Plasma-arc reactor and fine powder producing method

FIELD: powder metallurgy, namely process for producing sub-micron and nanometer size aluminum powder by plasma evaporation.

SUBSTANCE: plasma-arc reactor for producing powder of solid material such as wire includes first electrode and second electrode that may be spaced from first electrode by distance sufficient for plasma arc occurring in space between first and second electrodes. First electrode has duct passing through it; outlet opening of said duct is open to space between first and second electrodes. Reactor includes unit for feeding solid material such as wire through said duct into space between electrodes. If it is necessary to produce passivated aluminum powder, in reactor aluminum wire is fed to inert-gas plasma where aluminum evaporates. Evaporated aluminum is cooled by inert gas for condensing aluminum powder and oxidizing surface of aluminum powder particles with passivating gas.

EFFECT: enhanced efficiency, possibility for producing fine powders of highly constant size and small cohesion forces of particles.

46 cl, 8 dwg, 2 tbl, 1 ex

 

The invention relates to a device and method for the production of powders. In particular, the proposed plasma arc reactor that can be used in the plasma process of evaporation to obtain aluminum powders of submicron or nanometer size.

Metal and ceramic powders are used in sintering metallurgy and catalysis in the chemical industry. These powders can be used for the production of structural elements, magnetic films, chemical coatings, additives to oils, additives to rocket fuel, and in explosives.

For the production of such powders are known various methods. In the document EN 2133173 C1 B 22 F 9/14, from 20.07.1999 described method for the production of powder with a microcrystalline structure by means of widely known plasma torch or plasmatron. The paper describes the application of water-cooled plasmatron and refers to the use of the device straight polarity (plasma burner straight polarity), in which both the stationary electrode placed in a water cooled burner housing, both electrodes are made of copper. The document refers to the technology with the use of atomization, in which the wire is segmented and melt with the formation of droplets, i.e. the liquid phase.

Known is n document US 5593740 from 14.01.1997, which refers to a method of manufacturing submicron metal particles in the carbon shell, in which the evaporation of the solid material in the plasma, the mixing of the evaporated material with a gas containing carbon, and subsequent condensation of the mixture with the formation of submicron metal particles in the carbon shell.

The technical result achieved with the use of the claimed invention, is to increase productivity or output and ensure the production of high yield nanoscale and submicron powders with high constancy of dimensions and low forces of adhesion of particles.

In the present invention is proposed plasma arc reactor to obtain a powder of the solid feed material containing:

(a) a first electrode,

(b) a second electrode made with the possibility of removal from the first electrode by a distance sufficient to generate a plasma arc between them,

(c) means for entering a plasma-forming gas into the space between the first and second electrodes,

(d) means for forming a plasma arc in the space between the first and second electrodes,

the first electrode has a through channel, the outlet of which opens into the space between the first and second electrodes, is provided by the means for feeding solid material into the channel and through it to exit the channel through the outlet into the space between the first and second electrodes.

In this context, the term "electrode" includes a plasma torch.

The first electrode preferably is arranged to move relative to the second electrode from the first position, in which the arc portion in contact with the arc part of the second electrode in a second position, in which the arc portion are separated from each other by a distance sufficient to generate a plasma arc between them. This condition is preferred because the contact between the first and second electrodes facilitates the initiation of the plasma arc. Under arc part refers to those areas or points on the surfaces of the first and second electrodes, between which may be generated by the plasma arc.

The first electrode may be preferably made in the form of a hollow elongated element, the inner surface of which forms a closed channel (equivalent to the bore or passage). Elongated element ends arc working end, which is opposite to the arc of the second electrode. The outlet of the closed channel is located on the arc working end or next to it. In this case, the first electrode may be in the form of a hollow rod, cylinder, or tube. The first electrode may be initially made in the form of a hollow object. Alternatively, first the second electrode may be made solid with the subsequent execution holes in it or pass. If the outlet hole is located on the arc working end, the end surface of the elongated element forms an arc working end of the electrode and the discharge outlet of the closed channel. The first electrode is usually the cathode.

The second electrode acting as the counter-electrode may be of any appropriate form, to generate a plasma arc between it and the first electrode. The second electrode may have just mostly flat arc part. For example, the second electrode can be located as a flat layer on the bottom wall of the plasma reactor.

Arc of the first and/or second electrodes are usually made of carbon, preferably graphite.

The plasma reactor may be in the form of coated graphite capacity or graphite crucible, part of which performs the function of the second electrode. Accordingly, the second electrode may be integral with the reactor vessel.

In a preferred embodiment of the invention, some or all of the inner surface of the reaction chamber with a plasma arc is the second electrode. This camera can be a graphite reaction chamber or coated graphite reaction chamber.

It is also preferable to perform the second electrode is the anode, in the work of metal ions electro is catechesi departed from him.

Neither the first nor the second electrode do not require grounding.

Plasma-arc reactor preferably further comprises cooling means for cooling and condensation of solid material, which is evaporated in the plasma arc generated between the first and second electrodes. The cooling means preferably includes a source of cooling gas.

The second electrode preferably contains graphite vessel having a surface to guide the evaporated material further, in the cooling zone for cooling operation cooling gas.

