Sudden cooling

Regulators may be used in gas blanketing systems to maintain a protective environment above anv liquid stored in a tank or vessel as the liquid is pumped out. When the temperature of the vessel is suddenly cooled, the regulator maintains the tank pressure and protects the waUs of the tank from possible collapse. Regulators are known for their fast dynamic response. The absence of time delay that often comes with more sophisticated control systems makes the regulator useful in applications requiring fast corrective action. 

Sudden cooling of a vapour-filled vessel which is sealed, or inadequately vented, may cause an implosion due to condensation to liquid. 

Another type of probe is based on the principle of the sudden cooling of the heated element. When foam comes in contact with a heated electrical element, the hot surface detects sudden cooling, which is translated to an output signal. The major problem with the use of a heated element is fouling of the media the sensitivity decreases while it is used, so such detectors may not be reliable in practice. 

Perhaps the most obvious method of studying kinetic systems is to periodically withdraw samples from the system and to subject them to chemical analysis. When the sample is withdrawn, however, one is immediately faced with a problem. The reaction will proceed just as well in the test sample as it will in the original reaction medium. Since the analysis will require a certain amount of time, regardless of the technique used, it is evident that if one is to obtain a true measurement of the system composition at the time the sample was taken, the reaction must somehow be quenched or inhibited at the moment the sample is taken. The quenching process may involve sudden cooling to stop the reaction, or it may consist of elimination of one of the reactants. In the latter case, the concentration of a reactant may be reduced rapidly by precipitation or by fast quantitative reaction with another material that is added to the sample mixture. This material may then be back-titrated. For example, reactions between iodine and various reducing agents can be quenched by addition of a suitably buffered arsenite solution. 

Sudden Cooling of Emulsion (Thermal Shock) Sudden temperature drop or freezing i.e., giving a thermal shock) of an emulsion mostly enhances the interfacial tension between the two immiscible phases thereby causing coalescence. 

Steel It has a higher C content (usually 0.5-1%) and is harder than soft bon. An important property of steel is that it may be hardened. If heated to bright redness (to obtain an austenitic alloy) and suddenly cooled quenched), by putting it in water, oil, etc, it becomes hard and brittle due to the formation of the very hard martensite. Brittleness can be removed by tempering (that is by a carefully heating for a short time at, say, 250-300°C) to release or dimmish the internal strains resulted from quenching. 

Metallic grey, semi-metal. In addition to the metallic form there are other metastable modifications (yellow As, formed by sudden cooling of the vapour, and three amorphous forms beta (black As), gamma and delta As). 

The critical factor which thus determines the nature of the emerging iron peak is the combustion time. Only a hydrodynamic model can provide us with a full appreciation of fusion times, describing the sudden and brutal temperature increase as the shock wave passes through, and the equally sudden cooling that follows it. 

The blackt amorphous, form is produced by sudden cooling of Sb vapors. The black form is more active and more easily volatilized than the metallic form. It is said (Ref 5, p 51), that if Sb is distilled in high vacuum, it deposits as an amorphous powder which might explode on heating or scratching... 

Sulfur has a striking ability to catenate, or form chains of atoms. Oxygen s ability to form chains is very limited, with H2Oz, 03, and the anions 02,022-, and 03 the only examples. Sulfur s ability is much more pronounced. It appears, for instance, in the existence of S8 rings, their fragments, and the long strands of plastic sulfur that form when sulfur is heated to about 200°C and suddenly cooled. The — S—S— links that connect different parts of the chains of amino acids in proteins are another example of catenation. These disulfide links contribute to the shapes of proteins, including the keratin of our hair thus, sulfur helps to keep us alive and, perhaps, curly haired. 

I. Remsen and E. H. Keiser considered that they had obtained a special allotropic form of phosphorus by suddenly cooling the vapour of phosphorus by iced-water. The product is here red phosphorus, for, as shown by A. Stock and co-workers, red phosphorus can be produced by suddenly quenching phosphorus vapour at 900 -1175. H. M. Vernon reported that rhombic phosphorus, i.e. rhombic crystals of phosphorus, can be obtained by slowly cooling liquid phosphorus. This observation, however, remains unverified ... 

Techniques of chromatographic analysis continue to develop and for up-to-date methods, the specialist literature should be consulted [62, 63]. In all cases, reaction samples have to be taken at known time intervals and quenched by an appropriate method (sudden cooling, change of pH, dilution, etc.) before chromatographic analysis. It is important to check the stability of the reaction component to the chromatographic and work-up conditions. For example, are the compounds to be analysed thermally stable to the GC conditions (Conditions inside a GC injection port and, indeed, within the column are not unlike those of a heterogeneous catalytic reactor ) Are they stable to the pH of the HPLC eluent An obvious restriction is that chromatographic component analysis does not lend itself to the study of fast reactions. 

IR spectroscopy is not confined to stable substances. In recent years, matrix isolation IR spectroscopy has become important in the investigation of short-lived, unstable molecular species. A gas containing such highly-reactive molecules - produced by photolysis of a reaction mixture, or in a high-temperature furnace - is suddenly cooled by contact with an inert solid (e.g. argon at c. 40 K). The matrix-isolated molecules are protected by the low temperature from unimolecular decomposition, and - by sheer isolation, if the dilution is sufficient - from bimolecular processes such as dimerisation or disproportionation. For example, the photolysis of Mn(CO)5H by a laser produces the otherwise unstable Mn(CO)5 and Mn(CO)4H molecules whose IR spectra can be measured in an argon matrix. Because of the low temperature, the lack of inter-molecular interactions and the rigidity with which the molecules are trapped in the matrix, such spectra are often very well resolved, better than can be achieved by conventional methods. Thus matrix isolation spectroscopy is widely used in the study of stable species, in preference to conventional techniques. 

Quench the sudden cooling of hot material discharging from a thermal reactor. 

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