RU2198242C1 - Composition for cobalt chemical deposition - Google Patents

Abstract

FIELD: chemical deposition of cobalt coating on metal and ceramic surfaces. SUBSTANCE: composition contains, g/l: cobalt salt (in terms of metal), 1.8-4.7; hydrazine hydrate, 3-40; thiourea, 0.2-2; 25-% aqua ammonia, the balance. Coating of ceramic base with cobalt is carried out without preliminary activation with compounds of platinum metals. Produced coating contains no boron or phosphorus impurities. EFFECT: higher efficiency of use. 2 tbl, 3 ex

Description

 The invention relates to the field of chemical deposition of cobalt coatings on metal and ceramic surfaces. The use of the invention allows the application of cobalt pure coatings on parts of complex profile, including in the pores of ceramic materials, which opens up additional possibilities for its application in various fields of technology.

Known cobalt methods based on the decomposition of volatile chemical compounds. So, to obtain a cobalt coating using octacarbonyl cobalt, which decomposes at a temperature of 180-220 ^o [Syrkin V.G. Carbonyl metals. M.: Chemistry. 1978. 256 p.]. However, the use of organometallic compounds is limited by the high toxicity of the starting compounds, the need for heat treatment of the substrate, and the formation of cobalt carbide impurities in the surface layer. The disadvantage of such processes is the high reaction temperature.

Known compositions for producing cobalt coating in processes based on the reaction of reduction of cobalt ions in an aqueous solution to a metal using a reducing agent - sodium hypophosphite [Physicochemical basis of the chemical cobaltization process. Ed. Gorbunova K.M. M .: Science. 1974. 219 p.]. The disadvantages of these reactions are that the reaction mixture is unstable, and a noticeable (10 mg Co / 10 cm ² • 10 min) formation of a metal coating occurs only when heated to 90 ^o C. Another disadvantage of such methods is the high phosphorus content (3- 10%) in a cobalt coating in the form of CoP, Co ₂ P and CoP ₃ , which is acceptable only for obtaining magnetic coatings.

процесс необходимо проводить при нагревании не менее чем до 60^oС и обязательно после предварительной активации изделия раствором хлорида палладия. Вторым недостатком является образование в кобальтовом покрытии 0,3-5% бора в виде борида кобальта, что значительно ограничивает использование полученного таким образом покрытия.Closest to the proposed invention in technical essence is a solution containing 0.3-5.0 g / l of cobalt salt (in terms of metal), 0.04-1.2 g / l of hydrazinborane, 0.2-20 g / l of hydrazine and 0.1-1.0 g / l of gluconic acid or its salt (in terms of acid) [and.with. USSR 435305, Bull. 31, 1977] (prototype). Precipitation of cobalt from a solution containing a cobalt salt is carried out with a mixture of hydrazinborane and hydrazine in the presence of gluconic acid or its salt. The disadvantage of the prototype is that to obtain such a coating composition with a thickness of more

the process must be carried out when heated to at least 60 ^o C and always after pre-activation of the product with a solution of palladium chloride. The second disadvantage is the formation in the cobalt coating of 0.3-5% boron in the form of cobalt boride, which significantly limits the use of the coating thus obtained.

 The objective of the invention is to obtain pure cobalt on the surface of the ceramic substrate, since only in this case catalytically active cobalt is formed.

 The technical result of the invention is to obtain a cobalt coating on a ceramic substrate without prior activation by platinum metals and not containing impurities of boron or phosphorus.

This goal is achieved by the fact that the proposed composition for the chemical deposition of cobalt, including cobalt salt, characterized in that it further comprises hydrazine hydrate, thiourea and aqueous ammonia in the following ratios of components, g / l:
Cobalt salt (in terms of metal) - 1.8-4.7
Hydrazine Hydrate - 3-40
Thiourea - 0.2-2
Ammonia water - The rest
The cobaltation of the claimed solution is carried out as follows: a weighed portion of cobalt salt is dissolved in water, after which hydrazine and 25% aqueous ammonia are added. The workpiece is immersed at room temperature in this solution and thiourea is added, after which the cobalt process immediately begins, the speed of which is ~ 0.5 g / l • h. The selection of the components of the composition allows efficiently and with high speed to carry out the deposition of cobalt and to obtain a coating that does not contain impurities, since reagents that do not contain phosphorus and boron are used to reduce Co (II) ions.

