WO2001036133A1 - Process and equipment for preparing superfine powder by heating and evaporation - Google Patents

Abstract

The present invention relates to a process and equipment for preparing superfine powder by heating and evaporation. Under the condition of inertial atmosphere or reactive atmosphere, the metal or alloy is heated by use of induction, resistance or arc while high-power CO2 gas laser or YAG solid laser acts directly on the metal or alloy to speed up its fusion and evaporation. A high gradient of pressure and temp is generated near the surface of the metal or alloy to speed up the evaporation of molten metal and alloy, resulting in higher output rate of superfine powder. In the equipment for preparing superfine powder a heat-vacuum evaporation chamber provided with specially designed laser and heat means is used.

Description

 Method and equipment for preparing ultrafine powder by heating evaporation

 The invention relates to a technique for preparing ultrafine powder. Specifically, it relates to a method and equipment for preparing ultrafine powder by heating and evaporation.

Background technique

 When the induction heating evaporation method is used to prepare ultrafine powders of metals and alloys, the heating temperature is generally lower than 2000 *, which makes this method unsuitable for the preparation of ultrafine powders of high melting point metals and alloys and high boiling non-metals and compounds. This temperature is also lower than the boiling point of common metals and alloys. For example, the melting point of aluminum is 660t: but the boiling point is as high as 2450X; the melting point of copper is 1083; the boiling point is 25951 :; the melting point of iron is 1536 * and the boiling point is 3000 "C. The heating temperatures for preparing ultrafine powders of aluminum, copper and iron by induction heating evaporation methods are generally 1400 ", 1500 *, 1600, respectively, which are far below their respective boiling points. Therefore, it is not difficult to understand that the production of ultrafine powders of metals, alloys and non-metals and compounds by induction heating is low. In order to increase productivity and increase production, both at home and abroad have been adopted to increase the evaporation area (enlarge the crucible diameter) and increase the power (which has exceeded 200KW). However, due to the above reasons, the yield of ultrafine powders of metals and alloys prepared by this method is generally 0.1-0.5 Kg / hr, some of which are even lower than 0.1 Kg / h, and the energy consumption is huge, and the product is expensive.

Using a laser as a heat source, a solid metal or alloy is heated in an emotional gas (Ar, He, etc.) to evaporate, and the evaporated atoms are cooled in a continuous collision with the gas molecules, reaching a supersaturated state, producing agglomerated growth and forming ultrafine powder . The ultrafine powder prepared by the laser heating method has high purity, small particle size, concentrated distribution, and good sphericity. However, solid metals and alloys have a strong ability to reflect laser light, and a large amount of energy is required to dissipate heat from the substrate. Therefore, it is inefficient to directly melt and evaporate metals and alloys with lasers to prepare ultrafine powders. The research on the interaction between laser and materials shows that the absorption rate of laser light by materials changes with temperature, and the trend is that the absorption rate increases with temperature. The absorption rate of metal at room temperature is very small (for CO ₂ laser, the absorption rates of AI, Cu, and Fe are 1.9%, 1.5%, and 3.5%, respectively). When the temperature rises to near the melting point, its absorption rate Up to 40-50%; if the temperature is close to the boiling point, its absorption rate is as high as 90%. Summary of the invention

 The purpose of the present invention is to solve the shortcomings of the method and equipment for preparing ultrafine powder in the prior art, and to provide an improved method which can not only maintain the cleanliness and purity of the ultrafine powder produced, but also improve the yield and yield of ultrafine powder. Method and equipment for preparing ultrafine powder.

To achieve the above object of the present invention, the present invention provides a method of heating evaporation preparing ultrafine powders: The evaporation chamber is evacuated to IX 10 ¹ - starting material IX 10- ⁵ Pa, with a heating apparatus for heating for the preparation of superfine powder, During this period, a laser is introduced to the surface of the raw material to accelerate its melting and vaporization, and the evaporated vapor condenses to form ultrafine powder.

In the above method, after evacuation of the evaporation chamber, an inert gas is introduced to make the pressure of the evaporation chamber reach and maintain at IX 10 ¹ -IX 10 ⁵ Pa, and then the next steps are performed.

After the above-described method may also be evacuated evaporation chamber, introducing a reactive gas, the pressure of the evaporation chamber and maintained at ^{1 χ 10 1 - 1 X 10} 5 Pa, then the subsequent steps.

After the above-described method may also be evacuated evaporation chamber, introducing an inert gas and reactive gas, the pressure in the evaporation chamber and maintained at ^{1 X 10 1 - 1 X 10} 5 Pa, then the subsequent steps.

