5.

OTHER TESTING

Thermal Testing: Differential scanning calorimetry, Differential thermal

analysis.

Thermo-mechanical and Dynamic mechanical analysis: Principles,

Advantages, Applications.

Chemical Testing: X-Ray Fluorescence, Elemental Analysis by Inductively

Coupled Plasma-Optical Emission Spectroscopy and Mass Spectrometry.

Thermal Testing

Thermal analysis helps determine if materials are appropriate for the

intended application or use.

By using a model of temperature over time, these methods provide

accurate data about glass transition temperature (Tg), coefficient of linear
thermal expansion (CTE), specific heat, melting temperature, phase
transitions, and more. 

Thermal analysis methods are also useful for:

 Identifying unknown materials

 Molecular structures of crystalline and amorphous polymers

 New composite materials research and development. 

Thermal analysis methods measure physical, mechanical, chemical, and

thermodynamic changes taking place under differing temperatures and
loads, and can pinpoint when and at what temperature significant
changes occur.

Thermal testing includes:

 Differential Thermal analysis (DTA)

 Differential scanning calorimetry (DSC)

 Thermo-mechanical analysis (TMA)

 Dynamic mechanical analysis (DMA)

Differential Thermal analysis (DTA)

A technique in which the difference in temperature between the sample

and a reference material is monitored against time or temperature while
the temperature of the sample, in a specified atmosphere, is
programmed.

The sample and the reference are placed symmetrically in the furnace.
The furnace is controlled under a temperature program and the
temperature of the sample and the reference are changed. During this
process, a differential thermocouple is set up to detect the temperature
difference between the sample and the reference.

Also, the sample temperature is detected from the thermocouple on the

sample side.

Matters that do not change in the measurement temperature range

(usually α-alumina) are used as reference.

When the furnace heating begins, the reference and the sample begin
heating with a slight delay depending on their respective heat capacity,
and eventually heat up in according to the furnace temperature.
 ΔT changes until a static state is reached after the heating begins, and
after achieving stability, reaches a set amount compliant with the
difference in heat capacity between the sample and the reference. The
signal at the static state is known as the baseline.

When the temperature rises and melting occurs in the sample, for
example, the temperature rise stops as shown in graph (a) and the ΔT
increases. When the melting ends, the temperature curve rapidly reverts
to the baseline.

At this point, the ΔT signal reaches the peak, as shown in graph (b).

From this, we can detect the samples transition temperature and the
reaction temperature from the ΔT signal (DTA signal).

In graph (b), the temperature difference due to the sample’s

endothermic change is shown as a negative direction and the
temperature difference due to the sample’s exothermic change is shown
as a positive direction.

Graph (a) shows the temperature change of the furnace, the reference and
the sample against time.

Graph (b) shows the temperature difference (ΔT) against time detected
with the differential thermocouple.

ΔT signal is referred to as the DTA signal.

Differential scanning calorimetry (DSC)

A technique for determining the quantity of heat that is either absorbed or

released by a sample undergoing a physical or a chemical change

Heat Flux DSCs

A technique in which the temperature of the sample unit, formed by a

sample and reference material, is varied in a specified program, and the
temperature difference between the sample and the reference
material is measured as a function of temperature.

Power Compensation DSC

A technique in which amount of power change that is applied to the

sample and the reference material per unit of time is measured as a
function of the enthalpy change to equalize their temperature, while
temperature of the sample unit, formed by the sample and reference
material, is varied in a specified program.
DSC is a commercially available instrument which has two (2) types: Heat
Flux Type and Power Compensation Type. Figure 1 shows the block
diagram of Heat Flux DSC as an example. Heat Flux DSC comprises the
sample and reference holder, the heat resistor, the heat sink, and the
heater. Heat of heater is supplied into the sample and the reference
through heat sink and heat resistor. Heat flow is proportional to the heat
difference of heat sink and holders. Heat sink has the enough heat capacity
compared to the sample. In case the sample occurs endothermic or
exothermic phenomena such as transition and reaction, this endothermic
or exothermic phenomena is compensated by heat sink. Thus the
temperature difference between the sample and the reference is kept
constant. The difference the amount of heat supplied to the sample and the
reference is proportional to the temperature difference of both holders. By
calibrating the standard material, the unknown sample quantitative
measurement is achievable.
DSC enables the measurements of the transition such as the glass
transition, melting, and crystallization. Furthermore, the chemical reaction
such as thermal curing, heat history, specific heat capacity, and purity
analysis are also measurable.
Thermo-mechanical analysis (TMA)

A technique in which a deformation of the sample under non-oscillating

stress is monitored against time or temperature while the temperature
of the sample, in a specified atmosphere, is programmed.

