Projects / Programmes
A new and effective large-scale synthesis of sub-stoichiometric conductive tungsten nanowires as precursors for WS2 nanotubes
| Code |
Science |
Field |
Subfield |
| 2.04.02 |
Engineering sciences and technologies |
Materials science and technology |
Metallic materials |
| Code |
Science |
Field |
| P360 |
Natural sciences and mathematics |
Inorganic chemistry |
substehiometric tungsten oxides, nanowires, tungsten disulphide, nanotubes, fullerenes, chemical transport reaction, inductive heating, atomic force microscopy, scanning tunneling microscopy, sulphurization
Researchers (1)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
20003 |
PhD Maja Mrak |
Physics |
Head |
2007 |
39 |
Organisations (1)
| no. |
Code |
Research organisation |
City |
Registration number |
No. of publicationsNo. of publications |
| 1. |
0106 |
Jožef Stefan Institute |
Ljubljana |
5051606000 |
90,664 |
Abstract
One-dimensional system such as nanowires and nanotubes are especially attractive building blocks for nanodevices because they represent the smallest dimension wires for efficient transport of electrons and also electron field emitters. Substoichiometric tungsten oxides WO3-x are not only attractive because of wide variety of application of tungsten and their compounds, but particular because of the fact that their stoichiometric compound WO3 is non-conducting and diamagnetic. Many sub-stoichiometric tungsten oxide phases (WO3-x) are already known, but with an exception of semiconductive W18O49 (WO2,72) phase, it is very hard to synthesize them in a pure form. The aim of the project will be a high-yield synthesis of one-dimensional conductive or semi-conductive WO3-x nanowires, which will be for the first time studied by ultra-high vacuum atomic force microscopy (AFM) and scanning tunneling microscopy (STM) for their surface properties and will fill the void in the surface characterization of dense tungsten sub-stoichiometric oxide nanowires. Special attention will be taken on the synthesis of W5O14 (WO2.8) phase, which has a metallic behavior and interesting structure with 5- and 6- fold ring channels. W5O14 nanowires could be potentially used for many applications, but the limited yield and insufficient chemical homogeneity of the product was a serious drawback for a detail characterization. Optimization of the large-scale synthesis of WO3-x nanowires (gram quantities) will be carried out by chemical transport reaction with iodine and by induction heating with radio-frequency magnetic field. The WO3-x nanowires will be than used as precursors for the production of WS2 nanotubes and/or WS2 fullerenes by sulfidizing atmosphere. EU partners in FOREMOST project will use our nanotubes for lubricants and greases to lower the friction by which substantially reduced energy loss will be achieved, which could result in reduced maintenance requirements which cuts downtimes and increases productivity of mechanical systems.
Significance for science
My contribution to the science will be macroscopic synthesis of these nanomaterials with semiconductive and conductive properties. The synthesis of mainly W5O14 phase in gram quantity after 30 years of its discovery will finally give an opportunity for a detail characterization of their chemical and physical properties of W5O14 material. The chemical transport reaction will enable the growth of very long substoichiometric nanowires with less defect and higher purity. Furthermore, since the material is thermally stable and has 5- and 6- fold channels within a layer (large surface area) it could be used for lithium or hydrogen incorporation. Currently WS2 nanotubes can be synthesized only in small quantities and not in a pure form. The sulphurization of W5O14 phase at different stages could give a new insight into the grow mechanism of nanotubes. Planned optimization of the nanowires and nanotubes and macroscopic production is necessarily for all of predicted applications and for majority of the first investigations of applicable properties.
For EU project the supply of large quantity of nanotubes will give a possibility to develop more innovative coating processes and incorporation techniques for the production of the unique nanocomposites.
Significance for the country
The assimilation of nanomaterials by Europian industry (Renault, Rolls-Royce, EADS, etc.) and by indirect economic benefit also to the Slovenian industry will provide significant reductions in friction and wear leading to: substantially reduced energy loss in mechanical systems resulting in less pollution; significant savings in raw materials and capital expenditures by reducing component wear; enhanced reliability and durability of mechanical systems together with reduced maintenance requirements which cuts downtimes and increases productivity;
About 25% of the energy used in the world is wasted on overcoming and losses due to wear of materials have been estimated by various sources to be 1.3 to 1.6% of the GNP of an industrialized country. The cost of friction, wear and lubrication (including reduced life time, repair and maintenance costs) is estimated at 350 x 109 Euro/year. Breaking this down by activity sectors, the maximum cost are associated with Surface Transport (46.6%), Industrial manufacturing and processing (33%), Energy suppliers (6.8%), Aeronautic (2.8%) and Household (0.5%). Other sectors complete the remaining 10.3%.
New coatings incorporating WS2 nanotubes inorganic fullerene-like nanoparticles will contribute to significantly reduce these figures. For example, the effective coefficient of friction at the gear teeth in oil lubricated gearboxes generally lies in the range 0.04 to 0.08, with a resulting power loss in the range of 0.3% to 1.5% of the transmitted power. Considering the case of automotive gearboxes, if a coating could reduce the coefficient of friction by 20%, it could reduce the mesh friction loss in a typical automotive gearbox from 0.8% to 0.64%. This would mean a cost saving of 26 x 109 Euro/year, only in the Surface Transport Sector.
Inclusion of WS2 particles on main shaft drive splines would contribute to the Rolls Royce targets for reduction of wear due to fretting. In their aero-engine external gear box power losses due to gear mesh friction could reduce oil flow requirements leading to lower windage losses and reduced oil tank and heat exchanger size (reduced engine weight). Friction benefits for large high power marine gearboxes will reduce the energy wasted and heat dissipated. World-wide oil reserves, while once considered to be infinite, have been realized long ago to be extremely finite. As such taking advantage of the properties of the IF materials, will further promote the shift from petroleum-based oils to sustainable agricultural-based IF-enhanced vegetable oils.
By reducing the dependency on petroleum for lubrication applications, we will be extending the life-time of world-wide oil reserves for critical applications such as medicines. In fact, friction reduction may prove a very cost effective way of improving the fuel-efficiency. The successful application of fullerene-like nanoparticles in coatings, bulk materials or lubricants will lead to a breakthrough reduction in frictional losses in certain applications.
Road transport accounts for approximately 20% of CO2, thus a one percent reduction will account for as much as 1.4 million tons of CO2 that could be spared in Europe annually.
