Optimization of low carbon steel coating with corrosion inhibitor method based on siwalan (Borassus flabellifer) fiber extract

OBJECTIVES Siwalan fiber waste (SFW) has the potential as a source of lignin (7-25%) which is used as a green inhibitor to inhibit the corrosion rate of low carbon steel (LCS). The aims of this study were: (1) determine the optimum conditions(typesofHClandH 2 SO 4 , C inhibitor and C media , inhibition temperature,andcoatingtime)forLCScoatingprocessusing the inhibitory method using lignin extract from SFW, and (2) knowing the resistance of LCS coated with inhibitor at optimum conditions. METHODS Empirical research through laboratory experiments explains the relation between variables by analyzing numerical data. 185g of SFW produced 52.289g (28.26%) fine brown powder. RESULTS IR spectrum analysis on extract showed the wavelength was almost the same as the standard. IR spectrum analysis was also carried out on the extracted compounds that were adsorbed, and the absorption peaks confirmed the presence of lignin in the adsorbed compounds. CONCLUSIONS Based on the results of the analysis of the weighing data of the specimen before and after inhibition, the inhibitor concentration of 0.2–0.3 g/L in H 2 SO 4 at 313K is the optimum condition to suppress the corrosion rate on the surface of LCS by 76.2%.


INTRODUCTION
Straddling the equator, Indonesia is a tropical climate that produces endemic plant biodiversity, Siwalan (Borassus flabellifer). Based on data from the Department of Agriculture and Plantation of East Java Province in 2018, 93,000 -186,000 tons of palm fiber waste were produced every day (Ministry of Agriculture Directorate General of Plantation, 2019). This leads to the accumulation of siwalan fiber waste in Indonesia because it is not used. On the other hand, siwalan fiber waste can be a source of lignin (7-25%) which can be treated as a green inhibitor for coating on low carbon steel, which reduces the corrosion rate (Dehghani et al. 2019). Reducing the corrosion rate will prevent technical accidents such as bridge collapses, building construction, and tank leaks at oil refineries, resulting in various financial losses, health, and death. (Alcántara et al. 2017).
Based on a research by Hassannejad and Nouri (2018), regarding lignin extract from sunflower seeds and Ramlah et al. (2020) with flavonoid extract from beluntas leaves, it has several shortcomings, namely the availability of sunflower seeds and beluntas leaves, which are not abundant in Indonesia and are widely used as food (Ramlah et al. 2020). It was found that the sunflower seed extraction research conducted by Hassannejad and Nouri (2018) only produced lignin extract of less than 8%, and the beluntas leaves only produced a corrosion rate inhibitory effect of only 2.31% (Farimani et al. 2020).
The results of the analysis regarding the application of lignin extract from siwalan fiber waste (Borassus flabellifer) in LCS have been carried out by Khoirunnisa Susanti et al. (2021) and demonstrated that the highest LCS resistance value is estimated to occur in the state of the optimization value of lignin inhibitor concentration in the range of 0.5 mg/day. 2.0-3,0 mg/L with immersion time ½ hours-24 hours on 0,5 M H 2 SO 4 (Susanti et al. 2021). The results displayed that the lignin extract produced from siwalan fiber waste was predicted to have an inhibitory effect on the corrosion rate of up to 25.28% under conditions of optimum inhibitor concentration, temperature, and immersion time (Susanti et al. 2021).
Prof. Emeritus Dr. Carlton W. Dence mentioned that lignin has the potential as a corrosion inhibitor due to the presence of OH groups and aromatic rings in its structure as much as 82.71% (Divya et al. 2019). Thus, the objectives of this study are: (1) To find out the optimum conditions (types of HCl and H 2 SO 4 , inhibitor concentrations and acid media, inhibition temperature, and coating time) for the low carbon steel coating process using the inhibitory method using green inhibitor lignin extract of siwalan (Borassus flabellifer) fiber waste, and (2) Figuring out the percentage increase in the resistance of low carbon steel coated with green borer corrosion inhibitor at optimum conditions.
The significance of this research are: (1) The results of this study serve as a reference in dealing with corrosion rates in metals using the inhibition method and can provide a new source of literature in the development of science, especially in the field of local materials science in Indonesia, (2) The results of this research are the latest technological breakthroughs in overcoming the problem of the applicative resistance of LCS material to corrosive substances especially in Indonesia, (3) The results of this research provide innovations in a variety of inhibitor substances to provide solutions to prevent corrosion of metal materials, and (4) The use of siwalan fiber (locally fiber waste plant from Indonesia) can reduce waste that is not utilized, and optimize the use of abundant nature.

