What are the most important termical properties (from a technologycal viewpoint)?
thermal expansion
heat capacity
thermal conductiviy
thermal diffusivity
characteristic thermal transitions
Describe the dilatometric measurement. When is it called thermodilatometric?
A thermomechanical analysis, in which a sample is heated and the expansion is measured either optically or by a push rod, which can also exert a pressure. If the pressure is 0 the technique is called thermodilatometry.
How can the effect of thermal expansion be explained qualitativley?
The vibration around the initial radius C causes the mean radius to shift and grow, which results in thermal expansion.
How are the linear and volumetric thermal expansion coefficients defined?
What are the ranges of the thermal expansion coefficient?
Why is a change in thermal expansion difficult?
Because it is bond dependant. Change in thermal expansion needs change in large amount of composition.
What is the problem about a high missmatch in thermal expansion?
High thermal stresses develop at the interfaces.
How is the temperature change described in the literature?
percentage valueof the length expansion
What are the two methods for measuring the thermal expansion?
Optical analysis
Push rod analysis
How is the heat capacity defined?
A factor to relate the absorbed heat with the change in temperature.
What are the two ways of measuring heat capacity?
For constant volume or constant pressure.
How is the heat capacity calculated?
How is the function for heat capacity normally fitted?
Logharithmically:
How is the thermal conductivity defined?
Out of which components consists the thermal conductivity?
vibrational waves (quants=phonones)
electric contribution
How is the thermal conductivity factor k calculated for pure crystalline materials?
A, B = constants
How is the thermal conductivity factor k calculated for amorphous materials?
C, D = constants
How is the thermal conductivity factor k calculated for a combination of crystalline and amorphous materials?
A, B, C =constants
What are additional modifiers for the polymer thermal conductivity?
molecular weight distribution
crystallite orientation
degree of crystallinity
macromolecule size
thermo-mechanical history
What is the relation between electrical and thermal conductivity in metals? Name the equation.
k= thermal conductivity
sigma= electrical conductivity
Wiedmann-Franz law
Is thermal energy transferred by phonons or electrons in pure metal?
electrons
How is the function for the thermal conductivity factor fitted?
What are methods for thermal conductivity measurement?
Thermoflussimetry
material between warm and cold plate. Heat needed for cooling measured
Laser Flash analysis (LFA)
laser shot onto target sensor measures the diffusivity of the heat.
Hot disk
resistance heater is immerged in sample. Disscipated heat measured
How is the thermal diffusivity defined?
What are the different thermal property measurement methods?
Differential Thermal analysis
Differential Scanning Calorimetry
Thermo Gravimetric Analysis
Dynamic Mechanical Thermal analysis
Heat deflection temperature
How does differential thermal analysis function?
a atmosphere is heated in which the samples change in temperature is compared to a reference sample.
What is the optional parameter than can be applied besides temperature variations in the differential thermal analysis?
Pressure variations
How does differential scanning calometry work?
Temperature difference between two simultaniously heated probes is detected. The heat flow can be obtained from the difference in thermal power that needs to be supplied to the sample.
How do the Temperature change and the heat flow correlate?
They are proportional.
How can the Enthalphy be measured in the differential scanning Calorimetry?
The adiabatic conditions in the measurement lead to a equivalency of heat flow and enthalphy change.
What is concretely measured in the Heat flux Differential scanning calorimetry?
The deviation fron the furnace temperature delta T
What are the advantages of power compensated differential scanning calorimetry?
individual controllers of thermal power, which enables to heat without temperature difference.
Advantages:
quicker response
better adjustable heating rate
more suitable for heat capacity measurements
Which effect needs to be considered during the calibration of the differential scanning calorinmeter?
the effect of thermal inertia (delay in demperature change due to volumetric temperature change)
What is the most common application of the differential scanning calorimeter?
Detection of transition temperatures (glass, crystal, melting)
What is the difference in temperature modulation between Temperature modulated differential scanning calometry (TMDSC) and differential scanning calometry (DSC)?
In TMDSC the temperature exitation is performed in a sinusoidal fashion. (vs.linear in DSC)
How is the temperature change described in differential scanning calometry (DSC)?
How is the temperature change described in Temperature modulated differential scanning calometry (TMDSC)?
beta= linear growth component
At= amplitude
omega= frequency
What are the advantages of Temperature modulated differential scanning calometry (TMDSC)?
seperation of complex transitions into more easily interpretable ones
more accurate measurement in semicrystalline materials
improved resulution
improved sensitivity
thermal conductivity measurement
determination of heat flow & heat capacity
How is the heat flow described in Temperature modulated differential scanning calometry (TMDSC)?
individual measureing of both components
reversing heat flow= heat capacity component
non reversing heat flow= kinetic(time dependant) component (arithmethic differnce)
What is measured in Thermogravimetric (TGA) analysis?
TGA measures the mass change over temperature.
What is the name of the first derivation of the Thermogravimetry analysis curve?
Differential thermogravimetry curve.
What types of atmospheres can be used in thermogravimetry?
inert
oxidizing
static
dynamic
What are materials for thermogravimetric testing crucibles?
Al2O3, Pt/Rh, Al
Which information can be obtained by adding a gas analysis to the thermogravimetry analysis?
Information about composition and individual gas fingerprint
What is measured in dynamicall mechanical thermal analysis (DMTA)?
Stress behaviour under thermal influence.
Measured: deformation, temperature
Explain the Vicat Softening Temperature measurement.
Temperature at which a flat needle of 1 mm^2 penetrates 1mm into the material.
Penetration depth over temperature measured.
Explain the heat deflection measurement.
A probe is heated (in an oil bath) while a fixed force pressure is applied in a three point bending manner.
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