Preparation method of high-purity low-oxygen chromium evaporation particles

Abstract

The invention belongs to the technical field of metal particle preparation, and discloses a preparation method of high-purity low-oxygen chromium evaporation particles. The preparation method comprises the following steps: carrying out deoxidation treatment on an electrolytic chromium sheet, and crushing to obtain low-oxygen metal chromium powder; carbon powder and low-oxygen metal chromium powder are evenly mixed and pressed into a columnar green body, then reduction sintering is conducted under vacuum, and a high-purity low-oxygen metal chromium column is obtained; the method comprises the following steps: heating a high-purity low-oxygen metal chromium cylinder to 1200-1500 DEG C in a high-frequency coil under vacuum, irradiating by laser to partially melt the end surface of the high-purity low-oxygen metal chromium cylinder and form liquid drops, continuously and uniformly falling the liquid drops into a rotating water-cooling copper disc under the action of gravity, and cooling and solidifying to obtain the high-purity low-oxygen chromium evaporation particles. The preparation method is easy to operate, and the high-purity low-oxygen chromium evaporation particles can be continuously obtained; the content of Cr in the prepared high-purity low-oxygen chromium evaporation particles exceeds 99.96%, and no residual carbon exists.

Description

Technical Field

[0001] The invention relates to the technical field of metal particle preparation, and in particular to a method for preparing high-purity low-oxygen chromium evaporation particles. Background Art

[0002] Chromium target is a key raw material widely used in coating fields such as reflective films for automotive and architectural glass, chromium masking films for integrated circuits, multi-layer metal films in LEDs and semiconductor power devices, spectroscopic films in optical devices, and chromium carbide hard films on cutting tools. It has a wide range of uses.

[0003] Metallic chromium particles are the key raw material for vacuum-deposited chromium metal films. However, due to the extremely high melting point, active chemical properties and high brittleness of the metal, the chromium particles currently obtained by methods such as melt atomization, centrifugal granulation of chromium powder and mechanical cutting have low purity, less than 99.9%, which seriously limits the further application and development of metallic chromium particles.

[0004] Based on the above, it can be seen that it is currently difficult to obtain high-purity chromium particles with a purity greater than 99.95% in the prior art, so it is necessary to provide an effective means for obtaining high-purity chromium particles with a purity greater than 99.95% to promote the further application and development of high-purity chromium particles. To this end, the present invention provides a method for preparing high-purity low-oxygen chromium evaporation particles. Summary of the invention

[0005] In order to solve the deficiencies in the above-mentioned prior art, the present invention provides a method for preparing high-purity low-oxygen chromium vapor-deposited particles. The present invention analyzes the reasons why it is difficult to obtain high-purity chromium particles in the prior art, and finds that due to the high melting point of metallic chromium, about 1870°C, it is difficult to melt it, and the chemical activity of metallic chromium is high, and liquid chromium is easy to react with refractory materials such as crucibles, making it very difficult to obtain high-purity chromium melt. As a result, it is difficult to obtain high-purity chromium particles with a purity of more than 99.9% by using methods such as atomization, high-speed centrifugal granulation, and mechanical processing of the blocks obtained by solidifying the chromium melt. To this end, the present invention proposes a method for purifying metallic chromium in the solid state and obtaining a high-purity columnar metallic chromium sintered body, and then using high-frequency heating and laser dual heating in a high vacuum environment to cause micro-area melting of the solid metallic chromium to obtain high-purity chromium droplets, and the chromium droplets solidify in a high vacuum environment to obtain high-purity low-oxygen chromium vapor-deposited particles.

[0006] The preparation method of the high-purity low-oxygen chromium vapor-deposited particles of the present invention is achieved by the following technical scheme:

[0007] A method for preparing high-purity low-oxygen chromium evaporation particles comprises the following steps:

[0008] Step 1: using an electrolytic chromium sheet as a chromium source, deoxidizing it to obtain a reduced low-oxygen electrolytic chromium sheet.

[0009] It should be noted that in order to ensure the purity of the metallic chromium particles finally obtained, in some feasible embodiments of the present invention, high-purity chromium sheets prepared by electrolysis are used as raw materials. The impurity concentration of the chromium sheets prepared by electrolysis, except for oxygen and nitrogen elements, is less than 0.05%, that is, the purity of the obtained chromium sheets is ≥99.95%, which can be regarded as high-purity chromium sheets.

[0010] Considering that the oxygen content in the electrolytic chromium sheet is relatively high, about 5000 ppm, the present invention first performs a deoxidation treatment on it to reduce its oxygen content to below 500 ppm, so as to preliminarily obtain a low-oxygen chromium raw material.

