Materials Science Forum Vol. 553

Abstract: The control of a process dealing with heat pipe exploitation needs the thermal analysis of the evaporation-condensation cycle and noticeably the imposed external conditions (in instance modeling the heating). In this work a numerical model has been developed to describe the local coupling near the liquid/vapour interface. Simulations exhibits and quantify the response of the capillary motion to the thermal conditions.

Abstract: Many industrial and biological phenomena involve the evaporation of liquids in porous media. In drying processes the evaporation of a liquid meniscus from the solid is the key mechanism in the process and its efficiency. After a first steady stage of evaporation the meniscus becomes unsteady and recedes inside the pore. Diffusion of vapour becomes the controlling mechanism for evaporation in a later stage. In this work an experimental investigation is undertaken to study the various stages of evaporation of different liquids in capillary tubes (pores) of various sizes. The analysis of the data obtained from this investigation reveals some interesting behaviours and emphasizes the role played by vapour diffusion in the case of unsteady interface. The preliminary transient regime allowing the thermal field establishment, is followed by the first stage of evaporation is found to be dominated by thermocapillary effects associated with non-uniform evaporation and temperature gradients. The laste stage is a molecular diffusion-limited mode. The liquid volatility and the effect of the size of the tube (ranging from 200 to 900 μm) are also analysed to show the interaction between the various effects at different scales.

Abstract: A two-dimensional heat transfer model, extended phase change, is developed with an enthalpy formulation in order to predict the splat/substrate thermal story and its effects on plasma surface interaction. The model validated with respect to experimental results is used to estimate the early solidification of yttria stabilized zirconia splat deposited on a cooled substrate. Simulations quantify transfers in terms of some working parameters such that the splat thickness, the splat/substrate contact quality, the latent heat of solidification and the initial temperatures.

Abstract: Ultra precision machines are used for very precise machining as well as small parts. Due to their application, the accuracy of products has been upgraded in recent years. Thus, dimensional accuracies could be compared with surface texture dimensions like roughness and etc. In order to attain dimensions with surface texture accuracy, usually micro/nano meter, it is necessary to adopt ordinary machining technologies with micro/nano techniques. This measuring by adoption leads to nano-machining. Nano-machining researches deal with all three basic components of, machine tools, work piece, and cutting tool, which have fundamental importance for development of this technique. Despite of wide range of possible researches, only part of design points of ultra precision machines have been considered in this report. Air operated systems, like air slide table, and air spindle are examples of ultra precision machine tool components. These two components have been analyzed for some of their characteristics. Experiments have been planed to extract the relationship between stiffness, employing some of the effective parameters such as air pressure and air gap. The results describe the performance condition of air table and air spindle under different loadings.

Abstract: The fabrication of thin nanoporous TiO2 layers (thickness < 2 μm) on functionally graded porous alumina (thickness = 2 mm) is reported for the first time. The membrane is produced by dip coating TiO2 sols on the alumina support. The alumina porous support is produced using centrifugal casting with an acceleration of 3000g .The average pore size of the support is ca. 0.5 μm while its upper surface on which the membrane layer is deposited has an average pore diameter of 0.38 μm and average porosity of 10.7 %. The sol is produced by the peptization technique using tetrapropylorthotitanate as precursor. For the first time, a synthesis procedure has been implemented which allows the production of TiO2 sols with average particle sizes from12 to 22 nm. Using the BET technique, the average pore size and meso-porosity of the unsupported sintered TiO2 membranes as a function of sintering temperature and ZrO2 impurity concentration (0.0, 0.2, 0.6 and 1.0 wt. % of ZrO2) have been determined. The kinetics of the membrane layer anatase to rutile transformation reaction has been investigated as a function of ZrO2 impurity concentration introduced to the TiO2 sol during its preparation. The lack of macrocraks in the ultrafilter layer of the sintered composite was confirmed using the gas permeability and SEM techniques. The main outcome of this work is that the support has an outstanding low surface roughness (< 0.4 μm) allowing deposition of a defect free single layer of TiO2 in one step

Abstract: Monodispersed nanometer-sized particles proved to be very important and advantageous in many industrial applications. One of the notable groups of these particles is silica (SiO2) nanoparticles which are widely utilized in developing numerous products such as electrical and thermal insulators, humidity sensors, varnish, etc. Since the quality of some of these products depends highly on the purity and size distribution of the silica particles, it is necessary to produce silica nanoparticles of narrow size distribution and very high purity. In this research silica nanoparticles, with a relatively narrow size distribution, have been synthesized via the hydrolysis reaction of tetraethoxisilane (TEOS) in the solution of deionized water and ethanol (C2H5OH), and in the presence of ammonia (NH3) as a catalyst. The nature, morphology and the size of the silica particles has been studied using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-ray diffraction. Results indicate that the morphology, structure and the diameter of silica particles depend strongly on the molar ratios of the reactants.

Abstract: In the recent years, many researchers have been interested in nanoparticles because of their unique properties. In this study, a method for producing ZnO nanoparticle colloids is proposed. The colloids were characterized by spectroscopic analyzer. By absorption spectrum study, we found out that colloids were consisted of nanoparticles with less than 10 nanometer size. The quantum confinement effect in these spectrums was recognized through blue shift of onset absorption wavelengths. These wavelengths shift from 370 nm to 340 nm by decreasing the particles size. Transmittion electron micrographs showed formation of zinc oxide nanoparticles.

Abstract: In this research work, a high-energy ball mill has been applied to prepare an Al/SiC nanocomposite. The formation mechanism of the nanocomposite was investigated. This nanocomposite contained the nanocrystalline characteristics. Crystallite size, lattice strain and particle size of the nanocomposite as a function of milling time were determined. SEM micrographs showed that the nanocomposite powders agglomerated after milling. The particle size analysis confirmed the agglomeration of the nanocomposite particles. TEM observations showed that the SiC particles were in the nanometer size and these particles embedded in the Al matrix, and the nanocomposite produced in the final stage of mechanical alloying. In addition, a simple model checked for the refinement of the crystallite and the particle size of nanocomposite.

Abstract: Aluminum-titanate (tialite) based ceramics have found widespread applications due to their good thermal shock resistance and low thermal expansion. Tialite is presently used in automotive industry, thermal processing technology, metallurgy and glass industry. Eutectoid decomposition in to the initial oxides and low mechanical strength limit the well-known properties of aluminum-titanate. In the present work, good stabilizing behavior was achieved by addition of talc in micron size and appropriates properties were obtained by adding nano boehmite and colloidal silica that results mullite phase formation. The effect of mullite phase in the densification of tialite has been studied. XRD, DTA and SEM have been used to characterize the influence of these additives on phase transformation, sintering process and microstructure.