Thermomechanical Analysis (TMA)

Question 1

What are the basic principles of TMA?

Answer 1

1. change in dimension
2. sample subjected to temperature regime (heating or cooling)
3. Can include:
   a) linear rate of change
   b) stepwise temperature changes.

Question 2

What is meant by static force TMA?

Answer 2

When applied force is constant.

Question 3

What is meant by dynamic load TMA?

Answer 3

When force -> changed

-
When the force is changed and any alteration occurring of the force with time (dynamic).

Question 4

What are the instruments used in TMA?

Answer 4

1. Measuring probe
2. sample
3. sample support
4. sample length (as function of temperature at certain load)

Question 5

How does the TMA instrument work?

Answer 5

Sample:
1. mounted in instrument
2. surrounded by furnace
3. change in length measured
4. as a function of time or temperature

Question 6

What instrument is used in TMA?

Answer 6

Linear Variable Transducer (LVDT)

Question 7

How does the LVDT work?

Answer 7

1. Produces electrical signal from movement of probe (quartz) attached
2. Whole assembly enclosed in programmer controlled furnace

Question 8

What are the types of probes?

Answer 8

1. Expansion
2. Penetration
3. Tension
4. Dilatometer

a. normal probe
b. macroprobe
c. penetration
d. setup for films or fibers in tensile mode

Question 9

What are the application of probe types for different measurements?

Answer 9

1. Compression
2. Penetration
3. Flexure
4. Tension

Question 10

How does TMA apply to compression?

Answer 10

1. irregular shaped samples
2. low force 0.001N to 0.05N
3. sample behavior in immersion (e.g. paint films in water/solvent - swelling)

Question 11

How does TMA apply to penetration?

Answer 11

1. registers large change at glass transition Tg
2. force 0.05N to 0.5N

Question 12

How does TMA apply to flexure?

Answer 12

1. 3 point bending
2. stiff samples High force
3. 0.05N to 5N

Question 13

How does TMA apply to Tension?

Answer 13

1. used for fibers
2. force 0.005N to 5N
   (depending on fibers)

Question 14

How does TMA apply for polyethylene?

Answer 14

1. Shows glass transition Tg of coating
2. The displacement on melting gives thickness of coating

Question 15

How is the Temperature calibrated in TMA?

Answer 15

By melting of pure metal (e.g. Sn)

Question 16

How is the displacement calibrated in TMA?

Answer 16

By inserting accurately measured (height) samples and noting instrument output.
- Using AI with known coefficient of linear expansion α.

Question 17

What are the parameters measured in TMA?

Answer 17

1. Linear thermal expansion coefficient
2. Tg from TMA curve

Question 18

How is the linear thermal expansion coefficient calculated (α)?

Answer 18

α = dL/dT * (1/Lo)
Lo = length of sample at To (reference length at room temperature)

Question 19

What is the α for Quartz glass?

Answer 19

0.5

Question 20

What are the units of α?

Answer 20

10^-6 x K^-1

Question 21

What is the α for Aluminum?

Answer 21

24

Question 22

What is the α for PVC?

Answer 22

70

Question 23

What is the α for HDPE?

Answer 23

150

Question 24

How is the Young’s modulus calculated from TMA?

Answer 24

YM = (F/A) / (ΔL/L)

YM = Stress / Strain
Stress = Force x Unit Area
Strain = Change in displacement / original length