Advanced Materials Research Vols. 47-50

Abstract: In this research, the eggshell was thermally treated at 700°C for 1-3 hrs and 800°C for 1- 4 hrs. After the treatment, thermally treated eggshell was characterized via X-ray diffraction spectrometer, particle size analyzer and thermogravimetric analyzer. From the XRD patterns, it revealed that calcium carbonate was obtained when chicken eggshell was treated at 700°C. The content of calcium carbonate, however, decreased with increasing heating times and temperature. After the eggshell was heated at 800°C, calcium hydroxide was mainly obtained and eventually when the treatment time was 4 hrs, instead of calcium carbonate, calcium hydroxide and calcium oxide were obtained. The size of the treated eggshell was about 0.06 – 878.7 µm depending on the treatment times and temperatures. The size distribution of 800°C-treated eggshell was narrower than that of the 700°C-treated eggshell.

Abstract: Joining Si3N4 and Al2O3 using 15 layers has been achieved by a unique approach that introduces SiAlON polytypoids as a functionally graded material (FGM) bonding layer. Previously, the hot press sintering of multilayered FGM with 20 layers, each 500 µm thick, has been achieved successfully. In the present study, the number of layers for FGM was reduced from 20 to 15 to increase optimization. Samples were fabricated by hot pressing at 48 MPa during the temperature ramp to 1650°C and cooling at 2°C/min to minimize residual stresses from sintering. Moreover, a finite element method (FEM) program based on the maximum principal stress theory and the maximum tensile stress theory was applied to design optimized and reduced FGM layers that produced a crack-free joint. The sample had a 3-dimensional cylindrical shape that was transformed to a 2-dimensional axisymmetric mode. By determining the expected thermal stress from the calculated elastic modulus and coefficient of thermal expansion, we were able to predict and prevent damage due to thermal stresses. These analyses are especially useful for FGM samples where it is very difficult to measure the residual stresses experimentally. Finally, oriented Vickers indentation testing was used to qualitatively characterize the strengths of the joint and the various interfaces. The indentation cracks were deflected at the SiAlON layers, implying weak interfaces. In other areas, cracks were not deflected, implying strong interfaces.

Abstract: The martensite stabilization in Cu72Zn13Al15 (at %) alloy on heating at a heating rate of 5°C/min has been studied. During heating, the transition of the lattice parameters of the stabilized martensite is that lattice parameters a and c increase, b decreases and monoclinic angle β tends to 90º, the abnormal re-relief and RSME take place. These phenomena in the alloy during heating are irreversible and do not change upon air-cooling.

Abstract: In this research, a comparative study of the hydrostatic performances of 1-3 piezoelectric composites with a porous matrix is presented. The piezoelectric fibers PZT-5H and PZT-7A are considered in the present study. The micromechanics based Mori-Tanaka model is used. Results of the study show that PZT-5H/Aradite D composite have better hydrostatic performance than PZT- 7A/Aradite D composite, and this advantage of PZT-5H/Aradite D composite over PZT-7A/Aradite D composite increases with the increase of porosity in the matrix.

Abstract: Surface texturing, a sort of surface engineering, has been studied as an effective method to improve the tribological performance under lubricated contact. Those mechanisms of friction reduction, however, are not fully understood. Therefore, the sliding direction and the angle of micro-grooved crosshatch patterns for coefficient of friction were examined. The micro-grooved crosshatch pattern was fabricated by mechanical indentation method on the upper specimen and the pin-on-disc friction test was performed with lubricant of paraffin oil. The influence of angel on the friction was confirmed as friction coefficient increased proportional to the angle increase. The micro-grooved crosshatch patterns have also the potential to change the friction characteristics by sifting the lubrication regimes.

Abstract: Here we draw attention to the development of smart materials with embedded vasculatures that provide multiple functionality: volumetric cooling, self-healing, mechanical strength, etc. Vascularization is achieved by using tree-shaped (dendritic) and grid-shaped flow architectures. As length scales become smaller, dendritic vascularization provides dramatically superior volumetric bathing and transport properties than the use of bundles of parallel microchannels. Embedded grids of channels provide substantially better volumetric bathing when the channels have multiple diameters that are selected optimally and put in the right places. Two novel dendritic architectures are proposed: trees matched canopy to canopy, and trees that alternate with upside down trees. Both have optimized length scales and layouts. Flow architectures are derived from principle, in accordance with constructal theory, not by mimicking nature.

Abstract: The magnetic domain structures of the cubic parent phase (high-temperature phase) in ferromagnetic shape memory alloys (SMAs) have been studied by electron holography. In a Ni51Fe22Ga17 alloy, the magnetic flux distribution in the parent phase changes dramatically before the onset of martensitic transformation. In contrast, a Ni45Co5Mn36.7In13.3 alloy—a recently developed ferromagnetic SMA—does not show appreciable changes in the magnetic domain structure upon cooling. The anomaly observed in the Ni51Fe22Ga17 alloy appears to be due to lattice distortions, which become more pronounced as the temperature approaches the martensitic transformation start temperature, Ms.

Abstract: The experimental results on morphology evolution of macroscopic deformation domain during stress-induced phase transition under uniaxial tension in superelastic NiTi polycrystalline microtubes are reported in this paper. It focuses on morphology of the domain front during unloading process. A series of high-resolution digital photos were taken from the tube surface under equal incremental elongations. The 3D geometry of the front was quantified by an optical profiler. New propagation modes of the front such as rotation and crossing were found.

Abstract: We fabricated a crack-free joining of Ni and Al2O3 using a functionally graded method. Because porosity reduction is important, particle size of the Ni and Al2O3 powders was varied to improve green body density and minimize shrinkage during sintering. As a result, crack-free joining of a Ni–Al2O3 sample with 10 layers was obtained. The ANSYS simulation tool was used to calculate residual stress. The hardness and modulus of each graded layer were measured using an Vickers’ indenter. The experimental values matched the simulation results, showing that this analysis is useful when residual stresses are very difficult to measure experimentally.

Abstract: In this study, thermosensitive and magnetic nanoparticles were synthesized by reverse microemulsion and radical polymerization. Thermo-sensitive and magnetic nanoparticles consist of 6nm magnetite core (Fe3O4) and silica shell which then grafted by poly (N-isopropylacrylamide) (PNIPAM). The morphologies of these fabricated nanoparticles were observed by SEM and TEM, which is confirmed to be the core-shell structure. The property of PNIPAM could change from hydrophilic to hydrophobic from low temperature to high temperature. The lower critical solution temperature measured by DSC and DLS is at ~35°C. The magnetic characteristic of these nanoparticles is analyzed by SQUID. The result is illustrated as superparamagnetic behavior for the nanoparticles. Therefore, the nanoparticles could be introduced to the desired location by external magnetic field due to magnetite core. The absorption and desorption of Bovine serum albumin (BSA) were also discussed. At 50°C, the BSA can be absorbed by the polymeric shell presented as hydrophobic chains and be desorbed ~70% at room temperature. Combined thermosensitive and magnetic properties, nanoparticles could be utilized in controlled drug –targeting delivery.