CN114653960A - Method for preparing superfine high-purity spherical titanium powder by magnetizing radio frequency plasma - Google Patents
Method for preparing superfine high-purity spherical titanium powder by magnetizing radio frequency plasma Download PDFInfo
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- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 title claims abstract description 101
- 238000000034 method Methods 0.000 title claims abstract description 48
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims abstract description 29
- 150000002500 ions Chemical class 0.000 claims description 12
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 12
- 230000006698 induction Effects 0.000 claims description 7
- 239000010453 quartz Substances 0.000 claims description 3
- 239000002245 particle Substances 0.000 abstract description 68
- 239000010936 titanium Substances 0.000 abstract description 65
- 229910052719 titanium Inorganic materials 0.000 abstract description 65
- 229910052786 argon Inorganic materials 0.000 abstract description 15
- 229910052751 metal Inorganic materials 0.000 abstract description 13
- 239000002184 metal Substances 0.000 abstract description 13
- 238000010146 3D printing Methods 0.000 abstract description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 4
- 239000001301 oxygen Substances 0.000 abstract description 4
- 229910052760 oxygen Inorganic materials 0.000 abstract description 4
- 239000007769 metal material Substances 0.000 abstract description 2
- 239000007789 gas Substances 0.000 description 17
- 230000005684 electric field Effects 0.000 description 14
- 239000000843 powder Substances 0.000 description 11
- -1 argon ions Chemical class 0.000 description 8
- 230000007935 neutral effect Effects 0.000 description 8
- 230000008569 process Effects 0.000 description 7
- 230000009471 action Effects 0.000 description 6
- 238000000889 atomisation Methods 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 4
- 230000004907 flux Effects 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 239000004020 conductor Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 239000002923 metal particle Substances 0.000 description 3
- 230000004888 barrier function Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000005672 electromagnetic field Effects 0.000 description 2
- 230000004927 fusion Effects 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 230000001052 transient effect Effects 0.000 description 2
- 229910001111 Fine metal Inorganic materials 0.000 description 1
- 229910001069 Ti alloy Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000005468 ion implantation Methods 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910001338 liquidmetal Inorganic materials 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/14—Making metallic powder or suspensions thereof using physical processes using electric discharge
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Abstract
The invention belongs to the technical field of metal materials, and provides a method for preparing superfine high-purity spherical titanium powder by magnetizing radio frequency plasma. According to the method, the magnetic mirror position type magnetic field is utilized to restrain the electron escape of the radio frequency ionization section, so that the radial escape and longitudinal escape losses of plasma electrons are reduced, the electron density and the electron temperature of the radio frequency plasma are improved, and the electric energy utilization rate of the radio frequency plasma is improved. The large diameter titanium particles entering the discharge chamber with the argon are charged in the high electron density plasma, and when the electrostatic coulomb repulsion force is larger than the dynamic viscous resistance of the molten titanium metal, the large diameter titanium particles are driven to be split, so that the titanium particles with smaller diameters are formed. The method can prepare the pure titanium powder with superfine particle size less than 5 mu m, high purity (oxygen content less than 0.1%) and spherical shape (sphericity better than 98%) for 3D printing at lower cost and higher efficiency.
Description
Technical Field
The invention belongs to the technical field of metal materials, and particularly relates to a method for preparing superfine high-purity spherical titanium powder by using magnetized radio frequency plasma.
Background
With the technological progress, the preparation process of the micro spherical titanium powder is better developed, and the method is developed from the previous rotating electrode method and the electron beam rotating disc method to the plasma rotating electrode method. The plasma rotating electrode method has the main advantages of high sphericity of the prepared powder, good surface appearance and low impurity content. However, since the electrode rotation speed is limited by the problem of dynamic sealing, the average particle size of the powder prepared by the plasma rotating electrode method is large. The particle size of the powder is generally distributed in the range of 50-300 μm, and the average particle size of the powder is large, thereby resulting in a limited range of application.
The plasma atomization method has appeared, although the above-mentioned problems of the plasma rotary electrode method can be greatly improved. The plasma atomization is a process which takes titanium or titanium alloy wires as raw materials, takes a plasma arc gun as a heating source, the raw material wires are instantly melted by plasma and atomized by high-temperature gas, and formed micro-droplets are spheroidized under the action of surface tension and cooled and solidified into spherical particles in the falling process. It is reported that Pyrogenesis, canada, has developed a new plasma atomization process that enables the mass production of ultra-fine metal powders (5-20 μm). The canadian pyrogenes company is a patent holder of the plasma atomization method technology, but the company does not sell the plasma atomization equipment externally, and the research on the plasma atomization technology in China is slow due to patent protection and technical blockade.
