Deplating method for iron coating on surface of titanium workpiece

Abstract

The invention belongs to the technical field of metal layer deplating, and discloses a deplating method for an iron coating on the surface of a titanium workpiece. The deplating method comprises the following steps: taking an acidic deplating solution as an electrolyte, taking a titanium workpiece to be deplated as an anode, putting the workpiece to be deplated and a cathode into the acidic deplating solution, electrifying and applying a voltage of 0.1-5V to carry out electrolytic deplating until the electrolytic current lt is reached; when the current threshold value is stopped, electrolytic deplating is stopped; the anode is taken out after electrolytic deplating is finished, drying is conducted after ultrasonic cleaning is conducted, and the deplated titanium workpiece is obtained; the acidic stripping solution is one or more of a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution or a nitric acid aqueous solution. According to the deplating method, the iron plating layer can be selectively removed, use of a large amount of high-concentration acid is avoided, the operation process is simple, the treatment cost is low, the green and environment-friendly requirements are met, and large-scale use is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of metal layer stripping, in particular to a method for stripping an iron plating layer on the surface of a titanium workpiece. Background Art

[0002] Titanium alloys are widely used in aerospace, automobile, medical equipment, chemical and marine engineering fields due to their high strength, light weight, corrosion resistance, high temperature oxidation resistance, excellent toughness, good thermal stability, strong plasticity and easy processing and forming.

[0003] However, the easy scratching and poor wear resistance of titanium alloys limit their further application in some industrial fields, especially in the aviation industry. In order to improve the surface hardness and wear resistance of titanium alloys, and thus improve the mechanical properties and high temperature performance of titanium alloys, those skilled in the art have proposed a method for iron plating on the surface of titanium alloys. In the iron plating process of titanium alloys, due to the stability of the process and the quality of the coating, it is often necessary to strip and re-plate the workpiece.

[0004] At present, the existing technology mainly uses chemical methods to remove the iron coating on the surface of titanium alloy by strong acid treatment. However, the concentration of strong acid used in this treatment method is relatively high, making the degree of reaction difficult to control and easily causing corrosion to the titanium substrate. In addition, strong acid will cause the reaction temperature to rise during stripping, and then release pungent acidic gas, which does not meet the requirements of environmentally friendly green production. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for stripping the iron coating on the surface of a titanium workpiece.

[0006] The method for stripping the iron coating on the surface of a titanium workpiece of the present invention is achieved by the following technical scheme:

[0007] A method for stripping an iron coating on a titanium workpiece surface comprises the following steps:

[0008] Step 1: using an acidic deplating solution as an electrolyte and a titanium workpiece to be deplated as an anode, placing the workpiece to be deplated and a cathode in the acidic deplating solution, applying power for electrolytic deplating, and stopping the electrolytic deplating when the electrolytic current is less than a stop current threshold.

[0009] Step 2, after the electrolytic stripping is completed, the anode is taken out, ultrasonically cleaned and then dried to obtain a titanium workpiece that has completed stripping.

[0010] It should be noted that the present invention adopts an electrolytic stripping method according to the performance difference of electrochemical corrosion of titanium and iron, with an acidic stripping solution as an electrolyte, and a titanium workpiece to be stripped as an anode, and the voltage of the power supply is controlled to be 0.1V~5V, so that as the stripping time is extended, the electrolytic stripping current gradually decreases, and the iron coating content gradually decreases. When the electrolytic stripping is to the electrolytic current < stop current threshold, the electrolytic stripping is stopped. Due to the difference in electrochemical corrosion between titanium and iron, titanium has a higher corrosion resistance than iron, so that at a specific voltage of 0.1V~5V, iron reacts preferentially, and its current density is significantly higher than that of titanium. This characteristic enables the present invention to selectively remove the iron coating without damaging the titanium substrate, thereby achieving the removal of the iron coating on the surface of the titanium workpiece. It should also be emphasized that in the process of applying a voltage of 0.1V~5V for electrolysis, the titanium substrate is basically not chemically corroded, or the chemical corrosion is very slow and can be ignored.

[0011] The preferred acidic deplating solution of the present invention is one or more of a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution and a nitric acid aqueous solution, so as to achieve the effect of efficient iron removal.

