Chemical durability

A number of processes have been observed during the dissolution of glasses in aqueous solutions. If the glass contains any alkali or other 

Since most common commercial silicate glasses contain alkali ions, the initial step in their dissolution usually involves ion exchange between these ions and protonic species from the liquid. The interdiffu-sion coefficient for the alkali ion and the protonic species is given by Eq. 8.13, which can be rewritten in the form  

Since the ion exchange process is diffusion-controlled, it is not surprising to find that the depth of hydrogen penetration into glasses increases with the square root of time of exposure to the source of hydrogen. The alkali concentration in the surrounding solution also increases with the square root of time. 

Crystallization can alter the durability of glasses by altering the chemical composition of the phases present. Crystallization often removes mobile ions such as lithium from the glass and places them into very durable crystals. In this case, the durability of the crystallized material is usually superior to that of the base glass. It is possible, however, for the crystals to be less durable than the base glass, in which case the final material may be subject to leaching by dissolution of the crystalline phase. 

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Chemical Durability. The resistance of nontransparent vitreous sihca to chemical attack is slightly less than the resistance of transparent vitreous sihca. This difference results primarily from the higher surface area of the former caused by the presence of a large number of bubbles. Most data in the hterature are on the transparent material. 

Other applications of ceramics require clay, either raw or purified, sand, and feldspar. Brick, porcelain, and white wares are made from these raw materials the main expenditure in making these products is in firing the mixtures of powders to a dense solid. Ordinary brick made from fire-clay requires a small amount of energy even refractory brick for high temperatures and chemical durability, made partly from purified oxides such as alumina or chrome ore,... 

The slow rate of dissolution of, or leaching from, durable glasses has led to proposals for the vitrification of nuclear waste. Glasses based on the sodium borosilicate system appear to be favoured because of their ability to dissolve the waste, combined with good chemical durability. Intensive development has taken place over recent ycars and a regular journal is devoted to this topic . 

Bacon, F. R., The chemical durability of silicate glass, The Glass Ind. 

Transparent vitreous silica chemical durability of, 22 417 density of, 22 422 devitrification of, 22 421 manufacture of, 22 412-415 viscosity of, 22 424t Transpeptidases, 3 27 Transport. See also Transportation of ascorbic acid, 25 771 of hydrated lime, 15 56-57 of quicklime, 15 56 of radioactive waste, 25 855-856 in waste collection, 25 869-870 Transportation, 25 322-348. See also Shipping Transport aluminum applications, 2 340-341 cost of, 25 323... 

The phase structure of glasses has a significant effect on their physical properties, which is discussed below with reference to chemical durability. The magnitude of the phase separation can be altered by heat treatment, and enhanced or reduced by the addition of various oxides to the melt. In particular, the addition of alumina to commercial soda-lime-silica glasses reduces the tendency to phase separation, improving chemical resistance (Doremus, 1973). A detailed study of the microstructure of soda-lime-silica glasses has been published by Burnett and Douglas (1970). The control of phase separation in the melt is now commercially important for processes such as the... 

Dilmore, M.F. (1977). Chemical Durability of Multicomponent Silicate Glasses. 

El-Shamy, T.M. (1973). The chemical durability of K20-Ca0-Mg0-Si02 glasses. Physics and Chemistry of Glasses 14 1-5. 

El-Shamy, T.M., Morsi, S.E., Taki-Eldin, H.D. and Ahmed, A.A. (1975). Chemical durability of Na20-Ca0-Si02 glasses in acid solutions. Journal of... 

Eguchi, K., H. Tanaka, T. Yazawa and T. Yamagura. 1987. Chemically durable porous glass and process for the manufacture thereof. European Patent Appl. 0,220,764. 

Its chemical durability also makes it indigestible to plant eaters because of its bonding to cellulose and protein material. Formation of lignin also helps block the growth of pathogens and is often the response to partial plant destruction. 

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