Evacuated container

Die castings produced in a cavity which has been evacuated contain significantly less porosity and hence, are more ductile. Such castings were produced on an experimental basis in the 1980s. In the 1990s, this process is expected to compete with components either fabricated from sheet metal or... 

Evacuated container A sealed vacuum sampling container, which is opened for the collection of a given material. 

Consider what happens when a sample of N204, a colorless gas, is placed in a closed, evacuated container at 100°C. Instantly, a reddish-brown color develops. This color is due to nitrogen dioxide, NO2, harmed by decomposition of part of the N2O4 (Figure 12.1, p. 324) ... 

Admission of air to the evacuated container of the dry oximate led to explosion on 2 occasions nitrogen purging is advised. 

The protection of petroleum facilities follows the same overall philosophy that would be applied to any building or installation. These basic requirements are personnel evacuation, containment, isolation, and suppression. Since these are design features that cannot be immediately brought in at the time of an incident they must be adequately provided as part of the original facility design. What constitutes adequate is the definition fire, risk and loss protection professionals must provide. 

The activity of the solvent often can be obtained by an experimental technique known as the isopiestic method [5]. With this method we compare solutions of two different nonvolatile solutes for one of which, the reference solution, the activity of the solvent has been determined previously with high precision. If both solutions are placed in an evacuated container, solvent will evaporate from the solution with higher vapor pressure and condense into the solution with lower vapor pressure until equilibrium is attained. The solute concentration for each solution then is determined by analysis. Once the molality of the reference solution is known, the activity of the solvent in the reference solution can be read from records of previous experiments with reference solutions. As the standard state of the solvent is the same for all solutes, the activity of the solvent is the same in both solutions at equUibrium. Once the activity of the solvent is known as a function of m2 for the new solution, the activity of the new solute can be calculated by the methods discussed previously in this section. 

The chart in Fig. 1.1 represents schematically the venting (or airing) of an evacuated container through an opening in the envelope (venting valve), allowing ambient air at p = 1000 mbar to enter. In accordance with the information given above, the resultant critical pressure is Ap, = 1000 (1- 0.528) mbar = 470 mbar i.e. where Ap > 470 mbar the flow rate will be choked where Ap < 470 mbar the gas flow will decline. 

The detection, identification and estimation of impurities by various chromatographic techniques is so well documented that few comments are required here. It must be remembered, however, that since we are concerned with extremely low concentrations, one cannot be sure of finding an impurity whose retention time on a column is close to that of the main compound, and also that a very small fraction of the main compound may undergo transformations on the column, especially if it is at an elevated temperature, so that spurious impurities may be produced in this way. If the main compound is sensitive to any of the components of air, especial precautions must be taken in transferring the sample from its evacuated container to the inlet of the chromatograph. 

The sample preparation vacuum line (often called spray-on line ) should allow for (a) controlled mixing of the host gas with the substrate (or with other components that are added to the matrix) by manometric techniques and (b) the controlled release of the gas (mixture) toward the inlet system of the cryostat. These conditions are met by a vacuum line that incoporates a storage bulb for the gas (mixture), inlets for attachment of evacuable containers that allow degassing of the substrate prior to its mixing with the host gas, pressirre gauges that cover suitable ranges, a needle valve that allows the controlled release of the gas, possibly via a flowmeter, and interfaces to the bottles that contain the host gas(es), and to the inlet system that is attached to the vacuum shroud of the cryostat. 

Worker exposure to toxic vapors is monitored by collecting samples in the breathing zone of the worker. These samples are usually returned to a laboratory for analysis. A suitable sampling pump and collection device are required. Lightweight, battery-operated pumps are available in a variety of flowrates. Collection devices are usually sorbent tubes or bubblers or impingers, but bags and evacuated containers have also been used. This discussion will focus on solid sorbents as collection media. 

A large proportion of atmospheric samples will be obtained in containers similar to those shown in Figure 7.1. It should be recognized that these samples may have been taken under circumstances in which the temperature of the sample was much higher than the laboratory in which analyses are to be made. An immediate result of this would be that the sample contained, as available to the analyst, is present at an unknown pressure less than atmospheric. In addition, some samples are taken by using evacuated containers, then opening them at the site to transfer sample to the container. If the container was not opened for a sufficient period of time, the contents may still be below atmospheric... 

