文档介绍：processes for producing materials.
MSE 120 - 1999
Introduction.
All of our steel, copper, aluminum and silicon (including semiconductor grade silicon) is made by processes that at some point use high temperatures. In producing ceramic parts, high temperature “sintering” mon. This part of the course is therefore devoted to some of those high temperature operations. [By “high temperatures” is meant temperatures between about 400 and 15000C.] Earlier we learned that many oxides can be reduced to metals by the inexpensive reducing agents carbon and hydrogen at high temperatures. However, as shown on the next slide, many ores exist as sulfides.
MSE 120 - 1999
Oxide and sulfide ores.
Aluminum occurs in the lithosphere as an oxide.
Iron as oxides (mostly).
Copper as both sulfides and oxides.
Nickel (ditto).
Zinc as sulfides.
Silicon as oxides.
Lead as sulfides.
Gold and silver as metals.
Magnesium as chloride (in the hydrosphere).
MSE 120 - 1999
The problem with sulfides...
…is illustrated in the Ellingham diagram for sulfides (next slide) which should be contrasted with the Ellingham diagram for oxides. In contrast to the oxide diagram, the lines for the inexpensive reducing agents carbon and hydrogen (going to their sulfides) lie high in the diagram. Consequently the sulfides of most metals cannot simply be reacted with carbon or hydrogen to produce the metal. Expressed another way, neither carbon nor hydrogen have sufficient affinity for sulfur to be used to remove sulfur from most pounds.
MSE 120 - 1999
Alternative processes for sulfides....
…are illustrated on the next slide. One possibility is to oxidize the sulfide to an oxide and then carbon or hydrogen can be used to reduce the oxide. This works fine for metals that have a high affinity for oxygen ( metals about half-way down the Ellingham diagram for oxides, or lower, zinc is a good example) and is carried out in an operation known as “roasting”. An alternative route can be used for metals with a l