Chemical Formula:Zn
Molecular Weight:65.38
Properties:
Zinc is a bluish-white metal with a hexagonal close-packed crystal structure. It has a melting point of 419.58°C, a boiling point of 907°C, a Mohs hardness of 2.5, an electrical resistivity of 0.02 Ω·mm²/m, and a density of 7.14 g/cm³.
Zinc dust pigments come in two particle structures: spherical and flake-like. Flake-like zinc dust has greater covering power.
Chemically, zinc dust is quite reactive. In normal atmospheric conditions, it forms a thin, dense layer of basic zinc carbonate on its surface, which prevents further oxidation, making it highly corrosion-resistant in the atmosphere. However, it is not resistant to corrosion in acidic or alkaline salts. It dissolves in inorganic acids, bases, and acetic acid but is insoluble in water.
Zinc dust burns with a bright white flame in pure oxygen but is difficult to ignite in normal air, so it is not classified as a flammable solid. In normal environments, zinc dust reacts with moisture or water to produce hydrogen gas, but the rate of hydrogen production is relatively slow, far less than 1 L/(kg·h). Therefore, zinc dust is not classified as a substance that produces flammable gases upon contact with water. However, for safer storage and transportation, it is advisable to treat it as a Class 4.3 hazardous material (substances that are dangerous when wet). Currently, regulations on the storage and transportation of zinc powder vary across different regions in China, with some being more lenient and others more stringent.
Zinc dust can explode in air, a process involving gas-phase combustion. For example, micron-sized zinc dust has an optimal ignition delay time of 180 ms, with an explosion limit of 1500–2000 g/m³. At a concentration of 5000 g/m³, it reaches maximum explosion pressure, maximum explosion pressure rise rate, and maximum explosion index, which are 0.481 MPa, 46.67 MPa/s, and 12.67 MPa·m/s, respectively. The explosion hazard level of micron-sized zinc powder is classified as St1, indicating a relatively low explosion risk.
Production Methods:
1. Upstream—Zinc Ore Smelting:
China has abundant zinc ore resources, accounting for nearly 20% of global reserves, second only to Australia. China is also a major producer of zinc ore, contributing over one-third of global production, ranking first worldwide. The smelting process involves refining zinc ore to obtain zinc sulfide concentrate, which is then reduced to pure zinc through pyrometallurgical or hydrometallurgical processes, resulting in zinc ingots.
In 2022, China’s zinc ingot production reached 6.72 million tons. The cost of zinc ingots ultimately determines the price of spherical zinc powder, which can be estimated at 1.15–1.2 times the price of zinc ingots.
2. Zinc Dust—Atomization Method:**
High-purity (99.5%) zinc ingots are heated to 400–600°C in a reverberatory or rotary furnace until molten. The molten zinc is then transferred to a refractory crucible and atomized under heated and insulated conditions, with compressed air at a pressure of 0.3–0.6 MPa. The atomized zinc powder is collected in a dust collector and then passed through a multi-layer vibrating sieve to separate it into different particle sizes before packaging.
3. Zinc Dust—Ball Milling Method:**
This method can be either dry or wet, producing dry flake zinc dust or paste-like flake zinc dust. For example, wet ball milling can produce paste-like flake zinc dust slurry. Atomized zinc powder is mixed with aliphatic hydrocarbon solvents and a small amount of lubricant in a ball mill. Once the desired fineness and flake structure are achieved, the slurry is filtered to form a filter cake with over 90% zinc content. The filter cake is then mixed to produce zinc dust slurry for coatings, with a metal content of over 90%.
Uses:
Zinc dust is primarily used in the coatings industry, such as in organic and inorganic zinc-rich anti-corrosion coatings. It is also used in dyes, metallurgy, chemicals, and pharmaceuticals. The coatings industry accounts for about 60% of zinc powder demand, followed by the chemical industry (28%) and the pharmaceutical industry (4%).
Spherical zinc dust consists of nearly spherical particles, including standard zinc dust and ultra-fine high-activity zinc dust. The latter has higher zinc content, lower impurities, smooth spherical particles, good activity, minimal surface oxidation, narrow particle size distribution, and excellent dispersibility, making it a high-performance product. Ultra-fine high-activity zinc dust is widely used in coatings and anti-corrosion applications, particularly in zinc-rich primers or directly applied to anti-corrosion coatings. In coatings, zinc dust with a particle size of less than 28 μm is commonly used. High-performance ultra-fine zinc dust saves resources, improves utilization efficiency, and enhances coating anti-corrosion performance, offering broad market prospects.
Flake zinc dust has a flake-like structure and is produced by ball milling or physical vapor deposition (PVD). It has a high aspect ratio (30–100), excellent spreading, covering, and shielding properties, and is mainly used in DACROMET coatings (zinc-aluminum coatings). Flake zinc dust offers better coverage, floating ability, bridging ability, shielding ability, and metallic luster compared to spherical zinc powder. In DACROMET coatings, flake zinc dust spreads horizontally, forming multiple parallel layers with face-to-face contact, improving conductivity between the zinc and the metal substrate and among zinc particles. This results in a denser coating, extended corrosion pathways, optimized zinc consumption and coating thickness, and enhanced shielding and anti-corrosion properties. Anti-corrosion coatings made with flake zinc dust exhibit significantly better salt spray resistance than electroplated or hot-dip galvanized coatings, with lower pollution levels, meeting environmental protection requirements.
Post time: Feb-07-2025
