Due to the wide application of rare earth elements,lanthanum(La) is gradually accumulated in our living environment.Lanthanum can enter the body through a variety of routes,which has a series of effects on various sys...Due to the wide application of rare earth elements,lanthanum(La) is gradually accumulated in our living environment.Lanthanum can enter the body through a variety of routes,which has a series of effects on various systems.As a consequence,the safety of lanthanum deserves our attention.This study aims to compare the toxicity of lanthanum oxide nanoparticles(La_(2)O_(3) NPs) and lanthanum chloride(LaCl_(3)) and enrich the toxicity evaluation of lanthanum.Therefore,a 30 d intragastal experiment was conducted.C57BL/6j mice were given by La_(2)O_(3) NPs solution and LaCl_(3) solution respectively at doses of 0,30,60 and120 mg/kg BW(lanthanum content).The results show that,compared with the control group,both La_(2)O_(3)NPs and LaCl_(3) can reduce the body weight of female mice in the high-dose group,but for male mice,the high-dose La_(2)O_(3) NPs solution can increase the body weight,while LaCl_(3) has the opposite effect.The coefficients of liver,kidney,heart,lung,uterine and ovaries increase first and then decrease with the exposure dose,but testes and epididymides coefficient keep increasing with the exposure of LaCl_(3) and La_(2)O_(3) NPs.La_(2)O_(3) NPs and LaCl_(3) can reduce the concentration of triglycerides(TG) and increase the level of low density lipoprotein(LDL),but the effect of La_(2)O_(3) NPs is more obvious.La_(2)O_(3) NPs and LaCl_(3) can reduce the concentration of malondialdehyde(MDA),increase the total antioxidant capacity(T-AOC)and enhance the activity of catalase(CAT),but LaCl_(3) has more obvious protective effects on oxidative stress.La_(2)O_(3) NPs and LaCl_(3) have potential risks to liver,and the toxicity of La_(2)O_(3) NPs might be higher than that of LaCl_(3).展开更多
Graphitized carbon/carbon composites were prepared by the process of catalytic graphitization with the rare-earth catalyst, lantha-num oxide （La2O3）, in order to increase the degree of graphitization and reduce the ...Graphitized carbon/carbon composites were prepared by the process of catalytic graphitization with the rare-earth catalyst, lantha-num oxide （La2O3）, in order to increase the degree of graphitization and reduce the electrical resistivity. The modified coal tar pitch and coal-based needle coke were used as carbon source, and a small amount of La2O3 was added to catalyze the graphitization of the disordered carbon materials. The effects of La2O3 catalyst on the graphitization degree and microstructure of the carbon/carbon composites were investi-gated by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The results showed that La2O3 promoted the formation of more perfect and larger crystallites, and improved the electrical/mechanical properties of carbon/carbon composites. Carbon/carbon compos-ites with a lower electrical resistivity （7.0 ？？？m） could be prepared when adding 5 wt.% La2O3 powder with heating treatment at 2800 oC. The catalytic effect of La2O3 for the graphitization of carbon/carbon composites was analyzed.展开更多
This study evaluated the bacterial toxicity of lanthanum oxide micron and nano sized particles using shake flask method against gram-positive （Staphylococcus aureus） and gram-negative （Escherichia coli, Pseudomonas...This study evaluated the bacterial toxicity of lanthanum oxide micron and nano sized particles using shake flask method against gram-positive （Staphylococcus aureus） and gram-negative （Escherichia coli, Pseudomonas aeruginosa） bacteria. Particle size, morphology and chemical composition were determined using scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDS）. Results indicated that lanthanum oxide nanoparticles showed antimicrobial activity against Staphylococcus aureus, but not against Escherichia coli and Pseudomonas aeruginosa. It was speculated that lanthanum oxide produced this effect by interacting with the gram-positive bacterial cell wall. Furthermore, lanthanum oxide bulk particles were fotmd to enhance the pyocyanin pigment production in Pseudomonas aeruginosa.展开更多
The preparation of nano sized La 2O 3 powder by mechanochemical reaction of lanthanum carbonate with sodium hydroxide and subsequent heat treatment was studied using X ray diffraction, differential thermal and ther...The preparation of nano sized La 2O 3 powder by mechanochemical reaction of lanthanum carbonate with sodium hydroxide and subsequent heat treatment was studied using X ray diffraction, differential thermal and thermo gravimetric analysis and transmission electron microscopy. It was found that the mechanochemical reaction process can be divided into two steps: the first step is the multi phases mechanochemical reaction of lanthanum carbonate with NaOH to form amorphous lanthanum basic carbonate and lanthanum hydroxide, and the second step is the crystallization of basic lanthanum carbonate with the formula of La 2(OH) 2(CO 3) 2·H 2O under a quasi hydrothermal synthesis condition caused by the mechanical ball milling. The synthesized La 2O 3 powder appears clearly separated spherical like monodisperse nano size particles in which particle size ranges from 30 to 50 nm.展开更多
A new method for the determination of trace non-rare earth elements(NREEs)impurities in high-purity lanthanum oxide by HPLC combined with ICP-AES is proposed.The chromatographic retention behaviors of matrix(La)and NR...A new method for the determination of trace non-rare earth elements(NREEs)impurities in high-purity lanthanum oxide by HPLC combined with ICP-AES is proposed.The chromatographic retention behaviors of matrix(La)and NREEs were studied using 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate(P507)chelating resin as the stationary phase and dilute nitric acid as the mobile phase.It is found that the use of pH 1.7 nitric acid enables effective elution of NREEs from HPLC column,but the lanthanum remains on the column.The experimental results show that a favorable separation between matrix lanthanum and NREEs can be obtained within 15 min.The method proposed is applied to the determination of 8 NREEs impurities in high-purity La2O3.The recoveries of 8 NREEs are in the range of 90%similar to 110%.展开更多