For the cooling zone may be provided by the collection area designed to collect powder condensed evaporated material. The collection area may contain fabric that separates the powder particles from the gas stream. Filter fabric preferably is grounded on the frame, to prevent the formation of electrostatic charge. After that, the powder can be collected with filter cloth, preferably in the area with controlled atmosphere. The obtained powder product is then preferably sealed in an inert gas in the container under pressure above atmospheric.

The first electrode is preferably an additional channel that provides the plasma input gas into the space between Erwin and second electrodes. Therefore, the solid feed material and a plasma gas can pass through a common channel in and out of the electrode through a common outlet into the space between the first and second electrodes.

Means for generating a plasma arc in the space between the first and second electrodes typically contains a source of direct or alternating current.

If desired, you can use one or more additional electrodes, containing a conduit for supply of material, to be able to serve together different materials in a single plasma reactor. You can use a common counter-electrode, or alternatively can be separate protivoelektrodom, each of which is located opposite electrode with a channel in it. You can use a common or separate power supplies with separate power sources are preferred, as this allows you to apply different evaporation rates for different materials.

The device according to the present invention can operate without the use of any water-cooled elements inside the plasma reactor and also allows you to replenish the solid feed material without stopping the reactor. Water cooling can lead to thermal shock and the resulting destruction of the material. It can also trouble the AMB adverse reactions between water vapor and the material to be processed.

The device according to the invention may further comprise means for supplying solid feed material to the first electrode. If the solid material has the form of a wire, the device preferably contains a supply of wire. For example, the device may include a container or holder for wire, preferably, the coil or reel.

Preferably can be provided with means for feeding wire from the stock wire to the first electrode, and the wire is fed into the channel. For this you can use, for example, a motor.

According to the present invention is also a method for obtaining powder from a solid feed material, namely, that

(i) take plasma-arc reactor described above, (ii) introducing a plasma gas into the space between the first and second electrodes,

(iii) generating a plasma arc in the space between the first and second electrodes,

(iv) serves solid material through the channel to exit through its outlet in the plasma arc, in which the solid material is vaporized,

(v) cool the evaporated material for condensation powder and

(vi) collect the powder.

The proposed method can be seen as a way of condensation of the gas/vapor phase. In such a process for evaporating a solid downloadable what about the material to generate plasma in the vapor phase is fragmented material. Then the steam is cooled and transformed into solid particles.

Solid feed material usually contains or consists of a metal, such as aluminum, Nickel or tungsten, including alloys containing one or more of these metals. The preferred material is aluminum and its alloys. Solid feed material may be in any suitable form that allows you to serve it in the channel and release through the channel into the space between the electrodes. For example, the material may be in the form of wire, fibers and/or powder. Solid feed material does not require to supply any supporting carrier-phase type liquid media.

Solid feed material preferably has the form of a continuous wire. This form is preferred because it was found that the solids feed material in the form of a wire facilitates the transfer of material in the zone of the plasma in the core plasma.

Plasma gas typically contains or consists of an inert gas such as helium and/or argon.

The plasma gas is preferably introduced into the channel in the first electrode to exit into the space between the first and second electrodes. In this case, the plasma gas and the solid material is preferably extend from the first electrode through a common outlet. Plasma is the first gas and the solid material can be fed into the channel in the first electrode through a common inlet or alternatively, through a separate inlet. During operation of the plasma gas and the solid material is fed into the channel together.

Volumetric flow rate of the plasma gas is preferably controlled to optimize heat transfer between the material and the plasma and to ensure the separation of material in the vapor phase.

At least some cooling of the evaporated material can be secured using a stream of inert gas, such as argon and/or helium. Alternative or together with inert gas can be used a stream of reactive gas. The reactive gas can produce powders of oxides and nitrides. For example, the use of air for cooling the evaporated material can lead to oxide powders, for example powders of aluminum oxide. Similarly, the use of a reactive gas containing, for example, ammonia, can provide a nitride powders, for example powders of aluminum nitride. The cooling gas can be recycled through a water-cooled chamber conditioning.

The surface of the powder can oxidize with pestiviruses the gas stream. This is especially preferable when the material is aluminum or a material based on aluminum. Passivating gas may contain oxygen is a gas, especially preferred gas contains from 95 to 99% vol. inert gas, such as helium and/or argon, and from 1 to 5 vol.% oxygen, more preferably, about 98 vol.% inert gas (gases) and about 2 vol.% the oxygen. It was found that this gas mixture gives particularly good results for aluminum and materials based on aluminum. Pestiviruses gases are preferably pre-mixed, in order to exclude local enrichment of the gas phase and the possibility of explosions. Cooling (inert) gas can be recycled and then to dilute the oxygen with a speed of typically 1 Nm3per hour to get the flow pestiviruses gas. The aluminum acts as getpagetitle for oxygen and reacts with it, resulting in the partial pressure in the chamber falls. If the control pressure in the chamber, then the subsequent increase in the partial pressure means that the surface of the aluminum powder was almost completely passivated. Reactivity of some ultrafine powders is working the danger, if there is a possibility of contact, for example, water and/or air. Stage passivation powder makes the material more suitable for transportation.

