The Chemistry of Metal Casting and Refining

Introduction

Humans have been refining and working with metals since 7000 BCE, and making it one of the oldest modern practices. However, previous rudimentary procedures have been since replaced by more advanced methods and materials. As Refractory materials were perfected, higher forge temperatures were reached, eventually leading to the first Iron casting in 513 BCE. This was revolutionary considering iron’s melting point of 1528 degrees celsius.


I chose metal refining and casting because metal objects and their creation processes fascinate me. I have recently become enamored with forge technology, and casting methods. Because Aluminum has one of the lower melting temperatures of the common earth metals, I decided it would be the best material to make my first cast with. Casting is still the most common metal production method humans have used in industry. Since Aluminum is so common, I used empty soda cans as a source of aluminum, as well as a dented aluminum pot.

Composition of ...

    1. Crucibles
      1. Graphite (Carbon hexagonally bonded)
      2. Clay (Al2O, 2SiO, 2H₂O)
    2. Refractory Cement (Na₂O, K₂O), 2 Al(H₂PO₄)₃ + 3H₂O
    3. Aluminum and Aluminum oxide (Al), Al₂O₃
    4. Steel (Carbon and Iron)
    5. Casting Sand (SiO₂), (H₂O)

Main Chemicals, Compounds, Components

    1. Components
      1. Forge
        1. Steel Wall
        2. Refractory chamber
      2. Crucible
      3. Fuel Source
        1. Charcoal and air powered
        2. Propane powered
        3. Other fossil fuel burner
      4. High silica sand for casting
        1. Low water content
        2. Mix of fine sand and clay
      5. Wood casting frame
      6. Crucible tongs
      7. Metal
        1. Aluminum, Copper, Lead, Silver, Gold, Brass
      8. Acids for dissolving impurities

Chemistry's Role

    1. Materials with extremely high melting points must be used for the forge and crucible. Refractory cement can withstand up to 3500 degrees F. Carbon Graphite can take temperatures up to 6400 degrees F.
    2. Native crystal structures of certain metals can determine the yield
      1. Liquid Aluminum has a very low surface tension and high adhesion properties, so a significant amount will remain inside the crucible after pouring
      2. Copper, on the other hand, beads up like mercury with almost no adhesion to the crucible.

Resources

    1. http://www.istc.illinois.edu/info/library_docs/manuals/primmetals/chapter4.htm
      1. Aluminum Information
    2. http://www.themetalcasting.com/crucible.html
      1. The science of the crucible
    3. http://www.historyworld.net/wrldhis/plaintexthistories.asp?historyid=ab16
      1. History of metallurgy
    4. http://www.almatis.com/media/3986/high-calcium-aluminate-cements_and_chemical_binders.pdf
      1. Refractory Information

About the Author

Alex Campbell - Junior at Billings Senior High