Vessel sealing

The common microwave oven has been brought into the laboratory. Using special Teflon reaction vessels, components are mixed together, the vessel sealed and put into the microwave oven. Reaction times are greatly accelerated in many reactions, and reactions that took hours to be complete in refluxing solvents are done in minutes. Benzyl alcohol was converted to benzyl bromide, for example, using microwaves (650 W) in only 9 min on a doped Montmorillonite K-10 clay. This is a growing and very useful technique. 

In a Karl Fischer experiment, why is the titration vessel sealed off from the laboratory air ... 

In a first full scale attempt at a new polymerisation process, the thermally unstable initiator was charged and heated to reaction temperature, but there was then an unforeseen delay of an horn before monomer addition was started. The rate of polymerisation effected by the depleted initiator was lower than the addition rate of the monomer, and the concentration of the latter reached a level at which an uncontrollable polymerisation set in which eventually led to pressure-failure of the vessel seals. Precautions to prevent such occurrences are detailed. In another incident, operator error led to catalyst, condensing styrene and acrylonitrile being ducted into an unstirred weighing tank instead of a reactor. When the error was recognised, the reacting mixture was dropped into drums containing inhibitor. One of the sealed drums had insufficient inhibitor to stop the reaction, and it slowly heated and eventually burst [1], The features and use of... 

Following preliminary DSC studies, isothermal decompositions of small quantities (1-3 mg) of compound are performed at temperatures generally below the observed DSC exothermic maximum. Samples are usually thermolyzed in sealed Pyrex tubes. Use of Pyrex usually precludes reaction with the container that often occurs with metal reaction vessels. Sealed vessels also prevent corrosive decomposition products, e.g. NO2 or HF, from damaging laboratory instrumentation. Sealed reaction vessels confine the decomposition products where they can easily be identified and quantified. It is obvious that highly reactive decomposition products such as formaldehyde are not observed by this technique, but they would not be expected to survive over the time of these decomposition experiments (seconds to hours, depending on the temperature). Seal vessel thermoylses mimic real storage scenarios where the sample is self-confined. However, autocatalysis may occur in sealed vessels that would not be observed in open ones. On the other hand, in unsealed tubes sublimation of the sample may become competitive with decomposition. 

Sample Digestion Fortification Preparation Weigh a representative sample on a balance with 0.1-mg precision (see Weights and Balances under Apparatus for Tests and Assays, Appendix I). Transfer the sample to a digestion vessel that has been cleaned according to the manufacturer s specifications. Slowly add 5.0 mL of concentrated nitric acid to the digestion vessel, seal, and heat the vessel for 8 to 16 h at 210° 5°. Allow the vessel to cool to room temperature, and quantitatively transfer its contents into a clean, dry, tared 1-oz polyethylene bottle. Slowly add concentrated hydrochloric acid to achieve a final concentration of 10% (w/w), and dilute to an appropriate final mass with High-Purity Water. 

As the work with the salts progresses, you can blend together equal volumes of the alcohol and vinegar in a "roomy" glass vessel, seal it and allow it to circulate for a Lunar cycle. At the end of the month, add the dry and powdered salts to the cooled liquid slowly. Re-seal the container and allow this to circulate for another Lunar cycle. At the end of this second cycle, carefully distil the whole mixture to dryness. 

The reaction vessel is then closed and the cotton removed from the collection vessel. A heating tape is wrapped around the collection vessel to point B (Fig. 6), and the vessel is warmed to 65°. Because of the difference in vapor pressure (at 65°, 4 mm. for the oxytetrafluoride and 2 mm. for the pentafluoride3) the oxytetrafluoride will sublime more quickly through the vessel and collect in the trap, while the pure pentafluoride will collect just beyond point B (Fig. 6) as a bright yellow viscous oil. The heating tape is removed and the collection vessel sealed at constrictions C and D. 

Weight loss at 60°, % Open Vessel Sealed Vessel... 

With cryogenic trapping, the extraction mixture is cooled down until the supercritical fluid expands and the analytes deposit. The trapping temperature to be used depends on whether the analytes are to be isolated from the fluid or this is to be liquefied and the collection vessel sealed in order to avoid losses of analytes through partial crystallization or the formation of aerosols during cooling. When the temperature of the cryogenic trap is very low, the restrictor must be heated in order to avoid the formation of two phases. As with collection on a solid sorbent, an additional preparative step is required. 

Testing for seals and gaskets. Unlike lining for vessels, seals and gaskets cannot be tested in full simulation, so the total compatibility is determined piecemeal, i.e., chemical compatibility and evaluation of the material in the gasketed joint. It takes experience to put the information together to make a sound decision. 

After reaction vessel a has been opened, the filled crucible is placed in it and the vessel sealed directly above the side tube (dotted line in figure), leaving as little dead space as possible. The reaction vessel is placed inside the heater o and its top is wrapped as well as possible in asbestos wool, to prevent cold spots where later on the alkali metal vapor could condense. Heating under high vacuum is then started. The temperature is checked with a thermocouple, protected by a thin ceramic sheath and inserted between the vessel wall and the heater. The thermocouple sheath must not touch the vessel wall and is prevented from adhering to the latter by a few tufts of asbestos. 

Naturally, this arrangement is more expensive than the first, and the problem of high shaft deflection at the vessel seal is still present. 

FIGURE 10.23 Vessel-sealing bipolar electrode system with cutting device. (Courtesy Tormod Martinsen.)... 

Advanced bipolar technologies include the seahng of blood vessels, fusion of tissue, tissue ablation, and bipolar cutting. Vessel sealing and tissue fusion uses special instruments and control algorithms to fuse the collagen within tissue. The most common use of this technology is to permanently seal blood vessels. 

Controlling Critical Coagulation Processes in Vessel Sealing (LigaSure)... 

Sample vessel sealing presses for use with (I) open-type sample vessels and (II) and (III) hermetically sealed-type sample vessels... 

Measure the amount of water, e.g. 1 litre, with a graduated cylinder and pour into the zinc or brass vessel. Seal the vessel with a rubber bung and then shake it for 1 minute. This produces the vapour-space equilibrium between the liquid and gas phases. Carefully discharge any gauge pressure and then fit the dispersion cylinder and measuring head in position in the vessel. 

Figure 4.71 Phase diagrams of water-carboxymethylcell-ulose (CMC) sodium salt. Water content (WJ = mass of water/mass of dry CMC, (gg ) heating rate, 10°Cmin sample mass, ca 5 mg sample vessel, sealed-type aluminum...

Figure 4.72 DSC curve for water-ethanol (40 60) mixture. Sample mass, 4.7 mg scanning rate, 5 °C min sample vessel, sealed type...

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