Preparation method of toughened lead oxide particles suitable for industrial mass production

Abstract

The invention discloses a method for preparing toughened lead oxide particles by a dry pressing method, which belongs to the technical field of metal ceramic and is suitable for industrial batch production. The lead oxide particles are prepared by using a dry pressing forming cold isostatic pressing pressure maintaining method. The method focuses on solving the problems of low preparation efficiency, high cost, low hardness and density of produced pellets and the like of lead oxide particles prepared in a laboratory at present. Firstly, the tedious steps of binder adding, re-pressing, glue discharging and the like in the laboratory preparation process are omitted, loss of a machine and a metal mold caused by pressure maintaining of a molding press is avoided, production is greatly improved, production cost is reduced, and industrial large-batch production of lead oxide particles can be achieved; and secondly, due to dry pressing and cold isostatic pressing for pressure maintaining, a binder is not added, so that the influence of volatilization of the binder on the internal structure of the particles is avoided, and the prepared lead oxide particles are better in performance. The hardness and density of the material are tested, and the microstructure is characterized to be smooth and crack-free under a scanning electron microscope.

Description

Technical Field

[0001] The invention relates to the technical field of metal ceramic preparation, and in particular to a method for preparing toughened lead oxide particles by a dry pressing method suitable for industrial mass production. Background Art

[0002] At present, the development prospects of nuclear power generation technology are broad, and the treatment of spent fuel produced by nuclear power plants is also being promoted simultaneously. Liquid lead-bismuth alloy (LBE) is used as a coolant in lead-cooled fast reactors of the fourth generation reactors, and is also the preferred material for spallation targets and subcritical reactor coolants in accelerator-driven subcritical systems. However, experiments have shown that LBE will cause a certain degree of corrosion to metal structural materials in application scenarios, and long-term use will cause serious safety problems. Studies have shown that controlling the dissolved oxygen concentration in lead-bismuth alloy to 10 -6 -10 -8 wt.% range can effectively alleviate the corrosion of structural materials without introducing excess impurities. In actual applications, the interior of the reactor system is a fully sealed structure. As the operating time increases, the growth of the oxidized structure on the surface of the structural material consumes the dissolved oxygen in the liquid lead-bismuth alloy, and an additional oxygen source is needed to supply oxygen to the lead-bismuth alloy to maintain the oxygen concentration of the system. Lead oxide particles are an important oxygen source material in solid oxygen control in lead-cooled fast reactors and accelerator-driven subcritical systems. Under actual working conditions, it is necessary to carry out large-scale production under the premise of ensuring its density and structural stability to meet industrial needs, but the current preparation method of lead oxide particles is only suitable for small-scale laboratory preparation. Therefore, the present invention provides a new technology suitable for industrial large-scale production of lead oxide particles.

[0003] The technical problem solved by the present invention is to simplify the preparation steps of lead oxide particles and provide a new method for enhancing the physical properties of the pellets by dry pressing and cold isostatic pressing. This method directly eliminates the steps of adding a binder, pre-pressing, re-crushing, and debinding. Since the addition of a binder can form pores within the particles, reducing the performance of the sintered particles, affecting the internal structure of the particles, and thus the performance of the sintered ceramic particles, research on the binder addition amount and debinding process is a major challenge. Laboratory preparation can only produce one ceramic pellet at a time, and the molding machine requires long periods of pressure maintenance, which causes significant wear and tear on both the machine and the metal mold. Dry pressing, on the other hand, eliminates the need for binder-related issues and the need for pressure maintenance during the molding process. Dry pressing can produce large quantities of lead oxide particles at once, achieving high production efficiency and low production costs. The subsequent cold isostatic pressing process also ensures the performance of the pellets. In summary, this inventive method can produce lead oxide particles that meet the requirements of specific applications while also enabling industrial mass production and reducing production costs. Summary of the Invention

[0004] The present invention aims to provide a method for preparing toughened lead oxide particles by dry pressing suitable for industrial mass production. The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0005] A method for preparing toughened lead oxide particles by dry pressing suitable for industrial mass production is characterized by using dry pressing and cold isostatic pressing to enhance the physical properties of the pellets, eliminating the steps of adding a binder, pre-pressing, re-crushing, and debinding required in laboratory preparation.

[0006] Two powders, Bi2O3 and PbO, are used, and the purity of both powders is 99.9%.

[0007] A method for preparing toughened lead oxide particles by dry pressing suitable for industrial mass production comprises the following steps:

[0008] (1) Mix 97 wt.% PbO and 3 wt.% Bi2O3 powders and mix thoroughly using a ball mill.

[0009] (2) Using an experimental vibrating sieve machine, the sieves are 50 mesh and 100 mesh, and the powder particle size is uniform and meets the requirements;

[0010] (3) pressing the mixed powder obtained in step (2) into balls in large quantities using a dry pressing method;

[0011] (4) The lead oxide pellets obtained in step (2) are again subjected to cold isostatic pressing to maintain pressure;

[0012] (5) The lead oxide pellets obtained in step (4) are placed in a muffle furnace and heated and sintered, and then naturally cooled in the furnace to obtain ceramic pellets.

[0013] In step (3), the dry pressing process is used, and the powder molding parameters of the metal mold pressing are: compression ratio 2.1 and pressure 200 MPa.

[0014] The cold isostatic pressing process described in step (3) has a pressure of 200 MPa and a holding time of 2 min, which can make the powder evenly stressed and ensure that the powder is fully diffused inside the particles.

[0015] In step (5), a muffle furnace is used to uniformly heat the sintering temperature to 620° C., which is kept for 8 h and then cooled with the furnace.

