Blackening aluminum at home (for homemade adapters). Etchants for aluminum Galvanic etching of aluminum at home

Aluminum etching is carried out in an alkaline or acidic environment. A widely used etchant consists of concentrated H 3 PO 4 (76%), glacial acetic acid (15%), concentrated nitric acid (3%) and water (5%) by volume. According to research, the process consists of two stages - the formation of Al 3+ and the formation of AlPO 4, controlled by the rates of the corresponding reactions:

Al 2 O 3 slow Al -3е HNO3 Al 3+ fast fast Film slow Soluble AlPO 4 . (40)

Water in phosphoric acid prevents the dissolution of Al 2 O 3, but it promotes the dissolution of the secondary product AlPO 4. The current strength is proportional to the etching speed. If current is applied to aluminum, then anisotropy of etching is observed.

The activation energy for etching Al in H3PO4/HNO3 is 13.2 kcal/mol, which suggests that the process is limited by the rate of dissolution of Al2O3 in H3PO4. The gas released is a mixture of H 2, NO and NO 2. Adsorption of gases onto Al surfaces is a constant problem when using viscous etchants. Bubbles can slow down etching - islands of unetched metal are formed under them, which can short-circuit nearby conductors.

Rice. 17.

The preferential adsorption of gaseous products on the side wall limits lateral etching.

An unexpected application of bubble adsorption was its use for smoothing profile edges when etching iron-nickel films in HNO 3 (Fig. 17). As soon as the etching process begins, nitrogen oxide bubbles collect along the side edge. The adsorbed NO 2 intermediate acts as a strong oxidizing agent in metal etching, and lateral etching is accelerated. Adsorption of gases on the side wall (Fig. 17) was also used to reduce the lateral etching of Al during its etching in H 3 PO 4. Reducing the pressure in the etching chamber from 10 5 to 10 3 Pa led to a decrease in etching from 0.8 to 0.4 μm. As a result of the adsorption of small hydrogen bubbles on the side wall, an effective diffusion barrier was formed on it. To reduce the lateral etching of Al from 1.0 to 0.25 µm, several etchants (Table 9) containing additives of sucrose (polyalcohol) and surfactants were proposed.

Table 9. Etchants for aluminum.

1) AK - cyclo rubber with azides, KTFR type resists; DCN - novolac with quinone diazides, resists type AZ-1350.

Poor etching of Al is caused by several factors:

1) underdeveloped resist;
2) uneven thickness;
3) stress in the films over the steps;
4) galvanic acceleration of etching due to the presence of Al-Cu precipitates;
5) uneven oxide thickness;
6) temperature instability (>1 o C).

These factors lead to over-etching and short-circuiting.

Chromium is the second most commonly etched metal after aluminum. It is widely used in the manufacture of photo masks. Cerium sulfate/HNO 3 is used as an etchant.

Due to the induction effect (formation of the upper layer of Cr 2 O 3), the etching of the film is nonlinear, and therefore the moment of the end of etching cannot be determined by its initial thickness.

Chemical solutions for pickling iron and steel

The simplest effective solutions for etching iron and steel parts are diluted inorganic acids, especially 20% sulfuric acid, in which etching is carried out at 45-50 ° C, or 20-25% hydrochloric acid, in which parts are etched at room temperature. For etching, 10-15% is also used. orthophosphoric acid, heated to 60-70°C. Parts are etched in it, which will then be varnished or their surface will be left without further processing. If, after etching, galvanic coating of the surface is provided, then this bath is unsuitable.

Chemical etching of non-ferrous metal surfaces

Etching copper and brass

On brass the solution forms a light yellow coating, on copper it forms a light pink coating. The solution contains:

Concentrated nitric acid 250 ml;
- Concentrated hydrochloric acid 150 ml;
- Denatured ethyl alcohol 100 ml;
- Water 500 ml.

The parts are etched by briefly immersing them in a bath of solution, after which they are removed and immediately washed with water.

Brushed copper etching

After etching on copper, you will get a rough (to matte) surface. Bath composition:

Nitric acid 40% 600 g;
- Concentrated sulfuric acid 400 g;
- Sodium chloride 3 g;
- Zinc sulfate 2 g.

Brilliant etching of copper and its alloys

Concentrated sulfuric acid 500 ml;
- Concentrated nitric acid 500 ml;
- Concentrated hydrochloric acid 10 ml;
- Soot 5 g.

Working temperature baths 18-20°C. The degreased parts are immersed in a bath of solution for 10-30 s, after which they are removed, washed with water and dried.

Solution for etching aluminum and its alloys

The aqueous solution contains:

Sodium fluoride 40 g/l;
- Caustic soda 50 g/l.

The operating temperature of the bath is 70-80°C, the processing time is about 1 minute.

Another water solution contains

Chromium oxide 30 g/l;
- Concentrated sulfuric acid 150 g/l;
- Operating bath temperature 70°C, treatment time 1-1.5 minutes;

The simplest way to decoratively paint steel products

The electrochemical method can be used to paint steel products in any color. If the paint layer is varnished, it will reliably protect the product from corrosion. The solution in which steel products are painted includes the following components:

Copper sulfate 60 g;
- Refined sugar 90 g;
- Caustic soda 45 g;
- Water up to 1 liter.

