How to Anodize Steel at Home

Metal anodizing

• Characteristics
• Process
• Materials

• Aluminum
• Titanium
• Steel
• Copper
• Anodizing at home

In the modern world there are a large number of methods for processing metals and metal products. They are used both on an industrial scale and at home.

Anodizing Characteristics

Anodizing is a procedure for forming an oxide film on the surface of various metals by anodic oxidation. The growth of the oxide film is carried out in a conducting medium. This film adheres quite well to the metal surface.

The growth of the oxide film can also be carried out using the method of increasing the temperature regime. However, it turns out to be low in strength and does not last for a long time. Thanks to the electrochemical method of forming the oxide film, it is of optimal thickness and adheres well to the surface of the material.

Different types of metals can be anodized. The main requirement is that they must be able to form only one oxide. It must have the maximum level of stability. If a metal has the ability to form several oxides at once, this can lead to the film simply starting to crack and no protective effect appearing. It is for this reason that cases of anodizing iron or copper occur only at rare industrial facilities.

In addition, the oxide film on the surface of metals must have a porous structure. This is necessary so that electrolytes penetrate into it better. As a result, it turns out that only a small part of all metals on earth can satisfy these parameters. These include aluminum, tantalum, titanium. In the industrial and domestic spheres, the most common treatment is anodizing aluminum material.

Anodizing process

The technology for anodizing various types of metals is simple. The main thing is to have at hand everything you need to implement it.

It is carried out in several stages:

• Preparation of metals for the formation of an oxide film.

At this stage, preparatory work for anodizing is carried out. They consist of thoroughly cleaning and washing the metal surface. First, all dirt and deposits are removed. Then the material is washed using water or special solutions. After this procedure it must be dried.

At this stage, a solution with an acidic or any other medium is prepared and connected to the positive plus of the current source.

• Coating the surface of metals or their alloys with an oxide film.

At this stage, the metal or product made from it is immersed in the prepared solution.

Anodizing materials

Today, various metal materials are used for anodizing.

Currently, the following types of anodizing are distinguished depending on the materials used, such as:

Aluminum anodizing

This process is most common today. It consists of coating an aluminum material with an oxide film. In the process, aluminum is lowered into an acidic environment, and the positive plus of the current source is passed to it. As a result, a thin oxide film appears on the material.

Titanium anodizing

Everyone knows that titanium belongs to the category of metals that are widely used in industry, but they have a low level of wear resistance. To give it strength and resistance to different environmental conditions, an anodizing procedure is used. In this case, all anodic processing of the metal is carried out in an acidic environment at a temperature of 40 to 50 degrees Celsius.

Anodizing steel

Anodizing steel is a complex process. For this, either an alkaline or acidic medium is used. As a result, an oxide film is formed, which imparts a high level of strength.

Copper anodizing

Copper is a fairly flexible type of metal. Various methods are used to give it strength. One of them is anodizing. By placing the copper material in an acidic environment, a dense oxide film is formed on the surface, which gives the material a large number of useful characteristics.

Table. Compatibility table of metals and alloys

MaterialAluminiumBronzeDuraluminBrassCopperNickelTinTin-lead alloy (POS solder)Unalloyed steel (carbon) / cast ironChromeZinc

Aluminum	Joint	Not compatible	Joint	Not compatible	Not compatible	Not compatible	Not compatible	Not compatible	Joint	Not compatible	Joint
Bronze	Not compatible	Joint	Not compatible	Joint	Joint	Joint	Soldering	Soldering	Not compatible	Joint	Not compatible
Duralumin	Joint	Not compatible	Joint	Not compatible	Not compatible	Not compatible	Not compatible	Not compatible	Joint	Not compatible	Joint
Brass	Not compatible	Joint	Not compatible	Joint	Joint	Joint	Soldering	Soldering	Not compatible	Joint	Not compatible
Copper	Not compatible	Joint	Not compatible	Joint	Joint	Joint	Soldering	Soldering	Not compatible	Joint	Not compatible
Nickel	Not compatible	Joint	Not compatible	Joint	Joint	Joint	Soldering	Soldering	Joint	no data	Joint
Tin	Not compatible	Soldering	Not compatible	Soldering	Soldering	II	Joint	Joint	Joint	no data	Joint
Tin-lead alloy(POS solder)	Not compatible	Soldering	Not compatible	Soldering	Soldering	Soldering	Joint	Joint	Joint	no data	Joint
Unalloyed steel (carbon)/cast iron	Joint	Not compatible	Joint	Not compatible	Not compatible	Joint	Joint	Joint	Joint	Joint	Joint
Chromium	Not compatible	Joint	Not compatible	Joint	Joint	no data	no data	no data	Joint	Joint	Joint
Zinc	Joint	Not compatible	Joint	Not compatible	Not compatible	Joint	Joint	Joint	Joint	Joint	Joint

Anodizing at home

In the modern world, a large number of metal objects are used in the household sphere, which are used for various purposes. Each owner wants to protect them from corrosion so that they last a long period of time. Anodizing at home is suitable for this purpose.

Important: The procedure for home anodizing of any metal must be carried out outdoors or on the balcony.

First you need to prepare a solution. To do this, you need to mix distilled water and acid in a certain proportion. It is important to handle sulfuric acid with extreme care, because if it comes into contact with the eyes or skin, it can lead to an unpleasant situation.

After this, you can prepare metal parts for processing. All kinds of substances are used for this purpose. They are able to clean them for the procedure.

