Borate Melts

The viscosity of vitreous boric oxide is among the lowest reported for common oxide glasses. Boric oxide melts are also considerably more 

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A number of reviews have appeared covering the various aspects of borate glasses. The stmcture, physical properties, thermochemistry, reactions, phase equihbria, and electrical properties of alkah borate melts and glasses have been presented (73). The apphcation of x-ray diffraction, nmr, Raman scattering, in spectroscopy, and esr to stmctural analysis is available (26). Phase-equihbrium diagrams for a large number of anhydrous borate systems are included in a compilation (145), and thermochemical data on the anhydrous alkah metal borates have been compiled (17). 

Although electrical measurements have confirmed the ionic nature of borate melts, viscous flow and volumetric studies clearly indicated their difference from liquid silicates. Shartsia and co-workers (4 ) have suggested that an equilibrium exists in the melt between BOj triangles and B04 Letrahedra, this being both temperature and composition dependent. The only ionic model for the borates is that of Bockris and Mellors (8) which... 

The processes of electrocrystallization form the basis of methods for synthesizing the spinel superconductors Lii Nb02 [387] and Lii tTi204 [388-390]. The stoichiometric forms are obtained by the electrolysis of borate melts followed b) lithium extraction with HCl solution. 

The chemistry of borate melts is described in detail in special monographs devoted to this problem. Thus the above mentioned short characteristics are given here only. 

Isothermal emf of cell (VI) in a sodium borate melt as a function of temperature (dynamic measurements) showing validity of Equation (26-33) and thermodynamically correct functioning of the cell with respect to the inherent oxygen/oxide system of the melt, (b) Effect of internal short circuit of platinum measuring electrode during a 10 h halt of the dynamic measurement after (a). 

Very high oxidation rates can be expected when an alloy yields a scale consisting of a melt providing fast flow of ions and a sohd phase providing easy flow of electrons. A model experiment for such a case was also proposed by Wagner [122]. When Ni is covered by a borate melt, oxidation can take place only by dissolution and diffusion of oxygen in the melt to the metal surface. 

Fig. 15 Local cell action in high-temperature corrosion [118,122], (a) Growth of Agl on an Ag—Ta couple in I2 (gas), (b) Corrosion of Ni in a borate melt, reactions on a Ni—Pt couple.

Figure 6.5 Effect of composition on the 10 Pa s isokom temperature for lithium borate melts...

Figure 11.7. Galvanic cell—Pt Oj, borate melt Ni—illustrating accelerated oxidation of nickel through contact with platinum.

I. Inderite—186 °C endotherm, inderite dehydrates 763 °C exotherm, the dehydrated substance recrystallizes 1106 °C endotherm, borates melt. 

L Carboborite—240°C endotherm, carboborite dehydrates 566 °C endotherm, the dehydrated substance decomposes and releases CO2 642 °C exotherm, borate crystallizes 944 °C endotherm, borate melts. 

III. Hydroboracite—354 °C endotherm, hydroboracite releases H2O 697 °C endotherm, borates decompose and are transformed to MgB204 and 036407 751 °C exotherm, MgB204 crystallizes 797 °C exotherm, CaB407 crystallizes 896 °C endotherm, borates melt. 

IV. Priceite—338 °C endotherm, priceite releases crystalline water, 505 °C endotherm, priceite releases constitution water 684 °C endotherm, the dehydrated substance decomposes and is transformed to CaB204 and 036407 700 "C exotherm, CaB204 crystallizes 740 °C exotherm, 036407 crystallizes 967 °C endotherm, borates melt. 

II. Preobrazhenskite—590 ° endotherm, preobrazhenskite releases constitution water, 779 ° exotherm, borate crystallizes 1096 ° endotherm, borates melt. 

Malyshev, V. V, Uskova, N.N., Shapoval, V.I. and Sarychev, S. Yu. (1996) Electrochemical deposition and properties of tungsten coatings form tungstate-borate melts [in Russian]. Zashch. Met., 32, 653-657. 

Fig 2 Enthalpy of solution of synthetic diopside-CaTs pyroxenes in a lead borate melt at 970 K (Newton et al, 1976), compared with trends predicted by completely ordered, unit cell charge balanced, and completely disordered models of Wood (1975). 

Systems which may be described by physical solubility are the solutions of the noble and the so-called inert gases in molten salts. It should be emphasized that a given gas which is inert with respect to a given melt is not necessarily inert toward another system. For example, the solubility of CO2 in molten alkali halides, "- sodium borate melts, or soda-silica melts demonstrates this behavior. 

Quenching techniques have been widely applied. However, subsequent analysis of such quenched solutions is usually based on assumptions regarding the amount of gas escaping during the cooling period. Pearce measured the solubility of CO2 in sodium borate melts by this method and analyzed the amount of CO2 evolved under vacuum. Forland et... 

The solubility of in soda-silica and sodium borate melts... 

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