Papers by Keyword: Tungsten Powder

Abstract: Jet grading technology is an efficient process in different industries. In this research, tungsten powder with different particle size distribution was used as a raw material to produce tungsten products via isostatic pressing as well as sintering. The mechanism of jet grading and the morphology and particle size distribution of different precursors were analyzed. The results showed that jet grading technology had remarkable effect on tungsten powder classification. The appropriate grading treatment was helpful to the formation of tungsten products with high performance. After jet grading and the following process like pressing and sintering, the tungsten products with better properties were manufactured which was used fischer particle size of 3.0~3.5μm as the raw material. The obtained products’ density was 18.77g/cm³ and its hardness was 372.15HV_0.3.

Abstract: The experiment of laser cladding on the surface of 20 steel was made. The mixed powder of cobalt-based alloy powder (Co55) and tungsten powder was used as cladding material. There were three kinds of weight percent of tungsten powder, 5%, 10% and 15%. The microstructure and hardness of three kinds of laser cladding layer were studied. The microstructure of cladding zone was greatly refined after adding tungsten powder to Co55 powder. When the proportion of tungsten powder was 5%, the cladding zone was made up of dendritic crystal. The average hardness of cladding zone was 590 HV0.2. When the proportion of tungsten powder rose to 10%, there was reticular secondary carbide precipitating along the grain boundary. The average hardness of cladding zone was 648 HV0.2. When the proportion of tungsten powder rose to 15%, much granular carbide would diffusely distribute in Ni-based solid solution. The average hardness of cladding zone was 831 HV0.2.

Abstract: Tungsten-copper(W-Cu) alloy is employed for manufacturing heavy duty contactors, relays,switches etc. During production of such components, W-Cu turnings/borings aregenerated. At CSIR-NML, a process for recovering tungsten and copper fromtungsten-copper borings containing 46.01% W, 53.78% Cu, 0.13% Fe and otherminor metals as high purity tungsten powder and copper powder has beendeveloped. In the present work, a detailed investigation on reduction ofammonium paratungstate (APT) having purity 99.95% by hydrogen gas to produce highpurity tungsten powder is presented. The various process parameters such astemperature, time and flow rate of hydrogen gas have been optimized. At the temperatureof 800°C and 0.1 lpm flow rate a reduction of 77.78% was observed upto 2h time. At 900°C, with increase in flow rate from 0.1 lpm to 0.3lpm the increase in reduction was found to be from 63.88% to 99.99% at 1h time.At still high temperature of 1000°C, almost complete reduction was obtainedat 0.1 lpm flow rate in 1h time. The effect of bed-depth was also carried out. Atall temperatures chemical reaction was the rate determining step.

Abstract: The spherical tungsten powder was prepared by chemical reaction with ammonium tungstate and strong acids under ultrasonic and mechanical agitation. After precipitation reaction, the precipitate was dried and grinded, and then reduced into tungsten powder with hydrogen. The effects of acid kinds and dispersant on the fine tungsten powder were studied in this paper. The result shows that the acid kinds and its addition amount have great effect on the shape of tungsten particles. The tungsten powder with uniform particle size and spherical could be prepared by adding 17ml sulfric acid into 100ml ammonium tungstate. The tungsten particles can be finer and more dispersive, and have a spherical with addition of dispersant SDS (Sodium dodecyl sulfate). The particle size is about 1.5 micrometer.

Abstract: Experiments have been conducted to consolidate tungsten powder using hot-shock consolidation technique combining with underwater shock wave. An exothermic mixture (TiO2-C-Al-Fe2O3) was ignited by an electric wire coil to release a large mount of heat via a self-propagating high-temperature synthesis reaction which was used to pre-heat the sample powder. As getting the needed isothermal temperature, the powder was subsequently consolidated by shock wave generated by explosion of nitro methane, with a detonation velocity of 6.3 km/s and a detonation pressure of 11.9 GPa. The density and Vickers micro-hardness of the consolidated sample were determined and its microstructure was analyzed by scanning electron microscope (SEM). High-density tungsten samples were obtained by optimizing the experimental conditions. In this paper, the relative density and hardness of the recovered sample are 96.5% and 670 HV, respectively.

Abstract: To increase largely the performance of shaped charge, it is required to generate detonation velocity much higher than CJ velocity or detonation pressure much higher than CJ pressure of existing high explosives. One solution is the application of overdriven detonation phenomena. In this study, the effects of overdriven detonation in tungsten loaded high density explosive on the performance of shaped charge were demonstrated by experiments and numerical simulation. Sample shaped charge was composed of the inner layer tungsten loaded high density PBX and outer layer high velocity PBX. Concentration of tungsten powder in high density PBX was varied from 20 to 60% in mass. The pressure of overdriven detonation in inner layer PBX was measured by PMMA gauge, and was shown to be higher than 50GPa. The experimental results showed that the initial jet velocity and jet penetration velocity in target plates were largely increased by the effects of the overdriven detonation in tungsten loaded high density PBX.

Abstract: Underwater explosive compaction is a modified explosive compaction process that is used for manufacturing of parts by compaction of hard powders such as tungsten powder. In the present research work, equation of state (EOS) for tungsten powder was determined by a theoretical method and numerical simulation of the underwater explosive compaction process for tungsten powder was done using LS-DYNA program. The simulation results were utilized for the optimization of die design setups, which were used in our experimental test. Several experiments for compaction of tungsten amorphous powder with a mean grain size about 5 microns were performed using C4 explosive with a detonation velocity about 8.2 km/s. The hardness and density of consolidated samples were determined. The fragmented surfaces of samples were analyzed by scanning electron microscope (SEM). The experimental results indicated the usefulness of computer simulation for optimization of die design and the process parameters. In addition, the results indicated that the tungsten parts without cracks and with a high relative hardness and density could be obtained by underwater explosive compaction method.

Abstract: The research conducted was focused primarily on the development of a process for obtaining silver-coated tungsten powders for applications related to electrical-conducting devices. Particles of high strength material when coated with silver offer a means of obtaining desirable electrical properties and high strength. The coating process employed aqueous ammoniacal silvernitrate electrolytes with a formaldehyde solution as the reductant. Modifying additives were also applied. The reduction and subsequent deposition of silver occurred selectively on the surface of the tungsten particles. The morphologies of the coated particles were assessed by SEM imaging. The silver was uniformed coated on tungsten powder and its thickness was estimated to be approximately 100nm on the basis of a mass account.