SU645950A1 - Mrthod of obtaining powdery material - Google Patents

Description

The invention relates to the field of producing polycrystalline materials based on salts or oxides of various metals, such as special ceramics, raw materials for growing single crystals, optical glass melting, etc. The invention can be used in the chemical, metallurgical, electronic and other industries to obtain various chemical reagents, catalysts, powder metals and alloys, solid fuels, etc., as well as in other areas, where as final or intermediate products required such as are for powders with controlled uniformity SEASON Coy mixing components or kontroliruemo- high specific surface, or with both. quality at the same time. Methods are known for producing powdered materials, including the steps of preparing salt solutions or suspensions of substances capable of producing the desired composition of the final product, spraying the prepared solution or suspension in the form of freezing drops in a liquid or gaseous refrigerant that is practically incompatible with the original solution or suspension, and removing solvent or suspending medium from. frozen spherical particles by sublimation and the transfer of the powder remaining after sublimation into the final product using the appropriate heat treatment ij. The closest to the proposed invention is a method for producing powders for preparing polycrystalline materials by introducing a stream of fine droplets of salt solutions into a refrigerant followed by freeze-drying and heat treatment, in which a fine stream is pre-scattered to a single dispersed state by vibration with a frequency of 10 Hz MHz in an electrostatic field with a voltage from .10 volts to 2 sq. 2. The use of monodisperse drops instead of polydisperse makes the method more technolog This is due to the fact that it reduces the ablation of the product in the subsequent stages of the process and contributes to maintaining a more stable quality of the final product. However, this method of obtaining a powdery material is not free from a number of disadvantages, the most significant of which is the insufficiently high freezing rate of the solution and caused by the use of although monodisperse, but relatively large drops of solution (more than 50 micrometers in diameter), which leads to the occurrence of segregation of dissolved substances, and, as a consequence, to a deterioration in the homogeneity of the final product. In order to obtain a high freezing rate, which is necessary for chemical rotation of significant segregation of These substances require spraying the solution into extremely small droplets, micron and submicron in size (up to 0.1 micrometer and smaller). Obtaining monodisperse droplets of this size presents considerable difficulties and at present the solution of this problem is unknown. In addition, the spraying of the solution is carried out in an air medium with an electrostatic field loading up to 2 square meters, which creates restrictions on the choice of starting materials and solvents, since easily acidic or easily flammable air mixtures and solvents cannot be used in this process. Further, the conversion of a fluid stream into a monodisperse droplet stream is carried out in an open air volume, which creates considerable difficulty in the operation of a) sterile; b) highly toxic; c) radioactive substances. The purpose of the invention is to increase the uniformity and increase the specific surface of the powders while reducing the heat treatment times. This goal is achieved by the fact that in the method of obtaining a powder material. dispersion is carried out by emulsifying the solution in an immiscible state at a temperature higher than the freezing temperature of the solution, and freezing is carried out by evaporating the emulsion. Chills can be used as a volatile liquid. The process of emulsification is carried out at a pressure higher than or equal to atmospheric pressure, and the process of evaporation of emulsion of the properties of poronpsy iron oxide, obtained by the proposed and known methods.

Properties

WITH

Decomposition temperature, Decomposition time, min,

Proposed

Known method. method

850

850 10 gator is carried out at atmospheric pressure or in vacuum. Moreover, the evaporation of the volatile liquid is carried out with such intensity that the freezing process takes place at the required rate. Example 1. A sealed, heat-insulated container containing 3 liters of freon 22, which is under a pressure of 10 atm and room temperature, is injected with 0.5 liter of a 15% (based on anhydrous salt) aqueous solution (NH) SO -. Feso (103.5 g of salt per 426.5 ml of water). The mixture is emulsified with a propeller stirrer for. 30 minutes, after which this tank is connected through a vacuum seal to another 200 liter tank, connected through an aerosol filter to the atmosphere and the vacuum seal is opened, resulting in a result; rapid evaporation of the emulsifier (freon), and, as a consequence, the freezing of droplets of the solution emulsified in it. The resulting frozen solution, consisting of spherical particles with a size of less than 6 micrometers, is transferred to a sublimator, where at a total pressure of 10 Torr in the chamber and heat supply is heated. radiation from it over 8 hours removes the frozen solvent (ice). The mixture of substances obtained after freeze-drying is decomposed in a tunnel kiln in a continuous mode at a temperature rise rate of 300 degrees / hour to a temperature of 850 ° C and keeping it in a zone with a temperature of 850 ° C for 5 minutes after which it cools at a rate of 300 degrees per hour to room temperature. The obtained powder is pressed in vacuum molds at a specific pressure of 10 tons / cm into tablets with a diameter of O ml and a thickness of 4 mm, after which the sintering is carried out in the mode of: heating and cooling rates of 300 degrees / hour, isothermal holding temperature of 900 ° C, time isothermal you, cerzhki 1 hour T a b l and c a 1

Continued table. one

The specific surface of the powder after decomposition,

Average particle size, micrometers

Properties of ceramics of iron oxide, obtained by pressing. Pressing pressure, ton / cm

Sintering temperature, ° С Sintering time, hour.

The relative density of the powder

% of radiographic

Accuracy of the determination of the density of the cross-section is ± 0.01%,

Example 2 A 0.5 liter of an aqueous solution containing 30 g of copper acetate is introduced into a sealed, heat-insulated container containing 3 liters of refrigerant 22, which is under a pressure of 10 atm and room temperature. The mixture is emulsified with a pelletic stirrer for 15 minutes, after which this container is connected through a vacuum seal to another 206-liter container, previously evacuated to a pressure of 10 torr, and the first container is depressurized to the second.

Properties of copper powder, obtained by the proposed and known (2) methods.

Decomposition temperature, s

Decomposition time, h, Average particle size, A

22.3

30.2 0.36 0.28

Chart table and random methods

10,900 1.0

99.1

The resulting paramilitary frozen solution consisting of spherical particles with a diameter of 4-6 micrometers is transferred to a subzero and sublimated at atmospheric pressure in a stream of dry nitrogen at -35 ° C for 45 hours. The product obtained after freeze-drying is decomposed under hydrogen at a temperature of 280 ° C.

Electron microscopic studies showed that the resulting metallic copper powder had an average crystallite size of 110 L.

Table 3

280

five

about

1400