Dissolved oxygen and other gases can be removed from the solvent by the freeze-pump-thaw (FPT) method, or by the expansion of gases above the solvent into an evacuated container on the vacuum line. It is customary to freeze-pump-thaw the solvents before vapor transfer from the storage container to the vacuum electrochemical cell. Such FPT cycles should be done as soon as the solvent is brought into contact with the drying agent. The FPT method involves three basic steps (i.e., one cycle), which are often repeated ... 

A similar strategy is employed to purify zirconium, which is used as cladding for fuel rods in nuclear reactors (Section 22.6). The crude metal is heated at about 200°C with a small amount of iodine in an evacuated container to form the volatile Zrl4. The Zrl4 is then decomposed to pure zirconium by letting the vapor come in contact with an electrically heated tungsten or zirconium filament at about 1300°C ... 

The discussion of the high-temperature properties and thermal decomposition of carbonates in this chapter, a plan which will be followed for other classes of compounds in subsequent chapters, is given for each element. A brief discussion is followed by quantitative data on phase transitions, densities, and thermodynamic parameters for the carbonate, the corresponding oxide, and the decomposition reaction MC03 = MO + C02. If the carbonate and oxide are solids and form no solid solution, the equilibrium constant is the pressure of C02 which would be obtained if one begins with an evacuated container and lets the system come to equilibrium. In this case, the pressure is a unique function of the temperature. As pointed out in Chapter 1, this is no longer true... 

Partial pressures of the three gases can be calculated if the initial conditions are known. For example, if the decomposition is carried out in air, p(02) = 0.21. If it is carried out in a closed, originally evacuated container in which the only source of the gases is the decomposing sulfate, partial pressures can be calculated from the simultaneous solution of Equations 4.3 and 4.4, corresponding to Equations 4.1 and 4.2... 

A glass ampoule containing 1 mol of liquid water at 100°C is inside an evacuated container of volume V. The ampoule is broken, while the system is maintained at 1000 C. Calculate AS for the change in state (a) for the case that V — 10 liters, and (b) for the case that V - 100 liters. Make any reasonable approximations required. 

A sample of solid ammonium chloride was placed in an evacuated container and then heated so that it decomposed to ammonia gas and hydrogen chloride gas. After heating, the total pressure in the container was found to be 4.4 atm. Calculate Kp at this temperature for the decomposition reaction... 

An 8.00-g sample of SO3 was placed in an evacuated container, where it decomposed at 600.°C according to the following reaction ... 

A sample of iron(II) sulfate was heated in an evacuated container to 929 K, where the following reactions occurred ... 

The Vapor Pressure of Liquids. Vapor pressure is defined as the pressure exerted by a vapor in equilibrium with its liquid. Consider a closed, evacuated container which has been partially filled with a liquid. The molecules of the liquid are in constant motion but not all the molecules move with the same velocity and there will be some which possess a relatively high kinetic energy. If one of these fast moving molecules reaches the liquid surface, it may possess sufficient energy to overcome the attractive forces in the liquid and pass into tiie vapor space above. As the number of molecules in the vapor phase increases the rate of return to the liquid phase also increases and eventually a condition of dynamic equilibrium is attained when the number of molecules leaving the liquid is equal to the number returning. The molecules in the vapor phase obviously exert a pressure on the containing vessel and this pressure is known as the vapor pressure. 

The equilibrium constant for this reaction is 1.8 X 10 at 600 K. Gaseous CH4, H2O, and CO are introduced into an evacuated container at 600 K, and their initial partial pressures (before reaction) are 1.40 atm, 2.30 atm, and 1.60 atm, respectively. Determine the partial pressure of H2(g) that will result at equilibrium. 

Suppose some OF2 is introduced into an evacuated container at 298 K and allowed to dissociate until its partial pressure reaches an equilibrium value of 1.00 atm. Calculate the equilibrium partial pressures of F2 and O2 in the container. 

Pure solid NFd4lTSe is placed in an evacuated container at 24.8°C. Eventually, the pressure above the solid reaches the equilibrium pressure 0.0184 atm due to the reaction... 

Ammonium hydrogen sulfide, a solid, decomposes to give NH3(g) and H2S(g). At 25°C, some NH4HS(s) is placed in an evacuated container. A portion of it decomposes, and the total pressure at equilibrium is 0.659 atm. Extra NHslg) is then injected into the containei and when equilibrium is reestablished, the partial pressure of NH3(g) is 0.750 atm. 

If a quantity of water is introduced into an evacuated container at 37°C, evaporation will occur and the pressure in the container will rise to 47 mmHg the S VP of water is 47 mmHg at 37°C. 

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