**5. Results and discussion**

Ferrochrome slag is obtained as waste material during production of ferrochrome alloy in a smelter. Pouring temperature of Slag is around 1500°C. The slag contains oxides of magnesium, iron and chromium in their different oxidation states. Chromium present in the slag may either be trivalent (+3 oxidation state) and or hexavalent (+6 oxidation state). Some elemental chromium may also be present in the slag. The oxides are usually spinel phase (*i.e.* FeCr2O4). MgAl2O4 spinel phase is also there in the slag. Presences of these spinel phases help the slag to enhance mechanical, chemical and thermal properties both at ambient and elevated temperatures [27, 28]. **Table 1** depicts chemical analysis of ferrochrome slag. It is evident that SiO2, Al2O3, Fe2O3, and Cr2O3 are present in major quantities, while CaO, MgO, FeO are present in a minor quantities [29]. The ground and sieved (240 meshes) of as-received slag is dried for 2 h at 120°C for removal of moisture. The sieved HCFC slag is ready for Geopolymer preparation.

Geopolymer samples are made by treating with different molar concentration of sodium hydroxide (NaOH). Effect of different molar concentration of alkali materials on the compressive strength is studied. The strength properties of asprepared Geopolymers are shown in **Figure 3**. S1, S2, S3, S4 represent Geopolymer prepared with 6 M, 8 M, 10 M, and 12 M solution of NaOH, respectively. These are cured at 70°C in an oven, followed by 7-days and 24-days of curing in air. It is well known that sodium plays an important role for polymerization of alumina (Al2O3) and silica (SiO2), which is present in the slag. Each pair of bar drawn in **Figure 3** is

#### **Figure 3.**

*Compressive strength vs. molar concentration at 7-days and 28-days air curing of HCFC slag based GP samples prepared by optimized parameters [23].*

showing data on comparative strength scale for a Geopolymer prepared with different molar concentration, cured for 7 days and 28 days, respectively. It is found that maximum compressive strength has been achieved for the Geopolymer prepared with 8 M NaOH concentration [30–33].

**Figure 4A** and **B** show superimposed XRD pattern obtained from two different types of samples i.e., prepared with as-received HCFC slag (**Figure 4A**) and geopolymer prepared with optimal treatment combination (**Figure 4B**). Sharp XRD peaks can be seen in XRD pattern of as received slag (**Figure 4A**), whereas broaden peaks can be seen in geopolymer prepared with optimal treatment combination. It can infer that the slag material has crystalline phases and geopolymer has non-crystalline glassy phases. Sharp peaks in the as received material are identified to be quartzite and mulite phases, whereas broaden line profile of XRD pattern of geopolymer are glassy phases formed chemical and thermal treatment.

The morphology of HCFC slag and GP samples prepared with optimal treatment combination is studied (**Figure 5A** and **B**). **Figure 5A** shows SEM micrograph of HCFC slag which consists of fused mass of oxides with some glassy phase spread over the matrix. Since the slag material is poured from a high temp to a room temperature, therefore, faster cooling rate results. **Figure 5B** is a magnified image of Geopolymer as shown in the earlier slide. The picture shows morphology of Geopolymer prepared with optimal treatment combination. At lower magnification *i.e.,* 500 KX, it shows crystalline needle shape phase oriented in a random direction (**Figure 6B**). Additionally, there is some region of glassy phase co-exist together with the crystalline phase. The sample, therefore, is further investigated at a higher magnification *i.e.,* 1500 KX (**Figure 5B**). **Figure 5C** shows the bundles of rodshaped phase oriented in the same direction. This crystalline phase has occurred due to cross-linking of alumino-silicate Geopolymer phase by reacting with the sodium of sodium hydroxide [34]. EDS analyses are done during the SEM studies (**Figure 7**). The elements such as Na, O, Al, Ca, Mg, Cr are present both in crystalline and glassy phases of as-prepared HCFC slag based GP (**Figure 7B**). However, all the elements present in GP are found in as-received slag except element such as sodium (**Figure 7A**). Occurrence of element sodium in GP is due to the reaction sodium compound with slag during polymerization process.

