Effect Of La2O3 Research Articles

Effect of La2O3 on the optical, thermal, structural and radiation shielding properties of TeO2–ZnO–BaO glasses

Influence of lanthanum oxide (La2O3) on various properties of melt quenched zinc barium tellurite glasses (TeO2–BaO–ZnO) have been investigated. Lanthanum was limited to 10 mol% beyond which the glass formation ability was affected leading to crystallization in the proposed tie-line. Glass transition temperature improved with lanthanum oxide incorporation, while the density and energy band gap values showed a minimum at 5 mol%. The observed variation with lanthanum oxide doping was clearly elucidated from Raman spectral data, which indicated their influence in modifying the host ternary glass network. Radiation shielding parameter calculations showed a larger mass and linear attenuation coefficients for glasses doped with 10 mol% lanthanum oxide, indicating the influence of heavier oxides in improving the shielding properties and consequently acting as replacement candidate for toxic lead-based compounds.

La3+-adjusted optical and ligand field parameters in low CoO impurities Na2O–ZnO borate glass matrix

The effect of La2O3 on the ligand field and optical properties of the current glass system was investigated. In detail, the absorption band at (493–499 nm) is ascribed to 4T1g (F) → 2T1g (H) transition of Co2+ in octahedral symmetry. The absorption band at (574–580 nm) is ascribed to 4A2 (4F)→4T1(4P) transitions of Co2+ in tetrahedral symmetry. On the other hand, the electronic transition at (639–644 nm) is attributed to 5T2g→ 5Eg transition of Co3+ in octahedral symmetry. Moreover, the redshift of the absorption edges reduces the optical bandgaps from 3.42 eV to 3.24 eV. Additionally, the La2O3-free glass sample exhibited a transition at ∼230 nm in the UVC region. However, this glass sample showed an displayed transparency in the UVA and UVB regions. Furthermore, the redshift of the absorption edges resulted in the glass sample with the highest La2O3 content (i.e., 8 mol%) becoming UVA transparent while blocking UVC and UVB regions. The obtained data regarding the ligand field parameters indicate an increase in the ligand field splitting (10Dq), reflecting the increased interplay strength between Co2+ in tetrahedral symmetry and its ligands. Also, the values of the nonlinear refractive index and nonlinear optical parameters increased due to the enhancement of basicity within the glass network. These findings suggest that the glass with the greatest concentration has the potential to be utilized as an optical filter that allows UVA while blocking UVC and UVB electromagnetic waves.

Effect of La2O3 on hardness, wear resistance and corrosion resistance of WC/Fe90 iron-based composite coatings

In this paper, WC/Fe90 iron-based composite coatings were prepared using plasma spraying technology. The influence of rare earth oxide La2O3 on the microstructure and properties of the composite coatings was studied through microstructural characterization, phase identification, microhardness, wear resistance, and corrosion resistance. The results showed that the composite coatings were mainly composed of α-Fe, M7C3, Fe-Cr, FexCy, and other reinforcing phases. The addition of La2O3 promoted the decomposition of WC particles and improved the uniformity of the coatings. When the La2O3 content reached 1.0 wt%, the hardness was the highest, reaching 885.481 HV, which was 10% higher than that of the untreated coatings. The addition of La2O3 increased the friction coefficient but still improved the wear resistance. Compared to the coatings without La2O3, the mass loss due to wear was reduced by approximately 40%. Moreover, the addition of La2O3 formed a passive film on the surface of the coatings, effectively preventing the penetration of Cl- ions and refining the grain structure of the coatings, significantly enhancing the corrosion resistance. When the La2O3 content was 1.0 wt%, the corrosion resistance of the coatings was the best.

