Barium silicate glasses

The thermal expansion curve of a phase separated sample containing two glassy phases may show two glass transitions, as is shown in Figure 7.11. This type of curve will be observed if the more viscous phase is continuous, and if the immiscibility temperature for the glass lies above the Tg of the more viscous phase. Curves of this type have been observed for lead borate and barium silicate glasses, where the immiscibility temperature is greater than the Tg of either phase. 

In addition to the blend of monomers, composite resins contain fillers. These are typically finely divided quartz or barium silicate glasses, and their function is to provide strength for the fully formulated composite [2]. These fillers are linked to the polymer phase by coupling agents, which are typically silane-based substances [2]. Composite reins are characterized by the absence of a chemical reaction between the filler and the monomer or polymer phase. Also, they show no inherent adhesion to the tooth but instead they have to be bonded to the tooth with bespoke bonding agents. These are discussed in detail in Chapter 5. 

Lewis M.H., and Smith G., "Sperulitic Growth and Recrystallization in Barium Silicate Glasses," / Mater. Sci., 11, 2015-26 (1976). 

MacDowell J.F., "Nucleation and Crystallization of Barium Silicate Glasses," Proc. Brit Ceram. Soc., 3, 229-40 (1965b). 

Figure 19.9 Normal force AFM image of a fracture surface of barium silicate glass (see text) image size lOOOx lOOOnm, loading force F = 25nN (From Ref (20)).

Glocker and Frohnmayer determined the characteristic constant c for nine elements (Reference 2, Table 4) ranging in atomic numbers from 42 (molybdenum) to 90 (thorium). They proved that identical results could be obtained with the sample in the primary (polychromatic) or in the diffracted (monochromatic) beam. The method was applied with good results to the determination of barium in glass of antimony in a silicate of hafnium in the mineral alvite and of molybdenum, antimony, barium, and lanthanum in a solution of their salts—for example, 5.45% barium was found on 90-minute exposure by the x-ray method for a glass that yielded 5.8% on being analyzed chemically. 

With respect to pH sensitivity and an adequate speed of response (time constant r = RC where R is the resistance of the measuring circuit and C the capacitance of the electrode), a certain degree of superficial swelling is needed however, the gel layer thus formed should remain thin in order to minimize the solubility of the glass and to guarantee sufficient durability of the electrode. In this respect lithium barium silicates offer an attractive compromise32. 

Note The remainder of the composit consisted of 80 wt% filler consisting of barium- aluminum-boron silicate glass powder, silicon dioxide-zirconium dioxide, and ytterbium fluoride. For dental composites lower viscosities are preferred because of their flowability. 

Crystalline dispersions of several niobate crystals or barium titanate (up to 70 vol %) in a silicate glass phase form transparent ferroelectric glass ceramics. The small size of the crystals ( 500 A) accounts for transparency. 

The role of the fillers in composite resins is to reinforce their mechanical properties and provide a blended material whose overall properties make it suitable for the clinical repair of teeth. A limited range of materials has been used, with greater emphasis on variations in the particle size and size distribution than on chemical composition. Early materials were filed with powdered quartz, whereas modem composites are more likely to be filled with finely divided barium silicate or a radio-opaque silicate glass [8]. Filler loadings are typically of the order of 55% by volume, as they were in Bowen s original formulation [9]. 

Fillers are introduced into resin to form dental characteristics. Silica, silicate glass of barium aluminum, silica zirconia, ceramics, and colloidal silica are used for fillers. Polymerization initiators of dental resin are shown in... 

Energy transfer from Mn(II) to Nd(III) in calcium phosphate glass and from Mn(II) to Er(III) and Ho(III) in silicate glass was found to occur by a dipole-dipole interaction (Parke and Cole, 1971). The same mechanism takes place also for the energy transfer between Mn(II) and Nd(III) in barium borate glass (Kumar, 1977). 

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