Chrome/Nickel
(too old post to reply)
2005-03-27 19:01:08 UTC
Nickel plating?
I know that both are used to cover metal surfaces to
make them shiny and protect against corrosion.
Cost difference?
Oleg ICQ#168343240
Who gets up early - he gets everyone
Leizer A. Karabin
2005-03-28 04:58:10 UTC
Good afternoon, Oleg light Antoshkiv!
I actually just came out Monday March 28 2005 00:01,
here I hear - Oleg Antoshkiv says All (well, I butted in, of course):
OA> The question is purely out of curiosity: what is the difference between chrome plating and
OA> nickel plating?
I hope this question is rhetorical. Or explain.
OA> I know that both are used to coat metal
OA> surfaces to make them shiny and protect against corrosion.
OA> How to distinguish a chrome-plated surface from a nickel-plated one by eye?
Nickel is slightly yellowish, chrome is slightly bluer.
OA> What is the difference in mechanical strength, chemical resistance?
For improvised and home chemistry, both are absolutely resistant.
OA> The difference in cost?
Chrome plating is definitely more expensive.
OA> Is the coating technology the same?
Very different. For example, traditional bumper chrome plating technology
it's nickel - copper - nickel - glitter. nickel - chromium on steel. or without first
nickel sublayer, if you get permission for copper from a cyanide al-ta.
If it seemed to you that there are just single-layer
decorative anti-corrosion coatings, then only Chinese-underground watches.
Half a micron of chrome or gold on bronze is enough for a couple of weeks of wearing.
OA> Is there any difference what metals can be coated with both?
The difference is in technology, but in general, any can be covered with anything.
Why do you need to find out what is where, or did you gather yourself? The last "M-nee, no
I advise, they will eat it!" (C)
For sim forever and so on. Leizer (ICQ 62084744)
2005-03-28 08:07:29 UTC
Greetings, Oleg!
Monday March 28 2005 00:01, Oleg Antoshkiv -> All:
OA> The question is purely out of curiosity: what is the difference between chrome plating and
OA> nickel plating?
different metals
OA> I know that both are used to cover
OA>
OA> corrosion. How to distinguish a chrome surface by eye
OA> nickel-plated?
Nickel is usually just white and chrome plating can change color though
usually slightly purple.
OA> What is the difference in mechanical strength, chemical resistance?
Chrome plating gives a harder coating than nickel, chemically chromium
continues to protect the base metal (if it is steel) with minor damage
coating, in the case of nickel, corrosion only accelerates if the coating is damaged.
OA> The difference in cost?
who knows
OA> Is the coating technology the same?
At least on steel products, chromium is deposited directly, and nickel
through the substrate (copper).
OA> Is there any difference what metals can be coated with both?
Sincerely, Sergey Din.
Andrew Mitrohin
2005-03-28 13:26:07 UTC
*_Be healthy_*, /_Oleg_/!
OA> The question is purely out of curiosity: what is the difference between chrome plating and
OA> nickel plating? I know that both are used to cover
OA> metal surfaces to make them shiny and protect from
OA> corrosion.
OA> How to distinguish a chrome-plated surface from a nickel-plated one by eye
OA>?
The color is different.
OA> What is the difference in mechanical strength, chemical resistance?
Chrome is better in this regard.
OA> The difference in cost?
Before nickel plating, the metal is coated with copper and polished.
Before plating with chromium - the metal is first coated with copper, then with nickel and
then chrome. Then the cover is strong.
OA> Is the coating technology the same?
Different, it’s better to forget about chrome at home. Chromic anhydride is used
which is very toxic.
OA> Is there any difference what metals can be coated with both?
It all depends, if I'm not mistaken, on the activity of the metal.
/With respect/, _/Andrew/_...
- [Russian rock music] -
Start with a bath
Electrolyte compositions
Don't forget about chrome modes!
Chrome plating aluminum alloys
Intermediate Coatings
Galvanizing
Nickel Plating (Chemical)
Deposition of chromium through nickel salt
Chromium deposition through anodizing
Fixtures, fixtures.
Chrome plating of steel parts
Chrome defects and their causes
Based on the materials of the magazine "Modelist-Constructor". Beginning at #5, 1989
Chrome plating, one of the most needed coatings for engine builders, is one of the most labor-intensive processes in electroplating. It requires special care and cleanliness both in the preparation of the electrolyte and the substances themselves that make up its composition. Water is used distilled or (only as a last resort!) Thoroughly boiled.
Start with a bath
Classes in model electroplating, start with making a bath. First of all, pick up a 10-liter pot and a three-liter glass jar. It is better not to use smaller containers - this can complicate the adjustment of process parameters, and even with the given values, the volume of the bath is only enough for chrome plating of 6-8 cylinder liners. Having glued the body from 1-1.5 mm plywood, assemble the bath according to the figure shown and close everything with a plywood ring. Work on the bathroom ends with turning the lid of the pan and mounting heating elements and a contact thermometer on it. Now - electrical equipment. Any source can be used to power the bath. direct current with an electrolytic capacitor connected at the output 80000 microfarad X 25 V. Power wires must have a cross section of at least 2.5 mm2. A sectional rheostat can serve as a current regulator replacing the voltage regulator. It is connected in series with the galvanic bath and consists of parallel sections switched on by single-pole circuit breakers. Each subsequent one has twice the resistance of the previous one. The number of such sections is 7-8. Install two 15A sockets on the front panel of the lithium unit, one normal polarity and one reversed. This will allow you to quickly anodize the part and switch to chrome plating by simply rearranging the fork. Sockets with three outputs, so as not to be mistaken in polarity (of course, only two sockets are connected). To maintain a constant electrolyte temperature, the bath is equipped with a contact thermometer. It cannot directly control the operation of heating elements due to high currents, so it will be necessary to assemble a simple device, the diagram of which is shown in the figures.
