Contents lists available at ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest Short Communication: Analysis Method Significant hidden temperature gradients in thermogravimetric tests Carlos Gracia-Fernández a , Begoña Álvarez-García b , Silvia Gómez-Barreiro b , Jorge López-Beceiro b , Ramón Artiaga b,∗ a TA Instruments-Waters Cromatografía, Alcobendas, 20108, Madrid, Spain b University of A Coruña, EPS, Avda. Mendizábal s/n, 15403, Ferrol, Spain ARTICLE INFO Keywords: Thermogravimetry Temperature gradient Error Simulation ABSTRACT In thermal analysis, correct measurement of temperature is usually ensured by means of a calibration procedure. However, in addition to make sure that the right value of temperature is measured, estimation of temperature gradients into the sample is important. That is especially important in thermogravimetric (TG) analysis, where combinations of some of the common sample sizes heating rates could lead to important differences of tem- perature into the sample. If there is a significant gradient between different parts of the sample, then the temperature of the thermocouple, although correct, does not actually represent the temperature of the whole sample. While the correctness of the temperature is always important, errors in temperature measurement are critical in kinetic studies. Thus, estimations of the temperature gradients that appear into the sample as a result of a given treatment are of highest interest to choose the right operational conditions that minimize that gra- dient. That is particularly important for kinetic studies. In this work, thermal gradients originated into a sample during a typical TG test are estimated through a simulation study performed on the Comsol ™ software. A typical vertical TG furnace, sample size of about 125 mg, and several heating rates were used. Additionally, samples of different void contents were considered. The results of the simulation show that significant gradients of tem- perature can be achieved into the sample with experimental conditions like those that are often used. It is also observed that the difference of temperature between the sample and the furnace wall not only depends on the heating rate, which can be easily corrected by calibration at the corresponding heating rate, but also varies with temperature, which makes highly recommended to calibrate in more than one temperature point when broad ranges of temperature are considered. 1. Introduction Thermogravimetry is a technique that measures the mass of a sample as a function of temperature or time while it is subjected to a controlled temperature program in a controlled atmosphere [1]. The origin and first developments of this technique were thoroughly de- scribed by different authors [2–5]. Most of the early thermobalances were constructed by individual investigators [6], such as Nernst and Riesenfeld [7], Brill [8], Truchot [9], Urbain and Boulanger [10] and Honda [11] at the beginning of the twenty-first century. It is also re- markable the work of Duval [12], who developed an automated ana- lytical method based on thermogravimetry. His work provided a strong impetus for this technique [13]. The first commercial thermobalance appeared in 1945 and it was based on the work of Chevenard [14]. The evolution has been fast from the beginning up to now, and the sensi- bility and precision of the thermobalance were increasing continuously. Nowadays, TG is one of the most common thermal analysis techniques and it is used in many industrial and scientific fields. A clear review of TG and other thermophysical characterization techniques has been provided by K.P. Menard [15]. Temperature calibration is routinely performed in any thermal analysis technique. While there are many works discussing the im- portance of temperature calibration and several standards indicating the right procedures to calibrate temperature of different instruments [16–26], only a few works paid attention to the possible gradients of temperature originated into the sample while subjected to a typical thermo-analytical temperature program [27,28]. Thermal gradients originated into the sample during a typical thermogravimetric (TG) test are estimated here through a simulation study. For the simulation, a typical vertical TG furnace, samples of different porosity and thermal conductivity, and a few of the most common heating rates were used. https://doi.org/10.1016/j.polymertesting.2018.04.039 Received 4 December 2017; Received in revised form 5 April 2018; Accepted 26 April 2018 ∗ Corresponding author. E-mail address: ramon.artiaga@udc.es (R. Artiaga). Polymer Testing 68 (2018) 388–394 Available online 30 April 2018 0142-9418/ © 2018 Elsevier Ltd. All rights reserved. T