The inhibitive effect of vitamin B 2 , B 6 and vitamin C on the cooper corrosion

. Corrosion of copper (Cu) in sodium chloride (NaCl) and hydrochloric acid (HCl) can be inhibited by using inhibitors of vitamins B 2 , B 6 and Vitamin C. The concentration of each vitamin varies between 400 – 1.100 ppm. The copper used is type Cu-OF/CW008A measuring 5 cm x 5 cm x 0.5 cm. The concentration of NaCl solution used as a corrosion medium is 30,000 ppm and 0.4 M HCl concentration. The corrosion process is carried out within 6 – 12 days. The calculation of the corrosion rate on Cu was carried out using the gravimetric method. The corrosion rate in acidic media (HCl) is greater than in neutral NaCl media. This phenomenon happens as the H + ions in HCl acid is receptive to electrons from the oxidized Cu metal. The vitamin inhibitor layer on the surface of the Cu metal reduces the contact between the Cu metal and the corrosion medium, so that the interaction of H + ions in the corrosion medium with the Cu surface is inhibited. Vitamin C can have multiple functions, at certain concentrations it can function as an inhibitor but if the concentration is enlarged it functions as an activator.


Introduction
The environment around which we live is surrounded by chemical compounds.Everything that is around us consists of natural materials or synthetic chemical compounds.The consequences of this situation are detrimental and some are beneficial to human life [1].
Copper metal has many uses because of its good properties, for example for wires, sheets, tubes, and for forming alloys.Copper is resistant to atmospheric influences and resistant to chemical reagents due to the formation of an oxide layer which acts as a passive shield or a non-conductive corrosion layer forms on its surface [2].The reaction process for dissolving pure copper in a solution containing chloride is as follows [3]: These reactions take place reversibly.High chloride concentrations stabilize Cu(I) ions in the form of complex anions CuCl2 -and CuCl3 2- [3].These reactions take place reversibly.High chloride concentrations stabilize Cu(I) ions in the form of complex anions CuCl2 -and CuCl32-.In acidic conditions, the dissolution of copper is accompanied by the release of hydrogen and an increase in chloride concentration resulting in the stability of the solid phase CuCl2•3 Cu(OH)2 increasing compared to the stability of Cu2O and CuO.In this condition, there is potential for corrosion of Cu metal [3].
In the industrial business, there is a massive use of copper.And as such, the problem of copper corrosion and how to overcome it have received the attention of researchers in the field [4].The use of inhibitors to control the corrosion rate of copper is an inhibitor of organic compounds and their derivatives such as azoles, amines, amino acids and others.Inhibitors of these organic compounds are heteroatoms such as nitrogen, sulphur, and phosphorus [5].The interaction between the conjugated electrons in the ring of heterocyclic compounds and the vacant d orbitals on the copper atom also cause coordination bonds to occur [6].Currently, researchers are exploring environmentally friendly corrosion inhibitors (corrosion green inhibitors) that can reduce environmental pollution.One example of an environmentally friendly inhibitor is an active pharmaceutical compound.Pharmaceutical corrosion inhibitors are organic compounds that have a carboxyl functional group and are heterocyclic [6].Vitamin B2 (Riboflavin), vitamin B6 (pyridoxine) and vitamin C (ascorbic acid) as shown in Figure-1 (a), 1(b) and 1(c) are therapeutic molecules including active pharmaceutical compounds [7].These vitamins are a potential corrosion inhibitor.These compounds can be adsorbed by metal surfaces and form complexes with metals.The impact is that the contact of the metal surface with the corrosive medium is inhibited so that the corrosion rate can be inhibited [8].Vitamin C is non-toxic and easily soluble in water.The mechanism of metal corrosion inhibition is thought to be due to the chemical adsorption of ascorbic acid according to the Langmuir adsorption isotherm [9].Vitamin C that can inhibit around 83% in the corrosive medium HCl due to the adsorption of Dehydroascorbic acid (DHA) is an oxidized form of ascorbic acid onto the metal surface [10].Vitamin B6 can be used as a corrosion inhibitor because its chemical structure contains heteroatoms (oxygen and nitrogen) which can facilitate adsorption on metal surfaces and is environmentally friendly and non-toxic [11].

