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ChemWiki: The Dynamic Chemistry E-textbook > Wikitexts > UC Davis > UCD Chem 124A: Kauzlarich > ChemWiki Module Topics > Substitutional Alloys

Substitutional Alloys

Substitutional Alloys consist of a solid solution of metals. These metals bond together to form crystal structures that involve atleast two different metals. These metals often have similar bonding characteristics, but once combined can form an alloy with unique physical and chemical properties.

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Why Substitutional Alloys Occur: Bonding

The bonding between two metals is best described as a combination of metallic electron "sharing" and covalent bonding, one can't occur without the other and the proportion of one to the other changes depending on the constituents involved.(2 pg 6) Metals share there electrons throughout there structure, this flow of electrons is the reason behind many of the characteristics associated with metals, including their ability to act as conductors.(2 pg 6) The different amount and strength of covalent bonds can change depending on the different specific metals involved and how they are mixed.(2 pg 6) The covalent bonding is what is responsible for the crystal structure as well as the melting point and various other physical properties.(2 pg 6)

CC crystal.jpg

Examples of Substitutional Metal Alloys

FCC crystal.jpg

Depending on the specific type of substitutional alloy they can have multipile crystal structures. Two of the possible structures include Face Center Cubic(left), and Cubic Center Cubic(right). The structure of the metal alloy isn't limited to these two structures, but combined they represent a large portion of the common alloys.(2)

 

 

 

 

 

 

 

Chemical Charactaristics of Alloy vs. Pure metal

As the similarities between the electron structure of the metals involved in the alloy increase, the metallic characteristics of the alloy decrease.(2 pg 7) Pure metals are useful but their applications are often limited to each individual metal's properties.(1) Alloys allow metal mixtures that have increased resistance to oxidation, increased strength, conductivity, and melting point; Essentially any property can be manipulated by adjusting alloy concentrations.(1) An example could be Brass Door fixtures, they are strong and resist corrosion better then pure zinc or copper, the two major metals that constitute a brass alloy.(1) The combination also has a low melting point allowing it to be easily cast into many different shapes and sizes.(1) There are many other aspects of substitutional alloys that could be explored in depth, but the basic concept is the idea that each individual metal in an alloy give the final product its chemical and physical properties.(1)

Substitutional Alloys and Their Value to Humans

Substitutional alloys played an important role in the development of human society and culture as we know it today. The Bronze age itself is named after the Substitutional alloy consisting of tin in a metallic sollution of copper.(3) Ancient bronzes are very impure, or even mislabeled, containing large amounts of zinc and arsenic as well as lots of impurities.(3) These many substitutional alloys allowed for stronger tools and weapons, they allowed for increased productivity in the workshop as well as on the battlefield.(3) The need for raw materials like tin and copper for the production of bronze also spurred an increase in trade, since their ores are rarelly found together.(3) The current chemical understanding of substitutional alloys would not be so in depth if it weren't for the usefulness of the alloys to humans.

 

References

  1. Smallman, R. E., Ngan, A. H. W., & Smallman, R. E. (2007). Physical metallurgy and advanced materials. Amsterdam: Butterworth Heinemann.
  2. Wang, F. E.. (2005). Bonding theory for metals and alloys. Amsterdam: Elsevier.
  3. Dickinson, O. T. P. K. (1994). The Aegean Bronze age. Cambridge world archaeology. Cambridge: Cambridge University Press.

Outside Links

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Problems

Question 1: Are substitutional metal alloys naturally occuring on earths surface?

Question 2: What are two characteristics of a metal required for a substitutional alloy to form?

Question 3: Can Oxygen or Nitrogen be a part of the crystal structure of a substitutional alloy?

Answer 1: No, the oxidizing nature of the earths atmoshpere, as well as the need for specific and concentrated metals keeps these from being found naturally occuring.

Answer 2: Similar radii and similar electronegativity.

Answer 3: Only metallic elements can form the necessary metallic bonds that allow alloys to form.

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Last Modified
10:17, 2 Oct 2013

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