Autoclave synthesis

Once prepared the gel was stirred for 18 hours at room temperature and then transferred into a teflon-lined stainless steel autoclave. Synthesis took place at 180°C for 3 days, after which the reaction was quenched by plunging the autoclave into cold water. The resulting crystals were filtered with copious amounts of water, before being left to dry at 110°C overnight. 

Autoclave Synthesis of VPI-5. Table I shows how the properties of the gel change after various heating times. The TBA that is present in the starting gel is rapidly expelled into solution upon heating and is not found in any of solid samples collected. The pH was found to rise sharply after 45 minutes and reaches a final pH of 7.0 after 23 hours. The solid Al/P ratio decreases to a ratio of 1.06 over the course of the reaction while the liquid Al/P ratio rises to a value of 0.9. 

The synthesis of nanocrystalline Ti02, which is an important photocatalyst for the decomposition of toxic chemicals, is one of the more thoroughly investigated solvothermal/hydrothermal reactions. Approaches to this preparation have involved the decomposition of metal alkoxides, [158] a TOPO-capped autoclave synthesis of Ti02 by metathetic reachon [159] and decomposihon of a metal N-nitroso-N-phenylhydroxylamine complex [160,161]. In 1988, Oguri and coworkers reported the preparahon of anatase by hydrothermally processing hydrous htania prepared by the controlled hydrolysis of Ti(OEt)4 in ethanol [162]. The reachon condihons leading to monodispersed anatase nanoparhcles by this approach... 

Twenty grams of cobalt(II) carbonate (0.168 mol) and 150 ml. of c.p. pyridine (1.86 mols) are placed in a 500-ml. stainless-steel autoclave (synthesis 54). The autoclave is flushed three times with carbon monoxide at a pressure of 200 p.s.i. An equimolar mixture of carbon monoxide and hydrogen is admitted to a pressure of 3500 p.s.i. The rocking mechanism is started, and the temperature is raised to 155 to 160° and maintained in this range for 2 hours. The vessel is then allowed to cool to room temperature, and the gases are vented. The solution in the bomb contains about 2.5 g. of the pyridinium salt of the cobalt tetracarbonyl anion per 10 ml. (yield about 90%)4... 

Some of the important innovations in recent years are the decomposition of metal alkoxides for the synthesis of TiOj "" nanoparticles, TOPO capped autoclave synthesis of Ti02by metathetic reaction, 22i decomposition of metal N-nitroso N-phenyl... 

Many methods have been reported for production of nanodiamonds (NDs) such as laser ablation, " plasma-assisted chemical vapor deposition," autoclave synthesis from supercritical fluids, ion irradiation of graphite, chlorination of carbides, electron irradiation of carbon onions, and ultrasound cavitation. Smaller NDs can be prepared by detonation processes that yield aggregates of NDs with sizes of 4-5 nm embedded in a detonation soot composed of other carbon allotropes and impurities. An explosive mixture having an overall negative oxygen balance provides a source of both carbon and energy for the conversion. Because of their small size (2-10 nm) detonation NDs have also been referred to as ultradispersed, nanocrystalline... 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

High Osmolality Contrast Media. An important advance in radiopaques came with the synthesis of aminotriiodoben2oic acid and its acetylated derivative, acetrizoic acid [85-36-9] (5) (8,9). Aqueous solutions of sodium acetrizoate possessed the thermal stabiUty so that they could be autoclaved (10) with minimal decomposition. The higher iodine content, ie, 3 atoms/molecule, increased the contrast efficiency, and the clinical safety of acetrizoate was improved over that of the earlier urographic agents. 

The preferred method for synthesis of complex carbides is the powder metallurgy technique. Hot-pressed powder mixtures must be subjected to prolonged annealing treatments. If low melting or volatile components are present, autoclaves are used. 

Hydrogenation reduces the nitro group to amino which is then diazotized using sodium nitrite and tetrafluoroboric acid. The diazotized crown was not isolated but the aq. solution was treated directly with sodium acetate and bis(dibenzylideneacetone)-pal-ladium(O) in acetonitrile solution. Ethylene was then introduced to the autoclave and the solution was allowed to stir for 2 days. 4 -Vinylbenzo-15-crown-5 was isolated (30% from 4 -nitrobenzo-15-crown-5) as a colorless solid (mp 43.5—44.2°) °. The synthesis is illustrated in Eq. (3.16). 

Later a more convenient synthesis of 172 appeared heating di-ferf-butylacetylene with elemental sulfur in benzene at 190°C in an autoclave... 

High-pressure synthesis Here austenitic steels are applied to autoclaves and pressure-vessel linings, pipelines, valves and other equipment dealing with a variety of products, often at quite high temperatures. 

The main method of PA synthesis is by melt polymerization. The polymerization of PA-6,6 occurs in two stages, a prepolymerization of the PA salt at elevated pressures followed by a melt polymerization at atmospheric pressure. The prepolymerization stage requires an autoclave, preferably with a glass insert. The glass insert allows easy extraction of the polymer. PA-6 polymerization is simple it can be carried out at atmospheric pressure, and the evaporating water stirs the reaction medium. 

The partially aromatic PAs are exclusively made of die diamine-diacid type and not die amine-acid type. The aromatic diamines, similar to phenylene diamines, color easily and dieir polymers are conjugated, having a golden brown color. The aromatic diacids used in the formation of partially aromatic PAs are mainly terephthalic and isophthalic acids. Starting with the diacids, the PA salt is made first and with this the salt prepolymers are prepared. The prepolymerization is usually carried out in an autoclave to prevent die sublimation of the reactants. In a laboratory synthesis it would be preferable to avoid this autoclave step as one is not always available. It is possible to start with the more reactive esters, such as diphenyl isophtiialate, or with the acid chlorides starting with the reactive isocyanates is, in principle, also possible. The terephthalic and isophthalic acids are also used to modify PA-6,6 and PA-4,6 to more dimensionally stable copolymers.6,18... 

In zeolite synthesis (ref. 2) an aqueous mixture containing a silicon source, an aluminum source, an alkali source (usually NaOH) is autoclaved and subjected to hydrothermal treatment. Hydrated Na-ions are then filling the pore system in the as-synthesized zeolite. In the case of relatively high Si/Al zeolites an organic template is required which is usually a tetraalkylammonium compound, applied as the bromide or the hydroxide. 

The same periodic structures can also be formed from alternating AIO4 and PO4 tetrahedra the resulting aluminophosphates are not called zeolites but AlPOs. Zeolites are made by hydrothermal synthesis under pressure in autoclaves, in the presence of template molecules such as tetramethylammonium, which act as structure directing agents. 

In several investigations, the synthesis of [Tc2(CO)i0] was improved with respect to yield and reaction conditions. The lowest pressure allowing the isolation of [Tc2(CO)io] in acceptable yield was about 100 atm. However, even under these conditions, the use of an autoclave for high-pressure reactions is still necessary. This offers a clue as to how preparation of larger amounts of this synthon may currently be achieved, thereby providing a basis for fiirther development of the field of organotechnetium chemistry. 

With autoclave syntheses a high yield of clusters is achieved, and it is possible for researchers to follow the reaction path in solution by gradually changing (from experiment to experiment) the working parameters of the synthesis (temperature, pressure, exposure at working temperatures, etc). All these advantages of the autoclave technique have resulted in an abundance of new forms of technetium clusters (particularly, polynuclear ones) because it has been possible to develop and improve the method of obtaining these compounds. 

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