[0011] In order to ensure that the above-mentioned effects can be achieved through deoxidation treatment, in some feasible embodiments of the present invention, it is preferred to use a hydrogen atmosphere as a high-temperature reducing atmosphere to achieve deoxidation and reduction treatment of the electrolytic chromium sheet under a hydrogen atmosphere to obtain a reduced electrolytic chromium sheet.

[0012] The present invention takes into account the possibility of water vapor in hydrogen. In order to avoid water vapor contamination in hydrogen, in some preferred embodiments of the present invention, hydrogen with a dew point of ≤-70°C is used as a high-temperature reducing atmosphere, and the deoxidation and reduction treatment of the electrolytic chromium sheet is specifically achieved by the following steps:

[0013] The electrolytic chromium sheet is placed in a ceramic boat made of alumina, and the ceramic boat is placed in a high-temperature furnace chamber for hydrogen reduction; nitrogen with a purity of ≥99.9% is first introduced into the high-temperature furnace chamber to evacuate the air in the furnace chamber, and then hydrogen with a dew point of ≤-70°C is introduced into the furnace chamber, and the hydrogen at the outlet is ignited after passing an explosion test; after the hydrogen is ignited, the furnace chamber begins to gradually heat up, and the temperature rises to 1000°C to 1300°C and is kept warm for 1h to 3h, and then cooled to room temperature under hydrogen protection to obtain a reduced low-oxygen electrolytic chromium sheet.

[0014] Step 2: crush the low-oxygen electrolytic chromium sheet to obtain low-oxygen metal chromium powder; use carbon powder as a reducing agent, mix it with the low-oxygen metal chromium powder and press it into a columnar blank, and then sinter it in a vacuum environment to obtain a high-purity low-oxygen metal chromium column.

[0015] It should be noted that the present invention takes into account that the deoxidation effect of hydrogen reduction may not be thorough enough, so it is necessary to further deoxidize it to further remove oxygen in the low-oxygen electrolytic chromium sheet. In order to further improve the removal effect of oxygen in the low-oxygen electrolytic chromium sheet and improve the purity of the metal chromium vapor-deposited particles finally obtained, in some feasible embodiments of the present invention, the present invention first crushes the reduced low-oxygen electrolytic chromium sheet to make it powder, so as to facilitate further carbon thermal reduction deoxidation and molding.

[0016] Moreover, in order to ensure the contact between the obtained low-oxygen metallic chromium powder from the comminution process and the subsequent reducing agent, in some feasible embodiments of the present invention, the reduced low-oxygen electrolytic chromium flakes are comminuted by mechanical crushing in a liquid nitrogen environment and then screened to obtain low-oxygen metallic chromium powder with a particle size of 45 μm to 150 μm.

[0017] Considering that there may be some impurities on the surface of the low-oxygen electrolytic chromium flakes obtained from the reduction and deoxidation treatment, in some feasible embodiments of the present invention, before comminuting the low-oxygen electrolytic chromium flakes obtained from the reduction and deoxidation treatment, they are first washed with water to remove the possible impurities, and then dried to remove the residual water on the surface to obtain clean low-oxygen electrolytic chromium flakes, and then they are comminuted to ensure the purity of the low-oxygen metallic chromium powder.

[0018] In order to ensure that the reduction of oxygen in the low-oxygen metallic chromium powder can be achieved by the reducing agent, preferably, carbon powder is used as the reducing agent in the present invention. By adding carbon powder to the low-oxygen metallic chromium powder, during the subsequent sintering process, while the carbon reduction reaction occurs, sintering and shaping are realized, and at the same time, the remaining oxygen in the hydrogen-reduced metallic chromium powder is further removed and the chromium column has high mechanical strength for further operations.

[0019] It should also be noted that the present invention considers that the oxygen in the chromium powder mainly exists in two forms. One is the oxygen adsorbed on the surface of the chromium powder, and the other is the oxygen existing in the form of oxides on the surface and inside of the chromium powder. The oxygen adsorbed on the surface of the chromium powder can be removed by vacuum annealing degassing, while the oxygen existing in the form of oxides cannot be eliminated even by vacuum annealing at 1500°C. Due to the high stability of chromium oxides, to decompose them, the temperature of vacuum annealing must be increased or an ultra-high vacuum system must be equipped.

[0020] Taking the decomposition of Cr 2 O 3 as an example, its decomposition chemical equation is shown in Equation 1:

[0021] Cr 2 O 3 →2Cr + 3 / 2O 2 Equation 1.

