Effect of gas adsorption

Morookaef al. (M42) studied the effect of gas adsorption on mass transfer between bubbles and emulsion phase, while measuring the residence time distributions of tracer gases for helium, carbon dioxide. Freon 12, and Freon 22 in 12- and 19-cm-diam. free and baffled beds of cracking catalyst. The kob b values are calculated from the distributions for different gases according to the two-phase model, providing for the adsorption equilibrium. 

Study on effect of gas adsorptive constant under electro magnetic fields exerted... 

NOj(N02/N204) gas and the effect of gas adsorption was monitored using visible and infrared spectroscopy the high sensitivity surface-enhanced resonance-Raman spectroscopy (SERRS) allowed to observe the reversible chemical absorption of NO2 on a monomolecular LB layer of PrPc2 and PrPc. ... 

Kim C, Choi YS. et al.. The effect of gas adsorption on the field emission mechanism of carbon nanotubes. Journal of the American Chemical Society, 2002. 124(33) 9906-9911. 

Urita K., Seki S., Utsumi S., Noguchi D., Kanoh H., Tanaka H., Ochiai Y., Aoki N., Yudasaka M., lijima S. and Kaneko K., Effects of gas adsorption on the electrical conductivity of single wall carbon nanohorn. Nano. Lett. In press. 

First principles calculations of the effect of gas adsorption on the surface stress of Pt(lll) have been performed [97Fei], The adsorption of hydrogen and oxygen was found to relief the tensile stress of the clean Pt(l 11) surface partially. The results of this study are presented in section 4.4.7.11 in Table 11 and in Fig. 11 and Fig. 12. These calculations suggest that the modification, i.e. weakening, of the surface bonds of the substrate in the vicinity of the adsorbate is an important issue in the discussion of adsorbate-induced stress. 

It is interesting to observe that a fair correlation can be found between the pore size evaluated by the Washbum-Laplace model and the pore size evaluated by the BJH model of nitrogen adsorption in the case of SBA-15 [12] and other materials with interconnected pores [13], In the case of gas adsorption, the surface defects are filled at a lower pressure and do not affect the pressure of capillary condensation [10]. However, the BJH model does not take into account the effects of curvature on condensation and systematically underevaluates the size of the mesopores [7, 14]. 

In 1992 the cyclic voltammogram feature of Pt single crystals in sulfuric acid solution was examined by CO adsorption. Figure 13 shows the effect of CO adsorption on Pt(lll) in sulfuric acid solution, " where at ads=0-08,0.3, and 05 V(RHE), CO gas was introduced and the current... 

The data shown in Figure 9.10 indicate both the kind of data that may be obtained by direct calorimetric study of gas adsorption and some evidence of the effect of preheating on the properties of surfaces. The figure shows the calorimetric heat of adsorption of argon on carbon black. The broken line indicates the behavior of the untreated black, and the solid line is the same adsorbent after heating at 2000°C in an inert atmosphere, a process known as graphitization. The horizontal line indicates the heat of vaporization of argon. 

There are fundamentally two types of gas adsorption processes, which can be differentiated by the way in which adsorbed species are desorbed. In one type the adsorbed species are removed by raising the temperature of the adsorbent, thereby decreasing its capacity. In the second type the partial pressures of the adsorbed species are reduced to effect desorption. Of course a combination of the two desorption techniques can be and is sometimes used. In Figure 1 an isotherm diagram is shown which depicts these desorption techniques. 

Effect of gas pressure on adsorption and surface permeation processes. In order to understand the nature of this gas evolution following a previous charge of the furnace tube with gases, it is necessary to study the extent of adsorption and permeation of the gases into the tube material as a function of the pressure with the intermediate chamber evacuated. The extent of these processes is measured by apparent leak rate measurement 10 minutes after evacuation of the gas. 

Because of the importance of the surface chemistry of bone mineral in physiological systems, we have undertaken a series of gas adsorption studies on hydroxyapatite in the form of anorganic bone. In a recent publication from this laboratory (4) results of calorimetric studies of the adsorption of water and methanol vapors on bone mineral and on synthetic hydroxyapatite were reported. The adsorption potential for nitrogen on dehydrated hydroxyapatite, whether from bone or from synthetic sources, was rather profoundly altered by the addition to the surface of chemisorbed methanol or water prior to the adsorption of nitrogen at —195° C. This effect was reflected in the specific surface areas, in the BET C values, and in the resultant values of Ex — EL (net heats of adsorption) as shown in Table I of the above paper. 

The technique of gas adsorption manometry is now probably the most widely used it is simple and effective since the pressure transducer provides all the information required to determine the adsorption isotherm. Thus, the pressure and temperature of each dose of gas are measured and the gas is allowed to enter the adsorption bulb. After adsorption equilibrium has been established, the amount adsorbed is calculated from the change in pressure. The most critical features of adsorption manometry are summarized in the following checklist, with more detailed comments given in Section 3.4. 

The specific surface area of a ceramic powder can be measured by gas adsorption. Gas adsorption processes may be classified as physical or chemical, depending on the nature of atomic forces involved. Chemical adsorption (e.g., H2O and AI2O3) is caused by chemical reaction at the surface. Physical adsorption (e.g., N2 on AI2O3) is caused by molecular interaction forces and is important only at a temperature below the critical temperature of the gas. With physical adsorption the heat erf adsorption is on the same order of magnitude as that for liquefaction of the gas. Because the adsorption forces are weak and similar to liquefaction, the capillarity of the pore structure effects the adsorbed amount. The quantity of gas adsorbed in the monolayer allows the calculation of the specific surface area. The monolayer capacity (V ,) must be determined when a second layer is forming before the first layer is complete. Theories to describe the adsorption process are based on simplified models of gas adsorption and of the solid surface and pore structure. 

CA 69, 11871k(1968) (Effect of gas liberation from material blasted loose in coal mine atmospheres. Tests were conducted in coal mines of the Krivoi Rog Basin using Dinaftalit and Atnmonit-6ZhV> After removal of the blasted material the conen of CO NOg exceeded the stafidafds. To reduce adsorption of CO and NO 2 on the dust of blasted material, it was recommended to drill... 

The surface of all inorganic materials exposed to ambient (humid) air is always covered with a thin layer of water adsorbed from the gas phase. The thickness of the adsorbed water layer varies with the humidity and surface chemistry. This water layer has been shown to reduce wear in MEMS operation. However, the high surface tension of the water film can cause an in-use stiction problem. The gas-phase lubrication concept discussed here employs the same equilibrium adsorption principle as the water adsorption in humid environments. The difference is that our approach utilizes a surfactant-like molecule that can provide low adhesion and good lubrication. The entry summarizes the advantages of gas-phase lubrication for MEMS devices and discusses the effect of alcohol adsorption on the adhesion and lubrication of silicon oxide surfaces. 

Cal,. M.P., Strickler, B.W., and Lizzio, A.A. (2000). High temperature hydrogen sulfide adsorption on activated carbon. I. Effect of gas composition and metal addition. Carbon, 38, 1757-65. 

---