Dissolve in 200-300 ml of distilled water copper sulfate, then sugar is added to the resulting solution. Separately, caustic soda is dissolved in 250 ml of water and a solution of copper sulfate and sugar is added to it in small portions (with stirring). After mixing these two solutions, add distilled water to 1 liter. The part is cleaned, polished and degreased in a solution used for nickel plating, and then thoroughly washed in warm water. An additional electrode is made from red copper (preferably grades M0, M1). The part and electrode are connected to a flashlight battery (or other 4-6 V DC source), and the copper electrode should be connected to the plus of the battery, and the part to the minus. First, the copper electrode is lowered into the solution, and then the part. After 5-10 s, the battery is turned off, and coloring continues without electric current. While in the solution for 2 to 25 minutes, the part is painted in the following colors (in the order of their appearance): brown, purple, blue, cyan, light green, yellow, orange, red-lilac, greenish-blue, green, pink-red . The part can be removed from the solution (checking the color) and put back into the solution - the process will proceed normally. When the part is kept in the solution for more than 25-30 minutes, the process is repeated cyclically many times.

As the electrolyte evaporates, distilled water is added to the bath, since increasing the electrolyte concentration worsens the quality of the color. To obtain more contrasting colors, add 20 g of sodium carbonate (anhydrous soda) to the finished electrolyte. If the painting is unsuccessful, the film can be easily removed by wiping the part with ammonia. The painted parts are washed with water, dried and coated with colorless varnish.

Easy way decorative finishing aluminum surface with mother-of-pearl effect

The aluminum surface is cleaned with a metal brush, making small strokes in different directions (creating a certain pattern). Chips and dirt are removed from the surface with a clean rag. A clean aluminum surface is coated with an even layer of 10% caustic soda solution (working temperature of the solution is 90-100°C). After the solution dries, a beautiful film with a pearlescent tint forms on the aluminum surface. For better preservation, the film is coated with colorless varnish. A more beautiful film is obtained if the product or part is heated to 80-90°C before applying the caustic soda solution.

Chemical method of brightening products and parts made of silumin (restoration)

Products and parts made of silumin (an alloy of aluminum and silicon) are quickly covered with an oxide film of dark tones. However, they can remain shiny for a long time if they are lightened. Products or parts are cleaned and, if necessary, polished, then degreased, washed and immersed for 10-20 minutes in the following solution:

Chromic anhydride 100 g;
- Concentrated sulfuric acid 10 g;
- Water up to 1 liter.

The working temperature of the solution is 18-20°C.

After lightening, the products and parts are washed and dried, and so that the surfaces of the products and parts do not oxidize for a long time, they are coated with colorless varnish.

What you need to know about polishing steel and non-ferrous metals

Polishing is used to improve the cleanliness of the surface of parts and devices, and to eliminate traces of previous processing (strokes, scratches, small dents and tiny irregularities). There are two types of polishing - preliminary and final. Pre-polishing is used to mechanically remove surface irregularities with loose abrasives (in a free state) or grains fixed to work surface polishing wheel. Final polishing is carried out with fine grinding powders or soft elastic wheels with thin polishing pastes applied to them. The finest surface finish is achieved by rubbing a piece of felt or woolen cloth coated with a special metal polishing paste. After polishing, the surface acquires a mirror shine.

Lime paste is used for polishing nickel, brass, aluminum and other metals, its composition (in%) is as follows:

Vienna lime 71.8;
- Ceresin 1.5;
- Stearic acid 2.3;
- Solid oil T 1.5;
- Turpentine 2.2;

Composition of paste (in%) for polishing steel and other metals:

Paraffin 20;
- Stearin 10;
- Technical lard 3;
- Micropowder M50 67;

Note

Waxy and liquid materials are mixed and heated in a water bath (or low heat). Then the dry ingredients are mixed into the hot mass.

GOI pastes are intended for polishing steel and other metals and are chromium oxide mixed with waxy substances. Pastes are produced in three grades: coarse, medium and fine. In the absence of chrome paste, you can successfully use chromium oxide oil paint diluted with kerosene. Crocus paste (iron oxide) is sold in stores in finished form(in dentures they are used under the name “gold paste”). Crocus paste is used for polishing brass, bronze, silver and other metals. Glitter powder diluted with machine oil is used for fine polishing of metals.

Chemical method of polishing metals

Metals can be polished chemically, i.e. by simply immersing a part or object in a bath of polishing solution without the use of electric current. For this purpose, you can use porcelain glasses or baths. The polishing solution consists of the following substances:

Concentrated phosphoric acid 350 ml;
- Concentrated nitric acid 50 ml;
- Concentrated sulfuric acid 100 ml;
- Copper sulfate or nitrate 0.5 g.

The operating temperature of the bath is 100-110°C. Polishing time from 0.5 to 4 minutes. Polishing produces choking fumes, so the bath should be kept in a fume hood or outdoors.
This solution polishes aluminum and its alloys well. It is also suitable for polishing other metals, but the operating conditions (polishing time, temperature) must be different.

CHEMICAL PROCESSING OF METALS

Chemical nickel plating of steel, copper, brass and bronze products
Parts made of steel and copper alloys can be chemically coated with nickel. This coating not only protects parts well from corrosion and gives them a beautiful appearance, but also has increased wear resistance. Another advantage of chemical nickel plating is that nickel is evenly deposited on all, including internal, surfaces of parts.
The part to be decorated with nickel plating must be prepared in an appropriate way: sanded, polished and degreased. Steel parts are degreased in a solution containing per 1 liter of water 20-30 g of caustic potassium (or caustic soda), 25-50 g of soda ash and 5-10 g liquid glass(silicate glue); copper - in a solution containing (for the same amount of water) 100 g of trisodium phosphate and 10-20 g of liquid glass. Before nickel plating, copper parts must be kept on the iron for 0.5-1 minutes. It should also be borne in mind that alloys containing more than 1-2% lead or cadmium are not amenable to chemical nickel plating.

