# Can I cement < 20 micron silver particles from silver nitrate using Copper? Do dispersants help?



## baldwin_kevin (Jan 2, 2023)

Hi, Silver Forum.

*PROBLEM TO SOLVE
My cemented silver is all agglomerated, lumpy, and shows crystal faces. I need the finest, most dispersed silver sludge/powder possible.

BACKDROP*
I am a graphic artist who wants to branch out into silver-clay jewelry production. In art, I experiment a LOT before landing good designs, so I want to make lots of my own artisanal silver clay to experiment with. And it doesn't have to be _perfect _silver clay.

In the past, I have cemented 20 or 30 ounces of silver powder to create silver clay. Yes, I know all the standard warnings: The clay-making process is super-difficult, what with proper starch binders, organic conditioners, sintering temperature ranges, auto-fluxing, etc. I am currently climbing all these very real obstacles.

But as everyone here knows, the one saving grace is that you get to recycle metal from failed experiments into your current experiments.

*QUESTIONS
How can I cement a very small silver particle size (around 20 microns?) from aqueous silver nitrate using elemental copper? Would it help to add dispersants to the aqueous silver nitrate?*
. . . *Small silver particle size*: I need fine particles for great clay body plasticity, good shape definition/retention, and easy sintering.
. . . *Aqueous silver nitrate*: This is my current method of getting elemental silver into solution.
. . . *Silver cementation using copper*: I know that the resulting solid precipitate will not be 999 silver but rather silver-mixed-with-copper. For artisanal use, I am okay with this impurity.
. . . . . . BTW, to cement silver I have also used *ascorbic acid* (C6H8O6), but there's a HUGE drawback (which nobody discusses): In cementation, the silver particles bind with a coating of dehydroascorbic acid (C6H6O6), which later on makes sintering the silver clay object nearly impossible. The decomposition temperature of the C6H6O6 is almost the same as silver's fusing temp :-(
. . . *Adding dispersants*: Maybe the actual particle size is already good enough and perhaps it's just the agglomeration (lack of dispersal) that's the problem, I don't know.
. . . . . . Anyway, I have read a lot about adding *methyl cellulose* or *PVA *(= Elmer's glue) to the silver nitrate before cementing. Has anyone tried this?
. . . . . . I actually had some good results early on, adding methyl cellulose as dispersant to silver nitrate in an ultrasonic bath like this guy does. But my more recent problems with C6H6O6 coating makes me hesitate now. (Does the methyl cellulose intercede before the C6H6O6 can attach? I don't know.)
. . . *Am I over-thinking this?!!* Can I super-dilute the silver nitrate to achieve small particle size? Change the temperature? Can I stir vigorously (adding lots of shear force) during cementation? What have I overlooked here? I am looking for something simple that I have missed here.

*CURRENTLY OUT OF SCOPE*
. . . *Perfection*. (Small improvements are welcome.)
. . .* Mechanical sifting*. (I just want to cement and go.)
. . . *No industrial atomizing equipment*. (Who has the money for that?!)

Thanks in advance, --K


----------



## Yggdrasil (Jan 2, 2023)

baldwin_kevin said:


> Hi, Silver Forum.
> 
> *PROBLEM TO SOLVE
> My cemented silver is all agglomerated, lumpy, and shows crystal faces. I need the finest, most dispersed silver sludge/powder possible.
> ...


I think most fine metal powders are produced with Atomization by High pressure water directly from molten state.
Search the forum for Atomizing.


----------



## FrugalRefiner (Jan 2, 2023)

The first thought that comes to mind is to cement from a dilute solution. In general, when we cement or precipitate our precious metals, we want large particles that will agglomerate together and form large clusters that are easy to wash and melt. When we drop from dilute solutions, the particles are often smaller, so they don't agglomerate and settle as well. It's just my first thought.

This has been discussed before, but I don't remember what solutions people came up with. I don't think it was cementation, but precipitating by other means. You can try a search for PMC (precious metal clay) as a starting point.

Dave


----------



## baldwin_kevin (Jan 2, 2023)

FrugalRefiner said:


> The first thought that comes to mind is to cement from a dilute solution. In general, when we cement or precipitate our precious metals, we want large particles that will agglomerate together and form large clusters that are easy to wash and melt. When we drop from dilute solutions, the particles are often smaller, so they don't agglomerate and settle as well. It's just my first thought.
> 
> This has been discussed before, but I don't remember what solutions people came up with. I don't think it was cementation, but precipitating by other means. You can try a search for PMC (precious metal clay) as a starting point.
> 
> Dave


Thanks, Dave. I will test a small amount of highly-diluted silver nitrate and watch for good effects. Then (as you say) the problem becomes how to effectively filter/dry the precipitate.