Thermostat details: transistors MP 13 - MP16, MP39-MP42 (VT1); 213-217 (VT2) with any letter designations; resistors MLT-0.25, diode - D226, D202-D205; relay-TKE 52 PODG or OKN passport RF4.530.810.
Adjustment of the thermostat: if the relay does not work when shorting points 1-2, connect the emitter and collector VT1. Turning on the relay indicates a malfunction or low gain VT1. Otherwise, the transistor VT2 is faulty or it has insufficient gain. Gathered and set up bath device, you can start preparing the electrolyte.
For this you need:
1. - pour a little more than half of the prepared distilled water into the jar, heated to 50 °
2. - add chromic anhydride and stir
3. - add water to the calculated volume
4. - pour in sulfuric acid
5. - Work through the electrolyte for 3-4 hours at the rate of 6-8 A g/l.
The last operation is necessary for the accumulation of a small amount of Cr3 monos (2–4 g/l), the presence of which favorably affects the process of chromium precipitation.
Electrolyte compositions
Chromic anhydride-250 g/l or 150 g/l
Sulfuric acid-2.5 g/l or 1.5 g/l
Don't forget about chrome modes!
The chromium plating process is highly dependent on the electrolyte temperature and current density. Both factors affect appearance and coating properties, as well as the current output of chromium. It must be remembered that as the temperature rises, the current output decreases; with increasing current density, the current output increases; at lower temperatures and a constant current density, gray coatings are obtained, and at elevated temperatures, milky ones. The optimal mode of chromium plating was found by practical means: current density 50-60 A/dm2 at an electrolyte temperature of 52° - 55° ±1°.
To be sure that the electrolyte is working, several parts similar in shape and size to the working samples can be coated in the prepared bath. Having chosen the mode and knowing the current output by simply measuring the dimensions before and after chrome plating, you can start coating the sleeves.
According to the proposed method, chromium is applied to steel, bronze and brass parts. Their preparation consists in washing the surfaces to be chrome-plated with gasoline and then with soap (using a toothbrush) in hot water, charging into the mandrel and placing in the bath. After immersion in the electrolyte, you need to wait 3-5 s and then turn on the working current. The delay is needed in order for the part to warm up. At the same time, the surface of parts made of brass and copper is activated, since these metals are well etched in the electrolyte. However, you should not wait more than 5 s - these metals contain zinc, the presence of which in the electrolyte is unacceptable.
|
Determination of the content of chromic anhydride CrO3 depending on the specific gravity of the solution |
||
|
specific gravity at 15 C |
CrO3 content |
|
|
in moles |
in g/l |
|
|
1,07 |
1,00 |
|
|
1,08 |
1,14 |
|
|
1,09 |
1,29 |
|
|
1,10 |
1,43 |
|
|
1,11 |
1,57 |
|
|
1,12 |
1,71 |
|
|
1,13 |
1,85 |
|
|
1,14 |
2,00 |
|
|
1,15 |
2,15 |
|
|
1,16 |
2,25 |
|
|
1,17 |
2,43 |
|
|
1,18 |
2,57 |
|
|
1,19 |
2,72 |
|
|
1,20 |
2,83 |
|
|
1,21 |
3,01 |
|
|
1,22 |
3,16 |
|
|
1,23 |
3,30 |
|
|
1,24 |
3,45 |
|
|
1,25 |
3,60 |
|
|
1,26 |
3,75 |
|
|
1,27 |
3,90 |
|
|
1,28 |
4,06 |
|
|
1,29 |
4,22 |
|
|
1,30 |
4,38 |
|
|
1,31 |
4,53 |
|
|
1,32 |
4,68 |
|
Chrome plating aluminum alloys
Special attention should be paid to the processes of applying chromium to aluminum alloys. The implementation of such coatings is always associated with a number of difficulties. First of all, it is the need for preliminary application of an intermediate layer. Aluminum alloys containing a large amount of silicon (up to 30%, alloys of grades AK12, AL25, AL26, SAS-1) can be chrome-plated as follows:
- washing the part in gasoline,
- washing in hot water with washing powder or soap,
- processing of the part in a solution of nitric and hydrofluoric acids (ratio 5: 1) for 15-20 s,
- washing in cold water,
- installation of the part on the mandrel and chrome plating (loading into the bath under current!).
Another thing is if it is necessary to chrome-plated the AK4-1 alloy. It can only be chrome plated with an intermediate layer. These methods include: zincate treatment; on the nickel sublayer; through nickel salt; through anodic treatment of the part in a solution of phosphoric acid.
In all cases, the parts are prepared as follows:
- grinding (and lapping);
- cleaning (removal of fatty deposits after grinding in gasoline or trichlorethylene, then in an alkaline solution),
- washing in running cold and warm (50-60°) water,
- pickling (to remove particles remaining on the surface after grinding and lapping, as well as to improve the preparation of the surface of the part for chromium deposition).
For etching, a solution of caustic soda (50 g/l) is used, the processing time is 10–30 s at a solution temperature of 70–80°C.
For etching aluminum alloys containing silicon and manganese, it is better to use such a solution, in parts by weight:
nitric acid (density 1.4) -3, hydrofluoric acid (50%) -1. The processing time of parts is 30-60 s at a solution temperature of 25-28°. After etching, if it is a cylinder liner, it must be immediately rinsed in running water and immersed in a solution of nitric acid (50%) for 2-3 seconds, followed by rinsing with water.
