Rapid quench device

The rapid-quenching device employed will be described in Chapter 5. A polished cylindrical steel specimen, 11.28 mm diameter and 5 mm high, was held in a liquid aluminium alloy (volume 10 cm ) protected by a flux for 100 to 3600 s, and then the solid specimen together with the melt were rapidly cooled by quenching in water to arrest the reactions at the steel-aluminium interface. The time of cooling from 700°C down to room temperature did not exceed 2 s. The bimetallic specimen thus obtained was... 

The process of dissolution of a solid in a liquid can readily be investigated using a rapid-quenching device like that shown schematically in Fig. 5.3. Depending on the nature of substances to be studied, this may be carried out either in vacuum, or in a protective atmosphere (inert gases, hydrogen, nitrogen, etc), or under a flux.197,303309... 

Fig. 5.3. Rapid-quenching device for investigating the process of dissolution of a solid in a liquid by the rotating disc method.309 1, electric-resistance furnace 2, solid specimen 3, protective tube 4, electric motor 5, rotating shaft 6, stopper 7, thermocouple 8, flux 9, liquid.

Figure 8.43 Rapid Quench Device. Biocatalyst E and substrate S are combined in a mixing zone (hatched area) and the mixture ejected along a common outlet tube in order to be combined with quencher Q in another mixing zone. Different mixing times correlate with different reaction times t pre-quenching. Spectroscopic monitoring as a function of t gives first order relaxation curves for analysis.

Figure 2. Rebinding of [ C]ADP to oxidized ( ) and DTT-reduced ( ) thylakoid membranes following 150 saturating flashes. After a dark interval of between 20 ms and 500s, samples were mixed with an equal volume of reaction medium containing 50 uM [ C]ADP, using a rapid quench device (Update Instruments). The reaction temperature was 4°C.

The autoclave is not the only component of an LDPE plant which may be exposed to a decomposition. Local hot spots in a secondary compressor may initiate a decomposition reaction consequendy it is necessary to protect these units from serious overpressure by pressure relieving devices and to release the products of the decomposition reactions safely. The problem of the aerial decomposition referred to eadier has been largely overcome by rapidly quenching the decomposition products as they enter the vent stack. 

Recently, studies were reported measuring the kinetics of stimulation of both cAMP and 3 using a mixing device and rapid quenching, in the millisecond range, in rat olfactory cilia (67). The response to a mixture of < orants peaks within 25 to 50 milliseconds, the time frame expected for receptors, with both cAMP and IP3. Similar measurements of the change in concentration of cAMP or IP3 were also done in the taste cell. Here mice, which were bred as bitter tasters and nontasters , were used as subjects. The bitter stimuli, sucrose octaacetate, strychnine and denatonium benzoate, were shown to increase IP3 levels in a membrane preparation from "taster" mice in the presence of GTP-protein and Ca but not in membranes from "nontaster" mice (68). 

The US EPA defined Best Current Operating Practice (BOP) as being the use of GCP combined with a temperature limitation of 350 °F (approximately 175 °C) on the inlet to post-combustion control devices. Rapid quenching of the combustion gases to below 175 °C was also regarded as BOP. 

Figure 4 A schematic representation of the experimentai approach for time-resoived XAS measurements. XAS provides local structural and electronic information about the nearest coordination environment surrounding the catalytic metal ion within the active site of a metalloprotein in solution. Spectral analysis of the various spectral regions yields complementary electronic and structural information, which allows the determination of the oxidation state of the X-ray absorbing metal atom and precise determination of distances between the absorbing metal atom and the protein atoms that surround it. Time-dependent XAS provides insight into the lifetimes and local atomic structures of metal-protein complexes during enzymatic reactions on millisecond to minute time scales, (a) The drawing describes a conventional stopped-flow machine that is used to rapidly mix the reaction components (e.g., enzyme and substrate) and derive kinetic traces as shown in (b). (b) The enzymatic reaction is studied by pre-steady-state kinetic analysis to dissect out the time frame of individual kinetic phases, (c) The stopped-flow apparatus is equipped with a freeze-quench device. Sample aliquots are collected after mixing and rapidly froze into X-ray sample holders by the freeze-quench device, (d) Frozen samples are subjected to X-ray data collection and analysis.

Rapid-Mixing or Stop-Flow Monitoring To elucidate the mechanism of very fast enzyme reactions, it is critical to monitor the initial events before the system has a chance to attain a steady state. In many cases, the intermediate transient species exist for only few milliseconds. The fast enzyme reactions can be monitored readily by combining rapid mixing and quenching devices with mass spectrometry. The multiplex detection and fast scanning capabilities of time-of-flight (TOF) and Fourier transform (FT)-ion cyclotron resonance (ICR) mass spectrometers make them ideal for this combination. 

Enzyme reaction intermediates can be characterized, in sub-second timescale, using the so-called pulsed flow method [35]. It employs a direct on-line interface between a rapid-mixing device and a ESI-MS system. It circumvents chemical quenching. By way of this strategy, it was possible to detect the intermediate of a reaction catalyzed by 5-enolpyruvoyl-shikimate-3-phosphate synthase [35]. The time-resolved ESI-MS method was also implemented in measurements of pre-steady-state kinetics of an enzymatic reaction involving Bacillus circulans xylanase [36]. The pre-steady-state kinetic parameters for the formation of the covalent intermediate in the mutant xylanase were determined. The MS results were in agreement with those obtained by stopped-flow ultraviolet-visible spectroscopy. In a later work, hydrolysis of p-nitrophenyl acetate by chymotrypsin was used as a model system [27]. The chymotrypsin-catalyzed hydrolysis follows the mechanism [27] ... 

In recent years there has been renewed interest in treating coal at high temperatures both by rapid processing in the more conventional type of carbonization apparatus (I) and by using such devices as flash tubes (5, 12, 13), lasers (13), arc image furnaces (9, 11), and plasma jets (3). All these methods produce conditions whereby the coal can be heated rapidly to a temperature well in excess of 1000°C. followed by quenching of the products. The work described here is an investigation into the reactions of coal in a plasma jet and has been reported briefly elsewhere (3). 

Polyethylene is translucent to opaque white in thick sections, opacity increasing with density. Relatively clear film can be extruded from polyethylene, especially if it is quenched rapidly. The plastic accepts pigmentation readily. Most coloring is performed using dry-blend techniques. Color dispersion devices are required to ensure thorough mixing of resin and pigment. 

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