La Addition Research Articles

Role of cerium, lanthanum, and strontium additions in an Al – Si – Mg (A356) alloy

Abstract The effects of individual and combined additions of cerium (Ce), lanthanum (La), and strontium (Sr) on the eutectic modification and solidification characteristics of an Al – Si – Mg (A356) aluminum alloy were investigated using optical microscopy and thermal analysis techniques. Addition of Ce, La, and Sr resulted in different depression levels of the eutectic nucleation temperature and eutectic growth undercooling, generating modified eutectic structures exhibiting different levels of modification. Microstructural results showed that the best modification levels using individual additions were achieved by Sr which produced a fine fibrous eutectic structure, followed by La, which produced a refined lamellar structure, with Ce providing the lowest level of modification. On the other hand, a combined addition of Ce and Sr provided the highest modification level, with the production of a very fine fibrous eutectic silicon structure. In general, the addition of Sr helped to further increase the refinement obtained in the alloys containing La or Ce + La additions. In the latter alloy, the main intermetallic phases observed were La(Al,Si)2 and Al20(La,Ce)Ti2Si. The improved modification levels were found to be proportional to the depression in the eutectic nucleation temperature and the eutectic growth undercooling. A high cooling rate also improved the modification level by at least one level.

Significance of Lupus Anticoagulant in Children with Prolonged Prothrombin Time/activated Partial Thromboplastin Time

Methods: This study included 66 subjects, who showed prolonged PT/aPTT on routine examination and screening test prior to an invasive procedure. LA was investigated in subjects with only PT prolongation, only aPTT prolongation, and PT/aPTT prolongation. The aPTT prolongation subjects were subdivided into more prolonged (≥60 sec) and less prolonged (39.6≤aPTT<60 sec). In addition, the sensitivity and specificity of LA in PT or aPTT prolongation was evaluated by ROC (receiver operating characteristics) curve.

Structure alterations in Al-Y-based metallic glasses with La and Ni addition

The atomic structures of Al89Y11, Al90Y6.5La3.5, and Al82.8Y6.07Ni8La3.13 metallic glasses have been studied by using high energy X-ray diffraction, X-ray absorption fine structure combined with the ab initio molecular dynamics and reverse Monte Carlo simulations. It is demonstrated that the partial replacement of Y atoms by La has limited improvement of the glass forming ability (GFA), although La atoms reduce the ordering around Y atoms and also the fractions of icosahedron-like polyhedra centered by Al atoms. In contrast, Ni atoms can significantly improve the GFA, which are inclined to locate in the shell of polyhedra centered by Al, Y, and La atoms, mainly forming Ni-centered icosahedron-like polyhedra to enhance the spatial connectivity between clusters and suppress the crystallization.

Influence of rare earths addition on residual stress of Fe-based coating prepared by brush plating technology

AbstractThe effect of rare earths (La, Ce and Pr) addition on residual stress in iron coatings prepared by brush plating was investigated. The results showed that the addition of rare earth transformed the residual stress in the coating from tensile to compressive. To relieve the residual stress, on the one hand, RE elements segregated at the grain boundaries which restricted the coalescence of the grains and provided more capability of grain deformation. On the other hand, RE elements could purify detrimental element and absorb hydrogen atoms in the coating. Among the three rare earths, elements lanthanum showed the most significant effect on surface morphology and residual stress.

Energy storage properties of (Bi0.5Na0.5)0.93Ba0.07TiO3 lead-free ceramics modified by La and Zr co-doping

Lead-free [(Bi0.5Na0.5)0.93Ba0.07]1-xLaxTi1-yZryO3 (BNBLTZ) ceramics were investigated for energy storage applications. In order to adjust its energy storage properties, the La and Zr co-doping contents varied at 0.01 ≤ x, y ≤ 0.04. BNBLTZ ceramics show a single phase perovskite structure without phase transition after La and Zr co-doping. The compact and uniform microstructure with similar grain morphology and different grain sizes is obtained. The remnant polarization and coercive field decrease with the increase of La and Zr additions, and the energy storage density increases drastically. The maximum energy storage density of 1.21 J/cm3 is obtained when x = 0.04 and y = 0.01. There are two dielectric anomalies at Tp and Tm due to the phase transformation. The results suggest that lead-free BNBLTZ ceramics should be good candidates for energy storage applications.