The stress may be compression, tension, flexure or torsion.

The sample is inserted into the furnace and is touched by the probe which
is connected with the Length Detector and the Force Generator. The
thermocouple for temperature measurement is located near the sample.

The sample temperature is changed in the furnace by applying the force

onto the sample from the Force Generator via probe.
The sample deformation such as Thermal Expansion and Softening with
changing temperature is measured as the probe displacement by the
Length Detector. Linear Variable Differential Transformer (LVDT) is used
for Length Detection sensor.

TMA MEASUREMENT MODES

Figure below shows two copper wires with different coating materials

respondi
ng in penetration mode. Graph shows that Wire A is superior than wire B as
wire A has comparatively higher softening and decomposition
temperature.

Dynamic mechanical analysis (DMA)

Dynamic mechanical analysis (abbreviated DMA) is a technique used to

study and characterize materials.

It is most useful for studying the visco-elastic behaviour of polymers.

A sinusoidal stress is applied and the strain in the material is measured,
allowing one to determine the complex modulus.

The temperature of the sample or the frequency of the stress is often

varied, leading to variations in the complex modulus;

This approach can be used to locate the glass transition temperature of

the material, as well as to identify transitions corresponding to other
molecular motions.

TEMPERATURE SCAN – glass transition, crystallization, curing etc...

FREQUENCY SCAN - damping behaviour,

TIME SCAN – creep recovery,

AMPLITUDE SCAN – stress and strain.

How does DMA differ from Thermo-mechanical Analysis?

A Thermo-mechanical Analysis, or TMA, applies a constant static force to

a material and watches the material change as temperature or time varies.

It reports dimensional changes. On the other hand, DMA applies an

oscillatory force at a set frequency to the sample and reports changes in
stiffness and damping.

DMA data is used to obtain modulus information while TMA gives

coefficient of thermal expansion.

Both detect transitions, but DMA is much more sensitive.

WORKING OF DMA

A DMA works by applying a sinusoidal deformation to a sample of

known geometry. The sample can be subjected by a controlled stress or a
controlled strain.
For a known stress, the sample will then deform a certain amount. In DMA
this is done sinusoidally. Deformation of sample is related to its
stiffness. A force motor is used to generate the sinusoidal wave and this is
transmitted to the sample via a drive shaft.

A schematic of the analytic train of the DMA 8000, in Figure. shows its
innovative design that requires neither springs nor air-bearings to support
the drive shaft.
STRESS CYCLES OF DMA

DMA measures stiffness and damping, these are reported as modulus and
tan delta.

Because of application of a sinusoidal force, the modulus is expressed as

an in-phase component, the storage modulus, and an out of phase
component, the loss modulus.

The storage modulus, either E’ or G’, is the measure of the sample’s elastic
behaviour.

The ratio of the loss to the storage is the tan delta and is often called
damping.

It is a measure of the energy dissipation of a material.

 DMA GRAPH

X-ray Fluorescence Spectroscopy

XRF (X-ray fluorescence) is a non-destructive analytical technique used to

determine the elemental composition of materials. XRF analyzers
determine the chemistry of a sample by measuring the fluorescent (or
secondary) X-ray emitted from a sample when it is excited by a primary X-
ray source. So it is a process whereby electrons are displaced from their
atomic orbital positions, releasing a burst of energy that is characteristic of
a specific element.
 There are two main XRF methodologies - energy dispersive (EDXRF) and
wavelength dispersive (WDXRF)

XRF spectroscopy is the technique of analyzing the fluorescent X-rays in

order to gain information on the elemental composition of a particular
material.

