LT6119B - The process for electrodepositing of black chromium coatings - Google Patents

Abstract

The present invention relates to chemical industry, in particular to production coatings from electrolytes. An object of the invention is the process for electrodepositing, namely an intense black coating electrodepositing method on a steel, nickel, copper and alloys of these. The method may be used for forming solar collectors selective layers and a variety of industrial products or protection parts from corrosion and improvement of appearance (decorativeness). Parts from steel, copper, brass or nickel-plated parts immersed in the electrolyte containing trivalent chromium Cr (III) ions, chloride ions, nitrate ions, boric acid, amino-acetic acid or its salts is added to the electrolyte. Additionally inorganic zinc compound is added and electrolysis carried out using a cathodic current pulses in the range of 20 to 40 A / dm2, where cathodic pulse duration is 0.5 to 2.5 with 10-20 minutes of breaks. Electrolysis is carried out in cycles, starting with the right size of the cathodic current impulse, and after a brief pause, charged a second cathodic impulse. The number of impulses can be between 2 and 6, depending on the desired coating thickness.

Description

The invention relates to the chemical industry, which comprises coating coatings from electrolytes.

The present invention relates to a process for electrolytic deposition, namely a process for electrolytic deposition of intense black coatings on steel, nickel, copper and their alloys, which can be used to form selective layers in solar panels and in various industrial applications for protection against corrosion and appearance. ) to improve.

Given the growing need for alternative energy sources, it is appropriate to investigate black chromium coatings because of their unique optical properties and particularly high corrosion resistance. Black chromium plating is one of the most widely used solar energy converters [G.Zajac.G.B. Smith, A. Ignatiev, J. Appl. Phys. 51: 554 (1980); J.P. Houre, J. Electrochem. Soc. 126: 190 (1979). However, to date black coatings have been obtained from highly toxic hexavalent chromium [Cr (VI) j electrolytes.

There is a known method to obtain glossy black chromium coatings from an electrolyte containing (g / l): CrC> 3 - 150-250, NaNO3 or KNO3 - 2-4, H2C2O4 - 0.5-5.0, H3BO3 - 0.5 -1.0, Zn (BF ₄ ) ₂ - 0.5-0.7 or K ₂ SiF ₆ - 0.2-0.3, ZnO - 1-20 (LT 4110, Int.CI. C25D 3/08 , 1997).

Electrolytic deposition of selective black chromium coatings for the production of suitable solar collectors is also known (US 4,389,464 Int.CI: C25D 3/08; 3/02, 1983). In this method, intense black coatings are obtained from an electrolyte containing chromium (VI) oxide (CrO3), hexafluoro-silicic acid (H ₂ SiF ₆ ) and sodium molybdate (Na ₂ MoO _{4 2} H ₂ O).

Subsequently, a process for electrolytic deposition of black chromium has been proposed which allows the concentration of hexavalent chromium Cr (VI) ions to be improved and the coating characteristics to be improved (EP 1876268, Int.CI. C25D 3/06).

However, all of these methods for electrolytic deposition of black chromium are associated with the use of highly toxic hexavalent chromium Cr (VI) electrolytes.

There is a known chemical deposition of a black chromium coating from a trivalent chromium solution (EP 1995348 A1, Int.CI. C23C 22/12, 2008), whereby a conversion corrosion resistant black chromium film is formed on the surface of zinc or its alloy by immersion in a trivalent chromium solution, containing zinc ions, complexing agent, organic sulfite compound and phosphite ions.

However, from a technological point of view, this process is fundamentally different from the process of electrolytic deposition of the black chromium coating according to the invention in that the conversion black chromium film is very thin and formed only on the surface of the zinc or its alloy coating.

The closest technical solution in essence is the electrolytic deposition of black chromium, where the details are immersed in an electrolyte containing trivalent chromium Cr (III) ions, cobalt ions, sodium hypophosphite, sodium dihydrogen phosphate, sodium fluoride and electrolysis under conditions of: cathode current density 35 A / dm ² , electrolyte temperature 20-30 ° C, pH 0.5-1.0, coating time 1-5 min, [MR Bayati, MH Shariat, K. Janghorban, Renevable Energy 30 (2005) 2163-2178 ].

