RU2791652C1 - Method of obtaining ceramics - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemistry and can be used in the manufacture of high-strength ceramics, heating elements of devices, photocatalysts for wastewater treatment, microcomponents for electronics, as well as in the technology of preparing solid radioactive waste for preservation and long-term storage. First, the initial components are mixed, wt. %: 90-97 of fused MgO and 3-10 δ*-Bi₂O₃ as a binder. The mixture is heated to 700-900°C and stand for 5 hours. High-density ceramics with low porosity and high hardness are obtained.

EFFECT: invention reduces the synthesis, there is no release of by-products and gases.

1 cl, 5 dwg, 2 ex

Description

The method relates to the field of chemistry and can be used to obtain high-strength ceramics, to preserve solid radioactive waste in the technology of their preparation for long-term safe storage, to obtain heating elements for devices, as a promising photocatalyst for wastewater treatment, for the processing of oxide magnesium waste, as ceramic basis of microelements of modern electronics.

A known method for producing ceramics based on Bi ₂ O ₃ -MgO, including mixing components, filtering, heating and cooling [Not Haoyan, Chen Dongxu, Zhao Zhixiong. Research on the preparation of Bi ₂ O ₃ -MgO composite material and its photocatalytic activity // Industrial Water Treatment. V.35, No. 4, 53-55].

However, this method is laborious and time consuming due to the large number of operations.

Closest to the claimed is a method of obtaining Bi ₂ O ₃ -MgO, including mixing, heating and cooling, with a synthesis time of 43 hours. [E.-J. Li, K. Xia, S.-F. Yin, W.-L. Dai, S.-L. Luo, C.-T. Au. Preparation, characterization and photocatalytic activity of Bi ₂ O ₃ -MgO composites // Materials Chemistry and Physics 125 (2011) 236-241]. This method is taken as a prototype.

However, when using this method, it is not achieved:

1. quick receipt of ceramics, because this method is more laborious and requires a lot of time spent on synthesis;

2. ease of execution of the synthesis, due to the complex multi-stage process.

The objective of the invention is:

reduction in the synthesis time of ceramics based on fused MgO.

This is achieved by the fact that in the method of obtaining ceramics based on MgO using a solid binder, including pre-mixing of the initial components, heating and holding, δ*-Bi ₂ O ₃ is used as a binder, which is mixed with fused MgO in the following ratio of components, mass . %: 90-97 MgO - 3-10 δ*-Bi ₂ O ₃ , after stirring the resulting mixture is heated to 700-900°C and incubated for 5 hours.

The presence of a higher heating temperature in the proposed method helps to reduce the time required for synthesis, and the use of the metastable compound δ*-Bi ₂ O ₃ as a binder ensures its high reactivity at the time of the phase transition, and allows the process of ceramic synthesis to be carried out in less number of stages and less time. A unique feature of the use of such a binder is also the effect of superplasticity, which is realized during the decomposition of δ*-Bi ₂ O ₃ and provides the possibility of not only additional compaction of a ceramic product even under small loads, but also giving it a given shape in the "forging" mode. In this case, there is no release of by-products, gases, and the initial composition of the ceramic product does not change. The absence of outgassing and liquid makes it possible to obtain high-density ceramics with low porosity and high hardness.

The choice of boundary parameters for the amount of a metastable solid binder (3-10 wt. %) is due to the experimentally obtained values of the hardness of ceramics from fused MgO depending on the amount of δ*-Bi ₂ O ₃ introduced into it (Fig. 1). From the graph (Fig. 1) it can be seen that at 3 wt. % δ*-Bi ₂ O ₃ begins the most intensive increase in the hardness of sintered ceramics. A lower binder content leads to a significant decrease in the hardness of the synthesized material. Closer to 10 wt. % δ*-Bi ₂ O ₃ hardness growth reaches quite high values - over 920 HV (kgf/mm ² or 9200 N/mm ² ) and starts to slow down. The introduction of a higher content of a metastable binder into ceramics is possible, but impractical, due to its rather high cost, and also because of the high probability of brittleness of the synthesized ceramics.

