What is Isostatic Graphite?
Apr 28, 2025
Introduction
As a professional graphite & carbon materials expert, SHJ-CARBON understands the role isostatic graphite plays in industries. isostatic graphite, developed in the 1960s, is an advanced material with widespread applications, even though it is not always noticeable in everyday life. For example, mobile phone chips rely on isostatic graphite for heat dissipation; rocket engines depend on it as a thermal protection layer, withstanding extreme temperatures of up to 3000°C; and even in nuclear reactors, key components like control rods are made from isostatic graphite. This seemingly obscure material supports cutting-edge technologies across many industries. Let's explore what is isostatic graphite and how to use it in your projects.
What is Isostatic Graphite?
Before introduce isostatic graphite, it's essential to understand specialty graphite. Specialty graphite refers to graphite materials with a carbon content greater than 99.99%, characterized by high strength, high density, and high purity. isostatic graphite is a type of specialty graphite formed through the isostatic pressing process.
In the isostatic pressing process, uniform liquid or gas pressure is applied, ensuring the graphite's high density, homogeneous structure, and excellent strength and isotropic properties. Simply put, regardless of the size, shape, or sampling direction of the graphite, its performance remains consistent. This makes isostatic graphite an ideal material for high-tech manufacturing and extreme environments. Consequently, isostatic graphite is referred to as Isotropic Graphite in the industry. In the following sections, we will show the isostatic graphite manufacturing process, - let you exactly understand what gives it those qualities.
Manufacturing Process of Isostatic Graphite
The production of isostatic graphite involves several steps, including raw material crushing, sieving, milling, binder melting, mixing, molding, baking, impregnation, and graphitization. Each step directly influences the final product's quality and performance.
Products Description
The material for isostatic graphite is needle petroleum coke, which has low sulfur, ash, and volatile content. Graphite products made from needle petroleum coke typically feature higher graphitization levels, lower electrical resistance, and better surface lubricity. Petroleum coke is produced by distilling crude oil and cracking heavy oils.
Its main elements include carbon, hydrogen, oxygen, nitrogen, sulfur, and various metal elements (such as Al, Fe, Ca, etc.). Since the raw petroleum coke particles are relatively large, they must first be crushed using airflow mills or other grinding equipment to produce fine particles suitable for producing isostatic graphite.
The common particle size used for production is 0.075mm, while ultra-fine particles are required to be smaller than 0.02mm. Airflow grinding technology ensures uniform particle distribution, which is crucial for achieving high-quality isostatic graphite.
Mixing & Kneading
Once the petroleum coke powder is purified and reaches the right particle size, it is mixed with a binder (like coal tar pitch, asphalt, or resin) in a specific ratio to create a smooth, uniform mixture. The quality of the binder and how well the mixture blends together are key factors that affect the final product. It's important to carefully control the temperature and kneading time to ensure the best results.
After kneading, the paste is rolled into thin sheets (1-3mm thick) using a calender, which helps the binder and coke powder stick together well. The paste is then ground into a fine powder, getting it ready for the next step-Isostatic Molding.
Isostatic Pressing
Isostatic pressing technology works based on Pascal's Law, which says that pressure applied inside a sealed container is evenly distributed in all directions. In this process, pressure is applied uniformly to the graphite raw material using a liquid or gas medium, ensuring consistent density and creating high-strength graphite products.
There are three types of isostatic pressing:
- Cold Isostatic Pressing (CIP),
- Warm Isostatic Pressing (WIP),
- Hot Isostatic Pressing (HIP).
Usually, carbon/graphite materials first undergo Cold Isostatic Pressing, followed by Hot Isostatic Pressing, along with baking and densification, to achieve the desired performance.
Baking and Impregnation
Baking is an important step in increasing the density of the graphite. During baking, to avoid cracking, the temperature increase must be controlled gradually. For small-sized graphite products, a square or round container made from heat-resistant materials is used for baking, and filler material is added to isolate and protect the product.
The impregnation process is used to increase the density of the graphite. Graphite products typically undergo 2-4 impregnation cycles, with baking required after each cycle to remove excess impurities. The choice of impregnation agent, temperature, pressure, and other parameters must be strictly controlled to ensure optimal impregnation results.
Graphitization and Purification
Graphitization is the process in which carbon products are subjected to high temperatures of 2000-3000°C to convert them into graphite. Carbon products have disordered atomic arrangements, whereas graphitized carbon atoms form ordered, layered structures. The graphitization process occurs in a graphitization furnace, where chlorine and fluorine gases are introduced to remove impurities and purify the material. The use of chlorides and fluorides helps volatilize the impurities into low-boiling chlorides and fluorides. This process must be carried out under strict safety and environmental protection conditions.
Features of Isostatic Graphite
By analyzing the production process of isostatic graphite, we can clearly grasp its superior performance in key indicators like thermal conductivity and flexural strength, especially its performance consistency, with differences less than 5% across different directions-fully achieving high-performance, isotropic properties.
