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Specialty Chemistry Forums => Citizen Chemist => Topic started by: SteveE on March 15, 2017, 05:35:55 PM

Title: Silver Powder for Making PMC Metal Clay
Post by: SteveE on March 15, 2017, 05:35:55 PM
Hello,

I don't know if any of you have heard of PMC Metal Clay. It's silver powder combined with a binder of some type. It's used in making jewelry. You shape in into any form, fire it in a kiln. The binder burns off and the silver powder fuses together to make a solid piece of jewelry.

My question is.... How do you make silver powder? Surely you wouldn't grind metallic silver into a powder. My guess is they dissolve silver metallic silver into a solution of nitric acid, then precipitate it out with something. What would you use to precipitate it out?

It maybe someone has another way of making silver powder. I'm not trying to make it. I just want to know how it's done.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Corribus on March 15, 2017, 07:07:11 PM
Ultrafine metal colloids are made by reduction of a cationic metal source (Ag+ in this case). This is how nanoparticle dispersions are made as well. These particles would usually be stabilized by some sort of surface ligand.

A quick literature source shows that fine (dry) silver powder can also be made by a mechanochemical process in which metallic silver and sodium chloride are ball milled, which causes a solid state reaction that forms silver powder and sodium chloride. This is still fundamentally a chemical process, though - Ag+ is reduced to Ag0.

http://onlinelibrary.wiley.com/doi/10.1002/aoc.159/abstract

I'm not sure how chemical suppliers make silver powder in large scales. I would guess it involves some kind of chemical reduction. I do not believe metallic silver can be mechanically ground at low temperature, since apparently FCC metals like silver do not have a brittle-to-ductile transition.

http://physics.stackexchange.com/questions/74983/why-dont-fcc-metals-have-a-brittle-to-ductile-temperature-transition
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Arkcon on March 15, 2017, 08:00:42 PM
Surely you wouldn't grind metallic silver into a powder.

Like Corribus: explained, they do.  They just use a ball mill and a removable grinding powder.  A bar of metal could also be ground on an abrasive wheel, or filed and then pulverized.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Corribus on March 15, 2017, 10:30:54 PM
There was an error in my previous post. In the paper I mentioned, it wasn't metallic silver and sodium chloride that are ball milled, but silver chloride and sodium.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: billnotgatez on March 16, 2017, 03:33:01 AM
I seem to remember there being patents for PMC
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: SteveE on March 16, 2017, 06:10:40 AM
I'm sure there's a patent for PMC silver clay. I wasn't going to try and make it. I'm simply curious as to how it's done.

So then you ball mill silver chloride and metallic sodium?

However they do it, it's pretty expensive. Retail is 3 or 4 times spot.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: billnotgatez on March 17, 2017, 12:09:25 AM
If you look at our forum rules you will note
Quote
Chemical Forums is a place where you can ask your chemistry questions and discuss them with others. Our main goal is to help you learn chemistry, regardless of whether you are at school or whether you are treating chemistry as a hobby.

My suggestion was to try searching for the patents and reading them to get an idea how the process might be understood. Maybe you can return with your results and we can discuss further.

I apologize for not being clear.

Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on March 18, 2017, 07:46:16 AM
[...] PMC Metal Clay is silver powder combined with a binder of some type. [...] You shape in into any form, fire it in a kiln. The binder burns off and the silver powder fuses together to make a solid piece of jewelry.
Could you elaborate on this, or give a link maybe? I didn't find explanations.

If the silver part keeps the given shape, the metal doesn't melt. So does the binder completely disappear and the silver sinter, even without pressure? Or does the binder transform into some solid that holds the powder together?
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: SteveE on March 18, 2017, 10:03:03 AM
https://en.m.wikipedia.org/wiki/Metal_clay
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: billnotgatez on March 18, 2017, 10:19:57 AM
@SteveE beat me to it but here is some of my thoughts.
Here is the WIKI for Metal clay
https://en.wikipedia.org/wiki/Metal_clay (https://en.wikipedia.org/wiki/Metal_clay)
Quote
The binder burns away, leaving the pure sintered metal.

I do mostly ceramics but have taken a few classes using the silver version of the Metal clay.
In any case, the stuff handles much like clay.

At one time I looked up one of the patents and it went into extensive explanation of the stuff.
I do not remember if the patent information discussed what or how the metal part was made into the fine particles. That is why I suggested that @SteveE look up the patents and report back.
@SteveE might even post some links to some of the patents.
(This would keep us within the spirit of our forum rules.)

As an aside
It appears to me that the Base version of Metal clay could be used for many citizen science projects.
Even the PMC version could be used as well, if you can stand the cost.
A reminder that the metal is sintered and not as strong as regular cast metal.

