Alkali borate glasses

Colour centres in alkali borate glasses containing cobalt, nickel and copper. R. Juza, H. Seidel and J. Tiedemann, Angew. Chem., Int. Ed. Engl., 1966, 5, 85-94 (44). 

Alkali aluminate (5-calcium disilicate monosulfate), phase in Portland cement clinker, 5 472t Alkali aluminate (8-calcium disodium trialuminate), phase in Portland cement clinker, 5 472t Alkali belite, phase in Portland cement clinker, 5 472t Alkali blue toners, 14 318 Alkali borate glasses, 12 572, 573, 584 Alkali catalysed pad-dry-bake procedure, 9 485... 

Another widely studied phenomenon in alkali borate glasses is the mixed alkali effect, the nonlinear change in glass properties when a second kind of alkali oxide is added into the single-alkali glass. Models have been suggested to explain the mixed alkali effect (144), but a universally accepted model has not been developed as of this writing. 

Kawazoe, H., H. Hosono, and T. Kanazawa (1978a). Electronic structure and properties of oxide glasses (I) ir-electron distribution of alkali borate glass networks. J. Noncryst. Solids 29, 159-71. 

Shkrob lA, Tadjikov BM, Trifunac AD. (2000) Magnetic resonance studies on radiation-induced point defects in mixed oxide glasses. 1. Spin centers in BjOj and alkali borate glasses. / Non-Cryst Solids 262 6-34. 

Krogh-Moe, J. New Evidence on the Boron Coordination in Alkali Borate Glasses. Phys. Chem. Glasses 3, 1—6 (1962). 

B) Thermal treatment of glass obtained in stage A. The glass (in pieces or as crushed and sieved powder) is reheated for several hours to several days [16,17] to achieve phase separation and to increase the microheterogeneities which are the alkali-borate phase. The thermal history determines the later size of the CPG pores. The separation process for alkali-borate glasses occurs in the temperature range from about 500 to 700°C. 

Figure 6.10. N4 as a function of R for alkali borate glasses. L = lithium, N = sodium, K= potassium, R = rubidium, C = cesium and B = borate. Unhatched block in mixed alkali compositions represent excess N4. (After Zhong and Bray, 1989).

Levasseur et al. (1978, 1979) recognized two important factors which influence a. The first was that the replacement of O by S in alkali borate glasses (Li20-B203 to Li2S-B2S3), which increased the room... 

Figure 12.10. Different structural units present in alkali borate glasses.

Addition of alkali oxides to vitreous silica result in the formation of NBO. Examination of property trends for alkali silicate versus alkali borate glasses, however, suggests that this is not the case for alkali borate glasses. Small additions of alkali oxides to silica cause a decrease in Tg, while similar additions to boric oxide cause an increase in Tg. Conversely, small additions of alkali oxides to silica cause an increase in the thermal expansion coefficient, while similar additions to boric oxide cause a decrease in the thermal expansion coefficient. Any potential structural model for alkali borate glasses must directly address this extreme difference in behavior. 

Figure 5.4 Boroxol ring structures in vitreous boric oxide and alkali borate glasses...

Eventually, a number of new observations raised questions regarding the original explanation for the borate anomaly. First, and most importantly, nuclear magnetic resonance was used for the direct measurement of the concentrations of 3- and 4-fold borons in a large number of alkali borate glasses. The results of these studies clearly demonstrate that the coordination conversion process does occur as proposed, but also show that the maximum in the concentration of tetrahedrally coordinated borons, designated as N4, does not occur until the composition contains = 35 to 40 mol% alkali oxide. Since this concentration is well past the composition where the property trend reversals occur, a direct correlation between the borate anomaly and the value of N4 seems doubtful. 

Figure 5.5 Effect of alkali oxide concentration on the relative concentrations of intermediate range units in alkali borate glasses. Dashed lines indicate simple theory. Solid lines represent experimental results...

The connectivity number of the alkali borate glasses in this compositional region is determined by the sum of the contributions of the Q3 and Q4 groups. If we consider a glass containing 10 mol% alkali oxide,... 

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