Surface passivation treatment method of nickel-based alloy
Nickel-based alloy is a heat-resistant alloy with nickel as the base material (the content is generally greater than 50%), which has high strength and good tolerance and gas corrosion resistance in the range of 650-1000℃. Common nickel-based alloys include monel alloy, inconel alloy, hastelloy alloy, etc. Nickel-based alloys are often used in the manufacture of high-temperature parts on aviation, nuclear reactors and energy conversion equipment due to their excellent corrosion resistance. However, in some industries, such as nuclear reactors and spent fuel reprocessing, when strong fluorinating agents (such as F2, HF) are introduced, nickel-based alloys will still be corroded, resulting in problems such as reduced mechanical strength of the alloy.
Nickel-based alloys will reach their service life after being used in a strong fluorinating agent environment for a period of time. Therefore, in some industries, such as the nuclear industry, nickel-based alloy materials need to be continuously replaced. At present, the technology for corrosion of nickel-based alloys is to produce a layer of "frozen wall" on its surface for protection. The frozen wall refers to a protective lining formed by salts of certain specific compositions. However, the conditions for the formation of the freezing wall are very harsh, and the temperature difference between the inner wall and the outside of the nickel-based alloy needs to be strictly controlled; and during the use of the nickel-based alloy, it is difficult to maintain the dynamic state of the freezing wall.
However, no passivation technology that can make the nickel-based alloy resistant to strong fluorinating agents has been found.
Surface treatment method of nickel-based alloy
The technical problem to be solved by the present invention is to overcome the defect that the current nickel-based alloy is corroded in the environment of strong fluorinating agents, and provide a surface passivation treatment method for nickel-based alloys. Using the surface passivation treatment method provided by the present invention, a dense passivation layer is formed on the surface of the nickel-based alloy, which prevents the alloy from being corroded by strong corrosive gases such as fluorine gas, improves the corrosion resistance of the nickel-based alloy material, and prolongs the service life of the alloy.
Therefore, the present invention provides a surface passivation treatment method for nickel-based alloys, which includes the following steps: pre-treating and drying the nickel-based alloy, and then performing surface passivation treatment with a fluorine-argon mixed gas; the surface passivation treatment is divided into four stages:
1: heating the nickel-based alloy to 100℃～150℃, and further removing the water in the reaction system;
2: continuing to heat the nickel-based alloy to 350℃～550℃, such as to 400℃～500℃, so that the surface of the nickel-based alloy slowly produces a passivation layer;
3: keeping the nickel-based alloy at the temperature at the end of the second stage heating for 3h～6h, such as 4h～5h, and further producing a stable passivation layer on the surface of the nickel-based alloy;
4: cooling the nickel-based alloy to room temperature, and the above cooling is preferably natural cooling, so that the formed passivation layer is not broken. Each stage of the above surface passivation treatment is carried out under the condition of passing a fluorine-argon mixed gas.
In the present invention, the above-mentioned pretreatment is the pretreatment conventionally referred to in the art, which is generally for the treatment of impurities on the surface of the nickel-based alloy, preferably one or more of sandpaper polishing, acid cleaning and water washing; the above-mentioned acid is preferably a mixed solution of NaCl and HNO3; the concentration of the above-mentioned HNO3 is preferably 0.5mol/L~1.5mol/L, more preferably 1mol/L; the mass percentage of the above-mentioned NaCl is preferably 5%.
In the present invention, the above-mentioned drying method and conditions can refer to the conventional drying method and conditions in the art. The present invention preferably uses a blast drying oven or a vacuum drying oven, the above-mentioned drying temperature is preferably 90℃~110℃, and the above-mentioned drying time is preferably 1h~10h to clean the water on the surface of the nickel-based alloy.
According to common sense in the art, in the reaction system of the surface passivation treatment of the present invention, there will be no impurities that can react with nickel-based alloys or fluorine-argon mixed gas, such as water or oxygen; preferably, before the surface passivation treatment, a rare gas is used to clear the impurities in the reaction system with reference to the conventional method in the art; the above-mentioned rare gas is a rare gas conventionally used in the art, generally referring to a gas that does not react during the surface passivation treatment, preferably argon.
