Ljubica M. Nikolić

Effect of the silica sol-gel coatings on the properties of glass substrate

Abstract Strengthening of the glass substrate with silica sol-gel coatings was investigated. Sol–gel silica coating microstructure (is related to the degree of substrate strengthening), as it is known depends on the silica sol structure. In order to produce different microstructures of the silica coating, a variety of silica sols were prepared starting from TEOS and changing the water and solvent content, catalyst type and concentration, at room temperature. Carefully prepared glass surfaces were coated with silica sol using a dipping technique, with constant withdrawing rate (all physical parameters of the deposition were constant, since they can additionally change the coating microstructure). After specific heat treatment of the samples, the modulus of rupture was calculated using the measured flexural strength data. The degree of the substrate strengthening depends on the quantity of water used for the sol preparation, coating sol pH, state of the substrate surface and the degree of the coating bonding to the substrate (all mentioned parameters are discussed as to how they effect the silica sol structure). Results showed that strengthening of the glass substrate is effected by the microstructure of the silica coating.

Relationship between the microstructure of boehmite gels and their transformation to alpha-alumina

Abstract The gelation of aluminium hydroxide sols from aluminium propoxide and aluminium sec-butoxide has been studied at high temperature and high molar ratio of water under acidic conditions, up to 1.1 molar ratio of nitric acid per aluminium alkoxide. The resultant boehmite-type gel structure can vary to a broad extent as a function of the precursor type and the acid amount. On heating, these different boehmite gel structures transform, through transition forms of alumina to alpha-alumina, at 1100 °C. The rate of transformation of the gels to alpha-alumina depends on the boehmite microstructure. Short boehmite platelets (ordered) transform to alpha-alumina faster than larger ones, but for full densification, at a temperature as low as 1100 °C, it is necessary that the boehmite should be at least 70% of its theoretical density.

Low Temperature Synthesis of Nanocrystalline ZnFe2O4 Powders

Advances in nanoscale electronics require superior ceramic powders, preferable prepared with techniques for the direct synthesis of crystalline nanoparticles. Zinc ferrite (ZnFe2O4) nanopowders were prepared by co-precipitation method, from nitrate precursors. Crystalline powders having the single-phase cubic spinel structure were directly synthesized at temperature ≥80°C in the presence of NaOH. The obtained powders are agglomerated with ultra-fine crystallites having the average crystallite size about 3-4 nm.

Microstructural and sintering behavior of magnesia doped, seeded, different boehmite derived alumina

Abstract The effect of the original boehmite structure, seeding and magnesia doping on the microstructural development and sintering behaviour of alumina was investigated. Magnesia doping has a very important role in the sintering of the sol–gel derived alumina, but it is not the same as in the classical processing of alumina. It decreases the grain size, increases the rate of sintering and changes the temperatures of phase transformation of transitional aluminas. Seeding plays a beneficial role in processing of sol–gel alumina, as was already known. The origin of the boehmite plays an important role in all the phases of sol–gel processing of alumina.