RESEARCH METHODOLOGY
This empirical research uses laboratory experiments to confirm the relationship between variables by analyzing the numerical data obtained. The independent variables of this study used variations of acid type, the concentration of inhibitor and acid (HCl and H 2 SO 4 ), inhibition temperature, and coating time, with the control variable being LCS specimens

Materials
The materials needed are as follows: siwalan fiber waste dry in 100 mesh from Tuban East Java, LCS specimens (1 cm x 1.5 cm x 0.2 cm), 37% HCl, 98% H 2 SO 4 , NaOH p.a, technical acetone, and distilled water. The instrumentation needed are: sticky notes, grinder, analytical balance, universal pH indicator, thermometer, scissors, nylon thread, spray bottle, 70 mesh sieve, Whitman filter paper no. 1, 10 and 0.1 mL mohr pipettes, glass pipette, and stirrer, stand and clamp, Buchner funnel, oven, petri dish, 100 mL measuring flask, glass The first step is to separate and clean the siwalan, and then after that, it is crushed and mashed. Then it is left in the oven to dry at 60 o C for 24 hours. Next, the siwalan is dried, ground, and sieved. Furthermore, 185 grams of siwalan fiber powder was soaked in 2 L of 15% NaOH. The mixed solution was heated at 80 o C and stirred for 6 hours. It was then left to be cooled to form a precipitate. The precipitate is separated from the filtrate. The filtrate was acidified with 40% H 2 SO 4 to pH±2 and left for 1x24 hours to form a precipitate. The precipitate formed was filtered and dried in an oven at 60 o C for 12 hours.

Specimen preparation
The specimen used is low carbon steel which has been cut with dimensions of 1 cm x 1.5 cm x 0.2 cm. After that, the spec-  imens were sanded. Sanding is done in 2 steps, the first is sanding with 80 grit to remove the plating that sticks to the specimen surface, and then sanding with 150 grit to smooth the surface that has been clean from the plate so that it has a homogeneous surface. After sanding, specimen cleaned with distilled aquadest to rinse off the remaining sandpaper. After rinsed by aquadest, specimen rinsed with acetone, and then dried in an oven at 60 o C for 10 minutes. The dry sample was then cooled and then weighed (W 0 ).

Lignin adsorption process on LCS specimens
Specimens with known initial weight (W 0 ) was immersed in an acid solution (HCl and H 2 SO 4 ) with a concentration variation of 0.25; 0.5; and 1M for 2 hours (recorded mass every 15 minutes and dried for ± 3 minutes). Then the specimen was washed with distilled water, rinsed with acetone, dried in an oven at 60 o C for 15 minutes, then weighed the final mass of the whole process (W t ).
FIGURE 3. IR spectra of adsorbed lignin compounds.

Data collection
The results of LCS mass weighed before, during, and after the inhibition were recorded and tabulated with sample codes presented in Tables 1 and 2.

Characterization of lignin functional groups using FTIR
The extracted lignin in solid/powder was tested to determine the functional groups of lignin compounds using FTIR. Sample preparation (for solid samples, the sample is mixed with KBr in a ratio of 1:10 and for the sample it must be free of H 2 O and placed between 2 KBr plates) then analysis is carried out. Identification of functional groups was analyzed by observing the absorption peaks that appear at specific wavelengths and compared based on standard absorption references.

Microscopic characterization of specimens using SEM and EDAX
LCS specimens before and after adsorption with and without the addition of lignin inhibitors were characterized to examine their pore size and confirmed the presence of lignin constituents on the surface of the adsorbed specimen. The sample to be analyzed is placed in a holder measuring ± 10mm. the sample was prepared by coating using Au-Pd (this aims to make the sample more conductive). The sample is put into the SEM chamber then low vacuum pump. Characterization results were compared between specimens before inhibited, uninhibited, and after inhabited by lignin.

Data analysis and interpretation
In order to analyze the data, quantitative descriptive analysis is employed to help summarize the results and calculating the inhibition efficiency and the effectiveness of reducing the corrosion rate. Data is interpreted into tables and histograms.

Percentage of lignin extract yield from siwalan fiber
The yield of lignin resulting from the extraction of siwalan fibers is calculated using the equation1.

