Chip value estimation

[pinwheel]

To be clear, there are 700 pounds and every chip is identical.

 

[samuel-a]

Chris.

It amaze me time and again, how you (and the other "veterans") seems to have the bigger picture in mind and are willing to share your point of view with such detail. For that i pesonally would like to thank you.

The easiest and, probably, most accurate way on identical parts (at least, in appearance), such as these, is to fire assay the whole parts separately. To sample them, since they all appear to be identical, I would probably just grab a part here and a part there - I can't see how splitting down the lot by coning and quartering or using a sample splitter would give much improvement. In this case, you can probably run 2 parts per fire assay but, if the total copper and nickel is more than about 2 grams, you may only be able to run 1 part per assay. Since organics are involved, the parts must be incinerated before fluxing. This is easily done by weighing the 2 parts and placing them in an empty assay crucible. Then put them in a hot (say, 1850F) assay furnace, with the door opened just a crack to let in a little oxygen, and burn them until they fall apart into white ash. This might take 45-60 minutes. or more. Occasionally, you might have to pull the crucible out and give it a stir with a small diameter steel rod. If they aren't burned completely and any carbon remains, you'll probably end up with a too large lead button. After incineration, pre-mix the flux in a separate crucible, pour it onto the ash, stir it all up, and run a normal fire assay.

What flux composition will be needed for such material?
According to spec sheets, about 60-70% of package matrix is composed of fused silica with the rest being mostly epoxy of some sort (which wouldn't matter since incinerated)

 

[goldsilverpro]

Chris.

It amaze me time and again, how you (and the other "veterans") seems to have the bigger picture in mind and are willing to share your point of view with such detail. For that i pesonally would like to thank you.

The easiest and, probably, most accurate way on identical parts (at least, in appearance), such as these, is to fire assay the whole parts separately. To sample them, since they all appear to be identical, I would probably just grab a part here and a part there - I can't see how splitting down the lot by coning and quartering or using a sample splitter would give much improvement. In this case, you can probably run 2 parts per fire assay but, if the total copper and nickel is more than about 2 grams, you may only be able to run 1 part per assay. Since organics are involved, the parts must be incinerated before fluxing. This is easily done by weighing the 2 parts and placing them in an empty assay crucible. Then put them in a hot (say, 1850F) assay furnace, with the door opened just a crack to let in a little oxygen, and burn them until they fall apart into white ash. This might take 45-60 minutes. or more. Occasionally, you might have to pull the crucible out and give it a stir with a small diameter steel rod. If they aren't burned completely and any carbon remains, you'll probably end up with a too large lead button. After incineration, pre-mix the flux in a separate crucible, pour it onto the ash, stir it all up, and run a normal fire assay.

What flux composition will be needed for such material?
According to spec sheets, about 60-70% of package matrix is composed of fused silica with the rest being mostly epoxy of some sort (which wouldn't matter since incinerated)

That's a lot more silica than I expected, but since silica is usually used in assay fluxes, it may not cause a problem unless there is so much that it won't allow the epoxy to burn out. If the silica melts in the 1850F heat and coats the epoxy and prevents it from burning out, you might try incinerating at a much lower temperature - say, 1000F, for a longer period of time. It might also help to crush up the part in a cast iron mortar and pestle before incinerating. This won't work, though, if any of the gold sticks to the cast iron. It probably won't.

You might have to experiment with the flux mixture but, to start with, here's what I would try for these parts.

60-70 g litharge
30 g anhydrous borax or borax glass
20-30 g anhydrous soda ash
Sugar or flour
A little fluorspar (try 2-5 grams) if the molten flux is too thick. If you use too much, the crucible can be severely attacked and you can leak flux onto the furnace floor.

Except for the sugar or flour, the amounts of the ingredients are not that super critical and can vary somewhat.

Bismuth trioxide can be used instead of litharge and is much safer (and more expensive). I haven't used it so I can't comment on it. If you use litharge, make sure you have excellent furnace exhaust. You don't want to breathe that crap.