Degreasing of steel and copper parts at room temperature ends after 40-60 minutes, at a temperature of 75-85°C - after 20-30 minutes. Then the part is thoroughly washed in running water and immersed for 0.5-1 min in a 5% solution of hydrochloric acid to remove the oxide film, after which it is washed again in water and immediately transferred to the nickel plating solution. 30 g of nickel chloride and 10 g of sodium acetate are dissolved in 1 liter of water heated to 60°C. Then the temperature is brought to 80°C, 15 g of sodium hypophosphate is added - and the solution is ready. The part is immersed in it, the temperature is raised to 90-92°C and maintained at this level until the end of the nickel plating process. At lower temperatures, the speed of the process slows down sharply, and when heated above 95°C, the solution may deteriorate.

Required amount(volume) of the solution depends on the area of the nickel-plated part. The ratio of this area (in square decimeters) to the volume of the solution (in liters) should be in the range of 2.5-3.5.
So, for example, at S/V=3 in 1 hour the thickness of the nickel layer will be 10 μm.

The chemicals used are not toxic, degreasing and nickel plating are not accompanied by release harmful gases.
Chemical copper plating of steel and cast iron parts

Quite easily, copper is chemically deposited on iron, steel and cast iron. The coverage is satisfactory.

To coat these metals, a solution of the following substances is prepared:

Copper sulfate 8-50 g;
- Concentrated sulfuric acid 8-50 g;
- Water up to 1 liter.

Operating temperature 18-20°C. After thorough cleaning and degreasing, the parts are immersed in the solution for a few seconds. Parts coated with copper are removed from the solution, washed with water and dried.

Chemical chrome plating of metals

Parts made of steel, copper and brass are chemically chrome plated in a solution containing:

Chromium fluoride 14 g;
- Sodium hypophosphate 7 g;
- Sodium citrate 7 g;
- Glacial acetic acid 10 ml;
- Caustic sodium (20% solution) 10 ml;
- Water up to 1 liter.

Operating temperature is about 80°C. Cleaned and degreased parts are metallized within 3-8 hours. When chemically chrome-plating steel objects, it is recommended to first chemically coat them with copper. Parts with a deposited layer of chromium are washed in water and dried.

Electroless nickel plating of metals

The nickel plating solution consists of the following substances:

Nickel ammonium sulfate 50 g;
- Ammonium chloride 40 g;
- Water up to 1 liter.

A small amount of zinc metal is added to the solution and stirred continuously.

Chemical dyeing of pewter items bronze

Pewter products can be easily painted bronze using a chemical method. Products are immersed in a solution or wiped with a cloth soaked in a solution consisting of the following substances:

Copper sulfate 25 g;
- Ferrous sulfate 25 g;
- Water up to 500 ml.

Then the product is dried, cleaned with a brush, wiped with a cloth and again immersed in a solution consisting of the following substances:

Copper acetate 100 g;
- Acetic acid 10% 400 ml.

After this, the product is dried. If desired, it can be polished and coated with clear varnish.

"Gold plating" of brass

Brass and products made from it quickly tarnish and oxidize in air. To protect highly polished products from oxidation, brass parts are often coated with a special golden varnish. Simpler and affordable way is as follows: after thorough cleaning and polishing, a brass part is immersed in a 10-15% solution of some alkali to remove fat from its surface. Then the part is washed in water and immersed in a weak (2-3%) solution of sulfuric or hydrochloric acid for 1-2 s. Good results are obtained if brass is dipped in a solution of sodium bisulfite, then rinsed in water and dipped in a solution of copper acetate heated to 36-40°C.

Depending on the time the piece is in the solution, the brass will turn from a light golden color to a red gold color and even a reddish-violet hue. The color of the paint is monitored by removing the part from the solution from time to time. After painting, the part is washed with water and air dried. The color is permanent and does not change over time. Copper acetate is commercially available, but you can make it yourself. To do this, you need to dissolve 5 g of copper sulfate in 0.5 liters of water, then mix it with a solution of lead acetate (pharmacy lead lotion or lead sugar).

The second solution is made up of 8 g of lead acetate and 0.5 liters of water. When mixing the solutions, a precipitate of lead sulfate precipitates, and copper acetate remains in the solution. This solution will serve as the working solution. The precipitate can be filtered or left at the bottom of the vessel.

Copper gold coloring

4 g of caustic soda and 4 g of milk sugar are dissolved in 100 g of water, boiled for 15 minutes, then with constant stirring, 4 g of a solution of saturated copper sulfate is added in small doses. Well-cleaned copper products are immersed in the hot mixture. Depending on the duration of action, they acquire different colors - from gold, green to complete black.

Golden varnish for brass (passivation of brass)

When brass is passivated, a stable protective film similar to gold plating is formed. This film is not afraid of moisture, so fishermen passivate brass lures. The cleaned, polished and degreased part is dipped for 1 second in a solution prepared from 1 part nitric and 1 part sulfuric acid, and immediately transferred to a strong solution of potassium dichromate (chrompic) for 10-15 minutes.

After this, the part is washed and dried.

Chemical staining of brass

The cleaned, degreased and washed part is dipped into one of the following solutions.

1st solution:

Hyposulfite 11 g;
- Lead sugar 39 g;
- Water up to 1 liter.

Solution temperature 70°C.

2nd solution:

10 g of sodium hydroxide and 10 g of milk sugar are dissolved in 250 ml of boiling water. Then, stirring continuously, add 10 ml of a concentrated solution of copper sulfate to the solution.

Within 3-10 minutes, the part in one of the solutions turns golden, bluish, blue, violet and, finally, rainbow.

When the desired color is obtained, the part is removed, dried and polished with cloth.
Brass acquires a bluish-black color when the prepared part is immersed for 1-3 minutes in the following solution:

Ammonia (25% ammonia) 500 ml;
- Bicarbonate (or carbon dioxide) copper 60 g;
- Brass (sawdust) 0.5 g.

