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3 Experimental Methods in Characterization of Nanosystems
an integral effect of the entire annealing process). The reason why it is called a
differential analysis method is that the devices that can measure the heat effect of the
process are equipped with two identical sample holders. One of the sample holders
(or chambers) contains the sample to be tested, and the other is loaded with an equal
portion of standard material for comparison that does not undergo any transformation
upon annealing. The temperature of both sample holders is recorded as the device is
annealed. The temperature measurement is usually made with thermocouples. Since
the heat effect of the transformation taking place in the sample causes a deviation
in temperature as compared to the standard, it can be compensated by modulating
the heating programs in order to equilibrate the temperature of the sample holder
pair (differential scanning calorimetry, DSC). What is measured is the compensation
heating power that directly yields the excess energy absorbed/released during the
annealing process. Since practically no transformation takes place instantaneously,
the key parameters established are the onset temperature of a process and the integral
heat effect of the transformation that belongs to a peak (wave). The faster the heating
rate, the wider the temperature range over which the thermal peak of the same process
is smeared out.
Annealing processes are often accompanied with a weight change, too, when the
sample has a gas emission during a decomposition process. The weigh change can be
measured by observing the weight of the solid residue of the sample, often in parallel
to the recording of the heat effect. The correlation of the weight loss (gain) and the
heat effect is a tool of high performance to identify the processes taking place.
There are various ways to analyse the emission product accompanying the
annealing processes. Devices that can be attached to the outflow of a thermal analysis
instrument include chromatographs and mass spectrometers. Neither of the abovementioned devices can perform an absolute quantitative analysis, although their relative signal intensities can be calibrated. Nevertheless, the information yield of such
an analysis refers primarily to the quality of the gas released.
A fully quantitative analysis during a heat treatment is much easier if the product
to be released is a one-component material and its quality is well known. This is
the case when the absorbed hydrogen is emitted upon annealing. Degassing devices
designed to rate hydrogen emission are calibrated with heat conductivity detectors
since they are very sensitive to light molecules appearing beside a heavier carrier gas
(mostly argon). With this method, hydrogen solubility can be measured.
3.4 Mechanical Tests
Four major forms of mechanical tests are noteworthy of mentioning here: tensile,
hardness, wear and adhesion tests. Tensile tests are exact in the sense that coefficients
defined in physical formulae can be derived from them, but the other three test
methods are based on conventions and are more comparative.
3 Experimental Methods in Characterization of Nanosystems
an integral effect of the entire annealing process). The reason why it is called a
differential analysis method is that the devices that can measure the heat effect of the
process are equipped with two identical sample holders. One of the sample holders
(or chambers) contains the sample to be tested, and the other is loaded with an equal
portion of standard material for comparison that does not undergo any transformation
upon annealing. The temperature of both sample holders is recorded as the device is
annealed. The temperature measurement is usually made with thermocouples. Since
the heat effect of the transformation taking place in the sample causes a deviation
in temperature as compared to the standard, it can be compensated by modulating
the heating programs in order to equilibrate the temperature of the sample holder
pair (differential scanning calorimetry, DSC). What is measured is the compensation
heating power that directly yields the excess energy absorbed/released during the
annealing process. Since practically no transformation takes place instantaneously,
the key parameters established are the onset temperature of a process and the integral
heat effect of the transformation that belongs to a peak (wave). The faster the heating
rate, the wider the temperature range over which the thermal peak of the same process
is smeared out.
Annealing processes are often accompanied with a weight change, too, when the
sample has a gas emission during a decomposition process. The weigh change can be
measured by observing the weight of the solid residue of the sample, often in parallel
to the recording of the heat effect. The correlation of the weight loss (gain) and the
heat effect is a tool of high performance to identify the processes taking place.
There are various ways to analyse the emission product accompanying the
annealing processes. Devices that can be attached to the outflow of a thermal analysis
instrument include chromatographs and mass spectrometers. Neither of the abovementioned devices can perform an absolute quantitative analysis, although their relative signal intensities can be calibrated. Nevertheless, the information yield of such
an analysis refers primarily to the quality of the gas released.
A fully quantitative analysis during a heat treatment is much easier if the product
to be released is a one-component material and its quality is well known. This is
the case when the absorbed hydrogen is emitted upon annealing. Degassing devices
designed to rate hydrogen emission are calibrated with heat conductivity detectors
since they are very sensitive to light molecules appearing beside a heavier carrier gas
(mostly argon). With this method, hydrogen solubility can be measured.
3.4 Mechanical Tests
Four major forms of mechanical tests are noteworthy of mentioning here: tensile,
hardness, wear and adhesion tests. Tensile tests are exact in the sense that coefficients
defined in physical formulae can be derived from them, but the other three test
methods are based on conventions and are more comparative.