2 M HNO₃ and 1 M H₂SO₄ was prepared by diluting 69% HNO₃ and 98% H₂SO₄ with distilled water as corrosive medium. Plant inhibitor Aloe lateritia gel was obtained from the western part of Kahama district at Wendere village, Tanzania. The gel was obtained by cutting the leaves and squeezing, then filtering through the mesh of cloth to get pure gel. About 1 kg of fresh leaves was used to obtain 2 Litters of gel. It was kept cool in a refrigerator prior to testing this is, in similar to what reported by [12] . Concentration of inhibitors: (0%, 3.2%, 6.3%, 9.1%, 11.8%, 14.3% v/v) was used at room temperature.

Mild steel with following composition was used: C―0.15, Mn―1.26, V―0.017, Si―0.035, S―0.008, Cr―0.036, Ni―0.03, Al―0.083, Cu―0.038 and the remainder is Fe. The metal was cut into 2 cmx1 cm as working electrode for electrochemical measurements. The surface of metal was pre-cleaned using silicon carbide paper; it was made to silver mirror by cleaning using diamond paste. Finally, by using acetone and distilled water in an utrasonicator bath was washed and rinsed then stored for use.

The experiment was performed in a conversational cell with three electrodes connected to a potentiostat (PGSTAT 302N). Mild steel was used as working electrode in 2 M HNO₃ and 1 M H₂SO₄ corrosive medium. Platinum wire, saturated calomel electrode was used as a counter and reference electrodes respectively. The plots used to obtain the tafel curve were done by changing the potential from −250 to +250 mV at scan rate of 1mV∙s⁻¹ against open circuit potential.

The surface of Mild steel exposed to uninhibited 2 M HNO₃ and 1 M H₂SO₄ and to that containing optimal concentration of inhibitor, was examined by Field Scanning Electron Microscope (FE-SEM, Hilachi, S-4700). Before exposing to SEM the metal was cleaned thoroughly to remove the oxide layer and after 24 hours prior-o to measurement was washed using running distilled water and dried. Corrosion products were obtained by removing the oxide surface of the metal using the utrasonicator, and then were submitted for measurement.

The inhibitor gels and the corrosion products were subjected to Varian 660-IR for the determination of appropriate functional groups available. Few drops of Aloe lateritia gel and the corrosion products obtained after 24 hours of metal corrosion in optimal inhibitor were subjected to FTIR measurements.

It was used to obtain polarization curves for the Mild steel in 2 M HNO₃ and 1 M H₂SO₄ with and without the addition of Aloe lateritia gel.

The plots from Figure 1 and Figure 2 reveal that Tafel plot was obeyed by anodic and cathodic reactions. The linear part of the Tafel plots were extrapolated, at the point of intersection is where corrosion potential (E_corr)

and corrosion current density (i_corr) were obtained.

Related parameters like Cathodic Tafel slope (b_c), anodic Tafel slope (b_a), corrosion current density (i_corr) and corrosion potential (E_corr) were calculated and results are tablated in Table 1.

An increase in the concentration of inhibitor resulted in the following:

There is equal shift for the potential toward more negative and positive relating to cathodic and anodic respectively; this indicates that reaction mechanism was the same. From Table 1 it is observed that there is a decrease of corrosion current density (i_corr) contrary to inhibitor concentration. This is attributed by the ability of inhibitor to prevent interaction between metal and the corrosive medium which leads to corrosion. Although, the corrosion current density (i_corr) decrease as inhibitor’s concentration increases; no remarkable shift of corrosion potential (E_corr) was observed. This is to say a mixed type inhibition for both anodic and cathodic reactions took place, the observation is associated with that reported by [13] .

Inhibition efficiency (%IE) was obtained by Equation (11) when the concentration of inhibitor increased %IE increases too. From Table 1 at 14.3% v/v of inhibitor %IE reached maximum 77.4% for 1M H₂SO₄ while for 2M HNO₃%IE increased with concentration of inhibitor up to 11.8%v/v which attained 70.3%, then started to decrease as concentration increased. So the inhibitor performs better with H₂SO₄ than HNO₃.

Mild steel was exposed to 1M H₂SO₄ and 2M HNO₃ medium in the absence and presence of optimal amount

Aloe lateritia gel for 24 hours at room temperature. Their morphology was determined by SEM, the results from Figure 3(a) and Figure 3(c) verifies that the steel more corroded as the surface was more rough in blank medium. However, Figure 3(b) and Figure 3(d) is for the steel which was exposed in a corrosive medium with optimal concentrations of inhibitor.

The presence of inhibitor reduced the extent of corrosion, the surface become smoother compared to the uninhibited. This reveals the performance of inhibitor by protective layer formation; which separates the interaction between the metal and corrosive medium similar behavior observed by [14] . From Figure 3(a) and Figure 3(c) the metal exposed to blank 1 M H₂SO₄ and 2 M HNO₃ displayed uniform and pitting corrosion respectively.

For determination of the functional groups few drops of Aloe lateritia gel and that of corrosion products was used. The results were displayed for FT-IR spectrum as shown in Figure 4.

Aloe lateritia gel and that of corrosion product was exposed to IR spectrum and the results are shown in Figure 4(a) and Figure 4(b). The stretch for O-H which was around 3339.60 cm⁻¹ was shifted to 3360.29 cm⁻¹, from 1635.49 cm⁻¹ to 1641.08 cm⁻¹ for C=C when the pure inhibitor gel and corrosion product respectively. The presence of stretch at 551.87 cm⁻¹ indicates presence of g-Fe₂O₃ this verifies the interaction between the inhibitor and the metal surface was also observed as shown in Table 2 [15] .