INTRODUCTION:

Aluminum and its alloys are widely utilized materials due to their significant technological value and extensive industrial applications. They are commonly found in sectors such as aerospace, household industries, and marine applications. However, despite their inherent corrosion resistance, aluminum and its alloys can still be susceptible to corrosion under certain conditions^1,2.

Corrosion is a major concern when it comes to the use of aluminum and its alloys. While aluminum is known for its excellent corrosion resistance, it is still susceptible to certain environments and conditions. Understanding the corrosion behavior of aluminum and its alloys is crucial to ensure their long-term performance and durability. When aluminum is exposed to certain environments, such as moisture, oxygen, acids, or alkaline solutions, it undergoes a chemical reaction with its surroundings. This reaction can result in the formation of corrosion products and the degradation of the material^3,4.

one of the most important features of aluminum is its corrosion resistance, primarily attributed to the presence of a thin, adherent, and protective surface oxide film. This oxide film, primarily composed of aluminum oxide (Al₂O₃), forms naturally when aluminum is exposed to oxygen in the atmosphere. This passive oxide layer acts as a barrier, protecting the underlying aluminum from further corrosion. Due to this advantageous corrosion resistance, aluminum and its alloys find extensive use in various industries, including reaction vessels, pipes, machinery, and chemical batteries. However, there are certain conditions and environments where aluminum can still be susceptible to corrosion.

In the case of aluminum being exposed to different concentrations of hydrochloric acid (HCl) solutions, such as in pickling, chemical etching, or electrochemical etching processes, the corrosion inhibitors should be utilized. Hydrochloric acid can attack and dissolve the protective oxide film on aluminum, making it more vulnerable to corrosion. The solubility of the oxide film on aluminum increases at pH values below 4 and above 9. At these pH levels, the aluminum surface is more prone to uniform attack, where corrosion occurs evenly across the surface. The use of corrosion inhibitors in these situations is crucial to mitigate the corrosion process.

One of the common method to protect the metals against acid corrosion is the use of organic compounds containing functional group and π electron in their structure, as inhibitors^5,6. Many Schiff bases have been reported as effective corrosion inhibitors for different metals and alloys in the acidic media^7-10. Increasing the application of Schiff bases in the field of corrosion starting materials and their eco-friendly or low toxic properties^11-13. The effective inhibitory performance of these compounds results from the substitution of different heteroatoms (N, O, Cl, Br) and π electron in their structure besides the presence of imine functional group^14-16. These molecules form very thin and persistent adsorbed films that lead to decrease in the corrosion rate due to the slowing down of anodic, cathodic reaction or both^17-18. He efficiency of the inhibitor depends on the characteristics of the environment in which it acts, the nature of the metal surface and electrochemical potential at the interface.

EXPERIMENTAL:

All the melting point were determined in open capillary tubes and are uncorrected. The FT IR Spectra (ν_max cm^-1) were recorded on a Perkin Elmer 557 grating infrared spectrophotometer in KBr pallets. PMR spectra were recorded on Bruker Spectrometer (200mhz) using CDCl₃ as a solvent. TMS was used as internal standard (chemical shift in δppm). Mass spectra were recorded on kratos 30 and 50 mass spectrometer. A domestic microwave oven (LG, MS-194A) operating at 2450MHz (40 % power ,320 W) was used in the experiment- X-ray powder diffraction (XRD) is efficient and used to determine the phase and cell dimension of crystalline compounds. The Schiff base under investigation was finely powdered, homogenized and the bulk composition was calculated on an average. The purity of the compound was checked by TLC using silica Gel-G as adsorbent, UV light or iodine accomplished visualization 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide Schiff base was prepared by the literature method¹⁹.The used all chemicals for the preparation of Schiff base were AR grade (MERCK).

Investigation on X-Ray powder diffraction were examined at from an angle of 100 to 800.The range of the powder XRD patterns is 2Q=0-80A^o. Scherrer's formula was used to determine the Schiff bases' average crystalline size.²⁰In XRD X-axis shows the pattern is measured in 2θ and Y-axis is relative intensity of the diffracted beam. d_xrd=0.9λ/β cos θ

Scanning Electron Microscopy (SEM) is used to give the information of the surface topography, crystalline structure, chemical and electrical behaviour of Schiff bases.²¹ The corrosion rate (р), inhibition efficiency (IE%), mass loss (∆M), surface coverage (θ) determined from weight loss method.²²

Potentiodynamic polarization measurements: It is an electrochemical measurement. The electrochemical kinetic parameters were examined by using Gamry potentiostst/galvanostst. The anticorrosion behavior of inhibition was studied via anodic and cathodic polarization by plotting a curve between corrosion current density and corrosion potential. These curves are known as Tafel plot (figure-3).

