The TGA Technique
- TGA measures the amount of weight change of a material, either as a function of increasing temperature, or isothermally as a function of time, in an atmosphere of nitrogen, helium, air, other gas, or in vacuum.
- Thermal gravimetric analysis can be interfaced with a mass spectrometer RGA to identify and measure the vapors generated, though there is greater sensitivity in two separate measurements.
- Inorganic materials, metals, polymers and plastics, ceramics, glasses, and composite materials can be analyzed.
- Temperature range from 25°C to 900°C routinely. The maximum temperature is 1000°C.
- Sample weight can range from 1 mg to 150 mg. Sample weights of more than 25 mg are preferred, but excellent results are sometimes obtainable on 1 mg of material.
- Weight change sensitivity of 0.01 mg.
- Samples can be analyzed in the form of powder or small pieces so the interior sample temperature remains close to the measured gas temperature.
Applications of Thermogravimetry
- Determines temperature and weight change of decomposition reactions, which often allows quantitative composition analysis. May be used to determine water content.
- Allows analysis of reactions with air, oxygen, or other reactive gases (see illustration below).
- Can be used to measure evaporation rates, such as to measure the volatile emissions of liquid mixtures.
- Allows determination of Curie temperatures of magnetic transitions by measuring the temperature at which the force exerted by a nearby magnet disappears on heating or reappears on cooling.
- Helps to identify plastics and organic materials by measuring the temperature of bond scissions in inert atmospheres or of oxidation in air or oxygen.
- Used to measure the weight of fiberglass and inorganic fill materials in plastics, laminates, paints, primers, and composite materials by burning off the polymer resin. The fill material can then be identified by XPS and/or microscopy. The fill material may be carbon black, TiO2, CaCO3, MgCO3, Al2O3, Al(OH)3, Mg(OH)2, talc, Kaolin clay, or silica, for instance.
- Can measure the fill materials added to some foods, such as silica gels and titanium dioxide.
- Can determine the purity of a mineral, inorganic compound, or organic material.
- Distinguishes different mineral compositions from broad mineral types, such as borax, boric acid, and silica gels.
ASTM Test Methods Using Thermogravimetric Analysis
- ASTM D2584 – Standard Test Method for Ignition Loss of Cured Reinforced Resins
- ASTM E1131 – Standard Test Method for Compositional Analysis by Thermogravimetry
California Department of Pesticide Regulation Tests:
We have a web page dedicated to this test here.
Inquiries specifically about TGA analyses should be directed to Kevin A. Wepasnick, Ph.D. by phone or at e-mail address: email@example.com
Illustrative Example: Determination of weight % of composite material components
Thermogravimetric analysis was used as one of several complementary techniques in the identification of an unknown polymer composite, which microscopy revealed had fiberglass content. XPS identified the composition of the fiberglass and revealed the presence of CaCO3 as residues of a lower temperature TGA run than the high temperature run shown below. FTIR indicated a polymer consisting of polyester and, probably, polystyrene. TGA was then performed on the material to find the weight percent of each material. The sample was heated from room temperature to 900°C at a rate of 5°C/min in air. The TGA curve (below) is labeled in terms of the identity of the components. Here polyester (71% of the polymer), polystyrene (29% of the polymer), fiberglass (22.9% of the whole) and CaCO3 (49.3% of the whole) were easily identified by their different temperatures of combustion or evaporation. The combustion of the styrene polymer component produced enough energy that the temperature momentarily increased more than the programmed rate, which accounts for the unusual shape of the curve due to the cooling that followed the reactive overheating. The remaining material after the TGA analysis was completed was confirmed by XPS to consist only of CaCO3. The results obtained for the polymer matrix match the common blend co-polymer of 70% polyester and 30% polystyrene by weight.