[0016] Compared with the existing preparation process, the present invention has the following advantages: the present invention proposes a method for preparing toughened lead oxide particles by a dry pressing method suitable for industrial mass production. Compared with laboratory preparation, firstly, it can realize industrial mass production of lead oxide ceramic pellets, greatly improving production efficiency, and eliminating the process of holding pressure in a molding machine, avoiding damage to the molding machine and metal mold, and greatly reducing production costs; secondly, the binder will decompose and volatilize, and the decomposition products will generate pores inside the particles, reducing the density of the particles and affecting the internal structure of the particles. Compared with the compression molding process using an adhesive, the dry pressing cold isostatic pressing holding pressure process has simpler process steps, and cold isostatic pressing makes the pressure of the powder more uniform, so that the powder inside the pellet can be better diffused, so that the pressed pellets have uniform hardness and high density. Scanning electron microscopy (SEM) characterization shows that the microstructure surface is smooth and has no obvious cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Scanning electron microscope image of ceramic balls formed by dry pressing and cold isostatic pressing for implementation case;

[0018] Figure 2 For the implementation case, the density and hardness of ceramic balls formed by dry pressing and cold isostatic pressing are plotted as a function of sintering time.

[0019] Figure 3 Actual picture of sintering of ceramic pellets formed by dry pressing and cold isostatic pressing as an implementation case. Specific implementation methods

[0020] The following is a detailed description of the implementation scheme of the invention in conjunction with the drawings in the implementation case of the invention.

[0021] The following are the specific implementation steps for preparing toughened lead oxide particles by dry pressing:

[0022] (1) Weigh two powders with a purity of 99.9% according to the mass percentage of 97wt.% PbO and 3wt.% Bi2O3.

[0023] (2) Pour the two weighed powders into the ceramic pot of the ball mill and use the ball mill to mix the powders thoroughly.

[0024] (3) Pour the mixed powder into the sieve of the experimental vibrating screen machine. The two layers of sieve are 50 mesh and 100 mesh respectively, and sieve for 15 minutes.

[0025] (4) The mixed powder obtained in step (3) is placed in a metal mold of a dry pressing machine and pressed into small balls with a small diameter of 8 mm in large quantities;

[0026] (5) cold isostatically pressing the pellets obtained in step (4) for 2 minutes;

[0027] (6) The molding parameters of the metal mold used to compress the powder in step (4) are: mold inner diameter 8 mm, powder filling height 15 mm, compression ratio 2.1, and pressure 200 MPa;

[0028] (7) The ceramic balls obtained in step (6) were spread flat in a 20 cm × 20 cm crucible, placed in a muffle furnace, and uniformly heated to 620° C., kept at this temperature for 8 h, and then cooled in the furnace to obtain lead oxide ceramic balls.

[0029] The density and hardness of the lead oxide ceramic balls obtained by cold isostatic pressing at different sintering times are shown in Table 1. Figure 1 Summarized.

[0030] The lead oxide ceramics obtained in the implementation case were examined by scanning electron microscopy ( Figure 1 ), and found that the lead oxide ceramics obtained by dry pressing plus cold isostatic pressing and sintering at 620℃ for 8h had a smooth micro surface, dense structure, few pores, good crystallinity and sufficient grain growth.

[0031] In summary, the present invention provides a method for preparing toughened lead oxide particles using a dry-pressing process for industrial mass production. This method not only improves the production efficiency of lead oxide ceramic pellets but also enhances their density and hardness. The lead oxide ceramic pellets produced by this process are capable of stably controlling the dissolved oxygen concentration in lead-bismuth alloy (LBE) over a long period of time.

Claims

1. A method for preparing toughened lead oxide particles by dry pressing suitable for industrial mass production, characterized in that The granulation steps of dry pressing and cold isostatic pressing are used to enhance the physical properties of lead oxide pellets and simplify the steps of adding binder, pre-pressing, re-crushing and debinding in laboratory preparation.

2. The method for preparing toughened lead oxide ceramics by dry pressing according to claim 1, wherein: The purity of the Bi2O3 and PbO is 99.9%.

3. A method for preparing the lead oxide ceramic according to any one of claims 1 and 2, characterized in that: The preparation comprises the following steps: (1) Using 3wt.% Bi2O3 powder and PbO powder, they were fully mixed using a new ball mill. The addition of Bi2O3 was beneficial to improving the toughness of lead oxide particles. (2) Using a vibrating sieve machine, the sieves are 50 mesh and 100 mesh, and the powder particle size is uniform and meets the requirements; (3) pressing the mixed powder obtained in step (2) into balls in large quantities using a dry press; (4) The lead oxide pellets obtained in step (3) are again subjected to cold isostatic pressing to maintain pressure; (5) placing the lead oxide pellets obtained in step (4) into a muffle furnace and heating and sintering the pellets, and then naturally cooling the pellets to obtain toughened lead oxide ceramic pellets.

4. The preparation method according to claim 3, characterized in that In the step (3), the pressing is performed by dry pressing, and no binder is added to the powder. The cold isostatic pressing is performed and the metal mold pressing parameters of the powder are: compression ratio 2.1, pressure 200 MPa, and cold isostatic pressing holding time of 2 min.

5. The preparation method according to claim 3, characterized in that In the step (4), a muffle furnace is used for uniform heating, the sintering temperature is 620° C., and the temperature is kept for 8 hours.

6. The preparation method according to claim 3, characterized in that The cooling in step (4) is furnace cooling to reduce the temperature.

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