Papers by Keyword: Lanthanum Oxide

Abstract: Fe-10wt% La (OH)₃ composite powders have been fabricated by ball milling, under argon atmosphere for milling periods of 0, 5 and 10 h, respectively. Changes in structural, morphological, thermal and magnetic properties of the powders during mechanical alloying and during subsequent annealing have been examined by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM). XRD results: showed the formation of new phases (Fe and LaFeO3 perovskite) created through the ball milling. The results showed that the crystalline size of ball milled powders decreased with increasing the milling time. In fact, after 10 h of ball milling, La (OH)₃ changes from nanostructure in amorphous structure. The magnetic measurements display a distinct saturation magnetization and coercivity.

Abstract: In this paper, alumina ceramics were prepared with alumina powder and lanthanum nitrate. The influence of La₂O₃ on the microstructure and properties of alumina ceramics were studied. The result showed that the addition of La₂O₃ contributed to the mechanical property of the samples. The alumina ceramics with adding of 0.05wt% La₂O₃ sintered at 1490°C had the best mechanical properties. And the flexural strength, fracture toughness of the ceramics could reach 571.902MPa and 5.82MPa•m^1/2，which were improved by 37.55% and 10.65% respectively compared with the alumina ceramics without La₂O₃. Besides, the average grain size of alumina ceramic is about 2.8μm, and the effect of inhibition on grain growth of alumina ceramics was obvious.

Abstract: Lanthanum oxide (La₂O₃) has been proposed as the promising gate dielectric material for future complementary metal-oxide-semiconductor (CMOS) technology. However, unlike the conventional homopolar materials such as silicon oxide or silicon nitride, La₂O₃ is more ionic and in particular at the La₂O₃/Si interface is less thermally stable. This work investigates the chemical and compositional variations of La₂O₃ thin film on the silicon substrate during rapid thermal annealing by using angle-resolved x-ray photoelectron spectroscopy (ARXPS) measurements. Results show that thermal annealing at temperatures above 500 °C would result in the incorporation of substrate Si atoms deep into the bulk of the La₂O₃ film and forming silicate phases both at the interface and in the bulk. These effects would result in the characteristic degradation of CMOS devices.

Abstract: Titanium dioxide (TiO₂) has been recognized as an active photocatalyst for degradation of various organic pollutants. In this study, in order to improve the photocatalytic activity of TiO₂, the effect of lanthanum oxide modification was investigated by using commercial P25 as the benchmark. Lanthanum oxide/P25 TiO₂ composites with 0.1, 0.5, 1 and 5 mol% of La loadings were prepared via an impregnation method. The resultant composites were characterized by X-ray diffraction (XRD), UV-Vis absorption spectroscopy, transmission electron microscopy (TEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and electrochemical impedance spectroscopy (EIS). It was confirmed that the addition of lanthanum oxide did not much affect the crystallinity, crystal structure and the morphology of P25 TiO₂. The catalytic activities of the lanthanum oxide/P25 TiO₂ catalysts were tested by using 2,4-dichlorophenoxyacetic acid (2,4-D) as the test pollutant and UV light as the irradiation source. The reaction was caried out for 1 hour at room temperature and the percentage removal was determined using a UV spectrophotometer. The results showed that La loading was an important factor that influenced the photocatalytic activity of the composites. After 1 hour reaction, the best catalyst with 0.1 mol% of La loading showed 24% higher photocatalytic activity than the unmodified P25 TiO₂ catalyst. It is shown by EIS that the enhanced photocatalytic activity of the composites was due to the ability of lanthanum oxide in improving the charge separation of the photogenerated electron-hole pairs in TiO₂.

Abstract: In this work, composite ceramic was produced to base Al₂O₃ reinforced with 35% weight TiO₂ and variation 0-2% La₂O₃, were evaluated properties to study their microstructural characteristic and mechanical properties as applicable cutting tools. The ceramic composites were produced by thermo-mechanical process. It was observed from the results of XRD after sintering no new phase is formed, besides the characteristics of the precursor oxides. According to the result of particle size analysis before and 24 hours after milling, there was a reduction of the average diameter of agglomerate 95.25% which is suitable to assist sintering of the composite, because this reduction increases the reaction rate the raw material during firing. At microdurezavickers test it was observed that the sample with 1.5% La₂O₃ showed better hardness results.

