Preparation method of tungsten-based rare earth heating wire powder spheroidization and vertical melting sintering containing lanthanum oxide

Abstract

The application discloses a preparation method of tungsten-based rare earth heating wire powder spheroidization and vertical melting sintering containing lanthanum oxide, and relates to the technical field of heating wire preparation. The tungsten-based powder containing the rare earth element lanthanum oxide is adopted, and the tungsten-based heating wire with refined grains and dense oxide film is prepared by optimizing process parameters. The method can effectively improve the high-temperature strength and oxidation resistance of the heating wire, and prolong the service life of the heating wire. The application is suitable for high-temperature heating scenes, such as electric heaters, electric furnaces and the like, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heating wire preparation, and in particular to a preparation method of tungsten-based rare earth heating wire powder spheroidization and vertical melting sintering containing lanthanum oxide. BACKGROUND

[0002] Tungsten-based heating wire is widely used in high-temperature heaters, industrial kilns, household appliances and other occasions requiring high-temperature resistance and thermal shock resistance due to its extremely high melting point (about 3422℃), good high-temperature strength and thermal stability.

[0003] Patent document EP0765949A1 discloses a lanthana (La2O3) doped tungsten alloy wire for vibration resistant filament. It is pointed out in the document that the durability and fracture resistance of the wire in a vibrating environment can be improved by the presence of La2O3 as a second phase or dispersed phase inside the tungsten. After doping, La2O3 precipitates at the grain boundary, which helps to inhibit grain sliding and grain boundary diffusion, thereby improving tensile strength and vibration resistance.

[0004] Disadvantages: Although this patent involves lanthanum oxide doping and improvement of wire vibration resistance, it does not provide a systematic solution to the specific requirements of powder sphericity, spheroidization process (such as plasma spheroidization / radio frequency plasma spheroidization), sintering density control, post-processing (drawing, surface treatment, resistance stability) and other aspects.

[0005] Patent document CN102259186A discloses a method for preparing fine tungsten spherical powder. The core technology is to treat irregularly shaped raw tungsten powder by gas flow impact (or dispersion) and classification, and then by RF-plasma spheroidization to obtain spherical tungsten powder with a particle size of less than 10 μm. The spherical tungsten powder has the advantages of high sphericity, smooth surface and uniform particle size distribution.

[0006] Disadvantages: However, this document only focuses on the preparation of pure tungsten spherical powder, and does not involve rare earth doping (such as lanthanum oxide), doping dispersion, high-temperature stability testing, sintering compact density, and mechanical properties and service life of the final wire.

[0007] Patent document CN107470639A focuses on the preparation of spherical tungsten powder, and aims to solve the problems of severe agglomeration of raw tungsten powder, irregular shape, wide particle size distribution, particle growth or disappearance of fine powder after spheroidization. It adopts a combination process of dispersion, classification and RF-plasma spheroidization, and achieves spherical tungsten powder with high sphericity, narrow particle size distribution, high purity and high yield.

[0008] Disadvantages: still not combined with mineral rare earth oxide doping on grain stability, oxidation resistance and life, also did not specifically elaborate blank sintering density and wire drawing, surface roughness, resistance fluctuation and other performance indicators.

[0009] In addition, in actual use, there are problems such as low powder sphericity, insufficient blank density, and short service life of heating wire. SUMMARY

[0010] Based on the above problems, a lanthanum oxide-containing tungsten-based rare earth heating wire powder spheroidization and vertical melting sintering preparation method is proposed, and the technical solution is as follows:

[0011] A lanthanum oxide-containing tungsten-based rare earth heating wire powder spheroidization and vertical melting sintering preparation method, comprising the following steps, according to the mass fraction:

[0012] S1: raw material preparation and mixing

[0013] Dissolve 500-800 parts of lanthanum nitrate hexahydrate and 100 parts of polyvinylpyrrolidone in 1200-2000 parts of deionized water, stir and heat to crystallization at 60-80℃ and evaporate water, and dry at 50-60℃ for 36-72h to obtain lanthanum oxide powder;

[0014] In the ball mill tank, mix 20-50 parts of lanthanum oxide powder with 950-980 parts of tungsten powder, add grinding aid at a proportion of 0.5%-1.2% of the total mass of the mixed powder, add ball milling beads, and ball mill for 12-16h to obtain the mixed powder;

[0015] S2: calcination reduction and powder spheroidization

[0016] The mixed powder is calcined at 280-320℃ for 1-1.5h, then reduced in hydrogen atmosphere at 380-400℃ for 1-1.5h, and sieved through a 60 mesh sieve, and then reduced in hydrogen at 900-1200℃ for 2-4h and sieved through a 120 mesh sieve;

[0017] The reduced powder is sent to a plasma spheroidization device and treated under argon atmosphere at a powder feeding rate of 20-30g / min to obtain a pre-alloy powder with a sphericity of ≥0.85 and a particle size of 5-50μm;

[0018] S3: blank pressing and vertical melting sintering

[0019] The pre-alloyed powder is loaded into a stainless steel die coated with boron nitride coating, and the pressure is increased to 190-270 MPa at a rate of 5-10 MPa / min, and the pressure is maintained for 15-20 min to obtain a blank; the blank is placed into a vertical sintering furnace, preheated at 500℃ for 1h, preheated at 1100-1200℃ for 1-2h, then heated to 1300-1400℃ at a rate of 5-10℃ / min for 2-4h, and cooled in the furnace to obtain a sintered blank with a density of ≥18g / cm³;

