TGA and DSC

Thermal analysis ○Thermal analysis is a branch of materials science where the properties of materials are studied as they change with temperature. ○Several methods are commonly used--- these are distinguished from one another by the property which is measured:

○Other less common methods measures the sound or light emission from a sample or the electrical discharge from a dielectric material, or the mechanical relaxation in the stressed specimen. ○The essence of all techniques is that the sample’s response is recorded as a function of temperature and time.

○Thermal analysis is also often used as a term for the study of heat transfer through structures. ○Many of the basis engineering data for modeling such systems comes from measurements of heat capacity and thermal conductivity. ○TGA can also give an indication of thermal stability and the effects additives such as flame retardants.

Thermal analysis of polymers ○Polymers represents another area in which thermal analysis finds strong applications. ○Thermoplastic polymers are found in everyday packaging and households items, but for the analysis of the raw materials, effects of the many additive used and fine-tuning of the molding or extrusion processing used can be achieved by using DSC.

Thermal analysis of composite ○Thermal analysis of composite materials such as carbon fiber composites or glass epoxy composites are carried are often carried out using DMA or DMTA, which can measure the stiffness of materials by determining the modulus and damping(energy absorbing) properties of the materials.

Thermogravimetric analysis (TGA)

○TGA is a method of thermal analysis in which mass of the sample is measured over time as the temperature changes. ○This measurements provides information about physical phenomenon, such as phase transitions, absorption and desorption; as well as chemical phenomenon including chemisorption thermal decomposition, and solid gas reactions (e.g. oxidation and reduction)

Instrumentation ○TGA is conducted on an instrument referred to as a thermogravimetric analyzers, which is also known as thermo balance. ○It continuously measures mass while the temperature of the sample changed over time. ○Mass temperature and time in TGA are considered base measurements.

Thermogravimetric analyzer

Different parts of analyzers

Description of TG analyzer ○

○The thermal reaction may occurs under a variety of atmosphere including ○Vacuum ○Inert gas ○Oxidizing/reducing gases ○Corrosive gases ○Vapors of liquids ○Self generated atmosphere

○The data collected from a thermal reaction is complied in a graph form taking mass or percentage of initial mass on the y-axis versus either temperature or time on x–axis. This plot is referred to as a TGA curve.

Experimental conditions ○ Heating rate ○ Purge gas

Heating rate ○

Purge gas ○Nitrogen is the most common gas used to purge sample in TGA due to its inert nature. ○Whereas, helium provides the best baseline.

Applications of TGA ○A TGA can be used for materials characterization through analysis of characteristic decomposition patterns. ○It is especially useful technique for the study of polymeric materials, including thermoplastics, elastomers, composites fibers, coatings, paints and fuels.

Thermal stability ○TGA can to used to find out the thermal stability of a material. ○If a species is thermally stable, there will be no observe mass change. ○TGA also gives the upper use temperature of a material. Beyond this temperature the material will begin to degrade.

Thermally stable ceramics and polymers ○Ceramics usually melt before they decompose as they are thermally stable over a large range of temperature, thus TGA is mainly used to investigate thermal stability of polymers.

Oxidative stability of materials ○Oxidative mass losses are the most common observable losses in TGA. ○Oxidative degradation can occurs in alloys as copper oxides form in atmospheres that are rich in oxygen. ○Study the static oxidation of materials for practical use.

Thermo gravimetric kinetics ○It is used for study of reaction mechanisms of thermal decomposition involved in the pyrolysis and combustion processes of different materials. ○Activation energies of the decomposition process can also be calculated.

Differential scanning calorimeter (DSC)

○It is a thermoanalytical technique in which difference in amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. ○It is used to study thermal transitions of a polymer(the changes that take place on heating)

Principle ○The sample and reference are maintained at same temperature. ○The energy required to maintain to zero temperature difference between the sample and the reference is measured ○During thermal event in a sample, the sample will transfer heat to or fro from the sample to maintain the same temperature in the sample and reference pan.

Study of polymer when heated

○There are two pans, in sample pan, polymers is added while the other, reference pan left empty ○Each pan sits on top of the heater which are controlled by a computer ○The computer turns in heaters, and let the heat the two pans at specific rate, usually 10 Celsius/min. ○The computer makes sure that the heating rate remain same during the experiment.

Applications ○This technique is used to ○observe fusion crystallization events ○as well as glass transition temperature ○Study oxidation