*3.2.2. Characterization of Ni-P-SiC composites*

Figure 3 shows that the values of the thickness of the clarifying layer (∆H) in the upper portion of the aqueous SiCP suspension decreased significantly in the presence of the dispersant and increased over time. The best results were obtained for the highest concentrations of CTAB. During the time period from 0 to 13 h, the ∆H value of the aqueous SiCP suspensions with both 0.08 and 0.10 mM CTAB was only 0.85 mm, whereas for the suspension without surfac‐ tant, ∆H was 48 mm beginning in the first minutes of the experiment. After 20 h, the ∆H value

The greater stability of the SiCPs in the suspension with the dispersant is attributed to the modification of the solid surfaces of the SiC particles via the adsorption of CTAB. Because of its spatial structure and hydrophilic functional groups, CTAB can enhance the electrostatic

of the aqueous SiCP suspension with 0.08 mM CTAB was only 6.92 mm.

**Figure 3.** Effect of DTAB dosage on the clarifying-layer thickness (∆H) as a function of time (0 to 24 h).

*3.2.1. Hull cell studies and electrodeposition of Ni-P-SiC composites*

anodes.

**in solution, on the composition of SiC particles in the matrix Ni-P-SiC composites**

**3.2. Electrodeposition of composite Ni-P-SiC: Influence of the concentration of SiC particles**

A Hull electrochemical cell was used as a first step to find the suitable values of current density that promote uniform coatings of Ni-P-SiC. Prior to the test, an AISI 1018 steel plate was pickled and activated. For pickling, the steel plate was immersed in a 30% HCl solution for 10 s, immediately washed, and then subsequently activated by its immersion in a 10% HCl solution. Immediately after activation, the AISI 1018 steel plate was submerged in a Hull cell containing solution S (= 0.2 M NaCl + 0.65 M NiSO4⋅6H2O + 0.75 M NiCl2⋅6H2O + 0.1 M H3BO3 + 0.1 M H3PO3) + 0.084 mM DTAB + *x* g mL-1 SiC (*x* = 0.00125, 0.0025, 0.005, 0.01, 0.015, or 0.02) (see Figure 4a). Each test was repeated three times for each given SiC concentration. Tests were performed by applying a current of 1 A for 12 min. Ni plates (99%, Atotech) were used as the

repulsion and steric hindrance between SiC particles.

128 Electrodeposition of Composite Materials

Glow discharge spectroscopy (GDS) was used to obtain the elemental composition profiles of Ni-P-SiC coatings obtained from S solutions having different SiC concentrations. The analysis of the sample was performed at successive depths until the substrate (Fe) was reached.

Figure 6 shows a typical composition profile obtained by GDS. The thickness of the coating was approximately 15 μm. At the surface of the coating, a higher concentration of oxygen was present, presumably indicating surface oxidation. After the oxide layer was removed from the surface, Ni, P, Si, and C were observed; in the range of 2.5 to 25 μm, the composition of Ni and P changed slightly as a function of depth, whereas the Si concentration remained constant but increased inside the AISI 1018 steel matrix. Additionally, the oxygen concentration decreased. A similar behavior was observed for all the SiC concentration values tested.

**Figure 6.** Typical GDS elemental composition profiles of Ni-P-SiC coatings electrodeposited at 0.042 mA/cm2 , *t* = 10 min from solutions S (0.2 M NaCl + 0.65 M NiSO4⋅6H2O + 0.75 M NiCl2⋅6H2O + 0.1 M H3BO3 + 0.1 M H3PO3) + 0.084 mM DTAB + 0.02 g mL-1 SiC.

Figure. 7 shows the variation of the SiC content in the coating matrix as a function of SiC concentration in the electrolytic bath. With an increase in SiC concentration in the solution, the concentration of SiC dispersed in the obtained coating increases until a maximum value of 0.6 at.% is reached when a solution with a SiC concentration of 0.015 g/mL is used. With higher concentration values, the percentage of SiC in the coating matrix decreases.

**Figure 7.** Change in the SiC concentration in the Ni-P-SiC coating matrix as a function of the SiC concentration in the solution. Coatings were obtained at 0.042 mA/cm2 , *t* = 10 min.

Figure 8 shows the XRD patterns obtained for Ni-P-SiC coatings having different SiC concen‐ trations in the metallic matrix. The peaks that correspond to different crystallographic orientations of Ni are most prominent. No significant changes were found in the Ni XRD patterns recorded for coatings with different SiC concentrations in the metallic matrix.

**Figure 8.** XRD patterns for Ni-P-SiC coatings with different SiC contents in the metallic matrix that were electrodepos‐ ited onto AISI 1018 steel.
