High-temperature graphitization furnace's operating principle is mainly based on high-temperature heat treatment and graphitising process of carbon materials, through precise control of temperature, atmosphere and time and other parameters, to achieve the conversion of carbon materials to graphite. The following is a detailed analysis of the operating principle of high temperature graphitising furnace.

1. Basic principles of graphitisation

Graphitization is the process by which carbon materials are gradually transformed into graphite structures through pyrolysis, rearrangement and crystallisation at high temperatures. Graphite is a crystalline material consisting of carbon atoms arranged in a hexagonal layered structure with excellent electrical and thermal conductivity and chemical stability. The graphitising process of carbon materials mainly relies on thermal activation at high temperatures, whereby heat energy drives carbon atoms to rearrange themselves to form a regular layered structure.

During the graphitising process, carbon materials go through the following stages:

Pyrolysis stage: Carbon material undergoes pyrolysis at high temperature, non-carbon elements (such as hydrogen, oxygen, etc.) are removed and carbon atoms are gradually enriched.

Structural rearrangement stage: As the temperature rises, the carbon atoms begin to rearrange themselves to form a short-range ordered structure.

Crystallisation stage: At higher temperatures, the carbon atoms are further ordered to form a long-range ordered graphite crystal structure.

2. Composition of high-temperature graphitising furnace

High-temperature graphitising furnace usually consists of the following main parts:

Furnace body: The furnace body is the core part of the graphitising furnace, which is usually made of high-temperature-resistant materials (e.g. graphite, silicon carbide, etc.), and is able to withstand temperatures as high as 3,000°C or more. Inside the furnace body, there are heating and cooling zones designed to achieve uniform heating and rapid cooling.

Heating system: The heating system is the key component of the graphitising furnace, which usually adopts resistance heating or induction heating. Resistance heating heats the heating elements (e.g. graphite rods or graphite tubes) by energising them, while induction heating uses electromagnetic induction to generate eddy currents inside the material to generate heat.

Temperature Control System: The temperature control system is used to precisely control the temperature inside the furnace to ensure the stability and consistency of the graphitising process. The system typically consists of thermocouples, temperature controllers and feedback regulators.

Atmosphere Control System: The graphitising process usually needs to be carried out under inert gases (e.g. nitrogen, argon) or in a vacuum to prevent oxidation of the carbon material at high temperatures. The atmosphere control system is used to regulate the gas composition and pressure in the furnace.

Cooling system: The cooling system is used to quickly reduce the temperature in the furnace after the graphitising process, usually by means of water or air cooling.

3. The operating process of high-temperature graphitising furnace

The working process of high temperature graphitising furnace can be divided into the following steps:

Charging: Load the carbon material to be treated (e.g. carbon fiber, carbon/carbon composites, etc.) into the heating zone of the furnace to ensure uniform distribution of the material.

Heating up: Start the heating system and gradually increase the temperature in the furnace. The rate of heating needs to be controlled according to the characteristics of the material and process requirements, and usually adopts a segmented heating method to avoid material damage due to thermal stress.

Holding: When the temperature in the furnace reaches the set value (usually 2500℃~3000℃), hold it for a certain period of time (usually several hours), so that the carbon material is fully graphitised.

Cooling: After the graphitising process, the cooling system is activated to rapidly reduce the temperature inside the furnace. The cooling rate also needs to be controlled according to the material properties to avoid cracking of the material due to thermal stress.

Unloading: After the temperature inside the furnace has dropped to a safe range, the treated graphitised material is removed.

4. Key process parameters

The working effect of high temperature graphitising furnace mainly depends on the following key process parameters:

Temperature: Temperature is the core parameter of the graphitising process and directly affects the degree of graphitising and material properties. In general, the higher the graphitising temperature, the higher the degree of graphitization, but too high a temperature may lead to material evaporation or damage.

Rate of temperature increase: The rate of temperature increase affects the thermal stress and graphitising uniformity of the material. Too rapid a rate of heating may result in cracking or deformation of the material.

Holding time: The holding time determines the adequacy of the graphitising process. Too short a holding time may lead to incomplete graphitising, while too long a holding time may increase energy consumption.

Atmosphere: The atmosphere in the furnace has an important influence on the graphitising process. Inert gases or vacuum prevents oxidation of the carbon material, while certain gases (e.g. hydrogen) can facilitate the graphitising process.

5. Areas of application

High temperature graphitising furnaces have important applications in a number of fields:

Carbon fibers: graphitising polyacrylonitrile (PAN)-based carbon fibers or bitumen-based carbon fibers to improve their strength and modulus.

Carbon/Carbon Composites: High temperature resistant materials for aerospace applications, graphitised to improve thermal stability and mechanical properties.

Graphite Electrodes: Graphite electrodes used in electric arc furnace steelmaking need to be graphitised to improve their electrical conductivity and heat resistance.

Anode materials for lithium batteries: natural or artificial graphite is graphitised to improve its electrochemical properties.