La Addition Research Articles

Effects of La addition on the mechanical properties and thermal-resistant properties of Al–Mg–Si–Zr alloys based on AA 6201

In this paper, the influence of La addition on the aging behavior, microstructure, mechanical properties, and thermal-resistant properties of Al–Mg–Si–Zr aluminum alloy has been studied with the help of optical microscope (OM), Brinell hardness measurements and scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS). The results show that La addition decreases the peak-aged hardness during aging process. Electrical conductivity and thermal-resistant properties improve when the La addition exceed 0.2%. Increasing La content to 0.3% leads to a poor elongation at fracture. Most of La element exists in the form of compounds containing Si which result in improvement in thermal-resistant properties. The tensile strength of the material with 0.2% La addition reduces while the thermal-resistant properties and electrical conductivity improve. This amount of La addition added to the experimental alloy could be a compromise between the mechanical properties and others like electrical conductivity and thermal-resistant properties.

Influence of rare earth elements on corrosion behavior of Al-brass in marine water

The corrosion behaviors of Al-brass in stagnant and flowing marine water as a function of combinative rare earths (Ce and La) addition were investigated by electrochemical techniques, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was demonstrated that RE elements could make the corrosion product layer more protective and strengthen the cohesion between the film and matrix in stagnant seawater. The electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) analysis confirmed that a duplex layer, which was mainly composed of an inner Al 2O 3 with trace amounts of RE compounds and an outer basic chloride of copper or zinc like (Cu, Zn) 2Cl(OH) 3, Cu(OH)Cl and CuCl 2·3Cu(OH) 2 layer was formed on RE-contained Al-brass surface and that the inner layer was responsible for the good corrosion resistance of the alloy. While only a porous and non-protective corrosion product layer was formed on the Al-brass alloy without RE addition, which made small values of the corrosion resistance. Additionally, in flowing marine water with velocity about 2 m/s, pitting corrosion occurred on the Al-brass surface and RE addition could availably decrease pitting sensitivity of the alloy.

Hydrogen-Storage Properties of Nanocrystalline Mg-Based Materials Created through Controlled Devitrification of a Metallic Glass

Mg-based nanostructured materials with a composition of Mg85Ni15-xMx (M=Y, La, or Pd) have been fabricated by proper alloying additions and controlling the crystallization process of melt spun metallic glass ribbon. XRD suggests that the average crystallite sizes range from 100 nm in the binary materials to <30 nm in the ternary alloys. Hydrogen absorption/desorption measurements show improved properties compared to nanocrystalline alloys fabricated using other processing strategies. Surface treatment of the binary and Pd-containing ribbons by ball milling or submersion in aqueous NH4+ allows the materials to be activated at 473 K, significantly lower than conventional Mg-based hydrogen storage materials. Y and La additions improve the maximum storage capacity. Absorption kinetics are also improved the materials is alloyed with La, while Y slows the reaction kinetics. Some degradation in storage capacity is observed when the materials are exposed to a cyclic absorption/desorption process, likely due to microstructural coarsening. The Mg85Ni10Pd5 composition fully absorbs and desorbs ≈5 wt. % H at 473 K, while other bulk Mg-based materials require temperatures in excess of 573 K.

Effects of temperature and rare earth content on oxidation resistance of Ni-based superalloy

AbstractThe oxidation behaviors of the Ni-22Cr-14W-2Mo superalloys with various La contents were investigated at 1 000 °C and 1 100 °C up to 500 h. The experimental results show that the oxidation resistance is improved by La addition. The mechanism of the reactive-element effect (REE) exhibits some difference at various oxidation temperatures. The REE is dependent on the solutionized La content when the alloy is oxidized at 1 000 °C. The dispersed LaCrO3 segregates on the grain boundaries of Cr-oxides, and hence the diffusion of metallic ions, e.g., Mn2+ and Cr3+, are prevented. The oxidation resistance decreases with the increase of La content. However, the REE ascribes not only to the solutionized La, but also to the La-Ni intermetallic phases, when the alloy is oxidized at 1 100 °C. The oxidation resistance is influenced by two effects: firstly, the formation of the dispersed La2O3 from the solutionized La on the grain boundary of Cr-oxides reduces the oxidation rate, and secondly, the aggregation of the La-O oxides from the large amount of La-Ni phases accelerates the oxidation process. The alloy with 0.026% La (mass fraction) exhibited excellent oxidation resistance at 1 100 °C.

