Tungsten nanoparticles with size in the range of 60-100 nm are produced using a cluster source ba... more Tungsten nanoparticles with size in the range of 60-100 nm are produced using a cluster source based on magnetron sputtering combined with the gas aggregation technique. The metallic vapors obtained by sputtering are cooled down in the flow of the inert gas (argon); nucleation centers appear first, then the nanoparticles grow subsequently by accretion and coagulation and they are ejected from the cluster sources as a beam of particles. An undesired effect is the slowing down and cease of the deposition process in about 30 minutes, suggesting the dependence of the deposition rate on the presence of residual gases which are gradually consumed during the process. We show that by deliberately mixing the argon with small amounts of hydrogen the production of tungsten nanoparticles become continuous. Moreover, an oscillatory behavior of the main process parameters (target selfbias, pressure in the cluster source, intensity of the optical emission lines and the deposition rate) was noted. ...
ABSTRACT We present the synthesis of tungsten nanoparticles using a gas aggregation cluster sourc... more ABSTRACT We present the synthesis of tungsten nanoparticles using a gas aggregation cluster source based on a magnetron sputtering discharge. The nanoparticles have sizes between 70 and 100 nm and a dendritic morphology, with branches emerging from the center and evolving in a flower-like pattern. Structural investigations revealed the presence of α-W and residual β-W crystalline phases. Post deposition oxidation of the nanoparticles is also investigated.
IEEE International Frequency Control Sympposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003
ABSTRACT In context of the joining of Romania to the European union, the practical realization of... more ABSTRACT In context of the joining of Romania to the European union, the practical realization of a national metrological system and its integration into the European metrological activity is becoming increasingly important. One of the goals of our research is the realization of an accurate time standard and the maintenance of a time scale compatible with the standards adopted internationally.
Radiofrequency plasma jets generated in argon and nitrogen at low and atmospheric pressure have b... more Radiofrequency plasma jets generated in argon and nitrogen at low and atmospheric pressure have been investigated by means of Optical Emission Spectroscopy (OES) analysis. The local emissivity of the plasma along axial and radial direction of the plasma expansion has been determined by Abel inversion of the integral emission intensity. The gas temperature has been evaluated by simulating the roto-vibrational structure of the molecular bands.
ABSTRACT Tritium adsorption and desorption from well characterized tungsten dust are presented. T... more ABSTRACT Tritium adsorption and desorption from well characterized tungsten dust are presented. The dust used are of different types prepared by planetary milling and by aggregation technique in plasma. For the milled powder, the surface specific area (SSA) is 15.5 m2/g. The particles are poly-disperse with a maximum size of 200 nm for the milled powder and 100 nm for the aggregation one. Prior to tritiation the particles are carefully de-oxidized. Both samples are experiencing a high tritium inventory from 5 GBq/g to 35 GBq/g. From comparison with massive samples and considering that tritium inventory increases with SSA, it is shown that surface effects are predominant in the tritium trapping process. Extrapolation to the ITER environment is undertaken with the help of a Macroscopic Rate Equation model. It is shown that, during the life time of ITER, these particles can exceed rapidly 1 GBq/g.
2004 Conference on Precision Electromagnetic Measurements, 2004
The uncertainty budget of a primary frequency standard based on a continuous cold cesium beam bui... more The uncertainty budget of a primary frequency standard based on a continuous cold cesium beam builds up differently than with a pulsed fountain. This communication reports on a detailed theoretical and experimental analysis of three entries in the continuous case: the collisional shift, the light shift and the Zee-man shift
Tungsten and tungsten nanoparticles are involved in a series of processes, in nanotechnology, met... more Tungsten and tungsten nanoparticles are involved in a series of processes, in nanotechnology, metallurgy, and fusion technology. Apart from chemical methods, nanoparticle synthesis by plasma offers advantages as good control of size, shape, and surface chemistry. The plasma methods are also environmentally friendly. In this chapter, we present aspects related to the magnetron sputtering gas aggregation (MSGA) process applied to synthesis of tungsten nanoparticles, with size in the range of tens to hundreds of nanometers. We present the MSGA process and its peculiarities in the case of tungsten nanoparticle synthesis. The properties of the obtained particles with a focus on the influence of the process parameters over the particle production rate, their size, morphology, and structure are discussed. To the end, we emphasize the utility of such particles for assessing the environmental and biological impacts in case of using tungsten as wall material in thermonuclear fusion reactors
We present hybrid nanomaterial architectures, consisting of carbon nanowalls (CNW) templates deco... more We present hybrid nanomaterial architectures, consisting of carbon nanowalls (CNW) templates decorated with tungsten oxide nanoparticles, synthesized using a mechanism based on tungsten oxide sublimation, vapor transport, followed by vapor condensation, in the absence or presence of plasma. The key steps in the decoration mechanism are the sublimation of tungsten oxides, when are exposed in vacuum at high temperature (800 °C), and their redeposition on colder surfaces (400–600 °C). The morphology and chemical composition of the hybrid architectures, as obtained from Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, are discussed with respect to substrate nature and the physical conditions of synthesis. We pointed out that the decoration process is strongly dependent on the temperature of the CNW templates and plasma presence. Thus, the decoration process performed with plasma was effective for a wider range of template temperatures, in contrast with the decoration p...