 To achieve the above object of the present invention, the present invention also provides an evaporation chamber device for implementing the above method, including: a container with a laser inlet on the wall, a raw material heating zone and a heating device provided in the container, and a raw material heating zone provided above the raw material heating zone. Metal tube, which is fixed on the wall of the container and connected to the powder trap.

 The heating device in the above evaporation chamber device may be an induction heater, a resistance heater or an arc heater; a cooling device may be arranged on the outer surface of the metal tube; a raw material heating zone may be provided with a crucible for storing raw materials; The crucible is set and sent directly to the raw material heating zone.

 The wall of the container in the evaporation chamber device may be provided with a feed port through which raw materials are fed, and may also have one or two gas ports through which the inert gas and the reactive gas are introduced separately or simultaneously. The lower end of the metal tube in the container can also be equipped with a radiation protection cover communicating with it. The radiation protection cover can be designed in a spherical shape, and laser through holes and raw material through holes can be opened on it.

The invention has the advantages that when preparing ultrafine powder of metal or alloy, the metal or alloy is heated and melted by using a heating device to maintain a high temperature and has a large absorption rate for laser light, Then, the laser is introduced into the evaporation chamber, and acts on the surface of the liquid metal or alloy, so that its laser action zone reaches or approaches the boiling point, forming a high pressure gradient and temperature gradient near the upper part of the liquid metal or alloy surface, and accelerating the evaporation of the surface of the liquid metal or alloy When preparing non-metal or compound ultrafine powder, after heating the raw materials to a high temperature with a heating device, introducing a laser can quickly vaporize them. Therefore, whether it is metal and alloy or non-metal and compound, the preparation of ultrafine powder by using the present invention can increase the yield, increase the output, reduce energy consumption and production cost, and maintain the high purity and cleanliness of the ultrafine powder.

Overview of the drawings

 The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

 FIG. 1 is a schematic structural diagram of an embodiment of an evaporation chamber device used for a method of preparing ultrafine powder by laser and heating.

 Fig. 1 is a schematic structural view of another embodiment of an evaporation chamber device for a method of preparing ultrafine powder by laser and heating.

Best Mode of the Invention

 Fig. 1 shows a specific embodiment in which a crucible is provided in the raw material heating zone. On the wall of the double-layer internally cooled stainless steel container 6, there is a laser inlet 13, a gas inlet 7, or two gas inlets 7, 8, and a feed inlet 3 and an observation window 4 may also be opened. The raw materials in the container 6 The heating zone 14 is provided with a high temperature resistant crucible 9 and an induction heater 5, the crucible 9 contains a raw material 10 for preparing ultrafine powder, and a metal tube 2 is arranged above the crucible 9, the metal tube 2 and a trap and an exhaust The devices are connected, and a cooling device 1 is arranged on the outer surface. The cooling device 1 is composed of water-cooled or fluorine-cooled steel pipes, and is directly brazed to the outer wall of the metal pipe 2. The metal pipe 2 is fixed on the wall of the container 6. The metal tube 2 is a collecting channel of the ultrafine powder, and the cooling device 1 cools the evaporated raw material vapor through the wall of the metal tube, and suppresses the growth of the ultrafine powder. A radiation protection cover 11 is installed at the lower end of the metal tube 2 and communicates with the metal tube 2. A laser through hole 12 and a material opening 15 are opened thereon. When a metal or alloy is used as a raw material, it is used to block liquid metal or The alloy directly irradiates the laser. The radiation shield 11 adopts a spherical shape design, and improves the thermal efficiency of the evaporated metal and the alloy through spherical reflection.

The laser enters the evaporation chamber through the laser inlet 13 and interacts with the raw materials in the crucible 9. Before the laser enters the evaporation chamber, it can be changed by the adjusting device on the liquid surface of the raw materials. Laser spot size. The introduced laser can be a CO ₂ gas laser or a YAG solid laser. When one gas inlet 7 is opened, an inert gas or reactive gas (0 ₂ , N ₂ , NH ₃ , H ₂ , CH ₄ , C ₂ H _2, etc.) is introduced from the gas inlet 7; when two gas inlets are opened At 7, 8 hours, inert gas or reactive gas is introduced from the gas inlets 7, 8 respectively. The introduction of inert gas can better control the evaporation pressure and protect the molten pool. When only inert gas is introduced, ultrafine powder of metal, nonmetal or alloy is generated, and when only reactive gas or both inert gas and reactive gas are introduced, ultrafine powder of compound is generated. Through the dynamic feeding device connected to the feeding port, raw materials can be added dynamically and in real time, so that the liquid level of the raw materials in the crucible 9 is maintained within a fixed height range. Through the observation window 4, the evaporation process of the raw materials in the evaporation chamber can be observed.