Calculation of the weight loss measurement and method of calculation of inhibition efficiency
The test using the weight loss method refers to the ASTM G31-72 standard. The inhibited low carbon steel specimens were FIGURE 5. Inhibitor adsorption mechanism on Fe surface.
then weighed, and the percentage of inhibition efficiency and corrosion rate was determined.

Stage of research
Figure 1 is the stage of the research carried out. The data analysis technique used was quantitative descriptive analysis by summarizing the research results, calculating the % efficiency of corrosion inhibition and reduction, interpretation of IR spectrum data, and analysis of microscopic morphology and compound content in the specimen using SEM-EDAX.

Lignin extract yield
The siwalan fiber used as the material for this research was obtained from Tuban, East Java district. The extract obtained from 185 grams of siwalan fiber waste produced 52.289 grams (28.26%) of fine brown powder. Based on Figure  2   book.nist.gov). It is analyzed and confirmed that the compound obtained was a lignin compound. The IR spectrum of standard lignin has a narrower peak, on the other hand, the compound extract has a wider peak because it describes a bond that includes a lot of energy. The widening is because the intermolecular H-bonding shows a widening of the IR band due to the strength of the continuum bond.

Adsorbed lignin compound
The FT-IR test was also carried out on the solid brown coating the specimen to confirm the formation of new compounds after the inhibition process. Figure 3 is the IR spectrum of the extracted compound adsorbed on the specimen.
The absorption peaks at wavelengths 3487.3, 1612.49, 1508.33, 1373.32, and 10423 cm -1 respectively indicate the presence of stretching vibrations of phenolic OH groups, aromatic C=C, OH bending vibrations in the plane, and the stretching vibration of the aromatic ring CO which confirmed the presence of lignin content in the adsorbed compound. The fingerprint region shows a complex bond between the specimen and the extracted compound, which was adsorbed were Fe-O at the wavelength of 653,87 cm -1 and corrosion products -FeOOH and -Fe 3 O 4 at wavelength 804,32, dan 896,9 cm -1 .

SEM and EDAX microscopic analysis
SEM-EDAX characterization was carried out on low carbon steel specimens before inhibition and inhibited specimens in HCl and H 2 SO 4 media with and without inhibitors at 100x,  1000x, 5000x, and 10000x magnifications. Figure 4 (a) illustrated the condition of the specimen before the inhibition process, which demonstrated that holes and cracks had not yet formed. Figure 4 At 1000x magnification, clusters of various sizes on the specimen after inhibition are spread over almost every surface. 1000x magnification Figure 4. (b 2 ) and (c 2 ) clusters were formed in both specimens, but more clusters were formed in the specimens without inhibitor, almost evenly on the surface and 38.971µm larger than the specimens using 2.168 m inhibitors. At 5000x magnification, as shown in Figures 4 (b 3 ) and (c 3 ), the holes formed in the specimen without the inhibitor are almost uniformed on the surface and are larger than the holes in the specimen with the inhibitor on the uneven surface (Mobin et al. 2019). While at 10000x magnification in Figure 4 (b 4 ) and (c 4 ), cracks are seen in both specimens. Specimens without inhibitors had more cracks than those with inhibitors.
Lignin compounds consisting of monomers p-coumaryl-, coniferyl-, and sinapyl alcohol have the potential as corrosion inhibitors on metals. This makes lignin compounds potential as centers of adsorption inhibitors and can inhibit the rate of corrosion. The inhibition of corrosion rate of low carbon steel (LCS) in H 2 SO 4 by neutral and protonated monolignol lignin was explained based on molecular adsorption. Lignin monolignol inhibitors are predicted to be adsorbed on the LCS surface in the following manner: 1. Donor-acceptor interaction between the π electron of the aromatic ring of the inhibitor species and the vacant d or-bital of the iron atom on the surface, 2. The interaction between the lone pair of heteroatoms of the neutral inhibitor and the unpaired electrons of the protonated inhibitor with the empty d orbitals of the iron atom on the surface of the LCS.
Based on the MD simulation and MC calculation results thant have been conduct by Susanti et al. (2021), two interactive simulations can be predicted during the adsorption process. Neutral and protonated species of lignin compounds interact with sulfate ions previously adsorbed on the surface of the LCS, resulting in the physisorption of inhibitor molecules. With this, the inhibitor molecule competes with the H + proton of sulfuric acid to form bonds with the electrons of Fe atoms on the surface of the LCS, however, based on the plot calculation data E HOMO and E LUMO , protonated lignin compounds more easily form bonds with Fe atoms than protons H + .
Corrosion inhibitor species are adsorbed on the surface of the LCS through a chemisorption mechanism that involves the transfer of electrons from the inhibitor heteroatom to the Fe atom on the surface of the LCS in sulfuric acid media. Inhibitor molecules can also be adsorbed on the surface of LCS based on donor-acceptor interactions between electrons π from the heterocyclic ring to the empty d orbital of the surface iron. The corrosion inhibition mechanism is shown in Figure 5.
Cracks and holes formed are the main factors causing corrosion because they are the entrance for corrosive substances to oxidize iron on the surface of low carbon steel (Nathiya et al. 2019;Shi et al. 2018). The results of the EDAX test on specimens without and with inhibitors are shown in Figures 6 (b) and (c). The test results are compared with Figure 6 (a), which is the result of the EDAX test of the specimen before inhibition.
Based on the results of the EDAX test in before and after inhibition with and without inhibitor. EDAX test sample used in optimum condition specimenwhich is AA01 (C inhibitor 0 g/ 0.25 M in H 2 SO 4 ) and BB01 specimen (C inhibitor 0.2 g/ 0.25 M in H 2 SO 4 ). The specimens before inhibition showed the per-  centage of Fe elements of 92.77% and O 7.23%, while in the specimens after initiation without inhibitors, the Fe content was only 72.98%, and 27.02% of O elements formed due to acid reactions with the specimen in the inhibition process. Based on Figure 6. the percentage of elemental O content without inhibitor is more than with inhibitor (10.57%); this indicates an inhibitory effect on the formation of corrosion products (Fouda et al. 2016).

