US20090250350A1

US20090250350A1 - Detection device and method of anodic oxide film

Info

Publication number: US20090250350A1
Application number: US12/324,849
Authority: US
Inventors: Pai-Sheng Wei; Chia-Shou Chang
Original assignee: Foxconn Technology Co Ltd
Current assignee: Foxconn Technology Co Ltd
Priority date: 2008-04-03
Filing date: 2008-11-27
Publication date: 2009-10-08
Also published as: CN101551352A

Abstract

A device for detecting an anodic oxide film during an anodic oxidation treatment includes a container receiving an electrolyte therein, an aluminum sheet immersed in the electrolyte, a power source supplying a current to the aluminum sheet to form an anodic oxide film on the aluminum sheet, a data acquisition unit measuring a potential of the anodic oxide film at a time, a data processor unit calculating a differential value of the potential, and a display unit displaying a differential curve generated according to the differential values of the potentials at different times. The quality of the anodic oxide film can be judged by reading the shape of the differential curve.

Description

BACKGROUND

1. Field of the Disclosure
The disclosure generally relates to detection devices and detection methods, and more particularly to a detection device and method for detecting an anodic oxide film during an anodic oxidation treatment.
2. Description of Related Art
Anodic oxide films have drawn much attention for industrial and nanotechnology uses because of their unique pore formation capability, which not only increases corrosion resistance but has the added value of enhanced cosmetic appearance. The anodic oxide film is composed of a porous layer. During an anodic oxidation treatment, a current density, a bath temperature, and an acid concentration of an electrolyte may influence a pore formation capability of the anodic oxide film. For example, a burnt film may be formed at a higher current density, and pitting and burning tend to occur at a lower acid concentration or when a concentration of a sulfate increases. However, to examine the texture of the anodic oxide film always involves the use of an electronic microscope and preparation of specimens, which is tedious and laborious.
For the foregoing reasons, there is a need in the art for a detection device and method for detecting an anodic oxide film which overcome the limitations described.

SUMMARY

According to the disclosure, a device for detecting an anodic oxide film during an anodic oxidation treatment includes a container receiving an electrolyte therein, an aluminum sheet immersed in the electrolyte, a power source electrically connected to the aluminum sheet for supplying a current to the aluminum sheet to cause an anodic oxide film to grow on the aluminum sheet, a data acquisition unit measuring a potential of the anodic oxide film, a data processor unit calculating a first-order differential value of the potential at a time, and a display unit displaying a first-order differential curve generated according to the differential values of the potentials at different times. During a period between the time when the potential of the anodic oxide film reaches a maximum and the time when the potential of the anodic oxide film starts to become constant, if only one valley is formed on the first-order differential curve, the anodic oxide film is excellent; should there be more than one valleys formed on the first-order differential curve, the anodic oxide film has a poor quality.
Other advantages and novel features of the disclosure will be drawn from the following detailed description of the exemplary embodiments of the disclosure with attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a detection device according to an exemplary embodiment for detecting an anodic oxide film during an anodic oxidation treatment.

FIG. 2 is a flowchart of a detection method for detecting the anodic oxide film during the anodic oxidation treatment using the detecting device of FIG. 1.

FIG. 3 is a potential-time curve and an associated first-order differential curve of the anodic oxide film formed by anodizing an aluminum sheet in a sulfuric acid solution with a concentration of 15 wt % at a bath temperature of 293K and a current density of 15 mA/cm².

FIGS. 4-7 show microscopic images of the anodic oxide film of the aluminum sheet at different anodizing times under the condition of FIG. 3.

FIG. 8 is similar to FIG. 3, but shows the potential-time curve and the associated first-order differential curve of the anodic oxide film formed by anodizing the aluminum sheet in a sulfuric acid solution with a concentration of 10 wt % at a bath temperature of 303K and a current density of 27 mA/cm².

FIG. 9 shows a microscopic image of the anodic oxide film formed on the aluminum sheet under the condition of FIG. 8.

FIG. 10 shows the potential-time curve and the associated first-order differential curve of the anodic oxide film formed by anodizing the aluminum sheet in a sulfuric acid solution with a concentration of 20 wt % at a bath temperature of 283K and a current density of 24 mA/cm².

