Borates binary

Inspecting Figs. 14.3, 14.4 14.5 and Table 14.1 shows that, as stated earlier for Bi -doped alkali or alkali-earth borate binary glasses, the excitation peak regularly shifts red and the emission peak shifts blue with increasing concentration of alkali or alkali-earth elements. As a result, the Stokes shift decreases. How does all this happen To elucidate it, information on glass microstructural changes is helpful. 

Anhydrous metal borates may be prepared by heating the hydrated salts to 300—500°C, or by direct fusion of the metal oxide with boric acid or B2O2. Many binary and tertiary anhydrous systems containing B2O2 form vitreous phases over certain ranges of composition (145). 

Use of 10 pm LiChrosorb RP18 column and binary eluent of methanol and aqueous 0.1 M phosphate buffer (pH 4.0) according to suitable gradient elution program in less than 20-min run time with satisfactory precision sensitivity of spectrophotometric detection optimized, achieving for all additives considered detection limits ranging from 0.1 to 3.0 mg/1, below maximum permitted levels Simultaneous separation (20 min) of 14 synthetic colors using uncoated fused silica capillary column operated at 25 kV and elution with 18% acetonitrile and 82% 0.05 M sodium deoxycholate in borate-phosphate buffer (pH 7.8), recovery of all colors better than 82%... 

The binary representation is applicable to various other oxide materials. However, an important distinction can be made between borates and other main group element oxide systems, such as aluminates and silicates. In the latter systems cations predominantly reside at sites created by the demands of rigid anionic oxide frameworks. Although some degree of structural control may be obtained by varying cations or by use of template synthesis, the oxide frameworks of these systems tend to be relatively inflexible in comparison with... 

Recently, Silver and Bray (52) were able to differentiate and to estimate the relative proportions of three- and four-coordinated borons in binary borate glasses. This technique was thus adopted by the present author in order to ascertain the presence or absence of four-coordinated boron in liquid B203 (35). Glassy samples were quenched in liquid mercury from temperatures up to 1400°C but no four-coordinated boron was detected. (The lower limit of detectability was estimated to be about 2%.) Experiments were also carried out on liquid B203 up to 500°C but again no four-coordinated boron was found. It thus appeared that at least up to 500 or 600°C, the structural variation of liquid B203 with temperature is not primarily the result of a boron coordination change of from three to four. 

Primarily because of industrial interests in glass and slags, and, to a less extent, of the relative ease of experimentation, most of the binary liquid oxide systems studied have been silicates and borates. Hence these will be the only systems to be discussed in this section. 

Compared to the silicates, only a few systematic physico-chemical measurements have been carried out on the binary borates. Whereas in silica and silicates the Si04 tetrahedron is the only building unit, both B08 and BCb groups are known to be present in crystalline and glassy borates (52, 60). Structural interpretations similar to those for the silicates are thus more difficult. At present, no satisfactory model exists for the binary borates. Some very interesting results arc, however, available and these will be discussed below. 

Fio. 7. Energy of activation for electrical conduction in binary liquid borates 28). 

Boron forms strong bonds to fluorine (644kJmol ), usually combining with three or four fluorides in its compounds or salts. Several binary fluorides of boron are known including boron trifluoride, BF3, a stable gas of great industrial importance as a Lewis acid. Boron trifluoride is synthesized industrially by reaction of hydrofluoric acid with borates or boric oxides (equation 42). ... 

Wiegand S., Briggs M.E., Levelt Sengers, J.M.H., Kleemeier, M., and Schroer, W. Turbidity, light scattering, and coexistence curve data for the ionic binary mixture triethyl n-hexyl ammonium triethyl n-hexyl borate in diphenyl ether. 

Derivatives are synthesized by mixing 1.75 mL of 1M borate buffer (pH 9), 750 xL methanol, 1 mL of wine sample and 30 xL of DEEMM in a screw-cap tube. The solution is kept in an ultrasound bath for 30 min, then is heated at 70 °C for 2 hours in order to allow complete degradation of the DEEMM excess. Derivatives are stable for about one week. Analysis of DEEMM derivatives is performed with a C18 (250 x 4.6 mm, 5 xm) column at 16 °C using a binary solvent mixture and gradient program and conditions reported in Table 4.5. Detection... 

In the binary glass-forming systems of alkali metal borates, it is possible to observe change in the trend of a number of physico-chemical properties in the concentration range of approximately 20 mole % of alkali metal oxide. This phenomenon is known in the literature as boric acid anomaly , and it is due to the change in the structure of the B2O3 melt caused by the alkali metal oxide addition and is related to the ability of boron to change its coordination number. 

Thermodynamic data from solution calorimetry using molten lead borate [95, 101] for the perovskite and garnet phases have been combined with data for the YAM phase, and heat capacity data from adiabatic calorimetry and differential scanning calorimetry have been used to calculate the phase diagram for the binary system. This recent study shows unequivocally congruent melting of the perovskite phase and that it does not decompose to the YAM phase + liquid [95],... 

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