Effect of La2O3 as sintering aid on the structural, mechanical & electrical properties of Y2O3

Yttrium oxide (Y2O3) is a potential material in the development of transparent polycrystalline ceramics (PTCs). PTCs have possible applications in laser-materials, scintillators, Infrared windows, opto-electronic devices, displays etc. To obtain these, the ceramic must have a symmetric crystal structure, high purity and density. Highly dense ceramics require sophisticated sintering procedures as well as optimum sintering additives such as Lanthanum Oxide (La2O3) and Zirconium Oxide (ZrO2). In this manuscript, La2O3 is used as a sintering to embrace the sintering of Y2O3 with the aim to bring down the sintering temperature and systematically study the opto-electrical properties. La2O3 substituted Y2O3 (LaxY2−xO3, where, x = 0, 3, 6 and 9 at.%) ceramics are made, using co-precipitation method were examined for structural, morphological, physico-chemical and electrical properties by using XRD, SEM, TGA-DSC, and dielectric measurements. The obtained results serve as guidelines for the use of Y2O3 as a pathway to new dimensions opto-electronic applications.

Effect of La2O3 on Microstructure and Mechanical Properties of Mg–3Y Alloy

Effect of La2O3 on Microstructure and Mechanical Properties of Mg–3Y Alloy

Effect of La2O3 on Magnesium Borosilicate glasses glass for radiation shielding materials in nuclear application

As the radiation shielding is important for human health, alternative materials are under research for using this purposes. Thus in this study, Magnesium Borosilicate Glasses were inspected for their radiation defensive mechanism. The glass compositions are 40MgO–30SiO2 – (30-x)B2O3–xLa2O3, where x = 0,2.5,5,7.5 (mol%). Lanthanum (III) oxide, known as lanthana, is an inorganic compound and in it contains the rare earth element lanthanum and oxygen. It can be used as a component of optical materials such as glass as it was used in this study. The variation of the linear attenuation coefficient (LAC) and some other parameters such as half value length (HVL), mean free path (mfp), effective atomic number (Zeff) and Effective electron density (Neff) with the amount of La2O3 (0, 2.5, 5, 7.5 mol%) in glass samples was studied. The Phy-X/PSD program was utilized for this purpose. The results demonstrate that LaO-7.5 (with composition of 40MgO–30SiO2 – 22.5B2O3–7.5La2O3) has the highest LAC value out of the prepared glasses, while LaO-0 has the lowest.

Effect of La2 O3 and CeO2 on anaerobic methanogenesis process: Kinetics analysis and process mechanism study.

La2 O3 and CeO2 , as main rare earth oxides, with unique physical and chemical properties have been widely used in catalyst and grinding industry. In this study, the effects of La2 O3 and CeO2 on the anaerobic process were investigated. The biological methane production tests showed that 0-0.05 g/L La2 O3 and 0-0.05 g/L CeO2 enhanced anaerobic methanogenesis process. The result showed maximum specific methanogenic rates of La2 O3 and CeO2 were 56.26 mL/(h·gVSS) and 49.43 mL/(h·gVSS) and, compared with the control, increased 4% and 3%, respectively. La2 O3 significantly reduced the accumulation of volatile fatty acids (VFAs), whereas CeO2 had no similar effect. Dissolution experiments demonstrated that the content of extracellular La in the anaerobic granular sludge reached 404 μg-La/g volatile suspended solid (VSS), which was 134 times higher than that of extracellular Ce (3μg-Ce/gVSS). The content of intracellular La reached 206 μg-La/gVSS, which was 19 times higher than that of intracellular Ce (11 μg-Ce/gVSS). The different stimulation between La3+ and Ce3+ could be attributed to the different dissolution of La2 O3 and CeO2 . The result of this work is helpful to optimize anaerobic processes and to develop novel additives. PRACTITIONER POINTS: Novel anaerobic additives were developed. La2O3 and CeO2 in 0-0.05 g/L enhanced organics degradation and methane production. The addition of La2O3 significantly reduced the accumulation of volatile fatty acids. The solubilization of La2O3 was stronger than CeO2. The promoting effects of low concentrations of La2O3 and CeO2 were derived from dissolved La and Ce.

