فصلنامه مواد پیشرفته در مهندسی
سال سی و یکم شماره 2 (پاییز 1391)

Despite excellent bioactivity of bioactive ceramics such as hydroxyapatite, their clinical applications have been limited due to their poor mechanical properties. Using composite coatings with improved mechanical properties could be a solution to this problem. Therefore, the strength of metal substrate and the bioactivity of the improved composite coating combined could yield suitable results. The aim of this work was fabrication and characterization of hydroxyapatite-forsterite-bioactive glass nanocomposite coating. The sol-gel technique was used to prepare hydroxyapatite-forsterite-bioactive glass nanocomposite in order to coat on 316L stainless steel (SS) by deep coating technique. The X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive X-ray analysis (EDX) techniques were used to investigate the microstructure and morphology of the prepared coating. The results obtained from XRD analysis showed that the suitable temperature for calcination is 600 °C. At this temperature, the homogenous and crack-free coating could attach to the 316L SS substrate. The crystallite size of composite coatings determined via AFM was lower than 100 nm. Overall, the results obtained from this work indicate that hydroxyapatite-forsterite-bioactive glass nanocomposite coating can be a good candidate for biomedical applications.

Although titanium has been recognized for its excellent bio-compatibility with human tissues and good corrosion resistance in some specific environments, little attention has been paid to the surface enrichment of the components by titanium. In this paper, titanium diffusion coating was formed on the surface of Ni-based alloy B-1900 via pack cementation technique and the microstructure of the coatings obtained was studied. Diffusion titanizing was carried out via pack cementation technique at 850 and 950 °C for 3 hours in a mixture of commercially pure titanium, Al2O3 and NH4Cl powder. Microstructure, phase composition and concentration profile of the coatings were examined using optical and electron metallography, X-ray diffraction, and glow dischargeoptical spectroscopy. The results showed that Ti2Ni and AlNi2Ti were the main constituents of the coating. The formation mechanism of the coatings was also evaluated.

Polyethylene terephthalate (PET) based nanocomposites containing three differently modified silica particles were prepared by melt compounding. The influence of type and amount of nanosilica on various properties of nanocomposite was studied using atomic force microscope, thermal degradation, thermal-mechanical properties, scanning electron microscope, and reflectance spectra. AFM test was used to study the roughness of composites which indicated that the roughness is related to hydrophilicity degree of silica, increasing with an increase in hydrophilicity of particles. SEM images were studied on the surface, confirming that the surface roughness of nanocomposite depends on the type of nano-silica used. Results of thermal analysis showed that the interaction between nanosilica particle and polyethylene terephthalate chains is effective in thermal stability of composite. UVvis spectra of polyester nanocomposites indicated that the refraction of hydrophilic silica nanocomposites is more than hydrophobic one, indicating agglomeration of hydrophilic particles at the surface of nanocomposite compared with hydrophobic one.

In recent years, use of Sol-gel procedure for laboratory and industrial synthesis of Nanostructures and especially silica Nano-particles has increased. In this research, silica particles were synthesized by Sol-gel procedure and their physical properties were studied by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Thermal Gravimetric Analysis (TGA). Effect of structural modifiers on the morphology and diameter of Nano-particles was investigated. In addition, the reaction was carried out in the presence of ultrasonic waves in periods of 10, 30 and 60 minutes and the effect of these waves on different stages of reaction was studied by means of SEM. Finally, in this research, spherical particles of 50 to 80 nanometer sizes were synthesized and characterized. They can be very useful hosts for lanthanide complexes that can be used in drug delivery systems, radiotherapy, photoluminescence applications and manufacturing of special lasers. Also, different amounts of Lanthanum Nitrate hexahydrate were added to the mixture during the creation of Nano-particles. Then, Simulated Body Fluid (SBF) was produced for the study of ability of the Nanostructures in regulated delivery of drugs such as Lanthanides, and releasing of Lanthanides in 10 minute periods for 80 h was studied. Lanthanide concentration in SBF was also studied by means of Inductively Coupled Plasma (ICP). According to the results of ICP, loaded Lanthanide was not released from the silica network. Loaded Lanthanides in the mesopores can be used in radiation, especially in cases of liver cancer.

In this paper, preparation and characterization of a-SiNx thin films deposited by LPCVD method from free radicals of TCS and NH3 gaseous system were investigated. These radicals are made by passing each of the precursor gases separately over Pt-Ir/Al2O3 catalyst at the temperature of 600 C. Kinetics of this process was investigated at different total pressures, NH3/TCS flow rate ratios and temperatures. Surface topography and chemical concentrations were studied by Ellipsometry, XXPS, AFM and ADP. Our analyses of the performed experiments indicated that at the temperatures between 730 C and 830 C, the growth rate of thin films follows an Arrhenius behavior with activation energy of 166.3 KJ.mol-1. The measured H2 contamination in a-SiNx thin films is 1.05 at%, which is 17 times lower than the corresponding contamination in the films produced by PECVD and 3.4 times lower than the contamination in the LPCVD thin films with SiH4 or DCS and NH3. The created surface topography of the prepared films is smooth and uniform.

Composite and nanocomposite Ni-Co/SiC coatings were synthesized by electro-codeposition of micro and nano-sized SiC particles with average diameter of 10μm and 20nm using horizontal electrodes. Surface morphology, chemical composition, phase composition, hardness and corrosion resistance of the deposited coatings were studied using SEM observations and EDX, XRD, microhardness and polarization measurements as a function of the electrodeposition current density. The results indicated that the nanocomposite coatings exhibit higher hardness and corrosion resistance compared with the composite coatings containing micro-sized SiC particles despite their lower percentage of the SiC content. The maximum hardness values of 615HV and 490HV were obtained for nanocomposite and composite coatings deposited at current density of 3A/dm2. The observed properties were discussed based on the structural details.

Coherency elastic strain between γ and γ′ is one of the effective factors which affect the morphology,spatial re-arrangement and coarsening kinetics of γ′ precipitates in nickel-base superalloys. using X-ray diffraction (XRD) technique, the γ-γ′ constrained and unconstrained lattice misfits were calculated for different morphologies of the γ′ precipitates in Inconel 738LC nickel-base superalloy. The constrained and unconstrained misfits, hence the coherency elastic strains of different morphologies of the γ′ precipitates were calculated from the XRD patterns of the bulk sample and electrolytically extracted γ′ precipitates, respectively.According to the results, as the sizes of the γ′ particles increased the γ-γ′ coherency as well as the compressive strain of the γ′ precipitates was reduced and consequently their morphology changed from spherical to cubic, then flowerlike,and finally dendritic shapes.

The materials with spinel structures are important for their unique structural and physical properties. In the current research, nanocrystalline hercynite was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA) via sol-gel process. The gel was dried and then the precursor was preheated at1000oC in the air atmosphere and then calcined at different temperatures in the reducing atmosphere in the graphite bed. The preheated and calcined powders were characterized using simultaneous thermal analysis,X-ray diffraction (XRD) and field emission scanning electron microscopy(SEM). Results showed that fully crystalline hercynite was detected in the sample calcined at 900oC. The crystal size of hercynite was different at each calcination temperature, ranging from 30 to100nm.VSM analysis indicated that hercynite is a paramagnetic material.