20-1 thermal methods theory instrumentation thermal methods §physical properties of a substance are...
TRANSCRIPT
20-1
Thermal Methods
• Theory• Instrumentation
• Thermal methods Physical properties of a substance are evaluated as
a function of temperature May include reaction products Temperature is controlled
Methods Thermogravimetry Differential thermal analysis Differential scanning calorimetry
20-2
Thermogravimetric (TGA)
• Thermogravimetry is one of the oldest thermal analytical procedures has been used extensively in the study of polymeric
systems
• involves monitoring the weight loss of the sample in a given atmosphere as a function of temperature N2, O2, air, He
Ambient to 1000 °C Can record the first derivative of the mass loss
20-3
Thermogravimetric
• MS can be coupled to TGA On line analysis Evolution of gas
• evaluation of the thermal decomposition kinetics of materials Polymers Resins rubbers
provides information on thermal stability • provide information on the bulk composition of compounds
Oxidation heat resistance the amount of water compositional analysis measurement of ash content in a sample
20-4
20-5
65
70
75
80
85
90
95
100
0 100 200 300 400 500
We
igh
t lo
ss
(%
)
Temperature (°C)
152.19 °C7.831%
Analysis of Resin
20-6
Table 10. Phenomenological data on the thermal decomposition of the phenolic resins
Resin T1, ˚C T2, ˚C Weight loss at 500˚C, %
PF 241.62 - 17
CF 148.84 - 40
RF 152.19 - 32
CQF 145.48 221.53 30
RQF 155.54 292.51 24
Table 11. Phenomenological data on the thermal decomposition of the metal complexes of phenolic resins
Resin complex
T1, ˚C T2, ˚C T3, ˚C T4, ˚C Weight lossat 500˚C, %
PF-Eu 243.42
- - - 18
CF-Eu 172.31 445.06 - - 29
RF-Eu 193.55 457.36 - - 32
CQF-Eu 163.37 290.80 361.22 431.65 25
RQF-Eu 172.31 300.00 361.22 451.77 26
20-7
Differential thermal analysis
• temperature difference between a substance and a reference material is measured as a function of temperature substance and reference material are subjected
controlled temperature emissions of heat (exothermic) absorptions of heat (endothermic)
* comparison with a passive material such as alumina
• Can be used to identify samples Clay materials
• Peak areas depend upon sample mass and enthalpy A=-kGmH
A= peak area, G is geometry factor, k is constant related to thermal conductivity
20-8
New Zealand Halloysite. Premium
20-9
Differential Scanning Calorimetry
• Differences in heat flow are measured as a function of temperature Sample and reference
Energy difference measured• Power Compensated DSC
Two furnaces Heat flow evaluated Difference in power input montiored
In watts• Useful for glass transition temperatures• Purity of drug samples
20-10
20-11
Automated methods
• Automatic No feedback
• Automated Includes feedback
• Different methods Discrete/batch
sample remains isolated throughout Continuous
sample introduced into stream * Simpler instrumentation* more efficient
20-12
Flow Injection Analysis
• Samples carried by flow
• Flow can have chromatographic properties Good behavior in
system
20-13
20-14
Diffusion processes