E106 Problem 199

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E106 Problem 199

• Kevin Swartzlander
• February 7, 2007

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The Problem (199)

• Kovar is
• 54 weight percent iron (M 55.8450)
• 29 weight percent nickel (M 58.6934)
• 17 weight percent cobalt (M 58.9332)
• What is the composition of Kovar in atomic
  percent?

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Applications of Kovar

• Kovar is an iron-nickel-cobalt alloy
• Designed to have a coefficient of thermal
  expansion similar to that of borosilicate glass
• Commonly used in seals between metal and glass
  parts
• Power tubes, microwave tubes, transistors, diodes

http//www.espimetals.com/tech/kovar.pdf
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Weight Percent Composition

• The weight (mass) of an element relative to the
  total weight of the material (units wt)

mi mass of element i wi weight fraction of
element i
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Atomic Percent Composition

• The number of moles of an element relative to the
  total moles of all elements in the material
  (units at)

ni moles of element i xi mole fraction of
element i
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Solution Method 1

• Step 1 find mi
• Assume basis of 100g, then mi wt
• 54g iron, 29g nickel, 17g cobalt
• Step 2 find ni

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Method 1 (continued)

• Step 3 calculate CI

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Solution Method 2

• Derive general equations to convert directly
  between wt and at composition
• Faster conversions
• Limit rounding error
• Fewer values to keep track of

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wt ? at
where
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at ? wt
where
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Implications

• Easily convert between wt and at
• Weight composition used for
• Purchasing material
• Most measurements
• Atomic composition used for
• Determining chemical structure
• Unit cells and mer units
• Reactions (stoichiometry)

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Important Equations