Pickling is a metal processing process in which a layer of a certain thickness is removed from the surface under the influence of active chemicals (acids or salts with an acidic reaction), as well as direct current in an electrolyte bath.

Metal etching can serve various purposes and be used in industry and at home. The surface of an item subjected to etching receives a number of technological and decorative properties and allows one to examine its microstructure in a metallographic microscope, remove scale and other non-metallic inclusions from the surface, obtain the necessary jewelry ornament or prepare it for soldering.

Etching, also called electrochemical engraving, is most often used at home or in the garage to obtain relief images on various objects with decorative functions. Most often, it is used on steels with high hardness, the processing of which with conventional engraving tools requires great effort. This process is not very difficult even in the absence of artistic skills, if you follow its technology.

Metal surface preparation

In order for the etching process to proceed at a high speed and the thickness of the removed layer to be the same, all dirt and traces of oils should be removed from the surface of the product. For this purpose, ordinary detergents and cleaning products used for washing dishes and warm water are suitable. After washing and drying, the surface should be wiped with fiber soaked in a solvent, which, in addition to degreasing, helps remove residual moisture.

Separately, it is worth mentioning the quality of surface treatment. Mirror polishing is subsequently guaranteed to give a good contrasting pattern even with a small etching depth. But if its implementation is impossible for some reason, the surface can be treated with sandpaper so that the risks from it go in one direction. This will also give a good optical effect.

Drawing

To apply a design to metal, you can use a lot of different methods that work according to the same mechanism: areas that are not subject to etching are protected from exposure to an aggressive environment or electrolyte.

Method No. 1

The most affordable way is to apply regular nail polish to the protected areas. However, it has a number of significant disadvantages:

• The viscosity of the varnish does not allow the lines to be thin enough to obtain highly complex patterns;
• Good ability in visual arts required;
• Correcting inaccurate lines is difficult.

Method No. 2

First you need to apply a protective layer to the entire surface of the product. To do this, you can use primers GF-021, XV-062 or bitumen varnish, available in auto parts and household goods stores. After the coating has completely dried, you can use a gel pen or a thin marker to draw the contours of the future image. An experienced artist can be hired for this task.

Next, from a copper (or brass) wire or rod, the diameter of which is selected based on the ease of holding in the hand, you need to make a needle with a pointed end and scratch the primer along the image lines to the metal. Harder needle material may damage the polish on the surface of the product.

Already at this stage you can evaluate the relief of the future ornament. To obtain areas with different depths of metal etching, for example, contours and penumbra, this process can be carried out in two or more cycles.

Important! The primer should not chip off during the process. Before applying the design, you should experiment and make sure that it is suitable for the job.

Method No. 3

You will need a laser printer, glossy paper, image processing software and an iron. The selected picture must be formatted (adjusted to size, mirrored) and printed. The most affordable source of glossy paper is women's magazines.

The printed image is applied to the surface, covered with a regular landscape sheet (to protect the iron) and ironed. After cooling, the paper is washed off under running water, and the toner layer remains on the metal surface.

This method is often used for etching printed circuit boards. Its main drawback is that the design is applied only to a straight surface.

Important! The gloss is difficult to see under water. After drying, you need to make sure that it does not remain on the product.

Care must be taken to protect all surfaces of the product. Various substances can be used for this. You can cover the back surface with ordinary plasticine: it is a good dielectric.

Metal etching methods

The choice of a specific method depends on many factors: the chemical activity of the metal, the availability of chemical reagents and safety considerations.

Chemical etching

It is performed in a container with the active substance. For carbon steels, solutions of weak acids may be suitable: citric, acetic. Hydrochloric acid works well. Pickling in battery electrolyte, nitric acid and rust converter should be treated very carefully: the process can release toxic gaseous substances, so it is better not to work with such reagents in the absence of a fume hood and good ventilation.

One of the safest substances is a saturated solution of ferric chloride. It can be bought in stores that sell radio components. The advantages of the solution are its almost unlimited service life (when working with iron alloys) and the coloring of the etched surface in an even gray color.

The process time is selected experimentally depending on the concentration of the reagent used and the activity of the metal.

Electrochemical etching

Many stainless and acid-resistant steels, for example, 40Х13, 95Х18, 08Х10Н18, 03Х12Н14М2, do not react to acids, so an electrochemical method is used for etching them.