----------



## Lino1406 (Jan 3, 2023)

baldwin_kevin said:


> Hi, Silver Forum.
> 
> *PROBLEM TO SOLVE
> My cemented silver is all agglomerated, lumpy, and shows crystal faces. I need the finest, most dispersed silver sludge/powder possible.
> ...


From nanoparticles production, I take very high speed stirring, thousands of rpm


----------



## kurtak (Jan 3, 2023)

Use ascorbic acid to precipitate the silver from your silver nitrate









Mesh size of gold drop?


I would only add that when precipitating you really want the objective element as finely divided as possible in order to facilitate the removal of anything else, which would be considered a contaminant.




goldrefiningforum.com





In this link - read my post - (the fifth post up from the bottom) it has several links in that post about making PMC - Edit; - I see when you click on the link it goes right to my post with the other links - other links are at bottom of my post

Some of them show precipitating silver from silver nitrate with ascorbic acid to get 20 micron & finer silver particles to make PMC with

Kurt


----------



## Lou (Jan 3, 2023)

baldwin_kevin said:


> Thanks, Dave. I will test a small amount of highly-diluted silver nitrate and watch for good effects. Then (as you say) the problem becomes how to effectively filter/dry the precipitate.


can be reduced from dilute solutions of sodium formate with a variety of growth inhibitors to prevent agglomeration. Wash and decant with DI water via centrifuging and then lyophilize to dry.


----------



## orvi (Jan 3, 2023)

baldwin_kevin said:


> Hi, Silver Forum.
> 
> *PROBLEM TO SOLVE
> My cemented silver is all agglomerated, lumpy, and shows crystal faces. I need the finest, most dispersed silver sludge/powder possible.
> ...


As Lou very objectively suggests, preventing agglomeration is very important. Sometimes, polymeric additives as gelatine or other could act as disruptors of clumping the particles.
In other hand, processing of AgCl by lye/sugar also tend to process relatively fine precipitates. Borohydride reductions also.

Also, if you happen to have pure silver nitrate, cementing on more reactive metal like aluminium or iron zinc could result in much much quicker reaction, producing very fine sludge of silver.


----------



## baldwin_kevin (Jan 3, 2023)

Lino1406 said:


> From nanoparticles production, I take very high speed stirring, thousands of rpm


Thanks for the answer. I will soon purchase an *overhead stirrer* (up to 3000 rpm), which should provide shear force in a *dilute silver nitrate* solution. I hope that this addition will create the next step function down in particle size.

I see in your list of publications this item: "'*Ascorbic acid in precipitation of precious metals' 8 pages*." If I may:

Having used ascorbic myself many times, I have been struggling with what I assume is *a C6H6O6 (dehydroascorbic acid) coating* on the silver. In other words, when the silver cements out, it doesn't come out pure -- there are organic molecules bonded to it. If this assumption is true, *can I achieve pure silver by adding ascorbic acid to silver nitrate?* (The organic coating makes sintering a very high temperature affair indeed.) If this is not true, what am I actually dealing with here?


----------



## baldwin_kevin (Jan 3, 2023)

kurtak said:


> Use ascorbic acid to precipitate the silver from your silver nitrate
> 
> 
> 
> ...


Hi, Kurt. Thanks for your reply suggesting ascorbic acid. See my OP where I describe organic-coating issues with ascorbic and also see my reply on this page to Lino1406, who has published on this process. I might just be "doing it wrong," as they say, but I have measured 5% by weight organic coating of some kind in my silver cement using ascorbic :-(

Thanks, too, for all your links: Yes, I find going over all the old "literature" helps, mostly because I almost always miss something. Cementing fine particle sizes is way more nuanced than I ever thought it would be.


----------



## baldwin_kevin (Jan 3, 2023)

Lou said:


> can be reduced from dilute solutions of sodium formate with a variety of growth inhibitors to prevent agglomeration. Wash and decant with DI water via centrifuging and then lyophilize to dry.


