Vacuum line metal

The metal itself, having an appreciable vapour pressure, is also toxic, and produces headaches, tremors, inflammation of the bladder and loss of memory. The best documented case is that of Alfred Stock (p. 151) whose constant use of mercury in the vacuum lines employed in his studies of boron and silicon hydrides, caused him to suffer for many years. The cause was eventually recognized and it is largely due to Stock s publication in 1926 of details of his experiences that the need for care and adequate ventilation is now fully appreciated. 

A greater hindrance for paleoclimate studies, however, is that the traditional method required reduction in an all metal vacuum line at high temperature (in externally-heated nickel reaction vessels) with bromine pentafluoride (BrFs), a highly reactive gas (Clayton and Mayeda 1963). Handling this material in anything other than a dedicated geochemistry laboratory has proven extremely difficult and dangerous (Chivas 1984). 

The adsorbent—a powder generally, but it could be a metal or oxide film— is placed in a glass tube (the adsorption cell C in Fig. 15) which is connected to the volumetric and vacuum lines. The bottom part of the tube, which contains the adsorbent and is located in the calorimeter cell, is made of thin-walled (0.2-0.3 mm) blown tubing (A in Fig. 18). In order to avoid the slow diffusion of gases through a thick layer of adsorbent (see Section VII.A), the sample is often placed in the annular space between the inner wall of the adsorption cell and the outer wall of a cylinder made of glass,... 

Materials 1,3-Dioxolane (1) and 1,3-dioxepane (5) were prepared and purified conventionally. Compound 1 contained no impurities detectable by GLC, but 5 contained a trace of tetrahydrofuran (THF) which could not be removed even by distillation on a Fenske column with a reflux ratio of 50 1 4-methyl-l,3-dioxolane (4) was prepared by Astle s method [10]. All monomers were dried preliminarily by storage over LiAlH4 in reservoirs attached to a conventional high-vacuum line fitted only with all-metal valves, and then stored with liquid Na-K alloy until used. Methylene dichloride was purified conventionally, distilled on a Normatron 1.5 m column, dried i.vac. over LiAlH4 on a conventional high-vacuum line, and then stored for 24 h over a fresh sodium film immediately before use, in a reservoir attached to the vacuum line. 

Antimony pentafluoride (4.94 g, 22.8 mmole) is added, in a good dry box, to side B of the reaction flask using an all-glass syringe. Elemental mercury (2.74 g, 13.7 mmole) is added to side A. The reaction vessel is fitted at E and F with Nupro or similar metal valves, removed from the dry box, and attached to a vacuum line that has been thoroughly flamed before use. Approximately 10 mL of sulfur dioxide is transferred to side B by cooling with liquid N2, and the... 

Fig. 4. Schematic vacuum system for metal atom reactions. X represents the stopcock or Teflon-in-glass valve. Satisfactory components (for a general discussion of vacuum line design see References 1 and 4) forepump, 25 L/min free air capacity diffusion pump, 2 L/sec main trap is removable and measures about 300 mm deep main manifold has a diameter of about 25 mm, stopcock or valve in manifold should be at least 10 mm substrate container is removable container with 1-2 mm Teflon-in-glass needle valve connected to bottom of container. Connection between this needle valve and the reactor may be 1/8 in. od. Teflon tubing is used. Alternatively, the substrate may be added as shown in Fig. 3.

In a typical experiment the metal vacuum line and connections to the hexafluoride and HF storage tubes are pumped to at least KT4 torr over several hours. A 30-mL Kel-F reaction tube9 fitted with a metal valve closure is charged with silicon powder and a Teflon-covered stirring bar. The reaction tube is attached to the vacuum system and evacuated. 

Sodium was purified in the apparatus shown in Fig. 5.1(a), thus Ca. 12 g of sodium, cleaned as described in Section 4.4.3.1, was introduced into a tube A, which was then sealed to the apparatus at a this was evacuated for 8 h without heating the sodium, and then sealed off from the vacuum line at e. Tube A was then heated gently and the molten sodium poured swiftly into B, leaving its skin stuck to the tube, which was sealed off at b. This process was repeated by pouring the sodium successively into C and D and finally collecting the silvery metal in E, the sections being sealed off successively at c, d, and /. It is not known why this method of purification is more effective than distillation. The flask E was reattached to the vacuum line via the break-seal g (Fig. 5.1(i)) and then 300 ml of purified ethanol was distilled into E from the container F. 

