RU2066716C1 - Process of manufacture of tinted coast on valve metals and alloys - Google Patents

Abstract

FIELD: chemical industry, finishing materials. SUBSTANCE: process relates to tinting of articles from valve metals and their alloys into various shades of blue color while manufacturing panels, cases of instruments, finishing rooms, fabricating decorations, producing catalysts for chemical industry. process deals with expansion of spectrum of blue color from light blue up to saturated dark blue and dark violet color. In agreement with process electrolytic oxidation is conducted under conditions of microarc discharges with direct or alternating current with current density 0.5-20.0 A/sq. dm, final formation voltage 110-250 V in electrolyte containing sodium dihydrophosphate, borax, phosphorus-acid cobalt, sodium hexammetaphosphate and potassium or sodium wolframate with pH 3.0-6.0. EFFECT: expanded spectrum of blue color. 7 cl, 1 tbl

Description

 The invention relates to the electrochemical deposition of protective and decorative painted coatings on valve metals and their alloys, mainly on aluminum and its alloys, titanium and its alloys, zirconium and its alloys, niobium and its alloys, and can be used in various sectors of the economy when painting products from these metals in various shades of blue, decoration of devices, rooms, manufacturing of panels, cases, etc. in the production of decorative jewelry, catalysts in the chemical industry. In combination with other colors provides high decorative qualities of the appearance of products.

A known method of staining products from aluminum and some of its alloys, including blue, includes porous anodizing, non-porous anodizing and electrochemical staining of the anode film with alternating current in solutions of metal salts of Ni, Co, Sn, Fe, Cd, Zn, Pb, Au at a temperature of 15-30 ^o C, a current density of 0.3-1 A / dm ² , a voltage of 8-50 V for 1-10 minutes (AS USSR N 802409, publ. 07.02.81, ) By this method, anodic colored films are obtained, including from blue to dark blue. The disadvantage of this method is the complexity of the technology (mandatory degreasing, etching, porous anodizing, non-porous anodizing, electrochemical staining).

A known method of anodic production of colored silicate films on products from aluminum and its alloys (US Pat. US N 3812023. publ. 21.05.74,). The electrochemical processing of parts is carried out in aqueous solutions of alkali metal silicates with alternating current at a density of 3.2-15.6 A / dm ² , voltage 250-350 V, at a temperature of 100 ^o C, processing time from 1 minute to 1 hour. For coloring silicate coatings, various coloring pigments of inorganic and organic origin are introduced into the bath, depending on the desired color. In particular, blue ultramarine is added to obtain blue films. The disadvantage of this method is the complexity of the technology, low light resistance of the coatings.

Closest to the claimed is a method for producing colored protective coatings on aluminum products under the conditions of an electric spark discharge, which includes processing in the main electrolyte (M / L: NaF 0.5; NaH ₂ PO ₄ 0.5; Na ₂ B ₄ O ₇ • 10H ₂ O - 0.1; NH ₄ F 0.1) by pulsed or direct current at a density of 10-30 A / dm ² for 10 min. and a final voltage of 250-750 V (US Pat. GDR N 229163, publ. 30.10.85 g.). Various metal compounds Mn, Fe, Cr, V, Zn, including cobalt in the form of [Co (NH ₄ ) ₆ ] ²⁺ , at a concentration of 0.01-1 M / L, complexing agents or complexones are introduced as coloring substances. in excess of 5-10% relative to the stoichiometric amount of the coloring compound. As a result of processing, color coatings are obtained, including blue light-resistant ones, with good adhesion to metal. The disadvantage of this method is the presence of a high current density, which leads to a high energy intensity of the process, as well as the complexity of the technology, because to maintain the stability of the complex [Co (NH ₄ ) ₆ ] ²⁺ , which provides the blue color of the coating, it is necessary to constantly monitor the concentration of the complexing agent and, if necessary, introduce additionally. In this case, the coating turns out to be one tonality blue with a cobalt content of up to two percent.

 The problem solved by the proposed technical solution is to obtain on the surface of products from valve metals, mainly from aluminum and its alloys, titanium and its alloys, niobium and its alloys, zirconium and its alloys, a protective, uniformly colored film with a wide spectrum of blue tonality ( from light blue to deep dark blue and dark purple) with a cobalt content on the surface of up to 32 wt. on aluminum, 18.5% on titanium, 18% on niobium and zirconium, respectively.

