Issue 50

Q. Hu et alii, Frattura ed Integrità Strutturale, 50 (2019) 638-648; DOI: 10.3221/IGF-ESIS.50.54 642 Figure 3 : Morphologies of specimens before and after resistance-heating treatment TG/DSC TG/DSC analysis enables identifying of temperature-dependent characteristics of the granite. The TG and DSC curves are given on the common figure (Fig. 4). The TG curve shows the variation of mass as a function of temperature, and the DSC curve shows the amount of heat applied as a function of temperature. In course of the run, the maximum mass loss of approximately 0.21 % is detected at 664 °C, which is visible on the TG curve. This might be attributed to the multiple processes of water loss as temperature increased. The evaporation of free water takes up 0.06 % and the most of rest (0.15 %) is possibly related to the mineralogical variation. Seeing the wide endothermic band around 300 °C, it is perhaps induced by the iron mineral transition, e.g. the decomposition of goethite to form haematite at 300 °C [24]. Besides, it also can be due to pyrolysis of the organic matter. The slope variation on the TG curve for temperature between 350 °C and 400 °C, probably express the accomplishment of organic reaction. However, the specific reaction cannot be confirmed due to the complex composition of granite. For the temperature in excess of 400 °C, the dehydration and further dehydroxylation of biotite probably results in the further mass decline according to Labus and Lempart [25]. For temperature greater than 664 °C, the re-increase of TG curve may be due to the oxidation of some minerals in air atmosphere. In addition, the small endothermic peak representing α-β quartz phase transition at 573 °C is detected [19], which is visible on the DSC curve. This transition is accompanied by approximately 5 % of volume expansion which can induce numerous micro-cracks around the grain of quartz [26]. Figure 4 : TG-DSC patterns obtained from Danfeng granite