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The lead-tin equilibrium diagram is shown below - Leaving Cert Engineering - Question b - 2010
Question b
The lead-tin equilibrium diagram is shown below. (i) Identify the point A and the lines B, C and D. (ii) Describe the main features of the diagram. (iii) Determin... show full transcript
Worked Solution & Example Answer:The lead-tin equilibrium diagram is shown below - Leaving Cert Engineering - Question b - 2010
Step 1
Identify the point A and the lines B, C and D.
Answer
Point A is identified as the eutectic point, which is the composition where the lowest melting temperature occurs for the alloy. Line B represents the solvus line, which indicates the boundary where the two metals are completely soluble in each other. Line C is the solidus line, demarcating the start of solidification. Line D is the liquidus line, defining the temperature above which the alloy is completely liquid.
Step 2
Describe the main features of the diagram.
Answer
The lead-tin equilibrium diagram illustrates the phase relationships between lead and tin across varying compositions and temperatures. The main features include:
- Liquidus Line: Determines the temperature range in which the alloy is completely liquid.
- Solidus Line: Marks the beginning of solidification; below this line, the alloy is entirely solid.
- Solvus Line: Represents the limit of solubility for the two metals in each other.
- Solid Region: Located below the solidus line where all components are solid.
- Liquid Region: Found above the liquidus line where the alloy is entirely liquid.
- Pasty Region: The area between the solidus and liquidus lines where both solid and liquid phases coexist.
Step 3
Determine, from the diagram, the composition of the phases at 250°C for the alloy at 30% tin.
Answer
At 250°C and for the alloy with 30% tin, the diagram shows that the solid phase contains approximately 13% tin and 87% lead, while the liquid phase consists of about 38% tin and 62% lead. This indicates that at this temperature, the alloy is in a partly liquid and partly solid state.