Thermomechanical Analysis (TMA) Flashcards
What are the basic principles of TMA?
- change in dimension
- sample subjected to temperature regime (heating or cooling)
- Can include:
a) linear rate of change
b) stepwise temperature changes.
What is meant by static force TMA?
When applied force is constant.
What is meant by dynamic load TMA?
When force -> changed
-
When the force is changed and any alteration occurring of the force with time (dynamic).
What are the instruments used in TMA?
- Measuring probe
- sample
- sample support
- sample length (as function of temperature at certain load)
How does the TMA instrument work?
Sample:
1. mounted in instrument
2. surrounded by furnace
3. change in length measured
4. as a function of time or temperature
What instrument is used in TMA?
Linear Variable Transducer (LVDT)
How does the LVDT work?
- Produces electrical signal from movement of probe (quartz) attached
- Whole assembly enclosed in programmer controlled furnace
What are the types of probes?
- Expansion
- Penetration
- Tension
- Dilatometer
a. normal probe
b. macroprobe
c. penetration
d. setup for films or fibers in tensile mode
What are the application of probe types for different measurements?
- Compression
- Penetration
- Flexure
- Tension
How does TMA apply to compression?
- irregular shaped samples
- low force 0.001N to 0.05N
- sample behavior in immersion (e.g. paint films in water/solvent - swelling)
How does TMA apply to penetration?
- registers large change at glass transition Tg
- force 0.05N to 0.5N
How does TMA apply to flexure?
- 3 point bending
- stiff samples High force
- 0.05N to 5N
How does TMA apply to Tension?
- used for fibers
- force 0.005N to 5N
(depending on fibers)
How does TMA apply for polyethylene?
- Shows glass transition Tg of coating
- The displacement on melting gives thickness of coating
How is the Temperature calibrated in TMA?
By melting of pure metal (e.g. Sn)
How is the displacement calibrated in TMA?
By inserting accurately measured (height) samples and noting instrument output.
- Using AI with known coefficient of linear expansion α.
What are the parameters measured in TMA?
- Linear thermal expansion coefficient
- Tg from TMA curve
How is the linear thermal expansion coefficient calculated (α)?
α = dL/dT * (1/Lo)
Lo = length of sample at To (reference length at room temperature)
What is the α for Quartz glass?
0.5
What are the units of α?
10^-6 x K^-1
What is the α for Aluminum?
24
What is the α for PVC?
70
What is the α for HDPE?
150
How is the Young’s modulus calculated from TMA?
YM = (F/A) / (ΔL/L)
YM = Stress / Strain
Stress = Force x Unit Area
Strain = Change in displacement / original length