At the last stage of home anodizing, metal parts are immersed in a solution and an electric current is connected.

anodizing at home

Source: http://lkmprom.ru/clauses/tekhnologiya/anodirovanie-tekhnologiya-dannogo-protsessa/

Anodizing metal: description and types of coating, nuances of working at home - Machine

An attractive appearance and increased strength properties of a metal surface can be achieved by using special electrochemical reactions. One of these methods is anodizing the metal, during which a protective oxide film is formed on the surface, giving the material additional qualities.

Features of anodized

This procedure is widely used on an industrial scale; in addition, you can independently oxidize steel, aluminum or copper at home. The latter option will differ from the professional process, but it is convenient for processing small parts.

Products that have a film formed on their surface after anodizing have the following characteristics:

• increased resistance to corrosion;
• the strength of materials such as steel and aluminum increases;
• the product becomes non-toxic;
• lack of ability to conduct current;
• the prepared surface is suitable for further processing using galvanic coating.

The procedure of anodizing metal is used for the production of cookware - products processed by this method do not burn on the stove and are safe for cooking. Materials with an oxide film are used in the manufacture of some tools, building materials, lighting devices, and household items. In addition, silver products are processed.

Color anodizing is widespread, which allows you to give parts a variety of decor. Products painted in this way have a more even and deeper color.

The anodized surfaces of tools and devices do not crack during use, maintaining their original appearance for a long time. In addition, the plane becomes stronger, which allows it to withstand increased loads and mechanical stress.

How does the anodizing process work?

The whole procedure consists of three stages of work: preparing the metal, its chemical treatment and fixing the coating to the surface. We propose to take a closer look at each of these phases using the example of processing a material such as aluminum:

1. Preparatory stage. The metal profile is cleaned mechanically, after which it is polished and degreased. This must be done so that the coating is firmly fixed to the base. Next comes the use of alkalis. The part is placed in the solution for some time for etching, after which it is transferred to an acidic liquid, where the aluminum is brightened. The final stage of anodic preparation is the complete washing of parts from residual alkali and acid.
2. Chemical reaction. The prepared product is placed in an electrolyte. It is a solution of acid to which a current is connected. The material to be anodized is most often treated with sulfuric acid, and its oxalic analogue is used to achieve color. A successful result is achieved with the correct temperature and current density. Hard anodizing involves the use of low temperatures, but if the goal is to obtain a soft and porous film, the performance increases.
3. Stage of fixing the coating. The resulting aluminum parts with the film formed on them have a porous appearance, so they need to be strengthened. Several methods are used for this: dipping the product in hot water, treating with steam or a cold solution.

For further color painting of the product, there is no need to fix the anodizing. Existing paints and varnishes adhere perfectly to the porous surface, forming excellent adhesion to it.

It is worth noting that metals are coated with such anodizing at industrial enterprises. A particularly durable type of coating can be achieved with a hard type of procedure. This material is used in automobile production, aircraft construction and construction.

Method of procedure at home

When starting anodizing yourself at home, you must first prepare all the tools:

• container for placing the product;
• batteries with a capacity of 9 V (several pieces, depending on the desired result);
• aluminium foil;
• cable with good insulation;
• electrolyte solution;
• ticks.

As an experimental experience, you can try processing the bolts. The thickness of the finished coating is approximately 0.05 mm. Products must be prepared in advance. If stainless steel elements were selected, degrease and sand them in advance.

Prepare an electrolytic solution. To do this you will need sulfuric acid and distilled water. You can purchase acid for the electrolyte at auto stores that specialize in battery repair. The proportions of water and acid should be the same, but you should not use an undiluted substance.

It will take longer to achieve a black metal color than a light or bronze result.

First, etch the part in lye to prepare it. After this, place the part in a solution with electrolyte and connect the current. It is important to use a thermometer to monitor the temperature and ensure that the readings do not drop. When the level reaches the lower levels, it is necessary to end the process.

Source: https://regionvtormet.ru/beton/anodirovanie-metalla-opisanie-i-raznovidnosti-pokrytiya-nyuansy-raboty-v-domashnih-usloviyah.html

Steel oxidation

One of the important tasks in preserving metal structures is combating the harmful effects of the environment. High humidity and the presence of chemically active elements in the air that can destroy the integrity of metal, especially steel, lead to a deterioration in such indicators as reliability and strength.

To solve this problem, finished products are coated with various types of protective coatings.

Steel oxidation

There are various methods to improve surface stability and corrosion resistance.

One of these methods is to create a protective film on the surface of steel using special processing methods.

Understanding the essence of the purpose of this process requires an answer to the question - what is oxidation?

The essence is to use the properties of the oxidation-reduction reaction, as a result of which a protective film is formed on the surface of the steel. Steel oxidation is also carried out.

This process allows you to solve the following problems:

• Protect steel structures from corrosion (this is especially important in modern construction where metal structures are used).
• Limit exposure to aggressive components of the external environment (solutions of acids, alkalis, chemical elements that destroy the integrity of steel).
• Create a surface layer with good electrical insulating characteristics.
• Give details, individual elements, and the structure as a whole original decorative and aesthetic properties.

Metal oxidation is carried out using the following methods:

1. Using chemical reactions (chemical oxidation of steel).
2. Use of electrochemical processes (anodic oxidation).
3. Carrying out heat treatment (thermal method).
4. Creation of low-temperature plasma (plasma method).
5. Laser (special laser installations are used).

Anodized steel

Let's look at each method in more detail.

Chemical oxidation

This process involves the processing of metals with solutions, mixtures, melts of chemical elements (oxides such as chromium oxides). This oxidation allows for the so-called passivation of the metal surface. It involves the creation of an inactive (passive) formation in a metal layer close to the surface. A thin surface layer is created that protects the main part of the structure.

