Addition Of Lanthanum Oxide Research Articles

Unlocking the secrets of colored glass: Structural-optical behaviors and non-linear optical properties of [formula omitted] and [formula omitted] ions-doped borates

Investigations of structural-optical properties were performed for La3+-doped borate glass host based on a fixed ratio of Fe3+ ions, and within a lanthanum oxide concentration range of (0–8 mol%). The density was measured and confirmed the increase in bond density of the network, with increasing its volume. While infrared spectroscopy was carried out to investigate the dominant role of lanthanum on structural variations of glass, for example, the BO3 to BO4 conversion and the conspicuous decrease in NBO content. Optically, the d-d visible transitions of Fe3+ ions were suppressed by La3+ quenchers, preventing their peaking within the optical absorption spectra of glass samples. Further, in good coalescence with density and infrared spectroscopy results, Tauc gap energy increased with lanthanum oxide addition owing to the band structure modulations. Additionally, the metallization criterion changed from 0.262 (eV)0.5 to 0.325 (eV)0.5, owing to the Tauc gap energy increment, indicating that the lanthanum addition causes a shift toward the semiconducting nature of the prepared samples. On the other hand, Urbach energy decreased with increasing lanthanum oxide content, manifesting the glass structure's propensity toward less disorder and high polymerization. Besides, the increase in electron-phonon interaction energy indicates a high possibility of phonon consumption to bind free electrons as pairs, mitigating the network disorder. Surprisingly, the non-linear optical properties of the glass matrix were enhanced through lanthanum oxide addition. For the current glass host activated by La3+ ions, including Fe3+ color centers, the correlation between these above-mentioned structural modifications, and optical findings provide a decent paradigm for the optics realm.

Study of effect of lanthanum oxide on kinetics, morphology and properties of borated layers obtained by liquid method on different carbon content steels

Studies were carried out of the structure and properties of borated layers obtained on steels with different carbon contents by liquid electrolysis-free boriding in a melt with the addition of lanthanum oxide. It has been shown that the presence of lanthanum oxide additives makes it possible to increase the depth and reduce the microhardness values of borated layers. The microhardness values of the boride layers were 1650—1750 HV0,1, the microhardness values of the transition layer were about 650—750 HV0,1. Electron microscopy studies have revealed that lanthanum oxide additives can affect the morphology of borated layers. The energy dispersive analysis and the distribution maps of alloying elements showed that some of the alloying elements are concentrated in the transition layer.

Coalescing of lanthanum oxide and PPy @graphitic carbon nitride to achieve ultrahigh energy density electrode material for supercapacitors applications

Faster charging and discharging rate and long cycle life make supercapacitors compatible for energy storage devices. However, supercapacitors' poor energy density prevents them from replacing batteries. This study reports a facile method of synthesizing PPy/g-C3N4/La2O3 (LGP) nanocomposite electrodes via in-situ polymerization by varying the lanthanum oxide concentration. The electrochemical application of synthesized nanocomposites was performed in 1 M H2SO4 by cyclic voltammetry (CV), Galvanostatic Charge Discharge (GCD) and electrochemical impedance spectroscopy (EIS). It was observed that the addition of lanthanum oxide has a synergistic effect on already reported PPy/g-C3N4 composite resulting in a specific capacitance of 1763.56 F g−1 at 10 mV s−1 with ultrahigh energy density of 198.18 W h kg−1 and power density of 450.01 W kg−1 at a current density of 1 A g−1 for 0.4 LGP. From EIS studies, the solution resistance was 1.53 ohm and the charge transfer resistance was 0.50 ohm for PPy, while for 0.4 LGP it was 1.00 ohm and 0.23 ohm respectively. Additionally, the capacitance of 0.4 LGP composite increased to 131% after 10,000 cycles showing the enhanced cyclic stability of electrode material in 1 M H2SO4 electrolyte demonstrating its capability as an electrode material for future supercapacitors.

