School of material science and engineering

In this study, Eu3+/Gd3+ co-doped fluoroapatitååe (Eu/Gd:FAP) nanocrystals were synthesized by the hydrothermal method as a fluorescent bioimaging agent. The phase composition, morphology, fluorescence, and biosafety of the resulting samples were characterized. Moreover, the in vivo fluorescent bioimaging application of Eu/Gd:FAP nanocrystals was evaluated in mice with subcutaneously transplanted tumors. The results showed that the Eu/Gd:FAP nanocrystals were short rod-like particles with a size of 59.27 ± 13.34 nm × 18.69 ± 3.32 nm. With an increasing F substitution content, the Eu/Gd:FAP nanocrystals displayed a decreased size and enhanced fluorescence emission. Eu/Gd:FAP nanocrystals did not show hemolysis and cytotoxicity, indicating good biocompatibility. In vivo fluorescent bioimaging study demonstrated that Eu/Gd:FAP nanocrystals could be used as a bioimaging agent and displayed stable fluorescence emitting in tumors, indicating an accumulation in tumor tissue due to the pass...

Nano hydroxyapatite (Ca10(PO4)6(OH)2, HAp) has aroused widespread attention as a green and environmentally friendly adsorbent due to its outstanding ability in removing heavy metal ions, radio nuclides, organic pollutants and fluoride ions for wastewater treatment. The hexagonal crystal structure of HAp supports the adsorption mechanisms including ionic exchange reaction, surface complexation, the co-precipitation of new partially soluble phases and physical adsorption such as electrostatic interaction and hydrogen bonding. However, nano HAp has some drawbacks such as agglomeration and a significant pressure drop during filtration when used in powder form. Therefore, instead of using nano HAp alone, researchers have worked on modificationsand composites of nano HAp to overcome these issues and enhance the adsorption capacity. The modification of cationic doping and organic molecule grafting for nano HAp can promote the immobilization of ions and then increase adsorption capacity. De...

To improve the electrical conductivity of the dicyandiamide-cured electrically conductive adhesives (ECAs), short-chain difunctional acids with various structures including oxalic acid, succinic acid, adipic acid, phthalic acid and cis-hexahydrophthalic acid were introduced in-situ to replace the commonly used surfactant-stearic acid on the silver filler surface. Oxalic acid, phthalic acid and cis-hexahydrophthalic acid deteriorated the electrical conductivity of ECAs whereas the electrical conductivity was improved significantly with the addition of succinic acid and adipic acid. Moreover, the storage performance, viscosity, curing behavior, bulk resistivity and the shear strength of ECAs with varied content of adipic acid had been further studied. With the increment of adipic acid, the curing temperature of ECAs decreased, while the reaction between dicyandiamide and adipic acid happened as the content reached 0.3 wt%. And the adipic acid not just improved the electrical conductive, but also improved the shear strength without adversely affected the storage performance of ECAs. As the content of adipic acid reached 0.3 wt%, the lowest bulk resistivity 3.8 Â 10 −4 Ω cm was obtained, at the content of 0.5 wt%, the shear strength was improved to 18.5 MPa.

The aim of this work was to develop a new process for the synthesis of TiC and NiAl/TiC composite in which the combustion reaction was ignited using a high frequency induction heater. High density, two-layer TiC-NiAl composites were also produced using this process. Temperature profiles during synthesis were measured with an IR thermometer and a high resolution thermal image camera was used to monitor the reaction process. Phase transformation was investigated using XRD and SEM was used to characterize the microstructure of the synthesized composites. The mechanical properties of the products were evaluated by measuring hardness. The results show that the reaction was complete and that stoichiometric products of NiAl and TiC were produced. The properties of NiAl/TiC composites were found to be functions of composition and processing parameters. The reaction mechanism was analyzed using temperature monitoring, thermodynamic analysis and microstructure investigation.

Combustion synthesis of NiAl requires the combustion reaction to be ignited and fully controlled to maintain the geometry of the compressed parts. This paper describes a new ignition process using induction heating and investigates the effect of Al 2 O 3 on both the combustion synthesis process and the performance of the synthesized products. A high frequency induction heater was used to ignite the synthesis reaction. During synthesis the temperature profiles were measured with infrared thermometers to monitor the reaction process and X-ray Diffraction was used to investigate the phase transformation. The results show that single phase NiAl can be produced by this new process regardless of the addition of Al 2 O 3 . However, the addition of Al 2 O 3 was found to have a significant effect on heating rates, combustion behaviour and properties of the synthesized products. Additionally, there is a critical concentration for Al 2 O 3 above which the compacts cannot be ignited by induction heating. Mechanical properties of the products were tested to evaluate the performance of the synthesized composites.

