Dust-analog synthesis

To model experimentally the formation and properties of solid particles that form in the outflows of stars under realistic conditions appropriate to a circumstellar outflow, we would need a system large enough that the walls of the chamber are unimportant and the chamber itself needs to be pumped down to pressures that are several orders of magnitude less than the partial pressure of the least abundant reactant. In a typical stellar outflow SiO is present at 10-6 the abundance of hydrogen, while hydrogen is present at 1010 particles per cm3. In practical terms, this means that the experimental system must be capable of achieving a vacuum better than 10-15 atm and operate at about 10-9 atm or less. These conditions are barely achievable in terrestrial laboratories. However, for wall effects to be unimportant, the chamber radius must be several times the mean free path of the gas at 10-9 atm the mean free path is 100m. 

A spherical vacuum chamber several hundred meters in radius, capable of achieving a vacuum less than 10-15 atm and operating at 10 9 atm might be possible, but would be very expensive. Heating the system to more than 2000K only adds spice to the problem. If the system were built and, in the one-meter cube center, SiO molecules were introduced at 104 cm-3, then condensed to make 10 nm grains ( 105 SiO molecules per grain) that are allowed to settle onto a 10 m square collection plate, and if this experiment were repeated 10 times, then the collector would 

LI Vapor condensation, electrical discharge, and laser pyrolysis 

2 Melt solidification, sol-gel reactions, Czochralski, and floating-zone methods 

Sol-Gel reactions were developed in the 1950s as a method to synthesize pure silicate mineral grains such as forsterite or clinopyroxene. These techniques begin 

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Laboratory studies of simple dust analogs in astrophysical environments 153 5.5.2 Catalytic effects of dust on synthesis of biomolecules... 

Laboratory production of dust analogs is a highly specialized field that attempts to reproduce a subset of the basic properties of the solids that we expect to exist in a particular astrophysical environment. The synthesis of dust in the outflows of evolved stars, however, is a much more complex process that occurs under nonequilibrium, continuously changing conditions and with the participation of many more chemical elements than can be accommodated by any practical experimental... 

The NaSa-containing analog of sarcophaginate 3 was obtained from 5,5 -bis-(4-amino-2-thiabutyl)-3,7-dithianonane-l,9-diamine by Scheme 63 [144], After reduction with zinc dust the resultant NaSa-sarcophaginate underwent demetallation with NaCN. Thus, the ligand obtained may be employed for the synthesis of other metal ion complexes. 

This five membered hetero-cyclic compound is analogous to the two preceding ones having the oxygen of furfuran replaced by the imide group, (—NH—). Two methods of synthesis prove its constitution. Succinimide when distilled with sodium or zinc dust is reduced and pyrrole is obtained. 

Two important polycycles produced prior to 1920 were perylene 19 (Fig. 1.2a) and pyrene 7, both of note as parent structures for numerous fused benzenoid analogs produced in the following decades. In 1910, Scholl, Seer, and Weitzenbock first produced perylene from an AlCls-mediated cyclization of naphthalene and/or 1,1 -binaphthyl under heat in low yield [19]. A subsequent success with improved yield occurred via treatment of 1,8-diiodonaphthalene with Cu powder. Weitzenbock was responsible for the first synthesis of pyrene in 1913 [20]. The five-step synthesis began with bromination of o,o -ditolyl followed by conversion into dicar-boxylic add 20 via a dinitrile intermediate (Scheme 1.7). Cyclization and Zn-dust distillation afforded the tetra-fused structure in a well-designed synthesis, confirming its structure through intermediate analysis. 

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