[0022] Among them, the change in Gibbs free energy during the decomposition process is shown in Equations 2 and 3:

[0023] ΔG = ΔG 0 + RTlnP 2 / 3 Equation 2.

[0024] ΔG 0 = 1110140 - 247.316T Equation 3.

[0025] According to Equations 1 - 3, it can be calculated that to make Cr2 O 3 To decompose in the atmosphere, it must be heated to above 4500℃, which is difficult to achieve in practice. In a vacuum system, the oxygen generated by the reaction is pumped away by the vacuum system. The equilibrium reaction is related to the vacuum degree of the system. It can be seen that at 1500℃, Cr 2 O 3 The vacuum degree required for decomposition is 7×10 -14 Pa, this is also unattainable.

[0026] It should also be noted that there is always a certain amount of water vapor in hydrogen, and it is difficult to obtain hydrogen with an extremely low dew point; experiments have shown that hydrogen reduction cannot produce metallic chromium powder with an oxygen content of less than 350ppm.

[0027] If carbon is added to chromium powder at high temperature, Cr 2 O 3 React with carbon as shown in Formula 4 and Formula 5:

[0028]

[0029] ΔG+514340-337.905T+RTlnP 2 Formula 5.

[0030] Where P is the partial pressure of CO, it can be calculated that Cr at 1500℃ 2 O 3 The vacuum degree of decomposition is 7.4×10 4 Pa.

[0031] The Cr values ​​with and without carbon addition are shown in Table 1. 2 O 3 The relationship between decomposition temperature and vacuum degree.

[0032] It can be seen from Table 1 that the reduction and removal conditions of oxygen after adding carbon can be achieved in a general vacuum furnace. In practice, metal chromium powder with a minimum oxygen content of less than 20 ppm can be obtained, creating favorable conditions for preparing low-oxygen chromium columns using high-oxygen chromium powder.

[0033] Table 1Cr 2 O 3 Relationship between reduction temperature and vacuum degree

[0034] Temperature / ℃ <![CDATA[Cr 2 O 3 Decomposition vacuum degree / Pa]]> <![CDATA[Cr 2 O 3 Carbon reduction vacuum degree / Pa]]> 1100 - 4.10×10 1200 <![CDATA[2.49×10 -19 ]]> <![CDATA[4.27×10 2 ]]> 1300 <![CDATA[7.49×10 -17 ]]> <![CDATA[3.10×10 3 ]]> 1400 <![CDATA[9.96×10 -15 ]]> <![CDATA[1.70×10 4 ]]> 1500 <![CDATA[6.0×10 -13 ]]> <![CDATA[7.4×10 4 ]]> 1522 - <![CDATA[10 5 ]]>

[0035] Based on the above, the present invention preferably adopts reduction deoxidation treatment in a hydrogen atmosphere and carbon reduction treatment of carbon powder to gradually remove oxygen from the electrolytic chromium sheet.

[0036] It should be emphasized that the present invention takes into account the possible presence of residual carbon or its ash, so it is necessary to control the purity of the carbon powder and the degree of its deoxidation to achieve the purity of the chromium column.

[0037] In order to ensure that the degree of deoxygenation of the carbon powder can be controlled, in some feasible embodiments of the present invention, the oxygen content in the low-oxygen metal chromium powder is first measured, and then the amount of carbon powder required to reduce the total residual oxygen content in the low-oxygen metal chromium powder is calculated according to the measured oxygen content in the low-oxygen metal chromium powder according to the formula shown in Formula 4, and then 0.4wt% to 0.6wt% of the amount of carbon powder required to reduce the total residual oxygen content in the low-oxygen metal chromium powder is used as the actual amount of carbon powder added to achieve the purpose of deoxidation and no residual carbon. Among them, when measuring the oxygen content in the low-oxygen metal chromium powder, a Leco gas analyzer can be used for measurement.

[0038] The present invention takes into account the requirements of the material shape for subsequent induction heating, and first presses the mixed powder into a columnar blank, and then performs a sintering process to achieve the purpose of chromium powder molding. In some feasible embodiments of the present invention, the vacuum degree of the sintering process is ≤6.67×10 -3 Pa, the sintering temperature is 1250℃~1400℃, and the sintering time is 1h~2h.

[0039] The present invention does not limit the specific size of the columnar blank, and can be prepared according to the size of the high-frequency coil actually used, as long as the diameter of the prepared columnar blank is smaller than the inner diameter of the high-frequency coil insulation layer, so that the columnar blank can pass through the high-frequency coil, so that the columnar blank passing through the high-frequency coil can be heated and melted by laser irradiation to form droplets. For example, in some feasible embodiments of the present invention, the diameter of the columnar blank is 10 mm to 50 mm, and the length is 200 mm to 1000 mm.

