Nicholas Mondinos

Synthesis and characterisation of nanohydroxyapatite using an ultrasound assisted method.

Nanostructured hydroxyapatite (HAP) was prepared by a wet precipitation method using Ca(NO(3)) and KH(2)PO(4) as the main material and NH(3) as the precipitator under ultrasonic irradiation. The Ca/P ratio was set at 1.67 and the pH maintained at a minimum of 9. The temperature conditions and ultrasound influences were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FT-IR). The results showed that Nano-HAP can be obtained by this method and the particles were achieved to around 30 nm.

Effect of dilute gelatine on the ultrasonic thermally assisted synthesis of nano hydroxyapatite.

A series of nano hydroxyapatite-gelatine composites with different dilute solutions of gelatine concentrations were synthesized by a thermally assisted low-power ultrasonic irradiation method. The gelatine hydroxyapatite, (Gel-HAP) nanoparticles were prepared using Ca(NO(3))(2) and KH(2)PO(4) in the presence of gelatine in an aqueous solution. The synthesised products were heat treated between 100 and 400°C. The effect of the addition of gelatine on the nucleation and growth of synthesised nano HAP was investigated. Characterisation was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FT-IR). The characterisation results indicate that gelatine has been appended to the nano HAP forming regular spherical shaped crystals of nano sized Gel-HAP.

Chemical bonding states and solar selective characteristics of unbalanced magnetron sputtered TixM1−x−yNy films

Transition metal nitride TixM1−x−yNy (M = Al or AlSi) based thin films are evaluated as solar selective surfaces by correlating their spectral selective features with their crystal structure and chemical bonding state including mechanical strength. Ti0.5N0.5, Ti0.25Al0.25N0.5, and Ti0.25Al0.2Si0.05N0.5 films were synthesized on AISI M2 steel substrates via closed field unbalanced magnetron sputtering technology. These were investigated using XRD, SEM, XPS, UV-Vis, FTIR and nanoindentation techniques. Analysis of the optical properties showed the solar absorptance, in the visible range, of the TixM1−x−yNy films improved significantly from 51% to 81% with AlSi-doping and an increase of solar absorptance of up to 66% was recorded from films doped with Al. Moreover, the Al doping can reduce the thermal emittance in the infrared range from 6.06% to 5.11%, whereas doping with AlSi reduces the emittance to ca. 3.58%. The highest solar selectivity of 22.63 was achieved with TiAlSiN films. Mechanical studies showed enhanced hardness by ∼32%; enhanced yield strength by ∼16% and enhanced plastic deformation by ∼110% of Al and AlSi doped TiN matrix.

Investigation of the post-annealing electromagnetic response of Cu–Co oxide coatings via optical measurement and computational modelling

The optical frequency response and changes to the dielectric and optical parameters due to annealing temperature variation (200–500 °C) of sol–gel derived CuCoOx thin film coatings were investigated. The optical constants such as absorption coefficient, band-gaps, Urbach energy, complex refractive index, complex dielectric constants, optical dispersion parameters, and energy loss functions were determined from reflectance data analysis recorded in the ultraviolet to near-infrared (190–2200 nm) range. The absorption coefficient and the broadening of absorption edge (steepness parameter), energy band-gaps, Urbach energy, loss tangent and energy loss functions decreased with the increase in annealing temperatures. The refractive index displayed normal dispersion behaviors at higher frequency with the maximum value at a temperature of 500 °C. First-principles simulations, density functional theory (DFT+U) as implemented in the Cambridge Serial Total Energy Package (CASTEP), based on a cluster structure of Cu0.5Co2.5O4 system, optimized the crystalline structure and calculated the electronic structure of the framework. The calculated density of states (DOS) and associated absorption coefficient and dielectric constant results reasonably support the experimental findings.

