Catalytic effect of platinum and silver in a hydrogen peroxide monopropellant ceramic microthruster

Zahra Khaji ^a,b,*, Lena Klintberg ^b, Kristoffer Palmer ^c, Greger Thornell ^a,b

a. Ångström Space Technology Centre, Dept. of Engineering Sciences, Uppsala University, Box 35, 75103, Uppsala, Sweden
         b. Div. of Microsystems Technology, Dept. of Engineering Sciences, Uppsala University, Box 35, 75103, Uppsala, Sweden
         c. Nanospace AB, Ulls Väg 29A, 75651, Uppsala, Sweden

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 15-20 vol.% graphite sacrificial paste before screen printing it. Ag was in-situ electroplated on the porous Pt surface after sintering. Decomposition of 50 wt.% 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 behaviour 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.

Keywords: Monopropellant microthruster; HTCC; Catalytic bed; Platinum; Silver; Hydrogen peroxide; Electroplating