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Oxides of alkali metals and those of alkaline earth metals which cannot form glass by themselves but can form glassy structure with network formers mentioned above are known as network modifiers as they modify structure of glass network. Their addition reduces the bond strengths and viscosity of glass. However, their addition assumes importance as pure silica glass can be processed only at very high temperatures whereas addition of modifiers makes it feasible to process them at room temperatures. |
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Transition metal oxides, such as, TiO , Al O , SnO etc. which are known as intermediates, have strong absorption in visible and in the near infrared. If such oxides are present in the glass network, they will cause losses. Hence such impurities must be removed from the host. |
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