The Eulr2 alloy was prepared by direct combination of the metals. Europium chips, % in. on edge were placed in a V4 in.-diameter cavity of a die. Iridium metal powder, —325 mesh and 99.9% pure, was sprinkled over the rare earth element, and the mixture was compressed at 5000 psi. The compressed pellet was placed in a molybdenum boat, which then was transferred to a quartz sleeve, followed by insertion into a quartz reaction tube. The tube was attached to a glass vacuum line and evacuated. Argon was added to approximately 1 atm and the compressed pellet was heated to 900° C and held at the temperature for 14 hr. The product was air quenched to room temperature. The product was crushed in an agate ball mill, compressed into a pellet again, and reheated in the same manner as before. 

In a glove box several grams of benzophenone and freshly cut sodium metal were added to a glass tube (40 cm long, 2 cm ID) topped with a Kontes valve and vacuum line adapter. This glass tube was attached to the vaccum line and evacuated. The tube was immersed in a — 78°C isopropanol/COz slush bath. The lecture bottle valve on the (CH3)20 tank was opened slowly and (CH3)20 was condensed into the glass tube at — 78°C. The pressure of... 

The synthetically useful dianions [M3(CO)u]2- were first isolated by Shore and co-workers as the Ca2+ (M=Ru) and the K+ (M=Os) salts by the reduction of M3(CO)12 using alkali metal benzophenone solutions in THF.1 [Ru3(CO) J2 reacts with Ru3(CO) 2 to form the higher nuclearity clusters [Ru4(CO)13]2- and [Ru6(CO)i8]2- but the triruthenium anion can be obtained in high purity by slowly adding triruthenium dodecacarbonyl to an excess of reducing solution using vacuum-line techniques.2 Vacuum-line syntheses of both dianions have been described in detail.1... 

There are two basic evaporator designs that are typically used atmospheric and vacuum evaporation (Metals Handbook 1987). Atmospheric evaporation principles are similar to those of a heated open tank, with the exception that the heated liquid is sprayed over plastic packing in order to increase its surface area and accelerate evaporation. Atmospheric evaporators on chrome plating lines have sometimes been used simultaneously as evaporators and as plating bath fume scrubbers. Atmospheric evaporators are considerably less expensive than vacuum evaporators. Typical atmospheric evaporator capital costs range from 2500 to 4000, while vacuum evaporator costs can be an order of magnitude or more higher. In atmospheric evaporator systems, however, vaporized water is not recovered, as it can be in vacuum systems. 

The S4N4 is pumped in u vacuum line over silver wool al 220 °C, where it polymerizes slowly lo a lustrous golden material.w The resulting product is analytically pure, as is necessary for it to show metallic properties to a significant degree it has a conductivity near that of mercury at room temperature, and it becomes a superconductor al low temperatures (below 0 26 Kl. 

The reaction is carried out in a 100-mL, three-necked flask connected via a stopcock adaptor to the inert gas supply of a vacuum line. Mercury metal (0.40 g, 2.0 mmol) is added to a stirred solution of Ar2Te212 (1.09 g, 2.2 mmol)... 

The liquid sulfur dioxide solutions described in the preparations have a vapor pressure of about 3.3 atm at 21 °C. Therefore, well-constructed glass vessels and a glass (or metal) vacuum line must be employed to prevent pressure bursts. Thick leather gloves, safety goggles, a face shield, and a rubber apron should be worn and the experiments have to be conducted behind a safety shield or explosion-proof glass in a fume hood to prevent possible contact with the reaction mixtures as well as with AsF5 and SbFs. 

Fig. 5.3. Wayda-Dye greaseless vacuum line. This apparatus makes extensive use of metal bellows tubing and O-ring seals. Thus the reaction vessels, filters, and other items can be tilted and manipu lated like Schlenk ware, and high vacuum conditions can be achieved for the removal of atmospheric gases and for baking out residual moisture. Trap to-trap distillation of volatile solvents such as NH) or SO is readily accomplished with this apparatus. This version is not designed for the measurement of volatiles or trap-to-trap separation. (Reproduced from A.L. Way da and J. L. Dye, J. Chent. Educ. 62, 356 (1985) by permission of the copyright owner the Division of Chemical Education of the American Chemical Society.)...

The mechanical fore pump is a heavy item which sets up considerable vibration. This vibration disrupts the menisci of mercury manometers and is otherwise undesirable. To minimize the transfer of vibrations to the vacuum line, the fore pump generally is mounted on the floor (rather than on the bench of the vacuum rack) and the connection between the fore pump and the vacuum system is made with heavy-walled vacuum tubing or flexible corrugated metal tubing. 

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