Technologically, this process is implemented by lowering the prepared metal part into an alkali or acid solution of a given percentage.

They keep it there for a certain time, which allows the oxidation-reduction reaction to fully occur. Then the part is thoroughly washed, subjected to natural drying, and final processing.

Chemical oxidation of steel

To create an acid bath, three types of chemically active acids are used: hydrochloric, nitric, and orthophosphoric. The acceleration of the chemical reaction is stimulated by adding manganese, potassium, and chromium compounds to the acid solution. The oxidation reaction occurs at a solution temperature in the range from 30 °C to 100 °C.

The use of solutions based on alkaline compounds allows the use of additives of sodium nitrate and manganese dioxide compounds. In this case, the solution temperature must be increased to 180 °C, and with additives up to 300 °C.

After the procedure, the part is washed and dried. Sometimes potassium bichromate is used to consolidate the chemical reaction process. To increase the shelf life of the formed film, chemical oxidation with oiling is carried out. Sometimes this process is called chemical oxidation. The final coating with oil results in a reliable anti-corrosion coating with a striking, highly decorative black color.

This type is called electrochemical oxidation of steel. Sometimes it is called anodic oxidation of steel. The term anodizing is also used. It is based on the chemical process of electrolysis. It can be carried out in both solid and liquid electrolytes. The prepared workpiece is placed in a container with an oxide solution.

The electrolysis reaction is possible by creating a potential difference between two elements.

The surface of the oxidized product is characterized by a positive potential. Chemically active elements with a negative potential are isolated from the solution. The interaction of oppositely polar elements is called the electrolysis reaction (in our case, anodization).

Anodic oxidation

The anodization reaction can be performed at home. It is required to strictly comply with safety regulations. The reaction involves harmful reactive fluids and unsafe voltage.

The use of anodic oxidation makes it possible to create protective films of various thicknesses. The creation of thick films is possible through the use of a sulfuric acid solution.

Thin films are obtained in solutions of boric or phosphoric acid. Using anodization, you can give the surface layer of metal beautiful decorative shades. For this purpose, the process is carried out in organic acids. Oxalic acid, maleic acid, sulfosalicylic acid are used as such solutions.

Micro-arc oxidation is a special anodizing process. It makes it possible to obtain coatings with high physical and mechanical characteristics. These include: protective, insulating, decorative, heat-resistant and anti-corrosion properties. In this case, oxidation is carried out under the influence of alternating or pulsed current in special baths filled with electrolyte. Such electrolytes are weakly alkaline compounds.

Anodic oxidation at home

Anodizing allows you to obtain a surface layer with the following properties:

• reliable anti-corrosion coating;
• good electrical insulators;
• thin but durable surface layer;
• original color scheme.

Anodizing stainless steel requires a special approach. This is due to the fact that such steel is considered a neutral (inert) alloy. Therefore, in production, when anodizing a large number of parts, a two-step procedure is used.

At the first stage, stainless steel is anodized together with another metal that is more suitable for this process. It may be nickel, copper, other metal or alloy.

At the second stage, the stainless steel itself is oxidized directly. To simplify the oxidation process, special additives, so-called passivating pastes, are being developed today. These compounds speed up the reaction process of stainless steel.

According to the term, oxidation occurs at relatively high temperatures. The value of this indicator depends on the steel grade. For example, the process of thermal oxidation of ordinary steel occurs in special furnaces.

A temperature close to 350 °C is created inside. A class of alloy steels undergo thermal oxidation at higher temperatures. It is necessary to heat the workpiece to 700 °C. Treatment continues for one hour.

This process is called steel bluing.

Steel bluingSteel gun after bluing

Plasma oxidation

This oxidation is carried out in an environment with a high concentration of oxygen using low-temperature plasma. Plasma is created due to discharges that occur when high- or ultra-high-frequency currents are applied.

Plasma oxidation is used to form oxidized films on fairly small surfaces.

It is mainly used in electronics and microelectronics. With its help, layers are formed on the surface of semiconductor compounds, the so-called pn junctions. Such films are used in transistors, diodes (including tunnel diodes), and integrated circuits. In addition, it is used to increase the photosensitive effect in photocathodes.

Plasma oxidation

A type of plasma oxidation is oxidation using high-temperature plasma. Sometimes it is replaced by an arc discharge with an increase in temperature to 430 ° C and higher. The use of this technology can significantly improve the quality of the resulting coatings.

Laser oxidation

This technology is quite complex and requires special equipment. To carry out oxidation use:

• pulsed laser radiation;
• continuous radiation.

In both cases, infrared laser systems are used. Due to laser heating of the top layer of material, it is possible to obtain a fairly resistant protective film. However, this method is only applicable to a small surface area.

Laser oxidation

DIY oxidation

You can organize the process of oxidation of small metal products in your home laboratory. By strictly following the sequence of technological operations, high-quality oxidation is achieved.

The whole process should be divided into three stages:

1. Preparatory stage (includes preparation of the necessary equipment, reagents, and the part itself).
2. Direct oxidation stage.
3. The final stage (removing harmful traces of the chemical process).

At the preparatory stage the following work is carried out:

• Rough cleaning of the surface (use a metal brush, sandpaper, polishing machine with appropriate discs).
• Final mechanical polishing of the surface.
• Removing grease and polishing residues. It's called decopying. It is carried out in a five percent solution of sulfuric acid. The residence time of the workpiece in the solution is one minute.
• Washing the part. This procedure is carried out in warm boiled water. It is advisable to carry it out several times.
• The final operation is the so-called passaging. After washing the part after processing, place clean boiled water in which laundry soap is first dissolved. This solution, together with the part, is heated and brought to a boil. The boiling procedure is continued for several minutes.

