RU2723629C1 - Method of producing anode films of zinc oxide - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to a method of producing anode films of zinc oxide, involving electrochemical oxidation of zinc metal in an aqueous solution of alkali metal salts. Method is characterized by that electrochemical oxidation is carried out in aqueous solution of potassium chloride 0.1 M in potentiostatic mode at temperature 25 °C and oxidation voltage 7.5 V.

EFFECT: obtaining a film of zinc oxide with high specific surface area.

1 cl, 2 dwg, 1 tbl, 3 ex

Description

The invention relates to an electrochemical method for producing zinc oxide films, which can be used to create film transistors, solid-state lasers, backup chemical current sources, catalysts, and spin electronics devices. It can also be used as a coating for anticorrosive protection of equipment.

A known method for producing a single crystal film of zinc oxide (RU No. 2036218, IPC C09K 11/54, published May 27, 1995), comprising treating zinc oxide powder with hydrogen containing water vapor, depositing a film of zinc oxide on a substrate with a temperature gradient between the powder processing zone and the substrate cooling the substrate, characterized in that in order to improve the luminescent characteristics of the film, the substrate is heated to 890-1000 K after deposition of the film, kept at this temperature for 2 minutes, and cooling is carried out in an inert gas atmosphere.

Common features of the proposed method with an analogue are that the process of forming an oxide film proceeds under standard conditions (t = 25 ° C).

The disadvantages of the analogue are that, firstly, to improve the luminescent characteristics of the film, it is necessary to heat it to 617–727 ° C, and secondly, the thickness of the zinc oxide layer is too large (0.3-3 mm) for the previously described applied tasks.

A known method of producing a thin piezoelectric film of zinc oxide (SU No. 1812242, IPC С23С14 / 46, published on 04/30/1993). According to this method, a thin piezoelectric film of zinc oxide is produced by magnetron reactive sputtering of a film of zinc oxide on a dielectric substrate previously subjected to ion processing. The method can be used in the manufacture of acoustoelectronic devices operating in the microwave range.

A common feature of the proposed method with an analogue is that the process of forming an oxide film proceeds under standard conditions (t = 25 ° C).

The disadvantage of this method is that when using surfaces of freshly sprayed dielectric films, the effect is observed only on that part of the layered structure, which grew on the ion-treated part of the surface of the freshly sprayed film. The substrate, before sputtering, is pre-treated with inert gas ions with an energy of at least 300 eV. The film thickness applied to the substrate is less than 1 μm.

Known methods for producing zinc oxide powder by oxidation by heating zinc-containing raw materials (5-40 wt.% Zn) with air (RU No. 2077158, IPC C01G 9/02, published 04/10/1997) and zinc metal with oxygen (RU No. 2450972, IPC C01G 9 / 02, published on 05/20/2012).

A common feature of the proposed method with an analogue is that during their implementation, the formation of zinc oxide occurs on metal zinc.

The disadvantages of these methods are the use of high temperatures - 1300-1400 ° C and 850 ° C, respectively, the existing possibility of local overheating of the reaction mixture and, as a consequence, the destruction of the walls of the reactor, as well as the inability to use them to obtain films of zinc oxide.

Closest to the proposed invention, in technical essence and the achieved result, adopted as a prototype, is a method for producing zinc oxide (RU No. 2221748, IPC C01G 9/02, published January 20, 2004), including oxidation of metallic zinc and heat treatment, characterized in that carry out the electrochemical oxidation of metallic zinc in an aqueous solution of sodium chloride with a concentration of 2-5 mass. % at an alternating sinusoidal current density of industrial frequency 1.0-2.0 A / cm ² and a temperature of 50-90 ° C, heat treatment is carried out at 105-400 ° C.

The disadvantage of this method is the high cost of electricity for the oxidation of zinc metal and the impossibility of its use to obtain films of zinc oxide.

The task of the invention is the development of the most energy-efficient and simple in hardware execution method for producing zinc oxide with a high specific surface area.

The technical result of the claimed invention is to obtain a zinc oxide film with a high specific surface area.

The specified technical result is achieved in that the method of producing anode films of zinc oxide, including the electrochemical oxidation of metallic zinc in an aqueous solution of alkali metals, characterized in that the electrochemical oxidation is carried out in an aqueous solution of potassium chloride 0.1 M in a potentiostatic mode, at a temperature of 25 ° C and a voltage of 7.5 V, a zinc electrode obtained by melting granular zinc (99.99%) for 30 minutes in a furnace at a temperature of 450 ° C is used as an anode, and a platinum electrode is used as a cathode.

5 компании Struers. Завершающим этапом подготовки полученных цинковых электродов стала их шлифовка и полировка с использованием шлифовально

полировального станка Tegramin

25 компании Struers при скорости вращения 200

300 об/мин дисков различной зернистости (SiC, алмаз). Zinc electrodes were made of granulated zinc of the “chemically pure” qualification, which were melted in a furnace in refractory crucibles closed with lids at a temperature of 450 ° C for 10-15 minutes, and the molten zinc was cast into molds. After cooling the molds, the zinc ingots were removed, hardened and cut in the form of identical parallelepipeds on a Labotom manual cutting machine

5 Struers. The final step in the preparation of the obtained zinc electrodes was their grinding and polishing using grinding

polishing machine tegramin

25 Struers at 200

300 rpm of discs of different grain sizes (SiC, diamond).