Intermediate Coatings
Galvanizing
Aluminum products at room temperature are dipped for 2 minutes in a solution (caustic soda 400 g / l, zinc sulfate 120 g / l, Rochelle salt 5-10 g / l. Or: caustic soda 500 g / l, zinc oxide 120-140 g /l) with constant stirring. The coating is quite uniform and has a gray (sometimes blue) color.
If the zinc coating lay unevenly, the part is immersed in an etching 50% nitric acid solution for 1-5 seconds, and after washing, galvanizing is repeated. For magnesium-containing aluminum alloys, double galvanizing is mandatory. After applying the second layer of zinc, the part is washed, charged into the mandrel and under current (without voltage supply, zinc has time to partially dissolve in the electrolyte, polluting it) and installed in the bath. Previously, the mandrel with the part is immersed in a glass of water heated to a temperature of 60 °. The chrome plating process is normal.
Nickel Plating (Chemical)
If zinc does not lay down on aluminum (this happens most often on AK4-1 alloy), you can try to apply chromium through nickel. The order of work is as follows:
- lapping the surface,
- degreasing,
- etching for 5-10 s in a solution of nitric and hydrofluoric acids, mixed in a ratio of 3:1,
- Nickel plating.
The last operation - in a solution of the following composition: nickel sulfate 30 g/l, sodium hypophosphite 10-12 g/l, sodium acetate 10-12 g/l, glycol-30 g/l. It is compiled first without hypophosphite, which is introduced before nickel plating (with hypophosphite, the solution is not stored for a long time). The temperature of the solution during nickel plating is 96-98°. You can use the solution without glycocol, then the temperature should be reduced to 90 °. In 30 minutes, a nickel layer with a thickness of 0.1 to 0.05 mm is deposited on the part. Dishes for work - only glass or porcelain, since nickel is deposited on all metals of the eighth group of the periodic table. Brass, bronze and other copper alloys lend themselves well to nickel plating.
After nickel deposition, heat treatment is carried out to improve adhesion to the base metal (200-250°, exposure 1-1.5 h). Then the part is mounted on a mandrel for chromium plating and lowered for 15-40 s into a solution of 15% sulfuric acid, where it is treated with reverse current at the rate of 0.5-1.5 A/dm2. Nickel is activated, the oxide film is removed, and the coating acquires grey colour. Acid should be used only chemically pure (in the last resort battery). Otherwise, nickel becomes black, and chrome will never lie on such a surface.
After that, the mandrel with the part is loaded into the chromium plating bath. First, they give a current twice as large, then "within 10-12 minutes it is reduced to a working one.
Defects chemical nickel plating:
- no nickel plating: the part has not warmed up, you should wait a while,
- spots on the surface (typical for AK4-1): poor heat treatment of the part, it needs to be heat treated at 200-250 ° for 1.5-2 hours.
Removal of nickel from aluminum alloys can be produced in a solution of nitric acid.
Sometimes in the process of nickel plating, self-discharge occurs - precipitation of powdered nickel. In this case, the solution is poured out, and the dishes are treated with a solution of nitric acid to remove nickel from its surface, which will interfere with deposition on the parts.
I would like to note that nickel-phosphorus itself has very interesting properties that are not inherent in chromium coatings. This is the uniformity of the layer on the surface of the parts (after deposition, finishing is not required); high hardness after heat treatment (400 ° mode for an hour gives a coating hardness of HV 850-950 and more); low coefficient of friction compared to chromium; very slight expansion; high tensile strength.
Nickel-phosphorus without further chromium application can be used not only as an intermediate coating on liners, but also as a working, friction and wear reducing coating for spools and piston pins. After two years of active operation of the engine with parts of a similar finish, there was no obvious wear characteristic of hardened steel surfaces.
Deposition of chromium through nickel salt
The whole process comes down to this:
- etching in a solution of caustic soda (50 g/l, t=.80°, 20 s),
- application of the 1st intermediate layer (nickel chloride, 1 min),
- etching of the intermediate layer in a solution of nitric acid (acid solution 50%, 1 min),
- application of the 2nd intermediate layer (nickel chloride, 1 min),
- rinsing with water
- pickling (nitric acid 50%, 15s).
- washing in running water,
- loading into the chromium plating bath under current.
Chromium deposition through anodizing
Instead of intermediate layers, anodic treatment can be performed in a solution of 300–350 g/l of phosphoric acid at a temperature of 26–30°C, a terminal voltage of 5–10 V, and a current density of 1.3 A/dm2. The bath should be cool. For alloys containing copper and silicon, a solution of 150-200 g/l of phosphoric acid is used. Mode - 35 °, processing time 5-15 minutes.
After anodic treatment, short-term cathodic treatment in an alkaline bath should be carried out, which partially removes the oxide layer. Studies have shown that in the process of anodic treatment of aluminum alloys in phosphoric acid a rough surface is formed on the parts, which contributes to the strong adhesion of the subsequently applied coating.
Fixtures, fixtures.
Sleeve chrome plating 
To perform work with the cylinder liner, a mandrel is made. Its device is clear from the above figure, we will dwell only on individual details.
Anode - steel pin; from one end of it, lead with antimony (7-8%) is welded over a length of 50-60 mm. Lead is machined along the outer diameter up to 6 mm (for sleeves working 0 15 mm). On the other side of the stud, a thread is cut to fix the wire.
The cathode is a ring with an inner diameter of 0.5 mm greater than inner size sleeves. A piece of insulated wire is minted into it. It is better not to use copper and brass conductors - the electrolyte dissolves them, and the contact may be broken. Before mounting the mandrel in the bath, it is useful to check the reliability of the contacts with a tester.