The key components of a typical XRF spectrometer are:

 Source of X-rays used to irradiate the sample.

 Sample.
 Detection of the emitted fluorescent X-rays.

The resulting XRF spectrum shows intensity of X-rays (usually in counts

per second) as a function of energy (usually in eV).

There are two main types of XRF spectroscopy. Energy Dispersive XRF
(EDXRF) and Wavelength Dispersive XRF (WDXRF), which differ primarily
in the way the fluorescent X-rays are detected and analyzed. 

Energy Dispersive XRF

An energy dispersive detection system directly measures the different

energies of the emitted X-rays from the sample. By counting and plotting
the relative numbers of X-rays at each energy an XRF spectrum is
generated. 
The principle of the energy dispersive (ED) detector is based on the
generation of electron-hole pairs in a semiconductor material (often
silicon). An incident X-ray, of energy EX, is absorbed by the detector
material, and will cause one or more electron-hole pairs to form. The
energy, to do this is fixed for that particular material.

Once this has occurred, the electrons are pulled off the detector, and the
resulting current is proportional to the number of electron-hole pairs,
which in itself is directly related to the X-ray energy.

This analysis process is repeated at a very high rate, and the results sorted
into energy channels.

Wavelength Dispersive XRF

A wavelength dispersive detection system physically separates the X-rays

according to their wavelengths.

The X-rays are directed to a crystal, which diffracts the X-rays in different
directions according to their wavelengths (energies).

On a sequential system a detector is placed at a fixed position, and the

crystal is rotated so that different wavelengths are picked up by the
detector. The XRF spectrum is built up point by point. In a simultaneous
system, a number of crystal/detector units are used, so that a range of
elements can be detected simultaneously.
INDUCTIVELY COUPLED PLASMA- OPTICAL EMISSION SPECTROMETER

ICP-OES (Inductively coupled plasma optical emission spectrometry) is

also known as Inductively coupled plasma atomic emission spectroscopy
(ICP-AES) is used to detect the trace metals in particularly water dissolved
samples. It uses inductively coupled plasma which excites the ions from the
sample element.

ICP-OES has main two pacts: MCP and Optical spectrometer. Inductively
coupled plasma is produced from the torch which made up from 3
concentric quartz glass tubes. Argon is burned to create the plasma.

A pump transports the aqueous or organic sample to the analytical

nebulizer. The function of this analytical chamber is to convert the sample
into mist and to introduce into the plasma flame. This results into the
collision of the sample with the electrons and it is broken down into
charged ions. This breakdown induces radiation in particular wavelengths
according to the sample element. In next step, the radiated light is
separated into different wavelengths in optical chamber. This light is
measured by a photomultiplier tube which consists of semiconductor
photo detectors (Charged coupled devices' CCDs). These detector arrays
can measure the intensity of all wavelengths which allows analysis of every
element and quick analysis. This intensity is matched and compared with
the known concentration of element which is included in the calibration
curve of the instrument.

The accuracy of the instrument is dependent on the calibration curve

because the intensity from the range of known concentrations will be
matched to the element in the analyte.

INDUCTIVELY COUPLED PLASMA - MASS SPECTROMETRY

The ICP-MS instrument measures most of the elements in the periodic

table.

Most analyses performed on ICP-MS instrumentation are quantitative;

however, it also can serve as an excellent semi-quantitative instrument. By
using a semi-quantitative software package, an unknown sample can be
analyzed for 80 elements in three minutes, providing semi-quantitative
data that is typically within ±30% of the quantitative values.

Samples are introduced into an argon plasma as aerosol droplets. The

plasma dries the aerosol, dissociates the molecules, and then removes an
electron from the components, thereby forming singly-charged ions, which
are directed into a mass filtering device known as the mass spectrometer.
Most commercial ICP-MS systems employ a quadrupole mass spectrometer
which rapidly scans the mass range.

At any given time, only one mass-to-charge ratio will be allowed to pass
through the mass spectrometer from the entrance to the exit. The ions are
separated on the basis of their mass-to-charge ratio and a detector receives
an ion signal proportional to the concentration.

INDUCTIVELY COUPLED PLASMA MASS SPECTRUM