Electrodeposition and Surface Finishing by Stojan S. Djokić

Author:Stojan S. Djokić
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

The TG curves of the non-sintered HAP/Lig coatings containing 0.5, 3, and 10 wt% Lig, obtained in the temperature range between 25 and 1,000 °C, are shown in Fig. 3.59a, where three stages can be distinguished. The first stage was observed from 25 to 200 °C with sharp peaks on the DTG curves at 53, 55, and 63 °C for coatings with 0.5, 3, and 10 wt% Lig, respectively (Fig. 3.59b). This stage corresponds to desorption of water molecules adsorbed on the surface of the crystallites of the HAP/Lig coatings [28]. The second stage of weight loss of the TG curves was observed between 200 and 600 °C, with sharp peaks on the DTG curves at 227, 239, and 256 °C, which correspond to the thermal decomposition of lignin [163, 198]. The peaks at DTG curves at around 353, 383, and 392 °C (Fig. 3.59b) can be attributed to dehydroxylation of HAP. The third stage of weight loss of the TG curves was observed between 600 and 1,000 °C without distinguishable peaks on the DTG curves. This phase could still be attributed to dehydroxylation or to the early slow decomposition of HAP and of the remaining lignin. The total weight loss in the temperature range of 25–1,000 °C was 6, 7.5, and 11.8 wt% for the coatings containing 0.5, 3, and 10 wt% Lig, respectively, suggesting that increasing lignin concentration decreased the thermal stability of the HAP/Lig coatings. In other words, increasing HAP concentration increased the thermal stability of the HAP/Lig coatings.

Fig. 3.59TG curves (a) and differential TG (DTG) curves (b) of non-sintered HAP/Lig coatings with: 0.5, 3, and 10 wt% Lig (reprinted from [2] with permission from Elsevier)

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