[0012] The present invention takes into account the difference in electrochemical corrosion performance between titanium and iron, so the mass concentration of the hydrochloric acid aqueous solution preferably used is 0.1wt% to 6wt% to achieve the electrolytic stripping effect of the iron coating on the titanium workpiece.

[0013] The present invention takes into account the performance difference of electrochemical corrosion between titanium and iron, so the mass concentration of the sulfuric acid aqueous solution preferably used is 1wt% to 20wt% to achieve the electrolytic stripping effect of the iron coating of the titanium workpiece.

[0014] The present invention takes into account the difference in electrochemical corrosion performance between titanium and iron, so the mass concentration of the nitric acid aqueous solution preferably used is 1wt% to 15wt% to achieve the electrolytic stripping effect of the iron coating on the titanium workpiece.

[0015] It should be noted that the electrolytic stripping process of the present invention is monitored according to the change of the actual electrolytic current. When the electrolytic stripping reaches the electrolytic current < the stop current threshold, the electrolytic stripping is stopped to ensure that the iron coating on the surface of the titanium workpiece can be removed while avoiding damage to the titanium workpiece substrate. The stop current threshold is ≤ 1% to 3% of the initial current value of the electrolytic stripping.

[0016] In some preferred embodiments of the present invention, when the stop current threshold is ≤3% of the initial current value of electrolytic stripping, the iron coating content on the surface of the titanium workpiece is ≤2%, and the weight loss of the titanium workpiece is ≤0.5%.

[0017] In some preferred embodiments of the present invention, when the stop current threshold is ≤1% of the initial current value of electrolytic stripping, the iron coating content on the surface of the titanium workpiece is ≤1%, and the weight loss of the titanium workpiece is ≤1%.

[0018] In some preferred embodiments of the present invention, the temperature of the electrolytic stripping is 5° C. to 40° C. In some preferred embodiments of the present invention, the distance between the anodes is maintained at 0.5 cm to 50 cm to achieve uniform stripping.

[0019] In some preferred embodiments of the present invention, the cathode is any one of a stainless steel plate, a titanium plate and a lead plate.

[0020] In some preferred embodiments of the present invention, the ultrasonic cleaning has an ultrasonic frequency of 25 Hz to 40 Hz, so as to remove the acid on the surface of the workpiece.

[0021] In some preferred embodiments of the present invention, the ultrasonic cleaning temperature is 10° C. to 60° C., and the ultrasonic time is 0.1 min to 60 min.

[0022] In some preferred embodiments of the present invention, the titanium workpiece to be stripped is any one of titanium metal fibers, titanium wires, titanium rods, titanium plates and titanium sheets with an iron coating on the surface.

[0023] In some preferred embodiments of the present invention, the drying temperature is 50° C. to 120° C., and the drying time is 5 h to 24 h.

[0024] It should also be noted that in order to ensure that the final workpiece after stripping meets the requirements, it is subjected to quality inspection. If it meets the actual iron content requirements, it is stored in the warehouse. If it does not meet the requirements, it returns to the electrolytic stripping step to continue stripping the iron plating on its surface until the actual iron content requirements are met.

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

[0026] According to the performance difference of electrochemical corrosion between titanium and iron, the present invention uses a low-concentration acid stripping solution as an electrolyte, takes a titanium workpiece to be stripped as an anode, adopts an electrolytic stripping method, controls the voltage of power supply to be 0.1V-5V, so that iron reacts preferentially under a specific voltage of 0.1V-5V, and monitors the change of electrolytic current during the electrolytic stripping process. When the electrolytic stripping reaches an electrolytic current less than a stop current threshold, the electrolytic stripping is stopped, thereby realizing selective removal of the iron plating layer on the surface of the titanium workpiece without damaging the titanium substrate.

[0027] The acidic deplating solution used in the present invention is one or more of hydrochloric acid aqueous solution, sulfuric acid aqueous solution and nitric acid aqueous solution; wherein the mass concentration of the hydrochloric acid aqueous solution is 0.1wt% to 6wt%; the mass concentration of the sulfuric acid aqueous solution is 1wt% to 20wt%; the mass concentration of the nitric acid aqueous solution is 1wt% to 15wt%. Compared with the traditional scheme, the present invention avoids the use of a large amount of high-concentration acid, the treatment process of the present invention is simple to operate, and the treatment cost is low, green and environmentally friendly, and is conducive to promotion and large-scale use. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the process flow chart of stripping the iron coating on the surface of titanium workpiece.

