Preparation method of high-efficiency deoxygenated high-purity chromium

Abstract

The application discloses a preparation method of high-efficiency deoxidized high-purity chromium. Metal chromium powder and high-purity graphite powder are added into a three-dimensional mixer to be premixed to obtain premixed materials; a solid organic binder is added into an ethanol solution and continuously stirred to obtain the binder, and the solid organic binder is a mixture of polyvinyl alcohol, carboxymethyl cellulose and starch; the binder is added into the premixed materials and mixed in the three-dimensional mixer to obtain mixed wet materials; the mixed wet materials are transferred into an oven to be heated and dried, and are pressed into cylindrical chromium blanks by using a die pressing forming method; the cylindrical chromium blanks are loaded into a vacuum sintering furnace, high-purity argon gas is introduced into the vacuum sintering furnace as a protective gas to remove glue; the chromium blanks after the glue removal are continuously heated and sintered to obtain high-purity chromium blocks. The method has the advantages that the deoxidization effect is better, the obtained high-purity chromium blocks have high purity, the production cost is low, and the method can meet the requirements of mass production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material processing, and particularly relates to a preparation method of high-efficiency deoxidized high-purity chromium. BACKGROUND

[0002] Metal chromium is a silver-white inert metal with hard and brittle texture, and is often applied to manufacturing industry, alloy material, chemical industry and high-end science and technology field due to its excellent oxidation resistance and corrosion resistance. Metal chromium block is an important intermediate product for producing high-purity chromium metal, and can be used for subsequent manufacturing of metal chromium powder and other metal chromium products. The content of impurity oxygen in the metal chromium block is very important for subsequent application of the metal chromium.

[0003] Metal chromium is mainly produced by aluminum thermal method and electrolysis method, and both methods contain different contents of impurity oxygen which needs to be removed in the subsequent purification process of the metal chromium. At present, the main method for removing oxygen from the metal chromium is to mix chromium powder with high-purity graphite powder, press into a block, and then remove the oxygen in the block by vacuum carbon reduction in a vacuum sintering furnace. This method is simple to operate and low in cost in the production of high-purity chromium, but it also has obvious defects. Due to the large difference in density between the metal chromium powder and the high-purity carbon powder, the two substances will be stratified during mixing and pressing due to the difference in density, and simple mixing cannot mix the two substances uniformly. During the subsequent vacuum carbon reduction, the oxygen in the area with low carbon content cannot be removed, and the residual carbon in the area with high carbon content is obvious, which makes the production of high-purity chromium very unstable and even cannot meet the product requirements of high-purity chromium.

[0004] CN111922351A discloses a preparation method of high-purity low-oxygen metal chromium powder. In the method, 40-500 mesh chromium powder and high-purity graphite powder are mixed, and then pressed into chromium blocks with a thickness of 5-20 cm by using mold pressing forming. Then, the chromium blocks are pretreated by deoxidization, sintered into metal chromium blocks at 1000-1500 DEG C, and then ground and crushed at low temperature to obtain chromium powder. In this method, the chromium powder and the high-purity graphite powder are simply mixed, and the two substances will be stratified due to the difference in density during the subsequent operation. The oxygen content of the chromium powder treated by this method is still high, and the deoxidization effect of the chromium powder is not ideal. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a preparation method of high-efficiency deoxidized high-purity chromium, which has better deoxidization effect, high purity of the obtained high-purity chromium block, low production cost and can meet the requirements of mass production.

[0006] The technical scheme of the present application is as follows:

[0007] A preparation method of high-purity low-oxygen chromium block, comprising the following steps:

[0008] (1) Pre-mixing

[0009] The metal chromium powder and high-purity graphite powder are added into a three-dimensional mixer for pre-mixing to obtain a pre-mixed material;

[0010] (2) Preparation of the binder

[0011] First, anhydrous ethanol and pure water are prepared into an ethanol solution with a mass concentration of 10%-50%, and then the solid organic binder is added into the ethanol solution and stirred to obtain the binder;

[0012] The addition amount of the solid organic binder accounts for 2.5%-10% of the mass of the ethanol solution; if the addition amount of the solid organic binder accounts for less than 2.5% of the mass of the ethanol solution, the concentration of the binder is too low, and the adhesion effect of the graphite powder is not good; if the addition amount of the solid organic binder accounts for more than 10% of the mass of the ethanol solution, the concentration of the binder is too large, and the chromium powder is easy to be agglomerated, which affects the subsequent pressing process; the function of the binder is to adhere the graphite powder to the surface of the chromium powder particles, so that the two can be mixed uniformly in the powder flow process; wherein the solid organic binder is a mixture of polyvinyl alcohol, carboxymethyl cellulose and starch, the molecular weight of the polyvinyl alcohol is 110000-130000, the molecular weight of the polyvinyl alcohol is 16000-20000, the viscosity is not enough, and the carbon powder is easy to fall off; the molecular weight of the polyvinyl alcohol is 180000-200000, the viscosity is too large, the mixture is not uniform, and the components are segregated;

[0013] The mass ratio of polyvinyl alcohol to carboxymethyl cellulose and starch is 8.5:(1-2) and 8.5:(0.1-0.5) respectively;