Calculation results of corrosion rate and corrosion rate inhibition effect
Based on the results of weighing the specimens before and after inhibition in HCl and H 2 SO 4 media, data analysis can be carried out to determine the effect of independent variables on the optimum control of low carbon steel resistance (Pradityana et al. 2013).

Effect of lignin concentration on inhibition efficiency and corrosion rate
The calculation of the efficiency of inhibition and corrosion rate of steel in HCl and H 2 SO 4 0.25M media with and without inhibitors of siwalan fiber waste extract under immersion for 2 hours at 303K is shown in Figure 7  shows that the greater the concentration of inhibitor (lignin) used, the lower the corrosion rate, both in HCl and H 2 SO 4 media. This is because the adsorbed extract compounds bind to the iron to form a thin layer that protects the specimen from corrosive substances (Ahanotu et al. 2020). The inhibitor concentration of 0.2 -0.3 g/L in HCl and H 2 SO 4 is the highest optimization of the addition of inhibitors to achieve the percent inhibition efficiency and optimum corrosion rate.

The effect of acid concentration on inhibition efficiency and corrosion rate
The results of the calculation of the efficiency of inhibition and corrosion rate of steel in HCl and H 2 SO 4 at concentrations of 0.25, 0.50, 1.00M with and without inhibitors of si-walan fiber waste extract under immersion in 2 hours at 303K are shown in Figure 8 (a) and (b). Based on Figure 8 (a), the higher the acid concentration, the higher the percentage of inhibition efficiency. Figure 8 (b) also shows that the greater the acid concentration used, the higher the corrosion rate, both in HCl and H 2 SO 4 media. This is because high acid concentration and inhibitor adsorption process causes the iron on the low carbon steel surface to be oxidized and result in corrosion . However, the graph of the increase in the corrosion rate, which is more sloping than the percentage value of the inhibition efficiency, shows that the optimization of the function of the acid as an inhibitor adsorption medium is more substantial (Hassannejad and Nouri 2018). The type of acid used also affects the percentage of inhibition efficiency and corrosion rate. Hydrochloric acid (HCl) has a higher percentage of inhibition efficiency than sulfuric acid (H 2 SO 4 ). This is because HCl is a strong acid that is more stable than sulfuric acid with high reactivity ).

The effect of temperature on inhibition efficiency
The graph displaying the relationship between temperature and the calculation of the percent inhibition efficiency in HCl and H 2 SO 4 is shown in Figure 9. Figure 9 displays the percentage optimization of the highest inhibition efficiency at 313K in HCl and H 2 SO 4 media, 28.16 and 39.93%, respectively.

