RU2664149C2 - Method for producing fine-grained corundum - Google Patents

Abstract

FIELD: manufacturing technology.SUBSTANCE: invention relates to the production of abrasive refractory materials, in particular to the production of a powder-alumina (corundum), and can be used in a metalworking, machine-building, chemical-metallurgical industry. Electrical aluminum wire waste containing not less than 99.5 % aluminum (GOST 14838-78), are subjected to electrospark dispersion in distilled water at a pulse repetition rate of 50 Hz, a voltage on the electrodes of 90  V, and a capacitance of 65 mcF.EFFECT: invention makes it possible to obtain fine-grained corundum from aluminum waste with low cost, low energy costs and environmental purity of the process.1 cl, 10 dwg, 3 ex

Description

The invention relates to the production of abrasive refractory materials, in particular to the production of powder - aluminum oxide (corundum), and can be used in the metalworking, engineering, chemical and metallurgical industries.

The most common method for producing powder α-Al ₂ O ₃ (corundum) is high-temperature (above 1200 ° C) firing in air of aluminum hydroxide (hydrargillite) or aluminum oxyhydroxide (boehmite) without / with the addition of crystals - seeds and / or alloying substances [ RU 2076083, 1997, C04B 35/10]. The α-Al ₂ O ₃ powder obtained by this method mainly contains irregularly shaped coarse-grained agglomerated particles. The α-Al ₂ O ₃ powder is ground and then sized according to the dry and / or wet method, often using special additives [US 5277702, 1994, C09C 1/68; US 5387268, 1995, C09C 1/68; US C1 51/309]. The method is time-consuming and energy-intensive, since it consists of several operations and includes high-temperature firing. In addition, the method does not allow the synthesis process to control the crystal size of the obtained corundum.

A known method of producing a powder of α-A1 ₂ O ₃ comprising the step of calcining aluminum hydroxide 500-1500 ° C in an atmosphere of hydrogen halide in the presence of seed crystals and / or form-regulating agent (Mg, Ca, Sr, Y, V, Mo, Cu, Zn, B, Lf, Nd, Ce) and their compounds. The method allows to obtain α-A1 ₂ O ₃ powder with a crystal size in the range of 0.8-20 μm of various habit. However, the method has disadvantages: high energy costs and the use of aggressive media in the synthesis process (HCl, Cl ₂ and MeCl), which makes the method environmentally unfavorable [RU 2118612, 1998, C01F 7/02].

The disadvantages of the known methods are high energy consumption, the crystal size of the obtained corundum cannot be regulated, as well as environmental problems

The invention is aimed at solving the problem of producing corundum from aluminum waste with low cost, low energy costs and environmental cleanliness of the process.

The problem is achieved by the method of producing corundum from aluminum waste, which differs from the prototype in that the waste electrical aluminum wire (GOST 14838-78) is subjected to electroerosive dispersion in distilled water at a pulse repetition rate of 50 Hz; the voltage at the electrodes is 90 V and the capacitance of the capacitors is 65 μF.

Figure 1 describes the steps for producing corundum; figure 2 is a diagram of the EED process, figure 3 is a photograph of the obtained alumina powder (corundum), figure 4 is the size distribution of microparticles of corundum powder, figure 5 is the shape parameters of the microparticle powder, figure 6 is a micrograph of corundum powder particles; figure 7 is the elemental composition of corundum powder, table 1 is the numerical values of the elemental composition of corundum powder, figure 8 is an x-ray of corundum powder, figure 9 is an x-ray of corundum powder, and figure 10 is an x-ray of corundum powder.

The EED process is the destruction of conductive material as a result of local exposure to short-term electrical discharges between the electrodes [Nemilov, E.F. Electroerosive processing of materials. L .: Engineering, Leningrad. Department, 1983. - 160 s]. Obtaining aluminum powder in an experimental setup for producing nanodispersed powders from conductive materials [RU Patent for the invention No. 2449859] was carried out according to the scheme shown in figure 1 in four stages:

- 1 stage - preparation for the process of electroerosive dispersion;

- 2 stage - the process of electroerosive dispersion;

- 3 stage - unloading of powder from the reactor.

- Stage 4 - drying and weighing of alumina powder.

The powder materials obtained in this way are generally spherical and elliptical in particle shape. Moreover, by changing the electrical parameters of the dispersion process (voltage at the electrodes, capacitance of the capacitors and pulse repetition rate), it is possible to control the width and offset of the particle size interval, as well as the performance of the process.

At the first stage, aluminum waste was sorted, washed, dried, degreased, and weighed. The reactor was filled with a working medium - distilled water, the waste was loaded into the reactor. Mounted electrodes. Mounted electrodes were connected to a generator. The necessary process parameters were set: pulse repetition rate, voltage at the electrodes, capacitor capacitance.