For aluminum, designed for some applications, preferably, the plasma is essentially what the f happened oxidation. It is preferable that the cooling of the evaporated material was carried out using a stream of inert gas, such as argon and/or helium. Accordingly, the stage passivation preferably takes place only after the powder has cooled down. In a preferred embodiment, the solid feed material, such as aluminum wire, served at the core of the plasma, where it evaporates. The metal vapor is then served in a separate area rapid cooling, where it is rapidly cooled in a stream of inert gas and turns into a hardened powder. This solid powder is then exposed to oxygen in the low-temperature oxidation conditions so that the oxide was grown to restrictive thickness and began to self-regulate, i.e. the oxide began to inhibit further oxidation. This process of exposure to oxygen and reaction occur away from the core plasma.

The proposed method can be used to obtain a powder material, such as aluminum, almost all particles which have a diameter less than 200 nm. Preferably, the average particle diameter is in the range from 50 to 150 nm, more preferably from 80 to 120 nm, and most preferably from 90 to 110 nm.

Analysis of specific surface showed that the proposed method can be used to obtain a powder material, such as aluminum specific surface area which is in the range from 15 to 40 m 2g-1, preferably in the range from 25 to 30 m2g-1.

It is clear that for the workpiece material and the desired particle size of the finished powder you have to specifically select the machining conditions such as the feed speed of the material and gas, temperature and pressure.

It is preferable that the second electrode was a part of or the entire inner surface of the reaction vessel. The second electrode is preferably an anode and the first electrode is preferably a cathode. For certain applications, the first and/or second electrodes are preferably made of a material that does not react with downloadable material at the operating temperature.

The first and second electrodes are preferably made of carbon material, more preferably of graphite. Accordingly, the reaction vessel may be a graphite reaction chamber or coated graphite reaction chamber, which is the second electrode.

Usually is preferable that the reactor was preheated before evaporation of the solid feed material. The reactor can be preheated to a temperature of 2500°S, more preferably from 500 to 2500°C.

For aluminum loading the reactor is preferably heated to t is mperature from 2000 to 2500° S, more preferably from 2200° 2500°and most preferably from 2300 to 2500°C. preheating is possible to provide any suitable means, although it is preferable to use the plasma arc. Preferably previously heated almost all of the inner space of the reaction vessel.

The speed with which the solid feed material is fed into the channel in the first electrode affects the yield and the size of the powder. When using aluminum wire was used, the feed rate from 1 to 5 kg/hour, more preferably about 2 kg/hour. Aluminum wire typically has a diameter of 1-10 mm, preferably 1-5 mm

Inert plasma gas, for example helium, you can also enter through the channel in the first electrode at speeds from 2.4 to 6 Nm3/hour, more preferably 3 Nm3/hour.

If the generation of a plasma arc is used constant current source, the power constant current is typically set in the range from 400 to 800 A. Electrical characteristics DC usually be about 800 a and from 30 to 40 In the length of the plasma arc column from 60 to 70 mm

The proposed method and plasma-arc reactor typically operate at a pressure above atmospheric, more preferably above atmospheric pressure on the pressure 750 mm of water. This prevents or helps to prevent the entry into the zone of the plasma of atmospheric oxygen, which could cause undesirable chemical reactions. If the loaded material is aluminum, it is preferable that a plasma arc reactor was operating at a pressure exceeding atmospheric pressure of 45 inches of water, preferably from 15 to 35 inches of water. Work under pressure above atmospheric may also contribute to a higher yield of the powder material.

If as a cooling gas is used, the preferred inert gas, such as argon or nitrogen, for cooling and condensing the evaporated material, it was found that the flow rate from 60 to 120 Nm3/h is obtained aluminum powder, in which the majority of the particles, if not almost all, have a diameter of less than 200 nm (preferably ≤100 nm). After cooling the temperature of the gas and powder is 300 to 350°C.

When loaded aluminum material proposed method allows to obtain a powder material with a chemical composition which is a mixture of aluminum metal and aluminum oxide. It is assumed that the reason for this is the addition of oxygen into the material during processing in the conditions of low-temperature oxidation. Accordingly, the present invention is e provides obtained by the proposed method of powder material, containing particles having a core, which contains or consists predominantly of aluminum, and the surface layer, which contains or consists mainly of aluminum oxide.

Essentially oxidize only the surface of the particles and the specific surface analysis showed that the oxide component of the powder is mostly associated with the surface, and the oxide layer has a thickness of less than about 10 nm, preferably less than about 5 nm. Therefore, such a material can be described as discrete dispersed. Almost all particles coated with aluminum oxide have a diameter of less than 200 nm, the average particle diameter is from 50 to 150 nm, preferably from 80 to 120 nm, and more preferably from 90 to 110 nm. The specific surface is covered with oxide of aluminum particles is from 15 to 40 m2g-1preferably from 25 to 30 m2g-1.

Studies of the powder material using TEM and electron diffraction showed that the aluminum particles are essentially single crystals.

