Narrow Results

Nanocrystalline cobalt–ferrite particles of size 20–30 nm have been prepared by a reverse coprecipitation technique under the assistance of ultrasonic irradiation and heat-treatment at different temperatures (from 473 K to 1073 K). Both X-ray diffraction and transmission electron microscope analysis confirms the reduction of strain present in the material with annealing temperature. Enhancement of coercivity and magnetization value has been observed without increase in the particle size for whole range of annealing temperature. Temperature dependent magnetization loop shows considerable magnetic hardening at low temperature. The observed enhancement of the coercivity value has been attributed to the increase in magneto-crystalline anisotropy, surface effects and exchange anisotropy. The mechanical properties of the pure cobalt–ferrite samples and cobalt–ferrite reinforced alumina samples were also examined. The Vickers microhardness and the compressive properties obtained from the stress–strain relation showed higher value with annealing temperatures and higher nanoparticle content.

Modern ultrasound induction is very much useful in crystallization process. It uses piezoelectric transducers or quartz crystals to convert mechanical waves to electrical signals and vice versa. Growth of a crystal is environment dependent. The characteristics of grown crystals depend on impurities, temperature, preparation of the solution and mechanical agitation. The properties and size of a crystal can be tailored by controlling any one or all the above factors. The most interesting fact is that the ultrasound influences the properties and size of a crystal. It is found that the characteristics are improved and tailored for a specific need of the industry when a crystal is grown by radiating ultrasonic wave. In some cases, it produces nanocrystals. We used a device which generates the Ultrasonic wave of 15 MHz, which is applied to the crystal right from the time before nucleation till the crystal formation. The Dextrose monohydrate crystals are grown by conventional slow cool batch method. In the same slow cool batch method, Ultrasonic waves of 15 MHz are allowed to pass, influence the nucleation, crystal formation and growing process. The crystal formation process under the exposure of Ultrasound is allowed to continue for a sufficiently long time to yield the desired nanocrystals. The FTIR, UV, microhardness and SEM analysis are taken for the crystals with and without ultrasound.

With help of the method of the spark plasma sintering (SPS), the fine-grained (of micron approximately) ceramics based on various alumina nanopowders had created. A comparison of microhardness of ceramic samples obtained from 11 alumina nanopowders and 2 their composites was held. Microhardness of the ceramics obtained both by SPS, and by the traditional method (at successive pressing and sintering) is compared. The dependence of ceramics microhardness on the phase composition of the initial nanopowder and the average size of its particles was investigated. Besides alumina nanopowders (Al₂O₃), there were compared microhardness of ceramics from other 10 nanopowders of oxides (SiO₂, ZnO, Fe₃O₄, Gd₂O₃, CuO, WO₃, TiO₂, Y₂O₃, ZrO₂, MgO) obtained both by SPS, and by the traditional method. It is obtained that the microhardness of the ceramics created on the method of the spark plasma sintering, is significantly higher than a microhardness of the ceramics obtained by the traditional method; at the SPS method the average size of grain in ceramics decreases (to 1 micron and less).

A biocompatible and corrosion-resistant coating was progressed by depositing a thin film of calcium titanate (CaTi${\mathrm{\text{O}}}_3)$ on CoCr-based alloy substrate using a radiofrequency magnetron plasma sputtering process to improve the characteristics of the interface between the thin-film coating and the CoCr alloy substrate. In this technique, the best power was previously observed at 225 W to get good coating film deposition properties. This power was applied to a deposited thin film of CaTiO₃ on a heated CoCr-based alloy at $100^{\circ }$C using an argon gas atmosphere with purity (99.8%) under vacuum 1.00E-02 Torr. Different deposition rates and times were used to observe nanofilm, the thicknesses of (50 nm, 80 nm, 110 nm and 140 nm). Field-emission scanning electron microscopy (FESEM) was applied to study surface morphologies. X-ray diffraction (XRD) was used to study the crystalline structure of thin films deposited. The Vickers Micro-Hardness tests were implemented on each specimen. Vitro electrochemical corrosion tests (open circuit potential, Tafel polarization curve and cyclic polarization) of the coated and uncoated specimens were done, to find the optimal state that gives excellent resistance to corrosion in a simulated body fluid environment. The results of the experiments showed that as the thickness of the thin films increased, so did the hardness measurements. An enhancement in corrosion resistance also was clearly observed at a thickness of 140 nm CaTiO₃ thin-film compared with uncoated and coated specimens at other nanothicknesses.