# A different use for silver chloride



## 4metals (Dec 12, 2017)

I was at a client who had a request from a customer to provide sample of powdered silver chloride. The end user was using it as a component in a glaze he makes up for coloring glass. The glaze is painted on to the glass and fired. 

My first thought was easy, dissolve some fine silver in nitric and water, drop out the silver as a chloride with hydrochloric, filter, rinse and dry at 225ºF. Well, after drying we tried to break up the clumps to make powder in a mortar and pestle. The chlorides didn't just crumble, they clumped together into flat flakes and assumed the shape of the pestle. I assumed it still was a little moist and went to plan B. 

I put the silver chloride in a scorifier and put it in a furnace at 900ºF to melt the chlorides. They melted into a nice liquid looking like maple syrup but thinner. I poured that into a shallow stainless tray where it immediately hardened and peeled off quite easily. Now I figured it would crush up nicely. Well not so fast, the solidified silver chloride bent into the shape of the mortar and did not break up. It behaved like a plastic and had no intention of cracking into smaller pieces. 

I never worked with silver chlorides in this way, usually my molten chlorides were large chunks and were reduced in a large tumbler back to metal but now I needed it as a chloride powder. 

The customer told us his client used the silver chloride as a component in a glaze and sent me a picture of the silver chloride he was using. It was slightly gray in color and powdery with a few small clumps maybe 5 mm in size. I knew there was a bucket of rinsed silver chlorides from aqua regia digestions being saved to collect until it was worth processing so I took out a few ounces, rinsed it well, and dried it at 225ºF for an hour and it crushed up into powder easily. 

I assume the silver chloride I made from silver nitrate was too pure and exhibited the plasticity I described but the silver chloride from a refining operation, which had gold and base metals in the original alloy, apparently was "contaminated" enough that it did not exhibit the physical properties that prevented the crushing into powder of the finer silver. Weird. I do want to run an AA on a sample of the powder made this way just to check the purity but as these glazes do utilize other base metals, anything over 98% should be fine. (As long as that 2% isn't gold!) 

Has anyone else seen this behavior with silver chloride?


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## Iggy-poo (Dec 12, 2017)

Yes, I have melted Silver Chloride and it does form a plastic like material. It has an interesting property:
I melted mine in a beaker, which left a disk of AgCl. If you hold the disk in the center, you can strike the edge and it will ring like a tuning fork. What's interesting is that the sound isn't dampened by holding it, like you would get if you did that with a disk of metal.
Some have used AgCl for high temperature gaskets in limited applications.


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## Topher_osAUrus (Dec 12, 2017)

Very interesting 4metals. 
I knew some people used AgCl in cement mix for concrete to help with the antibacterial properties and prevent some growth of algae, or whatever.

I can't add anything of substance that you don't already know, but your anecdote just reminds me of in Collins' book on silver (silver is part 2,metallurgy of lead is part 1) where he talks about the different "types" of silver chloride, one of which being the "light and flaky" type, which is a bit soluble in regular ol' water (coincidentally, this type of AgCl is what is produced after diluting your AR and having the AgCl drop out)

So, it makes me wonder if there were ways to manipulate this reaction.

I remember GSP mentioning his study of the solubility of AgCl in AR and other chloride media. ..but, cannot recall what thread it is on? Hopefully he sees this.

I'm sure your client is wanting a very high weight, so dissolving it slowly in AR and then removing it by cooling and/or diluting is impracticable at best.

Wish I had some good ideas for you, but will watch this thread with great interest.


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## Platdigger (Dec 12, 2017)

What if you use sodium chloride instead of hcl?
In other words if you can get crystals they should be easy to crush.


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## mls26cwru (Dec 12, 2017)

two thoughts come to mind... maybe a three roll mill (sometimes called a dispersion mill) or an ultrasonic?


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## 4metals (Dec 12, 2017)

> What if you use sodium chloride instead of hcl?



OK, well we used Hydrochloric because we had it and we didn't have sodium chloride on hand and I didn't feel like going into the lunchroom and opening a bunch of salt packages, not that I even considered it. 

The bond on a silver chloride molecule is a polar covalent bond. Hydrochloric acid presents a lower ionic character than sodium chloride. Like 3 times less. (Don't think for a minute that I whipped that little factoid off the top of my balding head!) It would be an interesting exercise to see if the physical characteristics of the resultant silver chloride are different depending on the source of the chloride ion. If the samples provided worked and they get an order, I am sure I will be working that out.


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## g_axelsson (Dec 13, 2017)

Just an idea... if the end product is for glaze, maybe mixing the silver chloride with some of the other ingredients of the glaze would make it easier to grind into a fine powder.

Göran


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## 4metals (Dec 14, 2017)

> Just an idea... if the end product is for glaze, maybe mixing the silver chloride with some of the other ingredients of the glaze would make it easier to grind into a fine powder.



I had the same idea but after talking to the customer, I decided straight silver chloride powder should be offered first as per the request, and if discussions ensue mixing in with a pre determined (by experimenting) quantity of borax to allow milling to a fine powder will indeed be explored.


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## fishaholic5 (Jul 30, 2018)

How did this turn out?
The best method I've found is to dry on a low heat while stirring then use a stainless blender type grain or powder mill to reduce it to a fine powder

Cheers Wal


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