The choice of boundary parameters for the sintering temperature of ceramics (700–900°C) is determined primarily by the decomposition temperature of the metastable binder. According to the data shown in Fig. 2, the decomposition of δ*-Bi ₂ O ₃ occurs around a temperature of 600°C. Thus, the heating temperature must be above 600°C for the interaction of the binder with the sintered material. The second important factor will be the level of ceramic hardness. Figures 3 and 4 show examples of changes in the hardness values of the sintered ceramic material depending on the sintering temperature. It can be seen from them that the highest hardness values can be obtained at 800–900°C (depending on the amount of binder introduced). A decrease in the sintering temperature leads to a decrease in the hardness of the ceramic. However, depending on the purpose, there is a need for ceramic materials with a different set of mechanical (and other) properties, so the lower limit of the temperature range (700°C) was chosen as the temperature at which the decomposition of δ*-Bi ₂ O ₃ is also ensured. , and quite high values of the hardness of the synthesized ceramics are achieved with the possibility of their further increase with increasing synthesis temperature.

The upper limit of the temperature range corresponds to the liquidus temperature of the alloy δ*-Bi ₂ O ₃ (Bi ₂ O ₃ :SiO ₂ - 78:22 mol.%) on the phase diagram of the stable equilibrium of the Bi ₂ O ₃ -SiO ₂ system (Fig. 5). Those. the metastable phase δ*-Bi ₂ O ₃ with an increase in temperature above 600°C undergoes decomposition with a transition to a stable state and, upon further heating above 900°C, melts according to the phase diagram of stable equilibrium. In this case, during ceramic sintering, the formation of a liquid component is possible, which will more effectively interact with magnesium oxide, however, due to the high fluidity of melts based on Bi ₂ O ₃ , part of the liquid phase is able to move to the lower part of the ceramic sample, leading to interaction with the substrate , as well as causing heterogeneity of properties throughout the volume of the sintered material. Thus, heating above 900°C is impractical.

The choice of limiting holding parameters (5 hours) at sintering temperatures (700-900°C) includes slow heating with a furnace, holding at specified temperatures, and also slow cooling with a furnace. Slow heating and cooling are due to the brittleness of ceramic materials. Sharp temperature drops can lead to active cracking and destruction of ceramics. The synthesis process itself, which takes place during the decay of the metastable binder (δ*-Bi ₂ O ₃ ), is very fast and does not require much time for implementation. A holding time of less than 5 hours may lead to cracking or incomplete interaction of the powders of the original oxides. A holding time of more than 5 hours is inappropriate, due to higher energy, time and economic costs.

The method is illustrated graphically, where:

Fig. 1 - Dependence of the hardness of a sample of ceramics from MgO on the content of the binder (δ*-Bi ₂ O ₃ ); synthesis time - 5 hours; synthesis temperature - 900°C;

Fig. 2 - Influence of the phase and component composition of metastable samples on the temperature of their decomposition in the Bi ₂ O ₃ -SiO ₂ system (heating rate 6 K / min) [Zhereb V.P. Metastable states in oxide bismuth-containing systems // M.: MAKS Press, 2003. - 162 p.];

Fig. 3 - Dependence of the hardness of a sample of ceramics from MgO on the temperature of synthesis using a binder (δ*-Bi ₂ O ₃ ); duration of synthesis - 5 hours; when the content of the binder - 3 wt. %;

Fig. 4 - Dependence of the hardness of a sample of ceramics from MgO on the temperature of synthesis using a binder (δ*-Bi ₂ O ₃ ); duration of synthesis - 5 hours; when the content of the binder is 5 wt. %;

Fig. 5 - The boundaries of the temperature zones (1) in the liquid state on the phase diagram of stable equilibrium (2) of the Bi ₂ O ₃ -SiO ₂ system, built from the results of heating the melts [Zhereb V.P. Metastable states in bismuth-containing oxide systems // M.: MAKS Press, 2003. - 162 p.].

