Glass Technology: European Journal of Glass Science and Technology Part A Volume 50 Number 1 February 2009 1. Introduction Glass is oſten thought of as an ‘inert’ material. Most glasses have high corrosion resistance but one must note that all glass products are chemically reactive to some degree. It is oſten important to know how a glass alters a solution that it contacts or how the glass product is altered by the solution. The predic- tion of such effects, even when the conditions are well specified, is an inexact process; there are no neat formulas to account for the numerous variables involved. There is no absolute or explicit measure of chemical durability and glasses are usually graded relative to one another aſter being subjected to similar experimental conditions. (1) Chemical aack on glass occurs either by an ion exchange process or by a network disruption process. The former is considered as an aack on nonbridging oxygen atoms by reagents with an electron deficiency, and the laer as an aack on bridging oxygen atoms by reagents with an electron excess, such as an alka- line solution where unlimited numbers of OH − ions are available. This is an irreversible process resulting in permanent damage to the glass network. (2) The chemical durability of silicate glasses is critically dependent on pH and the nature of the at- tacking solution. Silicate glasses are among the most chemically inert commercially available materials. They react with almost no liquids or gases at low temperatures except water and aqueous HF, and even at high temperatures they react appreciably only with fluorine, gaseous hydrofluoric acid and alkaline solu- tions. However, silicate glasses become particularly susceptible to decomposition above pH ∼9–10. In the presence of HF or fluoride ions, silico-fluoride anions will be formed. Although this reaction is also pH-dependent, the equilibrium constant is so large and positive that the reaction will take place in all practically aainable acid and alkaline media. (1) The rate of alkali extraction from glass by aqueous solutions is largely determined by the glass compo- sition. Generally, the rate decreases with declining alkali content of the glass, with decreasing alkali ion radius or when part of the SiO 2 is replaced by almost any other divalent oxide; (1) Ca and Mg oxides are the ones most oſten used commercially. Addition of CaO makes the batch cheaper, makes it easier to obtain the desired properties and gives beer alkaline durabil- ity. Ca 2+ ions coordinate with nonbridging oxygen ions, lowering their polarisability and increasing the chemical resistivity of glass. Mg is a network modi- fier in the glass structure. Mg 2+ cations occupy one site while two monovalent cations are required for the same purpose. The replacement of more mobile alkali ions by less mobile divalent alkaline earth ions reduces the net mobility of the modifier ions through the structure, improving the chemical durability. (3) Effect of transition metal oxide additions on the chemical durability of SrO–MgO–ZrO 2 –SiO 2 glasses Gursoy Arslan,* Bekir Karasu, Emrah Dolekcekic, Guray Kaya & Goktug Gunkaya Anadolu University, Department of Materials Science and Engineering, Iki Eylul Campus, 26480 Eskisehir, Turkey Manuscript received 22 March 2007 Revised version received 16 June 2008 Accepted 7 July 2008 SrO–MgO–ZrO 2 –SiO 2 quaternary glasses, such as 26SrO, 20MgO, 14ZrO 2 , 40SiO 2 (wt%; Zrn glass) have been found to be highly alkaline resistant because of the high ZrO 2 and MgO contents of the composition. However, the presence of 26wt% SrO makes the glass expensive and may degrade the chemical durability. Therefore, glasses with MnO and/or Fe 2 O 3 partially replacing SrO have been made with the aim of improving the chemical durability and decreasing the cost. Comparison of chemical durability test results performed in a pH 14 NaOH solution showed that glass compositions with suitable amounts of Fe 2 O 3 or Fe 2 O 3 plus MnO enhanced the alkaline resistance of the reference Zrn glass. The improved durability of glasses containing iron is aributed to the presence of ferric iron as confirmed by the formation of a hydroxide layer with an iowaite-like structure, while the poorer performance of glasses with Mn is related to the possible absence of Mn 3+ ions. * Corresponding author. Email garslan@anadolu.edu.tr Glass Tech.: Eur. J. Glass Sci. Technol. A, February 2009, 50 (1), xxx–yyy