CN101774528A - Cross-scale biomimetic micro-nano branch structure array and preparation method thereof - Google Patents

Abstract

The invention relates to the fields of micro-nano materials and robots, in particular to a bionic adhesive material and a preparation method thereof, and also to an electrochemical anodic oxidation technology. The cross-scale bionic micro-nano branch structure array is composed of a substrate and a micro-nano multi-level branch structure array, and the micro-nano multi-level branch structure at least includes an array of one-level micro-cylindrical structures and an array of branched micro-nano-cylindrical structures. The preparation method is to firstly use argon ion beam etching to obtain an aluminum template with a first-level micron hole array; then use electrochemical anodic oxidation to prepare a micro-nano branch structure array at a fixed point on the template array; and then use the polymer replica method In the template, a film is molded, solidified, and finally the template is removed for molding to obtain the required micro-nano structure array, which becomes a bionic dry adhesive material. The invention utilizes the characteristics of the electric field to effectively solve the controllable problem of the cross-scale branch structure array from micron to nanometer, and has great significance for the development of bionic adhesive materials and the development of related dry bionic robots.

Description

Array with cross-scale biomimetic micro-nano branch structure and preparation method thereof

Technical field:

The invention relates to the fields of micro-nano materials and robots, in particular to a bionic adhesive material and a preparation method thereof, and also to an electrochemical anodic oxidation technology.

Background technique:

The miraculous ability of geckos to climb walls has attracted people to imitate them for thousands of years. The wall-climbing behavior of geckos is different from that of other insects or animals, leaving no mucus or scratch marks on the surface they have climbed. The crawling adhesion method of gecko toes, which can quickly adhere and detach on surfaces with various roughnesses, is called dry adhesion by researchers. The micro-nano structure of gecko's toe bristles is the secret to achieve rapid adhesion and detachment, and dry adhesion. The aggregation force of van der Waals force produced by this micro-nano structure array greatly exceeds the weight of its body many times. In 2000, Autumn and Full et al. reported on page 681 of volume 405 of Nature that the special adhesive force on gecko toes mainly comes from the van der Waals force generated by the setae array of millions of micro-nano structures on the toes. accumulation. This accumulation of molecular attraction must be generated in an appropriate array of micro-nanostructures, and this array of micro-nanostructures must match the materials used to form the micro-nanostructures. Combining gecko-like dry adhesive materials with robotic technology will make it possible to walk on irregular floors, walls and ceilings, and work in areas that are difficult for humans to reach. In aerospace technology, electronic packaging and high-temperature bonding, etc. The field has great application prospects. The adhesive strength of early dry adhesive materials is far lower than the expected value. With the application of micro-processing technology and nano-fabrication technology in this research direction, the adhesive force of dry adhesive materials has been greatly improved. However, there are many parameters related to the micro-nano structure of gecko toe bristles, and they are interrelated. It is a complicated work to find a suitable composition material and the best condition to match the micro-nano structure. Achieving fast and reversible switching between adhesion and desorption remains a challenge.

Although humans have done a lot of research on the dry adhesion of geckos, so far humans have not really found the most suitable micro-nano structure similar to the setae of gecko toes to achieve ideal dry adhesion. The main reason is that humans cannot effectively match the micro-nano structure with the constituent materials like the gecko toe bristles. Gecko reduces the effective elastic modulus of the whole toe setae array through the special structure of setae. Its unique high-density, high aspect ratio micro-nano multi-level branch structure setae array makes it easy to deform and can achieve close contact with various rough surfaces. Intermolecular contact to achieve dry adhesion.

There have been many reports on the preparation of gecko-like dry adhesive materials. Generally speaking, there are two types of preparation methods. That is, the top-down preparation method based on micro-processing means and the bottom-up method based on nanometer growth and assembly technology. The top-down preparation method mainly uses polymers as matrix materials. Traditional top-down micro-nano preparation techniques such as photolithography, electron beam lithography, and etching are used to directly prepare micro-nano arrays from the substrate, or use these micro-processing as a means to first fabricate micro-nano holes with vertical micro-nano holes. template, and then replicate the polymer using a template with upstanding micro- and nano-holes. As reported by Geim et al. in "Nature Materials" 2003, Volume 2, page 461, a nanohole template prepared by electron beam lithography was used, and then a polyimide replica was used to prepare a gecko-like adhesion array with a diameter of about 0.5 microns. As another example, Sitti et al reported a photoresist micro-array prepared by photolithography on page 3322 of Volume 23 of "Langmuir" in 2007, and they also reported that a polyurethane adhesion film with a diameter of 8 microns prepared by replicating a photoresist template array. For the bottom-up (Bottom-up) method, it is mainly based on the growth and preparation of carbon nanotubes (Carbon Nanotubes, CNTs), as reported by Dai et al. The growth of CNTs arrays on substrates with transition metal catalyst particles by deposition method belongs to this method.