Microstructure, toughness, and tribological properties of laser cladded Mo2FeB2-based composite coating with in situ synthesized WC and La2O3 addition

Mo2FeB2-WC-La2O3 composite coatings were prepared using a preplaced method of laser cladding. The forming quality, microstructure, distribution of La, microhardness, fracture morphology, fracture toughness, and tribological properties were examined. The effect of La2O3 on the microstructure and properties of the coatings was analyzed. The results showed that the metallurgical bonding between the coating and substrate was significantly improved. La2O3 had no significant effect on the phases of the composite coatings. The microstructure growth of the La2O3 coating had no obvious direction and a block-like structure. The microstructure was initially refined and then coarsened with an increase in La2O3; La was found to exist at the Mo2FeB2 phase grain boundaries. The microhardness of the Mo2FeB2-WC coating was 1584.6 HV0.5. The microhardness of the composite coating that contained 0.3 wt% La2O3 reached 1494.7 HV0.5; its coefficient of friction (COF), wear rate, and fracture toughness were 0.31, 3.13 × 10−5 mm3/Nm, and 14.35 MPa·mm1/2, respectively. The crack resistance of the composite coating was the highest at 0.3 wt% La2O3 addition. The wear mechanisms of the coatings containing La2O3 were typical abrasive wear, and the coating without La2O3 was a combined mechanism of slight adhesive and abrasive wear. The coating exhibited an evident brittle fracture morphology.

Effect of La2O3 on the microstructure and optical performance of (Tb0.8Y0.2-xLax)2O3 ceramics

(Tb0.8Y0.2-xLax)2O3 transparent ceramics were prepared by using co-precipitation method combined with pressure-less sintering in flowing H2 atmosphere. Microstructure, optical transmittance, elements composition, and Verdet constant of the (Tb0.8Y0.2-xLax)2O3 ceramics were studied. The amount of La2O3 is crucial for the formation of expected transparent (Tb0.8Y0.2)2O3. With increasing content of La2O3, the number of pores and the grain size of as-fabricated (Tb0.8Y0.2-xLax)2O3 ceramics both decrease. When 4 at.% La2O3 is doped, the (Tb0.8Y0.16)2O3 transparent ceramics shows the highest transmittance of 73.3% at 1400 nm wavelength. With holding time increasing from 8 h to 15 h, the average grain size of (Tb0.8Y0.16La0.04)2O3 ceramics gradually increases from 5 μm to 13 μm. The Verdet constant measured at 633 nm is −352 rad/T·m, which is 2.63 times higher than that of TGG. In addition, large-size ceramics with Φ 20 mm × 3 mm and Φ 30 mm × 3 mm were also successfully obtained.

Effect of La2O3 on Microstructure and Properties of Laser Cladding SMA Coating on AISI 304 Stainless Steel

Known as having a stress self-accommodation characteristic, the laser cladding shape memory alloy (SMA) coatings have been widely used in material failure repair. Nevertheless, their further development is greatly limited by their low microhardness (250 HV0.2) and corrosion resistance. Benefiting from the capability of refined grain and adjusted microstructure, rare earth oxides play a key role in improving the properties of materials. Herein, to improve the microhardness and anti-corrosion of laser cladding SMA coatings, different amounts of La2O3 were doped in SMA coating. The influence of the different La2O3 doping amounts on the phases, grain size and microhardness was studied. The anti-corrosion of the SMA/La2O3 composite coating was explored in 3.5 wt.% sodium chloride solution. Results showed that the grain of the SMA/La2O3 composite coating is significantly refined. When doping with 0.9 wt.%, the refinement rate reaches 19%. Furthermore, based on the Hall–Petch effect, the microhardness of the SMA/La2O3 composite coating is increased to 450 HV0.2. At the same time, the anti-corrosion of the composite coating is enhanced due to the smaller grain size and fewer defects.

