Add corrosion inhibitor protection

Electrochemical protection includes cathodic protection, anode protection and protector protection. The role of these corrosion inhibitors is to directly prevent metal ions from entering the solution, and the other is to form a protective film on the metal surface so as to reduce the anode surface. These materials are constantly in contact with atmospheric oxygen, water vapor, acid mist and acid, alkali, salt and other substances, so that the metal is eroded. It is evident that many commonly used metals can spontaneously form oxides with oxygen in the atmosphere. Metal erosion always begins at the surface and spreads inward or simultaneously to other parts of the surface. Therefore, iron is naturally white when it is eroded.

Metallurgy from ores requires energy, and metal erosion will restore it to a mineral-like state, so the erosion grounding of metals represents an important energy consumption. The reactants let us study the reaction of typical metals with oxygen. It is found that since the natural free energy of any solid element is zero, for the oxidation reactions mentioned above, there is a delta of oxides. The erosion of metals in organic liquids such as benzene and other non-electrolyte solutions, and in petroleum containing sulfur, is also chemical erosion. Anode protection is to use an external power supply to make the metal to be protected as anode, anodize, through the metal passivation method to be protected. The natural composition of the atmosphere affects the formation of erosive components, and we should take the problem of metal erosion seriously even if there are no pollutants in the surrounding environment. According to the electrode potential of the half cell, the direction of the reaction can be accurately judged, one by one. Having said this, we can say that any metal pair more active than hydrogen has a negative electrode potential and can be eroded in the atmosphere. Indeed, even if two metals are not in contact, the possibility of erosion exists whenever the metals come into contact with an aqueous solution. Thermodynamics reminds people that in practical use, the metal state should not be preferred.

Cathode corrosion inhibitor

Types of corrosion inhibitors Corrosion inhibitors are medium added to the corrosive medium which can greatly reduce the electrochemical reaction rate of metal erosion. Expansion indicates that the presence of oxygen aggravates the erosion of metals. An important method of covering metal with an corrosion-resistant protective coating is electroplating. Because of erosion and scrap metal equipment and materials, the number is very large, the loss to the national economy is very amazing. Even after cleaning, the use of a higher concentration of corrosion inhibitor is generally necessary. Thermodynamics, of course, can only tell us how likely a reaction is to happen spontaneously, not how fast, which is the domain of kinetics. After pickling to remove the residual acid on the metal products, and then immersed in appropriate alkali, phosphate or chromate washing, can also contain stearic acid in hot water washing, so that the surface of the protective metal to form a layer of hate water film. Organic corrosion inhibitors These corrosion inhibitors are commonly used in acidic solutions such as metal pickling. It is generally believed that the organic preservatives with low molecular weight are adsorbated on the surface of metals, which increases the superpotential of hydrogen and inhibits the discharge process of ions, thus slowing down the dissolution rate of metals. Some macromolecular organic preservatives, such as gelatin, dextrin and AGAR, are adsorbed on the metal surface, resulting in the so-called lock-in effect, which increases the resistance and reduces the current density. The acid dissolves the oxide on the surface and exposes the clean metal. If the corrosion inhibitor is added to the acid wash solution, the electrochemical erosion and corrosion of the metal in the first stage of the corrosion inhibitor are adsorbed to form a protective layer.

Red or gray rust forms in the presence of sufficient dissolved oxygen

Black magnet -

A? Green hydrating magnet

If dissolved oxygen in an aqueous solution is limited, the following reaction will occur

Metal such as iron in contact with oxygen saturated electrolyte solution, the oxidation of metal on the anode is natural ", the released electrons to a certain direction of the cathode move, at the cathode is oxygen reduction, so that the solution near the cathode is alkaline. The precise choice of corrosion inhibitor depends on the metal being protected and the acid used. Sometimes it is beneficial to add a detergent or foaming agent to the pickling tank. Some metal ions, such as antimony, can form a film on the cathode surface to slow down the process of hydrogen escape from the cathode, which is especially useful for acidic solutions. The commonly used corrosion inhibitors during pickling are amine, sulfur veins and aldehydes. Such as protective layer, electrochemical protection, corrosion inhibitor protection, etc.

Corrosion protection of metal

So the color of the iron product depends on the amount of oxygen.

When metal and electrolyte solution are in contact, the erosion caused by electrochemical action is called electrochemical erosion.

Electrochemical protection law

The protective layer of metal has two kinds of non-metallic and metal protective layer method, and the non-metallic materials that are used as the protective layer are paint, enamel, glass, rubber, plastic and so on.

