CORROSION INHIBITOR OF PLATANUS ACERIFOLIA LEAF EXTRACT AND APPLICATION THEREOF

TECHNICAL FIELD

The present invention relates to the technical field of corrosion inhibitor, and specifically relates to a corrosion inhibitor of Platanus acerifolia leaf extract and application thereof.

BACKGROUND ART

With the accelerated development of industrialization and urbanization, metal materials are more and more widely used in many fields such as construction, transportation, energy, and the chemical industry. However, metal materials are easily eroded by environmental factors such as atmosphere, water, and soil, resulting in corrosion and damage, which brings many problems and safety hazards to production and life. Consequently, the anti-corrosion technology of metal materials has become one of the hot demands in the current market. Currently, scientific and technological workers at home and abroad have adopted a variety of protection methods, including the development of new corrosion-resistant alloys, the use of electrochemical protection (such as cathodic protection and anodic protection), surface treatment, and the addition of corrosion inhibitors and coatings. Wherein, adding corrosion inhibitor is one of the most widely used methods, which has the advantages of less dosage, simple operation, low cost, remarkable effect, and strong versatility so that occupies an important position in various anti-corrosion methods. Most inorganic corrosion inhibitors, nitrites, and molybdates have been banned in many countries and regions due to their high biological toxicity and carcinogenicity; organic corrosion inhibitors usually require a relatively large dose to play a role, so the application is also limited; hybrid materials can be customized with good corrosion resistance and low toxicity, but the synthesis methods are usually expensive and not environmentally friendly. With the improvement of environmental awareness, the extraction of green corrosion inhibitors from natural plants has become a research hotspot in the field of anti-corrosion.

Research has shown that plant extracts are a natural green corrosion inhibitor, which has the characteristics of wide source, non-toxic, non-polluting, and low cost, and has an important position in the field of corrosion inhibitor research. At present, people have carried out a lot of research work on plant extracts, such as ginkgo leaves, luffa leaves, camphor leaves, olive leaves, and so on. The research on the use of plant extracts as environmentally friendly corrosion inhibitors is an important direction for optimal resource utilization in the future.

SUMMARY OF THE INVENTION

In view of the above technical problems, the present invention provides a corrosion inhibitor of Platanus acerifolia leaf extract and application thereof. The corrosion inhibitor of Platanus acerifolia leaf extract provided by the present invention has a good corrosion inhibition effect on copper in sulfuric acid systems, and has a good corrosion inhibition effect on steel in hydrochloric acid systems; and has more comprehensive and superior anti-corrosion performance, which can meet the anti-corrosion requirements of different materials.

The present invention is realized by the following technical scheme:

- a corrosion inhibitor of Platanus acerifolia leaf extract, the active components of the corrosion inhibitor of Platanus acerifolia leaf extract include: flavonoid compounds and oligopeptides; the flavonoid compounds include: 5,8-dihydroxy-2-(2-phenylethyl), astragalin, biondnoid, hyperoside, licochalcone A, pinocembrin, procyanidin B1; the oligopeptides include: cyclic (tyrosine-leucine) dipeptide, cyclic (L-phenylalanyl-L-phenylalanyl).

The preparation method for the corrosion inhibitor of Platanus acerifolia leaf extract is as follows:

- cleaning fresh Platanus acerifolia leaf with ultrapure water, drying and grinding into powder;
- adding the ground leaf powder of Platanus acerifolia into an ethanol aqueous solution, heating, stirring, and soaking, filtering to remove the leaf residue, placing into a refrigerator for refrigeration, and then freeze-drying to obtain a corrosion inhibitor of Platanus acerifolia leaf extract.

Further, the drying step is carried out in the oven, the drying temperature is 328˜338K, and the drying time is 36˜48 h.

Further, the mass fraction of the ethanol aqueous solution used is 30˜40%; the solid-liquid ratio of the powder of Platanus acerifolia leaf and the ethanol aqueous solution is (30-50): 1000, unit g/mL.

Further, the temperature of heating and stirring is 333˜343K; the soaking time is 1˜3 h; the refrigeration time is 12˜24 h; the freeze-drying temperature is 53K and the freeze-drying time is 20˜28 h.

An application of a corrosion inhibitor of Platanus acerifolia leaf extract, wherein Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper or steel in an acid solution.

Further, the Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper in sulfuric acid solution, or the Platanus acerifolia leaf extract is used as a corrosion inhibitor for steel in hydrochloric acid solution.