[0020] S4: subsequent processing and detection

[0021] The sintered blank is heated at 1400-1650℃ for 30min, and then the following steps are performed: 5-8% compression ratio for 3 die passes, 15-20% compression ratio for spinning, and finally 8-12% compression ratio for spinning to form a 5-10mm wire;

[0022] The wire is heated at 1300-700℃ for drawing, with a pass compression rate of 15-20% and a cumulative deformation of 60-70%, and then annealed at 1200-900℃ for 10-20min; followed by electrolytic polishing; the diameter is adjusted to a resistance fluctuation of <2%, and then stabilized annealing is performed at 1000-1450℃ in a nitrogen-hydrogen mixed atmosphere for 10-40min, and finally the finished heating wire is obtained through detection.

[0023] Optionally, the tungsten powder in S1 has a purity of ≥99.95% and a particle size of 2-10μm.

[0024] Optionally, the ball milling jar in S1 is made of agate, and the ball milling beads are made of zirconia.

[0025] Optionally, the ball milling material in S1 has a mass ratio of 1:0.4-1:0.6, and the ball milling speed is 200-300r / min.

[0026] Optionally, the hydrogen gas in S2 has a purity of ≥99.99% and a flow rate of 5-8L / min.

[0027] Optionally, the plasma spheroidization equipment in S2 has a power of 30-50kW.

[0028] Optionally, the argon gas in S2 has a purity of ≥99.999% and a flow rate of 8-12L / min.

[0029] Optionally, the vertical sintering furnace in S3 has a vacuum degree of ≤5×10 -3 Pa.

[0030] Optionally, the grinding aid is prepared by:

[0031] A1: 80-120 parts by mass of aminotridecanol monomethyl ether, 60-90 parts by mass of hydroxyethyl acrylate, 0.3-0.6 parts by mass of lanthanum acrylate, 500-800 parts by mass of anhydrous ethanol are added into a three-necked flask with stirring and reflux, 1-3 parts by mass of p-hydroxyanisole polymerization inhibitor is added, and stirring is carried out at a rotation speed of 200-250 r / min; nitrogen is introduced, 2-5 parts by mass of N,N-dimethylcyclohexylamine catalyst is added, and the temperature is raised to 60-70 DEG C for 6-8 h of heat preservation;

[0032] A2: post-treatment purification: the composite reaction liquid is transferred to a rotary evaporator, and is distilled under reduced pressure at 55-65 DEG C and -0.08 MPa for 2.5-3.5 h to remove anhydrous ethanol and low-boiling-point impurities, and is placed in a vacuum drying box and dried at 60-70 DEG C for 7-9 h to obtain the grinding aid.

[0033] Optionally, the electrolytic polishing process parameters in S4 are as follows:

[0034] Temperature: 30±5 DEG C;

[0035] Alkaline solution: 15-25wt% NaOH solution;

[0036] Voltage: 20-90V;

[0037] Wire speed: 25-60 m / min.

[0038] Optionally, the nitrogen and hydrogen mixed atmosphere in S4 has a volume ratio of nitrogen to hydrogen of 3-5:1.

[0039] Mechanism of action of the grinding aid

[0040] The grinding aid plays a key role in the production process of the above preparation method relying on its molecular structure characteristics: the hydroxyl and ether groups in the linear long chain of the grinding aid can form hydrogen bonds and van der Waals forces with the surfaces of tungsten powder and lanthanum oxide powder, weakening the adsorption force between particles; the coordination units formed by lanthanum acrylate and the addition product in the grinding aid can produce a synergistic dispersion effect with the lanthanum oxide in the raw material, reducing the powder agglomeration phenomenon; in the ball milling link of S1 "raw material preparation and mixing", the grinding aid molecules can adhere to the surface of the powder particles, not only alleviating the agglomeration problem caused by particle collision in the ball milling process, but also reducing the friction resistance between the particles and the ball milling beads and the inner wall of the agate material ball milling tank, promoting uniform particle breakage, and providing high-quality raw material guarantee for the subsequent S2 "calcination reduction and powder spheroidization" to prepare high-sphericity pre-alloy powder and S3 "billet pressing and vertical melting sintering" to form high-density sintered billets.

[0041] Compared with the prior art, the technical scheme of the present application has at least the following beneficial effects:

[0042] 1. Through the optimization of the whole process chain and the synergistic effect of special grinding aids, multiple technical breakthroughs are achieved: in the S1 raw material mixing stage, the grinding aid effectively reduces the agglomeration of tungsten powder and lanthanum oxide powder by means of hydroxyl, ether group and lanthanum propylene acid coordination unit, improves the uniformity of mixing, and the sintered body structure is more compact and has lower porosity.

[0043] 2. High sintered body density: In the sintering link of the blank, the method uses a mold coated with a special coating for pressing, combined with multi-stage preheating and precise temperature control vertical melting sintering process, while strictly controlling the vacuum degree of the sintering environment, so that the sintered body structure is compact and the porosity is significantly reduced. The high-density blank not only improves the structural stability of the material itself, but also lays a good foundation for the subsequent wire processing link.

