阅读说明：本技术 一种用于高温表面液滴定向输运的脊阵列结构及其制备方法 (Ridge array structure for directional transportation of liquid drops on high-temperature surface and preparation method thereof ) 是由 刘亚华 王国洪 刘聪 孙宽 冯诗乐 于 2020-05-12 设计创作，主要内容包括：一种用于高温表面液滴定向输运的脊阵列结构及其制备方法,属于金属基材表面处理技术领域。包括：选用基材,对基材进行研磨抛光预处理；采用线切割精加工技术在基材表面加工一级微米级斜脊阵列结构；利用湿法刻蚀在一级微米级斜脊阵列结构表面制备二级微纳米球颗粒结构。该微斜脊阵列结构表面为非对称表面,液滴撞击在高温表面上时,其底部产生沿斜脊间槽方向向下流动的气流,驱动液滴沿微脊倾斜的反方向定向运动,与常温浸润性梯度表面液滴定向运输效果相比,高温微斜脊结构表面上液滴定向运动的速度更快；且采用室温下在通用性不锈钢基材上加工微斜脊阵列结构的方法实现,制备方法简单、易于操作、效率高、成本低、可用于大规模生产。(A ridge array structure for directional transportation of liquid drops on a high-temperature surface and a preparation method thereof belong to the technical field of surface treatment of metal substrates. The method comprises the following steps: selecting a base material, and carrying out grinding and polishing pretreatment on the base material; processing a primary micron-grade oblique ridge array structure on the surface of the base material by adopting a linear cutting finish machining technology; and preparing a secondary micro-nano spherical particle structure on the surface of the primary micron-sized oblique ridge array structure by wet etching. The surface of the micro-oblique ridge array structure is an asymmetric surface, when liquid drops impact on a high-temperature surface, airflow flowing downwards along the direction of grooves between oblique ridges is generated at the bottom of the micro-oblique ridge array structure, the liquid drops are driven to directionally move along the oblique opposite direction of the micro-ridges, and compared with the directional transportation effect of the liquid drops on the normal-temperature wettability gradient surface, the directional movement speed of the liquid drops on the surface of the high-temperature micro-oblique ridge structure is higher; the method for processing the micro inclined ridge array structure on the general stainless steel substrate at room temperature is adopted, and the preparation method is simple, easy to operate, high in efficiency, low in cost and applicable to large-scale production.)

1. The ridge array structure for the directional transportation of liquid drops on the high-temperature surface is characterized in that the micro-oblique ridge structure comprises a primary micro-scale oblique ridge array structure and a secondary micro-nano-scale rough structure, the primary micro-scale oblique ridge array structure is processed on a metal substrate material, and the secondary micro-nano-scale rough structure is attached to the upper surface of the primary micro-scale oblique ridge array structure:

the metal substrate is made of stainless steel; the first-level micron-scale inclined ridge array structure is characterized in that the ridge width is 50-400 mu m, the ridge spacing is 100-800 mu m, the ridge height is 100-400 mu m, the ridge inclination angle is 15-60 degrees, and the ridge inclination angle is an included angle between the ridge inclination angle and a normal perpendicular to a processing surface; the secondary micro-nano coarse structure is spherical particles with the diameter of 0.1-5 mu m.

2. The method for preparing the ridge array structure for the directional transportation of the liquid drops on the high-temperature surface according to claim 1, which is characterized by comprising the following steps:

firstly, selecting stainless steel as a substrate material, and carrying out grinding and polishing pretreatment on the stainless steel substrate to ensure that the surface roughness range is 0.1-1 mu m;

secondly, processing a first-grade micron-grade oblique ridge array structure on the surface of the stainless steel substrate by adopting a linear cutting finish machining method; the wire cutting fine machining method is characterized in that the diameter of a wire cutting wire is 100 mu m, the feeding speed of the wire cutting wire is 1-20 mm/min, and the size machining precision is less than 0.015 mm;

and thirdly, placing the product prepared in the second step into a dilute hydrochloric acid solution, and preparing a secondary micro-nano spherical particle structure on the surface of the primary micron-sized inclined ridge array structure by wet etching.

3. The method for preparing the ridge array structure for the directional liquid drop transportation on the high-temperature surface as claimed in claim 2, wherein the types of the stainless steel substrate materials in the first step are 201, 202, 302, 304, 316 and 410.

4. The method for preparing the ridge array structure for the directional liquid drop transportation on the high-temperature surface according to claim 2, wherein the pretreatment of grinding and polishing the stainless steel substrate in the first step is to grind and polish a stainless steel sheet by using sandpaper with the granularity of 800 meshes, 1000 meshes and 1500 meshes, remove impurities and scratches on the surface, and polish the surface by using a polishing step.

