SK99698A3 - Process for the preparation of textured materials - Google Patents

Abstract

Texture materials preparation method by pressing the particl es in the powdered form, then by sintering and slow cooling to th e room temperature, eventually by subsequent annealing and re-coo ling consists in that before the pressing the particles in the po wdered form are placed in the gravitation field and are subjected to the energetic excitation by the transfer of the acoustic wave s with optimal frequency, which is determined pursuant to the rel ation (I).

Description

Method of preparation of textured materials.

Technical field

The invention relates to a process for the preparation of textured materials.

BACKGROUND OF THE INVENTION

For two-dimensional anisotropy, there are significant differences in the values of physical quantities measured within the material in the direction of the base crystallographic plane (planes ab} and in the direction perpendicular to that plane (direction of the c axis).

Said anisotropy is usually extinguished in the case of bulk bodies made of sintered materials prepared by heat treatment of the compressed powders due to the different orientation of the kristallographic axes within the material. However, polycrystalline materials with random crystal orientation are more of an exception than a rule in common practice. Particularly in the case of compact materials, a certain crystallographic direction in the crystals is preferably oriented with respect to the outer geometric dimensions of the sample. This preferred orientation of the crystallographic planes resulting from the technological processing is called texture.

The materials processing techniques known to date to produce a preferred crystallographic orientation are as follows: ₍ ,

1. Technology of extrusion of ceramic mixtures on vacuum presses, in which the components of the mixture with planar particle morphology (especially clays and kaolins) are oriented in the direction of flow of the mixture at the mouth of the press.

2. Process of zone melting, melt textured growth (MTG)

3. Quench melt growth (QMG)

4. The process of zonal heating of the sample (body), which consists in moving the sample through a temperature gradient furnace.

These and some other methods of preparing oriented (textured) material provide good results in the preparation of simple shape bodies. When creating a texture using melt processes, this is always a problem of heat treatment of the material, i. temperature regime during its production. .

In ceramic materials, particularly in the manufacture of shape-complicated materials in which it is necessary to achieve the existence of grain boundaries in order to achieve the desired physical properties of the material, it is important to create a suitably oriented internal structure of the material (texture) at sintering temperature.

SUMMARY OF THE INVENTION

These disadvantages are largely eliminated by the method of preparing textured materials by pressing the particulate powder, then sintering and slowly cooling to room temperature, or subsequent annealing and recooling, characterized in that the particulate powder is placed in a gravitational field and subjected to energy excitation by passing acoustic wines with optimum frequency, which is determined according to the relation:

in"

2πΙ ₀ (I) where g is the gravitational acceleration h is the height of the powder in the punch

I _o is the amplitude of acoustic wines.

π is Ludolf's number

In a powder system, which is located in a homogeneous gravitational field, under predefined conditions, directed mass transport in the direction of this

-3poľa. The condition is determined by the relationship between the value of the energy propagated by the discrete system by means of acoustic wines "w" and the value of the total energy of the coupling force field between the elementary discrete system "u". The formation of the direction of the preferred orientation of the particles in the powder is conditioned by the correlation between the shape aisotropy of the particles and the anisotropy of the physical properties of the material in the volume of each particle clearly defined in relation to its geometric shape.

There may be three cases of energy conditions in a powder system through which an acoustic signal passes:

1. The total energy of the coupling forces between the particles of the powder system 'u' is greater than that of the acoustic wines 'w'. In this case, there is no directed mass transport in the powder system.

2. The total energy of the coupling force 'u' shall be less than that of the acoustic wines 'w' propagating through the system. The system receives more energy than is necessary to release the bonds between the particles and therefore mass transport occurs, but the propagation of the acoustic signal through the system will cause permanent changes associated with the alignment of the elements due to the continuous increase of the potential energy of the whole system in the gravitational field. The system remains disordered.

3. If the energy value of the acoustic waves "w" propagating through the system is just equal to the total energy of the field of interparticle bonding forces "u", the bonding between the particles is released and consequently the mass transport (Fig. 1). There is no energy left to increase the system's potential energy in the gravitational field. The released particles move within the system, but the energy supplied in the form of acoustic wines no longer contributes to the change of their motion state. They move spontaneously under the influence of the gravitational field. As a result, changes caused by the supply of energy to the system will bring the system to the lowest potential energy value. The transition to the lowest energy condition requires the formation of a specific configuration of the system, which is associated with the directional orientation of its elements. For example, in the case of particles of flat shape (FIG. 2), this is the orientation in which the crystallographic axis c is oriented in the vertical direction.

