CN117821831A - A high electrical and thermal conductivity rare earth tungsten electrode material and preparation method - Google Patents

Abstract

A high-conductivity heat-conduction rare earth tungsten electrode material and a preparation method thereof relate to the technical field of refractory metal materials. The weight percentage of the material is as follows: 0.66 to 0.8 percent of lanthanum oxide, 0.66 to 0.8 percent of cerium oxide, 1.98 to 2.4 percent of yttrium oxide, 3.3 to 4 percent of rare earth oxide and the balance of tungsten; the rare earth oxide cerium oxide, lanthanum oxide and yttrium oxide are mixed according to the proportion of La ₂ O ₃ ∶C eO ₂ ∶Y ₂ O ₃ =1:1:3. The preparation method of the material comprises the following steps: solid doping, cold isostatic pressing, intermediate frequency induction sintering, rotary forging, wire drawing, straightening, cutting, polishing and the like. The density of the rare earth tungsten electrode material prepared by the invention is more than 98%, and the intensity is highThe electrode material has excellent electric conduction and heat conduction properties, can realize the rapid transmission of internal current and heat of the electrode during working, effectively avoids the ablation of the electrode, and has simple preparation process, easy processing and higher yield.

Description

A high electrical and thermal conductivity rare earth tungsten electrode material and preparation method

Technical Field

The invention relates to the technical field of rare earth refractory metal materials, and in particular to a high-electrical and thermal-conductive rare earth tungsten electrode material and a preparation method thereof.

technical background

Tungsten and its related products have been used as thermal electron emission materials for many years. They play an important role in the fields of modern welding industry, thermal spraying, plasma application and electric vacuum. The performance of the use of tungsten is the determining factor of key performance indicators such as output power, gain and reliability of related equipment. The performance of the electrode is closely related to the melting point, electrical and thermal conductivity and mechanical properties of the electrode material. On the one hand, the electrode material with excellent electrical and thermal conductivity can enable the electrode to achieve rapid transmission of current and heat inside the material during startup and just after startup, increase the surface temperature of the electrode, and enable some electrons to quickly obtain sufficient energy to achieve electron emission. On the other hand, the electrode material with high electrical and thermal conductivity has a high migration speed of rare earth oxides inside the material, which can ensure that the rare earth oxides migrate from the inside of the electrode to the surface in time, and achieve a dynamic balance between the replenishment rate of rare earth oxides in the electrode surface layer and the evaporation loss rate, avoiding the electrode ablation caused by oxide evaporation or excessive local current during the working process, especially under high current conditions, and achieving long-term stable operation of the electrode.

Summary of the invention:

The technical problem to be solved by the present invention is to provide a tungsten electrode material with excellent electrical and thermal conductivity and a preparation method thereof, wherein the prepared rare earth tungsten electrode material has high electrical conductivity and thermal conductivity while ensuring high density and high strength. The second phase inside the electrode material is evenly distributed, the work function is low, and the electron emission ability is strong. In addition, the preparation process of the rare earth tungsten electrode material is simple, economical and energy-saving, has no radioactive pollution, and has a high yield rate.

The solution adopted by the present invention to solve the technical problem is: on the one hand,

The invention discloses a rare earth tungsten electrode material, which comprises a tungsten electrode of three rare earth oxides of _La2O3 , _CeO2 and _Y2O3 , wherein the weight percentages _are as follows: _0.66 % to 0.8% of lanthanum oxide, 0.66% to 0.8% of cerium oxide, 1.98% to 2.4% of yttrium oxide, 3.3% to 4% of the total rare earth oxides, and the rest being tungsten; and preferably, the mass ratio of the three rare earth oxides is _{La2O3 :CeO2} : _Y2O3 =1: ₁ : ₃ .

On the other hand, the method for preparing the rare earth tungsten electrode material described above specifically comprises the following steps:

(1) Powder mixing: The particle size of the tungsten powder used is less than 3 μm, and the particle size of the rare earth oxide (cerium oxide, lanthanum oxide, yttrium oxide) powder is 50 nm. The required raw material powders are weighed according to the weight percentage, pre-mixed and loaded into a V-type mixer for powder mixing. The preferred mixer speed is 24 r/min, the mixing time is 12 h, and the mixing time is 15 min every 2 h.