Oxidation at home

This concludes the preliminary stage.

The main stage of oxidation consists of the following operations:

1. Water is poured into a neutral bowl (preferably with an enamel coating). About caustic soda is dissolved in it. The volume of a substance depends on the amount of water. It is advisable to obtain a solution of about 5 percent.
2. The workpiece is completely immersed in the resulting solution.
3. The solution with the immersed part is heated to 150 degrees. This is practically a boiling process. It lasts approximately two hours. Using the tool, the quality of the process is checked. If necessary, the time can be increased.

At the final stage, the following operations are performed on the part:

1. The part is removed from the reagent bath.
2. Place it on a flat surface and allow it to cool naturally (without forced cooling). It is advisable to create conditions that limit contact with ambient air.
3. Visually check the quality of the resulting oxidation. The absence of uncovered areas, the density of the formed film, the final color.

Thus, oxidation can be carried out at home. The main thing is to follow these recommendations.

Source: https://stankiexpert.ru/spravochnik/materialovedenie/oksidirovanie-stali.html

How to anodize metal at home?

• Aluminum
• Titanium
• Steel
• Copper
• Anodizing at home

In the modern world there are a large number of methods for processing metals and metal products. They are used both on an industrial scale and at home.

What is anodized metal surface

By anodizing a metal we mean a process of processing it, for which an electrolyte and an electric current of a certain magnitude are used. As a result, a high-strength oxide film is obtained on the surface of the products. It significantly increases the service life of products, corrosion resistance, and ensures the absence of streaks and scratches.

The strength and mechanical properties of the material also change significantly, which depends on the composition of the metal and other characteristics:

• characteristics of the electrolyte used;
• cathode properties;
• characteristics of the anode.

A feature of anodic oxidation is that as a result of its implementation, no substances are applied to the surface of the metal. The protective film is formed as a result of the transformation of the material itself during the occurrence of appropriate reactions.

Applicable devices and equipment

On an industrial scale, a sulfuric acid solution is used for anodizing steel, which ensures a high process speed and the greatest penetration depth. Modern installations are fully automatic lines with a minimum number of personnel, whose role is reduced to monitoring the work process.

All equipment can be divided into three types:

1. Basics. It includes a bath and a cathode. The container must be made of an inert material with high thermal insulation properties - in this case, the electrolyte will not heat up too quickly and will last much longer. The cathode material depends on the type of metal being processed. For example, to anodize aluminum, a lead sheet is used, the size of which should be twice the dimensions of the workpiece.
2. Serving. This includes units that are responsible for ensuring the operation of the installation: drive mechanisms and devices for transmitting current.
3. Auxiliary. We are talking about equipment on which work is carried out to prepare workpieces for anodizing. This also includes mechanisms for moving parts and storing them.

When selecting a suitable installation, the following features must be taken into account:

1. The most labor-intensive operations are loading and unloading the workpiece. Pay attention to the reliability and power consumption of these nodes.
2. Productivity depends on the power of the power plant. As practice shows, the optimal rectifier power is 2.5 kW. The presence of stepless voltage level adjustment will be an additional advantage, facilitating the process of anodizing steel.

Stepless regulation will occur after the formation of a protective layer of medium thickness, when in order to maintain the current level it will be necessary to gradually increase the voltage.

1. Contact pads made of flexible material should be installed along the rings of the container. Copper elements will cope best with this task.

Methods for performing the procedure

Anodizing copper and other metals can be done in several ways. Each of them has its own advantages and disadvantages and implementation features.

Warm method

Anodizing stages

The simplest method of performing anodizing, which can be used even at home. The processing takes place at room temperature. When using organic paint, iodine or brilliant green, the aesthetic qualities of the processed parts can be significantly improved.

Hard anodizing of metal using this technology cannot be carried out. If this is done, a thin oxide film forms on the surface of the material, which does not provide reliable protection against corrosion and is easily damaged. But if, after performing such a treatment, the products are painted, the adhesion of the coloring compositions to the surface will be excellent. It is in this way that high-quality protection against corrosion can be ensured and the service life of parts can be extended.

Cold method

To perform anodic oxidation using the cold method, it is necessary to ensure temperature stability. It should be within -10–+10°С. The optimal temperature is considered to be 0°C, which corresponds to the parameters at which an ideal electrochemical reaction occurs.

Aluminum color anodizing methods

When these indicators are achieved, anodic and cathodic processing of the metal will occur more efficiently, forming a durable film on the surface. It provides the best protection against corrosion.

Using the cold method, you can perform electroplating of copper, gold and other metals. To do this, you need to correctly calculate the current using special equations. The resulting parts are almost impossible to damage. They are characterized by a long service life in particularly aggressive environments (in contact with sea water).

A minor disadvantage of this technology is the impossibility of applying paint to the resulting surface. To change color, a metal spraying method is used or an electric current of a certain magnitude is used.

The main advantages of anodized metal

Anodized steel compares favorably with unprotected products in the following qualities:

1. Corrosion resistance. The barrier film prevents metal from contacting moisture, as well as chemically active compounds.
2. High strength. The protective layer is highly resistant to mechanical damage.
3. Dielectric properties. The oxide film practically does not conduct current.
4. Environmental friendliness. Treated dishes become resistant to intense temperature changes. The food does not burn during the cooking process.
5. Decorative properties. Some metals are treated to change their visual qualities. Basically, aluminum is used for these purposes as it has a good connection with oxygen. Adding certain salts to the electrolyte solution will change the original color, giving the painted products even and deep shades.