Abstract: A plasma enhanced atomic layer deposition process has been demonstrated for Lanthanum oxide films using La (thd)₃ precursor and oxygen plasma. The chemical and electrical properties of La₂O₃ ultra-thin films on Si (100) substrates before and after post-annealing in N₂ ambient have been investigated. X-ray photoelectron spectroscopic revealed that interface reactions take place after annealing process which lead to oxygen insufficiency, as well as the balance band offset decreases with the increase of annealing temperature. The capacitance-voltage and current-voltage characteristics show La₂O₃ capacitors annealed at 900 °C have negligible hysteresis, smaller interface trap density in comparison with as-deposited samples, but larger flat band voltage and higher gate-leakage current density due to the appearance of oxygen vacancy in the La₂O₃ films.

Abstract: With lanthanum chloride solution as raw material, and use the hydrogen peroxide of clean and pollution-freeobtained from oxidation reaction as auxiliary reagent, and with the carrier gas together form spray pyrolysis to obtain lanthanum oxide. On the one hand, in the hydrogen peroxide system, the temperature of direct pyrolysis reaction of lanthanum chloride solution decreased obviously, The reaction temperature is decreased from 1280°C to 1000°C or less. That reduce the energy consumption and simplify the requirements of pyrolysis equipment technology. The production process does not use NH₃^.H₂O and NaOH to precipitate. It does not produce the traditional process of NH⁴⁺, Na⁺ to pollute water. It can greatly reduce the damage to the environment, and can product with high yield, high purity of the rare earth oxide. This method not only applies to the pyrolysis of the rare earth chloride solution, also applies to metal chloride solution, such as FeCl₃, AlCl₃, NiCl₂. It was shown that the reaction temperature has been effectively reduced, V_LaCl3: V_H2O2 with 1: 1.5 can get high purity of La₂O₃.

Abstract: Nowadays, people should pay more attention on the environment problems that had advent along with the development of rare earth metallurgy industry. A large number of water pollutant, air pollutant and solid pollutant were discharged in the process of synthesis of rare earth compound by precipitation and roasting process. In order to solve the industry pollution problems, a new technology route was developed for the preparation of lanthanum oxide using lanthanum chloride as raw material by oxy-hydrogen flame route. The experiment results showed that lanthanum chloride could directly convert to lanthanum oxide under high temperature by the combustion of mixture gas of hydrogen-oxygen that provided by oxy-hydrogen generator continuously. The phase composition of obtained product was characterized by XRD and the conversion rate of lanthanum chloride and the reaction mechanism were discussed.

Abstract: It is well known that a minor addition of rare earth oxides can provide a beneficial effect towards various catalytic reactions. Use of rare earth oxide in different applications could improve commercial productivity in an affordable way. Among the rare earth oxides, ZrO2, La2O3 and CeO2 are very interesting due to their various characteristics showing a large range of applications in organic reactions. The changes in the molecular properties of materials at the nano scale level greatly enhance their physical properties as well as chemical properties and activity. Due to the extremely small size of the particles, an increased surface area is provided to the reactant enabling more molecules to react at the same time, thereby speeding up the process. In this work, the enhancement in the catalytic activity of these nano structured rare earth oxides has been studied under different reaction conditions. Nano crystalline ZrO2, La2O3 and CeO2 samples were synthesized using precipitation method and optimum reaction conditions have been established; whereas the corresponding bulk samples were synthesized by combustion method. The identification of phase and crystalline size of synthesized oxides have been done by X-ray diffraction, the band gape of these three oxides in both the forms has been analyzed by UV absorbance and surface area has been determined by gas adsorption analysis (BET). Moreover their different properties and the activity of nano crystallite oxides have also been compared with their bulk counterparts. Even the activity of ZrO2 is also compared with the rare earth oxides La2O3 and CeO2.

Abstract: NO_x emission in coke combustion with and without La₂O₃ was investigated in a fixed bed quartz reactor. The effects of La₂O₃ loading and lanthanum oxide particle size on NO_x emission were discussed. NO_x emission was also studied by sintering pot tests with lanthanum oxide modified coke as sintering fuel. The results showed that lanthanum oxide was catalytically active in promoting not only coke combustion but also NO_x reduction. In coke combustion experiments, NO_x and CO emission decreased with increasing lanthanum oxide loading up to 2.0wt% and decreasing lanthanum oxide particle size (28~150μm).