Papers by Keyword: Sintered

Abstract: In this work, preparation of Fe_1.025Se samples was done using a solid-state reaction. Iron and selenium powder were used as raw materials. The raw materials were milled using a shaker mill for 5 hours after weighed in an atomic ratio of Fe:Se=1.025:1. To find out the formation of polycrystalline Fe_1.025Se, the milled powder was then compacted in a stainless-steel tube and sintered at a temperature of 355°C (for sample 1) and 745°C (for sample 2) for 6 hours. All samples were sintered in the air atmosphere and cooled rapidly in the air. XRD was used to analyze the phase formation. Based on the diffraction pattern calculation, the sintered sample at a temperature of 745°C has a higher mass fraction of the tetragonal phase than the sample sintered at 355°C. The lattice parameters of the sample sintered at a temperature of 745°C are a = 3.7688 Å and c = 5.5236 Å. According to the resistivity measurement results, it appears that the sample sintered at 745°C has a critical temperature onset of ~13.28 K.

Abstract: The interest in perovskite ceramics has been increased in recent years due to its useful properties and applications in various fields. We report the systematic study to explain the surface morphology and crystallographic nature of LSMO, prepared by solid state reaction and ball milling technique. The Density of the samples was calculated by Archimedes’s principle. The X-ray diffraction method was used to study the structural properties of the sintered powder using Philips Pro X’pertPANalytical. It exhibit dominant peak at (110) , (024) reflections , which confirms a polycrystalline nature of the powder. The surface morphology and elemental analysis of the samples is done by FEG-scanning electron microscope and energy dispersive spectrometry (EDS), confirms the absence of impurities in the samples. The analysis of FEG-SEM results and crystallite size verify the arrangement of LSMO particles in the range of 40-60 nm. The results show that the synthesis of LSMO ceramics in nanoparticle range is possible by the said techniques.

Abstract: Heat pipes are widely used in electronic cooling and other applications that require efficient transport or spreading of heat from local sources of high heat flux. One factor that most affect the performance of this device is the wetting properties of the wick material, whereby a hydrophilic wick material is required to transport the liquid from the evaporator to the condenser. The performance of heat pipe will decrease when the wick surface becomes hydrophobic as indicated by changes in its contact angle (CA). This study aims to determine the effect of ambient air exposure on the wettability of wick material. Wettability for a surface by a certain liquid can be shown by measuring the contact angle of liquid droplets on the surface. In this experiment, the contact angle was captured using a high speed video camera followed by image processing and then measured using Image J software. The surface of the sample/wick is a sintered copper powder which in this study through a process of forming or compaction by various parameters such as powder particle size, compacting pressure and sintering temperature. From the results of this study was found that the longer wicks were exposed in the ambient air, the contact angle of the liquid on the wick surface will be getting increased. After 7 days were contaminated on the ambient air, then all samples have been turned into hydrophobic, CA>90°.

Abstract: The objective of this work is to study the structural, morphological and electrical characteristics of lithium triflate-alumina composite electrolytes which were prepared via sol-gel technique. For this purpose, the composite electrolyte pallet samples which were sintered at 300 °C for four hours were subjected to X-ray diffraction, scanning electron microscopy, impedance spectroscopy and transference number measurement. X-ray diffraction spectra and scanning electron micrographs indicated that the crystalline alumina was distributed over the amorphous lithium triflate phase implying that the two-phases of microstructure (lithium triflate and alumina) interspersed each other. The highest ionic conductivity of 2.86 × 10^-3 S cm^-1 at room temperature was obtained for the sample with 60 mol % alumina. Temperature dependence of conductivity study was performed in the 303 K to 423 K temperature range and the trend of conductivity-temperature plot suggested that the increase in conductivity was due to the increase in migration rate of ions with temperature. The non-Arrhenius plot of the conductivity-temperature was due to continuous freezing of cations within the amorphous triflate medium. The value of ionic transference number indicated that the majority charge carriers in this composite electrolyte were ions while the value of Li⁺ transference number suggested that the majority of the ions were anions.

