Wu C.,Xiamen Tungsten Co. |
Wu C.,Xiamen Golden Egret Special Alloy Co.
International Journal of Refractory Metals and Hard Materials | Year: 2011
Ultrafine tungsten powders with a grain size below 0.5 μm are key raw materials for fabricating ultrafine cemented carbides. Conventional hydrogen reduction technique has been utilized to prepare the ultrafine tungsten powders. In the present work, highly pure nano-needles of violet tungsten oxide (WO 2.72) were reduced by dry hydrogen. Nucleation and growth of the metallic tungsten in the early stage of hydrogen reduction have been studied by XRD, FESEM and HRTEM. Mechanism of formation of nano-size tungsten powders is proposed and a concept of in-situ hydrogen of the nano-needle WO 2.72 is presented. Empirical relations between an average diameter of nano-needle WO 2.72 and an average particle size of the resultant tungsten powders in both stage of nucleation and industrial conduction have been established. These empirical relations could be a reasonable guidance for suitably choosing the raw materials of nano-needle WO 2.72 to prepare ultrafine tungsten powders. It has been determined that the BET special surface areas of the in-situ hydrogen-reduced tungsten powders with the average particle size of 0.2 μm and 0.3 μm, which were produced from the raw nano-needle WO 2.72 powders with the average diameter of 60 nm and 80 nm, are 6.03 m 2/g and 4.65 m 2/g, and the oxygen contents are 0.35% and 0.29%, respectively. © 2011 Elsevier Ltd. All rights reserved.
Wu C.-H.,Xiamen Tungsten Co. |
Zhang T.-Q.,Xiamen Golden Egret Special Alloy Co.
International Journal of Refractory Metals and Hard Materials | Year: 2013
The characteristics and formation mechanisms of microstructure imperfections in two sets of submicron WC-10wt.%Co cemented carbides, which are fabricated by vacuum and low-pressure sintering, respectively, are deeply analyzed. Main imperfections are pore-Co-pool in the vacuum-sintered samples. The number of pore-Co-pool is obviously reduced by low-pressure sintering, but many porous microstructures with poor-Co or Co-free are easily introduced; the impurity segregation is also easily formed. Transverse rupture strength (TRS) of samples is strongly affected by the characteristics and size of imperfections. Two linear relationships between TRS and pore size are experimentally established, and a critical pore size has been calculated to be 28.8 μm. © 2013 Elsevier Ltd.
Wu C.-H.,Xiamen Tungsten Co. |
Wu C.-H.,Xiamen Golden Egret Special Alloy Co.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2011
The continuously dynamic-controlled combustion synthesis (CDCCS) was developed based on the continuous fluidization and combustion synthesis technologies. CoC2O4·2H2O powders were transformed to Co3O4 in a gas-solid fluid bed unit designed and build independently, where the reactant of CoC2O 4·2H2O powders and the reactant of air were poured and introduced from the top and the bottom of the bed at a certain rates respectively. The reagents met in the bed and ignited at a given low temperature, resulting in formation of Co3O4. The results show a significant difference in combustion wave models. In the case of CDCCS, there was an immobile combustion wave, floating in the combustion zone located in the middle of the bed, instead of propagating of the combustion wave. The temperature of the combustion wave can be controlled by adjusting the flow rate of carrier gas. The resultant Co3O4 powders (diameter size ≤0.8 μm) have a narrow particle size distribution and spherical or quasi-spherical shape. This novel technique has many advantages, such as continuation, efficiency, energy conservation and environmental friendly and has been used in mass production. © 2011 The Nonferrous Metals Society of China.
Xiamen Tungsten Co. | Date: 2013-12-31
A manufacturing method of a powder for rare earth magnet and the rare earth magnet based on evaporation treatment, includes the steps of: coarsely crushing an alloy for the rare earth magnet and then finely crushing to obtain a fine powder; and evaporating the fine powder and an evaporation material in vacuum or in inert gas atmosphere; wherein the weight ratio of the evaporation material evaporated to the fine powder and the fine powder is 10-60.05:1. By adding the process of evaporation treatment of fine powder before the process of compacting under a magnetic field and after the process of fine crushing, the sintering property of the powder is changed drastically; a magnet with a high coercivity, a high squareness and a high heat resistance is obtained.
Xiamen Tungsten Co. | Date: 2013-11-08
The present invention discloses manufacturing methods of a powder for compacting rare earth magnet powder and rare earth magnet that omit jet milling process, which comprises the steps as follows: 1) casting: casting the molten alloy of rare earth magnet raw material by strip casting method to obtain a quenched alloy with average thickness in a range of 0.20.4 mm; 2) hydrogen decrepitation: decrepitating the quenched alloy and a plurality of rigid balls into a rotating hydrogen decrepitation container simultaneously, the quenched alloy is crushed under a hydrogen pressure between 0.011 MPa, cooling the alloy and the balls, then screening the mixture to remove the rigid balls and obtain the powder. As the jet milling process is omitted, the oxygenation during the process of the jet milling may be avoided, therefore the process may be non-oxide, and the mass production of magnet with super high property may be possible.