[0014] (3) Mixing

[0015] The binder is added to the pre-mixed material, the addition amount of the binder accounts for 0.5%-2% of the mass of the metal chromium powder, and the mixing is carried out in the three-dimensional mixer at a speed of 8r / min-20r / min for 0.5h-4h to obtain mixed wet material;

[0016] (4) Drying

[0017] The mixed wet material is transferred into an oven, the thickness of the mixed wet material layer is 0.5cm-3cm, and the mixed wet material is heated and dried under the conditions of a temperature of 50℃-80℃ and a pressure of 0.1kPa-101kPa for 0.5h-5h to remove the solvent ethanol, thereby obtaining mixed dry material;

[0018] The thickness of the material layer is greater than 5cm, which will cause the chromium powder in the lower layer to be agglomerated, and the flowability of the chromium powder is poor; if the temperature is higher than 80℃, the thickness of the material layer is less than 0.5cm, which will increase the additional production cost; maintaining a certain vacuum degree of the system can accelerate the drying efficiency, and the negative pressure environment also makes the volatile solvent ethanol not easy to pollute the environment;

[0019] (5) Pressing

[0020] The mixed dry material is pressed into a cylindrical chromium blank by die molding;

[0021] (6) Degreasing

[0022] The chromium blank is loaded into a vacuum sintering furnace, high-purity argon gas is introduced as a protective gas, and the temperature is raised to 350-600°C for 3-8h under a vacuum of <120Pa to remove the solid organic binder. The selected solid organic binder can be effectively decomposed in this temperature range. If the temperature is lower than 350°C, the solid mixed additives will not decompose, and the residual binder will decompose rapidly during the subsequent temperature rise, causing cracks in the chromium block and affecting the appearance quality of the product. If the temperature is higher than 600°C, the binder will also decompose too quickly, increasing production costs.

[0023] The degreased chromium blank is further heated to 500-800°C to carbonize the binder for 3-5h, and then further heated to 1400-1500°C to deoxidize for 10-12h under a vacuum of <120Pa, and a high-purity chromium block is obtained by sintering.

[0024] Through vacuum sintering, the carbon powder reacts with oxygen to generate gas and is removed. High temperature is also beneficial to the forming temperature of the chromium block, which is lower than 950°C, the holding time is lower than 180min, and the vacuum degree is higher than 120Pa, which will affect the degree of deoxidization of the chromium blank. After holding, the temperature is reduced by natural cooling.

[0025] Further, the purity of the metallic chromium powder is ≥99.5%, and the particle size of the metallic chromium powder is 10-500μm; the particle size of the high-purity graphite powder is 0.1-1μm.

[0026] Further, in step (2), the solid organic binder is added to the ethanol solution within 30min, and the solid organic binder is added while stirring. Slowly adding a small amount of solid organic binder to the ethanol solution can reduce the formation of large chunks of solid organic binder and accelerate the dissolution of the solid organic binder.

[0027] Further, the addition amount of the high-purity graphite powder is 0.1%-2% of the mass of the metallic chromium powder. If the addition amount of graphite powder is less than 0.1% of the mass of the metallic chromium powder, the deoxidization of the chromium powder will not be complete. If the addition amount is greater than 2%, the residual graphite will become an impurity.

[0028] Further, during premixing, the mixing time is 0.5-4h, and the rotational speed of the three-dimensional mixer is 8-20r / min. The purpose of premixing is to preliminarily mix the chromium powder and the graphite powder. If the premixing time is less than 0.5h or the rotational speed of the three-dimensional mixer is lower than 8r / min, the premixing effect will be poor, affecting the uniformity of the subsequent mixing. If the premixing time is greater than 4h or the rotational speed of the three-dimensional mixer is higher than 20r / min, the production time and cost will be unnecessarily increased.

[0029] Further, when pressing, the pressure parameter of the die forming is 10MPa-25MPa, the thickness of the chromium blank is 0.5cm-4cm, and the diameter of the chromium blank is 0.5cm-5cm; the pressing into blocks facilitates the subsequent glue removal and sintering process, the pressure of the die forming is less than 10MPa, and the chromium powder is not easy to form; the thickness of the chromium blank is greater than 4cm, and the diameter is greater than 5cm, so that the binder and the gas generated by reduction in the interior of the chromium blank are not easy to discharge, and the subsequent glue removal and vacuum carbon reduction degree will be affected

[0030] The beneficial effects of the present application are that;

[0031] The metal chromium powder produced by electrolysis is deoxidized and purified, and a solid organic binder is used. By controlling the selection and ratio of the solid organic binder raw materials, the physical and chemical properties of the binder are controlled at a reasonable level, so that the high-purity graphite powder is finally adhered to the surface of the chromium powder particles. The high-purity graphite powder will not fall off the surface of the chromium powder during movement, effectively solving the problem of uneven mixing caused by too large density difference between the chromium powder and the graphite powder. The decomposition temperature of the solid organic binder is between 350℃ and 600℃. The wet material obtained is dried, pressed and sintered to remove the binder without introducing impurities. The chromium block obtained by sintering is more uniform in composition and better in deoxidization effect. The high-purity chromium block obtained has high purity and low production cost, and can meet the requirements of mass production. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the process flow chart of the present application. DETAILED DESCRIPTION

[0033] Example 1

[0034] (1) Premix

[0035] Purity 99.6% metal chromium powder and high-purity graphite powder are added to a three-dimensional mixer for pre-mixing to obtain a pre-mixed material. The metal chromium powder does not need to be sieved. The metal chromium powder used is a high-purity chromium powder produced by electrolysis, which can greatly reduce the production cost of producing high-purity chromium. The particle size is 10-500μm. The particle size of the graphite powder is 0.1-1μm. The addition amount of the high-purity graphite powder is 0.45% of the mass of the metal chromium powder. The pre-mixing time is 2h, and the rotational speed of the three-dimensional mixer is 12r / min.