Oxidation can also hide minor surface defects such as scratches or scuffs.

Unlike ordinary stainless steel, it is difficult to process as a conditionally inert metal. To solve this problem, stainless steel is coated with nickel, and only then oxidation is carried out. Scientists are actively developing special pastes that will reduce the inert properties of the outer layer of stainless steel.

Share on social networks:

Source: https://wizard-aerosol.com/spetsialnye-materialy/tehnologiya-anodirovaniya-metalla-i-ee-osobennosti.html

Anodized aluminum - what is it, cold and warm anodizing technology

Modern devices made of metal are very different from those made 30-50 years ago. They have become lightweight, resistant to harmful influences, and minimally dangerous to life. Anodized aluminum occupies one of the leading places among the metals that are used for the manufacture of such devices.

Anodized aluminum has long and firmly taken the place of steel and cast iron where, in addition to strength and resistance to external influences, other main qualities are required - lightness and ductility.

It is much lighter than steel, so it has successfully replaced it in tens of thousands of products used in a variety of fields - industry, medicine, tourism, sports.

With the advent of anodizing technology, the remarkable properties of aluminum were supplemented by the results of chemical modification - high corrosion resistance and resistance to mechanical stress.

Why is this done?

Anodized coating is used where it is necessary to provide protection against corrosion and avoid increased wear in the contacting parts of mechanisms and devices. Among other methods of surface protection of metals, this technology is one of the cheapest and most reliable.

The most common use of anodizing is to protect aluminum and its alloys. As is known, this metal, having such unique properties as a combination of lightness and strength, has an increased susceptibility to corrosion.

This technology has been developed for a number of other non-ferrous metals: titanium, magnesium, zinc, zirconium and tantalum.

Features of anodizing copper and its alloys

Most often, anodization of copper and its alloys is carried out by chemical or electrochemical methods. As a result, the surface of the material in most cases acquires a colored coating.

To obtain a film of copper, an acidic or cyanide liquid is used. Copper alloys, which contain alloying metals, undergo anodic oxidation much more difficult.

Features of silver anodizing

Anodic oxidation of silver allows you to give an initially white metal a black, purple or blue tint without changing the structure and quality characteristics of the material being processed.

Experts recommend processing silver items using sulfur liver. When anodizing, silver begins to change color after about half an hour.

After the product has acquired the required color, it must be removed from the liquid and rinsed thoroughly, first with hot, then warm and finally cold water.

Features of titanium anodizing

Anodizing titanium is a mandatory procedure, the main significance of which is to increase the wear resistance of this metal. The presence of an oxide film gives the product chemical strength and changes the color of the coating surface. Chromic, oxalic or any other acid can be used for the anodic oxidation of titanium.

Dependence of the color of the titanium oxide film on the current voltage during oxidation.

Features of aluminum anodizing

Anodic oxidation of aluminum is required, regardless of the fact that this metal can still look great after extrusion. This is due to the fact that aluminum is highly susceptible to corrosion. In addition, it is easily destroyed under the influence of a number of negative external factors.

Some features

The process under study, in addition to changing the microscopic texture on the surface, also changes the crystal structure of the metal at the interface with the protective film. However, with a large thickness of the anodized coating, the protective layer itself, as a rule, has significant porosity. Therefore, to achieve corrosion resistance of the material, additional sealing is required.

At the same time, a thick layer provides increased wear resistance, much greater compared to paints or other coatings, such as spraying. As the strength of the surface increases, it becomes more brittle, that is, more susceptible to cracking from thermal and chemical influences, as well as from impacts.

Cracks in the anodized coating during stamping are by no means a rare occurrence, and the developed recommendations do not always help here.

Decorative materials

The anodized aluminum coating has a rather interesting structure. The outer 35-50 micron films are a microporous, sponge-like surface with very narrow and deep pores.

Even a small amount of dye penetrates deeply into anodized aluminum, turning it into a very durable and at the same time bright coating. Colorless microcrystals refract the light falling on the anodized coating, as a result of which the colors become bright and saturated.

The applied paint coating does not fade or lose its intensity.

Most modern paints and varnishes with an iridescent effect are made by adding microscopic flakes coated with oxidized aluminum. The thinnest film of anodized metal ensures high resistance of the filler to ultraviolet radiation and organic solvents, so the paint does not lose saturation for decades.

The popularity of coatings has increased so much that metal is sprayed onto steel and even cast iron structural parts for subsequent oxidation and anodized protection.

Instead of unsafe zinc coating or very expensive alloy steels, anodized aluminum is widely used today.

For example, a metal facade made of double-glazed windows of a multi-story shopping center would have to be repaired within five years, but with anodized aluminum frames the structure could last for several decades.

Crystalline metal oxide coatings have seriously displaced the most resistant powder and ceramic paints, which were previously widely used to protect facades and structural elements made of aluminum alloys.

Invention

The first documented use of anodizing occurred in 1923 in England to protect seaplane parts from corrosion. Initially, chromic acid was used. Later, oxalic acid was used in Japan, but today in most cases, classic sulfuric acid is used in the electrolyte to create an anodized coating, which significantly reduces the cost of the process. Technology is constantly being improved and developed.

Aluminum

Anodized coating is done to improve corrosion resistance and prepare for painting. And also, depending on the technology used - either to increase roughness or to create a smooth surface.

At the same time, anodizing in itself is not capable of significantly increasing the strength of products made from this metal.

When aluminum comes into contact with air or any other gas containing oxygen, the metal naturally forms an oxide layer 2-3 nm thick on its surface, and on alloys its value reaches 5-15 nm.