Title: Re: Silver Powder for Making PMC Metal Clay
Post by: SteveE on March 18, 2017, 10:36:10 AM
If you look at our forum rules you will note
Quote
Chemical Forums is a place where you can ask your chemistry questions and discuss them with others. Our main goal is to help you learn chemistry, regardless of whether you are at school or whether you are treating chemistry as a hobby.

My suggestion was to try searching for the patents and reading them to get an idea how the process might be understood. Maybe you can return with your results and we can discuss further.

I apologize for not being clear.

I tried looking for it but ran into a number of issues. First being... I don't have a clue as to how to do it. Have never looked up one before.  Spent some time online but got very aggravated.

Will keep trying but it may take some time.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: SteveE on March 18, 2017, 10:54:02 AM

It appears to me that the Base version of Metal clay could be used for many citizen science projects.
Even the PMC version could be used as well, if you can stand the cost.
A reminder that the metal is sintered and not as strong as regular cast metal.
[/quote]

It also comes in a brass and copper version. Both are much, much cheaper then the silver version.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: billnotgatez on March 18, 2017, 11:00:56 AM
@SteveE
In this case the WIKI has a reference section at the bottom that has links to the background information that helped make the WIKI article.
One of them is a link to one of the patents.
I see where they discuss the binder making, but yet to find how they procure the metal particles.
But, I only did a quick reading.

In some cases we suggest using GOOGLE search.

Maybe someone else will chime in on other tools to find patents.
But, you have the WIKI references to look through for now.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: billnotgatez on March 18, 2017, 11:09:02 AM
@SteveE
copper and bronze are considered to be BASE metals for this application.
Silver, Gold, and Platinum are considered to be PRECIOUS metals for this application.
 
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Intanjir on March 18, 2017, 11:25:49 AM
Very finely powdered metal is going to be more prone to oxidation, a problem compounded by firing at high temperatures. So it makes sense that nobler precious metals were done first. However, firing in a reducing environment has enabled even iron alloys to be used for metal clays.

Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on March 19, 2017, 02:50:37 PM
Against oxidation, a soldering flux like rosin is very effective. Upon heating, it de-oxidises copper alloys, permitting the solder metal to wet them. Maybe the producer uses a similar compound (but without leftovers) for metal clay? This would permit long storage, needing a reductive atmosphere only in the kiln.

Sintering: it can achieve the full strength of an alloy, but only if using extreme pressure, hence my interrogation. Some alloys are produced that way, especially refractory ones which would be impractical to melt: molybdenum, tantalum, tungsten...

Produce a powder: wearing now my mechanical engineer hat, I'd say "grind it". Though, many metals catch fire then: titanium, iron. Neither did I try with gold, which may well clog the grinding wheel and produce zero powder.

I wouldn't be surprised if only a mix of powders with different grain sizes sinters well without pressure, because such a mix leaves less void between the grains - just like concrete uses sand, gravel and crushed stones.

Thanks for the links and explanation! I didn't know such materials. Maybe I find uses in industrial applications.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on March 19, 2017, 07:22:05 PM
One standard way to pulverize metals is to melt them and let an injector make the spray in a cooler gas that solidifies the droplets. Mind the nozzle material to resists liquid metal.

The gas shouldn't oxidise the metal. Nitrogen is doubtful, dry argon and hydrogen are candidates. Some hydrogen adsorbs on metals; to degas, put the powder in a gentle oven, like 10mn at 300°C.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on March 19, 2017, 07:45:13 PM
The mix of powders with different grain sizes would also shrink less when sintered. 30% presently is a drawback for jewellery parts.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on March 20, 2017, 10:38:34 AM
Mixing powders of different grain sizes would help sintering and reduce shrinkage when sintering under high pressure too, not only for metal clay - and for ceramics and polymers in addition to metals. I have an intuition that it's already done.
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on July 09, 2017, 01:42:03 PM
Said metal clay could be interesting for 3D printing too. Or was that the original intention?

Used much like a polymer, but as a clay instead of molten: the fine printing head deposits it where metal is wanted. The printed part must be sintered afterwards, which puts constraints on the materials and the objects' shape. But a seducing alternative to present methods, which involve local laser sintering of the metal powder as each complete layer is deposited.

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on February 04, 2023, 11:47:28 AM
Wondering how a metal powder ("metal clay") can constitute one solid part upon heating but keep its shape... The temperature range must be narrow, more so without applying the strong pressure typical of true sintering.

This should be much easier if the powder comprises initially separated components that combine in a eutectic. Heating between the melting points of the eutectic and the components produces a brazed joint of eutectic between the components. This process usual in microelectronics should work well with powders.