Further, when the Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper in sulfuric acid solution, the Platanus acerifolia leaf extract is added into sulfuric acid solution to obtain the inhibition test solution; the concentration of the sulfuric acid solution used is 0.1-1M; in the inhibition test solution, the concentration of Platanus acerifolia leaf extract is 100-400 mg/L;

- when the Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper in sulfuric acid solution, the inhibition efficiency is up to 96.7%.

Further, when the Platanus acerifolia leaf extract is used as a corrosion inhibitor for steel in hydrochloric acid solution, the Platanus acerifolia leaf extract is added into the hydrochloric acid solution to obtain the inhibition test solution; the concentration of the hydrochloric acid solution used is 0.01-2M; in the inhibition test solution, the concentration of Platanus acerifolia leaf extract is 50-400 mg/L;

Further, the Platanus acerifolia leaf extract is used as a corrosion inhibitor for Q235, X60, X70, and N80 carbon steel in hydrochloric acid solution.

Further, when the Platanus acerifolia leaf extract is used as a corrosion inhibitor for Q235 steel in hydrochloric acid solution, the inhibition efficiency is up to 93.1%.

In this invention, the Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper and steel, compared with other plant extracts, the components of Platanus acerifolia leaf are more abundant, and a large number of flavonoid compounds and oligopeptides are effective components with corrosion inhibition. The flavonoid compounds contained in the Platanus acerifolia leaf extract include: 5,8-dihydroxy-2-(2-phenylethyl), astragalin, biondnoid, hyperoside, licochalcone A, pinocembrin, procyanidin B1; the oligopeptides contained in the Platanus acerifolia leaf extract include: cyclic (tyrosine-leucine) dipeptide, cyclic (L-phenylalanyl-L-phenylalanyl), docosanoic acid.

Wherein, flavonoid compounds have super delocalization, complete π bond conjugated system, strong coordination oxygen atoms, and suitable spatial configuration, the adsorption active center of flavonoid compounds on the metal surface is the parent skeleton of flavonoids, and the adsorption mode is ‘horizontal adsorption’, which makes it easy to form chelating ligands with metals, and has great application potential in the field of anti-corrosion; in the present invention, the flavonoid compounds and the oligopeptides form a nitrogen-carbon protective film on the copper and carbon steel substrate through the donor-acceptor interaction of the reaction site, blocking the direct contact of the corrosion medium with the steel surface, thereby achieving the effect of slowing down the corrosion.

The beneficial technical effect of the present invention is:

- in view of the shortcomings of traditional corrosion inhibitors, such as non-degradability, toxicity, high cost, and pollution to the environment, the corrosion inhibitor of Platanus acerifolia leaf extract provided by the present invention adopts Platanus acerifolia leaf with biodegradability and wide source as the source of corrosion inhibitor, which ensures its biodegradability and low cost; moreover, the corrosion inhibitor of Platanus acerifolia leaf extract provided by the present invention is non-toxic and harmless to the environment when used; in the process of synthesis or extraction of corrosion inhibitor, it also has little or no effect on the environment;
- because there are many active ingredients in the Platanus acerifolia leaf, the corrosion inhibitor of the Platanus acerifolia leaf extract provided by the present invention has a good corrosion inhibition effect on copper in sulfuric acid system and steel in hydrochloric acid system, and has a more comprehensive and superior anti-corrosion performance, which can meet the anti-corrosion requirements of different materials.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a polarization curve of a copper sample in a 0.5M sulfuric acid environment with different concentrations of Platanus acerifolia leaf extract in the example of the present invention;

FIG. 2a is a Nyquist diagram of copper impregnated with different concentrations of Platanus acerifolia leaf extract in the example of the present invention;

FIG. 2b is a Bode diagram of copper impregnated with different concentrations of Platanus acerifolia leaf extract in the example of the present invention;

FIG. 3a is a sample surface of the copper sample immersed in 0.5M sulfuric acid for 6 hours at 298K in the example of the present invention;

FIG. 3b is a sample surface of the copper sample immersed in 0.5M sulfuric acid containing 300 mg/L Platanus acerifolia leaf extract for 6 hours at 298K in the example of the present invention;

FIG. 4a is a Nyquist diagram of Q235 steel in 1M HCl solution containing different concentrations of Platanus acerifolia leaf extract at 308K temperature in the example of the present invention;

FIG. 4b is a Nyquist diagram of Q235 steel in 1M HCl solution containing different concentrations of Platanus acerifolia leaf extract at 318K temperature in the example of the present invention;

