RU2640895C1 - Method for forming structured surface on aluminium and its alloys - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention can be used to create coatings with multimodal roughness on the surface of aluminium and its alloys, which, in the subsequent application of the hydrophobizing agent, impart to the parts hydrophobic properties. Method involves washing parts, processing them in a solution of lye, subsequent washing parts, their drying and anodizing at room temperature, wherein anodizing is carried out in a 10 m aqueous solution of nitric acid with a current density of 10-100 Ma/cmfor 5-10 min, and then washing of parts and their drying are performed.EFFECT: creation of a coating with micro- and nanoscale roughness, which can serve as a sublayer to create a hydrophobic surface, the proposed electrochemical treatment does not require complex equipment, large energy inputs, and is performed in a short time.3 dwg, 1 tbl, 2 ex

Description

The invention relates to the electrochemical processing of aluminum and its alloys to impart a multimodal surface roughness, which can serve as the basis for increasing the hydrophobicity of products and reducing their icing at low temperatures.

It is known that the superhydrophobic state of a surface can be achieved on rough surfaces with low surface energy, on which a heterogeneous wetting regime is realized [1]. Using various methods of surface structuring using substances that reduce surface energy, it is possible to increase the contact wetting angle to 150-160 °, reaching a state of superhydrophobicity. It is known that on hydrophobic (superhydrophobic) coatings, the icing conditions differ significantly from the icing conditions on smooth surfaces — the temperature decreases and the ice formation time increases [2]. Thus, an increased surface roughness is a prerequisite for reducing icing of products operated at low temperatures and high humidity.

It is known that the structuring of the surface of aluminum can be performed by chemical, mechanical or electrochemical methods [3, 4, 5].

In the known method proposed in [3], etchants are used based on concentrated acids - hydrochloric, hydrofluoric. When treating the surface of aluminum and its alloys with the proposed method, the samples are immersed in a mixture of concentrated acids, while the surface is etched by metal dislocations and the surface acquires an inhomogeneous roughness. The method requires the use of special protective equipment. The method is environmentally hazardous, because It uses concentrated acids.

A known method of preparing the surface of aluminum, including sandblasting the surface of the metal [4]. The metal is processed by sand particles with a size of 50-180 microns, which requires the use of special equipment, the use of sufficiently large capacities. In addition, machining ensures that only microinhomogeneities are created on the aluminum surface, and an additional procedure is required to form the nanoscale roughness component.

A known method of forming a hydrophobic surface on an aluminum alloy by anodizing a metal in phosphoric acid solutions followed by modification with organic substances, such as lauric or stearic acids [5]. To create such a surface, two-stage anodizing is carried out with intermediate removal of the primary porous oxide. Anodizing is carried out at high voltages for a long time; the pore broadening procedure is additionally performed. The method is quite time-consuming and energy-intensive.

Closest to the proposed method for creating a structured surface on aluminum and its alloys is the method of anodizing in acid solutions, which is adopted as a prototype. In this method, porous alumina is formed on the metal surface, the characteristics of which (thickness, diameter and wall thickness of the pores) are determined by the process parameters (chemical composition and temperature of the electrolyte, current density, voltage and anodization time) [6]. The pore diameter of the oxide varies between 20-200 nm, the thickness of the oxide is up to 100 μm, creating a bimodal roughness on the surface of parts made of aluminum and its alloys. Before anodizing, aluminum parts are washed, treated in alkali solutions and heat treated. After a long (up to 5 hours) anodizing, the procedure for broadening the pores of the oxide is carried out.

However, this method of obtaining a structured surface of the parts is quite complex, lengthy and energy-intensive.

The technical result of the proposed technical solution is that it provides the creation of a coating with multimodal (micro- and nanoscale) roughness, which can serve as a sublayer for the formation of a hydrophobic (superhydrophobic) surface. This will reduce the icing of aluminum products and its alloys during their operation at low temperatures.

The technical result is achieved by the fact that parts of aluminum or its alloys are washed, treated in an alkali solution, then washed again, dried and anodized at room temperature in a 10M nitric acid solution at a current density of 10-100 mA / cm ² for 5-10 minutes then washed and dried.

