Zn2+- Controlled Crystallization and Microstructure in K-Li-Mg-B-Si-Al-F Glass

Abstract

Text:The crystallization of (9-X) K2O-1Li2O-12MgO-10B2O3-40SiO2-16Al2O3-12MgF2-X PbO/BaO/ZnO (X =0/5) composition (wt.%) were studied by means of dilatometry, DSC, XRD, SEM and microhardness analysis. Density of base K-Li-Mg-B-Si-Al-F glass (2.59 g.cm–3) is found to be increased on addition of the network modifier oxides PbO, BaO and ZnO content. Addition of Pb2+, Ba2+ and Zn2+ furthermore increased the glass transition temperature (Tg.). A characteristic exothermic hump is found to be appeared in DSC thermograph at the temperature range 800-950°C; and that is ascribed to the formation of crystalline phase fluorophlogopite mica, KMg3(AlSi3O10)F2. Opaque glass-ceramics were prepared from K-Li-Mg-B-Si-Al-F glasses (with and without containing PbO, BaO and ZnO content) by controlled heat-treatment at 1000°C. Interlocked type microstructure combined of flake like fluorophlogopite mica crystals is obtained in ZnO-containing K-Li-Mg-B-Si-Al-F glass-ceramic; and such microstructural pattern is ascribed to cause large thermal-expansion (>11.5×10-6/K, 50-800°C).Vickers Microhardness of base glass-ceramic (5.12 GPa) is increased when contains ZnO (5.26 GPa). ZnO-containing boroaluminosilicate glass-ceramic is, hence, considered with potential interest as they can exhibit the microcrack resistivity in high temperature recycling operation (like SOFC).

Cr+6 Controlled Nucleation in SiO2-MgO-Al2O3-K2O-B2O3-F Glass Sealant (SOFC)

“…In the present case, the crystallization for Cr-doped glasses could have occurred both during cooling or annealing heat-treatment. For Cr-0 glass, the exothermic maximum is estimated at 768 ± 2 • C corresponding to crystallization temperature (Garai et al, 2018b). As is evident from DSC of Cr-2 to Cr-7 presented in Figures 2B-D, a slight exothermic range can be refereed at around 755-760 • C for a Cr-2 system ( Figure 2B), but that is not characteristic as an initiation of crystallization range.…”

“…Cr-0 glass, which is a typical boro-alumino-silicate system (K 2 O-MgO-Al 2 O 3 -B 2 O 3 -SiO 2 -F), is not crystallized upon such annealing temperature (Garai et al, 2015c;Garai and Karmakar, 2016b). Hence, Cr-0 is practically glass but Cr-2, Cr-4, or Cr-7 are not glass, rather those are glass-ceramic composite (Garai et al, 2018b;Aktas et al, 2019), and the endothermic and exothermic peaks in Figures 2B-D are due to minor residual glass phase. In a similar study on borosilicate system, (Aktas et al, 2019) argued that 0-1 wt% Cr 2 O 3 -containing borosilicate glasses are completely amorphous, but Cr 2 O 3 contents of >1 wt% makes those glasses crystalline.…”

“…Here, the interesting point to note that CTE of Cr-0 and Cr-2 glass is comparable in 50-700 • C, whereas the same is low for Cr-4 glass and became high for Cr-7. This is because Cr-0 is glass and its softening range starts at around 670-680 • C. So, the CTE is large at 50-700 • C. But Cr-2 to Cr-7 is basically glass-ceramic or in true senses, the glass-ceramic composite (Garai et al, 2018b;Aktas et al, 2019). These contain different crystalline phases in the matrix body and thus, the CTE depends on crystalline phases as well as the residual glass phase.…”

Nanocrystalline microstructure in Sm3+ and Gd3+ doped K2O–MgO–Al2O3–SiO2–F glass-ceramic sealant (SOFC)

“…Volume crystallization with a rather fine morphology was observed for all the glass-ceramics studied under same heat-treatment. [18][19][20] The examples of the FESEM micrographs (taken using etched G-1 to G-3 specimens) are given in Fig. 3.…”

“…Such a compact morphology is ascribed for its high density value (3.02 AE 0.02 g cm À3 ). 6,20 During the heat-treatment at 950 1C, the nucleating agents such as Sm 3+ or Gd 3+ ions can either support the heterogeneous phase separation or these can cause the accumulation in a specific microphase or nanophase of the phase separated glass. 3,10 Those trivalent ions Sm 3+ or Gd 3+ having large ionic field strength (charge/radius) and smaller critical nuclei tend to form 'cluster', which makes a minority of oxide ions involved in the Sm-O-Sm or Gd-O-Gd linkages, and hence isolated from the silicate glass network (Si-O-Si).…”