Surface films aging

Figure 3.16 presents the corrosion rates for GW103K in the different heat treatment conditions, measured by immersion in 5% NaCl solution for 3 days. The as-cast (F) condition had the highest corrosion rate due to micro-galvanic corrosion of the a-Mg matrix by the eutectic. Solution treatment led to the lowest corrosion rate, attributed to the absence of any second phase and a relatively compact protective surface film. Ageing at 250 °C increased the... 

The first case is the most likely to be a problem with new plastic samplers. Although there is little in the literature to substantiate the belief, folklore has it that aging most plastic samplers in seawater markedly reduces the subsequent leaching of plasticisers. The second case is known to be a problem in fact, the effect is used in the various Teflon surface film samplers already mentioned. This problem alone would seem to militate against the use of Teflon for any sampling of organic materials, unless a solvent wash of the sampler in included routinely. With such a solvent wash, we introduce all of the problems of impurities in the reagents. 

Garofalakis, G., Murray, B.S. (1999). Effect of film ageing on the surface properties of lactoglobulin and lactoglobulin + sucrose stearate monolayers. Colloids and Surfaces B Biointerfaces, 12, 231-237. 

Thus, the aged surface films formed in nonactive metals in alkyl carbonates contain a mixture of ROC02Li and Li2C03 (demonstrated in Figures 11-15). 

Flence, aged surface films formed on nonactive electrodes at low potentials in alkyl carbonate solutions of these two salts contain LiF and other salt reduction products of the Li PF, Li BFy,... 

Rigorous use of XPS by Kanamura et al. enabled a further understanding of the multilayer structure of the surface films formed on Li in solutions, as well as the aging processes of the surface films [101— 105],... 

The use of galvanostatic transients enabled the measurement of the poten-tiodynamic behavior of Li electrodes in a nearly steady state condition of the Li/film/solution system [21,81], It appeared that Li electrodes behave potentio-dynamically, as predicted by Eqs. (5)—(12), Section III.C a linear, Tafel-like, log i versus T dependence was observed [Eq. (8)], and the Tafel slope [Eq. (10)] could be correlated to the thickness of the surface films (calculated from the overall surface film capacitance [21,81]). From measurements at low overpotentials, /o, and thus the average surface film resistivity, could be measured according to Eq. (11), Section m.C [21,81], Another useful approach is the fast measurement of open circuit potentials of Li electrodes prepared fresh in solution versus a normal Li/Li+ reference electrode [90,91,235], While lithium reference electrodes are usually denoted as Li/Li+, the potential of these electrodes at steady state depends on the metal/film and film/solution interfaces, as well as on the Li+ concentration in both film and solution phases [236], However, since Li electrodes in many solutions reach a steady state stability, their potential may be regarded as quite stable within reasonable time tables (hours —> days, depending on the system s surface chemistry and related aging processes). 

Hence, surface films composed mostly of CaCl2 cover calcium electrodes in T. As is usual for SEI-type electrodes [32], the films grow and reach a steady thickness during storage. It is assumed that the major ionic conductor in these films is Cl-, as they are totally blocking for Ca deposition [32], Their resistivity was measured by transient techniques and impedance spectroscopy [28], and is around 109 Q cm for a fresh Ca electrode and 1010 Q cm for an aged Ca electrode (500-1000 h in a TC-Ca(AlCl4)2 solution) [28], The thickness of the surface films is estimated as several tens of A [32],... 

Figure 33.2 shows XPS spectra of the surfaces of the TMS plasma polymer film deposited on (Ar + H2) plasma-pretreated steel (a, b, c) and on O2 plasma-pretreated steel (d, e, f). As shown in the spectra, the surface of the plasma film is functional in nature with functional groups of C-OH, C=0, and Si-OH. Two films basically ended up with the same surface structure. This is also confirmed by XPS analysis of the film during the film aging in air after the film deposition, which indicated that the film surfaces were saturated with a fixed surface structure after a few hours of air exposure [4]. This is due to a well-known phenomenon that the residual free radicals of the plasma polymer surface reacted with oxygen after exposure to air [5]. Curve deconvolution of C Is peaks showed structures of C-Si, C-C, C-0, and C=0. The analysis clearly shows a silicon carbide type of structure, which is consistent with the IR results. The functional surfaces of TMS films provide bonding sites for the subsequent electrodeposition of primer (E-coat). 

Figures 46C and D present analogous measurements for unaged electrodes. All the results are consistent with the structural changes that accompany aging as well as oxidation or reduction of the surface films.

Fig. 43 Isothermal surface potential decay (ITPD) curves as a function of time at Tywn = 120°C of compression-molded Ultem 1000 films aged at rage = 200°C...

The scope of the present paper is to emphasize the role of wetting and spreading in the aging by sintering, and in the redispersion of supported metal catalysts. In the next section, some experimental results regarding the behavior of iron supported on alumina are presented to demonstrate that surface phenomena do play a major role. This is followed by stability considerations which are employed to explain the coexistence of multilayer surface films with crystallites in an oxygen atmosphere and the rupture of thin films into crystallites in a hydrogen atmosphere. 

Benjamins et al (24) studied the effects of aging on the elasticity of (i-casein and K-casein films. The dilatational modulus of K-casein was larger than that of -casein and increased by a factor of three with film age, whereas the dilatational modulus of -casein films changed little with time ( ). K-casein unfolds less at the air/water interface since it has less random structure than Q-casein. This can also be interpreted in terms of K-casein having less direct contact with the film surface at any given protein concentration (25). Significant protein-protein interactions i.e. steric/electrostatic repulsion, are believed to occur between segments of polypeptide chains which extend both above and below the plane of the air/water interface in surface protein films (16,26)... 

Physical aging also exists in thin films. The gas permeability of 400 run thick polysulfone decreases when the films continued to densify [9]. Thin films age faster in gas permeability [10]. Kawana and Jones reported [11] thin supported films of PS aged below Tg exhibit clear overshooting in expansivity temperature cmwes when reheated for thicknesses of 18 tun or more, but not for a thickness of 10 run, suggesting the existence of a surface layer of the order of 10 nm in which aging is complete within the time scale of 10 s, while the rest of the film essentially has thermal properties identical to bulk samples. 

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