A.R. Mirhabibi

Investigation of phase transition of γ-alumina to α-alumina via mechanical milling method

In this research, the results obtained from studying the phase transition of γ-alumina (γ-Al2O3) to α-alumina (α-Al2O3) during intense mechanical activation in high-energy ball milling are presented. The powder samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric and Differential thermal analyses (TG-DTA). With respect to the results achieved from above analyses, the transition of γ → α-alumina through δ- and θ-phases, can be initiated. Also, it was found that the pure γ-alumina phase showed a great stability during high-energy ball milling and there was no transformation to any other phase after a long milling time (30 h). On the other hand, γ-alumina containing a small amount of the α-alumina seed, showed a gradual phase transition from γ-alumina to α-alumina in milling. The phase transition mechanism during milling is nucleation and growth, which is promoted by the α-alumina seed.

Graphite flake carbon composites with a ‘sinterable’ microbead matrix: I. Mechanical properties

Abstract In this paper we report a study of the effect of graphite flakes of different size and volume fraction on the mechanical properties of a fine-grained carbon produced by the ‘sinterable’ route. Mesophase microbeads have been used as a matrix and the volume percent and size of the graphite flakes have been varied. It is shown that the flakes significantly increase the work of fracture of the composite, the effect being dependent on both flake size and volume fraction. However, there is a corresponding decrease in the Young Modulus and flexural strength of the composites. The flakes are not bonded to the structure and effectively act as inherent ‘crack-like’ pores. Flakes aligned perpendicular to the surface form the flaws that control the fracture stress. However, they also contribute significantly to the bridging stresses in the wake of the crack, so enhancing the work of fracture. The results should be useful in understanding the role of graphite-flake inclusions in modifying the properties of carbon materials.

Studies of luminescence property of long afterglow Eu2+, Dy3+ activated Sr2MgSi2O7 phosphor

Long afterglow Sr2MgSi2O7 (SMS) phosphor was prepared by Doubys methods at high temperature and reductive atmosphere. The excitation and emission spectra of this phosphor showed that both had broad bands and that the main emission peak at 469 nm was due to 4f‐5d transitions of Eu+2 and implied that the luminescence centres Eu+2 occupied the Sr+2 sites in the Sr2MgSi2O7 host. The phosphor doped only with Eu ions did not demonstrate the long afterglow phenomenon, but when co‐doped with Dy+3 ions in the SMS matrix, significant long afterglow was observed.

Synthesis of carbon nanotubes on alumina-based supports with different gas flow rates by CCVD method

Several methods for the synthesis of carbon nanotubes have been developed in the last decade. The CVD process and their associated parameters affect the structure of the resulting nanotubes. In this work CNT growth has been studied on different supported catalysts with different rates of gas flow as one of the critical points. Different supports were prepared by mixing nanosized alumina with tetraethyl orthosilicate (TEOS) by a chemical method at low temperature and iron as the metal catalyst was impregnated by 5%, 10% and 20% weight of the supports. Methane was used as a carbon source for the synthesis of CNTs at 800°C-1000°C. Aluminium-based support, supported catalysts and CNT samples have been characterised by TEM, SEM, BET and XRD.

Preparation of and photo‐ and electroluminescence characteristics of ZnS:Cu phosphor

ZnS:Cu phosphors were prepared by co‐precipitating Cu along with ZnS using H2S and thiourea. Phosphors giving luminescence at around 530 nm were prepared. The difference in the characteristic properties among the samples prepared appeared to be due to the formation of nanoparticles during the preparation of the samples by different methods.

