Plasma Spraying Process Flow

During plasma spraying, numerous process parameters influence the quality of the coating. The main ones include: ① Plasma gas: The selection of the gas is primarily based on availability and cost-effectiveness. Nitrogen (N2) is inexpensive and has a high enthalpy of ionization, resulting in rapid heat transfer that facilitates the heating and melting of powder particles. However, it is not suitable for powders or substrates that are prone to nitriding reactions. Argon (Ar) has a lower ionization potential, ensuring a stable plasma arc that is easy to ignite; its arc flame is relatively short, making it ideal for spraying small or thin components. In addition, Ar provides excellent shielding protection. Nevertheless, Ar has a lower enthalpy and is more expensive. The gas flow rate directly affects the enthalpy and velocity of the plasma jet, thereby influencing...

12-23

2019

Method for producing tungsten carbide

Using tungsten metal and carbon as raw materials, an average particle size of 3–5 μm tungsten powder is dry-mixed with an equal molar amount of carbon black using a ball mill. After thorough mixing, the mixture is pressed into shape and then placed in a graphite crucible. It is subsequently heated in a graphite resistance furnace or an induction furnace to a temperature ranging from 1400 to 1700°C, with the temperature carefully controlled between 1550 and 1650°C. In a hydrogen gas flow, W₂C is initially formed, and upon further reaction at high temperatures, WC is produced. Alternatively, tungsten powder can first be prepared by thermal decomposition of tungsten hexacarbonyl in a CO atmosphere at temperatures ranging from 650 to 1000°C. This tungsten powder is then reacted with carbon monoxide at 1150°C to yield WC; at temperatures higher than this, W₂C may form instead. The chemical reaction equations are as follows:

12-23

2019