The pretreated feedstock into a crucible and a dynamic of the charging device 9, the evaporation chamber is evacuated to ^{IX 10 1 - IX 10- 5 Pa} , and then introduced into the inert gas inlet 7 from the gas, the gas from the inlet 8 to a reactive gas, The evaporation chamber pressure was brought to IX 10 ¹ -IX 10 ⁵ Pa, the induction heater 5 was turned on, and the raw material in the crucible 9 was heated until it melted. At this time, the laser is introduced to act on the surface of the molten pool (it can also be introduced before the raw material is melted), so that the raw material is quickly evaporated. Depending on the degree of drop of the liquid level in the crucible 9, start the dynamic feeding device to add raw materials into the crucible 9. The generated ultrafine powder is dynamically and continuously collected by the cooled metal pipe 2 and the trap connected to it.

 Figure 2 shows an embodiment where the rod-shaped raw material enters the raw material heating zone directly through the feed port. A feeding port 3 is opened on the wall of the container 6, and the rod-shaped raw material 10 is dynamically and real-time fed into the raw material heating zone 14 from the feeding port 3, so that the top of the raw material 10 is maintained within a fixed height range, and the laser passes through the laser inlet. 13 and the laser through hole 12 directly act on the top of the raw material 10 in the raw material heating zone 14. The raw material 10 is melted by the resistance heater 16 and the laser and evaporated.

 Example 1:

99.99% block-shaped pure iron was used and placed in an A1 ₂ 0 ₃ crucible. The evaporation chamber was evacuated to IX 10- ^ a, and then filled with argon to lx l0 ³ Pa. Start the high-frequency power supply and heat the pure iron to melt. A CO ₂ laser is introduced, the laser passes through the focusing lens, the spot diameter is φ4ιη, and the laser power is 1000W. Pure iron ultrafine powder having an average particle diameter of 40 nm was obtained, and the yield was 0.8 kg / hour. Example 2:

99.99% block-shaped pure aluminum is placed in the A1 ₂ 0 ₃ crucible. The evaporation chamber was evacuated to IX 10 and then filled with trace oxygen to lx l0 ³ Pa. Start the high-frequency power supply and heat the pure aluminum to melt. A CO ₂ laser is introduced, the laser passes through a focusing lens, the spot diameter is φ4ππη, and the laser power is 800W. Γ-A1 ₂ 0 ₃ ultrafine powder was obtained, the particle size distribution is shown in the table, and the yield was 0.6 kg / hour.

实施例 3: γ-A1 ₂ 0 ₃ ultrafine powder particle size distribution

Example 3:

99.99% rod-shaped pure graphite is continuously fed from the feeding port. The evaporation chamber is pre-evacuated to 1 x 10- ^ a, and then filled with helium to 5 <10 ³ Pa. Activate the resistance heater to heat the graphite to a higher temperature. 400W YAG laser is introduced, and the laser is irradiated on the pure graphite rod through the focusing lens. Pure graphite ultrafine powder having an average particle diameter of 12 nm was obtained, and its yield was 0.3 kg / hour.

 Example 4:

99.99% rod-shaped pure titanium is continuously fed from the feeding port. The evaporation chamber is pre-evacuated to 1 x 10-iPa, and then filled with argon and a small amount of oxygen to 5 x ¹⁰³ Pa. The arc heater was started to heat the titanium rod to a higher temperature. A 400W YAG laser was introduced, and the laser was irradiated on a pure titanium rod through a focusing lens. 22nm average particle diameter of the ultrafine Ti0 _2, with a yield of 0.4 kg / hr.

Industrial applications

 The invention can be used for preparing ultrafine powder.