The radio frequency plasma spheroidizing technology is characterized in that irregular powder particles fed into plasma are rapidly heated and melted by utilizing the high-temperature characteristic of the plasma, and the melted particles are rapidly solidified under the combined action of surface tension and extremely high temperature gradient to form spherical powder. The plasma has the advantages of high temperature, large volume of the plasma torch, high energy density, no electrode pollution, high heat transfer and cooling speed and the like, and is a good way for preparing high-quality spherical powder with uniform components, high sphericity and good fluidity. However, according to the existing rf plasma spheroidizing technology, it is still impossible to prepare pure titanium powder which satisfies high purity (oxygen content < 0.1%), sphericity (sphericity better than 98%) and ultra-fine (particle size less than 5 μm) simultaneously and is suitable for 3D printing.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method for preparing superfine high-purity spherical titanium powder by using magnetized radio frequency plasma, and superfine (the particle size is less than 5 mu m), high-purity (the oxygen content is less than 0.1 percent) and spherical (the sphericity is better than 98 percent) pure titanium powder for 3D printing can be prepared at lower cost and higher efficiency by using the method.
In order to achieve the above purpose, the solution adopted by the invention is as follows:
the invention provides a method for preparing superfine high-purity spherical titanium powder by using magnetized radio frequency plasma, which comprises the following steps: and adding a magnetic field in a radio frequency ionization section of the radio frequency plasma spheroidized titanium powder.
Further, in the preferred embodiment of the present invention, two dc electromagnetic coils are respectively installed at two ends of the rf discharge coil of the dual-band rf plasma quartz discharge tube, so as to form a magnetic mirror type magnetic field on the dual-band rf discharge plasma.
Further, in the preferred embodiment of the present invention, the magnetic induction intensity of the magnetic field is 300-500Gs
Further, in the preferred embodiment of the present invention, the magnetically confined plasma is a non-thermal equilibrium magnetized plasma.
Further, in the preferred embodiment of the present invention, the electron density of the magnetically confined plasma is 5 × 1019m-3。
Further, in the preferred embodiment of the present invention, the electron temperature of the magnetically confined plasma is 15 eV.
Further, in the preferred embodiment of the present invention, the density of the magnetically confined ions and argon atoms is about 2 × 1024m-3。
Further, in the preferred embodiment of the present invention, the temperature of the magnetically confined ions and argon atoms is about 3000K.
The method for preparing the superfine high-purity spherical titanium powder by the magnetized radio frequency plasma has the beneficial effects that:
on the basis of spheroidized titanium powder of radio frequency plasma, a magnetic mirror type magnetic field with the magnetic induction intensity of 300-500Gs is added to a radio frequency ionization section of the spheroidized titanium powder, so that the electron escape of the radio frequency ionization section is restrained, the radial escape and longitudinal escape losses of plasma electrons are reduced, the electron density and the electron temperature of the radio frequency plasma are improved, and the electric energy utilization rate of the radio frequency plasma is improved:
(1) the large-diameter titanium particles entering the discharge chamber along with argon are charged in high-electron-density plasma, the accidental particle surfaces are raised to form a tip charging effect, when electrostatic coulomb repulsion force is larger than dynamic viscous resistance of molten titanium metal, electrostatic coulomb force drives large-radius particles and small-radius raised parts to generate coulomb repulsion force, large particles are generated to form small particles, input non-spherical titanium particles are converted into spherical titanium powder particles with smaller radius;
(2) in the application, because the titanium particles are charged, the titanium particles are separated to form a plurality of separated powders under the action of electrostatic coulomb repulsion force, the separated powders are continuously heated by electrons in radio frequency plasma, and the surface tension of the titanium particles drives the separated powders to form a more standard sphere; the satellite type titanium powder particles are separated under the action of electrostatic coulomb repulsive force, and the satellite type particles are difficult to form again;
(3) the method adopts an argon gas circulating working mode, so that the argon gas consumption can be reduced, and the production cost for preparing the high-quality superfine titanium powder is further reduced; in addition, the direct-current steady-state magnetic mirror position type magnetic field is adopted, radial and longitudinal escape of radio frequency plasma electrons is restrained, the effect of reducing electric energy consumption is achieved, and the production cost of high-quality superfine titanium powder can be further reduced;
(4) the inert gas and quartz glass discharge tube adopted by the method can not bring extra metal pollution in the melting process of spheroidizing and radius reducing of the non-spherical titanium powder.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides a method for preparing superfine high-purity spherical titanium powder by using magnetized radio frequency plasma, which comprises the following steps: and adding a magnetic field in a radio frequency ionization section of the radio frequency plasma spheroidized titanium powder. Specifically, the method comprises the following steps: two ends of a radio frequency discharge coil of the two-waveband radio frequency plasma quartz discharge tube are respectively provided with a direct current electromagnetic coil, so that a magnetic mirror position type magnetic field with the magnetic induction intensity of 300-500Gs is formed on the two-waveband radio frequency discharge plasma.
