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Describe any two of the following: (i) Crystalline and amorphous structures; (ii) The differences between a eutectic alloy and a solid solution alloy; (iii) Three crystal point defects; (iv) Age hardening - Leaving Cert Engineering - Question Question 1 - 2007
Question Question 1
Describe any two of the following: (i) Crystalline and amorphous structures; (ii) The differences between a eutectic alloy and a solid solution alloy; (iii) Three... show full transcript
Worked Solution & Example Answer:Describe any two of the following: (i) Crystalline and amorphous structures; (ii) The differences between a eutectic alloy and a solid solution alloy; (iii) Three crystal point defects; (iv) Age hardening - Leaving Cert Engineering - Question Question 1 - 2007
Step 1
Describe any two of the following: (i) Crystalline and amorphous structures
Answer
Crystalline structures are materials where atoms are arranged in a highly ordered, repeating pattern. This regular arrangement gives rise to well-defined geometric shapes and predictable properties. Examples include metals such as copper and aluminum, which form distinct crystal lattices. Conversely, amorphous structures lack this ordered arrangement; their atoms are positioned randomly. Common examples are glass and certain plastics, which do not exhibit a sharp melting point but soften gradually.
Step 2
Describe any two of the following: (ii) The differences between a eutectic alloy and a solid solution alloy
Answer
Eutectic alloys are mixtures of two metals that completely dissolve in each other in the liquid state but not in the solid state, forming distinct phases upon solidification. An example is the lead-tin alloy. In contrast, a solid solution alloy is formed when one metal completely dissolves in another to create a single phase without distinct separations, as seen in alloys such as bronze.
Step 3
Using the graph paper supplied: (i) Draw the equilibrium diagram according to the given data
Answer
To plot the equilibrium diagram, take the percentages of metal B on the x-axis and the temperatures on the y-axis. Draw the liquidus line connecting points at which the alloy is completely liquid and the solidus line where it is completely solid. The area between these lines represents the region where the alloy exists as a mixture of liquid and solid.
Step 4
Using the graph paper supplied: (ii) Label the diagram and describe the main features
Answer
Label the liquid, solid, liquid + solid regions on the diagram. The liquidus line indicates the temperature above which the alloy is entirely liquid. Below this line, the alloy begins to solidify, transitioning to a mix of solid and liquid, and eventually to solid at the solidus line. These features illustrate how different temperature compositions affect the state of the alloy.
Step 5
Using the graph paper supplied: (iii) For the alloy with 50% B determine, from the diagram, the ratio of the phases at 1250°C
Answer
At 1250°C, locate the 50% point on the x-axis. From the diagram, read the solid and liquid phase lines. Assume, for instance, the solid mass is found to be 24 units and the liquid mass to be 16 units. Therefore, the ratio can be calculated as:
ext{Ratio of solid to liquid} = rac{24}{16} = rac{3}{2}.
Step 6
Outline the relationship between cooling curves and the formation of equilibrium diagrams
Answer
Cooling curves plot temperature against time as a material cools. The points at which phase changes occur can be correlated to an equilibrium diagram, showcasing the temperatures at which solidification starts and ends. Thus, cooling curves provide crucial information leading to the development of thermal equilibrium diagrams by illustrating temperature profiles during the solidification process.
Step 7
Explain, using diagrams, the stages of dendritic growth as a metal solidifies
Answer
Dendritic growth begins when nucleation occurs at temperatures below the liquidus line. Initially, small crystals start to form, which then branch out into dendrites resembling tree-like structures. As solidification progresses, these branches continue growing, intertwining and forming grain boundaries. The final solid structure consists of numerous dendrites that create a stable solid metal with various grain sizes and orientations, enhancing mechanical properties.