The thickness of the anodized aluminum coating is 15-20 microns, that is, a difference of two orders of magnitude (1 micron is equal to 1000 nm). Moreover, this created layer is distributed in equal parts, relatively speaking, inside and outside the surface, that is, it increases the thickness of the part by ½ the size of the protective layer.

Although anodizing produces a dense and uniform coating, microscopic cracks in the coating can lead to corrosion. In addition, the surface protective layer itself is subject to chemical decomposition due to exposure to an environment with high acidity levels.

To combat this phenomenon, technologies are used that reduce the number of microcracks and introduce more stable chemical elements into the oxide composition.

Etching a metal surface

Pickling means lightly etching a metal surface. This treatment is necessary to remove a thin film of oxides from the metal that interferes with the application of a new coating.

Picking of steel products is carried out with a solution of sulfuric acid, 80 ml of which is diluted in 100 ml of water with the addition of 2-3 g of chromium. The resulting composition is applied for 20 seconds at room temperature.

An alternative is anodic pickling in an electrolyte consisting of 150 g of chromium, 0.5 ml of sulfuric acid and 1 liter of water.

Application

Processed materials are used very widely. For example, in aviation, many structural elements contain aluminum alloys under study, and the situation is the same in shipbuilding. The dielectric properties of anodized coating predetermined its use in electrical products.

Products made from processed material can be found in various household appliances, including players, flashlights, cameras, and smartphones. In everyday life, anodized iron coating is used, or rather, its soles, which significantly improves its consumer properties. When cooking, you can use special Teflon coatings to prevent food from burning.

Usually such kitchen utensils are quite expensive. However, an uncoated, anodized aluminum frying pan can provide a solution to the same problem. At the same time, with less money spent. In construction, anodized profiles are used for installation of windows and other needs.

In addition, multi-colored parts attract the attention of designers and artists, and they are used in various cultural and art objects around the world, as well as in the manufacture of jewelry.

Special anodized aluminum films

In addition to high decorative qualities, anodized aluminum films have a number of very useful properties. For example, high hardness and wear resistance. The microcrystalline structure of corundum is practically not afraid of any abrasive. Sand and cement dust, and even metal carbides and silicides are not able to significantly damage the corundum protection.

Therefore, anodized parts cannot be cleaned with sandpaper or polishing or grinding paste. A thick layer of crystalline Al2O3 on the surface of rubbing parts increases the service life of any mechanism by two to three times. Protection made of oxidized aluminum is used for high-temperature painting of wheel rims, suspension elements of quarry machines and long-haul equipment.

Application of anodized aluminum coating:

• Does not degrade under the influence of frost, heat, ultraviolet radiation or chemically active substances, withstands direct contact with acids, alkalis, and organic solvents;
• Does not generate dust and does not wear out during repeated washing, cleaning, or under abrasive loads;
• There is no filamentary or gaseous form of corrosion; if the anodized aluminum layer is manufactured in compliance with the technology, then the service life of the coating can easily reach 60-80 years.

The second interesting quality of anodized aluminum film is low thermal conductivity. The processed metal is used to make foundry molds for casting copper alloys, despite the fact that the temperature of aluminum is several hundred degrees lower than that of copper. A thin, just a couple of millimeters oxidized coating reliably protects the aluminum mold from overheated liquid copper.

Source: https://instanko.ru/drugoe/anodirovannyj-alyuminij.html

Anodizing at home - methods and technology

Many people associate the beautiful and incomprehensible word “anodizing” with complex physical and chemical technologies, laboratory conditions and other scientific paraphernalia. Few people know that this useful and simple process can be carried out using improvised means: it is possible to anodize titanium and other metals even at home. But what is it, and why is it needed for metal?

The name anodization is a process that occurs when using an electrolyte and electric current of various sizes and allows you to obtain a durable oxide foam on the product, which increases the strength of steel and provides protection against corrosion. Strength and mechanical characteristics vary depending on the composition of the metal, the density and type of electrolyte, the magnitude of the anodic and cathodic effects, calculated using special equations.

The protective coating itself is not applied, but is formed from the iron itself during an electrochemical reaction. The technology used at home looks schematically like this:

Scheme of the anodizing process at home

1. Electrolyte is poured into a dielectric (non-conducting) container.
2. A power supply is taken that can provide the required DC voltage at the output (this can be a battery or several batteries connected in electronic circuits).
3. The “+” clamp is connected to the object being processed, and the object is immersed in a container with the solution.
4. The “–” clamp is attached to a lead or stainless steel plate and is also lowered into the liquid.
5. An electric current of the required magnitude is connected, according to the electrochemical equation. Thanks to it, oxygen begins to be released on the surface of the product, promoting the formation of a durable protective film.

Anodic oxidation (anodizing) of various metals, carried out at home, is, of course, much inferior to that carried out using industrial equipment. But, nevertheless, it can provide the product with a number of advantages:

1. Increase resistance to corrosion - due to the fact that the oxide film prevents moisture from penetrating the metal base, providing reliable protection. The use of this process on quickly rusting household items or disks and parts of household appliances can significantly extend their service life.
2. Increase the strength of metal and steel: the oxidized coating is much more resistant to mechanical and chemical damage.
3. Dishes treated in this way are non-toxic, resistant to prolonged heating, and food does not burn on them.
4. After anodizing treatment, metal products acquire dielectric properties (they do not conduct current at all or almost not).
5. Possibility of electroplating of another metal (chrome, titanium). Made with your own hands, it can significantly increase the mechanical strength characteristics or improve the decorative qualities (gold plating).

