La Salt Research Articles

Ni–La coatings as electrocatalysts for hydrogen evolution reaction deposited from electrolytes based on a deep eutectic solvent

Ni–La electrocatalytic coatings were electrodeposited from electrolytes based on a eutectic mixture of choline chloride and ethylene glycol (the so-called deep eutectic solvent "ethaline") containing dissolved NiCl2 and LaCl3 salts. It was shown that in this case, nickel alloys containing up to approximately 1.75 wt.% lanthanum were formed. An increase in the cathodic current density and the content of La(III) salt in the solution contributed to a higher content of lanthanum in the electrodeposits. The presence of a lanthanum(III) salt in the electrolyte led to a noticeable leveling of the surface microprofile. The electrocatalytic activity of the deposited coatings towards the hydrogen evolution reaction was evaluated by linear voltammetry in an aqueous solution of 1 M NaOH at a temperature of 298 K. It was found that the polarization of hydrogen evolution decreased, and the exchange current density increased with an increase in the lanthanum content in the coating. For example, the calculated hydrogen evolution exchange current density is 4.2610–5 A cm–2 and 1.0310–3 A cm–2 for a lanthanum-free nickel deposit and a nickel-based coating containing 1.75 wt.% La, respectively. The increased electrocatalytic activity observed when lanthanum was introduced into the nickel matrix can be attributed to both the synergistic interaction of the nickel and lanthanum components of the alloy (as previously described, the catalytic effect resulting from the hypo-hyper-d-electron interaction of transition metals) and the presence of surface active sites with lanthanum in different oxidation states (La(III)/La(II)), which can serve as electron carriers. The significant electrocatalytic effect observed when nickel is doped with lanthanum during deposition from an electrolyte based on DES allows us to consider such electrode materials as very promising for use in the electrolytic synthesis of "green" hydrogen.

Behavioral and Lethal Effects of La Salt and a Mixture of Cu and La Salt on <i>Daphnia magna</i> Straus

Behavioral and Lethal Effects of La Salt and a Mixture of Cu and La Salt on <i>Daphnia magna</i> Straus

Modelling the Climate and Weather of a 2D Lagrangian-Averaged Euler\u2013Boussinesq Equation with Transport Noise

The prediction of climate change and its impact on extreme weather events is one of the great societal and intellectual challenges of our time. The first part of the problem is to make the distinction between weather and climate. The second part is to understand the dynamics of the fluctuations of the physical variables. The third part is to predict how the variances of the fluctuations are affected by statistical correlations in their fluctuating dynamics. This paper investigates a framework called LA SALT which can meet all three parts of the challenge for the problem of climate change. As a tractable example of this framework, we consider the Euler–Boussinesq (EB) equations for an incompressible stratified fluid flowing under gravity in a vertical plane with no other external forcing. All three parts of the problem are solved for this case. In fact, for this problem, the framework also delivers global well-posedness of the dynamics of the physical variables and closed dynamical equations for the moments of their fluctuations. Thus, in a well-posed mathematical setting, the framework developed in this paper shows that the mean field dynamics combines with an intricate array of correlations in the fluctuation dynamics to drive the evolution of the mean statistics. The results of the framework for 2D EB model analysis define its climate, as well as climate change, weather dynamics, and change of weather statistics, all in the context of a model system of SPDEs with unique global strong solutions.

Friction and Wear Behavior of Polyimide Composites Reinforced by Surface-Modified Poly-p-Phenylenebenzobisoxazole (PBO) Fibers in High Ambient Temperatures.

(1) In order to improve the properties of antifriction and wear resistance of polyimide (PI) composite under high temperature conditions, (2) 3-Aminopropyltriethoxysilane (APTES) and Lanthanum (La) salt modifications were employed to manufacture poly-p-phenylenebenzobisoxazole (PBO)/PI composites with different interface properties. The representative ambient temperatures of 130 and 260 °C were chosen to study the friction and wear behavior of composites with different interface properties. (3) Results revealed that while both modification methods can improve the chemical activity of the surface of PBO fibers, the La salt modification is more effective. The friction coefficient of all composites decreases with the increase of sliding velocity and load at two temperatures, and the specific wear rate is increases. Contrary to the situation in the 130 °C environment, the wear resistance of the unmodified composite in the 260 °C environment is greatly affected by the sliding velocity and load, while the modified composites are less affected. Under the same test parameters, the PBO–La/PI composite has the lowest specific wear rate and friction coefficient, and (4) La salt modification is a more effective approach to improve the properties of antifriction and wear resistance of PI composite than APTES modification in high ambient temperatures.

