Evacuation and outgassing

During outgassing, when the sample is being heated, a vacuum must be 

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Fig. 9.11. The vapor-pressure thermometer. The manometer is filled as described in the caption to Fig. 7.1. The manometer is then evacuated and outgassed through a joint attached at point A. A pure compound is condensed into the probe, and the apparatus is sealed off under vacuum at point A. For thermometric compounds which boil below room temperature, care must be taken not to overfill the apparatus.

Catalytic combustion experiments have been performed in a flow reactor operating below the lower explosion limits using HC/02/He mixtures. The product analysis was done by gas chromatography. FT-IR spectra have been recorded with a Nicolet Magna 750 instrument, using conventional IR cells connected with evacuation-gas manipulation apparatus. The powder was pressed into self-supporting disks, calcined in air at 773 K and outgassed at 773 K for 20 minutes before experiments. 

Wade and Hackerman (302) measured the heats of immersion in water of both anatase and rutile as a function of particle size and outgassing temperature. Apart from the distinct influence of the particle size, a maximum in the heat of immersion was observed after outgassing at 300 to 350°, indicating a rehydroxylation reaction. This is similar to the behavior of silica. Whereas, with silica, the decrease at higher evacuation temperatures is caused by the slowness of the reopening of siloxane bonds (see Section III,A,2), it is very probably caused by a decrease in surface area in the case of TiOj. The maximum in the heat of immersion curves was distinct only with samples of high surface area. Stbber et al. (225) observed a decrease in the surface area of fine particle size anatase already at 450°. 

Vacuum Drying Books. (A) Frozen (or wet) books are placed in a chamber and heated by warm air. Vacuum is applied to remove water vapor as the ice thaws (5, 7). This is sometimes called the purged air system. (B) Frozen (or wet) books are placed in an unheated chamber. Moist air is evacuated and replaced with dry heated air (0% r.h.). When the replacement air becomes saturated with moisture, it is evacuated and the process repeated until the books are dry (4, 5). (C) Thawing books are put in a chamber. Vacuum is applied and then controlled at a pressure of about 5 torr. Heat is then applied to books through shelves to replace latent heat of vaporization. As moisture is released from books in vapor form (outgassing), it is collected by pumps and reverted to ice on cooled condensers in the chamber. After most of the water leaves the books, the book temperature is increased gradually from 32 °F to 80°-85°F the chamber is opened after 48 hr, the books are removed from the shelves, and the condensers are defrosted (4,5,10). 

In order to cross-check the preceding results with a second "chemical" method, experiments able to detect selectively the fraction of alumina surface uncovered by ceria were looked for. As other alumina-supported oxides [12-16], adsorption of carbon dioxide was considered. Preliminary volumetric results of the adsorption of carbon dioxide at room temperature, after calcination and outgassing under vacmun at 673 K, were not fiilly conclusive, as both ceria and alumina are able to chemisorb carbon dioxide further, although the adsorption strength of carbon dioxide is much lower on alumina than on ceria, experiments for isolating selective contribution of ceria, after desorption of CO2 from alumina at 373 K were also unsatisfactory, as some 20% of CO2 adsorbed on ceria was also desorbed during evacuation. 

Consequently, the IR spectroscopy of adsorbed CO2 has been considered. IR spectra in the hydroxyl group range (3800-3400 cm"l), for both pure alumina and ceria, are shown in Figures 2a and 2b, respectively. Curves 1 refer to samples calcined at 673 K and outgassed at the same temperature and then, cooled to room temperature. Curves 2 refer to the catalysts after adsorption of CO2 at room temperature (pC02 = 9-15 torrs) and curves 3 to the samples after a further evacuation at room temperature for 1 h. 

The catalysts were characterized by X-ray diflfractometry (XRD) and infi-ared (IR) spectroscopy. Acidity of the catalysts was tested by pyridine adsorption monitored by IR spectroscopy. Self-supported wafers pressed fi-om zeolite powder (thickness 15 mg cm ) were placed in the sample holder and outgassed at 770 K in vacuum (final vacuimi was better than 10 Pa) for 2 horns followed by cooling to room temperature where the spectrum of the activated zeolites were registered. 1.33 kPa pyridine was adsorbed at 473 K for 1 hour followed by evacuation at the same temperature for 1 h. For calculating the concentration of acid sites extinction coefficients available in the literature were used [15]. 

Thermal conductivity of the skin should also be very low to minimise the heat transfer through the panel edges which can partially reduce the insulation efficiency of the evacuated panel ( edge effect , see Section 3.2.1). These properties have to be coupled with very low gas permeation and outgassing rates. 

In the pioneering study of rutile by Hollabaugh and Chessick, adsorption isotherms of water were determined after an outgassing at 450°C, and were repeated after evacuation at 90°C at the end of the run. The... 

A detailed study of the physical and chemical adsorption of water on three xerogels, ferric oxide, alumina and titania, as well as on silica (cf. p. 272) has been carried out by Morimoto and his co-workers. Each sample was outgassed at 600°C for 4 hours, the water isotherm determined at or near 20°C, and a repeat isotherm measured after an outgassing at 30 C. The procedure was repeated on the same sample after it had been evacuated at a... 

Special preparation of A/j is necessary to obtain maximum adhesion and to avoid outgassing of foreign matter during evacuation. Outgassing can be prevented by pre-coating the substrate with a lacquer which can further provide a smooth base for A/,. 

To see that this is true, qualitative models of the titania surface produced following each of the three pretreatments used in this study (i.e., evacuation at 600 K, evacuation at 720 K, and hydrogen reduction at 720 K) are developed below on the basis of earlier studies of Ti02 surfaces (5-6,10-22). Surface Type I Following outgassing at about 600 K the Ti02 surface should be almost entirely free of molecular water (except on the rutile fraction), but about one half of the surface should be covered... 

Using infrared spectroscopy, Yates (299) proved the existence of hydroxyl groups on anatase as well as on rutile. Both forms still contained some adsorbed molecular water after evacuation at 150°, as evidenced by the bending vibration at 1605 cm b After outgassing at 350°, no free water was detected. There remained two OH stretching absorptions in the case of anatase (at 3715 and 3675 cm ) and one weak band at 3680 cm with rutile. This is indication of the existence of two different types of OH groups on anatase. These results were confirmed by Smith (300). 

Hollabaugh and Chessick (301) concluded from adsorption studies with water, m-propanol, and w-butyl chloride that the surface of rutile is covered with hydroxyl groups. After evacuation at 450°, a definite chemisorption of water vapor was observed as well as of n-propanol. The adsorption of -butyl chloride was very little influenced by the outgassing temperature of the rutile sample (90 and 450°). A type I adsorption isotherm was observed after outgassing at 450°. Apparently surface esters had formed, forming a hydrocarbonlike surface. No further vapor was physically adsorbed up to high relative pressures. 

Spectro-grade pyridine was dried over calcium hydride, thoroughly outgassed on the vacuum line, distilled onto fresh barium oxide, and again outgassed. The liquid was finally distilled into a clean, dry, evacuated flask from which the samples for investigation were distilled. 

The field emission microscope utilizes the phenomenon of cold emission as follows A wire etched to a very sharp point is surrounded by a spherical anode, usually in the form of a fluorescent screen. The system is evacuated to pressures of the order of 10 to 10 mm, of Hg and the wire is heat-polished electrically. This outgasses the metal and produces a smoothly... 

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