In addition, the process allows for decoration. You can do color anodic oxidation. This result can be obtained by changing the equations of the applied current and the density of the electrolyte (this is possible when anodizing titanium and other hard materials) or by using paint (more often for aluminum and other soft metals, but this process is also used on hard substrates). Objects painted in this way have a more even and deeper color.

The industrial method provides higher coating strength, the ability to carry out deep anodizing with the simultaneous application of cathodic electrochemical foam, which provides additional protection against corrosion. But even anodic-cathode treatment carried out at home will help make disks or other parts of moving mechanisms more durable and wear-resistant.

Different ways

There are two ways to carry out the process of oxidizing steel at home. Each of them has its own disadvantages and advantages .

Anodic oxidation technology

The whole process, carried out with your own hands, can be divided into stages:

1. The surfaces of disks and other metal parts are well cleaned of dirt, washed, and polished.
2. Degreasing is carried out with white spirit or acetone.
3. The required time is maintained in the alkaline solution (it is calculated by the equation based on the structure of the material).
4. After this, the disks or other metal products are immersed in an electrolyte, where the anodic and cathodic reaction of growing an oxide film is carried out.
5. If the product was cold processed, then after removing it from the container it should be thoroughly rinsed from acid and dried. After completion of this process, it is provided with long-term reliable protection against corrosion.
6. During the thermal process, the film will be porous, soft, requiring additional strengthening, carried out by dipping in clean boiling water or by exposure to hot steam. Then you need to rinse it well.

Types of electrolytes

At home, not only industrial chemical acid solutions are used, but also simple products that can be found in any kitchen:

1. When anodizing titanium, you can take sodium chloride, sulfuric or phosphoric acid.
2. For aluminum, oxalic, chromic or sulfuric acids are used.
3. Instead of acids, you can use table salt and baking soda for anodic and cathodic treatment of disks or other steel objects. You can make the necessary electrolyte by mixing 9 parts of a concentrated soda solution with one part of saline.

The exposure time of disks, plates, and other metal objects in an electrolyte container under current is calculated according to the equation, based on physical and chemical parameters.

Dangerous moments

When using acids as electrolytes, safety precautions must be strictly observed. Neglecting them can lead to accidents:

1. In case of contact with skin, due to the fact that the drug is diluted, minor burns are possible. But such a concentration is dangerous for the eyes, so you should not neglect protective glasses and gloves.
2. Under the influence of current, oxygen and hydrogen vapors are released, which, when mixed, form an explosive gas. When working in a poorly ventilated area, you can get an explosion from any spark, which can be fatal.

By following safety precautions and the stages of technological processing, you can get durable, beautiful things: chrome plating car wheels, creating gold-look jewelry, adding strength to parts of household mechanisms, depending on the technologies used.

Source: https://kraska.guru/specmaterialy/drugie-pokrytiya/anodirovanie-v-domashnix-usloviyax.html

Metal anodizing technology and its features

An attractive appearance and increased strength properties of a metal surface can be achieved by using special electrochemical reactions. One of these methods is anodizing the metal, during which a protective oxide film is formed on the surface, giving the material additional qualities.

Anodizing steel at home

One of the important tasks in preserving metal structures is combating the harmful effects of the environment. High humidity and the presence of chemically active elements in the air that can destroy the integrity of metal, especially steel, lead to a deterioration in such indicators as reliability and strength.

To solve this problem, finished products are coated with various types of protective coatings.

Chemical oxidation

This process involves the processing of metals with solutions, mixtures, melts of chemical elements (oxides such as chromium oxides). This oxidation allows for the so-called passivation of the metal surface. It involves the creation of an inactive (passive) formation in a metal layer close to the surface. A thin surface layer is created that protects the main part of the structure.

Technologically, this process is implemented by lowering the prepared metal part into an alkali or acid solution of a given percentage.

They keep it there for a certain time, which allows the oxidation-reduction reaction to fully occur. Then the part is thoroughly washed, subjected to natural drying, and final processing.

To create an acid bath, three types of chemically active acids are used: hydrochloric, nitric, and orthophosphoric. The acceleration of the chemical reaction is stimulated by adding manganese, potassium, and chromium compounds to the acid solution. The oxidation reaction occurs at a solution temperature in the range from 30 °C to 100 °C.

The use of solutions based on alkaline compounds allows the use of additives of sodium nitrate and manganese dioxide compounds. In this case, the solution temperature must be increased to 180 °C, and with additives up to 300 °C.

After the procedure, the part is washed and dried. Sometimes potassium bichromate is used to consolidate the chemical reaction process. To increase the shelf life of the formed film, chemical oxidation with oiling is carried out. Sometimes this process is called chemical oxidation. The final coating with oil results in a reliable anti-corrosion coating with a striking, highly decorative black color.

Anodic" oxidation

This type is called electrochemical oxidation of steel. Sometimes it is called anodic oxidation of steel. The term anodizing is also used. It is based on the chemical process of electrolysis. It can be carried out in both solid and liquid electrolytes. The prepared workpiece is placed in a container with an oxide solution.

The electrolysis reaction is possible by creating a potential difference between two elements.

The surface of the oxidized product is characterized by a positive potential. Chemically active elements with a negative potential are isolated from the solution. The interaction of oppositely polar elements is called the electrolysis reaction (in our case, anodization).

The anodization reaction can be performed at home. It is required to strictly comply with safety regulations. The reaction involves harmful reactive fluids and unsafe voltage.

The use of anodic oxidation makes it possible to create protective films of various thicknesses. The creation of thick films is possible through the use of a sulfuric acid solution.

Thin films are obtained in solutions of boric or phosphoric acid. Using anodization, you can give the surface layer of metal beautiful decorative shades. For this purpose, the process is carried out in organic acids. Oxalic acid, maleic acid, sulfosalicylic acid are used as such solutions.