Microstructural evolution of copper-titanium alloy during in-situ formation of TiB2 particles

Bulk Cu−Ti alloy reinforced by TiB2 nano particles was prepared using in-situ reaction between Cu−3.4%Ti and Cu−0.7%B master alloys along with rapid solidification and subsequent heat treatment for 1−10 h at 900 °C. High-resolution transmission electron microscopy (HRTEM) characterization showed that primary TiB2 nano particles and TiB whiskers were formed by in-situ reaction between Ti and B in the liquid copper. The formation of TiB whiskers within the melt led to coarsening of TiB2 particles. Primary TiB2 particles were dispersed along the grain boundaries and hindered grain growth at high temperature, while the secondary TiB2 particles were formed during heat treatment of the alloy by diffusion reaction of solute titanium and boron inside the grains. Electrical conductivity and hardness of the composite were evaluated during heat treatment. The results indicated that the formation of secondary TiB2 particles in the matrix caused a delay in hardness reduction at high temperature. The electrical conductivity and hardness increased up to 8 h of heat treatment and reached 33.5% IACS and HV 158, respectively.

A new method of biomolecular recognition of avidin by light scattering of ZnS:Mn nano‐particles

Purpose – The purpose of this paper is to develop a new method for biomolecular recognition based on light scattering of ZnS:Mn nano‐particle functionalised with biotin.Design/methodology/approach – ZnS:Mn nano‐particles was successfully synthesised from quaternary water‐in‐oil micro‐emulsion system. The addition of biotin and the subsequent specific binding events alter the dielectric environment of the nano‐particle, resulting in a spectral shift of the particle plasmon resonance. Cyclohexane was used as oil, Triten X‐100 as surfactant, n‐hexanol as a co‐surfactant and mercaptoethanol for the best linking of biological part to nano‐particle. Measurement of the content of avidin was achieved by detecting the Department of Biomedical Engineering change in the excited emission. For qualitative and quantitative analyses of this product, scanning electron microscopy, transmission electron microscopy, energy dispersive X‐ray spectroscopy and spectrograph techniques were used.Findings – It was observed that wi...

Synthesis and Characterization of Silica Nanoparticles

Currently there are several models discussed to describe the formation of monodispersed silica particles. Monodisperse colloidal silica was prepared from tetraethoxysilane in mixture of ammonia, water and ethanol. Chemical system reaction permits the controlled growth of silica nanoparticles and subsequent condition of silicic acid in alcoholic solution. The molar ratio of NH4OH, C2H5OH and H2O has a significant effect on particle size and specific surface area of silica particles. The nature of particles was evaluated using X-ray diffraction, energy dispersive spectroscopy (EDS) and BET. The morphology of particles were determined by scanning electron microscopy (SEM) and transmission electron microscopy(TEM).

Preparation of some coloured chelates of 2-mercapto-4-picoline-N-oxide and their applications as new pigments

SummaryThe sulphur-containing ligand 2-mercapto-4-picoline-N-oxide (MPN) was prepared from 2-bromo-4-picoline by peracetic oxidation and the reaction of its oxidation product with thiourea, and finally hydrolysis with sodium hydroxide solution. The preliminary reaction of MPN with metal ions showed that from 25 common metal ions examined, only Fe(III) and Cu(II) gave 3:1 and 2:1 stable insoluble and intense coulored chelates which were violet and green respectively. Al(III), Y(III), Ce(IV), Th(IV), Pb(II), Mn(II), Mg(II), Sr(II), Ba(II) and Ca(II) gave no precipitate. Hg(II), Ga(III), Tl(II), Bi(III), W(IV), Zr(IV), Zn(II) and Ag(I) gave whites. Ti(IV), V(V), Co(II), Ni(II) and Pd(II) gave pale coloured chelates. The reaction of MPN with Fe(III) and Cu(II) ions were quantitative. Both complexes had good pigment properties and should prove suitable to plastics, inks, board markers and textile printing.

Synthesis and characterisation of chromium oxide as a pigment for high temperature application

In this paper, the synthesis and the application of chromic oxide as a high temperature pigment have been reported. To synthesise chromic oxide, solid‐state reaction using sulphur and sodium chromate tetrahydrate was undertaken. Morphology of the pigment synthesised was investigated by scanning electron microscopy. Formation of the chromic oxide was observed at 888°C in an oxidising atmosphere. Thorough washing of the resultant pigment played a vital role in the aggregation of the pigment particles, as demonstrated by a particle size characteristics.