A new method for determination of trace silicon in high purity lanthanum oxide by using electrothermal vaporization (ETV) ICP AES with polytetrafluoroethylene(PTFE) slurry as a fluorinating reagent has been proposed...A new method for determination of trace silicon in high purity lanthanum oxide by using electrothermal vaporization (ETV) ICP AES with polytetrafluoroethylene(PTFE) slurry as a fluorinating reagent has been proposed. Under the optimized experimental conditions, the fluorination reactions of analyte(Si) and matrix(La) with PTFE in the graphite furnace took place at high temperature, and the fractional volatilily between Si and La was observed. Based on this principle the matrix interference could be eliminated. The detection limit of Si was 4.0 μg·L -1 , and the RSD was 3.4%( C =0.2 mg·L -1 , n =10). The procedure proposed has been applied successfully to determine trace Si in La 2O 3 without any chemical pre treatment.展开更多
Ce3＋-doped yttrium lanthanum oxide （Y0.9La0.1）2O3 transparent ceramics is fabricated with nanopowders and sintered in H2 atmosphere. The spectral properties of Ce：（Y0.9La0.1）2O3 transparent ceramics are investig...Ce3＋-doped yttrium lanthanum oxide （Y0.9La0.1）2O3 transparent ceramics is fabricated with nanopowders and sintered in H2 atmosphere. The spectral properties of Ce：（Y0.9La0.1）2O3 transparent ceramics are investigated. There appear two characteristic absorption peaks of Ce3＋ ions at 230~nm and 400~nm, separately. It is found that Ce3＋ ions can efficiently produce emission at 384~nm from （Y0.9La0.1）2O3 transparent ceramic host, while the emission is completely quenched in Re2O3 （Re=Y, Lu, La） host materials.展开更多
In this paper, a series of Fe- and Co-doped lanthanum（hydr）oxides catalysts were prepared by a simple coprecipitationhydrothermal method. The as-prepared catalysts were characterized with various techniques includin...In this paper, a series of Fe- and Co-doped lanthanum（hydr）oxides catalysts were prepared by a simple coprecipitationhydrothermal method. The as-prepared catalysts were characterized with various techniques including powder X-ray diffraction（XRD）, N2 adsorption/desorption, inductively coupled plasma（ICP） and transmission electron microscopy（TEM）. The Fe-based catalysts exhibited consecutive phase changes of amorphous Fe Ox→FeLaO3→Fe2N under different stages（as-prepared→calcination→ammonia decomposition reaction）; as for Co-based catalysts, the phase transformation followed a sequence of Co（OH）2→Co3O4→metallic Co. It was revealed that Fe2N and metallic Co were most probably the active crystalline phase respectively for Feand Co-based catalysts in the decomposition of ammonia.展开更多
This paper investigates the feasibility of using a lanthanum oxide thin film （La2O3） with a high dielectric constant as a gate dielectric on GaAs pHEMTs to reduce gate leakage current and improve the gate to drain b...This paper investigates the feasibility of using a lanthanum oxide thin film （La2O3） with a high dielectric constant as a gate dielectric on GaAs pHEMTs to reduce gate leakage current and improve the gate to drain breakdown voltage relative to the conventional GaAs pHEMT. An E/D mode pHEMT in a single chip was realized by selecting the appropriate La2O3 thickness. The thin La2O3 film was characterized： its chemical composition and crystalline structure were determined by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. La2O3 exhibited good thermal stability after post-deposition annealing at 200, 400 and 600℃ because of its high binding-energy （835.6 eV）. Experimental results clearly demonstrated that the La2O3 thin film was thermally stable. The DC and RF characteristics of Pt/La2O3/Ti/Au gate and conventional Pt/Ti/Au gate pHEMTs were examined. The measurements indicated that the transistor with the Pt/La2O3/Ti/Au gate had a higher breakdown voltage and lower gate leakage current. Accordingly, the La2O3 thin film is a potential high-k material for use as a gate dielectric to improve electrical performance and the thermal effect in high-power applications.展开更多
A new process for electrolytic production of a perfluorinated compound, （CF3）3N, using lanthanum nickel oxide-coated Ni sheet anode in the （CH3）4NF· 4.0HF melt at room temperature, was developed. Thin films o...A new process for electrolytic production of a perfluorinated compound, （CF3）3N, using lanthanum nickel oxide-coated Ni sheet anode in the （CH3）4NF· 4.0HF melt at room temperature, was developed. Thin films of the lanthanum nickel oxides were prepared on Ni sheets by sol-gel coating method using polyvinlylpyrrolidone（PVP）. The main components of the thin films were La2O3, LaNiO3, and La2NiO4 at 500, 750 and 1000℃, respectively. The anode performance in the （CH3）4NF·4.0HF melt depends greatly on the main component of the thin film, and the LaNiO3-coated Ni sheet anode gives the best anode performance. The potential of LaNiO3-coated Ni sheet anode remains constant at 5.9 V during electrolysis at 20 mA·cm^-2 in the （CH3）4NF·4.0HF melt for 100 h. This is because LaNiO3 and NiF3 and/or Ni2F5, the latter of which was formed during electrolysis, in the film give a high electronic conductivity to the surface film during electrolysis. The maximum mole fraction of （CF3）3N （21.4%） was obtained at 20 mA·cm^-2 in （CH3）4NF·4.0HF melt using the LaNiO3-coated Ni sheet.展开更多