Experimental and predicted mechanical properties of Cr1−xAIxN thin films, at high temperatures, incorporating in situ synchrotron radiation X-ray diffraction and computational modelling

Cr1−xAlxN coatings, synthesised by an unbalanced magnetic sputtering system, showed improved microstructure and mechanical properties for ∼14–21% Al content. In situ SR-XRD analysis indicated various crystalline phases in the coatings that included: CrN, AlN, α-Cr with small amounts of AlO2 and Al2O3 over the 25–700 °C range. Al doping improves resistance to crystal growth, stress release and oxidation resistance of the coatings. Al doping also enhances the coating hardness (H) from 29 to 42 GPa, elastic modulus (E) from 378 to 438 GPa and increased the resistance to deformation. First-principles and quasi-harmonic approximation (QHA) studies on bulk CrN and AlN were incorporated to predict the thermo-elastic properties of Cr1−xAlxN thin film coatings in the temperature range of 0–1500 °C. The simulated results at T = 1500 °C give a predicted hardness of H = ∼41.5 GPa for a ∼21% Al doped Cr1−xAlxN coating.

Electronic properties and stability phase diagrams for cubic BN surfaces

Abstract This contribution investigates structural and electronic properties as well as stability phase diagrams of surfaces of the cubic boron nitride (c-BN). Our calculated parameters for bulk c-BN agree reasonably well with both experimental and computed values available in the literature. Based on the energies of the three experimentally recognised phases of bulk boron, i.e. α-B36, β-B105 and γ-B28, we estimate enthalpy of formation of c-BN to be −2.8 eV. The c-BN(1 0 0) surface offers separate B and N terminations (denoted as c-BN(1 0 0)_B and c-BN(1 0 0)_N), whereas c-BN(1 1 1) and c-BN(1 1 0) are truncated with combinations of boron and nitrogen atoms (denoted as c-BN(1 1 1)_BN and c-BN(1 1 0)_BN). Optimised geometries of surfaces display interlayer displacements up to the three topmost layers. Downward displacement of surface boron atoms signifies a common geometric feature of all surfaces. Bulk c-BN and its most stable surface c-BN(1 0 0)_N possess no metallic character, with band gaps of 5.46 and 2.7 eV, respectively. We find that, only c-BN(1 0 0)_B configuration exhibits a metallic character. c-BN(1 1 0)_BN and c-BN(1 1 1)_BN surfaces display corresponding band gaps of 2.5 and 3.9 eV and, hence, afford no metallic property.

Thermo-mechanical properties of cubic titanium nitride

Abstract The equilibrium structure, elastic constants Cij and thermodynamic functions of cubic titanium nitride (TiN) were calculated within the temperature range of 0–3100 K and under a pressure range 0–60 GPa. Properties were computed using the generalised gradient approximations (GGA) exchange-correlation functional. Calculated mechanical properties (Elastic constants, Young’s modulus and shear modulus) and phonon spectra of TiN obtained via robust DFT-QHA algorithm, were generally in a good agreement with available experimental and theoretical analogous values. In particular, a well-examined quasi-harmonic approximation method implemented in the Gibbs2 code is utilised herein to provide accurate estimation of thermal expansion coefficients, entropies, heat capacity values (at different combinations of temperature/volume/pressure) and Debye’s temperature. Parameters calculated herein shall be useful to elucidate the superior performance of TiN at harsh operational conditions encompassing elevated temperatures and pressures pertinent to cutting machineries and surface coatings.

3d Transition Metal Oxide based Sol-gel Derived Coatings for Photothermal Applications

Photothermal devices require high performance solar selective materials for the surface of solar energy converters. A good solar selective surface exhibits high spectral absorptance in the visible range and low thermal emittance in the infrared to far-infrared range of the solar spectrum. 3d transition metal oxide based thin film coatings are explored as high solar selective material to be used in solar energy harvesting devices. Solar selectivity of such coatings depends on the deposition conditions, crystal structure, chemical composition, microstructural morphology, composition uniformity and stoichiometry. This report highlights and summarizes the optical properties and mechanical characteristics of some recently developed sol-gel dip- coating derived from CuxCoyOz transition metal oxides based solar selective surfaces thinfilms. X-ray photoelectron spectroscopy (XPS), UV-Vis spectrometer, FTIR spectrophotometer, nanoindentation and Synchrotron radiation X-ray diffraction (SR-XRD) techniques are utilized to realize various features involved in such coatings.