Hereinafter will be described in more detail exemplary embodiment of the present invention with reference to the accompanying drawings, on which:

1 shows an embodiment of an electrode that can be used in plasma arc reactor according to the invention,

figure 2 - block the Hema execution of the method according to the invention,

figure 3(a) and (b) secondary electron of microsemi aluminum powders produced by the proposed method ((a) 100000-fold increase; (b) 200000-fold increase);

4 is a graph showing the change of the specific surface ideal nanometer aluminum powder, depending on the diameter of the particle;

5 is a diagram showing changes in the content of the oxide in an ideal nanometer aluminum powder, depending on the diameter of the particle;

6 is a graph of the primary (first heat) analysis of the DSC aluminum sample;

7 is a graph of the secondary (second heat) analysis of the DSC aluminum sample, and

Fig - researched range of nanometer aluminum powder, obtained using x-ray photoelectron spectroscopy (RFS).

Figure 1 shows the first electrode 5 made in the form of a cylindrical graphite rod, which ends arc working end 6. If desired, the upper part of the graphite electrode can be replaced by copper. The electrode 5 is made a Central bore passing through the length of the electrode 5. The surface of the bore forms a closed channel 7 (or passage)having the inlet opening 8 at one end and an outlet 9 for arc working end 6.

The second counter-electrode 10 is made as part of the coated graphite reaction vessel (13) (see figure 1 and 2). Figure 1 shows only the managed portion 11 on the inner surface of the bottom wall 12 of the reactor 13. The entire reactor 13 is shown in figure 2, where it is possible to notice that the counter-electrode to form with it one whole. Arc part 11 of the second electrode 10 is located opposite the arc of the working end 6 of the first electrode 5.

The first and second electrodes 5 and 10 connected to the source 15 DC. The first electrode 5 is a cathode and the second anode electrode 10, although it is clear that the polarity can be reversed.

The first electrode 5 is made movable relative to the second electrode 10 and therefore may fall to establish contact between the arc working end 6 and the arc part 11 of the second electrode 10 to complete the electrical circuit. Effect of direct current from the source 15 is usually set to a value between 400 to 800 A. If the rise of the first electrode 5 can be formed plasma arc direct current arc between a working end 6 of the first electrode 5 and the arc part 11 of the second electrode 10.

Solid feed material, for example aluminum wire 20 can be fed to the inlet 8, skipped down in the channel 7 and out of the outlet opening 9 in the space between the arc working end 6 of the first electrode 5 and the arc part 11 of the second electrode 10. Inert plasma gas 25, such as argon and/or helium, may similarly be introduced through the inlet 8 into the channel 7 and out of the first ele is trade 5 through the outlet 9. Consequently, the aluminum wire 20 and a plasma gas 25 can enter the first electrode 5 through the inlet opening 8 and the exit electrode 5 through a common discharge outlet 9 on arc working end 6.

The wire 20 may be stored, as usual, on a spool or reel and fed through a multi-speed motor to the inlet 8. Plasma gas 25 can be stored as usual in the gas tank and use the valve to be entered adjustable manner to the inlet. Therefore, the wire feed speed and the plasma gas can be controlled.

In the work of the coated graphite container 10 is heated to a temperature of at least about 2,000°With (preferably approximately 2200-2300° (C) using a plasma arc. After that enter the inert plasma gas 25 through the channel 7 in the first electrode 5 and include a power 15 power.

The reactor typically operates at a pressure in excess of atmospheric pressure is 750 mm of water.

After preheating the reactor aluminum wire 20 serves to the inlet 8 of the channel 7 in the first electrode 5 with a speed of typically 2 kg/hour. Inert plasma gas is also injected through the channel 7, at speeds from 2.4 to 6 Nm3/hour, preferably 3 Nm3/hour.

Electrical characteristics DC are over the and 800 a and from 30 to 40 In the length of the plasma arc column from 60 to 70 mm

Thus, the aluminum wire 20 is evaporated in a hot plasma gas (step a in figure 2). The wire 20 and the plasma gas 25 is continuously fed into the channel 7 of the first electrode 5 as the evaporation of the wire 20 in the plasma arc. Over time, achieved steady state. It is clear that the feed speed of the wire 20 and/or gas 25 can be adjusted in the process.

Evaporated aluminum and hot plasma gas out of the reaction vessel under the action of the gas fed through the channel 7 in the first electrode 5. Evaporated aluminum is then rapidly cooled in the cooling zone 30 with a flow of inert cooling gas, such as argon or helium, for condensation of submicron aluminum powder (stage 2). The flow rate of the cooling gas is from 60 to 120 Nm3per hour, and the particle diameter aluminum powder is ≤200 mm (preferably ≤100 mm). After rapid cooling the inert gas, the temperature of the gas and powder typically ranges from 300 to 350°C.

If desired, you can then implement phase passivation zone 35 passivation zone 30 cooling (stage 2). This can be achieved in different ways. Can be recycled cooling gas in a water-cooled chamber conditioning, and then back into the device together with oxygen in an amount up to 5% vol. to contact then Scam. Oxygen is usually introduced at a rate of about 1 Nm3/hour. Alternatively, you can use a separate source pestiviruses gas. Temperature during passivation is usually from 100 to 200°C.