The black chromium coatings obtained in this way exhibit good adhesion to the substrate and a high light absorption coefficient (0.96). However, these coatings are micro-cracked and therefore not sufficiently corrosion resistant. In addition, these coatings are easily damaged by needle swipe.

It is an object of the present invention to provide a method for electrolytic deposition of black chromium coatings on a trivalent chromium Cr (III) electrolyte which will provide decorative coatings having sufficient black saturation, high light absorption coefficient and sufficient corrosion resistance.

The essence of the invention is that the steel, copper, brass or nickel plated parts are electrolyte dipped into an electrolyte containing trivalent chromium Cr (III) ions, chlorine ions, nitrate ions, boric acid, aminoacetic acid or salts thereof in addition to the electrolyte Adds an inorganic zinc compound and electrolyses it using cathode current pulses in the range of 20-40 A / dm ² , where the cathodic pulse duration is 0.5-2.5 min. with 10-20 s breaks (pauses).

Electrolysis is performed in cycles, starting with a cathode current pulse of the required size, and after a short pause, delivering a second cathodic pulse. The number of pulses can be from 2 to 6, depending on the required coating thickness.

Pulsed electrolysis can be considered as a combination of precipitation and dissolution resulting in dissolution of chromium hydroxide and promoting electrolytic deposition of the coating.

A break between individual cathode pulses during electrolysis is required to smooth the coating surface. Its duration is 10-20 s. This is the optimum time for dissolving the irregularities on the surface of the pavement. If the break is longer than 20 s, the entire surface of the coating begins to melt. In addition, during the break, the diffusion layer formed during electrolysis is disassembled, resulting in a lower pH of the diffuse layer and a constant electron deposition rate.

The coatings obtained in this way consist of layers that are firmly bonded to the substrate and to each other, have better protective properties, have higher corrosion and abrasion resistance, a richer black color and a high light absorption coefficient.

Electrolysis is carried out from an electrolyte containing (g / l):

CrCI ₃ 6H ₂ O NaCl NaNO ₃ H ₃ BO ₃

NH ₂ CH ₂ COOH

ZnO

- 200-300,

-60,

-2.5-5.0, - 30-40,

-18-42, -2-10.

Electrolysis temperature 18-30 ° C.

The electrolyte is prepared in distilled water by dissolving the amounts indicated in the recipe.

Prior to electrolysis, the nickel plated (10 pm) parts are washed with water, placed in an electrolyte and discharged to a cathodic current in the range of 20-40 A / dm ² (1 min), then switched off and repeated for a short interval (10 s). current pulse (1 min). The pulses can be 2-3.

The coated parts are washed with water, dried and lubricated with oil. After 24 or. analyzes the properties of the skies.

The steel parts are cleaned, degreased, activated and coated before electrolysis, allowing a cathodic current of 20-40 A / dm ² pulses (1-2 minutes each) with 10-20 s breaks.

Only 4-6 pulses are used instead of two to three pulses.

Copper and brass parts are cleaned, degreased, activated and coated by pulsing cathodic current in the range of 20-40 A / dm ² (after 1-2 minutes) with 10-20 s breaks. The number of pulses can be up to six.

The corrosion resistance of coatings is determined by a salt fog chamber (LST EN ISO 9227: 2012), where details are held until the first corrosion foci appear.

The adhesion of the coating to the substrate is checked by bending the coated plates at 90 °.

The reflectance of the samples was measured using a device:

Spectrophotometer Spekord 250 flows from analytik Jena (Germany),

The angle of light incident on the samples was 12 °.

To evaluate the effectiveness of the proposed process, 10 solutions were prepared, nine of which were prepared according to the proposed process using a nickel-based coating (e.g. 1-3), steel (e.g. 4-6) and copper (e.g. 7-9). Control samples were prepared according to the prototype using base steel (for example 10).

