SU1171571A1 - Method of anodizing zirconium - Google Patents

Abstract

1. METHOD OF ANODIZING ZIRCONY, including processing in an acidic electrolyte with additives of hydrofluoric acid or its salts, characterized in that, in order to increase the service life of the electrolyte, anodization is carried out using niobium cathodes, on which an anodic barrier film is preliminarily formed a voltage of 60-100 V. 2. The method according to claim 1, about tl and h ayush and the fact that the process of anodizing zirconium is interrupted every 24-36 hours, niobium cathodes are removed from the solution, washed in water, (A reformed on shh anode ba core film, in water and then used for anodizing zirconia.

Description

U1 11 The invention relates to the electrochemical oxidation of valve metals, in particular zirconium, and can be used to form thick anodic oxides on zirconium. The purpose of the invention is to increase the service life of the electrolyte. An increase in the service life of the electrolyte is achieved by conducting anodization using niobium cathodes with a preformed anodic barrier film. Pr and measures. A 100 L bath with a total loading area of 0.25 m is used to anodize zirconium. The ratio of the anode surface to the cathode is 1: 4. The pre-oxidation of the niobium cathodes in order to form barrier films on them is produced in a special bath of the same volume. The bath is filled with a 0.05% sodium sulfate solution. The niobium cathodes in this bath act as anodes. The anode film is formed by direct current at a voltage of 80 V and. temperature of 20 ° C for 15 minutes Under these conditions, niobium forms a barrier layer with a thickness of 1700 A. The oxidized niobium is removed from the solution, washed in water, and placed in an anodizing bath of zirconium. Zirconia parts are hung in the bath, which serve as anodes in the process of zirconium anodizing. A constant voltage of 120 V is applied between the electrodes and an electric current is passed for 60 minutes. The process of anodizing zirconium is carried out at 20 ° C. Under such conditions, a layer of porous anodic oxide with a thickness of 40 microns is formed on the zirconium in a specified time. Anodized zirconia parts are removed from the bath and new zirconia, etc. parts are hung in it. After 30 hours of operation, the zirconium anodizing baths interrupt the anodization process, remove their niobium cathodes from their baths, and replace them with new niobium cathodes, on which the barrier oxide layer is preliminarily formed. After another 30 hours, the anodization process is again interrupted, the cathodes are replaced, and so on. In this electrolyte to anodize zirconium at 20 ° C, the corrosion rate of oxidized niobium is 10; therefore, over a year of operation of a solution of 100 liters, 0.5 g of niobium passes into it, i.e. an amount that does not affect the anodizing of zirconium at all. To implement the proposed method, it is not necessary to replace the worked niobium cathodes with new ones after every 30 hours of anodizing. Instead, the spent cathodes can be washed in water, re-installed in the niobium oxidation bath, and the barrier oxide can be reduced on niobium using the same procedure as the initial formation of barrier oxide on niobium. The mode of anodizing described in the example is not the only one for the implementation of the proposed method. High-quality anodizing of zirconium can be carried out in the range of electrolyte temperatures of 15–40 ° C when the concentration of ammonium hydrofluoride varies within 1-2 g / l, in the range of voltages applied between the cathode and the anode, 60-120 V. At the same time anodizing of zirconium and the thickness of the anode film on it. In tab. 1 shows examples of the use of various modes of anodizing. The initial formation of barrier oxide on niobium and its reduction on spent cathodes can be performed in the voltage range of 60–100 V at 15–30 s for 50–60 min in a solution that is non-aggressive to niobium and its oxide, for example, in solutions of sulfuric, oxalic or orthophosphoric acids, as well as in solutions of potassium, sodium and ammonium salts at their concentrations of 0.05-3%. In this case, a change in the thickness of the barrier oxide, and, consequently, of the time during which anodizing of zirconium without a stone of the cathodes can take place, occurs. In tab. 2 shows examples of practical implementation of solutions and modes of oxidation of niobium.

3

The time of one cycle of operation of the cathodes of niobium in Table. 2 corresponds to an ammonium hydrofluoride concentration of 2 g / l in the solution for thick-layer anodizing of zirconium and is 24-36 h (depending on the electrolyte selected, temperature, terminal voltage, and oxidation time). The main factor determining the time of a single cycle of cathode operation is the terminal voltage. The oxidation of niobium is impractical to carry out the above mentioned in table. 2 ranges of forming stresses and forming time. Oxidation of niobium for more than 60 minutes is impractical, since after 60 minutes the further passage of current through the electrolyte does not practically change the corrosion-chemical properties of the barrier film on this metal. When oxidizing less than 5 minutes, the film thickness is insufficient, due to which the film does not possess the necessary corrosion resistance. Oxydio715714

When forming voltage above 100 V, a niobium bath begins to cause electrical breakdowns and, consequently, deterioration of the properties of 5 films, and forming voltages below 60 V lead to the formation of a film with a thickness of less than 1200 A, which causes a sharp decrease in of the service life of the barrier film on niobium in the solution for anodizing zirconium

The proposed method provides high-quality anodizing of zirconium and long-term operation of the solution for any areas of the parts to be coated and any sizes of baths.

The elimination of lead from the zirconium anodization process significantly improves the hygienic conditions of operating the anodizing solution, since the latter is not contaminated with lead compounds. Lead compounds and waste water will also not be polluted when the working solutions change periodically.

Table 1

table 2

Claims (2)

1. METHOD FOR ZIRCONIUM ANODIZING, including treatment in an acidic electrolyte with the addition of hydrofluoric acid or its salts, characterized in that, in order to increase the life of the electrolyte, the anodization is carried out using niobium cathodes on which an anode barrier film is preliminarily formed at a voltage of 60 -100 V. 2. The method according to claim 1, characterized in that the zirconium anodization process is interrupted every 24-36 hours, the niobium cathodes are removed from the solution, washed in water, re-formed an anode barrier film on them, passed through water and then used for anodizing zirconium. SU „„ 1171571