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Sun X.-Y.,Xiamen Golden Egret Special Alloy Co. | Sun X.-Y.,Xiamen Tungsten Co. Technology Center
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2010

It is important to control carbon content during cemented carbide production. The conventional method for controlling carbon content is adjusting magnetic saturation intensity. Because of the limitation of the detecting system, the big manufactures can't be detected in magnetic saturation intensity equipment. In the view of cobalt as the binder phase of cemented carbide is magnetic, ferrite detecting method is proposed in this paper to replace the tradition method of detecting the carbon content of cemented carbide manufactures in large size. The WC-Co samples with different carbon content sintered in low pressure sintering furnace using WC and Co mixed powders as raw materials were used to detect the magnetic saturation intensity and the ferrite content. Besides, the relationships of carbon content, magnetic saturation intensity and ferrite content value were investigated. The results indicate that the relationship of carbon content and ferrite content value is linear, thus, ferrite content can be considered to be used to represent carbon content. Since detecting method of test ferrite content is simple, it's a good way to give benefit to the improvement of the cemented carbide quality. Source


Xiao M.-D.,Xiamen Tungsten Co. Technology Center | Xiao M.-D.,Xiamen Golden Egret Special Alloy Co.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2010

Raw material oxidation is the most strict problem in submicron grain (≤ 0.8 μm) cemented carbides production. By means of adding oxide, the morphology of pores induced by the oxide in samples prepared at different sintering temperature was investigated using SEM. The results show that pores induced by oxide have obvious characterization of coarse grain structure. In addition, the mechanism of the coarse grain structure formation is discussed and it is recognized that the coarse grain structure is resulted from gas participated reaction. TG-DSC result shows the temperatures of carbon reducing Co3O4 and WO3 are around 732°C and 1050°C, respectively. Source


Zhang T.-Q.,Xiamen Tungsten Co. Technology Center
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2010

Cobalt powder used in cemented carbides is mainly fabricated by hydrogen decomposition-reduction technology using cobalt compounds of cobalt oxalate (CoC2O4 · 2H2O), cobalt carbonate (CoCO3 · xH2O), or cobalt oxide (Co3O4) as raw materials. The decomposition-reduction mechanisms of the above three cobalt compounds have been analyzed and discussed in detail in the present paper. According to the decomposition-reduction mechanisms, the effects of the character of raw materials powders and the technology parameters on the quality of cobalt powders were also discussed based on nucleation and growth theories. The results indicate that the ultra-fine spherical raw materials powders are necessary to obtain ultra-fine spherical cobalt powders. It is very important to improve the nucleation rate of the cobalt particles and restrain their growth rate during decomposition-reduction, and the order of the raw materials from difficult to easy for controlling technology is CoC2O4 · 2H2O > CoCO3 · xH2O > Co3O4. Source


Wu C.-H.,Xiamen Tungsten Co. Technology Center | Wu C.-H.,Xiamen Golden Egret Special Alloy Co.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2010

A novel method to inhibit Mo codeposition from ammonium tungstate solution during ammonium paratungstate (APT) crystallization process by control the concentration of Cl- in the solution. Based on the plentiful APT production practices, the wonderful effect of Cl- on inhibition Mo co-deposition with APT during APT crystallization process has been found out. For a special ammonium tungstate solution with given Mo concentration, there is a corresponding threshold concentration of Cl- in order to achieve high crystallization rate and low Mo content for APT production. Using this high effective method, the primary crystallization rate of the APT increases from 80% to 96% and the resultant APT is zero-grade with very low Mo concentration (≤ 2 × 10-5). The APT products have perfect crystal morphology and homogenous particle size (40~50 μm). A possible mechanism of Cl- inhibiting molybdenum deposition is proposed. Source


Ma L.-L.,Xiamen Tungsten Co. Technology Center | Ma L.-L.,Xiamen Golden Egret Special Alloy Co.
Fenmo Yejin Cailiao Kexue yu Gongcheng/Materials Science and Engineering of Powder Metallurgy | Year: 2010

The WC-10%Co rods are adopted to study the corrosion behavior of cemented carbide in water. The finished grinding rods were stored at room temperature in the presence of water for a certain time. It can be found that there are many yellow "rusted spots" on the finished grinding rods. The SEM and EDS analysis results show that the formed "rusted spots" are yellow compact oxide films which indicate the corrosive effect of water on cemented carbide. Moreover there are cobalt-free defects on the corroded rods after the oxide films removed by finished grinding. The existence of cobalt-free defects on the rods also demonstrates that water has the effect of cobalt leaching from cemented carbide rods. In addition, the electrochemical mechanism of the cobalt corrosion and leaching is also discussed in this paper. Source

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