Differential thermal analysis (DTA) determines the temperature at which thermal reactions, such as phase transformation and thermal decomposition, take place in a material when it is heated continuously to an elevated temperature, and also the intensity and general characters
(endothermic or exothermic) of such reactions (Speyer 1994).
In contrast, thermogravimetric (TG) analysis
determines the weight gain or loss of a material (e.g.,
minerals, glasses, ceramics, polymers) due to absorption
or gas release as a function of temperature. DTA and TG
curves of the talc sample are shown in Figures 7a and 7b. The
DTA and TG curves indicate different temperature ranges
at which the mass losses accompanying 4 endothermic
reactions occurred. On the DTA curve of the talc- and
chlorite-bearing actinolite (E-1) and chlorite-bearing
talc (E-3) samples, endothermic peaks were observed
in the temperature ranges of 500–600 °C and 760–780
°C (Figure 7a), and hence mass loss (Figure 7b) resulted
from the dehydroxylation reaction of chlorite (Nkoumbou
2006). It was observed that these endothermic peaks
disappeared with increasing talc contents in the samples.
The endothermic peak of pure talc samples (with 95 wt.%
talc content) at a temperature of 895 °C and mass loss
indicate transformation of talc to enstatite (MgSiO3
) and
silica minerals (SiO2
) (Nkoumbou 2006). The endothermic
peak observed for sample E-1 (containing about 70%
actinolite) around 1220 °C resulted from deformation of
the crystal structure of actinolite (Taboadela & Aleixandre
Ferrandis 1957). The highest mass loss occurred in sample
E-3, which probably resulted from calcite content. Mass
loss (~5 wt.%) occurred in sample E-3 between the
temperatures of approximately 650 and 800 °C, and this
resulted from CO2
gas that was removed from the structure
after the thermal decomposition of calcite. Consistent with
this, on the DTA curve of the same sample, endothermic
peaks from 760 to 895 °C confirm this situation. Similar
results were obtained in thermal analyses performed using
various solids containing pure calcite (Hristova & Jancev
2003; Hojamberdiev et al. 2008). The total mass loss values
of the samples (Figure 7b) are corroborated by the loss on
ignition yielded by the chemical analysis (Table 2).