[0044] 3. High-temperature mechanical properties of heating wire: The method uses a synergistic process of multi-pass rotary forging, heating drawing and stage annealing to gradually shape and control the performance of the sintered blank. The design of the staged compression ratio in the rotary forging link and the temperature matching in the drawing process, combined with the optimization effect of annealing on the grain, make the final prepared heating wire have excellent high-temperature tensile strength, yield strength and plasticity, and can stably withstand the mechanical impact and stress changes in high-temperature heating scenarios.

[0045] 4. Long service life and excellent electrical properties of heating wire: On the one hand, the lanthanum oxide doped in the raw material can play an oxidation inhibition role in a high-temperature environment, stabilize the grain boundary structure and reduce the volatilization loss of tungsten, combined with the compact material structure, effectively prolonging the service life of the heating wire; on the other hand, by electrolytic polishing to remove surface defects of the wire, combined with diameter adjustment and resistance stabilization and annealing treatment, the wire has good and small fluctuation of resistance consistency, stable and reliable electrical properties, which can meet the stringent requirements of high-temperature heating scenarios on the electrical properties of the heating wire. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 Pictures of the heating wire prepared by the method before and after shaping. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0048] Example 1

[0049] A tungsten-based rare earth heating wire powder spheroidization and vertical melting sintering preparation method containing lanthanum oxide, comprising the following steps, according to the mass:

[0050] S1: Raw material preparation and mixing

[0051] 500g lanthanum nitrate hexahydrate and 100g polyvinylpyrrolidone (PVP) were dissolved in 1200g deionized water, and the solution was heated to crystallization at 60°C under stirring, and then the water was evaporated; the crystalline material was dried in an oven at 50°C for 36h to obtain lanthanum oxide powder;

[0052] 20g of the above lanthanum oxide powder and 980g of tungsten powder (purity ≥ 99.95%, particle size 2μm) were mixed, and a grinding aid was added at a proportion of 0.5% of the total mass of the mixed powder; the mixture was added to a ball mill tank made of agate, and zirconium oxide balls were loaded (mass ratio of material to ball 1:0.4); the mixture was ball milled at a speed of 200r / min for 12h to obtain a mixed powder.

[0053] The preparation method of the grinding aid is as follows:

[0054] A1: 80g of aminotridecanol monomethyl ether, 60g of hydroxyethyl acrylate, 0.3g of lanthanum acrylate, and 500g of anhydrous ethanol were sequentially added to a three-necked flask with a stirring reflux device; then 1g of p-hydroxyanisole was added as a polymerization inhibitor, the stirring device was turned on, and the stirring speed was set to 200r / min to preliminarily mix the materials in the flask uniformly; nitrogen was continuously introduced into the three-necked flask to remove air, and then 2g of N,N-dimethylcyclohexylamine was added as a catalyst; the three-necked flask was heated to 60°C, and the temperature was maintained for 6h, during which the stirring speed and nitrogen introduction were maintained;

[0055] A2: post-treatment and purification: after the reaction was completed, the composite reaction solution in the three-necked flask was transferred to a rotary evaporator; the temperature of the rotary evaporator was set to 55°C, the vacuum degree was set to -0.08MPa, and the equipment was started to perform vacuum distillation for 2.5h to remove anhydrous ethanol and low-boiling-point impurities in the reaction solution; after the distillation was completed, the remaining material was transferred to a vacuum drying oven, the drying temperature was set to 60°C, and the material was dried in a vacuum environment for 7h; the light yellow transparent liquid obtained after drying was the grinding aid.

[0056] S2: calcination reduction and powder spheroidization

[0057] The mixed powder was placed in a calcination furnace and calcined at 280°C for 1h; then it was transferred to a reduction furnace and reduced in a hydrogen atmosphere (hydrogen purity ≥ 99.99%, flow rate 5L / min) at 380°C for 1h, and then sieved through a 60 mesh sieve; the sieved powder was then placed in a reduction furnace and reduced in a hydrogen atmosphere at 900°C for 2h, and then sieved through a 120 mesh sieve;

[0058] The twice-reduced powder is sent into a plasma spheroidization device for treatment under the conditions of an argon atmosphere (purity of argon ≥ 99.999%, flow rate 8 L / min), device power 30 kW, and powder feeding rate 20 g / min, to obtain pre-alloyed powder with a sphericity ≥ 0.85 and a particle size of 5 μm.

[0059] S3: blank pressing and vertical melting sintering

[0060] The pre-alloyed powder is loaded into a stainless steel mold coated with a boron nitride coating, and the pressure is increased to 190 MPa at a rate of 5 MPa / min, and the blank is pressed at a pressure of 190 MPa for 15 min;

[0061] The blank is placed in a vertical melting sintering furnace (vacuum degree ≤ 5 × 10 -3 Pa), preheated at 500°C for 1 h, and then preheated at 1100°C for 1 h; then the temperature is increased to 1300°C at a rate of 5°C / min, and pre-sintering is performed for 2 h; after cooling in the furnace, a sintered blank with a density ≥ 18 g / cm³ is obtained.