To sum up, different preparation methods have their own characteristics, and arrays prepared from different materials also show different adhesion properties. However, because it is very difficult to assemble or grow nano-ordered structures in a fixed-point orientation on micro-structures, the array structures obtained in the prior art are either only in the micro-scale range, or only in the nano-scale range, and have not reached the cross-scale micro-nano The structural parameters can be adjusted, so it can't adapt to some specific usage requirements. How to find an effective method for the controllable preparation of cross-scale branched structure arrays, that is, how to assemble or grow nano-ordered structures on micro-structures is a difficult problem for today's technicians.

Contents of the invention

The purpose of the present invention is to provide a cross-scale bionic micro-nano branch structure array and its preparation method, which is used to prepare a dynamic adhesive material that can rapidly adhere and detach alternately, that is, a bionic dry adhesive material, to meet different needs. Useful needs.

In order to achieve the above object, the present invention adopts the following technical solutions.

The cross-scale bionic micro-nano branch structure array of the present invention is characterized in that it is composed of a substrate and a micro-nano multi-level branch structure array, and the micro-nano multi-level branch structure array includes at least one level of micron cylinder structure array and Branched micro-nano cylinder structure array, wherein the first-level micron cylinder structure array is arranged in a quadrangular or hexagonal close-packed arrangement, the diameter of the cylinder is 3-10 microns, the height is 5-100 microns, and the density is 0.25-3.21×10 ⁶ /cm ² ; or, on the top surface of the first-level micron cylinder, the second-level submicron cylinder array is arranged first, and then the branched nano-cylindrical array is set on the top surface of the second-level submicron cylinder, wherein the second-level submicron cylinder The body array is hexagonal close-packed arrangement, the diameter of the cylinders is 200-400 nanometers, the height is 1-5 microns, and the density is 0.4-1.3×10 ⁹ /cm ² ; or, on the top surface of each secondary submicron cylinder Then set a 2-3 branched three-level submicron cylinder structure array, and then set a 4-5 branched four-level nano-cylinder array on the top surface of the three-level submicron cylinder. The diameter of the three-level submicron cylinder is 100 -200 nanometers, 0.5-2 microns in height, 0.8-3.9×10 ⁹ /cm ² density, 50-100 nanometers in diameter, 100-500 nanometers in depth, and 0.32-1.95×10 ¹⁰ density in four-stage nano cylinders /cm ² ; the micro-nano multi-level branch structure array is perpendicular to the substrate or inclined at 0-30°.

The preparation method of the cross-scale biomimetic micro-nano branch structure array of the present invention includes firstly obtaining a photoresist mask pattern on the surface of the cleaned metal aluminum sheet through ultraviolet lithography, and then performing argon ion beam etching to obtain a required one. The aluminum template of the first-level micron hole array; it is characterized in that, after obtaining the aluminum template with the required first-level micron hole array, the electrochemical anodic oxidation method is used to prepare the desired micro-nano branch on the first-level micron hole array. An aluminum oxide template of a structure array; then, the polymer replica method is used to mold a film in the template, solidify, and finally remove the template for molding to obtain the desired structure array; the fixed-point oriented preparation means that when anodizing The aluminum template with a hole array is used as the anode electrode, and the lead plate is used as the cathode electrode, and the positive and negative electrodes are placed in parallel or at an angle of 0-30°, so that the axis of the hole array is parallel to the direction of the electric field or at an angle of 0-30° Tilting; by adjusting the voltage, oxidation time and using different electrolytes to control the required pore size and depth during the anodic oxidation process, the alumina template with the required micro-nano branch hole structure array is obtained at the end of the oxidation process.

