Study On Preparation Of Ultrafine Tungsten Powder By Micro-impinging Stream Reactor

Tungsten powder has attracted more and more attention because of its high melting point,corrosion resistance,low gas emission and high stability.It has been widely used in aerospace,national defense,electronic industry,mechanical manufacturing and etc.There are abundant tungsten resources in China;however,the manufacturing technology of tungsten powder industry is still behind the demands.Therefore,to find simple and more efficient preparation methods of ultrafine tungsten powder is essential.Micro-impinging stream reactor(MISR)is a promising process intensifying technology,which has an excellent microrrmixing property,simple structure and is easy to be industrialized.It is a new method for preparing nanomaterials.In this thesis,the micro-impinging stream reactor was applied to prepare ultrafine tungsten powder.The main research contents are as follows:(1)Using sodium tungstate as the tungsten source and hydrochloric acid as precipitant,tungsten oxide was prepared by a micro-impinging stream reactor.The effects of type and dosage of additives,aging time,precipitant concentration,feed flow rate,drying temperature,calcination temperature and calcination time were studied.The optimum reaction conditions were determined as follows:acetic acid was used as assistant agent,the concentration of precipitator was 1.5 mol/L,and the reaction was carried out in MISR at a feed flow rate of 100 mL/min.After 6 h of static aging and calcination at 600 ? for 3 h,tungsten trioxide with a particle size of about 40 nm could be obtained,which is superior to that of tungsten trioxide prepared by traditional precipitation method and microwave ultrasonic method,and the tungsten trioxide can reach the same level compared with the new method in the literature.Finally,the two-stage hydrogen reduction method was used to conduct the transition from WO3 to W,and ultrafine tungsten powder with a particle size of about 35 nm was obtained.(2)Based on the above work,ammonium tungstate was then used as tungsten source,instead of sodium tungstate,to prepare tungsten powder in MISR without sodium content.Due to the addition of ammonium in the reaction environment,it is necessary to study the primary influencing factors,such as additive dosage,aging time and precipitant concentration on the preparation.The optimum conditions were determined as follows:4.5 mL acetic acid was added to the reaction and aged for 6 h at the concentration of 1 mol/L hydrochloric acid.Finally,tungsten trioxide with particle size of about 40 nm was obtained,and high purity ultrafine tungsten powder of about 35 nm was obtained after hydrogen reduction.Such tungsten powder was compared with nano tungsten powder prepared by gas phase method from market sales and the particle size is a little better than that of tungsten powder prepared by gas phase method.