La Addition Research Articles

Ru-supported lanthania-ceria composite as an efficient catalyst for COx-free H2 production from ammonia decomposition

Ru doped on a series of LaxCe1-xOy composites by the deposition-precipitation (DP) method was studied in NH3 decomposition to generate COx-free H2. N2 physisorption, CO chemisorption, XRD, XPS, XAS, ICP-OES, HAADF-STEM, TPR, and TPD analysis were used to investigate the catalyst properties and to elucidate the beneficial properties for the reaction. Density functional theory (DFT) calculations provided insights into how the La addition promoted the high recombinative N2 desorption capacity leading to the high NH3 decomposition activity of the Ru-based catalysts at low temperatures. Among the tested catalysts, Ru/La0.33Ce0.67 exhibited superior catalytic activity and excellent stability. This study provides direct proof that the combination of the relatively small Ru size with strong interaction with the composite LaxCe1-xOy by the DP method and the optimized acidity–basicity property for the enhancement of both H2 and N2 desorption is essential to the development of Ru-based catalysts for NH3 decomposition.

Antimicrobial Efficacy of Aqueous Ozone and Ozone-Lactic Acid Blend on Salmonella-Contaminated Chicken Drumsticks Using Multiple Sequential Soaking and Spraying Approaches.

Ozone (O3) is an attractive alternative antimicrobial in the poultry processing industry. The optimal operational conditions of O3 for improving food safety concerns are poorly understood. The main objective of this study was therefore to characterize the microbial killing capacity of aqueous O3 and O3–lactic acid blend (O3–LA) at different operational conditions on chicken drumsticks contaminated with high Salmonella load using sequential soaking and spraying approaches. Four hundred forty-eight chicken drumsticks (280–310 g) were soaked into two-strain Salmonella cocktail, and the initial load on the surface of the skin was 6.9-log10 cell forming unit (CFU)/cm2 [95% confidence interval (CI), 6.8–7.0]. The contaminated drumsticks were then sequentially (10×) soaked and sprayed with aqueous O3 (8 ppm) and O3–LA. Following O3 exposure, quantitative bacterial cultures were performed on the post-soaking and post-spraying water, skin surface, and subcutaneous (SC) of each drumstick using 3MTM PetrifilmTM Rapid Aerobic Count Plate (RAC) and plate reader. The average killing capacity of aqueous O3/cycle on the skin surface was 1.6-log10/cm2 (95% CI, 1.5–1.8-log10/cm2) and 1.2-log10/cm2 (95% CI, 1.0–1.4-log10/cm2), and it was 1.1-log10/cm2 (95% CI, 0.9–1.3-log10/cm2) and 0.9-log10/cm2 (95% CI, 0.7–1.1-log10/cm2) in SC for soaking and spraying approaches, respectively. Six sequential soaking and seven sequential spraying cycles with ozonated water of 8 ppm reduced the heavy Salmonella load below the detectable limit on the skin surface and SC of drumsticks, respectively. Addition of LA seems to increase the microbial killing capacity of aqueous O3 with average differences of 0.3-log10/cm2 (P = 0.08) and 0.2-log10/cm2 (P = 0.12) on the skin surface using soaking and spraying approaches, respectively. Aqueous O3 did not cause any significant changes in the drumstick skin color. The Salmonella load of < 4.5-log10/cm2 was a strong predictor for the reduction rate (P < 0.001, R2 = 0.64). These results provide important information that helps the poultry processing facilities for selecting the optimal operational strategy of O3 as an effective antimicrobial.

Effect of La Addition on Solidification Behavior and Phase Composition of Cast Al-Mg-Si Alloy

The current study focusses on the phase composition, solidification path, and microstructure evaluation of gravity cast Al-4Mg-0.5Si-xLa aluminum alloy, where x = 0, 0.1, 0.25, 0.5, 0.75, and 1 wt.% La. A computational CalPhaD approach implemented in Thermo-Calc software and scanning electron microscopy technique equipped with electron microprobe analysis (EMPA) was employed to assess its above-mentioned characteristics. The thermodynamic analysis showed that the equilibrium solidification path of La-containing Al-Mg-Si alloys consists of only binary phases LaSi2 and Mg2Si precipitation along with α-Al from the liquid and further solid-state transformation of this mixture into α-Al + Al11La3 + Mg2Si + Al3Mg2 composition. Scheil–Gulliver simulation showed a similar solidification pathway but was accompanied by an increase in the solidification range (from ~55 °C to 210 °C). Furthermore, microstructural observations were congruent with the calculated fraction of phases at 560 °C and related to α-Al + LaSi2 + Mg2Si three-phase region in terms of formation of La-rich phase having both eliminating effect on the eutectic Mg2Si phase. Quantitative EMPA analysis and elemental mapping revealed that the La-rich phase included Al, La, and Si and may be described as Al2LaSi2 phase. This phase shows a visible modifying effect on the eutectic Mg2Si phase, likely due to absorbing on the liquid/solid interface.

