Borosilicate glass structure

Acid resistance This property is best appreciated when the glass structure is understood. Most enamel frits are complex alkali metal borosilicates and can be visualised as a network of Si04 tetrahedra and BO, triangular configurations containing alkali metals such as lithium, sodium and potassium or alkaline earth metals, especially calcium and barium, in the network interstices. 

In the broad use of the word polymer, ion-containing polymers are ubiquitous. They include inorganic substances such as silicate and borosilicate glasses discussed in Chapter 4, most biopolymers, solvent-swollen synthetic ion exchangers and some synthetic structural polymers. With few exceptions, these exhibit the characteristic feature of an electrolyte, ion mobility. In this chapter we consider the group of synthetic... 

WUes and Watts [48,53] have reported the use of a rather successful heterogenic catalytic system to carry out these reactions. They have tested a borosilicate glass microreactor (dimensions 3.0 x 3.0 x 0.6 cm) consisting of two etched layers with two inlets, mixing channels, a larger etched region and the outlet. A solid-supported catalyst was dry-packed in this structure (Fig. 4). 

Konijnendijk, W. H. Stevels, J. M. 1976. The structure of borosilicate glasses studied by Raman scattering. Journal of Non-Crystalline Solids, 20, 193-224. 

This material also has a porous structure by virtue of its being made by etching a phase-separated borosilicate glass. PS chains have also been introduced into the pores of this type of glass [146], but the only results to date involve mechanical property measurements, and scattering investigations. 

Boron s chemistry is so different from that of the other elements in this group that it deserves separate discussion. Chemically, boron is a nonmetal in its tendency to form covalent bonds, it shares more similarities with carbon and silicon than with aluminum and the other Group 13 elements. Like carbon, boron forms many hydrides like silicon, it forms oxygen-containing minerals with complex structures (borates). Compounds of boron have been used since ancient times in the preparation of glazes and borosilicate glasses, but the element itself has proven extremely difficult to purify. The pure element has a wide diversity of allotropes (different forms of the pure element), many of which are based on the icosahedral Bj2 unit. 

The Si NMR spectra of a series of sodium borosilicate glasses (Bunker et al. 1990) show that in compositions containing 30-40 mol% B2O3 the predominant structural unit is Q" (8 of about — 110 ppm), but at lower B2O3 contents the Si shift becomes less negative, reflecting an increase in the number of Q" (1B) (—105 ppm) and Q (OB) units (— 90 ppm). The latter component could also arise from the presence of Q (3B)... 

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