term correctly.

The only way to remove ions without also removing the silver particles is by reacting them with something which would produce an insoluble compound.  I can't think of any sodium compounds that are not soluble.  It is harmless though. 

Stabilizers for CS and CG fall into two main groups called electrostatic and steric.  Electrostatic stabilizers like sodium citrate keep the particles from aggregating by adsorbing onto the surface of the nanoparticle and repelling other nanoparticles because of the negative electrostatic charge created by the double layer.

Steric stabilizers like soluble starch, PVP, and maltodextrin keep the particles far enough apart just by their large size.

See http://wikis.lib.ncsu.edu/index.php/Nanoparticles for more information about how stabilizers work.

[silverFalcon]

That's what you call it a perfect setup...viruses and bacterias must be very scared now 

[Silvio]

Hi. I just got my shipment of sodium citrate, so I thought I'd post some results.

The recipe was:

500ml water (Boiling)
Added 80mg sodium citrate
18min electrolysis @ 8,3mA
Cut power, removed anode
Boiled an additional ~10min   
 
The batch went straight from a �straw� color (never bypassing clear yellow) to the �tea� color which can
be seen in the image. Even If diluted, the sample always has a slight red hue like amber. I heard somewhere
that silver NP's will only grow into spheres when using sodium citrate (as opposed to rods or cube shapes).
Would that account for the color variation? Not sure what to make of it, but It sure would be nice to be able
to measure particle size.

Cheers

[Kephra]

I think you used four times as much citrate as I did.  I used 40mg to make 250ml of 80 ppm CS.  Scaling for volume would make it 20 mg citrate for 500ml 20ppm.  I do not know if that would make any real difference, except that the excess sodium leads to less stable CS. 

When I tested citrate, my reasoning for the amount was: One sodium citrate molecule contains 3 sodium atoms, and can reduce 3 silver atoms.  Sodium citrate weighs almost 3 times as much as silver, so a one to one ratio of liberated silver to citrate would be a good minimum starting point, which would be 5 mg  citrate per 250ml of 20ppm CS.  But, sodium citrate also contains some water^*, so I arbitrarily doubled the weight of citrate.  For your water volume, current and time, I would have used 20 mg based on that reasoning.  It may not be optimum, and without knowing Formula Weight of the citrate, I cannot calculate it exactly.     

Also, if you are using a copper cathode, it is best to remove it also from the solution before turning off the power.  As soon as the power is turned off, the copper can become reactive.  Its more important to remove the cathode than the anode.  Butthis is probably not significant.

One other thing that might also happen is that silver oxide left over on the electrodes from previous runs may chemically react with the citrate, increasing the ppm.  I have not tried this, but it may happen.  Silver citrate is a lot more soluble than silver oxide.

I heard somewhere that silver NP's will only grow into spheres when using sodium citrate (as opposed to rods or cube shapes).

I have not heard that, but it may be true.  I do know that using citrate with gold first produces gold rods which evolve into spheres over time.  The rod shapes give the gold a dark blue to black color which changes to red as the rods become spheres.  The shape of the particles does influence the color.



--------------------
*Trisodium Citrate has two different crystal structures with water.  The formula weight depends on whether the crystals contain none, 2 or 5 water molecules.  So the FW could range from 258 gms/Mole to 346 depending on the crystal form.

[Silvio]

Very useful information Kephra, thank you.

I made another batch using 20mg sodium citrate and a shorter boiling time. I'm appending an image, but unfortunately the colors
aren't very accurate when compared to the real thing, which reminds me more of olive oil (green tint). I also took a picture of a
smaller (undiluted) sample from the same batch and it looks yellow to me.     

I'm glad I wasn't using a copper cathode. I got a "cheap" stirrer/heater from Ebay that requires an temp. probe to work,
and since it's hopefully steel I had it double as the cathode. It seems to work, but I don't really like it, so I'll use a proper
stainless steel probe from now on. 

Regards

Edit:
After reading this http://www.cgcsforum.com/index.php/topic,148.msg1331.html#msg1331
I have decided to scrap the batch, mostly because of the green tint, but also because the 500ml
quantity of liquid seems rather opaque when lit from the front.

[Silvio]

After reading some posts regarding home build magnetic stirrers, I thought I would share my own experiences from building one. 
The stirrer motor is a standard PC fan (3") with 4 Neodymium magnets mounted on the fan hub. I have seen people using the magnets
from scrapped hard drives, but I felt those might be a bit to powerful for this application. For heating, I used a
travel immersion heater in a double boiler-type arrangement. However, one probably shouldn't use electrical tape as a surface on
the stirrer as I did.





The fan motor control circuit is very simple and uses a adjustable voltage/current regulator (L200C). I omitted the current limiter
resistor (Rsc) because my 12VDC wall adaptor takes care of that, but I thought I'd add it in the schematic. The diode is my idea
and can probably also be omitted. I added it just for style points, as the DC motor is an inductive load.   
Finally, I used a 50Kohm potentiometer, but that more or less only affects sensitivity when adjusting the fan speed.   
   




The last picture illustrates the magnets and where one can place them.

Cheers

[Kephra]

Very nice!  This will probably help some of the forum members build their own. 

I presume the first magnet is glued to the fan motor, but are the top magnets glued on, or just held together by their own magnetic attraction? 

[Silvio]

Thank you.

The top magnets are not glued in place, but after checking them just now, I noticed that
they haven't shifted position even slightly. Neodymium magnets are impressive.

Best regards and a happy new year to all.