[0062] S4: subsequent processing and detection

[0063] The sintered blank is placed in a heating furnace and heated at 1400°C for 30 min; it is then transferred to a rotary swaging machine (frequency of 10 times / min), and is first swaged at a compression ratio of 5% for 3 passes, then rotary swaged at a compression ratio of 15%, and finally swaged at a compression ratio of 8% to form a wire with a diameter of 5 mm;

[0064] The wire is drawn at a heating temperature of 1300°C and a pass compression rate of 15%; when the cumulative deformation reaches 60%, the wire is annealed at 1200°C for 10 min;

[0065] The annealed wire is electrolytically polished at a temperature of 30°C using 15wt% NaOH solution at a voltage of 20V and a wire running speed of 25 m / min;

[0066] After polishing, the wire is sized and resistance-adjusted to have a resistance fluctuation of < 2%, and is then placed in a nitrogen-hydrogen mixed atmosphere (nitrogen:hydrogen = 3:1, volume ratio) furnace and annealed at 1000°C for 10 min for stabilization; finally, the finished heating wire is obtained through detection.

[0067] Example 2

[0068] A method for preparing a lanthanum oxide-containing tungsten-based rare earth heating wire powder by spheroidization and vertical melting sintering, comprising the following steps, according to mass:

[0069] S1: raw material preparation and mixing

[0070] 600g lanthanum nitrate hexahydrate and 100g polyvinylpyrrolidone (PVP) were dissolved in 1500g deionized water, heated to crystallization under stirring at 65°C, and evaporated to dryness; the crystalline product was dried in an oven at 55°C for 48h to obtain lanthanum oxide powder;

[0071] 30g of the above lanthanum oxide powder and 970g of tungsten powder (purity ≥ 99.95%, particle size 5μm) were mixed, 0.8% of the total mass of the mixed powder was added as a grinding aid, and the mixture was added to a ball mill tank made of agate, and zirconia balls were added (mass ratio of material to ball 1:0.5), and the mixture was ball milled at a speed of 250r / min for 13h to obtain a mixed powder.

[0072] The preparation method of the grinding aid is as follows:

[0073] A1: 90g of aminotridecanol monomethyl ether, 70g of hydroxyethyl acrylate, 0.4g of lanthanum acrylate, and 600g of anhydrous ethanol were sequentially added to a three-necked flask with stirring and reflux device; 1.5g of p-hydroxyanisole was added as a polymerization inhibitor, and the stirring was started with a speed of 220r / min to mix the materials uniformly; after purging oxygen with nitrogen, 3g of N,N-dimethylcyclohexylamine catalyst was added; the flask was heated to 63°C, and the reaction was maintained for 7h with stirring and nitrogen purging;

[0074] A2: post-treatment and purification: the reaction solution was transferred to a rotary evaporator, the temperature was set to 58°C, the vacuum degree was set to -0.08MPa, and the solution was distilled under reduced pressure for 3h to remove the solvent and low-boiling-point impurities; then the material was placed in a vacuum drying oven and dried at 63°C for 8h to obtain a uniform and transparent grinding aid product.

[0075] S2: calcination reduction and powder spheroidization

[0076] The mixed powder was placed in a calcination furnace and calcined at 300°C for 1.2h; then it was transferred to a reduction furnace and reduced at 390°C for 1.2h in a hydrogen atmosphere (hydrogen purity ≥ 99.99%, flow rate 6L / min), and then sieved through a 60 mesh sieve; the sieved powder was then placed in a reduction furnace and reduced at 1000°C for 3h in a hydrogen atmosphere, and then sieved through a 120 mesh sieve;

[0077] The twice-reduced powder was sent to a plasma spheroidization device and treated under the following conditions: argon atmosphere (argon purity ≥ 99.999%, flow rate 9L / min), device power 35kW, and powder feeding rate 23g / min, to obtain a pre-alloyed powder with a sphericity ≥ 0.85 and a particle size of 20μm.

[0078] S3: green compact pressing and vertical sintering

[0079] The pre-alloyed powder is loaded into a stainless steel die coated with a boron nitride coating, and the pressure is increased to 220 MPa at a rate of 7 MPa / min, and the pressure is maintained for 17 min to press the blank;

[0080] The blank is placed in a vertical sintering furnace (vacuum degree ≤5×10 -3 Pa), and preheated at 500°C for 1 h, and then preheated at 1130°C for 1.3 h; then the temperature is increased to 1330°C at a rate of 7°C / min, and pre-sintered for 3 h; after cooling in the furnace, a sintered blank with a density of ≥18 g / cm³ is obtained.

[0081] S4: Subsequent processing and detection

[0082] The sintered blank is placed in a heating furnace and heated at 1500°C for 30 min; it is transferred to a rotary swaging machine (frequency of 12 times / min), first swaged at a compression ratio of 6% for 3 die times, then rotary swaged at a compression ratio of 17%, and finally forged into a 7 mm diameter wire at a compression ratio of 9%;

[0083] The wire is drawn at 1100°C with a pass compression rate of 17%; when the cumulative deformation reaches 63%, it is annealed in a 1100°C furnace for 14 min;

[0084] The annealed wire is electrolytically polished: temperature 30°C, 18wt% NaOH solution, voltage 40V, wire speed 35m / min;

[0085] After polishing, the wire is sized and resistance adjusted to a resistance fluctuation of <2%, and then placed in a nitrogen-hydrogen mixed atmosphere (nitrogen:hydrogen =3.5:1, volume ratio) furnace for stabilization annealing at 1200°C for 20 min; finally, through detection, the finished heating wire is obtained.

