Desorption studies

Different types of chemisorption sites may be observed, each with a characteristic A value. Several adsorbed states appear to exist for CO chemisorbed on tungsten, as noted. These states of chemisorption probably have to do with different types of chemisorption bonding, maybe involving different types of surface sites. Much of the evidence has come initially from desorption studies, discussed immediately following. 

This article discusses why one would choose nonresonant multiphoton ionization for mass spectrometry of solid surfaces. Examples are given for depth profiling by this method along with thermal desorption studies. 

Chemisorption of simple diatomic molecules has usually been the object of thermal desorption studies. Recently, there has been a growing interest in the application of this method to the investigation of surface phenomena produced by more complex molecules which yield either fragment desorption products or catalytically formed species (35, 46a 46h). Also, physisorp-... 

Wolfsberg, K. Aguilar, R.D. Bayhurst, B.P. Daniels, W.R. DeVilliers, S.J. Erdal, B.R. Lawrence, F.O. Maestas, S. Mitchell, A.J. Oliver, P.Q. Raybold, N.A. Rundberg, R.S. Thompson, J.L. Vine, E.N. "Sorption-Desorption Studies on Tuff. III. A Continuation of Studies with Samples from Jackass Flats and Yucca Mountain, Nevada", Report LA-8747-MS, Los Alamos National Laboratory, 1981. 

P. Berlowitz, C. Megiris, J.B. Butt, and H.H. Kung, Temperature-Programmed Desorption Study of Ethylene on a Clean, a H-Covered, and an O-Covered Pt( 111) Surface, Langmuir 1, 206-212 (1985). 

An Auger Electron Spectroscopic and Electron-Stimulated Desorption Study... 

Kariis, H., Westermark, G., Persson, I. and Liedberg, B. (1998) Infrared Spectroscopic and Temperature-Programmed Desorption Studies of Dimethylphenylphosphine Adsorbed on the Coinage Metals. Langmuir, 14, 2736-2743. 

Jachimowski TA, Meng B, Johnson DP, Weinherg WH. 1995. Thermal desorption studies of high-coverage hydrogen overlayers on Ru(OOl) created with gas-phase atomic hydrogen. J Vac Sci Technol A 13 1564. 

Conventional techniques such as solvent extraction followed by gas chromatography mass spectrometry (GCMS), and acid digestions followed by GCMS have all been performed on meteorite samples but all information about the location within the sample is lost during a digestion processes. However, microprobe laser desorption studies allow the profiling of material within the meteorite sample. 

Ali MA, Baugh PJ (2003) Sorption-desorption studies of six pyrethroids and mirex on soils using GC/MS-NICI. Int J Anal Chem 83 923-933... 

Figure 2.10 Experimental set-up for thermal desorption studies in ultrahigh vacuum. The heat dissipated in the tantalum wires resistively heats the crystal the temperature is measured by a thermocouple spot-welded to the back of the crystal. Desorption of gases is followed with a mass spectrometer...

Further adsorption/desorption study 14-day earthworm toxicity Study of the effects on soil microorganisms Short-term toxicity to plants... 

In desorption studies, plots of the logarithm of the fraction remaining vs time tend to show a progressive decrease in slope, indicating increasing resistance to desorption. Hence, desorption in natural solid particles seems to be a continuum. 

Formic acid decomposes generally on metal surfaces to carbon dioxide and hydrogen. A thermal desorption study on Cu(l 10) showed that the reaction... 

Temperature programmed desorption studies of formic acid decomposition by metals was reviewed recently by Madix (7d) the significance of formate formation is paramount to the discussion. This is also apparent in the recent electron energy loss spectra of formic acid adsorption on Cu(lOO) reported by Sexton (77). 

In contrast to the detailed work on the Au(l 11) surface, desorption studies from the other low-index surfaces are scarce with, for example, MC9 and MC4/8 on Au(l 10) [45, 46] and MC4 [47] on Au(l 00). Compared to Au(l 11) thiols are more stable on Au(l 10) as reflected by a negative shift of the desorption peak by 200-300 mV, which was explained by the difference in the pzc for both surfaces [46]. N o obvious differences in the shape of the desorption peaks were found for Au( 1 0 0) compared to Au(l 11). Interestingly, for MC4 a higher thiol coverage compared to both MC4 on the Au(l 11) and MC2 Au(l 0 0) was concluded from the desorption studies. For polycrystalline surfaces the desorption signal is more complicated with additional features, possibly due to the presence of different crystallographic domains [94, 163, 164]. 

R. Harris, A. McGuiness, D.G.R. Jones, J.S. Abel, Nd-Fe-B permanent magnets Hydrogen absorption/desorption studies (HADS) on Ndl6Fe76B8 and Nd2Fel4B, Phys. Scr. T16B (1987) 435 40. 

Imamura et al. [137] studied absorption of Mg ball-milled with graphite and benzene as milling additives. In a Sieverts-type apparatus, the mixture after 20 h milling was able to absorb at 180°C. This in itself is nothing outstanding because milled, activated, and cycled MgH can also absorb at 200°C (Fig. 2.22a). Bouaricha et al. [138] also studied absorption of a Mg -i- graphite mixture at 300°C, which showed much better kinetics than that of just milled Mg. A number of researchers studied both absorption and desorption [25, 139-141] but unfortunately, all desorption studies were conducted in vacuum. However, it must be pointed out that even under vacuum conditions, desorption kinetics were no better than those obtained with a number of other additives discussed earlier in the text. The lowest desorption temperature applied was 290°C. 

Apparent hysteresis also may be caused by other phenomena. During the consecutive extractions and dilution steps used as a common technique in desorption studies, weathering of the sorbent may occur, resulting in a possible increase of contaminant sorption and decrease in its release. Degradation of the contaminant induced by physicochemical or biological factors, or a volatilization process leading to a decreased contaminant concentration in solution, are additional factors affecting a true hysteresis result. 

Takita, Y Tashiro, T Saito, Y Hori, F. The effects of water coadsorption on the adsorption of oxygen over metal oxides I. Temperatime-programmed desorption study of C03O4. J. Catal, 1986, Volume 97, Issue 1, 25-35. 

The epoxy resin formed by tetraglycidyl 4,4 -diamino diphenyl methane and 4,4 -diamino diphenyl sulfone was characterized by dynamic mechanical analysis. Epoxy specimens were exposed to varying dose levels of ionizing radiation (0.5 MeV electrons) up to 10,000 Hrads to assess their endurance in long-term space applications. Ionizing radiation has a limited effect on the mechanical properties of the epoxy. The most notable difference was a decrease of approximately 40°C in Tg after an absorbed dose of 10,000 Mrads. Sorption/desorption studies revealed that plasticization by degradation products was responsible for a portion of the decrease in Tg. 

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