After mixing the components, the solution is shaken vigorously 2-3 times, after which the part is immersed in it.
Brass turns brown when the part is immersed in one of the following solutions.

1st solution:

Hyposulfite 50 g;
- Copper sulfate 50 g;
- Water up to 1 liter.

Solution temperature 70°C.

2nd solution:

Sodium sulfide 100 g;
- Water up to 1 liter.

Solution temperature 70°C.

3rd solution:

Lead acetate 30 g;
- Hyposulfite 90 g;
- Water up to 1 liter.

The solution temperature is 80-90°C.

To prepare the 3rd solution, you need to dissolve both substances separately in half the volume of water, then drain them together and heat to 80-90°C. After painting the part is washed warm water, dried and coated with colorless varnish.

A simple method of silvering

Spent hyposulfite (fixer) is used as a silvering compound, which is no longer suitable for fixing photographic films or photographic paper. The method is extremely simple. Copper part cleaned until shiny, boiled in a soda solution and washed thoroughly with water. Then it is dipped into used hyposulfite. After some time, silver will settle on the part. After washing with water, the part is dried and polished with cloth. The quality of silver plating and the strength of adhesion of silver to copper depends on the concentration of silver in the hyposulfite solution.

Hot silvering of metal parts

Any metal can be silvered using this method. It consists of the following: a cleanly processed part is immersed on a zinc strip in a boiling solution consisting of the following components:

Potassium iron sulfide 120 g;
- Potash 80;
- Silver chloride 7.5 g;
- Distilled water up to 1 liter.

The silvering process ends after the surface of the part is completely covered with silver. The part is then removed from the solution, washed and polished. It should be remembered that when the solution boils, harmful substances, so boiling should be done in the open air or under a hood.

Chemical silver plating

1. Several sheets of Unibrom matte photographic paper are cut into pieces and dipped into a solution of fixing salt (the salt is diluted in the volume of water indicated on the package).

The cleaned and degreased part is placed in this solution and rubbed with an emulsion layer of paper until a dense layer of silver is formed on the surface of the part. After rinsing in warm water, wipe the part with a dry cloth.

2. Add 1-2 ml to 300 ml of used fixer (remaining after printing photographs) ammonia and 2-3 drops of formalin (the solution is stored and worked with only in the dark).
The cleaned and degreased part is placed in the solution for 0.5-1.5 hours, then washed in warm water, dried and wiped with a soft cloth.

Paste for silvering

Parts made of copper, bronze, brass, and copper-plated iron can be plated with silver using pastes.

1. Paste for silvering is prepared as follows: in 300 ml of distilled water or water obtained from ice in household refrigerators, dissolve 2 g of silver nitrate (lapis) and add a 10% solution of table salt to the solution until precipitation stops silver chloride precipitate. This precipitate is washed 5-6 times in running water. Separately, 20 g of hyposulfite and 2 g of ammonium chloride (ammonia) are dissolved in 100 ml of distilled water. Then silver chloride is added to the resulting solution in small doses until it stops dissolving. The resulting solution is filtered and mixed with finely ground chalk to the consistency of thick sour cream. The pre-degreased part is rubbed with a paste using cotton wool or gauze until a dense layer of silver is formed on its surface, after which the part is washed with water and wiped with a dry rag.

2. Rub the polished and degreased part with a cloth or piece of soft skin, onto which a paste of the following composition is applied:

Silver chloride 6 g;
- Table salt 8 g;
- Sour potassium tartrate (tartar) 8 g.

The listed substances are ground in a mortar and stored in a dark container; before use, the mixture is diluted with distilled water until liquid paste. When the part is covered with a layer of silver, it is washed in water and rubbed until shiny with soft flannel.

3. Paste for silvering is prepared as follows: pour 2 g of ammonia, 4 g of tartar and 1 g of silver nitrate (lapis) into a vessel, add a little distilled water until a semi-liquid slurry is obtained. Then, with a cloth with paste applied to it, the polished and degreased part is rubbed to a silver shine.

Chemical method of silvering non-metallic materials

Non-metallic parts, such as plastics, glass, ceramics, wood, etc., can also be metalized using a chemical method. The solution given below for silvering non-metallic materials gives very good results, especially when metallizing glass (silvering of mirror surfaces, vessels, incandescent lamp bulbs, reflectors for projection equipment, etc.).

The silver bath contains the following substances:

Composition A

Silver nitrate 12 g;
- Ammonium nitrate 18 g;

After complete dissolution of the substances, the solution is added with distilled water to 750 ml.

Composition B

Caustic soda (chemically pure) 19 g;
- Distilled water 500 ml.

After complete dissolution of caustic soda, the solution is added with distilled water to 750 ml.

Composition B

Sucrose 12.5 g;
- Tartaric acid 1.5 g;
- distilled water 125 ml;

The solution is boiled for 20 minutes, and then added with distilled water to 500 ml.

All solutions are stored separately in dark containers with ground-in stoppers.

The solution for silvering is prepared by mixing compositions A and B, to which composition B is added immediately before silvering. Parts intended for silvering are thoroughly cleaned in a hot soda solution and rinsed running water and immerse in a bath with a freshly prepared solution. The working temperature of the solution is 18-20°C. Silvering time - 10 min. Metallization can be carried out two or three times in succession, but each time in a fresh solution. Silver-plated parts are dried at a temperature of 50°C for 1 hour, and at a temperature of 18-20°C for 24 hours. The silver layer can be easily removed from glass, porcelain or ceramics with nitric acid.