Resistive switching devices with a high self-rectifying ratio are important for achieving the crossbar memristor array that overcomes the sneak current issue.Herein,we demonstrate a single amorphous lithium lanthanum ...Resistive switching devices with a high self-rectifying ratio are important for achieving the crossbar memristor array that overcomes the sneak current issue.Herein,we demonstrate a single amorphous lithium lanthanum titanium oxide(LLTO)layer based Pt/LLTO/Pt device possessing a self-rectifying ratio higher than 1 × 10^(4) that is comparable to the reported devices with complicated multi-layer stacking structures.Moreover,the device shows forming-free and highly uniform bipolar resistive switching(BRS)characteristic that facilitates the potential applications.The trap-controlled and trap-free space charge limited conductions are demonstrated to dominate the high and low resistance states of the device,respectively.The fast migration of lithium ions under external voltage accelerates the electron injection across the Pt/LLTO interface and also the space charge accumulation in the LLTO layer,and as a result,the high performance of the Pt/LLTO/Pt device was achieved.As demonstrated Pt/LLTO/Pt device sheds a light on the potential applications of the lithium ionic conductors in self-rectifying resistive switching devices.展开更多
The changes of the valence state of lanthanum in the Mo La 2O 3 model cathode specimens were systematically studied by in situ XPS/AES analyses from room temperature to 1550 ℃. The experimental results show that ...The changes of the valence state of lanthanum in the Mo La 2O 3 model cathode specimens were systematically studied by in situ XPS/AES analyses from room temperature to 1550 ℃. The experimental results show that the valence of lanthanum changes during the activation processes. As the temperature increases, the lattice oxygen in La 2O 3 is dissociated, resulting in partial reduction of the lanthanum to LaO x(x <3/2). In addition, the lanthanum rich phase diffuses from bulk into the surface of the sample. The lack of lattice oxygen in this phase has a favorable effect on emission, which leads to a lower work function for the Mo La 2O 3 cathode.展开更多
Platinum catalyst for CO oxidation has been studied for decades,due to its high activity and good stability.In this work,we prepared three different lantha num oxide or hydroxide supports(LaO_(x)(OH)_(y)),and deposite...Platinum catalyst for CO oxidation has been studied for decades,due to its high activity and good stability.In this work,we prepared three different lantha num oxide or hydroxide supports(LaO_(x)(OH)_(y)),and deposited platinum(Pt) with 0.5 at% via an impregnation approach to synthesize Pt/LaO_(x)(OH)_(y) catalysts.However,we find that these catalysts perform a poor stability for the CO oxidation reaction.The fresh and used samples were comprehensively characterized by multiple techniques including power X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),transmission electron microscopy(TEM),temperature-programmed reduction by carbon monoxide(CO-TPR) and thermogravimetric analysis(TGA),to demonstrate that the oxidized platinum atoms or clusters,without any component of Pt-Pt metallic bond,are highly dispersed on the surface of LaO_(x)(OH)_(y).Furthermore,the as-formed lanthanum carbonate(La_(2)O_(2)CO_(3)) during the exposure to ambient circumstances or in the reaction atmosphere of CO+O_(2),severely impair the reactivity of Pt/LaO_(x)(OH)_(y).On the basis of the obtained experimental results,we have drawn a conclusion that the oxidized P_(t)O_(x) atoms or PtxOy clusters are the active species for CO oxidation,while the formation of lanthanum carbonate is the origin of deactivation on reactivity.展开更多
Nickel-alumina catalysts supported on cordierite monoliths of honeycomb structure surpass essentially the conventional granulated ones with respect to the output in carbon dioxide reforming of methane. Adjusting the s...Nickel-alumina catalysts supported on cordierite monoliths of honeycomb structure surpass essentially the conventional granulated ones with respect to the output in carbon dioxide reforming of methane. Adjusting the surface acid-base properties of catalysts by introduction of alkali metal （Na, K） oxides inhibits the carbonization and as a result, improves the operational stability of these catalysts. An effect of promotion of nickel-alumina based composite doped by lanthanum oxide is found. This effect, caused by an additional route for the CO2 activation on Ni-La2O3/Al2O3/cordierite catalyst, is displayed in increase of methane conversion under conditions of an oxidant excess.展开更多
Hydrogen was produced over noble metal（Ir, Ru, Rh, Pd） catalysts supported on various oxides, including γ-Al2O3, CeO2, ZrO2 and La2O3, via the autothermal reforming reaction of ethanol （ATRE） and oxidative reform...Hydrogen was produced over noble metal（Ir, Ru, Rh, Pd） catalysts supported on various oxides, including γ-Al2O3, CeO2, ZrO2 and La2O3, via the autothermal reforming reaction of ethanol （ATRE） and oxidative reforming reaction of ethanol （OSRE）. The conversion of ethanol and selectivites for hydrogen and byproducts such as methane, ethylene and acetaldehyde were studied. It was found that lanthana alone possessed considerable activity for the ATRE reaction, which could be used as a functional support for ATRE catalysts. It was demonstrated that Ir/La2O3 prevented the formation of methane, and Rh/La2O3 encumbered the production of ethylene and acetaldehyde. ATRE reaction was carried out over La2O3-supported catalysts （Ir/La2O3） with good stability on stream, high conversion, and excellent hydrogen selectivity approaching thermodynamic limit under autothermal condition. Typically, 3.4H2 molecules can be extracted from a pair of ethanol and water molecules over Ir（5wt%）/La2O3. The results presented in this paper indicate that Ir/La2O3 can be used as a promising catalyst for hydrogen production via ATRE reaction from renewable ethanol.展开更多