FIG. 5 is an equivalent circuit for electrochemical impedance spectroscopy fitting in accordance with the example of the present invention;

FIG. 6a is a potential dynamic polarization curve of Q235 steel in 1M HCl solution containing different concentrations of Platanus acerifolia leaf extract at 308K temperature in the example of the present invention;

FIG. 6b is a potential dynamic polarization curve of Q235 steel in 1M HCl solution containing different concentrations of Platanus acerifolia leaf extract at 318K temperature in the example of the present invention;

FIG. 7a is a scanning electron micrograph (a) of Q235 steel immersed in 1M HCl solution (without the addition of Platanus acerifolia leaf extract) at 308K temperature for 4 h in the example of the present invention;

FIG. 7b is a scanning electron micrograph of Q235 steel immersed in 1M HCl solution (the concentration of Platanus acerifolia leaf extract is 400 mg/L) at 308K temperature for 4 h in the example of the present invention;

FIG. 8a is a scanning electron micrograph of Q235 steel immersed in 1M HCl solution (without the addition of Platanus acerifolia leaf extract) at 318K temperature for 4 h in the example of the present invention;

FIG. 8b is a scanning electron micrograph of Q235 steel immersed in 1M HCl solution (the concentration of Platanus acerifolia leaf extract is 400 mg/L) at 318K temperature for 4 h in the example of the present invention;

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to make the objective, technical solution, and advantages of the present invention clearer and more specific, the present invention will be further described in detail below with reference to accompanying drawings and examples. It should be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention.

On the contrary, the intention is to cover all alternatives, modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. A full appreciation of the invention can be gained by those skilled in the art without the description of the details.

A corrosion inhibitor of Platanus acerifolia leaf extract, the active components of the corrosion inhibitor of Platanus acerifolia leaf extract include: flavonoid compounds and oligopeptides;

- the flavonoid compounds include: 5,8-dihydroxy-2-(2-phenylethyl); the oligopeptides include: cyclic (tyrosine-leucine) dipeptide.

In this example, the corrosion inhibitor of Platanus acerifolia leaf extract is in powder form; the preparation method for the corrosion inhibitor of Platanus acerifolia leaf extract is as follows:

- the fresh Platanus acerifolia leaf is cleaned with ultrapure water, dried, and ground into powder;
- the ground leaf powder of Platanus acerifolia is added into an ethanol aqueous solution, heated stirred and soaked, filtered to remove the leaf residue, placed into a refrigerator for refrigeration, and then freeze-dried to obtain a corrosion inhibitor of Platanus acerifolia leaf extract.

Specifically, the Platanus acerifolia leaves used in this invention are collected from Platanus acerifolia.

Specifically, the Platanus acerifolia leaf is cleaned with ultrapure water, and then dried in an oven at 328˜338K (preferably 333K) for 36˜48 h (preferably 40 h). Then ground into powder and sieved with a sieve with a pore size of 1.25 mm to obtain dry leaf powder; the 30-50 g dry leaf powder after grinding is added to 1000 mL ethanol aqueous solution with a mass fraction of 30-40%, heated and stirred in a magnetic stirrer and soaked, the temperature of heating and stirring is 333-343K; the soaking time is 1˜3 h; then the vacuum filtration device is used to remove the Platanus acerifolia leaf residue, and the filtered solution is placed in a glass container and refrigerated in a refrigerator for 12˜24 h (preferably 18 h); finally, the extract obtained by vacuum freeze-drying is freeze-dried with a vacuum freeze-drying machine, the freeze-drying temperature is 53K and the freeze-drying time is 20˜28 h; the corrosion inhibitor (brown solid) of Platanus acerifolia leaf extract is obtained.

The present invention also provides an application of a corrosion inhibitor of Platanus acerifolia leaf extract, the Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper in sulfuric acid solution, or the Platanus acerifolia leaf extract is used as a corrosion inhibitor for steel in hydrochloric acid solution.

Specifically, when the Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper in sulfuric acid solution, the Platanus acerifolia leaf extract is added into sulfuric acid solution to obtain the inhibition test solution; the concentration of the sulfuric acid solution used is 0.1-1M; in the inhibition test solution, the concentration of Platanus acerifolia leaf extract is 100-400 mg/L. When the Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper in sulfuric acid solution, the inhibition efficiency is up to 96.7%.

