Refining Mechanisms Of Phosphorus-assisted Arsenic To Nano Tungsten And The Preparation Of Ultrafine Tungsten Carbide Powders

In tungsten metallurgy industry,arsenic and phosphorus are usually removed as main impurity elements in tungsten ore raw materials.It is found that As elements have a significant refining effect on tungsten powder,and nano tungsten powder with uniform particle size and good dispersibility can be prepared.However,P and As elements are associated in the process of tungsten metallurgy.It is difficult to prepare nano tungsten powder by removing phosphorus and arsenic.To prepare nano-tungsten powder and high performance WC-Co cemented carbide by using the As and P element in the process of tungsten metallurgy,it is necessary to understand the influence mechanism of As and P in the preparation of WC-Co cemented carbide.In this paper,a certain amount of As and P elements were added to the compound in the precursor powder,and the nano W-As-P and ultrafine WC-As-P composite powder with uniform particle size was prepared by calcining,hydrogen reduction and carbonization processes.The effects of As and P elements on the morphology and phase structure of tungsten powder and tungsten carbide powder were analyzed by means of XRD,SEM,TEM and ICP in the process of the study,and the detailed mechanism of P assisted As to W powder was discussed.In addition,the growth model of WC was established by analyzing the effects of the As and P elements on the nucleation and growth of WC powder.The main conclusions of the study are as follows:1.By adding P and As elements together,the average particle size of W-As-P composite powder with uniform particle size and good dispersion was 79 nm.In the process of APT-As-P calcination,thermal decomposition reaction of APT were advanced and accelerated because of the existence of P and As elements.At the same time,the large release of As₂O₃ and P₂O₃ gas made the tungsten oxide powder structure more porous,which is beneficial to the hydrogen reduction of tungsten oxide.In the process of hydrogen reduction,the release of more gaseous P₂O₃ could further reduce the water pressure in the furnace and prevent the tungsten particles from growing up through chemical vapor deposition.And more arsenic remains in the form of WAs₂.Therefore,adding P and As elements is more significant than adding As elements to tungsten powder,and can eliminate the adverse effect of P on the morphology of tungsten powder.2.The WC-As-P composite powder with uniform particle size and good dispersion can be obtained after carbonization of W-As-P composite powder at 1400^o C for 2h.And the average particle size of WC-As-P powder was 210 nm.The WAs₂ and WP₂binary phase and W₅As_2.5P_1.5.5 ternary phase were existed in tungsten carbide powder,and attached on the edge of the WC powder particles,hindered the WC particles through the grain boundary migration and grow up.Besides,the growth mode of WC-As-P and WC-As is different from that of pure WC.The WC-As-P and WC-As particles are all grown in a direct combination,which is different from the way in which the pure WC granules first burst and then merged.In this paper,the influence mechanism of P and As in the preparation of WC-Co cemented carbide was studied systematically.The uniform nano tungsten powder and ultrafine tungsten carbide powder were prepared by conventional method.The bending strength of YG6-As-P alloy was increased by 11.5%compared with the blank sample.It can provide theoretical basis and practical basis for resource utilization of P and As elements in tungsten mines and large-scale preparation of high performance ultra-fine grained WC-Co cemented carbide in the future.