CN105256373A - Method for preparing superfine nano powder by introducing airflow - Google Patents

Abstract

The invention provides a method for preparing ultra-fine nano-powder through an air flow, which is used in an ultra-fine nano-powder calcination furnace. Sufficient separation to prevent particle growth caused by long-term contact between particles during high-temperature sintering, specifically including the following steps: a. Nano-powder materials that need high-temperature sintering are placed at the bottom of the furnace liner; b. Gas is introduced from the air inlet , to control the airflow rate, under the interaction of the buoyancy of the airflow and the gravity of the powder particles, it is fully dispersed in the furnace body; c. The fully dispersed nano-powder sample is sintered at high temperature to achieve sufficient crystallization; d. The gas flows out from the gas outlet. The invention avoids the grain growth caused by the long-term contact between the grains, thereby realizing the preparation of the superfine nanometer powder with good crystal structure obtained through high-temperature sintering without grain size growth.

Description

Method for preparing ultrafine nanopowder by air flow

technical field

The invention relates to the design of a novel high-temperature furnace to realize the high-temperature preparation process of ultrafine nanometer powder.

Background technique

Nanomaterials are becoming more and more important in today's industrial production and social life. Although there are various chemical preparation methods, the output is not high. The most suitable method for industrial production is the high-temperature sintering preparation process. However, as the sintering temperature of nanomaterials increases, although the crystal structure will be more complete, the particle size will also increase sharply, and the particle size has a crucial impact on the performance of nanomaterials. Generally, in order to obtain ultra-fine nano-powders, the sintering temperature can only be lowered, and low-temperature sintering will lead to incomplete crystallization of particles, resulting in a decrease in the performance of the final material. How to effectively control the growth of particle size and fully realize the special functions of nano-powder materials while improving the crystal structure during high-temperature sintering is an urgent problem to be solved. In order to achieve this function, we modified the existing high-temperature furnace and designed a unique high-temperature sintering preparation process that uses airflow to disperse nano powder particles.

Invention content:

Technical problem: The purpose of the present invention is to provide a method for preparing ultrafine nanopowder through air flow, so as to realize the high temperature preparation of ultrafine nanopowder.

Summary of the invention: In order to solve the above technical problems, the present invention provides a method for preparing ultra-fine nano-powder through air flow. The method is used in an ultra-fine nano-powder calcination furnace. Medium blowing to achieve sufficient separation between particles and prevent particle growth caused by long-term contact between particles during high-temperature sintering, which specifically includes the following steps:

a. The nano-powder material that needs to be sintered at high temperature is placed at the bottom of the furnace liner;

b. Introduce gas from the air inlet, control the airflow rate, and make it fully dispersed in the furnace body under the interaction of airflow buoyancy and powder particle gravity;

c. Fully dispersed nano powder samples are sintered at high temperature to achieve sufficient crystallization;

d. The gas passed in flows out from the gas outlet.

Preferably, electric furnace wires, silicon carbon rods or silicon molybdenum rods are used for heating the furnace body, the temperature is measured by thermocouples, and the temperature is controlled by a temperature controller.

Preferably, the gas inlet and the gas outlet at both ends of the liner are respectively connected with sealing devices to isolate the air.

Beneficial effects: the present invention blows the ultrafine nano-powder inside the furnace body through air flow, avoiding the long-term contact between particles during sintering, which leads to the growth of particles at high temperature, thereby preventing the particle size from changing while improving the crystal structure. Grow up to obtain high-quality ultra-fine nano-powder materials. The device is not only suitable for the preparation of nanometer materials in the laboratory, but also can be used in industrial production to prepare high-quality ultrafine nanometer powder products.

Description of drawings

Figure 1 Schematic diagram of the principle of sintering ultrafine nano-powder through atmosphere, including:

1-furnace body

2- liner

3- Gas inlet

4-Gas outlet

5-Ultrafine Nano Powder

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

The principle of the method for preparing ultrafine nanopowder by airflow provided by the present invention is as shown in the accompanying drawings. The ultrafine nanopowder material to be sintered is placed at the bottom of the inner container, and a certain airflow is passed through the gas inlet to make a constant rate or a pulse Under the interaction of the buoyancy of the airflow and the gravity of the powder, the nanometer ultrafine powder is suspended in the middle of the inner tank and fully dispersed. The furnace is heated to a specific temperature, and the ultrafine nano powder is fully sintered to obtain a well crystallized nano powder sample.

The method for preparing ultra-fine nano-powder provided by the invention is used in an ultra-fine nano-powder calcination furnace. The method uses air flow to blow away the nano-powder material that needs high-temperature sintering in the furnace body to achieve sufficient separation between particles. , to prevent particle growth caused by long-term contact between particles during high-temperature sintering, specifically including the following steps:

a. The nano-powder material that needs to be sintered at high temperature is placed at the bottom of the furnace liner;

b. Introduce gas from the air inlet, control the airflow rate, and make it fully dispersed in the furnace body under the interaction of airflow buoyancy and powder particle gravity;

c. Fully dispersed nano powder samples are sintered at high temperature to achieve sufficient crystallization;

d. The gas passed in flows out from the gas outlet.