Anodic oxide films of zinc oxide in an aqueous KCl solution (0.1 M, 0.5 M and 1 M) were obtained by the electrochemical oxidation of metallic zinc. A zinc electrode was used as an anode, and a platinum plate was used as a cathode. The effect of the concentrations of KCl solutions and the voltage applied to the electrochemical cell on the morphology of the anode ZnO films and their thermodynamic stability is studied. Analysis of current-voltage curves with a linear potential sweep and chronoamperometric dependences showed that oxidation in a 0.1 M KCl solution at a voltage of 7.5 V allows one to obtain continuous stable defect-free ZnO films on metal zinc.

The claimed invention is illustrated by examples.

Example 1

To determine the influence of the conditions of electrochemical synthesis of zinc oxide in a KCl solution (0.1 M) on the morphology and stability of the anode films, chronoamperometric dependences (i – τ) were obtained at a voltage of 7.5 V (Fig. 1), as well as current – voltage curves (i – U) in the range of potential from -2 to 10 V (FIG. 2). An analysis of current – voltage curves with a linear potential sweep and chronoamperometric dependences showed that oxidation in a 0.1 M KCl solution allows one to obtain a continuous anode film on metal zinc with minimal surface defects. At an oxidation voltage of 7.5 V, the most gentle and smooth course of the i – τ curve was observed, which is associated with the appearance of a continuous thick and stable film. The sample placed in the electrolyte at 7.5 V had the maximum yield of the product - zinc oxide ZnO, which is associated with a longer time before passivation and a not very aggressive environment.

Example 2

The dependences of the i – τ of the zinc anode in a KCl solution (0.1 M) at oxidation voltages of 5 V and 10 V are shown in FIG. 1. In the chronoamperometric dependence at 5 V, a maximum is observed at the time instant τ _max = 13 min, which indicates the formation of a continuous film on the surface of the anode. The type of dependence in the entire time range is smooth, without obvious kinks before and after the maximum. A shorter course of the i – τ curve compared to the similar curve obtained at 7.5 V indicates a lower stability of the formed oxide film in the electrolyte, which in turn negatively affects the morphology of the film.

When the voltage increases to 10 V, the electrolyte exhibits more aggressive properties, which is reflected in the receipt of a defective oxide film on the surface of zinc.

Example 3

The voltage of 7.5 V had the best effect on the surface morphology of the ZnO zinc oxide film. In KCl solutions, 0.1 M and 0.5 M zinc oxide films were obtained practically without defects. Given that the preparation of a 0.1 M electrolyte solution requires a lower consumption of KCl, it should be concluded that the formation of a continuous stable defect-free film takes place in a 0.1 M KCl solution in a potentiostatic mode at a voltage of 7.5 V.

Table 1 shows the effect of the concentration of electrolyte (potassium chloride) and oxidation voltage on the quality of the resulting zinc oxide film.

Table 1 - Effect of electrolyte concentration and oxidation voltage on the quality of the resulting zinc oxide film

Electrolyte Concentration, M Oxidation voltage, V 5 v 7.5 V 10 V 0.1 M KCl - A continuous film is formed with minor defects. - Formed continuous high-quality stable film of zinc oxide without defects - A continuous film is formed with minor defects. 0.5 M KCl - A continuous film is formed with minor defects. - A continuous, stable, defect-free zinc oxide film is formed. - An uneven, continuous film forms 1M KCl - An uneven non-continuous film forms - The formation of an uneven continuous film is expected with a longer experiment (τ ≥ 60 min) - Impossible to form a continuous film

An analysis of current – voltage curves with a linear potential sweep and chronoamperometric dependences showed that oxidation in a 0.1 M KCl solution allows one to obtain a continuous stable anode film on metal zinc with minimal surface defects. In this case, there is practically no process of dissolution of the obtained oxide film.

The above examples demonstrate that the oxidation voltage of 7.5 V has the best effect on the morphology of the film surface. In 0.1 M and 0.5 M KCl solutions, zinc oxide films were obtained with virtually no defects. Since a lower consumption of KCl is required to prepare a 0.1 M electrolyte solution, it should be concluded that the formation of a continuous stable defect-free zinc oxide film takes place in a 0.1 M KCl solution in the potentiostatic mode at a voltage of 7.5 V.

Claims (2)

1. The method of producing anode films of zinc oxide, including the electrochemical oxidation of zinc metal in an aqueous solution of alkali metal salts, characterized in that the electrochemical oxidation is carried out in an aqueous solution of potassium chloride 0.1 M in a potentiostatic mode at a temperature of 25 ° C and an oxidation voltage of 7, 5 V. 2. The method according to p. 1, characterized in that the anode uses a zinc electrode obtained by melting granular zinc (99.99%) for 30 minutes in an oven at a temperature of 450 ° C, and a platinum electrode is used as a cathode.

Images