Vacuum-generation methods

This section reviews various vacuum-generation methods applicable to process industries. There are many types of equipment that can be used for vacuum generation in industries. 

Three generations of latices as characterized by the type of surfactant used in manufacture have been defined (53). The first generation includes latices made with conventional (/) anionic surfactants like fatty acid soaps, alkyl carboxylates, alkyl sulfates, and alkyl sulfonates (54) (2) nonionic surfactants like poly(ethylene oxide) or poly(vinyl alcohol) used to improve freeze—thaw and shear stabiUty and (J) cationic surfactants like amines, nitriles, and other nitrogen bases, rarely used because of incompatibiUty problems. Portiand cement latex modifiers are one example where cationic surfactants are used. Anionic surfactants yield smaller particles than nonionic surfactants (55). Often a combination of anionic surfactants or anionic and nonionic surfactants are used to provide improved stabiUty. The stabilizing abiUty of anionic fatty acid soaps diminishes at lower pH as the soaps revert to their acids. First-generation latices also suffer from the presence of soap on the polymer particles at the end of the polymerization. Steam and vacuum stripping methods are often used to remove the soap and unreacted monomer from the final product (56). 

Characterization methods. The 100 kV Vacuum Generator HB-5 STEM was used to mlcroanalyze samples. The HB-5 has a KEVEX SI(LI) energy dispersive X-ray spectrometer (EDS) and micro area electron diffraction (MAED) capabilities In conjunction with simultaneous bright and dark field Imaging capabilities. A more detailed explanation of the Instrumental operation can be obtained In a publication by C. Lyman(12). 

The bromoketone 17 was prepared via bromination of 15 with PTAB in DME. Hydrogen bromide, formed during the reaction, reacted with DME to generate methyl bromide and 2-methoxyethanol, both of which could be easily removed from the reaction medium under vacuum. This method was more convenient than the bromination reaction in TH F because the resulting 4-bromobutanol by-product formed from THF was not volatile. The bromide 17 was used directly in the next reaction, partly because 17 is rather reactive with limited stability. 

Electroless deposition as we know it today has had many applications, e.g., in corrosion prevention [5-8], and electronics [9]. Although it yields a limited number of metals and alloys compared to electrodeposition, materials with unique properties, such as Ni-P (corrosion resistance) and Co-P (magnetic properties), are readily obtained by electroless deposition. It is in principle easier to obtain coatings of uniform thickness and composition using the electroless process, since one does not have the current density uniformity problem of electrodeposition. However, as we shall see, the practitioner of electroless deposition needs to be aware of the actions of solution additives and dissolved O2 gas on deposition kinetics, which affect deposit thickness and composition uniformity. Nevertheless, electroless deposition is experiencing increased interest in microelectronics, in part due to the need to replace expensive vacuum metallization methods with less expensive and selective deposition methods. The need to find creative deposition methods in the emerging field of nanofabrication is generating much interest in electroless deposition, at the present time more so as a useful process however, than as a subject of serious research. 

Under the headline of instmmentation we shall mainly discuss the different types of mass analyzers in order to understand their basic principles of operation, their specific properties and their performance characteristics. Of course, this is only one aspect of instmmentation hence topics such as ion detection and vacuum generation will be addressed in brief. As a matter of fact, sample introduction is more closely related to particular ionization methods than to the type of mass analyzer employed, and therefore, this issue is treated in the corresponding chapters on ionization methods. The order of appearance of the mass analyzers in this chapter neither reflects the ever-changing percentage they are employed in mass spectrometry nor does it strictly follow a time line of their invention. Instead, it is attempted to follow a trail of easiest understanding. 

The present procedure uses sodium methoxide in methanol for generation of the tosylhydrazone salt. This procedure gives the highest reported yield and, unlike other procedures, also gives pure diazo compounds free from solvents. This vacuum pyrolysis method appears applicable to the formation of relatively volatile aryldiazomethanes from aromatic aldehydes. Table I gives yields of diazo compounds produced by this vacuum pyrolysis method. The yields have not been optimized. The relatively volatile diazo esters, ethyl a-... 

However, we concentrate here on the generation methods in which we are able to get directly the FD quantum state desired. Namely, we shall describe the models involving quantum nonlinear oscillator driven by an external field [11-13,22]. For this class of systems we are able to get the quantum states that are very close for instance, to the FD coherent states [2,3] or to the FD squeezed vacuum [10]. 

Vacuum ultraviolet (VUV) photolysis of liquid water (Aexc <185 nm) provides a clean source of HO radicals and H atoms and, with much lower efficiency, hydrated electrons (Caq ). Formate reacts efficiently with HO and H, as shown in reactions (R2-R5). The quantum yields of hydrated electron formation, (eaq ), are very low, and in acidic solutions of pH <4 the concentration of Caq is further decreased owing to the efficient scavenging of Caq by HaO to yield H atoms (k = 2A x 10 ° ImoF s ) (see below). Consequently, VUV irradiation (Aexc= 172 nm) of N2-saturated aqueous solutions (pHw4) containing formic acid/formate ions yields mainly CO2 radicals and this generation method was used for experiments under steady-state conditions. 

The vortex method, one existing vacuum generation technique, allows mobile robots to maintain a solid grip by means of a constant airflow that creates a suction that in turn produces negative pressure in this closed area, resulting in the necessary force of attraction between the robots and the wall. 

The choice of the precursor will depend on the reaction medium. High vacuum deposition methods use volatile organometallic precursors or ion, atom or molecule beams. Normal pressure vapor methods use similar volatile precursors, or sprayed metal salt solutions. Aqueous solution methods use water soluble salts, and organic solution methods use organometallic soluble compounds. Typical chemical reactions to generate the growth units are ... 

Synthesis. Iminoboranes, thermodynamically unstable with respect to oligomerization can be isolated under laboratory conditions by making the oligomerization kineticaHy unfavorable. This is faciUtated by bulky substituents, high dilution, and low temperatures. The vacuum gas-phase pyrolysis of (trimethylsilylarnino)(aLkyl)haloboranes has been utilized as an effective method of generating iminoboranes RB=NR as shown in equation 19 for X = F,... 

The most common impurities are the corresponding acid and hydroxy compound (i.e. alcohol or phenol), and water. A liquid ester from a carboxylic acid is washed with 2N sodium carbonate or sodium hydroxide to remove acid material, then shaken with calcium chloride to remove ethyl or methyl alcohols (if it is a methyl or ethyl ester). It is dried with potassium carbonate or magnesium sulfate, and distilled. Fractional distillation then removes residual traces of hydroxy compounds. This method does not apply to esters of inorganic acids (e.g. dimethyl sulfate) which are more readily hydrolysed in aqueous solution when heat is generated in the neutralisation of the excess acid. In such cases, several fractional distillations, preferably under vacuum, are usually sufficient. 

---