The effect of immersion time on changes in weight and corrosion rate
The graph illustrating the relationship between immersion time on changes in specimen weight and corrosion rate in 0.25M HCl and H 2 SO 4 are presented in Figure 10. (a) and (b), respectively. Based on Figure 10. (a) shows the length of immersion time (inhibition process), which varies with the influence of changes in specimen weight (∆W). This is caused by the formation of corrosion products that make the specimen porous during the inhibition process. In the 75 th to 90 th minute, there was an increase in the weight of the specimen, which was indicated by a negative value of W. This is due to the presence of inhibitors adsorbed on the surface of low carbon steel (Rosli et al. 2019). The difference in the acid concentrations used also influences the weight loss of the specimen. Figure 10 (a) shows that H 2 SO 4 experienced a significant change in the weight of the specimen. This event is because H 2 SO 4 oxidizes iron strongly and adsorbs corrosion inhibitors rather than HCl. While in Figure 10 (b) is a graph of the effect of immersion time on the corrosion rate. The graph shows at 75 th minute in H 2 SO 4 media, which is the optimum condition to suppress the corrosion rate on the surface of low carbon steel.

Reactivity of Lignin Species as Corrosion Inhibitor
From a previous literature review, it is acknowledged that the value of the transferred electron fraction (∆N), which is higher than zero (positive value), indicates the fact that the inhibitor molecule can transfer its electrons to Fe atoms on the surface of the LCS. However, if the value of this parameter is lower than zero, it proves the existence of electron transfer derives from the metal to the inhibitor. The data collected in table 1 explained that if N's value for neutral and protonated inhibitors is positive, it indicates that all neutral and protonated lignin molecules tend to donate electrons to empty orbitals of Fe atoms. The highest PI value explained that the molecule had the highest adsorption reactivity as a corrosion inhibitor. Table 3. shows the pattern of increasing the value of the ionization potential, which is correlated with the pattern of increase in E HOMO . Based on equation 3, the PI value is obtained from the negative value E HOMO . The PI of the protonated p-coumaryl alcohol compound is 0.19024 eV, the highest among the ionization potential values of other compounds. This proves that the highest adsorption reactivity is in the protonated monolignol lignin compound p-coumaryl alcohol. Moreover, Table 3. also indicates the value of the difference in electronegativity of each neutral and protonated monolignol lignin molecule. The value of a slight difference in electronegativity in a molecule indicates that the molecule tends to reach electron equilibrium, making the molecule less reactive than other molecules and vice versa. This signifies that protonated p-coumaryl alcohol compounds are in a very reactive condition as corrosion inhibitors. Protonated p-coumaryl alcohol compounds are more easily bound to Fe atoms on the surface of LCS to achieve electron distribution equilibrium than other compounds. Table 4 exhibited the results of the calculation of the inhibition efficiency (IE theory %) of neutral and protonated pcoumaryl-, coniferyl-, and sinapyl alcohol compounds. The data showed irregular %IE values in each analyzed lignin molecule. The calculation results explain that adding electron donor groups such as hydroxyl and methoxy groups to the inhibitor compound may not necessarily increase the percentage of inhibition efficiency. Based on the data in Table 4. and according to the results of the pattern calculation E HOMO , ionization potential, and electronegativity can be predicted that the p-coumaryl alcohol molecule has the highest inhibition efficiency value of 23.4100% compared to other compounds. This is because the donor-acceptor interaction between the electrons of the aromatic ring and the lone pair of inhibitor heteroatoms with the empty d orbital of the iron atom on the surface of the LCS is stable on the phenolic group, causing the p-coumaryl alcohol molecule bound to the Fe atom to be more stable than other molecules.

