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Guo S.,Jiangxi University of Science and Technology | Guo S.,HIGH-TECH | Yang J.,Jiangxi University of Science and Technology | Yang J.,HIGH-TECH | And 5 more authors.
Xiyou Jinshu/Chinese Journal of Rare Metals | Year: 2015

Nanophase WC-Co composite powder has an important engineering application and large market potential. As for the problem that the morphology of nanophase WC-Co composite powder was difficult to control accurately, using ammonium metatungstate (AMT), soluble cobalt salt, and organic carbon source as raw materials and distilled water as solvent, without adding any growth inhibitor of WC grain, the mixed solution with components of tungsten, cobalt and carbon elements was prepared, and the effects of the spray conversion process such as solution concentration, feed rate, centrifugal speed and transition temperature on the apparent density, grain size of WC and micro morphology of nanophase WC/Co composite powders fabricated by spray conversion (SCP) and low temperature reduction-carbonization methods were studied. The results showed that the appearance of composite powder was a kind of spherical shell, Co phase was melted and most of the WC was bonded together; sintering neck was observed between WC particles, there were a lot of pores existing on particle surfaces, and some of the particles were broken; the mean grain size of WC was less than 200 nm; centrifuge speed was the most important factor which affected the apparent density, grain size of WC and morphology of WC/Co composite powder; the particle size of composite powder was smaller and the apparent density became bigger with greater centrifugal speed; meanwhile, the composite powder ruptured more easily and the grain size of WC became smaller with higher conversion temperature. ©, 2015, Editorial Office of Chinese Journal of Rare Metals. All right reserved. Source


Guo S.-D.,Jiangxi University of Science and Technology | Guo S.-D.,HIGH-TECH | Yang J.-G.,Jiangxi University of Science and Technology | Yang J.-G.,HIGH-TECH | And 4 more authors.
Gongneng Cailiao/Journal of Functional Materials | Year: 2015

Using ammonium metatungstate (AMT), soluble cobalt salt, and organic carbon source as the raw materials, the WC-Co composite powder was fabricated by spray conversion method and direct carbonized in-situ synthesize method. The phase compositions, powder morphology of WC-Co composite powder were characterized by XRD, SEM. Results show that W was carbonized completely at 900℃ because of the promoting effect of Co phase, the carbonize temperature in this experiment of W was lower than the normal carbonize temperature far; The carbonization process of W depends on the reaction of the surface of tungsten powder particles and carbon which resolved from carbon atmosphere, and the diffusion of carbon to the inside of W particles, was a solid-solid reaction, W was carbonized into W2C firstly, and then carbonized into WC further because of the Gibbs free energy of W2C is lower than WC; The W/Co/C system reacted along the specific steps of WCo3, Co6W6C, W2C-Co and WC-Co; With the increasing of carbonize temperature, the reaction system can skip the first two steps, and generated W2C-Co directly, then carbonized into WC-Co composite powder further. ©, 2015, Journal of Functional Materials. All right reserved. Source


Guo S.-D.,Jiangxi University of Science and Technology | Guo S.-D.,HIGH-TECH | Yang J.-G.,Jiangxi University of Science and Technology | Yang J.-G.,HIGH-TECH | And 4 more authors.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2014

Nanophase WC-Co composite powder is applied widely with the fast development of modern industry and has a large market potential. Through the use of ammonium metatungstate (AMT), soluble cobalt salt, organic carbon and carbon black as raw materials, composite powders were prepared by spray conversion and low temperature reduction-carbonization methods. The effects of atomization speed, transition temperature and selection of carbon to morphology of nanophase WC-Co composite powder were studied. The results show that, the appearance structure of composite powders is shell spherical, grain size is less than 100 nm, while a phenomenon of pores and particle breakage exist, Co-phase presents fcc-structure. Within a certain range, the particle size increases with decreasing atomization speed; the degree of spherical powder decreases with increasing transition temperature; the particle size of composite powder prepared by organic carbon is bigger and the shell wall is thinner than that of prepared by carbon black. ©, 2014, Central South University. All right reserved. Source


Guo S.,Jiangxi University of Science and Technology | Guo S.,HIGH-TECH | Yang J.,Jiangxi University of Science and Technology | Yang J.,HIGH-TECH | And 4 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2016

Using ammonium metatungstate, soluble cobalt salt, and organic carbon as the raw materials, the WC-Co composite powder was fabricated by spray conversion, calcinations and low temperature reduction-carbonization. The phase composition, grain size of WC, powder morphology and particle size distribution of precursor powder and composite powder were characterized. Results show that the composite powder is composed of WC and Co phases, and the grain size of WC is about 60 nm. The appearance of precursor powder is a kind of spherical shell structure, some of which are broken. Powder morphology does not change after calcinations. After reduction and carbonization, a large number of pores are produced on particle surface, the powder morphology is similar to that of precursor powder, and genetic characteristics of morphology is fine; the mean grain size of composite powder is smaller than that of precursor powder and the particle size distribution is narrow; the mean particle size increases with the increase of the slurry concentration as well as liquid feeding rate and the decrease of centrifugal speed, but the particle size changes slightly with different inlet temperatures. © 2016, Science Press. All right reserved. Source


Zhu E.-T.,Jiangxi University of Science and Technology | Yang J.-G.,Jiangxi University of Science and Technology | Yang J.-G.,Advanced Corporation for Materials & Equipment | Dai Y.,Advanced Corporation for Materials & Equipment | And 4 more authors.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2015

Using ammonium metatungstate (AMT), cobalt acetate (Co(CH3COO)2∙4H2O) and organic carbon source as raw materials, precursor powder was prepared through spray drying, then was calcined in N2 to prepare W-Co oxide composite powder. TG-DSC-DTA analysis was applied on AMT, cobalt acetate and precursor powder, XPS was used to analyse valence state of W-Co oxide composite powder; XRD was used to analuse phase composition of W-Co oxide composite powder, SEM was used to analyse morphology of the powder. The results show that, the particle size of W-Co oxide powder prepared at 550 ℃ with 6.5 m3/h N2 for 20 min is 10~125 μm, and average particle size is 50 μm. The products by calcining W-Co oxide are cracking carbon, WO3 and Co3O4. It is at 550 ℃ that WO3 generated by AMT decomposition can be avoided to produce WO2(OH)2 under the effect of water vapor, WO2(OH) 2 can be avoided from reducing to W powder in H2, W powder can be avoided from depositing on W core, which makes W powder particles growing. ©, 2015, Central South University. All right reserved. Source

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