Papers by Keyword: MgO

Abstract: The bulk samples with the composition Bi_1.8Pb_0.4Sr_1.9Ca_2.1Cu_3.5O_y + x wt% MgO + (5-x) wt% Ag₂O (x = 0, 1, 2, 3, 4 and 5) were prepared by sintering at 840°C for 240 h after partial­melting at 870°C for 1 h. The sample with individual Ag₂O addition shows the lowest melting temperature and the lowest proportion of the Bi-2223 phase, whereas the sample with individual MgO addition shows the highest melting temperature. The highest proportion of the Bi-2223 phase appears in the sample with 1wt% MgO and 4 wt%Ag₂O mix-additions. With increasing MgO content, the width of hysteresis loop ΔM of the bulk samples at 77 K increases (0≦x≦2), and then decreases (2≦x≦5). The largest ΔM appears in the sample with 2 wt% MgO and 3 wt% Ag₂O mix-additions.

Abstract: The performance of zirconia toughened alumina with addition of MgO additives is investigated. Optimized composition of MgO at 1.1 wt% was used in the composition with alumina/yittria stabilized zirconia (YSZ). The composition was mixed, uniaxially pressed into rhombic 80o cutting inserts with 0.8 mm nose radius and sintered at 1600oC for 4 h in pressureless condition. For machining analysis, commercial stainless steel 316L with 12 mm diameter were used as workpiece. The workpiece was machined at 625 to 1750 rpm. Tool wear and surface roughness of workpiece were measured. Result shows three types of wear behaviour appear which are flank wear, notch wear and chipping. Flank wear and notch wear increased with the cutting speed but decrease by increasing the feedrate before increased after passing the 0.2mm/rev feedrate. While chipping very much related to the feedrate as the chipping area increased when the feedrate increased. Meanwhile, surface roughness increase with increment of cutting speed and feedrate which match the wear pattern.

Abstract: The effect of MgO-Y₂O₃ additives on densification, microstructure and mechanical properties of hot-pressed Al₂O₃-TiCN composites was studied. The MgO-Y₂O₃ additions had little influence on densification of Al₂O₃-TiCN composites. The Al₂O₃-TiCN composites without additives had coarsening microstructure, whereas that containing 0.25wt%MgO-0.5wt%Y₂O₃ had a noticeable finer microstructure and good mechanical properties. The increase of fracture toughness were attributed to the addition of MgO and Y₂O₃ together with the TiCN particles to inhibit the abnormal grain growth of Al₂O₃.

Abstract: We report the current status of our development of spin-transfer torque magnetic RAMs (STT-MRAMs) and their integration with the back-end-of-line (BEOL) process to replace conventional embedded SRAM cache memories. Our MRAM technology features a top-pinned, perpendicular magnetic tunnel junction (MTJ) and a highly reliable MTJ for a cache memory. We could obtain a higher density cache memory than that with conventional SRAMs with our STT-MRAMs, and leakage free characteristics, as well as unlimited write and read cycling times and 10-year time-dependent dielectric breakdown (TDDB) characteristics. They were integrated into Cu interconnects with 300 mm facilities. We also discuss variations in MTJ pattern sizes that are very important for memory applications from the viewpoint of high density embedded cache memories.

Abstract: Concrete plate is mainly anti-seepage structure for rockfill dam and essential to avoid dam destruction. Cooling shrinkage will be effectively compensated by mix MgO, as a result, it have been widely used in hydraulic structure. However, with large radiating surface, uniform heat exchange and small bottom restriction, stress characteristic of concrete plates is much different from conventional massive concrete structure. Therefore, impact of MgO on stress characteristic of concrete plates is unclear. In view of this, construction process using MgO concrete and ordinary concrete are simulated based on practical project data. Conclusions indicate that tensile stress of concrete plates in cooling stage can be reduced by adding MgO.