Effects of La intermetallics on the structure and tensile properties of thin section gravity die-cast A357 Al alloy

In current research different amounts of La (0.01, 0.03, 0.05, 0.07, 0.1, 0.3, 0.5 and 1wt.%) were added to A357 aluminum alloy to investigate the structure and tensile properties of thin section parts prepared by gravity die-casting. The cast specimens were examined by using optical microscopy (OM), scanning electron microscopy (SEM), tensile testing and determination of quality index values to evaluate the modification efficiency of the alloy by La addition. Obtained results revealed that La reduces the grain size of A357 alloy from 620μm to minimum 300μm and improves the morphology of eutectic silicon in as-cast condition. Al4La and AlSiLa intermetallic phases were detected through the microstructural studies. The optimum amount of La was found to be 0.1wt.% by enhancing ultimate tensile strength (UTS) of the alloy from 226MPa to 267MPa. Further improvement in tensile strength was achieved after T6 heat treatment for 0.1wt.% La added specimens, in which UTS showed the highest value (420MPa). The addition of 0.1wt.% La also increased El.% values from 3.8% to 6.8% in non-heat treated and from 6.2% to 9% in T6 heat treated alloys.

Effects of La and Ce Addition on the Modification of Al-Si Based Alloys

This study focuses on the effects of the addition of rare earth metals (mainly lanthanum and cerium) on the eutectic Si characteristics in Al-Si based alloys. Based on the solidification curves and microstructural examination of the corresponding alloys, it was found that addition of La or Ce increases the alloy melting temperature and the Al-Si eutectic temperature, with an Al-Si recalescence of 2-3°C, and the appearance of post-α-Al peaks attributed to precipitation of rare earth intermetallics. Addition of La or Ce to Al-(7–13)% Si causes only partial modification of the eutectic Si particles. Lanthanum has a high affinity to react with Sr, which weakens the modification efficiency of the latter. Cerium, however, has a high affinity for Ti, forming a large amount of sludge. Due to the large difference in the length of the eutectic Si particles in the same sample, the normal use of standard deviation in this case is meaningless.

Promotional role of La addition in the NO oxidation performance of a SmMn2O5 mullite catalyst

A series of LaxSm1−xMn2Oδ (x = 0, 0.1, 0.3, 0.5) catalysts were synthesized through a co-precipitation method. The catalytic activity for NO oxidation was enhanced with La substitution, and the maximum activity was achieved at x = 0.3.

Sudden transition from columnar to equiaxed grain of cast copper induced by rare earth microalloying

A sudden columnar-to-equiaxed transition (CET) of cast copper with rare earth (RE) microalloying has been examined. Some solidification parameters of Cu–La alloys were determined by using optical microscopy and differential scanning calorimetry, and simulation of temperature field in copper ingot solidification process. It is noted that the addition of RE microalloying can purify the alloy and make an interaction between equiaxed nucleation and constitutional undercooling, which results in a sudden CET. Furthermore, a new prediction model of the critical alloy composition condition for the CET induced by RE microalloying is established. The critical compositions of a sudden CET of cast copper with La addition is 0.14wt.%, which is in good agreement with the experimental results. It is suggested that increasing the alloy content is very necessary at a high gradient in order to promote the CET. However, the number N0 of effective nucleation sites should also be increased with the decrease of the alloy composition. Meanwhile, it can be found that the columnar region can be expanded with the increase of the temperature gradient. It is obvious that lowering temperature gradient contributes to promote the CET. The prediction model can also be used in the common CET very well.

Effects of the addition of lanthanum and ultrasonic stirring on the microstructure and mechanical properties of the in situ Mg2Si/Al composites

In this study, an in situ Mg2Si/Al composite was fabricated with the addition of lanthanum (La) combined with ultrasonic stirring at different powers during solidification. The composite exhibited simultaneously enhanced tensile strength and elongation because of the positive effects of La addition and ultrasonic stirring on microstructure. X-ray diffraction analysis, optical microscopy and scanning electron microscopy were used for the microstructural characterization. Hardness and tensile tests were used for the evaluation of the mechanical properties. The results indicated that the Mg2Si/Al composite with the addition of 0.4wt.% La combined with ultrasonic stirring at a power of 150W exhibited a unique combination of mechanical properties including a hardness of 132HB, a tensile strength of 201MPa, and an elongation of 5.28%; while the composite without La addition nor ultrasonic stirring exhibited a hardness 76HB, a tensile strength 84MPa and an elongation 2.02%. This study demonstrated that a minor La addition combined with 150W ultrasonic stirring is a promising approach in modifying the microstructure and enhancing the mechanical properties of the in situ Mg2Si/Al composite for industrial applications.

Effects of lanthanum and sodium on the structural, optical and hydrophilic properties of sol–gel derived ZnO films: A comparative study

The technological applications of the transparent ZnO films could be broadened via incorporation of small amounts of some special elements. In this work, the optical and surface properties of the spin coated Zn1−xMxO films (M=Na or La and x≤0.075) grown on glass substrates, are reported. According to X-ray diffraction (XRD) results, all films consist of a single phase with a hexagonal structure and the ZnO crystallites are preferentially oriented towards (002) direction. The plane surface of the pure ZnO film turned to be wrinkle network structure after Na and La addition. The reflectance (R%) of the films decreased after Na doping and significantly increased with increasing La content. The optical band gap of pure ZnO is 3.26eV and red-shifted after Na and La incorporation. The dependence of the refractive index and film's wettability on the structural and morphological changes are reported. The obtained results of these two systems are compared with those of similar materials and some expected applications are explored.