[0040] Step 3: In a vacuum environment, use a high-frequency coil to heat the high-purity low-oxygen metal chromium column to 1200° C. to 1500° C. to obtain a heated high-purity low-oxygen metal chromium column; then, use a laser to irradiate the heated high-purity low-oxygen metal chromium column to melt it to form droplets; allow the droplets to fall continuously and evenly onto a rotating water-cooled copper disk under the action of gravity, and cool and solidify on the water-cooled copper disk to obtain high-purity low-oxygen chromium vapor-deposited particles.

[0041] It should be noted that the present invention takes into account the fact that chromium is easy to sublime. Preferably, a high-frequency coil is used to heat the high-purity low-oxygen metal chromium column to 1200°C to 1500°C, so that the temperature of the high-purity low-oxygen metal chromium column is heated to a temperature close to the melting point of metallic chromium, so that the high-purity low-oxygen metal chromium column is fully heated but the chromium is not obviously sublimated, so as to reduce the requirement for laser power during subsequent laser irradiation, so that the high-purity low-oxygen metal chromium column can be melted and droplets can be formed by laser irradiation under lower requirements.

[0042] In order to ensure that the high-frequency coil used can heat the high-purity low-oxygen metal chromium column to a temperature close to the melting point of metal chromium, in some feasible embodiments of the present invention, when the high-purity low-oxygen metal chromium column is heated by the high-frequency coil, the high-purity low-oxygen metal chromium column is slowly passed through the center of the high-frequency induction coil at a descending speed of 3mm / min to 5mm / min, so that the high-purity low-oxygen metal chromium column is heated to 1200°C to 1500°C in the process of passing through the high-frequency coil.

[0043] In order to further ensure that the high-frequency coil used can heat the high-purity, low-oxygen metal chromium column to a temperature close to the melting point of metal chromium, in some feasible embodiments of the present invention, the high-frequency coil used is made of a water-cooled copper coil, and the power supply adopts automatic frequency regulation, with a power supply power of 20kW to 50kW and an operating frequency of 10000Hz to 50000Hz.

[0044] It should also be noted that the present invention takes into account the factors of reducing the laser power and not producing obvious chromium metal vapor. In some feasible embodiments of the present invention, after the high-purity low-oxygen metal chromium column is heated to 1200°C to 1500°C by a high-frequency coil, it is irradiated by laser to melt the high-purity low-oxygen metal chromium column in a high-temperature state in a vacuum environment by laser irradiation to form droplets, and the formed droplets fall continuously and evenly on the rotating water-cooled copper disk under the action of gravity. The water-cooled copper disk is cooled by circulating water inside, which can cool the high-temperature droplets. The rotating water-cooled copper disk can also increase the spheroidization of the droplets during the solidification process, thereby forming spherical solid particles on the water-cooled copper disk, that is, obtaining high-purity low-oxygen chromium vapor-deposited particles. In a feasible embodiment of the present invention, the rotation speed of the water-cooled copper disk is 10r / min to 50r / min.

[0045] In order to ensure that the high-purity, low-oxygen metal chromium column in a high-temperature state in a vacuum environment can be melted to form droplets by laser irradiation, in some feasible embodiments of the present invention, the process parameters during laser irradiation are: laser power of 200W to 800W, scanning spacing of 0.1mm to 0.2mm, and scanning rate of 200mm / s to 500mm / s.

[0046] It should also be noted that since the high-purity low-oxygen metal chromium column of the present invention is continuously heated by passing through a high-frequency coil, and the heated high-purity low-oxygen metal chromium column is continuously melted to form droplets after being irradiated by a laser, and the formed droplets fall continuously and evenly onto a rotating water-cooled copper disk under the action of gravity, the entire preparation process is carried out continuously, and high-purity low-oxygen chromium vapor-deposited particles can be continuously obtained.