Abstract: The research investigates various methods to identify magnesium oxide influences on the crystal structure and hydration properties of tricalcium silicate. The f-CaO content of the clinkers were analyzed by chemical analysis. The complex disordered superstructure of the tricalcium silicate has been studied by a joint XRD, NMR and TEM. The results show that MgO exerts a remarkable influence on the polymorphisms of C₃S. Mg is not only substitutional atom but also interstitial atom in the crystal lattice of tricalcium silicate. The HRTEM pattern of C₃S doped with MgO is covered by the various irregular lattice. The addition of appropriate amount of MgO in raw meal can change the formation kinetic of C₃S, slightly perturb the environment of SiO₄^4- tetrahedral, modify the crystal structure of C₃S and affect the hydration activity. Doped with MgO in the raw meal can slow down the hydration rate of alite slightly in early stage.

Abstract: The effect of MgO on phase composition, alumina leaching properties and the self-disintegrating rate of calcium aluminate slag were investigated by X-ray diffraction and another analysis method. And a feasible method is proposed to eliminate the negative effects of MgO. The results shows that: the phase of 2CaO·SiO₂(C₂S)、20CaO·13Al₂O₃·3MgO·3SiO₂(Q phase) and 12CaO·7Al₂O₃(C₁₂A₇) are formed when there is MgO in slag with the C/A=1.4 and A/S=1.3. The content of Q phase increase and the leaching rate of slag reduce with increasing the temperature and the content of MgO. MgO would reduce self-disintegrating rate of slag. CaSO₄·2H₂O can improve the self-disintegrating the leaching properties of slag by promoting the synthesis of C₁₂A₇ and inhibit the synthesis of Q phase.

Abstract: Nephelium lappaceum L. peels was effectively used for the synthesis of magnesium oxide nanoparticles as a natural ligation agent. The XRD and SEM revealed the crystallinity and spherical morphology of the biosynthesized nanoparticles. The size of the particles was found to be 60-70 nm as deduced from XRD and SEM analysis. The particle size of as-synthesized magnesium oxide powders measured by PSA was approximately 100 nm. The successful formation of magnesium oxide nanoparticles was confirmed employing XRD, SEM-EDX and PSA analysis.

Abstract: Geometric structure and electronic structures of Zn_1-xMg_xO alloy under different Mg doped concentrations have been investigated by performing the first-principle calculations based on density functional theory under the generalized gradient approximation (GGA). The calculated results show that there is substantial change in electronic structure of Mg doped Mg_xZn_1-xO alloy, with the constant increase of Mg content, cell parameter a shall be on the gradual increase, with c on gradual decrease and band gap width of Mg_xZn_1-xO alloy on the increase. The research findings show that the position of conduction band bottom is dependent on Mg 2p and Zn 4s. Mg doping results in drift of Mg 2p and Zn 4s toward high energy region, being the root cause for the increase in band gap width,the research results in the paper are in accordance with other experimental results. The above results provide theoretical guidance to the preparation of Zn_1-xMg_xO alloy in experiment.

Abstract: BaZr_xTi_1-xO₃-based (BZT) ceramics with Al₂O₃ and MgO addtives were prepared by the conventional solid state method with BaCO₃, ZrO₂, TiO₂, Al₂O₃ and MgO as raw materials and B₂O₃ and Li₂CO₃ as sintering additive. The morphologies were analysized by scanning electron microscopy (SEM). The dielectric constant and dielectric loss of ceramics were measured by LCR meter. The temperature dependences of dielectric constant were measured by high-low temperature incubator tank and LCR meter at 1 MHz and a temperature range-55 to 125 °C. The tunabilities were tested by C-T-V converter and LCR meter at 1 MHz at room temperature. The results show that with the increase of Zr/Ti, BZT ceramic dielectric constant increases, the loss increases, the Curie temperature moves to a lower temperature, and dielectric bias field coordination is relatively lower. The SEM images show that the grain size reaches about 1-2 μm when the sintering temperature is 1100 °C, and the addition of Al₂O₃ and MgO promote the grain growth and densification of the composite ceramics. The Curie peaks are broadened and depressed with the addition of Al₂O₃ and MgO. The tunability is improved to 9.59% under a DC electric field of 7.0 kV/cm after the addition of Al₂O₃. The dielectric constant and dielectric loss of BaZr_0.25Ti_0.75O₃-30wt%Al₂O₃ and BaZr_0.25Ti_0.75O₃-30wt%MgO are 586, 0.011 and 486, 0.003, respectively. The optimistic dielectric properties make it a promising candidate for the application of tunable capacitors and phase shifters.