Microstructural, mechanical and phase formation behaviour of sintered mullite prepared from kaolinite and reactive alumina: effect of La2O3

Microstructural, mechanical and phase formation behaviour of sintered mullite prepared from kaolinite and reactive alumina: effect of La2O3

Effect of La2O3- decorated SiO2 on the performance of CuCo catalyst for direct conversion of syngas to ethanol

The specific synthesis of ethanol from syngas is particularly important for C1 chemistry platforms. Herein, the uniformly decorated xLa/SiO2-supported CuCo catalysts were prepared by a facile incipient wetness impregnation (IM) method. On the basis of detailed characterization and catalytic performance, the relationship between the distribution of active Cu and Co species and intrinsic catalytic activity was established and discussed. The La2O3 preferentially enhances the dispersion of copper and inclines to generate stable Cu+ from Cu-O-La units. Additionally, SiO2 is conducive to the generation of Cu0, and then promotes the reduction of adjacent Co2+ to Co0 through hydrogen spillover. It was found that the CuCo/(5La/Si) catalyst showed a highest CO conversion of 44.2% and the space time yield of total alcohols (STYROH) of 61.6 mg/mLcat·h, which was 8.0-fold and 3.3-fold higher than that of undecorated CuCo/(Si) catalyst, respectively. Moreover, a superior ethanol selectivity in total alcohols is as high as 34.0 wt%. The significant improvement in catalytic performance is attributed to the abundant Cu+-Co0 in the interface with strong capacity on C–C chain growth. This work provides a novel and simple model for the rational design other related CuCo catalyst with beneficial performance, which is of great significance to reveal the unique synergistic interface between Cu and Co species.

Effect of La2O3 on the properties of vanadium phosphate glasses: Structure-conductivity relation by molecular dynamics with self-assembly

Glasses in the yP2O5–xLa2O3–(100-y-x)V2O5 system have been obtained in the composition ranges of y = 5, 10, and 15 mol% and x = 1, 2, 3, 4, and 5 mol% using the melt quenching method. The concentration dependences of characteristic temperatures and density are found to pass through the maximum and minimum, respectively. In all studied composition ranges, the introduction of 1 mol% La2O3 leads to a slight increase in conductivity; after that, the conductivity gradually decreases. Such behavior is explained by the results of non-constant field molecular dynamics simulation in terms of the mean coordination number of the V…V pair. The conductivity value at a temperature of 50 °C reaches 3.2·10−4 S·cm−1 for the composition x = 1 and y = 5.

Molecular dynamics study on the mechanical and tribological properties of polyimide reinforced by lanthana

Purpose The purpose of this paper is to investigate the effect of lanthana (La2O3) on the mechanical and tribological properties of polyimide (PI). Design/methodology/approach The mechanical and tribological properties of PI nanocomposites filled with La2O3 were studied by molecular dynamic simulations to explore the deep mechanisms from an atomic or molecular view. Findings The results showed that the hardness of the PI matrix increased after La2O3 modification with a decrease of 72.4% nanoindentation depth. Besides, the friction coefficient of PI decreased by 72.2% after filling La2O3, and the shear deformation was largely reduced under the same conditions. The adsorption effect of La2O3 on the PI molecular, which reduced the atomic relative concentration, velocity, interaction with counterpart Fe layer and the temperature rise in the frictional interface, contributed to the improvement of the mechanical and tribological performance. Originality/value This study reveals the friction and wear mechanism of PI composites filled with rare earth oxide at the nanoscale.

The effect of La2O3 and CeO2 modifiers on properties of Ni–Al catalysts for LNG prereforming

Ni/La–Al2O3 and Ni/Ce–Al2O3 catalysts with a small amount of promoters intended for prereforming of LNG were characterized by XRF, N2 adsorption-desorption, XRD, H2 chemisorption, HRTEM and XPS. The catalytic activity was evaluated in methane steam reforming both in the kinetic and diffusion regime, at temperatures characteristic of pre-reforming. Carbonaceous deposit was analysed by TPO-MS method. The nature and location of the coke were studied by HRTEM.La or Ce addition into Ni–Al system causes the increase of the active surface area of Ni by enhancing its dispersion. Studies at kinetic regime have shown that the promoted catalysts have almost twice the activity than reference Ni–Al catalyst. This effect was not confirmed by measurements in the diffusion regime on whole catalyst tablets. Almost identical textural properties of catalysts and diffusive limitations related to them but not the catalytic properties of the material itself appeared to be crucial factors. The presence of La (but not Ce) causes a significant increase in resistance to coking.