Effects of La Addition on Properties of Sr2Nb2O7 Thermoelectric Ceramics

Thermoelectric ceramics Sr2−x La x Nb2O7 prepared by a reaction-sintering process were investigated. Dense Sr2Nb2O7 (SNO) with 5.15 g/cm3 (97.9% of the theoretical density) was obtained after 1400°C/6 h sintering. Grain size decreased as La was substituted into SNO. Resistivity of SNO is 3.07 × 108 Ωcm at 200°C and decreased to 4.77 × 104 Ωcm at 700°C. The resistivity of Sr1.97La0.03Nb2O7 (SNL3) and Sr1.95La0.05Nb2O7 (SNL5) at 300–700°C, 2.19 × 106–2.29 × 108 Ωcm, are 1–2 orders higher than SNO. Activation energy E a for SNO was 0.7 eV. E a for SNL3 and SNL5 increased from 0.16 eV to 0.19 eV at 200–400°C to 0.72–0.74 eV at 400–700°C. The Seebeck coefficient for SNO was S = 26.93 μVK−1 at 200°C and S = 57.15 μVK−1 at 500°C. This implies that SNO is a p-type thermoelectric ceramic. S = –30.73 μVK−1 at 200°C and S = –60.75 μVK−1 at 500°C for Sr1.9La0.1Nb2O7 (SNL10). This implies Sr2−x La x Nb2O7 is an n-type thermoelectric ceramic. Power factors 7.17 × 10−9, 1.93 × 10−10, 1.11 × 10−10 and 2.61 × 10−10 μWcm−1 K−2 were obtained at 500°C for SNO, SNL3, SNL5 and SNL10, respectively.

Effect of Lanthanum Addition on Microstructure and Hardness as Cooling Rate Function of ADC12 Eutectic Cast Alloy

This paper presents the experimental investigation conducted on ADC12 cast alloy. The main objective of the research is to investigate the effect of 1.5%La addition with different cooling rate on microstructure and hardness value of ADC12 cast alloy. The Ceramic Mold with different thickness dimensions was use to obtained different cooling rate. The Si structure became modified by increase the cooling rate of base alloy. With La addition the Si size observed smaller area than base alloy when the cooling rate increases. In addition, the higher cooling rate and La addition improves the hardness specially at lower thickness with La addition.

Effect of Lanthanum Addition on Fluidity of Complex Al-11Si-Cu-Mg Cast Alloy

This research was to determine the effect of rare earth metal (REM) on the fluidity of eutectic Al-11Si-Cu-Mg cast alloy. The rare earth metal used here is Lanthanum to produce Al-11Si-Cu-Mg-0.1La, Al-11Si-Cu-Mg-0.5La and Al-11Si-Cu-Mg-1.0La alloys. The fluidity was measured by permanent spiral mold, pre-heated at 450°C. The microstructure was characterized by optical microscope. The fluidity of complex Al-11Si-Cu-Mg eutectic alloy decreased with the increase of La addition. The 1.0 % of La addition led to refinement of silica particles, which reduced the fluidity length by 25%.

Effects of rare earth La on microstructure and properties of Ag–21Cu–25Sn alloy ribbon prepared by melt spinning

Abstract Ag–21Cu–25Sn alloy ribbon as a promising intermediate temperature alloy solder (400–600 °C) was prepared by melt spinning technique in this paper. Rare earth La was added into Ag–21Cu–25Sn alloy to refine the microstructures and improve the wettabilities of as-prepared alloy solders. The phase constitutions, microstructures, melting temperatures and wettabilities of selected specimens were respectively tested. The results showed that the dominant phase constitutions of Ag–21Cu–25Sn– x La alloy ribbons were Ag 3 Sn and Cu 3 Sn. The grain size of Ag–21Cu–25Sn– x La alloy decreased with the addition of La increasing. La addition reduced the melting temperatures of Ag–21Cu–25Sn– x La alloy ribbons, and effectively improved the wettabilities of the alloy ribbons. When the addition of La was 0.5 wt%, the wettability of as-prepared alloy solder achieved the optimal value of 158 cm 2 g −1 under brazing temperature 600 °C and dwell time 15 min. In addition, raising brazing temperature and prolonging dwell time could improve the wettability of Ag–21Cu–25Sn– x La alloy ribbon.