1. Preparation of multiferroic oxide BiFeO ₃ ultrafine powder

BiFeO ₃ is a multiferroic oxide with ferroelectricity and antiferromagnetism above room temperature at the same time. There is a small dip angle between the spins of adjacent Fe ions, and there is a certain net magnetic moment. At the same time, the magnetic structure has The helical periodic structure of 64 nm causes the macroscopic magnetic moment of the large _- grained BiFeO3 to be offset to almost zero. In order to obtain enhanced ferromagnetism in BiFeO ₃ , one method is to keep the size of BiFeO ₃ particles below 64 nm, so that there is no complete helical periodic structure inside the particles, and the particles will have a certain net magnetic moment, thus showing externally Certainly ferromagnetic. Usually, the low-temperature sintering process is used in experiments to obtain powder materials with a size below 64 nanometers. However, due to low-temperature sintering, the crystal structure of BiFeO ₃ is incomplete, and there are a large number of defects, which affect its magnetic and ferroelectric properties.

By adopting the furnace of the present invention, the low-temperature sintered BiFeO3 nano _- powder material that has been phased can be put into the inner container, and air or oxygen is introduced to maintain a certain air flow, so that the _BiFeO3 powder is blown into the inner container. In the middle of the tank, intermittent ventilation can also be used to maintain a certain low-speed air flow to provide the reaction oxygen atmosphere required for sintering, and then intermittently enter the large air flow to blow the powder into the middle of the inner tank and disperse it completely. As the gravity falls, the powder is blown away again by the next pulsed airflow, keeping it in a dispersed state in the inner tank. Raise the furnace temperature to 600 to 800 degrees and keep it warm for 2 to 10 hours. Under high temperature, BiFeO ₃ will achieve sufficient crystallization and obtain a good crystal structure. At the same time, the powder particles will be in a dispersed state during sintering and will not grow up. Thereby realizing the preparation of the BiFeO ₃ ultra-fine nano-powder with good crystal structure, and controlling its particle size below 64 nanometers.

2. Preparation of LiFePO ₄ ultrafine powder as cathode material for lithium battery

Lithium batteries play an increasingly important role in today's social life. The performance of cathode materials in lithium batteries is crucial. LiFePO ₄ is a very important cathode material with high energy density, high safety and long service life, which can be applied to the power battery of electric vehicles. However, its poor electrical conductivity and low mobility of lithium ions also greatly limit its application, especially the charge-discharge performance at high rates. Generally, LiFePO ₄ is nanometerized to reduce its size, thereby shortening the diffusion distance of lithium ions to improve its fast charging performance.

LiFePO ₄ needs to be prepared by high temperature sintering. Although the phase has been formed during low-temperature sintering, the particle size is very small, about 50 nanometers to 100 nanometers, but the crystallization is incomplete, resulting in poor electrochemical performance. Although high-temperature sintering greatly improves its crystal structure, the particle size grows significantly to micron and sub-micron sizes, resulting in a significant drop in performance at high magnifications.

Adopt the furnace of the present invention, can put the _LiFePO4 powder body material prepared by sintering at low temperature into the furnace liner, because the preparation of _LiFePO4 needs to isolate the air, prevent divalent Fe from being oxidized into trivalent Fe, can pass through in the furnace Into the protective atmosphere, such as argon or nitrogen, etc., maintain a certain air flow to blow the LiFePO ₄ powder in the middle of the liner, or keep a certain low air flow of the protective gas, and then indirectly introduce the pulsed atmospheric air flow of the protective gas, so that The powder is fully dispersed in the middle of the liner, the furnace temperature is raised to 700 to 800 degrees, and sintered for 10 to 30 hours, which can fully crystallize the LiFePO ₄ powder at high temperature and avoid particle growth caused by long-term contact between particles. Large, so as to obtain high-quality LiFePO ₄ ultrafine powder materials, and prepare high-performance lithium battery cathode materials.

It is necessary to design a furnace with a special structure, which is characterized in that the furnace body adopts a vertical style, the bottom of the furnace can be sealed and insulated, and the upper end of the furnace is open to facilitate the insertion of a ventilated liner. After the liner is placed, the upper part of the furnace body can be made of heat-insulating cotton, etc. For further heat insulation treatment, electric furnace wire, silicon carbon rod or silicon molybdenum rod can be used for heating the furnace body, the temperature can be measured by thermocouple, and the temperature can be controlled by temperature controller.

