Abstract: The use of conventional lubricant such as hexadecane and toluene in micro-bearings has shown poor performance due to their hydrophilicity. High friction between the lubricated surfaces could lead to the occurrence of stiction which limits the functionality of a micro-bearing. In order to assess this strategy, a lubrication model of a micro-slider bearing with modified surface was used to simulate the technology. Friction, hydrophobic zone and hydrophobicity coefficient were evaluated based on the modified Reynolds equation. Results showed that in general the application of a hydrophobic coating has a significant improvement in reducing friction. Further, particular care must be taken in choosing the hydrophobic coating zone; an inappropriate choice of this zone will lead to a deterioration of the friction. This finding may have useful implications to accelerate the development of micro-bearings.
Abstract: The effect of magnetic fields on the swelling of liquid crystal elastomers (LCE) dissolved in liquid crystal (LC) solvent have been studied. The Flory-Huggins model used to calculate the free energy of an isotropic mixing and the Maier-Saupe model used to calculate the free energy of a nematic mixing. Numerical integration method used to calculate the orientational order parameter and the total free energy of system (consists of : nematic free energy, elastic free energy, isotropic mixing free energy and magnetic free energy) and the calculation results graphed as a function of temperatures for various magnetic fields and as function of magnetic fields for various of temperatures. We find that the magnetic field shifts the transition points towards higher temperatures, increases the energy transition, and induces an isotropic phase to paranematic phase.
Abstract: The indentation technique has been proven to be useful in determining mechanical properties of materials, but it is rarely applied to rubber-like materials (elastomers). It is difficult to describe accurately the mechanical properties of an elastomer by theoretical formulation due to its complex material behaviour. Indentation of a Styrene Butadiene Rubber (SBR-0) material by a rigid straight blade with a tip angle of 45 and 60 degrees was performed to estimate the elastic modulus. Indentation was carried out numerically by finite element analysis (FEA) and for the elastomer the hyper-elastic material model of Mooney-Rivlin is used. The estimated elastic modulus was calculated based on the contact depth. The predicted result was also verified by tensile test results. It was found that the predicted elastic modulus of the elastomer agrees with the tensile test result.
Abstract: Van der Waals (vdW) interaction is one of the important properties in the composite. The usual measurement used to investigate the vdW interaction between filler and polymeric binder is FTIR spectroscopy where the result obtained is the band shift appearance, however, it has not been used yet to estimate the vdW magnitude. Using the Lennard-Jones potential, we developed a new analysis method to obtain approximately its magnitude and further the distance between filler atoms and polymeric group. We used our model proposed to several data reported by some authors, and interestingly we also found an appearance of anharmonic vibration of the atoms.
Abstract: The effects of B2O3 addition (0, 0.2, 0.5, 1 and 2 wt %) on the change of microstructure and magnetic properties of barium hexaferrite (BHF) has been made and analyzed. The purpose of this work is to higher the magnetic properties of BHF by B2O3 additive. It was found that the distribution average diameter particle, true density, sintered density, and magnetic flux density of BHF are modified obviously as a small amount of B2O3 is added. The best quality of materials is obtained which 0.5 wt % B2O3 addition and showed excellent properties with average particle size of 1.78 µm , true density of 5.00 g/cm3, sintered density of 4,66 g/cm3, and flux density of 722.5 Gauss. Furthermore, the surface morphology by SEM revealed that the grain is around 1.2 µm and more homogeneity. The results can be interpreted that the preferential addition of B2O3 at low level is 0.5 wt%.
Abstract: We performed an experiment to characterize the four samples of main chain liquid crystal elastomers (MCLCEs) by using differential scanning calorimetry (DSC) method. Basic principle of this method is that difference in the amount of heat required to increase the temperature of the sample and reference is measured as a function of temperature. The temperature between the sample and reference is maintained nearly the same throughout the experiment. There were four samples with different concentrations of crosslinker we have taken, namely 8%, 12%, 14%, and 16%. The results showed that the phase transition from nematic to isotropic obtained by this method had correlation with their thermo-mechanical effects.
Abstract: The study of the perovskite manganites La0.47Ca0.53Mn1-xCuxO3 with x = 0, 0.06, 0.09, and 0.13 has been done. The magnetic structure was determined using high-resolution neutron scattering at room temperature and low temperature. All samples were paramagnetic at room temperature and antiferromagnetic at low temperature. Using the SQUID Quantum Design, the samples showed that the doping of the insulating antiferromagnetic phase La0.47Ca0.53MnO3 with Cu doping resulted in the temperature transition from an insulator to metal state, and an antiferromagnetic to paramagnetic phase. The temperature transition from an insulator to metal state ranged from 23 to 100 K and from 200 to 230 K for the transition from an antiferromagnetic to paramagnetic phase.
Abstract: ZIF - 8 material has been successfully synthesized through a reaction between zinc nitrate hexahydrate with 2 - metilimidazol in the dimethylformamide solvent in solvotermal condition. Synthesis process is carried out at 120oC for 24 hours . The results show that the characterization by XRD diffractogram synthesized ZIF - 8 has a characteristic peak at 2θ = 7.4o; 12.7o; 16.5o and 18.0o corresponding to the characteristic peaks of ZIF - 8 standard . The results of ZIF - 8 templated carbon show the XRD pattern of amorphous carbon material, while the carbon activated KOH show peak K2CO3 at 2θ = 31.6o. FTIR spectra of synthesized ZIF - 8 has a absorption peak at 420; 760 ; 990 ; 1147 and 1585 cm-1 which is the characteristic absorption peak of ZIF-8 solids. Then ZIF - 8 characteristic peaks disappear after activated with KOH. Morphology of the ZIF-8 has plumage regular rectangular in shape , and morphology of the resulting carbon particles are also the same rectangular shape with ZIF-8 template.
Abstract: In this paper, the physical and magnetic properties of isotropic bonded magnet Pr-Fe-B manufactured at atmospheric and low vacuum condition were discussed. The commercials Pr-Fe-B melt spun ribbon which mixed with epoxy resin binder was used as starting materials. The compaction method was using hydraulic press of 3 grams sample (ϕ9 mm) with force of 3 tons. The atmospheric and low vacuum (P ~ 10 mbar) environment during curing process were sets with temperature varied from 100 °C to 200 °C. The curing time (t) variations of 30 minutes to 4 hours were also done in the selected temperature to understand the short term aging effect. The optimum curing time was generated in 4 hours which produced at the low vacuum curing that increased the sample density and magnetic flux with the value of 5.846 g/cm3 and 2.51 kG, respectively. Generally it can be concluded that the process of low vacuum curing give a positive trends for manufacturing the bonded magnet Pr-Fe-B. The analysis of microstructure for mentioned parameters using SEM were also discussed.
Abstract: Commercially, NdFeB powder (type MQP-B+) with difference in particle sizes were used in this study. The powders were isotropically compressed and heat cured at 150°C for 30 minute. The samples were then magnetized and characterized by impulse magnetizer K series and permagraph MAGNET-PHYSIK Dr. Steingroever GmbH, respectively. According to the results of SEM characterization, compacted powder showed a homogeneous plate distribution. The surface morphology also indicated the presence of pores in the bonded NdFeB magnet. X-ray diffraction analysis from all samples revealed that the diffraction peaks were detected as tetragonal Nd2Fe14B-phase. There was no significant different in magnetic properties of bonded magnets with different in particle size. The optimum Br, Hcb, and (BH)max were achieved at particle size range of 150-297 mm.