Papers by Keyword: La₂O₃

Abstract: Coal fly ash (CFA) and bottom ash (BA) obtained from coal fired power plants in Thailand and local supplier were characterized using XRF, XRD and N₂ adsorption-desorption techniques. Their possibilities for conversion of palm oil into biodiesel were investigated. Selected CFA was also modified with lanthanum (La) at different La loading and the influence of La loading on biodiesel conversion was evaluated. The resulted showed that the Class C CFA as contained large amount of CaO (free lime) could catalyze the transesterification to achieve the highest FAME content of 89% under the operation conditions; the reaction temperature of 200 °C, the reaction pressure of 39 bars, the catalyst loading of 5 wt% of oil, the molar of oil to methanol of 1:30 and the stirring speed of 600 rpm for 5 h. The addition of La on the Class C CFA had a negative effect on conversion of palm oil. The FAME content decreased gradually from 89 to 62% with increasing La loading from 0 to 1 wt%.

Abstract: This research aims to study the preparation and characterization of La₂O₃ supported coal fly ash catalyst. Studied La₂O₃ and coal fly ash (CFA) were obtained from Thai monazite ore processing and local supplier, respectively. The catalyst was prepared by wet impregnation method. The influences of La₂O₃ loading and impregnation temperature on the chemical composition, crystalline phase and surface morphology of the catalyst were examined by varying the amount of La₂O₃ (5, 10 and 20 wt%) and the impregnation temperature (room temperature, 100, 150 and 200 °C). Characterizations such as WDXRF, XRD and SEM were carried out. The XRD results demonstrated that the La₂O₃ was highly dispersed on the CFA support. A high La₂O₃ loading resulted in an increase free CaO dissolvation during the impregnation which inhibited the interaction between SiO₂ and La₂O₃. The impregnation temperature had no significant effect on the chemical and physical properties of the catalyst. The coexist of Fe₃O₄ in the CFA support might impact to hinder the incorporation of La₂O₃ into SiO₂ matrix.

Abstract: La₂O₃ derived from Thai monazite ore chemical processing was used as a precursor to prepare SO₄^-1-1%La₂O₃/ZrO₂ solid acid catalyst. The SO₄^-1-1%La/ZrO₂ catalyst was synthesized by co-precipitation with subsequent impregnation method. Various characterization techniques such as X-ray diffraction (XRD), nitrogen adsorption-desorption (BET) and Fourier transform infrared spectroscopy (FTIR) were used to study crystalline structural, textural and acid properties of the prepared catalysts. XRD results revealed that the presence of stable La₂O₃/ZrO₂ tetragonal phase for SO₄^-1-1%La₂O₃/ZrO₂ was observed at calcined temperature up to 600 °C. No diffraction peaks of La₂O₃ appeared in the profile of SO₄^-1-1%La₂O₃/ZrO₂, indicated that the La₂O₃ was finely dispersed on the ZrO₂ support. The doping of SO₄^-1-ZrO₂ with La₂O₃ led to a significant decrease in its BET surface area, total pore volume and pore diameter. A relatively uniform pore size distribution of SO₄^-1-1%La₂O₃/ZrO₂ catalyst with average pore diameter of 6 nm was found at the calcined temperature of 600 °C. Lewis acid sites existed in the synthesized SO₄^-1-1%La₂O₃/ZrO₂ were lower than that counterpart. A loss of sulfate species was noted at high calcined temperature. The prepared SO₄^-1-1%La₂O₃/ZrO₂ will be further used as a solid catalyst for transesterification of waste cooking oil to biodiesel, and the addition of La₂O₃ on the support could lead to enhance the catalytic activity and thermal stability.

Abstract: In this paper for the first time, the performance of Dielectric Engineered Tunnel Field Effect Transistors (DE-TFETs) is evaluated on the InGaAs channel. Two DE-TFETs based on gate-dielectric structures, namely, Device-A and Device-B are modeled and characterized for both n-type and p-type operations to attain low subthreshold slope (SS) and drain induced barrier lowering (DIBL) using La₂O₃ as high-k gate dielectric. A structural modification of Device-B is illustrated that improves the on-state current (I_on), SS, and DIBL. Then, performance of both devices are analyzed based on physical oxide thickness (T_ox). The simulation results show that the modified Device-B has the lowest SS of 15.31 mV/dec and 54.64 mV/dec, I_on/I_off ratio of ~10⁹ and ~10⁶ with off-state current (I_off) of ~10^-15 A/µm and ~10^-12 A/µm for n-DE-TFET and p-DE-TFET, respectively. Furthermore, the performance parameters of both devices are studied for digital and analog applications and it is found that the modified Device-B can be a potential candidate for future digital applications due to its low power dissipation of 13.55 µW/µm and 27.56 µW/µm for n-DE-TFET and p-DE-TFET, respectively. On the other hand, Device-A shows high transconductance (g_m) of 722.52 µS/µm and 424.3 µS/µm and cut-off frequency (f_T) of 211.95 GHz and 290.86 GHz for n-DE-TFET and p-DE-TFET, respectively, and can be a viable candidate for future low power analog applications.

