Tungsten Crucibles
Challenge
To clean tungsten crucible used in gold deposition physical vapor deposition system by a large LED manufacturer. To not only recoup the gold, but to potentially reuse the tungsten crucible for further production.
Recoup
Gold
Substrate
Tungsten
Results
Our new patented solution was again used to solve a typical production problem and with low cost but high gain of gold. The recoup was close to optimum and both our client and the end customer benefited from the use of our novel process.
A large producer of LED equipment sent physical vapor deposition crucibles after use in the coating processes, which were filled with gold, to a refiner to recoup the gold.
The refiner was not able to fully clean the tungsten crucibles filled with gold, their option was to heat them to the melting temperature of gold and pour out most of the gold, but certainly not all of the gold.
It was our estimation that this current process was not economical due to the (i) high energy invested into the heating, (ii) the tungsten does not get completely cleaned, and (iii) quite a bit of the gold remained on the surface of the tungsten crucible, which not only reduced the recoup of the gold, but may also be contribute to lag time in getting the coating system to equilibrium for coating after new gold was added to he crucible and re-used in the coating chamber.
We were contacted to try to come up with a technology that would solve this situation.
First, we understood that the tungsten surface is not so sensitive, as many chemicals cannot damage it.
Second, we reviewed the current situation and what existing technologies were available?
• The cyanides can be used because they work on gold. We ruled them out due to their high toxicity;
• The current state-of-the-art aqua regia would damage the tungsten, so the customer would have to keep buying new crucibles;
• Blasting the crucible by different blasting media would mean consequent extraction (dissolution of gold from the media utilizing liquid chemicals) most probably by the current state-of-the-art aqua regia. Since this process of extractions cause huge losses of precious metals, we ruled this possibility out.
• The other available technologies (please see our FAQs for more details) like weaker aqua regia, potassium iodide/iodine, thiourea/sulfuric acid/iron(III) sulfate and some other processes were ruled out, because they are (a) too expensive for the recycling of gold from such etching solutions and because (b) we would be adding iodine or sulfur into the very pure gold that comes directly from the physical vapor deposition process and chamber.
The ultimate solution would be to look for a technology that would (i) visibly dissolve gold, (ii) preserve and completely clean the tungsten precision parts and (iii) be “clean” enough not to introduce any other impurities into the gold.
Since the tungsten’s surface is not so sensitive to strong chemicals, we decided to use the strongest version of our patented solution. In addition, this new solution also contains no additional metals or non-precious metals that would hinder reaching the highest possible purity of the recycled gold.
We optimized and demonstrated this technology to the refiner mentioned above with confidence that the technology would meet the challenges and also provide the highest yield in gold, as well as provide recycled crucible for re-use if the customer so desired.