In this example, when the Platanus acerifolia leaf extract used as a corrosion inhibitor for steel in hydrochloric acid solution, the Platanus acerifolia leaf extract is added into the hydrochloric acid solution to obtain the inhibition test solution; the concentration of the hydrochloric acid solution used is 0.01-2M; in the inhibition test solution, the concentration of Platanus acerifolia leaf extract is 50-400 mg/L.

Specifically, the Platanus acerifolia leaf extract is used as a corrosion inhibitor for Q235, X60, X70, and N80 carbon steel in hydrochloric acid solution; when the Platanus acerifolia leaf extract is used as a corrosion inhibitor for Q235 steel in hydrochloric acid solution, the inhibition efficiency is up to 93.1%.

The specific experimental process of the Platanus acerifolia leaf extract is used as a corrosion inhibitor for copper in sulfuric acid solution is as follows:

(1) Preparation of Electrode and Copper Pickling Solution:

the cut copper sheet (2 cm×2 cm×0.2 cm) is placed in a self-made oil removal solution heated to 70° C. for 10 min, the oil stain on the surface of the copper sheet is removed by emulsification and saponification of the oil with a hot alkali solution, and then the copper sheet is immersed in deionized water for 10 min to obtain an oil-free copper sheet; after that, the copper sheet is placed in 125 ml/L HCl for 10 min, and the oxide film on the surface of the copper sheet is removed by hydrochloric acid solution, then the copper sheet is immersed in deionized water for 10 min to remove the residual hydrochloric acid solution on the surface of the copper sheet; finally, the copper sheet is washed in ultrasonic ethanol solution for 10 min, and the ultrasonic cavitation is used to accelerate the removal of the dirt layer on the surface of the copper sheet, so as to obtain a clean and oil-free copper sheet. In the electrochemical process, the acid solution is 0.5M sulfuric acid solution, which was prepared from concentrated sulfuric acid (98%) and ultrapure water. The Platanus acerifolia leaf extract is added to 0.5M sulfuric acid solution to obtain 100 mg/L, 200 mg/L, 300 mg/L, and 400 mg/L Platanus acerifolia leaf extract solutions, respectively.

(2) Electrochemical Test:

Electrochemical impedance spectroscopy (EIS) is performed on an electrochemical workstation (CHI660E, Shanghai Chenhua Instrument Co., Ltd.), the electrode is a saturated calomel electrode (SCE), the counter electrode is a platinum sheet, and the copper sheet sample is a working electrode (working area 1×1 cm²). The scanning frequency range is 10⁻²Hz˜10⁵Hz, and the EIS data are fitted by Zsimpwin software, the corresponding inhibition efficiency (n) is calculated according to Formula (1-1):

$\begin{matrix} η (%) = \frac{i_{corr, o} - i_{corr}}{i_{corr, 0}} \times 1 0 0 & (1 - 1) \end{matrix}$

where, i_corrand i_corr,0represent the corrosion current densities of the experimental groups with and without the Platanus acerifolia leaf extract, respectively.

Surface Morphology Observation:

the pretreated copper sample (0.5 cm×0.5 cm×0.5 cm) is immersed in 0.5M sulfuric acid solution without Platanus acerifolia leaf extract and with 300 mg/L Platanus acerifolia leaf extract, respectively, and the FE-SEM test is performed after immersed for 6 h at 298K.

In order to study the surface properties of the copper electrode and the kinetic process of the adsorption of the Platanus acerifolia leaf extract on the copper surface, the copper electrode is tested by electrochemical impedance measurement at 298 K in different concentrations of the Platanus acerifolia leaf extract.

FIG. 1 is the polarization curves of the Cu electrode with different concentrations of Platanus acerifolia leaf extract in a sulfuric acid environment. With the increase of the concentration of Platanus acerifolia leaf extract, the value of the corrosion potential moves to the negative potential direction. In terms of corrosion current density, the value decreased by an order of magnitude after the addition of Platanus acerifolia leaf extract, and decreased with the increase of the concentration of Platanus acerifolia leaf extract, when the concentration is 300 mg/L, the corrosion current density is the smallest. It shows that the corrosion rate of copper is inhibited. This shows that the Platanus acerifolia leaf extract forms a protective film at the Cu interface and inhibits the corrosion of the Cu electrode. Table 1 shows the corresponding polarization curve data, in the test solution without the Platanus acerifolia leaf extract, the i_corrvalue on the surface of the copper electrode is 0.1234 mA/cm². When the concentration of Platanus acerifolia leaf extract reached 300 mg/L, the i_corrof the copper electrode interface decreased to 0.004351 mA/cm²; the corrosion inhibition efficiency of Platanus acerifolia leaf extract can reach 96.7%.

