Lead/Tin Solder Lab. 1. Select a labeled cup(s) and sign your names on the table of lead/tin percentages.

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1 Lead/Tin Solder Lab 1. Select a labeled cup(s) and sign your names on the table of lead/tin percentages. 2. Mass out 50 grams total of your assigned lead and tin alloy. 3. Melt the metals together in an evaporating dish using a hot plate 4. Mix with a glass stirring rod and gently scrape the oxidation to the side. Hold the evaporating dish with needle-nose pliers. 5. Using pliers, pour the molten metal into one depression in the spot plate try to make the metal level with the surface of the spot plate. CAUTION: Make sure the spot plate is absolutely dry!!!!!!!!!! 6. Pour the remaining metal into the warm sinker mold. 7. Quench the metal pieces in a can of water. 8. Put the metal spot into a labeled plastic bag and give it to the teacher. You may keep the sinkers.

2 Tin Lead Solder Observations 1. Cup #1: Percentage of tin lead mass of tin used mass of lead used 2. Cup #2: Percentage of tin lead mass of tin used mass of lead used 3. Describe the appearance of tin: 4. Describe the appearance of lead: 5. Which metal melted first? 6. Color of the oxidation: 7. Is the oxidation more or less dense than the metal? 8. Describe the appearance of the solidified solder: 9. Describe the flow characteristics of molten metal:

3 10. Additional observations and impressions:

4 100% Pb 0% Sn 90% Pb 10% Sn 80% Pb 20% Sn 70% Pb 30% Sn 60% Pb 40% Sn 50% Pb 50% Sn 40% Pb 60% Sn 30% Pb 70% Sn 20% Pb 80% Sn 10% Pb 90% Sn 0% Pb 100% Sn

5 Basic phase diagram: -heating/cooling curve for water Typical diagram for pure substances o elements and compounds o same typical shape - different temps for different substances Label: o Heating a solid o melting a solid o heating a liquid o boiling a liquid o heating a gas (vapor) Heat is changing the whole time Temperature does not increase during a phase change (change of state) Heat total energy, potential and kinetic Temperature average kinetic energy

6 Figure 11.9: Heating curve for water.

7 The diagram on the left shows the uptake of heat by 1 kg of water, as it passes from ice at -50 ºC to steam at temperatures above 100 ºC, affects the temperature of the sample. A: Rise in temperature as ice absorbs heat. B: Absorption of latent heat of fusion. C: Rise in temperature as liquid water absorbs heat. D: Water boils and absorbs latent heat of vaporization. E: Steam absorbs heat and thus increases its temperature. The above is an example of a heating curve. One could reverse the process, and obtain a cooling curve. The flat portions of such curves indicate the phase changes. Phase material that has its own structure and/or composition

8 Phase change Two types: o Change in state o Change in crystalline structure (solid state phase change) Energy is absorbed or released Temperature does not change Particles held together more tightly energy was released Particles less closely attracted energy was absorbed phase diagram for iron Same as for water backwards shows a release of energy instead of an absorption in energy Has additional flat lines phase changes that are not changes of state represent solid state phase changes such as a change in crystalline structure binary phase diagram for Pb/Sn solder Plots percent composition versus temperature Pass out student copy Does not include gas state Label the all liquid region Label the all solid region Label the liquidus line only liquid above the line Label the solidus line only solids below the line Ask what is between the 2 lines slush zone Slush o combination of solid and liquid o amounts of each varies based on temperature and percentage composition o compare to a slurpee Eutectic mixture that acts like a pure substance o Eutectic composition composition with the lowest melting temp varies from alloy to alloy o Eutectic point lowest melting temperature of the alloy temp at which eutectic composition freezes varies from alloy to alloy

9 The solidus line touches the liquidus line in 3 places: o on the left edge of the graph melting point of a pure metal (element) o on the right edge of the graph melting point of a pure metal (element) o the eutectic point. Pure substances have a melt point o a temperature at which it melts o no temp change until melting is completed Mixtures have a melt range o a temperature at which it starts melting and a higher temperature at which it completes melting -melt an ice cube on the griddle point out that it goes directly from solid to liquid, no slush. -melt the solder spots on the griddle gradually turning up the temperature (heat) -compare the phase diagram to what they are seeing with the melting spots on the griddle -have the students predict: o Which spot will melt first o Which spot should melt start melting second, etc o Which spots will have slush as they melt o What will happen if you stop increasing the temperature while a spot is in the slush zone o Which spot has the biggest slush range o Which spots won t melt o What will happen if you turn off the heat After melting, resolidifying, and melting again, review the phase diagram. Have students pick out the liquidus line, solidus line, and eutectic point on other sample binary phase diagrams.

10 Websites: Very useful for your own study and learning. Some are much more in depth. lead/tin solder and phase diagrams tutorials and quizzes on phase diagrams looks excellent phase diagrams and the lever rule phase diagrams and solidification list of websites about phase diagrams lots of good ones