Synthesis of machinable quality magnesium aluminium silicate (MgO-Al₂O₃-SiO₂) for fabrication of insulators/spacers usable in high voltage applications under high vacuum conditions has been carried out following two different routes i.e. (i) sintering route, and (ii) glass route. A three-stage heating schedule involving calcination, nucleation and crystallization, has been evolved for the preparation of magnesium aluminium silicate (MAS) glass ceramic with MgF₂ as a nucleating agent. The effect of sintering temperature on the density of compacted material was studied. Microstructure and machinability of samples obtained from both routes were investigated. They were also characterized for microhardness. Initial studies on material obtained by glass route reveal that these samples are superior to those obtained from sintered route in respect of their high voltage breakdown strength and outgassing behaviour. Outgassing rate of 10⁻⁹ Torr l·s⁻¹ cm⁻² and breakdown strength of 160 kV/cm were obtained. Different types of spacers, lugs, nuts and bolts have been prepared by direct machining of the indigenously developed glass ceramic.

Sodium aluminophosphate glasses having compositions of 𝑥Al₂O₃(1 – 𝑥)NaPO₃ (𝑥 = 0.05–0.2) were prepared using conventional melt-quench technique. Density, glass transition temperature, microhardness (MH), thermal expansion coefficient (TEC) and transmission characteristics were measured as a function of alumina content for different samples. They were found to depend on O/P ratio with pronounced changes taking place for O/P ratio ≥ 3.5. Density, glass transition temperature and microhardness were found to increase up to 15 mol% of alumina and then they showed a decreasing trend. Thermal expansion coefficient decreased continuously with alumina content. Optical gaps for different glass samples as measured from transmission characteristics were found to be in the range 3.13–3.51 eV. It initially decreased with alumina content up to 15 mol% and then increased. The behaviour was explained on the basis of change in the average aluminum coordination number from six Al(6) to four Al(4) (i.e. Al(OP)₆/Al(OP)₄ ratio) along with the changes in polyhedra linkages in the glass network due to change in O/P ratio.

Phosphate glasses having composition, 40Na₂O–10BaO–𝑥B₂O₃–(50–𝑥)P₂O₅, where 𝑥 = 0–20 mol% were prepared using conventional melt quench technique. Density of these glasses was measured using Archimedes principle. Microhardness (MH) was measured by Vicker’s indentation technique. Structural studies were carried out using IR spectroscopy and ³¹P and ¹¹B MAS NMR. Density was found to vary between 2.62 and 2.77 g/cc. MH was found to increase with the increase in boron content. ³¹P MAS NMR spectra showed the presence of middle 𝑄² groups and end 𝑄¹ and 𝑄⁰ groups with P–O–B linkages. FTIR studies showed the presence of BO₃ and BO₄ structural units along with the depolymerization of phosphate chains in conformity with ³¹P MAS NMR. ¹¹B NMR spectra showed increase in BO₄ structural units with increasing boron content. The increase in MH with B₂O₃ content is due to the increase of P–O–B linkages and BO₄ structural units as observed from MAS NMR studies resulting in a more rigid borophosphate glass networks.

The electrical conductivity of lithium zinc silicate (LZS) glasses with composition, (SiO₂)_0.527 (Na₂O)_0.054(B₂O₃)_0.05(P₂O₅)_0.029(ZnO)_0.34–𝑥(Li₂O)_𝑥 (𝑥 = 0.05, 0.08, 0.11, 0.18, 0.21, 0.24 and 0.27), was studied as a function of frequency in the range 100 Hz–15 MHz, over a temperature range from 546–637 K. The a.c. conductivity is found to obey Jonscher’s relation. The d.c. conductivity ($\sigma_{d.c.}$) and the hopping frequency($\omega_{h}$), inferred from the a.c. conductivity data, exhibit Arrhenius-type behaviour with temperature. The electrical modulus spectra show a single peak, indicating a single electrical relaxation time, 𝜏, which also exhibits Arrhenius-type behaviour. Values of activation energy derived from $\sigma_{d.c.}, \omega_{h}$ and 𝜏 are almost equal within the experimental error. It is seen that $\sigma_{d.c.}$ and $\omega_{h}$ increase systematically with Li₂O content up to 21 mol% and then decrease for higher Li₂O content, indicating a mixed alkali effect caused by mobile Li⁺ and Na⁺ ions. The scaling behaviour of the modulus suggests that the relaxation process is independent of temperature but depends upon Li⁺ concentration.

The degradation behaviour of phosphate glass with nominal composition, 40Na₂O–10BaO–𝑥B₂O₃–(50–𝑥)P₂O₅, where 0 ≤ 𝑥 ≤ 20 mol%, was studied in water, HCl and NaOH solutions at room temperature to 60°C for different periods extending up to 300 h. These glasses were synthesized by conventional melt-quench technique. Dissolution rates were found to increase with B₂O₃ content in the glass. The dissolution rates for the glass having 10 mol% B₂O₃ were found to be 0.002 g/cm² and 0.015 g/cm² in distilled water and 5% NaOH solution, respectively, at room temperature after 225 h of total immersion period, whereas it increased considerably to 0.32 g/cm² in 5% NaOH at 60°C after 225 h. However, glass samples with 𝑥 = 15 and 20 mol% B₂O₃ were dissolved in 5% HCl solution after 5 h immersion. The degradation behaviour has been correlated with the structural features present in the glass. The optical microscopy of the corroded surface revealed that the corrosion mechanism were different in acid and alkali media.