# A High Thermal Conductivity of MgO-H\({}_{2}\)O Nanofluid Prepared by Two-Step Technique
## 3 Results and Discussion
### Stability Measurement of MgO-DW Nanofluid  
The stability of the nano suspension contents in the base medium must be carefully monitored since it has a significant influence on the thermal characteristics. Nanoparticle aggregation may cause precipitation and blockage, hence, decreasing the thermal conductivity of the nanofluid. The zeta potential refers to the quantity of electrostatic repulsion potential presented between the charged nanoparticles and the base fluid. The zeta potential was investigated at various volume concentrations and ultrasonication times of MgO-DW nanofluid, as listed in the Table 5A,B. It can be seen that all the values of zeta potential have a negative sign, due to the adsorption of the OH-ions (negative ions) on the surface of MgO nanoparticles. The states of zeta potential values were determined according to the ASTM standard in Table 2 (experimental part). The specimens in part A were conducted with an ultrasonication time of 90 min. Mostly, the zeta potential values exhibited that as the volume ratios increased from 0.05 to 0.25 vol.%, the ZP values of the synthesized MgO-DW nanofluid decreased from \(-41.0\) to \(-30.3\) mV. This behavior cannot be extended as a general rule, as shown in the 0.15 vol.% MgO nanofluid sample, which recorded a zeta potential value of \(-47.0\) mV. Hence, in the case of this sample, an increase in solid volume concentration did not cause a decrease in the zeta potential value, as shown in other samples.  
Good stability was obtained when the electrostatic repulsion forces overcame the attraction forces such as Van der Waals forces between the MgO nanoparticles. For this reason, this phenomenon could prevent accumulation, therefore, no sedimentation of dispersion nanoparticles occurred within the base fluid. A low zeta potential value was found at 0.25 vol.% MgO-DW nanofluid, which indicated the presence of some clusters or aggregates. However, this sample was moderately stable. All the samples in part B were prepared with a concentration ratio of 0.15 vol.% nanoparticles. It can be seen that ultrasonication time is directly proportional to zeta potential values. Therefore, as ultrasonication time increased from 45 to 180 min, the ZP values of the synthesized MgO nanofluids also increased from \(-38.9\) to \(-62.1\) mV. The portion of nanoparticles that survive in a well dispersed state in nanofluid increases as the ultrasonication treatment period increases, raising the zeta potential values. The last result confirmed the possibility  
\begin{table}
\begin{tabular}{c} **The State** \\ **The State** \\ \end{tabular} \\ \hline
0.05 & \(-41.0\) & Good stability & 45 & \(-38.9\) & Moderate stability \\
0.1 & \(-38.2\) & Moderate stability & 90 & \(-45.0\) & Good stability \\
0.15 & \(-45.0\) & Good stability & 135 & \(-54.7\) & Good stability \\
0.2 & \(-35.7\) & Moderate stability & 180 & \(-62.1\) & Good stability \\
0.25 & \(-30.3\) & Moderate stability & & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Zeta potential analysis of MgO nanofluids prepared using the two-step technique.  
of improving the dispersion stability of the nanofluids via an increasing ultrasonication agitation time. The current findings agree with those reported in [61].