DE102021134542A1 - Alumina particles, method for producing high-purity aluminum or alumina particles, and use of a foil as a raw material - Google Patents

Abstract

The application relates to a method for forming high-purity aluminum or aluminum oxide particles, micro- and nanoparticles formed by the method, a method for recovering an electrolyte, the use of nanoparticles and the use of an etched foil. In particular, a method for forming high purity aluminum and/or aluminum oxide particles from etched and/or anodized foils is provided.

Description

The application relates to a method for producing high-purity aluminum or aluminum oxide particles, micro- and nanoparticles produced by the method, a method for recovering an electrolyte, the use of nanoparticles and the use of an etched foil.

Among the particulate materials, aluminum and alumina play an important role in various technical fields such as catalysis, ceramics, and some others.

In this context it is advantageous to have new access possibilities to aluminum or aluminum oxide materials.

This aim is at least partly achieved by a method according to claim 1. Additional effects are achieved by implementations addressed in further independent or dependent claims.

According to a first aspect, a method for forming high purity aluminum and/or aluminum oxide particles from etched and/or anodized foils is provided.

Etched and/or anodized foils, especially if they comprise aluminum or contain aluminum as a main component, can be etched and/or anodized in order to increase the surface area in an anodic reaction. Various types of surface enlargement can be achieved by electrochemical anodic etching of aluminum. In particular, tubular structures can be formed. The tubular structures can have sizes in the micrometer or nanometer range. In this case, micrometer- or nanometer-sized structures, which can be referred to as micro- or nanostructures, can be electrochemically formed on the surface.

According to the present invention, it is possible to use the etched and/or anodized foil as a raw material for the production of high-purity aluminum and/or aluminum oxide particles.

The method according to the invention thus enables new access to aluminum and/or aluminum oxide particles, in particular to nanoparticles or microparticles which contain aluminum or aluminum oxide.

The method according to the invention can also be used as a means for recycling. In particular, if an aluminum foil with an increased surface area was formed in a previous process, but for some reason is defective and thus not fully suitable for the originally intended purpose, the defective foil can still serve as raw material to produce nano- or microparticles from it.

The aluminum or aluminum oxide particles formed by the process can either be a product themselves for various applications or serve as a precursor material that is used as a raw material for another process or sub-process.

According to one aspect, the etched and/or anodized foil has been micro- and/or nanostructured by an etching or anodizing process.

Etching and/or anodizing are highly efficient processes for micro or nano structuring of an aluminum foil.

In other words: a method is proposed in which an aluminum-containing foil is first electrochemically etched and/or anodized and then used to produce aluminum and/or aluminum oxide particles from it.

With this method it is possible to form structures on the surface of the film and then to form particles from the film which retain or can retain structural motifs of the film. In other words, the surface of the foil can be structured in two or three dimensions by easily controllable electrochemical processes, and then micro- or nanoparticles are formed from the foil, which retain certain features of the structure of the foil. That is, the method makes it possible to define part of the particle structure in a two- or three-dimensional surface process before the particles are shaped.

The etching and/or anodizing process can be performed either in a static process or in a roll-to-roll process.

A static process can be any process in which the foil is completely immersed in an electrolyte during etching. During etching, the foil remains in the electrolyte and is not moved out of the electrolyte. After etching, the entire foil can be taken out of the electrolyte.

In a roll-to-roll process, the film is wound onto a first roll. In the roll-to-roll process, the first roll is unwound and the film is wound onto a second roll. A part (fraction) of the unwound film is located between the two rolls. A part (fraction) of this developed part is passed through an electrolytic bath while a voltage or current is applied, so that the foil can be continuously etched while passing through the electrolytic bath.

The roll-to-roll process is a highly efficient method of etching aluminum foil to produce large quantities of etched or micro- or nano-structured aluminum foil.

According to a further aspect, the etched and/or anodized foil is either suitable for use as an electrode foil in an electrolytic capacitor or is a foil which can only be used as an electrode in a capacitor to a limited extent. The capacitor can be a wound capacitor, for example.

According to this aspect, the foil used in the method may be a foil that has been used, can be used, or was intended to be used in an electrolytic capacitor. In this case, the method according to the invention enables an alternative use of the foil as a raw material for the formation of aluminum and/or aluminum oxide particles from the foil.

This approach can be particularly beneficial when the foil has reduced utility in an electrolytic capacitor for some reason. In this case it may be more useful to use the foil for the method according to the invention than to use it in a capacitor. If a foil of reduced utility were to be used in a capacitor, a capacitor of reduced performance, such as e.g. B. reduced capacity or reduced stability, which leads to a reduced service life. Therefore, prior to the present invention, such film was often discarded. However, the inventors have recognized such foils as a valuable raw material. The method according to the invention enables the formation of valuable, high-purity aluminum and/or aluminum oxide particles, as a result of which the value of the high-purity aluminum foil can be maintained or even partially increased. This means that foils which do not meet high technical requirements can also be used advantageously in the process according to the invention.