In the present invention, in the above-mentioned fluorine-argon mixed gas, the volume fraction of fluorine gas is preferably 5% to 30%, such as 10% to 20%.
In the present invention, in the above-mentioned stages, the flow rate of the fluorine-argon mixed gas is preferably 0.01L/min to 0.1L/min, such as 0.05L/min; in other stages, the flow rate of the fluorine-argon mixed gas is preferably 0.01L/min to 0.3L/min, such as 0.1L/min to 0.2L/min; in the above-mentioned third stage, the flow rate of the fluorine-argon mixed gas is preferably 0.01L/min to 0.2L/min, such as 0.1L/min; in the above-mentioned fourth stage, the flow rate of the fluorine-argon mixed gas is preferably 0.01L/min to 0.1L/min, such as 0.05L/min.
The surface passivation treatment method of the nickel-based alloy provided by the present invention is suitable for various parts made of nickel-based alloys, such as reaction tanks, pipes and screws, etc., but is not limited thereto; the surface passivation treatment method provided by the present invention is also suitable for various forms of nickel-based alloys, such as various plates, cables and pipes of nickel-based alloys, etc.
Without violating the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred cases of the present invention.
The reagents and raw materials used in the present invention are all commercially available.
The positive and progressive effect of the present invention is that the surface passivation treatment method of the nickel-based alloy provided by the present invention is selected to obtain a golden passivation layer on the surface of the nickel-based alloy; the passivation layer has good adhesion, is uniform and dense, and can withstand highly corrosive gases such as fluorine gas and hydrogen fluoride at room temperature to 600°C, thereby increasing the corrosion resistance of the nickel-based alloy material and thus extending the service life of the nickel-based alloy material.
Specific implementation methods
The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the above-mentioned examples. The experimental methods for which the specific conditions are not specified in the following examples are selected according to conventional methods and conditions, or according to the product instructions.
Example
The nickel-based alloy reaction tank is pickled with a 0.5mol/LHNO3-5%NaCl solution, then washed with water, and then placed in a 90°C blast drying oven for drying for 1h. Use high-purity argon to replace the gas in the reactor, and perform passivation treatment on the nickel-based alloy reactor according to the following passivation treatment scheme 1.
Passivation treatment scheme 1 is as follows:
1: Heat the nickel-based alloy reactor to 100°C, and introduce a 30% F2/Ar mixed gas at a flow rate of 0.01L/min during this period;
2: Heat the nickel-based alloy reactor from 100°C to 350°C, and introduce a 30% F2/Ar mixed gas at a flow rate of 0.2L/min during this period;
3: Keep the nickel-based alloy reactor at a constant temperature of 350°C for 3h, and introduce a 30% F2/Ar mixed gas at a flow rate of 0.1L/min during this period;
4: Cool the nickel-based alloy reactor naturally from 350°C to room temperature, and introduce a 30% F2/Ar mixed gas at a flow rate of 0.01L/min during this period.
After passivation, the surface of the nickel-based alloy reaction tank formed a uniform and dense golden passivation layer. The reaction tank was placed in a KF-ZrF4-UF4 molten salt system and fluorine gas was introduced at 500°C for fluorination reaction. As a result, the passivation layer did not separate from the surface of the nickel-based alloy and the reaction tank was not corroded.
Example 2
The nickel-based alloy reaction tank was pickled with 1.0 mol/L HNO3-5% NaCl solution, then washed with water, and then placed in a 100°C blast drying oven for 5 hours. The gas in the reactor was replaced with high-purity argon gas, and the nickel-based alloy reaction tank was passivated according to the following passivation treatment scheme 2.