Micro-arc oxidation is a special anodizing process. It makes it possible to obtain coatings with high physical and mechanical characteristics. These include: protective, insulating, decorative, heat-resistant and anti-corrosion properties. In this case, oxidation is carried out under the influence of alternating or pulsed current in special baths filled with electrolyte. Such electrolytes are weakly alkaline compounds.

Anodizing allows you to obtain a surface layer with the following properties:

• reliable anti-corrosion coating;
• good electrical insulators;
• thin but durable surface layer;
• original color scheme.

Anodizing stainless steel requires a special approach. This is due to the fact that such steel is considered a neutral (inert) alloy. Therefore, in production, when anodizing a large number of parts, a two-step procedure is used.

At the first stage, stainless steel is anodized together with another metal that is more suitable for this process. It may be nickel, copper, other metal or alloy.

At the second stage, the stainless steel itself is oxidized directly. To simplify the oxidation process, special additives, so-called passivating pastes, are being developed today. These compounds speed up the reaction process of stainless steel.

Thermal oxidation

According to the term, oxidation occurs at relatively high temperatures. The value of this indicator depends on the steel grade. For example, the process of thermal oxidation of ordinary steel occurs in special furnaces.

A temperature close to 350 °C is created inside. A class of alloy steels undergo thermal oxidation at higher temperatures. It is necessary to heat the workpiece to 700 °C. Treatment continues for one hour.

This process is called steel bluing.

Read also: Attaching the corrugation to the wall with clips

Anodizing operation and its specifics

Here you can see 2 baths with washing liquid (blue) and anodizing liquid (green liquid)

Anodizing metal as a procedure is not particularly difficult and, if desired, can be done on your own. Performing this operation involves performing the following work steps:

Stage 1. Preparing the metal surface

Before starting anodic oxidation, the metal surface should be carefully prepared: polished, ground. The surface is degreased using organic solvents (for example, gasoline, acetone or alcohol). Then the surface is treated with any alkali.

At home, an ordinary soap solution can be used. Ferrous metals are perfectly degreased using a solution of caustic potassium or soda, which is preheated to 80 degrees. As for aluminum, a 10% sodium phosphate solution is better suited for it.

Stage 2. Etching (picking) the metal surface

Etching a metal surface is carried out in order to remove oxides that interfere with the high-quality application of a new coating. To carry out the procedure, sulfuric acid is used (in a ratio of 80 milliliters of acid per 100 milliliters of input with the addition of 2 grams of chromium.

Stage 3. Anodizing the metal

The process of anodic oxidation of a metal is carried out in an electrolyte solution under the influence of direct current. It is important that the container in which anodizing is performed does not allow current to pass through. A 20% sulfuric acid solution is most often used as an electrolyte.

IMPORTANT! When preparing an electrolyte solution, it is necessary to pour sulfuric acid into water, and not vice versa.

In the absence of sulfuric acid, a solution of table salt and soda can be used.

The anodic oxidation process itself occurs as follows. A metal product is attached to the anode using a special suspension, and a lead plate is attached to the cathode (for products with complex shapes, several lead plates will be required).

The distance to the plate should be no more than nine centimeters . The procedure is carried out at a temperature of 20 degrees. In this case, the electric current density should vary from 2 to 3 A/sq. dm .

Voltage required is from 12 to 15 V. The whole process takes about one hour.

Devices and tools

Before you begin anodic oxidation, you should prepare the following equipment and tools that will be needed to complete the job:

• aluminum foil;
• rubber gloves;
• plastic container for placing a metal product;
• 9V batteries (from 1 to 8 pcs.);
• insulated cable (about one and a half meters);
• electrolyte solution;
• spoon;
• organic solvent;
• plastic glass;
• mites;
• a device designed for stripping cables.

Installations for anodizing metals and their design features

Any large installation for anodic oxidation is a rather complex complex, including electrical, chemical and mechanical equipment. When choosing it, you should take into account a number of significant points:

1. The highest operating costs are for unloading as well as loading procedures . And this is precisely what makes anodic oxidation a very labor-intensive procedure.
2. The maximum throughput of the anodizing installation is determined by the power of the DC rectifier , with the help of which anodic oxidation is carried out. The most commonly used rectifier is 25 Watt . It is good if the installation has stepless voltage regulation under load from zero to maximum , as well as an automatic function of returning the voltage to zero at the end of the cycle. High-quality anodic oxidation requires the presence of an oxide film on the metal surface. At the very beginning of the anodizing process, the film is relatively thin and has low resistance. Accordingly, in order to maintain the current density, a small voltage is sufficient . As the thickness of the oxide film increases, its resistance increases, and accordingly the current decreases. In order to maintain the same current density throughout the procedure, the voltage must be gradually and smoothly increased. And this is where the infinitely variable voltage control of the anodizing machine comes in very handy.
3. The contacts between the plates and the busbars require precision design. Therefore, it is advisable to install flexible contact pads (for example, made of copper) at the ends of the anodizing baths.

Why is metal anodizing necessary?

The scope of application of anodic oxidation is quite diverse. Metals that have undergone anodic oxidation acquire:

• excellent protective properties;
• homogeneous surface;
• no stripes or scratches;
• high decorative characteristics

Recently, decorative anodizing of metal has been in quite high demand, which can be done both with or without mechanical processing.

Most often, anodic oxidation of a metal is carried out to protect the alloy from the development of corrosion.

Below is a short video of the aluminum anodizing operation.

Source: https://steelfactoryrus.com/anodirovanie-stali-v-domashnih-usloviyah/