The "metal clay" could comprise powders of different components, or grains of one components covered with the other by displacement in an electrolyte, vapour deposition or any method.

This applies to jewelry and to more technical products and includes 3D printing. Mixing different grain sizes applies too.

Or is it already usual?

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on February 04, 2023, 06:32:02 PM
Some parts of cast titanium alloy get pressed in hot silicone to compact and harden them. The process is known as HIP for Hot Isostatic Pressure.

I've already suggested to apply the process to polymer parts made by 3D printing
  chemicalforums (http://www.chemicalforums.com/index.php?topic=90705.msg324993#msg324993)

Hot Isostatic Pressure could also densify and harden parts obtained from metal powder, be it from metal clay or by 3D printing, or other processes that make porous parts. Silver and its alloys, first discussed here, melt well below titanium, so it's a candidate, as well as copper and its alloys, gold and its alloys, pure or alloyed Zn, In, Sn, Sb, Te, Pb, Bi and more.

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on February 05, 2023, 06:34:50 PM
Electrically conductive glue uses to contain a fine powder of silver or other metal. It too would improve if mixing different grain sizes to make more contact points. A matrix that shrinks much upon curing should stabilize the contacts too, but I suppose this is banal.

==========

Thermal paste often contains a fine powder of thermally conductive ceramic in a liquid matrix, and here too, mixing different grain sizes should improve the conductivity while keeping an acceptable viscosity.

==========

In all uses, a continuous distribution of grain sizes doesn't suffice. It takes well separated sizes to fill the matrix better, as is done for concrete.

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on February 21, 2023, 05:12:15 PM
Most conductive paints include powder of graphite or metal in a binder. They serve to electrodeposit metal on or in an insulating mold, and other purposes.

Some polymer parts also include powders, to shield against electrostatic discharges or electromagnetic interferences, improve tribological properties, adjust the expansion ratio, reduce the cost, and more.

A powder mix of very different grain sizes lets increase the volume fraction of powder, to give a higher and more reliable conductivity, reduce further the thermal expansion or the cost, and so on.

Fullerenes can provide the finest grain.

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on March 12, 2023, 08:46:33 AM
More filler and less matrix, as enabled by a mix of very different grain sizes, can have more uses.

A cermet, which embeds a ceramic powder in a metal matrix, would have properties closer to the ceramic: thermal expansion, stiffness, hardness and more.

A lubricating grease could embed more graphite, MoS2... or be more fluid.

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on March 15, 2023, 07:41:09 PM
Molds can be made of wax, paraffin and other easily molten materials. Gypsum and other fillers improve the stiffness, strength, thermal expansion.

With mixes of very different grain sizes, more powder can fill the matrix for better behaviour.

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on April 09, 2023, 05:45:05 PM
Solid propellants for launchers comprise aluminium powder, ammonium perchlorate powder, and a prepolymer that makes a castable paste, cures, and adds combustion gases. Casting without cracks imposes far less perchlorate than the combustion optimum.

Maybe the perchlorate could consist of several very different grain sizes, so it fills more volume and the paste can still be cast. Or maybe not, because the combustion speed depends on grain size, I suppose at aluminium more.

Vega and Ariane 6 achieve a higher perchlorate proportion than Ariane 5 does. Maybe they apply this idea already? Aluminium grain size very different from perchlorate, or perchlorate of several grain sizes?

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on April 24, 2023, 06:52:22 PM
I mentioned here on 21 Feb 2023 that fillers can reduce the thermal expansion of polymer parts. Epoxy is filled with fine silica powder to encapsulate semiconductor chips. This reduces the shrinkage at polymerization as well as the thermal expansion to protect the chip and its fragile connection against big epoxy movements.

Several very different grain sizes would further improve the dimension stability, or make the encapsulating paste more fluid, possibly improve the shock resistance, or all.

Marc Schaefer, aka Enthalpy
Title: Re: Silver Powder for Making PMC Metal Clay
Post by: Enthalpy on April 26, 2023, 11:46:05 AM
Silica brings an extremely low expansion coefficient, but if different grain sizes increase enough the powder's volume fraction, chip encapsulation can use other powders with different benefits, alone or mixed with silica.

For instance alumina conducts heat better than silica.

I already suggested a high optical index:
  scienceforums (http://www.scienceforums.net/topic/69058-antireflective-package-for-optoelectronics/)

==========

Was it done before? Around 2001, I suggested to mix a high-index nanopowder in a polymer to produce lenses.

Different grain sizes would make lenses thinner (increased powder fraction) or less brittle (fewer contacts between the grains) or easier to inject. Vision glasses and others improve.

The biggest grain size must stay <<λ/4.

Marc Schaefer, aka Enthalpy