Abstract: Dental zirconia ceramics have been widely used in dental restorations due to their superior aesthetical and mechanical properties. Ultrasonic vibration assisted grinding (UVAG), as a novel effective machining process for hard and brittle materials, is introduced into directly machining sintered dental zirconia ceramics. This study is dedicated to investigating the influence of input variables (spindle speed, feedrate and cutting depth) on surface roughness during UVAG of sintered dental zirconia ceramics. The experiment is conducted through single-factor method, and the experimental results are statistically analyzed by One-Way ANOVA. Besides, the influence tendency of input variables on surface roughness is also obtained. The results indicate that the influence of spindle speed on surface roughness is highly significant. The value of surface roughness rises with the increase of spindle speed, feedrate, and cutting depth. Therefore, a better surface quality will be achieved with the combination of lower spindle speed, cutting depth and feedrate.

Abstract: Fully developed turbulence single phase convection heat transfer of water in pipes filled with sintered porous metal inner rings or solid inner rings was investigated numerically respectively. Numerical calculations were conducted with the Fluent 6.3 code, using the SST k-ω turbulence model. Comparing to solid-ring turbulator pipes, porous-ring turbulator pipes have better comprehensive heat transfer effect. The maximum PEC for porous-ring turbulator pipes is 4.4 and the PEC of solid-ring turbulator pipes is less than 1. It was also analyzed effect of geometric structures on porous-ring turbulator pipe performance. f/f₀ for porous-ring turbulator pipes increases with the increasing of Re while Nu/Nu₀ decreases with the increasing of Re ,and PEC decreases with the increasing of Re. With the same Re, if the width of the porous ring is equal to the width of groove, f/f₀, Nu/Nu₀ increases and PEC decreases with the increasing height of porous ring. When the height of porous ring is constant, the f/f₀, Nu/Nu₀ and PEC decreases with the increasing height of porous ring under the same Re.

Abstract: This paper explains sintering properties of Al2O3-70(referred to as the 70 green sample) natural mullite that was prepared by the process of homogenization, wet grinding, vacuum extrusion and high-temperature tunnel kiln sintering. The results show that 70 green sample's dehydroxylation temperature started in 528 °C; 70 green sample's sintering densification started in 1500 °C; 70 green sample had not completed sintering in the 1600 °C, and at this temperature, to prolong the holding time also won't realize densification. After sintering at 1600 °C, the sample's bulk density is 2.82. In this sample, the mullite phase was uniform distribution, density, low porosity and most are closed porosity.

Abstract: (100-x) LiCF3SO3 + (x) CeO2 composite electrolytes were prepared using sol-gel technique followed by sintering at 300 °C for four hours. Structural property and conductivity of the prepared composite electrolytes were studied using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) analysis and Impedance Spectroscopy. The XRD spectra show only crystalline peaks of CeO2 indicating that LiCF3SO3 exists in the form of amorphous phase. This is confirmed by SEM and EDX analyses. The highest ionic conductivity at room temperature is found to be in the order of 10-3 S cm-1 for the composite of 70 mol % LiCF3SO3 - 30 mol % CeO2. The conductivity of the composite electrolytes is observed to increase gradually with temperature.

Abstract: Composite solid electrolyte systems composed of different compositions of lithium triflate (LiCF3SO3) as host, and cerium oxide (CeO2) as dispersoid were prepared using sol-gel method. The electrical, structural and morphological properties of the composite solid electrolytes were investigated using impedance spectroscopy (IS), X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). Maximum room temperature conductivity was obtained for the system of 60 mol % LiCF3SO3 – 40 mol % CeO2.

Abstract: Elaboration of complex multifunctional materials with nanometric structure and controlled characteristics for special applications, implies the use of advanced techniques of powder metallurgy such as mechanical alloying, allowing the structural modeling and designing of material properties. The aims of paper consist in the development of complex multifunction materials with nanometric structure for special use (civil and/or military) for industrial applications. The paper presents briefly some aspect regarding the present stage in production of homogenous mixtures of W-Ni-Cu powders system for manufacturing the materials made of heavy alloys type.