Hard vacuum

Hard Vacuum Use a balanced o-ring seal for industrial vacuum. For absolute pressure less than 1 kpa (1 kilopascal) use a torsion balanced seal. (Must verify this measurement)... 

The operating principle of steam-jet ejectors is explained in Volume 1, Chapter 8. Then-specification, sizing and operation are covered in a comprehensive series of papers by Power (1964). Diffusion pumps are used where very low pressures are required (hard vacuum) for processes such as molecular distillation. 

A solution of 20.6 g of 3,4,5-trimethoxphenylacetonitrile in 70 g pyridine was treated with 15 mL 99+% D20 and held at reflux for 24 h. All volatiles were stripped first under vacuum and finally with a hard vacuum at room temperature in a Kugelrohr apparatus. The dark residue was treated again with another 30 mL pyridine and another 15 mL 99+% D20. The flask was protected with a drying tube and held at reflux for another 24 h. Again, all volatiles were stripped, and the residue distilled at 110-130 °C at 0.25 mm/Hg to yield 16.77 gofan almost white solid. The GCMS verified this chemical to be 3,4,5-trimethoxy-B,B-dideuterophenylacetonitrile, with a parent peak at m/e 209 and no visible peak at m/e 207. 

Amixtureof 2.2 g 3-bromo-4,5-methylenedioxybenzaldehydeand 3.6 mL cyclohexylamine in a distillation flask was heated to 100 °C to effect solution, and then with an open flame until the signs of H,0 evolution were evident. This was then placed under a hard vacuum to remove the generated water and excess cyclohexylamine, and the product distilled at 120-125 °C at 0.2 mm/Hg. There was obtained 2.4 g of the Schiff base of the aldehyde and the amine, melting at 86-96 °C. Recrystallization of an analytical sample from 5 volumes of MeOH gave 3-bromo-... 

The relationship between pressure ratio and selectivity is important because of the practical limitation to the pressure ratio achievable in gas separation systems. Compressing the feed stream to very high pressure or drawing a very hard vacuum on the permeate side of the membrane to achieve large pressure ratios both require large amounts of energy and expensive pumps. As a result, typical practical pressure ratios are in the range 5-20. 

The calculations shown in Figure 11.18 assume that a hard vacuum is maintained on the permeate side of the membrane. The operating and capital costs of vacuum and compression equipment prohibit these conditions in practical systems. More realistically, a carrier facilitated process would be operated either with a compressed gas feed and atmospheric pressure on the permeate side of the membrane, or with an ambient-pressure feed gas and a vacuum of about 0.1 atm on the permeate side. By substitution of specific values for the feed and permeate pressures into Equation (11.19), the optimum values of the equilibrium constant can be calculated. A plot illustrating this calculation for compression and vacuum operation is shown in Figure 11.19. 

G. Ottaviani and M. Costato have investigated the process of compound formation at the platinum-silicon interface. Platinum films, 115, 205, 268 and 357 nm thick, were sputtered on Si(l 11) single crystals under hard vacuum. The interaction of the Pt and Si phases during isothermal annealing was followed using Rutherford backscattering spectroscopy of helium ions. 

Lithium tantalate is a single-crystal material that is produced in quantity by the Czochralski method (see Section 3.11) for piezoelectric applications and is therefore readily available. It is stable in a hard vacuum to temperatures that allow outgassing procedures. It is insensitive to humidity. It is widely used where precise measurements are to be made. 

The laser is used in two ways. In the first strike, it is defocused and its beam is used simply to clear adsorbed impurities, films, etc., from the area, a small portion of which (say, a micron in dimension) is to be the object of a pothole excavation. In the second strike, the laser is intensely focused after passing through a lens system, and the intensity of its strike vaporizes metal to form a hole. The size of the potholes is as little as 0.1 pm in diameter and about 1 pm in depth. A hard vacuum (10 10 to 10 y mm Hg) is necessary to give the quadrupole mass spectrometer the required sensitivity. A diagram of the technique is shown in Fig. 12.95. 

To a solution of 66 mg nor-LSD in 2 mL freshly distilled DMF under a nitrogen atmosphere, there was added 48 mg anhydrous K2CO3 and 38 mg ethyl iodide. When TLC analysis indicated that the nor-LSD had been consumed (4 h) all volatiles were removed under a hard vacuum. The residue was solubilized in... 

In order to determine surface characteristics and particle thickness, it is usual to deposit obliquely a film of heavy metal on to a specimen or its replica. The metal is applied by deposition in a hard vacuum by a small source in order that a nearly parallel beam may reach the specimen. The technique was originated by Williams and Wyckoflf [175] in 1946 and has been used extensively since. 

The cells are vacuum treated. 35% of the electrolyte volume is filled and the cells are vacuum treated again. Another 35% of the electrolyte is added. The cells are vacuum treated and the remaining 30% of the electrolyte volume is filled. Most often, however, this procedure is reduced to two vacuum treatments only. The method is applied mainly to gel designs of VRLA battery. There are two types of vacuum treatment (i) soft vacuum , in which a pressure slightly lower than atmospheric pressure is maintained in the cells (ii) hard vacuum , in which the cell pressure is < 15 mm Hg column. The hard vacuum treatment ensures faster filling of the plate group with electrolyte. 

TABLE 19-3. COEFFICIENTS OF FRICTION OF M0S2 SLIDING ON M0S2 IN HARD VACUUM... 

The apparatus comprised a tube, containing a fine tungsten wire, to which was attached a pirani gage calibrated for hydrogen, and a gas pipette. As before, the apparatus was pumped to a hard vacuum and the wire flashed... 

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