When the acoustic signal passes through the powder system, energetic excitations of the particles in the gravitational field occur. Excitation processes lead at a certain frequency

The acoustic wines characteristic of each powdered material and arrangement to spontaneously produce a preferred orientation of the crystallographic axis c of the particles in the powder.

An advantage of the method according to the invention is that it allows the formation of a preferred direction of orientation of the crystallographic axes c prior to the heat treatment of bodies with different geometrical shapes as well as complicated materials, which favorably affects their physical properties. In the case of high temperature superconducting materials, the use of the method according to the invention leads to an increase in critical currents and thus to a significant improvement in the properties in the superconducting region.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

To verify the process of the invention, a superconducting ceramic material based on copper oxides - YBaCuO powder was used.

Prior to the experiment, a physico-chemical analysis of YBaCuO powder was performed to determine the quality, crystallographic structure of the powder and the physical quantities necessary to calculate the frequency of acoustic waves inducing a preferential particle orientation. The powder analysis consisted of the following steps:

(a) Chemical analysis to determine the presence of the chemical elements Y, Ba, Cu. Their percentage by weight was: 12.780% Y, 40.510% Ba, 27.050% Cu.

b) X-ray (X-ray) analysis of the free-flowing powder, which showed that no secondary phase was present in the puffed YBaCuO powder. All reflections pointed to the presence of a pure orthorhombic phase of YBaCuO. The powder particles could be considered "perfectly oriented" before the acoustic signal began to spread. The X-ray spectrum of such a powder was used as a starting point in evaluating the orientation effect.

c) Measurement of the particle distribution function of the powder particles, which made it possible to estimate the particle size distribution of the powder particles. The partitioning function had a maximum around 7pm.

The shape similarity of the powder particles and the clear correlation between the shape of the particles and the orientation of the crystallographic axes of the material (Fig. 2) were guaranteed by the nature of the crystalline growth of the material.

Then, 1g of YBaCuO powder was placed in a cylindrical punch with a diameter of 8mm and exposed to an acoustic signal from a controllable frequency generator for 1 hour. The acoustic signal was transmitted to the powder after passing through the amplifier and the electromechanical transducer from the vibrating mat. A diagram of the apparatus used is shown in Fig. 3. The signal frequencies used were in a relatively wide spectrum of frequencies in the acoustic range of 20 Hz to 3000 Hz.

Values were used and ^"_2 10 m from _the ΚΓ ~ ⁴ m where the characteristic frequency calculated from equation (I) was = 498.74 Hz.

A quantitative evaluation of the process of gradual alignment of powder particles as the acoustic signal transitions were made by measuring spatial X-ray spectra using a scanning device, the scheme of which is shown in FIG. 4th

The orientation of the crystallographic axes c of the YBaCuO powder particles was determined from the measured diffraction values from the crystallographic planes [0,0,2].

The distribution functions of the pressed powder particles were constructed from the measured spatial X-ray spectra according to the orientation of their basic crystallographic planes in space. The procedure for determining the partitioning functions is shown in Figure 5. The partitioning function of the compacted powder particles obtained from the spatial X-ray spectrum from the sample surface is shown in FIG. 6, and FIG. 7 is the particle distribution function of the powder particles obtained from the spatial X-ray spectrum of the sample volume.

From the above particle distribution functions, it can be seen that the propagation of the acoustic signal at a given frequency results in a direction of preferential orientation of the crystallographic axes c of the particles in the powder.

-6Default usability

The method according to the invention is applicable in ceramic technologies in which the raw material composition of the processed compositions or some of their constituents has a layered structure and the material fulfills the anisotropy criterion, i.e. the composition of the composition. when the material exhibits anisotropy of physical properties at the particle level of the powder.

PVWČ-W

Claims (2)

Method for the preparation of textured materials by powder particles, sintering and slow cooling to room temperature, optionally followed by annealing and recooling, characterized in that they are placed in a gravitational field and subjected to energy excitation by passing acoustic wines before pressing the powder particles. with an optimal frequency to be determined according to: Jgh y »Jl— 2πΖ ₀ (I) where g is the gravitational acceleration h is the height of the powder in the punch I _o is the amplitude of acoustic wines π is the Ludolf number