Chemical dyeing of silver objects purple

Silver or silver-plated objects acquire a purple color in a solution consisting of the following substances:

Anhydrous sodium sulfate 12.5 g;
- Sodium carbonate 5 g;
- Water 500 ml.

The solution is heated to 80°C and the object is immersed in it for a few seconds. The item is then allowed to dry. The surface of the object can be coated with transparent varnish.

Chemical solution for dyeing silver objects black
Silver or silver-plated objects become black after boiling them in a solution of sodium sulfate (100 g per 500 ml of water). After boiling in this solution, the objects are dried and coated with a clear varnish.

Hot gilding of metal products

Mix 20 g of nitric and 20 g of hydrochloric acid in a glass vessel. 1 g of gold is dissolved in this mixture. When the gold dissolves, 1 g of antimony chloride and 1 g of pure tin are added to the solution. The vessel with the solution is placed in hot water and boiled until the tin dissolves, after which 20 g of a saturated solution is added boric acid. Products intended for gilding are cleaned, polished and boiled in a solution of caustic potassium or soda. The solution is applied to the product with a brush; the dried product is heated on the flame of an alcohol lamp or on a fire made of charcoal. After heating, a good gilding is obtained that does not require polishing. Store the solution in a glass container with a ground-in stopper in a dark place.

Gold plating without an external current source Contact gold plating is used to obtain very dense and uniform coatings, characterized by high adhesion strength, and if a large coating thickness is not required. Electrolysis by this method does not require an external current source. The potential difference required for gold deposition is created by a galvanic cell, in which the cathode is the coated product, immersed in a gold-plating electrolyte, and the anode is a zinc plate located in a concentrated solution of table salt and connected to the product with a wire, as shown in Fig. 1. Any heated gold-plating electrolyte from those indicated in the table can be used for electrolysis.

Gilding by immersion is based on the creation of a potential difference at the boundary of the surface of the metal being coated and the adjacent electrolyte layer. Coatings good quality are formed only on brass or brass plated parts. Therefore, parts made of other metals are pre-brass-plated (minimum layer thickness 1-2 microns). The gilding process automatically stops when a gold layer about 0.1 microns thick is obtained, but the coating is dense, glossy and has good adhesion to the surface of the parts.

Compositions of solutions and operating modes for gilding using the immersion method

Removal of poor-quality gold coatings

To remove poor-quality coatings, gold-plated silver items are suspended as anodes in a 5% solution of hydrochloric acid at a temperature of 18-20°C. Iron or lead plates serve as cathodes. Anodic current density 0.1 - 1 A/dm?. Copper pendants. Besides, gold plating Can be removed in "royal vodka". "Royal vodka" is a mixture of acids (50% nitric acid mixed in 50% hydrochloric acid). The mixture is used for etching copper, brass, iron, steel, zinc, etc. This solution acts on metals almost instantly; Corrosion and dirt disappear and the metal surface becomes shiny or, more often, matte. Jewelers use this mixture to determine pure gold.

Note

When using active acids, safety rules must be strictly observed. It should be remembered that when diluting an acid with water (for example, sulfuric acid), you need to pour the acid into the water, and not vice versa, since otherwise the acid will splash, which can lead to severe burns.

Simple ways extracting silver from waste hyposulfite (fixer)
Only part of the silver contained in the photosensitive layer of the photographic material is consumed to construct a photographic image. Most of the silver goes into the fixer and developer; it can be isolated and collected.

1st method.

Allows you to highlight pure silver. It consists of the following: iron filings or small iron nails, well washed from grease with gasoline, are poured into a vessel with depleted fixer. Shake the solution from time to time. After 7-10 days, the solution is drained and the nails are dried in air. Silver deposited on nails falls off as a black powder, which can then be smelted into ingots.

2nd method.

The depleted fixer and an equal volume of spent metholhydroquinone developer are poured into one vessel. A 30% solution of sodium hydroxide is added to the resulting mixture at the rate of 100 ml for each liter of used fixer. The silver is deposited in the form of the finest pure silver powder. The process lasts at least 48 hours.
The silver precipitate formed during this time is filtered and dried. The remaining aqueous solution of sodium thiosulfate, i.e. fixer, can be used again in work.

3rd method.

A polished sheet of brass is placed in the used fixer, which is in a glass vessel. After 48 hours, almost all the metallic silver from the depleted solution will have deposited on it. After deposition, the sheet is washed well with water and dried. Then the layer of silver is carefully scraped off its surface.

4th method.
To 1 liter of used fixing solution add 5-6 g of sodium hydrosulfite and 5-6 g of anhydrous soda. After 19-20 hours, the metallic silver formed in the form of a black fine powder is filtered, and the desilvered fixing solution is acidified with sodium bisulfite and used again for work.

5th method.
To do this, prepare a 20% solution of sodium sulfate and pour it into the used fixer at the rate of 20 ml of solution for each liter of fixer. After thoroughly mixing the solution, it is allowed to stand for 24 hours. Then the solution is drained from the sediment, and the sediment is dried on paper. The precipitate is silver sulfide. Precipitation is carried out in the open air or with increased ventilation; to reduce the release of hydrogen sulfide, the spent fixing solution is pre-alkalinized.

COLORING OF METALS

Coating metal with moiré varnish
Before coating with “moire” varnish, the surface of the metal part is degreased by heating it in an oven (oven) for 15-20 minutes at a temperature of 80-100°C, then primed with heat-resistant enamel, puttied with varnish putty and dried. When the part is thoroughly dry, it is treated with pumice with water and sandpaper, wiped dry, coated with an even layer of “moire” varnish using a spray bottle and placed for 10-15 minutes in an oven at a temperature of about 80°C.

