[SteveE]

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.

[Corribus]

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

[Arkcon]

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.

[Corribus]

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.

[billnotgatez]

I seem to remember there being patents for PMC

[SteveE]

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.

[billnotgatez]

If you look at our forum rules you will note

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.

[Enthalpy]

[...] 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?

[SteveE]

https://en.m.wikipedia.org/wiki/Metal_clay

[billnotgatez]

@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

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.

[SteveE]

If you look at our forum rules you will note

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.

[SteveE]

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.

[billnotgatez]

@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.

[billnotgatez]

@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.
 

[Intanjir]

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.