Optimized NaOH and KOH treatments for interfacial and mechanical enhancement of agro-marine ash reinforced aluminum composites

A systematic comparative study evaluated NaOH and KOH alkali activation of three agro-marine ashes (periwinkle shell powder, plantain stem ash, eucalyptus wood ash) as reinforcements for AA6061 aluminium matrix composites. Treatments were performed at 4 M and 30-120 min and characterized by SEM, EDS, BET, XRD, FTIR, cyclic voltammetry, and statistical modelling (regression, ANOVA). NaOH produced uniform surface etching, a 32.5% reduction in mean particle size (125.3 → 84.6 μm, p < 0.05, mean ± SD, n = 3) and a more homogeneous hydroxylation ( ≈ + 26% FTIR O-H; surface O 8.1 ± 0.4 wt%). KOH generated a markedly higher specific surface area (1850 ± 92.5 m² g⁻¹ vs. 572.3 ± 29.7 for NaOH), greater microporosity (82% vs. 71%), and higher electrochemical capacitance (Na₂SO₄: 185.0 ± 7.2 F g⁻¹ vs. 61.27 ± 3.5 F g⁻¹). Regression models show excellent predictive accuracy (NaOH: R² = 0.9842, RMSE = 1.7 μm; KOH: R² = 0.9883, RMSE = 1.9 μm) and ANOVA indicates treatment chemistry explains 71% of variance (η² = 0.71, p = 5.79 × 10⁻⁴). Void content rose from 3.24% (untreated) to 3.85% (NaOH, 60 min) and 6.12% (KOH, 90 min); applying established porosity-strength correlations implies an estimated tensile-strength penalty of ≈ 15-20% for the highest-porosity KOH route. NaOH, therefore, yields dense, chemically uniform particles that favour interfacial bonding and predictable load transfer; KOH yields high-surface-area, porous particulates advantageous for adsorption/energy applications and mechanical interlocking at the expense of fatigue and tensile reliability. The study defines process windows and energy metrics (NaOH ≈ 2.4 kWh·kg⁻¹; KOH ≈ 4.0 kWh·kg⁻¹) and provides a mechanistic framework for selecting alkali routes according to target composite function. Figure 1 shows key findings.