[0047] In order to prevent the formed high-purity low-oxygen chromium vapor-deposited particles from affecting the subsequent droplets to form high-purity low-oxygen chromium vapor-deposited particles, the descent method of the high-purity low-oxygen metal chromium column can be adjusted, such as intermittent descent. During the intermittent descent, a scraper is used to remove and collect the high-purity low-oxygen chromium vapor-deposited particles on the water-cooled copper plate, and then the high-purity low-oxygen metal chromium column continues to descend through the high-frequency coil.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention uses an electrolytic chromium sheet as a chromium source, and performs a deoxidation treatment on the electrolytic chromium sheet in a high-temperature reducing atmosphere to achieve deoxidation and reduction treatment of the electrolytic chromium sheet, so as to reduce the oxygen content in the chromium source. Then, the low-oxygen electrolytic chromium sheet is crushed, and carbon powder is used as a reducing agent, and a sintering treatment is performed, so that sintering and molding are achieved while a carbon reduction reaction occurs, and the remaining oxygen in the hydrogen-reduced metal chromium powder is further removed, and the chromium column has high mechanical strength. Subsequently, the high-purity low-oxygen metal chromium column obtained by the sintering treatment is heated by laser irradiation to a temperature close to the melting point of metal chromium, so that the high-purity low-oxygen metal chromium column is fully heated but the chromium is not obviously sublimated, so as to reduce the requirements for laser power during subsequent laser irradiation, so that the high-purity low-oxygen metal chromium column can be melted and droplets can be formed by laser irradiation under lower requirements. Then, laser irradiation is used to irradiate the high-purity low-oxygen metal chromium column in a high-temperature state in a vacuum environment, so that it melts and forms droplets, and the formed droplets fall continuously and evenly onto a rotating water-cooled copper disk under the action of gravity. The water-cooled copper disk is cooled by circulating water inside, which can cool the high-temperature droplets. The rotating water-cooled copper disk can also increase the spheroidization of the droplets during the solidification process, thereby forming spherical solid particles on the water-cooled copper disk, that is, obtaining high-purity low-oxygen chromium vapor-deposited particles.

[0050] The preparation method of the present invention is simple to operate and can be carried out continuously, and high-purity low-oxygen chromium vapor-deposited particles can be continuously obtained. The Cr content in the high-purity low-oxygen chromium vapor-deposited particles prepared by the present invention exceeds 99.96%, and no residual carbon is present, indicating that the method of the present invention can successfully prepare high-purity low-oxygen chromium vapor-deposited particles, making up for the deficiency that it is difficult to obtain high-purity chromium particles in the prior art. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present invention will be described clearly and completely below.

[0052] Example 1

[0053] This embodiment provides a method for preparing high-purity low-oxygen chromium evaporation particles, comprising the following steps:

[0054] Step 1, deoxidation treatment:

[0055] 1) Placing the electrolytic chromium sheet in a ceramic boat made of alumina, and placing the ceramic boat in a high-temperature furnace chamber for hydrogen reduction.

[0056] 2) First, nitrogen with a purity of ≥99.9% is introduced into the high-temperature furnace chamber to evacuate the air in the furnace chamber, and then hydrogen with a dew point of ≤-70°C is introduced into the furnace chamber. After passing the explosion test, the hydrogen at the outlet is ignited.

[0057] 3) After the hydrogen is ignited, the furnace chamber begins to gradually heat up, and after the temperature rises to 1200°C, it is kept at 1200°C for 2 hours, and then cooled to room temperature under the protection of hydrogen to obtain reduced low-oxygen electrolytic chromium sheets.

[0058] Step 2, preparation of low oxygen metallic chromium powder:

[0059] 1) The reduced low-oxygen electrolytic chromium sheet was washed with deionized water for 3 times, and then dried to remove the residual water on the surface to obtain a clean low-oxygen electrolytic chromium sheet.

[0060] 2) The clean low-oxygen electrolytic chromium flakes obtained above are crushed in a liquid nitrogen environment and then sieved to obtain low-oxygen metal chromium powder with a particle size of 45 μm to 150 μm.

[0061] Step 3, sintering treatment:

[0062] 1) Measure the oxygen content in the low-oxygen chromium metal powder, and then calculate the amount of carbon powder required to reduce the total remaining oxygen content in the low-oxygen chromium metal powder according to the measured oxygen content in the low-oxygen chromium metal powder according to the formula shown in Formula 4, and then use 0.5wt% of the amount of carbon powder required to reduce the total remaining oxygen content in the low-oxygen chromium metal powder as the actual amount of carbon powder added, and weigh the corresponding mass of carbon powder for later use.

[0063] 2) The weighed carbon powder and the low-oxygen metal chromium powder obtained above are mixed evenly, and then pressed into a slender columnar blank with a diameter of 30 mm and a length of 500 mm.

[0064] 3) The slender columnar blank obtained above is formed into a -3 Pa high vacuum and 1350 ° C high temperature environment, and then hot carbon reduction for 1.5 h to obtain high-purity low-oxygen metal chromium column.