The solution to this problem is provided due to the fact that painted decorative protective coatings on these valve metals are obtained under microplasma discharges in a galvanostatic mode at constant current at a density of 0.5-6 A / dm ² and a final formation voltage of 150-180 V for aluminum and its alloys, 110-140 V for titanium, zirconium, niobium and their alloys or on alternating current at a density of 3-20 A / dm ² and a final formation voltage of 180-250 V for aluminum and its alloys and a current density of 8-30 A / DM ² and the final voltage formiro 150-220 V for titanium, zirconium, niobium and their alloys in an aqueous electrolyte containing sodium dihydrogen phosphate, will, cobalt (II) phosphate, sodium hexametaphosphate, potassium or sodium tungstate in the following ratios of components, g / l:
sodium dihydrogen phosphate NaH ₂ PO ₄ 3-7
borax Na ₂ B ₄ O ₇ • 10H ₂ O 4-7
cobalt phosphate (II) Co ₃ (PO ₄ ) ₂ • 8H ₂ O 6-15
sodium hexametaphosphate Na ₆ P ₆ O ₁₈ 20-60
potassium tungstate K ₂ WO ₄ 4-8
or sodium tungstate Na ₂ WO ₄ • 2H ₂ O 4-8
The method is as follows. A part that is defatted if necessary (in order to preserve the purity of the electrolyte) is immersed in the electrolyte and oxidized at the current density and formation voltage described above under microplasma discharges in the galvanostatic mode for 2-20 minutes. The workpiece is an anode; alloys of nickel, titanium, and stainless steel can be used as a cathode. An electrolyte for oxidation is prepared by separately dissolving each component and then draining it into a total volume. The pH of the prepared electrolyte is 3-6, the temperature of the electrolyte is 0-40 ^o C.

 As a result of processing, a smooth, enamel-like coating is formed on the surface of the product, painted in color from light blue to saturated dark blue or violet, depending on the conditions of formation and the alloy being processed, with a thickness of 3-20 microns.

 The maxima of the reflection spectrum for Al are 420 nm, Ti 430 nm, Zr - 440 nm, Nb 435 nm.

 The resulting films have high light fastness. When the ERT 250 mercury lamp was irradiated with unfiltered light at a distance of 20 cm for 2 hours, the color of the film did not change. Unfiltered light contains more than 50% hard ultraviolet and corresponds to a wavelength of λ 365 nm.

 The films exhibit good adhesion to the substrate, low porosity, and high decorative qualities.

 In addition, they are characterized by high electrical protective properties (the breakdown voltage in the metal-oxide-metal system with positive and negative polarity is 400-900 V for Al and its alloys and 550-750 V for Ti, Nb, Zr and their alloys, respectively).

Using X-ray phase analysis, the presence of CoAl ₂ O ₄ , Co ₂ O ₃ and AlPO ₄ spinels on aluminum alloys was established. For titanium, niobium, zirconium alloys, the presence of a compound of the type Co (II) Co (III) Me (PO ₄ ) _x (Me Ti, Zr, Nb), Co ₂ O ₃ and the oxide of the corresponding metal (TiO ₂ rutile, b- Nb ₂ O ₅ is a high-temperature crystalline modification, ZrO ₂ cubic). In addition, the presence of the compound NaZr ₂ (PO ₄ ) _{2 was} found in the colored coating on zirconium.

Microprobe analysis of the elemental composition of the surface (excitation depth 3-5 microns) of the films obtained at a direct current density of 0.03 A / dm ² for 10 minutes showed the presence of the following elements in mass percent: for aluminum alloy AMtsM 7.5 Al; 32 Co; 17.3 P; 4.5 W; 0.8 Na; 0.3 K; for titanium alloy VT1-0 19.8 Ti; 18.5 Co; 17.9 P; 4.1 W; 1 Na; 0.3 K; for the niobium alloy NbCCU 17.2 Nb, 18 Co; 18 P; 3.9 W; 0.9 Na; 0.2 K.

The elemental composition of the obtained coatings was studied using an electron microprobe using a UHA-5A X-ray analyzer at an accelerating voltage of U 20 kV, I 48 nA. X-ray diffraction patterns were obtained on a DRON - 2.0 setup (CuK _$$$ radiation). The reflection spectra on the film for the visible region of light were taken on a SPECORd M-40 instrument.

Based on the quantitative analysis data, it follows that the outer layer of the film on aluminum alloys consists of a spinel of the composition CoAl ₂ O ₄ , which due to the existence of a cobalt (II) ion in tetrahedral coordination has a blue color. In the same coordination, the Co (II) ion is also found in the compounds Co (II) Co (III) Ti (PO ₄ ) ₃ , Co (II) Co (III) Zr (PO ₄ ) ₃ and Co (II) Co (III ) Nb (PO ₄ ) ₄ formed on alloys of titanium, niobium, zirconium, providing a blue color of the latter.