In-situ hydrodeoxygenation of phenol by supported Ni catalyst – explanation for catalyst performance

In-situ hydrodeoxygenation of phenol with aqueous hydrogen donor over supported Ni catalyst was investigated. The supported Ni catalysts exerted very poor performance, if formic acid was used as the hydrogen donor. Catalyst modification by loading K, Na, Mg or La salt could not make the catalyst performance improved. If gaseous hydrogen was used as the hydrogen source the activity of Ni/Al2O3 was pretty high. CO2 was found poisonous to the catalysis, due to the competitive adoption of phenol with CO2. If formic acid was replaced by methanol, the catalyst performance improved remarkably, with major products of cyclohexanone and cyclohexanol. The better effect of methanol enlightened the application of the supported Ni catalyst in in-situ hydrodeoxygenation of phenol.

Hydration and ion pair formation in common aqueous La(III) salt solutions--a Raman scattering and DFT study.

Raman spectra of aqueous lanthanum perchlorate, triflate (trifluorosulfonate), chloride and nitrate solutions were measured over a broad concentration (0.121-3.050 mol L(-1)) range at room temperature (23 °C). A very weak mode at 343 cm(-1) with a full width at half height at 49 cm(-1) in the isotropic spectrum suggests that the nona-aqua La(III) ion is thermodynamically stable in dilute perchlorate solutions (∼0.2 mol L(-1)) while in concentrated perchlorate solutions outer-sphere ion pairs and contact ion pairs are formed. The La(3+) nona-hydrate was also detected in a 1.2 mol L(-1) La(CF3SO3)3(aq). In lanthanum chloride solutions chloro-complex formation was detected over the measured concentration range from 0.5-3.050 mol L(-1). The chloro-complexes in LaCl3(aq) are fairly weak and disappear with dilution. At a concentration <0.1 mol L(-1) almost all complexes disappeared. In LaCl3 solutions, with additional HCl, a series of chloro-complexes of the type [La(OH2)(9-n)Cln](+3-n) (n = 1-3) were formed. The La(NO3)3(aq) spectra were compared with a spectrum of a 0.409 mol L(-1) NaNO3(aq) and it was concluded that in La(NO3)3(aq) over the concentration range from 0.121-1.844 mol L(-1), nitrato-complexes, [La(OH2)(9-n)(NO3)n](+3-n) (n = 1, 2) were formed. These nitrato-complexes are quite weak and disappear with dilution <0.01 mol L(-1). DFT geometry optimizations and frequency calculations are reported for a lanthanum-nona-hydrate with a polarizable dielectric continuum in order to take the solvent into account. The bond distances and angles for the cluster geometry of [La(OH2)9](3+) with the polarizable dielectric continuum are in good agreement with data from recent structural experimental measurements and high quality simulations. The DFT frequency of the La-O stretching mode at 328.2 cm(-1), is only slightly smaller than the experimental one.

Incorporation of Trinuclear Lanthanide(III) Hydroxo Bridged Clusters in Macrocyclic Frameworks

A cluster of lanthanide(III) or yttrium(III) ions, Ln3(μ3-OH)2, (Ln(III) = Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Yb(III), or Y(III)) can be bound in the center of a chiral macrocyclic amines H3L1(R), H3L1(S), and H3L2(S) obtained in a reduction of a 3 + 3 condensation product of (1R,2R)- or (1S,2S)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol or 2,6-diformyl-4-tertbutylphenol. X-ray crystal structures of the Nd(III), Sm(III), Gd(III), Dy(III), and Y(III) complexes reveal trinuclear complexes with Ln(III) ions bridged by the phenolate oxygen atoms of the macrocycle as well as by μ3-hydroxo bridges. In the case of the Nd(III) ion, another complex form can be obtained, whose X-ray crystal structure reveals two trinuclear macrocyclic units additionally bridged by hydroxide anions, corresponding to a [Ln3(μ3-OH)]2(μ2-OH)2 cluster encapsulated by two macrocycles. The formation of trinuclear complexes is confirmed additionally by (1)H NMR, electrospray ionization mass spectrometry (ESI MS), and elemental analyses. Titrations of free macrocycles with Sm(III) or Y(III) salts and KOH also indicate that a trinuclear complex is formed in solution. On the other hand, analogous titrations with La(III) salt indicate that this kind of complex is not formed even with the excess of La(III) salt. The magnetic data for the trinuclear Gd(III) indicate weak antiferromagnetic coupling (J = -0.17 cm(-1)) between the Gd(III) ions. For the trinuclear Dy(III) and Tb(III) complexes the χ(M)T vs T plots indicate a more complicated dependence, resulting from the combination of thermal depopulation of mJ sublevels, magnetic anisotropy, and possibly weak antiferromagnetic and ferromagnetic interactions.