[0086] Example 3

[0087] A method for preparing a lanthanum oxide-containing tungsten-based rare earth heating wire powder by spheroidization and vertical sintering, comprising the following steps, according to mass:

[0088] S1: Raw material preparation and mixing

[0089] 700g of lanthanum nitrate hexahydrate and 100g of polyvinylpyrrolidone (PVP) are dissolved in 1800g of deionized water, and the solution is heated to crystallization under stirring at 75°C and then evaporated to dryness; the crystalline material is dried in an oven at 58°C for 60h to obtain lanthanum oxide powder;

[0090] Take 40g of the above lanthanum oxide powder and 960g of tungsten powder (purity ≥ 99.95%, particle size 8μm) and mix them. Add grinding aids at a proportion of 1.0% of the total mass of the mixed powder. Put the mixed powder into a ball mill tank made of agate, and add zirconium oxide balls (mass ratio of material to balls is 1:0.55). Mill at a speed of 275r / min for 15h to obtain the mixed powder.

[0091] The preparation method of the grinding aid is as follows:

[0092] A1: Add 110g of aminotridecanol monomethyl ether, 85g of hydroxyethyl acrylate, 0.5g of lanthanum acrylate, and 700g of anhydrous ethanol into a three-necked flask with stirring and reflux device in sequence. Add 2.5g of p-hydroxyanisole polymerization inhibitor, start stirring, and set the stirring speed to 240r / min to mix the materials thoroughly. After purging the air in the flask with nitrogen, add 4g of N,N-dimethylcyclohexylamine catalyst. Heat the flask to 67℃ and maintain the temperature for 7.5h, maintaining the stirring speed and nitrogen atmosphere during the reaction.

[0093] A2: Post-treatment purification: Transfer the reaction solution to a rotary evaporator, set the temperature to 62℃ and the vacuum degree to -0.08MPa, and distill under reduced pressure for 3.2h to remove anhydrous ethanol and low-boiling-point impurities. Place the treated material in a vacuum drying oven and dry at 67℃ for 8.5h to obtain a grinding aid with the required purity.

[0094] S2: Calcination reduction and powder spheroidization

[0095] Place the mixed powder in a calcination furnace and calcine at 310℃ for 1.4h. Then transfer it to a reduction furnace and reduce at 395℃ in a hydrogen atmosphere (hydrogen purity ≥ 99.99%, flow rate 7L / min) for 1.4h. After cooling, pass the powder through a 60 mesh sieve. Then place the sieved powder in a reduction furnace and reduce at 1100℃ in a hydrogen atmosphere for 3.5h. After cooling, pass the powder through a 120 mesh sieve.

[0096] Send the twice-reduced powder to a plasma spheroidization device and process it under the following conditions: argon atmosphere (argon purity ≥ 99.999%, flow rate 11L / min), device power 45kW, and powder feeding rate 27g / min. This results in a pre-alloyed powder with a sphericity ≥ 0.85 and a particle size of 40μm.

[0097] S3: Green compact pressing and vertical fusion sintering

[0098] Place the pre-alloyed powder in a stainless steel mold coated with a boron nitride coating. Increase the pressure at a rate of 8MPa / min to 250MPa and maintain the pressure for 18min to press the powder into a green compact.

[0099] Put the blank into the vertical melting sintering furnace (vacuum degree ≤5×10 -3 Pa), preheat at 500℃ for 1h, then preheat at 1170℃ for 1.7h; then increase the temperature to 1370℃ at a rate of 8℃ / min, and pre-sinter for 3.5h; after cooling in the furnace, the sintered blank with a density ≥18g / cm³ is obtained.

[0100] S4: Subsequent processing and detection

[0101] Put the sintered blank into the heating furnace, heat at 1600℃ for 30min; transfer to the rotary swaging machine (14 times / min frequency), first punch the corner 3 times with a compression ratio of 7%, then rotary swage with a compression ratio of 18%, and finally swage into a 8mm diameter wire with a compression ratio of 11%;

[0102] Draw the wire at 900℃, with a pass compression ratio of 18%; when the cumulative deformation reaches 67%, anneal in a 1000℃ furnace for 17min;

[0103] Electrolytic polish the annealed wire: temperature 30℃, use 22wt% NaOH lye, voltage 70V, wire speed 50m / min;

[0104] After polishing, size the wire to a resistance fluctuation of <2%, then place it in a nitrogen-hydrogen mixed atmosphere (nitrogen:hydrogen =4.5:1, volume ratio) furnace, stabilize at 1350℃ for 30min; finally, through detection, obtain the finished heating wire.

[0105] Example 4

[0106] A method for preparing a lanthanum oxide-containing tungsten-based rare earth heating wire powder by spheroidization and vertical melting sintering, comprising the following steps, according to mass:

[0107] S1: Raw material preparation and mixing

[0108] Dissolve 800g lanthanum nitrate hexahydrate and 100g polyvinylpyrrolidone (PVP) in 2000g deionized water, stir and heat at 80℃ until the solution crystallizes and evaporate the water; place the crystalline material in a 60℃ oven and dry for 72h to obtain lanthanum oxide powder;

[0109] Take 50g of the above lanthanum oxide powder and mix with 950g of tungsten powder (purity ≥99.95%, particle size 10μm), add grinding aids at a proportion of 1.2% of the total mass of the mixed powder, add to a marbled ball mill tank, load zirconia ball mill beads (mass ratio of material to ball 1:0.6), and ball mill at 300r / min for 16h to obtain the mixed powder.