At the second stage - the stage of electroerosive dispersion included installation. The EED process is presented in figure 2. The pulse voltage of the generator 2 is applied to the electrodes 5 and then to the aluminum waste 8 (aluminum waste also serves as the electrodes). Aluminum waste is located in the reactor 3. When a voltage of a certain value is reached, an electrical breakdown of the working medium 10 occurs, located in the interelectrode space, with the formation of a discharge channel. Due to the high concentration of thermal energy, the material at the discharge point melts and evaporates, the working medium evaporates and surrounds the discharge channel with gaseous decomposition products (gas bubble 9). As a result of significant dynamic forces developing in the discharge channel and the gas bubble, droplets of molten material are ejected outside the discharge zone into the working medium surrounding the electrodes and freeze in it, forming droplet-like particles of aluminum powder 7. Voltage regulator 1 is designed to set the necessary voltage values, and the shaker 4 moves one electrode, which ensures the continuous flow of the EED process.

At the third stage, the working fluid with the powder is unloaded from the reactor.

At the fourth stage, the solution is evaporated, dried, weighed, packaged, packaged and then analyzed with powder.

This achieves the following technical result: the production of aluminum oxide (corundum) with particles of the correct spherical shape with low energy costs and environmental cleanliness of the process by electroerosive dispersion (EED).

The method allows to obtain corundum without the use of chemicals, which significantly affects the cost of the powder and avoids contamination of the working fluid and the environment with chemicals.

The average specific cost of electricity in the production of aluminum electroerosive powder is 2.1 kg / kW⋅h, which is lower than other methods for producing corundum. Electroerosive dispersion allows efficient disposal of aluminum waste with low energy costs and environmental frequency of the process and to obtain aluminum oxide.

Corundum obtained by electroerosive dispersion of aluminum waste can be used in the metalworking, engineering and chemical-metallurgical industries. Corundum is also used as a refractory material. Alumina-based ceramics have high hardness, fire resistance and antifriction properties, and is also a good insulator. It is used in gas-discharge lamp burners, integrated circuit substrates, in shut-off elements of ceramic pipeline valves, in dentures, etc.

Example 1

To obtain aluminum oxide (corundum) in an experimental setup by the method of electroerosive dispersion, we used waste products of GOST 14838-78 aluminum wire, pre-cut to 5 ... 7 cm. The wire was loaded into a reactor filled with a working fluid - distilled water. The following electrical parameters of the installation were used:

- pulse repetition rate of 50 Hz;

- voltage at the electrodes 90 V;

- capacitance of 65 microfarads.

The resulting alumina (corundum) (Figure 3) was investigated by various methods. The particle size distribution of alumina powder obtained by electroerosive dispersion in distilled water was studied on a Analysette 22 NanoTec laser particle size analyzer. (Figure 4). The Figure 5 presents the parameters of the shape of the microparticles of corundum powder, it was found that the elongation coefficient (elongation) of particles with a size of 25.489 microns is 1.245, which indicates the spherical shape of the particles of corundum powder. It was found that the average particle size is 28.5 μm, the arithmetic value is 28.503 μm, and the specific surface area is 16266.5 cm ² / cm ³ .

The study of the elemental composition of the powder samples was carried out on an electron-ion scanning (raster) microscope with field emission of electrons "QUANTA 600 FEG" (Figure 6) and energy-dispersive x-ray analyzer company "EDAX" (Figure 7).

A phase analysis of the obtained powder was carried out on a Rigaku Ultima IV X-ray diffractometer, the results of which are shown in Figure 8.

Example 2

To obtain aluminum oxide (corundum) in an experimental setup by the method of electroerosive dispersion, we used waste products of GOST 14838-78 aluminum wire, pre-cut to 5 ... 7 cm. The wire was loaded into a reactor filled with a working fluid - distilled water. The following electrical parameters of the installation were used:

- pulse repetition rate of 140 Hz;

- voltage at the electrodes 100 V;

- capacitance of 65 microfarads.

A phase analysis of the obtained powder was carried out on a Rigaku Ultima IV X-ray diffractometer, the results of which are shown in Figure 9.

The Figure 9 presents the x-ray diffraction pattern of aluminum powder obtained with the following electrical parameters: capacitance of discharge capacitors 65 μF, voltage 100 V, pulse frequency 140 Hz., By which it can be established that the main phases in the aluminum powder are Bayerite - Al (OH) ₃ and Gibbitsite - Al (OH) ₃ .

Example 3

To obtain aluminum nanodispersed powder in an experimental setup by the method of electroerosive dispersion, we used waste products of GOST 14838-78 aluminum wire, pre-cut to 5 ... 7 cm. The wire was loaded into a reactor filled with a working fluid - distilled water. The following electrical parameters of the installation were used:

- pulse repetition rate of 50 Hz;

- voltage at the electrodes 100 V;

- capacitance of 65 microfarads.

Phase analysis of the obtained powder was carried out on a Rigaku Ultima IV X-ray diffractometer, the results of which are shown in Figure 10. On the presented X-ray diffraction pattern of aluminum powder obtained with the following electrical parameters: capacitance of discharge capacitors 65 μF, voltage 50 V, pulse frequency 100 Hz. that the main phases in the aluminum powder are aluminum - Al and boehmite - AlO (OH).

Claims (1)

A method of producing fine crystalline corundum, characterized in that the waste electrical aluminum wire containing not less than 99.5% aluminum (GOST 14838-78) is subjected to electroerosive dispersion in distilled water at a pulse repetition rate of 50 Hz, voltage on the electrodes of 90 V and discharge capacitance 65 uF capacitors.

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