The pattern of the pattern depends on the thickness of the coating and the duration of heating of the part. When a pattern forms on the part, it is removed from the oven for a short time to partially cool and then put back into the oven to dry the varnish completely. At a temperature of 120-150°C, the varnish finally dries within 30-40 minutes, and at a lower temperature - within 2-3 hours.
To protect the painted surface from dust, it is coated with celluloid varnish: celluloid is dissolved in acetone to the consistency of liquid oil varnish and applied to the surface in an even layer using a swab. After the acetone dries, a strong protective film remains on the surface.

A durable coating is obtained if BF-2 glue is added to aluminum paint. BF-2 glue is dissolved in alcohol until the enamel becomes thick, then dry aluminum powder is poured into the resulting solution and mixed thoroughly, after which alcohol is added again until normal viscosity is obtained.

The paint prepared in this way adheres well when painted with a brush or with a spray gun, it does not crumble and retains its appearance for a long time.

Painting steel products to look like aluminum

To give steel products beautiful view and to protect them from corrosion, the metal is often coated with aluminum paint - a varnish with aluminum powder. To do this, 15 g of powder is poured into colorless nitro varnish diluted with acetone (110 g).
In the same proportion, the paint can be diluted not in nitro varnish, but in celluloid glue - acetone, in which 5-10 g of X-ray film, cleared of the emulsion, is dissolved.
The surface of the product is first thoroughly cleaned and then a thin layer of paint is applied using a spray gun.
A durable coating is obtained if BF-2 glue is added to aluminum paint. BF-2 glue is dissolved in alcohol until the enamel becomes thick, then dry aluminum powder is poured into the resulting solution and mixed thoroughly, after which alcohol is added again until normal viscosity is obtained. The paint prepared in this way adheres well when painted with a brush or with a spray gun, it does not crumble and retains its appearance for a long time.

What you need to know about paint incompatibility and the peculiarities of paint color perception

All paint components are chemicals. Metals (copper, zinc, aluminum), which are part of paints in the form of powder, affect the corrosion of the paint. metal surface and on the binder. Metal oxides and salts affect the binder, accelerating film formation. Dissimilar types of binders cannot be combined with each other, and some oil paints made with the same binder, but based on different pigments, cannot be mixed.

Pigment incompatibility. When mixing pigments, it is very important to consider the nature of their interaction. If pigments are incompatible, they are destroyed and their anti-corrosion properties are lost.
When mixing paints with incompatible pigments, their color is lost.

Incompatibility of binders. You can mix oil paints only with oil paints (on a homogeneous basis), glypthal - with glypthal, pentaphthalic - with pentaphthalic, epoxy - with epoxy, bitumen varnishes - with asphalt and coal tar varnishes, etc. However, all thick oil paints can be diluted with drying oils and varnishes made on the basis of only light natural and artificial resins, excluding asphalt and bitumen resins.
Incompatibility of paint with surface material. All primers without exception can be applied to a steel surface: oil, phosphating, tread, glyphthalic, phenol-formaldehyde, vinyl chloride copolymers, ethylene, acrylic, etc.

Etching is a process in which part of the metal is removed from the surface by chemical means. This method is used for final processing of a part, when preparing a workpiece before applying a coating (electroplating), as well as for creating all kinds of drawings, ornaments and inscriptions.

The essence of the method

Metal etching involves careful surface treatment. A protective coating is applied to the product, which is erased in the place of the design. Then either acids or an electrolyte bath are used. Unprotected places are destroyed. The longer the exposure time, the deeper the etching of metals occurs. The drawing becomes more expressive and clear. There are various ways to obtain an engraving (inscription): the image itself or the background can be etched directly. Often such processes are combined. Multilayer etching is also used.

Types of etching

Depending on the substance used to destroy the surface of the material, the following etching methods are distinguished.

1. Chemical method (also called liquid method). In this case, special acid-based solutions are used. In this way, ornaments and inscriptions are applied to alloys.

2. Electrochemical etching of metal - involves the use of an electrolyte bath. It is filled with a special solution. Lead salts are also often used to prevent over-etching. This method has a number of advantages. Firstly, the drawing is clearer, and the time required to complete the process is significantly reduced. In addition, this metal processing is economical: the volume of acid used is much less than with the first method. Another undoubted advantage- absence of harmful gases (mordant does not contain caustic acids).

3. There is also an ion plasma method (the so-called dry method). In this case, the surface is damaged minimally. This method is used in microelectronics.

Steel pickling

This treatment is mainly used to remove scale and various oxides. This procedure requires careful adherence to technology, since over-etching of the base metal is undesirable. In the process it is used as chemical method, and electrolyte baths. Hydrochloric and sulfuric acids are used to prepare solutions. All parts require thorough degreasing of the surface. Even a small fingerprint can ruin the workpiece. As protective coating use varnish based on rosin, turpentine, tar. However, it is worth remembering that the components are flammable substances, so preparing the varnish requires great concentration and caution. After the metal processing is completed, the etching process itself occurs. Upon completion, the part must be cleaned of varnish.

Mordants used for steel

Very often, a solution of nitric acid is used for pickling steel. Salt and tartar are also used (with small additions of nitrogen). Hard steel grades are pickled with a mixture of nitric and acetic acids. Glyphogen is a special liquid based on water, nitric acid and alcohol. The surface is treated with this composition for several minutes. Then they are washed (a solution of wine alcohol in purified water) and quickly dried. This is pre-etching. Only after such manipulations are the workpieces placed in the etching solution. Cast iron pickles well in a sulfuric acid solution.