EXAMPLES:

example

The nickel plated parts are immersed in a solution containing (g / l):

CrCl ₃ 6H ₂ O - 200 NH ₂ CH ₂ COOH -18.75

H ₃ BO ₃

NaCl

NaNO ₃

PH

- 60 -3.0 - 1.4

Temperature 20 ° C

The cathodic current is supplied by pulses: first pulse - 40 A / dm ² (60 s), break s; second pulse 40 A / dm ² (60 s), break 10 s, third pulse 40 A / dm ² .

The parts are then washed with water, dried and lubricated with oil.

example

The nickel plated parts are immersed in a solution containing (g / l):

CrCl ₃ 6H ₂ O - 250

NH ₂ CH ₂ COOH -18.75

H ₃ BO ₃ - 30

NaCl - 60

NaNO ₃ - 3.0

ZnO - 5.0 pH - 1.2

Temperature 20 ° C

The cathodic current is supplied by pulses: first pulse - 20 A / dm ² (60 s), break for 10 s; second pulse - 20 A / dm ² (60 s). The parts are then washed with water, dried and lubricated with oil.

example

The nickel plated parts are immersed in a solution containing (g / l):

CrCl ₃ 6H ₂ O - 300 NH ₂ CH ₂ COOH -18.75 H3BO3 - 30

NaCl - 60

NaNO ₃ - 3.0

ZnO - 5.0 pH - 1.2

Temperature 20 ° C.

The cathodic current is supplied by pulses: first pulse - 40 A / dm ² (60 s), break for 10 s; second pulse - 40 A / dm ² (60 s). The parts are then washed with water, dried and lubricated with oil.

example

Steel parts are cleaned, degreased, rinsed with water, activated (approx

(s), wash with water and soak in a solution containing (g / l):

CrCl ₃ 6 H ₂ O - 250 NH ₂ CH ₂ COOH -18.75

H ₃ BO ₃

NaCl

NaNO ₃

PH

-3.0 - 1.4

Temperature 20 ° C

The cathodic current is supplied by 6 pulses at a 10 s break between pulses: first pulse 30 A / dm ² (60 s), second pulse 40A / dm ² (60 s), third pulse 30 A / dm ² (60 s) , fourth pulse 40 A / dm ² (60 s), fifth pulse 30 A / dm ² (60 s), sixth pulse 40 A / dm ² (60 s). The parts are then washed with water, dried and lubricated with oil.

example

The steel parts are cleaned, degreased, rinsed with water, activated (about 10 s), washed with water and soaked in a solution containing (g / l):

CrCl ₃ 6H ₂ O - 250

NH ₂ CH ₂ COOH -18.75

H ₃ BO ₃ - 30

NaCl - 60

NaNO ₃ - 3.0

ZnO - 5.0 pH - 1.2

Temperature 20 ° C

The cathodic current is supplied by 4 pulses at a 10 s break between pulses: the first pulse is 20 A / dm ² (60 s), the second pulse is 20 A / dm ² (60 s), the third pulse is 20 A / dm ² (60 s) ), fourth pulse - 20 A / dm ² (60 s). The parts are then washed with water, dried and lubricated with oil.

example

Steel parts are cleaned, degreased, rinsed with water, activated (approx

(s), wash with water and immerse in a solution containing (g / l):

CrCl ₃ 6H ₂ O - 250 NH ₂ CH ₂ COOH - 18.75 H ₃ BO ₃ - 30

NaCl - 60

NaNO ₃ - 3.0

ZnO - 5.0 pH - 1.2

Temperature 20 ° C

The cathodic current is supplied by 2 pulses at a 10 s break between pulses: the first pulse is 40 A / dm ² (60 s), the second pulse is 40 A / dm ² (60 s). The parts are then washed with water, dried and lubricated with oil.

example

Copper parts are degreased, greased, washed with water, activated, washed with water and immersed in a solution containing (g / l):