In an alternative scenario, the foil can be a used foil. The foil may be one that has already been used or employed in an electrolytic capacitor. If, for example, the capacitor has been damaged or its performance has deteriorated, the foil can still be used as raw material for the method according to the invention.

In this context, the method according to the invention allows material to be reused or recycled, thus avoiding waste, as shown by the above scenarios.

In another aspect, the foil may have macroscopic defects that reduce its utility as a capacitor foil.

Macroscopic defects can occur, for example, when winding in a roll-to-roll process. Macroscopic defects can e.g. B. folds or tearing of the film. Aluminum foils can be wound in high-speed machines and are exposed to mechanical stress. Because the foil can be quite thin, it can easily tear or further disintegrate, which can be viewed as the formation of macroscopic defects.

Macroscopic defects can reduce the usefulness of a foil in a capacitor compared to a foil that does not have such defects. The inventors of the present invention have found that macroscopic defects hardly affect the microscopic or nanoscopic structure of the foils, so that foils with macroscopic defects can also serve as a suitable raw material for the formation of aluminum and/or aluminum oxide particles.

Accordingly, the general method of the present invention can be advantageously applied to macroscopically defective foils. This allows the economic value of the material to be maintained and waste to be avoided.

In another aspect, the formation of high purity aluminum and/or aluminum oxide particles includes grinding the foil.

In other words, the means of forming the high purity aluminum and/or alumina particles from the etched and/or anodized foils may include grinding.

The inventors of the present invention have found that grinding is an efficient method to form particles from the etched and/or anodized foil.

Alternatively, chemical means can also be used to form particles from the film.

Both chemical means and grinding can be used to form the particles.

In another aspect, the grinding involves applying shear forces or impact forces.

The inventors have found that it is possible to form particles from the film by shearing or impact forces, preferably having a size in the micrometer or nanometer range. The grinding with shearing or impact forces can also make it possible to at least partially preserve the structures formed by etching and/or anodizing the foil. Correspondingly, these structures can be transferred from the film to the aluminum and/or aluminum oxide particles.

According to another aspect, the grinding is a milling process. It has been shown that grinding processes can be carried out in a technically simple manner and enable the preservation of structural motifs of the two- or three-dimensional nanostructures in the nanoparticles or microparticles.

Furthermore, for certain applications of the particles, it can be preferred if structural motifs of the structures on the film are retained in the particles during the formation of the particles. This is particularly preferred in grinding as a means of particle formation.

The preservation of structural motifs makes it possible to determine a structure on the film surface in two or three dimensions by etching and/or anodizing, from which at least part of the structural motif can be transferred to the aluminum and/or aluminum oxide particles.

According to a further aspect, the high purity aluminum and/or aluminum oxide particles formed by the above method are subjected to a thermal plasma process to form spherical aluminum or aluminum oxide nanoparticles. In other words, after the formation of the high-purity aluminum and/or aluminum oxide particles from the foil, they can be used as a raw material for a thermal plasma process that forms spherical aluminum or aluminum oxide particles.

Since the foils used for the etching process have a high degree of purity, the particles formed from them also have a high degree of purity. Since thermal plasma processes place high purity requirements on the raw material introduced into the process, the inventors found that the particles formed by the above processes can be advantageously used as raw material for the thermal plasma process, thereby forming spherical aluminum or aluminum oxide particles.

A plasma torch can be used for the thermal plasma process, in which gas is ionized between an electrode and a nozzle between which a voltage is applied. Alternatively, inductively coupled plasma technology can also be used, in which a high-frequency alternating current is applied to a spiral coil, which generates heat that leads to plasma formation.

According to a further aspect, the microparticles and/or nanoparticles that can be formed by one of the methods are described.

Microparticles can be understood as meaning particles which have a size in the micrometer range. Analogously, nanoparticles can be understood to mean particles that have a size in the nanometer range.

Particle sizes obtained directly from the etched and/or anodized foil, e.g. B. by grinding, preferably have an average size in the micrometer range. The particle sizes can be between 3 µm and 300 µm, for example. An average particle diameter can be 100 μm, for example.

The particles formed directly from the etched and/or anodized foil can be a mixture of micro and nanoparticles.

The particles generated by the thermal plasma process are mostly spherical nanoparticles. Accordingly, the size range can be below 1 µm. However, it is possible that at least part of the particles are also larger, e.g. B. particles with sizes below 10 microns.

Particle sizes between 0.1 and 1 μm are particularly preferably achieved with the thermal plasma process. The average particle diameter of the thermal plasma process can be 200 nm.

It is pointed out that the particles formed directly from the foil can serve as raw material for the formation of the nanoparticles of the thermal plasma process.

The thermal plasma process also allows access to much smaller particles. For example, particle sizes below 50 nm can be achieved, for example in the range between 20 and 30 nm.