We report on the performance of La203/InA1N/GaN metal-oxide-semiconductor high electron mobility transistors （MOSHEMTs） and InA1N/GaN high electron mobility transistors （HEMTs）. The MOSHEMT presents a maximum drai...We report on the performance of La203/InA1N/GaN metal-oxide-semiconductor high electron mobility transistors （MOSHEMTs） and InA1N/GaN high electron mobility transistors （HEMTs）. The MOSHEMT presents a maximum drain current of 961 mA/mm at Vgs = 4 V and a maximum transconductance of 130 mS/mm compared with 710 mA/mm at Vgs = 1 V and 131 mS/mm for the HEMT device, while the gate leakage current in the reverse direction could be reduced by four orders of magnitude. Compared with the HEMT device of a similar geometry, MOSHEMT presents a large gate voltage swing and negligible current collapse.展开更多
The collection of different cations in the A and B sites of ABO3 was explored for the regularity of perovskites phase formability.Here,Sr2？,La3？,and Ce4？are selected as the cations of site A.The site B is considere...The collection of different cations in the A and B sites of ABO3 was explored for the regularity of perovskites phase formability.Here,Sr2？,La3？,and Ce4？are selected as the cations of site A.The site B is considered to be Mn or Co cations.XRD analysis and Fourier transform infrared spectroscopy results confirm the formation of perovskite structure for catalysts in which La3？and Sr2？are considered as the cations of site A.Ceria is detected as the main crystalline phase when Ce4？is selected to be cation of site A.It is found that the octahedral factor（rB/rO） takes the same important role as the tolerance factor to form cubic perovskite.Average crystallite size of the products was calculated by data of the XRD and measured by the TEM analysis.Results of the XRD and TEM studies were supported by the study of the particles size distribution,which was carried out in a particle size analyzer.The perovskite samples were also used for stoichiometric oxidation of carbon monoxide with air.展开更多
Density‐functional theory calculations were carried out to study the strontium(Sr)‐doping effect on methane activation over a lanthanum‐oxide(La2O3)catalyst for the oxidative coupling of methane(OCM)using the clust...Density‐functional theory calculations were carried out to study the strontium(Sr)‐doping effect on methane activation over a lanthanum‐oxide(La2O3)catalyst for the oxidative coupling of methane(OCM)using the cluster model.Eight Sr‐doped La2O3cluster models were built from pure La2O3clusters that were used previously to model the La2O3catalyst.These form two distinct categories,namely,those without a radical character(LaSrO2(OH),La2SrO4,La3SrO5(OH),and La5SrO8(OH))and those with a radical character(LaSrO3,La2SrO4(OH),La3SrO6,and La5SrO9).The potential‐energy surface for CH4activation to form a CH3radical at different Sr-O and La-O pair sites on these Sr‐doped La2O3clusters was calculated to study the Sr‐doping effect on the OCM catalytic activity.CH4physisorption and chemisorption energies,and activation barriers,and CH3desorption energies were predicted.Compared with the pure La2O3clusters,in general,the Sr‐doped La2O3clusters are thermodynamically and kinetically more reactive with CH4.For the Sr‐doped La2O3clusters without the radical character,the Sr-O pair site is more reactive with CH4than the La-O pair site,although a direct release of the CH3radical is also highly endothermic as in the case of the pure La2O3clusters.In contrast,for the Sr‐doped La2O3clusters with a radical character,the activation of CH4at the oxygen radical site and the release of the CH3radical are much easier.Thus,our calculations suggest that the Sr dopant prompts the OCM catalytic activity of the La2O3catalyst by providing a highly active oxygen‐radical site and by strengthening the basicity of the M-O pair site,which leads to lower CH4activation energies and lower CH3desorption energies.展开更多
In order to improve the wear resistance, a kind of alumina ceramic with good wear resistance was created in an Al_2O_3-CaC_O3-SiO_2-MgO-La_2O_3（ACSML） system. The effects of La_2O_3 content on sintering temperature,...In order to improve the wear resistance, a kind of alumina ceramic with good wear resistance was created in an Al_2O_3-CaC_O3-SiO_2-MgO-La_2O_3（ACSML） system. The effects of La_2O_3 content on sintering temperature, bulk density, and wear rate were investigated. The wear rate of sample was as low as 0.0393‰. The wear resistance of the sample containing La_2O_3 has improved 43% than that of the sample without La_2O_3. Appropriate La_2O_3 doping could inhibit grain growth, enhance density, and purify grain boundary. La_2O_3 could diffuse into Al_2O_3 to form a solid solution and react with Al_2O_3 to form high-aluminum low-lanthanum complex oxides. The combination among Al_2O_3, the solid solution layer, and the layer of high-aluminum low-lanthanum complex oxides combined closely, which could improve grain boundary cohesion. Besides, the homogeneous distributions of elements made uniform structure. Finally, the wear resistance of alumina ceramic was improved.展开更多