The mechanism of formation of colored coatings can be represented as follows. It is known that a solution of sodium hexametaphosphate (GMF) has a slightly acidic reaction and firmly binds divalent metal cations, in particular the Co ²⁺ cation, by exchange decomposition with the formation of compounds Na ₄ CoP ₆ O ₁₈ or Na ₂ Co ₂ P ₆ O ₁₈ . As a result of the dissociation of these compounds under the influence of an electric potential difference, complex complex anions with cobalt (II) [CoP ₆ O ₁₈ ] ^4- , [Co ₂ P ₆ O ₁₈ ] ^2- approach the anode, where in the conditions of microplasma discharges the high-temperature synthesis of the above stained compounds. The color intensity depends on the formation conditions (time, current density).

 The introduction of potassium or sodium tungstate improves the conditions of sparking at the anode, which contributes to the production of even, dense, uniformly colored films.

 The presence of borax in the electrolyte helps to accelerate the formation of colored compounds, improves the appearance of coatings (smoothness, continuity, uniformity).

 Sodium dihydrogen phosphate in this electrolyte acts as a buffer, regulating the pH of the solution, and stabilizes the formation of a complex anion with cobalt during the anode process.

 The claimed technical solution is feasible at concentrations of electrolyte components and values of the formation parameters in accordance with the claims.

 When the content of hexametaphosphate is less than 20 g / l, the pH of the electrolyte solution is shifted to the alkaline region, which leads to the precipitation of cobalt in the form of hydroxide. With an increase in the concentration of hexametaphosphate over 60 g / l, the appearance of the coating worsens, the color continuity is violated.

 When the borax concentration is less than 4 g / l, the pH of the solution approaches 2–3, while the final formation stress increases, the substrate is etched, the color becomes spotty, in the form of a “jam”. At a borax concentration of more than 7 g / l, the pH of the electrolyte solution is shifted to the alkaline region, which leads, as described above, to cobalt precipitation.

 When the concentration of potassium or sodium tungstate is less than 4 g / l, the appearance of the films deteriorates, fading appears. At a concentration of potassium or sodium tungstate above 7 g / l, uneven coloring appears, the final formation stress increases, which leads to etching of the substrate.

 When the content of sodium dihydrogen phosphate is less than 3 g / l, the pH of the solution is shifted to the acidic region (2-3), while the samples are etched, and fading appears in the color. At a concentration of more than 7 g / l, the appearance of the films does not change, the color is bright, uniform, and a further increase in the concentration of dihydrogen phosphate is impractical.

The claimed technical solution is feasible with the following values of the formation parameters. The formation of colored coatings with direct current with a density of less than 0.5 A / dm ² and with alternating current of less than 3 A / dm ² for aluminum and its alloys and 8 A / dm ² for alloys of titanium, niobium, zirconium gives thin, slightly colored films in the case of aluminum and anode in the case of titanium, niobium and zirconium.

At a direct current density of more than 8 A / dm ² and an alternating current of more than 20 A / dm ² for aluminum and its alloys and 30 A / dm ² for titanium, niobium and zirconium, films with visible mechanical damage along the edges are obtained due to severe overheating of the electrolyte in areas of the anode space.

 Thus, the claimed values of the parameters of the method provide the possibility of its implementation with obtaining a technical result, which consists in the formation of colored coatings from blue to dark blue on the surface of parts of aluminum, titanium, niobium, zirconium and their alloys, respectively.

 To implement the method using standard equipment designed for electrochemical oxidation of metals and their alloys, including a current source.

 The possibility of implementing the proposed method is confirmed by examples of its specific implementation.

For oxidation, samples were taken in the form of plates with an area of 0.1-5 dm ^{2 of the} following alloys (chemical composition,):
1. aluminum AMtsM (Mn 1-1.6; Si 0.6; Cu 0.2; Ti 0.2; Zn 0.1; Mg 0.05), AOO (Fe 0.3; Si 0.3; Cu 0.02; Mn 0.025; Zn 0.1; Mg - 0.05), AL-2 (Si 10-13; Mg 0.1; Fe 0.8-1.5; Mn 0.5; Cu 0 , 6; Zn - 0.3), AMG6 (Mg 5.8-6.8; Mn 0.5-0.8; Ti 0.02-0.1; Si 0.4; Cu 0.1; Zn 0.2)
2. titanium VT1-O (Fe 0.2; Si 0.1; C 0.07; N 0.04; O 0.12), 3B (Al 3.5-5; V 1.2-2.5 , other elements at the level of impurities),
3. niobium NbTsU (Zr 1-1,4; C 0,08-0,12),
4. zirconium (Nb 0.01-0.02; Su, Fe at the level of impurities).