[0065] Step 4: High frequency coil heating followed by laser irradiation:

[0066] 1) The high-purity low-oxygen metal chromium column obtained above is slowly passed through a high-frequency coil with an inner diameter greater than the diameter of the columnar blank and a length of 80 mm at a descending speed of 4 mm / min in a vacuum environment, so that the high-purity low-oxygen metal chromium column is heated to 1350°C in the process of passing through the high-frequency coil, and the column and the coil are perpendicular to the ground during the movement.

[0067] 2) Outside the vacuum chamber, a laser is used to irradiate the lower end face of a metal chromium cylinder heated by a high-frequency coil, so that the irradiated position of the end face of the chromium cylinder is melted, forming droplets, which fall under the action of gravity onto a water-cooled copper disk that rotates slowly at a speed of 30 r / min in the vacuum chamber. The copper disk is cooled by circulating water to cool the high-temperature droplets, and the rotating water-cooled copper disk can also increase the spheroidization of the droplets during the solidification process, thereby forming spherical solid particles on the water-cooled copper disk, thereby obtaining high-purity low-oxygen chromium vapor-deposited particles.

[0068] In this embodiment, liquid chromium particles solidify on a water-cooled copper disk and rotate with the metal disk, and are cleaned out of the copper disk by a scraper before returning to the casting position next time; the laser continuously irradiates the metal chromium column that slowly moves downward in the high-frequency coil, and the molten chromium droplets in the irradiated area fall down to cool down, and continuously solidify on the water-cooled copper disk to form high-purity low-oxygen chromium vapor-deposited particles and are scraped out of the disk.

[0069] The present invention has tested the performance of the chromium particles prepared in the above embodiment, and the test results are shown in Table 2.

[0070] Table 2 Chromium particle size and chemical composition

[0071] element Cr Fe Al Si Mo W Content / wt% 99.97 0.0091 0.000097 0.0011 0.0063 0.0011

[0072] And from the test results in Table 2, it can be seen that the purity of the chromium particles prepared by the present invention is 99.97% and there is no residual carbon, which shows that the method of the present invention can prepare high-purity low-oxygen chromium vapor-deposited particles.

[0073] Example 2

[0074] This embodiment provides a method for preparing high-purity low-oxygen chromium vapor-deposited particles, comprising the following steps:

[0075] Step 1, deoxidation treatment:

[0076] 1) Placing the electrolytic chromium sheet in a ceramic boat made of alumina, and placing the ceramic boat in a high-temperature furnace chamber for hydrogen reduction.

[0077] 2) First, nitrogen with a purity of ≥99.9% is introduced into the high-temperature furnace chamber to evacuate the air in the furnace chamber, and then hydrogen with a dew point of ≤-70°C is introduced into the furnace chamber. After passing the explosion test, the hydrogen at the outlet is ignited.

[0078] 3) After the hydrogen is ignited, the furnace chamber begins to gradually heat up, and after the temperature rises to 1000°C, it is kept at 1000°C for 3 hours, and then cooled to room temperature under the protection of hydrogen to obtain reduced low-oxygen electrolytic chromium sheets.

[0079] Step 2, preparation of low oxygen metallic chromium powder:

[0080] 1) The reduced low-oxygen electrolytic chromium sheet was washed with deionized water for 3 times, and then dried to remove the residual water on the surface to obtain a clean low-oxygen electrolytic chromium sheet.

[0081] 2) The clean low-oxygen electrolytic chromium flakes obtained above are crushed in a liquid nitrogen environment and then sieved to obtain low-oxygen metal chromium powder with a particle size of 45 μm to 150 μm.

[0082] Step 3, sintering treatment:

[0083] 1) Measure the oxygen content in the low-oxygen chromium metal powder, and then calculate the amount of carbon powder required to reduce the total remaining oxygen content in the low-oxygen chromium metal powder according to the measured oxygen content in the low-oxygen chromium metal powder according to the formula shown in Formula 4, and then use 0.4wt% of the amount of carbon powder required to reduce the total remaining oxygen content in the low-oxygen chromium metal powder as the actual amount of carbon powder added, and weigh the corresponding mass of carbon powder for later use.

[0084] 2) The weighed carbon powder and the low-oxygen metallic chromium powder obtained above are mixed evenly, and then pressed into a slender columnar blank with a diameter of 10 mm and a length of 200 mm.

[0085] 3) The slender columnar blank obtained above is formed into a -3 Pa high vacuum and 1250 ° C high temperature environment, and then hot carbon reduction for 2 h to obtain high-purity low-oxygen metal chromium columns.