Strengthening of solid solution (Ti,La)(C,N)-based cermets by LaB6 addition

(Ti,La)(C,N)-based solid solution cermets are fabricated from self-prepared (Ti,La)(C,N) carbonitrides by powder metallurgy with LaB6 addition in the solid solution. Based on the results of XRD and SEM analyses, it is confirmed that there is complete dissolution of (Ti,La)(C,N) powder. The presence of La can effectively suppress grain overgrowth and thus enhance the homogeneity of porcelain microstructure, consequently increasing the particle size of black phase. On the basis of equal mass fraction of La, the performance of (Ti,La)(C,N)-based cermets is better than that of Ti(C,N)-La-based cermets prepared by simple addition of LaB6 to Ti(C,N)-based cermet powder. The discrepancy can be directly related to the effect of adding LaB6 in the solid solution. The physical and mechanical properties of (Ti,La)(C,N)-based cermets comes to optimum when the content of dissolved La is 0.25 wt%, and there is hardness elevation of 20%. With suitable La addition, there is decrease of oxygen content in the solid solution of cermets. It is hence deduced that LaB6 can improve the performance of cermets as a deoxidizer.

Thermal stability of high-temperature compound La2Fe14B and magnetic properties of Nd-La-Fe-B alloys

The thermal stability and refined crystal structure of ternary La2Fe14B compound were investigated by integrating X-ray powder diffraction, electron probe microanalyzer and differential scanning calorimetry techniques. It was found that La2Fe14B is a high-temperature stable ternary compound, which decomposes with a eutectoid reaction: La2Fe14B→La + Fe + LaFe4B4 at 794 °C and melts via a peritectic reaction: Fe + Fe2B + Liquid→La2Fe14 B at 926 °C. By investigating the effects of La substitution on the magnetic properties of Nd2-xLaxFe14B alloys, it was revealed that the Nd1.3La0·7Fe14B alloy still keeps excellent maximum energy product (113 kJ/m3), intrinsic coercivity (523 kA/m) and high remanent magnetic polarization (0.83 T). Moreover, the magnetic improvement mechanisms of Nd2-xLaxFe14B alloys were also discussed in detail. The present work is beneficial to design high-performance 2:14:1-type magnets with low-cost and abundant La addition.

Improvement of mechanical properties in micro-alloying Al-Si-Mg-Zn cast alloy

The strengthening effects of micro Mo, Zr, La and Ce addition and short-time artificial aging (STAA) on mechanical properties of high pressure die-casting (HPDC) Al-Si-Mg-Zn alloy were investigated. The additions of Mo, Zr, La and Ce induced the formation of nanoscale phases in rapid solidification of HPDC. After the STAA, the supersaturated α-Al matrix solidified rapidly resulted in the fast and adequate precipitation of nano β'-Mg2Si phases. The combination of nano-phases containing the micro elements and nano β'-Mg2Si precipitates improved hardness and yield strength of the Al-Si-Mg-Zn cast alloy.

One-Step Fabrication of PtSn/γ-Al2O3 Catalysts with La Post-Modification for Propane Dehydrogenation

The catalytic dehydrogenation of propane to propene is an alternative technique to supplement the traditional steam cracking and catalytic cracking process for satisfying the continuously increasing demand for propylene downstream products. In this study, the parent PtSn/γ-Al2O3 catalyst was fabricated via the one-step method for the subsequent La post-modification to prepare the catalysts for propane dehydrogenation. The prepared and spent catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscope (SEM), NH3 temperature-programmed desorption (NH3-TPD), H2 temperature-programmed desorption (H2-TPR), and thermogravimetric (TG) analysis. The catalytic performance and characterization results demonstrated that the addition of La into the parent catalyst could significantly improve the catalytic performance of the prepared catalyst. Especially, the PtSn-La2.2 catalyst with the 2.2 wt.% La addition exhibited the stable and highest propylene selectivity (&gt;84%) under the investigation time of 800 min. The introduced La exhibits the ability to adjust the textural properties of the obtained catalysts, curb the acidity of support, promote the reduction of Pt species, and reduce the carbon accumulation on the prepared catalysts.