[0036] (2) Binder preparation

[0037] The solid organic binder is obtained by mixing polyvinyl alcohol, carboxymethyl cellulose and starch in a mass ratio of 8.5:1:0.5, using a 10% ethanol solution as the solvent, the polyvinyl alcohol is selected from medium viscosity polyvinyl alcohol with a molecular weight of 110000-130000, the solid organic binder is added into the ethanol solution within 30 minutes (the feeding time of the solid organic binder is 30 minutes), the amount of the solid organic binder added accounts for 2.5% of the mass of the ethanol solution, and the solid organic binder is stirred with a stirring paddle while being added, and the mixture is uniformly mixed to obtain the binder;

[0038] (3) Mixing

[0039] The prepared binder is added to the pre-mixed material, and the three-dimensional mixer is used again for mixing to obtain mixed wet material; the binder is added in an amount of 1% of the mass of the chromium powder, the mixing time is 2h, and the rotating speed of the three-dimensional mixer is 12r / min;

[0040] (4) Drying

[0041] The mixed wet material is heated to 80℃ in an oven for drying to remove the solvent ethanol, and mixed dry material is obtained, the pressure is 1kPa, the drying time is 0.5h, and the material layer thickness is 1cm;

[0042] The drying is to first remove the solvent ethanol in the binder, and the drying efficiency is reduced when the drying temperature is lower than 50℃, the material layer thickness is greater than 3cm, and the time is less than 0.5h;

[0043] (5) Pressing

[0044] The mixed dry material is pressed into a cylindrical chromium blank by using a die forming press, and the pressure parameter of the die forming press in the pressing is 20MPa, the thickness of the chromium blank is 3cm, and the diameter of the chromium blank is 4cm;

[0045] (6) Degreasing

[0046] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as a protective gas, and heating is performed for degreasing, the degreasing temperature is controlled at 350℃-600℃, the holding time is 180min, and the vacuum degree is 100Pa;

[0047] (7) Sintering

[0048] The chromium blank after the degreasing of step (6) is continuously heated to 800℃ and held for 3h, and high-purity chromium block is obtained by sintering, the sintering temperature is controlled at 1400℃, the holding time is 600min, and the vacuum degree is <120Pa.

[0049] Example 2

[0050] (1) Pre-mixing

[0051] The 99.6% pure metal chromium powder and high-purity graphite powder are mixed in a three-dimensional mixer to obtain a premixed material; the metal chromium powder does not need to be sieved, and the metal chromium powder used is high-purity chromium powder produced by electrolysis, which can greatly reduce the production cost of high-purity chromium, and the particle size is 10-500 μm; the particle size of the graphite powder is 0.1-1 μm, and the addition amount of the graphite powder is 2% by weight of the metal chromium powder; the mixing time is 4 h, and the rotation speed of the three-dimensional mixer is 8 r / min;

[0052] (2) Preparation of binder

[0053] An ethanol solution with a mass concentration of 40 wt.% is used as a solvent, and polyvinyl alcohol, carboxymethyl cellulose and starch are mixed in a mass ratio of 8.5:2:0.1 to obtain a solid organic binder; the polyvinyl alcohol is selected to be medium-viscosity polyvinyl alcohol with a molecular weight of 110,000-130,000; the solid organic binder is added to the ethanol solution within 30 min, and the addition amount of the solid organic binder accounts for 5% of the mass of the ethanol solution; the solid organic binder is stirred with a stirring paddle while being added, and is uniformly mixed to obtain a binder;

[0054] (3) Mixing

[0055] The prepared binder is added to the premixed material, and the three-dimensional mixer is used again to mix to obtain mixed wet material; the binder is added in an amount of 2 wt.% of the mass of the metal chromium powder, and the mixing time is 4 h, and the rotation speed of the three-dimensional mixer is 8 / min;

[0056] (4) Drying

[0057] The mixed wet material is heated to 50°C in an oven for drying to remove the solvent ethanol, and mixed dry material is obtained; the pressure is 1 kPa, the drying time is 5 h, and the material layer thickness is 0.5 cm;

[0058] (5) Pressing

[0059] The mixed dry material is pressed into a cylindrical chromium blank by mold pressing; the pressure parameter of the mold pressing is 10 MPa, the thickness of the chromium blank is 0.5 cm, and the diameter of the chromium blank is 0.5 cm;

[0060] (6) Degreasing

[0061] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as a protective gas, and heating is performed for degreasing; the degreasing temperature is controlled at 350-600°C, the holding time is 8 h, and the vacuum degree is 100 Pa;

[0062] (7) Sintering: continue to heat the degummed chromium blank of step (6) to 800 °C for 5 h, and sinter to obtain high-purity chromium block. The sintering temperature is controlled at 1500 °C, the holding time is 720 min, and the vacuum degree is < 120 Pa.