Effect of Lanthanum Oxide on the Activity Ni-Co/Diatomite Catalysts in Dry Reforming of Methane

The effect of modifying additive (La2О3) on the activity of Ni-Co oxides was studied for the dry reforming of methane (DRM). The catalysts were prepared by impregnation of the granulated diatomite (D) and characterized by SEM, EDX, H2-TPR, XRD, and AES. It is shown that the addition of 1.5 wt.% La2O3 into the Ni-Co/D composition leads to an increase in the activity of the catalyst, providing a methane conversion that is close under thermodynamic equilibrium conditions in the temperature range of 700‒850 °С. The highest activity is achieved at T = 850 °C, the conversion of methane is 96%, and carbon dioxide is 92%. The addition of lanthanum oxide to the Ni-Co/D composition led to an increase in catalyst stability; after testing in the DRM reaction for 360 min, the deactivation coefficient for methane was 3.4%, and for carbon dioxide 2.5%. While significant deactivation is observed for Ni-Co/D, the deactivation coefficient for methane is 19%, and for carbon dioxide 36%. Many characterization results (SEM, H2-TPR, and XRD) confirm that Ni-Co-La/D has abundant surface oxygen and the presence of spinel structures that contribute to the reactivity of CH4 and CO2, which positively affect its activity.

Effect of Lanthanum Oxide Addition on Microstructure and Wear Performance of Iron-Chromium Alloy Manufactured by Laser Direct Deposition Additive Manufacturing.

Additive Manufacturing (AM) has become increasingly common, and its use in various industries is increasing. However, the microstructure, friction and wear performance of metals made by AM, such as the inexpensive and relatively good-performing iron-chromium alloys, require further investigation. Generally, adding rare earth elements can effectively improve the performance of AM alloys, such as tensile strength, wear resistance, corrosion resistance, creep resistance, etc. This work aims to study the variation of microstructure, friction and wear properties of laser additive manufacturing processed iron-chromium alloys after adding different mass fractions of La2O3. The observations obtained by scanning electron microscopy showed that, with the addition of La2O3, the microstructure of AM alloy becomes more uniform and the grains are significantly refined. It is found by friction test that the running-in period is significantly shortened after the addition of La2O3. The coefficient of friction is reduced to a minimum of 0.68. Compared with AM alloys without La2O3, the wear rate of AM alloys with La2O3 is significantly reduced, with a maximum reduction of 38%. Using an optical microscope to observe the surface morphology of the wear scar, it is found that, after adding rare earth oxide, the wear mechanisms changed from adhesive wear and abrasive wear to abrasive wear, with the spalling of hard particles at the same time.

Effect of lanthanum oxide addition on physical, electrical and dielectric properties in lithium borosilicate glasses

In the present study, lanthanum oxide doped lithium borosilicate glasses were synthesized using standard melt-quenching technique. The synthesized glass materials were characterized by XRD, FTIR, density calculation, Electrical and dielectric properties measurements. The amorphous nature of the studied glasses was established through XRD spectra. FTIR spectra were used to investigate the different functional groups. Improvements in density and molar volume values were reported as the La2O3 content increased, it can be attributed to higher molecular weight of La2O3. Numerous other physical parameters such as lanthanum ion concentration (N), inter-nuclear distance (ri), polaron radius (rp), and field intensity (F) were determined using density values and are discussed in detail here. Electrical conductivity and dielectric measurements were carried out by impedance spectroscopy. The dynamical processes taking place in the glass system was studied by introducing conductivity and composition scaling. The dielectric constant (ε’) and dielectric loss (Tan δ) with frequency at various temperatures are extensively explored. There is a fairly good correlation among the physical parameters, FTIR, electrical conductivity and dielectric properties for the glasses studied in the present work.

