A lead tin alloy of composition 30

MATERIALS LABORATORY

Fall 2008

Lab 5: Phase Diagrams

THE LAB:

· Construction of a phase diagram utilizing cooling curve data for a molten binary alloy.

THE SAMPLES:

Tin-lead alloys of the following weight percent compositions:image1.jpg

· 30%Sn-70%Pb

· 50%Sn-50%Pb

· 63%Sn-37%Pb

· 70%Sn-30%Pb

· 90%Sn-10%Pb

THE EQUIPMENT:

· Safety Glasses

· Stopwatch/timer

· Steel crucible

· Hot plate

· Thermocouple with calibrated digital display

THE PROCEDURE:

1. Wear safety glasses and ensure all lab participants are wearing safety glasses prior to beginning the Phase Diagram Experiment.

2. Assign members of your team to the following:

· Monitor the stopwatch and announce the ten-second intervals.

· Monitor the thermocouple and announce the temperature reading.

· Record the temperature reading with respect to the time.

3. Heat the sample to a temperature above 500 ° F at which the alloy reaches the molten liquid state, and then turn off the hot plate.

4. Once the temperature reaches 500oF, record the temperature of the sample at ten- second intervals, as the specimen cools.

5. Continue this process until the thermocouple temperature falls below 190 ° F when the alloy reaches the solidified state.

6. Plot the cooling curve data as temperature (oC) as a function of time (minutes) using Microsoft Excel.

THE REPORT:

Your Company is interested in the Pb-Sn alloy system as a possible solder material. Your Boss would like you to check the eutectic composition and temperature of the Sn-Pb system. Therefore, to accomplish this assignment you must conduct the following:

· Determine the cooling curve for the 90 Sn-10 Pb alloy.

The report (no more than five pages), should include (but not limited to) the following:

· A detailed drawing/photograph illustrating the experimental setup.

· A plot of your cooling curve experimental data (Temperature (in °C) as a function of time (in minutes) (E.g. Fig.3.), identify on the plot both the liquidus temperature and the eutectic temperature.

· Your actual experimental data should be included in an appendix.

· A plot of the complete phase diagram (Fig.4, also provided electronically).

· Your conclusion as to what is the eutectic composition and temperature of this system.

· Also comment on and discuss any difference between experimental and published data if any.

Your report should fully conform to the format and organization as given in the

REPORTS & TECHNICAL WRITING DOCUMENT provided on blackboard.

APPENDIX
BACKGROUND
The purpose of this experiment is to study and record phase transitions that occur because of thermal disturbances in binary compositions, and the graphical relationships between them. Phase diagrams define the specific quantities of the binary composition, and illustrate equilibrium states at any given temperature. This behavior can be modeled utilizing a series of temperature versus time plots called cooling curves.

image5.jpg

Fig. 1. Cooling curves for the copper-nickel alloy.

A series of cooling curves for the copper-nickel alloy is shown in Fig. 1. The cooling curves illustrate the change in temperature as a function of time for various copper-nickel weight percent. The linear parts of the cooling curve (although does not always have to be linear) identify the temperature (in °C) for the two-phase regions; i.e. the liquid phase and the solid phase. The upper and lower parts of the cooling curve define the temperature (in °C) for the single-phase region; i.e. the liquid phase or the solid phase. These temperature readings can be utilized in conjunction with the alloy’s corresponding composition to plot the copper-nickel phase diagram illustrated in fig. 2.

image2.jpg

Fig. 2. Phase diagram for the copper-nickel alloy.

(Fig.1 & 2: from: R. Higgins, Properties of Engineering Materials, Hodder & Stoughton, London, (1986), 149-150).

Table 1. Temperature (in ° C) versus time (in minutes) for 90 wt% sn-10 wt% pb alloy

Time

Temperature

( °F)

Time

Temperature

( °F)

Time

Temperature

( °F)

0:00

3:10

6:20

0:10

3:20

6:30

0:20

3:30

6:40

0:30

3:40

6:50

0:40

3:50

7:00

0:50

4:00

7:10

1:00

4:10

7:20

1:10

4:20

7:30

1:20

4:30

7:40

1:30

4:40

7:50

1:40

4:50

8:00

1:50

5:00

8:10

2:00

5:10

8:20

2:10

5:20

8:30

2:20

5:30

8:40

2:30

5:40

8:50

2:40

5:50

9:00

2:50

6:00

9:10

3:00

6:10

9:20

Table 1. (continued) Temperature (° C) versus time (minutes) for 90 wt% Sn-10 wt% Pb alloy

Time

Temperature

( °F)

Time

Temperature

( °F)

Time

Temperature

( °F)

9:30

12:40

15:50

9:40

12:50

16:00

9:50

13:00

16:10

10:00

13:10

16:20

10:10

13:20

16:30

10:20

13:30

16:40

10:30

13:40

16:50

10:40

13:50

17:00

10:50

14:00

17:10

11:00

14:10

17:20

11:10

14:20

17:30

11:20

14:30

17:40

11:30

14:40

17:50

11:40

14:50

18:00

11:50

15:00

18:10

12:00

15:10

18:20

12:10

15:20

18:30

12:20

15:30

18:40

12:30

15:40

18:50

Table 1. (continued) Temperature (° C) versus time (minutes) for 90 wt% Sn-10 wt% Pb alloy

Time (minutes)

Temperature ( °F)

19:00

19:10

19:20

19:30

19:40

19:50

20:00

image3.emf

Cooling Curve

Temperature (in °C) versus Time (in minutes)

80

100

120

140

160

180

200

220

240

260

280

0:002:004:006:008:0010:0012:0014:0016:0018:0020:00

Time (minutes)

Temperature ( °C)

90 wt% Sn-10 wt% Pb

Fig. 3. Temperature (in °C) versus time (in minutes) for 90 wt% Sn-10 wt% Pb alloy.

Table 2. Compositions and corresponding liquidus temperatures (determined experimentally)

Composition (Sn-Pb)

Liquidus temperature (oC)

30-70

257

50-50

210

63-37

187

70-30

196

90-10

?

image4.emf

Lead-Tin Phase Diagram

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

0102030405060708090100

Composition (wt% Sn)

Temperature (°C)

Liquidus Temp. (oC)

Fig. 4. Incomplete binary phase diagram for the lead-tin alloy.

Fig. � SEQ Figure \* ARABIC �1�. Phase diagram lab set-up

Hot plate

Digital Display

Thermocouple