Pickling of non-ferrous metals

Copper and alloys based on it are etched using sulfuric, hydrochloric, phosphoric or nitric acids. The process is accelerated by solutions of chromates or nitrates. The first stage is the removal of scale, then the brass is directly etched. Aluminum (and its alloys) are etched in a caustic alkali solution. For casting alloys, nitric and hydrofluoric acids are used. Spot welded workpieces are treated with phosphoric acid. Titanium alloys are also etched in two stages. First - in caustic alkali, then in a solution of sulfuric, hydrofluoric, nitric acids. Titanium etching is used to remove the oxide film before electroplating. Molybdenum is treated with a solution based on sodium hydroxide and hydrogen peroxide. In addition, metals (such as nickel, tungsten) are etched using water, hydrogen peroxide and formic acid.

There are several ways to etch boards. In the first case, water and ferric chloride are used. You can make it yourself. To do this, iron filings are dissolved in hydrochloric acid. The mixture is kept for some time. Printed circuit boards are also etched using nitric acid. The whole process lasts about 10 minutes. At the end of the process, the board must be thoroughly wiped with baking soda, as it perfectly neutralizes the remaining caustic substance. Another etching composition includes sulfuric acid, water, hydrogen peroxide (in tablets). Etching boards with the following composition takes much more time: hot water, table salt, copper sulfate. It is worth noting that the solution temperature must be at least 40 degrees. Otherwise, etching will take longer. You can also etch boards using direct current. As a utensil for this process you can use glass plastic container(it does not conduct current). Fill the container with a solution of table salt. It is this that is the electrolyte. You can use copper (brass) foil as a cathode.

Etching process for other materials

A type of glass processing called etching is currently widespread. Vapors of hydrofluoric acid and hydrogen fluoride are used. First, the surface is acid polished, then a pattern is applied. After these manipulations, the product is placed in a bath with an etching solution. Then the glass is thoroughly washed and cleared of the protective coating. As the latter, you can use a mixture based on beeswax, rosin, and paraffin. Etching glass with hydrofluoric acid is used to give it a haze. There is also the possibility of color etching. Silver salts give the surface yellow, red, blue shades, copper salts - green, black, red. To obtain a transparent, shiny pattern, sulfuric acid is added to hydrofluoric acid. If deep etching is necessary, the process is repeated several times.

Pickling safety precautions

Metal etching is a rather unsafe activity that requires a lot of concentration. This is due to working with aggressive materials - acids and their mixtures. First of all, for this process it is necessary to wisely choose a room with good ventilation. Ideal when used for etching pull out drobe. If one is not available, then you need to take care of a respirator to avoid inhaling harmful fumes. When working with acids, you should wear rubber gloves and an apron. Should always be at hand baking soda, which - if necessary - can neutralize the effect of the acid. All etching solutions must be stored in special containers (glass or plastic). Don’t forget about the stickers that will indicate the composition of the mixture and the date of preparation. There is one more rule: jars of acids should not be placed on high shelves. Their fall from a height is fraught with serious consequences. Artistic metal etching is not complete without the use of nitric acid, which is quite caustic. In addition, in some mixtures it can be explosive. More often nitric acid used for sterling silver. Etching solutions are prepared by mixing acids with water. It is also worth remembering that in all cases the acid is added to the water, and not vice versa.

Greetings, chemists and radio amateurs!

Since the beginning of the year, our Endurance (LaserLab) team has been asked the question: can we make beautiful laser engravings on aluminum? And will it be available to everyone?

Finally we answer! :)

Aluminum is a common metal, so it's no surprise that people want to put their own engravings on it. I was happy to do this for the aluminum key fob, flash drive and case of my mobile phone.

What are the properties of aluminum?! Yes, metal. Melting temperature is 600 degrees, with high thermal conductivity and often has aluminum oxide on its coating, which has a melting point of more than 1100 degrees. Therefore, heat treatment will not be so simple. Let's look at another option. As you know, wires are made of copper and aluminum. Aluminum is an excellent conductor, which means we can use the process of electrolysis. This is the trick, about which read further! Namely, aluminum etching.

It's simple!) We will need:

Water (no more than 1 l).
Electric current source (9 to 12 V).
Regular table salt NaCl.
Dielectric capacitance (for example, made of plastic).
A nail or other sharp, hard object.

And of course the L-Cheapo laser! Power 3-5 W.

1. Prepare the design you want to engrave on the aluminum plate.

For example, a raster image of a logo.

2. Get rid of the fat on your aluminum sample. Cover it with any of the following materials: brown tape, paint, varnish, tape.

3. Place the product on the 3D printer and start the laser (you need to destroy the surface layer from step 2 and you will get open areas).

4. Mix the salt in the water to obtain a concentrated solution.

5.1. Take a current source (in the photo there is a red “plus” and a white “minus” wire).
5.2. Attach an iron object to the minus and lower it into the saline solution.
5.3. Attach a sample of aluminum to the plus and lower it into the solution in the same container.
6. Apply current!

7. Wait for the electrolysis (etching) process in the solution for about 5 minutes. Depending on the concentration of the solution and the current strength, estimate the time required for etching. We were able to etch the sample in the photograph in 3 minutes.

8. Remove the sample from the solution.

Class!!)

Before placing it in a container with a solution, do not forget that your sample on which you want to apply a pattern must be carefully isolated from external environment, except in those areas where engraving is to be applied.

You can carry out this experiment both at home and in your workshop.

With this technology, anyone can become a metal engraver (at least aluminum).

All this is valuable and practical knowledge. We will be glad if you subscribe to Endurance news

Engrave? Easily!

The boss once set me a task. It is necessary to make a duplicate keyboard to control the machine controller, since the factory one quickly became unusable, because it was made of transparent self-adhesive film, onto which a design was applied at the factory.

