| Abstract: |
SUMMARY AND CONCLUSIONSCorrosion behavior of some binary glasses (lead borate, lithium borate and sodium borate glasses), ternary glasses as well as some multicomponent optical and opthalmic glass compositions were studied. For these glasses the weight loss of the glass grains Glasses were prepared from high pure raw materials. The glass melting was continued for about 3-8 hours depending on the type and composition of the glass. The melt was cast into rectangular and circular slabs, which were annealed at the appropriate tempeThe experimental results comprise numerous data obtained from different varieties of glasses with variable chemical compositions. The summary of the results and their interpretation are given afterwards:(A) Results and their interpretation of the results from binary borate glassesI) Alkali borate glasses:(1) The dissolved quantities of glass No.3 are larger than that obtained from glassNo.4 in all leaching solutions. As Li2O content increases the fraction (N4 ) of the four-coordinated boron and consequently the BO4 : BO3 increases.(2) The high dissolution rate of sodium borate glass [glass No.5] in all solutions are due possibly to the small fraction of the four-coordinated boron (N4) and consequently the BO4: BO3 decreases and also due to the high solubility of all the ionized con(3) The alkali borate (lithium or sodium borate) glasses are highly attacked by acidic solutions because both the alkali and borate species are highly soluble in solutions especially with completely ionized acidic solutions in relatively short time.(4) The corrosion weight loss of alkali borate glasses in NaOH solution reveals the weight loss of almost half the weight after the specified time (1h) at temperature (100oC). This result can be rationalized by assuming that both constituents of these gla(5) The difference between the attack of sodium borate and lithium borate can be related to the differences in the binding strength between the lithium or sodium and oxygen and the ratio of BO4 / BO3 groups. The relatively small and highly polarized lithi(6) The observed increasing dissolution of alkali borate glasses in distilled water rather than that of sodium hydroxide solution can be interpreted by recalling that it is understood that water attacks easily both constituents of the alkali borate glass (7) The observed similar behavior of H2SO4 and HCl solutions on the corrosion of alkali borate glasses may be explained as follows. The ionization of the mentioned acids (even if it is weakly dissociated) is sufficient to supply the leaching solution with(8) The corrosion effect of the ethyl alcohol on the glass can be related to the solubility of the modifier cations in alcohol and the ability of silicate or borate ions to form surface protective layer with the specified alcohol.II) Alkali borate glasses:(1) The rate of dissolution weight of glass No.2 is higher than that obtained from glass No.1 in all leaching solutions. As the PbO content increases the fraction of the four-coordinated boron (N4) and consequently the BO4: BO3 ratio increased.(2) The corrosion mechanism of binary lead borate glass is expected to be different from the corrosion of binary alkali borate glasses. The corrosion of lead borate is lower than that of sodium or lithium borate glasses. This can be explained by assuming (3) Experimental results obtained from EDAX measurements indicate and verify the previous postulation that there are several corrosion routes during the action of the various leaching solutions on the studied glasses. These different corrosion routes depea) The action by water seems to proceed through the corrosion of both constituent components PbO and B2O3 with the same rate as the experimental result indicates that the lead oxide content on the surface remains unchanged.b) The same lead borate glass PbO 70%, B2O3 30%, seems to corrode by the action of sodium hydroxide solution (0.1N NaOH) by preferential attack of more lead ions than borate phase and this is verified by the progressive decrease of PbO content on the surfC) The action of acid solution seems to depend on the type of acid and the ability of forming insoluble protective rayer during the corrosion process.(B) The results and their interpretation obtained from ternary borate glasses:The introduction of ZnO replacing PbO causes slight improvement in the corrosion of the lead borate glasses. This change can be correlated with:(1) The improvement of the chemical resistance of glasses containing ZnO is possibly due to the formation of zinc-rich surface layers.(2) The ability of zinc ions is to exist partly as a network-former. The formed tetrahedral ZnO4 groups strengthen the network improving the durability of the glass.(3) Zn ions can assume a dual role in glass structure like Al2O3. If ZnO prefers to act as network-former ions (ZnO4), the number of nonbridging oxygens is expected to decrease. This means that the leaching process is somewhat difficult.(4) The ion-exchange process is slightly changed as the Zn2+ (ionic radius ≈ 0.74Ao and Pb2+ ionic radius ≈ 1.2 Ao) cations are substituted both having the same charge but the latter ions having higher ionic radii. It is expected that the interdiffusion pThe effect of CaO replacing PbO on the corrosion process can be understood and explained as follows(1) The ion-exchange process is slightly changed as the Ca2+ (ionic radius ≈ 0.99 Ao and Pb2+ ionic radius ≈ 1.2 Ao) cations are substituted both having the same charge but the latter ions having higher ionic radii. It is expected that the interdiffusion (2) The change in the amounts of corrosion weigh loss can be also correlated with the extent of solubility of the Ca2 or Pb2+ ions in the respective solutions.(3) Also, the decrease in the CaO content in the glass composition decreases the capability for forming a gel protective film layer of calcium hydroxide during leaching with sodium hydroxide. The corresponding zinc compounds are quite soluble, enhancing t(C) The results and their interpretation obtained from multicomponent glasses:1) Ophthalemic glass [glass No.11]:The ophthalemic lenses contain aluminum oxide and zinc oxide. These combined oxides are known to be chemically stable towards the action of acidic and alkaline solutions. Zinc oxide can exist as a network former or as a network modifier. The structural roFrom previous considerations, it is expected that zinc ions can assume a dual role in glass structure like Al2O3. If the preference for ZnO is to act as network-former due to the [ZnO/M2O] ratio equal 0.58, this will decrease the number of non-bridging ox2) Ophthalemic glasses [glass No.12]:The studied ophthalemic lenses are known to contain SiO2, B2O3, Al2O3 and ZnO. This glass contains two network formers (silicon and boron). The added alkali may act as modifier with silicon network, creating a NBO as SiO-M+, or act with boron network, pre3) Ophthalemic glasses [glass No.13]:The chemical durability of the ophthalemic glass No.13 is close to glass No.12 because both having the almost same components SiO2, Al2O3, Na2O, K2O, CaO, BaO and relatively low mol% of ZnO. The presence of enough alkali increases the ability to share in 4) Slide glass [glass (14)]:Experimental results indicate that this glass contains both alumina and boric oxide leading to better chemical durability. In alkali aluminosilicate glasses, the trivalent aluminium ion does not always act as a network former. The structural configurationwhen [Al2O3/M2O]5) The results and their interpretation obtained from television screen glass:The results obtained reveal that this special optical glass possesses high chemical durability towards the action of water and hydrochloride acid solution but is slightly corroded by sodium hydroxide solution. This behavior can be interpreted referring to(D) Interpretation of the results obtained the infrared absorption spectra(1) Lead borate glass (glass No.1):The infrared absorption spectra of this glass before immersion in leaching solutions show absorption peaks at: (i) the first peak observed at 720 cm-1 is attributed to the bending vibrations of B-O-B linkages in borate networks, (ii) the second peak obserWe introduce a review of the definitions of hypermedia and hypertext as well as the difference between them and multimedia. Also the basic concepts of hypermedia system and techniques relevant to the field of hypermedia. Also we illustrated the famous hypFinally, this thesis presented an object oriented hypermedia database for building an online magazine, which is treated as an enhanced hypermedia application. 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