It will require an electrolyte bath made of plastic or glass, wires, terminals and a direct current source. A saturated solution of table salt will work as an electrolyte. When choosing a container for it, you should remember that the process can proceed quite violently, so its volume should be 2 times larger than that of the electrolyte.

You can use rechargeable batteries as a current source, but it is better to use a charger (3 - 10A) with an ammeter and the ability to adjust the current parameters to select their optimal value. The workpiece is connected to the anode (positive contact) using terminals and a conductor; any stainless plate placed in the bath parallel to the front surface of the workpiece can be used as a cathode. After this, the device is connected to the network.

The entire process can take from two minutes to half an hour, depending on the current strength and the area of ​​the pattern. The etching depth should be controlled by periodically removing the part from the bath. At the same time, do not forget to turn off the power.

At the end of the process, the protective coating can be removed with a suitable solvent and the results of the work can be assessed. Thanks to good adhesion of the etched surface, it is possible to create a colored pattern.

To do this, the entire surface of the product is blown out of a cylinder with nitro enamel, and after it dries, it is wiped with a piece of clean leather, felt or other non-abrasive material. The paint is removed from the polished surface, remaining only in the depressions.

Dear readers, if you have any questions, please ask them using the form below. We will be glad to communicate with you;)

Select the image you want to etch onto the steel. You can draw the image by hand or reproduce an existing image on the surface of the steel. Depending on the image transfer method you choose, you may end up with either a very simple pattern or a rather complex one.

• If you're planning on reproducing an existing pattern, then choose something with a high contrast of black and white.
• If you plan to make and sell prints of your etched designs, select a public domain image or obtain permission from the copyright holder if one exists.

Transfer your design onto the surface of the steel. You can translate the pattern using one of the following methods. However, keep in mind that no matter the transfer method, the result will be the opposite of the image produced by etching onto the steel. If you plan to use the etched plate solely as a decoration and not for printing with it, then this will not matter to you.

• The oldest method of transferring images is to coat steel with a liquid varnish or wax-like substance (such as beeswax), or even enamel paint or nail polish. This coating is called soil. You can scratch your image directly into the ground using needles or cutting tools. (This process is reminiscent of wood carving.) The primer will serve as a resist, isolating the areas of steel it coats from the action of the etching acid.
• Another method is to cover the surface of the steel with permanent marker marks in the areas you don't want to etch. To determine the best resist, you will have to experiment with several permanent markers of different brands and colors.
• The third method is to create a stencil that is transferred to steel using an iron, either by photocopying the image onto transfer paper, or by printing it on glossy photo paper with a laser printer. Place the paper face down on the steel surface and, using an iron set to high temperature, smooth it with smooth circular movements for 2-5 minutes. (If you're using transfer paper, press down gently; if you're using photo paper, press down firmly with the iron.) You can then remove the paper. (The transfer paper will peel off on its own, and removing the photo paper requires placing it in a tray of hot water to soften it.) The transferred ink will become a resist for the etching acid.

Cover the edges of the steel piece. You can apply duct tape to the edges of the steel or paint over them. Both methods prevent etching of the steel edges

Select the acid you will use to etch the steel. Possible alternatives are hydrochloric acid (HCl), nitric acid (HNO3), or sulfuric acid (H2SO4). Certain substances that are not acids but produce an acidic environment in water, such as iron (III) chloride (FeCl3) or copper sulfate (CuSO4), can be used as etching agents. The strength of the acid determines the rate of pickling of the steel. You can purchase pickling acids and compounds from chemical or electronics supply stores.

• To make a solution of hydrochloric acid, iron (III) chloride is usually mixed with water in equal quantities. It is most often used for etching copper, but it also works well on stainless steel. It is used in combination with a wider range of resist materials compared to other acids; however, without proper attention, it can cause pitting corrosion of the surface.
• Copper sulfate is more suitable for pickling mild and stainless steels. It is better to mix it with sodium chloride (NaCl - ordinary table salt) in a ratio of 1 to 1 to prevent the formation of copper deposits on the surface of the steel, which will stop the etching process. The blue solution gradually fades as the etching process progresses and becomes colorless when it is complete.
• Nitric acid is usually mixed in a ratio of 1 part nitric acid to 3 parts water. It can also be mixed with acetic acid (vinegar) in a 1 to 1 ratio, or with hydrochloric acid.
• Sulfuric acid can only be used at a concentration of 10 to 25 percent. A dilute solution of sulfuric acid is usually more effective than a concentrated solution. However, acids etch steel longer than compounds that form acids with water.