Lead-free piezoelectric ceramics of (Bi1/2Na1/2)TiO3-BaTiO3(BNT-BT) were prepared by the conventional piezoelectric ceramic preparation technique (free air atmosphere sintering). The influence of BaTiO3 additive amoun...Lead-free piezoelectric ceramics of (Bi1/2Na1/2)TiO3-BaTiO3(BNT-BT) were prepared by the conventional piezoelectric ceramic preparation technique (free air atmosphere sintering). The influence of BaTiO3 additive amount and La2O3 additive amount on the properties of BNT-BT lead-free piezoceramics were investigated. The results show that the dielectric constant(ε) and piezoelectric strain constant(d33) of materials start increasing and then decreasing while BaTiO3 additive amount increasing, the e and d33 of materials have maximum value (ε= 1650, d33 = 120 PC·N -1 ) while x (BaTiO3) =0.06 mol. Theεand d33 of materials start increasing and then decreasing while La2O3 additive amount increasing, the e and d33 of materials have maximum value (ε= 1684, d33 = 153 PC·N-1) while w(La2O3) =0.3% . The influence of La2O3 additive amount on the microstructure of BNT-BT piezoelectric ceramics was analysed by SEM( scanning electron microscope). The influence mechanism of La2O3 additive amount on the properties of BNT-BT piezoelectric ceramics was discussed. The BNT-BT ceramics with optimum comprehensive properties were obtained.展开更多
基金Project supported by the National Natural Science Foundation of China(81903364)the National Natural Science Foundation of Jiangxi Province(20202BABL206123)the Postgraduate Innovation Special Fund Project of Jiangxi Province(YC2021-S795)。
文摘Due to the wide application of rare earth elements,lanthanum(La) is gradually accumulated in our living environment.Lanthanum can enter the body through a variety of routes,which has a series of effects on various systems.As a consequence,the safety of lanthanum deserves our attention.This study aims to compare the toxicity of lanthanum oxide nanoparticles(La_(2)O_(3) NPs) and lanthanum chloride(LaCl_(3)) and enrich the toxicity evaluation of lanthanum.Therefore,a 30 d intragastal experiment was conducted.C57BL/6j mice were given by La_(2)O_(3) NPs solution and LaCl_(3) solution respectively at doses of 0,30,60 and120 mg/kg BW(lanthanum content).The results show that,compared with the control group,both La_(2)O_(3)NPs and LaCl_(3) can reduce the body weight of female mice in the high-dose group,but for male mice,the high-dose La_(2)O_(3) NPs solution can increase the body weight,while LaCl_(3) has the opposite effect.The coefficients of liver,kidney,heart,lung,uterine and ovaries increase first and then decrease with the exposure dose,but testes and epididymides coefficient keep increasing with the exposure of LaCl_(3) and La_(2)O_(3) NPs.La_(2)O_(3) NPs and LaCl_(3) can reduce the concentration of triglycerides(TG) and increase the level of low density lipoprotein(LDL),but the effect of La_(2)O_(3) NPs is more obvious.La_(2)O_(3) NPs and LaCl_(3) can reduce the concentration of malondialdehyde(MDA),increase the total antioxidant capacity(T-AOC)and enhance the activity of catalase(CAT),but LaCl_(3) has more obvious protective effects on oxidative stress.La_(2)O_(3) NPs and LaCl_(3) have potential risks to liver,and the toxicity of La_(2)O_(3) NPs might be higher than that of LaCl_(3).
基金Project supported by the National High-Tech R&D Program (863 Program) of China (2009AA06Z102)the Fundamental Research Fund for the Central Universities and State Key Laboratory of Exploration Fund of China
文摘Graphitized carbon/carbon composites were prepared by the process of catalytic graphitization with the rare-earth catalyst, lantha-num oxide （La2O3）, in order to increase the degree of graphitization and reduce the electrical resistivity. The modified coal tar pitch and coal-based needle coke were used as carbon source, and a small amount of La2O3 was added to catalyze the graphitization of the disordered carbon materials. The effects of La2O3 catalyst on the graphitization degree and microstructure of the carbon/carbon composites were investi-gated by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The results showed that La2O3 promoted the formation of more perfect and larger crystallites, and improved the electrical/mechanical properties of carbon/carbon composites. Carbon/carbon compos-ites with a lower electrical resistivity （7.0 ？？？m） could be prepared when adding 5 wt.% La2O3 powder with heating treatment at 2800 oC. The catalytic effect of La2O3 for the graphitization of carbon/carbon composites was analyzed.
文摘This study evaluated the bacterial toxicity of lanthanum oxide micron and nano sized particles using shake flask method against gram-positive （Staphylococcus aureus） and gram-negative （Escherichia coli, Pseudomonas aeruginosa） bacteria. Particle size, morphology and chemical composition were determined using scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDS）. Results indicated that lanthanum oxide nanoparticles showed antimicrobial activity against Staphylococcus aureus, but not against Escherichia coli and Pseudomonas aeruginosa. It was speculated that lanthanum oxide produced this effect by interacting with the gram-positive bacterial cell wall. Furthermore, lanthanum oxide bulk particles were fotmd to enhance the pyocyanin pigment production in Pseudomonas aeruginosa.
文摘The preparation of nano sized La 2O 3 powder by mechanochemical reaction of lanthanum carbonate with sodium hydroxide and subsequent heat treatment was studied using X ray diffraction, differential thermal and thermo gravimetric analysis and transmission electron microscopy. It was found that the mechanochemical reaction process can be divided into two steps: the first step is the multi phases mechanochemical reaction of lanthanum carbonate with NaOH to form amorphous lanthanum basic carbonate and lanthanum hydroxide, and the second step is the crystallization of basic lanthanum carbonate with the formula of La 2(OH) 2(CO 3) 2·H 2O under a quasi hydrothermal synthesis condition caused by the mechanical ball milling. The synthesized La 2O 3 powder appears clearly separated spherical like monodisperse nano size particles in which particle size ranges from 30 to 50 nm.