Studies of the conversion coatings formed by combined use of lanthanum salt and benzotriazole on commercial brass

PurposeThe aim of this paper is to investigate the synergism effect between lanthanum salt (La(NO3)3) and benzotriazole (BTAH) on the corrosion inhibition of commercial brass and to further study the inhibition mechanism.Design/methodology/approachPotentiodynamic polarization curves were carried out on bare brass and brass treated with additions of optimum concentration of BTAH, La salt and La salt+BTAH to the basal deposition solutions in 3.5 wt. percent sodium chloride solution. The inhibition mechanism of the composite conversion coatings on brass obtained in optimal deposition techniques were investigated by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X‐ray diffraction (XRD), and FT‐IR reflection spectra.FindingsA “Critical La(NO3)3 content” and “Critical BTAH content” were both observed, at which the coatings prepared performs the highest protectiveness, and La(NO3)3 and BTAH had an excellent synergism effect on the corrosion inhibition of brass. The corrosion mechanisms for uncoated and coated brass are different. A remarkable enhancement of the brass's corrosion protection was obtained by the formation of composite conversion coatings consisted of Cu(I)BTA and La coordinate thing except for Cu2O and La2O3, which acted as a barrier avoiding the release of metal ions and inhibited the diffusion of the oxygen.Originality/valueThe results from this paper showed that La(NO3)3 and BTAH could be used together to prepare the novel composited conversion coatings on commercial brass for the good corrosion inhibition.

Effect of surface modification of poly-p-phenylenebenzobisoxazole fiber with lanthanum salt on flexural and tribological properties of composite with polyimide

The effect of lanthanum (La) salt on surface treatment of poly-p-phenylenebenzobisoxazole (PBO) fiber on flexural and tribological properties of PBO fibers reinforced polyimide (PI) composites was investigated. Experimental results revealed that flexural strength and modulus were largely improved by La salt treatment. The La salt treated composite had lower friction coefficient and specific wear rate than that of untreated one under the same testing condition. The principle of improvement in interfacial adhesion between PBO fiber and PI matrix after La salt treatment was discussed. The surface characteristics of PBO fibers were characterized by X-ray photoelectron spectroscopy. It was found that the content of polar groups on the surface of PBO fiber treated by La salt increased compared with the untreated fiber. The increase in the amount of polar groups strengthened the interfacial adhesion between PBO fibers and PI matrix, and accordingly enhanced the flexural and tribological properties.

Enhanced corrosion resistance of A3xx.x/SiCp composites in chloride media by La surface treatments

The influence of silicon carbide particles (SiCp) proportion and matrix composition of aluminium metal matrix composites (A3xx.x/SiCp) modified by lanthanum-based conversion or electrolysis coating was evaluated in 3.5 wt% NaCl aerated solution. The intermetallic compounds were preferentially covered by lanthanum-based conversion coatings obtained by immersion in 50 °C solution of La(III) salt, and the intermetallic compounds, SiCp and aluminium matrix were covered by lanthanum electrolysis treatment. The corrosion process was studied on the basis of gravimetric tests and electrochemical impedance spectroscopy (EIS) during immersion in 3.5 wt% NaCl aerated solution. The composition of both La coating and corrosion products was analyzed before and after accelerated testing, by scanning electron microscopy (SEM), atomic force microscopy (AFM), low-angle X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to determine the influence of surface microstructural changes on corrosion behaviour during exposure to the corrosive environment. The corrosion process was more influenced by the concentration of alloy elements in the matrix than by the proportion of SiCp reinforcement. Both lanthanum treated surfaces presented better behaviour to chloride solution corrosion than original composite surfaces without treatment; however, electrolysis afforded a higher degree of protection than the conversion treatment because the coating was more extensive.

Effect of La surface treatments on corrosion resistance of A3 xx. x/SiC p composites in salt fog

The influence of the SiC p proportion and the matrix concentration of four aluminium metal matrix composites (A360/SiC/10p, A360/SiC/20p, A380/SiC/10p, A380/SiC/20p) modified by lanthanum-based conversion or electrolysis coating was evaluated in neutral salt fog according to ASTM B 117. Lanthanum-based conversion coatings were obtained by immersion in 50 °C solution of La(III) salt and lanthanum electrolysis treatments were performed in ethylene glycol mono-butyl ether solution. These treatments preferentially covered cathodic areas such as intermetallic compounds, Si eutectic and SiC p. The kinetic of the corrosion process was studied on the basis of gravimetric tests. Both coating microstructure and nature of corrosion products were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDS) and low angle X-ray diffraction (XRD) before and after accelerated testing to determine the influence of microstructural changes on corrosion behaviour during exposure to the corrosive environment. The corrosion process was more influenced by the concentration of alloy elements in the matrix than by the proportion of SiC p reinforcement. Both conversion and electrolysis surface treatments improved the behaviour to salt fog corrosion in comparison with original composites without treatment. Additionally, electrolysis provided a higher degree of protection than the conversion treatment because the coating was more extensive.

