Vacuum exposure

The implementation of high-pressure reaction cells in conjunction with UFIV surface science techniques allowed the first tme in situ postmortem studies of a heterogeneous catalytic reaction. These cells penult exposure of a sample to ambient pressures without any significant contamination of the UFIV enviromnent. The first such cell was internal to the main vacuum chamber and consisted of a metal bellows attached to a reactor cup [34]- The cup could be translated using a hydraulic piston to envelop the sample, sealing it from... 

Anthracene and maleic anhydride. In a 50 ml. round-bottomed flask fitted with a reflux condenser, place 2 0 g. of pure anthracene, I 1 g. of maleic anhydride (Section 111,93) and 25 ml. of dry xylene. Boil the mixture under reflux for 20 minutes with frequent shaking during the first 10 minutes. Allow to cool somewhat, add 0 5 g. of decolourising carbon and boil for a further 5 minutes. Filter the hot solution through a small, preheated Buchner funnel. Collect the solid which separates upon coohng by suction filtration, and dry it in a vacuum desiccator containing paraffin wax shavings (to absorb traces of xylene). The yield of adduct (colourless crystals), m.p. 262-263° (decomp.), is 2-2 g. Place the product (9 10-dihydroanthracene-9 10-cndo-ap-succinic anhydride) in a weU-stoppered tube, since exposure to air tends to cause hydration of the anhydride portion of the molecule. 

Prior to determination of an isotherm, all physisorbed material has to be removed from the surface of the adsorbent. This is best achieved by exposure of the surface to high vacuum, the exact conditions required (temperature and residual pressure) being dependent on the particular gas-solid system. In routine determinations of surface area it is generally advisable not to remove any chemisorbed species which may be present thus, the hydroxylated oxides are usually outgassed at 1S0°C. Microporous adsorbents such as zeolites or active carbons however require higher temperatures (350-400 C, say) for complete removal of physisorbed material from their narrowest pores. An outgassing period of 6-10 hours (e.g. overnight) is usually sufficient to reduce the residual pressure to 10 Torr. 

Direct-inlet probe. A shaft or tube having a sample holder at one end that is inserted into the vacuum system of a mass spectrometer through a vacuum lock to place the sample near to, at the entrance of, or within the ion source. The sample is vaporized by heat from the ion source, by heat applied from an external source, or by exposure to ion or atom bombardment. Direct-inlet probe, direct-introduction probe, and direct-insertion probe are synonymous terms. The use of DIP as an abbreviation for these terms is not recommended. 

K. H. Brown, Proc. Soc. Photo-Opt. Instr. Eng. 2438, 33 (1995). A good source of information on the new exposure technologies can be found in the Proceedings of the International Conference on Electron, Ion and Photon Beam Technology and Nanofabrication, pubhshed annuaUy in Issue 6 of the Journal of Vacuum Science and Technology B. 

Naphthalenol. 2-Naphthol or p-naphthol or 2-hydroxynaphthalene/7i3 -/5 -i7 melts at 122°C and boils at 295°C, and forms colorless crystals of characteristic, phenoHc odor which darken on exposure to air or light. 2-Naphthol [135-19-3] is manufactured by fusion of sodium 2-naphthalenesulfonate with sodium hydroxide at ca 325°C, acidification of the drowned fusion mass which is quenched ia water, isolation and water-washing of the 2-naphthalenol, and vacuum distillation and flaking of the product. A continuous process of this type has been patented (69). The high sulfate content ia the primary effluent from 2-naphthol production is greatiy reduced ia modem production plants by the recovery of sodium sulfate. 

The radioactive isotopes available for use as precursors for radioactive tracer manufacturing include barium [ C]-carbonate [1882-53-7], tritium gas, p2p] phosphoric acid or pP]-phosphoric acid [15364-02-0], p S]-sulfuric acid [13770-01 -9], and sodium [ I]-iodide [24359-64-6]. It is from these chemical forms that the corresponding radioactive tracer chemicals are synthesized. [ C]-Carbon dioxide, [ C]-benzene, and [ C]-methyl iodide require vacuum-line handling in weU-ventilated fume hoods. Tritium gas, pH]-methyl iodide, sodium borotritide, and [ I]-iodine, which are the most difficult forms of these isotopes to contain, must be handled in specialized closed systems. Sodium p S]-sulfate and sodium [ I]-iodide must be handled similarly in closed systems to avoid the Uberation of volatile p S]-sulfur oxides and [ I]-iodine. Adequate shielding must be provided when handling P P]-phosphoric acid to minimize exposure to external radiation. 

