| 1. |
- Berglund, Martin, 1985-, et al.
(författare)
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Extreme-temperature lab on a chip for optogalvanic spectroscopy of ultra small samples – key components and a first integration attempt
- 2016
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Ingår i: 27th Micromechanics And Microsystems Europe Workshop (MME 2016). - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- This is a short summary of the authors’ recent R&D on valves, combustors, plasma sources, and pressure and temperature sensors, realized in high-temperature co-fired ceramics, and an account for the first attempt to monolithically integrate them to form a lab on a chip for sample administration, preparation and analysis, as a stage in optogalvanic spectroscopy.
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| 2. |
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| 3. |
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| 4. |
- Khaji, Zahra, et al.
(författare)
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Alumina-based monopropellant microthruster with integrated heater, catalytic bed and temperature sensors
- 2016
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Ingår i: 27th Micromechanics And Microsystems Europe Workshop (Mme 2016). - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- A liquid propellant alumina microthruster with an integrated heater, catalytic bed and two temperature sensors has been developed and tested using 30 wt. % hydrogen peroxide. The temperature sensors and the catalytic bed were screen-printed using platinum paste on tapes of alumina that was stacked and laminated before sintering. In order to increase the surface of the catalytic bed, the platinum paste was mixed with a sacrificial paste that disappeared during sintering, leaving behind a porous and rough layer. Complete evaporation and combustion, resulting in only gas coming from the outlet, was achieved with powers above 3.7 W for a propellant flow of 50 μl/min. At this power, the catalytic bed reached a maximum temperature of 147°C. The component was successfully operated up to a temperature of 307°C, where it cracked.
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| 5. |
- Khaji, Zahra, et al.
(författare)
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Catalytic Effect of Platinum and Silver in a Hydrogen Peroxide Monopropellant Ceramic Microthruster
- 2020
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Ingår i: Propulsion and power research. - : Elsevier. - 2212-540X. ; 9:3, s. 216-224
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic microthrusters with an embedded Pt resistive heater, two temperature sensors, and a Pt or Ag catalytic bed were made of high-temperature co-fired alumina ceramics. To increase the surface area by a factor of 1.21, and so the catalytic effect, the Pt catalytic bed was made porous by mixing the Pt paste with 15–20vol.% graphite sacrificial paste before screen printing it. Ag was in-situ electroplated on the porous Pt surface after sintering. Decomposition of 50wt.% hydrogen peroxide as a monopropellant was studied both qualitatively and quantitatively by changing the catalyst (between Ag and Pt), flow rate (15–55 μl/min), and operating temperature (115–300 °C). A reference device without catalyst exhibited an unstable behavior as a result of no, or very little, decomposition, whereas the Ag catalyst was more stable, and the Pt one even more stable. Also, Pt was found to be slightly more effective. Quantitatively, there were small differences between Pt and Ag in the power needed to maintain the temperature. The inventive methods to make the Pt bed porous as well as in-situ electroplating Ag were successfully demonstrated.
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| 6. |
- Khaji, Zahra, et al.
(författare)
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Design and fabrication of a miniaturized combustor with integrated oxygen storage and release element
- 2014
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Ingår i: 25th Micromechanics and Microsystems Europe workshop (MME 2014),2014, P19 (4 pp).
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Konferensbidrag (refereegranskat)abstract
- A miniature combustor for converting organic samples into CO2 with application in carbon isotopic measurements of small samples has been manufactured and evaluated. The combustor was made by machining and laminating High-Temperature Co-fired Ceramic (HTCC) 99.99% alumina green tapes and screen printing platinum conductors on them. The device has a built-in heater and a temperature sensor made of platinum, which were co-sintered with the ceramic. A metal oxide (copper oxide) oxygen supply was added to the combustor after sintering by in-situ electroplating of copper on the heater pattern followed by thermal oxidation. Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Thermal Gravimetric Analysis (TGA) were used to study electroplating, oxidation and the oxide decompo-sition processes.
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| 7. |
- Khaji, Zahra, et al.
(författare)
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Endurance and Failure of an Alumina-based Monopropellant Microthruster with Integrated Heater, Catalytic Bed and Temperature Sensors
- 2017
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Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 0960-1317 .- 1361-6439. ; 27:5, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Monopropellant ceramic microthrusters with an integrated heater, catalytic bed and two temperature sensors, but of various designs, were manufactured by milling a fluidic channel and chamber, and a nozzle, and screen printing platinum patterns on green tapes of alumina that were stacked and laminated before sintering. In order to increase the surface area of the catalytic bed, the platinum paste was mixed with a sacrificial paste that disappeared during sintering, to leave behind a porous and rough layer. As an early development level in manufacturing robust and high-temperature tolerant microthrusters, the influence of design on the temperature gradients and dry temperature tolerance of the devices was studied. On average, the small reaction chambers showed a more than 1.5 times higher dry temperature tolerance (in centigrade) compared to devices with larger chambers, independent of the heater and device size. However, for a given temperature, big devices consumed on average 2.9 times more power than the small ones. It was also found that over the same area and under the same heating conditions, devices with small chambers were subjected to approximately 40% smaller temperature differences. A pressure test done on two small devices with small chambers revealed that pressures of at least 26.3 bar could be tolerated. Above this pressure, the interfaces failed but the devices were not damaged. To investigate the cooling effect of the micropropellant, the endurance of a full thruster was also studied under wet testing where it was fed with 31 wt.% hydrogen peroxide. The thruster demonstrated complete evaporation and/or full decomposition at a power above 3.7 W for a propellant flow of 50 mu l min(-1). At this power, the catalytic bed locally reached a temperature of 147 degrees C. The component was successfully heated to an operating temperature of 307 degrees C, where it cracked. Under these firing conditions, and assuming complete decomposition, calculations give a thrust and specific impulse of 0.96 mN and 106 s, respectively. In the case of evaporation, the corresponding values are calculated to be 0.84 mN and 92 s.