RESULT AND DISCUSSION:

Synthesis: A reaction mixture of 0.01mol of 3,4,5-trihydroxy benzohydrazide in water, 0.01mol of 3,4-dimethoxy benzaldehyde and 2 drops of Conc.H₂SO₄ was incubated inside a microwave oven running at 160 W for 7-8 minutes. The reaction mixture was placed into water when the reaction completed and it cooled at room temperature The resultant solid proceeds to recrystallization. TLC checked on the reaction's progression every two minutes.²³ After some time, TLC revealed a complete conversion. The TLC spots were found using UV light at 254nm, and H₂SO₄ in ethanolic solution (5%,v/v) was sprayed on before being heated to 100°C.²⁴ By the condesation reaction to afford the desired schiff base 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide was obtained. (Scheme-I). The physical and anayltical data of schiff base 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide is shown in Table-1.

Scheme-I:

Table 1: The Physical and Analytical Data of 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide Schiff base

Molecular formula

Exact Mass

Molecular weight

M.P.(^oC)

Yields

Elemental Analysis Found (Calculated) %

C₁₆H₁₅N₂O₆

331

262

89.36

57.99

(58.00)

4.51

(4.53)

8.44

(8.45)

28.99

(29.00)

Table 2: Spectral analyses of 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide Schiff Base

Molecular formula

IR(KBr) ν _max cm^-1.

¹H NMR(CDCl₃) δppm

Mass (m/z)

XRD

C₁₆H₁₅N₂O₆

1632-1619cm^-1

(>C=N-Str. mode)

1510-1405,1115-1055 and 980-710 cm^-1 (Aromatic C-H),3200-3180 cm^-1

(-NH- str.)

8.1(S, CH=N,1H),

7.3-7.4(m,Ar-H,3H)

331(M⁺)

38-59nm (Average Size of Grains)

In the IR spectra of 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide (Schiff Base) characteristic absorption due to >C=N- group appears at 1630-1620 cm^-1. -NH- absorption appears as a broad band from 3250-3180 cm^-1. The vibration bands at 1500–1400, 1100–1050, and 900–700 cm^-1 show the presence of an aromatic ring in the Schiff base.

In the ¹H NMR Spectra of Schiff Base 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide benzo hydrazide -CH=N- proton resonance signal appears as a sharp singlet at δ 8.2 ppm. This up field confirms the conversion of formyl group (-CHO) into imino group(-CH=N-). Aromatic Proton signals appears as multiplates at δ7.2-7.5 ppm. Final confirmation is obtained by the fast atomic bombardment (FAB) mass spectra as M⁺ at 331 that corresponds to their molecular mass which is C₁₆H₁₅N₂O₆ respectively.

X-Ray powder Diffraction (Figure-1) of synthesized Schiff base showed that crystalline nature and average size of grain were 36-59nm. Scanning Electron Microscopy (SEM) image (Figure-2) of synthesized base detected the existence of microscopic grains with non-uniform, size and morphological agglomeration.

Figure 1: XRD pattern of Schiff Base 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide

Figure 2: SEM image of Schiff base 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide

Figure 3: Potentiodynamic Diagram

The percentage of inhibition efficiency and surface coverage obtained from weight loss method at different concentrate of inhibitor for the corrosion of Schiff base in 0.5N, 1N, 2N HCl for an immersion period of 1hour, 6 hours, 24 hours (0.5N and 1N HCl) and 30 min, 1hour, 6 hour (2N HCl) at 298+0.1K, area of exposure 7.7cm² are shown in Table 3,4 and 5. The results show that inhibitor actually inhibited the corrosion of aluminium in 0.5N, 1N, 2N HCl at constant temperature (298+0.1K) the IE% increases with increasing inhibitor concentration. This behaviour is the result of increased adsorption oh the inhibitor on the meal surface. The inhibition efficiency (IE %) and degree of surface coverage (θ) were calculated using these equations (i) and (ii) respectively^25-26.