After step passivation powder material and the gas flow passing into the zone 40 of the collection containing the filter cloth (not shown) to separate the powder from the gas (see step D in figure 2). Filter fabric preferably is grounded on the frame, to prevent the formation of electrostatic charge. The gas can be recycled.

After that, the powder can be collected with filter cloth, preferably in the area with controlled atmosphere.

The obtained powder product is then preferably sealed in an inert gas in the container under pressure above atmospheric.

If desired, you can use one or more additional electrodes, provided with a channel for simultaneous filing of various metals in a single reactor capacity, to obtain, for example, powder alloys, submicron and nanometer mixtures, oxides, and nitrides. You can use a common counter-electrode or, alternatively, a separate protivoelektrodom, each of which is located opposite electrode with a channel in it. You can use public or private sources : the I, although it is preferable to have a separate power supply, as it allows you to use different evaporation rates for different metals.

Example

This example relates to the production of nanometric aluminum powder with the help of technology atmospheric plasma DC, which is a clean, controlled and directed heat source. Such aluminum powders can be used in sintering metallurgy and catalysis in the chemical industry. Powders can be used for the manufacture of structural elements, magnetic films, chemical coatings, additives to oils, additives to rocket fuel, and in explosives.

This process uses the mechanism of condensation of the gas phase. The process provides high yields (kg/hour) in the technological conditions of the mixed inert gas, followed by a controlled passivation material with pneumatic transport and dispersion at a pressure above atmospheric. The material was obtained, cooled, Passepartout (i.e. oxidize the surface under low temperature conditions), harvested and Packed in strict control and high degree of automation.

The source wire (precursor)used in this process is a wrought alloy with m is rtirovki A, ASTM=ER1100, DIN=S-A1 9915. This wire has a nominal composition of 99.5 wt.% A1, the main impurities are Si and Fe with a maximum content of 0.25 and 0.40 wt.%, respectively.

The content of aluminium and aluminium oxide cannot be determined directly, therefore performed quantitative elemental analysis of the main component powder. In the calculations it was assumed that all the oxygen is bound in the aluminum oxide with a stoichiometry of Al2About3. To determine the oxygen content was used pre-calibrated oxygen analyzer and nitrogen Leco TC436. For carbon analysis were used pre-calibrated analyzer Leco carbon and sulfur CS344. For analysis of powder at high levels of contamination were applied x-ray fluorescence analysis method energy dispersion (RFID). For the quantitative analysis of solutions to the high levels of contamination identified HAD used atomic emission spectrometer ARL 3410 with inductively coupled plasma (AESOP).

Analysis AESOP showed significant levels of calcium, although the detected levels of other contaminants such as, Fe, Na, Zn and Ga, were very low. Therefore, the quantitative analysis was focused on, and Sa. The Al content can be defined as a majority of the powder remaining after subtraction of aluminum oxide, calcium and carbon. The carbon content of b is lo made for elementary because of the insoluble residue, remaining in the container during analysis AESOP. The results of the analysis are presented in table 1.

Table 1
The results of combined analysis of material
Identification sampleWith wt.%Sa wt.%About* wt.%Al2O3Calculated. wt.%Al Calculated. wt.%
6AL2,480,1714,9
6AL2,410,1715,4
6AL16,3
Average2,440,1715/53364,4
*Oxygen were added specifically in the low-temperature oxidation conditions.

Samples of aluminum powder were studied under the scanning electron microscope brand Leica Cambridge S360. E-microsemi were prepared to show the size and shape of the particles. Quantitative x-ray analysis based on the method of energy variance was performed to determine e the elements of, present in the sample using x-ray analysis system, complementary to SAM.

Secondary electron analysis was used to obtain topographic texture images of the particles of the aluminum powder and the corresponding agglomerates. At low magnification (350 times) it was noticeable that powder agglomerated product. The size of the agglomerates ranged from less than 5 microns to more than 200 microns. At high magnification (20000 and 50000 times) it was possible to obtain images of individual particles. Their size (i.e. the largest) was approximately 100 nm ± 50 nm, however, the particles still looked like clusters. It was determined that the agglomerates consisted of these smaller particles. The particles had an irregular shape, a spherical or oval. It is assumed that this form of individual particles and the sintering process occurs, to minimize the excess free surface energy inherent in so finely divided material. Figure 3(a) and (b) shows two secondary electron mikronika.

Research under transmission electron microscope (TEM) showed that the particles have in common spherical morphology. Relevant work electron diffraction shows that the particles are predominantly single crystals.

Specific surface area (UE) was determined by absorption of nitrogen, use the method I continuous stream, described in BS 4359, part 1. Research the UE has shown that it is in the range from 25 to 30 m2g-1. Figure 4 shows the change in specific surface area depending on the particle size ideal for chemically pure spherical aluminum powder. Figure 4 shows that the average particle size of 90 nm corresponds to a specific surface area of 25 to 30 m2g-1. Thus, the TEM images demonstrate compliance analysis pack.

With decreasing particle size of the powder fraction of oxide in the powder will change adversely, i.e. will increase the proportion of oxide on the proportion of metal. This trend is graphically presented in figure 5, where the assumption of a uniform oxide layer thickness of 4.5 mm, This layer is a limited diffusion, adhering, coherentnoye uniform oxide film associated with aluminum material, formed as a result of exposure to oxygen-enriched atmosphere in the low-temperature mode.