Immerse the steel piece in a bath of pickling acid. Typically, you should place the steel plate face down in the solution so that the metal being etched flakes down from the plate. This gives cleaner lines when etching steel. If you placed the plate face up, you can use a light brush or feather to brush away the flakes as they form, which will also remove any bubbles that form. (The bubbles slow down the etching process, but if left they can form interesting patterns.) Leave the steel plate until the lines are the depth you want.

• Regardless of whether you place the steel plate face up or face down, somehow lift it off the bottom of the tub. (This is especially important when the plate is face down.)
• Shake the pickling bath occasionally to ensure the solution is well mixed.

Technologies for a beginner radio amateur

Perhaps not a single radio amateur now can do without printed wiring, the advantages of which - a high density of parts, reliability of the assembled circuits - are obvious.
However, inexperienced radio amateurs may have difficulties with the manufacture of printed circuit boards: first of all, you need to apply a drawing, then you need to purchase (or make) a solution for etching the board, in the end you also need to have the appropriate utensils in order to place this board for etching.

In general, all this is not so difficult; you can find a lot of information about this on the Internet. And our site is no exception to this: here, for example:
Manufacturing of printed circuit boards using the laser-iron method
Solution for etching printed circuit boards from scrap materials
Simple PCB Etching Tank

But here we will present you another method of printed wiring, which does not require any drawing. no etching of printed circuit boards. Ask - how is it? And here it is: in the magazine Modelist-Designer 1967 No. 5, S. BELOTSERKOVETS, A. OVSYANNIKOV from Moscow proposed an extremely simple and effective method make a printed circuit board parallel path method. Printed-parallel boards are made of foil getinax and differ from conventional ones in that the connecting conductors on them are arranged in parallel. Circuit elements are installed on the connecting conductors. If necessary, the conductors can be cut into separate parts or connected together with jumpers.

And here is a real example of manufacturing a device on such a printed circuit board:

Of course, this will require some skills, in particular the ability to arrange all the parts as compactly as possible.

For example, let’s assemble a circuit of a simple amplifier, like this:

C1, C2 - EM or "Tesla": C3 - ETO-1; R1 - variable resistor with switch; R2 - ULM or MLT - 0.25; loudspeaker - 0.2 GD-1 with a voice coil resistance of 28 Ohms.

Let's look at how to prepare a board for mounting an amplifier. First, a rectangular plate of specified dimensions is cut out of a piece of foil getinax or textolite. Then, using a caliper, divide the foil into seven equal strips, between which the foil is cut (as in the figure)

After this, holes are marked and drilled on the side of the foil layer. The drill should have a diameter of 1.0-1.2 mm. Where necessary, incisions are made with a sharp scalpel

Circuit details and connecting jumpers (single-core tinned wire with a diameter of 0.5-1.0 mm) between the individual strips are installed on the back side of the board

You need to solder the circuit with a small soldering iron, and its tip should be no wider than the foil strip. When soldering, make sure that the solder does not spread and short-circuit adjacent areas.

Printed-parallel boards can be made without foil getinax. To do this, use BF-2 glue to glue strips of thin copper foil onto any insulating material (textolite, getinaks. plexiglass, etc.) with a thickness of 1.5-2.0 mm and heat the plates at a temperature of 100-120° for two hours .

Note:
Although the source of this material was published back in 1967, this topic has not lost its relevance. Moreover, nowadays printed circuit boards are produced that do not require soldering. If anyone is interested in what they look like and where they can be purchased, I recommend taking a look here

Stainless steel often requires surface treatment to achieve the desired aesthetic or performance properties. Treatment with shot blasting and sandblasting devices is limited due to the high probability of hardening. Modern production uses etching of stainless steel, after preliminary thermal or mechanical treatment. The complexity of this process, compared to conventional black, low-alloy steels, is explained by the presence of a chromium oxide film that acts as a protective barrier. It is this that forms hard scale that does not interact well with reagents. Technological influences may cause color changes on the surface. These include welding, soldering, and other operations involving high temperatures. Iridescent tarnish can be removed by etching. For different chemical compositions of stainless steel, individual pickling methods and compositions have been developed, taking into account the influence of the steel elements, to achieve maximum results.

Predominant methods of etching stainless steel steels are alkaline and acidic, which can be intensified by electrolysis or occur without it.