According to a further aspect, the micro- and/or nanoparticles can have a rod-shaped, tubular or spherical shape.

Particularly in the case of particles which are formed from the foil by grinding, a rod-shaped or tubular shape can be achieved in that tubular or rod-shaped structures were present on the foil before grinding. These structural features are retained in the particles. A spherical shape can be achieved by grinding or particularly preferably by the thermal plasma process.

According to one aspect, the microparticles and/or nanoparticles can have pores. These can originate from structures obtained from the etched and/or anodized foil. The pores can be an order of magnitude smaller than the average size of the particle. The smaller pores in the larger particles form a hierarchical structure. In this case, the particle size can be B. be on average 200 microns. The pores can be of the same size as the pores created by anodization and/or etching. The size of the pores can be below 10 µm here. Preferably the sizes are less than 2 µm. Sizes can range from 0.5 to 0.7 µm.

The hierarchical structure allows a high surface area material to be formed, which is useful for various applications where high surface area materials are required, such as: B. support material in catalysis or catalyst material, can be used in many ways.

According to a further aspect, the microparticles and/or nanoparticles contain aluminum oxide, ie alumina, or metallic aluminum or mixtures of these substances.

Aluminum or aluminum oxide particles are very versatile materials with great technical importance in various fields such as ceramics or catalysis.

According to a further aspect, a method is provided in which an aluminum-containing electrolytic solution that has been produced by the etching and/or anodizing process is recovered. This principle can be extended for any etching of aluminum foils independent of the particle formation process described above. However, it can be advantageously applied to the process.

As already mentioned, the etched aluminum foils are of high purity and therefore generally a valuable resource. During etching, up to 30% by weight of the etched foil is dissolved in the electrolyte. The inventors have found that highly pure compounds containing aluminum ions are formed in the electrolyte by the etching and/or anodizing process. Accordingly, the inventors of the present invention have identified the electrolyte containing these compounds as a very valuable resource of high-purity aluminum. According to this aspect, the electrolyte from the etching or anodizing process is used as a resource or raw material for further processing.

In the prior art, solution recovery was not performed or only very impure materials were recovered, i.e. the high purity of the aluminum compounds in the electrolyte was not maintained.

According to one aspect of this method, the method includes forming high purity alumina particles from the recovered solution. In particular, the particles formed can have the form of nanoparticles.

The inventors have identified the electrolyte solution as a very valuable source for the precipitation, separation or other formation of particles. In one aspect, the recovery of the aluminum-containing electrolyte can be performed such that alumina particles are formed from the recovered solution by precipitation, hydrothermal synthesis, flame spray pyrolysis, or thermal plasma synthesis. The inventors have found that highly pure particles can be formed with high efficiency by these methods.

In addition, the electrolyte solution can contain aluminum chlorohydrate as an aluminum compound. The aluminum chlorohydrates can be represented by the formula ((Al _n (OH) _m Cl) _3n-m ) _x where n, m and x are natural numbers.

Corresponding aluminum chlorohydrate complexes are formed in the electrochemical etching reaction, and the inventors have found that these can be used as a precursor for particle formation. For example, they can be incorporated into the particle formation techniques mentioned above.

Compared to other precursor salts, such as aluminum chlorides or aluminum nitrides, the typically used in the formation of aluminum nanoparticles from solution, the aluminum chlorohydrates formed or used in an etching and/or anodizing process contain, on average, higher amounts of aluminum with a high ratio of aluminum ions to anions. The amount of aluminum can be more than twice as high as in the conventionally used precursor molecules. Accordingly, such solutions were identified by the inventors as an ideal precursor for the production of alumina particles or alumina nanoparticles from solution. An example of the aluminum chlorohydrates is Al ₂ (OH) ₅ Cl.

According to a further aspect, the use of the above particles includes use as pigments, explosives or precursors for surface treatments or use as a substrate in catalyst applications.

