Search Results

1 - 10 of 117 items :

Clear All

References Ahmed H.A., Harbi H.M. & Habtoor A.M. 2012: Compositional variations and tectonic settings of podiform chromitites and associated ultramafic rocks of the Neoproterozoic ophiolite at Wadi Al Hwanet, northwestern Saudi Arabia. J. Asian Earth Sci. 56, 118-134. Arai S. 1992: Chemistry of chromian spinel in volcanic rocks as a potential guide to magma chemistry. Mineral. Mag. 56, 173-184. Arai S., Shimizu Y., Ismail S.A. & Ahmed A.H. 2006: Low-T formation of high-Cr spinel with apparently primary chemical characteristics within podiform chromitite from

Abstract

A new method of preparation of nanocrystalline zinc aluminate (ZnAl2O4) powder is described in this paper. Different organic acids are used as template material and nitric acid as an oxidant. Single phase ZnAl2O4 spinel can be formed at a much lower temperature through this route which gives nanocrystalline powder with uniform particle size and morphology. The powders are characterized by thermo gravimetric analysis (TGA), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), BET surface area analysis and field emission scanning electron microscopy (FE-SEM). The average crystallite size of the single phase material was of 20 to 30 nm and the surface area was found to be 21 to 27 m2g−1.

Abstract

In this study, some types of composites consisting of multi-walled carbon nanotubes (MWCNTs) and spinel oxide (Co, Ni)3O4 were synthesized by simple evaporation method. These composites were characterized by UV–Vis diffuse reflectance spectroscopy, X-rays diffraction(XRD), Scanning electron microscopy (SEM) and specific surface area(SBET). The photocatalytic activity of the prepared composites was investigated by the following removal of Bismarck brown G (BBG) dye from its aqueous solutions. The obtained results showed that using MWCNTs in combination with spinel oxide to produced composites (spinel/MWCNTs) which succeeded in increasing the activity of spinel oxide and exhibited higher photocatalytic activity than spinel oxide alone. Also it was found that, multiwalled carbon nanotubes were successful in increasing the adsorption and improving the activity of photocatalytic degradation of Bismarck brown G dye(BBG). The obtained results showed that spinel/MWCNTs was more active in dye removal in comparison with each of spinel oxide and MWCNTs alone under the same reaction conditions. Also band gap energies for the prepared composites showed lower values in comparison with neat spinel. This point represents a promising observation as these composites can be excited using a lower energy radiation sources.

Hopkinson Effect Study in Spinel and Hexagonal Ferrites

The magnetic susceptibility shows a Hopkinson peak just below the Curie temperature TC when heating the selected hexagonal and spinel ferrite samples. It is proposed that this peak can be associated with a transition from stable magnetic state to super-paramagnetic relaxation above the blocking temperature up to the TC. The Hopkinson effect results are compared with SEM micrographs of both studied hexagonal and spinel ferrites.

Abstract

Strontium aluminate (SrAl2O4) and the indium aluminate (SrIn2O4) spinels have been proven to be efficient host materials, which offer the possibility of generating broadband emission after doping with rare earth trivalent ions. The present work is devoted to the calculation of the crystal field parameters and the energy levels of the trivalent europium doped in SrAl2O4 and SrIn2O4 spinels, using the superposition model of the crystal field. Using the intrinsic parameters for Eu3+-O2− bonds, and the geometry structure of the each crystal, we modeled the CFPs and simulated the low-lying energy levels schemes. The obtained results are compared with the experimental data and discussed.

Abstract

In the present study, the dopant effect of Zn on the crystal structure, thermal properties and morphology of magnesium aluminate (MgAl2O4) spinel (MAS) structure was investigated. A pure and two Zn-containing MASs (e.g. MgAl1.93Zn0.07O4 and MgAl1.86Zn0.14O4) were synthesized for this purpose via a wet chemical method, and the as-prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, differential thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy techniques. It was found that the crystal structure, thermal properties and morphology of the MAS system change with the increase in the amount of Zn. MgO phase formation was observed. The values of the lattice parameter, unit cell volume and crystallite size increased, and the crystallinity percentage decreased. The morphology was also affected by adding of Zn.

References 1. Hill, H. J., Craig, J. R., & Gibbs, G. V. (1979). Systematics of the spinel structure type. Phys. Chem. Minerals , 4 , 317–339. 2. Dormann, J. L., Seqqat, M., Fiorani, D., Nogues, M., Soubeyroux, J. L., Bhargava, S. C., & Renaudin, P. (1990). Mössbauer studies of FeAl 2 O 4 and FeIn 2 S 4 spin glass spinels. Hyperfine Interact. , 54 , 503–508. DOI: 10.1007/s10751-004-7332-8. 3. Russo, U., Carbonin, S., & Giusta, A. D. (1996). Mössbauer spectral studies of natural substituted spinels. In G. J. Long & F. Grandjean (Eds.), Mössbauer spectroscopy

1 Introduction Lithium manganese oxide (LiMn 2 O 4 ) spinel has been extensively studied as a cathode material for Li-ion batteries, as an alternative to LiCoO 2 , LiNiO 2 or LiFePO 4 used today. Initially, LiMn 2 O 4 spinel has been synthesized mainly using conventional solid state methods [ 1 , 2 ]. Nowadays, other synthetic routes are applied too. One of them is a modified sol-gel (Pechini) technique, which seems to be appropriate for preparation of nanocrystalline cathode materials. Being a solution-based route, it offers a possibility of molecular level

Properties of a Nickel-Zinc Ferrite”, Journal of Physics: Condensed Matter, 1994, vol. 6, no. 29, pp. 5707–5716. [7] J. P. Sing, H. Kumar, A. Singha, N. Sarin, R.C. Srivastava and K. H. Chae, “Solubility Limit, Magnetic Interaction and Conduction Mechanism in Rare Earth Doped Spinel Ferrite”, Applied Science Letters, 2016, vol. 2, no. 1, pp. 3–11. [8] M. Šoka, M. Ušáková, E. Ušák, R. Dosoudil and E. Dobročka, “Magnetic and Structural Properties of Nickel Zinc Ferrites Doped with Yttrium”, IEEE Transactions on Magnetics, 2015, vol. 51, no. 1, Art. no. 2000504. [9] E

References 1. Sickafus, K. E., Wills, J. M., & Grimes, N. W. (1999). Structure of spinel. J. Am. Ceram. Soc., 82(12), 3279-3292. DOI: 10.1111/j.1151-2916.1999. tb02241.x. 2. Amirkhanyan, L., Weissbach, T., Kortus, J., & Aneziris, Ch. G. (2013). On the possibility of hercynite formation in a solid state reaction at the Al2O3-iron interface: A density-functional theory study. Ceramics Int., 40(1, Pt. A), 257-262. 3. Verwey, E. J. W., & Heilmann, E. L. (1947). Physical properties and cation arrangement of oxides with spinel structures. I. Cation arrangements in