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Thermal analysis of Tin, Lead-Tin Alloy and Polyethylene Using DSC and TG-DTA
Eman Mousa Alhajji
North Carolina State University
Department of Materials Science and Engineering
MSE 3 3 5 Lab Report
A
Jessica Liu
November 18 2016
Abstract
The objectives of the experiment were to determine phase transformations and reaction
enthalpies in metals using differential scanning calorimetry (DSC) and to determine phase
transformations and thermal degradation behavior in polymers using thermogravimetric
/differential thermal analysis (TG-DTA). Two 99.9% tin (Sn) samples and one lead-tin (Pb/Sn)
alloy sample composed of 37% lead and 63% tin were tested in PerkinElmer instruments Diamond
DSC at a rate of 5, 10 and 20 ºC/min, respectively. One polyethylene terephthalate (PET) sample
was examined in SII Nano technology Inc. TG/DTA6200. The melting points were determined to
be 232. 32 ºC for tin run at 5 ºC/min and 232. 53 ºC for tin run at 10 ºC/min, indicating a limited
effect of the heating rate on the thermograms. The specific heat of fusion for tin was found to be
59.65 mJ/mg. The melting point of the lead-tin alloy was determined to be 18 5 .40°C. The melting
point for PET was determined to be 249 °C, and significant degradation and loss of molecular
weight started at 350°C. The degradation of PET does not begin until above the melting point,
implying that PET is a safe material used in food and drink packing. Good agreements are found
between the literature thermal characteristics and the values obtained experimentally, which
suggests that DCS and TG/DTA are very accurate in determining thermal characteristics and
identifying the melting points for Sn and Sn/Pb alloy.
Introduction
Thermal analysis is a method used in materials science and engineering to characterize the
properties of materials as they change with temperature.
1 Thermal analysis is important because
it can determine phase transformations, reaction enthalpies and thermal degradation behaviors.
1
A physical change indicates a phase change in metals or a glass transition temperature in polymers.
A chemical change indicates the onset of oxidation or degradation of the material.
2 , There are
three main methods commonly used in thermal analysis: differential scanning calorimetry (DSC),
differential thermal analysis (DTA), and thermal gravimetric analysis (TGA).
1 Differential
scanning calorimetry measure the change in heat whereas differential thermal analysis measures
the change in temperature and thermogravimetric analysis measures the change in mass, as
summarized in Figure 1.
Figure 1. Methods of thermal analysis: (a) Thermogravimetric analysis, (b) differential thermal
analysis, and (c) differential scanning calorimetry. 2
In TGA, the weight of the sample is continuously measured as temperature increases.
1,
The same heat source is used to heat the sample and the reference material. The decrease in the
mass of the sample indicates oxidation, decomposition or chemisorption.
2
DTA and TGA curves are usually combined together to give a more comprehensive study
of the thermal events occurring in the tested materials. While TG only measures changes caused
by mass loss, DTA record changes in material where no change in mass occurs such as melting
temperature and glass transition. 2 Figure 2 shows that different sizes and shapes of peaks in a DTA
plot correspond to different events occurring in an idealized polymathic material.
Figure 2. DTA curve of an idealized polymer.
2
The objectives of the experiment were to determine phase transformations and reaction
enthalpies in metals using DSC and to determine phase transformations and thermal degradation
behavior in polymers using TG-DTA. Two 99.9% tin (Sn) samples and one lead-tin (Pb/Sn)
alloy sample composed of 37% lead and 63% tin were tested in PerkinElmer instruments
Diamond DSC at a rate of 5, 10 and 20 ºC/min, respectively. One polyethylene terephthalate
(PET) sample was examined in SII Nano technology Inc. TG/DTA6200.
Experimental procedure
The instruments used for the thermal analysis of metals and polymers were PerkinElmer
instruments Diamond DSC and SII Nano technology Inc. TG/DTA6200. The metallic materials
being examined were 99.9% tin (Sn) and lead-tin (Pb/Sn) alloy composed of 37% lead and 63%
tin. The polymeric material being examined was polyethylene terephthalate (PET) obtained from
a plastic water bottle. The experiment was performed at a pressure of 1 atm. All samples and DSC
pans were handled with tweezers in order to minimize any transformation of oils or dust to the
samples.
1
The first part of this experiment was to preform thermal analysis of two Sn samples and
one Pb/Sn alloy sample using Differential Scanning Calorimetry (DSC). Each sample was
prepared as following. First, the weight of the sample was measured to be about 10 mg and was
recorded to the nearest 0.1 mg. Then, the sample was placed in an empty aluminum DSC pan. A
caution was taken when the sample was handled. An aluminum cover disk was placed over the
DSC sample pan. The DSC sample pan was sealed using the Perkin-Elmer pan crimper. Then, the
sample was inserted into the appropriate heating chamber contained within the DSC. An empty
pan was obtained to serve as the reference pan and was inserted into the appropriate heating
chamber contained within the DSC. The following parameters were entered into the software.