[0063] Example 3

[0064] In the preparation of the solid organic binder of this example, the polyvinyl alcohol, carboxymethyl cellulose and starch are mixed in a mass ratio of 8.5:1.5:0.3, and the other conditions are the same as in Example 1. The specific conditions are as follows:

[0065] (1) Premixing

[0066] The pure metal chromium powder with a purity of 99.6% and high-purity graphite powder are mixed in a three-dimensional mixer in advance to obtain a premixed material. The metal chromium powder does not need to be sieved, and the metal chromium powder used is a high-purity chromium powder produced by electrolysis, which can greatly reduce the production cost of high-purity chromium. The particle size of the metal chromium powder is 10-500 μm. The particle size of the graphite powder is 0.1-1 μm. The addition amount of the high-purity graphite powder is 0.45% of the mass of the metal chromium powder. The premixing time is 2 h, and the rotation speed of the three-dimensional mixer is 12 r / min.

[0067] (2) Binder preparation

[0068] An ethanol solution with a mass concentration of 10% is used as a solvent. The polyvinyl alcohol, carboxymethyl cellulose and starch are mixed in a mass ratio of 8.5:1.5:0.3 to obtain a solid organic binder. The polyvinyl alcohol is selected to be a medium-viscosity polyvinyl alcohol with a molecular weight of 110000-130000. The solid organic binder is added to the ethanol solution within 30 min. The addition amount of the solid organic binder is 2.5% of the mass of the ethanol solution. The solid organic binder is stirred with a stirring paddle while being added, and the mixture is uniformly mixed to obtain a binder.

[0069] (3) Mixing

[0070] The prepared binder is added to the premixed material, and the three-dimensional mixer is used again for mixing to obtain mixed wet material. The binder is added in an amount of 1% of the mass of the metal chromium powder. The mixing time is 2 h, and the rotation speed of the three-dimensional mixer is 12 r / min.

[0071] (4) Drying

[0072] The mixed wet material is heated to 80 °C in an oven for drying to remove the solvent ethanol and obtain mixed dry material. The pressure is 1 kPa, the drying time is 0.5 h, and the material layer thickness is 1 cm.

[0073] The drying is to first remove the solvent ethanol in the binder. If the drying temperature is lower than 50 °C, the material layer thickness is greater than 3 cm, or the time is less than 0.5 h, the drying efficiency will be reduced.

[0074] (5) pressing

[0075] The mixed dry materials are pressed into cylindrical chromium blanks by mould pressing, the pressure parameter of mould pressing is 20 MPa, the thickness of the chromium blank is 3 cm, and the diameter of the chromium blank is 4 cm;

[0076] (6) degreasing

[0077] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as protective gas, and heating is performed for degreasing, the degreasing temperature is controlled at 350-600 ℃, the holding time is 180 min, and the vacuum degree is 100 Pa;

[0078] (7) sintering

[0079] The chromium blank after degreasing in step (6) is continuously heated to 800 ℃ and held for 3 h, high-purity chromium blocks are obtained by sintering, the sintering temperature is controlled at 1400 ℃, the holding time is 600 min, and the vacuum degree is less than 120 Pa.

[0080] Example 4

[0081] In the preparation of the binder in this example, the solid organic binder accounts for 10% of the mass of the ethanol solution, and the other conditions are the same as in Example 1. The specific conditions are as follows: (1) premixing

[0082] The pure metal chromium powder with a purity of 99.6% and high-purity graphite powder are mixed in a three-dimensional mixer in advance to obtain a premixed material; the metal chromium powder does not need to be sieved, and the metal chromium powder used is a high-purity chromium powder produced by electrolysis, which can greatly reduce the production cost of high-purity chromium, and the particle size is 10-500 μm; the particle size of the graphite powder is 0.1-1 μm, and the addition amount of the high-purity graphite powder accounts for 0.45% of the mass of the metal chromium powder, the premixing time is 2 h, and the rotating speed of the three-dimensional mixer is 12 r / min;

[0083] (2) binder preparation

[0084] An ethanol solution with a mass concentration of 10% is used as a solvent, polyvinyl alcohol, carboxymethyl cellulose and starch are mixed according to a mass ratio of 8.5:1:0.5 to obtain a solid organic binder, the polyvinyl alcohol is selected to be a medium-viscosity polyvinyl alcohol with a molecular weight of 110000-130000, the solid organic binder is added to the ethanol solution within 30 min, the addition amount of the solid organic binder accounts for 10% of the mass of the ethanol solution, and the solid organic binder is stirred with a stirring paddle while being added, and the mixture is uniformly mixed to obtain the binder;

[0085] (3) mixing

[0086] The prepared binder is added into the premixed material, and the three-dimensional mixer is used again to mix to obtain mixed wet material; the binder is added according to 1% of the mass of the metal chromium powder, the mixing time is 2h, and the rotating speed of the three-dimensional mixer is 12r / min;

[0087] (4) Drying

[0088] The mixed wet material is heated to 80℃ in an oven to dry, and the solvent ethanol is removed to obtain mixed dry material, the pressure is 1kPa, the drying time is 0.5h, and the material layer thickness is 1cm;