Nonoxide fibers, such as carbides, nitrides, and carbons, are produced by high temperature chemical processes that often result in fiber lengths shorter than those of oxide fibers. Mechanical properties such as high elastic modulus and tensile strength of these materials make them excellent as reinforcements for plastics, glass, metals, and ceramics. Because these products oxidize at high temperatures, they are primarily suited for use in vacuum or inert atmospheres, but may also be used for relatively short exposures in oxidizing atmospheres above 1000°C. 

One concern in conventional processing is the achievement of uniform reagent appUcation and uniform cross-linking (18). An area in which adequate treatment of aU fibers is necessary is in flame-retardant finishing. One means of obtaining thorough treatment has been the use of vacuum impregnation, in which the fabric is first passed over a vacuum slot to remove air from the fabric interstices, foUowed by exposure to the phosphoms flame-retardant solution in the precondensate ammonia system (19). 

It has been suggested that gold does not have a stable surface oxide (227), and therefore, its surface can be cleaned simply by removing the physically and chemically adsorbed contaminants. However, more recently it has been shown that oxidation of gold by uv and ozone at 25°C gives a 1.7 0.4 — nm thick AU2O2 layer (228), stable to extended exposure to ultra high vacuum (UHV) and water and ethanol rinses. 

Photochromic silver—copper haUde films were produced by vacuum evaporation and deposition of a mixture of the components onto a sUicate glass substrate (13). The molar ratio of the components was approximately 9 1 (Ag Cu) and film thicknesses were in the range of 0.45—2.05 p.m. Coloration rate upon uv exposure was high but thermal fade rates were very slow when compared with standard silver haUde glass photochromic systems. 

Vacuum-packed coffee retains a high quaUty rating for at least one year. The slight loss in fresh roasted character that occurs is because of chemical reactions with the residual oxygen in the can and previous exposure to oxygen prior to packing (29). 

Indirect Heating If the process material cannot tolerate exposure to the combustion gas or if a vacuum or an atmosphere other than air is needed in the furnace chamber, indirect firing must be employed. This is accomplished in a muffle furnace or a radiant-tube furnace (tubes carrying the hot combustion gas run through the furnace). 

Tetracyanoethylene [670-54-2J M 128.1, m 199-200 (sealed tube). Crystd from chlorobenzene, dichloroethane, or dichloromethane [Hall et al. J Org Chem 52 5528 1987]. Stored at 0° in a desiccator over NaOH pellets. (It slowly evolves HCN on exposure to moist air.) It can also be sublimed at 120° under vacuum. Also purified by repeated sublimation at 120-130°/0.5mm. [Frey et al. J Am Chem Soc 107 748 1985 Traylor and Miksztal J Am Chem Soc 109 2778 1987.]... 

Triphenylmethane [519-73-3] M 244.3, m 92-93 . Crystd from EtOH or benzene (with one molecule of benzene of crystallisation which is lost on exposure to air or by heating on a water bath). It can also be sublimed under vacuum. It can also be given a preliminary purification by refluxing with tin and glacial acetic acid, then filtered hot through a glass sinter disc, and ppted by addition of cold water. 

Vanadium (metal) [7440-62-2] M 50.9, m 1910°, d 6.0. Cleaned by rapid exposure consecutively to HNO3, HCl, HF, de-ionised water and reagent grade acetone, then dried in a vacuum desiccator. 

After dilution with 200 ml. of benzene, the solution is transferred to a 2-1. separatory funnel containing 800 ml. of ice water and shaken thoroughly. The aqueous layer is separated, acidified to pH 3-4 with 2-3 ml. of concentrated hydrochloric acid, and extracted with three 100-ml. portions of benzene. All the organic layers are then combined and dried over anhydrous sodium sulfate. Filtration and concentration of the solution with a rotary evaporator, followed by exposure to high vacuum for 2-3 hours, affords 17.3-19.3 g. of the crude product (Note 3). Low-boiling impurities are removed by vacuum distillation (Note 4), the residual oil (14-15 g.) is transferred to a 50-ml. flask equipped with a short-path distillation apparatus, and vacuum distillation is continued. A forerun is taken until no rise in boiling point is observed, and then 7.2-8.6 g. (23-27%) of dimethyl nitrosuccinate is collected as a colorless oil, b.p. 85° (0.07 mm.), 1.4441 (Note 5). 

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