Scale morphology

Many studies have shown that surface pretreatment of Fe-Cr alloys has a strong effect on the scale morphology and subsequent oxidation rate For instance, Caplan indicated that several Fe-Cr alloys show improvement in the corrosion resistance due to cold work, with greater than 16% Cr required to show the optimum benefit. Khanna and Gnanamoorthy examined the effect of cold work on 2.25%Cr-l%Mo steels at temperatures between 400°C and 950°C over 4h in 1 atm O2. They found that up to 90% reduction by cold rolling had a negligible effect on the oxidation rate up to 700°C. However, above 700°C there was a general reduction in the kinetics... 

Lees and Whitehead" have shown that differences in boiler design lead to differences in furnace atmospheres, which are subsequently reflected in differences in scale morphology and corrosion performance. Hence they report that there is no unique scale morphology which is characteristic of furnace wall corrosion. They also warn that the scale that is examined during an investigation may not be an exact reflection of the scale on the tube surfaces during operation due to the possible hydrolysis of the scale on cooling (when hot flue gas is replaced by moist air) and the redistribution of phases in the scale due to the loss of the incident heat flux. 

CFPs are normally manufactured as submillimetric beads or powders (Figure 2) [15]. A convenient simplified comparison between the micrometer and nanometer scale morphology of gel-type and macroreticular resins is illustrated in Figure 3. 

C -CP-MAS NMR provides subtle information about the degree of solvation of the polymer chains of a CFP in a given solvent and consequently it may be qualitatively correlated with the nanometer scale morphology of the polymer matrix. In fact, the prerequisite that enables a polymer framework to develop a nanoporosity is the ability of the polymer chains and its pendants to be suitably solvated by the liquid medium [26-28]. Therefore, C -CP-MAS NMR spectra provide the basis for a first level screening of the possibility of a CFP in a given solvent to be employed as an hexo-template, able to accommodate metal nanoclusters chemically produced in its interior (see below and Ref. [29]). 

For macroreticular CFPs, the accessibility of reagents and removal of the products is guaranteed by the intrinsic micrometer- and nanometer-scale morphology of the support. For gel-type CFPs, the same positive features are enabled by the proper choice of cross-linking degree and swelling medium. 

The scale morphology is dependent on the conditions of readmit. Ihe time of oxidation, the composition of the corrosive medium, and the type and composition of the particular alloy involved. Complex alloys may form two or more layers differing in either composition or inicrostructurc or both. In order to maintain good oxidation resistance at least one of the layers must he compact and preferably be a slow growing oxide. 

D) objects, allows a fine control of the nanometer-scale morphology, which is a relevant parameter in the fabrication of efficient Pc-based devices. 

PF solution studies are interesting for two chief reasons. First, PFs can be easily processed from solution and any structures adopted in solution will impact those that evolve in the subsequent processing. As might be expected, the solvent plays a major role in establishing the large length-scale morphology of solvent-processed PF thin films [21]. Second, the composition may... 

Fig. 3.24 TM-AFM height images of large scale morphology (left) and flat on lamellae (right) spincoated PEO Aims on silicon [60]...

Sandgren, C.D., Hall, S.A. and Barlow, S.B. (1996) Siliceous scale production in chrysophyte and synurophyte algae. 1. Effects of silica-limited growth on cell silica content, scale morphology, and the construction of the scale layer of Synura petersenii. Journal of Phycology, 32, 675—692. 

By considering the EL spectra from Section 2.2.3, we have shown that the amount of EL observed from the endothermically generated bulk excitons is dependent on the film morphology, and we introduced the concept of retrapping of excitons. For nm-scale morphologies, excitons are likely to encounter again an interface during their lifetime and get retrapped into an exciplex, which can reduce exciton EL by more than 70%. 

In the present contribution, the possibilities of local in-situ STM and SFM probing at non-ideal electrodes are illustrated with recent SPM work performed in the electrochemistry group of the University of Bern STM studies of underpotential deposition of Pb and Tl at non ideal (chemically polished) Ag(l 11) electrodes are presented to show the influence of the nanometer-scale morphology of the non-ideal Ag(lll) substrate upon the local progress of adsorbate formation and the long-term stability of the resulting adsorbates. More detailed reports of the experiments are given elsewhere [3,4]. 

Fig. 5. SEM secondary electron images of the scale surface after 2 h at 1200°C in Oz, the substrates were made from (a) unmilled, extruded Fe-28Al-2Cr powder, (b) milled, extruded powder which contains an A1203 dispersion and (c) milled, extruded powder which contains a Y203 dispersion. At high magnification, there is little effect of the A1203 dispersion on the scale morphology compared to a Y203 dispersion.

B. A. Pint The Oxidation Behaviour of Oxide-Dispersed [3-NiAl I. Short-Term Cyclic Data and Scale Morphology, submitted to Oxidation of Metals. 

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