Hi, Lou. Thanks for your suggestions on process improvements "growth inhibitors," "centrifuging," and "lyophilizing" (which I assume to be freeze-drying?). I will try DIY solutions for the latter two, which fit right into my less-is-more approach here. Experimenting with growth inhibitors is further on down the road for me, I think, because I have difficulty enough understanding the organics in my process (using ascorbic acid) already. --K


----------



## kurtak (Jan 3, 2023)

orvi said:


> Also, if you happen to have pure silver nitrate, cementing on more reactive metal like aluminium or iron could result in much much quicker reaction, producing very fine sludge of silver.


Aluminum does not react with nitric so is not going to work for cementing silver from silver nitrate

Cementing with iron is likely going to contaminate the silver with iron oxyhydroxide so would need to be cleaned up - not a good choice for making you PMC 

For making PMC you want a particle precipitation size of 20 micron & less & want the precipitation to be a "clean" drop

Watch this video - this is what baldwin_keven is looking for --------------



Kurt


----------



## Lino1406 (Jan 3, 2023)

baldwin_kevin said:


> Thanks for the answer. I will soon purchase an *overhead stirrer* (up to 3000 rpm), which should provide shear force in a *dilute silver nitrate* solution. I hope that this addition will create the next step function down in particle size.
> 
> I see in your list of publications this item: "'*Ascorbic acid in precipitation of precious metals' 8 pages*." If I may:
> 
> Having used ascorbic myself many times, I have been struggling with what I assume is *a C6H6O6 (dehydroascorbic acid) coating* on the silver. In other words, when the silver cements out, it doesn't come out pure -- there are organic molecules bonded to it. If this assumption is true, *can I achieve pure silver by adding ascorbic acid to silver nitrate?* (The organic coating makes sintering a very high temperature affair indeed.) If this is not true, what am I actually dealing with here?


Many articles deal with producing nanometals with ascorbic acid. I suggest Google for it. However for producing nano you use capping materials of organic origin. My booklet deals with thermodynamics, not nano, not silver.


----------



## RogueGeochemist (Jan 3, 2023)

baldwin_kevin said:


> Hi, Silver Forum.
> 
> *PROBLEM TO SOLVE
> My cemented silver is all agglomerated, lumpy, and shows crystal faces. I need the finest, most dispersed silver sludge/powder possible.
> ...


Nanoparticles can be stabilized to form a stable colloidal system using silica. Although 20 microns is big for a colloidal particle, you might try adding some sodium silicate (sparingly) before you reduce the silver nitrate. I’m guessing too fine a particle would not be an issue.


----------



## baldwin_kevin (Jan 3, 2023)

Lino1406 said:


> Many articles deal with producing nanometals with ascorbic acid. I suggest Google for it. However for producing nano you use capping materials of organic origin. My booklet deals with thermodynamics, not nano, not silver.


Hi, Lino1406. Yes, it's the "capping materials" function of the ascorbic-acid process that has forced me to try the silver-cementation-by-copper method. Using ascorbic, I ended up with 5% organic admixture by weight in my silver cement. At least with copper as reducer, the silver cement is 100% inorganic. (The cement is not necessarily 100% *pure* silver, because <5% copper contamination occurs. But this 95/5 ratio still qualifies as "sterling" by legal definition. --K

P.S. Yes, I have googled extensively on the use of ascorbic acid as reducer for silver nitrate to produce silver. Can't remember where, but I found a description of the post-reduction, organic C6H6O6 bond to the elemental silver, which maps to my observed results when trying to sinter the silver clay body: Boy, that organic bond is a strong one! I nearly have to fuse the elemental silver before the organic coating decomposes! (If indeed, that's what's going on here.)


----------



## baldwin_kevin (Jan 3, 2023)

RogueGeochemist said:


> Nanoparticles can be stabilized to form a stable colloidal system using silica. Although 20 microns is big for a colloidal particle, you might try adding some sodium silicate (sparingly) before you reduce the silver nitrate. I’m guessing too fine a particle would not be an issue.


Hi, RogueGeochemist. Now, this is a new twist for me: *sodium silicate*. I'll have to give that a try. (I just happen to have some on hand, too, for a lab-created petrified wood project, per patent US4612050A.) Thanks for the suggestion. --K


----------



## orvi (Jan 3, 2023)

kurtak said:


> Aluminum does not react with nitric so is not going to work for cementing silver from silver nitrate
> 
> Cementing with iron is likely going to contaminate the silver with iron oxyhydroxide so would need to be cleaned up - not a good choice for making you PMC
> 
> ...