5. The method for preparing the ridge array structure for the directional transportation of the liquid drops on the high-temperature surface according to claim 2, wherein the processing times in the wire-electrode cutting finishing method in the second step are 1-5 times of circulating filament walking.

6. The method for preparing the ridge array structure for the directional transportation of the liquid drops on the high-temperature surface according to claim 2, wherein in the wet etching method in the third step: the concentration of the dilute hydrochloric acid solution is 1-4 mol/L, and the soaking time is 1-5 min; and after soaking, ultrasonically cleaning the soaked materials by using acetone, absolute ethyl alcohol and deionized water in sequence, and finally drying the soaked materials by using nitrogen.

Technical Field

The invention belongs to the technical field of metal substrate surface treatment, and relates to a method for preparing a micro-oblique ridge structure which has a primary micro-scale oblique ridge array structure and a secondary micro-nano-scale rough structure and can be used for directional transportation of liquid drops on a high-temperature surface by a wire cutting finish machining technology and a wet etching technology.

Background

Spontaneous directional transport of liquid droplets is widely existed in natural systems and actual engineering in different forms on various scales, such as millisecond-level raindrops, micron-level morning dew, fog and the like, covers various environmental systems from dehumidification of water collected in arid desert to wet rainforests, micro-flow control in lab-on-a-chip to condensation heat exchange in energy and power systems, anti-icing on the surface of an airplane to interface drag reduction of oil and gas transportation and the like, and is a hot spot and frontier field of research of domestic and foreign scholars. The method for realizing spontaneous directional transportation of liquid drops in the current experimental research mainly breaks the symmetry of a solid/liquid interface three-phase contact line by designing an asymmetric surface structure and chemical composition and provides a non-mechanical directional driving force, thereby promoting the spontaneous directional transportation of micro liquid drops. However, the adhesion and friction of these surfaces can limit the speed and distance of droplet transport. In addition, most of the preparation methods require precise processing techniques, and the preparation process is complex and difficult to produce in large scale and with high precision.

In recent years, research on "Leidenfrost effect" has become a hot spot of domestic and foreign research. The liquid drop "Leidenfrost effect" is the phenomenon that when the liquid drop contacts the surface of a solid far higher than the boiling point of the liquid drop, a layer of vapor film is rapidly generated between the liquid drop and the solid due to solid-liquid heat exchange, so that the liquid drop is suspended above the vapor layer. Research shows that the droplet motion in the Leidenfrost state is not influenced by the interface adhesion force, so that the droplet motion in the Leidenfrost state has larger transport speed and distance, and the method provides inspiration for the design of a surface with a rapid long-range droplet directional transport function.

Disclosure of Invention

Aiming at the problems, the invention provides a method for preparing a micro-oblique ridge structure which has a first-level micro-scale oblique ridge array structure and a second-level micro-nano coarse structure and can be used for directional transportation of liquid drops on a high-temperature surface by a wire cutting finish machining technology and a wet etching technology. The surface of the micro-inclined ridge structure of the liquid drop is an asymmetric surface, when the liquid drop impacts on a high-temperature surface, the bottom of the liquid drop can generate an air flow flowing downwards along the direction of the grooves between the inclined ridges, the liquid drop is driven to directionally move along the inclined opposite direction of the micro-ridges, compared with the directional transportation effect of the liquid drop on the normal-temperature asymmetric surface, the directional movement speed of the liquid drop on the surface of the high-temperature micro-inclined ridge structure is higher, and the maximum horizontal average speed reaches 46 cm/s. In addition, the preparation method is simple, short in period, low in product cost, convenient to use and capable of realizing large-scale production.

The specific technical scheme of the invention is as follows:

a ridge array structure for directionally conveying liquid drops on a high-temperature surface comprises a primary micron-scale ridge array structure and a secondary micro-nano-scale rough structure, wherein the primary micron-scale ridge array structure is processed on a metal substrate material, and the secondary micro-nano-scale rough structure is attached to the upper surface of the primary micro-ridge array structure.

The metal substrate is made of stainless steel, and the types of the metal substrate are 201, 202, 302, 304, 316, 410 and the like. The first-level micron-grade oblique ridge array structure is characterized in that the ridge width is 50-400 mu m, the ridge spacing is 100-800 mu m, the ridge height is 100-400 mu m, and the ridge inclination angle (the included angle between the ridge inclination angle and the vertical normal of the processing surface) is 15-60 degrees. The secondary micro-nano coarse structure is spherical particles with the diameter of 0.1-5 mu m.

