Mohammed Es-Souni

On the properties of two binary NiTi shape memory alloys. Effects of surface finish on the corrosion behaviour and in vitro biocompatibility

The present paper compares the transformation behaviour and mechanical properties of two orthodontic wires of close chemical compositions. The effects of surface topography and surface finish residues on the potentiodynamic corrosion behaviour and biocompatibility are also reported. The cytotoxicity tests were performed on both alloys in fibroblast cell cultures from human gingiva using the MTT test. It is shown that the surface finish and the amounts of surface finish residues affect dramatically the corrosion resistance. Bad surface finish results in lower corrosion resistance. The in vitro biocompatibility, though not affected to the extent of corrosion resistance, is also reduced as the surface roughness and the amounts of residues increase. This is thought to be due to surface effects on corrosion and metallic ions release.

On the transformation behaviour, mechanical properties and biocompatibility of two NiTi-based shape memory alloys:: NiTi42 and NiTi42Cu7

The transformation behaviour, mechanical properties and cytotoxicity of a binary NiTi42 and a ternary NiTi42Cu7 alloy have been investigated. The transformation temperatures were determined via differential scanning calorimetry, the mechanical properties have been investigated in 3-point bending tests in the temperature range between 6 and 60 degrees C. The cytotoxicity tests were performed on both alloys in cultured epithelial cells from human gingiva. The cytotoxicity investigations included both MTT tests and morphological observations. It is shown that although the ternary alloy is characterised by a narrower hysteresis and superior mechanical properties, including fatigue resistance, its cytotoxicity is higher than that of the binary alloy. This is thought to arise from the release of copper ions in the medium, which upon atomic absorption spectroscopy measurements amount to approximately 2.8 microg cm(-2) for an incubation period of 7 days.

Morphology and property control of NiO nanostructures for supercapacitor applications.

We process one-dimensional (1D) NiO nanostructures in anodized alumina templates starting from electrochemically deposited Ni nanotubes (NTs), and characterize their morphology-dependent supercapacitance behavior. The morphology of the 1D NiO nanostructures is controlled by the time of annealing at 450°C. After 25 min of annealing, the NTs start to close but maintain the tubular structure, and after a further 300 min of annealing time, the tubes are completely closed and nanorods (NRs) are formed. We show that the structures obtained are highly promising for supercapacitor applications; the performance of the NiO NT structure is with a specific capacitance of 2,093 F/g, the highest ever obtained for NiO, approaching the theoretical capacitance of this material. A suitable combination of nanocrystalline grain size and the high surface area akin to the tubular structure is responsible for this high performance. In contrast, the NiO NR structure is characterized by lower performance (797 F/g). A further attribute of the proposed structure is its high stability against galvanostatic charging-discharging cycling at high current densities, with almost no alteration to performance after 500 cycles.

Mn-doped 0.71Pb(Mg1∕3Nb2∕3)O3–0.29PbTiO3 pyroelectric crystals for uncooled infrared focal plane arrays applications

3mol%Mn-doped 0.71Pb(Mg1∕3Nb2∕3)O3–0.29PbTiO3 single crystals were grown by a modified Bridgman technique. The pyroelectric properties and thermal stability of the crystals were investigated. Mn substitution resulted in an enhanced pyroelectric coefficient and a lower dielectric loss, which led to the improvement of the detectivity figure of merit of doped crystals by about a factor of 4 at 50Hz compared with that of pure crystals. Moreover, the thermal stability was enhanced by Mn substitution. The mechanism of doping effect is explained by the fact that the domain walls are pinned by the dopant dipolar defects, which optimizes the pyroelectric performance of 0.71Pb(Mg1∕3Nb2∕3)O3–0.29PbTiO3 for uncooled infrared focal plane arrays applications.

