مجله مواد مهندسی
سال دوم شماره 3 (پیاپی 7، 2010)

In the fibre-reinforced ceramic-matrix composites، the fibre-matrix interface plays an important role. Tailoring the interfacial bond strength improves mechanical properties of the materials. Micro-mechanical experiments indicate that the sliding surface of fibre/matrix interface is rough. The interface roughness plays an important role on the frictional slid and hence on the interfacial shear stress (ISS). The interfacial properties of SiCf/SiC mini-composites with different interphase structures have been determined by indentation، with pushes the top of a selected fibre on a polished cross section. The displacement of that fibre-end is measured. The push-in test on thick specimens shows that the fibre debonds at a given fibre stress and then slides under a certain frictional shear stress. Both parameters increase when the TiC layers become discontinuous، like aligned TiC clusters in a Pyrocarbon matrix. The load-displacement behaviour is in very good agreement with theory when the interfacial shear stress is kept constant، non depending on relative slip displacement. The push-out test on thin composite slices gives directly access to the force which is directly related to the interfacial shear stress associated to slip، without taking into account the elastic compression of the fibre (generally is very small). During push-back، a seating drop was recorded as the fibre returns in its initial position، illustrating a certain effect of roughness. The results obtained by push in on thick specimens are higher than of those of push-out on thin films.

The optical properties of PbTiO3 such as interband transition strength، electron energy-loss spectroscopy (EELS) and dielectric function have been studied by first principles using the density functional theory. The calculated EEL spectrum yield plasmon energy of 23eV and maximum interband transition strength occurs at 3. 8eV. The result also yields a static refractive index of 2. 8 for PbTiO3 in paraelectric phase that are in better agreement with the experimental data.

In this paper an analitical investigation for performance analyses of a dehumidification wheel system with solid desiccant by the mathematical simulation of solid desiccant wheel and with the conservation of mass، energy and mumentum for the air flow and moiture content of desiccant bed in prossess air and regeneration air flow have been presented. Solid desiccant wheel have long been used in dehumidification and cooling systems. In this study a mathematical model has been derived to show the dehumidification trend of desiccant wheel. Four equation concerning water content balance and energy conservation and one momentum equation are used to describe the complicated heat and mass transfer and momentum occurring in moisture adsorption and regeneration. In this model، variation of several parameters such as air humidity ratio، air temperature، water content of desiccant bed and temperature of desiccant according to the length of bed and time were investigated. The mathematical model was confirmed by doing experimental tests on a solid desiccant wheel filled with silica gel. The results indicated that dehumidification rate during the length of desiccant Wheel depended mostly on input humidity ratio، air stream velocity، heat and mass transfer from air stream to bed. The results also described that air stream velocity was one of the most effective parameter on dehumidification rate of wheel.

The chemical corrosion behavior of fusion cast ZAS (ZrO2-Al2O3-SiO2) refractories inside lead silicate glass melt with 68. 5 wt% PbO content was investigated at temperatures of 1200، 1250، 1300 and 1350ºC. Scanning Electron Microscopy (SEM)، Energy Dispersive Spectroscopy (EDS)، Thickness Reduction and Archimedes Principle were used to evaluate morphology/composition/structure of (corroded and un-corroded) refractory probes. The attack of lead silicate glass melt was taken place by inter-diffusion of the more mobile constituents into glassy matrix. chemical reactions produced a low viscosity secondary glass composition and deteriorated the durability.

In this research the effective parameters on properties of chamotte based low cement castable with vibration during installation was investigated so that to reach high strength in these castables. \"In this regard the most important parameters are type & amount of deflocculant additives and particles size distribution about which their effect on flow ability، amount of water needed، physical and chemical properties of these bodies had been evaluated after dried to 110 º C. Results show that chamotte based low cement castable with high strength can be obtained using suitable particles size distribution according to Andreasen equation with distribution coefficient (q) of 0. 26. This also requires the best suited deflocculant additives with optimum amount of Polycarboxylate ether with 0. 08 %wt.

In this paper، the effect of a magnetic field on transient and laminar natural convection in a square cavity with constant temperature side walls filled with liquid gallium (Pr=0. 02) is investigated numerically. Governing equations are discretized using the control volume method. The results are presented in the form of streamlines، isotherms، heat lines and plots of Nusselt number versus time. The results have shown that with increasing magnetic field strength and therefore the Hartmann number، velocity inside the cavity reduces. Thus maximum absolute value of stream function and the heat transfer between the hot and cold walls of the cavity decreases and the free convection has been weakened. Applying the magnetic field (high enough) suppresses the convection flow and decreases the heat transfer rate and thus conduction heat transfer mechanism become dominant in the cavity.

In this paper، the effect of a magnetic field and its angle on steady and laminar natural convection in a tilted square cavity with constant temperature side walls filled with liquid gallium (Pr=0. 02) is investigated numerically. Governing equations are discretized using the control volume method. The results are presented in the form of streamlines، isotherms، heat lines and plots of Nusselt number. The results have shown that with increasing the Hartmann number، velocity inside the cavity reduces. Thus maximum absolute value of stream function and the heat transfer coefficient decreases and free convection has been weakened. By applying a proper magnetic field (high enough)، convection flow suppresses and conduction heat transfer mechanism become dominant in the cavity. The weaken convection at high magnetic field can be disappeared by increasing the inclination angle from 0 to 90 degrees CCW. Also it is observed that the minimum heat transfer rate is occurred by applying the magnetic field perpendicular to gravity.

In this paper Zinc Sulfides nanoparticles were synthesized via hydrothermal method and the effects of hydrothermal period on the obtained nanoparticles and aggregates morphologies were studied. XRD analyses were carried out for investigation about structure and also for investigation about its morphologies and growth SEM analyses were carried out. The results show that the synthesis period influence on the particles size and also the morphologies of the aggregates. Moreover، in this paper the mechanisms of the nanoparticles and aggregates growth and reformation of the aggregates were studied carefully.

The aim of this work was preparation، characterization and bioactivity evaluation of bioactive glass Nanopowder with three different compositions (58S، 63S، and 72S) by sol–gel technique. TEOS، TEP and Ca (NO3) 2. 4H2O were used as precursors. The prepared bioactive glass nanopowders were immersed in the simulated body fluid (SBF) solution at 37 ºC for 7 and 30 days. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) was utilized to recognize and confirm of the formation of apatite layer on prepared bioactive glass nanopowders. Characterization techniques such as XRD، XRF and TEM were used to investigate the microstructure، composition and morphology of nanopowders. XRD patterns showed that the prepared bioactive glass nanopowders were amorphous.