Effect of La addition on precipitation hardening in Mg–10Dy alloy

The effect of a small lanthanum (La) addition on Mg–10 wt% Dy alloy has been studied using isothermal aging at 120 °C. A combination of scanning transmission electron microscope (STEM) imaging and high-angle annular dark field (HAADF) based electron tomography has been used to characterize the precipitates. βF′ and β′ precipitates were determined, where βF′ precipitates form a bridge connecting two β′ precipitates, thus forming a continuous network of precipitates. This network results in a significant increase in hardness.

Relationship between La and Ce additions on microstructure and corrosion resistance of hot-dip galvanized steel

Scanning electron microscopy, X-ray diffraction, a neutral salt spray test, and electrochemical methods were applied to observe the microstructure and test the corrosion resistance of hot-dip galvanized steel before and after the addition of La and Ce. La/Ce mixture existed in the form of (La, Ce)Zn13 on the coated surface, decreased the coating thickness and accelerated the zinc dendritic growth. The corrosion current density of Zn–0.1La–0.1Ce coating was 63% less than that of pure Zn coating. This phenomenon can be explained that La/Ce mixture inhibited the transformation of Zn5(OH)8Cl2·H2O into Zn5(CO3)2(OH)6 or ZnO, reduced the time for appearance of red rust, and thus enhanced the stability of corrosion products and delayed the oxidation and corrosion processes of galvanized coating. La/Ce mixture improved the corrosion resistance compared to a single La or a single Ce addition. A competitive relationship between La and Ce was observed in the corrosion resistance improvement of hot-dip galvanized steel.

Preparation and properties of La and Nb co-doped TiO2 colossal dielectric ceramic materials

In this study, La + Nb co-doped TiO2 (LNTO; x = 0, 0.02, 0.05, 0.07) ceramics were prepared by the solid-state reaction method with high-purity TiO2, La2O3 and Nb2O5 powders. LNTO ceramics show dense microstructures with the second phase at the grain boundary, and La and Nb addition can inhibit the grain growth. Results of dielectric properties show that the dielectric constant of LNTO ceramics are enhanced largely (e′ > 104) and that the dielectric loss is relatively low (tan δ ~ 0.1) compared with that of pure TiO2 (e′ ~ 102) at low frequency. Within the test temperature range (30–500 °C) and test frequency range (0.5–1000 kHz), dielectric constants of LNTO ceramics display relatively high stability. The two peaks in modulus spectra could be explained by Maxwell–Wagner polarization. The results of dielectric and impedance spectra prove that the internal barrier layer capacitance model can be used to explain the colossal permittivity in (La + Nb) co-doped TiO2.

Effect of minor lanthanum on the microstructures, tensile and electrical properties of Al-Fe alloys

Wheel belt continuous casting and hot extrusion experiments were performed with the Al-0.5wt.%Fe alloys. The effects of minor lanthanum (La) on the microstructures as well as the electrical conductivity and tensile properties have been investigated. The microstructure analyses indicated that minor addition of rare earth element La (500 ppm) not only can achieve the α-Al grain refinement, but also can modify the Al13Fe4 intermetallic phase. The test results of tensile and electrical properties indicated that minor La addition can concurrently enhance the yield strength, ultimate tensile strength, elongation as well as the electrical conductivity of Al-Fe alloys. The improvements of strength, ductility and electrical conductivity are mainly ascribed to the α-Al grain refinement, the modification of Al13Fe4 intermetallic phase and the reduction of the solubility of Fe and Si elements in α-Al, respectively. The minor La addition is a promising approach for altering the microstructures and simultaneously enhancing the tensile properties and electrical conductivity of Al-Fe alloys. This study lays foundation for manufacturing Al-Fe alloys with good tensile and electrical properties.

Austenite Grain Growth Behaviors of La-Microalloyed H13 Steel and Its Effect on Mechanical Properties

Controlling austenite grain size is an effective method to improve mechanical properties of alloy steels. This article shows that La addition can effectively restrain the growth of austenite grains in H13 steel and make the grain size distribution more uniform. When holding at 1050 °C from 10 to 180 minutes, the average austenite grain of La-microalloyed H13 steel increases by 35.7 pct, while that of La-free H13 steel increases by 66.7 pct. With the extension of austenitizing time, the decrease in the strength and the plasticity of tempered La-microalloyed H13 steel is considerably less than those of tempered La-free H13 steel. Austenitized at 1050 °C for 180 minutes, the tensile strength and the elongation to failure of the tempered La-microalloyed steel are 1895 MPa and 9.3 pct, respectively. The addition of La increases the amount of undissolved carbide V8C7 and refines the carbide, and La2O2S particles with high melting point are detected. Because of the combined effect of these fine dispersed second-phase particles, the pinning effect on grain boundary migration increases, and the grain growth is restrained. Some martensitic substructures transform from twin configuration to dislocation configuration because of La addition, and the lath bundles of martensite are refined. As a result, the strength and the toughness of the steel are improved.