• 1 zeigt einen Ausschnitt aus einem Querschnitt eines Elektrolytkondensators.
• 2 zeigt eine schematische Darstellung eines elektrochemischen Aufbaus.
• 3 zeigt eine elektronenmikroskopische Querschnittsaufnahme einer Hochspannungskondensatorfolie nach dem ersten Ätzen.
• 4 zeigt eine elektronenmikroskopische Querschnittsaufnahme einer Hochspannungskondensatorfolie nach einem Aufweitungsprozess.
• 5 zeigt das Stromwellenprofil eines Stromwellenpuls-Ätzprozesses.
• 6 zeigt eine elektronenmikroskopische Aufnahme einer pulsgeätzten Tunnelstruktur.
• 7 zeigt eine elektronenmikroskopische Aufnahme einer pulsgeätzten Blumenkohlstruktur.
• 8 zeigt eine elektronenmikroskopische Aufnahme der resultierenden geätzten Struktur einer mit sinusförmigem Wechselstrom geätzten Aluminiumfolie.
• 9 zeigt eine transmissionselektronenmikroskopische Aufnahme eines Querschnitts eines einzelnen Tunnels einer Hochspannungsfolie während des Bildungsprozesses und nach der Einwirkung von Wasser.
• 10 zeigt eine transmissionselektronenmikroskopische Aufnahme eines Querschnitts eines einzelnen Tunnels einer Hochspannungskondensatorfolie nach vollständiger Umwandlung bei Hochspannung.
• 11 zeigt eine elektronenmikroskopische Aufnahme von hochreinen Gamma-Aluminiumoxid-Partikeln, die aus bei Hochspannung geformten Folien gewonnen wurden.
• 12 zeigt ein elektronenmikroskopisches Bild einer Röhre der in 11 gezeigten Gamma-Aluminiumoxid-Strukturen.
• 13 zeigt die Partikelgrößenverteilung von Partikeln aus geätzten Folien.
• 14 zeigt das Röntgenbeugungsmuster der aus geätzten Folien gebildeten Partikel.
• 15 zeigt eine rasterelektronenmikroskopische Aufnahme eines Aluminiumpulvers, das aus einer geätzten Folie gebildet wurde.
• 16 zeigt eine vergrößerte rasterelektronenmikroskopische Aufnahme eines Aluminiumpartikels.
• 17 zeigt ebenfalls eine rasterelektronenmikroskopische Aufnahme eines Oberflächendetails eines anderen Aluminiumpartikels.
• 18 zeigt eine elektronenmikroskopische Aufnahme einer Aluminiumoxid-Verbundbeschichtung, die durch ein Hochgeschwindigkeitssauerstoff-Brennverfahren hergestellt wurde.
• 19 zeigt eine elektronenmikroskopische Aufnahme einer Aluminiumoxid-Kompositbeschichtung, die durch Plasmasprühen in kontrollierter Atmosphäre hergestellt wurde.
• 20 zeigt eine schematische Querschnittsdarstellung eines Plasmabrenners, der für die Beschichtung eines Substrats eingerichtet ist.
• 21 zeigt eine schematische Darstellung der Bildung von Nanopartikeln durch induktiv gekoppelte Plasmatechnologie mit beigeordneter Temperaturkurve.
• 22 zeigt eine rasterelektronenmikroskopische Aufnahme von durch induktiv gekoppelte Plasmatechnologie gebildeten Nano-Aluminiumoxidpartikeln.
• 23 zeigt ein Diagramm der Größenverteilung der durch induktiv gekoppelte Plasmatechnologie gebildeten Nanopartikel.

The invention is described in more detail below using exemplary embodiments and with reference to the figures. The figures contain both exemplary embodiments and process-related information. It is noted that components in the schematic drawings are not drawn to scale. In these, the components can be distorted in terms of their sizes, lengths or aspect ratios. Accordingly, the sizes or ratios should not be taken from the schematic drawings.

• 1 shows a section of a cross section of an electrolytic capacitor.
• 2 shows a schematic representation of an electrochemical structure.
• 3 Figure 12 shows a cross-sectional electron micrograph of a high voltage capacitor foil after the first etch.
• 4 shows an electron microscopic cross-sectional image of a high-voltage capacitor foil after a widening process.
• 5 shows the current wave profile of a current wave pulse etch process.
• 6 shows an electron micrograph of a pulse-etched tunnel structure.
• 7 shows an electron micrograph of a pulse-etched cauliflower structure.
• 8th Figure 12 shows an electron micrograph of the resulting etched structure of an aluminum foil etched with sinusoidal alternating current.
• 9 Figure 12 shows a transmission electron micrograph of a cross section of a single tunnel of high voltage foil during the formation process and after exposure to water.
• 10 Figure 12 shows a transmission electron micrograph of a cross section of a single tunnel of a high voltage capacitor foil after full conversion at high voltage.
• 11 Figure 12 shows an electron micrograph of high purity gamma alumina particles recovered from high voltage formed foils.
• 12 shows an electron micrograph of a tube in 11 gamma alumina structures shown.
• 13 shows the particle size distribution of particles from etched foils.
• 14 shows the X-ray diffraction pattern of the particles formed from etched foils.
• 15 Figure 12 shows a scanning electron micrograph of an aluminum powder formed from an etched foil.
• 16 shows an enlarged scanning electron micrograph of an aluminum particle.
• 17 also shows a scanning electron micrograph of a surface detail of another aluminum particle.
• 18 Figure 12 shows an electron micrograph of an alumina composite coating prepared by a high velocity oxygen firing process.
• 19 Figure 12 shows an electron micrograph of an alumina composite coating produced by controlled atmosphere plasma spraying.
• 20 shows a schematic cross-sectional view of a plasma torch that is set up for coating a substrate.
• 21 shows a schematic representation of the formation of nanoparticles by inductively coupled plasma technology with associated temperature curve.
• 22 Figure 12 shows a scanning electron micrograph of nano-alumina particles formed by inductively coupled plasma technology.
• 23 shows a diagram of the size distribution of the nanoparticles formed by inductively coupled plasma technology.