TABLE 1

the polarization curves of Cu electrode with different concentrations

of Platanus acerifolia leaf extract in a sulfuric acid environment.

Concentration
E_corr
i_corr
β_c
β_a
η

(mg/L)
(mV/SCE)
(mA/cm²)
(V dec⁻¹)
(V dec^−l)
(%)

Blank
20
0.1234
−5.424
9.544
—

100
8
0.03059
−5.721
13.396
75.2

200
−40
0.008188
−5.504
16.951
93.4

300
−39
0.004351
−5.970
15.367
96.7

400
−44
0.004402
−5.725
17.712
96.4

FIG. 2a-FIG. 2b shows that the Nyquist and Bode data of copper samples are subjected to an EIS test at 298K with different concentrations of Platanus acerifolia leaf extract are added, for the Nyquist data of FIG. 2a, the addition of Platanus acerifolia leaf extract increases the diameter of the capacitive reactance arc, with the increase of concentration, the capacitance radius is greatly increased, when 300 mg/L Platanus acerifolia leaf extract is added, the radius of the capacitive reactance arc has reached the maximum. This phenomenon indicates that the corrosion degree of copper in these solutions is reduced. This is due to the fact that the copper surface can be covered by the Platanus acerifolia leaf extract. For the Bode data of FIG. 2b, |Z|_{0.01 HZ}can be selected to evaluate the corrosion rate of the electrode. Obviously, when the copper sample is immersed in 0.5M sulfuric acid solution, |Z|_{0.01 HZ}value is about 2.952. With the increase of concentration, the |Z|_{0.01 HZ}value remained near 4Ω in the Platanus acerifolia leaf extract, the |Z|_{0.01 HZ}value reached 4.15Ω in the 300 mg/L Platanus acerifolia leaf extract solution, which reached the maximum. In addition, two time constants are observed on all the phase angle curves, the peak height increased with the increase of the concentration of the Platanus acerifolia leaf extract, and the frequency range of the phase angle became wider, the peak height and peak width reached the peak when the concentration of the Platanus acerifolia leaf extract is 300 mg/L, which indicated that the adsorption of the Platanus acerifolia leaf extract at the copper/solution interface had a strong response.

The EIS parameters are fitted by the conventional equivalent circuit diagram, and the fitted parameters are shown in Table 2. It can be clearly found that with the increase of the concentration of Platanus acerifolia leaf extract, the Q_fand Q_d1values decrease significantly with the increase of Platanus acerifolia leaf extract, and reach the minimum at the concentration of 300 mg/L. The decrease in Q_fand Q_d1values is due to the fact that the Platanus acerifolia leaf extract forms a tight and orderly protective film, which replaces the water molecules on the copper surface and adsorbs on the copper surface, thus reducing the area of the copper electrode exposed to the corrosive environment. The R_ctand R_fvalues increased with the increase of the concentration of the Platanus acerifolia leaf extract, and reached the maximum at the concentration of 300 mg/L, indicating that the adsorption of the Platanus acerifolia leaf extract on the copper surface hindered the transfer of charge. Therefore, the electrochemical impedance spectroscopy data can strongly prove that the Platanus acerifolia leaf extract has high corrosion inhibition performance.

TABLE 2

EIS data of copper electrode immersed in different

concentrations of Platanus acerifolia leaf extract

Concen-
R_s
Q_f

R_f
Q_d1

R_ct

tration
(Ω
(μF

(Ω
(μF

(Ω

(mg/L)
cm²)
cm²)
n₁
cm²)
cm²)
n₂
cm²)

Blank
15.38
128.3
0.6966
—
—
—
763.6

100
10.96
38.07
0.8844
3890
415.1
0.4482
3985

200
10.38
31.52
0.9211
4671
511.2
0.4215
4985

300
11.41
22.43
0.8999
9460
316.4
0.624
4543

400
10.34
28.64
0.8924
6814
473.0
0.5959
3935

FIG. 3a-FIG. 3b are the SEM images of copper samples after different experimental treatments. FIG. 3a is an image of a copper sample exposed to 0.5M sulfuric acid solution for 6 hours. The surface of copper is seriously corroded, the surface is rough, there are many pits, and there are many corrosion products. FIG. 3b is the surface image of the copper sample in 0.5M sulfuric acid solution with 300 mg/L Platanus acerifolia leaf extract. The surface protected by Platanus acerifolia leaf extract showed a relatively smooth morphology than the unprotected surface. These observations indicate that an inhibition film is formed on the surface of the copper sample. Therefore, the Platanus acerifolia leaf extract can effectively inhibit the corrosion behavior of copper samples in 0.5M sulfuric acid solution, which is consistent with the electrochemical results.