Yep, you are right  I chosen two bad examples without much thinking about it. But zinc will work for sure  

This aside, strong mixing would be probably easiest to try and it could indeed deliver good results.


----------



## baldwin_kevin (Jan 3, 2023)

orvi said:


> As Lou very objectively suggests, preventing agglomeration is very important. Sometimes, polymeric additives as gelatine or other could act as disruptors of clumping the particles.
> In other hand, processing of AgCl by lye/sugar also tend to process relatively fine precipitates. Borohydride reductions also.
> 
> Also, if you happen to have pure silver nitrate, cementing on more reactive metal like aluminium or iron could result in much much quicker reaction, producing very fine sludge of silver.


Hi, Orvi. Thanks for your response. Yes, even when I have succeeded in creating fine-sand or fine-silt silver cement, I do notice physical clumping occurring almost immediately (perhaps even more so at the higher rinse-water temperatures). Early on, I had success using methyl cellulose as polymeric additive, and I'll definitely try MC again (and begin experimenting with PVA) after I better understand the physical temperature, dilution, and stirring controls. (Ultrasonic cavitation during cementation should help, too.) --K


----------



## Platz (Jan 3, 2023)

I once made a silver powder so fine it was a nightmare to handle and was incredibily abrasive. The combination of Tergitol TMN 6 surfactant and oleic acid both capping agents added before reduction works well. Be warned the silver was <3um by laser diffraction and when dry would go everywhere.


----------



## baldwin_kevin (Jan 3, 2023)

Platz said:


> I once made a silver powder so fine it was a nightmare to handle and was incredibily abrasive. The combination of Tergitol TMN 6 surfactant and oleic acid both capping agents added before reduction works well. Be warned the silver was <3um by laser diffraction and when dry would go everywhere.


Hi, Platz. Thanks for the *Tergitol TMN 6* and *oleic acid* suggestions. After I understand the physical constraints better (temp, shear, dilution), I'll go back to additives like these.

*What proportions did you use?* My own use of surfactants has been in the eyeballed range of "a drop or two." *Can you help me dial that in a little?* What worked for you? 

Oleic acid as a capping agent makes sense. I wonder how it would burn off in sintering? In my own experience, burning off methyl cellulose occurs at a delightfully low temp, whereas the C6H6O6 (dehydroascorbic) cap requires a too-high temperature, preventing an easy sinter.

Last thing: You mention, "...when dry would go everywhere." Yes! When I have purchased silver powders in the past, I noticed this quality AND their extreme hydrophobic behaviors: I cannot wet them in pure form for the life of me! (I have always resorted to methyl cellulose and surfactants to help.) --K


----------



## Platz (Tuesday at 3:12 PM)

I cant remeber exact volumes but it was minimal few mL per litre of each. There are a few papers on using this and other tergitol combinations. The order of addition makes no difference. However for best results it must be added before the reductant. I think both either end up washed out in the mother liquor and washings or burn off at low temperatures if adhered to the silver giving minimal carbon conatmination after firing.


----------



## Platz (Tuesday at 3:13 PM)

You could wash the silver powder with ethanol to remove residual organic also


----------



## baldwin_kevin (Tuesday at 3:32 PM)

Platz said:


> You could wash the silver powder with ethanol to remove residual organic also


This makes total sense, Platz. I will try the tergitol organic route after I experiment further with my purely inorganic physical constraints (stirring shear force, temperature, and dilution). FYI, I am planning to try one additional physical constraint, which I should have thought of, earlier: Using finely-divided copper as reductant instead of solid copper plate/bar. We'll see. My "known unknown" in this scenario is the possible hydrophobic nature of bare metals like copper when they are finely divided. Wetting agents might come into play at that point, so I might as well try tergitol organics with the copper reductant if I run into hydrophobic copper at the powder level.


----------



## orvi (Tuesday at 3:39 PM)

baldwin_kevin said:


> This makes total sense, Platz. I will try the tergitol organic route after I experiment further with my purely inorganic physical constraints (stirring shear force, temperature, and dilution). FYI, I am planning to try one additional physical constraint, which I should have thought of, earlier: Using finely-divided copper as reductant instead of solid copper plate/bar. We'll see. My "known unknown" in this scenario is the possible hydrophobic nature of bare metals like copper when they are finely divided. Wetting agents might come into play at that point, so I might as well try tergitol organics with the copper reductant if I run into hydrophobic copper at the powder level.