1 shows a cross section through an electrolytic capacitor 7 with an anode 9, a cathode 8 and a dielectric material with an electrolyte 10 separating the anode 9 and the cathode 8.

Electrolytic capacitors are passive components that z. B. be used in electrical circuits for charge storage. the inside 1 The basic structure shown consists of two conductive electrodes, the anode 9 and the cathode 8, and a dielectric material with electrolyte 10 in between. In the present example, the electrodes have aluminum as the main component. Accordingly, the present capacitor 7 is an aluminum capacitor. One of the electrodes, in this case the anode 9, is coated with aluminum oxide, which has a dielectric function. Both electrodes have a high specific surface area in order to store as much charge as possible, according to the capacitor equation: C = E × A/D. where C is the capacitance; E is the electrical constant; A is the surface area of the capacitor; D is the thickness of the dielectric material.

The formation of high surface area films is addressed below.

2 1 shows a schematic representation of an electrochemical structure 1. In the electrochemical structure 1, an anode 2 and a cathode 3 are connected to a voltage supply 6. FIG.

It should be noted that the anode 2 and the cathode of the electrochemical assembly are not necessarily the same as the anode and the cathode of the capacitor and must not be mixed.

In addition, the anode 2 and the cathode 3 are immersed in an electrolyte 4 . The anode 2 includes or consists of an aluminum material. The anode 2 is preferably made of pure aluminum with certain additives and a few impurities. For example, additives can be present in an amount of 100 to 150 mg of heteroatoms per kg of aluminum material. The purity of the aluminum used for the foil can range from 99.99% or more. Depending on the etching process used, the aluminum foil is preferably highly crystalline and a high cubic texture orientation may be desirable. For example, a foil with high cubic texture orientation may have an alignment of the (100) planes of the aluminum crystal unit cells with the surface of the foil of 98% or more, i. H. the [100] direction of all unit cells has an average alignment of 98% or more with the surface normal of the film.

A voltage and a current are applied between the anode 2 and the cathode 3 in the electrochemical structure 1 via a voltage and current source 6 . Optionally, another electrode, which in the example of 2 not shown, can be used in an electrochemical setup, resulting in a typical three-electrode electrochemical setup, in which the voltage of the anode 2 is defined against a reference electrode and the cathode 3 has the role of a counter-electrode supplying the current.

When a positive voltage is applied to the anode 2, the foil can be partially dissolved and etched and/or anodized, as a result of which an increase in surface area can be achieved. Aluminum ions are introduced into the electrolyte 4 in the process. The aluminum ions are represented here by Al ³⁺ . However, it should be noted that complex ions can also form, for example involving ligands originating from the electrolyte 4 .

The following simplified reactions can take place at the anode 2 or at the cathode 3: Anodic reaction: 2A1 → 2A1 ³⁺ + 6e ^- Cathodic reaction: 6H ⁺ + 6e ^- → 3H ₂

The electrolyte 4 can be any suitable electrolyte, preferably an aqueous electrolyte. Aluminum chlorohydrates are formed in the aqueous electrolyte by etching and/or anodizing. The aluminum chlorohydrates can have the formula ((Al _n (OH) _m Cl) _3n-m ) _x . In particular, one of the aluminum chlorohydrates formed can be Al ₂ (OH) ₅ Cl. These substances can serve as raw material for particle production.

At the in 2 The method shown is a static method in which the electrodes (anode 2 and cathode 3) are fully immersed in the electrolyte 4 during etching. After the etching process is completed, the electrodes are taken out of the electrolyte 4 .

As an alternative to a static method, a roll-to-roll method can also be used. In the roll-to-roll process, a ribbon-shaped foil is pulled through the electrolyte, with part of the foil always being in contact with the electrolyte and being etched as long as it is in contact with the electrolyte. The voltage is accordingly applied to the foil running through the electrolyte. In the roll-to-roll process, the film is preferably wound onto a first roll hangs, unwound from the first roll and rewound on a second roll. The unwound portion (fraction) between the rollers passes through the electrolyte, with part of the unwound portion (fraction) being in contact with the electrolyte as it passes through it.

An etched foil is formed on the anode side by the method described above. The foil formed can be referred to as etched and/or anodized foil. The etched and/or anodized foil is preferably surface-enhanced, i.e. it has a larger effective surface area than before etching. The surface can be micro- and/or nano-structured, for example. This means that the foil can have structures in the micrometer range or in the nanometer range or both. The structures can be tubes, for example.

Possible structures on aluminum foils are discussed in more detail below. The 3 and 4 show electron micrographs of foils after an intermediate step and a final step of an etching process.

The morphology created in aluminum foil is generally the result of several process parameters and foil properties. Depending on the process parameters, different etching structures can be created in the nanometer or micrometer range. The crystal structure of the aluminum foil, the composition of the etching solution or the voltage and current form of the anodic polarization can be of particular interest.