Torque Transmission between Square Wire and Bracket as a Function of Measurement, Form and Hardness Parameters

Abstract: The aim of the study was to investigate the influence of cross section, edge geometry and structural hardness on torque transmission between square wire and bracket.For this purpose, 5 different brands of stainless steel square wire in 3 dimensions (0.016”× 0.016”, 0.016”× 0.022” and 0.017”× 0.025”) were inserted into edgewise brackets with a slot size of 0.018” and loaded with different torques (1 and 3 Ncm). The slot and wire geometries were analyzed by computer on ground specimens before and after loading. In addition, the Vickers hardness and micro-hardness of the unstressed and stressed metal surfaces were determined.While the slot size was very accurately maintained, the wire dimensions deviated downwards by an average of 10%. Torque transmission led to notching and bending-up phenomena on the bracket slot flanks. A torque loading of 3 Ncm increased the torque play of 0.016”× 0.022” wires by 3.6°, and of 0.017”× 0.025” wires by 3.7°. In the case of 0.016”× 0.016” wires, an effective torque transmission was no longer possible. The average Vickers hardness of the wires was 533 kp/mm2, and that of the brackets 145 kp/mm2. The micro-hardness in the deformation area of stressed internal slot walls increased with increasing load transmissions from 204 to 338 kp/mm2.As a result of excessively small wire dimensions and plastic deformation of the brackets, a relatively large torque play occurs. Deformation and notching in the area of the internal slot walls are inconsistent with demands for recycling brackets. A standardization of bracket wire systems stating the actual torque play would be desirable.Zusammenfassung: Ziel der Studie war es, den Einfluss von Querschnittsmaß, Kantengeometrie sowie Gefügehärte auf die Torquedrehmomentübertragung zwischen Vierkantdraht und Bracket zu untersuchen.Dazu wurden Vierkantdrähte aus rostfreiem Stahl von fünf Herstellern in drei Dimensionen (0,016 ”× 0.016”, 0,016”× 0,022” und 0,017”× 0,025”) in Edgewise-Brackets mit dem Slotmaß 0,018” eingebracht und mit unterschiedlichen Drehmomenten (1 und 3 Ncm) belastet. Slot- und Drahtgeometrie wurden vor und nach Belastung an Schliffpräperaten rechnergestützt analysiert. Außerdem wurden die Vickers- und Mikrohärte der unbelasteten und belasteten Metallflächen bestimmt.Während das Bracketlotmaß recht genau eingehalten wurde, wichen die Drahtdimensionen im Mittel um 10% nach unten ab. Drehmomentübertragung führte zu Einkerbungs- und Aufbiegungserscheinungen an den Bracketslotflanken. Eine Drehmomentbelastung von 3 Ncm erhöhte das Torquespiel von 0,016”× 0,022”-Drähten um 3,6°, von 0,017”× 0,025”-Drähten um 3,7°. Bei 0,016”× 0,016”-Drähten war eine wirksame Drehmonentübertragung nicht mehr möglich. Die Vickers-Härte der Drähte betrug im Mittel 533 kp/mm2, die der Brackets 145 kp/mm2. Die Mikrohärte im Deformationsbereich belasteter Slotinnenwände nahm mit zunehmender Kraftübertragung von 204 auf 338 kp/mm2 zu.Infolge zu kleiner Drahtdimensionen und plastischer Deformation der Brackets kommt es zu einem relativ großen Torquespiel. Deformationen und Einkerbungen im Bereich der Slotinnenwände widersprechen der Forderung nach einem Recycling von Brackets. Eine Normung der Bracketdrahtsysteme unter Angabe des tatsächlichen Torquespiels wäre wünschenswert.

Orientation and phase transition dependence of the electrocaloric effect in 0.71PbMg1/3Nb2/3O3-0.29PbTiO3 single crystal

In this letter, the electrocaloric effect (ECE) of 〈111〉- and 〈001〉-oriented 0.71PbMg1/3Nb2/3O3-0.29PbTiO3 (0.71PMN-0.29PT) single crystals is investigated with emphasis on the effects of phase transitions and their dependence on electric field. We show that crystal orientation and more specifically the complex phase transitions taking place in the specific composition above have large effects on the maximum ECE temperature, ΔTmax, its peak temperature, TEC, and the width of the ECE peak of the ΔT(T) curve. The investigation shows that ECE may be tuned by a proper choice of 0.71PMN-0.29PT crystal orientations.