1 - cover (viniplast), 2 - upper part of the mandrel (fluoroplastic), 3 - lower part of the mandrel (fluoroplastic), 4-anode (steel), 5 - cathode, 6 - through window for electrolyte passage, 7 - coated sleeve, 8 - nozzle insulator
Chrome plating of steel parts
(crankshaft, crank pin, piston pin, bearing races)
Chrome plating of steel parts is carried out according to the following technology:
- removing grease stains with gasoline,
- washing in hot water with soap,
- treatment of the part with reverse current for 2-3 minutes,
- switching to the chromium plating mode with a current 2-2.5 times greater than the calculated one, and a gradual decrease in current for 10-15 minutes.
The rated current is determined by multiplying the area of the chrome plated surface by the process current. For steel, the last value is 50 A/dm2. When chrome plating, for example, seat under the main bearing on the crankshaft of the KMD-2.5 engine, the rated current will be 0.03 dm2 x 50 A / dm2 x 1.5 A.
You will need a new mandrel to chrome the crank pin. As in the processing of the crankshaft, all open areas surfaces are closed with AGO glue. The anode is machined from steel, followed by pouring lead and boring a hole for the finger. The use of a steel part is explained by the need to ensure reliable contact - in lead threaded connections unreliable. Current calculations are similar. Work is carried out in the mandrel of the shaft using a special nozzle.
The chrome plating of the bearings is practically the same. The only thing is that to protect the inside of the part, it is filled with grease or other grease, which, after coating, is washed out with gasoline. Mandrel for chrome plating of the outer race of the ball bearing:
1-bearing mandrel housing; 2-ball bearing; 3-shaped nut; 4-anode (lead); 5-central part of the mandrel for chrome plating; 6-cathode (steel); 7-cover; 8-through window for electrolyte passage.
Chrome defects and their causes
1. Chrome does not settle on the product:
- poor contact at the anode or cathode,
- small cross-section of conductors,
- a thick film of oxides has formed on the surface of the anode (it is removed in a hydrochloric acid solution),
- low current density,
- little distance between the electrodes,
- excess sulfuric acid.
2. The coating peels off:
- poor degreasing of the surface,
- power supply interrupted
- fluctuation of temperature or current density.
3. On the surface of chromium - craters, holes:
- hydrogen lingers on the surface of the part
- change the suspension so that the gas is freely removed,
- there is graphite on the surface of the base metal,
- the surface of the base metal is oxidized, porous.
4. Thickened coating on protruding parts:
- increased current density.
5. The coating is hard, flakes off:
- low current density, increased electrolyte temperature,
- in the process of chromium plating, the temperature of the electrolyte changed,
- the product overheated during the grinding process.
6. Chrome does not settle around the holes of the part:
- a large release of hydrogen - close the holes with ebonite plugs.
- excess sulfuric acid.
7. Brown spots on the coating:
- lack of sulfuric acid,
- an excess of trivalent chromium (more than 10 g / l) - withstand the bath under current without parts, increasing the surface of the anodes and reducing - cathodes.
8. Soft "milky" coating:
- high electrolyte temperature,
- low current density.
9. Matt finish, uneven, difficult to rub:
- lack of chromic anhydride.
- high current density,
- lack of sulfuric acid,
- an excess of trivalent chromium.
10. The finish is spotty and matte:
- during the chrome plating process, the power supply was interrupted,
- the product was cold before loading.
11. In some places the coating is shiny, in others it is matte:
- high current density,
- low electrolyte temperature,
- uneven current density on the protruding and recessed parts of the part.
The concentration of chromic anhydride in the electrolyte is controlled using a hydrometer. The concentration of sulfuric acid can be determined only, unfortunately, indirectly, by the quality of the coating. During chromium plating, the electrolyte evaporates. In these cases, add water to the desired level. This is done without installing parts - it is possible to change the temperature of the electrolyte. After chromium plating, all products are subjected to heat treatment for 2-3 hours to remove hydrogen, at a temperature of 150-170°. All work is carried out under a fume hood, wearing rubber gloves and goggles.
1. NICKEL PLATE
2. CHROME PLATE
LIST OF USED SOURCES
1. NICKEL PLATE
Nickel-plated coatings have a number of valuable properties: they are well polished, acquiring a beautiful long-lasting mirror finish, they are durable and well protect the metal from corrosion.
The color of nickel plating is silvery white with a yellowish tint; they are easily polished, but fade over time. The coatings are characterized by a fine-grained structure, good adhesion to steel and copper substrates, and the ability to passivate in air.
Nickel plating is widely used as a decorative coating for parts of lamps intended for lighting public and residential premises.
To cover steel products, nickel plating is often carried out over an intermediate copper sublayer. Sometimes a three-layer nickel-copper-nickel coating is used. In some cases, a thin layer of chromium is applied to the nickel layer, and a nickel-chromium coating is formed. On parts made of copper and alloys based on it, nickel is applied without an intermediate sublayer. The total thickness of two and three-layer coatings is regulated by mechanical engineering standards, usually it is 25–30 microns.
On parts intended for operation in a humid tropical climate, the coating thickness should be at least 45 microns. In this case, the regulated thickness of the nickel layer is not less than 12–25 µm.
To obtain brilliant coatings, nickel-plated parts are polished. Recently, brilliant nickel plating has been widely used, which eliminates the laborious operation of mechanical polishing. Brilliant nickel plating is achieved by introducing brighteners into the electrolyte. However, the decorative qualities of mechanically polished surfaces are higher than those obtained by bright nickel plating.
Nickel deposition occurs with significant cathodic polarization, which depends on the temperature of the electrolyte, its concentration, composition, and some other factors.