Enhanced Magnetic and Ferroelectric Properties and Current-Voltage Hysteresis by Addition of La and Ti to BiFeO3 on 0.7%Nb-SrTiO3

By adding La and Ti, we improve the magnetic and ferroelectric properties of Bi0.8La0.2Fe0.92Ti0.08O3 and Bi0.8La0.2FeO3 films on 0.7% Nb-SrTiO3. In Bi0.8La0.2Fe0.92Ti0.08O3 and Bi0.8La0.2FeO3, the saturation magnetization and the coercivity are several times higher than those in BiFeO3. The La and Ti additions reduce the leakage current, and increase the remnant electric polarization. A resistance switching is observed in Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb-SrTiO3 and Bi0.8La0.2FeO3/0.7%Nb-SrTiO3 interfaces. Also, it is observed that Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb-SrTiO3 has a wider current-voltage hysteresis and a larger resistance difference than Bi0.8La0.2FeO3/0.7%Nb-SrTiO3. In the interface of Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb-SrTiO3, the ratio of high to low resistance is 103 and 105 times, at 300 K and 10 K, respectively. The voltage pulses can switch the resistance to vary in the 2 states. The transport mechanisms show that a trap-controlled space-charge-limited current induces current-voltage hysteresis and resistance switching. The current of Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb-SrTiO3 decays with the Curie—Von Schweidler law.

Nano Crystalline La Substituted Barium Hexaferrite Synthesized by Coprecipitation Method

La substituted barium hexaferrite Ba1-yFe12LayO19 with 0≤ y ≤0.5 was synthesized by chemical co-precipitation method using aqueous solutions of metallic chlorides at ambient temperature. NaOH was used as a precipitant. The co-precipitated products were annealed at 900 and 1000°C. The effects of La addition on the phase composition, morphology and thermal behavior of samples were studied using XRD, SEM and DTA/TGA, respectively. XRD results indicated that barium hexaferrite forms together with some intermediate phases in samples annealed at 900°C and the amount of intermediate phases decreased significantly by increasing annealing temperature to 1000°C. XRD results also showed that in sample annealed at 1000°C, the crystallite size of magnetic phase decreases from 98 to 64 nm by increasing the amount of La. Thermal analysis (DTA/TGA) implies that formation temperature of barium hexaferrite is increased with addition of La.

Influence of La and Ce additions on the magnetocaloric effect of Fe–B–Cr-based amorphous alloys

The magnetic entropy change (ΔSM), temperature of peak ΔSM (Tpk) and refrigerant capacity (RC) in Fe(RE)80B12Cr8 (RE=La, Ce, or Gd) alloys were studied. Increasing La, Ce, and Gd content led to relatively constant, decrease, and increase in Tpk, respectively. Both the phenomenologically constructed universal curve for ΔSM and field dependence power laws demonstrated that these alloys exhibited similar critical exponents at Curie temperature. With 5% Ce added to Fe80B12Cr8, Tpk could be tuned near room temperature with relatively constant peak ΔSM. Fe79B12Cr8La1 exhibited enhanced RC compared to Gd5Si2Ge1.9Fe0.1. The tunable Tpk and enhanced RC are needed in active magnetic regenerators.

A deficit in zinc availability can cause alterations in tubulin thiol redox status in cultured neurons and in the developing fetal rat brain

Zinc (Zn) deficiency during early development can result in multiple brain abnormalities and altered neuronal functions. In rats, a gestational deficit of Zn can affect the fetal brain cytoskeleton and signaling cascades involved in cellular processes that are central to brain development. In this paper, we tested the hypothesis that oxidative stress is involved in Zn deficiency-induced altered tubulin dynamics and the associated dysregulation of transcription factor NF-κB. For this purpose, we used two cell culture models (rat cortical neurons, human IMR-32 neuroblastoma cells) and an animal model of Zn deficiency. A low rate of in vitro tubulin polymerization, an increase in tubulin oligomers, and a higher protein cysteine oxidation were observed in the Zn-deficient neuronal cells and in gestation day 19 fetal brains obtained from dams fed marginal-Zn diets throughout pregnancy. These alterations could be prevented by treating the Zn-deficient cells with the reducing agent tris(2-carboxyethyl)phosphine or by the presence of N-acetylcysteine (NAC) and α-lipoic acid (LA). Consistent with the above, Zn deficiency-induced tubulin-mediated alterations in transcription factor NF-κB nuclear translocation were prevented by treating IMR-32 cells with LA and NAC. Binding of the NF-κB protein p50, dynein, and karyopherin α (components of the NF-κB transport complex) to β-tubulin as well as the expression of NF-κB-dependent genes (Bcl-2, cyclin D1, and c-myc) was also restored by the addition of LA and NAC to Zn-deficient cells. In conclusion, a deficit in Zn viability could affect early brain development through: (1) an induction of oxidative stress, (2) tubulin oxidation, (3) altered tubulin dynamics, and (4) deregulation of signals (e.g., NF-κB) involved in critical developmental events.

