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Explain any two of the following: (i) Allotropy; (ii) Interstitial solid solution; (iii) The difference between amorphous structures and crystalline structures; (iv) The degree of brittleness in body-centred cubic (bcc) structures and the degree of brittleness in face-centred cubic (fcc) structures - Leaving Cert Engineering - Question 4 - 2011
Question 4
Explain any two of the following: (i) Allotropy; (ii) Interstitial solid solution; (iii) The difference between amorphous structures and crystalline structures; (iv... show full transcript
Worked Solution & Example Answer:Explain any two of the following: (i) Allotropy; (ii) Interstitial solid solution; (iii) The difference between amorphous structures and crystalline structures; (iv) The degree of brittleness in body-centred cubic (bcc) structures and the degree of brittleness in face-centred cubic (fcc) structures - Leaving Cert Engineering - Question 4 - 2011
Step 1
Explain any two of the following: (i) Allotropy
Answer
Allotropy is the ability of a material to exist in multiple structural forms. For instance, carbon can exist as graphite or diamond, which have distinct properties due to their different arrangements of atoms. In metals, allotropy can change with temperature and pressure. An example is iron, which can transform from alpha (ferrite) at room temperature to gamma (austenite) at high temperatures, affecting their mechanical properties.
Step 2
Explain any two of the following: (ii) Interstitial solid solution
Answer
An interstitial solid solution occurs when smaller atoms fit into the spaces (interstices) between the larger atoms of a crystal lattice. This can enhance the strength of the material by distorting the lattice and creating additional stress fields. Common examples include carbon in iron, which forms steel and significantly increases hardness.
Step 3
Using the graph paper supplied: (i) Draw the thermal equilibrium diagram according to the given data
Answer
To draw the thermal equilibrium diagram, plot the melting points of metal A (1083 °C) and metal B (1453 °C) on the temperature axis. Mark the solidus and liquidus lines based on the given data points. Connect the points with appropriate curves, ensuring to highlight the regions of liquid, solid, and pasty states.
Step 4
Using the graph paper supplied: (ii) Label the main features of the diagram
Answer
The main features to label on the diagram include the liquidus line (the boundary where all material is liquid), the solidus line (where all material is solid), and the regions indicating pure solid, pure liquid, and pasty regions where both solid and liquid coexist.
Step 5
Using the graph paper supplied: (iii) Determine, from the diagram, the ratio of phases at 1250 °C for 50% metal B
Answer
At 1250 °C, refer to the graph to identify the mass of solid and liquid phases. For 50% metal B, if the mass of solid is 24 and the mass of liquid is 16, the ratio can be calculated as:
Step 6
Outline the various stages of solidification as a metal cools, from X to the crystal at Y
Answer
The stages of solidification from the liquid phase to the crystal involve the following:
- Cooling: As the metal cools, temperature drops, leading to reduced kinetic energy of particles.
- Nucleation: Tiny solid crystals (nuclei) start to form as temperature decreases.
- Dendritic Growth: These nuclei develop into dendrites that branch out in all directions.
- Grain Formation: As solidification continues, the dendrites connect, forming grain boundaries that define the solid's structure.
- Complete Solidification: Eventually, the entire volume solidifies, and the metal takes on a solid crystal structure.
These stages illustrate the transition from a liquid state to a structured solid.