Effect of La on microstructure and corrosion behavior of 10%TiB2(p)/Al–5%Cu composites

The effect of La on microstructure and corrosion behavior of 10%TiB2(p)/Al–5%Cu composites was studied by using computer-aided cooling curve analysis (CA-CCA), X-ray diffraction, EDS, SEM, TEM and electrochemical testing. The experimental results showed that the La addition reduced the solidification rate of composites, decreased the nucleation temperature of primary α-Al, enhanced the transformation temperature of Al–Cu eutectic and narrowed the liquid–solid interval. Meanwhile, Al2.12La0.88 phase formation was found after adding La to the composites, and the precipitation of CuAl2 phase decreased with the increase of La content. The segregation of large agglomerates containing TiB2 clusters and second phases was improved obviously after the addition of La, which resulted in more uniform microstructure of composites. Moreover, proper La enhanced the corrosion resistance of 10%TiB2(p)/Al–5%Cu composite in 3.5% sodium chloride solution.

Effect of La addition on microstructures and properties of TiB2(-TiB)/Cu hybrid composites prepared by in situ reaction

TiB2p(-TiBw)/Cu hybrid copper matrix composites were fabricated by in situ reaction of Cu–Ti and Cu–B double-beam melts in combination with rolling. La was added on both sides of the melts and the effect of La addition on the microstructure and properties of TiB2(-TiB)/Cu hybrid composites were investigated. The results show that both the hybrid reinforcements and copper matrix are refined, and the reinforcements are more evenly distributed in the matrix with the addition of La. Meanwhile, the addition of La has no effect on the type of reinforcements. Accordingly, a good comprehensive performance of TiB2(-TiB)/Cu composites was achieved with addition of La and post-rolling treatment. Besides, the refinement mechanisms of reinforcements and copper matrix are analyzed. The reasons for the improved performance are also discussed.

Multi-Refinement Effect of Rare Earth Lanthanum on α-Al and Eutectic Si Phase in Hypoeutectic Al-7Si Alloy

The effect of La addition on primary α-Al and the eutectic Si phase of Al-7Si alloy is investigated systematically in this work. The results indicate that La addition causes a multi-refining efficiency on the microstructure of Al-7Si alloy, including refinement of α-Al grains and secondary dendrite arm spacing as well as eutectic Si particles. The grain size, secondary dendrite arm spacing and area of eutectic Si particles are decreased by 26.8%, 7.7% and 26.7%, respectively, with the addition of 0.1 wt.% La. It is also found that La-rich phases of Al2Si2La form and distribute in the vicinity of the eutectic Si phase. The crystal structure and lattice parameter of Al2Si2La phase are determined to be hexagonal (a = b = 0.405 nm, c = 6.944 nm) based on the TEM analysis results. The multi-refinement effects are mainly attributed to the increased constitutional undercooling caused by the low solubility of La in Al alloy and the growth-restricting factor caused by the Al2Si2La phase.

Improving the Performance of Zinc Oxide Photocatalysts for Phenol Degradation through Addition of Lanthanum Species

One green approach to degrade organic pollutants, such as phenol, is through the photocatalytic reaction. Despite having large band gap energy, which is enough for phenol degradation, zinc oxide (ZnO) has low photocatalytic efficiency. In this study, ZnO was modified by lanthanum (La) species, and the improved photocatalytic activity was confirmed for degradation of phenol under visible and ultraviolet (UV) light irradiation. The ZnO and its modified photocatalysts were prepared by the hydrothermal method in the absence and presence of La species (0.01‒2 wt%). X-ray diffraction (XRD) patterns showed that the addition of La did not disturb the structure of ZnO, but slightly decreased the crystallite size. While the La addition up to 1 wt% did not affect the optical properties of the ZnO, the addition of 2 wt% La slightly red-shifted the absorption band edge of the ZnO. The Fourier-transform infrared (FT-IR) spectra showed La oxide formation observed at 515-540 cm-1 after 2 wt% La addition. Fluorescence emission spectra revealed that synthesized ZnO has oxygen vacancies at 558 nm, and the presence of 1 wt% La did not significantly affect the emission intensity. The photocatalytic activity of ZnO was influenced by the La addition, where the best performance was obtained on the ZnO with 1 wt% La. This study demonstrated that the optimum amount of La species could increase the performance of the ZnO.