The Bi-based lead-free frit for silicon solar cell front contact has a shortage of conversion efficiency compared with traditional products that contain Pb. One feasible method to increase conversion efficiency is by improving the current flow at the interface. The current flow establishment is controlled by the reaction of Bi ions to Ag, SiNx, and the Si wafer. However, the microstructure of Bi ions in the glasses remains unclear. In this work, two groups of Bi 2 O 3 -B 2 O 3 -SiO 2 glasses were studied through differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared, and Raman and X-ray photoelectron spectroscopies. The results suggest that the Bi 3+ to Bi 5+ transformation is induced by the increase in B 2 O 3 content in both the 30 mol% and 60 mol% Bi glasses. The coexistence of [BiO 3 ] and [BiO 6 ] is confirmed in all ternary samples. The [BO 4 ] units exhibit in all borosilicate glass. The [BO 3 ] structure only emerges in a high boron concentration. The glass transition temperature (T g ) is strongly affected by the ratio of Non-Bridging Oxygen. The Oxygen packing density also has influence on T g but not obvious.

The objective of this work was to develop a new technique to synthesize and fabricate NiAl coatings on a steel
substrate in one processing step. Induction heating was used as the ignition source to initiate the selfpropagation
high-temperature synthesis (SHS) reaction of Ni/Al, while titanium was used as the underlayer to
facilitate the adhesion between the coating and the substrate. The temperature profiles during the process
were measured to monitor the heating and synthesis reaction in the coating and underlayer. The microstructure
and the phase compositions of the synthesized products were studied using SEM and XRD. The results showed
that the SHS reactions of Ni/Al produced stoichiometric and substoichiometric NiAl such as Ni0.58Al0.42 and
Ni1.04Al0.96 in the coating. The Ti underlayer joined the reaction. The reacted part changed into Ti3Al–Ti2Ni composite
and the unreacted Ti formed an alloywith theNiAl. Themechanical properties of the synthesized products,
evaluated using Vickers indentation, showed that the hardness of the underlayer was higher than that of the
coatings and substrate, while the test at the substrate/underlayer interface indicated that the existence of a Ti
underlayer had improved the adhesion between the coating and the substrate.

Stainless steel was investigated in terms of the evolution mechanism of chemical elements during selective laser melting. It was found that 21% carbon was lost and the decarburization occurred. The carbon-gradient structure contributes to a low Young's Modulus and hardness in molten pool boundary and also anisotropic tensile properties.

The aim of this work was to develop a new process for the synthesis of TiC and NiAl/TiC composite in which the combustion reaction was ignited using a high frequency induction heater. High density, two-layer TiC-NiAl composites were also produced using this process. Temperature profiles during synthesis were measured with an IR thermometer and a high resolution thermal image camera was used to monitor the reaction process. Phase transformation was investigated using XRD and SEM was used to characterize the microstructure of the synthesized composites. The mechanical properties of the products were evaluated by measuring hardness. The results show that the reaction was complete and that stoichiometric products of NiAl and TiC were produced. The properties of NiAl/TiC composites were found to be functions of composition and processing parameters. The reaction mechanism was analyzed using temperature monitoring, thermodynamic analysis and microstructure investigation.

The elastic and anelastic properties of three different samples of Fe x O have been determined in the frequency range 0.1-2 MHz by resonant ultrasound spectroscopy and in the range 0.1-50 Hz by dynamic mechanical analysis in order to characterize ferroelastic aspects of the magnetic ordering transition at T N ∼ 195 K. No evidence was found of separate structural and magnetic transitions but softening of the shear modulus was consistent with the involvement of bilinear coupling, λe 4 q, between a symmetry-breaking strain, e 4 , and a structural order parameter, q. Unlike a purely ferroelastic transition, however, C 44 does not go to zero at the critical temperature, T * c , due to the intervention of the magnetic ordering at a higher temperature. The overall pattern of behaviour is nevertheless consistent with what would be expected for a system with separate structural and magnetic instabilities, linear-quadratic coupling between the structural (q) and magnetic (m) driving order parameters, λqm 2 , and T N > T * c . Comparison with data from the literature appears to confirm the same pattern in MnO and NiO, with a smaller difference between T N and T * c in the former and a larger difference in the latter. Strong attenuation of acoustic resonances at high frequencies and a familiar pattern of attenuation at low frequencies suggest that twin walls in the rhombohedral phase have typical ferroelastic properties. Acoustic dissipation in the stability field of the cubic phase is tentatively attributed to anelastic relaxations of the defect ordered structure of non-stoichiometric wüstite or of the interface between local regions of wüstite and magnetite, with a rate controlling step determined by the diffusion of iron.

Anelastic loss mechanisms associated with phase transitions in SrZr 1−x Ti x O 3 perovskites (x = 0.375, 0.450, 0.550, 0.775) have been investigated by dynamic mechanical analysis between 128 and 723 K at frequencies of 0.1-50 Hz. Distinctive patterns of changes in the elastic moduli due to octahedral tilting transitions correlate closely with data for the shear modulus obtained previously by resonant ultrasound spectroscopy at high frequencies (∼0.5 MHz). The I 4/mcm ↔ I mma transition is first order and has a characteristic minimum in the shear modulus and Young's modulus. For x = 0.450 and 0.550, a dissipation peak occurs at the transition temperature, the maximum of which varies with frequency according to a power law relationship of the form tan δ = A f n , with n ≈ −0.3. Debye-like dissipation peaks in the stability field of the I mma structure at x = 0.375 have a frequency and temperature dependence consistent with twin wall pinning by defects with an activation energy ∼184 kJ mol −1 . These results indicate that there is diversity of pinning and relaxation processes for transformation twin walls and interfaces in different perovskites with I 4/mcm, I mma and Pnma structures.