The purpose of the sugar or flour (I use sugar) is to reduce part of the litharge (lead oxide) to lead metal, which is formed in droplets wherever a sugar particle contacts a litharge particle and these rain down through the mixture to collect the PMs. The remaining unreduced litharge acts as an important part of the flux. The sugar or flour is burned to carbon and that's what reduces the lead. Ideally, about a 25 gram lead button is formed. For the brand of granulated sugar I was using, that took about a level 1/2 teaspoon. Since sugar and flour can vary tremendously, you'll have to experiment with the amount. In general, it takes less flour than sugar. If the epoxy doesn't burn out completely, a lot more lead can be reduced and you may need no sugar or flour at all. If way too much lead is formed, you can either use a huge cupel or split 1 part into 2 pieces and run it in 2 crucibles.

If you're interested in both Au and Ag: cupel the lead button, weigh the Au/Ag bead, wrap the bead in lead foil along with enough silver to give about a 4-6/1 silver/gold ratio, cupel, part, weigh the gold, calculate the silver from the 2 weighings. If you're only interested in the gold: add the silver to the flux mixture, cupel the lead button, part, weigh the gold.

Were I doing this, I would probably run a few experimental assays before settling on the method I would use. The high silica could cause problems and change the whole approach. I sold my assay equipment so I have no way to play with it. Good luck!

 

[Harold_V]

Keeping in mind I have never assayed, my experience in processing waste materials taught me that silica is not melted (about 3,300° F required to melt silica), but dissolved by soda ash. If there's an excessive amount of silica present, more soda ash should handle it in stride. I can't address the issue of the epoxy, but I certainly would recommend full incineration before any attempt at melting. A slag cover may preclude full incineration, otherwise.

I certainly agree with the comments about fluorspar. It does an amazing job of thinning slag--and is, indeed, very aggressive in dissolving things, including furnace lining.

Harold

 

[goldsilverpro]

Keeping in mind I have never assayed, my experience in processing waste materials taught me that silica is not melted (about 3,300° F required to melt silica), but dissolved by soda ash. If there's an excessive amount of silica present, more soda ash should handle it in stride. I can't address the issue of the epoxy, but I certainly would recommend full incineration before any attempt at melting. A slag cover may preclude full incineration, otherwise.

I certainly agree with the comments about fluorspar. It does an amazing job of thinning slag--and is, indeed, very aggressive in dissolving things, including furnace lining.

Harold

You're right, of course, about the melting point. I don't know what I was thinking.

 

[samuel-a]

Thank you Chris for that detailed answer.
Looks like a promising point to start with. At the moment i don't have assaying equipment and my knowladge about fluxes and smelting is somwhere at 2 out of 10, but was very interested to know how one would fire assay them IC's.
I'm saving this post for when the time comes and it will be relevant.

silica is not melted (about 3,300° F required to melt silica), but dissolved by soda ash.

Thaks Harold for pointing this out, i had a hunch this might be the case. I guess it's good you point that out for those that know about smelting even less then i do.

With this amount of soda ash melted, i assume the clay/fused silica dish will probably be a disposable one, right?
What would you use in case smelting large volumes is part of the process rather then assaying in small disposable crucibles?

 

[Anonymous]

Silicon Carbide would work well.
This is a good place http://www.budgetcastingsupply.com/Crucibles.php
They also have a 5 pack of carbon stirring rods (12" long x 1/2 "thick) for $30,which is an excellent deal.
Their prices include shipping,and they have an option where you can be emailed for every step of the shipping/delivery process.
I have always had my stuff delivered quickly,and packaged well.
The A10 silicon carbide crucible is a very good deal at $55.70,and should be large enough to handle most "backyard" refiners.

 

[Harold_V]

Silicon Carbide would work well.

You did pay attention to my mention that soda ash dissolves silica, yes?

Food for thought:

When I melted my (cement) silver, I used flux. Using a #8 silicon carbide crucible, I could get about eight heats from each one before it was thinned beyond reasonable use, and often sprung a leak at the flux line. Fluxing in a crucible is a recipe for very short lifespan.

When I processed my waste materials, I knew they were high in silica, but I still added silica sand to each lot. The results I achieved in my tilting furnace were outstanding. I was fortunate to land on a flux recipe (my own) that served the purpose perfectly well. An assay of the flux revealed a content too low to justify further processing, so I was elated.

That being said, I did my melting directly in the furnace, no crucible. In spite of using a 94% alumina lining, erosion was severe. Were it not for the extremely high value of the material in question, it would have been a mistake to process the material because of wear and tear on the furnace. I shudder to think of the cost of the crucibles I'd have destroyed instead.