In the above preparation method, the oxidation process can be divided into one time or two or more than two times, one oxidation process can obtain aluminum templates with secondary hole arrays, and two oxidation processes can obtain aluminum templates with tertiary hole arrays. Template, the aluminum template with four-level hole array can be obtained in three oxidation processes, for example, first in the inorganic acid electrolyte with a pH value of 2-3.5, such as phosphoric acid electrolyte, sulfuric acid electrolyte, etc., for the described one-level micron The aluminum template of the hole array is anodized once, and hexagonal close-packed secondary submicron holes are obtained on the bottom surface of the micron holes. The secondary submicron holes have a diameter of 200-400 nanometers, a depth of 1-5 microns, and a density of 0.4- 1.3×10 ⁹ /cm ² ; and then carry out secondary anodic oxidation in the above phosphoric acid electrolyte by the depressurization method to obtain a tertiary pressure micropore structure with 2-3 branches, and the diameter of the tertiary micropores is 100-200 nanometers , with a height of 0.5-2 microns and a density of 0.8-3.9×10 ⁹ /cm ² , and finally perform anodic oxidation three times in an organic acid electrolyte with a pH value of 0.8-1.2, such as oxalic acid electrolyte, etc. to obtain a quaternary alumina template with a 4-5 branch structure, a pore diameter of 50-100 nanometers, a depth of 100-500 nanometers, and a density of 0.32-1.95×10 ¹⁰ /cm ² .

In the above preparation method, controlling the required pore size and depth by adjusting the voltage, oxidation time and using different electrolytes in the anodic oxidation process is a conventional technology in the existing electrochemical anodic oxidation technology, high voltage, oxidation If the time is long, the aperture will be large and the depth will be long, otherwise the aperture will be small and the depth will be short. For example, in the present invention, when carrying out primary oxidation, use inorganic acid electrolyte with pH value of 2-3.5, its concentration is 0.1%-2%, oxidation voltage is 180-190V, oxidation time is 5-20 hours, the obtained The hole diameter is 200-400 nanometers, and the depth is 1-5 microns; during the secondary oxidation, the electrolyte remains unchanged, the oxidation voltage is gradually reduced to 105-135V, and the oxidation time is reduced to 5-10 hours, and the obtained hole diameter is 100- 200 nanometers, 0.5-2 microns in depth; three times of anodizing, using an organic acid electrolyte with a pH value of 0.8-1.2, with a concentration of 0.1%-0.5%, an oxidation voltage of 40-50V, and an oxidation time of 10-30 minutes. The obtained pores have a diameter of 50-100 nanometers and a depth of 100-500 nanometers.

In the above preparation method, the array of micron holes obtained by the argon ion beam etching is distributed in a four-corner arrangement or a hexagonal close-packed arrangement, with a hole diameter of 3-10 microns, a depth of 5-100 microns, and a density of 0.25 -3.21×10 ⁶ /cm ² ; the said “Using the polymer replica method to form a film in the template, solidify, and finally remove the template for molding to obtain the required structure array” is a conventional technology, that is, to first create a micro-nano branch The aluminum oxide template of the hole structure array is completely penetrated, and then the liquid polymer, such as polyurethane (TPU), polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS) and so on The polymer is covered on the template under vacuum conditions. After it is solidified and shaped, the aluminum layer on the back of the alumina template is removed by a saturated SnCl ₄ solution replacement reaction, and finally the template is removed by soaking in 0.2M sodium hydroxide solution to obtain A cross-scale biomimetic micro-nano branch structure array composed of polymer materials.

The specific operation steps related to the oxidation process are:

(1) First anodize the aluminum template with a first-level micron hole array for 5-20 hours, and the oxidation voltage is 180-190V to obtain an aluminum oxide template with a second-level multi-branched structure, that is, an aluminum oxide template with a diameter of 200-400 nanometers The aluminum oxide layer has a depth of 1-5 microns, a pore density of 0.4-1.3×10 ⁹ /cm ² , and a hexagonal close-packed arrangement of pores. In the oxidation process, the electrolyte used is an inorganic acid electrolyte with a pH value of 2-3.5, and its concentration is 0.1%-2%;

(2) Then gradually reduce the voltage to 105-135V, and carry out secondary anodic oxidation on the secondary alumina template for 5-10 hours to obtain a tertiary alumina template with a 2-3 branch structure, with a pore size of 100-200 nanometers and a depth of 0.5-2 microns, the electrolyte used is an inorganic acid electrolyte with a pH value of 2-3.5, and its concentration is 0.1%-2%;

(3) Gradually reduce the voltage to 40-50V, anodize the tertiary alumina template three times for 10-30 minutes, and obtain a quaternary alumina template with a 4-5 branch structure, with a pore size of 50-100 nanometers and a depth of 0.2 -1 micron, the electrolyte used is an organic acid with a pH value of 0.8-1.2 and a concentration of 0.1-0.5M.