. The latter depends on the acidity of the solution and the dissolved oxygen. Because rust is usually porous, it provides no protection, so that water can permeate into the base metal, causing erosion until the iron is completely converted into a loose oxide film, which is weathering. Electrochemical principles of Erosion Electrochemical erosion is an electrochemical process. "It is certain that it also dissolves spontaneously on contact with copper. Mixed corrosion inhibitor Some compounds, such as zinc chromate, can dissociate the natural cation and anion 1 in solution, thus inhibiting the bipolar reaction. Because the ionic radius is small and relatively flexible, it is easy to diffuse to the metal surface, replacing the protective and insoluble hydroxide with soluble metal chloride, resulting in local erosion, especially in the low pits. Erosion of thermodynamics basis erosion processes including the metal or alloy spontaneously into erosion products, such as carbonate, sulfide, silicate hydrate, oxide or oxide hydrate, its general reaction equation is less, it is well known that the spontaneous chemical reaction, the delta must be negative free energy change, the scale state ℃, Journal of Xiabaoji College of Arts and Sciences, Natural Science Edition. Metal erosion can be divided into two categories: chemical erosion and electrochemical erosion. There are anodic protective layer and cathodic protective layer. When two metal products are in contact with each other, and there are other media such as moist air or other gases, water or electrolyte solution, the galvanic cell is formed, and the electrochemical process including oxidation reaction and reduction reaction occurs. For example, when sodium nitrite and sodium chromate are in near-neutral solutions, their anions migrate at the sun's pole and, in the absence of oxygen, naturally develop a protective oxide film on the surface of iron. The reaction formula is as follows: The difference between the two is that nitrite produces only insoluble oxides, while chromate is naturally formed by the edge.

Institute for petroleum, chemical, machinery, engineering, electronics, instruments, ships, pipelines, coal, power plants and other related materials corrosion and related inspection, evaluation, design, research and development of application technology, services, and transfer as the main business scope, such as in anticorrosion materials research and development, production, sales and engineering construction as the main business, such as continuous state, serve the society. In the industrial production, especially in the chemical production, because of the erosion and damage of equipment, the phenomenon of running, risking, dropping, leakage and so on occurs, which pollutes the environment, deteriorates the labor premise, harms human health, affects the quality of products, and even causes accidents, and its loss is inestimable. The importance of studying the problem of metal erosion prevention is obvious. The greater harm of metal erosion is not the loss of the metal itself but the destruction of its products. It has been estimated that approximately the world's steel production is consumed by erosion, with the United States alone losing more than 30 million tons of steel to erosion every year.

It is generally believed that sodium nitrite solution has a better anticorrosive effect on steel parts in seawater. According to the relation of "one by one expansion, the expansion is positive, which means △. Put iron pipe on the brass, for example, or put the faucet copper on the iron pipe, or on a piece of copper nail some iron rivets, long-term exposure to the wet surface of iron in the air will condense a thin layer of water film and in the air, some factories from soluble in water, such as medium will dissolve into the water film electrolyte solution by nature. Really common metal products belong to this category.

Use of corrosion inhibitors Because coarse and unclean metal surfaces require a higher concentration of corrosion inhibitors than clean surfaces, it is necessary to clean the metal products before the use of corrosion inhibitors. The erosion caused by simple chemical action between metal surface and medium is called chemical erosion.

Coating method

In the struggle against nature, people created and developed many effective antisepsis methods by studying the electrochemical nature of metal erosion.

Some cations can act in a neutral solution and diffuse to the cathode table, and react with the resulting ion insoluble protective film. These macromolecules may also reduce the rate of diffusion of reactants and products over the metal surface. Is negative, indicating that in this case, the rust of iron products must be caused by the electrochemical erosion and corrosion of the first metal. Moreover, most metal products are heated during the manufacturing process, so oxidation is more likely to occur. For example, carbon steel composed of, and graphite with the nearby medium,,, and reaction at high temperature, the result of its surface hardness is reduced, fatigue resistance function is reduced. This film protects the metal from erosion, but it can be damaged by external forces or by acid decomposition. In many cases, acid pickling is used to remove the corroding layer on metal products and the oxide scale formed during heating during manufacturing. The former is more negative than the base metal in terms of electrode potential, such as galvanizing iron, while the latter is more negative than the base metal in terms of electrode potential. These preservatives are more effective against iron at lower concentrations of gram-liter. A piece of

In fact, all metals except gold form oxide films when exposed to air at room temperature.

Since at the cathode there may be two reactions ① ② from the air one, expanding, and two "because of half the battery electrode potential. This is the focus of this article. Of the membrane.

The machinery and equipment, containers and a large number of pipes used in production are mostly made of metals and their alloys. Some silicates and phosphates also have this effect. In most media, the rate of oxidation of the metal at the anode is faster because the anode and the resistance must be equally reactive, so the rate of erosion is controlled by the slower cathodic reaction. In addition, there are phosphates, borates and so on only in dissolved oxygen and generally high concentrations such as chocoll will have a certain effect. The high chloride content in seawater, and many chlorides are absorbent, can promote electrochemical erosion. As the name suggests, cathodic protection is the use of applied dc electricity, scrap iron as the sacrificial anode, and to be protected metal as the cathode protection. Even using galvanized pipe or sheet is difficult to improve this situation, because the scale electrode potential of zinc half cell is one. This method is often used in the carbonization tower of nitrogen fertilizer plant to prevent corrosion. Large colloidal cations can also migrate to the cathode to form a shielding film, thus inhibiting the cathode reaction. The scale of typical metal oxides is natural free energy oxides △, one by one

Erosion is the destruction of metals by external factors.