文摘A new method for the determination of trace non-rare earth elements(NREEs)impurities in high-purity lanthanum oxide by HPLC combined with ICP-AES is proposed.The chromatographic retention behaviors of matrix(La)and NREEs were studied using 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate(P507)chelating resin as the stationary phase and dilute nitric acid as the mobile phase.It is found that the use of pH 1.7 nitric acid enables effective elution of NREEs from HPLC column,but the lanthanum remains on the column.The experimental results show that a favorable separation between matrix lanthanum and NREEs can be obtained within 15 min.The method proposed is applied to the determination of 8 NREEs impurities in high-purity La2O3.The recoveries of 8 NREEs are in the range of 90%similar to 110%.
文摘A new method for determination of trace silicon in high purity lanthanum oxide by using electrothermal vaporization (ETV) ICP AES with polytetrafluoroethylene(PTFE) slurry as a fluorinating reagent has been proposed. Under the optimized experimental conditions, the fluorination reactions of analyte(Si) and matrix(La) with PTFE in the graphite furnace took place at high temperature, and the fractional volatilily between Si and La was observed. Based on this principle the matrix interference could be eliminated. The detection limit of Si was 4.0 μg·L -1 , and the RSD was 3.4%( C =0.2 mg·L -1 , n =10). The procedure proposed has been applied successfully to determine trace Si in La 2O 3 without any chemical pre treatment.
基金supported by the National Natural Science Foundation of China (Grant No. 60578041)the Shanghai Leading Academic Disciplines (Grant No. S30107)
文摘Ce3＋-doped yttrium lanthanum oxide （Y0.9La0.1）2O3 transparent ceramics is fabricated with nanopowders and sintered in H2 atmosphere. The spectral properties of Ce：（Y0.9La0.1）2O3 transparent ceramics are investigated. There appear two characteristic absorption peaks of Ce3＋ ions at 230~nm and 400~nm, separately. It is found that Ce3＋ ions can efficiently produce emission at 384~nm from （Y0.9La0.1）2O3 transparent ceramic host, while the emission is completely quenched in Re2O3 （Re=Y, Lu, La） host materials.
基金Project supported by the National Natural Science Foundation of China(21301107,21501109)Fundamental Research Funding of Shandong University(2014JC005)+1 种基金the Taishan Scholar Project of Shandong Province(China)Doctoral Funding of Ministry of Education of China(20130131120009)
文摘In this paper, a series of Fe- and Co-doped lanthanum（hydr）oxides catalysts were prepared by a simple coprecipitationhydrothermal method. The as-prepared catalysts were characterized with various techniques including powder X-ray diffraction（XRD）, N2 adsorption/desorption, inductively coupled plasma（ICP） and transmission electron microscopy（TEM）. The Fe-based catalysts exhibited consecutive phase changes of amorphous Fe Ox→FeLaO3→Fe2N under different stages（as-prepared→calcination→ammonia decomposition reaction）; as for Co-based catalysts, the phase transformation followed a sequence of Co（OH）2→Co3O4→metallic Co. It was revealed that Fe2N and metallic Co were most probably the active crystalline phase respectively for Feand Co-based catalysts in the decomposition of ammonia.
基金Project supported by the Vanung University of the Republic of China,Taiwan (No.VIT-97-EE-02)
文摘This paper investigates the feasibility of using a lanthanum oxide thin film （La2O3） with a high dielectric constant as a gate dielectric on GaAs pHEMTs to reduce gate leakage current and improve the gate to drain breakdown voltage relative to the conventional GaAs pHEMT. An E/D mode pHEMT in a single chip was realized by selecting the appropriate La2O3 thickness. The thin La2O3 film was characterized： its chemical composition and crystalline structure were determined by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. La2O3 exhibited good thermal stability after post-deposition annealing at 200, 400 and 600℃ because of its high binding-energy （835.6 eV）. Experimental results clearly demonstrated that the La2O3 thin film was thermally stable. The DC and RF characteristics of Pt/La2O3/Ti/Au gate and conventional Pt/Ti/Au gate pHEMTs were examined. The measurements indicated that the transistor with the Pt/La2O3/Ti/Au gate had a higher breakdown voltage and lower gate leakage current. Accordingly, the La2O3 thin film is a potential high-k material for use as a gate dielectric to improve electrical performance and the thermal effect in high-power applications.
文摘A new process for electrolytic production of a perfluorinated compound, （CF3）3N, using lanthanum nickel oxide-coated Ni sheet anode in the （CH3）4NF· 4.0HF melt at room temperature, was developed. Thin films of the lanthanum nickel oxides were prepared on Ni sheets by sol-gel coating method using polyvinlylpyrrolidone（PVP）. The main components of the thin films were La2O3, LaNiO3, and La2NiO4 at 500, 750 and 1000℃, respectively. The anode performance in the （CH3）4NF·4.0HF melt depends greatly on the main component of the thin film, and the LaNiO3-coated Ni sheet anode gives the best anode performance. The potential of LaNiO3-coated Ni sheet anode remains constant at 5.9 V during electrolysis at 20 mA·cm^-2 in the （CH3）4NF·4.0HF melt for 100 h. This is because LaNiO3 and NiF3 and/or Ni2F5, the latter of which was formed during electrolysis, in the film give a high electronic conductivity to the surface film during electrolysis. The maximum mole fraction of （CF3）3N （21.4%） was obtained at 20 mA·cm^-2 in （CH3）4NF·4.0HF melt using the LaNiO3-coated Ni sheet.