The present invention uses the electrochemical anodizing method in the prior art, uses an aluminum template with a micron hole structure array as the anode electrode, and a lead plate as the cathode electrode, and places the negative and positive electrodes in parallel or at an angle of 0-30°, cleverly utilizing The characteristics of the electric field are obtained, so that the ordered structure of the fixed-point oriented assembly of the nano-array on the micro-structure array is obtained, and the cross-scale combination from the micro-structure to the nano-structure is realized. When the two electrodes of yin and yang are placed in parallel, under the action of the electric field, only the bottom end surface of the hole perpendicular to the direction of the electric field is anodized and a new hole structure is formed, and the axis of the new hole formed is parallel to the axis of the original hole, and the side wall of the original hole Parallel to the direction of the electric field, anodic oxidation cannot be performed, and no new holes will be generated; or when the positive and negative electrodes are placed at an angle of 0-30°, that is, the axis direction of the hole array and the cathode electrode have an angle of 0-30° When tilting, make the tilted hole axis direction parallel to the direction of the electric field. Under the action of the electric field, anodic oxidation will only occur on the bottom surface of the tilted hole and form a new hole structure. The new hole axis and the original hole axis have a distance of 0-30 °Inclination angle; similarly, the side wall of the original hole is parallel to the direction of the electric field, so anodic oxidation cannot be carried out.

The invention effectively combines photolithography, ion beam etching and electrochemical anodic oxidation to prepare an alumina template with a multi-level and multi-branched cross-scale micro-nano hole array, and through the liquefied polymer The material replica obtained a micro-nano array with a branched structure, which became a more effective dry adhesive material. The invention assembles the nanometer ordered structure on the micrometer structure in a fixed-point and oriented manner, and effectively solves the problem of the controllability of the cross-scale branch structure array from the micrometer scale to the nanometer scale. The invention has very important significance for the development of bionic micro-nano array dry adhesive materials and the development of related bionic robots.

Description of drawings

Figure 1 is a schematic diagram of the cross-scale biomimetic micro-nano branch structure adhesion array prepared in Example 1 of the present invention.

Fig. 2 is a schematic diagram of preparing the alumina template with micro-nano branch structure holes described in Example 1.

FIG. 3 is a scanning electron micrograph of the cross-scale biomimetic micro-nano branch structure adhesion array obtained in Example 2.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Example 1:

(1) The high-purity aluminum sheet is ultrasonically cleaned in acetone and ethanol in sequence to remove oil stains on the surface of the aluminum sheet.

(2) After drying the decontaminated high-purity aluminum sheet, place it in a tube furnace in N ₂ or an inert atmosphere, and anneal at 500°C for 4 hours.

(3) The aluminum sheet after annealing is carried out electrochemical polishing in the mixed solution (ethanol:perchloric acid=9:1 volume ratio) of absolute ethanol and perchloric acid, with graphite as negative electrode, voltage is 20V, eliminates aluminum Scratches and oxide layers on the chip surface.

(4) Obtain a photoresist mask pattern on the surface of the aluminum sheet by ultraviolet lithography.

(5) Perform argon ion beam etching on the aluminum sheet with a photoresist mask, the ion energy is 500eV, the ion beam is vertically incident, the beam current density is 0.5mA/cm ² , and the working pressure is 2×10 ^-2 Pa, to obtain An aluminum template with a micron hole array has a diameter of 3 microns, a depth of 5 microns, and a hole spacing of 3 microns, and the hole distribution is in a hexagonal arrangement.

(6) The photoresist on the surface of the aluminum template is removed, and the surface is cleaned and electrochemically polished again.

