Ahmed Bachar

Catalytic decomposition of N2O over Ni and Mg-magnetite catalysts

The total decomposition of N2O was performed on the partially nanocrystalline substituted MxFe3−xO4 magnetite (M2+ = Ni2+ and Mg2+ with x = 0–1). The given results showed that the partial incorporation of Fe2+ by Ni2+ and Mg2+ into Fe3O4 spinel frameworks led to a significant amelioration in the catalytic activity for the N2O catalytic reaction. Furthermore, the catalytic activity of synthesized substrates depended on the Fe2+ substitution amount by Ni2+ and Mg2+ cations. The N2O conversion reached 20% (chemical regime) over the Ni0.75Fe2.25O4 and Mg0.58Fe2.42O4 catalysts at 395 and 404 K for N2O (5000 ppm), respectively. A relative increase of decomposition temperatures was observed after O2 addition. Moreover, other results show that the N2O conversion shifted to higher temperatures at high space velocities.

Catalytic Decomposition of Ammonium Dinitramide (ADN) as High Energetic Material over CuO-based Catalysts

CuO supported on a La2O3-doped alumina catalyst was prepared and tested in the decomposition process of an ADN–water energetic propellant. The decomposition products were investigated via on-line analysis. Moreover, CuO/Al2O3–La2O3 shows better results of ADN decomposition in comparison with CuO/Al2O3. Both catalysts were characterized by physico-chemical techniques.

Retracted article: A novel approach for N2O decomposition over Rh-substituted hexaaluminate catalysts

We, the authors, Rachid Amrousse, Akimasa Tsutsumi and Ahmed Bachar, hereby wholly retract this Catalysis Science & Technology article. This article has been retracted as it contains significant overlap with the writing in the article, “A novel Ir-hexaaluminate catalyst for N2O as a propellant”, Chem. Commun., 2007, 1695–1697, without sufficient attribution to this earlier work being given. Signed: R Amrousse, A Tsutsumi and A Bachar, November 2013. This retraction is endorsed by Jamie Humphrey, Managing Editor. Retraction published 29 November 2013.

Synthesis and Characterization of Doped Bioactive Glasses

Abstract Bioactive glasses have been studied for several years. Hench has been the first to show their interest as bone substitutes. Bioglass 45S5 is the best known. This work reviews bioactive glasses of the SiO 2 , CaO, and Na 2 O domain. P, F, and N dopings are also presented. Mixture designs have been used to synthesize the best bioactive glass and to limit the essays. Structures have been studied by NMR analyses. Mechanic properties have been studied as a function of N ratios. Bioactivity has been determined by Fourier Transform Infrared (FTIR) spectroscopy in terms of time of HCA layer’s nucleation. The layer’s thickness has been estimated by Scanning Electron Microscopy coupled with Energy Dispersion Spectroscopy (SEM-EDS) analyses. The last part is about sol-gel synthesis and the Ag doping of an invert glass with 47% SiO 2 , 26.5% CaO, 21.5% Na 2 O, and 5% P 2 O 5 composition.

Mechanical properties, structure, bioactivity and cytotoxicity of bioactive Na-Ca-Si-P-O-(N) glasses

Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids. However, because of their poor strength their use is restricted to non-load-bearing applications. The effects of nitrogen addition on the physical and mechanical properties and structure of bioactive oxynitride glasses in the system Na-Ca-Si-P-O-N have been studied. Glasses with compositions (mol.%): 29Na2O-13.5CaO-2.5P2O5-(55 -3x)SiO2-xSi3N4 (x is the no. of moles of Si3N4) were synthesised with up to 1.5 at% P and 4.1 at% N. A novel 3-step process was used for addition of P and N and this proved successful in minimising weight losses and producing homogeneous glasses with such high SiO2 contents. The substitution of 4.12 at% N for oxygen results in linear increases in density (1.6%), glass transition temperature (6%), hardness (18%) and Youngs modulus (74%). Vickers Indentation Fracture (VIF) resistance (Kifr) was calculated from various relationships depending on the load, indent diagonal, crack lengths and Youngs modulus to hardness (E/H) ratio. Firstly, Meyers index n is calculated from the slope of the logarithmic plot of load versus indent diagonal. Then by comparing the experimental slopes of the logarithmic plots of crack lengths versus load it is concluded that the cracking mode is Radial Median type. The substitution of 4.12 at% N for oxygen results in an increase in Kifr of 40%. These increases in properties are consistent with the incorporation of N into the glass structure in three-fold coordination with silicon which results in extra cross-linking of the glass network. The structure of these bioactive oxynitride glasses was investigated by solid state nuclear magnetic resonance (MAS NMR) of 31P and 29Si. The structure reveals that all the N atoms are bonded to Si atoms with the formation of SiO3N, SiO2N2 and Q4 structural units with extra bridging anions at the expense of Q3 units. The bioactivity of the glasses has been evaluated by soaking them in simulated body fluid (SBF) and results confirm that all these oxynitride glasses are bioactive. Cytotoxicity tests based on different concentrations of these bioactive glass powders in a cell growth environment have also shown that they are not cytotoxic.

Bioactivity and Cytotoxicity of Oxynitride Glasses

Different kinds of bioactive materials are used as bone substitutes. In particular, bioglasses containing Si, Ca, Na and O, bind to host tissues with a stable chemical bond. The phenomenon of bioactivity is associated with the formation of a crystallized hydroxycarbonated apatite (HCA) layer on the bioglass surface when soaked in a simulated physiological fluid. This layer is similar to the mineral phase of bone. However, they do not have sufficient strength for use in load-bearing situations and therefore improving their mechanical properties would allow their use in more robust applications. Within the previously studies, we have shown that the density, glass transition temperature, hardness and elastic modulus have increased linearly with nitrogen content. The purpose of this work was to study the effects of nitrogen addition on the bioactivity in a simulated body fluid (SBF) and cytotoxicity tests have complemented the study.