CrCl ₃ 6H ₂ O - 250 NH ₂ CH ₂ COOH -18.75 H ₃ BO ₃ - 30

NaCl - 60

NaNO ₃ - 3.0 pH - 1.4

Temperature 20 ° C

The cathodic current is produced by 3 pulses: first pulse - 40 A / dm ² (60 s), break for 10 s; second pulse 40 A / dm ² (60 s), third pulse 40 A / dm ² (60 s). The parts are then washed with water, dried and lubricated with oil.

example

Copper parts are degreased, degreased, rinsed with water, activated, washed with water and soaked in a solution containing (g / l):

CrCl ₃ 6H ₂ O - 250

NH ₂ CH ₂ COOH -18.75

H ₃ BO ₃ - 30

NaCl

NaNO ₃

ZnO

- 60 -3.0 -5.0 pH - 1.2

Temperature 20 ° C

The cathodic current is supplied by 2 pulses at a 10 s break between pulses: the first pulse is 20 A / dm ² (60 s), the second pulse is 20 A / dm ² (60 s). The parts are then washed with water, dried and lubricated with oil.

example

Copper parts are degreased, greased, washed with water, activated, washed with water and immersed in a solution containing (g / l):

CrCl ₃ 6H ₂ O - 250

NH 2 CH 2 COOH -18.75

H ₃ BO ₃ - 30

NaCl - 60

NaNO ₃ - 3.0

ZnO - 5.0 pH - 1.2

Temperature 20 ° C

The cathodic current is supplied by 2 pulses at a 10 s break between pulses: the first pulse is 40 A / dm ² (60 s), the second pulse is 40 A / dm ² (60 s). The parts are then washed with water, dried and lubricated with oil.

Control samples (K1 and K2)

Steel parts are cleaned, degreased, rinsed with water, activated (approx

(s), wash with water and immerse in a solution containing (g / l):

Cr ³⁺ ion concentration - 1M

NaH ₂ PO ₂

NaH ₂ PO ₄

NaF

0.75 M -4 g / L

- 0.5 M

Co ²⁺ ion concentration -15 g / l pH - 1.0

Temperature 20 ° C

K1) A cathodic current of 35 A / dm ^{2 is} allowed for 5 min. The parts are then washed with water and dried.

K2) A cathodic current of 70 A / dm ^{2 is} allowed for 5 min. The parts are then washed with water and dried.

The properties of the coatings are analyzed after 24 hours.

Comparative data for black coatings obtained in the optimum current density range (20-40 A / dm ² ) are shown in Table 1.

Experimentally, the optimum black coating thickness was found to be about 1.0 µm for nickel Ni, about 2.0 µm for copper and more than 2.0 µm for steel.

The table shows that all black coatings have good adhesion to the substrate.

Coatings derived from an electrolyte containing zinc oxide ZnO 5 g / l have a fine-grained structure with a micro-crack network.

The results show that the black color becomes richer and the light reflectance is lower when the coatings are obtained from an electrolyte containing ZnO zinc oxide. The best selectivity for black chromium coatings was found in examples where steel was used as substrate (for example 5 and 6). However, samples (2 and 3) on nickel layers obtained from an electrolyte containing ZnO zinc exhibit the best corrosion resistance and sufficiently low reflectivity (99%).

Claims (2)

DEFINITION OF INVENTION A process for electrolytic deposition of black chromium coatings, wherein the details are immersed in an electrolyte containing trivalent chromium Cr (III) ions, chlorine and nitrate ions, boron and amino-acetic acid or their salts, characterized in that additional inorganic zinc is added to the electrolyte. and electrolysis is performed using cathodic current pulses in the range of 20-40 A / dm ² with a cathodic pulse duration of 0.5 to 2.5 min. with 10-20 s breaks (pauses). 2. The method of claim 1, wherein the electrolysis is carried out in cycles starting with a cathode current pulse of the required size, and after a short pause supplies a second cathodic pulse, wherein the number of pulses can be from 2 to 6, depending on the required coating thickness.