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Catalytic coating and method of manufacturing thereof

a catalytic coating and catalytic technology, applied in the field of catalytic coating, can solve the problems of limited resistance to such penalties, and achieve the effects of reducing the overvoltage of the coating towards anodic chlorine evolution, increasing the resistance to chloride attack, and increasing the stability of the coating to acid attack

Inactive Publication Date: 2017-07-13
IND DE NORA SPA
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention relates to a coating for valve metal surfaces that includes a titanium-free catalytic layer. The coating is made by applying a mixture of tantalum and ruthenium compounds in a solution, followed by thermal decomposition. The resulting coating is more resistant to chloride attack and has a better stability in acidic solution compared to coatings without tantanium. The coating also exhibits a reduced overvoltage for anodic chlorine evolution. The ratio of ruthenium oxide to tantalum oxide in the coating is important for its stability and function. The coating can be applied in one or two layers, with the second layer containing a higher amount of ruthenium oxide. The coating can also be combined with a protective pre-layer to improve its anchoring to the substrate. The method for manufacturing the coating involves applying a solution of tantalum and ruthenium compounds, followed by thermal decomposition. The resulting coating has been found to be effective in various applications such as catalytic activation of anodic structures.

Problems solved by technology

The magnitude of such resistive penalty can be however very limited, provided the pre-layer has a suitably limited thickness.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 2

[0020]The electrode samples shown in the table were subjected to a test of standard potential under anodic evolution of chlorine at the current density of 3 kA / m2, in 15% wt. HCl at a temperature of 60° C. The potential data obtained are reported in Table 3 (SEP). The table shows also the related data of an accelerated lifetime test, expressed in terms of hours of operation before deactivation under anodic evolution of chlorine at the current density of 6 kA / m2, in 20% wt. HCl at a temperature of 60° C., using a zirconium cathode as counterelectrode. The deactivation of the electrode is defined by a 1 V increase in the cell with respect to the initial value.

TABLE 3# SampleSEP (V)Lifetime (hours)11.175402021.168488031.160470041.170577051.173506061.166598071.161455081.154452091.161569010 1.1585540C11.1903660C21.1833900C31.1833280

example 3

[0021]Duplicates of electrode samples 2, 6 and C2 were subjected to a corrosion test which simulates the crevice corrosion conditions that can occur on the flanges of electrolysers for the production of chlorine or other occluded zones. A first series of samples was immersed in a known volume of 20% wt. HCl at 45° C. under nitrogen stream, to simulate electrolyte stagnation conditions; a second (control) series was immersed in the same volume of 20% wt. HCl at 40° C. under a stream of oxygen, in order to maintain passivation. In both cases, the concentration of chromium and nickel released from the substrate in the course of 24 hours was detected: for samples 2 and 6, the concentration of both metals in the volume of HCl was less than 2 mg / l, while sample C2 showed concentrations slightly higher than 2 mg / l of Cr and 4 mg / l of Ni under a stream of oxygen, which increased significantly under a stream of nitrogen (up to 6.5 mg / l for nickel).

[0022]The test was repeated with another set...

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PUM

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Abstract

The invention relates to a catalytic coating of surfaces of valve metals, for example titanium, suitable for operation in highly aggressive electrolytic environments such as electrolysis cells of hydrochloric acid. The coating may be used as catalytic activation of electrodes, for example for anodic evolution of chlorine, or for protection from crevice corrosion of flanges and other elements of electrolysers subject to stagnation of liquid.

Description

FIELD OF THE INVENTION[0001]The invention relates to a catalytic coating of valve metal articles suitable for use in highly aggressive electrolytic environments, for example in hydrochloric acid electrolysis cells.BACKGROUND OF THE INVENTION[0002]Hydrochloric acid electrolysis is an electrochemical process gaining increasing interest at present, being hydrochloric acid the typical by-product of all major industrial processes making use of chlorine: the increase in the production capacity of plants of new conception entails the formation of significant amounts of acid, whose placement on the market presents significant difficulties. The electrolysis of the acid, typically carried out in two-compartment electrolytic cells separated by an ion-exchange membrane, leads to the formation of chlorine at the anode compartment, which can be recycled upstream resulting in a substantially closed cycle of negligible environmental impact. The construction materials of the anodic compartment must ...

Claims

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Application Information

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IPC IPC(8): C25B11/04C25B1/26
CPCC25B1/26C25B11/0484C25B11/093C25B11/04
Inventor BONOMETTI, VALENTINACALDERARA, ALICE
Owner IND DE NORA SPA