Abstract: SiO₂ with varying thickness (0, 4.45, and 8.05 nm) were grown on n type 4H-SiC epilayer by thermal oxidation and La₂O₃ were stacked on them using atomic layer deposition (ALD). The La₂O₃/SiO₂/4H-SiC metal-oxide-semiconductor (MOS) capacitors were analyzed by X-ray photoelectron spectroscopy (XPS) and capacitance-voltage (C-V) measurements. C-V curves show that introducing an ultrathin SiO₂ can reduce the effect of lattice mismatch of La₂O₃/4H-SiC structure and then improve interface property. However, the interface quality is reduced as SiO₂ was grown thicker. XPS data show that more carbon cluster remains at the interfacial between SiO₂ and 4H-SiC as the oxidation time increases.

Abstract: TiC-based cermets with four different components of La₂O₃ content were prepared via vacuum sintering to investigate the effect of La₂O₃ addition on the microstructure and mechanical properties. The microstructure and phase structure were investigated by XRD, SEM, EDS and the mechanical properties were measured. Experimental results show that TiC-based cermets with La₂O₃ addition were also a typical core-rim structure but did not form a new phase. Along with the increase of La₂O₃ content, the density of TiC-based cermets was reduced, EDS analysis revealed La₂O₃ was partly dissolved in the Mo/Ni binder and hindered dissolution and separation of carbides. A moderate amount of La₂O₃ can favor the microstructure refinement and improve its mechanical properties in the form of La₂O₃ particles embedded in Mo/Ni particles. Compared with undoped sample, the cermets doped with 1 wt.% La₂O₃ showed optimum comprehensive properties: the bending strength of 1041.4 MPa, Vickers hardness of 13.19 GPa and the fracture toughness of 14.18 MPa• m^1/2.

Abstract: Development of creep-resistant 8mol% Yttria-stabilized Zirconia (YSZ) ceramic has received much interest due to its potential use in fuel cells and thermal barrier coatings. In this research, Spark Plasma Sintering was used to develop a high-density 10 mol% La₂0₃ + YSZ composite. Compressive creep testing was performed at 1300 oC at 45 – 78 MPa load. The mechanism of plastic deformation of the composite was studied using Scanning Electron Microscopy and X-Ray Diffraction. The results suggest that lattice diffusion and grain boundary sliding were the active creep mechanisms.

Abstract: Barium strontium titanate glass-ceramics with different La₂O₃ concentrations have been prepared by a melting-annealing technique. The effect of La₂O₃ concentration on phase evolution, microstructure and electrical properties of (Ba,Sr)TiO₃-Al₂O₃-SiO₂ glass-ceramics has been investigated. The X-ray diffraction results showed the volume fraction of the major perovskite (Ba,Sr)TiO₃ crystalline phase increased with increasing La₂O₃ concentration. In addition, the scanning electron microscopy observations revealed that small amounts of La₂O₃ could accelerate the growth of crystals. When the La₂O₃ concentration was increased to 1.5 mol%, the microstructure of these samples displayed nonuniform distribution of the crystals. The dc conductivity measurements showed an increasing temperature dependence of conductivity with La₂O₃ doping at high temperature range above 400 °C. Impedance spectroscopy analysis indicated that the additive of La₂O₃ changed the major polarization mechanism to the relaxation polarization and the relaxation time for the La₂O₃ doped samples was much shorter than the undoped ones. The frequency dependence of dissipation factor curve displayed a peak at the range of 1 to 10 kHz due to the La₂O₃ addition. And the peak value decreased with increasing La₂O₃ concentration.

Abstract: In this work, we have developed a novel gate stack to enhance the mobility of Si face (0001) 4H-SiC lateral MOSFETs while maintaining a high threshold voltage. The gate dielectric consists a thin lanthanum silicate layer at SiC/dielectric interface and SiO₂ deposited by atomic layer deposition. MOSFETs using this interface engineering technique show a peak field effect mobility of 133.5 cm²/Vs while maintaining a positive threshold voltage of above 3V. The interface state density measured on MOS capacitor with lanthanum silicate interfacial layers is reduced compared to the capacitors without the silicate. It is shown that the presence of the lanthanum at the interface reduces the formation of a lower quality SiO_x interfacial layer typically formed at the SiC surface during typical high temperature anneals. This better quality interfacial layer produces a sharp SiC/dielectric interface, which is confirmed by cross section Z-contrast STEM images.

Abstract: FeNiCr alloy with various amount of La₂O₃ powders were thermal sprayed onto 1045 carbon steel substrate. Properties of sprayed coatings were studied by an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. Electron probe microscopy analysis (EPMA), X-ray photoelectron spectroscopy (XPS), were employed to this study. The results show that La₂O₃ can refine the microstructure effectively, and make the element distribution uniform, which leads to the improvement on the properties of the coatings. Meanwhile, the wear rate of the FeNiCr alloy with 1.5% La₂O₃ is smaller than other coatings. Interestingly the rare earth can reduce the friction coefficient, and act as self-lubricant in the oxide debris layer formed on the worn surface in friction. Wear mechanism of the coatings is oxidation wear and a large amount of counterpart material is transferred to the coatings.