The specific experimental process of the Platanus acerifolia leaf extract is used as a corrosion inhibitor for steel in hydrochloric acid solution is as follows:

(1) Preparation of Electrode and Inhibition System

five different corrosion inhibition systems are designed to examine the corrosion inhibition effect of Platanus acerifolia leaf extract and the effect of different concentrations on the corrosion inhibition performance. 1M HCl (0.01-2M HCl) solution as the solvent, respectively prepare the solutions containing 0, 50, 100, 200, and 400 mg/L Platanus acerifolia leaf extract as the inhibition test system.

The metal material used in the present invention is Q235 carbon steel with a purity of 99.8%. The size of the electrochemical sample is 1 cm×1 cm×1 cm, except for the working surface (the working area is 1×1 cm²), other parts are sealed and cured with epoxy resin to make electrodes.

(2) Electrochemical Test:

the electrochemical test is carried out on the Gamry Reference 600+ electrochemical workstation, using a classic three-electrode system, in which the treated Q235 carbon steel is used as the working electrode, the 1 cm²platinum sheet is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode. Before each experiment, the working electrodes are polished with a series of different grades of sandpaper (400,800,1200 and 2000), washed with distilled water, and degreased with acetone. Tests are carried out in temperature-controlled water baths at 308K and 318K. First, the working electrode is immersed in the test solution for 1800 seconds to obtain a stable open circuit potential. Then the electrochemical impedance spectroscopy (EIS) test is carried out, a sine wave of ±5 mV is applied to the open circuit potential as an AC signal, and the scanning frequency range is 10⁻²˜10⁵Hz, the experimental data are fitted by ZsimDemo fitting software. Finally, the potential dynamic polarization curve is recorded at a scanning rate of 2 mV/s, and the open circuit potential is set to positive and negative 250 mV.

Electrochemical impedance spectroscopy tests were performed at 308K and 318K temperatures to illustrate the kinetic characteristics of the electrochemical process of Q235 steel in 1M HCl solution and the corrosion inhibition effect after the addition of Platanus acerifolia leaf extract, the obtained Nyquist diagrams are shown in FIG. 4a-FIG. 4b, the Nyquist diagrams of Platanus acerifolia leaf extract with various concentrations are composed of an approximately semi-circular capacitive reactance arc in the high-frequency region, and the capacitive arc in the high-frequency region is related to the charge transfer resistance and the electric double layer capacitance. After adding the Platanus acerifolia leaf extract to the solution, the radius of the capacitive arc increases greatly with the increase of its concentration. This indirectly indicates that a protective film is formed between the metal surface and the solution when the 1M hydrochloric acid solution contains the Platanus acerifolia leaf extract, and with the increase of the concentration of the Platanus acerifolia leaf extract, the protective film becomes denser, so that the capacitance value increases. In addition, by comparing the Nyquist diagrams at 308K (FIG. 4a) and 318K (FIG. 4b), the size of the capacitor arc semicircle decreases as the temperature increases, which means that the high temperature accelerates the corrosion. Nevertheless, compared with the blank solution, the impedance value increased significantly after adding the Platanus acerifolia leaf extract, which proved the high inhibition ability of the Platanus acerifolia leaf extract at high temperatures.

The impedance data of the Q235 steel electrode in 1M HCl solution are fitted by Zsimpwin software, the equivalent circuit is shown in FIG. 5, the obtained electrochemical parameters are listed in Table 3 and Table 4. Wherein including solution resistance R_s, film resistance R_f, charge transfer resistance R_ct, CPE is a phase angle element, indicating non-ideal capacitance, that is, the capacitance value of the electric double layer at the electrode interface. The constant phase angle elements CPE_d1and CPE_frepresent the double-layer capacitance C_d1and the film capacitance C_f, respectively. The value of CPE can be calculated by Equation (2-

$\begin{matrix} 1) &  \\ Z_{CPE} \frac{1}{{Y_{0} (j ω)}^{n}} & (2 - 1) \end{matrix}$

where Y₀is the film value of CPE, ω is the angular frequency, j is the imaginary number (j²=−1), and n is the dispersion effect index, reflecting the inhomogeneity of the electrode surface. When n is different values of −1, 0, 0.5 and 1, CPE represents different components, which can be regarded as inductance, resistance, Warburg impedance, and capacitance.