Electrolytes for nickel plating are relatively simple in composition. Currently, sulfate, hydroboric fluoride and sulfamic electrolytes are used. Lighting factories use exclusively sulfate electrolytes, which allow them to work with high current densities and at the same time obtain high-quality coatings. The composition of these electrolytes includes salts containing nickel, buffer compounds, stabilizers and salts that contribute to the dissolution of the anodes.
The advantages of these electrolytes are the lack of components, high stability and low aggressiveness. Electrolytes allow a high concentration of nickel salt in their composition, which makes it possible to increase the cathode current density and, consequently, to increase the productivity of the process.
Sulfate electrolytes have high electrical conductivity and good dissipation ability.
An electrolyte of the following composition, g/l, has been widely used:
NiSO4 7H2O 240–250
*Or NiCl2 6H2O - 45 g/l.
Nickel plating is carried out at a temperature of 60°C, pH=5.6x6.2, and a cathodic current density of 3–4 A/dm2.
Depending on the composition of the bath and its mode of operation, coatings with varying degrees of gloss can be obtained. For these purposes, several electrolytes have been developed, the compositions of which are given below, g/l:
for matte finish:
NiSO4 7H2O 180–200
Na2SO4 10H2O 80–100
Nickel plated at a temperature of 25–30°C, at a cathodic current density of 0.5–1.0 A/dm2 and pH=5.0–5.5;
for a semi-gloss finish:
Nickel sulfate NiSO4 7H2O 200–300
Boric acid H3BO3 30
2,6–2,7-Disulfonaphthalic acid 5
Sodium fluoride NaF 5
Sodium chloride NaCl 7–10
Nickel plating is carried out at a temperature of 20–35°C, a cathode current density of 1–2 A/dm2, and pH=5.5–5.8;
for a shiny finish:
Nickel sulfate (hydrate) 260–300
Nickel chloride (hydrate) 40–60
Boric acid 30–35
Saccharin 0.8–1.5
1,4-butyndiol (in terms of 100%) 0.12-0.15
Phthalimide 0.08–0.1
Nickel plating operating temperature 50–60°C, electrolyte pH 3.5–5, cathodic current density with intensive stirring and continuous filtration 2–12 A/dm2, anode current density 1–2 A/dm2.
A feature of nickel plating is a narrow range of electrolyte acidity, current density and temperature.
To maintain the composition of the electrolyte within the required limits, buffer compounds are introduced into it, which are most often used as boric acid or a mixture of boric acid with sodium fluoride. In some electrolytes, citric, tartaric, acetic acid or their alkaline salts.
A feature of nickel coatings is their porosity. In some cases, dotted spots, the so-called "pitting", may appear on the surface.
To prevent pitting, intensive air mixing of the baths and shaking of the suspensions with parts attached to them are used. The reduction of pitting is facilitated by the introduction of surface tension reducers or wetting agents into the electrolyte, which are used as sodium lauryl sulfate, sodium alkyl sulfate and other sulfates.
The domestic industry produces a good anti-pitting detergent"Progress", which is added to the bath in the amount of 0.5 mg / l.
Nickel plating is very sensitive to impurities that enter the solution from the surface of parts or due to anodic dissolution. When nickel plating steel de-
hoists, the solution is clogged with iron impurities, and when coating copper-based alloys - with its impurities. Impurities are removed by alkalizing the solution with carbonate or nickel hydroxide.
Organic pitting contaminants are removed by boiling the solution. Sometimes nickel-plated parts are tinted. In this case, colored surfaces with a metallic sheen are obtained.
Toning is carried out by a chemical or electrochemical method. Its essence lies in the formation of a thin film on the surface of the nickel coating, in which light interference occurs. Such films are obtained by applying organic coatings several micrometers thick to nickel-plated surfaces, for which the parts are treated in special solutions.
Black nickel coatings have good decorative qualities. These coatings are obtained in electrolytes in which zinc sulfates are added in addition to nickel sulfates.
The composition of the electrolyte for black nickel plating is as follows, g/l:
Nickel sulfate 40–50
Zinc sulfate 20-30
Potassium thiocyanate 25–32
Ammonium sulphate 12–15
Nickel plating is carried out at a temperature of 18–35°C, a cathode current density of 0.1 A/dm2, and pH=5.0–5.5.
2. CHROME PLATE
Chrome coatings have high hardness and wear resistance, low coefficient of friction, are resistant to mercury, adhere strongly to the base metal, and are chemically and heat resistant.
In the manufacture of lamps, chromium plating is used to obtain protective and decorative coatings, as well as reflective coatings in the manufacture of mirror reflectors.
Chrome plating is carried out on a pre-applied copper-nickel or nickel-copper-nickel sublayer. The thickness of the chromium layer with such a coating usually does not exceed 1 μm. In the manufacture of reflectors, chromium plating is currently being replaced by other coating methods, but in some factories it is still used for the manufacture of reflectors for mirrored lamps.
Chromium has good adhesion to nickel, copper, brass and other materials to be deposited, however, when other metals are deposited onto chromium, poor adhesion is always observed.
A positive feature of chromium coatings is that the parts are shiny directly in galvanic baths, this does not require them to be polished mechanically. Along with this, chromium plating differs from other galvanic processes by more stringent requirements for the operating mode of the baths. Minor deviations from the required current density, electrolyte temperature and other parameters inevitably lead to deterioration of coatings and mass rejects.
The scattering power of chromium electrolytes is low, which leads to poor coating of internal surfaces and recesses of parts. To improve the uniformity of coatings, special suspensions and additional screens are used.
For chromium plating, solutions of chromic anhydride with the addition of sulfuric acid are used.