Effect of lanthanum addition on microstructure and corrosion behavior of Al-Sn-Bi anodes

Novel Al-Sn-Bi anodes with and without lanthanum (La) were prepared. To evaluate the corrosion properties of the anodes, constant current and dynamic loop tests were carried out to determine its efficiency and corrosion rate. Optical microscopy (OM), transmission electron microscopy (TEM) and energy spectrum analysis techniques were used to examine and analyze microstructure and corrosion behavior of the specimens. The result showed that the Al-Sn-Bi anodes with La additions revealed higher current efficiency and anticorrosion in artificial environment. Segregation phase of anodes with La additions got more homogenous than that without La additions. Its grains were fined and the amount of segregation Fe-phase was reduced.

Effects of rare earth La on the microstructure and melting property of (Ag-Cu28)-30Sn alloys prepared by mechanical alloying

To obtain novel intermediate temperature ahoy solders with a melting temperature of 400-600℃, nominal (Ag-Cu28)-30Sn alloys without or with a trace addition (0.5 or 1.0 wt.%) of rare earth (RE) element La were prepared by mechanical alloying. The aim of this research is to investigate the effects of the addition of La on the microstructures, alloying process and melting properties of (Ag-Cu28)-30Sn alloys. The results show that the addition of La produces no new phase. A trace amount of La addition can effectively refine the grain size, but the excessive addition of 1.0 wt.% La inhibits the alloying process. The influence of La on the melting temperatures of solder alloys is negligible. However, the trace addition of 0.5 wt.% La can distinctly reduce the fusion zone and improve the melting property of (Ag-Cu28)-30Sn alloys.

Effect of La addition on adhesive strength and fracture behavior of Sn–3.5Ag solder joints

This study investigates the effects of trace amounts of La addition on the microstructure, adhesive strength and fracture behavior of Sn–3.5Ag solder joints. The electron backscatter diffraction (EBSD) results confirmed that the face-centered cubic (fcc) structure of LaSn 3 compounds distributed randomly in the β-Sn matrix had no obvious preferred orientation. La additions reduced the ripening reaction rate of the scallop-type Cu 6Sn 5 compounds at the interface layer. In spite of the significant refinement of microstructure and suppression of the growth of intermetallic Cu 6Sn 5 compounds caused by the La additions, the expected enhancement of adhesive strength and ductility did not occur apparently. With the aid of Argon Beam Milling, we have found defects and voids inside the LaSn 3 compounds; these features were closely related to the crack initiation and formation during the adhesive tensile test. Consequently, the beneficial effect due to the refinement of microstructure and suppression of interfacial layer compounds was retarded. In the aged samples, trace amounts of La addition suppressed the Sn diffusion and retarded the growth of the Cu 6Sn 5 layer, but not that of the Cu 3Sn layer.

690合金と316Lステンレス鋼異材多層盛溶接部のミクロ割れ発生抑制に対するREM添加効果

The microcracking susceptibility in dissimilar multipass welds of alloy 690 to type 316L stainless steel was investigated by the Varestraint test and the multipass welding test using the four different stainless steels varying the amounts of impurity elements such as P and S, and using the nine different filler metals of alloy 690 varying the REM(La) content. In order to simulate the dissimilar weld metals, stainless steels were gas tungsten arc (GTA) welded using alloy 690 filler metals with varying the dilution ratio. Microcracks occurring in the reheated weld metals were classified into ductility dip, liquation and solidification cracks. The ductility dip cracking susceptibility decreased with increasing the La content in the weld metal, while the liquation and solidification cracking susceptibilities increased contrarily when the La content in the weld metal exceeded ∼0.02 mass%. The relation among the microcracking susceptibility, the (P+S) and La contents in every weld pass of the multipass welding was investigated. Ductility dip cracks occurred in the compositional range (atomic ratio) of La/(P+S)<0.13 and solidification/liquation cracks occurred in that of La/(P+S)>0.55, while any cracks did not occur at La/(P+S) being between 0.13-0.55. The ductility dip cracking susceptibility could be improved by adding La due to the scavenging of the impurity elements. The excessive La addition to the weld metal resulted in the solidification/liquation cracking alternatively attributed to the formation of Ni-La intermetallic compounds with low eutectic point. The optimal filler metal for the dissimilar multipass welding of alloy 690 to stainless steel was selected as La/(P+S) would be 0.13-0.55 for every weld pass.

