Babita Tiwari

Effect of highest temperature invoked on the crystallization of LiB3O5 from boron-rich solution

Abstract The crystallization behavior of LiB3O5 (LBO) has been investigated by performing differential thermal analysis (DTA). When the measurements are carried out with the highest temperature limited to a few degrees above the melting point, a clear indication of the crystallization is revealed by the presence of exotherms at 787°C and 772°C in the DTA plot. On the other hand, the crystallization of LBO phase gets inhibited if the melt is subjected to a much higher temperature, prior to cooling. Powder X-ray diffraction patterns recorded in the two cases are also in agreement with these observations. The results obtained have been explained in terms of the microstructure of the melt, which besides other factors, is shown to be dependent upon the highest temperature to which the melt is raised prior to crystallization. The inference drawn has been vetted by growing LBO single crystals by top seeded solution growth technique. The results obtained also help to understand the difficulties encountered in nucleating LBO from a boron-rich solution with a Pt wire, as reported in literature [1] .

Some recent studies on glass/glass-ceramics for use as sealants with special emphasis for high temperature applications

Glass-ceramics owing to a combination of useful properties such as tuneable thermal expansion coefficient (TEC), good mechanical durability and chemical inertness find widespread uses in a variety of applications including seals and coatings. Glass-ceramic-to-metal seals have been fabricated with various silicate, phosphate and borate based oxide glasses depending upon the intended application. In this article, we review our studies on various glass and glass-ceramics materials development with a view to understand bonding behaviour with metals/alloys at ambient and high temperatures through a comprehensive structure property correlation investigations. Detail studies on BaO-CaO-Al2O3-B2O3-SiO2 (BCABS), barium strontium alumino-silicate, and strontium alumino-silicate with different additives (like Nd2O3, La2O3, NiO, TiO2, V2O5, ZrO2, Cr2O3, and P2O5) and barium/strontiun zinc silicate (B/SZS) glass-ceramics for high temperature sealing. We shall illustrate the role of various thermo-physical and structural characterization techniques that allowed optimum selection of materials and processing parameters. We particularly highlight the complementary role of NMR and XRD in studying the material at the short range and long range length scales.

NMR Studies of Strontium Zinc Silicate Based Glass/Glass-Ceramic Sealants for High Temperature Applications

Glass having composition 40SrO-10ZnO-40SiO2-2B2O3-2Al2O3-2TiO2-2Cr2O3-2Y2O3 (mol%) was prepared by melt-quench technique and converted into glass-ceramics by controlled crystallization. Formed crystalline phases in glass-ceramics were identified using powder XRD. MAS-NMR spectroscopy shows the presence of mainly Q1 and Q2 silicate structural units and BO3 structural units of boron in the glass network. It is inferred from 29Si NMR and XRD that glass-ceramics have high crystallinity and during crystallization initially Sr2ZnSi2O7 crystalline phase is formed and later SrSiO3 crystalline phase is crystallized. 11B and 27Al MAS-NMR of glass-ceramics depict an increase in the BO4 and AlO4 structural units with the crystallization. In accordance with XRD, NMR results also suggest the formation of solid solution of Sr2ZnSi2O7 phase with substitution of Zn/Si tetrahedral sites with B/Al.

Studies on some Glasses and Glass-Ceramics for Various Applications Including Seals

Glass and glass-ceramics (GCs) find wide applications in various disciplines of science and technology including sealing, vacuum, energy devices because of their desired thermomechanical, electrical, optical properties and chemical durability. We shall report here some recent studies carried out on thermo-physical and structural properties of TiO2 doped sodium aluminophosphate (NATP) glasses, interface studies on Li2O-ZnO-SiO2-P2O5-B2O3-Na2O (LZS) glassceramics for matched type of seal with Cu metal and machinability of magnesium aluminium silicate (MAS) glass-ceramics suitable for high voltage and ultra high vacuum applications. Structural studies have been carried out using XRD, FTIR, Raman and scanning electron microscopy(SEM). Thermo-physical measurements carried out on NATP glasses have been discussed in the light of structural properties.