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| 8. |
- Khaji, Zahra, 1983-
(författare)
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Extending Microsystems to Very High Temperatures and Chemically Harsh Environments
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aiming at applications in space exploration as well as for monitoring natural hazards, this thesis focuses on understanding and overcoming the challenges of extending the applicability of microsystems to temperatures above 600°C as well as chemically harsh environments. Alumina and zirconia high-temperature co-fired ceramics (HTCC) with platinum as the conductor material, have in this thesis, been used to manufacture a wide range of high-temperature tolerant miniaturized sensors and actuators, including pressure and flow sensors, valves, a combustor, and liquid monopropellant microthrusters.Interfacing for high temperatures is challenging. One solution is to transfer the signal wirelessly. Here, therefor, wireless pressure sensors have been developed and characterized up to 1000°C.It is usually unwanted that material properties change with temperature, but by using smart designs, such changes can be exploited to sense physical properties as in the gas flow sensor presented, where the temperature-dependent electrical conductivity of zirconia has been utilized. In the same manner, various properties of platinum have been exploited to make temperature sensors, heaters and catalytic beds. By in-situ electroplating metals after sintering, even more capabilities were added, since many metals that do not tolerate HTCC processing can be added for additional functionality. An electroplated copper layer that was oxidized and used as an oxygen source in an alumina combustor intended for burning organic samples prior to sample analysis in a lab on a chip system, and a silver layer used as a catalyst in order to decompose hydrogen peroxide in a microthuster for spacecraft attitude control, are both examples that have been explored here.Ceramics are both high-temperature tolerant and chemically resistant, making them suitable for both thrusters and combustors. The corresponding applications benefit from miniaturization of them in terms of decreased mass, power consumption, integration potential, and reduced sample waste.Integrating many functions using as few materials as possible, is important when it comes to microsystems for harsh environments. This thesis has shown the high potential of co-fired ceramics in manufacturing microsystems for aggressive environments. However, interfacing is yet a major challenge to overcome.
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| 9. |
- Khaji, Zahra, et al.
(författare)
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Integrated cooling system for microfluidic PDMS devices used in biological microscopy studies
- 2022
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Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 0960-1317 .- 1361-6439. ; 32:8, s. 087001-
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a two-channel, water-based cooling system was integrated into a PDMS-glass microfluidic device for application in single-cell biological studies. This system is designed to cool living cells to single-digit temperatures in situ, without requiring any features of the electron-beam fabricated master mould to be changed, and without interfering either biologically or optically with the cells themselves. The temperature profile inside the device was mapped using multiple thermocouples mounted inside the device, over time. A parametric study including coolant flow rate, distance between the cooling channel and the fluidic channel, and number of active cooling channels were performed to evaluate the performance of the system. By using ice water as the coolant, we have demonstrated stable on-chip cooling reaching an average temperature of 4.9 °C when operated at a coolant flow rate of 23 ml/min and using two active cooling channels, positioned only 400 μm away from the cell trapping sites. The maximum observed temperature deviation during an 80 min stability test was ± 0.2 °C. We have observed that flowing room temperature culture media through the device with active cooling had no influence on the temperature inside the chip, demonstrating its suitability for use in live cell culture experiments. Finally, we have also demonstrated that the active cooling system successfully decreased the cell metabolism of trapped E. coli resulting in a decreased growth rate of the bacteria.
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| 10. |
- Khaji, Zahra, et al.
(författare)
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Investigation of the storage and release of oxygen in a Cu-Pt element of a high-temperature microcombustor
- 2014
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Ingår i: The 14th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications(PowerMEMS 2014). - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- A miniature combustor for converting organic samples into CO2 with application in carbon isotopic measurements has been manufactured and evaluated. The combustor was made of High-Temperature Co-fired Ceramic (HTCC) alumina green tapes. The device has a built-in screen printed heater and a temperature sensor made of platinum, co-sintered with the ceramic. A copper oxide oxygen supply was added to the combustor after sintering by in-situ electroplating of copper on the heater pattern followed by thermal oxidation. Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Thermal Gravimetric Analysis (TGA) were used to study electroplating, oxidation and the oxide reduction processes. The temperature sensor was calibrated by use of a thermocouple. It demonstrates a temperature coefficient resistance of 4.66×10−3/°C between 32 and 660 °C. The heat characterization was done up to 1000 °C by using IR thermography, and the results were compared with the data from the temperature sensor. Combustion of starch confirmed the feasibility of using copper oxide as the source of oxygen of combustion.
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