A preparation method of a ridge array structure for directional transportation of liquid drops on a high-temperature surface comprises the following steps:

firstly, selecting stainless steel as a substrate material, and carrying out grinding and polishing pretreatment on the stainless steel substrate;

the metal substrate is made of stainless steel, and the types of the metal substrate are 201, 202, 302, 304, 316, 410 and the like. The dimensions are 50mm by 20mm by 3 mm. The pretreatment of grinding and polishing the stainless steel substrate refers to grinding and polishing a stainless steel sheet by using sand paper with the granularity of 800 meshes, 1000 meshes and 1500 meshes, removing surface impurities and scratches, and then polishing and polishing the surface by using a polishing step, wherein the surface roughness range is 0.1-1 mu m.

Secondly, processing a first-grade micron-grade oblique ridge array structure on the surface of the stainless steel substrate by adopting a linear cutting finish machining technology;

the wire-electrode cutting finish machining technology is characterized in that a micro-oblique ridge array structure is machined on the surface of a base material by a wire-electrode cutting finish machining method, the diameter of a wire electrode of the wire electrode cutting is 100 micrometers, the machining frequency is 1-5 times of circulating wire feeding, the wire feeding speed is 1-20 mm/min, and the size machining precision is smaller than 0.015 mm.

And thirdly, preparing a secondary micro-nano spherical particle structure on the surface of the primary micron-sized oblique ridge array structure by wet etching.

The step of preparing the secondary micro-nano spherical particle structure on the surface of the primary micron-sized inclined ridge array structure by wet etching is to soak the primary micron-sized inclined ridge array structure for 1-5 min by using a dilute hydrochloric acid solution with the concentration of 1-4 mol/L, then ultrasonically clean the primary micron-sized inclined ridge array structure for 8-20 min by using acetone, absolute ethyl alcohol and deionized water in sequence, and blow-dry the primary micron-sized inclined ridge array structure by using nitrogen.

The invention has the advantages that:

(1) the invention combines the linear cutting fine machining technology and the wet etching technology to realize the preparation of the micro-oblique ridge structure which has a primary micro-scale oblique ridge array structure and a secondary micro-nano-scale rough structure and can be used for directional transportation of liquid drops on the high-temperature surface.

(2) The surface of the micro-oblique ridge array structure prepared by the invention is an asymmetric structure surface, when liquid drops impact on a high-temperature surface, the bottom of the liquid drops can generate airflow flowing downwards along the direction of the grooves between the oblique ridges to drive the liquid drops to directionally move along the oblique opposite direction of the micro ridges, compared with the normal-temperature wettability gradient surface liquid drop directional transportation effect, the speed of the directional movement of the liquid drops on the surface of the high-temperature micro-oblique ridge structure is higher, and the maximum horizontal average speed reaches 46 cm/s.

(3) The method is realized by adopting a method for processing the micro-oblique ridge array structure on the general stainless steel substrate at room temperature on the basis of a linear cutting finish machining technology, and has the advantages of simple preparation method, easy operation, high efficiency and low cost.

Drawings

FIG. 1 is a SEM image of a micro-oblique ridge array structure; wherein, FIG. 1(a) is a side view SEM image of a primary micro-oblique ridge array structure with 15 degree ridge inclination angle. FIG. 1(b) is a side SEM image of a primary micro-oblique ridge array structure with 60 degree ridge inclination angle. FIG. 1(c) is a top SEM image of a first-level micro-oblique ridge array structure with 15 degree ridge inclination angle. FIG. 1(d) SEM image of second-order micro-nano spherical particles.

FIG. 2 is a timing diagram of directional movement of a droplet with a diameter of 2.85mm on the surface of a micro-oblique ridge array when the temperature of the surface of a sample is 380 ℃; wherein, FIG. 2(a) is a timing chart of directional movement of a droplet with a diameter of 2.85mm on a surface of a micro-inclined ridge array with a ridge inclination angle of 15 degrees when the surface temperature of the sample is 380 ℃; FIG. 2(b) timing diagram of the directional movement of a droplet with a diameter of 2.85mm on the surface of a slightly inclined ridge array with a ridge inclination angle of 60 ℃ at a sample surface temperature of 380 ℃.

FIG. 3 is a horizontal maximum velocity average of droplets having a diameter of 2.85mm at a temperature of 350 to 480 ℃.

Detailed description of the preferred embodiments

The technical solution of the present invention will be further described in detail with reference to the following embodiments and the accompanying drawings.