The composition analysis showed that the oxide content of 33 wt.%, that implies a particle size of from 90 to 100 μm. This is also consistent with the analysis of UE and TEM images.

Thermal analysis was carried out using differential scanning calorimetry (DSC). The device was first tested on the calibration of temperature and energy use were believed what CSOs indium standard. The sample was heated to 750°With a speed of 10°min-1in the air flow at a speed of 5 ml min-1. Range of DSC showed an exothermic peak (release of energy) with the extrapolated initial temperature 538°C. the Intervals of the peak was 538-620°with maximum at 590°C. After the initial heating, the sample was cooled and again heated in the same conditions, and ectothermy was not observed. This shows a complete and irreversible chemical reactions, i.e. the oxidation of aluminum. This result is graphically shown in Fig.6 and 7.

X-ray photoelectron spectroscopy (RFS) is sensitive to the surface and usually analyzes 2-3 of the top layer material (i.e. 1 nm above). It gives information on the composition and chemical state. For example, the RFU can distinguish Al as bulk metal from Al that is associated with the oxide of Al2About3. Table 2 shows the species found in the analyzed spectrum.

Table 2
The distribution of components on the pikes
284,7ClsCarbon pollution OCD. environment
72,2Al2Metal
74,2Al2Al2O3
531,6 Al2O3
1071,5NalsNa2CO3
2061,3The parameter Na augerNa2CO3
289,4ClsNa2CO3

The analyzed spectrum presented on Fig and shows the presence of carbon (19 at.%), oxygen (50 at.%), aluminum (27 at.%), nitrogen (0.6 at.%), sodium (3.3 at.%) and calcium (0.7 at.%). These values were calculated using the published sensitivity coefficients (Briggs and Seah, 1990). Detailed spectra were taken from the main peak to obtain chemical information in the form of energy, this was not taken into account factors such as the morphology, topography and heterogeneity. The carbon peak was used for calibration of the spectrum, i.e. accidental contamination with carbon (from the environment), the binding energy 287,4 eV. Information on the composition relates to the two or three outer layers of material and, therefore, should not be interpreted as bulk chemical composition of the material.

Peak A12 showed two superimposed component due to metal and native oxide with the binding energies for 72.1 eV and 74,1 eV, respectively. The fact that it was possible to detect metallic aluminum, which is connected through the oxide with the interior of the particles, i.e. with metal bases, the witness is there about the presence of a thin layer less than 2-3 monolayer (crystallography: corundum has a rhombohedral crystal system, where a=b=C=12,98 angstroms). It was observed that the carbon peak consisted of two components, i.e. pollution of the environment and carbide. Carbon was not strongly associated with any of the detected metals. Sodium is probably present in the form of carbonate (Na2CO3).

The thickness of the monolayer can be estimated using equations De Beers-Lambert and relevant assumptions.

The equation of De Beers-Lambert, option 1

Iox=I0ox[1-exp(-d/λsinθ)]

(1) the Equation of De Beers-Lambert, option 2:

Ielement=I0element[exp(-d/λsinθ)]

(2)

where λ inelastic mean free path of electron,

λ=0,05(KE)0,5nm=0,5(1486,6-73)0,5=1,8799 nm (KE=kinetic energy of the emitted electron).

If the oxide is native to this element of metallic material, I0and λapproximately equal. Therefore, dividing equation 1 by equation 2, one can obtain the equation relating the relative intensity of the signal A1 with the thickness of the oxide layer:

Iox/I0element=exp(-d/λsinθ)-1

(3)

For this equation used the following assumptions:

(i) the surface is flat,

(ii) the oxide layer has rawname the reduction in thickness,

(iii) this layer is continuous and

(iv) planar surface.

The result of this calculation, it was determined that the oxide layer has a thickness of approximately 2-3 nm, which is consistent with the analysis of the composition, analysis of UE and images of SAM. Variability is related to the inaccuracy of the assumptions adopted in the calculations. These calculations are very inaccurate, but this method analyzes the sample to a maximum depth of the upper nanometer sample. This means that, as in the spectral region of observation of the detected signal of the base metal, the thickness of the oxide should be less than 5 nm, which is a particular conclusion associated with characterizing the nature of the radiation.

Powder material according to the present invention has the following characteristics:

1. The composition of the material is a mixture of aluminum metal and aluminum oxide, which is consistent with the addition of oxygen into the material during processing in conditions of low temperature oxidation, i.e. oxidized practically only the surface.

2. The images show that the formed material has a morphology of small spherical particles with an average diameter of from 70 to 130 nm (more preferably from 80 to 120 nm, and more preferably approximately 100 nm). This confirms the classification of the material as a nanomaterial.

3. H is Stacy agglomerated thus, that accumulation of particles associated weak forces, which can be overcome by appropriate means, for example, by destroying ultrasound.

4. Analysis of specific surface showed that the material has a specific surface area in the range from 15 to 40 m2g-1more preferably in the range from 25 to 30 m2g-1. This is consistent with a particle size of from 75 to 95 nm.