It can be seen from the data in Table 3 and Table 4 that the values of charge transfer resistance R_ctand film resistance R_fincrease with the increase of the concentration of Platanus acerifolia leaf extract, that is, the resistance of corrosion behavior increases, showing better corrosion inhibition performance. In addition, the value of C_d1showed a decreasing trend with the increase of corrosion inhibitor concentration, indicating the adsorption behavior of corrosion inhibitor molecules on the surface of metal copper. It can be explained by the following expression:

$\begin{matrix} C_{d 1} \frac{ε^{0} ε}{d} S & (2 - 2) \end{matrix}$

where, ε and ε⁰represent the dielectric constant and vacuum dielectric constant, respectively. S represents the effective area of the working electrode, d represents the thickness of the electric double layer, and its value is variable. It can be seen from Table 3 and Table 4 that with the increase of the concentration of Platanus acerifolia leaf extract, the value of C_d1decreases gradually, which is attributed to the fact that the water molecules on the steel surface are replaced by the corrosion inhibitor molecules. Because the volume of corrosion inhibitor molecules is larger than that of water molecules, and the dielectric constant is smaller than that of water, the thickness of the electric double layer increases and the local dielectric constant decreases. In addition, the S value decreases with the adsorption of the Platanus acerifolia leaf extract molecules on the steel substrate, these elements together promote the reduction of C_d1and provide significant support for the development of barrier films to protect steel. The inhibition efficiency η can be determined by Equation (2-3):

$\begin{matrix} η = \frac{R_{p} - R_{p, 0}}{R_{p}} \times 100 % & (2 - 3) \end{matrix}$

where, R_pand R_p,0are the polarization resistances without and with Platanus acerifolia leaf extract in 1M hydrochloric acid solution, respectively. It can be seen from Table 3 and Table 4 that the inhibition efficiency n increases with the increase of the concentration of the Platanus acerifolia leaf extract, and the slow release efficiency at 318K is lower than that at 308K, which means that the high-temperature accelerates the corrosion.

TABLE 3

Impedance parameters of Q235 steel in 1M HCl solution containing different

concentrations of Platanus acerifolia leaf extract at 308K

CPE_d1

CPE

C
R
R_ct
Y₀

R_f
Y₀

(mg/L)
(Ω cm²)
(Ω cm²)
(μF cm²)
n
(Ω cm²)
(μF cm²)
n
η %

Blank
0.8272
0.7525
0.00004139
0.9134
4.028
0.0004806
0.7906
—

50
0.705
2.102
0.0000852
0.8942
16.19
0.0001967
0.8134
73.87

100
0.8095
1.244
0.00001824
0.8756
29.06
0.0002061
0.791
84.22

200
0.7878
32.31
0.000187
0.8272
3.072
0.04132
0.9058
86.49

400
0.7088
39.76
0.000222
0.7794
3.531
0.03261
1
88.96

TABLE 4

Impedance parameters of Q235 steel in 1M HCl solution containing different

concentrations of Platanus acerifolia leaf extract at 318K

CPE_d1

CPE

C
R
R_ct
Y₀

R_f
Y₀

(mg/L)
(Ω cm²)
(Ω cm²)
(μF cm²)
n
(Ω cm²)
(μF cm²)
n
η %

Blank
0.7407
0.5244
0.0000570
0.9723
3.886
0.0006857
0.8139
—

50
0.9751
13.24
0.0004155
0.8063
1.751
0.2277
0.8129
70.70

100
0.7749
15.92
0.0004829
0.7574
0.8773
1.119
0.9998
73.85

200
0.598
22
0.0003609
0.7579
1.753
0.6035
0.9122
81.51

400
0.7878
23.3
0.000244
0.7356
3.793
0.1301
0.5384
83.79

(3) Polarization Curve Analysis

the polarization test of the Q235 steel electrode was carried out in 1M hydrochloric acid without and with different concentrations of Platanus acerifolia leaf extract at 308K and 318K, the results of anodic and cathodic polarization curves are shown in FIG. 6. The corresponding corrosion kinetic parameters are summarized in Table 5 and Table 6, where E_corrrepresents the corrosion potential, i_corrrepresents the corrosion current density, θ represents the degree of surface coverage, and η represents the corrosion inhibition efficiency. β_cand β_aare the cathode Tafel slope and the anode Tafel slope obtained by extrapolation, respectively. θ and η are calculated by the following formula:

$\begin{matrix} θ = \frac{i_{corr, 0} - i_{corr}}{i_{corr, 0}} & (2 - 4) \end{matrix}$

$\begin{matrix} η = θ \times 1 0 0 & (2 - 5) \end{matrix}$

where, i_corr,0, and i_corrrefer to the corrosion current density without and with Platanus acerifolia leaf extract, respectively. From FIG. 6a to FIG. 6b, it can be seen that the corrosion potential is negatively shifted after adding the Platanus acerifolia leaf extract, because the Platanus acerifolia leaf extract only inhibits the cathodic reaction, and the corrosion potential shift is less than 85 mV, indicating that the Platanus acerifolia leaf extract is a ‘moderate’ cathodic corrosion inhibitor. In addition, the corrosion current density decreased, and with the increase of the concentration of Platanus acerifolia leaf extract, the corrosion current density continued to decrease, and the corrosion inhibition efficiency gradually increased, the corrosion inhibition efficiency reached a maximum of 93.1% (308K) and 87.8% (318K) at 400 mg/L, indicating that the Platanus acerifolia leaf extract molecules formed a layer of protective film on the surface of Q235 steel, which blocked the direct contact between the corrosive medium and the steel surface, thus achieving the effect of corrosion inhibition.

TABLE 5

Polarization curve parameter of Q235 steel in 1M

HCl solution containing different concentrations

of Platanus acerifolia leaf extract at 308K

C
E_corr
i_corr
β_c
β_a

(mg/L)
(mV/SCE)
(μA Cm⁻²)
(mV/dec)
(mV/dec)
θ
η(%)

0
−406
4388
−189
92
—
—

50
−457
812
−144
78
0.815
81.5

100
−468
453
−137
111
0.897
89.7

200
−470
313
−135
82
0.929
92.9

400
−467
303
−150
76
0.931
93.1

TABLE 6

Polarization curve parameter of Q235 steel in 1M

HCl solution containing different concentrations

of Platanus acerifolia leaf extract at 318K

C
E_corr
i_corr
β_c
β_a

(mg/L)
(mV/SCE)
(μA Cm⁻²)
(mV/dec)
(mV/dec)
θ
η(%)

0
−402
5849
−179
86
—
—

50
−435
1458
−186
69
0.751
75.1

100
−445
1217
−170
64
0.792
79.2

200
−440
866
−179
53
0.852
85.2

400
−462
712
−164
72
0.878
87.8

(4) Surface Morphology Observation

the surface morphology of Q235 steel Is analyzed by field emission scanning electron microscope (ZEISS MERLIN COMPACT). Before the test, the surface of Q235 steel needs to be polished in sequence by 500 to 5000 mesh water phase sandpaper, and the six sides are polished to a smooth surface like a mirror. After that, the ultrasonically cleaned in deionized water and anhydrous ethanol solution are carried out, respectively, and finally, the surface is dried by cold air for later use. The treated Q235 steel is immersed in 1M HCl solution without and with 400 mg/L Platanus acerifolia leaf extract at 308K and 318K (273-373K) for 4 hours, respectively. After the soaking is completed, deionized water and anhydrous ethanol are used for ultrasonication in turn, and cold air drying is used for detection.

FIG. 7a-FIG. 7b and FIG. 8a-FIG. 8b show the scanning electron micrograph of Q235 steel immersed in 1M HCl solution and 1M HCl solution containing 400 mg/L Platanus acerifolia leaf extract for 4 h at 308K and 318K. It can be seen that the Q235 steel immersed in the blank solution is seriously corroded, the surface is very rough, there are different sizes of corrosion pits, and there are more oxidation products on the surface, with the increase in temperature, the surface corrosion of Q235 steel at 318K is more serious. Under the same corrosion condition, the surface of Q235 steel at different temperatures is relatively flat and the corrosion products are significantly reduced after the addition of Platanus acerifolia leaf extract, and the corrosion products at 308K are significantly less than those at 318K, indicating that the Platanus acerifolia leaf extract effectively prevented the corrosion of Q235 steel matrix by HCl solution. Therefore, it can be concluded that the Platanus acerifolia leaf extract has a certain corrosion inhibition performance, which is consistent with the results of electrochemical experiments.

The above examples are merely preferred examples of the present invention, but are not intended to limit the present invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the disclosure should fall within the scope of protection of the present invention.

CORROSION INHIBITOR OF PLATANUS ACERIFOLIA LEAF EXTRACT AND APPLICATION THEREOF

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