(7) The aluminum template is oxidized once in a phosphoric acid electrolyte with a DC voltage of 190V and an oxidation time of 12 hours to obtain an alumina template with a secondary multi-branched array of holes with a diameter of 400 nm and a depth of 2 microns. The electrolyte is a phosphoric acid solution with a pH value of 3, and its concentration is 0.2%.

(8) After the secondary oxidation, the voltage drops to 110V, the electrolyte remains unchanged, and the oxidation is continued for 8 hours to obtain an alumina template with a tertiary branched array of holes with a diameter of 150 nm and a depth of 1 micron.

(9) After the third oxidation, continue to reduce the voltage. After the voltage drops to 40V, the electrolyte is replaced with an oxalic acid electrolyte with a pH value of 1, the concentration is 0.3M, and the oxidation is continued for 30 minutes to obtain a hole with a diameter of 60 nanometers and a depth of 500 nanometers. Alumina templates for arrays of quaternary branch structures. Its schematic diagram is shown in Figure 2. It can be seen from the figure that the axes of the four different micro-nano holes are all parallel.

(10) Utilize the saturated _SnCl4 solution displacement reaction to remove the aluminum on the back of the alumina template, and float the template in a 6w% phosphoric acid solution, and corrode it at 30°C until the solution permeates out of the surface of the alumina template membrane, that is, a complete Through double-pass aluminum oxide formwork.

(11) Cover thermoplastic polyurethane (TPU) on the template, remove the template after it is shaped, and obtain the adhesive array of polyurethane bionic micro-nano branch structure, as shown in Figure 1. In Fig. 1, the first-level micron cylinder array 2 is vertically connected on the substrate 1, the second-level submicron cylinder array 3 is vertically connected on the top surface of the first-level micron cylinder array, and the third-level submicron cylinder array 4 is vertically connected On the top surface of the second-level micro-cylinder array, the fourth-level nano-cylinder array 5 is vertically connected to the top surface of the third-level submicron cylinder array.

Example 2:

(1) The high-purity aluminum sheet is ultrasonically cleaned in acetone and ethanol in sequence to remove oil stains on the surface of the aluminum sheet.

(2) Dry the degreased high-purity aluminum sheet, place it in a tube furnace in N ₂ or an inert atmosphere, and anneal at 500°C for 4 hours.

(3) The aluminum sheet after annealing is carried out electrochemical polishing in the mixed solution (ethanol:perchloric acid=9:1 volume ratio) of absolute ethanol and perchloric acid, with graphite as negative electrode, voltage is 20V, eliminates aluminum Scratches and oxide layers on the chip surface.

(4) Obtain a photoresist mask pattern on the surface of the aluminum sheet by ultraviolet lithography.

(5) Carry out argon ion beam etching on the aluminum sheet with a photoresist mask, the ion energy is 600V, the ion beam incident angle is 30°, the beam current density is 0.6mA/cm ² , and the working pressure is 2×10 ^-2 Pa , to obtain a micro-hole array with a diameter of 5 microns and a depth of 10 microns.

(6) Removing the photoresist on the surface of the aluminum sheet and performing cleaning and electrochemical polishing on the surface of the aluminum sheet again.

(7) The alumina template is oxidized once. The electrolyte is a phosphoric acid solution with a pH value of 2.5, a phosphoric acid concentration of 1.2%, a DC voltage of 190V, and an oxidation time of 18 hours to obtain alumina with a diameter of 400 nanometers and a depth of 4 microns. layer.

(8) After the secondary oxidation, the voltage drops to 135V, the electrolyte remains unchanged, and the oxidation is continued for 10 hours to obtain an aluminum oxide layer with a diameter of 200 nanometers and a depth of 2 microns with bifurcated holes.

(9) The aluminum layer on the back of the alumina template is removed by a saturated _SnCl4 solution displacement reaction, and the alumina template is floated in a 6w% phosphoric acid solution, which is corroded at 30°C until the surface of the alumina template film has a solution seeping out, that is A fully through double-pass alumina template is obtained.

(10) Cover thermoplastic polymethyl methacrylate (PPMA) on the template, remove the template after it is shaped, and obtain a three-level biomimetic micro-nano branch structure adhesion array.