[0089] The drying is to discharge the solvent ethanol in the binder, and the drying efficiency is reduced when the drying temperature is lower than 50℃, the material layer thickness is greater than 3cm, and the time is less than 0.5h;

[0090] (5) Pressing

[0091] The mixed dry material is pressed into a cylindrical chromium blank by using mold pressing, and the pressure parameter of the mold pressing is 20MPa in the pressing, the thickness of the chromium blank is 3cm, and the diameter of the chromium blank is 4cm;

[0092] (6) Degreasing

[0093] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as a protective gas, and heating is performed for degreasing, the degreasing temperature is controlled at 350℃-600℃, the holding time is 180min, and the vacuum degree is 100Pa;

[0094] (7) Sintering

[0095] The chromium blank after the degreasing in step (6) is continuously heated to 800℃ and held for 3h, and high-purity chromium block is obtained by sintering, the sintering temperature is controlled at 1400℃, the holding time is 600min, and the vacuum degree is less than 120Pa.

[0096] Example 5

[0097] In this embodiment, the material after mixing is dried with a material layer thickness of 3cm, and the others are the same as in Example 1, and the details are as follows:

[0098] (1) Premixing

[0099] The metal chromium powder with a purity of 99.6% and high-purity graphite powder are added into a three-dimensional mixer to be premixed to obtain premixed material; the metal chromium powder does not need to be sieved, the metal chromium powder used is high-purity chromium powder produced by electrolysis, which can greatly reduce the production cost of producing high-purity chromium, and the particle size is 10-500μm; the particle size of the graphite powder is 0.1-1μm, the addition amount of the high-purity graphite powder accounts for 0.45% of the mass of the metal chromium powder, the premixing time is 2h, and the rotating speed of the three-dimensional mixer is 12r / min;

[0100] (2) Binder preparation

[0101] A 10% ethanol solution by mass concentration is used as a solvent, polyvinyl alcohol, carboxymethyl cellulose and starch are mixed in a mass ratio of 8.5:1:0.5 to obtain a solid organic binder, the polyvinyl alcohol is selected to be a medium viscosity polyvinyl alcohol with a molecular weight of 110000-130000, the solid organic binder is added to the ethanol solution within 30 min, the amount of the solid organic binder added accounts for 2.5% of the mass of the ethanol solution, and the solid organic binder is stirred with a stirring paddle while being added, mixed uniformly to obtain a binder;

[0102] (3) Mixing

[0103] The prepared binder is added to the pre-mixed material, and the three-dimensional mixer is used again for mixing to obtain mixed wet material; the binder is added in an amount of 1% of the mass of the metal chromium powder, the mixing time is 2 h, and the rotation speed of the three-dimensional mixer is 12 r / min;

[0104] (4) Drying

[0105] The mixed wet material is heated to 80°C in an oven for drying to remove the solvent ethanol, to obtain mixed dry material, the pressure is 1 kPa, the drying time is 0.5 h, and the material layer thickness is 3 cm;

[0106] Drying is to first remove the solvent ethanol in the binder, and a drying temperature lower than 50°C, a material layer thickness greater than 3 cm, and a time less than 0.5 h all reduce the drying efficiency;

[0107] (5) Pressing

[0108] The mixed dry material is pressed into a cylindrical chromium blank by mold pressing, and the pressure parameter of the mold pressing in the pressing is 20 MPa, the thickness of the chromium blank is 3 cm, and the diameter of the chromium blank is 4 cm;

[0109] (6) Degreasing

[0110] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as a protective gas, and heating is performed for degreasing, the degreasing temperature is controlled at 350°C-600°C, the holding time is 180 min, and the vacuum degree is 100 Pa;

[0111] (7) Sintering

[0112] The chromium blank after degreasing in step (6) is continuously heated to 800°C for 3 h, and high-purity chromium blocks are obtained by sintering, the sintering temperature is controlled at 1400°C, the holding time is 600 min, and the vacuum degree is <120 Pa.

[0113] Example 6

[0114] The binder is added in the amount of 0.5% of the mass of the metallic chromium powder, and the rest is the same as in Example 1.

[0115] (1) Premixing

[0116] The 99.6% pure metallic chromium powder and high-purity graphite powder are mixed in a three-dimensional mixer to obtain a premixing material; the metallic chromium powder does not need to be sieved, and the high-purity chromium powder produced by electrolysis is used, which can greatly reduce the production cost of high-purity chromium, and the particle size is 10-500 μm; the particle size of the graphite powder is 0.1-1 μm, and the addition amount of the high-purity graphite powder is 0.45% of the mass of the metallic chromium powder, and the premixing time is 2 h, and the rotating speed of the three-dimensional mixer is 12 r / min;

[0117] (2) Preparation of the binder

[0118] An ethanol solution with a mass concentration of 10% is used as a solvent, and polyvinyl alcohol, carboxymethyl cellulose, and starch are mixed in a mass ratio of 8.5:1:0.5 to obtain a solid organic binder; the polyvinyl alcohol is selected to be medium viscosity polyvinyl alcohol with a molecular weight of 110000-130000; the solid organic binder is added to the ethanol solution within 30 min, and the addition amount of the solid organic binder is 2.5% of the mass of the ethanol solution; the solid organic binder is stirred with a stirring paddle while being added, and is uniformly mixed to obtain the binder;