[0029] Figure 2 This is a curve showing the change of current over electrolysis time during the electrolytic stripping process of Example 1.

[0030] Figure 3 The open circuit voltage test results of the titanium sheet and the iron sheet in the acidic deplating solution of Example 1 are shown.

[0031] Figure 4 The electrochemical impedance spectroscopy of the titanium sheet and the iron sheet in the acidic deplating solution of Example 1 is shown.

[0032] Figure 5 1 and 2 are polarization curves of titanium sheet and iron sheet in the acidic deplating solution of Example 1. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be described clearly and completely below.

[0034] Example 1

[0035] See also Figure 1 This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0036] Step 1: Mix hydrochloric acid and deionized water to prepare a hydrochloric acid aqueous solution with a mass concentration of 0.9 wt%.

[0037] Step 2, taking 2000g of the above-prepared hydrochloric acid aqueous solution with a mass concentration of 0.9wt% and placing it in an electrolytic cell as an electrolyte.

[0038] Step 3, using an iron-plated titanium plate with an iron content of 40wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and cathode 10cm.

[0039] Step 4, at room temperature, power is turned on to apply a voltage of 3V to perform electrolytic stripping, the initial current is 0.4A, and the stripping is stopped when the reaction current of the electrolytic stripping is less than 0.003A. The total time is 120 minutes.

[0040] Step 5, placing the electrolytically stripped titanium plate into an ultrasonic cleaning device, and cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the surface acid residue.

[0041] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium plate after stripping.

[0042] The present invention has been tested and found that in the titanium plate after stripping in this embodiment, the iron content is 0.15wt% and the titanium weight loss is 0.58wt%.

[0043] Example 2

[0044] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0045] Step 1: Mix hydrochloric acid and deionized water to prepare a hydrochloric acid aqueous solution with a mass concentration of 0.3 wt%.

[0046] Step 2: Take 2000 g of the above-prepared hydrochloric acid aqueous solution with a mass concentration of 0.3 wt % and place it in an electrolytic cell as an electrolyte.

[0047] Step 3, using a discarded iron-plated titanium plate with an iron content of 40wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0048] Step 4, at room temperature, power is turned on to apply a voltage of 3V to perform electrolytic stripping, the initial current is 0.4A, and the stripping is stopped when the reaction current of the electrolytic stripping is less than 0.015A. The total time is 305min.

[0049] Step 5, placing the electrolytically stripped titanium plate into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the surface acid residue.

[0050] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium plate after stripping.

[0051] That is, the difference between this embodiment and embodiment 1 is only that:

[0052] The concentration of the hydrochloric acid aqueous solution used in this embodiment is 0.3 wt %.

[0053] The present invention has been tested and found that in the titanium plate after stripping in this embodiment, the iron content is 1.14wt% and the titanium weight loss is 0.1wt%.

[0054] Example 3

[0055] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0056] Step 1: Mix hydrochloric acid and deionized water to prepare a hydrochloric acid aqueous solution with a mass concentration of 6 wt%.

[0057] Step 2: Take 2000 g of the above-prepared 6 wt% hydrochloric acid aqueous solution and place it in an electrolytic cell as an electrolyte.

[0058] Step 3, using a discarded iron-plated titanium plate with an iron content of 40wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0059] Step 4, at room temperature, power is turned on to apply a voltage of 2V to perform electrolytic stripping, the initial current is 0.4A, and the stripping is stopped when the reaction current of the electrolytic stripping is less than 0.004A. The total time is 130 minutes.

[0060] Step 5, placing the electrolytically stripped titanium plate into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the surface acid residue.

[0061] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium plate after stripping.

[0062] That is, the difference between this embodiment and embodiment 1 is only that:

[0063] The voltage applied in this embodiment is 2V; the concentration of the hydrochloric acid aqueous solution used is 6wt%.

[0064] The present invention has been tested and found that in the titanium plate after stripping in this embodiment, the iron content is 0.75wt% and the titanium weight loss is 0.52wt%.

