Defect and Diffusion Forum Vols. 312-315

Abstract: This study focuses on the effect of electrolyte concentration of the micro arc oxidation process on the surface morphology of a Ti6Al4V alloy. Micro arc oxidation was performed in “(CH3COO)2Ca.H2O + Na3PO4” containing electrolytes. Micro arc oxidation developed a porous oxide layer mainly consisted of rutile form of titanium oxide on the surface of Ti6Al4V alloy with some calcium titanate (CaTiO3) and Hydroxyapatite. The increase of CH3COO)2Ca.H2O + Na3PO4 concentration of the electrolyte caused disappearance of the pores, reduction of surface roughness and decrease of wettability.

Abstract: This study focuses on tribological performance of as-received and borided Ti6Al4V alloys against ceramic counterfaces (Al2O3 and Si3N4 balls) in water. The wear mode of the alloy changed from ploughing to polishing by achieving a remarkable reduction in wear loss upon boriding. On the borided surface, the destructive action of the Si3N4 ball was very limited, when compared to that of the Al2O3 ball.

Abstract: Gas nitriding of a commercial purity Grade 4 titanium at 1120°C for 5 h formed hard TiN layer (2450 HV) on the surface with a thickness of about 35 m. When compared to the as-received state, nitrided titanium exhibited excellent wear resistance along with a relatively low coefficient of friction (CoF) against Al2O3 ball under dry sliding conditions.

Abstract: Miniature heat pipe is a compact heat transfer device with very high heat transfer capability. The miniature heat pipes have been widely accepted for thermal management in laptop computer. Generating heat from chip-set is rapidly transferred to a heat sink via the miniature heat pipe which occupies small space, resulting in smaller and more attractive size of the laptop. Heat pipe bending is unavoidable in such small space. However, tube bending decreases thermal performance of heat pipe and it stops working in some cases. In this study, a computer program to simulate heat transfer characteristics of a bending water-copper-sintered-wick heat pipe has been established. Domains of heat pipe consist of three parts; vapor of working fluid in vapor core which transfer heat and mass from evaporator section to condenser section, liquid of working fluid in wick which transfer heat and mass from condenser section to evaporator section in porous media by capillary force, and container wall. In simulation, fluid flow and heat transfer were assumed to be steady, laminar and incompressible. The porous media is saturated with liquid and working fluid is assumed to be Newtonian fluid. The governing equations, i.e. continuity, Navier-Stokes, and energy equations, and boundary conditions were solved by using the Finite Element Method (FEM). Several bending angles (0 and 90; angle measured from straight pipe) with 6 mm outer diameter and 200 mm length were simulated and tested. It was found that the predicted and experimental thermal resistances of heat pipe, when bending angle increases from 0 to 90, increased from 0.47°C/W to 0.65°C/W and 0.67°C/W to 0.88°C/W respectively, due to rising of the vapor pressure drop in vapor channel. The simulation results are in agreement with experimental data with 26-29% error.

Abstract: In this paper are illustrated the principal aspects connected with the numerical evaluation of thermal stress induced by LNG (liquefied natural gas) in a concrete tank. In order to investigate the thermal induced tensile stresses, the ANSYS finite element code has been employed for performing a sequential, non linear, transient thermal-structural analysis, taking into account the thermal dependant properties of the concrete such as thermal conductivity and specific heat. Temperature distribution data of thermal analysis is required in the coupled field analysis finally to obtain and analyze thermal stresses.

Abstract: This paper investigated the electrical properties of nanostructured Titanium Dioxide (TiO2) thin films prepared by the sol-gel method at different annealing temperatures. The precursor used was Titanium (IV) butoxide at concentration of 0.4 M. The TiO2 thin films were deposited on the glass and silicon substrates by using the spin coating technique. The influence of annealing temperatures on the electrical, structural, surface morphology and optical properties of the films were characterized by I-V measurement, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and UV-Vis Spectroscopy, respectively. It was found that the electrical properties of TiO2¬ thin films were changed due to the changes of annealing temperatures. As the annealing temperatures rises, the resistivity of the film found to be decreased. The result also shows that films which does not applied annealing temperature called as deposited were found to be amorphous while the films with annealing temperature T = 350oC and above became crystalline structure. The anatase phase can be obtained at annealing temperatures from T = 350oC up to T = 500oC.