[0119] (3) Mixing

[0120] The prepared binder is added to the premixed material, and the three-dimensional mixer is used again for mixing to obtain a mixed wet material; the binder is added in the amount of 0.5% of the mass of the metallic chromium powder, and the mixing time is 2 h, and the rotating speed of the three-dimensional mixer is 12 r / min;

[0121] (4) Drying

[0122] The mixed wet material is heated to 80°C in an oven for drying to remove the solvent ethanol, and a mixed dry material is obtained; the pressure is 1 kPa, the drying time is 0.5 h, and the material layer thickness is 1 cm;

[0123] The drying is to first remove the solvent ethanol in the binder; the drying temperature is lower than 50°C, the material layer thickness is greater than 3 cm, and the time is less than 0.5 h, which all reduce the drying efficiency;

[0124] (5) Pressing

[0125] The mixed dry material is pressed into a cylindrical chromium blank by mold pressing; the pressure parameter of the mold pressing is 20 MPa, the thickness of the chromium blank is 3 cm, and the diameter of the chromium blank is 4 cm;

[0126] (6) Degreasing

[0127] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as a protective gas, and degreasing is performed by heating. The degreasing temperature is controlled at 350-600°C, the holding time is 180 min, and the vacuum degree is 100 Pa;

[0128] (7) Sintering

[0129] The degreased chromium blank of step (6) is continuously heated to 800°C and held for 3 h to obtain a high-purity chromium block by sintering. The sintering temperature is controlled at 1400°C, the holding time is 600 min, and the vacuum degree is <120 Pa.

[0130] Example 7

[0131] In this example, the graphite powder accounts for 0.1% of the weight of the metallic chromium powder, and the other conditions are the same as in Example 1. The specific conditions are as follows:

[0132] (1) Premixing

[0133] The 99.6% pure metallic chromium powder and high-purity graphite powder are mixed in a three-dimensional mixer to obtain a premixed material. The metallic chromium powder does not need to be sieved, and the high-purity chromium powder produced by electrolysis is used, which can greatly reduce the production cost of high-purity chromium. The particle size is 10-500 μm. The particle size of the graphite powder is 0.1-1 μm, and the addition amount of the high-purity graphite powder accounts for 0.1% of the mass of the metallic chromium powder. The premixing time is 2 h, and the rotational speed of the three-dimensional mixer is 12 r / min.

[0134] (2) Preparation of binder

[0135] A 10% ethanol solution is used as a solvent, and polyvinyl alcohol, carboxymethyl cellulose, and starch are mixed in a mass ratio of 8.5:1:0.5 to obtain a solid organic binder. The polyvinyl alcohol has a medium viscosity and a molecular weight of 110000-130000. The solid organic binder is added to the ethanol solution within 30 min, and the addition amount of the solid organic binder accounts for 2.5% of the mass of the ethanol solution. The solid organic binder is stirred with a stirring paddle while being added, and the mixture is uniformly mixed to obtain a binder.

[0136] (3) Mixing

[0137] The prepared binder is added to the premixed material, and the three-dimensional mixer is used again for mixing to obtain a mixed wet material. The binder is added in an amount of 1% of the mass of the metallic chromium powder, and the mixing time is 2 h. The rotational speed of the three-dimensional mixer is 12 r / min.

[0138] (4) Drying

[0139] The mixed wet material is heated in an oven to 80°C to dry and remove the solvent ethanol, to obtain a mixed dry material, the pressure is 1 kPa, the drying time is 0.5 h, and the material layer thickness is 1 cm;

[0140] The drying is to first remove the solvent ethanol in the binder, and the drying efficiency is reduced when the drying temperature is lower than 50°C, the material layer thickness is greater than 3 cm, and the time is less than 0.5 h;

[0141] (5) pressing

[0142] The mixed dry material is pressed into a cylindrical chromium blank by using a die pressing forming, the pressure parameter of the die pressing forming is 20 MPa, the thickness of the chromium blank is 3 cm, and the diameter of the chromium blank is 4 cm;

[0143] (6) degreasing

[0144] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as a protective gas, and heating is performed for degreasing, the degreasing temperature is controlled at 350°C-600°C, the holding time is 180 min, and the vacuum degree is 100 Pa;

[0145] (7) sintering

[0146] The chromium blank after the degreasing of step (6) is continuously heated to 800°C and held for 3 h, and high-purity chromium blocks are obtained by sintering, the sintering temperature is controlled at 1400°C, the holding time is 600 min, and the vacuum degree is <120 Pa.