[0065] Example 4

[0066] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0067] Step 1: Mix hydrochloric acid and deionized water to prepare a hydrochloric acid aqueous solution with a mass concentration of 0.9 wt%.

[0068] Step 2, taking 2000g of the above-prepared hydrochloric acid aqueous solution with a mass concentration of 0.9wt% and placing it in an electrolytic cell as an electrolyte.

[0069] Step 3, using a discarded iron-plated titanium plate with an iron content of 40wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0070] Step 4, at room temperature, power is turned on to apply a voltage of 1 V to perform electrolytic stripping, the initial current is 0.4 A, and the stripping is stopped when the reaction current of the electrolytic stripping is less than 0.004 A. The total time is 305 min.

[0071] Step 5, placing the electrolytically stripped titanium plate into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the surface acid residue.

[0072] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium plate after stripping.

[0073] That is, the difference between this embodiment and embodiment 1 is only that:

[0074] In this embodiment, the applied voltage is 1V.

[0075] The present invention has been tested and found that in the titanium plate after stripping in this embodiment, the iron content is 1.54wt% and the titanium weight loss is 0.09wt%.

[0076] Example 5

[0077] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0078] Step 1: Mix hydrochloric acid and deionized water to prepare a hydrochloric acid aqueous solution with a mass concentration of 0.9 wt%.

[0079] Step 2, taking 2000g of the above-prepared hydrochloric acid aqueous solution with a mass concentration of 0.9wt% and placing it in an electrolytic cell as an electrolyte.

[0080] Step 3, using a discarded iron-plated titanium rod with an iron content of 8wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0081] Step 4, at room temperature, power is turned on to apply a voltage of 3V to perform electrolytic stripping, the initial current is 0.08A, and the stripping is stopped when the reaction current of the electrolytic stripping is 0.89mA. The total time is 24min.

[0082] Step 5, placing the titanium rod after electrolytic stripping into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the acid residue on the surface.

[0083] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium rod after stripping.

[0084] That is, the difference between this embodiment and embodiment 1 is only that:

[0085] In this embodiment, the workpiece to be stripped is a discarded iron-plated titanium rod with an iron content of 8 wt%.

[0086] Furthermore, the present invention has been tested and found that in the titanium rod after stripping in this embodiment, the iron content is 0.25wt% and the titanium weight loss is 0.45wt%.

[0087] Example 6

[0088] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0089] Step 1: Mix sulfuric acid and deionized water to prepare a sulfuric acid aqueous solution with a mass concentration of 1 wt%.

[0090] Step 2: Take 2000 g of the above-prepared 1 wt% sulfuric acid aqueous solution and place it in an electrolytic cell as an electrolyte.

[0091] Step 3, using a discarded iron-plated titanium rod with an iron content of 8wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0092] Step 4, at room temperature, power is turned on to apply a voltage of 2V to perform electrolytic stripping, the initial current is 0.08A, and the stripping is stopped when the reaction current of the electrolytic stripping is 1mA. The total time is 280min.

[0093] Step 5, placing the titanium rod after electrolytic stripping into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the acid residue on the surface.

[0094] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium rod after stripping.

[0095] That is, the difference between this embodiment and embodiment 5 is only that:

[0096] In this embodiment, the electrolyte used is a sulfuric acid aqueous solution with a mass concentration of 1 wt %; and the applied voltage is 2V.

[0097] Furthermore, the present invention has been tested and found that in the titanium rod after stripping in this embodiment, the iron content is 0.77wt% and the titanium weight loss is 0.51wt%.

[0098] Example 7

[0099] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0100] Step 1: Mix sulfuric acid and deionized water to prepare a sulfuric acid aqueous solution with a mass concentration of 20 wt%.

[0101] Step 2: Take 2000 g of the above-prepared 20 wt% sulfuric acid aqueous solution and place it in an electrolytic cell as an electrolyte.

[0102] Step 3, using a discarded iron-plated titanium rod with an iron content of 8wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0103] Step 4, at room temperature, power is turned on to apply a voltage of 1 V to perform electrolytic stripping, the initial current is 0.08 A, and the stripping is stopped when the reaction current of the electrolytic stripping is 5 mA. The total time is 75 minutes.

[0104] Step 5, placing the titanium rod after electrolytic stripping into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the acid residue on the surface.