[0110] The method for preparing the grinding aid is:

[0111] A1: 120 g of aminotridecanol monomethyl ether, 90 g of hydroxyethyl acrylate, 0.6 g of lanthanum acrylate, 800 g of anhydrous ethanol were sequentially added into a three-necked flask with stirring and reflux device; 3 g of p-hydroxyanisole polymerization inhibitor was added, stirring was started, and the rotation speed was set to 250 r / min to mix all the materials in the flask uniformly; nitrogen was continuously introduced into the flask to isolate air, and then 5 g of N,N-dimethylcyclohexylamine catalyst was added; the three-necked flask was heated to 70°C, and the temperature was kept for 8 h, during which stirring and nitrogen introduction were continuously performed;

[0112] A2: post-treatment purification: after the reaction was completed, the composite reaction solution was transferred to a rotary evaporator, the temperature was set to 65°C, the vacuum degree was set to -0.08 MPa, and vacuum distillation was started for 3.5 h to remove anhydrous ethanol and low-boiling-point impurities; the distilled material was transferred to a vacuum drying oven and dried at 70°C for 9 h, finally obtaining a transparent viscous grinding aid.

[0113] S2: calcination reduction and powder spheroidization

[0114] The mixed powder was placed in a calcination furnace and calcined at 320°C for 1.5 h; then it was transferred to a reduction furnace and reduced at 400°C for 1.5 h in a hydrogen atmosphere (hydrogen purity ≥ 99.99%, flow rate 8 L / min), and then sieved through a 60-mesh sieve after cooling; the sieved powder was then placed in a reduction furnace and reduced at 1200°C for 4 h in a hydrogen atmosphere, and then sieved through a 120-mesh sieve after cooling;

[0115] The twice-reduced powder was sent to a plasma spheroidization device and treated under the following conditions: argon atmosphere (argon purity ≥ 99.999%, flow rate 12 L / min), device power 50 kW, and powder feeding rate 30 g / min, to obtain a pre-alloyed powder with a sphericity ≥ 0.85 and a particle size of 50 μm.

[0116] S3: blank pressing and vertical fusion sintering

[0117] The pre-alloyed powder was loaded into a stainless steel mold coated with a boron nitride coating, and the pressure was increased to 270 MPa at a rate of 10 MPa / min, and the pressure was maintained for 20 min to press the blank;

[0118] The blank was placed in a vertical fusion sintering furnace (vacuum degree ≤ 5 × 10 -3 Pa), preheated at 500°C for 1 h, and then preheated at 1200°C for 2 h; then the temperature was increased to 1400°C at a rate of 10°C / min, and pre-sintering was performed for 4 h; after cooling in the furnace, a sintered blank with a density ≥ 18 g / cm³ was obtained.

[0119] S4: Subsequent processing and detection

[0120] The sintered blank is placed in a heating furnace, heated at 1650 DEG C for 30 min, transferred to a swaging machine (15 times / min frequency), first with 8% compression ratio to punch the corner 3 mold times, then swaged with 20% compression ratio, and finally forged into a 10mm diameter wire rod with 12% compression ratio;

[0121] The wire rod is drawn under the condition of heating at 700 DEG C, with a pass compression rate of 20%; when the cumulative deformation reaches 70%, it is annealed in a 900 DEG C furnace for 20 min;

[0122] The annealed wire rod is electrolytically polished: temperature 30 DEG C, 25wt% NaOH lye is used, voltage 90V, wire speed 60m / min;

[0123] After polishing, the wire rod is sized and resistance-adjusted to a resistance fluctuation of <2%, and then is placed in a nitrogen-hydrogen mixed gas atmosphere (nitrogen:hydrogen = 5:1, volume ratio) furnace, and is stabilized annealed at 1450 DEG C for 40 min; finally, through detection, the finished heating wire is obtained.

[0124] Comparative example

[0125] In this embodiment, no grinding aid is added, and the rest of the technical solutions are the same as those in example 2.

[0126] The heating wires prepared in examples 1-4 and the comparative example are detected, and the detection results are as follows:

[0127] Table 1 Detection results

[0128]

[0129] From the test results, the tensile strength, yield strength, elongation after fracture, specific heat, thermal conductivity and service life of the heating wire of the embodiment of the application are significantly better than those of the comparative example, which is mainly due to the innovative design of the special grinding aid, the precise control of the whole process chain and the synergistic effect of lanthanum oxide and tungsten-based raw materials:

[0130] Key role of grinding aid: the example uses a special grinding aid prepared by reacting aminotricateaole monomethyl ether, hydroxyethyl acrylate and lanthanum acrylate. The hydroxyl and ether groups in the linear long chain of the grinding aid can form hydrogen bonds and van der Waals forces with the surface of tungsten powder and lanthanum oxide powder, weakening the adsorption force between particles. At the same time, the coordination units formed by lanthanum acrylate in the grinding aid can produce a synergistic dispersion effect with the raw material lanthanum oxide, effectively solving the problem of powder agglomeration. In the ball milling process, the grinding aid can also reduce the frictional resistance between particles and ball milling beads and the inner wall of the agate jar, promoting uniform particle breakage. This makes the mixed powder in the example more uniformly dispersed, laying a foundation for high-quality raw materials for subsequent spheroidization and sintering, and ultimately achieving a sintered body density of ≥18 g / cm 3 , a tensile strength of the wire of 686-694 MPa, and a service life of 51330-51510 h. In the comparative example, without the addition of the grinding aid, the problem of powder agglomeration is prominent, and the mixed uniformity is poor, resulting in a tensile strength of only 642 MPa, a service life of only 4928 h, and significantly lower elongation after breakage (29%) and specific heat (0.42 J / g.℃) than the example.