FIG. 11 shows a microscopic image of the anodic oxide film formed on the aluminum sheet under the condition of FIG. 10.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, a detection device for detecting an anodic oxide film in an anodic oxidation treatment includes a power source 1, a data acquisition unit 8, a data processor unit 10, a display unit 11 and a container 14.
An electrolyte 6, such as a solution including sulfuric acid, phosphoric acid, chromic acid, and organic acid, is filled in the container 14. The container 14 is received in a constant temperature device 7 to maintain a constant anodizing temperature during the anodic oxidation treatment. An aluminum sheet 9 functions as an anode and has a bottom end extending into the electrolyte 6 and a top end electronically connected to a positive pole 2 of the power source 1. An aluminum post 4 functions as a cathode and has a bottom end extending into the electrolyte 6 and a top end electronically connected to a negative pole 3 of the power source 1. Thus the power source 1 can supply a current to the aluminum sheet 9. The power source 1 can be adjusted to change a current density flowing through the aluminum sheet 9. A calomel electrode 5 is utilized as a reference electrode. The calomel electrode 5 has a bottom end extending into the electrolyte 6, and a top end connected to a reference terminal 82 of the data acquisition unit 8. An input terminal 81 of the data acquisition unit 8 is connected to the top end of the aluminum sheet 9, an earth terminal 83 of the data acquisition unit 8 is connected to the ground, and an output terminal 84 of the data acquisition unit 8 is connected to an input terminal 13 of the data processor unit 10. The display unit 11 is connected to an output terminal 12 of the data processor unit 10.
During the anodic oxidation treatment, the power source 1 supplies the current to the aluminum sheet 9 to cause an anodic oxide film to continuously grow on the aluminum sheet 9 until reaching a quasi-steady state. A pore formation capability of the anodic oxide film can be detected during the anodic oxidation treatment according to a detecting method shown in FIG. 2. The detecting method mainly includes the following steps: (a) obtaining different potentials U of the anodic oxide film at different anodizing times t by the data acquisition unit 8, recording and processing the recorded potentials U and times t by the data processing unit 10 to obtain a potential-time curve 20 and displaying the potential-time curve 20 by the display unit 11 which has a potential-time coordinates; (b) differentiating the different potentials U at different times t by the data processing unit 10 to obtain first-order differential values U′ at different times t; (c) generating a first-order differential curve 21 by the data acquisition unit 8 according to the first-order differential value U′ at different times t and displaying the first-order differential curve 21 by the display unit 11; and (d) judging the pore formation capability of the anodic oxide film according to a shape of the first-order differential curve 21. Details of the detection method will be expatiated with specific anodic oxidation treatment examples as follows.
In one specific anodic oxidation treatment, the electrolyte 6 is a sulfuric acid solution with a concentration of 15 wt %. The aluminum sheet 9 is anodized in the sulfuric acid solution at a bath temperature of 293K and a current density of 15 mA/cm². The data acquisition unit 8 measures the potential U of the anodic oxide film at a frequency f of 100 Hz. The potential U of the anodic oxide film is converted to digital signal and sent to the data processor unit 10. The data processor unit 10 records the potential U of the anodic oxide film at the anodizing time t as U(t). Accordingly, the potential U of the anodic oxide film at the anodizing time t−1 is recorded as U(t−1), and the potential U of the anodic oxide film at the anodizing time t+1 is recorded as U(t+1). Then the data processor unit 10 calculates the first-order differential value U′ of the potential U according to a formula of U′=[U(t)−U(t−1)]*f. Thus a potential-time curve 20 is obtained according to the potentials U of the anodic oxide film at the anodizing times t, and a first-order differential curve 21 is obtained according to the first-order differential values U′ at the anodizing times t. Finally both of the potential-time curve 20 and the first-order differential curve 21 are displayed on the display unit 11, as shown in FIG. 3.
The potential-time curve 20 and the first-order differential curve 21 can be divided into four segments, which correspond to four stages of the growth of the anodic oxide film, i.e., a barrier layer formation stage, a nanopore initiation and growth stage, a pore widening stage, and a quasi-steady state stage. The four stages are divided by three anodizing times, t_U′max, t_Umax, and t_Uconst. The anodizing time t_U′maxis the time that the first-order differential curve 21 has a maximum value: U′max. The anodizing time t_Umaxis the time that the potential-time curve 20 has a maximum value: Umax, and at this time, the first-order differential value U′ of the potential U is zero. The anodizing time t_constis the time that the first-order differential curve 21 and the potential-time curve 20 start to become straight and horizontal. In other words, from the anodizing time t_const, the potential U of the anodic oxide film is constant, the first-order differential value U′ of the potential U is zero. The barrier layer formation stage is from the start of formation of the anodic oxide film (i.e., t=0) to the anodizing time t_U′max. The nanopore initiation and growth stage is from t_U′maxto t_Umax. The pore widening stage is from t_Umaxto t_Uconst. After the anodizing time t_Uconstis the quasi-steady state stage. The pore formation capability of the anodic oxide film is judged according to an amount of valleys of the first-order differential curve 21 in the pore widening stage. If the first-order differential curve 21 has only one valley in the pore widening stage, the anodic oxide film formed on the aluminum sheet 9 is excellent. In contrast, if the first-order differential curve 21 has more than one valleys in the pore widening stage, the quality of the anodic oxide film is poor.