Most electrons of the radio frequency plasma are restricted by the magnetic field of the magnetic mirror, so that the radial escape and the longitudinal escape of the electrons are reduced, and the electron density of the magnetically restricted radio frequency plasma is improved to 5 multiplied by 1019m-3Electron temperature of 15eV, density of ion and neutral argon atom of 2X 1024m-3And the temperature is 3000K, and non-thermal equilibrium magnetized plasma is formed. The large-diameter, high-purity and non-spherical titanium particles (800 meshes, about 18 mu m) are conveyed by argon carrying, and higher charge is formed in high electron density magnetized plasma, so that the electron charge density on the surface of the molten titanium metal particles is improved. The molten titanium metal is a conductor with a conductivity of about 2.6X 106S/m, electron charges are distributed on the surface of the molten titanium metal particles, the titanium particles form an equipotential body in magnetized plasma, the potential of the equipotential body is about-15V relative to the zero potential of the plasma, the molten titanium metal particles are split under the action of electrostatic coulomb repulsive force which is larger than the flowing viscous force of the metal liquid, and spherical titanium particles with smaller diameters are formed.
More specifically, it is derived as follows:
the embodiment adopts two-waveband (50kHz, 50MHz) radio frequency electromagnetic waves to generate the magnetized non-thermal equilibrium plasma ionized by argon atoms in the quartz glass tube. The 50kHz antenna penetrates through quartz glass, and forms a Dielectric Barrier Discharge (DBD) in the tube together with a direct current electromagnetic coil, and can be used for high gas density (2 multiplied by 10)25m-3) An initial discharge is formed under the conditions. The DBD discharge power is about 100W; and the radio frequency of 50MHz is a main power source for heating electrons, and the heating power is between 10kW and 100kW according to the gas flow and the delivery flow of the titanium particles.
The 50MHz radio frequency electromagnetic wave generates an angular induction electric field E on the cross section of the quartz glass tubeθ(r) in a cylindrical coordinate system (r, theta, Z) with the axis of the quartz glass tube as the Z axis and the central point of the radio frequency coil as the origin, the current of the radio frequency coil:
the coil generates a transient magnetic field in the quartz glass tube:
assuming that the rf electromagnetic coil is infinitely long, the transient induced magnetic field generated inside the quartz glass tube is spatially uniform inside the tube, with only the z-direction magnetic field (for the sake of simplicity and clarity of the following analysis), and varies with time. A time-varying magnetic field will induce an angular electric field Eθ(r) in a cylindrical coordinate system O (r, θ, z) with the discharge tube axis of symmetry as the origin according to maxwell's equations:
in an infinitely long solenoid, the magnetic field is axisymmetric, and the induced electric field generated by the time variation of the magnetic field also has axial symmetry, and the derivative of the induced electric field to the angular direction theta is zero. Thus:
derived from equations (A), (B) and (C):
the radio frequency electricity and the magnetic field excited by the radio frequency coil in the cylindrical discharge tube are as follows:
the fluence created by the rf electric and magnetic fields within the discharge tube is about:
the energy flux density vector of the radio frequency electromagnetic wave radiated by the radio frequency induction coil points to the radial direction of the discharge tube. In the radio frequency induced electric field, there are initial ionization electrons and argon ions (e) generated by Dielectric Barrier Discharge (DBD)-，Ar+). The electron's gyral angular frequency in a steady state magnetic field of 500Gs is about:
the cyclotron frequency of electrons is much greater than the frequency of the 50MHz radio frequency heating source, so that the accelerated motion of electrons in the induced radio frequency electric field can be regarded as a process accelerated in a quasi-steady-state electric field. It is assumed that the electron temperature generated by the DBD discharge is about 1eV and the temperature of the argon ion is about 0.2 eV. The thermal velocity of the electrons is approximately:
the thermal rate of the argon ions is:
the cyclotron radius of electrons in a steady-state magnetic field of 500Gs is:
and the radius of gyration of the argon ion is:
the radio frequency induction electric field is increased along with the increase of the radial radius, and electrons obtain energy from the radio frequency electric field in the electron cyclotron motion process, so that the kinetic energy of the electrons is increased. Within one period of electron cyclotron motionce＝2π/ωce＝1/fce＝7.14×10-10(s) time intervals, radio frequency electric field
And radio frequency magnetic field
Can be considered as a quasi-steady state electromagnetic field that does not vary substantially with time, and further assumes an initial phase at radio frequencies
At time ω t ═ π/3:
under the assumption that the steady-state magnetic field Bo is much larger than the radio-frequency magnetic field, the perturbation of the radio-frequency magnetic field to the electron cyclotron motion can be ignored.