FIG. 3 is a photo obtained by scanning the adhesion array of the cross-scale biomimetic micro-nano branch structure obtained in Example 2 with an electron microscope. It can be seen from the photo that its structure is consistent with the above, that is, the three-level bionic micro-nano branch structure adhesion array, in which the first-level micron cylinder structure array is arranged in four corners; the second-level sub-micron cylinders are in the first-level micron The top surface of the cylinders is arranged in a hexagonal close-packed arrangement; the third-level nano cylinders are on the top surface of the second-level micron cylinders, and the axes of all the micro-nano cylinders are parallel to each other.

Claims (6)

1. A cross-scale bionic micro-nano branch structure array, characterized in that it consists of a substrate and a micro-nano multi-level branch structure array, and the micro-nano multi-level branch structure array includes at least one level of micron cylinder array and Branched micro-nano cylinder arrays, in which the first-order micron cylinder arrays are arranged in a quadrangular or hexagonal close-packed arrangement, the diameter of the cylinder is 3-10 microns, the height is 5-100 microns, and the density is 0.25-3.21×10 ⁶ /cm ² ; or, on the top surface of the first-level micron cylinder, the second-level submicron cylinder array is set earlier, and then the branched nano-cylinder array is set on the second-level submicron cylinder top surface, wherein the second-level submicron cylinder array Arranged in hexagonal close-packed cylinders with a diameter of 200-400 nanometers, a height of 1-5 microns, and a density of 0.4-1.3×10 ⁹ /cm ² ; or, on the top surface of each secondary submicron cylinder Set up a 2-3 branched three-level submicron cylinder array, and then set a 4-5 branched four-level nano-cylinder array on the top surface of the three-level submicron cylinder, and the third-level submicron cylinder has a diameter of 100-200 nanometers , with a height of 0.5-2 microns and a density of 0.8-3.9×10 ⁹ /cm ² , four-level nano-cylinders with a diameter of 50-100 nanometers, a depth of 100-500 nanometers, and a density of 0.32-1.95×10 ¹⁰ /cm ² ; The micro-nano multi-level branch structure array is perpendicular to the base or inclined at 0-30°. 2. The method for preparing the cross-scale bionic micro-nano branch structure array according to the claim, comprising first obtaining a photoresist mask pattern on the surface of the cleaned metal aluminum sheet by ultraviolet lithography, and then performing argon ion beam etching to obtain the The aluminum template of the required first-level micron hole array; It is characterized in that, after obtaining the aluminum template with the required first-level micron hole array, it is prepared on the first-level micron hole array by electrochemical anodic oxidation method. An aluminum oxide template of the micro-nano branch structure array; then, the polymer replica method is used to mold a film in the template, solidify, and finally remove the template for molding to obtain the desired micro-nano branch structure array; the fixed-point oriented preparation refers to the When performing electrochemical anodization, the aluminum template with a hole array is used as the anode electrode, and the lead plate is used as the cathode electrode, and the positive and negative electrodes are placed in parallel or at an angle of 0-30°, so that the hole axis direction of the hole array is in line with the electric field The direction is parallel or inclined at 0-30°; by adjusting the voltage, oxidation time and using different electrolytes to control the required pore size and depth during the anodic oxidation process, the desired micro-nano branch hole structure array is obtained after the oxidation process is completed. Aluminum formwork. 3. The preparation method according to claim 2, characterized in that, the oxidation process is divided into one or two or more than two times, one oxidation process obtains an aluminum template with a secondary hole array, and two oxidation processes obtain An aluminum template with a three-level hole array, an aluminum template with a four-level hole array is obtained through three oxidation processes. 4. The preparation method according to claim 3, characterized in that, the oxidation voltage used in the primary oxidation process is 180-190V, the oxidation time is 5-20 hours, and the electrolyte used is an inorganic acid with a pH value of 2-3.5. Acid electrolyte, its concentration is 0.1%-2%. 5. preparation method as claimed in claim 3 is characterized in that, the oxidation voltage used in the described secondary oxidation process drops to 105-135V gradually, and oxidation time is 5-10 hours, and the electrolytic solution used is that pH value is 2- 3.5 Inorganic acid electrolyte, its concentration is 0.1%-2%. 6. The preparation method according to claim 3, characterized in that, the oxidation voltage used in the third oxidation process is 40-50V, the oxidation time is 10-30 minutes, and the electrolyte used is an organic acid with a pH value of 0.8-1.2. acid, the concentration is 0.1-0.5M.

Images