Acid etching

Maximum effect pickling stainless steel with acids is achieved by sequential interaction of the stainless steel surface in baths with two types of acids - sulfuric and nitric. The sequence of stages is as follows

1. Degreasing, removal of large snags, scale
2. Pickling in a sulfuric acid bath (concentration 10-12%) or sulfuric acid bath (8% sulfuric acid, 4% hydrochloric acid). In this case, corrosion of scale and roughness on the surface occurs. The ideal temperature for the process is between 60 and 80 degrees Celsius. Monitoring this parameter is important for process control. The duration of treatment depends on the steel grade, the presence of a controlled ratio, and the concentration of acids. If the bath is depleted, pitting corrosion may occur. For example, steel with 18% Cr, 8% Ni requires 23 to 45 minutes of pickling in a sulfuric acid bath. Reducing the processing time by half can be achieved if this operation is carried out in a controlled atmosphere.
3. Rinsing with plenty of running water
4. Immersion of the workpiece in a bath filled with a solution of nitric acid and hydrofluoric acid (10 - 20, 1-2 weight percent, respectively). At a bath temperature of 60–70 degrees, the treatment time is 7–15 minutes.
5. Repeated rinsing with large volumes of water

The presented method is basic and has many variations. Etching in one nitrate bath with an admixture of hydrofluoric acid increases the etching time to 30 minutes. Sodium fluoride can act as a substitute for hydrofluoric acid. Increasing the concentration of hydrofluoric acid to 10% allows the process to be carried out at low temperatures, avoiding preliminary immersion in sulfuric acid.

Reducing the etching time in sulfuric acid can be achieved by adding no more than 5% sodium chloride. This move gives the desired effect in 15 minutes, but at the same temperature, about 80 degrees Celsius.

Be careful: if it is necessary to carry out the procedure in a room with insufficient aspiration, replace the components of the second stage of etching. Acids produce harmful fumes when etching. A solution of ferrous sulfate (7%) and hydrofluoric acid (2%) is proposed as a replacement.

To correctly select the acid etching method, you need to know and take into account the state of the oxide film on the surface of stainless steel. Appearance can tell you about the composition of the film. The green color of the scale indicates a high content of chromium oxides. Accordingly, the action of acidic environments will be difficult and will require more time.

Electrolytic etching

One option common in modern factories is electrolytic etching. A workpiece or part placed in an acid bath is connected to a positive or negative terminal. When current passes through the surface of stainless steel, oxygen is released. The gaseous phase has a mechanical effect on the oxide film. This helps speed up the processing process and the quality of the resulting surface.

Etching with ready-made pastes

Modern industry offers a variety of etching products on the market. pastes for stainless steel . Their main purpose is local processing of welds, the consequences of changes in the uniformity of surface coloring under the influence of temperature. The principle of working with such pastes is simple and can be used even in small workshops.

• Apply the paste in a thick layer up to 2 cm, using a brush
• Exposure 60-90 minutes
• Water jet rinsing

The use of pastes is advisable for processing welding seams of stainless steel grades. The treated seam is able to resist corrosion even in the damp conditions of a car wash.

Alkaline etching

Treating the surface of stainless steel with molten caustic soda is called alkaline etching. It should be noted that during this process the oxide film is destroyed, while the chemicals do not react with the metal. An increase in temperature promotes corrosion of the oxide film, improving the quality of the treated surface. Rapid cooling in liquid also helps to improve the treated surface.

It is almost impossible to achieve 100% results with this type of processing. Residual films from chromium oxides, nickel and iron oxides are possible on the metal. Among the recommendations for final finishing of such defects is a short-term treatment in a nitrate bath.

Alkaline etching methods

The following methods are distinguished:

• Aging in soda. The sodium nitrate content should range from 20-40%, heated to a temperature of 460-500 degrees Celsius. Etching in such an environment lasts for 15 minutes. Some austenitic grades of stainless steel are prohibited from being heated above 450 degrees. This can lead to intergranular corrosion. This is followed by a rinsing step in a large amount of water, followed by a 5-minute immersion in a sulfuric acid bath and up to 10 minutes in a nitrate bath.
• Known in England since the first half of the 19th century, the etching method is combined with passing an electric current through the part being etched. At a current density of 11 A/m2, 15 seconds is sufficient. This reaction rate is associated with the electrolysis process. The release of sodium and hydrogen at the cathode contributes to the reduction of oxides. The reduced metal is deposited on the surface. This type of etching allows you to obtain degreased metal, characterized by purity and uniformity. This method uses soda. Variations are possible with the composition and addition of calcium chloride. This method is used for etching flat, rod blanks, and drawn products.
• Treatment with sodium hydrides is based on reduction by exposing the metal to sodium and hydrogen. The presence of sodium hydride is achieved by the interaction of hydrogen and sodium, which is in a molten state. A cylinder without a bottom plane is placed in molten caustic soda. The top plane has a hole. Sodium is poured into this hole, it reacts on the surface of the bath. A stream of hydrogen is passed through a spot of sodium on caustic soda. A hydride is formed and diffuses throughout the bath. Achieving the required concentration of 1-2% sodium hydride occurs within controlled threshold values. In the absence of an air separation product, dissociated ammonia is used. The parts are heated in such a bath to 400 degrees Celsius. Stainless steels show good pickling results with this technique and duration of 4-17 minutes. After etching, it is recommended to thoroughly rinse the parts. If necessary, carry out additional treatment in a nitrate bath. Given the high cost of this method, its obvious advantage is the fact that the metal does not interact with the etchant. Metal losses are minimal. Lower process temperatures reduce coolant costs and reduce operational safety.

There are certain rules that must be followed for any of the presented methods. Among them, priority is the treatment of the metal surface before etching, removal of the oxide film, and degreasing. The etching process is no less important.

Bath materials

Choosing the right material for making etching baths is a difficult task for chemists and materials scientists.

• ceramic coated
• glass covered brick
• wood, lead-coated concrete
• rubber derivatives
• Certain grades of stainless steel for acid baths.

The content of nitrogenous acid with impurities of hydrofluoric or hydrochloric acid allows the use of the same materials. The only exceptions are lead as a coating, ceramics with a high silicon content, due to their interaction. It is quite possible to use steel in alkali baths, monitoring the progress and intensity of electrolysis in close proximity to the material. Under certain conditions and acid content, its temperature, and nature, it is possible to use stainless steel grades for pickling tanks. Such, for example, as 8Х18Н8М or 10Х20Н25М4.

From the information provided in this review, we can conclude that the processing mode, the chemical composition of the bath, the need for additional mechanical processing, and the use of electrolysis should be determined based on specific initial conditions (steel grade, state of the oxide film, technological capabilities) and regulated in the context of the expected final result .

Pickling is the process of cleaning and processing a metal workpiece. Chemical, acidic, alkaline, electrochemical - there are many ways to perform this technological operation. Where is metal etching used, why is it used in industry, what are the processing methods using this technology, all these issues are discussed in detail in the article below.

What is etching

This is a technology for removing the top layer from the surface of a metal part. The technology is used to clean workpieces from scale, rust, oxides and remove the top layer of metal. Using this method, the top layer is removed to search for internal defects and study the macrostructure of the material.

Using etching, they clean the part and increase surface adhesion. This is done for the subsequent connection of the metal surface with another workpiece, before applying paint, enamel, galvanic coating and other protective coatings.

The method allows you not only to quickly clean the part, but also to create the desired pattern on the metal surface. Using this method, the finest channels and complex images are cut out on a metal surface. You can clean large parts or rolled products. The processing depth is adjustable with an accuracy of several microns, which makes it possible to produce complex parts with small grooves and other complex elements.

Application of etching in industry

1. For cleaning parts made of carbon, low-alloy and high-alloy steel, titanium and aluminum from oxide film.
2. To improve adhesion before applying galvanic and other types of protective coatings.
3. To prepare steel surfaces for hot-dip galvanizing.
4. To conduct macroanalysis to detect the formation of intergranular corrosion in stainless steels.
5. This technology is used to process small metal parts, such as watch gears.
6. Copper processing is used to make semiconductor chips and printed circuit boards in electronics. This method applies a conductive pattern to the microcircuit.
7. For quick cleaning of hot rolled metal products, heat-treated parts, from oxides.
8. In the aircraft industry, this technology is used to reduce the thickness of aluminum sheets to reduce the weight of the aircraft.
9. In the manufacture of metal inscriptions and drawings. Etching produces relief images drawn by removing a layer of metal according to a specific stencil.

Types of etching

The main types of metal processing used in industry:

• electrolytic - there are cathode and anodic;
• chemical;
• plasma.

Electrolytic etching

Electrolytic or galvanic metal processing is used to quickly clean parts, apply engravings and produce grooves. Metal parts are immersed in an acid or salt electrolyte. The part becomes a cathode - a negative electrode or an anode - a positive electrode. Therefore, two types of electrolytic etching are classified - cathodic and anodic.