Claims

Rights request 1. A method for preparing ultrafine heating evaporation, wherein: the evaporation chamber is evacuated to ^{IX 10 1 - IX 10- 5 Pa} , with a heating means for heating the feedstock preparation of superfine powder, during which the laser is introduced It acts on the surface of the raw material to accelerate its melting and vaporization, and the evaporated vapor condenses to form ultrafine powder. The heating method for evaporating the ultrafine powder prepared as claimed in claim 1, wherein: after the evaporation chamber is evacuated, an inert gas is introduced, the pressure in the evaporation chamber and maintained at ^{1 X 10 1 - 1 X 10} 5 Pa, go on to the next step. The heating method evaporation superfine powder prepared according to claim 1, wherein: after the evaporation chamber is evacuated, the reaction gas is introduced, the pressure in the evaporation chamber and maintained at ¹ X 10 1 - 1 X 10 ⁵ Pa, proceed to the next step. 4. The method for preparing ultrafine powder by heating and evaporation according to claim 1, characterized in that: after the evacuation chamber is evacuated, an inert gas and a reactive gas are introduced so that the pressure in the evaporation chamber reaches and is maintained at 1 X 10 ^1- 1 X 10 ⁵ Pa, proceed to the next step.  5. An evaporation chamber device for implementing the method of claim 1, comprising a container, a heating device and a raw material heating zone located in the container, characterized in that: a laser inlet is opened on the wall of the container, and A metal tube is arranged above the raw material heating zone, and the metal tube is fixed on the wall of the container and connected to the powder trap.  6. The evaporation chamber device according to claim 5, wherein: the heating device is an induction heater.  7. The evaporation chamber device according to claim 5, wherein: the heating device is a resistance heater.  8. The evaporation chamber device according to claim 5, wherein: the heating device is an arc heater.  The evaporation chamber device according to claim 5, characterized in that: a cooling device is disposed on the outer surface of the metal pipe. 10. The evaporation chamber device according to claim 5, 6, 7, 8 or 9, characterized in that: the raw material heating zone is provided with a crucible, and a feeding opening is opened on the wall of the container, The raw material enters the crucible through the feed port.  11. The evaporation chamber device according to claim 10, characterized in that: a radiation protection cover is installed at the lower end of the metal tube, and communicates with the metal tube, and the radiation protection cover is provided with a laser through hole. And raw through holes.  12. The evaporation chamber device according to claim 11, wherein the radiation protection cover adopts a spherical shape design.  13. The evaporation chamber device according to claim 12, characterized in that: a gas inlet is opened on the wall of the container.  14. The evaporation chamber device according to claim 5, 6, 7, 8 or 9, characterized in that: a feeding port is opened on the wall of the container, and the raw material is fed into the raw material through the feeding port. Heating zone.  15. The evaporation chamber device according to claim 14, characterized in that: the lower end of the metal pipe is provided with a radiation shielding cover communicated therewith, and the radiation shielding cover is provided with a laser through hole.  16. The evaporation chamber device according to claim 15, wherein: the radiation shielding cover is designed in a spherical shape. 17. The evaporation chamber device according to claim 16, characterized in that: a gas inlet is opened on the wall of the container. Amended claims  Date of receipt by the International Bureau: October 27, 2000 (27.10.00)  Replaced original claims 1-17 with new claims 1-6 (2 pages total) 1. A method for preparing ultrafine powder by heating evaporation, comprising the following steps:  The evaporation chamber is evacuated, and then at least one of the inert gas and the reactive gas is introduced, so that the evaporation chamber reaches a certain pressure, and the raw material for preparing ultrafine powder is heated by a heating device. At the same time as the above heating, a laser is introduced to act on the raw material. Surface, which accelerates its vaporization,  Condensing the evaporated vapor to form ultrafine powder,  It is characterized in that the raw material for preparing ultrafine powder is directly placed in a heating and vaporization area, and the raw material is directly vaporized from a solid state during the heating process. 2. The method according to claim 1, characterized in that, in said vacuuming stage, the degree of vacuum reaches 1 x 10 L 1 x ^{10 5} Pa, and in the step of introducing at least one of an inert gas and a reactive gas, evaporates the pressure chamber and maintained at ^{1 O 1 - 1 xl0 5 Pa} .  3. The method according to claim 1 or 2, characterized in that: the raw material for preparing the ultrafine powder is selected from one of a metal or an alloy, an oxide, a carbide, a nitride, and a carbon group material.  4. A method for preparing ultrafine powder by heating evaporation, comprising the following steps:  Evacuate the evaporation chamber, and then introduce at least one of inert gas and reactive gas to make the evaporation chamber reach a certain pressure,  The heating device is used to heat the raw material for preparing ultrafine powder placed in the crucible. At the same time as the above heating, a laser is introduced to act on the surface of the raw material to accelerate melting and vaporization.  Condensing the evaporated vapor to form ultra-fine powder,  It is characterized by introducing a reactive gas or a mixture of a reactive gas and an inert gas in a step of introducing at least one of the inert gas and the reactive gas. 5. The method according to claim 4, characterized in that: the page is modified in said vacuum stage (Article 19 of the Treaty) Section, degree of vacuum reached 1 χΐθ〗 - 1 χΐθ ⁵ Pa, the step of introducing at least one inert gas and the reaction gas of the two, the pressure in the evaporation chamber and maintained at ^{1 O 1 - 1 x 10 5} Pa.  6. The method according to claim 4 or 5, characterized in that: said raw material for preparing ultrafine powder is selected from one of metal or alloy, oxide, carbide, nitride and carbon group material. -9- Revised page (Article 19 第)