Views: 4 Author: Site Editor Publish Time: 2022-09-09 Origin: Site
As the name implies, tungsten carbide is a compound composed of metallic tungsten and non-metallic carbon, with the molecular formula of WC. Due to its special crystal structure, tungsten carbide has extremely novel physical and chemical properties and is widely used in manufacturing industry.
WC is a black hexagonal crystal with metallic luster, molecular weight of 195.85, melting point of 2870 ℃, boiling point of 6000 ℃, density of 15.63 g/cm, microhardness of 17300 MPa, elastic modulus of 710GPa, compressive strength of 56MP. The thermal expansion coefficient is 6.9×10-6/K, with good electrical and thermal conductivity, insoluble in cold water, good acid resistance and other advantages, but easily soluble in nitric acid and hydrofluoric acid mixed acid and aqua regia, and easy to be reduced, that is, in air above 500℃ will start active oxidation.
As one of the most important raw materials for the production of cemented carbide, tungsten carbide (WC) powder particle morphology, size, particle size distribution range and impurity content and other performance indicators will directly affect the quality and use of cemented carbide. According to the different particle size, WC powder can be divided into ultra-coarse WC, micron WC, sub-micron WC, sub-nano WC and nano WC, etc. Compared with other sizes of WC powder, what are the advantages and disadvantages of sub-micron WC particles?
From the point of physical and chemical properties, the appearance of the WC for black powder particles, melting point 2870 ℃, boiling point is about 6000 ℃, insoluble in water, hydrochloric acid and sulphuric acid, but soluble in acid mixture of nitric acid, hydrofluoric acid, there are similar to diamond hardness, good conductive thermal conductivity, low thermal expansion coefficient, high elastic modulus and compressive strength, etc.
It is worth noting that the particle size of sub-micron WC powder is between micron and sub-nanometer, that is, between 100nm and 1.0μm, so it will not be as easy to agglomerate as sub-nanometer WC under certain circumstances, that is, it will have better dispersion performance. At the same time, it does not need longer ball milling time like micron WC, which is more conducive to the preparation of sub-microcrystalline cemented carbide. But it is not suitable for use in 3D printing technology because the particles are too large and the resulting product is relatively coarse.
Production of WC
With tungsten and carbon as raw materials, with a ball mill dry mixing, after pressure molding into graphite disk, and then heated to 1400 ~ 1700℃, in the hydrogen environment, Mr. W2C, and continue at high temperature can be generated WC.
Tungsten carbide is mainly used to make hard alloy, but according to the different uses of the alloy, the WC particles used are not the same. Ultrafine WC particles are used in finishing alloy. Coarse alloy using medium particle WC; Medium and coarse WC particles are used in gravity cutting and heavy cutting alloys; Coarse particle or medium particle WC is used as the mining tool; When its wear resistance, compression resistance and surface finish are emphasized, ultrafine and subfine medium particle WC is used. WC can not only be used to produce hard alloy, but also be a good additive for aerospace cables.
From the point of production process, submicron WC powder is ammonium tungstate solution as raw material, macromolecule surfactant as dispersant and alcohols or ketones improved dispersion, using rapid crystallization of spray drying, dry, for fine particles in the hollow thin wall spherical ammonium tungstate crystals, then through pyrolysis, hydrogen reduction and carbonization, generated in situ.
From the point of use, sub-micron tungsten carbide powder is mainly used to produce hard alloy, super hard cutting tool, jet engine parts and kiln structure parts.
Storage of WC
WC should be stored in a cool and dry warehouse to prevent rain or exposure. At the same time, it should be noted that the packaging containers should be intact during transportation.