#### **Figure 4.**

*XRD pattern of grinded with sieved as received HCFC slag (A) and as-prepared HCFC slag GP prepared by optimized parameters [23].*

*Synthesis and Characterizations of High Carbon Ferrochrome (HCFC) Slag Based Geopolymer DOI: http://dx.doi.org/10.5772/intechopen.97140*

**Figure 5.**

*SEM images of grinded with sieved of as-received HCFC slag (A), slag based GP samples prepared by optimized parameters [23].*

**FTIR spectra** of the slag and GP material are shown in **Figure 6**. FTIR spectra indicate the presence of different absorption bands in each category of material. **Figure 6A** indicates the presence of different absorption bands occurring at different wave numbers *i.e.*, 3441, 2918, 1638, 1442, and 887 cm−1. Bands are in agreement with stretching vibrations of O-H bonds (3441 cm−1 wave number) and H-O-H bending vibrations (1638 cm−1 wave number) of interlayer adsorbed H2O molecule [35]. The hydroxyl-stretching band of water plays an important role and peak shift of the FTIR spectra is significant. Absorption band ensue at 887 cm−1 wave number is attributed to Si-O band and signifies the occurrence of silicate groups. Presences of Al3+O2− absorption bands are also indicated near 805 cm−1 wave number [35]. Stretching bands is found at 440 cm−1 wave number and signifies the occurrence of Fe-O band [36]. However, the absorption bands are not found to occur in asreceived HCFC slag. This is due to the formation of Geopolymer after treating and curing of as-received HCFC slag.

#### **Figure 6.**

*FTIR spectra of grinded with sieved as-received HCFC slag (A) and HCFC slag based GP prepared from optimized parameters (B) [23].*

#### **Figure 7.**

*EDS of grinded with sieved of as-received HCFC slag (A) and slag based GP samples prepared (B) by optimized parameters [23].*

In TGA analysis, the weight loss is estimated for different temperature, ranging between 50 and 800°C and data are plotted as shown in **Figure 8**. **TGA runs** are taken from two samples, HCFC slag and GP. There is a sharp decrease in weight percentage beyond 100°C. This is attributed to the loss of water molecules. Between 100 to 350°C, there is a rapid declination the curve. Beyond 350°C, a little change is observed. The average total loss in weight (%) increases and decreases within the range of temperature 350–700°C [37, 38].

Differential scanning calorimetry (DSC) studies are made for both the samples i.e. HCFC slag and the GP formed it. It may be observed that there is no change in heat flow for slag (**Figure 9A**) whereas; there is significant change in heat flow for GP made from slag (**Figure 9B**) at 141°C. This is due to expulsion of physically bound water within the GP materials [39].

*Synthesis and Characterizations of High Carbon Ferrochrome (HCFC) Slag Based Geopolymer DOI: http://dx.doi.org/10.5772/intechopen.97140*

#### **Figure 8.**

*TGA curve of grinded with sieved as-received HCFC slag (A) and HCFC slag based GP prepared with optimized parameters (B) [23].*

#### **Figure 9.**

*DSC isotherm of grinded with sieved as-received HCFC slag (A) and HCFC slag based GP prepared with optimized parameters [23].*

### **6. Conclusions**

Geopolymers are prepared from HCFC slag successfully by treating with the alkali materials. The structure and morphology of Geopolymer are studied using different characterization technique. The microstructure of Geopolymer shows needle-shaped, randomly oriented crystalline phase, embedded in glassy phases. Together with microstructural observation, SEM/EDS analyses show presence of alkali materials in the Geopolymer which indicates occurrence of reaction of the HCFC slag with alkali solution during the Geopolymerization process. The

maximum compressive strength is obtained to be 15 MPa by curing at 70°C in an oven for 24 h followed by cooling for 28-days in air. XRD pattern has clearly shown conversion of crystalline phase present in the slag has been transformed to glassy phase during the formation of Geopolymer. There is a marked difference observed in the FTIR spectrums. The numbers of peaks of as-prepared samples are much more in comparison to peaks present in as-received samples. This is due to formation of new bonds within the phases. TGA curves have revealed, for both the materials there is a gradual degradation material in the temperature range studied. DSC results show that there is a exothermic peak in Geopolymer at 150°C. This is due to elimination of water during condensation polymerization process occurring in the geopolymer.
