High-pressure methods

Sohds or mixed solids are compressed in flexible compressible containers and on applying a high pressme, dense, high coordination nimiber phases are formed. Depending on the geometry of the device, different techniques have been apphed [3] piston-cylinder press can achieve 50 kbar and 1800 K multianvil press up to 200 kbar and above 2000 K and belt design up to 150 kbar and 2300 K. 

Zeolites are generally prepared under hydrothermal conditions in the presence of alkali (Barrer, 1982). The alkali, the source of silicon and the source of aluminium are mixed in appropriate proportions and heated (often below 370 K). A common reactant mixture is a hydrous gel composed of an alkali (alkali or alkaline-earth metal 

The hydrothermal method has been employed in recent years to synthesize a variety of solids that include aluminium phosphates (ALPOs) and other microporous transition-metal phosphates and transition-metal polychalcogenides (Davis Lobo, 1992 Haushalter Mundi, 1992 Liao Kanatzidis, 1990, 1992). Unlike zeolites, synthesis of ALPOs requires acidic or mildly basic conditions and no alkali metal cations. A typical synthetic mixture for making ALPO consists of alumina, H3PO4, water and an organic material such as a quaternary ammonium salt or an amine. The hydrothermal reaction occurs around 373-573 K. The use of fluoride ions, instead of hydroxide ions as mineralizer, allows synthesis of novel microporous materials under acidic conditions (Estermann et al, 1991 Ferey et ai, 1994). 

In the belt apparatus, the sample is contained in a noble metal capsule (a BN or MgO container is used for chalcogenides) and surrounded by pyrophyllite and a graphite sleeve, the latter serving as an internal heater. In a typical high-pressure run, the sample is loaded, the pressure raised to the desired value and then the temperature increased. After holding the pressure for about 30 minutes, the sample is quenched (400 K s ) while still under pressure. The pressure is then released after the sample has cooled to room temperature. 

High-pressure research requires suitable calibration and measurement of pressures. 

Calibration is carried out by making use of standard substances which are known to undergo structure transitions at definite pressures. 

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F. Haber s catalytic synthesis of NH3 developed in collaboration with C. Bosch into a large-scale industrial process by 1913. (Hater was awarded the 1918 Nobel Prize in Chemistry for the synthesis of ammonia from its elements Bosch shared the 1931 Nobel Prize for contributions to the invention and development of chemical high-pressure methods , the Hater synthesis of NH3 being the first high-pressure industrial process.)... 

C. Bosch and F. Bergius (Heidelberg) the invention and development of chemical high pressure methods. 

A knowledge of processing methods will be useful to the designer to help determine what tolerances can be obtained. With such high-pressure methods as injection and compression molding of 2,000 to 30,000 psi... 

High-pressure gas separation, hollow-fiber membrane modules for, 15 823 High pressure liquid chromatography (hplc), 9 234 21 275 in herbicide analysis, 13 312 polymer analysis using, 19 566 High-pressure methanol, production process, 16 300-301 High pressure methods, specialized, 13 430-431... 

High-pressure methods have been used for the synthesis of new solids that cannot possibly be made otherwise. In general, the formation of a new compound from its... 

The last kind of devices used in high-pressure service are level indicators. The knowledge of the level of fluids in different apparatus is important for safe and continuous operation of chemical plants. Levels must be measured under high pressure, methods using various physical properties have been developed for this purpose. A selection of methods used in high-pressure technology is presented in Table 4.4-3. 

BERGIUS, FREDERICK (1884-1949). A Gentian chemist who won the Nobel prize in 1931 with Carl Bosch for chemical high-pressure methods. He invented a method of converting coal dust into oil via pressunzed hydrogen, He also invented a method for production of cattle... 

Interest has been generated in the high-pressure method since it was demonstrated that high pressure is not only useful in effecting cyclo addition reactions, but also several kinds of ionic reactions [9-16]. The aim of the present article is to review recent examples of the use of high pressure for the synthesis of hetero cycles related to biologically interesting molecules, and to predict some further possibilities. The present review covers either representative or most recent examples. 

While ambient pressure studies must rely on discrete changes of crucial parameters, the high pressure method is capable of generating continuous changes of interatomic distances or relative energies of different electronic states. Moreover, at the same time the chemical composition of the rare-earth compound is conserved under pressure, while ambient pressure studies usually have to consider different compounds. In this sense, the application of high pressure can solve physical problems which can not be accessed by any other method. 

Although the high-pressure method itself is rather simple to use, high-pressure physics is still a somewhat exotic tool for investigating rare-earth compounds. This seems rather surprising if the unique possibilities for example for the determination of intrinsic crystal-field parameters are considered. In many cases, theories explicitly predict certain distance dependences, which can be verified straightforward by the application of pressure, which continuously alters the interatomic distances. 

Many of the traditional methods continue to be exploited to synthesise novel materials. In the area of cuprates, the synthesis of a superconducting ladder cuprate and of car-bonato- and halocuprates is noteworthy. High pressure methods have been particularly useful in the synthesis of certain cuprates and other materials.36,44 The combustion method has come of age for the synthesis of oxidic and other materials.45 Microwave synthesis is becoming popular46 while sonochemistry has begun to be exploited.47... 

C.C. Bradley, High Pressure Methods in Solid State Research (London, Butter-worths, 1969.)... 

High-pressure methods are discussed in detail under High Pressure Synthesis of Solids. Hydrothermal methods are discussed in the previous Section. A few examples relative to oxide synthesis are given here. Descriptions of the equipment used are given by Rao and GopaUcrishnan and by Rooymans. ... 

Finally, the application of high-pressure methods (85S1) to the amination of chloro- and bromoquinolines and chloro- or bromopyridines (88H3I9) has been described. Thus, 2-chloropyridine (86) reacts at 60°C and 8 kbar pressure with piperidine to form 2-piperidinopyridine (111) in 12% yield. Analogously, 3-chloropyridine (112) reacts at I00°C with pyrrolidine to give a 10% yield of 3-pyrrolidinopyridine (113), which is, however, obtained in 71% yield under the same reaction conditions from 3-bromo-pyridine (99) (88H3I9). 

High Pressure Method. Sometimes, certain solid phases or compounds which defy synthesis at ambient pressure can be prepared at high pressures. Conditions are particularly favorable if the product molar volume is appreciably less than that of the reactants. Since the other techniques failed to produce either NiU04 or ZnU04, the preparation of these compounds was attempted by a high pressure method. 

Two additional hydrofluoric acid methods have been reported (1,2), and are similar to that described above. The method of Hughes et al. has also been the subject of two comparative studies relevant to the analysis of ceramics (2,31). Techniques that retain silicon have been discussed (1,2) and involve either fusion with lithium metaborate [or sodium carbonate (2)] or high pressure dissolution in a PTFE bomb. An alternative high pressure method, developed by Price and Whiteside (32), was evaluated in the course of this investigation but was found to be unreliable for stained glass of medieval composition in many experiments dissolution was incomplete. Attempts to modify the procedure by varying the prescribed dissolution parameters produced insufficiently consistent results although superior conditions were established (Table I). 

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