Ultrafine nickel powder generally refers to nickel metal with a particle size of less than 1 μm. There are four main methods for its preparation: chemical vapor deposition (CVD), physical vapor deposition (PVD), atomization drying, and liquid phase reduction.

Chemical Vapor Deposition (CVD):

Chemical vapor deposition (CVD) is also known as vapor-phase hydrogen reduction. It involves reducing gaseous metal halides with hydrogen and is one of the methods used to produce ultrafine nickel powder for multilayer ceramic capacitors (MLCC). In this process, nickel chloride is evaporated at high temperatures, then reduced to elemental nickel atoms in a hydrogen atmosphere. The atoms subsequently nucleate, grow, and condense into ultra-fine nickel powder. The nickel powder produced by this method is generally ultra-fine nickel powder and can be produced at a relatively low cost with uniformly sized spherical particles of metallic nickel powder.

Physical Vapor Deposition (PVD):

Physical Vapor Deposition (PVD) is a preparation technique that utilizes vacuum environments to vaporize and condense metals into ultra-fine powders. Its core principle involves: in high-vacuum or inert atmospheres, metal nickel atoms are detached from solid surfaces via high-temperature evaporation, sputtering, or arc discharge, entering the gas phase. These atoms then condense into nanoparticles ranging from nanometer to submicron sizes in low-temperature regions. It offers advantages such as controllable particle size and morphology, high purity and low defects, clean surfaces requiring no post-processing, and environmental friendliness. However, it also has drawbacks, including susceptibility to oxidation, complex equipment, high technical requirements, and high costs.

Atomization Drying:

The atomization method for producing ultrafine nickel powder is a typical physical preparation process, which mainly consists of three stages: melting, atomization, and cooling. The advantages of this method are its simplicity, low cost, and suitability for large-scale production (with a single batch yield of up to tons). However, the powder has a wide particle size distribution and is prone to surface oxidation (requiring subsequent reduction treatment). It is mainly used in mid- to low-end MLCC, metal injection molding (MIM), and thermal spray coating applications.

Liquid Phase Reduction:

The liquid-phase chemical reduction method for preparing ultrafine nickel powder is a process based on solution chemical reactions, typically involving the following steps: using nickel salts as precursors, dissolving them in water or organic solvents to form a uniform solution, then adding a strong reducing agent, and converting nickel ions into metallic nickel particles through a reduction reaction under alkaline conditions. During the reaction, temperature must be precisely controlled (50–90°C), and surfactants are added to prevent agglomeration of nanoparticles. The final product is obtained through centrifugation, ethanol washing, and vacuum drying, yielding nickel powder with particle sizes ranging from 50 to 200 nm. This method is simple to operate, cost-effective, and scalable. However, residual reducing agents may affect purity (typically ≤99.5%), necessitating subsequent acid washing or heat treatment for purification. It is primarily applied in mid-range MLCC electrodes, catalysts, and conductive pastes.