History
Graphite is one of the most interesting elements found on the earth. It is found naturally in its mineral form as well as produced in synthetic processes. The earliest use of graphite dates back to primitive man, who used it to draw on cave walls. It was also used by Egyptians to decorate pottery. During the Middle Ages, graphite was used as a refractory to line molds for the purpose of making smoother cannon balls, which could be fired farther. Throughout history, graphite has been confused with other minerals, especially galena and molybdenum. Names like plumbago and black lead have been used to describe the mineral and over time, the term graphite (meaning “to write”) was finally used to describe this mineral.
Characteristics
Graphite is gray to black in color, opaque with a metallic luster. It is a fairly soft crystalline form of carbon with a Mohs hardness of 1 to 2. Stable and chemically inert at normal temperatures, graphite has a very high sublimation point, in the absence of air. In its pure form, it is odorless, tasteless and nontoxic. It has a hexagonal, multi-layer planar microstructure which gives it a number of unique characteristics, the sum of which is not found in any other single material. The layers are alternating and honeycomb in structure, and are spaced at 1.42 angstroms apart (strong bonds), with 3.354 angstroms between layers (weak bonds).
Fig. 01
Graphite Structure
This unique structure provides for specific characteristics such as:
- Chemical Inertness
- Electrical Conductivity
- Lubricity
- Thermal Conductivity
Graphites, including graphite powder form, also possess both Primary and Secondary Properties that make them valuable in many applications. As you can see below, the Primary Properties of Impurities, Graphitization, Particle Size Distribution, and Morphology in combination determine the Secondary Properties of Lubricity, Reactivity, Resiliency/Strength, and Conductivity.
Fig. 02
Properties of Graphite
Forms of Graphite & Carbons
The family of graphite materials includes natural graphite types, such as amorphous graphite, crystalline flake and vein graphites, and synthetic (artificial) graphite, along with various purified or treated graphitic products. These materials are sourced from selected and qualified mines and sources from around the world, or are produced or treated in various, unique ways, including Electro-Thermal Treatment/Purification Technology created by Superior Graphite. The various forms of graphite are as follows:
Amorphous Graphite
This variety of graphite is typically formed by the metamorphism of coal beds or carbon rich sediments in association with igneous activity. It is generally a soft, darker black colored graphite, less reflective than other varieties of natural crystalline graphite. Commonly found as “microcrystalline” particles, this variety of graphite has a lower graphitic carbon level when compared to other naturally occurring crystalline graphite varieties.
Fig. 03
SEM of Amorphous Graphite
Crystalline Flake Graphite
Typically formed as flat plate–like particles, this variety of graphite is disseminated throughout layers of metamorphic rock, either in isolated pockets or more broadly distributed throughout the parent rock matrix. Generally, very brilliant in color, the size and thickness of the individual flakes can vary depending on the ore deposit. Unlike other varieties of natural crystalline graphite, flake needs to be mechanically/chemically processed or “upgraded” to reach the necessary carbon levels for industrial applications.
Fig. 04
SEM of Crystalline Flake Graphite
Crystalline Vein Graphite
This variety of graphite is typically found in fractures or fissures associated with metamorphic and/or igneous formations, hypothesized as being deposited in the vapor, or fluid state. Generally, a soft, very brilliant variety of natural crystalline graphite, it exhibits one of the highest degrees of crystallinity and in some formations, the most pure form of the natural crystalline graphite found. Vein can range from finer, needle–like grain to a more coarse massive lump.
Fig. 05
SEM of Crystalline Vein Graphite
Synthetic Graphite
Synthetic graphite, sometimes referred to as artificial graphite, is found in two forms: Primary Synthetic, and Secondary Synthetic. Primary Synthetic is produced through the high temperature treatment of specific coke precursors. Secondary Synthetic is the by-product of graphite electrode and part manufacturing. They have a dark gray to black, flat appearance. Manufactured from calcined cokes, and graphitized at temperatures approaching 3000°C, these materials offer high purity, excellent lubrication, and electrical conductivity.
Fig. 06
SEM of Synthetic Graphite
Purified/Heat Treated Graphites & Carbons
Various forms of graphites and carbons can be processed in our continuous Electro-Thermal Treatment/PurificationTechnology to produce unique materials with unparalleled characteristics such as high purity, porosity, resiliency, lubricity, and electrical and thermal conductivity. These materials can be customized for specific applications upon request.
Fig. 07
SEM of Purified/Heat Treated Graphites
Please contact us if you’d like to receive more information about graphite innovation.