[0086] Step 4: High frequency coil heating followed by laser irradiation:

[0087] 1) The high-purity low-oxygen metal chromium column obtained above is slowly passed through a high-frequency coil with an inner diameter greater than the diameter of the columnar blank and a length of 80 mm at a descending speed of 3 mm / min in a vacuum environment, so that the high-purity low-oxygen metal chromium column is heated to 1200°C in the process of passing through the high-frequency coil, and the column and the coil are perpendicular to the ground during the movement.

[0088] 2) Outside the vacuum chamber, a laser is used to irradiate the lower end face of a metal chromium cylinder heated by a high-frequency coil, so that the irradiated position of the end face of the chromium cylinder is melted, forming droplets, which fall under the action of gravity onto a water-cooled copper disk that rotates slowly at a speed of 20 r / min in the vacuum chamber. The copper disk is cooled by circulating water to cool the high-temperature droplets, and the rotating water-cooled copper disk can also increase the spheroidization of the droplets during the solidification process, thereby forming spherical solid particles on the water-cooled copper disk, thereby obtaining high-purity low-oxygen chromium vapor-deposited particles.

[0089] In this embodiment, liquid chromium particles solidify on a water-cooled copper disk and rotate with the metal disk, and are cleaned out of the copper disk by a scraper before returning to the casting position next time; the laser continuously irradiates the metal chromium column that slowly moves downward in the high-frequency coil, and the molten chromium droplets in the irradiated area fall down to cool down, and continuously solidify on the water-cooled copper disk to form high-purity low-oxygen chromium vapor-deposited particles and are scraped out of the disk.

[0090] Furthermore, according to tests, the Cr content in the high-purity low-oxygen chromium vapor-deposited particles prepared in this embodiment is 99.96%, and no residual carbon exists, which indicates that the method of the present invention can prepare high-purity low-oxygen chromium vapor-deposited particles.

[0091] Example 3

[0092] This embodiment provides a method for preparing high-purity low-oxygen chromium vapor-deposited particles, comprising the following steps:

[0093] Step 1, deoxidation treatment:

[0094] 1) Placing the electrolytic chromium sheet in a ceramic boat made of alumina, and placing the ceramic boat in a high-temperature furnace chamber for hydrogen reduction.

[0095] 2) First, nitrogen with a purity of ≥99.9% is introduced into the high-temperature furnace chamber to evacuate the air in the furnace chamber, and then hydrogen with a dew point of ≤-70°C is introduced into the furnace chamber. After passing the explosion test, the hydrogen at the outlet is ignited.

[0096] 3) After the hydrogen is ignited, the furnace chamber begins to gradually heat up, and after the temperature rises to 1300°C, it is kept at 1300°C for 1 hour, and then cooled to room temperature under the protection of hydrogen to obtain reduced low-oxygen electrolytic chromium sheets.

[0097] Step 2, preparation of low oxygen metallic chromium powder:

[0098] 1) The reduced low-oxygen electrolytic chromium sheet was washed with deionized water for 3 times, and then dried to remove the residual water on the surface to obtain a clean low-oxygen electrolytic chromium sheet.

[0099] 2) The clean low-oxygen electrolytic chromium flakes obtained above are crushed in a liquid nitrogen environment and then sieved to obtain low-oxygen metal chromium powder with a particle size of 45 μm to 150 μm.

[0100] Step 3, sintering treatment:

[0101] 1) Measure the oxygen content in the low-oxygen chromium metal powder, and then calculate the amount of carbon powder required to reduce the total remaining oxygen content in the low-oxygen chromium metal powder according to the measured oxygen content in the low-oxygen chromium metal powder according to the formula shown in Formula 4, and then use 0.6wt% of the amount of carbon powder required to reduce the total remaining oxygen content in the low-oxygen chromium metal powder as the actual amount of carbon powder added, and weigh the corresponding mass of carbon powder for later use.

[0102] 2) Mix the weighed carbon powder with the obtained low-oxygen metal chromium powder, and then press them into an elongated columnar blank with a diameter of 50 mm and a length of 1000 mm.

[0103] 3) Place the obtained elongated columnar blank in a high vacuum of less than 6.67×10 -3 Pa and a high-temperature environment of 1400 °C, and carry out thermal carbon reduction for 1 h to obtain a high-purity low-oxygen metal chromium column.

[0104] Step 4, laser irradiation after high-frequency coil heating:

[0105] 1) Place the obtained high-purity low-oxygen metal chromium column in a vacuum environment and slowly pass it through a high-frequency coil with an inner diameter larger than the diameter of the columnar blank and a length of 80 mm at a descending speed of 5 mm / min, so that the high-purity low-oxygen metal chromium column is heated to 1500 °C during the process of passing through the high-frequency coil, and the columnar body and the coil are perpendicular to the ground during the movement.

