Controlled vacuum outgassing

Outgassing the adsorbent sample 79 Aim of the outgassing 79 Conventional vacuum outgassing 80 Controlled vacuum outgassing by means of CRT A 81 Outgassing with a carrier gas 83... 

All measurements have been made on homogeneous membranes of Eastman Kodak 398-3 cellulose acetate (6). The membranes were cast on glass plates and evaporated slowly to dryness from 2% w/v solution in pure acetone in a controlled atmosphere. The membranes were carefully outgassed under vacuum at 40°C before annealing in water for 30 minutes at 80°C during which they became detached from their casting plates. 

The amount of water adsorbed after the samples were outgassed was controlled by adjustment of the pressure in one of three ways use of a sensitive Cartesian diver manostat, use of a water source at a controlled temperature, or use of the mixed magnesium perchlorate hydrates mentioned above. The amount of water adsorbed by the sample was measured either by the gain in weight of a companion sample or by interpolation from the isotherm at 23.5° C. The heat of immersion of samples with no water adsorbed was determined with samples sealed off from the vacuum line while they were still in the furnace at 500° C. 

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). 

Surface acid densities were estimated using pyridine adsomtion monitored by combined thermogravimetric and infi-a-red spectroscopic techniques. Thermogravimetric analyses were carried out using a PC controlled Cl microbalance attached to a conventional vacuum line fitted with rotary and diffusion pumps. Approximately 100 mg of sample as a fragmented disc (prepared as per FTIR experiments, see below) was outgassed for 2 h at 573 K, then exposed to 1 Torr pyridine and cooled to 373 K. A further... 

Prior to each adsorption experiment, the sample was outgassed using Sample Controlled Thermal Analysis (SCTA) [27] which consisted of heating the sample xmder a constant residual vacuum pressure up to a final temperature of 450°C with specific conditions previously reported in detail [13]. 

To ensure complete wetting, the solid sample must be adequately evacuated before it is exposed to the given liquid. The usual procedure is to insert a known amount into a glass bulb which is then attached to a vacuum system. The outgassing conditions (rate of heating, temperature and residual pressure) are controlled in the same manner as for physisorption measurements, but the sample bulb is then sealed off from the vacuum system. After it has been placed under the liquid in the calorimeter cell and time allowed for the temperature to equilibrate, a small brittle tip of the bulb is broken to allow the liquid to reach the solid surface. 

When introducing substrate materials that can absorb moisture, such as many polymers, the history of the material may be an important variable in the amount of water vapor released by outgassing in the deposition chamber. In this case the history of the material must be controlled and perhaps the materials outgassed before they are introduced into the deposition chamber. In some web coaters, the web material is unwound in a separately pumped vacuum chamber before it is introduced into the deposition chamber. This isolates the deposition chamber from most of the water vapor released dixring the unrolling operation. 

Besides the investigation of the properties of clean surfaces, the majority of surface science experiments are directed to the properties of adsorbed or deposited atomic or molecular layers and films and their interaction with the surface. These studies require a precise control of the adsorbate pressure or the deposition flux, of the background vacuum (due to outgassing of the hot evaporation source), and of the sample temperature. 

Evolution of the external surface area and the two types of microporosity of atiapulgite (structural and inter-fiber) were examined as a function of a vacuum thermal treatment upt to 500°C. The methods used include controlled transformation rate thermal analysis, N2 and Ar low temperature adsorption calorimetry, water vapor adsorption gravimetry and quasi equilibrium gas adsorption procedure of N2 at 77K and CO2 at 273 and 293K. Depending on the outgassing conditions,i.e. the residual pressure, the structure folds 150 to 70 C. For lower temperature, only a part (18%) of the structural microp< osity is available to N2,13% to argon and 100% to CC>2.With water, the structure can rehydrate after the structure is folded up to an outgassing temperature of 225°C. 

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