Papers by Keyword: Zinc Aluminate

Abstract: Zinc aluminate (ZnAl₂O₄) and zinc ferrite (ZnFe₂O₄) nanocrystalline structures dispersed into SiO₂ matrix were prepared by sol-gel method. Phase formation of ZnAl₂O₄ and ZnFe₂O₄ was confirmed by X-ray diffraction (XRD) analysis. The crystallite sizes was determine using Scherer’s equation from the broadening of dominant peak at (311) plane. It was found the crystallite size of both compound decreased due to the decrement compositions of Zn²⁺ ion and Al³⁺ / Fe³⁺ ions. The crystallite sizes for ZnAl₂O₄ and ZnFe₂O₄ was calculated to be around ~ 14.16 – 11.27 nm and ~ 11.27 – 4.72 nm, respectively. FTIR analysis was done to determine the formation of spinel structures. FTIR results analysis confirmed that the formation of spinel structure where it has been observed that the bands around 800 cm^-1 was associated to the vibrations of aluminum-oxygen and metal-oxygen-aluminum bonds. This characteristic was identified to the formation of zinc aluminate spinel structure. The optical properties have been done to determine the energy bandgap of ZnAl₂O₄ and ZnFe₂O₄ samples. The Uv-Visible absorption spectra have been done within wavelength 300 – 800 nm and the graph was plotted into the Tauc plot. This new dielectric material was purposed to improve the value of dielectric permittivity with addition of SiO₂ where it can be applied as microwave dielectric material without changing the original spinel structures.

Abstract: Zinc aluminate (ZnAl₂O₄) nanopowders were synthesized by co-precipitation method using zinc chloride and aluminum chloride as starting precursors. The crucial preparation factors including pH and calcination temperature were varied and their influence on relevant physical properties of the product is investigated. Structural properties of as-synthesized nanoparticles were investigated by X-ray diffraction, scanning electron microscope and Raman spectroscopy. XRD results suggested that ZnAl₂O₄ in spinel structure with high crystallinity could be obtained by this process after calcination beyond specific temperature. Meanwhile, SEM images revealed that surface morphologies and structure of ZnAl₂O₄ were in spherical structure with average size of few hundred nanometer range at high pH condition. Raman result indicated the correlated chemical bonding relating to the formation of ZnAl₂O₄ structure.

Abstract: The effect of morphological structures and optical band gap of (1-x)ZnAl₂O₄ xSiO₂ samples with compositions of x = 0.00, 0.05, 0.10 and 0.15 were prepared by sol-gel method. Spin coating technique was used to deposited the (1-x)ZnAl₂O₄ xSiO₂ as a thin film and to investigate the structural and optical band gap. The produced thin film samples were annealed at 450 °C for 1h. Field emission scanning electron microscope (FESEM) was used to investigate the surface morphology of the samples. The average particle size for (1-x)ZnAl₂O₄ xSiO₂ is about 331.23 nm. The particle size are tend to increase as the composition of SiO₂ increased. XRD analysis shows the formation of cubic structure phase and dominant peak has been observed with Miller Indices (311) plane. The average crystallite size, D was calculated with average size about 8 13 nm. The optical band gap was calculated for (1-x)ZnAl₂O₄ xSiO₂ samples and it was found within range of 3.34 to 3.94 eV.

Abstract: This paper proposes to assess the efficiency of ZnAl₂O₄ obtained by combustion reaction on the process of esterification and transesterification of soybean oil to biodiesel production. In the synthesis it was used three heating conditions: spiral resistance, muffle furnace, and microwave oven. In order to investigate the influence of the heating source on the structure, morphology, and on the catalytic activity, the samples were characterized by XRD, FTIR, granulometric analysis, TGA, carbon content, TEM, and gas chromatography. The results showed that it was possible to obtain the ZnAl₂O₄ cubic phase with traces of ZnO. The ZnAl₂O₄ monophasic was just obtained by the synthesis carried out in the microwave oven and in the electrical resistance. All the samples showed a typical morphology of dense agglomerates and low carbon content. The samples also presented low catalytic activity in the esterification and transesterification process under the adopted conditions.

Abstract: This work shows the influence of the fuels aniline, carbohydrazide and glycine on structural and morphological characteristics of ZnAl₂O₄ synthesized by combustion reaction. Samples were prepared according to the propellants and explosives theory using a vitreous silica crucible and a muffle furnace as heating source. During the synthesis was measured the time and temperature of the reaction. After The samples were structurally and morphologically characterized by the following techniques: XRD, nitrogen adsorption / desorption (BET / BJH), and SEM. The higher temperature was achieved by the synthesis using aniline, whose value was of 876°C. XRD results showed that all the samples presented the ZnAl₂O₄ spinel as majority phase and, ZnO and Al₂O₃ as segregated phases. The samples also showed low surface area, varying of 23.6 to 28.7 m²/g, and particle size of 45 to 55 nm, besides mesoporous characteristic and irregular agglomerates formation.

Abstract: ZnAl_1.,9Eu_0.1O₄ nanoparticles were functionalization used of the 3-aminopropyltrimethoxysilane silane and chitosan, in 5:1 proportion of the nanoparticles to chitosan, in order to obtain hybrid materials for the development of luminescent markers. The samples were characterized by XRD, FTIR, TEM, excitation and emission. After functionalized the nanoparticles showed formation of crystalline phase of spinel and chitosan. TEM results have revealed that the samples presented before particle size less than 100 nm and after functionalization was observed that the particle size increases. Emission peak of Eu centered at 614 nm, corresponding to the transition ⁵D₀ ⁷F₂. Nanoparticles before and after functionalization showed the spectral lines characteristics of Eu ion ⁵D₀ ⁷F_j where (J = 0,1,2,3,4). After functionalization the sample presented an increase of luminescence intensity.

Abstract: Zinc oxide (ZnO) ceramics was coupled and reacted with alpha aluminum oxide (α-Al2O3) ceramics at 1200oC for 24 h. SEM observation and energy dispersive X-ray spectroscopy (EDS) analysis revealed the existence of diffusion layer of 10 μm thickness on the α-Al2O3 side of interface between ZnO and α-Al2O3. The diffusion layer is considered to consist of a ZnAl2O4, from the result of XRD. The cathodoluminescence of the diffusion layer was compared with that of zinc aluminate (ZnAl2O4) ceramics synthesized by conventional solid state reaction method. The single phase ZnAl2O4 showed weak emission peaked at 4.6 eV. On the other hand, the diffusion layer showed intense emission peaked at 3.75 eV. The ZnAl2O4 on the α-Al2O3 side of the interface synthesized by coupling of ZnO and α-Al2O3 is considered to be a excellent material as an ultraviolet light emitter.