Advanced Ceramics Progress
Volume:2 Issue: 4, Fall 2016

The aim of this work was WC distribution in base Al-Si-Mg (A356) alloy as reinforcing agent. WC Solid particles in the sub-23-nm size range added to melted alloy by centrifuge casting. The cylinder tube without gap was obtained. FESEM and OPM results show that the distribution depends upon the rotational speeds of the mould and centrifugal casting conditions. According to the MAP results, during solidification, Nano size WC phase, by the Eutectic Silicon and around primary Aluminum phase, was precipitated and distributed significantly. The wear tests were carried out using pin on disk method. Results revealed the 0.0272g wear rate by 500gr load at 1200 m for samples that are casted at 1500RPM centrifugal casting speed. According to SEM micrographs, the sliding load transfer by Nano WC particles occurred.

Cadmium sulfide (CdS) photosensitizers were successfully formed on the mesoporous titania films using the successive ionic layer adsorption and reaction (SILAR) method in five cycles, and the effects of particles size distribution and their occupied surface area on the morphology, topography, optical property, and photovoltaic performance were investigated. Scanning electron microscope (SEM) images demonstrated that the increase in the number of SILAR cycles increased the number of deposited particles as well as their sizes so that the surface morphology after the third SILAR cycle changed from non-uniform particles to a uniform layer. The surface topography of all layers was hill-valley like, the roughness of which decreased as homogeneous layers formed. The absorbance spectra measured by UV-Vis spectrophotometer revealed that the absorbance spectra of the films increased and shifted towards longer wavelengths as the number of SILAR cycles increased, which is due to the increase in the particles size distribution. Photovoltaic measurements clarified that increase in the particles size distribution had the dominant effect up to the third SILAR cycle and increased the power conversion efficiency to a maximum of 4.65 %. However, as the occupied surface area increased due to the extreme formation of CdS particles and blocking of porosities in the mesoporous titania film, the efficiency dropped to 2.64 %.

In this study, spherical Nb2O5 nanoparticles were synthesized by a novel chemical method as a simple, robust, surfactant-free, non-toxic and widely applicable approach. In order to investigate the effect of initial concentration on particle sizes, nanoparticles with different initial concentration were synthesized. Ultrasonic assisted method was applied and the effects of ultrasonic treatment and concentration on particle sizes have been investigated. The structure and morphology of Nb2O5 nanoparticles were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FE-SEM). Particle size measurement was estimated by Digimizer software and particle size distribution was plotted. The results showed that ultrasonic treatment and different suspension concentration impact on particle sizes. Nanoparticles with average particle size of 41 nm in diameter were achieved by using 2 gr/L of Nb2O5 in initial suspension with ultrasonic assist.

This study deals with the effect of gelatin on physical and mechanical properties of calcium phosphate bone cements. The mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate (DCPA) as the cement powder was mixed with 6 wt% Na2HPO4 solution containing different amount (0, 2, 5 and 8% in w/w) of foamed gelatin as liquid phase. The physical properties were determined in the terms of setting time and macroporosity. The compressive strength was also checked before and after soaking the cements in simulated body fluid (SBF). The phase composition, microstructure and chemical groups were respectively determined using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Fourier transformation Infrared Spectroscopy (FTIR). The results showed that gelatin accelerated hydroxyapatite (HA) precipitation during setting and reduced the initial setting time from 35 min for cement without gelatin to 23 min for cement with the most amount of gelatin. Moreover, 17% (in v/v) macroporosity was induced in the cement structure using 8% solution of gelatin as the cement liquid. Gelatin addition promoted compressive strength of the set cement from 1.13 MPa (for gelatin-free cement) to 5.8 MPa.

Porous silicon was successfully prepared using metal-assisted chemical etching method. The Effect of HF/H2O2 concentration in etching solution as an affecting parameter on the prepared porosity type and size was investigated. Field emission electron microscopy (FE-SEM) confirmed that all etched samples had porous structure and the sample which was immersed into HF/H2O2 withmolar ratio of 7/3.53 had the smallest porosities. The average roughness of 288 nm and reflectivity as low as 7% could be achieved using this molar ratio. The Raman peak appeared at 520.09 cm-1 confirmed that there weren’t any defect and stress in the porous structure. The prepared porous silicon had potential candidate for replacement with antireflective layer in photovoltaic devices because of their low production cost, high antireflective property, and possibility of integration process relative to other antireflection layers.

Air plasma spray (APS) process is used to produce high density and flowability spherical powders. Phase transformation that occurred in this process isn’t well known. In this paper, the YSZ powders have been sprayed in water to investigate the morphology changes and phase transformations via air plasma spray (APS) method. Phase analysis of powders was examined by XRD and the crystallite size and lattice strain of YSZ calculated by the Williamson-Hall method. Morphology and particle size measurement observed by scanning electron microscope. Therefore, results showed the good spherical YSZ powders morphology and also phase transformations were in order to improve the properties of the fabricated powders. During the YSZ powders plasma process, some monoclinic phases transform to stable tetragonal phase.

In this study, the effect of surface roughness and roughness morphology on the bond strength of WC-Co-Cr coatings has investigated. The three different surfaces morphology are use for this purpose. The first and tow samples sandblasted with alumina and silicon carbide respectively. Other sample no sandblasted before spraying process. The same WC-10Co-4Cr coating deposited on the substrates with HVOF methods. The morphology of powder, coating and substrate surface roughness has investigated with scanning electron microscopy (SEM) and the surface roughness meter used for measurement of surface roughness. The phase study of powder and coating are doing with X-ray diffractometry. Coatings bond strength has investigated with pull off test. The phase investigated show that decomposition of WC phase is very low during thermal spray process. Porosity in the WC-10Co-4Cr coating that calculated with image analysis is about %1.6, whereas the hardness is 1180 HV. The pull off test results show the non-sandblasted substrate after coating process shows higher bond strength. Probably work hardening during sandblasting prevent of WC particles penetration into copper substrate. This phenomenon to cause the fracture mode in alumina and SiC was adhesion and cohesion respectively, while Fracture in the non-sandblasted coating occurs in epoxy.

In the current work, the effect of surface morphology on light emission property and absorption behavior of quasi-columnar macro-porous silicon (PS) was investigated. PS structures with different morphology were synthesized using photo-electrochemical etching method by applying different etching current densities. SEM micrographs showed that empty macro-pores size and porosity of PS layers were increased by increasing the current density due to passivity breakdown in initiated pore walls. Also, a decrease in pore density and a diminishing of nanocrystallites density on PS samples surface was observed. By increasing etching current density, a red shift in Raman peak position of PS samples was observed which was due to the residual stress and quantum confinement (QC) effect in the PS structures. PL peak position was also shifted to higher frequencies and it was in good agreement with Raman red shift due to QC effect in finite size crystallites. Maximum PL intensity was observed for sample with higher pore density and smaller pore size. Although, the PS structure with maximum pore size had the maximum porosity, but it showed a remarkable decrease in PL intensity because of trapping of irradiated light in quasi-columnar empty macropores. We report that porosity is not necessarily increase in order of creation more pores and more nanocrystallites formation in PS structures. Therefore porosity can not the only effective parameter for determination of optical properties such as photoluminescence efficiency. The morphology and size of pores can also be outstanding parameters for changing optical behavior of PS nanostructures.