The principle of gold and silver ingot casting

When gold or silver ingot cast, should be generally appropriate amount of the oxidizing agent and flux. Add saltpeter generally added sodium carbonate or borax plus saltpeter. The addition of sodium carbonate can also release active oxygen to oxidize impurities, so it can not only act as a flux to dilute the slag, but also can play a certain oxidation.

The amount of flux and oxidant added increases or decreases depending on the purity of the metal. For example, if electrolytic silver powder containing more than 99.88% of silver is melt-casted, only 0.1% to 0.3% of sodium carbonate is generally added to oxidize impurities and dilute slag. To smelt silver with high impurities, an appropriate amount of nitrate and borax may be added to enhance the oxidation of a part of the impurities to remove the slag. At this time, the amount of carbonic acid should also be appropriately increased. Since silver can dissolve a large amount of oxygen when it is melted, in general, the amount of the oxidizing agent added should not be excessive because it is necessary to protect the body from damage by strong oxidation. And graphite crucible is an acidic material, so it is not suitable to add too much sodium carbonate.

Electrolytic gold containing 99.9% or more of gold is cast, generally about 0.1% of potassium nitrate and borax are added, and 0.1% to 0.5% of sodium carbonate is added to make slag. For gold of lower purity, the flux and oxidant may be appropriately added.

In the process of melting gold and silver, if there is a possibility of "burning through" near the surface of the sputum due to strong oxidation, an appropriate amount of clean and dry cullet may be added to neutralize the slag to avoid damage to the sputum and loss of gold and silver. Through the smelting process of oxidation and slagging, the gold and silver grades of the ingots are improved compared with the raw materials. Therefore, it is necessary to add an appropriate amount of flux and oxidant during the casting process.

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