Effect of Minor Similar Elements Substitution on Glass Forming Ability and Fragility of Al-Ni-based Amorphous Alloys

Compared with the Al84Ni10Ce6 alloy, the glass forming ability (GFA) of Al84Ni10(Ce3La3) was improved and the melt fragility was decreased through the method of La addition (similar to Ce element), which is in contrary to the conventional rules of dissimilar elements (large atomic size differences) addition. This phenomenon can be understood from the thermodynamics of decrease in ΔGl-x. Furthermore, the effects of other similar RE elements (Pr, Nd, Gd) substitution on GFA and different fragility parameters were investigated in Al84Ni10 (Ce3RE3) alloys, and it was found that smaller M corresponds to a better GFA in these alloys. In addition, it can be also confirmed that m could be just used in an individual alloy system which may attribute to the different formation mechanism of metallic glasses.

無粒界腐食型25Cr-35Ni系超高純度ステンレス鋼の高温割れ感受性

The hot cracking susceptibility of type 25Cr-35Ni extra high-purity stainless steels was evaluated by the transverse-Varestraint test with varying the contents of Cr as well as P and S. Two types of hot cracks occurred in these steels by Varestraint test; solidification and ductility-dip cracks. The solidification cracking susceptibility was reduced as the amount of Cr in steels increased, and 25Cr-35Ni stainless steel was negligibly susceptible to solidification cracking. On the other hand, the ductility-dip cracking susceptibility adversely increased with an increase in Cr content as well as P and S contents in steels. There was a good linear relationship between the compositional parameter of (P+1.22S) and the DTR, as well as between (P+1.19S) and the BTR in 25Cr-35Ni stainless steel welds. Accordingly, the quantitative influence of S to an increase in the ductility-dip as well as solidification cracking susceptibility was approx. 1.2 times as large as that of P. The amount of P+1.22S in steels should be limited to approx. 90ppm in order to obtain the sufficiently low ductility-dip cracking susceptibility in 25Cr-35Ni stainless steel welds. Numerical simulation of segregation behaviours of P and S revealed that they were segregated at the grain boundary in the ductility-dip temperature range during welding. Molecular orbital analysis suggested that ductility-dip cracking was attributed to the grain boundary embrittlement due to the grain boundary segregation of P and S. In order to further inhibit the ductility-dip cracking in 25Cr-35Ni extra high-purity stainless steel welds, the effect of La addition on hot cracking susceptibility was investigated. The solidification and ductility-dip cracking susceptibilities could be improved by adding 20-70ppmLa to the extra high-purity steel containing P and S of 6-8ppm. The ductility-dip cracking susceptibility was decreased as a result of the desegregation of P and S to grain boundaries due to the scavenging effect of La.

Highly stable, mesoporous mixed lanthanum–cerium oxides with tailored structure and reducibility

Pure and mixed lanthanum and cerium oxides were synthesized via a reverse microemulsion-templated route. This approach yields highly homogeneous and phase-stable mixed oxides with high surface areas across the entire range of La:Ce ratios from pure lanthana to pure ceria. Surprisingly, all mixed oxides show the fluorite crystal structure of ceria, even for lanthanum contents as high as 90%. Varying the La:Ce ratio not only allows tailoring of the oxide morphology (lattice parameter, pore structure, particle size, and surface area), but also results in a fine-tuning of the reducibility of the oxide which can be explained by the creation of oxygen vacancies in the ceria lattice upon La addition. Such finely controlled syntheses, which enable the formation of stable, homogeneous mixed oxides across the entire composition range, open the path towards functional tailoring of oxide materials, such as rational catalyst design via fine-tuning of redox activity.

Effect of Si, Pd and La additions on glass forming ability and thermal stability of Zr–Ni-based amorphous alloys

In the present paper, the influence of minor additions of Si, Pd and La with representative atomic sizes on glass forming ability (GFA) and thermal stability of Zr–Ni-based amorphous alloys has been investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The results show that minor additions of La, Pd and Si can improve GFA of Zr–Ni-based alloys and La exhibits the optimum effect on enhancing GFA. The efficient cluster packing model can well explain the correlation between atomic sizes of additional elements and GFA of amorphous alloys. In addition, the relationship of the atomic size between the additional element and Zr has a more important effect on GFA than that between the additional element and Ni. The activation energy for crystallization of the Zr–Ni-based amorphous alloys with Si, Pd and La additions is obviously higher than that of the Zr 66.7Ni 33.3 amorphous alloy, and increases with decreasing distance between neighboring atoms. The thermal stability has a relation with topological short-range ordering of amorphous alloys. The proper addition of small atoms is preferential to enhance thermal stability of amorphous alloys due to stronger short-range ordering. Moreover, the small or intermediate atom addition can produce even better effect on thermal stability than the large atom addition.

