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), answer the following questions a) With reference to the Pb-Sn phase diagram for a 25wt% Pb-75wt% Sn alloy that is cooled from the liquid phase: (i) At what temperature does the first solid form (ii) What is the composition of this solid phase (iii) At what temperature does the material become completely solidified (iv) What are the amounts of the phases present just below the temperature when the material completely solidifies b) Sketch the expected microstructures, with the phases labeled, after slow cooling from the liquid phase to 190 °C and 100 °C

), answer the following questions a) With reference to the Pb-Sn phase diagram for a 25wt% Pb-75wt% Sn alloy that is cooled from the liquid phase: (i) At what temperature does the first solid form (ii) What is the composition of this solid phase (iii) At what temperature does the material become completely solidified (iv) What are the amounts of the phases present just below the temperature when the material completely solidifies b) Sketch the expected microstructures, with the phases labeled, after slow cooling from the liquid phase to 190 °C and 100 °C

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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### Text Transcription for Educational Website: **a) With reference to the Pb-Sn phase diagram, answer the following questions for a 25wt% Pb–75wt% Sn alloy that is cooled from the liquid phase:** (i) At what temperature does the first solid form? (ii) What is the composition of this solid phase? (iii) At what temperature does the material become completely solidified? (iv) What are the amounts of the phases present just below the temperature when the material completely solidifies? **b) Sketch the expected microstructures, with the phases labeled, after slow cooling from the liquid phase to 190 °C and 100 °C.** --- ### Explanation of the Phase Diagram and Microstructures: The problem references various phases and transitions using the Pb-Sn (Lead-Tin) phase diagram, which is a type of binary alloy phase diagram. This particular diagram helps identify temperatures and compositions at which various physical changes occur in the alloy. - **Phase Diagram Overview:** - Generally plots temperature against composition for different phases. - Shows liquidus, solidus, and solvus lines indicating different phase boundaries. - Useful for determining temperatures at which certain phases appear or disappear. - **Microstructures:** - **At 190 °C and 100 °C:** - Depict distributions of the β and α phases (typical phases in Pb-Sn alloys). - As the alloy cools, different phases appear and change, which can be shown through grain structures or phase proportions. The goal is to relate the phase diagram details to practical cooling scenarios, explaining at which temperatures and compositions various phases form as the alloy transitions from liquid to solid state.
Transcribed Image Text:### Text Transcription for Educational Website: **a) With reference to the Pb-Sn phase diagram, answer the following questions for a 25wt% Pb–75wt% Sn alloy that is cooled from the liquid phase:** (i) At what temperature does the first solid form? (ii) What is the composition of this solid phase? (iii) At what temperature does the material become completely solidified? (iv) What are the amounts of the phases present just below the temperature when the material completely solidifies? **b) Sketch the expected microstructures, with the phases labeled, after slow cooling from the liquid phase to 190 °C and 100 °C.** --- ### Explanation of the Phase Diagram and Microstructures: The problem references various phases and transitions using the Pb-Sn (Lead-Tin) phase diagram, which is a type of binary alloy phase diagram. This particular diagram helps identify temperatures and compositions at which various physical changes occur in the alloy. - **Phase Diagram Overview:** - Generally plots temperature against composition for different phases. - Shows liquidus, solidus, and solvus lines indicating different phase boundaries. - Useful for determining temperatures at which certain phases appear or disappear. - **Microstructures:** - **At 190 °C and 100 °C:** - Depict distributions of the β and α phases (typical phases in Pb-Sn alloys). - As the alloy cools, different phases appear and change, which can be shown through grain structures or phase proportions. The goal is to relate the phase diagram details to practical cooling scenarios, explaining at which temperatures and compositions various phases form as the alloy transitions from liquid to solid state.
### Lead-Tin (Pb-Sn) Phase Diagram This phase diagram represents the binary alloy system of Lead (Pb) and Tin (Sn), illustrating the phases present at various compositions and temperatures. #### Key Features: 1. **Axes:** - The horizontal axis represents the composition, given in weight percent (wt% Sn) and atomic percent (at% Sn), ranging from pure Lead on the left (0 wt% Sn) to pure Tin on the right (100 wt% Sn). - The vertical axis shows the temperature, with the left side in degrees Celsius (°C) and the right side in degrees Fahrenheit (°F). 2. **Phases:** - **α (Alpha) Phase:** A solid solution of Sn in Pb. - **β (Beta) Phase:** A solid solution of Pb in Sn. - **Liquid Phase:** The region where the alloy is fully molten. - **α + L (Alpha + Liquid):** A two-phase region where α and liquid coexist. - **β + L (Beta + Liquid):** A two-phase region where β and liquid coexist. - **α + β (Alpha + Beta):** A two-phase region where both solid phases coexist. 3. **Key Temperatures and Compositions:** - **Eutectic Point:** 61.9 wt% Sn at 183°C (361°F), where the liquid phase solidifies into a mixture of α and β phases. - **Melting Points:** - Pure Lead (Pb) melts at 327°C (621°F). - Pure Tin (Sn) melts at 232°C (450°F). 4. **Lines:** - The downward sloping line from the pure Lead side (327°C) represents the liquidus line for the α + L region. - The upward sloping line from the pure Tin side (232°C) represents the liquidus line for the β + L region. - The horizontal line at 183°C represents the eutectic isotherm, where transformation from liquid to solid phases occurs. Understanding this diagram is crucial for applications involving Pb-Sn alloys, significantly impacting their use in soldering due to the low melting point at the eutectic composition. The various phase regions inform decisions regarding alloy selection based on desired thermal and mechanical properties.
Transcribed Image Text:### Lead-Tin (Pb-Sn) Phase Diagram This phase diagram represents the binary alloy system of Lead (Pb) and Tin (Sn), illustrating the phases present at various compositions and temperatures. #### Key Features: 1. **Axes:** - The horizontal axis represents the composition, given in weight percent (wt% Sn) and atomic percent (at% Sn), ranging from pure Lead on the left (0 wt% Sn) to pure Tin on the right (100 wt% Sn). - The vertical axis shows the temperature, with the left side in degrees Celsius (°C) and the right side in degrees Fahrenheit (°F). 2. **Phases:** - **α (Alpha) Phase:** A solid solution of Sn in Pb. - **β (Beta) Phase:** A solid solution of Pb in Sn. - **Liquid Phase:** The region where the alloy is fully molten. - **α + L (Alpha + Liquid):** A two-phase region where α and liquid coexist. - **β + L (Beta + Liquid):** A two-phase region where β and liquid coexist. - **α + β (Alpha + Beta):** A two-phase region where both solid phases coexist. 3. **Key Temperatures and Compositions:** - **Eutectic Point:** 61.9 wt% Sn at 183°C (361°F), where the liquid phase solidifies into a mixture of α and β phases. - **Melting Points:** - Pure Lead (Pb) melts at 327°C (621°F). - Pure Tin (Sn) melts at 232°C (450°F). 4. **Lines:** - The downward sloping line from the pure Lead side (327°C) represents the liquidus line for the α + L region. - The upward sloping line from the pure Tin side (232°C) represents the liquidus line for the β + L region. - The horizontal line at 183°C represents the eutectic isotherm, where transformation from liquid to solid phases occurs. Understanding this diagram is crucial for applications involving Pb-Sn alloys, significantly impacting their use in soldering due to the low melting point at the eutectic composition. The various phase regions inform decisions regarding alloy selection based on desired thermal and mechanical properties.
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