Three types of electrolytes have found industrial application: diluted, universal and concentrated (Table 1). To obtain decorative coatings and to obtain reflectors, a concentrated electrolyte is used. In chromium plating, insoluble lead anodes are used.
Table 1 - Electrolyte compositions for chromium plating
During operation, the concentration of chromic anhydride in the baths decreases, therefore, to restore the baths, daily adjustments are made by adding fresh chromic anhydride to them.
Several formulations of self-regulating electrolytes have been developed, in which the concentration ratio is automatically stored.
The composition of such an electrolyte is as follows, g/l:
Chrome plating is carried out at a cathode current density of 50–80 A/dm2 and a temperature of 60–70°C.
Depending on the relationship between temperature and current density, different types of chromium coating can be obtained: milky shiny and matte.
The milky coating is obtained at a temperature of 65–80 ° C and
low current density. A brilliant coating is obtained at a temperature of 45–60°C and an average current density. A matt finish is obtained at 25–45°C and high current density. In the production of fixtures, a shiny chrome coating is most often used.
To obtain mirror reflectors, chromium plating is carried out at a temperature of 50–55°C and a current density of 60 A/dm2. in the manufacture of mirror reflectors, copper and nickel are pre-deposited. The reflective surface is polished after applying each of the layers. The technological process includes the following operations:
grinding and polishing the surface;
copper plating;
nickel plating;
polishing, degreasing, pickling;
chrome plating;
clean polishing.
After each technological operation, a 100% quality control of the coating is carried out, since non-compliance with the requirements of the technology leads to peeling of the sublayer along with the chromium coating.
Products made of copper and copper alloys are chromium-plated without an intermediate sublayer. The parts are immersed in the electrolyte after applying voltage to the bath. When applying multilayer coatings to steel products, the layer thickness is regulated by GOST 3002-70. Thickness values are given in table 2.
Table 2 - Minimum thickness of multilayer galvanized coatings
Chrome plating baths are equipped with powerful exhaust ventilation to remove poisonous chromic acid vapors.
During chromium plating, part of the hexavalent chromium Cr6+ gets into wastewater, therefore, to prevent Cr6+ emissions into open water, protective measures are used - neutralizers and treatment facilities are installed.
LIST OF USED SOURCES
Afanas'eva E.I., Skobelev V.M. "Light sources and ballasts: Textbook for technical schools", 2nd ed., Rev., M: Energoatomizdat, 1986, 270s.
Bolenok V.E. "Production of electric lighting devices: Textbook for technical schools", M: Energoizdat, 1981, 303s.
Denisov V.P. "Production of electric light sources", M: Energy, 1975, 488s.
Characterization of solid wastes of the chromium plating process. Titration with ferrous sulfate and permanganate. The theory of determining chromium experimentally. Qualitative Analysis solid waste components of the chromium plating process. Colometric methods for the determination of chromium.
The metal objects around us rarely consist of pure metals. Only aluminum pans or copper wire are about 99.9% pure. In most other cases, people are dealing with alloys. So, different kinds iron and steel, contain, along with metal additives, insignificant ...
Ministry of Education Russian Federation State educational institution of higher and professional education IRKUTSK STATE UNIVERSITY
Physico-chemical and thermodynamic properties of concentrated aqueous solutions containing components of iron-nickel alloy deposition electrolytes. Kinetic regularities of anodic dissolution of iron-nickel alloy under non-stationary conditions.
Nickel-plated coatings have a number of valuable properties: they are well polished, acquiring a beautiful long-lasting mirror finish, they are durable and well protect the metal from corrosion.
The color of nickel plating is silvery white with a yellowish tint; they are easily polished, but fade over time. The coatings are characterized by a fine-grained structure, good adhesion to steel and copper substrates, and the ability to passivate in air.
Nickel plating is widely used as a decorative coating for parts of lamps intended for lighting public and residential premises.
To cover steel products, nickel plating is often carried out over an intermediate copper sublayer. Sometimes a three-layer nickel-copper-nickel coating is used. In some cases, a thin layer of chromium is applied to the nickel layer, and a nickel-chromium coating is formed. On parts made of copper and alloys based on it, nickel is applied without an intermediate sublayer. The total thickness of two and three-layer coatings is regulated by mechanical engineering standards, usually it is 25–30 microns.
On parts intended for operation in a humid tropical climate, the coating thickness should be at least 45 microns. In this case, the regulated thickness of the nickel layer is not less than 12–25 µm.
To obtain brilliant coatings, nickel-plated parts are polished. IN Lately Brilliant nickel plating is widely used, which eliminates the laborious operation of mechanical polishing. Brilliant nickel plating is achieved by introducing brighteners into the electrolyte. However, the decorative qualities of mechanically polished surfaces are higher than those obtained by bright nickel plating.
Nickel deposition occurs with significant cathodic polarization, which depends on the temperature of the electrolyte, its concentration, composition, and some other factors.
Electrolytes for nickel plating are relatively simple in composition. Currently, sulfate, hydroboric fluoride and sulfamic electrolytes are used. Lighting factories use exclusively sulfate electrolytes, which allow them to work with high current densities and at the same time obtain high-quality coatings. The composition of these electrolytes includes salts containing nickel, buffer compounds, stabilizers and salts that contribute to the dissolution of the anodes.
The advantages of these electrolytes are the lack of components, high stability and low aggressiveness. Electrolytes allow a high concentration of nickel salt in their composition, which makes it possible to increase the cathode current density and, consequently, to increase the productivity of the process.
Sulfate electrolytes have high electrical conductivity and good dissipation ability.
An electrolyte of the following composition, g/l, has been widely used:
NiSO4 7H2O240–250
*Or NiCl2 6H2O - 45 g/l.