(2) Pressing: After being fully mixed in a mixer, a single mixed alloy powder with a weight of 1800±100g is placed in an elastic film sleeve, and after being fully vibrated, it is pressed into shape using a cold isostatic press. The maximum pressing force is 227Mpa, and the pressure is maintained at 192MPa and 95MPa, respectively, and the holding time is 100s (i.e., the pressure is first increased to a maximum pressure of 227Mpa, and then the pressure is reduced to 192MPa and maintained for 100s, and then the pressure is reduced to 95MPa and maintained for 100s). After pressing, a tungsten billet with a size of 21-22mm × 300mm in length is obtained; (3) Sintering: The tungsten billet obtained in step (2) is placed in a tungsten crucible of a medium frequency induction furnace and sintered at a flow rate of ^2.5m3. /h of hydrogen protection, and the sintering process goes through five stages of heating and five stages of insulation. The first stage is from room temperature to 1100℃~1200℃, and insulation for 1h; the second stage is heated to 1500℃~1600℃, and insulation for 2h; the third stage is heated to 1800℃~1900℃, and insulation for 1h; the fourth stage is heated to 2100℃~2200℃, and insulation for 1h; the fifth stage is heated to 2330℃~2400℃, and insulation for 3h. The highest sintering temperature is 2330℃, and the total sintering time is 15.5h

More preferably, in step (2), the particle size of the tungsten powder is less than 3 μm, and the particle size of the rare earth oxide (cerium oxide, lanthanum oxide, yttrium oxide) powder is 50 nm.

Further preferably, in step (3), medium frequency induction sintering is carried out under the protection of hydrogen with a flow rate of 2.5 m ³ /h. The sintering process is carried out through five stages of heating and five stages of heat preservation, the highest sintering temperature is 2330°C, and the total sintering time is 15.5h.

The present invention adds three kinds of rare earth oxides to a tungsten matrix by solid-solid doping, and the ratio is La ₂ O ₃ ∶CeO ₂ ∶Y ₂ O ₃ =1∶1∶3. The prepared rare earth tungsten electrode has a density of more than 98%, high strength, excellent electrical and thermal conductivity, strong electron emission ability, and second phase particles are evenly distributed in the tungsten matrix. There is no agglomeration of large second phase particles caused by excessive rare earth oxide content. The preparation process is simple, the production process is pollution-free, and the yield rate is high.

Description of the drawings:

In order to describe the present invention more clearly, the present invention is further described here with reference to the accompanying drawings.

FIG. 1 is a SEM image of the rare earth tungsten electrode prepared in Example 1 of the present invention.

FIG. 2 is a SEM image of the rare earth tungsten electrode prepared in Example 2 of the present invention.

Detailed ways:

The present invention is described in detail below, but the present invention is not limited to the specific embodiments.

Example 1

Weigh 10kg of powder according to the proportion, including 0.066kg of cerium oxide powder, 0.066kg of lanthanum oxide powder, 0.198kg of yttrium oxide powder, and the rest of tungsten powder. Mix the weighed powders and put them into a V-type mixer for mixing. The mixer speed is 24r/min, the mixing time is 12h, and it stops for 15min every 2h.

After the powders are fully mixed, a single mixed alloy powder weighing 1.80 kg is loaded into an elastic film sleeve and pressed into shape using a cold isostatic press. The maximum pressing force is 227 MPa, and the pressure is maintained at 192 MPa and 95 MPa, respectively, with a holding time of 100 s, to obtain a tungsten billet with a size of Ф22.2 mm × 300 mm long.

The obtained tungsten billet is loaded into the tungsten crucible of the medium frequency induction furnace and sintered under the protection of hydrogen with a flow rate of ^2.5m3 /h. During the sintering process, it undergoes five stages of heating and five stages of insulation. The first stage is heated from room temperature to 1167℃ and kept warm for 1h; the second stage is heated to 1505℃ and kept warm for 2h; the third stage is heated to 1810℃ and kept warm for 1h; the fourth stage is heated to 2104℃ and kept warm for 1h; the fifth stage is heated to 2330℃ and kept warm for 3h. The highest sintering temperature is 2330℃, and the total sintering time is 15.5h. After sintering, it undergoes processes such as rotary forging, wire drawing, and straightening to obtain the rare earth tungsten electrode and complete the preparation. The density of the electrode material in this case is 98.7%, the hardness is 408.4HV, the test data of electrical conductivity and thermal conductivity are 24.9%IACS and 155W/(m*k) respectively. The electron emission performance test of the electrode material of this composition shows that the electrode work function is 2.71eV. The SEM image of the electrode material shown in Figure 1 shows that the second phase particles are evenly distributed in the tungsten matrix, and no large particle agglomeration occurs.

Example 2

Weigh 10kg of powder in proportion, including 0.08kg of cerium oxide powder, 0.08kg of lanthanum oxide powder, 0.32kg of yttrium oxide powder, and the rest of tungsten powder. Mix the weighed powders and put them into a V-type mixer for mixing. The mixer speed is 24r/min, the mixing time is 12h, and it stops for 15min every 2h.