IE (%) = (W_u- W_i)/W_u X100 ………………...(i)

θ = (W_u-W_i)/W_u …………………..................(ii)

Where W_u and W_i are the weight loss of mild steel in 0.5N, 1N, 2N HCl in the absence and presence of Schiff base. The degree of surface coverage using Langmuir adsorption isotherm. The assumption of Langmuir adsorption isotherm can be expressed as Equation (iii)

C/ θ = 1/k + C ……………………………….. (iii)

Where C is the concentration of the inhibitors, θ is the degree of surface coverage of the inhibitor 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide and k is the adsorption equilibrium constant. Taking logarithm of equation (iii).

log C/ θ = log C – log k ……………………. (iv)

Figure - 4,5,6 shows Langmuir adsorption isotherm for the adsorption of Schiff 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide on the Aluminum surface. The valves of adsorption parameters deduced from the isotherm are given in the Table 3,4 and 5. From the results obtained, it is significant to note that these plots are linear with the slopes equal to the unity, which indicates a strong adherence of the adsorption data to the assumption establishing Langmuir adsorption isotherm. As we can see from Figure 3,4,5 of 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide inhibitor was found to obey the Langmuir adsorption isotherm.

Figure 4: Variation of log (θ /1-θ) with log C for Schiff’s bases inhibitors for Aluminum in 0.5N HCl at 298+ 0.1K, Time at 1h,6h,24h, Area of exposure -7.75cm²

Figure 5: Variation of log (θ /1-θ) with log C for Schiff’s bases inhibitors for Aluminum in 1N HCl at 298+ 0.1K, Time at 1h,6h,24h, Area of exposure -7.75cm²

Figure 6: Variation of log (θ /1-θ) with log C for Schiff’s bases inhibitors for Aluminum in 2N HCl at 298+ 0.1K, Time at 1h,6h,24h, Area of exposure -7.75cm²

Table 3: Mass Loss measurement (∆M), Corrosion Rate(mmpy), Inhibition Efficiency (η%), Surface Coverage(θ) of Schiff's bases inhibitors for Aluminum in 0.5N HCl at 298+ 0.1K, Time at 1h,6h,24h, Area of exposure -7.75cm²

Inhibitor Concentration (%) (w/v)	Mass Loss (∆M)			Inhibition Efficiency(η%)			Surface Coverage(θ)
Inhibitor Concentration (%) (w/v)	1h	6h	24h	1h	6h	24h	1h	6h	24h
-	132	233	317	0.00	0.00	0.00	0.0	0.0	0.0
0.1	94	105	162	28.79	54.94	48.24	0.2879	0.5494	0.4824
0.2	77	83	137	41.67	64.38	56.23	0.4167	0.6438	0.5623
0.3	59	71	95	55.30	69.53	69.65	0.5530	0.6953	0.6965
0.5	34	51	67	74.24	78.11	78.59	0.7424	0.7811	0.7859

Continue Table No. 3:

log(θ /1-θ)			log c	log(c/θ)			Corrosion Rate(ρ)
1h	6h	24h	log c	1h	6h	24h	1h	6h	24h
0.0	0.0	0.0	-				92.10	162.57	221.18
-0.3933	0.0860	-0.0305	-1.00	-0.4593	-0.7399	-0.3165	65.58	73.26	113.03
-0.1461	0.2570	0.1088	-0.698	-0.3179	-0.5068	-0.448	53.72	57.91	95.58
0.0925	0.3583	0.3607	-0.522	-0.2648	-0.3642	-0.365	41.16	49.53	66.28
0.4597	0.5525	0.5649	-0.301	-0.1717	-0.1938	-0.1964	23.72	35.58	46.74

Table 4: Mass Loss measurement (∆M), Corrosion Rate(mmpy), Inhibition Efficiency (η%), Surface Coverage(θ) of Schiff's bases inhibitors for Aluminum in 1N HCl at 298+ 0.1K, Time at 1h,6h,24h, Area of exposure -7.75cm²