Thermodynamic and structural basis for electrochemical response of Cu–Zr based metallic glass

Cu–Zr based metallic glasses were prepared by hyperquenching strategy to explore the thermodynamic and structural basis for electrochemical response. The thermodynamic parameters and the local atomic structure were obtained. Corrosion resistance in seawater was investigated via potentiodynamic polarization curve. The results indicate that increasing thermodynamic parameter values improves the corrosion resistance. The topological instability represented by the nearest neighbor atomic distance yields same tendency as the corrosion resistance with La addition.

Effects of La addition on the microstructure and tensile properties of Al-Si-Cu-Mg casting alloys

The effects of La addition on the microstructure and tensile properties of B-refined and Sr-modified Al-11Si-1.5Cu-0.3Mg casting alloys were investigated. With a trace addition of La (0.05wt%–0.1wt%), the mutual poisoning effect between B and Sr can be neutralized by the formation of LaB6 rather than SrB6. By employing a La/B weight ratio of 2:1, uniform microstructures, which are characterized by well refined α-Al grains and adequately modified eutectic Si particles as well as the incorporation of precipitated strengthening intermetallics, are obtained and lead to appreciable tensile properties with an ultimate tensile strength of 270 MPa and elongation of 5.8%.

Effect of La-substitution on the structure, dielectric and ferroelectric properties of Nb modified SrBi8Ti7O27 ceramics

The effect of La substitution on the electrical properties of SrLaxBi8−xTi6.88Nb0.12O27 intergrowth Aurivillius phase ferroelectric ceramic was investigated. La content ‘x’ was ranging from 0.0 to 1.0 in a step of 0.2. The ceramic phase was synthesized through a modified oxalate route. X-ray diffraction was used to identify the phase and to investigate the change in lattice parameter and microstrain with the substitution. La-substitution does not affect the crystal structure of the intergrowth. Microstructural investigation revealed that the grain size of the ceramic decreases with La addition. The lattice parameters and orthorhombicity of intergrowth structure were found to decrease with increasing La substitution. The temperature dependence of dielectric behavior was investigated in the temperature range 30–700°C and the frequency of 100kHz. The remnant polarization 2Pr increased and the Curie temperature Tc decreased with the increase in the La substitution.

Al2O3-based passive NOx adsorbers for low temperature applications

NOx storage on Pt/Al2O3 and Pt/La-Al2O3 in the temperature range 80–160°C was investigated by means of microreactor and in situ DRIFTS experiments, to ascertain their suitability for passive NOx adsorber applications. Addition of 1wt% La to Al2O3 resulted in the creation of new NOx storage sites and improved NOx storage efficiency. However, according to TPD measurements, Pt/La-Al2O3 exhibited slightly lower NOx desorption efficiency below 250°C than Pt/Al2O3. During repeated NOx adsorption–desorption cycles, almost no benefit of La addition was observed after five cycles, due to the inability to regenerate the strong NOx storage sites associated with the La at 250°C. DRIFTS measurements indicated that during NOx-TPD, nitrites and weakly bound nitrate species were initially removed from the surface of Pt/Al2O3 and Pt/La-Al2O3. NOx desorption at higher temperatures (>250°C) was mainly associated with nitrate decomposition. DRIFTS measurements on Pt/Al2O3 revealed that NOx was mainly stored on the Al2O3 surface when oxidized Pt was present, although when a reductive re-treatment was applied NOx storage on reduced Pt sites became significant and total NOx storage efficiency was improved. However, compared to bare Al2O3, NOx desorption efficiency below 250°C significantly dropped when Pt was present, and was even lower after pre-reduction in H2. Overall, the Pt-Al without pre-reduction showed the highest amount of NOx desorption below 250°C.

The Effect of La-intermetallic Compounds on Tensile Properties of Al-15%Mg2Si In-situ Composite

In this work, an attempt was made to examine the effect of different La-intermetallic on the microstructure and tensile properties of Al-15%Mg2Si metal matrix composite (MMC). The composite was made via in-situ process and characterized by optical microscope (OM), scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. Microstructural characterization revealed that La changes not only the morphology of primary Mg2Si particles from irregular to polyhedral and cubic shape. But also alter the eutectic Mg2Si phase from flakes to rods and the volume fraction of Mg2Si decreases while volume fraction of α-Al phase increases. La addition change the size of primary Mg2Si from (∼17μm) to (∼10μm) and the size of eutectic Mg2Si phase is reduced from more than 4.0μm to less than 0.5μm. This is mainly due to the formation of LaSi2 phase during solidification, as detected by XRD analysis. Further results revealed that as the amount of fine La-intermetallic is increased, ultimate tensile strength (UTS) and elongation values of the MMC were also significantly increased. The fracture study of the composite showed the La-intermetallic changes the mode of fracture from brittle to more ductile.