Iron and its compounds

Bakalářská práce je zaměřena na možnosti přípravy vybraných sloučenin železa. V teoretické části jsou podrobně popsány chemické a fyzikální vlastnosti síranu železitého, dodekahydrátu síranu amonno-železitého, oxidu železitého, hydroxidu železitého a tris(oxaláto)železitanu draselného. Z výsledků experimentální části je navržen optimální postup přípravy navazující řady tří sloučenin železa.The focus of the bachelor’s thesis are possibilities of synthesis of selected compounds of the iron. In theoretic part there are closely described chemical and physical properties of ferric sulfate, ammonium ferric sulfate dodecahydrate, ferric oxide, ferric hydroxide and potassium ferric oxalate. The optimal procedure of preparation of tree follow-up compounds of the iron is devised from the result of experimental section.

Catalytic Systems for Cyclic Ester Polymerization

Jednou z významných oblastí výzkumu organokovových sloučenin lanthanoidů, které je v poslední dekádě věnována pozornost, je využití komplexů v homogenní katalýze pro syntézu funkčních materiálů s definovanými vlastnostmi např. pro polymerace za otevření kruhu (ring opening). Polymerací za otevření kruhu mohou být připraveny alifatické polyestery, které díky své biodegradabilitě a biokompatibilitě nachází mimo jiné uplatnění i v biomedicíně. Teoretická část předložené práce se zabývá přípravou lathanidocenů, jejich charakterizací a možnostmi jejich využití při syntéze polymerů. Cílem experimentální části bylo provedení a optimalizace syntézy série lanthanocenových chloridových komplexů (Sm, Nd a Pr) a monopentamethylcyklopentadienylových komplexů. Uvedené strukturní typy byly vybrány s ohledem na možnost polymerační aktivity nebo možnosti jejich aktivace přidáním alkylačních činidel. Komplexy byly spektrálně charakterizovány pomocí NMR a IR spektroskopie a byla určena jejich struktura pomoci rentgenové strukturní analýzy. U vybraných chloridových komplexu neodymu a samaria komplexů byly provedeny studie katalytické aktivity pro polymerace ?-caprolactonu za laboratorní teploty v toluenu. Polykarpolakton byl poté charakterizován pomoci gelové permeační chromatografie a NMR.Usage of complexes in homogeneous catalysis for synthesis functional materials with defined properties is one of the most significant areas of research organometallic compounds of lanthanides in the last decade. One of the way became polymers with defined properties is for example ring opening polymerization. Aliphatic polyesters, which are biodegradable and biocompatible (useful for biomedicine), can be prepared by this method. Theoretical part of this work includes preparation of lanthanidocenes, their characterization and possibilities of their use for polymer synthesis. The aim of experimental part was performance and optimizing synthesis of series lanthanocen chlorides complex (Sm, Nd a Pr) and new monopentamethylcyklopentadienyl complexes. Introduced structural types were chosen for their possibility of polymerization activity or their activation by adding alkyl reagents. The complexes were spectral characterized by 1H NMR, and IR spectroscopy. Structure was defined by roentgen structural analysis. Catalytic activities for polymerization of ?-caprolacton in toluen (laboratory temperature) were performed for selected complexes. Polycaprolactone was characterized by gel permeation chromatography and NMR.

Micromachined electrospray thrusters for spacecraft propulsion

Micromachining has enabled the downscaling of large, massive and power hungry systems into small batch-produced integrated devices. Recent progress in electrospray thruster technology, in particular the discovery of an ionic emission mode using the ionic liquid EMI-BF4 as fuel has sparked interest in miniaturizing this thruster technology, initially developed in the 1950's and lying dormant for several decades. Electrospray thrusters operate by applying a potential difference between a conductive liquid, usually on the tip of a needle or capillary, and an extractor electrode. Once a threshold voltage is reached the electric stress at the apex of the liquid surface overcomes surface tension and a spray of particles is ejected toward a counter electrode. The purely electrostatic nature of this type of thruster makes it an ideal candidate for miniaturization and the use of ionic liquids, also known as molten salts, as fuel allows operating the thruster in bipolar mode eliminating the need for an additional neutralizer. This thesis describes a process flow to fabricate planar arrays of silicon capillaries with integrated individual extractor electrodes. The developed process flow offers the possibility to manufacture arrays on the wafer scale allowing, in principle, to increase thrust from a fraction of micronewton for a single capillary to the millinewton level for large arrays. This process flow has been validated by microfabricating several thruster prototypes, which were packaged using Low Temperature Co-Fired Ceramic (LTCC) technology. In conjunction with this microfabrication process an onset voltage model was developed intended as design tool during thruster layout. This model allows to predict the voltage at which particle emissions initiate for complex geometries and to estimate the effect of dimensional variations on parameters such as crosstalk in large arrays. Tests carried out with thruster prototypes using single capillaries show a well defined energy distribution of the particles and the possibility to modulate spray current by changing the voltage. Controlled variations in the fluidic impedance of the emitters allow to spray in either ionic or droplet mode. Time-of-flight measurements with arrays show a beam composed of ions (monomers, dimers), thus yielding a high specific impulse. A first life test finally shows thruster operation for several hours with stable beam properties

A method to determine the onset voltage of single and arrays of electrospray emitters

