Pyrometallurgy is used to make bronze, which is the alloy of choice for most large statues.
Pyrometallurgy is a process by which ores and metals are heated to produce a finished product of usable compounds, purer metals and alloys. The process can be any of the following: drying, roasting, smelting, refining and alloying, among others. Using high temperatures can cause chemical and exothermic reactions in materials. Various heating methods can be performed, all of which can be referred to as pyrometallurgy. All processes use heat to change some aspect of the material being worked on. The change can be as simple as heating water or other liquids to a gaseous state and then removing them. Or it could be as complex as chemically bonding metals, as when copper and tin are combined to form bronze.
Pyrometallurgy is a process by which ores and metals are heated to produce a finished product of usable compounds, purer metals and alloys.
Drying is a type of pyrometallurgy in which moisture is removed from the material. Heat is applied to make the metal hotter than the boiling point of water, and then moisture can be extracted from the material. Roasting is another type of pyrometallurgy. This occurs when metal sulfide is heated to a point where oxygen reacts to form solid metal oxide and sulfur dioxide gas.
Smelting is another form of pyrometallurgy that involves thermal reactions in a molten phase. Smelting normally takes place at a temperature above the melting point of the metal and removes carbon dioxide from the material, leaving a more refined metal. Refining is another pyrometallurgical process that removes impurities by heating metals.
Alloys are combinations of metals with other metals or of metals with non-metals. A common example of this is bronze, a combination of copper and tin. If one heats copper to about 2000° Fahrenheit (1100° Celsius) and adds tin, bronze can be made. Alloying is another form of pyrometallurgy.
In all types of pyrometallurgy, fuel or electricity is needed as a source of heat. Sometimes exothermic reactions can provide enough heat for the pyrometallurgical process to take place. At this point, when no additional fuel or electricity is needed to work the metal, the process is known to reach an autogenous phase.
Generally, pyrometallurgical processes are used on materials that tend not to be very reactive, as reactive materials can be stimulated to explode when heat is applied. Non-reactive elements can be extracted by heat and refined using heat to apply other materials and make the impurities bind and become easier to remove, allowing for a purer form.