Anelastic loss mechanisms associated with phase transitions in BaCeO 3 have been investigated at relatively high frequency ϳ1 MHz and low stress by resonant ultrasound spectroscopy ͑RUS͒, and at relatively low frequency ϳ1 Hz and high stress by dynamic mechanical analysis ͑DMA͒. Changes in the elastic moduli and dissipation behavior clearly indicate phase transitions due to octahedral tilting: Pnma ↔ Imma ↔ R3c ↔ Pm3m structures at 551 K, 670 K, and 1168 K, and strain analysis shows that they are tricritical, first-order, and second-order phase transitions, respectively. Structures with intermediate tilt states ͑R3c and Imma structures͒ show substantial anelastic softening and dissipation associated with the mobility of twin walls under applied stress. The Pnma structure shows elastic stiffening which may be due to the simultaneous operation of two discrete order parameters with different symmetries. In contrast with studies of other perovskites, BaCeO 3 shows strong dissipation at both DMA and RUS frequencies in the stability field of the Pnma structure. This is evidence that ferroelastic twin walls might become mobile in Pnma perovskites and suggests that shearing of the octahedra may be a significant factor.

Advantage is taken of the wealth of experimental data relating to the evolution with temperature of spin states of Co3 + in LaCoO3 in order to undertake a detailed investigation of the mechanisms by which changes in electronic structure can influence strain, and elastic and anelastic relaxations in perovskites. The macroscopic strain accompanying changes in the spin state in LaCoO3 is predominantly a volume strain arising simply from the change in effective ionic radius of the Co3 + ions. This acts to renormalize the octahedral tilting transition temperature in a manner that is easily understood in terms of coupling between the tilt and spin order parameters. Results from resonant ultrasound spectroscopy at high frequencies (0.1-1.5 MHz) reveal stiffening of the shear modulus which scales qualitatively with a spin order parameter defined in terms of changing Co-O bond lengths. From this finding, in combination with results from dynamic mechanical analysis at low frequencies (0.1-50 Hz) and data from the literature, four distinctive anelastic relaxation mechanisms are identified. The relaxation times of these are displayed on an anelasticity map and are tentatively related to spin-spin relaxation, spin-lattice relaxation, migration of twin walls and migration of magnetic polarons. The effective activation energy for the freezing of twin wall motion below ~ 590 K at low frequencies was found to be 182 ± 21 kJ mol - 1 (1.9 ± 0.2 eV) which is attributed to pinning by pairs of oxygen vacancies, though the local mechanisms appear to have a spread of relaxation times. It seems inevitable that twin walls due to octahedral tilting must have quite different characteristics from the matrix in terms of local spin configurations of Co3 + . A hysteresis in the elastic properties at high temperatures further emphasizes the importance of oxygen content in controlling the properties of LaCoO3.

A new series of 1,3,4-oxadiazoles derivatives was synthesized, characterized and evaluated for their in vitro and in vivo anti-thrombotic activity. Compounds (3a-3i) exhibited significant clot lysis with respect to negative control and reference drug streptokinase (30,000 IU) while enhanced clotting time (CT) values were observed (130-342 sec) for these tested compounds than the standard drug heparin (110 sec.). High affinity towards 1NFY with greater docking score was observed for the compounds (3a, 3i, 3e, 3d and 3h) than the control ligand RPR200095. In addition, very good inhibitory potential against factor Xa (F-Xa) was observed with higher docking scores (5612-6270) with ACE values (–189.68 to –352.28 kcal/mol) than the control ligand RPR200095 (Docking score 5192; ACE –197.81 kcal/mol. In vitro, in vivo and in silico results proposed that these newly synthesized compounds can be used as anti-coagulant agents.

In the original version of this Article, the affiliation for Hussein A. Younus with “Chemistry Department, Faculty of Science, Fayoum University, Fayoum 63514, Egypt” was omitted. This has now been corrected in both the PDF and HTML versions of the Article.

Novel mono-and dinuclear dimethyltin(IV) complexes were synthesized using tridentate Schiff base ligands, derived from 2-amino-2-hydroxymethyl-propane-1,3-diol and various aldehydes. These diorganotin(IV) compounds displayed good catalytic activity for solvent-free cycloaddition of CO 2 to epoxides at ambient pressure. These catalysts efficiently completed the insertion of CO 2 to various epoxides at low catalyst loadings (0.1-1.0 mol%) in 1-6 hours giving high values of TONs around 1000. The catalyst further usability for three continuous reaction runs in the reaction mixture gives the same activity revealing the remarkable stability of these compounds under the given reaction conditions. Therefore, organotin(IV) complexes are efficient catalysts for the synthesis of the industrially important cyclic carbonates from epoxides at ambient pressure under solventfree conditions.