This paper reports on an accurate and rapid method to compute the onset voltage for a single or for an array of electrospray emitters with complex geometries and on the correlation of the simulation with experimental data. This method permits the exact determination of the onset voltage based only on the surface tension of the sprayed liquid and of the emitter geometry. The approach starts by determining the voltage at which electrostatic forces and surface tension forces are equal for a sharpening conic surface at the tip of a capillary as a function of the apex radius of the liquid. By tracing the curve of this computed equilibrium voltage as a function of apex radius, the onset voltage for a liquid surface with the Taylor half-angle of 49.3{degree sign} or larger can be determined. For smaller cone half-angles the method is only applicable to ionic sprays as an approximate knowledge of the critical field for ion emission is necessary. The combination of analytical models and finite element tools used to compute the necessary parameters are described. The method is validated on a complex MEMS emitter geometry as well as on a linear array of electrospray emitters. Finally an empirical model of the behavior of the electric field near the apex of a conic surface with asymptotes at a fixed half-angle is proposed which allows establishing a simple method for onset voltage determination

Integrated out-of-plane nanoelectrospray thruster arrays for spacecraft propulsion

Nanoelectrosprays, well known for their use in sample injection for the mass spectrometry of large biomolecules, can also be used in other applications such as spacecraft propulsion. The thrust generated by a single electrospray emitter is well below 1 μN, which is several orders of magnitude below the required thrust for planned formation flying missions. This paper presents the process flow and the microfabrication of large 2D arrays of out-of-plane nanoelectrospray capillary emitters with integrated extractor electrodes as well as electrospray results. The capillaries, 70 μm high and with 24 μm inner diameter, are etched from one silicon-on-insulator wafer. The extractor electrodes are from another silicon-on-insulator wafer. Both parts are passively aligned to within 2 μm, centering each capillary under one extractor electrode, thus ensuring highly uniform emitter characteristics over large arrays. Low hydraulic impedance has been a major problem in out-of-plane electrospray designs in the past, which is solved here by adding a post-processing step in which the capillaries are filled with 5 μm silica microspheres fixed in place by silanization. Finally, this paper reports on successful spray tests carried out under vacuum conditions with single and arrays of capillaries spraying the ionic liquid EMI-Tf2 N demonstrating the operation of our nanoelectrospray thrusters in an ionic mode

Microfabricated out-of-plane arrays of integrated capillary nano-electrospray emitters

This paper presents the fabrication and operation of an integrated nano-electrospray thruster consisting of an array of microfabricated silicon capillary emitters and microfabricated silicon extractor electrodes. Based on previous work in which we showed operation of single microfabricated capillaries, the improved thruster presented here allows simultaneously operation of arrays of emitters. In addition, we control the hydraulic impedance of the capillaries by filling them with silica beads, thus tailoring the flow rate in order to spray either in droplet regime or in ionic regime for two ionic liquids. Operation in both modes is confirmed by mass spectrometry and retarding potential analysis. In ion regime, a specific impulse of 3500 s is obtained at 1.2 kV for the ionic liquid EMI-BF4

Microfabrication and test of an integrated colloid thruster

This paper reports on the design, fabrication and test of an integrated colloid micropropulsion system for spacecraft attitude control using the ionic liquid EMI-BF4 as fuel. The principle of operation of the thruster is identical to electrospray ionization. The objective of the project was to demonstrate the feasibility and operability of arrays of microfabricated capillary emitters with individual extractor electrodes. This design approach results in an identical electric field distribution from one capillary to the other, avoids crosstalk and therefore allows for a more finely modulated thrust control. Spraying tests with different thruster configurations were conducted under vacuum conditions. Tests were performed with different thruster configurations and starting voltages around 700V were observed

Performance of a micro-fabricated Colloid thruster system

In order to fully characterize the performance of the colloid thruster system the electrospray (ES) beam must itself be fully characterized. This may be achieved by measuring various properties such as flow rate, current, droplet/ion charge to mass ratio and current profile. Beam properties of both standard electrospray mass spectrometry (ESMS) emitters and arrays of custom made micro-fabricated emitters have been determined. By varying the geometries of the micro-fabricated emitters two basic modes of thruster operation have been identified a high Isp with lower thrust density and a lower Isp with higher thrust density. The versatility of this system allows for a thruster design that has a thrust range spanning two orders of magnitude from ~ 5 to 500μN with highly competitive power requirements ~ 0.05W/μN. The proposed thruster system is designed to meet the needs of future formation flying missions

A new concept for a low-cost Earth sensor: Imaging oxygen airglow with arrays of single photon detectors

This paper presents a novel concept for a compact low-cost Earth sensor based on imaging atmospheric oxygen emission at 762nm using arrays of single photon avalanche diodes (SPADs). In both nighttime and daytime there is continuous emission at 762nm due to oxygen recombination. The SPADs high sensitivity enables the ES to operate at night and day, over a wide temperature range, with a very compact optical system (e.g. aperture of 10mm, focal length of 14mm) and no scanning elements. A modular and low-cost instrument design is described with uses the same wavelength band, the same detector technology, the same optics, the same power and data interfaces and similar algorithms for LEO and GEO applications. Using the visible band rather than the LWIR band offers several advantages including much lower cost detectors, no need for cooling, a more relaxed thermal design, simpler optics, higher sensitivity and hence lower cost