 Before oxidation, the samples were degreased, washed with water, ethyl alcohol. An electrolyte was prepared by dissolving each component separately, then poured into the total volume.

Electrodes are immersed in an electrolytic cell equipped with a stirrer. The anode is an oxidizable product, a nickel alloy was used as a cathode. The process was carried out at a given density of direct or alternating current for 10 minutes, the temperature of the electrolyte was 15-22 ^o C.

 The values of the parameters of the method (concentration of electrolyte components, density of direct and alternating current, final formation potential), as well as the values of the cobalt content (wt.) On the film surface are shown in the table.

 In addition, the table shows the oxidation results for aluminum of the AOO brand and its three alloys (АМцМ, АЛ-2, АМГ6), for titanium VT1-0 and its alloy 3В, one niobium alloy NbTsU and an alloy of direct and alternating current. Moreover, for aluminum alloy AMtsM, oxidation was carried out at values of electrolyte concentrations, current density, and voltage that went beyond the declared limits.

 The table also shows the results of oxidation for the prototype.

 As can be seen from the table (examples 1-2, 7, 8), the inventive method provides deep and evenly colored coatings from blue to dark blue or violet on aluminum, titanium, niobium, zirconium and their alloys.

 In this case, the coating obtained by the method in accordance with the prototype, is quite equal, bluish in color. More intense shades of blue, this known method does not allow to obtain.

Claims (4)

1. The method of obtaining painted coatings on valve metals and alloys of microarc oxidation methods in an aqueous electrolyte containing sodium dihydrogen phosphate, borax and cobalt compound, characterized in that the oxidation is carried out at a constant current density of 0.5 to 6.0 M / dm ² , with the final voltage of coating formation is 110 180 V, and sodium hexametaphosphate, potassium tungstate or sodium are additionally introduced into the electrolyte, while cobalt phosphate is used as a cobalt compound in the following ratio of components, g / l:
Sodium dihydrogen phosphate NaH ₂ PO ₄ 3 7
Borax Na ₂ B ₄ O ₄ • 10H ₂ O 4 7
Cobalt Phosphate Co (PO ₄ ) ₂ • 8H ₂ O 6 15
Sodium hexametaphosphate Na ₆ P ₆ O _{1 8} 20 60
Sodium tungstate Na ₂ WO ₄
or
potassium tungstate K ₂ WO ₄ • 2H ₂ O 4 8
2. The method according to p. 1, characterized in that upon receipt of the painted coatings on aluminum and its alloys, the oxidation is carried out at a final voltage of 150-180 V.  3. The method according to p. 1, characterized in that upon receipt of colored coatings on titanium, niobium, zirconium and their alloys, oxidation is carried out at a final voltage of 110 140 V. 4. The method of obtaining painted coatings on vertical metals and alloys by the method of microarc oxidation in an aqueous electrolyte containing sodium dihydrogen phosphate, borax and cobalt compound, characterized in that the oxidation is carried out with alternating current density of 3 30 A / dm ² with a final coating formation voltage of 150 250 B, and sodium hexametaphosphate, potassium tungstate or sodium are additionally introduced into the electrolyte, while cobalt phosphate is used as the cobalt compound in the following ratio of components, g / l:
Sodium dihydrogen phosphate NaH ₂ PO ₄ 3 7
Borax NaB ₄ O ₇ • 10H ₂ O 4 7
Cobalt Phosphate Co ₃ (PO ₄ ) ₂ • 8H ₂ O 6 - 15
Sodium hexametaphosphate Na ₆ P ₆ O _{1 8} 20 60
Sodium tungstate Na ₂ WO ₄
or
potassium tungstate K ₂ WO ₄ • 2H ₂ O 4 8
5. The method according to p. 4, characterized in that upon receipt of the painted coatings on aluminum and its alloys, oxidation is carried out at a current density of 3 20 A / dm ² and a final voltage of 180,250 V. 6. The method according to p. 4, characterized in that to obtain colored coatings on titanium, niobium, zirconium and their alloys, oxidation is carried out at a current density of 8 30 A / dm ² and a final voltage of 150 220 V.

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