[0105] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium rod after stripping.

[0106] That is, the difference between this embodiment and embodiment 5 is only that:

[0107] In this embodiment, the electrolyte used is a sulfuric acid aqueous solution with a mass concentration of 20 wt %; and the applied voltage is 1V.

[0108] The present invention has been tested and found that the iron content in the titanium rod after stripping in this embodiment is 1.81wt%, and the titanium weight loss is 0.18wt%.

[0109] Example 7

[0110] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0111] Step 1, mixing nitric acid and deionized water to prepare a nitric acid aqueous solution with a mass concentration of 3wt%.

[0112] Step 2, taking 2000g of the above-prepared nitric acid aqueous solution with a mass concentration of 3wt% and placing it in an electrolytic cell as an electrolyte.

[0113] Step 3, using a discarded iron-plated titanium rod with an iron content of 8wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0114] Step 4, at room temperature, power is turned on to apply a voltage of 2V to perform electrolytic stripping, the initial current is 0.08A, and the stripping is stopped when the reaction current of the electrolytic stripping is 5mA. The total time for stripping is 20min.

[0115] Step 5, placing the titanium rod after electrolytic stripping into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the acid residue on the surface.

[0116] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium plate after stripping.

[0117] That is, the difference between this embodiment and embodiment 5 is only that:

[0118] In this embodiment, the electrolyte used is a nitric acid aqueous solution with a mass concentration of 3wt%; and the applied voltage is 2V.

[0119] The present invention has been tested and found that in the titanium plate after stripping in this embodiment, the iron content is 1.7wt% and the titanium weight loss is 0.17wt%.

[0120] Example 8

[0121] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0122] Step 1, mixing nitric acid and deionized water to prepare a nitric acid aqueous solution with a mass concentration of 1wt%.

[0123] Step 2, taking 2000g of the above-prepared nitric acid aqueous solution with a mass concentration of 1wt% and placing it in an electrolytic cell as an electrolyte.

[0124] Step 3, using a discarded iron-plated titanium rod with an iron content of 8wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0125] Step 4, at room temperature, power is turned on to apply a voltage of 1 V to perform electrolytic stripping, the initial current is 0.08 A, and the stripping is stopped when the reaction current of the electrolytic stripping is 5 mA. The total time is 25 minutes.

[0126] Step 5, placing the titanium rod after electrolytic stripping into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the acid residue on the surface.

[0127] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium rod after stripping.

[0128] That is, the difference between this embodiment and embodiment 7 is only that:

[0129] In this embodiment, the applied voltage is 1V.

[0130] The present invention has been tested and found that the iron content of the titanium rod after stripping in this embodiment is 1.85wt%, and the titanium weight loss is 0.15wt%.

[0131] Example 9

[0132] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0133] Step 1, mixing nitric acid and deionized water to prepare a nitric acid aqueous solution with a mass concentration of 15wt%.

[0134] Step 2, taking 2000g of the above-prepared nitric acid aqueous solution with a mass concentration of 15wt% and placing it in an electrolytic cell as an electrolyte.

[0135] Step 3, using a discarded iron-plated titanium rod with an iron content of 8wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0136] Step 4, at room temperature, power is turned on to apply a voltage of 0.8V to perform electrolytic stripping, the initial current is 0.08A, and the stripping is stopped when the reaction current of the electrolytic stripping is 4mA. The total time is 40min.

[0137] Step 5, placing the titanium rod after electrolytic stripping into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the acid residue on the surface.

[0138] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium rod after stripping.

[0139] That is, the difference between this embodiment and embodiment 7 is only that:

[0140] In this embodiment, the electrolyte used is a nitric acid aqueous solution with a mass concentration of 15wt%; the applied voltage is 0.8V.

[0141] The present invention has been tested and found that the iron content of the titanium rod after stripping in this embodiment is 1.83wt%, and the titanium weight loss is 0.19wt%.

[0142] Example 10

[0143] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0144] Step 1, mixing sulfuric acid, hydrochloric acid and deionized water to prepare a mixed acid solution with a sulfuric acid mass concentration of 1 wt % and a hydrochloric acid mass concentration of 0.9 wt %.

[0145] Step 2: Take 2000 g of the prepared mixed acid solution and place it in an electrolytic cell as an electrolyte.