Materials and methods
Corrosion rate is calculated by dividing the result of the multiplication of conversion constant (K) and the difference between the initial weight of Cu before corrosion (W0) and the weight of Cu after corrosion (W1) by the result of the multiplication of specific gravity of Cu (D), surface area of Cu (A), and length of time of the corrosion process (T).The Calculation of the corrosion rate using the gravimetric method can be formulated in the following equation-1 [12].CR = corrosion rate (milli inches/year, mpy) K = conversion constant to mpy: 3.45 x 106 W0 = weight of Cu before corrosion (g) W1 = weight of Cu after corrosion (g) D = specific gravity of Cu (8.93 g/cm 3 ) A = surface area of Cu (cm 2 ) T = length of time of the corrosion process (hours) The gravimetric method has the advantage of being able to determine the corrosion rate and inhibitor efficiency.The disadvantage of the gravimetric method is that it is not flexible because it requires repeated weighing.The concentrations of vitamin B2, B6 and vitamin C each range between 400 -1,100 ppm.The copper used is type Cu-OF/CW008A measuring 5 cm x 5 cm x 0.5 cm.The concentration of the NaCl solution used as a corrosion medium is 30,000 ppm and for HCl the concentration is 0.4 M. The corrosion process is carried out within 6 -12 days.

Corrosion rate of Copper in NaCl and HCl Corrosion media without Inhibitor
The Cu corrosion rate was determined at various concentrations of the NaCl corrosion medium between 26,000 ppm to 35,000 ppm without inhibitors.The results are shown graphically in Figure -4.It can be seen in Figure 4 that the corrosion rate without inhibitors was greatest at a NaCl concentration of 30,000 ppm for 10 days reaching 55,789 mpy. Figure 6, 7 and 8 shows the corrosion rate of Cu without inhibitors at various concentrations of HCl solution.The corrosion rate on the 12th day decreased because it was predicted to be due to the formation of a passive layer on the metal plate which inhibited it corrosion of metal [13].The concentration of the NaCl corrosion medium is determined based on the range of NaCl concentrations in seawater.Meanwhile, the concentration of the HCl solution is determined to be less than 1.5 M because HCl is very corrosive [14].

Copper Corrosion Rate in NaCl Corrosion Media using Inhibitors
Cu Corrosion Rate in 30,000 ppm NaCl Corrosion Media at various concentrations of vitamin B2, B6, and vitamin C inhibitors is shown in Figures 6, 7 and 8.The copper oxidation process can increase depending on the conditions of the acidic environment or the presence of easy compounds ionized like NaCl [15].The media containing aggressive anions such as chloride, Cl − cause the passive film on the metal surface to become unstable and locally degraded.As a result, the thin layer/film is damaged and ultimately corrosion occurs on the metal surface [16].Therefore, in this research, Cu corrosion is carried out using NaCl corrosion media.Inhibitors of vitamin B2, B6, and vitamin C can reduce the rate of Cu corrosion.If the concentration of vitamin B2, B6 and vitamin C inhibitors increases to 1,100 ppm, the Cu corrosion rate decreases.This is because organic inhibitors of vitamins B2, B6, and vitamin C contain heteroatoms such as nitrogen (N) and oxygen (O).This organic inhibitor also has lone pairs of electrons and phi (π) electrons which can interact with the metal surface to form an adsorption system [17].Organic inhibitors of vitamins B2, B6, and vitamin C can reduce the rate of Cu corrosion.The highest vitamin B2 inhibitor efficiency is 18.12% at a vitamin B2 concentration of 1,100 ppm for 8 days.Meanwhile, the greatest efficiency of the vitamin B6 inhibitor is 30.06% with 30,000 ppm NaCl corrosion media and an inhibitor concentration of 1,100 ppm for 8 days.The highest vitamin C inhibitor efficiency is 40.68% if the vitamin C concentration is 1,100 ppm and the corrosion time was is 12 days.