Passivation treatment scheme 2 is as follows:
1: Heat the nickel-based alloy reaction tank to 130℃, during which a fluorine gas volume fraction of 20% F2/Ar mixed gas is introduced at a flow rate of 0.05L/min;
2: Heat the nickel-based alloy reaction tank from 100℃ to 400℃, during which a fluorine gas volume fraction of 20% F2/Ar mixed gas is introduced at a flow rate of 0.1L/min;
3: Keep the nickel-based alloy reaction tank at a constant temperature of 400℃ for 6h, during which a fluorine gas volume fraction of 20% F2/Ar mixed gas is introduced at a flow rate of 0.2L/min;
4: Heat the nickel-based alloy reaction tank from 400℃ to room temperature, during which a fluorine gas volume fraction of 20% F2/Ar mixed gas is introduced at a flow rate of 0.05L/min.
After passivation, the surface of the nickel-based alloy reaction tank formed a uniform and dense golden passivation layer. The reaction tank was used in the FLiNaK-ZrF4-UF4 molten salt system, and fluorine gas was introduced at 550°C for fluorination reaction. As a result, the passivation layer did not separate from the surface of the nickel-based alloy and the reaction tank was not corroded.
Example 3
The nickel-based alloy reaction tank was pickled with 1.5mol/LHNO3-5%NaCl solution, then washed with water, and then placed in a vacuum drying oven at 110°C for 10 hours. The gas in the reactor was replaced with high-purity argon gas, and the nickel-based alloy reaction tank was passivated according to the following passivation treatment scheme 3.
Passivation treatment scheme 3 is as follows:
1; Heat the nickel-based alloy reaction tank to 150°C, during which a fluorine gas volume fraction of 5% F2/Ar mixed gas is introduced at a flow rate of 0.1L/min;
2; Heat the nickel-based alloy reaction tank from 150°C to 500°C, during which a fluorine gas volume fraction of 5% F2/Ar mixed gas is introduced at a flow rate of 0.3L/min;
3; Keep the nickel-based alloy reaction tank at a constant temperature of 500°C for 5h, during which a fluorine gas volume fraction of 5% F2/Ar mixed gas is introduced at a flow rate of 0.2L/min;
4; Naturally cool the nickel-based alloy reaction tank from 400°C to room temperature, during which a fluorine gas volume fraction of 5% F2/Ar mixed gas is introduced at a flow rate of 0.1L/min.
After passivation, the surface of the nickel-based alloy reactor formed a uniform and dense golden passivation layer. The reactor was used in the FLiNaK-UF4 molten salt system, and fluorine gas was introduced at 550°C for fluorination reaction. As a result, the passivation layer did not separate from the surface of the nickel-based alloy and the reactor was not corroded.
Example 4
The nickel-based alloy reactor was polished with sandpaper and then washed with water, and then placed in a 100°C blast drying oven for 8 hours. The gas in the reactor was replaced with high-purity argon gas, and the nickel-based alloy reactor was passivated according to the following scheme 4.
Passivation treatment scheme 4 is as follows
1; Heat the nickel-based alloy reaction tank to 100°C, during which a fluorine gas volume fraction of 10% F2/Ar mixed gas is introduced at a flow rate of 0.1L/min;
2: Heat the nickel-based alloy reaction tank from 100°C to 550°C, during which a fluorine gas volume fraction of 10% F2/Ar mixed gas is introduced at a flow rate of 0.01L/min;
3: Keep the nickel-based alloy reaction tank at a constant temperature of 550°C for 4h, during which a fluorine gas volume fraction of 10% F2/Ar mixed gas is introduced at a flow rate of 0.01L/min;
4: Naturally cool the nickel-based alloy reaction tank from 550°C to room temperature, during which a fluorine gas volume fraction of 10% F2/Ar mixed gas is introduced at a flow rate of 0.05L/min.
After passivation, a uniform and dense golden passivation layer was formed on the surface of the nickel-based alloy reaction tank. The reaction tank was used in a FLiNaK-ThF4-UF4 molten salt system and fluorine gas was introduced at 600°C for fluorination reaction. As a result, the passivation layer did not separate from the nickel-based alloy surface and the reaction tank was not corroded.