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

Twelve phosphomolybdate compounds were synthesized via cationic exchange and were of the form: M x H3–3x [PMo12O40] (M = Al, La or Ce; 0 ≤ x ≤ 1). These compounds were analyzed by XRD and adsorption isotherm. Aluminum addition causes a primitive cubic phase, while lanthanum and cerium yield body-centered structures. La and Ce addition reduces surface area of phosphomolybdate structure. Temperature-programmed experiments for the selective oxidation of isobutane yielded methacrolein, 3-methyl-2-oxetanone (lactone), acetic acid (not with aluminous compounds), propene (only with aluminous compounds), carbon dioxide and water. The preference for propene rather than acetic acid formation with Al3+ may be due to the smaller cation size, or primitive cubic structure. These products form via two distinct reaction processes, labeled categories 1 and 2. Category 1 formation is associated with isobutane forming products on the surface, but reaction rate determined by bulk migration of charged particles. Category 2 formation is concerned with isobutane penetrating deep within the bulk of the substrate and forming products which subsequently desorb in a series of bell-shaped humps. Methacrolein forms via both category 1 and 2, whilst all other products form via category 2 exclusively. Kinetic analysis showed apparent activation barriers for category 1 methacrolein formation range from 67 ± 2 kJ mol−1 to >350 kJ mol−1, and occur in groups with small, medium and large activation barriers. The addition of +3 metal cations to the phosphomolybdate anion increase thermal stability, significantly decreasing deactivation; IR spectroscopy shows that the Keggin structure remains intact during temperature-programmed experiments with the Al, La and Ce salts.

The impact of ruthenium, lanthanum and activation conditions on the methanation activity of alumina-supported cobalt catalysts

The influence of catalyst activation conditions and the presence of promoters (La, Ru) on the performance of γ-alumina-supported Co catalysts for the methanation reaction has been investigated. Physicochemical properties, Co crystallite size and the extent of Co 3O 4 reduction to metallic Co for both the monometallic and promoted catalysts were evaluated. Combined La and Ru addition produced the greatest activity improvement for converting carbon monoxide (CO) and hydrogen (H 2) to methane. Reduction conditions used to activate the catalyst were also found to have a direct influence on methanation activity. Maintaining the catalyst at 400 °C for 10 h during reduction enhanced catalyst activity, as well as increasing the H 2 concentration in the reducing gas stream. Characterisation of the reduced catalysts demonstrated that the extent of Co-oxide reduction to Co metal was the key to the improved methanation activity.

Effect of La addition on glass-forming ability and stability of mechanically alloyed Zr–Ni amorphous alloys

In this study, the role of La in the microstructural evolution of Zr66.7−xNi33.3Lax (x=1, 3, 5at.%) alloys during mechanical alloying has been investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results show that the single amorphous phase of Zr–Ni–La can be obtained through mechanical alloying. The minor La addition can improve the glass forming ability of Zr–Ni–La, enhance the mechanical stability of the amorphous phase against the mechanically induced crystallization and lead to an altered crystallization mode of Zr–Ni alloy. Moreover, the stability of the Zr–Ni–La amorphous phase decreases with further increasing La content. The best effect is obtained for the Zr65.7Ni33.3La1 alloy. Additionally, the effect of La addition in contrast with the small atomic size C addition plays a more significant role in promoting the stability of the amorphous phase. In addition, the reasons of La addition effect on GFA and stability have also been discussed from three factors of negative heat of mixing, distance between neighboring atoms and atomic size mismatch, respectively.

Effect of La Addition in W Skeleton on Microstructure and Properties of WCu Alloy

In order to improve properties of WCu alloy, the different La were introduced into W skeleton during sintering process. The hardness, electrical conductivity and the compression stress were tested, and the microstructure and composition were characterized by a scanning electron microscope. The results show that an appropriate rare earth La addition can purify W/W interface, enhance the bonding of W /W, and improve the densification and the integral properties of WCu alloy. In the range of experiments, WCu alloy with 0.3wt% La addition has the largest hardness value of 198HB and the maximum compression stress of 823N/mm2. In comparison with that without La addition, 0.3wt%La addition decreases the electrical conductivity slightly, but improves the hardness and the maximum compression stress significantly, which are increased by 23.6% and 57.2%, respectively.