Absorptivity of Fe Atoms on the Surface of LCS in H 2 SO 4
The interfacial adsorption of monolignol lignin compounds (p-coumaryl-, coniferyl-, and neutral and protonated sinapyl alcohol) on the surface of the Fe(110) target was theoretically simulated using a combination of Monte Carlo (MC) calculations and Molecular Dynamic (MD) modeling. The graphical results of the MD modeling are visualized in Figure 11. The side view proves that the protonated and neutral p-coumaryl, coniferyl, and sinapyl alcohol molecules tend to approach the crystallographic plane of Fe (110).
The top vertical cross-section view of the resulting graphic Figure 11 demonstrates molecules' adsorption in a flat frame orientation. The lignin molecule has a larger size than the Fe atom so that the predicted bond does not occur at the junction of the iron crystals. This can cause a steric effect on the monolignol lignin molecule, but based on the results of the MC calculation, the molecule will be adsorbed on the Fe surface and form an absorbent layer with solid chemical bonds that the iron element does not undergo direct contact with corrosive substances. The results of the MC calculation explained that the optimization of the highest negative value of adsorption energy was in the condition of 0.50M H 2 SO 4 media with an inhibition temperature of 303K. This explains that the 0.50M H 2 SO 4 medium with an inhibition temperature of 303K is the optimum condition for the inhibitor adsorption process, which is characterized by the largest binding energy value among other control conditions. Table 5 is the MC optimization data at optimum conditions. The quantitative results of the respective MC simulations showing the calculation of the adsorption energies of the neutral and protonated p-coumaryl-, coniferyl-, and synapyl alcohol molecules.
Based on the data in Table 5, the adsorption energy of p-coumaryl-, coniferyl-, and sinapyl alcohol molecules, both neutral and protonated, presents a negative value of adsorption energy. This indicates the tendency of monolignol lignin molecules to bind to Fe atoms on the surface of the LCS. The ease of adsorption of neutral and protonated monolignol lignin molecules occurs when the molecules that make up the media (H 2 O, HSO 4 -, and H + ) are at the interface, this is because the added H 2 SO 4 media functions as an oxidizer on the target iron surface which can facilitate the adsorption process of neutral and protonated monolignol lignin molecules. In addition, the results of the MC calculation of predicted molecules in H 2 SO 4 media also show that protonated p-coumaryl alcohol molecules have the highest negative adsorption energy value compared to other molecules. The negative value of the greater adsorption energy indicates that the value of the binding energy of the molecule is increasingly positive. The positive value of the binding energy of the inhibitor molecule indicates the bond strength of neutral and protonated monolignol lignin compounds adsorbed on Fe LCS. The protonated p-coumaryl alcohol molecule has the highest binding energy, indicating that the molecule has the strongest bond (chemisorption) with Fe atoms compared to other molecules. A negative enthalpy indicates that the bond energy being broken is greater than the binding energy formed. The enthalpy value of the Fe atom bonded to the sulfate anion is negative, which indicates that the binding energy between the broken Fe atoms is greater than the binding energy of the Fe-acid formed (it is difficult to form a product). The binding energy between Fe atoms is smaller than the binding energy of the Fe-inhibitor formed, which causes the acid to function as a medium for adsorption of lignin molecules on Fe atoms. The MC calculations proved that the adsorption energy of inhibitor molecules in sulfuric acid media is more negative than without sulfuric acid; this more negative value signifies how easily inhibitor molecules are adsorbed on Fe atoms on the surface of the LCS.

CONCLUSIONS
Based on the research that has been done, siwalan fiber waste produces 28.26% of fine brown powder. The results of the IR spectrum analysis on the extract confirms that the extraction compound obtained is a lignin compound. The analysis of the IR spectrum presented that indicated presence of lignin compounds in the adsorbed compounds. The results of the SEM test at 1000x magnification showed the presence of an inhibitor can hinder the formation of corrosion products in the specimen. At 5000x magnification, the holes formed in the specimen without the inhibitor are almost uniform on the surface than the holes in the specimen with the inhibitor, which are uneven. At 10000x magnification, cracks occur in both specimens. Specimens without inhibitors had more cracks than those with inhibitors. This is the main factor causing corrosion. Based on the results of the analysis of the data weighing specimens before and after inhibition showed: a) The condition of the inhibitor concentration of 0.2 -0.3 g/L in HCl and H 2 SO 4 was the highest optimization of the addition of inhibitors to achieve the percent inhibition efficiency and optimum corrosion rate; b) the graph of the increase in the corrosion rate which is more sloping than the percentage value of the inhibition efficiency shows the optimization of the function of the acid as a stronger inhibitor adsorption medium; c) the effect of temperature on inhibition efficiency showed that the highest percentage optimization of inhibition efficiency was at a temperature of 313K in HCl and H 2 SO 4 , which were 28.16 and 39.93%, respectively; d) at 75 th minute in H 2 SO 4 , as the optimum condition to suppress the corrosion rate on the surface of low carbon steel.

ACKNOWLEDGEMENTS
A deep sense of gratitude to the Universitas Negeri Malang and the Ministry of Education, Culture, Research, and Technology for funding the implementation of PKM-Exact Research.