Correlation between structure, dielectric, and ferroelectric properties in BiFeO3–LaMnO3 solid solution thin films

Chemical solution processed BiFeO3 thin films usually show high leakage currents and poor ferroelectric properties. The optimizations of processing conditions and doping with appropriate elements have been among the most promising strategies to enhance the overall properties of BiFeO3 thin films. However, detailed studies on the effects of doping elements on the structure and through it on the properties are still lacking. In this work we investigate the interplay between structure and dielectric-electric-ferroelectric properties of BiFeO3–LaMnO3 [Bi1−xLaxFe1−xMnxO3 (0≤x≤0.1)] solid solution thin films grown on Pt-terminated silicon substrates. The BiFeO3–LaMnO3 system is shown to undergo a structural transition from monoclinic to orthorhombic-tetragonal with various degrees of orthorhombic distortion. All LMO-containing films show a Debye-like dielectric relaxation with the activation energy of 0.90 eV. Both dielectric relaxation and leakage current mechanisms were interpreted in terms of ionized oxygen ...

Microstructure and properties of sol–gel processed Pb1−x Lax(Zr0.52, Ti0.48)1−x/4 O3 thin films. The effects of lanthanum content and bottom electrodes

Abstract PLZT {lanthanum doped PZT [Pb(Zr 0.52 , Ti 0.48 )O 3 ]} thin films with 5, 8 and 10 mol% lanthanum were processed via chemical solution deposition on (111)-Pt/TiO 2 /SiO 2 /Si (100) and LaNiO 3 (LNO)/(111)-Pt/TiO 2 /SiO 2 /Si (100). The thin films were investigated in terms of the influence of lanthanum content and substrate heterolayer structure on the microstructure and dielectric properties. It is shown that deposition on (111)-Pt leads to a (100)/(111) preferred texture and a coarse grained microstructure with PbO depleted areas. Deposition on LNO results in a randomly oriented, fine grained microstructure. The dielectric constants decrease with increasing lanthanum content and are higher for the films deposited on Pt. They take values between 1630 (0.05 mol La 3+ ) and 865 (0.1 mol La 3+ ) for deposition on Pt and between 1090 and 808 for deposition on LNO. The fatigue properties depend also on the lanthanum content and substrate type. The PLZT thin films with lanthanum concentration above 0.05 deposited on LNO show no fatigue.

Macro–meso-porous TiO2, ZnO and ZnO–TiO2-composite thick films. Properties and application to photocatalysis

We report on a new and versatile method for preparing homogenous, crack-free and macro–meso-porous thick films of TiO2, ZnO and ZnO–TiO2 composites using a single step coating procedure and fairly low annealing temperatures of a maximum of 400 °C. The method relies on an oxide nanopowder filler in an optimized precursor solution. The films are well adherent to the substrate, show homogeneously distributed open porosity, and are hydrophilic. The photocatalytic activity of these films was characterized using methyl orange as a model dye. We show that the TiO2 films have better photocatalytic activity than ZnO and ZnO–TiO2 composite films. The advantages of these composite films over particulate photocatalysts lie in their robustness and ease of application as no filtration is needed. Furthermore it is possible to apply them on suitable large area membranes.

Doping and thickness effects on dielectric properties and subswitching behavior of lead titanate thin films

Dielectric and ferroelectric properties of sol-gel derived PbTiO3 and (Pb,Er)TiO3 films with thickness in the range from 134 to 420 nm have been investigated. It is demonstrated that 1% Er doping improves the shape of the ferroelectric hysteresis loop probably due to compensation of p-type conductivity. The dielectric constant is shown to be linearly dependent on the amplitude of the measuring signal. It is shown that the Rayleigh equation can be used to discriminate between reversible and irreversible contributions to the dielectric properties of the films. Both reversible and irreversible Rayleigh components were found to be affected by donor doping and film thickness. Introducing 1% of Er is thought to counteract domain wall pinning on “dead layer” near the film–electrode interface.