The traditional preparation of tungsten powder process is divided into two steps: First, roasting APT to tungsten oxide, and then carrying on a secondary reduction in hydrogen to get tungsten powder. In the process of preparation tungsten powder in one-step reduction method, chemical vapor transport and local hydrogen reduction exist at the same time, and it will be more obvious at high temperature. With chemical vapor transport becoming faster, tungsten powder particles will gradually grow up. So temperature and water will play an important role in the reduction process. At the same time, in the process of local hydrogen reduction, gases- solid reaction will happen, and the rate is slow, also the shape of production change not obviously. So, solid state reduction is beneficial to prepare finer tungsten powder.

 

3 Introduction to the reduction process

Material requirements: APT quality complies with the requirements of GB/T3548-2006 standard; hydrogen and nitrogen are industrial grade (more than 99%). Take a certain number of APT into the quartz boat, put it into hydrogen reduction furnace under nitrogen for 20min. Then set a temperature program, electricity and keep furnace atmosphere always in the weak reduction state in a certain proportion of hydrogen and nitrogen mixed gas. After the temperature rises to settled value, holding for a certain time, making APT water and ammonia desorption completely. Continually heating to the specified hydrogen reduction temperature in a certain rate, inlet hydrogen again for the second phase reduction, turn off valve at the time e prescribed, turn on ammonia to cool down to required temperature at the same time.

 

In existing process that producing blue tungsten oxide from APT, we usually inlet a certain amount of ammonia at the time calcining APT. Because of the property of ammonia decomposed at high temperature, the reaction remained in weak reducing atmosphere condition. But, the decomposition of ammonia is often incomplete, and exhaust with tail gas, thus cause environment pollution and do greatly harm to human health. From the perspective of environmental protection and safety, the traditional ammonia process is not conducive to safety and environmental protection. Meanwhile, it proved that in the purpose of controlling blue tungsten, we inlet a certain proportion of hydrogen and nitrogen mixed gas instead of ammonia in the first step can achieve the same effect.