During all of the three DSC runs, purge gas of N 2 was flowing at approximately 20 mL/min. All
of the three samples were held initially at 150.00 ºC for four minutes and tested with heat ranging
from 150.00 ºC to 300.00C. The first run was performed at 5.00 ºC/min for the Sn sample measured
to be 10.6 mg. The second run was performed at 10.00 ºC/min for the Sn sample weighted 10.
mg. The third run was performed at 20.00 ºC/min for the Pb/Sn of 10.6 gm. An indium (99.999%,
4.7 mg) heating curve was provided in the course locker. This curve was used as the reference
Figure 3. DSC curves of the heat flow versus temperature for Indium and Tin at 5 ºC/min.
As a result, the specific heat of fusion for tin was determined to be 59.65 mJ/mg, calculated
as following:
s r r s r s s
A H m H A H m
3320 𝑝𝑖𝑥𝑒𝑙𝑠 (
- 45 𝑚𝐽 𝑚𝑔 )( 4. 7 𝑚𝑔)
702 𝑝𝑖𝑥𝑒𝑙𝑠 ( 10. 6 𝑚𝑔)
𝑚𝐽
𝑚𝑔
The melting temperature for the Sn sample run at 10 ºC/min was determined to be 232. 53
ºC using the intersection method on the DSC curve shown in Figure 4. No significant change in
the melting temperature was found between the Sn sample run at 5 ºC/min and the Sn sample run
at 10 ºC/min.
0
10
20
100 150 200 250 300 350
Heat Flow (mW)
Temperature (ºC)
DSC Curves for Indium and Tin at 5 ºC/min
In
Sn
Figure 4. DSC curve of the heat flow versus temperature for Tin at 10 ºC/min.
Figure 5 shows DSC curve of the heat flow versus temperature for Pb/Sn Alloy at 20
ºC/min. The melting temperature of the Pb/Sn Alloy was estimated to be 18 5. 40 ºC.
Figure 5. DSC curve of the heat flow versus temperature for Lead-Tin Alloy at 20 ºC/min.
0 140 160 180 200 220 240 260 280 300 320
Heat Flow (mW)
Temperature (ºC)
DSC curve for Tin at 10 ºC/min
0 140 160 180 200 220 240 260 280 300 320
Heat Flow (mW)
Temperature (ºC)
DSC curve for Lead-Tin Alloy at 20 ºC/min
Figure 6. Pb/Sn phase diagram. 3
For PET, the thermogravimetric analysis and differential thermal analysis results were
plotted as shown in Figure 7. TGA curve, in blue, shows a steady horizontal line then a rapid
decrease in the mass of the sample starting at approximately 350°C. DTA curve, in green, shows
peaks at 249 °C, 375° C and 425°C. Since no mass change was observed near the peak at 2 49 °C
and the peak was downward indicating endothermic process, the melting point was determined to
occur at this temperature.
1 , With changes in mass, oxidation was determined by the upward point
peak around 375°C and decomposition by the downward pointing peak at approximately 425°C. 1
Figure 7. TG (blue)-DTA (green) curves of temperature change and change in mass as a function
of temperature for PET.
The DTA curve for PET shows similar events happening in the DTA curve for ideal
polymers shown in Figure 2. The melting temperature of PET was determined to be 249 °C, which
agreed with the literature value of 248°C.
5 PET degrades significantly above a temperature of
350 °C as it rapidly loses mass.
2 These results agree with the literature findings. The degradation
of PET does not begin until above the melting point, implying that PET is a safe material used in
food and drink packing.
1 ,
Conclusion
The objectives of the experiment were to determine phase transformations and reaction
enthalpies in metals using differential scanning calorimetry (DSC) and to determine phase
transformations and thermal degradation behavior in polymers using thermogravimetric
Temp Cel
50.0 100.0 150.0 200.0 250.0 300.0 350.0 400.0 450.
DTA uV
TG mg
References
1 Y. Zhu, Thermal Analysis of Metals and Polymers, MSE 3 35 experiment description, 2010.
2 R.E. Smallman, A.H.W. Ngan, Physical Metallurgy and Advanced Materials , 7 th ed.
(Elsevier, Oxford, UK, 2007), pp 234 - 237.
3 W.D. Callister Jr., Materials Science and Engineering: An Introduction, Seventh Edition (Wiley,
New York, 2007).
4 Y.T. Zhu and J.H. Devletian, “Determination of Equilibrium Solid-phase Transition
Temperatures Using DTA,” Metallurgical Transaction , 22A , 1993-98 (1991).
5 B. Demirel, A. Yaras, H. Elcicek, Crystallization Behavior of PET Materials , (BAÜ Fen Bil.
Enst. Dergisi Cilt, 2011), 13(1) 26 - 35.