1. Cathodic etching. The method is used to remove scale from the surface of carbon steel products after hot rolling or oil quenching. In cathodic etching, the material for the anode is lead, and the electrolyte is a solution of hydrochloric, sulfuric acid or an alkali metal salt. During the electrolysis process, hydrogen gas is actively released at the cathode, which interacts with iron and removes scale. During the cathode method, the metal surface is actively saturated with hydrogen, which increases the fragility of the workpiece. Therefore, the cathode method is not used for thin-walled products.
2. Anodic electrochemical cleaning. This is the most common method in mechanical engineering. The process involves mechanically tearing off the oxide film on the anode with oxygen and mixing metal molecules with the electrolyte. An electrolyte is a solution of acids or salts of the metal being processed. Lead, copper and other metals are used as the cathode. During anodic treatment, the surface of the product becomes clean, with slight roughness, and the metal dissolves in the electrolyte. With this method, there is a risk of reducing the thickness of the workpiece and over-etching.

Chemical etching

The chemical treatment method is used to clean the surface of a part from oxide film, scale and rust for workpieces made of the following materials:

• ferrous metals;
• stainless and heat-resistant steels;
• titanium and its alloys;
• aluminum

For etching, sulfuric, hydrochloric or nitric acid is used. The workpiece is immersed in an acid or alkaline solution, molten salt and kept for the required time interval. The required cleaning time can range from 1 to 120 minutes.

The cleaning process occurs due to the release of hydrogen when the acid interacts with the metal. Acid molecules penetrate through pores and cracks under the oxide film. There they interact with the metal surface and hydrogen is released. The released gas tears off the oxide film and cleans the part.

Simultaneously with the oxides, the metal being treated dissolves in the acid. To prevent this process, corrosion inhibitors are used.

Plasma etching

With the ion-plasma method, cleaning and removal of the surface layer occurs by bombarding the part with ions of inert gases that do not react chemically with the molecules of the material being processed. Allows you to make high-precision notches and grooves with an accuracy of up to 10 nm. The technology is used in microelectronics.

The plasma-chemical method involves excitation of plasma in a chemically active medium, which causes the formation of ions and radicals. Active particles falling on a metal surface cause a chemical reaction. In this case, light compounds are formed, which are removed from the surrounding air by vacuum pumps.

The method is based on chemical reactions that occur when using reactive gases, such as oxygen, which are highly reactive. These gases actively interact in the gas discharge plasma. Unlike plasma treatment in inert gases, with this cleaning method, the active gas reacts only with certain molecules.

The disadvantage of this method is the lateral expansion of the grooves.

Etchants

Pickling of carbon steels is carried out in an 8-20% solution of sulfuric or 10-20% hydrochloric acid. With the obligatory addition of corrosion inhibitors (KS, ChM, UNIKOL) to eliminate the fragility of the material and reduce the possibility of over-etching.

Products made of stainless or heat-resistant steel are processed using a solution consisting of: 12% hydrochloric, 12% sulfuric, 1% nitric acid. If required, processing is done in several stages. The first is that scale is loosened in 20% hydrochloric acid. The second stage is immersion in a 20-40% nitric acid solution to completely remove surface contaminants.

The thick layer of scale that forms on stainless steel is removed during its production by 75-85% molten caustic soda with 20-25% sodium nitrate. After which, complete removal of oxides is carried out in 15-20% nitric acid.

Processing of aluminum and alloys based on it involves removing the refractory oxide film from the surface of the workpiece. For this purpose, alkaline or acidic solutions are used. Usually 10-20% alkali is used, at a temperature of 50-80 ºС, the etching procedure takes less than 2 minutes. The addition of sodium chloride and sodium fluoride to the alkali makes this process more uniform.

The purification of titanium and its alloys, carried out after heat treatment, is carried out in several stages. At the first stage, scale is loosened in concentrated caustic soda. Then the scale is removed in a solution of sulfuric, nitric or hydrofluoric acid. To remove the remaining pickling sludge, use hydrochloric or nitric acid with the addition of a small amount of hydrofluoric acid.

When processing copper and its alloys, etchants from hydrogen peroxide, chromic acid and the following salts are used:

• copper chloride;
• ferric chloride;
• ammonium persulfate.

This information material describes in detail the pickling process used in metallurgical plants. The method allows you to quickly clean the metal surface from oxides, scale, rust and other contaminants. Thanks to etching, it is possible to apply various designs to metal, create complex microcircuits and make microscopic channels of the desired shape.