Oxidation process method for preparing aluminum oxide film with high humidity sensing capacity

Abstract

The invention belongs to the technical field of film production, and discloses an oxidation process method for preparing an aluminum oxide film with high humidity sensing capacity. The method comprises the steps of machining of an aluminum sheet, polishing and cleaning of the aluminum sheet, micro-arc oxidation treatment of the aluminum sheet, secondary anodic oxidation treatment of the aluminum sheet subjected to micro-arc oxidation, and aging treatment of the aluminum sheet subjected to twice oxidation. According to the invention, through intense-reaction micro-arc oxidation, the aperture of the thin film is obviously improved, larger and deeper holes are obtained, the oxidation process time is obviously shortened, more stable crystal structures are obtained, and the stability of the thin film is obviously improved. After micro-arc oxidation is combined with anodic oxidation, the problems that micro-arc oxidation holes are too deep, and the bottoms of the holes are aluminum substrates and not barrier layers can be effectively avoided, and the aluminum substrates with the bottoms not oxidized are oxidized to form the barrier layers through mild anodic oxidation process treatment. Due to the advantages, the prepared humidity sensor has higher sensitivity and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of film production, and in particular relates to an oxidation process method for preparing an aluminum oxide film with high moisture sensitivity. Background Art

[0002] Alumina thin films are prepared for the production of humidity sensors, which belong to the resistance-capacitance humidity sensor. This type of equipment has the advantages of high precision, simple structure, low cost, good portability, and is widely used. The specific working principle is that the water molecule content in the humidity environment affects the material carrier mobility and dielectric constant, and then affects the size of resistance and capacitance, corresponding to different humidity values. Its humidity sensing performance is affected by factors such as pore size, pore depth, porosity, and crystal phase structure.

[0003] The preparation methods of porous alumina films include sol-gel method, powder sintering method and anodic oxidation method. The film obtained by sol-gel method has the advantages of high specific surface area and controllable pore size, but it is easy to break during the growth process. The powder sintering method is simple to prepare thin films, but the film stability is poor. The anodic oxidation method is to prepare the film with controllable pore size and thickness at low voltage, but the crystal phase of the film is unstable, which has an adverse effect on humidity performance. The micro-arc oxidation process is to prepare large-pore films at higher voltage to form a more stable crystal phase structure, but there is a problem of incomplete oxidation deep in the pores, causing short circuits.

[0004] The micro-arc oxidation process can be divided into three main stages:

[0005] Stage 1: In the initial stage of oxidation, part of the generated aluminum ions react with oxygen-containing ions in the electrolyte to form aluminum oxide, and a dense aluminum oxide film forms on the aluminum surface.

[0006] Stage 2: As the voltage continues to increase to the critical value, local tiny arc discharges occur on the surface, and the oxidation rate increases significantly, forming a dense, complex ceramic-like aluminum oxide layer.

[0007] Stage 3: Oxidation enters a stable stage and a stable porous structure is formed inside. Summary of the invention

[0008] The present invention aims to improve the deficiencies of the existing process technology and provides an oxidation process method for preparing an aluminum oxide film with high moisture sensitivity.

[0009] In order to solve the above process problems, the present invention provides an oxidation process method for preparing a highly moisture-sensitive aluminum oxide film. The process of this method includes using a metal rod used as an electrochemical cathode, an electrochemical anode substrate, a clamp for fixing the substrate, and a beaker for placing an electrolyte, a substrate, and a metal rod.

[0010] In the oxidation process method for preparing an aluminum oxide film with high moisture sensitivity, the metal rod material is high-purity titanium.

[0011] In the oxidation process method for preparing an aluminum oxide film with high moisture sensitivity, the substrate material is high-purity metal aluminum.

[0012] In the oxidation process method for preparing an aluminum oxide film with high moisture sensitivity, the fixture uses aluminum and iron.

[0013] In the oxidation process method for preparing an aluminum oxide film with high moisture sensitivity, a quartz beaker is used as the beaker.

[0014] Furthermore, the oxidation process method for preparing the aluminum oxide film with high moisture sensitivity comprises the following steps:

[0015] Step 1: Mechanically cut the high-purity aluminum sheet to obtain a high-purity aluminum sheet with customized shape and size.

[0016] Step 2: Mechanically polish and ultrasonically clean the high-purity aluminum sheet to remove surface roughness and impurities.

[0017] Step 3: The high-purity aluminum sheet after polishing and cleaning is subjected to a micro-arc oxidation process to obtain a large-pore aluminum oxide film.

[0018] Step 4: The aluminum oxide film after micro-arc oxidation is subjected to a secondary anodizing process to eliminate the phenomenon that the bottom of the hole is an aluminum substrate instead of a barrier layer due to incomplete micro-arc oxidation.

[0019] Step 5: Perform an aging process on the film after secondary anodization to improve the stability of the aluminum oxide film.