Inhibitor Concentration (%) (w/v)	Mass Loss (∆M)			Inhibition Efficiency(η%)			Surface Coverage(θ)
Inhibitor Concentration (%) (w/v)	1h	6h	24h	1h	6h	24h	1h	6h	24h
-	176	212	281	0.0	0.0	0.0	0.0	0.0	0.0
0.1	99	129	171	43.75	39.15	39.15	0.4375	0.3915	0.3915
0.2	73	99	132	58.52	53.30	53.02	0.5852	0.5330	0.5302
0.3	57	63	72	67.61	70.28	74.38	0.6761	0.7028	0.7438
0.5	36	41	57	79.55	80.66	79.72	0.7955	0.8066	0.7972

Continue Table No. 4

log(θ /1-θ)			log c	log(c/θ)			Corrosion Rate(ρ)
1h	6h	24h	log c	1h	6h	24h	1h	6h	24h
0.0	0.0		-				12280	147.91	196.06
-0.1091	-0.1915	-0.1916	-1.00	-0.641	-0.5928	-0.5928	69.07	90.00	119.31
0.1495	0.0574	0.0526	-0.698	-0.4654	-0.4248	-0.4225	50.93	69.07	92.10
0.3197	0.3738	0.4628	-0.522	-0.3521	-0.3689	-0.3935	39.77	43.95	50.23
0.5898	0.6202	0.5944	-0.301	-0.2017	-0.2077	-0.2026	25.11	28.60	39.77

Table 5: Mass Loss measurement (∆M), Corrosion Rate(mmpy), Inhibition Efficiency (η%), Surface Coverage(θ) of Schiff's bases inhibitors for Aluminum in 2N HCl at 298+ 0.1K, Time at 30min,1h,4h, Area of exposure -7.75cm²

Inhibitor Concentration (%) (w/v)	Mass Loss (∆M)			Inhibition Efficiency(η%)			Surface Coverage(θ)
Inhibitor Concentration (%) (w/v)	30 m	1h	4h	30 m	1h	4h	30 m	1h	4h
-	243	316	378	0.0	0.0	0.0	0.0	0.0	0.0
0.1	162	207	246	33.33	34.49	34.92	0.3333	0.3449	0.3492
0.2	137	148	135	43.62	53.16	64.29	0.4362	0.5316	0.6429
0.3	81	85	110	66.67	73.10	70.90	0.6667	0.7310	0.7090
0.5	52	61	65	78.60	80.70	82.80	0.7860	0.8070	0.8280

Continue Table No. 5:

log(θ /1-θ)			log c	log(c/θ)			Corrosion Rate(ρ)
30 m	1h	4h	log c	30 m	1h	4h	30 m	1h	4h
			-				169.54	220.48	263.74
-0.3010	-0.2785	-0.2704	-1.00	-0.6397	-0.5377	-0.5431	113.03	144.43	171.64
-0.1114	0.0550	0.2553	-0.698	-0.2209	-0.4236	-0.5062	95.58	103.26	94.19
0.3010	0.4342	0.3867	-0.522	-0.346	-0.3860	-0.3727	56.51	59.30	76.75
0.5650	0.6212	0.6826	-0.301	-0.1965	-0.2079	-0.2191	36.28	42.56	45.35

CONCLUSION:

The 3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide showed promising results for corrosion inhibition of aluminium in the presence of different concentrations of HCl. The synthesized Schiff bases inhibits the corrosion of aluminium in different concentrations of HCl solutions with inhibition efficiency of 78.59% (0.5N HCl), 79.72% (1N HCl) of 0.5 %v/v of Schiff base concentration for 24-hour exposure time, which are effective in reducing corrosion of the aluminium surface at temperature of 298+0.1K. The adsorption of the inhibitor Schiff base was consistent with the Langmuir adsorption isotherm. The inhibitor molecule (3,4,5-trihydroxy-N-(3,4-dimethoxy benzylidene) benzo hydrazide) adsorbed on the aluminum metal surface and tend to retard the rate of corrosion by reducing the number of available sites for corrosion. Overall, the results indicate that this Schiff base compound has the potential to be an effective corrosion inhibitor for aluminum in acidic environments. Its adsorption behavior and inhibition efficiency demonstrate its ability to protect the aluminum surface and reduce corrosion.

CONFLICT OF INTEREST:

The authors have no conflicts of interest regarding this investigation.

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Received on 21.06.2023 Modified on 11.08.2023

Research J. Science and Tech. 2023; 15(4):175-182.

DOI: 10.52711/2349-2988.2023.00029