Nickel plating is carried out at a temperature of 60°C, pH=5.6÷6.2 and a cathodic current density of 3–4 A/dm2.
Depending on the composition of the bath and its mode of operation, coatings with varying degrees of gloss can be obtained. For these purposes, several electrolytes have been developed, the compositions of which are given below, g/l:
for matte finish:
NiSO4 7H2O180–200
Na2SO4 10H2O80–100
Nickel plated at a temperature of 25–30°C, at a cathodic current density of 0.5–1.0 A/dm2 and pH=5.0÷5.5;
for a semi-gloss finish:
Nickel sulfate NiSO4 7H2O200–300
Boric acid H3BO330
2,6–2,7-Disulfonaphthalic acid5
Sodium fluoride NaF5
Sodium chloride NaCl7–10
Nickel plating is carried out at a temperature of 20–35°C, cathodic current density 1–2 A/dm2 and pH=5.5÷5.8;
for a shiny finish:
Nickel sulfate (hydrate) 260–300
Nickel chloride (hydrate) 40–60
Boric acid30–35
Saccharin0.8–1.5
1,4-butyndiol (in terms of 100%) 0.12-0.15
Phthalimide 0.08–0.1
Nickel plating operating temperature 50–60°C, electrolyte pH 3.5–5, cathodic current density with intensive stirring and continuous filtration 2–12 A/dm2, anode current density 1–2 A/dm2.
A feature of nickel plating is a narrow range of electrolyte acidity, current density and temperature.
To maintain the composition of the electrolyte within the required limits, buffer compounds are introduced into it, which are most often used as boric acid or a mixture boric acid with sodium fluoride. In some electrolytes, citric, tartaric, acetic acid or their alkaline salts are used as buffer compounds.
A feature of nickel coatings is their porosity. In some cases, dotted spots, the so-called "pitting", may appear on the surface.
To prevent pitting, intensive air mixing of the baths and shaking of the suspensions with parts attached to them are used. The reduction of pitting is facilitated by the introduction of surface tension reducers or wetting agents into the electrolyte, which are used as sodium lauryl sulfate, sodium alkyl sulfate and other sulfates.
The domestic industry produces a good anti-pitting detergent "Progress", which is added to the bath in an amount of 0.5 mg / l.
Nickel plating is very sensitive to impurities that enter the solution from the surface of parts or due to anodic dissolution. When nickel plating steel de-
hoists, the solution is clogged with iron impurities, and when coating copper-based alloys - with its impurities. Impurities are removed by alkalizing the solution with carbonate or nickel hydroxide.
Organic pitting contaminants are removed by boiling the solution. Sometimes nickel-plated parts are tinted. In this case, colored surfaces with a metallic sheen are obtained.
Toning is carried out by a chemical or electrochemical method. Its essence lies in the formation of a thin film on the surface of the nickel coating, in which light interference occurs. Such films are obtained by applying organic coatings several micrometers thick to nickel-plated surfaces, for which the parts are treated in special solutions.
Black nickel coatings have good decorative qualities. These coatings are obtained in electrolytes in which zinc sulfates are added in addition to nickel sulfates.
The composition of the electrolyte for black nickel plating is as follows, g/l:
Nickel sulfate40–50
Zinc sulfate20–30
Potassium thiocyanate25–32
Ammonium sulphate12–15
Nickel plating is carried out at a temperature of 18–35°C, cathodic current density of 0.1 A/dm2 and pH=5.0÷5.5.
2. CHROME PLATE
Chrome coatings have high hardness and wear resistance, low coefficient of friction, are resistant to mercury, adhere strongly to the base metal, and are chemically and heat resistant.
In the manufacture of lamps, chromium plating is used to obtain a protective decorative coatings, as well as reflective coatings in the manufacture of mirror reflectors.
Chrome plating is carried out on a pre-applied copper-nickel or nickel-copper-nickel sublayer. The thickness of the chromium layer with such a coating usually does not exceed 1 μm. In the manufacture of reflectors, chromium plating is currently being replaced by other coating methods, but in some factories it is still used for the manufacture of reflectors for mirrored lamps.
Chromium has good adhesion to nickel, copper, brass and other materials to be deposited, however, when other metals are deposited onto chromium, poor adhesion is always observed.
A positive feature of chromium coatings is that the parts are shiny directly in galvanic baths, this does not require them to be polished mechanically. Along with this, chromium plating differs from other galvanic processes by more stringent requirements for the operating mode of the baths. Minor deviations from the required current density, electrolyte temperature and other parameters inevitably lead to deterioration of coatings and mass rejects.
The scattering power of chromium electrolytes is low, resulting in poor coverage. internal surfaces and recessed parts. To improve the uniformity of coatings, special suspensions and additional screens are used.
For chromium plating, solutions of chromic anhydride with the addition of sulfuric acid are used.
Three types of electrolytes have found industrial application: diluted, universal and concentrated (Table 1). To obtain decorative coatings and to obtain reflectors, a concentrated electrolyte is used. In chromium plating, insoluble lead anodes are used.
Table 1 - Electrolyte compositions for chromium plating
During operation, the concentration of chromic anhydride in the baths decreases, therefore, to restore the baths, daily adjustments are made by adding fresh chromic anhydride to them.
Several formulations of self-regulating electrolytes have been developed, in which the concentration ratio is automatically stored
.The composition of such an electrolyte is as follows, g/l:
Chrome plating is carried out at a cathode current density of 50–80 A/dm2 and a temperature of 60–70°C.
Depending on the relationship between temperature and current density, different types of chromium coating can be obtained: milky shiny and matte.