[0146] Step 3, using a discarded iron-plated titanium rod with an iron content of 40wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and the cathode 10cm.

[0147] Step 4: At room temperature, power is applied to apply a voltage of 2V to perform electrolytic stripping, the initial current is 0.4A, and the stripping is stopped when the reaction current of the electrolytic stripping is less than 0.003A. The total time is 120 minutes. The total time is 60 minutes.

[0148] Step 5, placing the titanium rod after electrolytic stripping into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the acid residue on the surface.

[0149] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 100° C. for drying for 10 hours to obtain a titanium rod after stripping.

[0150] That is, the difference between this embodiment and embodiment 1 is only that:

[0151] In this embodiment, the electrolyte used is a mixed acid solution with a sulfuric acid mass concentration of 1 wt % and a hydrochloric acid mass concentration of 0.9 wt %; the applied voltage is 2V.

[0152] The present invention has been tested and found that the iron content in the titanium rod after stripping in this embodiment is 0.3wt%, and the titanium weight loss is 0.42wt%.

[0153] Embodiment 11

[0154] This embodiment provides a method for stripping an iron coating on a titanium workpiece surface, comprising the following steps:

[0155] Step 1: Mix hydrochloric acid and deionized water to prepare a hydrochloric acid aqueous solution with a mass concentration of 0.9 wt%.

[0156] Step 2, taking 2000g of the above-prepared hydrochloric acid aqueous solution with a mass concentration of 0.9wt% and placing it in an electrolytic cell as an electrolyte.

[0157] Step 3, using an iron-plated titanium plate with an iron content of 40wt% as an anode, connecting it to the positive electrode of a power source; using a titanium foil as a cathode, connecting it to the negative electrode of a power source, placing the connected anode and cathode in an electrolyte, and making the distance between the anode and cathode 50cm.

[0158] Step 4, at room temperature, power is turned on to apply a voltage of 5V to perform electrolytic stripping, the initial current is 0.42A, and the stripping is stopped when the reaction current of the electrolytic stripping is less than 0.003A. The total time is 150 minutes.

[0159] Step 5, placing the electrolytically stripped titanium plate into an ultrasonic cleaning device, and ultrasonically cleaning it at 25° C. and an ultrasonic frequency of 28 Hz for 15 minutes to clean the surface acid residue.

[0160] Step 6, placing the titanium plate after ultrasonic cleaning in an oven at 120° C. for drying for 5 hours to obtain a titanium plate after stripping.

[0161] The present invention has been tested and found that in the titanium plate after stripping in this embodiment, the iron content is 0.2wt% and the titanium weight loss is 0.72wt%.

[0162] Comparative Example 1

[0163] This comparative example provides a method for stripping an iron coating on a titanium workpiece surface, and the difference between this comparative example and Example 1 is only that:

[0164] In this comparative example, the voltage used is 10V.

[0165] After inspection, the iron content was less than 0.01wt%, the titanium weight loss was 13wt%, and chlorine evolution reaction also occurred.

[0166] Comparative Example 2

[0167] This comparative example provides a method for stripping an iron coating on a titanium workpiece surface, and the difference between this comparative example and Example 1 is only that:

[0168] In this comparative example, the electrolyte used is a hydrochloric acid aqueous solution with a mass concentration of 60 wt%.

[0169] After inspection, the iron content was less than 0.01wt%, the titanium weight loss was 20wt%, and chlorine evolution reaction also occurred.

[0170] In the electrolytic stripping process of this comparative example, not only the iron coating on the surface of the titanium workpiece was stripped, but also part of the titanium substrate was corroded, which indicates that the acid concentration of the electrolyte should not be too high.

[0171] Comparative Example 3

[0172] This comparative example provides a method for stripping an iron coating on a titanium workpiece surface, and the difference between this comparative example and Example 6 is only that:

[0173] In this comparative example, the voltage used is 10V.

[0174] In the electrolytic stripping process of this comparative example, the iron plating layer is passivated and an electrolytic water reaction occurs.

[0175] Comparative Example 4

[0176] This comparative example provides a method for stripping an iron coating on a titanium workpiece surface, and the difference between this comparative example and Example 6 is only that:

[0177] In this comparative example, the concentration of sulfuric acid used was 40 wt %.

