GOLD ANNEALING CRUCIBLES & PARTING FLASKS
GOLD ANNEALING CRUCIBLES, PARTING AND ANNEALING QUARTZ CRUCIBLES AND PARTING FLASKS
After cupellation, we obtain a bead made of gold and silver. Therefore, it is still necessary to separate the silver from the gold. To achieve this, we attack two times the bead with boiling nitric acid and then we anneal it. This process is called “parting” and “annealing”. Gold annealing crucibles and parting flasks are the key instruments to achieve this.
The reason for using nitric acid, is that silver is soluble in it but gold is not. However, to ensure that no silver is secluded into the gold, and therefore protected from being dissolved, it is first necessary to laminate the bead into a cornet.
It is possible to do the nitric acid attack in quartz parting and annealing crucibles or in borosilicate parting flasks. Quartz parting and annealing crucibles have the advantage of requiring less manipulation of the bead because the next step of the process (gold annealing) is done using this same crucible.
After the nitric acid attack, the obtained pure gold cornet is very brittle because it is covered by a multitude of holes left by the dissolved silver. At this point, it would be unsafe to weight the gold cornet due to the risk of breaking it and losing a part of the sample. This is why it is necessary to anneal the gold cornet in a quartz parting and annealing crucible or in a fireclay gold annealing crucible.
The Annealing process consists of just heating the gold cornet above it recystalization tempearute at 850ºC but without melting it. After annealing the cornet is more “solid” and can be weighted safely withou risk of breaking it.
Fire Assay SL supplies the parting and annealing accessories to achieve this:
QUARTZ PARTING & ANNEALING BASKETS – QUARTZ GOLD ANNEALING CRUCIBLES – Allowed by ISO11426
We supply a range of quartz baskets that allow to carry out the successive parting and annealing operations in the same container, and substitute, both parting flasks, and gold annealing crucibles.
These quartz baskets are capable of withstanding:
- Attack of concentrated nitric acid
- High temperature necessary for annealing (up to 1000ºC)
- Thermal shock due to very low coefficient of thermal expansion.
They are therefore suitable for processing samples in parallel during the two nitric acid attacks (the first with nitric acid 33%, the second with nitric acid 49%), and then go directly in the gold annealing furnace (after rincing with water).
On the other hand, we also supply the borosilicate beakers in various sizes to fit the diagonal of the baskets. The beakers are supplied with watch lids or with a chimney to avoid nitric acid spillage at boiling point or to conduct the vapours.
The quartz thimbles are provided with thin slits to evacuate the nitric acid / distilled water and possess a flange at the top to fit the holes of the basket.
It is possible to supply them as spares in case of breakage. There are two types of quartz thimbles / crucibles and they suit most cornet sizes.
The following parting and annealing baskets configurations are available:
|Dimensions (L x W x H)|
|QBR-6||42x57x70||6 (2 x 3)|
|QBR-12||57x72x70||12 (3 x 4)|
Advantages of parting & annealing baskets
Quartz parting and annealing baskets resist temperatures up to 1000ºC.
Furthermore, quartz has an extremely low thermal expansion coefficient (5.5×10−7/°C ; 20–320°C). This allows our parting and annealing baskets to resist rapid and large temperature changes without cracking (they have a great resistance to thermal shock).
EFFICIENY IMPROVEMENT IN OPERATIONS
Quartz parting and annealing baskets allow full scalability to mass analysis production stage.
Extends inherent parallel processing capabilities of Fire Assay.
Save time and reduce manipulation hazards.
Quartz parting and annealing baskets save Labour, Reagents (HNO3 – H2O), Reduced Energy consumption.
Parting Flask made with low thermal expansion borosilicate glass withstands both nitric acid attack and thermal shock.
Additionally, they have a tall narrow neck designed to fit inside gold annealing cups.
Finally, the dimensions of our parting flasks are: 230 x Ø 48 x Ø 18
Fireclay Annealing Cups / gold annealing crucibles possess a smooth unglazed surface and thin walls that provide them with excellent resistance against thermal shock.
Furthermore, they have a tronco-conical form designed for gold bead annealing and for ignition of precipitates such a barium sulphate and copper sulphide.
|CORNET ANNEALING CUPS nº 227||25||25|
|CORNET ANNEALING CUPS nº 230||32||30|
|CORNET ANNEALING CUPS nº 231||33||34|