Abstract: This work addresses damage evaluation of porous mullite refractory subjected to thermal shock. Incommunicating circular pores were distributed randomly at a volume percentage up to 40% in a cylinder of 20 cm diameter. The analysis was performed by means of the software ANSYS® combined with a pre-program that generates randomly distributed pores of given size. The analysis procedure was divided into two stages. In the first, transient thermal analysis considering temperature-dependent material property was dealt with different thermal shock temperatures under natural cooling condition. The following structure analysis ran based on the obtained temperature distribution. The material damage was defined by that the local tensile stress reached to or was over the strength of the refractory. The extent of damage was determined as the ratio of the area of the damaged regions to the section area of the cylinder. The results show that the porosity, thermal shock temperature and cooling time have a high effect on the material damage. The lower the porosity is, the larger the extent of damage. The thermal damage increases with the raise of thermal shock temperature and the cooling time. The damage develops rapidly within 10 minutes but slows down after one hour cooling. The damage difference at high shock temperature stage (≥ 1000°C) is less than at low shock temperature stage. The pore size effect gets into practice only at high shock temperature stage: the damage increases with the raise of the pore size. The present research confirms that high porosity and small pore size could decrease greatly thermal shock damage and should be considered in the micro structural design of refractory.

Abstract: In this study, MgxZn1-xO thin film with x varied from 0 to 0.3 was deposited on silicon with the orientation of [1 0 0] using the sol-gel method and spin coating technique. The thin film was annealed at 550°C before being used as a template to grow vertically aligned carbon nanotubes (VACNTs). Field emission scanning electron microscopy (FESEM) indicates that the top view of VACNTs’ topography are very similar to the topography of the template used, MgxZn1-xO thin film. When the value of x increased, the grain size of the template becomes larger and rougher, which were also true with the VACNTs. The electrical properties were measured using IV measurement system, which indicates that the conductivity of the VACNTs is directly proportional to the grain size of the template. Raman spectroscopy was used to inspect the crystal orientation.

Abstract: In this paper, the study of supergrowth VACNTs after being immersed in zinc oxide solution were presented. Vertically aligned carbon nanotubes (VACNTs) were first deposited on silicon with the orientation of [1 0 0] before being immersed in an aqueous solution of zinc nitrate hexahydrate and hexamethylenetetramine. Physical changes have been observed by scanning electron microscopy, SEM in the VACNTs, where the significant expansion of length of up to almost 0.8 mm was achieved after the immersion of 4.5 hr. The supergrowth of VACNTs was observed and analyzed by energy dispersive x-ray spectroscopy, EDX to substantiate the incorporation of CNTs and ZnO of the sample. Raman spectroscopy and x-ray diffraction, XRD were used to inspect the crystal orientation to support our findings.

Abstract: Molecular diffusion of gases in crude oils plays a crucial role in several oil recovery processes especially in cold-based production process. However, experimental data concerning CO2 diffusivity in heavy oils due to the tedious nature of diffusivity measurements are relatively rare in the open literature. In this work, a comprehensive experimental investigation of the effective molecular diffusion determination of CO2-heavy oil systems in homogeneous porous media was studied. The so-called pressure decay method was applied to measure the molecular diffusivity of carbon dioxide in heavy oil. Furthermore, effect of various parameters such as initial pressure, temperature and porous media on molecular diffusion coefficient have been analyzed and based upon experimental results, a new mathematical correlation for prediction of CO2-heavy oil molecular diffusion coefficient in presence of porous medium as a function of temperature was proposed.