[0131] The example achieves performance improvement through multi-stage process parameter optimization:

[0132] Roasting and reduction and powder spheroidization: using a hierarchical process of “280-320℃ roasting → 380-400℃ first hydrogen reduction → 900-1200℃ second hydrogen reduction”, combined with hydrogen gas with a purity of ≥99.99% (flow rate 5-8 L / min), effectively removes impurities from the powder; then treated by a 30-50kW plasma spheroidization equipment (argon purity ≥99.999%, powder feeding rate 20-30g / min), to obtain a pre-alloyed powder with a sphericity of ≥0.85 and a particle size of 5-50μm, ensuring the density of the subsequent green body pressing.

[0133] Green body pressing and vertical melting sintering: using a mold coated with a boron nitride coating, pressurized to 190-270MPa at a rate of 5-10MPa / min and held for 15-20min, combined with a multi-stage sintering process of “500℃ preheating → 1100-1200℃ second preheating → 1300-1400℃ pre-burning” (vacuum degree ≤5×10 -3 Pa), to reduce the internal porosity of the green body and improve the structural stability.

[0134] Subsequent processing and annealing: through the process of "1400-1650℃ heating → hierarchical compression ratio swaging (5-8% cornering, 15-20% main swaging, 8-12% fine swaging) → 1300-700℃ heating drawing (pass compression rate 15-20%) → staged annealing (cumulative deformation 60-70% at 1200-900℃ annealing)", the grain structure of the wire material is optimized, and the mechanical properties are enhanced; and then through electrolytic polishing (30±5℃, 15-25wt% NaOH lye) and nitrogen-hydrogen mixed atmosphere (volume ratio 3-5:1) stabilization annealing, the electrical performance consistency (resistance fluctuation <2%) is ensured.

[0135] Although the comparative example follows similar process steps, the process optimization effect is offset due to uneven mixing of raw materials (without auxiliary agent), and finally the green body density and wire forming quality are inferior to the examples.

[0136] Synergistic effect of lanthanum oxide doping and tungsten-based raw materials: the examples use tungsten powder with purity ≥99.95% and particle size 2-10μm as the matrix, and 20-50 parts of lanthanum oxide powder. Lanthanum oxide can act as a second phase particle to stabilize the tungsten grain boundary at high temperature, inhibit grain sliding and grain boundary diffusion, and reduce the loss of tungsten evaporation at high temperature, significantly improving the high-temperature strength and oxidation resistance of the heating wire. The examples have stable high-temperature mechanical properties, with a maximum use temperature of 1350℃, and the service life gradually increases with the gradient optimization of lanthanum oxide dosage (from 51330h to 51510h for examples 1-4). The comparative example has poor powder dispersibility, and lanthanum oxide cannot be uniformly distributed in the tungsten matrix, so its grain boundary stabilization and oxidation resistance do not fully play a role, resulting in a service life of only about 1 / 10 of the examples.

[0137] Overall synergistic effect: grinding aid, precise process and rare earth doping do not act independently, but form a synergistic system: grinding aid solves the problem of raw material mixing, providing high-quality "basic raw materials" for process optimization; multi-link process control ensures the quality of each step of powder spheroidization, green body sintering and wire forming, realizing the transformation of "raw material advantage → process landing → performance output"; the synergistic effect of lanthanum oxide and tungsten-based raw materials strengthens the high-temperature performance and durability from the composition level. The three work together to make the examples have overall advantages in mechanical properties, thermal properties, electrical properties and service life, significantly better than the comparative example which does not use this synergistic system.

[0138] Although the embodiments of the present application have been disclosed as above, they are not limited to the use listed in the specification and embodiments, and can be fully applied to various fields suitable for the present application, and additional modifications can be easily realized by those skilled in the art, therefore the present application is not limited to specific details and examples shown and described herein, without departing from the general concept defined by the claims and equivalent scope.