Stirring will be the case - and also dilution. With high dilution and rapid stirring, particle size would be certainly smaller than from concentrated solutions staying still. 
Cementing with powdered copper could definitely work - even without wetting agents. Be careful and be sure you use excess of silver in solution, to consume the copper as fully as possible


----------



## baldwin_kevin (Tuesday at 5:24 PM)

orvi said:


> Stirring will be the case - and also dilution. With high dilution and rapid stirring, particle size would be certainly smaller than from concentrated solutions staying still.
> Cementing with powdered copper could definitely work - even without wetting agents. Be careful and be sure you use excess of silver in solution, to consume the copper as fully as possible


Hi, Orvi. Yes, thanks. I have already gotten some excellent results from high dilution with rapid stirring (in a low-ph solution, to boot). The mostly-fine particle sizes were only ruined by crusts of solid silver metal that preferentially formed in the lee of the copper bar where the fluid shear was not strong. Regarding your suggestion to "use excess of silver in solution," I have already wondered how visual inspection might be able to tell how much copper powder was still in suspension. There should be a slight color shift as copper powder gives way to silver powder.


----------



## FrugalRefiner (Tuesday at 5:59 PM)

I don't know if you would be able to detect copper in suspension by color, but you could test the precipitated silver. Take a small sample of the silver cement and add a small amount of nitric acid. Any copper in the cement should give a blue tint to the acid.

If you're in doubt as to whether you're really seeing a blue tint, take a couple drops of the acid solution and add a few drops of ammonia. If there is copper, the blue color will intensify. Be sure to promptly reacidify the test sample to avoid creating any explosive compounds.

Dave


----------



## RogueGeochemist (Tuesday at 11:17 PM)

baldwin_kevin said:


> Hi, RogueGeochemist. Now, this is a new twist for me: *sodium silicate*. I'll have to give that a try. (I just happen to have some on hand, too, for a lab-created petrified wood project, per patent US4612050A.) Thanks for the suggestion. --K


Google Peter Scales. He has at least one patent in this area.


----------



## baldwin_kevin (Tuesday at 11:46 PM)

FrugalRefiner said:


> I don't know if you would be able to detect copper in suspension by color, but you could test the precipitated silver. Take a small sample of the silver cement and add a small amount of nitric acid. Any copper in the cement should give a blue tint to the acid.
> 
> If you're in doubt as to whether you're really seeing a blue tint, take a couple drops of the acid solution and add a few drops of ammonia. If there is copper, the blue color will intensify. Be sure to promptly reacidify the test sample to avoid creating any explosive compounds.
> 
> Dave


Thanks for the pro tip, Dave, with the nitric acid and ammonia tests. Also, not blowing up (accidental silver fulminate, I imagine.) --K


----------



## kurtak (Wednesday at 8:59 AM)

baldwin_kevin said:


> Thanks for the pro tip, Dave, with the nitric acid and ammonia tests. *Also, not blowing up (accidental silver fulminate, I imagine.)* --K


Just to clarify - silver fulminate can be unintentionally made by adding alcohol to a silver nitrate solution due to a CNO ion (fulminate ion) being attached to an Ag ion --- Silver fulminate = AgCNO 

There are a number of other silver explosive compounds that exist &/or can be created

Examples - silver nitride - silver azide - silver acetylide --- these silver explosive compounds are sometime referred to as "fulminating" silver - which is not the same thing as silver fulminate 

Silver nitride is created when silver is complexed with ammonia ------

Silver nitride - Wikipedia 

Kurt


----------



## baldwin_kevin (Thursday at 2:39 PM)

kurtak said:


> Just to clarify - silver fulminate can be unintentionally made by adding alcohol to a silver nitrate solution due to a CNO ion (fulminate ion) being attached to an Ag ion --- Silver fulminate = AgCNO . There are a number of other silver explosive compounds that exist &/or can be created. Examples - silver nitride - silver azide - silver acetylide --- these silver explosive compounds are sometime referred to as "fulminating" silver - which is not the same thing as silver fulminate. Silver nitride is created when silver is complexed with ammonia.


Thank you, kurtak, for these important safety distinctions. I did not know. --K


----------