For use in a capacitor, as in 1 shown, it may be necessary to grow an oxide layer, for example. The oxide gives the layer a dielectric function. The voltage used to create the oxide increases with the thickness of the oxide. For example, a voltage increase of 1 V per nanometer of oxide growth can be observed. For the structure on the surface and the dimensions of the structure on the surface, it is also important to ensure that the surface structures are created in a size in which it is still possible to form a sufficiently thick oxide to ensure an adequate dielectric function, without the pores being blocked by the oxide.

3 shows an electron microscopic cross-sectional image of an anodic high-voltage foil after the production of the etched structure in a first etch. In the electron microscopic cross-sectional image in 4 shows the same film after an expansion step. In the first step, the etching step, tunnels are produced with a pore diameter of 0.5 to 0.7 μm with a tunnel density of around 20 million per cm ² and a stochastic tunnel distribution. In the widening stage, a tunnel diameter of around 1 to 2 µm is achieved.

It is desirable that a core of the foil in the middle of the foil remains unetched during all etching processes. For example, since etching is typically done on both sides, the depth of the tunnels formed is less than half the foil used. The foil thickness can be in the order of 10 to 150 μm. The thickness can be 120 µm, for example. The depth of the tunnels etched into the foil can be 30 to 40 µm with a foil thickness of more than 90 µm.

In addition, for the example 3 and 4 used a film with a high cubic texture orientation of 98%. Such a foil can be produced by certain solidification, rolling and annealing processes.

Etching is followed by surface cleaning, which removes the residues of the etching reagents and the electrolyte from the foil. The final etching step is a heat treatment that serves to dry and passivate the surface of the etched foil.

In 5 shows the current curve of a pulse etching process. The pulse etching process is suitable for generating a morphology in the nanometer range.

A pulsed current is used in the pulse etching process. The basic parameters that determine the result are the pulse frequency, the duty cycle and the anodic and cathodic current densities. By varying these and other parameters along with the morphology of the raw material, various structures such as micrometer-sized tunnel structures or cauliflower-like structures on the nanometer scale can be formed. 6 Figure 1 shows an electron micrograph of micron-sized tunnels formed by certain pulse etching processes. 7 12 shows an electron micrograph of a cauliflower structure with cauliflower structures in the nanometer range.

In this process in particular, the crystal morphology of the raw film can play an important role. The dimensions of the structures formed are influenced by two factors. On the one hand, this is the anodic pulse length and, on the other hand, the crystallites of the foil. For example, if cold-formed foils are used for etching, three-dimensional networks of small etching units can be created develop. If such a foil is instead moderately annealed and etched with a sinusoidal alternating current, structures are obtained which have exactly the geometry of the cubic crystallized units. Accordingly, cube-like nanostructures can be formed, as shown in the electron micrograph of 8th you can see.

In addition, the surfaces of the surface-enlarged, i.e. etched and/or anodized foils can be chemically functionalized. Possible functionalizations are phosphate or silicate functionalizations. These layers can be formed by immersion in a solution containing the appropriate chemicals or by high temperature reactions with water to create a boehmite-like coating.

In 9 Figure 1 shows a cross-sectional transmission electron micrograph of a single tunnel produced by high voltage foil etching as an intermediate step in an electrode foil anodizing process. The etched foil was reacted with boiling water to form a boehmite layer 12 on the surface. The boehmite layer 12 forms a fibrous structure inside the tunnel. In the center of the tunnel 11 and the boehmite layer 12 is a hole 13. The boehmite layer 12 can be seen between the hole 13 and the tunnel wall 11 of alumina. The tube wall has a thickness of 0.9 µm.

In 10 is the same tube in a transmission electron micrograph after transformation of the boehmite 12 from 9 shown in gamma alumina. Thus the formed tube consists of a tube wall 11 with the gamma alumina and a hole 13 in the middle. The gamma aluminum oxide is formed at a formation voltage of about 560 V. In the present case, the aluminum oxide layer thickness achieved is 0.56 μm. This roughly corresponds to the sum of the previous tube wall 11 and the boehmite layer 12.

11 and 12 show electron micrographs of high purity gamma alumina particles obtained from high voltage formed foils, ie, etched and/or anodized foils. A tube 14 can be seen in particular.

Post-treatment of the etched and/or anodized foils after the etching process makes it possible to separate the metallic aluminum matrix from the structures formed. Post-treatment may include any process that allows surface structures of alumina to be separated from aluminum. Preferably, the alumina is completely separated from any residual aluminum. Post-treatment may involve chemical means or shearing or impact grinding, or a combination of both.

The in the 11 and 12 Nanoparticles shown contain or consist of high purity alumina of different crystallographic phases, ie gamma alumina, amorphous alumina or others.

The geometric shape of such structures can be varied by the etching process. With suitable post-treatment, the motifs of the tubular structures formed by etching and/or anodizing are preserved in the alumina nanostructures.