Effect of Cooling Rates on the Microstructure and Mechanical Property of La Modified Al7SiMg Alloys Processed by Gravity Die Casting and Semi-Solid Die Casting

Rare earth (RE) additions are capable of refining the α-Al phase as well as modifying the eutectic Si particles of alloys. The cooling rate in casting process should be carefully concerned when the Al-Si alloys are refined and modified by adding RE elements. In this study, the effect of cooling rates on the microstructure and mechanical properties of La modified Al-7.0Si-0.3Mg alloys was studied in gravity die casting and semi-solid die casting. It is found that in La modified Al-7.0Si-0.3Mg alloys, with increasing the cooling rate from 0.2 to 9 K/s in gravity die casting, the α-Al grains are greatly refined and the Si particles are modified to branching morphology, which evidently increases the UTS and elongation of alloys. In addition, when increasing the cooling rate from 30 to 130 K/s in semi-solid die casting, the α-Al grains are refined from 140 to 47 μm, and the Si particles are modified to fibrous morphology, which increases the UTS from 190 to 230 MPa and elongation from 10% to 11%. However, the 0.4 wt.% La addition results to La-rich phases formed in microstructure, which impairs the mechanical properties of Al-7.0Si-0.3Mg alloys in semi-solid die casting.

Oxidation characteristics and electrical properties of La- or Ce-doped MnCo2O4 as protective layer on SUS441 for metallic interconnects in solid oxide fuel cells

In this study, we discuss the evolution of area specific resistance (ASR) of SUS441 which was coated with MnCo2O4, La-doped MnCo2O4, and Ce-doped MnCo2O4, respectively. These systems are meant to simulate as protective layers for metallic interconnects in solid oxide fuel cells (SOFCs) and were tested at 800 °C in 2 L/min air flow for 5600 h. The protective coatings were deposited by using pulsed DC magnetron sputtering and the thickness was 5.0 ± 1.0 μm. The compositions and microstructures were observed by SEM/EDS and XRD. Results show that a trace amount of La addition into MnCo2O4 is beneficial to keep stable electrical resistance and inhibit the growth of the oxide scale between the SUS441 substrate and the protective layer for this coating system. However, visible cracks can be seen in MnCo2O4 and Ce-doped MnCo2O4 specimens at the interfacial layer between the oxidation scale on SUS441 and the coatings after heat treatment at elevated temperatures.

Effect of La addition on microstructure evolution of hypoeutectic Al–6Si alloys

Solidification experiments were carried out for Al–6Si alloys with different La addition levels. The results demonstrate that the average sizes of the α-Al grains and the eutectic Si have a tendency of first decreasing and then almost keeping constant with the La addition. About (0.04–0.06) wt% La addition is enough to achieve a satisfactory grain refinement and modification. An analytical model based on the Wilson equation, the Miedema model and the thermodynamics was proposed to investigate the mechanisms of the α-Al grain refinement and the eutectic Si modification in the hypoeutectic Al–6Si alloys with the trace La addition. The La effect on the grain refinement of α-Al and the modification of the eutectic Si are mainly attributed to the increase in the efficiency of the heterogeneous nucleation substrates to nucleate α-Al and the amount of La atoms in the eutectic Si. The grain refinement and the modification results achieve the maximum when the La concentration is near its maximum solid solubility in the primary α-Al phase.

Effect mechanisms of micro-alloying element La on microstructure and mechanical properties of hypoeutectic Al-Si alloys

The rare earth influence on the as-cast microstructures and mechanical properties of aluminum alloys attracted great attentions in the last decades. But up to date no reports can be found on the effect of micro-alloying element La (La addition is below 0.1 wt.%) on the solidification of hypoeutectic Al-Si alloys. This study carried out solidification experiments with Al-6Si alloys micro-alloyed by element La. The α-Al grain refinement, the eutectic Si modification and the tensile properties improvement caused by micro-alloying element La were investigated. The effect mechanisms of La were discussed. It is demonstrated that the addition of La as low as 100 ppm can deprave the more effective heterogeneous nucleation conditions for the eutectic Si caused by the impurity P. The addition of 0.06 wt.% La is sufficient to achieve an ideal α-Al grain refinement, eutectic Si modification and ductility improvement of the alloys. LaAlSi phase forms in the Al-Si alloy with the additive amount of La higher than 0.06 wt.%. It has a tetragonal structure. Micro-alloying element La refines the α-Al grains by working as a surfactant and modifies the eutectic Si by promoting the formation of the significant multiple Si twins.