TA

Question 1

Define Thermal analysis

Answer 1

group of techniques in which a physical property of a substance is measured as a function of temperature whilt the substance is subjected to a thermal programme

Question 2

What do you use TA for

Answer 2

Structural changes (phase transitions, melting, crystallisation)
Mechanical properties - Expansion, hardness
Thermal constants - enthalpy, melting point, Curie T
Reactivity - dehydration, oxidation, reduction, decomposition, thermal stability, curing reactions
Characterisation - fingerprinting

Question 3

Principles of dilatometry

Answer 3

changes in diameter are measured by an optimal, mechanical or electrical transducer as a function of temperature during controlled temperature regime

Question 4

Key parts of dialtometer

Answer 4

furnace, sample, holder, push rod, purge gas inlet, transducer, vacuum flange

Question 5

Applications of dilatometry

Answer 5

1. Thermal coefficient
   alpha=(L2-L1)/(L1(T2-T1))
2. Phase changes
   Since there will be a change in flow of the specimen
3. Sintering Studies
4. Glass transition and softening studies

Question 6

define Thermogravimetry + how conducted

Answer 6

Uses mass of sample as a function of temperature and or time in a given Temp regime
2 ways:
-isothermally - sample mass recorded at a constant T
- dynamically - sample heated/cooled at constant rate

Question 7

Requirements of thermogravimetry

Answer 7

1. Precision balance (usually microbalance)
2. programmed furnace
3. controlled atmosphere
4. means to accurately measure sample temperature

Question 8

applications of TG

Answer 8

1. Reactions with gases: oxidation, evaporation, dehydration
2. investigating thermal stability
3. study reaction kinetics of thermal decomposition
4. Study of oxygen exchange
5. w/DSC DTA - to study fingerprinting particularly useful for clay soils and some organics
6. Determine Curie temperature by placing in furnace with magnetic field and observing shift in weight

Question 9

DTA - how does it work

Answer 9

Differential Thermal Analysis
Measure difference in T between sample and inert material with respect to temperature or time while undergoing heating/cooling programme

Question 10

Enthalpy in DTA plot

Answer 10

peak area proportional to enthalpy however constant dependent on reaction and experimental conditions so difficult to callibrate

Question 11

Effect of heating rate in DTA

Answer 11

increase heating rate increases onset and peak temperatures

Question 12

Reaction kinetics DTA

Answer 12

d(ln(alpha/peak T^2))/d(1/peak T)=-activation energy/R

Question 13

DSC - how

Answer 13

Differential scanning calorimetry
measures energy necessary to maintain 0 temperature difference between sample and inert reference material as a function of temprature in controlled T regime

Question 14

heat flux DSC

Answer 14

can operate at higher T than normal DSC
no individual heaters, heat flux between sample and reference is measured through calibration and linearisation of instrument

Question 15

DSC peak area

Answer 15

area=change in enthalphy*mass/K where K is a constant dependent on temperature

Question 16

Applications of DTA/DSC

Answer 16

DSC gives better enthalpy values

• reaction temperatures
• heat of reaction
• reaction kinetics
• specific heat measurements
• fingerprinitng
• Quantitive determinations