**3. Results and discussion**

The results of contact angle measurement are represented in **Table 1** and plotted against FeO content of slag in **Figure 4**. Data from the sources [8, 9] were approximated by the curves and also represented in **Figure 4** (for the data from [8] molar concentration was converted to mass concentration). As can be observed from **Figure 4**, slags with higher FeO content exhibit substantially lower contact angles with iron: Increase of FeO content from 28 to 62% is followed by fivefold drop in contact angle. The obtained results are generally consistent with the trends reported in literature [8, 9]. At the same time, it is interesting to mention that, as seen from **Figure 5**, surface tension of the slag slightly grows with the increasing of FeO content (data were calculated using the spreadsheet available from [13], representing modified partial molar method developed by Mills [16]). Such discrepancy might be explained by better wetting of the solid iron surface (due to chemical interaction of FeO and iron) at higher FeO content, which offsets the slight increase of surface tension.

Although, both in our experiments and in studies of the other authors, contact angle decreases with the increased FeO content in slag, our data show substantially higher values of contact angle for the comparable slag compositions (e.g., around 28% FeO). This difference can be explained by higher temperatures of measurement, applied in the referred studies [8, 9].

*Wetting of Solid Iron by Molten FeO-Containing Slag DOI: http://dx.doi.org/10.5772/intechopen.110701*

**Figure 5.** *Surface tension calculated using method of Mills [13] versus FeO content in slag.*

#### **Figure 6.**

*Contact angle versus slag basicity. Slags compositions presented in* **Table 1** *are grouped here according to crystallization fields as follows: 1, 2 and 3—wollastonite; 4 and 5—eutectic valley between olivine and wollastonite; 7 and 8—olivine; 6 and 9—Wüstite.*

At the first sight, the experimental data for dependency of the contact angle upon the slag basicity are substantially scattered; however, as demonstrated in **Figure 6**, after the slags are grouped by the FeO content, it is possible to observe that, for the slags with FeO content of 28% and 46%, the increased basicity enhances wettability of the iron (contact angle decreases). On the contrary, for the slags with 62% FeO, contact angle increases with the increased basicity. Such ambivalent influence of CaO might be explained by the surface tension increase. A similar effect was previously reported by Kozakevitch [17] who studied surface tension of various slag mixes-addition of CaO to pure FeO is initially followed by surface tension's decrease; however, after CaO content in binary FeO-CaO melt reaches approximately 15%, surface tension starts increasing. Our slags with 62% FeO content may follow the behavior of the FeO-CaO binary system. Grouping of the slags by the crystallization fields in the ternary phase diagram (also demonstrated in **Figure 6**) shows that the

wetting conditions in the studied system can be efficiently controlled by tuning the slag composition and adjustment of the reduction degree of iron ore material (resulting in certain FeO content in slag).

In the study of Iguchi et al. [8], increase of the slag basicity was followed by increased contact angle; however, analysis of their data shows that the contact angles for the CaO-SiO2-FeO slags with the basicity ratios (CaO/SiO2) of 1.0 and 1.1 (both from the Wollastonite crystallization field) are higher when compared to the slag with the basicity of 0.5 from the Tridymite crystallization field. Therefore, it is possible to presume that the effect of slag basicity on the wettability of solid iron is rather complex and depends upon FeO content in the slag and other parameters of slag composition.

As discussed above in the introduction, wetting conditions between FeO-rich primary slag and the freshly reduced iron sponge determine iron carbonization and its intake of sulfur and silicon. Therefore, the obtained results might be used to develop a method for controlling the composition of metallic phase by tuning the composition of iron ore material and the regime of reduction. In our further studies, we aim to reveal the primary slag compositions (FeO content and basicity) favorable for limiting the transfer to the iron sponge of such elements as silicon, sulfur and probably even phosphorus (the latter under the blast furnace conditions is by 100% reduced to the hot metal), which might be applied for developing of a novel ironmaking method.

**Table 2** outlines the expected aspects of such novel technology in comparison with blast furnace (major ironmaking technology within an integrated steelmaking route), Midrex® (major technology in relevant segment of integrated steelmaking) producing Direct Reduced Iron/Hot Briquetted Iron (DRI/HBI) and ITmk3® (one


#### **Table 2.**

*Parameters of product in ironmaking technologies.*

*Wetting of Solid Iron by Molten FeO-Containing Slag DOI: http://dx.doi.org/10.5772/intechopen.110701*

of the alternative ironmaking technologies, commercialized in 2010, so far at a single plant). As shown in **Table 2**, we expect that thermodynamic conditions of iron ore reduction can be adjusted to prevent carbonization of metallic phase as well adsorption of silicon, sulfur and phosphorus. Certain losses of iron with FeO-containing slag are an unavoidable aspect of such approach to some extent, and this can be considered as a rebirth of an ancient bloomery process but on a current technology control level. However, we believe that novel technology should have competitive advantages to offset this drawback. Such advantages include


Certainly, the precise aspects and, needless to say, technological layout of the proposed concept are yet to be considered in our further research where study of the wettability phenomena should play substantial role.