The power of the radio frequency electric field accelerating electrons and ions is respectively as follows:
equation (E) shows that the rf induced electric field accelerates electrons at a power that is 600 times the power of the accelerated argon ions. This mainly means that the radio frequency induced electric field mainly heats electrons, which transfer their kinetic energy to gas molecules and ions by collisions with them.
The gas pressure in the quartz glass discharge tube is about one atmosphere, and electrons and ions are heated continuously by the radio frequency electromagnetic field, resulting in an electron temperature of about 15eV and a gas molecule and ion temperature of about 0.3 eV. The density of ionized electrons is about 5X 1019m-3. The steady state magnetic field in the plasma is about 500Gs and the radial pressure in the discharge vessel is about
nokTo＝Pr-Pe-PB＝1.013×105-120-995＝1.002×105(Pa)＝Po
The average density of the gas in the discharge vessel is about 2.1X 1024m-3The collision of electrons with neutral gas molecules is the main collision process of energy exchange, and the collision cross section of argon atoms is about 2 × 10-19m-2The mean free path of electrons in the discharge vessel is about:
the energy of the average accelerated electrons of the radio frequency electric field is about:
the electron density of plasma generated by the dual-band radio frequency plasma is about 5 x 1019m-3The electron temperature was 15eV, the temperature of neutral gas atoms and ions was 3000K (0.3eV), and the gas density was 2.1X 1024m-3. The internal gas pressure of the discharge tube is 1 atmospherePressing (1.013X 10)5Pa), and the background steady-state magnetic field is 300-500 Gs.
Because the electron temperature of the dual-band radio frequency plasma is about 15eV, the potential of the surface of the titanium particle is about-15V, and the plasma electrons are prevented from being further accumulated on the surface of the titanium particle. The surface potential distribution of the charged titanium particles in the plasma is thus:
wherein R is ≧ RoR is the distance from the space point to the spherical center of the titanium particle, RoIs the radius of the titanium particle.
Is the debye screen coulombic potential of the charged titanium particles in the plasma; lambda [ alpha ]DIs the debye radius of the plasma,
εo＝8.85×10-12(F/m), vacuum dielectric constant, QoIs the total charge carried by the titanium particles, k is the Boltzmann constant, Te is the temperature of the electrons, e is the electronic charge, neIs the electron density of the magnetized plasma. The temperature of the electrons in the magnetized plasma is about 15eV, and the thermal velocity of the electrons is about:
the electron has a cyclotron radius in a magnetic field of 500Gs of about
The magnetic moment of an electron when the electron moves along the direction of the magnetic field in the magnetic mirror magnetic field is a gradual invariant, namely the magnetic moment of the electron:
in addition to rotating around the magnetic lines of force, the electrons also reciprocate between the ends of the mirror in the magnetic field of the mirror if the velocity profile of the electrons is within the capture zone of the mirror. The magnetic field of the magnetic mirror position type restrains the longitudinal and radial escape of plasma electrons, so that electrons generated by radio frequency are restrained in the magnetic mirror; the magnetic field of 500Gs restrains the radial escape of electrons and also plays a role in improving the electron density of the plasma. The electron density of the dual-band radio-frequency magnetized plasma is 5 multiplied by 1019m-3Electron temperature of 15eV, and density of neutral gas of about 2.1X 1024m-3The temperature of the neutral gas is about 3000K. The elastic collision cross-sectional area of argon atoms is about 2X 10-19m2Mean free path of electron collision with argon atom:
the collision frequency of electrons with neutral gas atoms is about:
electrons in the magnetic mirror type cause partial radial escape due to collisions and longitudinal escape from the loss cone of the magnetic mirror. The heat flux density delivered by the dual band rf magnetized plasma electrons to the titanium particles is about:
Γeth＝0.5nevethkTe＝0.5×5*1019×2.6×106×24×10-19
＝156(MWm-2)
while the heat flux density imparted to the titanium particles by the neutral atoms is approximately:
189MWm is provided for coarse titanium powder particles by electrons and neutral gas atoms of radio frequency magnetized plasma-2Heat flux density, a 500um diameter titanium particle, with a surface area of about:
