Page 275 - Handbook of Thermal Analysis of Construction Materials

Section 12.0 - Water Reducers/Retarders 255

the type of water reducer. Lignosulfonates decomposed at around 700°C in
oxygen. Three stage decomposition occurred in TG curves. Most lignosul-
fonates gave a common peak in the region of 400–500°C. DTA showed one
endothermic peak and three exothermic peaks.
Sodium salts of gluconic acid and α-glucoheptonic acid indicate
different thermal behaviors from lignosulfonate. [40] An exothermic peak of
large intensity was evident at 710–850°C for gluconate whereas Na α-
glucoheptonate gave an exothermic peak at 800°C.
An extensive investigation was carried out by Milestone on various
types of admixtures by subjecting them to DTA in the presence of oxy-
gen. [41] DTA of admixtures based on lignosulfonates is given in Fig. 25. [41]
Although the overall pattern of the thermograms is similar, no two samples
had exactly the same pattern. Hence, it was concluded that the pattern serves
as a fingerprint for identification of these admixtures. The temperature of
the exotherm, number of exotherms, and the intensity of the exotherms can
be used for differentiating one lignosulfonate from the other.
Hydroxycarboxylic acids and their salts also show characteristic
peaks in the thermograms. It was found that the high temperature exother-
mal peaks (500–700°C) were common for many hydroxycarboxylic acids
salts, but they are absent in pure acids. It was also observed that two
admixtures, supposedly identical, in fact, had different thermal patterns. [41]