Vacuum treatment

Condensation of metal vapors followed by deposition on cooler surfaces yields metal powders as does decomposition of metal hydrides. Vacuum treatment of metal hydrides gives powders of fine particle size. Reaction of a metal haHde and molten magnesium, known as the KroU process, is used for titanium and zirconium. This results in a sponge-like product. 

Other Continuous Processes. Various pasteurization heat treatments ate identified by names such as quick time, vacuum treatment (vacreator), modified tubular (Roswell), small-diameter tube (MaHotizer), and steam injection. The last three methods are ultrahigh temperature (UHT) processes (see Fig. 3). Higher treatment temperatures with shorter times, approaching two seconds, are preferred because the product has to be cooled quickly to prevent deleterious heat effects. 

Vacuum Treatment. Milk can be exposed to a vacuum to remove low boiling substances, eg, onions, garlic, and some silage, which may impart off-flavors to the milk, particularly the fat portion. A three-stage vacuum unit, known as a vacreator, produces pressures of 17, 51—68, and 88—95 kPa (127, 381—508, and 660—711 mm Hg). A continuous vacuum unit in the HTST system may consist of one or two chambers and be heated by Hve steam, with an equivalent release of water by evaporation, or flash steam to carry off the volatiles. If Hve steam is used, it must be cuUnary steam which is produced by heating potable water with an indirect heat exchanger. Dry saturated steam is desired for food processing operations. 

The purification of Hquid nitro alcohols by distillation should be avoided because violent decompositions and detonation have occurred when distillation was attempted. However, if the distillation of a nitro alcohol cannot be avoided, the utmost caution should be exercised. Reduced pressure should be utilised, ie, ca 0.1 kPa (<1 mm Hg). The temperature of the Hquid should not exceed 100°C hot water should be used as the heating bath. A suitable explosion-proof shield should be placed in front of the apparatus. At any rise in pressure, the distillation should be stopped immediately. The only commercially produced Hquid nitro alcohol, 2-nitro-1-butanol, is not distilled because of the danger of decomposition. Instead, it is isolated as a residue after the low boiling impurities have been removed by vacuum treatment at a relatively low temperature. 

Unlike traditional surface science techniques (e.g., XPS, AES, and SIMS), EXAFS experiments do not routinely require ultrahigh vacuum equipment or electron- and ion-beam sources. Ultrahigh vacuum treatments and particle bombardment may alter the properties of the material under investigation. This is particularly important for accurate valence state determinations of transition metal elements that are susceptible to electron- and ion-beam reactions. Nevertheless, it is always more convenient to conduct experiments in one s own laboratory than at a Synchrotron radiation focility, which is therefore a significant drawback to the EXAFS technique. These focilities seldom provide timely access to beam lines for experimentation of a proprietary nature, and the logistical problems can be overwhelming. 

Fig. 33. The ESR spectra of V/Si02 after vacuum treatment at 500° spectra at —253° (a) without further treatment, (b) after contact with H20 vapor (151).

Studies of V4+, which is also a 3d1 ion, have been carried out by several investigators (151, 162, 163). The spectra are often complex due to a nuclear spin of i however, good resolution has been achieved for the ion in a particular symmetry. After a vacuum treatment of vanadium on silica gel at 500° van Reijen and Cossee (151) observed the spectra shown in Fig. 33. Both spectra were obtained with the sample at 20°K. The authors attributed the first spectrum to the (V04)4" ion and the second to the... 

Ukuku DO, Fan X and Kozempel MF. 2006. Effect of vacuum-steam-vacuum treatment on microbial quality of whole and fresh-cut cantaloupe. J Food Prot 69(7) 1623-1629. 

Fito, P., Andres, A., Chiralt, A., and Pardo, P. 1996. Coupling of hydrodynamic mechanism and deformation-relaxation phenomena during vacuum treatments in solid porous food-liquid systems. J. Food Engineer. 27, 229-240. 

Relation 9.77 is usually called the Washburn equation [55,237], One should consider it as a special case of the fundamental Young-Laplace equation [3,9-11], Washburn was the first to propose the use of mercury for measurements of porosity. Now, it is a common method [3,8,53-55] of psd measurements for a range of sizes from several hundreds of microns to 3 to 6 nm. The lower limit is determined by the maximum pressure, which is applied in a mercury porosimeter the limiting size of rWl = 3 nm is achieved under PHg = 4000 bar. The measurements are carried out after vacuum treatment of a sample and filling the gaps between pieces of solid with mercury. Further, the hydraulic system of a device performs the gradual increase of PHg, and the appropriate intmsion of mercury in pores of the decreasing size occurs. 

C02(C0)s ZnO Adsorption from solution and vacuum treatment Ion-pairing species stable up to 160°C under CO/H2 high selectivity to C1-C3 alcohols in CO hydrogenation, performance in ethylene hydroformylation [139]... 

Vanadium loaded AIPO -S showed broad bands. The broad features of EPR bands are attributed to the undispersed species. However, the EPR bands of the sample gradually changed on successive oxidation-reduction treatment followed by vacuum treatment, resulting in a clear hyperfine structure. This indicates that vanadium ions are finely dispersed in AIPO4-5. 

On the positive side, thermization and minimum pasteurization should not cause the formation of undesirable flavours and aromas and should, in fact, result in improved flavour by reducing bacterial growth and enzymatic activity, e.g. lipolysis. If accompanied by vacuum treatment (vacreation), pasteurization removes indigenous off-flavours, i.e. those arising from the cow s metabolism or from feed, thereby improving the organoleptic qualities of milk. 

P2O5 b) vacuum treatment of 1-bydro-peroxyethanol at 70-75° c) dehydration of di-(l-hydroxyethyl) peroxide with P2O5 and d) from butene ozonide Refs 1) Beil 19, [449] 2) H Wieland ... 

Carbon dioxide is, of course, in equilibrium with bicarbonate ion almost the entire CO2-HCO3- system can be removed by heat or vacuum treatment (Smith 1964). The oxygen content of pasteurized bottled... 

Shipe, W. F. 1964. Effect of vacuum treatment on freezing point of milk. J. Assoc. Offic. Agr. Chem. 47, 570-572. 

The assumption is made that the combining ratio for the alcoholate is identical to that for the hydroxide adduct. Percentages are in mole percent. Solvent remaining after vacuum treatment at 25° foi 16 hr. 3-Hydroxy-2-methyl-4ff-pyran-4-one. d Use of methanol instead of ethanol gave a 1.8 1 complex that consisted of 70% of alcoholate and 30% of adduct. 

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