the heat flow transferred to the titanium powder particles in the magnetized radio frequency plasma unit time is about:
q＝(Γeth+Γoth)Sσo＝189×106×7.85×10-7＝148(J/s)
titanium metal has a specific heat capacity of about Cth＝520J*kg-1*K-1Density of about 4510kgm-3The volume of a 500um diameter titanium particle is about:
titanium particles having a mass of about
M＝ρV＝4510×65.5×10-12＝3.0×10-7(kg)
The titanium powder particles are heated to the melting temperature 1941K from 300K, the temperature rise is about delta T-1641K, and the heat quantity required to be supplied from the outside is about the same as that of the titanium particles when the temperature of the titanium particles is raised to 1941K
ΔQth＝(CthMΔT)＝520×3.0×10-7×1641＝0.256(J)
Latent heat required for melting titanium particles (heat of fusion of titanium metal is about C)m＝322kJkg-1),
ΔQm＝CmM＝0.332×106×3×10-7＝0.1(J)
Thus, 500um diameter titanium particles enter the magnetized radio frequency plasma and are completely melted within time τ:
if the titanium particles move longitudinally in the RF plasma at a velocity of about 100m/s, the titanium particles move longitudinally during melting at a velocity of about 0.24 m. The quartz glass radio frequency discharge tube is about 1.5m in length, and can meet the physical process of fusion, electrostatic repulsion force splitting and re-spheroidization of titanium particles with the diameter of 500 um.
Electrons are restricted by magnetic field of magnetic mirror in magnetized RF plasma to increase electron density to 5 × 1019m-3The electrons are accelerated by a two-band radio frequency induced electric field to raise the temperature to 15eV, and the electron current density of the plasma electrons injected into the titanium particles is about:
Je＝-0.5eneveth＝-0.8×10-19×5×1019×2.1×106＝8.4(MAm-2)
the thermal velocity of the argon ions is approximately:
the ion current density for argon ion implantation is about:
Ji＝0.5enivArth＝0.8×10-19×5*1019×1300＝5.2(kAm-2)＜＜Je
assuming that the secondary electron emission current density of titanium particles in plasma is about 1000Am-2＜＜JeThus, in a magnetized plasma, the predominant carrier charged by the titanium particles is the plasma electron current, and both the ion current and the secondary electron current are negligible. When the charge potential of the titanium particles is about-15V relative to the zero potential of the plasma, the negative potential at the surface of the titanium particles prevents plasma thermal electrons of 15eV from continuing to charge the titanium particles, the negative potential of the titanium particles cannot continue to rise, and the titanium particles are maintained at a negative potential of-15V. A metallic titanium particle having a diameter of about 500 μm, the surface of which is charged to-15V and which has a total charge of about QoThe potential of the spherical surface of the conductor can be simplified into a spherical center QoTotal charge at radius RoThe coulomb potential at the sphere is:
the total charge carried by the metallic titanium particles is:
Qo＝-60πεoRo＝-60×3.14×8.85×10-12×2.5×10-4＝-4.2×10-13(C)
titanium metal spheres of 500 μm diameter were charged in magnetized plasma with a surface charge density of about:
if a small hemisphere with a diameter of 10 μm protrudes from a spherical titanium particle with a diameter of 500 μm, the potential of the surface of the small hemisphere remains-15V (the conductivity of titanium metal is about 2.6X 10)6S/m, the surface of the liquid metal is an equi-potential body), and the surface of the titanium particle is an equi-potential body. But the charge density of the surface of the small hemisphere is greater than that of the large sphere because the tip of the conductor is charged. The charge density of the small hemisphere is approximately:
wherein R isoIs the radius of the large sphere, RsIs the radius of the pellet. The surface area of the small convex hemisphere is about
The charge carried is about:
Qs＝σqsAs＝2πRsRoσqo＜＜Qo
assuming that the surface area of the small hemispheres of the protrusions is much smaller than the surface area (R) of the large diameter titanium dropletss＜＜Ro) The total charge on the surface of the large sphere becomes (Q)o-Qs) The distance between the big ball and the small convex hemisphere is about RoThe electrostatic coulomb repulsion between two charged spheres is about:
the viscous attraction between the small hemisphere and the large sphere is about
Where η ═ 0.326(Pa · s) is the kinetic viscosity coefficient of titanium metal.
