Boehmite sols were obtained by peptizing boehmite precipitates with glacial acetic acid. The sols were aged at room temperature (30 ± 1°C) under closed condition. Rheological properties of the sols were studied at different ageing times. The sol characteristics were interpreted by measuring their viscosity, areas of hysteresis of the flow curves and yield stress (𝜏_y). Viscosity and the area of hysteresis of the flow curves increased with increasing ageing time of the sols. A sharp change of yield stress was observed during the ageing period from 15 to 36 days. The change in viscous to elastic nature and the appearance of gel point of the sol was observed by studying their oscillatory flow behaviour, i.e. by measuring loss modulus (𝐺''), elastic modulus (𝐺'), and loss tangent (tan 𝛿) of the sols. Gel point of boehmite sol was found at 36 days of ageing under closed condition at room temperature (30 ± 1°C).

Synthesis and characterization of undoped and Mn²⁺ doped ZnS nanocrystallites (radius 2–3 nm) embedded in a partially densified silica gel matrix are presented. Optical transmittance, photoluminescence (PL), ellipsometric and electron spin resonance measurements revealed manifestation of quantum size effect. PL spectra recorded at room temperature revealed broad blue emission signal centred at ∼ 420 nm and Mn²⁺ related yellow–orange band centred at ∼ 590 nm while ESR indicated that Mn in ZnS was present as dispersed impurity rather than Mn cluster.

Crystal behaviours such as crystallization temperature (amorphous to tetragonal (𝑡) zirconia), tendency of phase transformation (tetragonal to monoclinic (𝑚) zirconia) and lattice strain were studied with mechanical property e.g. tensile strength of sol–gel derived ZrO₂–2 mol% RE₂O₃ (RE = La, Pr, Nd, Sm, Gd and Dy) spun fibres. Rare earth cations of varying sizes played a significant role in changing the above mentioned properties of ZrO₂–2 mol% RE₂O₃ fibres. It was found that with decreasing the ionic size difference between the zirconium and RE ions, crystallization temperature (amorphous $\rightarrow \ t$-ZrO₂) decreased, the probability of phase transformation ($t \rightarrow m$) decreased, lattice strain which is related to lattice distortion decreased and tensile strength increased.