Synthesis,microstructure and optical characterization of zirconium oxide nanostructures

Zirconium oxide (ZrO₂) nanostructures were synthesized by hydrothermal route. Surface morphology analysis depicts the formation of the nanobars and hexagonal-shaped nanodiscs at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO₂ product is of pure monoclinic phase (m-ZrO₂) with crystallite size of about 25 nm. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of the m-ZrO₂. The UV–vis absorption spectrum showed a strong absorption peak at about 292 nm and the estimated optical band gap was around 3.57 eV. Photoluminescence (PL) spectrum of ZrO₂ nanostructure showed a strong and broad emission peak at around 410 nm at room temperature, which can be attributed to the ionized oxygen vacancy in the material.     

Octane number enhancement studies of naphtha over noble metal loaded zeolite catalysts

An Indian industrial naphtha containing mixture of various hydrocarbons belong to n-paraffins, isoparaffins, naphthenes and aromatics falling in C₅ to C₉ carbon range has been studied for its octane boosting through the production of isoparaffins over various Pt loaded zeolite catalysts possessing different acidity and porosity properties. Optimum balance of acid and metal functionalities in 0.6 wt.% Pt loaded on BEA zeolite helped in achieving highest increase in research octane number (RON) from 44 to 80, suitable for gasoline applications, through the production of lower isoparaffins (iC₄-iC₆) along with C₇+ isoparaffins.     

Fully dense hot pressed calcium cobalt oxide ceramics

The processing parameters have been optimized to achieve highly pure and fully dense pellets of calcium cobalt oxide (Ca₃Co₄O₉) from solid-state ball milled calcium carbonate and cobalt oxide mixtures, calcined at optimized temperature and time, and consolidated by hot-pressing. The microscopic, spectroscopic, and thermal analysis suggest samples with longer ball-milling time require less calcination time for synthesizing highly pure crystalline phases of Ca₃Co₄O₉, and provide 99.2 ± 0.5% relative density.     

Bulk modulus and thermal expansion coefficient of mechano-chemically synthesized Mg2FeH6 from high temperature and high pressure studies

Mg₂FeH₆ was synthesized by ball milling MgH₂ and Fe (2:1 molar ratio) mixture for 72 h followed by heating at 400 °C under H₂ pressure. The hydride formation, its structure and homogeneity were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. High pressure in situ synchrotron X-ray diffraction and Vienna ab initio simulation were used to determine bulk modulus of the sample. The bulk modulus of Mg₂FeH₆ was found to be 75.4(4) GPa by optimized experiment and 76.3 GPa by theoretical simulation. From high temperature in situ X-ray diffraction study the volumetric thermal expansion coefficient of Mg₂FeH₆ was found to be α_v = 5.85(3) × 10⁻⁵ + 7.47(7) × 10⁻⁸ (T − T_o)/°C. Decomposition of Mg₂FeH₆ was observed at 425 °C and the decomposition products were Mg, Fe and H₂.     

Use of the nanoindentation technique for studying microstructure/crack interactions in the fatigue of 4340 steel

The objectives of this research are to study the influence of microstructure on the fatigue crack growth behavior in 4340 steel and to explore the application of the nanoindentation technique for determining the plastic deformation zone at a fatigue crack tip. Two heat treatment conditions were chosen for the steel: annealed and quenched plus tempered. The annealed steel consists of coarse pearlite and proeutectoid ferrite, while the quenched and tempered steel consists of fine tempered martensite. Fatigue crack propagation tests were conducted on disklike compact (DCT) specimens. Subsequently, the nanoindentation technique was applied to quantitatively determine the plastic deformation zone at fatigue crack tips. The plastic deformation zone size determined by the nanoindentation test seems larger than the cyclic deformation zone calculated using the fracture mechanics equation, which involves many assumptions. The fatigue crack growth test results show that the annealed steel has a higher resistance to crack growth than the quenched and tempered steel. The fatigue crack in the annealed steel tends to grow along pearlite domain boundaries, or the cementite/ferrite interfaces within a pearlite domain. In contrast, the fatigue crack in the quenched and tempered steel tends to traverse the fine martensite laths. Consequently, the actual crack path in the annealed steel is rougher than in the quenched and tempered steel and more secondary cracks are observed in the annealed steel.