The vented atmosphere liner has an asymmetric U-shaped structure, the reaction gas enters from the upper end of the thin tube, blows the powder to be sintered from the bottom, and the gas flows out from the other end of the thick tube.

The furnace can be raised to a specific temperature according to the sintering requirements to sinter the powder particles at high temperature. Sufficient dispersion between particles avoids particle growth caused by long-term contact between particles during high-temperature sintering, and high-temperature sintering promotes the crystallization of particles.

According to the process for preparing ultra-fine nano-powder through airflow according to claim 1, it is characterized in that the gas inlet and the gas outlet at both ends of the inner tank can be connected with sealing devices to isolate the air and pass in special reaction gas or protective gas.

The present invention provides a preparation process of ultra-fine nano-powder material which prevents grain growth due to long-term contact between particles during the sintering process. By designing a special furnace body structure, it can flow from the gas inlet 3 to the bottom of the furnace inner tank 2. The atmosphere is introduced. During the sintering process of the powder material, a certain flow of gas is introduced from the bottom, which can be ventilated continuously or intermittently. The powder is blown from the bottom of the furnace body to the middle of the inner tank 2. By controlling the rate of airflow , so that the powder that needs to be sintered is blown to the middle of the inner tank 2 by the air flow, and the powder is scattered in the middle of the inner tank 2, which avoids the grain growth caused by the long-term contact between the particles, so that the particle size does not grow, and at the same time, it is passed through the high temperature Preparation of ultrafine nanopowders with good crystal structure obtained by sintering.

It is a nano-powder preparation process in which the atmosphere is introduced to disperse the nano-powder particles and avoid the particle size growth caused by the long-term contact of the particles during the high-temperature sintering process. The present invention designs a high-temperature furnace with a special structure, and uses airflow to blow away the nano-powder material that needs high-temperature sintering in the furnace body to achieve sufficient separation between particles, which can improve the crystal structure of nano-powder particles through high-temperature sintering, At the same time, the problem of particle growth during sintering can be avoided. The designed furnace body includes a furnace body part, an inner tank part and a sealing device. It is characterized in that: the furnace body adopts a vertical style, the bottom of the furnace can be sealed and insulated, and the upper end of the furnace is open to facilitate the insertion of the ventilated liner. The furnace body can be heated by electric furnace wire, silicon carbide rod or silicon molybdenum rod, and the temperature can be measured by thermocouple. Control equipment, wherein the control equipment includes a manual control device and an automatic control device, which are used to adjust the transmittance of the glass and automatically generate heat. The vented atmosphere liner has an asymmetric U-shaped structure, the reaction gas is passed in from the upper end, the powder to be sintered is blown away from the bottom, and the gas flows out from the other end. The two ends of the liner can be connected with a sealing device to isolate the air and allow special reaction gas or protective gas to be introduced. The invention blows the ultra-fine nano-powder inside the furnace body through the air flow, avoiding the long-term contact between the particles during sintering, which leads to the growth of the particles at high temperature, thereby preventing the growth of the particle size while improving the crystal structure. Obtain high-quality ultrafine nano-powder materials. The device is not only suitable for the preparation of nanometer materials in the laboratory, but also can be used in industrial production to prepare high-quality ultrafine nanometer powder products.

The present invention provides a simple and practical idea and implementation method for the sintering preparation of ultrafine nano-powder materials. For personnel, under the premise of not departing from the principle of the present invention, some improvements can also be made, such as the shape of the inner tank and the body of the furnace can be further improved, and a single gas path can be improved into multiple gas paths, etc. These improvements also It should be regarded as the protection scope of the present invention.

Claims (3)

1. A method for preparing ultra-fine nano-powder through airflow, characterized in that the method is used in an ultra-fine nano-powder calciner, and the method utilizes air-flow to blow away the nano-powder material that needs high-temperature sintering in the body of furnace to realize particle The sufficient separation between the particles prevents the particles from growing due to the long-term contact between the particles during the high-temperature sintering process, which specifically includes the following steps: a. The nano-powder material that needs to be sintered at high temperature is placed at the bottom of the furnace liner; b. Introduce gas from the air inlet, control the airflow rate, and make it fully dispersed in the furnace body under the interaction of airflow buoyancy and powder particle gravity; c. Fully dispersed nano powder samples are sintered at high temperature to achieve sufficient crystallization; d. The gas passed in flows out from the gas outlet. 2. the method for preparing ultra-fine nano-powder by ventilating flow according to claim 1, is characterized in that, furnace body heating adopts electric furnace wire, silicon carbon rod or silicon molybdenum rod, adopts thermocouple to measure temperature, utilizes temperature controller to control temperature. 3. the method for preparing ultra-fine nano-powder by ventilation flow according to claim 1, is characterized in that, the gas inlet and the gas outlet at both ends of the inner bag are respectively connected with sealing devices to isolate the air.