Heat treatment is a crucial basic technology in the machinery industry and modern manufacturing. N₂ is used to protect materials during heat treatment, preventing metal oxidation. It serves as the atmosphere in controlled - atmosphere furnaces, a purging gas in vacuum annealing furnaces, a cooling gas for high - pressure gas quenching, and a backfill gas during heating. For the heat treatment industry, N₂ typically requires a purity of 99.99% - 99.999%.

Powder metallurgy is an industrial technique using metal powder as raw material, shaping and sintering to make metal materials, composites and various products. Typical items include powder metallurgy parts (bearings, gears), cemented carbide tools, etc. Widely applied in machinery, electronics, aerospace, etc., it's a dynamic branch of new material science. In this industry, N₂ serves for spray powder production, powder conveying and sintering protection, with a general purity demand of 99.999%.

Lithium-ion batteries usually have lithium alloy metal oxides as the cathode material, graphite as the anode, and a non-aqueous electrolyte. Praised as the "green energy of the 21st century", they feature high energy density, low self-discharge, long life and environmental friendliness. Their applications are diverse, covering energy storage, power, consumer goods and specialties. In the lithium battery industry, N₂ is used for sintering protection and powder processing of cathode and anode materials (purity requirement: 99.999%) and for cell production like liquid injection and baking (purity requirement: 99.99% - 99.999%).

SMT is short for Surface Mount Technology. In it, Surface Mount Devices (SMD) are fixed on the surface of a Printed Circuit Board (PCB) for soldering, and SMD assembly can be automated. After component placement, reflow soldering ovens are used for soldering. SMT's exponential growth meets the demands of complex PCB systems and mass production of electronics. As IC and SMD devices miniaturize, SMT dominates PCB manufacturing. In the SMT industry, N₂ protects SMD during soldering like reflow and wave soldering, with a purity of 99.99% - 99.999%.

Chemical fibers are textile - grade fibers produced from natural or synthetic polymers via processes like dope preparation, spinning and post - treatment. Polymer materials, with unique properties, serve various applications. The three major high - performance fibers globally are carbon fiber, aramid fiber and UHMWPE. In the chemical fiber industry, N₂ with 99.999% purity protects during raw silk production.