и более в керамической подложке. Судя по данным ЯМР и ЭПР, воздух, находящийся в порах керамики, окисляет гидразин до перекиси водорода, что в свою очередь приводит к синтезу в порах керамики диоксидтиомочевины (ДОТМ) в результате взаимодействия Н₂О₂ с тиомочевиной. Сильное восстановительное действие образующегося ДОТМ еще больше усиливается высоким значением рН (~11) в присутствии гидразина, что позволяет восстанавливать ионы кобальта(II) на поверхности и в порах образца без предварительной активации соединениями платиновых металлов.An important advantage of the claimed composition is that without prior activation of the substrate with platinum metal compounds, pores with a diameter of 40 are filled with cobalt metal

and more in a ceramic substrate. Judging by the NMR and EPR data, the air in the ceramic pores oxidizes hydrazine to hydrogen peroxide, which in turn leads to the synthesis of dioxi thiourea (DOTM) in the pores of the ceramic as a result of the interaction of H ₂ O ₂ with thiourea. The strong reducing effect of the resulting DOTM is further enhanced by a high pH (~ 11) in the presence of hydrazine, which allows the reduction of cobalt (II) ions on the surface and in the pores of the sample without prior activation by platinum metal compounds.

 It should be noted that the direct reduction of cobalt ions by dioxythiourea does not lead to complete cobaltation of the ceramics, since In this case, cobalt metal deposits only on the surface and does not enter the pores of ceramics, which is fundamentally important in the preparation of catalysts.

The increased content of hydrazine hydrate compared with the prototype due to the need to obtain DOTM. The choice of thiourea concentration is explained by the fact that when the content is less than 0.2 g / l, cobalt precipitation does not occur, and with an increase in the concentration of more than 2 g / l, in addition to the deposition of metallic cobalt, cobalt sulfate is also formed. So, in the case of a thiourea content of 3 g / l, judging by the data of X-ray electron spectroscopy, the cobalt coating contains 25% CoSO ₄ .

The dependence of the Co (II) reduction rate on the content of aqueous ammonia and hydrazine in the solution is given in Table 1. In the case of excess hydrazine, a decrease in the Co (II) ion reduction rate is observed due to the strong polarization of the ceramic surface by the hydrazine decomposition products. The concentration of ammonia in the solution is also important. So, with a decrease in the relative concentration of ammonia (at pH <11), the formation of Co (OH) 2 resistant to reduction occurs, and with an increase in the concentration of ammonia (at pH ≥ 13), a stable ion forms in the solution [Co (NH ₃ ) ₆ ] ²⁺ .

 The following are examples of the proposed composition for the chemical deposition of cobalt.

 Example 1

Cobalt (II) chloride six-water (in terms of metal) - 3.5 g / l
Hydrazine hydrate - 30 g / l
Thiourea - 1 g / l
Ammonia water - 360 g / l
Cobaltation is carried out as follows. Ceramic samples from γ-AlO ₃ are immersed in an aqueous ammonia solution containing cobalt salt and hydrazine. Then thiourea is added. The process takes 2 hours at a temperature of 10-30 ^o C. Formed coating with a thickness of 14-15 microns with optimal filling of pores. Data on the metallization rate are given in table. 2.

 Example 2

Cobalt (II) chloride, six-water - 4.7 g / l (in terms of metal)
Hydrazine hydrate - 40 g / l
Thiourea - 2 g / l
Water ammonia - 420 g / l
Cobaltation is carried out as in example 1. Get a coating thickness of 12-13 microns.

 Example 3

Cobalt (II) chloride, six-water - 1.8 g / l (in terms of metal)
Hydrazine hydrate - 3 g / l
Thiourea - 0.2 g / l
Ammonia water - 36 g / l
Cobaltation is carried out as in example 1. Get a coating thickness of 3-4 microns.

Claims (1)

Composition for the chemical deposition of cobalt, including cobalt salt, characterized in that it further comprises hydrazine hydrate, thiourea and aqueous ammonia in the following ratio, g / l:
Cobalt salt (in terms of metal) - 1.8 - 4.7
Hydrazine Hydrate - 3 - 40
Thiourea - 0.2 - 2
Ammonia water 25% - The rest

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