Sources of Error in Thermogravimetry

Errors in thermogravimetry can lead to inaccuracy in temperature and weight data. Proper placement of the TGA instrument in the laboratory, away from sources of vibration and heat, is essential to minimize fluctuations in the balance mechanism. Older instruments suffered from an apparent gain in weight of a sample container when heated, known as the buoyancy effect. This effect, due to the decreased buoyancy of the atmosphere. 

Errors in thermogravimetry can lead to inaccuracy in temperature and weight data. Proper placement of the TGA instrument in the laboratory, away from sources of vibration and heat, is 

The TGA mass loss from 50°C to 150°C suggests loss of water in more than one form because of the change in slope seen during the step. The first-derivative DTG plot clearly shows three separate mass losses due to water bound in different forms. [ 1993-2014 PerkinElmer, Inc. All rights reserved. Printed with permission, (www.perkinelmer.com).] (b) Partial TGA (bottom curve) and DTG (top curve) thermal curves for a mixture of hydrated barium, strontium, and calcium oxalates. Erdey et al. (1962) showed that the three hydrated oxalates lost water at three different temperatures. The TGA seems to show only one step, but the DTG clearly shows the three separate losses, one for each salt. 

Placement of the thermocouple is critical to accurate temperature measurement. Ideally, having the thermocouple in the sample itself would give the most accurate reading of the sample temperature. 

IGA and DTG thermal curves showing desorption of basic compounds from the acidic sites of a zeolite catalyst. Losses from weakly acidic sites can be distinguished from strongly acidic sites using the DTG curve, despite the fact that the overall mass loss is only about 1%. The mass scale is on the lefty-axis. (Courtesy of TA Instruments, New Castle, DE, from Thermal Analysis Applications Brief TA-231.) 

The first mass loss at 280°C is due to loss of HCI. [ 1993-2014 PerkinElmer, Inc. All rights reserved. Printed with permission, (www.perkinelmer.com).] 

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The sources of error in thermogravimetry can lead to considerable inaccuracies in the temperature and mass-change data obtained. Accurate thermogravimetry requires that a correction be applied for these errors or that at least some recognition be made of their magnitude. Many of these errors are interrelated and hence cannot be considered separately. Full consideration must be given to all these factors in thermogravimetry. 

The possible sources of error in thermogravimetry are many among them can be listed the following ... 

It should be mentioned that thermogravimetry versus T, or p o suffers from many potential sources of error. This includes buoyancy effects (especially of T and p J, dissolution of H in balance materials such as Pt wires, adsorption of H2O on balance parts (especially cold counterweights) and slow changes and equilibria because H2O and D2O adsorb on apparatus and tubing walls and are changed/exchanged slowly. 

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