[0178] In the electrolytic stripping process of this comparative example, the iron plating layer is passivated and an electrolytic water reaction occurs.

[0179] Experimental Section

[0180] The present invention found in the electrolytic stripping process of Examples 1 to 10 that the stripping methods of Examples 1 to 10 can achieve selective removal of the iron plating layer without damaging the titanium substrate.

[0181] In the electrolytic stripping process of Comparative Example 1, not only the iron plating layer on the surface of the titanium workpiece was stripped, but also part of the titanium substrate was corroded. The iron plating layer of Comparative Example 3 was passivated, and the electrolytic water reaction occurred, and the plating layer could not be removed, which shows that the voltage applied in the present invention should not be too high, so it is preferably 0.1V to 5V.

[0182] During the electrolytic stripping process of Comparative Example 2, Comparative Example 1 not only stripped the iron coating on the surface of the titanium workpiece, but also caused a portion of the titanium substrate to be corroded. The iron coating of Comparative Example 4 was passivated, and an electrolytic water reaction occurred, and the coating could not be removed. This shows that the acid concentration of the electrolyte used in the present invention should not be too high. Therefore, preferably, the mass concentration of the hydrochloric acid aqueous solution used is 0.1wt% to 6wt%. The mass concentration of the sulfuric acid aqueous solution used is 1wt% to 20wt%; and the mass concentration of the nitric acid aqueous solution used is 1wt% to 15wt%. The present invention also takes Example 1 as an example, and records the change of current with electrolysis time during its electrolytic stripping process as follows: Figure 2 shown.

[0183] Depend on Figure 2 It can be seen that the electrolytic stripping of the iron coating on the surface of the iron-plated titanium plate with an iron content of 40wt% is divided into three stages. The first stage: react with a constant current for a period of time. This stage is the time to remove the outer iron coating, and the withdrawn iron exists in the form of oxide. The second stage: most of the outer iron layer has been removed, and a small amount of residual iron begins to be removed, and the current drops rapidly to a low current. The fourth stage: the removal of residual trace iron, the current slowly decreases, tends to be stable, and approaches zero and the reaction stops.

[0184] In order to verify the deplating effect of the deplating method of the present invention, the surface of the titanium workpiece was subjected to energy spectrum test and analysis by a handheld X-ray fluorescence analyzer after the reaction was completed, and no iron element was found in the test results, indicating that the deplating method of the present invention can effectively realize the deplating of the iron plating on the surface of the titanium workpiece.

[0185] The present invention also uses titanium sheets and iron sheets as metal samples to be tested, and performs the following electrochemical tests on them respectively.

[0186] The electrochemical test adopted a three-electrode system, with the metal sample to be tested as the working electrode, graphite as the counter electrode, a saturated calomel electrode as the reference electrode, and the 0.9 wt % hydrochloric acid aqueous solution in Example 1 as the electrolyte. The test temperature was 25°C.

[0187] 1) Open circuit voltage test

[0188] According to the electrochemical test conditions, the open circuit voltage test of the titanium sheet and the iron sheet in the acidic deplating solution of Example 1, i.e., 0.9wt% hydrochloric acid aqueous solution, was tested, and the test results were as follows: Figure 3 shown.

[0189] Depend on Figure 3It can be seen that the open circuit potential of titanium in 0.9wt% hydrochloric acid aqueous solution is 0.35V (vsSCE), while the open circuit potential of iron is -0.48V (vsSCE). The open circuit voltage is positively correlated with the corrosion resistance of the metal. The open circuit potential of titanium is much higher than that of iron, indicating that titanium has stronger corrosion resistance than iron in 0.9wt% hydrochloric acid aqueous solution. This indicates that when electrolytic stripping is carried out in this electrolyte environment, due to the difference in electrochemical corrosion between titanium and iron, the present invention can achieve selective removal of iron without damaging the titanium substrate at a specific voltage.

[0190] 2) Electrochemical impedance spectroscopy

[0191] Based on the above electrochemical test conditions, the present invention adjusts the voltage to -0.48V and the frequency range to 10 -2 ~10 5 Hz, the AC excitation signal amplitude is 5mV, to perform electrochemical impedance test, and the test results are as follows Figure 4 shown.