After the powders are fully mixed, a single mixed alloy powder weighing 1.81 kg is loaded into an elastic film sleeve and pressed into shape using a cold isostatic press. The maximum pressing force is 227 MPa, and the pressure is maintained at 192 MPa and 95 MPa, respectively, with a holding time of 100 s, to obtain a tungsten billet with a size of Ф21.8 mm × 300 mm long.

The obtained tungsten billet is loaded into the tungsten crucible of the medium frequency induction furnace and sintered under the protection of hydrogen with a flow rate of ^2.5m3 /h. During the sintering process, it undergoes five stages of heating and five stages of insulation. The first stage is heated from room temperature to 1167℃ and kept warm for 1h; the second stage is heated to 1505℃ and kept warm for 2h; the third stage is heated to 1810℃ and kept warm for 1h; the fourth stage is heated to 2104℃ and kept warm for 1h; the fifth stage is heated to 2330℃ and kept warm for 3h. The highest sintering temperature is 2330℃, and the total sintering time is 15.5h. After sintering, it undergoes processes such as rotary forging, wire drawing, and straightening to obtain the rare earth tungsten electrode and complete the preparation. The density of the electrode material in this case is 99.2%, the hardness is 419.4HV, and the test data of electrical conductivity and thermal conductivity are 25.7%IACS and 138W/(m*k) respectively. The electron emission performance of the electrode material of this composition is tested, and the electrode work function is measured to be 2.60eV. The SEM image of the electrode material shown in Figure 2 shows that the second phase particles are evenly distributed in the tungsten matrix, and no large particle agglomeration occurs.

The composition of electrode materials for each implementation case is shown in Table 1:

Case W(wt%) La ₂ O ₃ (wt%) CeO ₂ (wt%) _{Y2O3 (} wt%) Example 1 96.7 0.66 0.66 1.98 Example 2 96 0.8 0.8 0.8

The density, hardness, electrical conductivity, thermal conductivity and work function data of the electrode materials of each implementation case at room temperature are shown in Table 2:

Example 1 Example 2 Density(%) 98.7 99.2 Hardness (HV) 408.4 419.4 Conductivity (%IACS) 24.9 25.7 Thermal conductivity (W/(m*k)) 155 138 Work function (eV) 2.71 2.60

Claims (3)

1. A rare earth tungsten electrode material, characterized in that: the tungsten electrode _contains three rare earth oxides of _La2O3 , _{CeO2 and Y2O3} , the weight percentages of which are: 0.66% to 0.8% of lanthanum oxide, 0.66% to 0.8% of cerium oxide, 1.98% to 2.4% of yttrium oxide, the total amount of rare earth oxides is 3.3% to 4%, and the rest is tungsten; the mass ratio of the three rare earth oxides is _La2O3 : _{CeO2 : Y2O3} = 1:1: ₃ . 2. The method for preparing a rare earth tungsten electrode material according to claim 1, characterized in that it comprises the following steps: (1) Powder mixing: The particle size of the tungsten powder used is less than 3μm, and the particle size of the rare earth oxide (cerium oxide, lanthanum oxide, yttrium oxide) powder is 50nm. The required raw material powders are weighed according to a certain weight percentage, pre-mixed and loaded into a V-type mixer for powder mixing. The mixer speed is 24r/min, the mixing time is 12h, and it stops for 15min every 2h; (2) Pressing: After being fully mixed in a mixer, a single mixed alloy powder with a weight of 1800±100g is placed in an elastic film sleeve, and after being fully vibrated, it is pressed into shape using a cold isostatic press. The maximum pressing force is 227MPa, and the pressure is maintained at 192MPa and 95MPa respectively. The holding time is 100s. After pressing, a tungsten billet with a size of 21-22mm × 300mm in length is obtained; (3) Sintering: The tungsten billet obtained in step (2) is loaded into the tungsten crucible of the medium frequency induction furnace and sintered under the protection of hydrogen at a flow rate of 2.5m3/h. The sintering process undergoes five stages of heating and five stages of insulation. The first stage is heating from room temperature to 1100℃~1200℃ and insulation for 1h; the second stage is heating to 1500℃~1600℃ and insulation for 2h; the third stage is heating to 1800℃~1900℃ and insulation for 1h; the fourth stage is heating to 2100℃~2200℃ and insulation for 1h; the fifth stage is heating to 2330℃~2400℃ and insulation for 3h. The highest sintering temperature is 2330℃ and the total sintering time is 15.5h. (4) After sintering, the rare earth tungsten electrode is obtained through processes such as rotary forging, wire drawing, and straightening to complete the preparation. 3. A rare earth tungsten electrode material and a preparation method thereof according to claim 2, characterized in that the ratio is _{La2O3 : CeO2 : Y2O3} = 1:1: ₃ , and the density of the prepared rare earth tungsten electrode is above 98%.