Glasses alkaline-earth aluminosilicate

Standards. REE phosphates should be used as standards for the REE. Silicates or phosphates of U, Th, and Pb are also suggested as standards for these elements. For EMP dating of monazite, use of lead silicate or phosphate results in smaller ZAF corrections for typical monazite composition than does the use of lead chromate or sulfide. Lead-doped (500-5000 ppm) alkaline earth aluminosilicate glass produces the smallest ZAF corrections for typical monazite compositions, but may generate insufficient X-ray counts due to low lead concentration, compromising its use as a standard. 

Most studies have dealt exclusively with vitreous silica, which compacts by only a few hundred ppm at doses as great as 10 rad. Some commercial borosilicate glasses compact up to 40 times as much as vitreous silica for comparable radiation doses. Limited data for alkaline earth aluminosilicate glasses suggests that they expand slightly under these same conditions. 

Alkaline earth ions are also very effective in blocking the diffusion of helium atoms, with a similar trend toward decreasing helium permeability in the order Ba > Sr > Ca > Mg for glasses having otherwise identical compositions. The least permeable traditional commercial glasses are based on alkaline earth aluminosilicate compositions. 

Alkaline-Earth Aluminosilicate Glasses. These glasses are free from alkali oxides, and contain 52-60% Si02, 15-25% AI2O3, and about 15% alkaline earths. A typical feature is a very high transformation temperature. 

Alkaline-earth aluminosilicate glass for high-temperature applications, for sealing to molybdenum... 

The feldspathic ingredients, for the most part, remain in the residual glass as a complex alkali—alkaline earth aluminosilicate. 

The T. of alkaline earth aluminosilicate glasses of the type used for halogen headlamp inner bulb application may be estimated by the relation ... 

Two synthesis variables seemed to have received most attention in the work reviewed here, the cation composition and the nature and source of the aluminosilicate reactant. Extensive use of mixed bases of the alkali, alkaline earth, and organic cations have been reported as well as a wide variety of reactant aluminosilicates including solutions, hydrogels, glasses, kaolin (raw and calcined), and naturally occurring zeolites. 

It is generally accepted that aluminum is tetrahedrally coordinated in aluminosilicate glasses and melts, provided that cations such as alkali metals or alkaline earth metals are present in sufficient amounts to charge compensate the replacement of Si by AF+ [i.e., Si + —> AP" -t- (1/ )M" +, where monovalent or divalent M ions occur in nonframework sites associated with the tetrahedral aluminosilicate framework]. Experimental data for aluminosilicate glasses derived from both low-angle x-ray-scattering experiments and EXAFS studies show that as aluminum is substituted for silicon, the average T (tetrahedrally coordinated ion) -O bond... 

Alkaline-earth borosilicate glasses (8486 and 8412) and aluminosilicate glasses (8252 and 8253) have the necessary sealability and thermal resistance to be particularly suitable for the tungsten and molybdenum seals frequently used in heavy-duty lamps. 

Alkaline earth feldspar glass with excess Si02 (Types E and F). Thirty to fifty wt% of an aluminosilicate glass matrix of the 7 0 Al203 wSi02 type where R = Ca, Ba, Sr and n = 2 can be incorporated for alkaline earth feldspars. 

As expected, given the above review, one of the principal apphcations of XPS in the study of glass corrosion, is the evolution of surface composition throughout the corrosion process. In particular, it has been shown erqrerimentally, an alkali and/or alkaline-earth depleted leached layer forms on the surfaee of a glass reacted in a variety of aqueous and/or humid envirorunents [13-15, 25-28]. For example, figure 7 shows the surfaee eomposition of a calcium-sodium aluminosilicate glass reacted in an acidic solution as a fimction of time. 

---