基金supported by the National Key Research and Development Program of China(No.2019YFB2005801)the National Natural Science Foundation of China(Nos.52061135205,51731003,51971024,51971023,51971027,51927802)the Beijing Natural Science Foundation Key Program(No.Z190007)。
文摘Resistive switching devices with a high self-rectifying ratio are important for achieving the crossbar memristor array that overcomes the sneak current issue.Herein,we demonstrate a single amorphous lithium lanthanum titanium oxide(LLTO)layer based Pt/LLTO/Pt device possessing a self-rectifying ratio higher than 1 × 10^(4) that is comparable to the reported devices with complicated multi-layer stacking structures.Moreover,the device shows forming-free and highly uniform bipolar resistive switching(BRS)characteristic that facilitates the potential applications.The trap-controlled and trap-free space charge limited conductions are demonstrated to dominate the high and low resistance states of the device,respectively.The fast migration of lithium ions under external voltage accelerates the electron injection across the Pt/LLTO interface and also the space charge accumulation in the LLTO layer,and as a result,the high performance of the Pt/LLTO/Pt device was achieved.As demonstrated Pt/LLTO/Pt device sheds a light on the potential applications of the lithium ionic conductors in self-rectifying resistive switching devices.
文摘The changes of the valence state of lanthanum in the Mo La 2O 3 model cathode specimens were systematically studied by in situ XPS/AES analyses from room temperature to 1550 ℃. The experimental results show that the valence of lanthanum changes during the activation processes. As the temperature increases, the lattice oxygen in La 2O 3 is dissociated, resulting in partial reduction of the lanthanum to LaO x(x <3/2). In addition, the lanthanum rich phase diffuses from bulk into the surface of the sample. The lack of lattice oxygen in this phase has a favorable effect on emission, which leads to a lower work function for the Mo La 2O 3 cathode.
基金Project supported by the National Natural Science Foundation of China(21773288)National Key Basic Research Program of China(2017YFA0403402)。
文摘Platinum catalyst for CO oxidation has been studied for decades,due to its high activity and good stability.In this work,we prepared three different lantha num oxide or hydroxide supports(LaO_(x)(OH)_(y)),and deposited platinum(Pt) with 0.5 at% via an impregnation approach to synthesize Pt/LaO_(x)(OH)_(y) catalysts.However,we find that these catalysts perform a poor stability for the CO oxidation reaction.The fresh and used samples were comprehensively characterized by multiple techniques including power X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),transmission electron microscopy(TEM),temperature-programmed reduction by carbon monoxide(CO-TPR) and thermogravimetric analysis(TGA),to demonstrate that the oxidized platinum atoms or clusters,without any component of Pt-Pt metallic bond,are highly dispersed on the surface of LaO_(x)(OH)_(y).Furthermore,the as-formed lanthanum carbonate(La_(2)O_(2)CO_(3)) during the exposure to ambient circumstances or in the reaction atmosphere of CO+O_(2),severely impair the reactivity of Pt/LaO_(x)(OH)_(y).On the basis of the obtained experimental results,we have drawn a conclusion that the oxidized P_(t)O_(x) atoms or PtxOy clusters are the active species for CO oxidation,while the formation of lanthanum carbonate is the origin of deactivation on reactivity.
文摘Nickel-alumina catalysts supported on cordierite monoliths of honeycomb structure surpass essentially the conventional granulated ones with respect to the output in carbon dioxide reforming of methane. Adjusting the surface acid-base properties of catalysts by introduction of alkali metal （Na, K） oxides inhibits the carbonization and as a result, improves the operational stability of these catalysts. An effect of promotion of nickel-alumina based composite doped by lanthanum oxide is found. This effect, caused by an additional route for the CO2 activation on Ni-La2O3/Al2O3/cordierite catalyst, is displayed in increase of methane conversion under conditions of an oxidant excess.
基金supported by the National Natural Science Foundation of China (No. 50675070)
文摘Hydrogen was produced over noble metal（Ir, Ru, Rh, Pd） catalysts supported on various oxides, including γ-Al2O3, CeO2, ZrO2 and La2O3, via the autothermal reforming reaction of ethanol （ATRE） and oxidative reforming reaction of ethanol （OSRE）. The conversion of ethanol and selectivites for hydrogen and byproducts such as methane, ethylene and acetaldehyde were studied. It was found that lanthana alone possessed considerable activity for the ATRE reaction, which could be used as a functional support for ATRE catalysts. It was demonstrated that Ir/La2O3 prevented the formation of methane, and Rh/La2O3 encumbered the production of ethylene and acetaldehyde. ATRE reaction was carried out over La2O3-supported catalysts （Ir/La2O3） with good stability on stream, high conversion, and excellent hydrogen selectivity approaching thermodynamic limit under autothermal condition. Typically, 3.4H2 molecules can be extracted from a pair of ethanol and water molecules over Ir（5wt%）/La2O3. The results presented in this paper indicate that Ir/La2O3 can be used as a promising catalyst for hydrogen production via ATRE reaction from renewable ethanol.
基金Project supported by the Basic Science Research Fund for the Central Universities （Grant No. K50511250009）.