[0147] Example 8

[0148] In this embodiment, the graphite powder accounts for 1.0% of the weight of the metallic chromium powder during premixing, and the others are the same as in Example 1, and the details are as follows:

[0149] (1) premixing

[0150] The metallic chromium powder with a purity of 99.6% and high-purity graphite powder are added to a three-dimensional mixer for pre-mixing to obtain a premixed material; the metallic chromium powder does not need to be sieved, and the metallic chromium powder used is a high-purity chromium powder produced by electrolysis, which can greatly reduce the production cost of high-purity chromium, and the particle size is 10-500 μm; the particle size of the graphite powder is 0.1-1 μm, the addition amount of the high-purity graphite powder accounts for 1.0% of the mass of the metallic chromium powder, the pre-mixing time is 2 h, and the rotation speed of the three-dimensional mixer is 12 r / min;

[0151] (2) binder preparation

[0152] The solid organic binder is obtained by mixing polyvinyl alcohol, carboxymethyl cellulose and starch in a mass ratio of 8.5:1:0.5 with an ethanol solution of a mass concentration of 10% as a solvent, the polyvinyl alcohol is selected from polyvinyl alcohol of medium viscosity, and the molecular weight of the polyvinyl alcohol is 110000-130000, the solid organic binder is added into the ethanol solution within 30 min, the amount of the solid organic binder accounts for 2.5% of the mass of the ethanol solution, and the solid organic binder is stirred with a stirring paddle while being added, and the mixture is uniformly mixed to obtain the binder;

[0153] (3) Mixing

[0154] The prepared binder is added into the pre-mixed material, and the three-dimensional mixer is used again to mix to obtain mixed wet material; the binder is added in an amount of 1% of the mass of the metal chromium powder, the mixing time is 2 h, and the rotating speed of the three-dimensional mixer is 12 r / min;

[0155] (4) Drying

[0156] The mixed wet material is heated to 80°C in an oven to dry, and the solvent ethanol is removed to obtain mixed dry material, the pressure is 1 kPa, the drying time is 0.5 h, and the material layer thickness is 1 cm;

[0157] The drying is to first remove the solvent ethanol in the binder, and the drying efficiency is reduced when the drying temperature is lower than 50°C, the material layer thickness is greater than 3 cm, and the time is less than 0.5 h;

[0158] (5) Pressing

[0159] The mixed dry material is pressed into a cylindrical chromium blank by using a die forming press, the pressure parameter of the die forming press in the pressing is 20 MPa, the thickness of the chromium blank is 3 cm, and the diameter of the chromium blank is 4 cm;

[0160] (6) Degreasing

[0161] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as a protective gas, and heating is performed for degreasing, the degreasing temperature is controlled to be 350°C-600°C, the holding time is 180 min, and the vacuum degree is 100 Pa;

[0162] (7) Sintering

[0163] The chromium blank after the degreasing in step (6) is continuously heated to 800°C and held for 3 h, and high-purity chromium blocks are obtained by sintering, the sintering temperature is controlled to be 1400°C, the holding time is 600 min, and the vacuum degree is less than 120 Pa.

[0164] Example 9

[0165] The graphite powder is 2.0% of the weight of the metallic chromium powder in the premix of this embodiment, the oxygen content of the metallic chromium powder is 0.895%, the purity of the metallic chromium powder is 99.1%, and the others are the same as in Embodiment 1, and the details are as follows:

[0166] (1) Premix

[0167] The metallic chromium powder with a purity of 99.1% and high-purity graphite powder are added to a three-dimensional mixer for pre-mixing to obtain a premix; the metallic chromium powder does not need to be sieved, and the metallic chromium powder used is a high-purity chromium powder produced by electrolysis, which can greatly reduce the production cost of high-purity chromium, and the particle size is 10-500 μm; the particle size of the graphite powder is 0.1-1 μm, and the addition amount of the high-purity graphite powder is 2.0% of the mass of the metallic chromium powder, and the pre-mixing time is 2 h, and the rotation speed of the three-dimensional mixer is 12 r / min;

[0168] (2) Preparation of binder

[0169] An ethanol solution with a mass concentration of 10% is used as a solvent, polyvinyl alcohol, carboxymethyl cellulose, and starch are mixed in a mass ratio of 8.5:1:0.5 to obtain a solid organic binder, the polyvinyl alcohol is selected to be medium-viscosity polyvinyl alcohol with a molecular weight of 110000-130000, the solid organic binder is added to the ethanol solution within 30 min, the addition amount of the solid organic binder is 2.5% of the mass of the ethanol solution, and the solid organic binder is stirred with a stirring paddle while being added, and the mixture is uniformly mixed to obtain a binder;

[0170] (3) Mixing

[0171] The prepared binder is added to the premixed material, and the three-dimensional mixer is used again for mixing to obtain mixed wet material; the binder is added in an amount of 1% of the mass of the metallic chromium powder, and the mixing time is 2 h, and the rotation speed of the three-dimensional mixer is 12 r / min;

[0172] (4) Drying

[0173] The mixed wet material is heated to 80°C in an oven for drying to remove the solvent ethanol, and mixed dry material is obtained, the pressure is 1 kPa, the drying time is 0.5 h, and the material layer thickness is 1 cm;

[0174] The drying is to first remove the solvent ethanol in the binder, and a drying temperature lower than 50°C, a material layer thickness greater than 3 cm, and a time less than 0.5 h all reduce the drying efficiency;

[0175] (5) Pressing

[0176] The mixed dry material is pressed into a cylindrical chromium blank by mold pressing, and the pressure parameter of the mold pressing is 20 MPa, the thickness of the chromium blank is 3 cm, and the diameter of the chromium blank is 4 cm;

[0177] (6) Degreasing

[0178] The pressed chromium blank is loaded into a vacuum sintering furnace, nitrogen gas is introduced as a protective gas, and heating is performed for degreasing, the degreasing temperature is controlled at 350-600 DEG C, the holding time is 180 min, and the vacuum degree is 100 Pa;

[0179] (7) Sintering

[0180] The degreased chromium blank of step (6) is continuously heated to 800 DEG C and held for 3 h, high-purity chromium blocks are obtained by sintering, the sintering temperature is controlled at 1400 DEG C, the holding time is 600 min, and the vacuum degree is <120 Pa.

