Glass, corrosion rate

Elemental solubility limits are a very important constraint on the releases of many radionuclides and selecting a set of more conservative values of this parameter significantly alters the profile of calculated doses as a function of time. Decay during near-field and geosphere transport minimizes the consequences of such changes for some nuclides as does the fact that, as solubilities increase, the glass corrosion rate takes over as a constraint on releases. 

Vitreous silica is susceptible to attack by alkaline solutions, especially at higher concentrations and temperatures. For 5% NaOH at 95°C, although craving may be evident, surface corrosion is only 10 p.m after 24 h (87). For 45 wt % NaOH at 200°C, dissolution proceeds at 0.54 mm /h (88). The corrosion rates in other alkaline solutions are Hsted in Table 3. Alkaline-earth ions inhibit alkaline solution attack on vitreous siUca. Their presence leads to the formation of hydrated metal siUcate films which protect the glass surface (90). 

Materials of Construction. Glass has excellent corrosion-resistance to wet or dry bromine. Lead is very usefiil for bromine service if water is less than 70 ppm. The bromine corrosion rate increases with concentrations of water and organics. Tantalum and niobium have excellent corrosion-resistance to wet or dry bromine. Nickel has usefiil resistance for dry bromine but is rapidly attacked by wet bromine. The fluoropolymers Kynar, Halar, and Teflon are highly resistant to bromine but are somewhat permeable. The rate depends on temperature, pressure, and stmcture (density) of fluoropolymer (63). 

An apparatus for testing enamel with acid and alkaline liquids (and their vapours) was later proposed in an attempt to standardise corrosion ratings on an international basis. After surveying enamel properties and their relationship with resistance to liquids of different pH values, the concept of modifying the resistance by including specific elements in the glass structure has been outlined. ... 

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. 

Grambow, B. 1985. A general rate equation for nuclear waste glass corrosion. In Jantzen, C. M., Stone, J. A. Ewing, R. C. (eds) Scientific Basis for Nuclear Waste Management VIII. Materials Research Society Symposia Proceedings, 44, 16-27. 

Towards a consistent rate law glass corrosion kinetics near saturation... 

This burgeoning set of reviews serves as a starting point for our discussion of glass corrosion resistance, although our review differs from those noted above by emphasizing dissolution behaviour near saturation with respect to potential rate-limiting phases. 

There are a number of mechanisms that pose potential problems to predicting dissolution rate kinetics as the system approaches saturation. Part of this conundrum originates from current models of glass corrosion kinetics that cannot yet incorporate these unanticipated phenomena into a mathematical equation that is consistent with the constraints of thermodynamics or kinetics. These phenomena include (1) alkali-hydrogen exchange (2) dissimilar reactivity of... 

Over the last 20 years investigators have reported that predpitation of secondary phases can accelerate the corrosion rate of glass. This is because predpitation can cause a sudden drop in the activity of a key aqueous species. In other words, we hypothesize that the rate is affected through the chemical affinity of the system. 

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. 

Grambow, B. 1985. A general rate equation for nuclear waste glass corrosion. Materials Research Society Symposium Proceedings, 44, 15-27. 

The alkah silicate glasses are easily corroded by aqneons acids and the main reaction is an exchange between H3O+ of the solntion with the alkah M+ of the glass the corrosion rate increases with the ionic raduofM+, that is, K+ > Na+ > Li+. The chemical durabihty is greatly increased by addition of divalent CaO or bivalent AI2O3 oxides, leading to conunercial soda-hme sihca compositions. 

Onuki et al. have screened a number of materials in an acid mixture of H2SO4 (50 wt%) and HI (0.1 wt%) at temperatures up to 120°C (table 4.7). This simulates the composition of the upper liquid phase. They found Ta, Zr, Pb, and quartz glass to be corrosion resistant in this acid complex, whereas common construction material such as stainless steel and Hastelloy did not possess acceptable corrosion rates. PFA (Teflon) also showed satisfactory corrosion performance, but I2 absorption by perfluoroalkoxy or PFA has been observed, which raises questions about its longterm viability. 

When the final column is run at atmospheric pressure, even a highly alloyed stainless steel such as UDDEHOLM 904 L containing 20 % Cr, 25 % Ni, 4.5 % Mo, 1.5 % Cu, 0.4 % Si, and 1.7 % Mn was found to be unsatisfactory. In one known case, the column was made of glass, but a less expensive solution of the problem is rurming the column at reduced pressure to lower all temperatures. As the rate of any chemical reaction, the corrosion rate contains the factor... 

Corrosion of the glass-making melters must be maintained at an absolute minimum to increase the lifespan of the melter. Laboratory-measured corrosion rates indicate that melter lifetimes of several years can be achieved with high chrome oxide or zircon refractories metallic melters may have lifetimes of several months if alloys such as Inconel 690 are used. These conclusions have been reached on the basis of extrapolation of laboratory tests. Long-term tests, particularly with waste glasses in engineering-scale continuous melters, have not yet been made. 

Morphological studies explain the mechanisms of E-glass corrosion. According to these studies, acid corrosion of E-glass is caused by calcium and aluminum depletion which varies depending on the acid type, fiber type, and acid concentration. Oxalic and sulfuric acids are more corrosive than nitric and hydrochloric acids. This difference is due to the fact that, in oxalic acid, precipitated products are formed which decrease the concentration of leachates in solution. In addition to the loss of mineral content, fibers develop axial and spiral cracks. Crack formation depends on the rate of material depletion. 

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