文摘We report on the performance of La203/InA1N/GaN metal-oxide-semiconductor high electron mobility transistors （MOSHEMTs） and InA1N/GaN high electron mobility transistors （HEMTs）. The MOSHEMT presents a maximum drain current of 961 mA/mm at Vgs = 4 V and a maximum transconductance of 130 mS/mm compared with 710 mA/mm at Vgs = 1 V and 131 mS/mm for the HEMT device, while the gate leakage current in the reverse direction could be reduced by four orders of magnitude. Compared with the HEMT device of a similar geometry, MOSHEMT presents a large gate voltage swing and negligible current collapse.
文摘The collection of different cations in the A and B sites of ABO3 was explored for the regularity of perovskites phase formability.Here,Sr2？,La3？,and Ce4？are selected as the cations of site A.The site B is considered to be Mn or Co cations.XRD analysis and Fourier transform infrared spectroscopy results confirm the formation of perovskite structure for catalysts in which La3？and Sr2？are considered as the cations of site A.Ceria is detected as the main crystalline phase when Ce4？is selected to be cation of site A.It is found that the octahedral factor（rB/rO） takes the same important role as the tolerance factor to form cubic perovskite.Average crystallite size of the products was calculated by data of the XRD and measured by the TEM analysis.Results of the XRD and TEM studies were supported by the study of the particles size distribution,which was carried out in a particle size analyzer.The perovskite samples were also used for stoichiometric oxidation of carbon monoxide with air.
基金supported by the National Natural Science Foundation of China(21473233,21403277)the Frontier Science Program of Shell Global Solutions International B.V.(PT32281)+1 种基金the Ministry of Science and Technology of China(2016YFA0202802)the Shanghai Municipal Science and Technology Commission(14ZR1444600)~~
文摘Density‐functional theory calculations were carried out to study the strontium(Sr)‐doping effect on methane activation over a lanthanum‐oxide(La2O3)catalyst for the oxidative coupling of methane(OCM)using the cluster model.Eight Sr‐doped La2O3cluster models were built from pure La2O3clusters that were used previously to model the La2O3catalyst.These form two distinct categories,namely,those without a radical character(LaSrO2(OH),La2SrO4,La3SrO5(OH),and La5SrO8(OH))and those with a radical character(LaSrO3,La2SrO4(OH),La3SrO6,and La5SrO9).The potential‐energy surface for CH4activation to form a CH3radical at different Sr-O and La-O pair sites on these Sr‐doped La2O3clusters was calculated to study the Sr‐doping effect on the OCM catalytic activity.CH4physisorption and chemisorption energies,and activation barriers,and CH3desorption energies were predicted.Compared with the pure La2O3clusters,in general,the Sr‐doped La2O3clusters are thermodynamically and kinetically more reactive with CH4.For the Sr‐doped La2O3clusters without the radical character,the Sr-O pair site is more reactive with CH4than the La-O pair site,although a direct release of the CH3radical is also highly endothermic as in the case of the pure La2O3clusters.In contrast,for the Sr‐doped La2O3clusters with a radical character,the activation of CH4at the oxygen radical site and the release of the CH3radical are much easier.Thus,our calculations suggest that the Sr dopant prompts the OCM catalytic activity of the La2O3catalyst by providing a highly active oxygen‐radical site and by strengthening the basicity of the M-O pair site,which leads to lower CH4activation energies and lower CH3desorption energies.
基金supported by the National Natural Science Foundation of China(51172049)State Key Laboratory of Advanced Technology for Materials Synthesis and Processing(WUT,China)(2015-KF-4)Guangxi Ministry-Province Jointly-Constructed Cultivation Base for State Key Laboratory of Processing for Non-ferrous Metal and Featured Materials(13AA-1)
文摘In order to improve the wear resistance, a kind of alumina ceramic with good wear resistance was created in an Al_2O_3-CaC_O3-SiO_2-MgO-La_2O_3（ACSML） system. The effects of La_2O_3 content on sintering temperature, bulk density, and wear rate were investigated. The wear rate of sample was as low as 0.0393‰. The wear resistance of the sample containing La_2O_3 has improved 43% than that of the sample without La_2O_3. Appropriate La_2O_3 doping could inhibit grain growth, enhance density, and purify grain boundary. La_2O_3 could diffuse into Al_2O_3 to form a solid solution and react with Al_2O_3 to form high-aluminum low-lanthanum complex oxides. The combination among Al_2O_3, the solid solution layer, and the layer of high-aluminum low-lanthanum complex oxides combined closely, which could improve grain boundary cohesion. Besides, the homogeneous distributions of elements made uniform structure. Finally, the wear resistance of alumina ceramic was improved.
文摘Lead-free piezoelectric ceramics of (Bi1/2Na1/2)TiO3-BaTiO3(BNT-BT) were prepared by the conventional piezoelectric ceramic preparation technique (free air atmosphere sintering). The influence of BaTiO3 additive amount and La2O3 additive amount on the properties of BNT-BT lead-free piezoceramics were investigated. The results show that the dielectric constant(ε) and piezoelectric strain constant(d33) of materials start increasing and then decreasing while BaTiO3 additive amount increasing, the e and d33 of materials have maximum value (ε= 1650, d33 = 120 PC·N -1 ) while x (BaTiO3) =0.06 mol. Theεand d33 of materials start increasing and then decreasing while La2O3 additive amount increasing, the e and d33 of materials have maximum value (ε= 1684, d33 = 153 PC·N-1) while w(La2O3) =0.3% . The influence of La2O3 additive amount on the microstructure of BNT-BT piezoelectric ceramics was analysed by SEM( scanning electron microscope). The influence mechanism of La2O3 additive amount on the properties of BNT-BT piezoelectric ceramics was discussed. The BNT-BT ceramics with optimum comprehensive properties were obtained.