Claims

1. A method for preparing spheroidized and vertically melted sintered tungsten-based rare earth heating wire powder containing lanthanum oxide, characterized in that, Includes the following steps, measured in parts by weight: S1: Raw material preparation and mixing Dissolve 500-800 parts of lanthanum nitrate hexahydrate and 100 parts of polyvinylpyrrolidone in 1200-2000 parts of deionized water, stir and heat at 60-80℃ until crystallization and evaporate the water, and dry at 50-60℃ for 36-72 hours to obtain lanthanum oxide powder. In a ball mill jar, 20-50 parts of lanthanum oxide powder and 950-980 parts of tungsten powder are mixed, and grinding aid is added at a ratio of 0.5%-1.2% of the total mass of the mixed powder. Then, grinding balls are added, and the mixture is ball-milled for 12-16 hours to obtain the mixed powder. S2: Calcination reduction and powder spheroidization The mixed powder was calcined at 280-320℃ for 1-1.5h, then reduced in a hydrogen atmosphere at 380-400℃ for 1-1.5h and passed through a 60-mesh sieve. It was then reduced again in a hydrogen atmosphere at 900-1200℃ for 2-4h and passed through a 120-mesh sieve. The reduced powder was fed into a plasma spheroidizing device and processed under an argon atmosphere and a powder feeding rate of 20-30 g / min to obtain a pre-alloyed powder with a sphericity ≥0.85 and a particle size of 5-50 μm. S3: Billet pressing and vertical melting sintering Pre-alloyed powder is loaded into a stainless steel mold coated with boron nitride, and pressurized at a rate of 5-10 MPa / min to 190-270 MPa, and held at the pressure for 15-20 min to obtain a billet. The billet is placed in a vertical melting sintering furnace, preheated at 500℃ for 1 h, preheated at 1100-1200℃ for 1-2 h, and then pre-fired at 1300-1400℃ for 2-4 h at a rate of 5-10℃ / min. The billet is then cooled in the furnace to obtain a sintered billet with a density ≥18 g / cm³. S4: Subsequent processing and testing The sintered billet is heated at 1400-1650℃ and held for 30 minutes. It is then forged in a rotary forging mill at a frequency of 10-15 times / min. First, it is forged into 3 rounds with a compression ratio of 5-8%, then rotary forged at a compression ratio of 15-20%, and finally forged into 5-10mm wire at a compression ratio of 8-12%. The filament is heated and drawn at 1300-700℃ with a compression rate of 15-20% per pass. When the cumulative deformation reaches 60-70%, it is annealed at 1200-900℃ for 10-20 minutes. Then, it is electrolytically polished, sized and resisted until the resistance fluctuation per meter is <2%, and stabilized by annealing at 1000-1450℃ in a nitrogen-hydrogen mixed atmosphere for 10-40 minutes. Finally, the finished heating wire is obtained through testing.

2. The method for preparing spheroidized and sintered lanthanum oxide-containing tungsten-based rare earth heating wire powder according to claim 1, characterized in that, The tungsten powder in S1 has a purity of ≥99.95% and a particle size of 2-10μm.

3. The method for preparing spheroidized and vertically melted sintered tungsten-based rare earth heating wire powder containing lanthanum oxide according to claim 1, characterized in that, The grinding jar in S1 is made of agate, and the grinding beads are made of zirconium oxide.

4. The method for preparing spheroidized and sintered lanthanum oxide-containing tungsten-based rare earth heating wire powder according to claim 1, characterized in that, In S1, the mass ratio of the grinding media balls is 1:0.4-1:0.6, and the grinding speed is 200-300 r / min.

5. The method for preparing spheroidized and vertically melted sintered tungsten-based rare earth heating wire powder containing lanthanum oxide according to claim 1, characterized in that, The hydrogen in S2 has a purity of ≥99.99% and a flow rate of 5-8 L / min.

6. The method for preparing spheroidized and sintered lanthanum oxide-containing tungsten-based rare earth heating wire powder according to claim 1, characterized in that, The plasma spheroidizing device in S2 has a power of 30-50kW.

7. The method for preparing spheroidized and vertically melted sintered tungsten-based rare earth heating wire powder containing lanthanum oxide according to claim 1, characterized in that, In S2, the argon gas purity is ≥99.999% and the flow rate is 8-12 L / min; in S3, the vacuum degree of the vertical melting sintering furnace is ≤5×10⁻⁶. -3 Pa.

8. The method for preparing spheroidized and sintered lanthanum oxide-containing tungsten-based rare earth heating wire powder according to claim 1, characterized in that, The grinding aid is prepared by: A1: By weight, add 80-120 parts of aminotridecyl glycol monomethyl ether, 60-90 parts of hydroxyethyl acrylate, 0.3-0.6 parts of lanthanum acrylate, and 500-800 parts of anhydrous ethanol to a three-necked flask equipped with a stirrer and reflux, add 1-3 parts of p-hydroxyanisole polymerization inhibitor, and stir at 200-250 r / min; purge with nitrogen gas, add 2-5 parts of N,N-dimethylcyclohexylamine catalyst, and heat to 60-70℃ and maintain the temperature for 6-8 h; A2: Post-processing purification: Transfer the composite reaction solution to a rotary evaporator and distill under reduced pressure at 55-65℃ and -0.08MPa for 2.5-3.5h to remove anhydrous ethanol and low-boiling-point impurities. Place it in a vacuum drying oven and dry it at 60-70℃ for 7-9h to obtain the grinding aid.

9. The method for preparing spheroidized and sintered lanthanum oxide-containing tungsten-based rare earth heating wire powder according to claim 1, characterized in that, The electropolishing process parameters in S4 are as follows: Temperature: 30±5℃; Alkaline solution: 15-25 wt% NaOH solution; Voltage: 20-90V; Wire feed speed: 25-60m / min.

10. The method for preparing spheroidized and sintered lanthanum oxide-containing tungsten-based rare earth heating wire powder according to claim 1, characterized in that, The nitrogen-hydrogen mixed atmosphere in S4 has a nitrogen to hydrogen volume ratio of 3-5:1.

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