RU2449061C1 - Method for obtaining coating from metal oxides on steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to electrochemistry, and namely to application of wear-resistant and protective polymer composite coatings on steel products and can be used for operation in friction assemblies, electroplating, radioelectronic and paint-and-varnish industries. Method involves oxidation using alternating current at temperature of 30 - 40°C in electrolyte containing hydroxy tricarballylic acid; at that, electrolyte also includes salts of cobalt, nickel, molybdenum and iron, gelatine and boric acid, and oxidation is performed using alternating asymmetric current at ratio of cathode and anode current components of 2 : 1, cathode current density of 1.2 A·dm^-2 , voltage of 15 - 20 V and at ratio of components in electrolyte, g·l^-1: cobaltic sulphate 100 - 150, cobaltichloride10 - 16, ferric sulphate 8 - 10, nickel sulphate 15 - 20, ammonium polymolybdate 35 - 40, boric acid 20 - 30, hydroxy tricarballylic acid 2.5 - 3, gelatine 2-4.

EFFECT: improving wear resistance and corrosion stability of steel surface, reducing power consumption and increasing coating adhesion to the base.

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Description

The invention relates to the field of electrochemistry, in particular to the application of wear-resistant and protective polymer composite coatings on steel products, and can be used in friction units, electroplating and paint and varnish industry.

A known method of deposition of a coating from an electrolyte containing, g · l ^-1 : ferric chloride 350-400, cobalt chloride 5-50 and hydrochloric acid 0.5-2.0 at a temperature of 30-50 ° C, in the range of cathodic current densities 30 -60 A · dm ^-2 at alternating asymmetric current with an asymmetry coefficient of 1.2-6.0 (US Pat. RU 2230836, C25D 3/56. Method of electrolytic deposition of an iron-cobalt alloy. 2002. Serebrovsky V.I. (RU ), Serebrovskaya L.N. (RU), Serebrovsky V.V. (RU), Konyaev N.V. (RU)). The disadvantage of this method is the low microhardness, wear resistance and poor adhesion of the coating to the base. As well as the high energy intensity of the process, since the deposition of the coating is carried out at high cathodic current densities.

The closest in technical essence and the achieved result to the proposed method is a method of electrolytic deposition of an alloy of iron - molybdate - cobalt (Pat. RU 2239672, C25D 3/56. Method of electrolytic deposition of an alloy of iron - molybdenum - cobalt. 2004, Serebrovsky V.I. (RU), Serebrovskaya L.N. (RU), Serebrovsky V.V. (RU), Konyaev N.V. (RU)).

The coating deposition process is carried out from an electrolyte containing, g · l ^-1 : iron chloride - 350-400, ammonium molybdate - 0.2-1.2, cobalt chloride - 5-30 and citric acid - 0.5-2.0 at a temperature of 30-40 ° C, cathodic current density of 40-60 A · dm ^-2 with an asymmetry coefficient of 1.2-6.0.

The disadvantages of this method are the high density of the cathode current (40-60 A · dm ^-2 ), i.e. high energy intensity of the process; insufficiently high adhesion strength of the coating to the base; the impossibility of obtaining polymer composite coatings from metal oxides (molybdenum, cobalt, iron, nickel) that are easily immobilized in a gelatin massif with the formation of nanostructured systems.

The objective of the invention is to increase the corrosion resistance and wear resistance of the steel surface, reducing energy consumption, increasing the thickness of the oxide coating and its adhesion to the base.

The objective is achieved in that a method of producing a coating of metal oxides on steel, including oxidation using alternating current at a temperature of 30-40 ° C, in an electrolyte containing citric acid, while the deposition of metal oxides is carried out from an electrolyte containing cobalt salts, nickel, molybdenum, iron, gelatin and boric acid, using asymmetric alternating current at a ratio of cathodic and anodic current components 2: 1, the cathodic current density of 1.2 a dm ^2, voltage of 15-20 V, and the ratio, · L ^-1:

cobalt sulfate (CoSO ₄ · 7H ₂ O) 100.0-150.0 cobalt chloride (CoCl ₂ · 6H ₂ O) 10.0-16.0 iron sulfate (FeSO ₄ · 7H ₂ O) 8.0-10.0 nickel sulfate (NiSO ₄ · 7H ₂ O) 15.0-20.0 ammonium polymolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O) 35.0-40.0 boric acid (H ₃ BO ₃ ) 20.0-30.0 lemon acid (C ₆ H ₈ O ₇ ) 2.5-3.0 gelatin 2.0-4.0

The use of gelatin allows you to get a polymer matrix. The use of an alternating asymmetric current makes it possible to obtain a coating of metal oxides immobilized into a polymer matrix on steel. Carrying out electrochemical processes on an asymmetric alternating current makes it possible to flexibly control the technological process, influence the microstructure of oxides, and the ratio of various phases in oxides. The cycling of the polarizing voltage leads to the formation of oxide phases in the anode half-cycle of the current due to the oxidation of metal ions, which are deposited on the surface of the steel in the cathode half-period. In addition, due to cycling processes, a transition layer of spinel is formed on the surface of the steel, which is a mixture of oxides (steel and oxide deposited from a solution), which ensures high adhesion of the resulting coating.

The proposed method for coating steel from metal oxides (molybdenum, iron, cobalt and nickel) immobilized in a polymer matrix, allowed:

- reduce tens of times the current density and voltage during oxidation;

- double the thickness of the oxide coating;

- increase the adhesion of the coating to the base;

- get a polymer composite coating;

- increase tens of times the protective properties of the base and its microhardness;

- implement complexation processes in the solid phase.

