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Electrothermal characterization of tungsten-coated carbon microcoils for micropropulsion systems
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
2007 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 45, no 3, 484-492 p.Article in journal (Refereed) Published
Abstract [en]

Laser-induced chemical vapor deposition is used to deposit tungsten-coated carbon microcoils from the gas phase. Because the microcoils are used as heating elements in cold/hot gas microthrusters in nanosatellites, it is important to characterize their electrothermal behavior so that the performance of the thruster may be predicted. The coils are deposited using an argon-ion laser (wavelength 514.5 nm) at 360 mW and 930 mbar of C2H4. Bent arms are then deposited at the ends of the 1 mm long coils using 600 mW of laser power and 700 mbar of C2H4. The arms serve as electrical contacts and as mechanical supports to hold the coils in the thruster by a locking mechanism. A layer of tungsten is then applied to the carbon coils by the hydrogen-reduction of WF6 using a 20 : 1 (H2 : WF6) pressure ratio at a total pressure of 105 mbar and 400 mW of laser power. High-resolution scanning electron microscopy analysis showed the tungsten coating to be 1.5–3.5 μm thick on the body of the coil and less than 2 μm on the contact arms. The tungsten coating reduced the resistance of the carbon coils by an order of magnitude and reached higher temperatures at lower voltages. In vacuum, the tungsten coating is the dominant current carrier below 1300–1700 °C; above this range carbon dominates. Peak temperatures for the tungsten-coated coils are 2050 °C in vacuum and 1940 °C in N2 – several hundred degrees higher than the non-coated coils.

Place, publisher, year, edition, pages
2007. Vol. 45, no 3, 484-492 p.
Keyword [en]
Transition elements, Carbon, Tungsten, Characterization
National Category
Engineering and Technology Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-94083DOI: 10.1016/j.carbon.2006.11.001ISI: 000244878200003OAI: oai:DiVA.org:uu-94083DiVA: diva2:167812
Available from: 2006-03-03 Created: 2006-03-03 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Laser-assisted CVD Fabrication and Characterization of Carbon and Tungsten Microhelices for Microthrusters
Open this publication in new window or tab >>Laser-assisted CVD Fabrication and Characterization of Carbon and Tungsten Microhelices for Microthrusters
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Laser-induced chemical vapor deposition (LCVD) is a process enabling the deposition of solid material from a gas phase in the form of free-standing microstructures with high aspect ratios. The deposition rate, wire diameter, and material properties are sensitive to changes in temperature and gas pressure. Through experimentation these dependencies are clarified for carbon and tungsten-coated carbon microhelices to be used as heating elements in cold gas microthrusters for space applications. The integration of heaters into the thruster will raise the temperature of the gas; thus, improving the efficiency of the thruster based on specific impulse.

Deposition rate is measured during the fabrication process, and the geometrical dimensions of the spring are determined through microscopy analysis. By experimentally measuring the spring rate, material properties such as shear modulus and modulus of elasticity for LCVD-deposited carbon can be determined as a function of process parameters.

Electrothermal characterization of carbon and tungsten-coated microcoils is performed by resistively heating the coils and measuring their surface temperature and resistance in atmospheres relevant to their operating environments. Through high-resolution microscopy analysis, sources having detrimental effects on the coils are detected and minimized. The results gained from these experiments are important for efforts in improving the performance of cold gas microthrusters.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. x+39 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 151
Keyword
Engineering physics, LCVD, Carbon, Tungsten, Microspring, Resistance, Teknisk fysik
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-6551 (URN)91-554-6480-7 (ISBN)
Public defence
2006-03-24, Polhemsalen, The Ånsgström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:00
Opponent
Supervisors
Available from: 2006-03-03 Created: 2006-03-03Bibliographically approved

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