Glass corrosion layers

BinsteadN (1998) EXCURV98 Program. CLRC Daresbuiy Laboratory, Warrington, UK Biwer BM, Soderholm L, Greegor RB, Lytle FW (1997) Uranium speciation in glass corrosion layers an XAFS study. Mat Res Soc Symp Proc 465(Scientific Basis for Nuclear Waste Management XX) 229-236... 

The failure of models based on application of TST rate laws to glass/water systems does not mean, however, that diffusion through a leach layer is by default the answer to this dilemma. Clearly, the set of recently reported data on glass corrosion resistance shows that it is not an either-or situation between affinity- and diffusion-based rate laws. Finding a mathematically stable form of the rate equation appears to be more worthy of pursuit. 

Metal ions that diffuse to the surface react with atmospheric gases to form hydroxides in a thin layer of high pH [36]. Fowkes improved adhesion of a basic polymer to glass with an acid wash [6, 7] a similar treatment also improved adhesion to epoxy [37], an acidic polymer. The former effect was attributed to replacement of sodium silicate with silanols by ion exchange the latter may result from removing a corrosive layer of metal hydroxides from the interface. IGC and PTD measurements in this study demonstrate a measurable basicity on bare fibers, which other investigators also noted [6,14,17],... 

Alkoxysilanes, including tetraalkoxysilanes, are utilized as crosslinking components in silicone rubbers, in the manufacture of silicone resins, as adhesion promoters with special organofunctional groups e.g. glass fiber layers, in the formulation of corrosion-resistant paints and in mold construction. 

Oxides are widely used and encountered in technical applications, such as high-temperature ceramics, nuclear fuels, glasses, and corrosion layers on superalloys. 

As expected, given the above review, one of the principal apphcations of XPS in the study of glass corrosion, is the evolution of surface composition throughout the corrosion process. In particular, it has been shown erqrerimentally, an alkali and/or alkaline-earth depleted leached layer forms on the surfaee of a glass reacted in a variety of aqueous and/or humid envirorunents [13-15, 25-28]. For example, figure 7 shows the surfaee eomposition of a calcium-sodium aluminosilicate glass reacted in an acidic solution as a fimction of time. 

Thus, an excess of hydroxyl ions is produced during the reaction and, depending on the environment of the glass, the OH" species may accumulate in the corrosion layer increasing the pH of the attacking solution and accelerating the process. Generally, the wet environment... 

Figure 5 Corroded aluminum-bondpad metallization layer taken under back-lit conditions. A photograph of the entire test device prior to any corrosion is shown on the right. The photograph of the corroded structure shows the importance of galvanic interactions and the existence of crevice corrosion (under the passivation layer) and was taken after imderlying silicon and glass insulation layer were etched away.

Corrosion layers formed on ZBLA glass (From D. G. Chen, Graduate Thesis, University of Florida, 1987, p. 101). (a) the two kinds of precipitates, (b) the bulk glass, transform layer, and precipitate layer. 

D. G. Chen, C. J. Simmons, and J. H. Simmons, Corrosion layer formation of ZrF4-based fluoride glasses. Mater. Sci. Forum, 19-20 315-320,1987. 

Laminated composite materials consist of layers of at least two different materials that are bonded together. Lamination is used to combine the best aspects of the constituent layers and bonding material in order to achieve a more useful material. The properties that can be emphasized by lamination are strength, stiffness, low weight, corrosion resistance, wear resistance, beauty or attractiveness, thermal insulation, acoustical insulation, etc. Such claims are best represented by the examples in the following paragraphs in which bimetals, clad metals, laminated glass, plastic-based laminates, and laminated fibrous composite materials are described. 

Studies on hot water tank enamelsin media of varying pH demonstrate a minimum corrosion rate at pH value of 4. In citric acid (pH 2), IR measurements indicate that ion exchange is the principal mode of corrosion. Distilled water (pH 7) showed evidence of a bulk dissolution mechanism with no silica enrichment of the surface layer. In neutral solutions, the first stage of attack is leaching of alkali ions, raising the pH of solution, which subsequently breaks down the glass network of the acidic oxides. 

The so-called hydro-vac pump, shown in Fig. II, 22, 2 (the upper half of the mercury reservoir and the column above it are insulated by a layer of asbestos), is an inexpensive, all-glass, mercury diffusion pump, which can be used in series either with an oil piunp or with a water filter pump (compare Fig. II, 21,1) capable of producing a vacuum of at least 2 mm. It is accordingly of particular value in the organic laboratory for vacuum distillations, fractionations, sublimations and pyrolyses as well as for molecular distillations (see Section 11,26). The hydro-vac pump, unlilce an oil pump, may be used in operations which evolve moisture and non-condensable or corrosive vapoius. In use the piunp is clamped in a vertical... 

The choice of the filter medium is often the most important consideration to ensure efficient operation of a filter. Its function is generally to act as a support for the filter cake, while the initial layers of cake provide the actual filter. The filter medium should be selected primarily on the basis of its ability to retain solids without binding. It should be mechanically strong and corrosion resistant, and should offer as little resistance as possible to the flow of the filtrate. The media are made from widely different materials such as cotton, wool, linen, nylon, jute, silk, glass fiber, porous carbon, metals, rayon and other synthetics, and miscellaneous materials like porous rubber. Cotton fabrics are most commonly used because they are available in a wide variety of weaves, and are cheap. 

Dynamic SIMS is used for depth profile analysis of mainly inorganic samples. The objective is to measure the distribution of a certain compound as a function of depth. At best the resolution in this direction is < 1 nm, that is, considerably better than the lateral resolution. Depth profiling of semiconductors is used, for example, to monitor trace level elements or to measure the sharpness of the interface between two layers of different composition. For glass it is of interest to investigate slow processes such as corrosion, and small particle analyses include environmental samples contaminated by radioisotopes and isotope characterization in extraterrestrial dust. 

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