The present invention is a new way to obtain a coating on the surface of steel from metal oxides deposited from aqueous solutions of their salts and immobilized in a polymer matrix. The developed electrolyte composition makes it possible to obtain a polymer gelatin matrix on the surface of the steel, in which oxygen compounds of the elements included in its composition are immobilized. The use of components containing complex anionic complexes in the electrolyte provides additional opportunities for the formation of oxide structures. Therefore, the introduction of ammonium polymolybdate into the electrolyte made it possible to obtain refractory metal oxides in the polymer matrix, giving the base high protective properties and wear resistance.

Confirmation that complex oxide systems of molybdenum, cobalt, iron, and nickel are formed on the surface of the steel are X-ray spectral microanalysis data obtained using a QUANTA 200 scanning electron microscope (table).

X-ray microanalysis data Element From the surface of the coating wt.% at.% Carbon 20.18 45.31 Oxygen 20.89 35.22 Iron 10.87 05.22 Cobalt 03.31 01.52 Nickel 00.71 00.33 Molybdenum 44.04 12.38

Based on these data, the approximate phase composition of the coating on steel was calculated: Mo, MoO ₂ , spinels — Fe ₂ O ₃ and CoFe ₂ O ₄ , highly dispersed carbon and molybdenum intermetallics. The presence of finely dispersed carbon in the coating confirms the formation of a polymer gelatin matrix on the steel surface during electrolysis.

The presence of a gelatin matrix was also confirmed by IR spectroscopy data obtained on a Varian 3100 FT - IR Excalibur Series instrument using the method of impaired total internal reflection. All spectra contain absorption bands in the region of 1650–1600 cm ^–1 , 1407, and 1409 cm ^–1 , which correspond to stretching vibrations of the C = O, С – N, and N – Н, С – H groups in С = C – Н, respectively. All this indicates the formation during the electrolysis of a polymer gelatin matrix, in which metal oxides are precipitated from an electrolyte solution. In addition, IR spectroscopy made it possible to draw conclusions about the complexation processes that occur along with the deposition of oxides.

The deposition of oxides from an aqueous electrolyte solution was carried out on a previously prepared surface, according to the standard electroplating technique, of flat steel samples of steel St.3 of size 20 × 30 × 1 mm, with polarization by an alternating asymmetric triangular shape current, frequency 50 Hz, with an equal duration of the cathode and anode pulses, at a certain ratio of the amplitude of the currents of the cathode and anode half-periods in an electrolyte containing salts of cobalt, molybdenum, iron, nickel, gelatin, citric and boric acid.

The current source was a device consisting of two diodes connected in parallel and conducting current in different directions through adjustable resistances.

As a counter electrode, stainless steel plates were used, the sizes of which were two times larger than the sizes of the processed samples. The electrolysis was carried out at a temperature of 30-40 ° C and stirring the solution with an electromagnetic stirrer. The duration of the oxide film formation was 60 min.

For experimental verification of the proposed method, coatings were formed on the surface of steel St.3 from metal oxides (molybdenum, cobalt, iron and nickel) immobilized in a polymer matrix.

Example. A high-quality coating of cobalt, molybdenum, iron and nickel oxides was obtained from an electrolyte of the following composition (at pH 4.5-4.8), g · l ^-1 :

cobalt sulfate (CoSO ₄ · 7H ₂ O) 100.0-150.0 cobalt chloride (CoCl ₂ · 6H ₂ O) 10.0-16.0 iron sulfate (FeSO ₄ · 7H ₂ O) 8.0-10.0 nickel sulfate (NiSO ₄ · 7H ₂ O) 15.0-20.0 ammonium polymolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O) 35.0-40.0 boric acid (H ₃ BO ₃ ) 20.0-30.0 lemon acid (C ₆ H ₈ O ₇ ) 2.5-3.0 gelatin 2.0-4.0

with a ratio of the average cathodic and anodic components of the current 2: 1, the cathodic current density of 1.2 A · dm ^-2 , a voltage of 15-20 V, a temperature of 30-40 ° C.

The adhesion strength of the coating to steel is 650 MPa. The coating thickness determined using the TM-4 vortex thickness gauge is 20 μm. Corrosion tests in a 3% (by weight) sodium chloride solution showed that, when an oxide coating is applied to the steel surface, the protective properties of the metal are increased tenfold compared to an unprotected surface, and in combination with a 32 LN fluoroplastic varnish - hundreds or more times. The wear resistance of the steel surface increases by 6-8 times and the coefficient of friction determined on the end friction machine is 0.035.

Claims (1)

A method of producing a coating of metal oxides on steel, including oxidation using alternating current at a temperature of 30-40 ° C in an electrolyte containing citric acid, characterized in that the electrolyte further comprises salts of cobalt, nickel, molybdenum, iron, gelatin and boric acid, and oxidation is carried out using an alternating asymmetric current at a ratio of the cathodic and anodic components of the current 2: 1, the cathodic current density 1.2 A · dm ^-2 , voltage 15 - 20 V and the ratio of the components in the electrolyte, g · l ^-1 :
cobalt sulfate (CoSO ₄ · 7H ₂ O) 100.0-150.0 cobalt chloride (CoCl ₂ · 6H ₂ O) 10.0-16.0 iron sulfate (FeSO ₄ · 7H ₂ O) 8.0-10.0 nickel sulfate (NiSO ₄ · 7H ₂ O) 15.0-20.0 ammonium polymolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O) 35.0-40.0 boric acid (H ₃ BO ₃ ) 20.0-30.0 citric acid (C ₆ H ₈ O ₇ ) 2.5-3.0 gelatin 2.0-4.0