I work at a small enterprise that produces spices. I am engaged in servicing packaging machines, electrical equipment, local network etc., in short, all the technology, smart and not so smart.
So there you go! After much thought and debate with the boss, I finally convinced him that for our lammer-operators the keyboard case would be best suited from “alloy gun steel”, :cool:, but in the absence of it we decided to use a high-strength aluminum case type 203-125B , dimensions 121x66x35 mm from Pros Kit.

Idea

The milling machine ordered aluminum buttons. The case was purchased from a store. And then the question arose of how to make indelible inscriptions on the buttons and body. I tried to scratch it and fill it with paint. It came out completely “meh”! Can be engraved! So I don’t have a Dremel, but I can’t help but search through friends.

Laziness, my friends, is the most powerful engine of progress. After some thought, I remembered that I had once accidentally dripped ferric chloride onto an aluminum radiator. While I wiped away the drop, there was a stain on the radiator and a small indentation. Yeah...

What if you make a stencil from photoresist and then etch it? The guinea pig was a piece of duralumin plate. Everything turned out great!

Preparing the surfaces

Let's start with preparing the surfaces. Sand dry first sandpaper No. 80-100, spreading it on a flat substrate, then remove large scratches with an emery sponge No. 180-200, moistening the surface and sponge with water. From time to time we rinse everything with water.

Rice. 1. Surface preparation.

I was quite happy with this roughness. If desired, you can polish it.

Rice. 2. Case and buttons after polishing.

Rolling photoresist

Next, we measure out the photoresist for the body and buttons.

Rice. 3. Film photoresist.

I can't say anything about the photoresist. I bought it in the online store. All that was indicated: “Film negative indicator photoresist.”

We measure a little with a margin around the edges so that it is convenient to roll. Film photoresist consists of 4 layers: the bottom (it is matte) - polyethylene, then a thin layer of glue, then, in fact, the photoresist itself, and on top there is a glossy protective layer (lavsan). Carefully pry up the matte layer with a needle or scalpel, tear off a strip 5-8 millimeters wide and glue it to the body. It is easier to roll the photoresist along the length of the body.

Yes! One more nuance. It is better to heat the housing over gas to a temperature of approximately 40 degrees. Then the photoresist sticks better. Gradually tearing off the base, we roll the photoresist onto the surface with a hard photo roller, or, at worst, with your finger. We cut off the protruding edges of the photoresist with a file to the body or a sharp knife.

Make sure that no dust particles or air bubbles get under the photoresist. In this place, ferric chloride may get in and there will be a problem. If air bubbles do occur, you can carefully pierce them with a sharp needle and roll them firmly with a photo roller.
We do not remove the top protective layer yet, because the photomask may stick to the photoresist (there have been cases).

Rice. 4. Rolled photoresist.

Making a photo template

Next, use any convenient program to prepare a photo template and print it on transparent film for printers. When printing, we indicate the maximum contrast and minimum brightness, but here you have to try. I have an Epson RX610. The settings are as follows: print quality “Best Photo”, “Shades of Gray”, paper type “Epson Matte”, brightness: -25, contrast +25.

Photoresist is negative! That is, where there is no paint on the template, the photoresist will glow and will not wash off during development! Be careful.

Rice. 5. Photo template. I use film sparingly. Therefore, I print different projects on one sheet while there is space left.

Illuminate with a UV lamp

We apply a photomask and press it with glass onto the photoresist.

Rice. 6. Preparing for exposure.

Hide the buttons before exposing them. If they light up, you will need to re-roll the photoresist.
We illuminate the photoresist with a UV lamp. Exposure time is about 1 min.

Rice. 7. Photoresist exposure

Rice. 8. After illumination, the contours of the drawing appear.

We illuminate the buttons in the same way. Now you can remove the top protective film photoresist.

We show

Next is development. We prepare a solution for development from: a household glass jar 0.5 l - 1 piece, soda ash (not baking soda) - 0.5 teaspoon, hot tap water - 0.5 l (full jar).
Stir the solution until the soda is completely dissolved. Then we take a not very hard clothes brush, dip it into the solution more often and brush it almost without pressing over the photoresist. The unexposed photoresist is gradually washed off and the following picture is obtained:

Rice. 9. Developed photoresist.

We poison in ferric chloride

We cover exposed areas of metal that do not need to be etched (for example, the ends) with colorless nail polish (you can steal it from your wife, like I did). Now we take a photo bath, pour in ferric chloride and throw the body and buttons there with the image DOWN.

Rice. 10. Etching.

The solution immediately begins to bubble. Aluminum displaces iron from the solution and it settles right there, at the site of etching. It should be removed with a soft, unnecessary toothbrush approximately once every 30 seconds. In this case, you need to be careful: chips of the photoresist may appear at the edges of the image. If this happens, immediately rinse, dry and correct the chip with a waterproof marker or the same nail polish. However, the varnish can corrode the photoresist, so be careful.

I etched for about 5 minutes. After etching, I get indentations about 0.5 mm deep.
We remove the photoresist. When making printed circuit boards, photoresist can be removed with a solution of caustic soda (caustic soda) or slightly diluted “Mole” for cleaning sewer pipes. But this is not suitable for aluminum. It darkens on contact with caustic. If the etched recesses are deep, then you can remove the photoresist with an emery sponge and water, if not very deep, then you can throw it in a bowl with acetone or solvent No. 646 or 647 for 15-20 minutes.

Rice. 11. After etching and removal of photoresist.

Final operations

Next we cut out the holes for the buttons.

Rice. 12. The holes are ready.

We seal the outline around the inscription with construction tape. I didn’t have construction tape, so I sealed it with aluminum.