Ultrafine Tungsten Powder Oxidation and Spontaneous Combustion Solution

Generally speaking, ultrafine tungsten powder refers to powder with average particle size less than 1μm, which can be divided into three levels: submicron tungsten powder (<1μm), ultrafine tungsten powder (<0.5μm) and nanometre tungsten powder (<1μm).

So small the size of ultrafine powder is, that the number of surface atoms and surface energy increase sharply, resulting in surface effects, small size effects and quantum effects which are invisible to macroscopic objects. Therefore, ultrafine tungsten powder, especially ultrafine tungsten powder less than 0.5μm, is easy to be oxidized when exposed to the air and is prone to spontaneous combustion when subjected to friction or mechanical vibration.

In the process of hydrogen reduction, the passivation measures of air separation and surface energy lowering to ultrafine tungsten powders should be taken, which is also the key to realize the industrialization of producing superfine tungsten powder. Currently, there are two main solutions to solve the problem of spontaneous combustion by hydrogen reduction.

1, Hydrogen aeration reduction
Hydrogen blows the water vapor from the furnace to the furnace tail with the water content in the atmosphere gradually increasing. When ultrafine tungsten powder reaches the cooling zone, it has come into contact with the wet hydrogen. So, before it leaves the furnace its surface has been saturated with water vapor, forming a layer of protective film which can greatly reduce the surface energy of ultrafine tungsten powder.

2, Special atmosphere protection
Protect freshly baked ultrafine tungsten powder by keeping it in inert gas or other inert gas such as CO2, CH4, and N2. Before carbon handing, the air will be removed from the ball crusher by above gases.

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