Tungsten nanoparticles with size in the range of 60-100 nm are produced using a cluster source ba... more Tungsten nanoparticles with size in the range of 60-100 nm are produced using a cluster source based on magnetron sputtering combined with the gas aggregation technique. The metallic vapors obtained by sputtering are cooled down in the flow of the inert gas (argon); nucleation centers appear first, then the nanoparticles grow subsequently by accretion and coagulation and they are ejected from the cluster sources as a beam of particles. An undesired effect is the slowing down and cease of the deposition process in about 30 minutes, suggesting the dependence of the deposition rate on the presence of residual gases which are gradually consumed during the process. We show that by deliberately mixing the argon with small amounts of hydrogen the production of tungsten nanoparticles become continuous. Moreover, an oscillatory behavior of the main process parameters (target selfbias, pressure in the cluster source, intensity of the optical emission lines and the deposition rate) was noted. ...
ABSTRACT We present the synthesis of tungsten nanoparticles using a gas aggregation cluster sourc... more ABSTRACT We present the synthesis of tungsten nanoparticles using a gas aggregation cluster source based on a magnetron sputtering discharge. The nanoparticles have sizes between 70 and 100 nm and a dendritic morphology, with branches emerging from the center and evolving in a flower-like pattern. Structural investigations revealed the presence of α-W and residual β-W crystalline phases. Post deposition oxidation of the nanoparticles is also investigated.
IEEE International Frequency Control Sympposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003
ABSTRACT In context of the joining of Romania to the European union, the practical realization of... more ABSTRACT In context of the joining of Romania to the European union, the practical realization of a national metrological system and its integration into the European metrological activity is becoming increasingly important. One of the goals of our research is the realization of an accurate time standard and the maintenance of a time scale compatible with the standards adopted internationally.
Radiofrequency plasma jets generated in argon and nitrogen at low and atmospheric pressure have b... more Radiofrequency plasma jets generated in argon and nitrogen at low and atmospheric pressure have been investigated by means of Optical Emission Spectroscopy (OES) analysis. The local emissivity of the plasma along axial and radial direction of the plasma expansion has been determined by Abel inversion of the integral emission intensity. The gas temperature has been evaluated by simulating the roto-vibrational structure of the molecular bands.
ABSTRACT Tritium adsorption and desorption from well characterized tungsten dust are presented. T... more ABSTRACT Tritium adsorption and desorption from well characterized tungsten dust are presented. The dust used are of different types prepared by planetary milling and by aggregation technique in plasma. For the milled powder, the surface specific area (SSA) is 15.5 m2/g. The particles are poly-disperse with a maximum size of 200 nm for the milled powder and 100 nm for the aggregation one. Prior to tritiation the particles are carefully de-oxidized. Both samples are experiencing a high tritium inventory from 5 GBq/g to 35 GBq/g. From comparison with massive samples and considering that tritium inventory increases with SSA, it is shown that surface effects are predominant in the tritium trapping process. Extrapolation to the ITER environment is undertaken with the help of a Macroscopic Rate Equation model. It is shown that, during the life time of ITER, these particles can exceed rapidly 1 GBq/g.
2004 Conference on Precision Electromagnetic Measurements, 2004
The uncertainty budget of a primary frequency standard based on a continuous cold cesium beam bui... more The uncertainty budget of a primary frequency standard based on a continuous cold cesium beam builds up differently than with a pulsed fountain. This communication reports on a detailed theoretical and experimental analysis of three entries in the continuous case: the collisional shift, the light shift and the Zee-man shift
Tungsten and tungsten nanoparticles are involved in a series of processes, in nanotechnology, met... more Tungsten and tungsten nanoparticles are involved in a series of processes, in nanotechnology, metallurgy, and fusion technology. Apart from chemical methods, nanoparticle synthesis by plasma offers advantages as good control of size, shape, and surface chemistry. The plasma methods are also environmentally friendly. In this chapter, we present aspects related to the magnetron sputtering gas aggregation (MSGA) process applied to synthesis of tungsten nanoparticles, with size in the range of tens to hundreds of nanometers. We present the MSGA process and its peculiarities in the case of tungsten nanoparticle synthesis. The properties of the obtained particles with a focus on the influence of the process parameters over the particle production rate, their size, morphology, and structure are discussed. To the end, we emphasize the utility of such particles for assessing the environmental and biological impacts in case of using tungsten as wall material in thermonuclear fusion reactors
We present hybrid nanomaterial architectures, consisting of carbon nanowalls (CNW) templates deco... more We present hybrid nanomaterial architectures, consisting of carbon nanowalls (CNW) templates decorated with tungsten oxide nanoparticles, synthesized using a mechanism based on tungsten oxide sublimation, vapor transport, followed by vapor condensation, in the absence or presence of plasma. The key steps in the decoration mechanism are the sublimation of tungsten oxides, when are exposed in vacuum at high temperature (800 °C), and their redeposition on colder surfaces (400–600 °C). The morphology and chemical composition of the hybrid architectures, as obtained from Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, are discussed with respect to substrate nature and the physical conditions of synthesis. We pointed out that the decoration process is strongly dependent on the temperature of the CNW templates and plasma presence. Thus, the decoration process performed with plasma was effective for a wider range of template temperatures, in contrast with the decoration p...
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