5. Thermal analysis showed that there is a complete and irreversible chemical reaction in air at 550-650°C. This corresponds to thermally caused by oxidation.

5. Specific surface analysis showed that the oxide component of the powder is associated with the surface and that this layer has a thickness of less than approximately 5 nm. Therefore, this material can be described as discrete dispersed.

The proposed apparatus and method provide a simplified technology of obtaining and collecting powders of submicron and nanometer dimensions. In a preferred embodiment, transferred plasma arc is formed between the arc working end of the elongated graphite electrode and counter-electrode made as part of the graphite reactor crucible.

The proposed device can be used without the use of any water-cooled elements inside the plasma reactor and allows you to replenish raw materials without stopping the eector.

The reactivity of submicron and nanometer metals, such as aluminum, is work the risk, if there is a possibility of contact with water reactive liquids or reactive gases such as air and oxygen. Described stage passivation powder makes the material more suitable for transportation.

1. Plasmino arc reactor to obtain a powder of hard material in the form of a wire containing a first electrode, (b) a second electrode made with the possibility of removal from the first electrode by a distance sufficient to generate a plasma arc between them, (c) means for entering plasmablade gas in the space between the first and second electrodes, (d) means for forming a plasma arc in the space between the first and second electrodes, the first electrode has a through channel, the outlet of which opens into the space between the first and second electrodes, and provided means for feeding solid material in the form of a wire through the channel to exit through the outlet into the space between the first and second electrodes.

2. Plasmino arc reactor according to claim 1, further containing a means for feeding solid material in the form of a wire to the first electrode.

3. Plasmino arc reactor according to claims 1 and 2, additionally soda is shaking the container or holder for solid material in the form of a wire.

4. Plasma-arc reactor according to claim 3, further containing a means for feeding wire from a container or holder of the first electrode.

5. Plasma-arc reactor according to any one of claims 1 to 4, in which the first electrode is configured to move relative to the second electrode from the first position, in which the arc portion in contact with the arc part of the second electrode in a second position, in which the mentioned arc parts separated from each other by a distance sufficient to generate a plasma arc between them.

6. Plasma-arc reactor according to any one of claims 1 to 5, in which the first electrode is made in the form of a hollow elongated element, the inner surface of which forms a closed channel, and an elongated element ends arc working end being opposite the second electrode, and the discharge outlet of the closed channel is located on the arc working end or next to it.

7. Plasma-arc reactor according to any one of claims 1 to 6, in which the arc of the first and/or second electrodes are made of graphite.

8. Plasma-arc reactor according to any one of claims 1 to 7, optionally containing a cooling means for cooling and condensation of solid material evaporated in the process in a plasma arc between the first and second electrodes.

9. Plasma-arc Rea the tor of claim 8, in which the cooling means includes a source of cooling gas.

10. Plasma-arc reactor according to claim 9, in which the second electrode contains graphite vessel having a surface made with the possibility of the direction of the evaporated solid material further into the cooling zone for cooling process cooling gas.

11. Plasma-arc reactor according to any one of claims 1 to 10, optionally containing a collection area which is used to collect the powder material.

12. Plasma-arc reactor according to any one of claims 1 to 11, in which the channel in the first electrode is additionally configured to input a plasma-forming gas into the space between the first and second electrodes.

13. Plasma-arc reactor according to any one of claims 1 to 12, in which the means for generating a plasma arc in the space between the first and second electrodes includes a source of direct or alternating current.

14. The method of obtaining powder of hard material in the form of wire, namely, that (i) take plasma-arc reactor according to any one of claims 1 to 13, (ii) introducing a plasma-forming gas into the space between the first and second electrodes, (iii) generate the plasma arc in the space between the first and second electrodes, (iv) serves solid material in the form of a wire through the channel to exit through its outlet in the plasma is strong arc in which the solid material is vaporized, (v) cool the evaporated material for condensation powder and (vi) collect the powder.

15. The method according to 14, in which the solid material contains or consists of a metal or alloy.

16. The method according to item 15, in which the solid material is aluminum or its alloy.

17. The method according to any of p-16, in which a plasma-forming gas contains or consists of an inert gas.

18. The method according to 17, in which a plasma-forming gas contains or consists of helium and/or argon.

19. The method according to any of PP-18, in which a plasma-forming gas is injected through the channel of the first electrode to exit into the space between the first and second electrodes.

20. The method according to claim 19, in which a plasma-forming gas and the solid material extend from the first electrode through a common outlet.

21. The method according to claim 19 or 20, in which a plasma-forming gas and the solid material is included in the channel in the first electrode through a common inlet.

22. The method according to any of PP-21, in which at least partial cooling of the evaporated material is carried out using a stream of inert gas.

23. The method according to any of PP-21, in which at least partial cooling of the evaporated material is carried out using a flow of reactive gas.

24. The method according to any of PP-23, in which the surface paraskakis using flow pestiviruses gas.

2 5. The method according to paragraph 24, in which the passivating gas is an oxygen-containing gas.

