Browsing by Author "Ahmed, Ahmed A."

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    Attack on soda-lime-silica glass bottles by acetic, citric and oxalic acids
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Ahmed, Ahmed A.; Youssuf, Ibrahim M.
    The corrosion resistance of soda-lime-silica glass bottles toward the action of aqueous Solutions of citric, acetic and oxalic acids was studied and compared with that toward HCl and water. The corrosion resistance was tested by subjecting the internal surface of the bottles to the action of Solutions of different concentrations of the organic acids at 95 °C for periods in the ränge of 15 min to 6 h. The quantities of Na₂O and SiO₂ extracted from the bottles under the conditions of attack were taken as a measure of the resistance to corrosion. The results obtained indicated that the extraction of Na₂O by Solutions of low concentrations of the different acids and wate? can be arranged in the following order: H₂O > citric acid > acetic acid > HCl > oxalic acid. Such behaviour was found to follo\ the order of the solubility of the corresponding sodium salts formed with the aqueous Solutions rather than the proton availabilit: in these Solutions. The relative magnitude of dissolution of SiO₂ was found to follow another order: H₂O > HCl > oxalic acid > citric acid > aceti acid. The decreasing solubility of SiO₂ by the organic acids, in comparison with that by HCl or water, was attributed to the formatio; of Oxalate, citrate and acetate complexes with silica which cover the glass surface and retard further dissolution of silica. Differences between the various organic acids in the dissolution of Na₂O or SiO₂ were not observed by increasing their concer trations. This behaviour was attributed to the increase in the concentration of the organosilicon Compound formed which is adsorbe on the glass surface acting as an effective barrier to further dissolution of glass.
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    Interaction between lead crystal glass (24 % PbO) and acetic acid
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Ahmed, Ahmed A.; Youssuf, Ibrahim M.
    On commercially available lead crystal glass tumblers (24 % PbO), the interaction between their bulk and grain forms and aqueous Solutions of various concentrations of acetic acid at different temperatures (22 to 95 °C), and for different times (30 min to 300 d) was studied. The extent of interaction was evaluated by determining the concentrations of K⁺, Na⁺, Pb²⁺ and Si⁴⁺ ions extracted by acetic acid, the change in the pH value of aqueous acetic acid Solutions and the weight loss of glass grains. The results showed that: a) Pb²⁺ was released from the glass studied under the Standard testing conditions in concentradons that were smaller than those specified in the various Standard specifications. b) The extraction of the different cations was significantly affected by the form of the test sample; glass grains were more reactive than the bulk form. c) Extraction of modifier cations, K⁺, Na⁺ and Pb²⁺, during short times of attack, up to 6 h at temperatures u p to 95 °C or during long-time attack up to 20 d at 22 °C, could be represented by a straight-line relationship when plotted against t^(1/2).Deviation was observed for times longer than 20 d but the straight-line relationship could be restored by plotting the extraction data against t. Such behaviour indicates that the leached layer became sufficiently thick after 20 d, so that the leaching and etching reactions proceeded at equal rates. d) The dissolution of glass increased with increasing temperature of attack up to 95 °C, but the mechanism of attack remained essentially of the leaching type. e) The extraction of K⁺, Na⁺, Pb²⁺ and Si⁴⁺ ions was affected by changing the concentration of acetic acid, which was correlated with the corresponding change in its pH value. f) The quantities of Pb^^ ions released by 4 % acetic acid Solution were several Orders of magnitude greater than that released by 40% ethyl alcohol Solution indicating that the Standard 4 % acetic acid test Solution is quite suitable for Pb²⁺ release safety.