Group 3 metal (Sc, La) triflates as catalysts for the carbomethoxylation of aliphatic amines with dimethylcarbonate under mild conditions

The activity of Sc(OTf) 3 and La(OTf) 3 (OTf=SO 3CF 3) as catalysts for the phosgene-free synthesis of carbamate esters via carbomethoxylation of aliphatic amines with dimethylcarbonate (DMC) has been investigated. In the presence of M(OTf) 3 (M=Sc, La), primary and secondary aliphatic amines easily react with dimethylcarbonate, under very mild conditions (20 °C), to afford carbamate esters with good yield and excellent selectivity (≌100%). Sc(OTf) 3 is a more effective catalyst than the homologue La salt. The carbomethoxylation reaction requires as strict anhydrous conditions, as, at 20 °C, the presence of water inhibits markedly the catalytic activity of both triflate salts. Temperature influences carbamate selectivity, which is lower at higher temperature because of deleterious formation of N-methylation side-products.

Elucidation of reaction process between solid tricalcium silicate and a lanthanum salt solution in connection with the precipitation pH. Extension to other elements

Dissolution of tricalcium silicate is strongly accelerated in a La salt solution and releases the amounts of OH, Ca and silicate ions just required to precipitate all of lanthanum at pH 8. It remained to be proved that (1) La silicate hydrate could form at pH 8, and (2) Ca silicate hydrate could not precipitate simultaneously. The plot of silicate hydrate and hydroxide precipitation pH of La, Ca and other elements (Th, Zr) against the dropped volume of K 2SiO 3 and KOH solution and some physico-chemical characterization methods bring affirmative answers to these questions and allow the immobilization process of La and other elements in the presence of tricalcium silicate to be better understood.

The addition of hydroxyl compounds to unsaturated carboxylic acids homogeneously catalysed by lanthanide(III)

La(III) is a good catalyst for the addition of hydroxyl compounds to unsaturated carboxylic acids, yielding etherpolycarboxylates. The La(III) can be applied as the chloride, the alkoxide, or the oxide. In the latter case in situ conversion to the La(III) salt of the unsaturated carboxylic acid is required. Lanthanum alkoxides, which combine the activation of the reactants by La(III) with a high basicity of the solution, give the highest addition reaction rates. The addition of ethylene glycol to acetylenedicarboxylate yields the dioxolane 12 upon removal of La(III). 13C and 17O NMR prove that the production of this ketalised oxaloacetate proceeds via two intermediates, namely the monoadduct 10 and the diadduct 11, of which the latter only exists as a La(III)-complex. The addition of glycerol to 8 yields a mixture of two dioxolanes 15 and 16 in a molar ratio of about 2:5, which indicates that the cyclisation is thermodynamically controlled.

N-pyridoxylidenehydrazine-N',N'-diacetic acid. III. Formation of metal chelates in solution.

Metal chelate formation of N-pyridoxylidenehydrazine-N ', N '-diacetic acid (1) and related hydrazines in solution was studied by means of absorption spectroscopy. Compound 1 and N-pyridoxylidene-N'-methylhydrazine (2) in methanol formed Cu (II) chelates of the same spectral character, which indicated the chelation of the phenolate oxygen and the hydrazine nitrogen atoms to Cu (II). The compositions of the chelates were 1 : 1 for 1 and 1 : 2 for 2, indicating that 1 acts as a tri- or tetradentate ligand. N- (3-Hydroxy-4-pyridylmethylene) hydrazine-N', N'-diacetic acid formed a Cu (II) chelate similar to that of 1 but N-pyridoxylidene-N', N'-dimethylhydrazine and N-pyridoxylidene-N', N'-diphenylhydrazine did not form chelates under similar conditions. Addition of an equimolar or excess amount of Co (II), Ni (II), Zn (II), Cd (II) or La (III) salt to 1 in methanol gave rise to absorption assignable to the chelate of 1, whereas 2 did not form metal chelates under the same conditions. It was concluded that the iminodiacetic acid moiety of 1 coordinated to the metal ions and enhanced the stability constant of the metal chelates.