Thermogravimetric analyzer[ edit ] Thermogravimetric analysis TGA is conducted on an instrument referred to as a thermogravimetric analyzer. A thermogravimetric analyzer continuously measures mass while the temperature of a sample is changed over time. Mass, temperature, and time are considered base measurements in thermogravimetric analysis while many additional measures may be derived from these three base measurements.
A typical thermogravimetric analyzer consists of a precision balance with a sample pan located inside a furnace with a programmable control temperature. The temperature is generally increased at constant rate or for some applications the temperature is controlled for a constant mass loss to incur a thermal reaction. The thermogravimetric data collected from a thermal reaction is compiled into a plot of mass or percentage of initial mass on the y axis versus either temperature or time on the x-axis.
This plot, which is often smoothedis referred to as a TGA curve.
The first derivative of the TGA curve the DTG curve may be plotted to determine inflection points useful for in-depth interpretations as well as differential thermal analysis.
A TGA can be used for materials characterization through analysis of characteristic decomposition patterns. It is an especially useful technique for the study of polymeric materials, including thermoplasticsthermosetselastomerscompositesplastic filmsfiberscoatingspaintsand fuels.
Types of TGA[ edit ] There are three types of thermogravimetry: Isothermal or static thermogravimetry: In this technique, the sample weight is recorded as a function of time at constant temperature.
Quasistatic thermogravimetry: In this technique, the sample temperature is raised in sequential steps separated by isothermal intervals, during which the sample mass reaches stability before the start of the next temperature ramp.
Dynamic thermogravimetry: In this technique the sample is heated in an environment whose temperature is changed in a linear manner.
Thermal stability[ edit ] TGA can be used to evaluate the thermal stability of a material. In a desired temperature range, if a species is thermally stable, there will be no observed mass change. Negligible mass loss corresponds to little or no slope in the TGA trace.
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TGA also gives the upper use temperature of a material. Beyond this temperature the material will begin to degrade.
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TGA is used in the analysis of polymers. Polymers usually melt before they decompose, thus TGA is mainly used to investigate the thermal stability of polymers. For example, a combustion reaction could be tested by loading a sample into a thermogravimetric analyzer at normal conditions.
The thermogravimetric analyzer would cause ion combustion in the sample by heating it beyond its ignition temperature. The resultant TGA curve plotted with the y axis as percentage of initial mass would show the residue at the final point of the curve.
Oxidative mass losses are the most common observable losses in TGA. For example, NASA National Aeronautics and Space Administration is conducting research on advanced copper alloys for their possible use in combustion engines. However, oxidative degradation can occur in these alloys as copper oxides form in atmospheres that are rich in oxygen.
Resistance to oxidation is very important because NASA wants to be able to reuse shuttle materials.
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TGA can be used to study the static oxidation of materials such as these for practical use. Combustion during TG analysis is identifiable by distinct traces made in the TGA thermograms produced.
One interesting example occurs with samples of as-produced unpurified carbon nanotubes that have a large amount of metal catalyst present.
Due to combustion, a TGA trace can deviate from the normal form of a well-behaved function. This phenomenon arises from a rapid temperature change. When the weight and temperature are plotted versus time, a dramatic slope change in the first derivative plot is concurrent with the mass loss of the sample and the sudden increase in temperature seen by the thermocouple.
The mass loss could be the result of particles of smoke released from burning caused by inconsistencies in the material itself, beyond the oxidation of carbon due to poorly controlled weight loss. Different weight losses on the same sample at different points can also be used as a diagnosis of the sample's anisotropy.
Generalmente un gas inerte azoto o elio viene utilizzato durante le varie fasi di calibrazione; i flussi vengono controllati e, se necessario, regolati mediante un flussimetroindipendente da quelli eventualmente presenti nel macchinario. Eventuali incrementi nel peso durante l'analisi possono essere direttamente correlati al livello di impurità del gas inerte selezionato. In particolari applicazioni, nelle quali è richiesto un grado di purezza quasi assoluto, è possibile inserire sulla linea delle trappole ad alto rendimento al fine di eliminare i residui di impurità. Tali parametri sono strettamente correlati ai differenti componenti della strumentazione:  quantità di materiale analizzato: idealmente identica per tutte le analisi condotte in una sessione di prove su uno specifico materiale o differenti materiali da confrontare; programma termico utilizzato: in particolare influisce in modo significativo la velocità di riscaldamento; tipologia di crogiolo utilizzato per contenere il campione: si deve tenere in considerazione che anche il materiale con il quale è realizzato il crogiolo, sebbene adatto per resistere alle alte temperature, possiede un'intrinseca inerzia termica.
For instance, sampling the top side and the bottom side of a sample with dispersed particles inside can be useful to detect sedimentation, as thermograms will not overlap but will show a gap between perdita di peso derivato tga if the particle distribution is different from side to side.
For example, the kinetic parameters of the carbonization of polyvinyl butyral were found using a constant mass loss rate of 0.
As the temperature increases, various components of the sample are decomposed and the weight percentage of each resulting mass change can be measured.
Comparison of Thermal gravimetric analysis and Differential thermal analysis techniques: Sr. In DTA the temperature difference between a sample and reference is measured as a function of temperature. The DTA curve shows upward and downward peaks. DTA does not require a change in mass of the sample in order to obtain meaningful information.
DTA perdita di peso derivato tga be used to study any process in which heat is absorbed or liberated.