[0020] Preferably, in the oxidation process method for preparing a highly moisture-sensitive aluminum oxide film, the specific size of the aluminum sheet is: the effective size of the aluminum sheet is 20mm×10mm×1mm, and a 20mm×1mm×1mm long and thin strip of aluminum sheet is retained at one end for connection and fixation with the clamp.

[0021] Preferably, the oxidation process for preparing a high moisture-sensitive aluminum oxide film comprises the following specific polishing processes: polishing on two types of sandpaper, 800 mesh and 1200 mesh, including manual polishing of the four sides of the aluminum sheet and mechanical polishing of the two surfaces of 20 mm×10 mm. In the cleaning stage, the aluminum sheet after polishing is placed in ethanol for ultrasonic cleaning to remove impurities.

[0022] Preferably, the oxidation process method for preparing a high moisture-sensitivity aluminum oxide film, the specific micro-arc oxidation process is: the electrolyte NaHSO4:KHSO4 is mixed in a mass ratio of 3:1, and is in a molten state at 200°C under the operation of a heating instrument, and a high-purity aluminum sheet is used as the anode and a high-purity titanium rod is used as the cathode. In the molten electrolyte, the power system operates in a 200mA constant current mode for micro-arc oxidation for 120s to obtain an aluminum oxide film.

[0023] Preferably, the oxidation process method for preparing a high moisture-sensitivity aluminum oxide film, the specific secondary anodizing process is: prepare an electrolyte solution with a mass fraction of 3% with ammonium tartrate, use the aluminum oxide film after micro-arc oxidation as the anode, and a high-purity titanium rod as the cathode, and anodize for 20 minutes at room temperature with a power system operating in a 100V constant voltage mode to prepare the film.

[0024] Preferably, the oxidation process method for preparing an aluminum oxide film with high moisture sensitivity, the specific aging process is: placing the aluminum oxide film after secondary anodization in boiling deionized water for 1 hour.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) Compared with the sol-gel method, anodization method, and powder sintering method, micro-arc oxidation has a fierce reaction, which significantly increases the pore size of the film and obtains larger and deeper holes. At the same time, the oxidation process time is significantly shortened, more stable crystal structures are obtained, and the stability of the film is significantly improved. From theoretical analysis, it can be seen that these advantages make the prepared humidity sensor have higher sensitivity and stability.

[0027] (2) Combining micro-arc oxidation with anodizing can effectively prevent the micro-arc oxidation holes from being too deep. The bottom of the hole is the aluminum substrate, not the barrier layer. A mild anodizing process is used to oxidize the unoxidized aluminum substrate at the bottom to form a barrier layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A high-purity aluminum sheet size diagram of an oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of a micro-arc oxidation structure of an oxidation process method for preparing an aluminum oxide film with high moisture sensitivity according to an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of a secondary anodizing structure of an oxidation process method for preparing an aluminum oxide film with high moisture sensitivity according to an embodiment of the present invention;

[0031] Figure 4A schematic diagram of an aging structure of an oxidation process method for preparing an aluminum oxide film with high moisture sensitivity according to an embodiment of the present invention;

[0032] Figure 5 A preparation process flow chart of an oxidation process method for preparing an aluminum oxide film with high moisture sensitivity according to an embodiment of the present invention;

[0033] In the accompanying drawings, the components of the oxidation process represented by each reference numeral are listed as follows:

[0034] 1. Fixture; 2. Aluminum substrate; 3. Electrolyte; 4. Titanium metal rod; 5. Heating device (with thermocouple); 6. Power supply device. DETAILED DESCRIPTION

[0035] The structure and process of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0036] As shown in the figure, the present invention provides an oxidation process method for preparing a high moisture-sensitive aluminum oxide film, including an electrochemical cathode metal rod 4, an electrochemical anode substrate 2, and a fixture 1 for fixing the substrate.

[0037] Optionally, the metal rod 4 is made of high-purity titanium.

[0038] Optionally, the substrate 2 is made of high-purity metal aluminum.

[0039] Optionally, the material used for the clamp 1 is aluminum or iron.

[0040] Specifically, the oxidation process method for preparing a high moisture-sensitivity aluminum oxide film has the following specific preparation process steps:

[0041] The high-purity aluminum sheet 2 is obtained by mechanical processing, and the shape and size are Figure 1 The effective size of the aluminum sheet is 20mm×10mm×1mm, and a 20mm×1mm×1mm thin strip of aluminum sheet is retained at one end for connection and fixation with the clamp.

[0042] Place the high-purity aluminum sheet 2 on the polishing platform, manually polish the four sides of the aluminum sheet on two types of sandpaper with 800 mesh and 1200 mesh, and mechanically polish the two surfaces of 20mm×10mm. The polishing speed is set to 60r / min and the polishing time is 5min. In the cleaning stage, place the polished aluminum sheet in anhydrous ethanol for ultrasonic cleaning for 5min to eliminate impurities.