If the viscous attraction force is smaller than the electrostatic coulomb repulsion force applied to the small hemisphere, the small hemisphere is separated from the large sphere to form titanium particles with small radius.
The above formula shows that as long as the radius of the small convex hemisphere is smaller than half of the radius of the large sphere, the electrostatic coulomb repulsion force between the two spheres is larger than the viscous resistance of titanium metal flow, and the titanium particles are split to form titanium powder with smaller diameter. That is, in the magnetized RF plasma, the small radius convex part on the surface of the large titanium particle due to the accidental fluctuation factor will overcome the viscous resistance of the interface between the molten titanium metals and break into smaller particles under the action of electrostatic coulomb repulsion force.
In conclusion, the method for preparing the superfine high-purity spherical titanium powder by using the magnetized radio frequency plasma provided by the invention is characterized in that a magnetic mirror position type magnetic field is added in a radio frequency ionization section of the radio frequency plasma spheroidized titanium powder. According to the method, the magnetic mirror position type magnetic field is utilized to restrain the electron escape of the radio frequency ionization section, so that the radial escape and longitudinal escape losses of plasma electrons are reduced, the electron density and the electron temperature of the radio frequency plasma are improved, and the electric energy utilization rate of the radio frequency plasma is improved. The large diameter titanium particles entering the discharge chamber with argon are charged in the high electron density plasma, and when the electrostatic coulomb repulsion force is greater than the dynamic viscous resistance of the molten titanium metal, the large diameter titanium particles are driven to be split, so that the titanium particles with smaller diameter are formed. The method can prepare the pure titanium powder which is used for 3D printing, superfine (the grain diameter is less than 1-5 mu m), high in purity (the oxygen content is less than 0.1 percent) and spherical (the sphericity is better than 98 percent) with lower cost and higher efficiency.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A method for preparing superfine high-purity spherical titanium powder by using magnetized radio frequency plasma is characterized by comprising the following steps: the method comprises the following steps: and adding a magnetic field in a radio frequency ionization section of the radio frequency plasma spheroidized titanium powder.
2. The method for preparing the ultrafine high-purity spherical titanium powder by using the magnetized radio frequency plasma according to claim 1, wherein the method comprises the following steps: the method comprises the following steps: two ends of a radio frequency discharge coil of the two-waveband radio frequency plasma quartz discharge tube are respectively provided with a direct current electromagnetic coil so as to form a magnetic mirror position type magnetic field on the two-waveband radio frequency discharge plasma.
3. The method for preparing the ultrafine high-purity spherical titanium powder by using the magnetized radio frequency plasma according to claim 2, wherein the method comprises the following steps: the magnetic induction intensity of the magnetic field is 300-500 Gs.
4. The method for preparing the ultrafine high-purity spherical titanium powder by using the magnetized radio frequency plasma according to claim 3, wherein the method comprises the following steps: the plasma after magnetic confinement is non-thermal equilibrium magnetized plasma.
5. The method for preparing the ultrafine high-purity spherical titanium powder by the magnetized radio frequency plasma according to claim 3, wherein the method comprises the following steps: the electron density of the magnetically confined plasma was 5X 1019m-3。
6. The method for preparing the ultrafine high-purity spherical titanium powder by using the magnetized radio frequency plasma according to claim 3, wherein the method comprises the following steps: the electron temperature of the magnetically confined plasma was 15 eV.
7. The method for preparing the ultrafine high-purity spherical titanium powder by using the magnetized radio frequency plasma according to claim 3, wherein the method comprises the following steps: the density of magnetically confined ions and argon atoms is about 2X 1024m-3。
8. The method for preparing the ultrafine high-purity spherical titanium powder by using the magnetized radio frequency plasma according to claim 3, wherein the method comprises the following steps: the temperature of the magnetically confined ions and argon atoms was about 3000K.
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