Control of heating rate in each stage of carbon material graphitization process

The graphitization process of carbon materials is a complex temperature control process, in which the control of heating rate has a crucial impact on the quality and performance of products. Generally speaking, the graphitization process can be roughly divided into three stages: repeated roasting stage, strictly controlled heating stage, and free heating stage. The following will discuss in detail the control methods of heating rate in these three stages.

1、 Repeated roasting stage (room temperature to 1250 ° C)

During the repeated roasting stage, the carbon material gradually heats up from room temperature to 1250 ° C. The heating rate in this stage is usually fast, with the aim of completing the preheating transition phase of carbon materials in the early stage of graphitization. Specifically, the carbon billet that has been roasted at around 1250 ° C already has certain thermoelectric and heat-resistant impact properties, so a faster heating rate can be adopted. For example, in some graphitization furnaces, the initial heating rate can reach 30-40 ° C/h, then gradually increase, and finally reach 70-80 ° C/h.

2、 Strictly control the heating stage (1250 ° C to 1800 ° C)

The strict control of temperature rise stage is a crucial stage in the graphitization process, with a temperature range of 1250 ° C to 1800 ° C. At this stage, the physical structure and chemical composition of carbon materials undergo significant changes, and the disordered layer structure of amorphous carbon gradually transforms into graphite crystal structure. At the same time, accompanied by the decomposition and escape of unstable low molecular weight hydrocarbons and impurity element groups, structural defects are generated and thermal stress is relatively concentrated. In order to reduce the effect of thermal stress, prevent the generation of cracks, and maintain a certain temperature maintenance time, it is necessary to strictly control the heating rate during this stage.

At this stage, the heating rate is usually controlled between 30-50 ° C/h. The selection of this speed is to ensure that carbon materials can be fully transformed during the graphitization process, while avoiding thermal stress concentration and crack generation caused by rapid heating. In fact, the temperature rise in this stage is the least easy to control, which is also the main reason why the curve used in practice is much more conservative than the calculated curve.

3、 Free heating stage (1800 ° C to maximum graphitization temperature)

During the free heating stage, the temperature continues to rise from 1800 ° C to the highest temperature for graphitization. At this stage, the graphite crystal structure of carbon materials has basically formed, and further heating is mainly aimed at further improving their graphitization degree. Due to the fact that the degree of perfection of graphite crystals mainly depends on the highest temperature, and the influence of holding time is already very small, the heating rate at this stage can be accelerated.

However, it should be noted that although the heating rate can be accelerated, it is difficult to increase the actual heating rate due to the increased heat loss at high temperatures. Therefore, in practical operation, it is necessary to flexibly adjust the heating rate and insulation time according to specific situations to ensure the smooth progress of the graphitization process and the stability of product quality.

In summary, controlling the heating rate at each stage of the graphitization process of carbon materials is the key to ensuring product quality and performance. By reasonably controlling the heating rate and holding time, efficient conversion of carbon materials to graphite can be achieved and excellent product performance can be achieved.