The effect of lanthanum addition on the microstructure and mechanical properties of Mg-modified hydroxyapatite ceramics

In the present paper, the effect of La2O3 (0.25, 0.5 and 1 wt.%) addition on the phase stability, porosity, density, hardness, fracture toughness, compressive strength and brittleness index of hydroxyapatite modified with 1 wt.% of MgO was investigated. Hydroxyapatite (HA) without additives sintered at 1300?C has mixture of dominant hydroxyapatite phase with beta-tricalcium phosphate (?-TCP), alpha-tricalcium phosphate (?-TCP) and calcium oxide (CaO) phases. The microstructure is characterized with transgranular microcracks and oversized grains. Although the density and hardness of the pure HA increased with increasing temperature, a steady decrease in fracture toughness (from 0.96 to 0.71MPa?m1/2) and compressive strength (from 130.2 to 65.6MPa) was observed. For the HA modified with 1 wt.% of MgO the highest compressive strength (183.2MPa) and fracture toughness (1.47MPa?m1/2) were obtained at 1200?C and at this temperature the brittleness index was 3.24 ?m-1/2. Increase in the sintering temperature led to the increase of the brittleness index of the pure HA,MgO modified HA and La2O3-MgO modified HA samples. The addition of 1 wt.%La2O3 to 1 wt.% MgO-HA contributed to the increase in the compressive strength of about 10%(from 183.2 to 202.0MPa), fracture toughness of about 69% (from 1.37 to 2.32MPa?m1/2) and also decrease of the brittleness index from 3.24 to 2.18 ?m-1/2. The best performance after sintering at 1300?C was obtained for the MgO-HA sample with 0.25wt.% La2O3. As a result of this study, a new candidate material for biomedical application with superior mechanical properties and the phases that do not cause adverse reactions in the human body could be 1 wt.% MgO-HA modified with 1 wt.% La2O3 and sintered at 1200?C.

Catalytic Performance of Lanthanum Promoted Ni/ZrO2 for Carbon Dioxide Reforming of Methane

Nickel catalysts supported on zirconium oxide and modified by various amounts of lanthanum with 10, 15, and 20 wt.% were synthesized for CO2 reforming of methane. The effect of La2O3 as a promoter on the stability of the catalyst, the amount of carbon formed, and the ratio of H2 to CO were investigated. In this study, we observed that promoting the catalyst with La2O3 enhanced catalyst activities. The conversions of the feed, i.e., methane and carbon dioxide, were in the order 10La2O3 > 15La2O3 > 20La2O3 > 0La2O3, with the highest conversions being about 60% and 70% for both CH4 and CO2 respectively. Brunauer–Emmett–Teller (BET) analysis showed that the surface area of the catalysts decreased slightly with increasing La2O3 doping. We observed that 10% La2O3 doping had the highest specific surface area (21.6 m2/g) and the least for the un-promoted sample. The higher surface areas of the promoted samples relative to the reference catalyst is an indication of the concentration of the metals at the mouths of the pores of the support. XRD analysis identified the different phases available, which ranged from NiO species to the monoclinic and tetragonal phases of ZrO2. Temperature programmed reduction (TPR) analysis showed that the addition of La2O3 lowered the activation temperature needed for the promoted catalysts. The structural changes in the morphology of the fresh catalyst were revealed by microscopic analysis. The elemental compositions of the catalyst, synthesized through energy dispersive X-ray analysis, were virtually the same as the calculated amount used for the synthesis. The thermogravimetric analysis (TGA) of spent catalysts showed that the La2O3 loading of 10 wt.% contributed to the gasification of carbon deposits and hence gave about 1% weight-loss after a reaction time of 7.5 h at 700 °C.