In the 13 until 17 examples and data are presented for particles formed by milling etched and/or anodized foils.

13 Figure 12 shows the particle size distribution of particles formed from etched and/or anodized foils by milling with shear and impact forces applied to the foil. In 13 two diagrams are shown. The distributional curve with a maximum above 100 µm is associated with the right axis "%channel". The other curve, with an integral-like shape, is mapped to the left axis %passing.

As can be seen from the curves, the average particle size is about 100 µm. The distribution shows a particle size distribution between 3 and 300 µm. The maximum of the particle size distribution is found at over 100 µm.

In 14 an X-ray diffraction pattern can be seen. It distinguishes between the peaks of the aluminum component (top spectrum) and the aluminum oxide component formed from the foil (bottom spectrum). As in 14 can be seen, sharp X-ray diffraction peaks can be observed, indicating high crystallinity of the materials.

It should be noted that the foil contains both aluminum oxide and aluminum. The aluminum oxide can be on the surface of the foil. The aluminum can be in the center of the foil. Accordingly, a mixed particulate material can be formed from the film. In further steps, this mixed material can be converted into pure aluminum oxide or, if necessary, into pure aluminum.

In the 15 , 16 and 17 shows electron micrographs of particles formed by milling using shear and impact forces. In the 15 Particles shown are consistent with the particles of the distribution 14 connected. The 16 and 17 show detailed images of individual particles from the distribution.

As in the 16 and 17 can be seen, the surfaces of the particles are porous. This porosity results from the porosity of the etched and then ground foil, as a result of which the surface structure motifs of the foil are at least partially preserved in the particles.

In 18 Figure 12 is a secondary electron micrograph of an aluminum-alumina surface coating using the aluminum-alumina powder of US Pat 15 until 17 to see. Here, the particle powder was applied to a surface using high velocity oxygen fuel processing (HVOF). This means that the ground material can serve as an ideal raw material for the production of surface coatings.

In 18 circular shapes can be seen. They indicate that the structures of the particles are preserved in the coating. In particular, the porous or tubular structures in the particles are at least partially retained in the coating. The circular shapes are derived from alumina tubing, thus indicating the presence of alumina material evident in the coating.

In 19 was an aluminum-alumina particle composite, which is similar or identical to the particles in the 15 until 17 was applied to a resin surface by controlled atmosphere plasma spray (CAPS). With this technique, a more homogeneous and finer mixing of aluminum and aluminum oxide from the particles is achieved, with no phases or structures clearly emerging in the electron image.

In addition, depending on the deposition technique, a pure aluminum oxide or a pure aluminum coating can be achieved. Various mixed coatings are also possible, as shown.

In summary, a wide range of aluminum and/or aluminum oxide surface coating materials can be produced from the powders obtained from etched and/or anodized foils.

In 20 A schematic representation of a plasma torch 15 for coating applications can be seen.

The plasma torch includes a nozzle 18 to which a gas for plasma formation is supplied via the plasma gas channel 16 . The gas flows past an electrode 17 . A voltage is applied between the nozzle 18 and the electrode 17 via a voltage supply 20 . As a result, the gas is ionized and forms a plasma.

The plasma torch 15 also includes a cooling water supply 21 to cool the system.

The plasma torch 15 includes an insulator 19 which insulates the electrode 17 from the nozzle 18 .

The shape of the nozzle 18 and the arrangement of the electrode 17 in relation to the nozzle together with the inlet pressure of the gas result in a plasma stream flowing out of the nozzle 18 . A powder is guided past the outlet opening of the nozzle 18 together with a carrier gas via a preliminary product feed 22 . The plasma entrains part of the powder and carrier gas and chemical reactions can take place therein. A spray jet 23 can be generated by these processes.

In one application, the spray jet 23 is directed onto a substrate 25 and produces a spray deposit 24 on the substrate 25.

The plasma sprayer can be operated in three modes. There is controlled atmosphere plasma spraying (CAPS), vacuum plasma spraying (VPS) and atmospheric plasma spraying (APS).

The following gases can be used both as a carrier gas and as a plasma gas: argon, hydrogen, nitrogen and helium. Mixtures of these gases can also be used.

As an alternative to the in 20 Inductively coupled plasma technology can also be used with the plasma torch shown. In this technology, a spiral coil 31 is impressed with a high frequency of alternating current. The conductor arranged in the center of the spiral coil 31 is heated by the alternating electromagnetic field. The advantage of this method is that these reactors can work without electrodes and can be fed with solid, liquid or gaseous precursors. The reactor design allows for the use of plasma generating gas, sheath gas and reactive gas together. The precursors are vaporized or evaporated by the high temperature generated in the reactor. They are transported to the quench zone at the bottom of the plasma reactor.

A description of this approach is given in 21 to see. The brightness represents the temperature, with lighter parts indicating hotter areas of the device or zones near the device. The temperature of the reactive mixture containing precursor 26 is shown on the axis in a temperature diagram.