[0106] 2) Use a laser to irradiate the lower end face of the metal chromium column heated by the high-frequency coil outside the vacuum chamber, so that the irradiated position of the chromium column end face melts, forms droplets, and falls onto a water-cooled copper disk slowly rotating at 50 r / min in the vacuum chamber under the action of gravity. The inside of the copper disk is cooled by circulating water, which can cool the high-temperature droplets, and the rotating water-cooled copper disk can also improve the spheroidization of the droplets during solidification, so that spherical solid particles are formed on the water-cooled copper disk, that is, high-purity low-oxygen chromium evaporation particles are obtained.

[0107] In this embodiment, the liquid chromium particles solidify on the water-cooled copper disk and rotate with the metal disk, and are scraped out of the copper disk by a scraper before returning to the casting position next time; the laser continuously irradiates the metal chromium column slowly moving downward in the high-frequency coil, and the melted chromium droplets in the irradiated area fall and cool down, continuously solidify into high-purity low-oxygen chromium evaporation particles on the water-cooled copper disk and are scraped out of the disk.

[0108] Moreover, through testing, the Cr content in the high-purity low-oxygen chromium evaporation particles prepared in this embodiment is 99.97%, and there is no residual carbon, indicating that the method of the present invention can prepare high-purity low-oxygen chromium evaporation particles.

[0109] Obviously, the above embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A method for preparing high-purity low-oxygen chromium evaporation particles, characterized in that: The following steps are involved: Using electrolytic chromium flakes with a purity of ≥99.95% as a chromium source, subjecting them to reduction and deoxidation treatment to obtain low-oxygen electrolytic chromium flakes; The low-oxygen electrolytic chromium sheet is crushed to obtain low-oxygen metal chromium powder; carbon powder is mixed with the low-oxygen metal chromium powder and then pressed into a columnar blank; the columnar blank is sintered in a vacuum environment so that the carbon powder reduces the remaining oxygen in the low-oxygen metal chromium powder to obtain a high-purity low-oxygen metal chromium column; In a vacuum environment, the high-purity low-oxygen metal chromium column is heated to 1200-1500° C. using a high-frequency coil to obtain a high-purity low-oxygen metal chromium column in a high-temperature state; Subsequently, a high-purity, low-oxygen metal chromium column in a high-temperature state is irradiated with a laser to partially melt its end surface and form droplets; the droplets are allowed to fall continuously and evenly onto a rotating water-cooled copper disk under the action of gravity, and are cooled and solidified on the water-cooled copper disk, thereby obtaining high-purity, low-oxygen chromium vapor-deposited particles.

2. The preparation method according to claim 1, characterized in that The reduction deoxidation treatment is carried out in a hydrogen atmosphere with a purity of ≥99.95%; The temperature of the reduction deoxidation treatment is 1000°C to 1300°C.

3. The preparation method according to claim 1, characterized in that: The particle size of the low-oxygen metal chromium powder is 45 μm to 150 μm.

4. The preparation method according to claim 1, characterized in that: The purity of the carbon powder is ≥99.99%, and the particle size of the carbon powder is 10 μm to 45 μm.

5. The preparation method according to claim 1, characterized in that: The amount of the carbon powder added is 0.4 wt % to 0.6 wt % of the amount of carbon powder required to reduce all the remaining oxygen content in the low-oxygen metallic chromium powder.

6. The preparation method according to claim 1, characterized in that: The vacuum degree of the sintering process is ≤6.67×10 -3 Pa, the sintering temperature is 1250℃~1400℃.

7. The preparation method according to claim 1, characterized in that: When the high-purity low-oxygen metal chromium column is heated by a high-frequency coil, the high-purity low-oxygen metal chromium column is slowly passed through the center of the high-frequency induction coil so that the high-purity low-oxygen metal chromium column is heated to 1200° C. to 1500° C. during the process of passing through the high-frequency coil.

8. The preparation method according to claim 1, characterized in that: The process parameters during the laser irradiation are: The laser power is 200W to 800W, the scanning interval is 0.1mm to 0.2mm, and the scanning rate is 200mm / s to 500mm / s.

9. The preparation method according to claim 1, characterized in that: The rotation speed of the water-cooled copper disk is 10 r / min to 50 r / min.

10. The preparation method according to claim 1, characterized in that: The pulverization is performed by freezing pulverization in a liquid nitrogen environment.

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