Copper corrosion rate in HCl Corrosion Media using Inhibitors
Cu Corrosion Rate in 0,4 M HCl Corrosion Media at various concentrations of vitamin B2, B6, and vitamin C inhibitors shown in Figures 9,10 and 11.HCl is a strong reducing acid, so it is very corrosive.HCl has a high dissociation rate in water.As a result, it produces H + ions so the pH is very low.This property makes HCl very corrosive [18].In the 0.4 M HCl corrosion medium, vitamin B2, B6 and vitamin C inhibitors can reduce the Cu corrosion rate.The highest efficiency of the vitamin B2 inhibitor is 18.34%, the highest efficiency of the vitamin B6 inhibitor is 18.24% all for 8 days with an inhibitor concentration of 1,100 ppm.Meanwhile, the highest vitamin C inhibitor efficiency is 25.18% for 6 days with a vitamin C inhibitor concentration of 1,100 ppm.Even though the corrosion medium is HCl which is very corrosive, vitamins B2, B6 and vitamins can still function as inhibitors.If the magnitude of the inhibitor efficiency is significantly different, it is the efficiency of the vitamin B6 inhibitor in the corrosion media NaCl and HCl.It turns out that the ability to inhibit the corrosion rate of vitamin B6 inhibitors is greater if the corrosion medium is NaCl.This indicates that HCl is more corrosive than NaCl [19].HCl has the electrolyte H + and Cl - all of which can attack Cooper, while NaCl only has Cl -which can cause corrosion on Cooper [19].As a result, the corrosion rate in the HCl medium is greater than in the NaCl medium.

Conclusion
The result of this research reveals that vitamin B2, B6 and vitamin C inhibitors can inhibit the corrosion rate of Cu metal.Vitamin B6 inhibitor with the same concentration, namely 1,100 ppm, has different inhibitor efficiency in different corrosion media.In the HCl corrosion

Fig. 2 .
Fig. 2. Cu corrosion process.Cu corrosion process is presented in Figure-2 and Cu corrosion is presented in Figure-3.

Fig. 4 .
Fig. 4. Corrosion Rate of Copper in NaCl Corrosion Media without Inhibitor.

Fig. 5 .
Fig. 5. Corrosion Rate of Copper in HCl Corrosion Media without Inhibitor.

Figure- 5
shows that the largest Cu corrosion rate without inhibitors was in 0.4 M HCl for 10 days reaching 80.85 mpy.The corrosion rate on the 12th day decreased because it was predicted to be due to the formation of a passive layer on the metal plate which inhibited it corrosion of metal[13].The concentration of the NaCl corrosion medium is determined based on the range of NaCl concentrations in seawater.Meanwhile, the concentration of the HCl solution is determined to be less than 1.5 M because HCl is very corrosive[14].Figure-5 and Figure6, 7 and 8 shows that the experiment to determine the corrosion rate of Cu in organic shows that the largest Cu corrosion rate without inhibitors was in 0.4 M HCl for 10 days reaching 80.85 mpy.The corrosion rate on the 12th day decreased because it was predicted to be due to the formation of a passive layer on the metal plate which inhibited it corrosion of metal[13].The concentration of the NaCl corrosion medium is determined based on the range of NaCl concentrations in seawater.Meanwhile, the concentration of the HCl solution is determined to be less than 1.5 M because HCl is very corrosive[14].Figure-5 and Figure6, 7 and 8 shows that the experiment to determine the corrosion rate of Cu in organic

Fig. 6 .
Fig. 6.Cu Corrosion Rate in 30,000 ppm NaCl Corrosion Media at various concentrations of vitamin B2 inhibitors

Fig. 11 .
Fig. 11.Cu Corrosion Rate in 0,4 M HCl Corrosion Media at various concentrations of vitamin C inhibitors.