[0043] The electrolyte 3 of NaHSO4:KHSO4 mixed in a mass ratio of 3:1 is placed in a quartz beaker, and the electrolyte is heated to a molten state of 200°C by a constant temperature electric heating jacket instrument 5. When the electrolyte reaches a molten state, the accessory thermocouple in the electric heating jacket 5 is placed in the beaker for real-time temperature monitoring. When the electrolyte reaches a molten state of 200°C, a customized fixture 1 is used to fix the high-purity substrate 2 and place it in the molten electrolyte 3, and the positive electrode of the power supply system 6 is connected. The high-purity titanium rod 4 is placed in the molten electrolyte 3 and connected to the negative electrode of the power supply system 6. Among them, the thermocouple in the electric heating jacket 5 in the quartz beaker, the high-purity substrate 2, and the high-purity titanium rod 4 do not contact each other. The power supply system 6 is turned on, and micro-arc oxidation is performed at a constant current of 200mA for 120s. After oxidation, the electrolyte is quickly removed by washing with boiling water, and ethanol is used for ultrasonic cleaning for 5min to remove residual impurities to obtain an aluminum oxide film.

[0044] A 3% by mass ammonium tartrate electrolyte solution 7 is prepared and placed in a beaker, and a high-purity titanium rod 4 and a substrate 2 fixed with a customized fixture 1 after micro-arc oxidation are placed in the solution 7. The substrate 2 and the high-purity titanium rod 4 do not contact each other. The negative electrode and the positive electrode in the power supply system 6 are connected to serve as the cathode and the anode respectively, and connected to the power supply system 6. Anodization is carried out at a constant voltage of 100 V for 20 minutes at room temperature. After oxidation, ultrasonic cleaning is carried out with ethanol for 5 minutes to obtain an oxidized film.

[0045] The substrate 2 after secondary anodization is fixed by a custom-made fixture 1 and placed in deionized water 8 heated to boiling and aged for 1 hour to obtain the final film after oxidation.

[0046] The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. An oxidation process for preparing a highly moisture-sensitive aluminum oxide film, comprising a metal rod used as an electrochemical cathode, an electrochemical anode substrate, a fixture for fixing the substrate, and a beaker for placing an electrolyte, substrate, and metal rod.

2. The oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to claim 1, characterized in that The material of the metal rod is high-purity titanium.

3. The oxidation process for preparing a high moisture-sensitive aluminum oxide film according to claim 1, characterized in that The substrate material is high-purity metal aluminum.

4. The oxidation process for preparing a high moisture-sensitive aluminum oxide film according to claim 1, characterized in that The clamp is made of aluminum or iron.

5. The oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to claim 1, characterized in that The beaker material uses quartz.

6. An oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: Step 1: Mechanically cut the high-purity aluminum sheet to obtain a high-purity aluminum sheet with customized shape and size; Step 2: Mechanically polish and ultrasonically clean the high-purity aluminum sheet to remove surface roughness and impurities; Step 3: subjecting the treated high-purity aluminum sheet to a micro-arc oxidation process to obtain a large-pore aluminum oxide film; Step 4: The aluminum oxide film after micro-arc oxidation is subjected to a secondary anodizing process to eliminate the phenomenon that the bottom of the hole is an aluminum substrate instead of a barrier layer due to incomplete micro-arc oxidation; Step 5: Perform an aging process on the film after secondary anodization to improve the stability of the aluminum oxide film.

7. The oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to claim 6, characterized in that: The effective size of the aluminum sheet obtained by the mechanical processing in step 1 is 20mm×10mm×1mm, and a 20mm×1mm×1mm thin strip of aluminum sheet is retained at one end for connection and fixation with the clamp.

8. The oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to claim 6, characterized in that: The polishing and cleaning process described in step 2 is: polishing on two types of sandpaper, 800 mesh and 1200 mesh, including manual polishing of the four sides of the aluminum sheet and mechanical polishing of the two surfaces of 20mm×10mm respectively. During the cleaning stage, the polished aluminum sheet is placed in ethanol for ultrasonic cleaning to eliminate impurities.

9. The oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to claim 6, characterized in that: The micro-arc oxidation process described in step 3 is: the electrolyte NaHSO4:KHSO4 is mixed in a mass ratio of 3:1, and is in a molten state at 200°C under the operation of a heating instrument. A high-purity aluminum sheet is used as the anode and a high-purity titanium rod is used as the cathode. In the molten electrolyte, the power system operates in a 200mA constant current mode for micro-arc oxidation for 120s to obtain an aluminum oxide film.

10. The oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to claim 6, characterized in that The secondary anodizing process described in step 4 is: prepare an electrolyte solution with a mass fraction of 3% by ammonium tartrate, use the aluminum oxide film after micro-arc oxidation as the anode, and a high-purity titanium rod as the cathode. The power system operates in a 100V constant voltage mode at room temperature for anodic oxidation for 20 minutes to prepare a film.

11. The oxidation process for preparing an aluminum oxide film with high moisture sensitivity according to claim 6, characterized in that The aging process described in step 5 is: placing the film after secondary anodization in boiling deionized water for 1 hour.

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