Uniform Structure
Isostatic graphite uses a uniform pressure molding process, unlike traditional molding processes where particles are oriented in a specific direction. The random particle arrangement breaks the limitations of conventional molding technology, making the physical properties (such as thermal conductivity, electrical resistance, and mechanical strength) of isostatic graphite consistent in all directions, thus enhancing its isotropic characteristics.
High-Density Uniformity
Isostatic graphite features precise density control, with a density deviation of less than 0.02 g/cm³, far exceeding the 0.1 g/cm³ deviation of traditional molded products. This high density uniformity is achieved by strictly controlling the pressure distribution during the molding process, ensuring consistent physical properties across each piece of graphite. The high-density structure also provides enhanced thermal conductivity and mechanical stress resistance, making it suitable for high-precision, high-performance applications.
Precise Porosity Control
The porosity of isostatic graphite can be precisely controlled between 8%-15%, providing a solid foundation for subsequent impregnation and modification processes. The fine control over porosity ensures the graphite's compactness and stability, allowing for uniform impregnation, which optimizes the material's conductivity and high-temperature resistance.
Products Application
The excellent features make isostatic graphite an excellent choice for precision machining. Therefore, the special graphite materials are widely used in various industries due to their unique combination of thermal, mechanical, chemical, and physical properties, such as in the manufacturing of semiconductors, metallurgy, motors and more.
In the Semiconductor & Photovoltaic Industries
In the semiconductor and photovoltaic industries, isostatic graphite is essential due to its excellent isotropic properties, thermal conductivity, heat shock resistance, and high flexural strength. It helps reduce internal stresses caused by rapid heating and cooling, extending the lifespan of equipment. This makes isostatic graphite widely used in semiconductor silicon crystal growth equipment.
As the single crystal silicon production process advances, the size of graphite heat field components has increased, and the technical requirements have become stricter, particularly for graphite purity. isostatic graphite is used to make components like crucibles, heaters, electrodes, thermal shields, and seed crystal holders in the vertical single crystal silicon heat field. Recently, as the demand for larger single crystal silicon rods has increased, the size of graphite crucibles and heaters has also grown significantly, often reaching diameters of 800mm or more. This puts higher demands on the purity and performance of graphite components.
Single Crystal Pulling Furnace Heat Field Systems
Single crystal pulling furnaces are key in both the photovoltaic and semiconductor industries for growing single crystal silicon. While the equipment and processes are similar, the main difference lies in the purity requirements for the heat field materials. Photovoltaic silicon crystals typically need a purity of 99.9999999%, while semiconductor silicon crystals require even higher purity (99.999999999%). The ash content control for graphite is less strict in the photovoltaic industry, but extremely strict in the semiconductor industry.
Multicrystalline Casting Furnace Heat Field Systems
The multicrystalline casting furnace is critical in the photovoltaic industry for multicrystalline silicon casting. isostatic graphite is used to manufacture components such as top plates, heating elements, cover plates, and protective plates. These parts must have excellent high-temperature resistance and thermal conductivity to ensure the temperature inside the furnace is evenly distributed.
Electrical Discharge Machining (EDM)
Electrical discharge machining (EDM) is irreplaceable in modern manufacturing, especially for machining super-hard and high-temperature alloys. The electrodes used in EDM are often made from graphite or copper, with about 70% of the electrodes being graphite. isostatic graphite, as an electrode material, has several advantages over copper electrodes. It does not melt at high temperatures and maintains good strength. It also experiences less wear, has a faster machining speed, and maintains thermal stability during cutting, making it less likely to deform.
Additionally, isostatic graphite electrodes provide superior surface quality and dimensional accuracy, making them ideal for precision machining. As technology advances, EDM is moving toward more precise, smaller, faster, and environmentally friendly processes. This trend requires graphite electrodes to have finer particle structures and the ability to handle larger sizes. isostatic graphite will continue to grow in this field, especially for high-speed, low-wear precision machining applications.
Continuous Casting Industry Applications
In the continuous casting industry, the mold is one of the most crucial components of the casting process. isostatic graphite is widely used in the manufacturing of continuous casting molds due to its excellent high-temperature resistance, corrosion resistance, and thermal and electrical conductivity. Compared to metal molds, graphite molds offer several advantages, such as being resistant to erosion from liquid metals and having a low friction coefficient, reducing friction during casting and ensuring high-quality cast surfaces without additional machining.
Moreover, graphite molds have a longer lifespan and lower maintenance costs, making them commonly used in the continuous casting of metals like steel and aluminum alloys.
Conclusion
Isostatic graphite, with its excellent isotropic properties, thermal conductivity, high-temperature resistance, and mechanical strength, has become an essential material in many advanced manufacturing and technology sectors. From semiconductor and photovoltaic crystal silicon manufacturing heat field systems to EDM and continuous casting, isostatic graphite's wide applications and outstanding performance continue to drive progress in modern industries.
As technology evolves, the demand for isostatic graphite across industries will grow, especially for high-precision and efficient materials. If your business faces challenges with high-temperature, high-strength, and high-precision materials, isostatic graphite is the reliable solution you need.
To learn more about how isostatic graphite can benefit your industry or to getcustomized graphite solutions, contact our technical experts today. We are here to provide professional product support and technical consulting to help your business stand out in a competitive market.