2 6. The method according A.25, in which oxygen-containing gas contains from 95 to 99% vol. inert gas and from 1 to 5 vol.% the oxygen.

27. The method according to p, in which oxygen-containing gas contains approximately 98% vol. inert gas and about 2 vol.% the oxygen.

28. The method according to any of PP-27, in which the powder contains particles, almost all which has a diameter less than 200 nm.

29. The method according to any of PP-28, in which the reactor is preheated to a temperature of from 2000 to 2500°C, preferably from 2200 to 2300°With, before evaporation of the solid material.

30. The method according to any of PP-29, in which the pressure in the reactor is maintained at above atmospheric.

31. The method according to any of PP-30, in which the powder contains particles having a core containing or consisting mainly of aluminum, and the surface layer containing or consisting mainly of aluminum oxide.

32. The method according to p, in which the surface layer of aluminum oxide has a thickness of <10 nm, preferably <5 nm, more preferably <3 nm.

33. The method according to p or 32, in which almost all the particles have a diameter of ≤200 nm.

34. The method according to any of PP-33, in which the average particle diameter is in the range from 50 to 150 nm, more PR is doctitle from 70 to 130 nm, and most preferably from 80 to 120 nm.

35. The method according to any of PP-34, in which the powder material has a specific surface area in the range from 15 to 40 m2g-1preferably, from 25 to 30 m2g-1.

36. The method according to any of PP-35, in which the particles are monocrystalline kernel.

37. The method of obtaining passivated aluminum powder of hard material in the form of aluminum wire, which consists in the fact that (a) take plasma arc reactor, (b) serves an inert gas into the reactor and generating a plasma of the inert gas in the reactor, (c) served aluminum wire in the plasma of inert gas, in which aluminum is evaporated, (d) cool the evaporated aluminum inert gas for condensation of the aluminum powder, and (e) oxidizing the surface of the aluminium powder pestiviruses gas.

38. The method according to clause 37, in which the reactor using the reactor according to any one of claims 1 to 13.

39. The method according to any of p-38, in which the reactor is preheated to a temperature of from 2000 to 2500°C, preferably from 2200 to 2300°With, before evaporation of the solid material.

40. The method according to any of p-39, in which the pressure in the reactor is maintained at above atmospheric.

41. The method according to any of PP-40, in which the powder contains particles having a core containing or consisting mainly of aluminum, and the surface layer containing or sostojashie is mainly aluminum oxide.

42. The method according to paragraph 41, in which the surface layer of aluminum oxide has a thickness of ≤10 nm, preferably ≤5 nm, more preferably ≤3 nm.

43. The method according to paragraph 41 or 42, in which almost all the particles have a diameter of ≤200 nm.

44. The method according to any of PP-43, in which the average particle diameter is in the range from 50 to 150 nm, more preferably from 70 to 130 nm, and most preferably from 80 to 120 nm.

45. The method according to any of PP-44, in which the powder material has a specific surface area in the range from 15 to 40 m2g-1preferably, from 25 to 30 m2g-1.

46. The method according to any of PP-45, in which the particles are monocrystalline kernel.



 

Same patents:

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The invention relates to powder metallurgy and can be used to obtain powders of metal oxides

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FIELD: production of powders by electric explosion of wire.

SUBSTANCE: installation includes reactor for electric explosion of wire with high-voltage and low-voltage electrodes that are connected to pulse current sources; mechanism for feeding wire to reactor; gas and powder circulation system; unit for separating gas and accumulating powder. According to invention gas and powder circulation system is in the form of tubular gas discharging pipes communicated by their one ends with reactor in front of inter-electrode gap and by their other ends - with unit for separating gas and accumulating powder. Said unit is in the form of successively connected through branch pipes expanders. Each expander is provided with powder accumulator at providing relation Si/Si+1 ≥ 1.43 where i = 1, 2…, Si - total surface area of effective cross section of tubular gas discharging pipes; S2, S3 - surface area of connection branch pipes.

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2 dwg, 2 tbl

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3 dwg, 1 tbl, 1 ex

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46 cl, 8 dwg, 2 tbl, 1 ex

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4 cl, 1 dwg, 1 tbl

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FIELD: inorganic protective coatings.

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7 cl, 5 dwg, 1 tbl

FIELD: metallurgy.

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EFFECT: increase in thermal stability of aluminum powder to 580 °C.

2 tbl, 1 ex

FIELD: technological processes.

SUBSTANCE: invention pertains to plasma technology, and specifically to methods of obtaining metal powder. The method involves igniting a discharge between two electrodes, one of which is an anode, made from the spray material, with diameter of 10-40 mm. The cathode is in form of an electrolyte. The process is carried out under the following parameters: voltage between electrodes - 800 - 1600 V, discharge current - 750-1500 mA, distance between the anode and the electrolyte - 2-10 mm. According to the alternative method, the spray material is the anode, and the cathode is the electrolyte. The process takes place under the following parameters: voltage between electrodes - 500-650 V, discharge current - 1.5-3 A, distance between the cathode and electrolyte - 2-10 mm. The technical outcome is the increased efficiency of obtaining metal powder.

EFFECT: increased efficiency of obtaining metal powder.

2 cl, 8 dwg

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