A Study On Preparation Of Nanometer Powders Of Tungsten-based Materials

Tungsten-based materials play an important and unique role in defence and high-tech industries. Owing to the high melting point of tungsten, their applications rely on high temperature powder metallurgy processes. Therefore, refinement of their powders to ultrafine or nanometer size is valuable, as this will lower their sintering temperature and improve their properties.Nanometer tungsten powders, W-20%Cu (mass fraction) nanocomposite powders and nanometer tungsten nitride powders were synthesized from metal-salt solution by means of spray drying,calcination, milling,reduction in hydrogen or nitrogen treatment in pure ammonia. Phases, morphologies, particle size and distribution of agglomerated quadric particle size in each process were analysed and characterized by using XRD, SEM and Particle Sizer.The mainly conclusions in our research are as flowing: tungsten trioxide powders with 100 nm primary particle are obtained by spray drying,calcination and wet milling process, and an average size of quadric particle composed of agglomerated particles is 0.64 μm; tungtsen powders with 39 nm grain size and 60 -100 nm primary particle are produced directly from previous tungsten trioxide using one step reduction in hydrogen at 700℃, and an average size of quadric particle of tungsten powder is 2.91 μm; tungsten trioxide and copper tungstate compound powders with 100 nm - 200 nm primary particle are produced using ammonia metatungsten and copper nitrate as raw materials by spray drying,calcination and wet milling process;the compound powders are transformed completely into tungsten and copper compound powders by reduction in hydrogen at 700℃,in which tungsten grain size is 59 nm and copper grain size is 51 nm; primary particle size of compound powders is 80 - 120 nm,and an average size of agglomerated quadric particle is 1.86 μm; tungsten nitride powders with 35 nm grain size are prepared from tungsten trioxide powders by nitrogen treatment thoroughly in pure ammonia at 650℃, and an average size of agglomerated quadric particle is 0.64 μm in normal temperature. It is nitrogen treatment in pure ammonia that possessed merit such as more stable procedure and production,and simpler process than nitrogen treatment in mixture of hydrogen and nitrogen reported in document.