The essence of the invention is illustrated by diagrams, as well as the results of measuring the hardness of sintered ceramics depending on the sintering temperature and the amount of binder introduced into the ceramics (δ*-Bi ₂ O ₃ ).

It was experimentally determined that when 3-10 wt. % binder (δ*-Bi ₂ O ₃ ) and sintering it at temperatures of 700-900°C ensures reliable production of a dense ceramic material with high hardness values (HV). This is explained by the fact that at temperatures of 600°C and above, the metastable binder δ*-Bi ₂ O ₃ decomposes, during which its crystal structure acquires high lability and actively interacts with the surface of particles of fused magnesium oxide. A unique feature of the use of such a binder is also the effect of superplasticity, which is realized during the decomposition of δ*-Bi ₂ O ₃ and provides the possibility of not only additional compaction of a ceramic product even under small loads, but also the possibility of giving it a given shape in the "forging" mode. In this case, there is no release of by-products, gases, and the initial composition of the ceramic product does not change. The absence of outgassing and liquid makes it possible to obtain high-density ceramics with low porosity and high hardness.

The presented data are confirmed by the high hardness values of the obtained ceramic samples. By varying the sintering temperature in the specified range, it is possible to control the hardness of the sintered material.

According to the results of the analyzes shown in Fig. 1, 3, 4, we can conclude that the decisive role in the sintering of MgO-based hard ceramics using the δ*-Bi ₂ O ₃ binder is played by the amount of the binder introduced into the ceramics and the sintering temperature.

The claimed method "Method for producing ceramics" can be implemented using the following material objects:

1. furnace - a heating device with a working chamber that provides heating of the material to a predetermined temperature in the range up to 900 ° C;

2. press - for compacting a mixture of raw materials (δ*-Bi ₂ O ₃ and fused MgO and), large loads are not required;

3. forms - to give the form required in the production of a sintered product or workpiece.

Concrete example 1:

1. As initial components, we take cast magnesium oxide and δ*-Bi ₂ O ₃ in a ratio of 97 wt. % MgO - 3 wt. % δ*-Bi ₂ O ₃ ;

2. thoroughly mix the initial components with each other;

3. compact (compress) the resulting mixture;

4. heat the resulting mixture to 900°C;

5. withstand 5 hours;

6. remove the resulting finished ceramics from the furnace.

Case Study 2:

1. As initial components we take fused magnesium oxide and δ*-Bi ₂ O ₃ in a ratio of 90 wt. % MgO - 10 wt. % δ*-Bi ₂ O ₃ ;

2. Thoroughly mix the initial components with each other;

3. compact (compress) the resulting mixture;

4. heat the resulting mixture to 700°C;

5. withstand 5 hours;

6. remove the resulting finished ceramics from the furnace.

As shown by the results of experimental verification, when using the proposed method, the following results are achieved:

1. A high-density hard ceramic based on cast MgO has been obtained;

2. synthesis of ceramics occurs in the absence of a liquid component (solution, melt), which makes it possible to obtain homogeneous high-density ceramics with low porosity and high hardness;

3. synthesis does not require additional equipment, except for a compacting device, and does not require the introduction of additional reaction components;

4. due to the use of a highly active metastable binder (δ*-Bi ₂ O ₃ ) the process of ceramic synthesis requires much less time to implement than analogues and prototype.

Claims (1)

A method for producing ceramics based on MgO using a solid binder, including pre-mixing of the initial components, heating and holding, characterized in that δ*-Bi ₂ O ₃ is used as a binder, which is mixed with fused MgO in the following ratio of components, wt. %: 90-97 MgO - 3-10 δ*-Bi ₂ O ₃ , after stirring, the resulting mixture is heated to 700-900°C and incubated for 5 hours.

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