New Crucible

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Gwar

Well-known member
Joined
Feb 1, 2022
Messages
259
Location
Grand Rapids, MI
I am getting ready to fire up my new furnace this week, going to take 59 ozt (.925) and make shot and then through the cell, the wooden pipe holder is just for height, I plan on using some of my broken fire brick for a proper holder, the hole on top is being fitted to hold a standard 2-3 kilo graphite crucible and I am re-using the lid from my former electric model as well..
 

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Watch out for a burn through of your crucible. Be prepared to catch the molten metal in something or pry it out of your furnace if you plan to use it in the gas powered one. The flame will eat through the graphite fast.
These crucibles are for electric furnaces or induction furnaces if i'm not mistaken.
 
Thanks for the heads up Martijn, I am actually going to perform a few small test runs and a project I have wanted to do for some time, I am going to fill a small mold with silver crystals, about 4 ozt. with a graphite lid on top, and see if this results in a better-looking bar, I am optimistic as to the results. I also have one of these on order as well, again, Thanks
 

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Thanks for the heads up Martijn, I am actually going to perform a few small test runs and a project I have wanted to do for some time, I am going to fill a small mold with silver crystals, about 4 ozt. with a graphite lid on top, and see if this results in a better-looking bar, I am optimistic as to the results. I also have one of these on order as well, again, Thanks
If your purpose is to get a homogenous shiny bar, the most important is the heat profile you are following. Allthough this procedure is mostly working with gold, i am not 100% sure the same result will be achievable with silver.
The best result you can get is in a closed electric furnace with heat controller. Could work with gas furnace if you can control the flame (hmm could be a future project for me to try)
The heat profile is as follows:
Linear heating (start with low flame and increase the flame gradually, ex: if you can control it with a valve then small turns every 10-15 seconds) until you reach 1000-1050 C, you have to stay at this temperature a few minutes, then this is the tricky part since the cooling is the most critical.
Now for cooling you will do exactly the opposite but with even longer periods and smaller steps, ex: from 1050C you need to lower to 1047C stay 30 to 60 sec then lower the temp to 1044-1045C and so on...all until you go below 200C
Very time consuming if you`ll do it in gas furnace, with electric you can set the steps from the controller.
The crucible you use has to have a good closing lid which prevents air to enter and spoil your finish. All the time the furnace has to be air free.(as free as it can be)
I have experimented with this up until i broke my furnace (an old calcinating furnace) and still didn`t repair it..(well my kids use up all my time, so probably will
repair it in the distant future)

Good luck, it all goes by experimenting, but fast cooling always spoils the finish on the silver, no matter what process is used.
 
I had to use the neighbors furnace, turns out the #2 crucible was too large for my new heat source, the person who originally made the bar didn't follow any known way to make it except he claims he used nitric / water and the cemented out the silver, dried, melted and poured, this is what I have after re-melting his bar into shot, it looks like a hodge podge of base metals with lots of gold coloration, silver and some purple-ish material, I'm going to use some HNO3 and distilled water with heat to eat away the base metals, and then re-cement, what are your thoughts on the coloration and could there be traces of other PM's ?
 

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As for running it thru the cell, the time savings is much better going the Ag---> AgCl--> Ag via the lye sugar method. Quicker, easier, and less up front investment for the same end result...99.9%+ purity Ag.

Steve
 
Thanks for the response lazersteve, I've always wanted to try that method, I just haven't invested a lot of time in that direction, also, it seems there are tooo many ways to do it, which one is right ?
 
If time is a factor, as it is for me, then converting 8 pounds (typical maximum sized batch in 5 gallon bucket) of AgCl to Ag in 15 minutes verse days in the electrolytic cell to get 99.9%+ purity Ag after melting, then the choice is obvious. I've setup up several silver cells, even did a DVD on one...hands down the lye sugar method is far superior and 10x plus faster for similar purity.

Steve
 
Just as a side note, gold with alu give beautiful purple alloy :), brittle tho. That looks rather like copper tho.
 
Started the batch last week, rinsing today, I'm not sure about using my silver cell, I don't think the return is worth the effort at this point, may just pour into a bar and wait for a bigger batch, then add the bar to the crucible for more shot to feed the cell.
 

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Many thanks Steve, I will try with a small sample batch !
Be aware of the exothermic nature of this reaction. It isn´t that hard to produce a runaway reaction spattering 120 °C NaOH silver sludge all over the place.

Thing with regular sugar is, the reaction speed up with temperature, and it is relatively slow below 85-90 °C. Base acts as reagent which break the glycosidic bond in sucrose to give fructose and glucose. In this basic enviroment, even sucrose acts as reducing sugar - because it is decomposed to reducing sugar by these harsh conditions. Even more, whole sugar molecule is then completely oxidized, not only the aldehyde part. Even CO2 is produced as oxidation product. That is why it take so little sugar to convert everything to silver.

I studied this reaction quite a bit and found out it can be done safely and in controlled fashion. Sreetips has for example few videos regarding lye and sugar, but he does it with "dump, stir and run" method, which is in my opinion very dangerous.

Better is to heat up the Ag2O to 90 °C and start adding sugar, spoon by spoon, stirring and watching temperature of the slurry. After addition of sugar, you will see temperature rise. When temperature stabilize/start to decline, add another spoon. You can go to roughly 110 °C, then it is hazardous as you can create some "popping" when reaching higher temperatures. Reaction is completely self-sufficient and in larger quantities, you will need to wait some time for it to cool to the good temp range for another addition. When the temperature does not rise after two following additions, you are done and all Ag2O reacted. Just be sure you are above 90 °C when observing, as being lower can prolong reaction times and skew your judging.
You can easily do up to 500-700g in 5L beaker, if you can stir it well. Just bring it to the 90 °C and start adding tablespoon or two at the time, watching the temperature. It usually take minute or two for temperature to somewhat peak, so be patient.
I do not say that it won´t work at lower temperatures, but in my eyes it is dangerous to be regularly used and implemented to the refining scheme of the shop.
 
I have a clever setup in the works for my small graphite crucible. I can set it inside a piece of the wide cast iron pipe I have. This will block airflow onto the crucible, keeping it fairly anoxic. Therefore, I can increase its lifespan, plus the iron will keep the heat more regular as it heats up and releases that heat around the crucible in a very stable manner.

I'm always thinking of how to adapt my wood and coal-burning 'chimney' furnace for more applications. Wood and coal are FREE for me, and I have enormous amounts of both available. Coal is plentiful from old rail lines which criss-cross all over the place near me, and have lumps of coal lying by the TON per mile of old track. It's PA anthracite from the early 1900's, washed in the rain for nearly 100 years. It burns completely smokeless and VERY hot.
 
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