[0192] Figure 4 The electrochemical impedance spectroscopy of the titanium sheet and the iron sheet in the acidic deplating solution of Example 1 is shown in FIG. Figure 4 It can be seen that the radius of the titanium semicircle is much larger than that of iron, which indicates that compared with titanium, iron has a smaller reaction impedance and is more susceptible to corrosion.

[0193] 3) Polarization curve test

[0194] Based on the above electrochemical test conditions, the present invention adjusts the scanning rate of the polarization curve to 5mV / s to perform the polarization curve test, and the test results are as follows Figure 5 shown.

[0195] right Figure 5 It can be seen from the fitting of the polarization curve that in the acidic stripping solution of Example 1, the corrosion potential of iron is -0.454V, and the corrosion potential of titanium is 0.011V, that is, the corrosion potential of titanium is greater than that of iron; the corrosion current density of iron is 6.15×10 -4 mA / cm 2 The corrosion current density of titanium is 3.32×10 -5 mA / cm 2 , that is, the corrosion current density of titanium is lower than that of iron by 6.15×10 -4 mA / cm 2 Based on the above, it can be seen that the positive corrosion potential and small corrosion current density of titanium indicate that titanium has higher corrosion resistance than iron in the acidic stripping solution environment of Example 1. In the range of 0V to 3V, the current density of iron is much higher than that of titanium, which means that iron will react preferentially in this system.

[0196] Obviously, the above embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for stripping an iron coating on a titanium workpiece surface, characterized in that: The following steps are involved: Using an acidic deplating solution as an electrolyte and a titanium workpiece to be deplated as an anode, placing the workpiece to be deplated and a cathode in the acidic deplating solution, applying a voltage of 0.1V to 5V to perform electrolytic deplating, and stopping the electrolytic deplating when the electrolytic current is less than a stop current threshold; After the electrolytic stripping is completed, the anode is taken out, ultrasonically cleaned and then dried to obtain a titanium workpiece that has completed stripping; The acidic deplating solution is one or more of a hydrochloric acid aqueous solution, a sulfuric acid aqueous solution and a nitric acid aqueous solution; wherein the mass concentration of the hydrochloric acid aqueous solution is 0.1wt% to 6wt%; The mass concentration of the sulfuric acid aqueous solution is 1wt% to 20wt%; The mass concentration of the nitric acid aqueous solution is 1wt% to 15wt%.

2. The method for stripping the iron coating on the surface of a titanium workpiece according to claim 1, characterized in that: The temperature of the electrolytic stripping is 5°C to 40°C.

3. The method for stripping the iron coating on the surface of a titanium workpiece according to claim 1, characterized in that: The distance between the anodes is 0.5 cm to 50 cm.

4. The method for stripping the iron coating on the surface of a titanium workpiece according to claim 1, characterized in that: The cathode is any one of a stainless steel plate, a titanium plate and a lead plate.

5. The method for stripping the iron coating on the surface of a titanium workpiece according to claim 1, characterized in that: The ultrasonic cleaning has an ultrasonic frequency of 25 Hz to 40 Hz, an ultrasonic temperature of 10° C. to 60° C., and an ultrasonic time of 0.1 min to 60 min.

6. The method for stripping the iron coating on the surface of a titanium workpiece according to claim 1, characterized in that: The stopping current threshold is ≤ 1% to 3% of the initial current value of the electrolytic stripping.

7. The method for stripping the iron coating on the surface of a titanium workpiece according to claim 6, characterized in that: When the stop current threshold is ≤3% of the initial current value of electrolytic stripping, the iron coating content on the surface of the titanium workpiece is ≤3%, and the weight loss of the titanium workpiece is ≤0.5%.

8. The method for stripping the iron coating on the surface of a titanium workpiece according to claim 6, characterized in that: When the stop current threshold is ≤1% of the initial current value of electrolytic stripping, the iron coating content on the surface of the titanium workpiece is ≤1%, and the weight loss of the titanium workpiece is ≤1%.

9. The method for stripping the iron coating on the surface of a titanium workpiece according to claim 1, characterized in that: The titanium workpiece to be deplated is any one of titanium metal fibers, titanium wires, titanium rods, titanium plates and titanium sheets with an iron coating on the surface.

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