[0181] Example 10

[0182] The concentration of the solvent ethanol solution of the solid organic binder used in the application can be 10-50%, and the final use effect is not significantly different between the ethanol solutions with concentrations in this range.

[0183] Example 11

[0184] When the three-dimensional mixer is used for mixing in steps (1) and (3) of the application, the rotational speed of the three-dimensional mixer can be 8-20 r / min, and the mixing effect is quite good.

[0185] Comparative Example 1

[0186] The polyvinyl alcohol used in this example has a molecular weight of 16000-20000, and the other conditions are the same as in Example 1.

[0187] Comparative Example 2

[0188] The polyvinyl alcohol used in this example has a molecular weight of 180000-200000, and the other conditions are the same as in Example 1.

[0189] Comparative Example 3

[0190] The binder used in this example is polyethylene glycol 6000, and the other conditions are the same as in Example 1.

[0191] The chromium powder before treatment by the method of the application is untreated chromium powder, and the treated chromium powder is low-oxygen chromium powder. The oxygen content and carbon content of the untreated chromium block (chromium block without adding binder) and the low-oxygen chromium block in Examples 1-9 are tested, and the results are shown in Table 1.

[0192] Table 1 Oxygen content and carbon content of untreated chromium block and low-oxygen chromium block in Examples 1-9

[0193]

[0194] As can be seen from Table 1, the oxygen content of the low-oxygen chromium block prepared by the present application is significantly lower than that of the untreated chromium block, and the residual amount reaches a very low level, and the content of the remaining carbon is also very low, and new impurities are not introduced.

Claims

1. A method for preparing high-purity chromium with high deoxidization efficiency, characterized by comprising the following steps: (1) premixing; adding metal chromium powder and high-purity graphite powder into a three-dimensional mixer to perform premixing, thereby obtaining a premixed material; (2) preparing a binder; preparing an ethanol solution with a mass concentration of 10%-50% by mixing anhydrous ethanol and pure water, then adding a solid organic binder into the ethanol solution while continuously stirring, thereby obtaining the binder; the amount of the solid organic binder added accounts for 2.5%-10% of the mass of the ethanol solution; the solid organic binder is a mixture of polyvinyl alcohol, carboxymethyl cellulose and starch, the molecular weight of the polyvinyl alcohol is 110000-130000, and the mass ratio of the polyvinyl alcohol to the carboxymethyl cellulose and the starch is 8.5:(1-2) and 8.5:(0.1-0.5) respectively; (3) mixing; adding the binder into the premixed material, the amount of the binder added accounts for 0.5%-2% of the mass of the metal chromium powder, mixing in a three-dimensional mixer at a rotating speed of 8r / min-20r / min for 0.5h-4h, thereby obtaining mixed wet material; (4) drying; transferring the mixed wet material into an oven, the thickness of the material layer is 0.5cm-3cm, and the mixed wet material is heated and dried under the conditions of a temperature of 50℃-80℃ and a pressure of 0.1kPa-101kPa for 0.5h-5h, thereby obtaining mixed dry material; (5) pressing; pressing the mixed dry material into a cylindrical chromium blank by die forming; (6) degumming; loading the chromium blank into a vacuum sintering furnace, introducing high-purity argon as a protective gas, heating to 350℃-600℃ under a vacuum degree of <120Pa for 3h-8h to perform degumming; (7) sintering; continuing to heat the degummed chromium blank, carbonizing the binder at a temperature of 500℃-800℃ for 3h-5h, and continuing to heat to 1400℃-1500℃ for 10h-12h to perform deoxidization under a vacuum degree of <120Pa, thereby obtaining a high-purity chromium block. The purity of the metal chromium powder is ≥99.5%, and the particle size of the metal chromium powder is 10μm-500μm. The particle size of the high-purity graphite powder is 0.1μm-1μm. The amount of the high-purity graphite powder added accounts for 0.1%-2% of the mass of the metal chromium powder. The mixing time during premixing is 0.5h-4h, and the rotating speed of the three-dimensional mixer is 8r / min-20r / min. The pressure parameter of the die forming during pressing is 10MPa-25MPa, the thickness of the chromium blank is 0.5cm-4cm, and the diameter of the chromium blank is 0.5cm-5cm. In step (2), the solid organic binder is added into the ethanol solution within 30min, and the solid organic binder is added while continuously stirring during the adding process. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The method of claim 1, wherein the method is characterized by: ​ 3. The method of claim 1, wherein the method is characterized by: ​ 4. The method of claim 1, wherein the method is characterized by: ​ 5. The method of claim 1, wherein the method is characterized by: ​ 6. The method of claim 1, wherein the method is characterized by: ​ 7. The method of claim 1, wherein the method is characterized by: ​

Images