Alkali Alkaline Earth Silicate Glasses

Reiner K. On the mobility of alkaline earth ions in mixed alkali alkaline earth silicate glasses. Journal of Non-crystalline Solids. 2003 328(l-3) 157-163.DOI 10.1016/ 50022-3093(03)00474-5. 

Low expansion surface regions can be obtained by removal of alkali from the surface region of alkali-alkaline earth-silicate glasses. Exposure to SO2 vapor, which is often carried out to improve chemical durability, leaches alkali ions from the surface, producing a silica-rich near-surface region. The reduction in alkali concentration reduces the thermal expansion coefficient and produces a compressive layer after cooling the glass. 

Ni/23Co/Fe 8454 ALkali-alkaline-earth silicate, sealable Intermediate sealing glass... 

Alkali-Alkaline-Earth Silicate Glasses (Soda-Lime Glasses). This is the oldest glass type, which is produced in large batches for windows and containers (see Sect. 3.4.3). Such glasses contain about 71% Si02,... 

Structure of Alkali-Alkaline Earth-Silicate Glass... 

Alkali alkaline earth silicate (or soda lime silicate) glasses are the most commonly used and oldest known glasses. They contain mainly Si02 and a small amount of AI2O3 as network former oxides. The network modifiers are the alkali oxides Na20 and K2O and the alkaline earth oxides CaO and MgO. 

As a further consequence microstructured glass components caimot be used at T exceeding T j. Micron-sized holes and channels, sharp edges or walls will deform by viscous flowing of the glass. Microstructured alkali alkaline earth silicate glasses can be safely used up to temperatures of about 350° C (see also Fig. 1.27, it shows the temperatures of the annealing point... 

The thermal expansion coefEcient a of alkali alkaline earth silicate glasses varies from 7 to 10 x 10 K depending on the actual chemical composition of the glass and is many times greater than for silica (quartz) glass. 

Besides the chemical composition the size of the cooled glass devices also depends on the cooling rate in the transformation range (Fig. 1.31). Therefore the cooling rate plays also a part if a joining between an alkali alkaline earth silicate glass with another material exhibits inner stresses. 

The specific electrical resistivity of alkali alkaline earth silicate glasses at room temperature is still high enough (ranging from 10 ° to 10 " H cm) for them to be electrical insulators. However, with increasing temperature the electrical resistivity decreases. A material is classified as insulator if the specific electrical resistivity exceeds 10 Q cm, which is only given for alkali alkaline earth silicate glasses if the temperature does not exceed about 150°C. This temperature is the maximum service temperature for alkali alkaline earth... 

Unfortunately the addition of large amounts of alkali oxides to silica leads to a reduction of the chemical durability of the resulting glass. Although commercial alkali alkaline earth silicate glasses are used as bottles and other containers for liquids, these glasses are compared with silica glass rather susceptible to dissolution in water and chemical reactions with acids and alkaline lyes. 

All these remarks are very important for appljdng alkali alkaline earth silicate glasses in microdevices. Nevertheless, absolutely regarded in comparison with other materials, also these glasses are chemically resistant. 

Lead silicate glasses having different mole ratios of Si02 to PbO and containing different amounts of alkali/alkaline earth metal oxides were prepared by conventional melt-quench method. The different structural units of Si present in these glasses were identified by Si MAS NMR. ... 

A simple model for alkali-alkaline earth-silica glasses strongly resembles that proposed for the alkali silicate glasses. If we now write the general composition in the form xR2O-yRO-(100-x-y)SiO2, we can... 

The network-forming structure of silicate glasses, such as alkali or alkaline-earth silicate glasses, is composed of (SiO ) tetrahedra (Kreidl 1983). Because of the tetravalence of silicon, (SiO ) tetrahedra can link together on four corners by means of oxygen ions to form a fiilly three-dimensional network. In alkali or alkaline-earth silicate glasses, the alkali and alkaline-earth ions break Si-O-Si bonds, loosening the (SiO ) tetrahedra network. 

Alkali, alkaline earth, iron, and similar impurities that are present largely combine with the siliceous material to form a low-melting-point glass and decrease the refractoriness of the brick. 

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