Precursor 26 enters spiral coil 31 and is vaporized in precursor vaporization zone 27 . In a condensation zone 28, which is at some distance from the precursor evaporation zone 27, the previously evaporated precursor condenses into particles. The particles are formed in the quench zone 29 . Here, the nucleation and growth of the nanoparticles takes place. In particular, there is a radial deterrent 30. On the right side of 21 shows the on-axis temperature of the reactive mixture. It can be seen that an almost linear drop in temperature with a decrease of about 10 ⁵ K/s leads to the formation of the particles.

22 Figure 12 shows a secondary electron micrograph of nanoalumina (alumina nanoparticles) prepared using inductively coupled plasma technology fed with precursor particles from an etched and/or anodized aluminum foil.

In the 22 The aluminum oxide particles shown are spherical and have sizes in the nanometer range. In 23 shows the particle size distribution of the spherical nanoparticles formed by the inductively coupled plasma process. The distribution curve, which has a maximum at around 0.2 µm, is assigned to the right-hand axis labeled "%channel". The curve with integral form is assigned to the left axis "%passing".

Both diagrams together show that good particle size homogeneity is achieved with an average particle size in the range of 100 to 200 nm. A few particles ranging in size from 2 to 10 µm can be formed as minority species. In particular, it can be shown that the majority of around 95% of the particles have a size of less than 1 µm and are therefore in the nanometer range.

Alternatively, the method is also able to generate sizes in the range of 20 to 30 nm.

Reference List

1

electrochemical structure

2

anode

3

cathode

4

electrolyte

5

reaction vessel

6

power supply

7

electrolytic capacitor

8th

Electrolytic capacitor cathode

9

Electrolytic capacitor anode

10

separator and electrolyte

11

tube wall

12

boehmite layer

13

Hole

14

tube

15

plasma torch

16

plasma gas channel

17

electrode

18

jet

19

insulator

20

power supply

21

cooling water supply

22

pre-product feeding

23

spray jet

24

spray coating

25

substrate

26

preliminary product

27

evaporation zone

28

condensation zone

29

deterrent zone

30

radial deterrent

Claims (23)

Process for the production of high-purity aluminum and/or aluminum oxide particles from etched and/or anodized foils. procedure after claim 1 , wherein the etched and/or anodized film has been microstructured and/or nanostructured by an etching or anodizing process. procedure after claim 1 or 2 , wherein the film is structured by an electrochemical etching process. procedure after claim 3 , wherein the film is formed in a static process or a roll-to-roll process. Procedure according to one of Claims 1 until 4 , wherein the foil is a foil suitable for use as an electrode in an electrolytic capacitor or whose use as an electrode in a capacitor is restricted. procedure after claim 5 , where the foil may have macroscopic defects that reduce its utility as a capacitor foil. Procedure according to one of Claims 1 until 6 , wherein the formation of high purity aluminum or aluminum oxide particles involves grinding the foil. procedure after claim 7 , wherein the grinding is performed using shear forces or impact forces. procedure after claim 7 or 8th , where grinding is a milling process. Procedure according to one of Claims 1 until 9 , whereby the structural motifs of the structures on the film are retained during the grinding process. Procedure according to one of Claims 1 until 9 , wherein the high-purity aluminum or aluminum oxide particles are subjected to a thermal plasma process to form spherical aluminum or aluminum oxide nanoparticles. Micro- and / or nanoparticles by the method according to at least one of Claims 1 until 10 are formed. Micro- and / or nanoparticles after claim 12 , which comprise particles having a rod-like, tubular or spherical shape. Micro- and / or nanoparticles after claim 12 or 13 , Wherein the particles have pores as structures obtained in the micro- and/or nano-structured film. Micro- and / or nanoparticles after Claim 14 , where the pores are an order of magnitude smaller than the average size of the original particles. Micro- and / or nanoparticles according to one of Claims 12 until 15 that contain aluminum oxide or metallic aluminum or mixtures of the substances mentioned. Method for obtaining an aluminum-containing electrolytic solution, which is produced by the electrochemical etching method according to one of claims 2 or 3 is formed. procedure after Claim 17 , which involves the formation of high purity alumina particles from the recovered solution. procedure after Claim 18 , wherein the alumina particles are formed by precipitation, hydrothermal synthesis, flame spray pyrolysis or thermal plasma synthesis. procedure after Claim 18 or 19 , the solution containing an aluminum compound having the formula ((Al _n (OH) _m Cl) _3n-m ) _x . Use of the micro- and / or nanoparticles according to one of Claims 12 until 16 as pigments, explosives, precursors for surface treatments. Use of an etched and/or anodized foil as raw material for the production of micro- and/or nano-particles. Use of micro- and / or nanoparticles according to one of Claims 1 until 10 as a raw material for use in a thermal plasma process to produce spherical aluminum or aluminum oxide nanoparticles.

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