3.2 Thermal Analysis of Lithium Chloride
23
is connected to the melting of the dehydrated LiCl. It was further shown that at high
temperatures, molten LiCl is partly hydrolyzed by the atmospheric moisture to form
LiOH which later decomposes into Li 2 O. These two transitions are portrayed by a
solitary endothermic reaction at high heating rates [15]. As a result, the third peak
in the DSC curve of LiCl, detected at 943 °C, is credited to the creation of lithium
oxides, and the fourth peak at 1212 °C is because of the augmented co-evaporation
of lithium oxide and lithium chloride [15].
3.3 Thermal Analysis of the Graphite–LiCl Mixture
The DSC and TG analyses were conducted on 50 mg mixtures of graphite and LiCl.
The experiments were performed at the rate of 80 °C min
−1 under an airflow rate of
100 mL min
−1 , and the results are displayed in Fig. 3.2. The thermographs of the
pristine graphite and LiCl are additionally shown in Fig. 3.2 for the aim of contrast.
The peaks observed on the DSC thermograph of the graphite–LiCl mixture can be
pinpointed by juxtaposing the curves shown in Fig. 3.2. Consequently, the foremost
DSC peak at 135 °C is credited to dehydration of LiCl and the second peak at 641 °C to
the melting of the dehydrated LiCl. It is to be noted that the area under the DSC peaks
conforms to the enthalpy change for the phase transition per mass unit of the sample.
Hence, the height of the peak linked to the melting of LiCl was decreased when LiCl
was diluted by the introduction of graphite (see Fig. 3.2). Likewise, the third and
fourth peaks, at 1047 °C and 1196 °C, can be delegated to the formation of lithium
oxide, and the co-evaporation of lithium oxide and lithium chloride, respectively.
As maintained by Fig. 3.2, the peak associated with the formation of lithium oxide
appeared at a noticeably lower temperature in the graphite–LiCl mixture relatively
with that of LiCl. It should be marked that the formation of lithium oxide is because
of the interaction of the LiCl melt with atmospheric moisture, as seen in Eq. (3.1)
[15]. Despite that, in the graphite–LiCl mixture, the interaction between molten LiCl
and the atmospheric moisture is decreased, which is attributable to the presence of
graphite particles. Consequently, the respective reaction is liable to take place at
higher temperatures.
In agreement with the DSC analysis, the TG thermogram of the graphite–LiCl
mixture, shown in Fig. 3.2, presents a mass loss of 1.8 wt% between 100 and 140 °C,
which is credited to the elimination of hydration water. The major mass loss of 45
wt% transpires between 950 and 1190 °C and is attributed to the evaporation of LiCl.
From looking at the DSC and the TG measurements, it can be noted that the
evaporation of lithium chloride is the sole leading event which happens during the
heat treatment of the graphite–LiCl mixture at higher temperatures. That is to say that
the graphite component was not considerably oxidized, and this behavior is assigned
to a combination of effects, including the oxidation-protective effect of molten LiCl
and the high heating rate employed. The heat-treated powders were studied by various
techniques.
23
is connected to the melting of the dehydrated LiCl. It was further shown that at high
temperatures, molten LiCl is partly hydrolyzed by the atmospheric moisture to form
LiOH which later decomposes into Li 2 O. These two transitions are portrayed by a
solitary endothermic reaction at high heating rates [15]. As a result, the third peak
in the DSC curve of LiCl, detected at 943 °C, is credited to the creation of lithium
oxides, and the fourth peak at 1212 °C is because of the augmented co-evaporation
of lithium oxide and lithium chloride [15].
3.3 Thermal Analysis of the Graphite–LiCl Mixture
The DSC and TG analyses were conducted on 50 mg mixtures of graphite and LiCl.
The experiments were performed at the rate of 80 °C min
−1 under an airflow rate of
100 mL min
−1 , and the results are displayed in Fig. 3.2. The thermographs of the
pristine graphite and LiCl are additionally shown in Fig. 3.2 for the aim of contrast.
The peaks observed on the DSC thermograph of the graphite–LiCl mixture can be
pinpointed by juxtaposing the curves shown in Fig. 3.2. Consequently, the foremost
DSC peak at 135 °C is credited to dehydration of LiCl and the second peak at 641 °C to
the melting of the dehydrated LiCl. It is to be noted that the area under the DSC peaks
conforms to the enthalpy change for the phase transition per mass unit of the sample.
Hence, the height of the peak linked to the melting of LiCl was decreased when LiCl
was diluted by the introduction of graphite (see Fig. 3.2). Likewise, the third and
fourth peaks, at 1047 °C and 1196 °C, can be delegated to the formation of lithium
oxide, and the co-evaporation of lithium oxide and lithium chloride, respectively.
As maintained by Fig. 3.2, the peak associated with the formation of lithium oxide
appeared at a noticeably lower temperature in the graphite–LiCl mixture relatively
with that of LiCl. It should be marked that the formation of lithium oxide is because
of the interaction of the LiCl melt with atmospheric moisture, as seen in Eq. (3.1)
[15]. Despite that, in the graphite–LiCl mixture, the interaction between molten LiCl
and the atmospheric moisture is decreased, which is attributable to the presence of
graphite particles. Consequently, the respective reaction is liable to take place at
higher temperatures.
In agreement with the DSC analysis, the TG thermogram of the graphite–LiCl
mixture, shown in Fig. 3.2, presents a mass loss of 1.8 wt% between 100 and 140 °C,
which is credited to the elimination of hydration water. The major mass loss of 45
wt% transpires between 950 and 1190 °C and is attributed to the evaporation of LiCl.
From looking at the DSC and the TG measurements, it can be noted that the
evaporation of lithium chloride is the sole leading event which happens during the
heat treatment of the graphite–LiCl mixture at higher temperatures. That is to say that
the graphite component was not considerably oxidized, and this behavior is assigned
to a combination of effects, including the oxidation-protective effect of molten LiCl
and the high heating rate employed. The heat-treated powders were studied by various
techniques.