Referring to FIG. 3 again, in the barrier layer formation stage, the anodic oxide film initially and continuously grows on the aluminum sheet 9. The initially formed anodic oxide film significantly increases the electric resistance of the aluminum sheet 9. The potential U of the anodic oxide film increases with the increase of the electric resistance. An increasing rate of the potential U of the anodic oxide film is more and more faster, and thus the first-order differential value U′ of the potential U increases remarkably until reaching the maximum U′max. According to the first-order differential curve 21, the maximum first-order differential value U′max is about 3.96, and the anodizing time t_U′maxis about 2.37s. In other words, a period for the barrier layer formation stage is about 2.37s. An intersection point A of the potential-time curve 20 with a vertical line of t=t_U′maxis about (2.37s, 10.08V), i.e., the potential U of the anodic oxide film reaching 10.08V at the end of the barrier layer formation stage. FIG. 4 shows the anodic oxide film formed on the aluminum sheet 9 in the barrier layer formation stage at the anodizing time of about 2s, which is substantially a barrier layer consisting mainly of amorphous type oxide which is compact and free of pores.
In the nanopore initiation and growth stage, the potential U of the anodic oxide film continues to rise until reaching the maximum Umax. However, the increasing rate of the potential U of the anodic oxide film in the nanopore initiation and growth stage is slower. As shown in FIG. 3, the first-order differential value U′ of the potential U decreases to zero when the potential U of the anodic oxide film reaches the maximum Umax. A point B (8.51s, 25.54V) indicates the peak of the potential-time curve 20, i.e., the maximum potential Umax of the anodic oxide film is about 25.54V, and the anodizing time t_Umaxis about 8.51s. The nanopore initiation and growth stage is from 2.37s to 8.51s. In this stage, initially, nanopores are formed on the surface of the anodic oxide film, which result in the decrease of the first-order differential value U′ of the potential U. Then the current supplied by the power source 1 to the aluminum sheet 9 for growing the anodic oxide film thereon functions as a pore current and an anodic oxide film formation current. The pore current increases because of growing of the nanopores, while the formation current decreases due to increase of the resistance of the anodic oxide film. Finally affected by the pore current, nanopores persistently increase in size to become pores. FIG. 5 shows the anodic oxide film formed on the aluminum sheet 9 in the nanopore initiation and growth stage at the anodizing time of about 6s, which has a plurality of pores.
In the pore widening stage, the anodic oxide film continues to growth until it reaches the quasi-steady state at the anodizing time t_Uconst. The pores of the anodic oxide film widen persistently and become apparent. According to the first-order differential curve 21 and the potential-time curve 20 of FIG. 3, the anodizing time t_Uconstis about 20.08s. At the anodizing time t_Uconst, the potential Uconst of the anodic oxide film decreases to about 17.15V, as indicated by point C. As shown in FIG. 6, the pores of the anodic oxide film at the anodizing time of about 12s are apparent. After the anodizing time t_Uconst, i.e., in the quasi-steady state stage, the potential U of the anodic oxide film is constant, being 17.15V, and thus the first-order differential value U′ of the potential U is also constant, being zero. Both of the first-order differential curve 21 and the potential-time curve 20 in the quasi-steady state stage after the anodizing time t_Uconstare straight and horizontal.
In the pore widening stage, the potential-time curve 20 declines, and the potential U of the anodic oxide film decreases gradually form Umax to U_const. The first-order differential curve 21 goes from zero to a minimum, and then lifts to zero again when the potential U of the anodic oxide film reaches U_const. One valley is formed in the pore widening stage of the first-order differential curve 21 when the first-order differential value U′ of the potential U reaches the minimum U′min, which is indicated by point D. The time t and the minimum U′min at the point D are about 10.27s and −1.71. According to the yardstick, if the first-order differential curve 21 has only one valley in the pore widening stage, the anodic oxide film formed in this specific anodic oxidation treatment that the aluminum sheet 9 is anodized in a sulfuric acid solution of 15 wt % concentration at a bath temperature of 293K and a current density of 15 mA/cm²has a good quality. FIG. 7 shows the pores of the anodic oxide film at the anodizing time of about 22s; it is obvious that the anodic oxide film has an excellent pore formation.
FIG. 8 shows the potential-time curve 22 and the first-order differential curve 23 of a second specific anodic oxidation treatment. In this anodic oxidation treatment, the aluminum sheet 9 is anodized in the electrolyte 6 with a concentration of 10 wt % at a bath temperature of 303K and a current density of 27 mA/cm². It is obvious that the first-order differential curve 23 has two valleys in the pore widening stage, and thus the anodic oxide film is poor in quality. As shown in FIG. 9, pitting is generated in the anodic oxide film, and thus the pore formation of the anodic oxide film is bad.
FIG. 10 shows the potential-time curve 24 and the first-order differential curve 25 of a third specific anodic oxidation treatment. In the third specific anodic oxidation treatment, the aluminum sheet 9 is anodized in the electrolyte 6 with a concentration of 20 wt % at a bath temperature of 283K and a current density of 24 mA/cm². Similar to FIG. 8, the first-order differential curve 25 in FIG. 10 has more than one valleys in the pore widening stage, and thus the anodic oxide film has a poor quality. As shown in FIG. 11, pitting also occurs in the anodic oxide film.
It is to be understood, however, that even though numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. A method for detecting an anodic oxide film during an anodic oxidation treatment, comprising steps of:

acquiring potentials of the anodic oxide film at different anodizing times by a data acquisition unit;

calculating differential values of the potentials at the different anodizing times by a data processor unit;

generating a differential curve according to the differential values of the potentials and displaying the differential curve on the display unit; and

judging a pore formation capability of the anodic oxide film according to a shape of the differential curve.

2. The method of claim 1, further comprising generating a potential-time curve according to the potentials of the anodic oxide film at the different anodizing times, and displaying the potential-time curve associated with the differential curve on the display unit.

3. The method of claim 2, wherein during a period of the anodizing times from a time when a corresponding potential of the anodic oxide film reaches a maximum to a time when a corresponding potential of the anodic oxide film starts to become constant, if only one valley is formed on the differential curve, the anodic oxide film is excellent, and if more than one valleys are formed on the differential curve, the anodic oxide film is bad.

4. A device for detecting an anodic oxide film during an anodic oxidation treatment, comprising:

a container receiving an electrolyte therein;

an aluminum article extending into the electrolyte;

a power source electrically connected to the aluminum article for supplying a current to the aluminum article to cause an anodic oxide film to grow on the aluminum article;

a data acquisition unit measuring potentials of the anodic oxide film at different times;

a data processor unit calculating differential values of the potentials at the different times; and

a display unit displaying a differential curve generated according to the differential vales of the potentials.

5. The device of claim 4, wherein the container is received in a constant temperature device for maintaining a constant anodizing temperature during the anodic oxidation treatment.

6. The device of claim 4, wherein the power source can be adjusted to change a current density through the aluminum article.

7. The device of claim 4, wherein the aluminum article is connected to a positive pole of the power source, the device further comprising another aluminum article connected to a negative pole of the power source, and a calomel electrode function as a reference electrode.

8. The device of claim 7, wherein the calomel electrode has one end extending into the electrolyte, and another end connected to a reference terminal of the data acquisition unit, an input terminal of the data acquisition unit being connected to the aluminum article, and an output terminal being connected to the data processor unit.

9. The device of claim 7, wherein the data processor unit generates a potential-time curve according to the potentials of the anodic oxide film at the different times, and the display unit displays the potential-time curve associated with the differential curve.

10. The device of claim 4, wherein the electrolyte is a solution including one of sulfuric acid, phosphoric acid, chromic acid, and organic acid.