The method includes surface preparation (washing, treatment in an alkali solution, followed by washing and drying) and anodizing in a 10M aqueous solution of nitric acid in the galvanostatic mode at a current density of 10-100 mA / cm ² at room temperature for 5-10 minutes. Then the parts are washed and dried.

As a result of this treatment, an aluminum oxide coating with a roughness of both micro- and nanoscale levels is created on the surface of aluminum or its alloy.

The proposed technical solution is illustrated by an example.

Example 1. Samples of flat aluminum sheet were washed in a solution of sodium bicarbonate, washed in distilled water, treated in a 3% NaOH solution at 50 ° C for 30 s, washed in distilled water and anodized at a current density of 10 mA / cm ² and 50 mA / cm ² for 10 min, at a current density of 100 mA / cm ² for 5 min. Then the samples were washed in distilled water and dried. In FIG. Figure 1 shows the surface images of anodized samples obtained using a digital optical microscope and their surface profiles: a - current density 100 mA / cm ² , b - 50 mA / cm ² , c - 10 mA / cm ² . The roughness parameters of the coatings were evaluated using the ScanMaster program. The results are shown in the table.

From the obtained images and roughness parameters presented in the table, it can be seen that with increasing anodizing current density, the roughness parameters are R _max is the maximum height of the profile, R _g is the square root of the mean square deviation of the point from the profile, R _z is the height of the profile irregularities in ten points, R _a is the arithmetic mean deviation of the profile — for oxides formed at a current density of 100 mA / cm ^{2 is} noticeably higher than for oxides obtained at lower currents.

In FIG. Figure 2 shows a photograph of the surface of aluminum anodized at a current density of 100 mA / cm ² , obtained using a SolverNexT atomic force microscope. The image shows both microinhomogeneities and oxide pores of 50-100 nm in size.

Example 2. On the surface of samples prepared similarly to Example 1, a thin layer of hydrophobic liquid (fluorocarbon resin) was applied. In FIG. Figure 3 shows snapshots of 5 μl distilled water droplets deposited on treated surfaces. The contact wetting angle on all samples exceeds 90 °, which indicates that the surfaces exhibit hydrophobic properties. The wetting angle depends on the anodization mode and increases with increasing anodization current density. The contact angle of wetting of the surface of the oxide formed at 100 mA / cm ² is ~ 149 °, which is comparable with the contact angle of contact of superhydrophobic coatings.

Thus, the structuring of the surface of aluminum and its alloys by the proposed method makes it quite simple to form a coating with multimodal roughness on the surface, which, after applying a thin layer of a hydrophobic agent to it, acquires hydrophobic properties, which allows to reduce the possible icing of products at low temperatures.

Information sources

1. Boynovich LB, Emelianenko A.M. Hydrophobic materials and coatings: principles of creation, properties and application // Advances in Chemistry. 2008, t. 77, p. 619-638.

2. G. Momen, M. Farzaneh and J.M. Asselin. Wettability behavior of superhydrofobic silicone rubber coatings at supercooled temperatures. The 14th International Workshop on Atmospheric Icing of Structures, Chongqing, China, May 8 - May 13, 2011.

3. Qian, W.T .; Shen, Z.Q. Fabrication of superhydrophobic surfaces by dislocation-selective chemical etching on aluminum, copper, and zinc substrates. Langmuir 2005, 21, 9007-9009.

4. US application 2010/0028615. laid out. 02/04/2010. A method of manufacturing a superhydrophobic surface and a solid with a superhydrophobic surface obtained by this method.

5. Cui Guo, Xue-wei Wang, Zhi-hao Yuan. Pore diameter-dependence wettability of porous anodized aluminum oxide membranes. J. Porous Mater (2013) 20: 673-677 DOI 10.1007 / s 10934-012-9641-7.

Claims (1)

A method of forming a structured surface of aluminum and its alloys with multimodal roughness, including washing the parts, processing them in an alkali solution, subsequent washing of the parts, drying and anodizing them at room temperature, characterized in that the anodizing is carried out in a 10 M aqueous solution of nitric acid at a current density of 10 -100 mA / cm ² for 5-10 minutes, after which the parts are washed and dried.

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