1.What is graphite
Graphite is an important non-metallic mineral resource and an allotrope of carbon.
The molecular formula of graphite is C and the molecular weight is 12.01. Natural graphite is iron black or steel gray, with bright black streaks, metallic luster, and opaque. The crystal belongs to the complex hexagonal bipyramidal crystal type. Common single forms include parallel bifaces, hexagonal bipyramids, and hexagonal columns, but intact crystal forms are rare and are generally scaly or plate-like.
Graphite is an allotrope of elemental carbon (other allotropes include diamond, carbon 60, carbon nanotubes and graphene). Each carbon atom is connected to three other carbon atoms (arranged in a honeycomb-like hexagon) by covalent bonds to form a covalent molecule. Since each carbon atom releases an electron, those electrons can move freely, so graphite is a conductor. The cleavage plane is mainly composed of molecular bonds, which have weak attraction to molecules, so it has good natural floatability. In view of the special bonding method of graphite, it cannot be simply considered that graphite is a single crystal or a polycrystal. It is now generally believed that graphite is a mixed crystal.
2.Graphite classification
1.According to the crystal form and process characteristics of graphite, natural graphite is divided into three categories: According to the Chinese Pharmacopoeia, it is crucial to conduct research on the effectiveness of crystalline drugs. Commonly used detection methods include:
(1) Dense crystalline graphite
Dense crystalline graphite is also called block graphite. This type of graphite has obvious crystals and the crystals are visible. The particle diameter is greater than 0.1 mm, the specific surface area range is concentrated in the range of 0.1-1m2/g, the crystals are arranged in a disorderly manner, and have a dense block structure. This type of graphite ore has a high grade, generally with a carbon content of 60-65%, sometimes up to 80-98%, but its plasticity and slipperiness are not as good as flake graphite.
(2)Flake graphite
Flake graphite crystals are in the form of flakes; they are metamorphosed under high temperature and high pressure, and are divided into large flakes and fine flakes. The grade of this type of graphite ore is not high, generally between 2-3%, or 10-25%. It is one of the best floatable ores in nature. After multiple grinding and selection, high-grade graphite concentrate can be obtained. According to the fixed carbon content, it is divided into four categories: high-purity graphite, high-carbon graphite, medium-carbon graphite, and low-carbon graphite. This type of graphite has superior floatability, lubricity, and plasticity than other types of graphite, so it has the greatest industrial value.
(3) Cryptocrystalline graphite
Cryptocrystalline graphite is also called microcrystalline graphite or earthy graphite. The crystal diameter of this graphite is generally less than 1 micron, and the specific surface area ranges from 1 to 5 m2/g. It is an aggregate of microcrystalline graphite, and the crystal shape can only be seen under an electron microscope. This type of graphite is characterized by an earthy surface, lack of luster, and slightly worse lubricity than flake graphite. It has a higher grade, generally with a fixed carbon content of 60 to 85%. A few are as high as 90% or more. It is generally used in the foundry industry. It is mainly found in Lutang, Chenzhou city, Hunan Province. With the improvement of graphite purification technology, the application of earthy graphite will become more extensive.
2.Artificial graphite (special graphite) can be divided into the following according to the molding method:
(1) Isostatic graphite (three-high graphite), but not all three-high graphite is isostatic;
(2) Molded graphite;
(3) Extruded graphite, mostly electrode materials.
3.Application of graphite
Graphite has unique physical and chemical properties such as high temperature resistance, corrosion resistance, thermal shock resistance, high strength, good toughness, high self-lubricating strength, thermal conductivity, electrical conductivity, plasticity, and coating properties. It is widely used in metallurgy, machinery, electronics, batteries, diamond superhard materials, nuclear industry, chemical industry, light industry, military industry, national defense, aerospace and refractory materials and other industries. It is an indispensable non-metallic material for the development of modern high-tech.
4. XRF fluorescence analysis of sulfur content in graphite
Sulfur content is an important indicator for evaluating the quality of graphite and its graphite products. The sulfur content directly affects the price of graphite products and even affects its product performance. Therefore, it is very important to quickly and accurately determine the sulfur content in graphite and its graphite products.
In China's current standard system, the main methods for determining sulfur content in graphite and its products are combustion iodine titration, Eschka gravimetry and high-temperature combustion neutralization titration. Although the combustion iodine titration and Eschka gravimetry are widely used, they have many detection steps and cumbersome analysis processes, which can easily lead to large deviations in the test results; the high-temperature combustion neutralization method is easy to operate, but the precision and accuracy of the measurement results are poor. The X-ray fluorescence spectrometry method is easy to operate, has fast analysis speed, and has high precision and accuracy.
5.Application Case
ScopeX benchtop XRF analyzer from LANScientific is easy to operate and has flexible configuration. It is an ideal tool for fluorescence analysis of the S element content in graphite. When ScopeX was used to detect and analyze the S element content in two different levels (90%/99.5%) of graphite materials. The accuracy test results showed that the relative error of the sample was small and the repeatability test results were stable and reliable.
