¿Cómo hacer grafito en polvo?

With the electrical conductivity, lubrication and high-temperature resistance, graphite powder is widely used in fields such as batteries. And its manufacturing process varies depending on the raw materials, which embodies material and industrial technological innovation. It includes the purification of natural graphite, the synthesis and transformation of artificial graphite, and the preparation of new nano-scale graphite.

Raw Materials for Graphite Powder Manufacturing

Grafito natural

Grafito natural exists in mineral form in geological structures such as gneiss and schist. The distribution of its resources is regional and according to its crystal form, it can be classified as:

Grafito en escamas

The crystals are arranged in layers and their diameters range from a few micrometers to several millimeters. Because of the high purity and good electrical conductivity, you can use it as anode materials for high-end batteries and flexible electronic materials.

Earthy graphite

The crystal structure is disordered, which is also known as “cryptocrystalline graphite”. You need to enhance its performance through deep purification. And it is widely used in refractory materials, casting coatings and other fields.

Raw Materials for Artificial Graphite

The core raw material of artificial graphite is a carbon-containing solid, commonly including:

Coque de petróleo

This is a by-product of petroleum refining, whose carbon content exceeds 90%. After calcination, it becomes a graphitization precursor and is the main raw material for the negative electrode of lithium batteries.

Asphalt

It is divided into coal tar pitch and petroleum pitch, which are used as binders and carbon sources. And they are carbonized at high temperatures to form a graphite layered structure.

Coca-Cola

It is a product of coal dry distillation, with low cost but more impurities. And it is suitable for medium and low-end scenarios such as refractory materials.

Negro de humo

You can use it as an auxiliary material in some special processes to regulate the pore structure.

Manufacturing Process of Natural Graphite Powder

Primary Processing

Crushing and Grinding

You should crush natural graphite ore to the millimeter level using equipment such as jaw crushers and cone crushers. And then ground it to the micron-level particles by ball mills, Raymond mills, etc. During the grinding process, you need to control the particle size distribution  to avoid damage to the crystal structure caused by overgrinding.

Classification and Screening

Classify the particles by particle size using equipment such as vibrating screens and air flow classifiers. And return the coarse particles for re-grinding, while fine particles enter the purification process. The air classification method can precisely control the particle size within the range of 1 to 100μm, which meets the requirements of different applications.

Purification Treatment

Método de flotación

This method takes advantage of the difference in hydrophobicity between graphite and hydrophilicity of gangue minerals. First add the collectors such as kerosene and turpentine oil, as well as foaming agents. Then through a flotation machine, graphite particles are made to adhere to air bubbles and float up. Thus achieving separation from impurities such as quartz and feldspar and the purity can reach 85%-95%.

Alkali-Acid method

Alkali melting

You should mix the graphite and sodium hydroxide in proportion and melt them at 500-700℃. After that, the impurities (such as SiO2) are transformed into soluble silicates.

Acidification

After cooling, add hydrochloric acid or sulfuric acid to dissolve the silicate. And through washing and drying, the purity can reach over 98%, used for medium and high-end battery materials.

High-temperature Method

Place the graphite powder in an inert atmosphere furnace at a high temperature of 2500-3000℃. During this process, impurities (such as boron and aluminium) volatilize in gaseous form, with a purity of over 99.9%. You can use it in high-end fields such as semiconductors and nuclear industries, but the energy consumption is relatively high.

Raw Material Pretreatment

Calcination of petroleum coke

As a key raw material for artificial graphite powder, raw coke contains hydrocarbon compounds and moisture, which needs to be calcined. You should place it in a tank calcination furnace or rotary kiln at 1200-1400℃ to allow the volatile components to escape. This process can increase the carbon content, enhance the density, strength and electrical conductivity, and reduce impurities.

Asphalt kneading

After calcination, you need to mix the petroleum coke with coal tar pitch in proportion. Then put the mixture in a powerful kneader and stir and knead it at a specific temperature to form a mixture with good plasticity. Its viscosity and plasticity are precisely controlled, which can meet the requirements of the molding process. ​

Forming and Heat Treatment

Forming Process

There are three common methods: extrusion molding, compression molding and isostatic pressing. Extrusion molding extrudes the blank through a die, which is suitable for continuous production. Compression molding involves applying pressure in a mold to form products such as cylinders and sheets. Isostatic pressing is a process of isotropic compression under high pressure to increase density, which is used for high-performance products.​

Carbonization process

Slowly heat in an inert gas to 800-1200℃ to carbonize the binder and form an initial carbon structure. Then the organic matter decomposes to produce carbon and volatile gases, forming a pore structure, which affects the performance of the final product. ​

Graphitization process

At high temperatures of 2000-3000℃, the amorphous carbon in the carbonized green body is rearranged into hexagonal lattice graphite crystals. This significantly enhances key properties such as electrical conductivity, lubricity, and high-temperature resistance. ​

Post-processing

Crushing and Grinding

Graphite blocks were crushed by using equipment such as ball mills, vibration mills and jet mills to obtain different particle sizes.

Grading and Packaging

Classify the crushed graphite powder and produce different products according to the particle size specifications. After passing the quality inspection, it is packed in plastic woven bags, paper bags or sealed drums. It ensures that transportation and storage are not contaminated.

New graphite powder preparation technology

Preparation of Nano-Graphite Powder

5.1.1 Chemical Vapor Deposition

The CVD method uses methane and other gaseous carbon sources to form nano-graphite layers. This process requires the decomposition and deposition of the carbon source on the substrate at 800-1200℃ and under the action of a catalyst. The product has the high purity, which is suitable for the high-end electronic field, but the efficiency is low.

5.1.2 Ultrasound-assisted liquid-phase exfoliation method

This is to disperse natural graphite in solvents such as NMP, break the interlayer forces of graphite, and peel off to obtain nano-powder. The process is simple and features low energy consumption, allowing for mass production, suitable for scenarios with low uniformity requirements.

Manufacturing of Composite Graphite Powder

Composite process with metals and polymers

Metal composite

Powder metallurgy mixed sintering, then it has the lubrication and metal strength, which is used for self-lubricating components.

Polymer compounding

When graphite powder is compounded with polymers, the commonly used methods include solution blending and melt blending. It has electrical and thermal conductivity, which is used in industrial products that conduct electricity and heat.

Quality Control and Environmental Protection Measures in the Manufacturing Process

Inspección de calidad

The final finished product needs to be tested for properties such as particle size, purity and electrical conductivity. And appearance defects should be analyzed with instruments to ensure that the finished product meets the standards.

Environmental Protection Treatment

After manufacturing graphite powder, you need to carry out environmental protection treatment to prevent air pollution, water pollution, etc. For example, you can neutralize, settle and filter the wastewater to purify it. And remove the dust and harmful gases by using bag filters, electrostatic precipitators and scrubbers to reduce environmental impact.

Conclusión

The production of graphite powder requires the selection of processes based on the characteristics of raw materials. Natural graphite focuses on purification, artificial graphite emphasizes graphitization, and new technologies promote nanoscale and composite processes. Meanwhile, you need to take into account both quality control and environmental protection requirements.