Effect of La2O3 as a Promoter on the Pt,Pd,Ni/MgO Catalyst in Dry Reforming of Methane Reaction

Pt,Pd,Ni/MgO, Pt,Pd,Ni/Mg0.97La3+0.03O, Pt,Pd,Ni/Mg0.93La3+0.07O, and Pt,Pd,Ni/Mg0.85La3+0.15O (1% of each of the Ni, Pd, and Pt) catalysts were prepared by a surfactant-assisted co-precipitation method. Samples were characterized by the XRD, XPS, XRF, FT-IR, H2-TPR, TEM, the Brunauer–Emmett–Teller (BET) method, and TGA and were tested for the dry reforming of methane (DRM). TEM and thermal gravimetric analysis (TGA) methods were used to analyze the carbon deposition on spent catalysts after 200 h at 900 °C. At a temperature of 900 °C and a 1:1 CH4:CO2 ratio, the tri-metallic Pt,Pd,Ni/Mg0.85La3+0.15O catalyst with a lanthanum promoter showed a higher conversion of CH4 (85.01%) and CO2 (98.97%) compared to the Ni,Pd,Pt/MgO catalysts in the whole temperature range. The selectivity of H2/CO decreased in the following order: Pt,Pd,Ni/Mg0.85La3+0.15O > Pt,Pd,Ni/Mg0.93La3+0.07O > Pt,Pd,Ni/Mg0.97La3+0.03O > Ni,Pd,Pt/MgO. The results indicated that among the catalysts, the Pt,Pd,Ni/Mg0.85La23+0.15O catalyst exhibited the highest activity, making it the most suitable for the dry reforming of methane reaction.

Effect of La2O3 on dielectric and ferroelectric properties of Ba1−xLax(Ti0.98Zr0.02)O3 lead-free piezoceramics

Lead-free Ba1−xLax(Ti0.98Zr0.02)O3 with x = 0.00, 0.02, 0.04, 0.06 ceramics were prepared by solid state reaction method. The nomenclatures for the compositions are: BLZT-00, BLZT-02, BLZT-04 and BLZT-06 for x = 0.00, 0.02, 0.04, 0.06, respectively. The powders were calcined at 1000 °C for 4 h and sintered at 1400 °C for 2 h. X-ray diffraction patterns of sintered pellets confirm pure perovskite phase. The samples after sintering were leveled, electrode and characterized for dielectric constant at different temperatures, hysteresis loop, etc. The maxima of dielectric constant peak shifted to lower temperature with the increase in La2O3 concentration which indicates the decrease in Curie temperature (Tc). The Tc values are 375 °K, 355 °K, 325 °K and 250 °K for BLZT-00, BLZT-02, BLZT-04 and BLZT-06, respectively. Ferroelectric loop measurement showed the remnant polarization decreased with the increase in La2O3 concentration.

Texture evolution of tungsten materials during recrystallization

Some functional and structural performance of tungsten (W) are related to its texture characteristics. Usually, W serves in high temperature and may undergo recrystallization. Thus it’s necessary to evaluate the recrystallization texture of W. In our previous studies, pure W (PW) and W-1.0wt%La2O3 (WL10) were deformed via unidirectional rolling (UNR), cross rolling (CRR) and clock rolling (CLR) with 80% reduction. In the present paper, PW-UNR, PW-CRR, PW-CLR and WL10-UNR were subjected to annealing at 2073 K for 2 h to achieve recrystallization and figure out the evolution mechanism of recrystallization texture in W materials. Besides, the effect of La2O3 on recrystallization texture of W was discussed. The results indicated that the fiber textures in rolling state were transformed into isolated textures after recrystallization. {001}〈uvw〉 isolated texture formed in the recrystallized W may be mainly resulted from the texture inheritance. {113}〈361〉 isolated texture formed in the recrystallized WL10-UNR may be attributed to the orientated growth of {113}〈361〉 grains with high grain boundary mobility facilitated by La2O3. Generally, isolated textures near θ-fiber were strengthened while γ-fiber was weakened for W during recrystallization, which is an effective method to achieve W with more {001} and less {111} textures.