The presented training courses are to help beginners who love decorative chrome plating of chemical plating. The purpose of the training courses is to fill the gap of systematized knowledge on the topic of decorative chrome plating by chemical plating and make this technology more accessible to beginners. The submitted texts, photos and videos are personal experience the author, who does not claim to be professional. The author of the training courses is not responsible for possible injuries, burns and poisoning associated with the use of hazardous chemicals such as concentrated acids, alkalis, ammonia. Therefore, do not neglect protective equipment and care when handling reagents.
Decorative chrome plating, chemical plating, all these terms and processes were not known to me not so long ago. Dear friend, since you are on this site, it means that you are also hooked on this topic and you are looking for answers to questions. Questions that haunt you ... How to make any thing with a mirror shine? However, the answers are very close, just sit back and carefully look at the contents of this page. In fact, this is a technology of mirror silvering by spraying. This is also called chemical silver plating. So, there is no talk of real chrome plating, but the name has taken root and is misleading. When I started collecting information on this topic, I was faced with the fact that there is a lot of information on the topic of decorative chrome plating, but to my amazement, nothing specific. All around, yes. Here are a lot of videos where garage craftsmen, as well as pros selling equipment, are happy to demonstrate the process of transforming a nondescript detail into a product sparkling with a mirror. But step by step all the technology, no one lays out for nothing, inflating a big one out of it, a big secret... There are many questions, but the answers are paid ...
After reading a mountain of sites and textbooks, a mess formed in my head, probably, like many others, faced with such a task. So that a clear picture appeared in my head, I decided to immediately practice. It is clear that without chemistry, you will not learn how to chemistry, so I began to search and bypass the offices that sell chemistry. First of all, I asked the price for silver nitrate, since this is the most expensive component. Decide on a supplier. For bought on the list of chemicals, dishes and other necessary utensils. The question arose how to try without equipment. The solution is simple - manual household sprayers. The search and experiments began to create a miracle solution of silvering and application technology. And then one interesting detail about the preparation of chemistry emerged ... All the available information posted on the Internet is a copy of the materials of mainly Soviet textbooks on the topic of chemical metallization ...
Draining a fair amount of silver (respectively, money) to the ground in the process of unsuccessful experiments. Came for a pretty good recipe. In other words, everything is in order. This is the end of the lyrical introduction and the beginning of a short course on how to make a thing a mirror. I will not ship the theory, I will leave it for self-study. There is a lot of this goodness on the Internet. Let's get straight to the point. Short, concise, to the point. I will show you on the example of silvering a glass cup.
Technology of chemical metallization with silver, sputtering method
To get the first experience of silver coating on the surface, by spraying, you should learn the technology. And to put it simply - the sequence of actions.
I will list them:
1. preparation of solutions
2. surface preparation
3.surface activation
4. plating
ladies short review listed items. To get the big picture in my head. Let's take a closer look at the lessons of the same name.
Preparation of solutions
To prepare solutions you will need:
- stannous chloride
- Hydrochloric acid
- Nitrate silver
- Sodium hydroxide
- Ammonia
- Glucose
- Formalin
- Distilled water
From the equipment you will need:
- Measuring cup for 1 liter
- Measuring cup for 200 - 250 ml.
- 100 ml bottles - 3 pcs.
- Disposable syringes for 5, 20 and 50 cubes
- Disposable cups per 50 ml
- Disposable knives and spoons
- Electronic scales, measuring up to 200 gr.
You can start preparing solutions with a solution of tin dichloride. Required to activate the surface. For this we take:
1. Stannous chloride
2. Hydrochloric acid
3. Distilled water
The next solution is "silver". We take:
1. Nitrate silver
2. Sodium hydroxide
3. Ammonia
4. Distilled water
Surface preparation
To prepare the surface, it must be degreased. To do this, you can prepare a simple degreasing solution, consisting of:
1. Sodium hydroxide
2. and water temperature 40-60 degrees
The surface should be carefully wiped with a sponge moistened with a degreasing solution. Then wash off the solution with distilled water, wiping, but with another sponge. A sign of good degreasing is the wettability of the surface with water. That is, watering with water, the entire surface should be covered with a water film. If there are dry islands, silver will not stick there.
Surface activation
In order for the metallization reaction to take place precisely on the surface, and not in the sink, it is necessary to activate it, as they say. That is, to help the silver stick to the surface. It is for this that we take a solution of tin dichloride. It's very important point procedure time. Water the part with a solution of stannous chloride for one minute. Then pour with distilled water - three minutes. This is very milestone and non-observance of the surface treatment time leads to marriage, that is, to a waste of time, effort and money. Watering should be as even as possible so that all areas of the surface are equally moistened.
Metallization
This is the most interesting stage of obtaining a mirror film of silver on the surface. Actually for the sake of this, the whole idea. To do this, you need only a silver solution and a reducing agent solution. This will require some skill, which comes with experience. It is necessary to spray so that the solutions mix on the surface and nothing else. And sprayed in equal amounts by volume. Having reached such accuracy, we get an ideal mirror, without defects.
In addition, you should be aware that the mirror film not durable and in order for it to retain its properties, it should be protected with a layer of transparent or tinted varnish. But that's a completely different story.
The process of decorative chrome plating can be repeated even at home in the bathroom without buying expensive equipment with minimal cost. You can get acquainted with the technology in more detail by studying the email course Technology of decorative chrome plating and trying it in practice, it will allow you to decide whether it is worth moving further in this direction.
What does the email course "Technology of decorative chrome plating" consist of?
- Chemistry and equipment.
- Recipes and preparation of solutions for silvering.
- Surface preparation for silver application.
- Metallization