Harold

 

[samuel-a]

Harold.
From your words, i understand that the higher the alumina content the more resistant it will be to the carbonate erosion, am i correct with that thinking?

I do have a pure alumina crucible.
Thing is, dou to it's cost i shutter from thinking it might become a one timer...

 

[Anonymous]

Silicon Carbide would work well.

You did pay attention to my mention that soda ash dissolves silica, yes?

Actually I did pay close attention....I just didn't make the connection between silica and silicon carbide.I'm not sure why it didn't register in my head,I should have known that.
Do you think graphite would work better?If so that would be better for me,because of the price.I have some magnesium oxide,I also have fireclay.Maybe lining the insides of the crucible would help?
Please advise,because this is something I will be starting as soon as next week(weather permitting).

 

[macfixer01]

In general I don't find anything in these PLCC type chip packages. However make sure you crack open any of them made by Rockwell. I have found several different part numbers (usually on modems or communications boards) that have a hybrid design with a ceramic wafer inside that has gold traces. I know there is at least one thread already here on the forum that talks about them.

macfixer01

 

[patnor1011]

Steve posted picture with rockwell chip opened and I did the same with chip from zip drives board. I would say most or nearly all chips contain gold but mostly in form of super thin bonding wires which are not visible with naked eye. You can see them when you crush package to fine dust, remove wires with magnet (80-90%). 10-20% are copper. Try to pan that crushed powder and as you will do that this gold wires will accumulate so you can see them. I like to look for them with help of watch repairer or jewelers magnifying glass.

 

[samuel-a]

mic,

what are planing to smelt?

 

[Harold_V]

Please advise,because this is something I will be starting as soon as next week(weather permitting).

Frankly, the only thing that provides longevity is not using flux. High alumina, and similar products offer decent resistance to dissolution, but even they have a finite life. Remember, the purpose of using flux is to do exactly what it does---liquefy solids, at which time it also absorbs oxides and other contaminants. Samual will have to balance his needs and decide if using his alumna vessel is a wise decision. It will hold up better than silicon carbide or graphite, but it will slowly dissolve.

Harold

 

[samuel-a]

OK Harold thank you.

That's sound like the resonable thing to do.

If i could pull at least 10 melts from that crucible i think i'll be fine, the capacity is about 500 ml and have a lid. I guess using the lid will help reduce damage to surrounding refactory.

I'll post a new thread once it become more relevant.

 

[Anonymous]

Frankly, the only thing that provides longevity is not using flux.

Since I am using litharge(lead oxide) ,couldn't I use glass as my gathering medium?I am not sure what to call it other than that,since I technically cannot call it flux.
Either way,Since I will be using borax and soda,I guess the only thing to do is use graphite,as opposed to silicon carbide,or fused silica.

 

[qst42know]

What is it you are working on mic?

A crucible will produce a lead alloy button, cover over with a very fluid lead borosilicate slag at temperature and pretty much stop reacting. Disposable or what they consider to be disposable fire clay crucibles are sold for this use.

 

[Anonymous]

What is it you are working on mic?

mic,

what are planing to smelt?

Sorry guys,I have been hurt(yet again),and I've had to coordinate the rest of that big shipment from that company last week.And on top of all of that I have a very large shipment coming in tomorrow.
I have not had time to breathe,much less coordinate what the next project will be.I am very sorry,and I will try to get something ready for you guys next week.My litharge came in today,so I should be ready to go on the new melting/smelting project,as soon as I can catch up on everything else.

 

[Harold_V]

Since I am using litharge(lead oxide) ,couldn't I use glass as my gathering medium?

No. Glass will absorb prills and may keep them in suspension. When you gather, a metal is desirable, so it will alloy with the prills, making them larger, encouraging them to combine instead of remaining in suspension in the flux (glass). By the way, common glass is nothing more than silica dissolved in soda ash.

Harold

 

[Anonymous]

Sorry Harold,
what I meant was,couldn't I just use glass,instead of borax and soda?
I have tons of borosilicate glass here,and just thought I could use it for this purpose.
I was definitely using the litharge as my "gatherer".Sorry again,just having an off-day.