Different classifications of high-purity graphite

High-purity graphite is the most widely used basic material among artificial specialty graphites. The industry generally defines high-purity graphite as graphite with a fixed carbon content of ≥99.9% and an impurity content of less than 50 ppm. With its advantages such as extremely low ash content, high temperature resistance, balanced thermal and electrical conductivity, and chemical stability, it has become a core consumable in the photovoltaic, non-ferrous metal smelting, semiconductor, and vacuum heat treatment industries. Many procurement processes focus only on purity when selecting graphite, neglecting density, particle size, and thermal shock resistance, leading to short-term cracking and flaking of products, significantly increasing production costs.

The production process of high-purity graphite is complex. Raw materials undergo mixing, molding, multiple calcinations, high-temperature graphitization, and purification treatment to ultimately remove harmful impurities such as silicon, iron, and calcium.

Based on the molding process, high-purity graphite is classified into three main categories: molded high-purity graphite, extruded high-purity graphite, and isostatically pressed high-purity graphite. Molded high-purity graphite boasts high density and strength, making it suitable for machining precision small graphite parts; extruded graphite offers high cost-effectiveness and is suitable for long strips and rods; isostatically pressed high-purity graphite exhibits isotropy, making it the preferred choice for hot zones and single-crystal furnace applications. Key performance indicators determine service life: conventional high-purity graphite can withstand temperatures up to 2200℃ in an inert atmosphere, but in a vacuum environment, it is recommended to control the temperature below 1800℃; its density ranges from 1.75 to 1.85 g/cm³, with higher density resulting in better wear resistance; fine-grained materials offer high surface smoothness, reducing the likelihood of molten contamination, making fine-structure high-purity graphite essential for precious metal smelting and sapphire sintering.

Key points for practical selection and avoiding pitfalls: First, high-purity graphite is easily depleted in oxidizing environments and needs to be paired with an anti-oxidation coating; Second, do not blindly pursue ultra-high purity. 99.9% high-purity graphite is sufficient for ordinary aluminum alloy smelting, while 99.995% ultra-high purity is required for semiconductor crystal growth; Third, in high-temperature rapid cooling and heating conditions, prioritize materials with a lower coefficient of thermal expansion to reduce the risk of thermal shock cracking.

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