A MEMS-based solid propellant microthruster array for space and military applications

Since combustion is an easy way to achieve large quantities of energy from a small volume, we developed a MEMS based solid propellant microthruster array for small spacecraft and micro-air-vehicle applications. A thruster is composed of a fuel chamber layer, a top-side igniter with a micromachined nozzle in the same silicon layer. Layers are assembled by adhesive bonding to give final MEMS array. The thrust force is generated by the combustion of propellant stored in a few millimeter cube chamber. The micro-igniter is a polysilicon resistor deposited on a low stress SiO2/SiNx thin membrane to ensure a good heat transfer to the propellant and thus a low electric power consumption. A large range of thrust force is obtained simply by varying chamber and nozzle geometry parameters in one step of Deep Reactive Ion Etching (DRIE). Experimental tests of ignition and combustion employing home made (DB+x% BP) propellant composed of a Double-Base and Black-Powder. A temperature of 250 therefore degrees C, enough to propellant initiation, is reached for 40 mW of electric power. A combustion rate of about 3.4 mm/s is measured for DB+20% BP propellant and thrust ranges between 0.1 and 3,5 mN are obtained for BP ratio between 10% and 30% using a microthruster of 100 mu m of throat wide

Structural and electronic properties of doped oligothiophenes in the presence of p-toluenesulfonate acids

We investigate the geometric and electronic structure of singly oxidized oligothiophenes in the presence of the counterion named p-toluenesulfonate acid (p-TSA) by performing ab initio density functional theory calculations using Becke-Half-and-Half-Lee-Yang-and-Parr hybrid functional on chains of up to 12 thiophene rings. Different possibilities of positioning the counterion along the conjugated chain are studied. The calculations indicate that the side orientation is the most stable structure of pTh/pTSA complex. Further, the influence of the counterion on the charge distribution and structural geometry of charged oligothiophenes is also investigated. In the last part of the work, the solid-state packing effects are considered by studying the stacking of two conjugated chains in the presence of two counterions. Our results are consistent with several experimental observations on similar conjugated polymers

A theoretical study of standard heat of formation of systems involving in the zinc reduction of silicon tetrachloride

The gas phase zinc reduction of silicon tetrachloride produces the silicon for solar cells. While this reaction provides a new low-cost production route for silicon materials for photovoltaic cells, little is known about the chemistry of this process. Theoretical methods, based on quantum chemistry predictions, in the gas phase, are now fully capable of providing molecular thermochemistry and kinetic parameters with sufficient accuracy for modeling purposes. This kind of kinetic information is crucial for reactor design and scale-up of reaction systems. In this spirit, we have developed two test sets, one for silicon and another for zinc compounds, for evaluating the performance of various computational methods: density functional theory (B3LYP, BH and HLYP, BMK, and M05-2X), and composite methods (G3 and CBS-QB3). The new generation of DFT methods BMK and M05-2X and the composite CBS-QB3 method allow to predict the standard heat of formation, Delta H-f(0), of the silicon compounds with MAD of, respectively, 7, 13, and 15 kJ mol(-1), whereas the previous DFT methods are less reliable. At least triple zeta, for basis set, is needed in order to predict correctly the standard heat of formation. For the zinc compounds, BMK, B3LYP, and CBS-QB3 are the best performing methods for the calculation of Delta H-f(0) with MADs of 24, 25, and 28 kJ mol(-1), respectively. We recommend BMK and CBS-QB3 methods for investigating the new solar silicon process

Evidence of Self-Assembled Monolayers Preorganization Prior to Surface Contact: a First Principles Study

International audienceno abstrac

Off-Lattice Flory–Huggins Approximations for the Tailored Calculation of Activity Coefficients of Organic Solutes in Random and Block Copolymers

Predicting activity coefficients in polymers for arbitrary solute and polymers is of general interest for packaging, environmental, and membrane applications. We examined the extensions of the proposed off-lattice approach [Gillet et al. <i>Ind. Eng. Chem.Res.</i> <b>2009</b>, <b>2010</b>] for random and block copolymers. Based on a comparison with an explicit representation of random copolymers, the principles of a mean-field approximation using only the properties of homopolymers have been established. The approach was successfully validated against the Flory–Huggins coefficients collected by Fornasiero et al. [<i>AIChE J</i>. <b>2002</b>] for 19 aromatic solutes in ethylene-vinyl acetate with acetylation rates varying from 33% to 100%. The role of substituents and isomerism is elucidated. Previously collected data and this study suggest that the real chemical affinity of substituted aromatic compounds for water could be strongly underestimated by previous oversimplified rules and that tailored methods, such as this one, would be preferable

The electrostatic probe: a tool for the investigation of the A beta(1-16) peptide deformations using the static modes

International audienceno abstrac