HIGH-FREQUENCY ELECTROMAGNETIC PROPERTIES OF BOROSILICATE GLASSESWITH ADDITIVES OF La2O3, TiO2, ZrO2

The results of studies of high-frequency electromagnetic properties of alkaline borosilicate glasses modified with lanthanum, titanium, and zirconium oxides concerning their structure are presented. The values of the spectral reflection and transmission coefficients are experimentally measured in the frequency range 12–18 GHz. The article presents typical spectra of the complex dielectric constant of the studied glass samples inthe range of 20 Hz–1 MHz, according to which both the real and imaginary parts decrease with increasing frequency, while the imaginary part decreases much faster. It is shown that the studied glasses can be used as a vacuum-tight dielectric base with low losses in the development of high-frequency devices operating in the microwave range. The influence of the chemical composition of the experimental glasses on the value of their dielectric permittivity in the frequency ranges of 20 Hz –1 MHz and 12–18 GHzis established. The structure of the studied glasses was studied by Raman spectroscopy. The influence of lanthanum, titanium, and zirconium oxides on the degree of polymerization of the structural framework was revealed. The presence of La2O3in sodium borosilicate glass causes a decrease in the polymeriza-tion of the borosilicon-oxygen framework of glass in the entire range of introduced concentrations since La2O3is in the octahedral position and acts as a modifier in the glass structure. The intro-ductionof zirconium oxide into the composition of sodium borosilicate glass has a more significant effect on the depolymerization of the glass structure than the addition of lanthanum oxide. The most serious structural changes are observed when TiO2is introduced into the compositions of such glasses, since it acts as a glass–forming agent, forming structural motifs [TiO4], which will combine with the silicon–oxygen component, forming Si–O–Ti type bridges.

Optical properties of new zirconia-based dental ceramics: literature review

The first generation of polycrystalline zirconia-based ceramic used to produce dental prosthesis showed excellent mechanical behavior; however, its low translucency limited the indication for aesthetic monolithic restorations. Thus, various strategies have been tested in order to develop a material that has high strength and good optical properties. The aim of this study was to characterize, through a literature review, the translucency of different types of zirconia-based ceramics indicated for monolithic restorations. The literature search was performed in PubMed/Medline database, from 2010 to 2019, using as keywords: zirconia, translucency, and optical properties. The 3rd (monochromatic) and 4th (multichromatic) generations of zirconia, which have high cubic phase content, showed the highest translucency among the zirconia-based ceramics investigated. Additionally, other strategies, such as the addition of lanthanum oxide and the infiltration of feldspathic glass in the zirconia surface (graded-zirconia), resulted in a good balance of optical and mechanical properties.

Synergistic Effects of Bimetallic AuPd and La2O3 in the Catalytic Reduction of NO with CO

Bimetallic AuPd nanoparticles supported on TiO2 are known to catalyze the reduction of NO with CO. Here, we investigated the effects of the addition of lanthanum oxide to a AuPd/TiO2 catalyst with a AuPd particle size of 2.1–2.2 nm. The addition of La2O3 enhanced the catalytic activity; for example, at 250 °C, there was 40.9% NO conversion and 49.3% N2-selectivity for AuPd/TiO2, and 100% NO conversion and 100% N2-selectivity for AuPd-La (1:1)/TiO2. The temperature requiring 100% NO conversion dropped from 400 °C to 200 °C by the simple post-impregnation of La2O3 onto AuPd/TiO2. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with modulation excitation spectroscopy (MES) demonstrated that CO adsorption occurs first on Au atoms and then, within 80 s, moves onto Pd atoms. This transformation between two adsorption sites was facilitated by the addition of La2O3.

Zr-rich basalt continuous fibers with increased alkali resistant properties

Zirconium-rich basalt continuous fibers with zirconium oxide content from 5.1 to 8.1 wt% with the addition of 1% lanthanum oxide were obtained in a laboratory facility. The production temperature range were measured. It was shown that lanthanum oxide addition allows to decrease production temperature by 50° and to make wider the production temperature range by 10°. Weight loss and tensile strength loss of fibers after refluxing in alkali solution were determined. The weight loss after boiling in 1 M NaOH and 0.5 M Na2CO3 solution is comparable to the weight loss of zirconium-rich glass fibers (AR glass). The addition of lanthanum oxide leads to an increase in the tensile strength of Zr-rich basalt continuous fibers by 15–20%. Based on the obtained data, it can be concluded that the presented approach will not only improve the alkali resistance of basalt continuous fibers for reinforcing cements and concretes, but also significantly reduce their cost.

Additive manufacturing of high-strength commercially pure titanium through lanthanum oxide addition

Preventing the formation of columnar grains and refining the microstructure in an effective way have been great challenges in additive manufacturing of titanium and its alloys. In this paper, the effect of La2O3 addition on the microstructure and mechanical properties of commercially pure titanium (CP-Ti) fabricated through selective laser melting (SLM) was comprehensively studied. Experimental results revealed that the microstructure of CP-Ti were composed of massive phase and fine parallel laths, whereas a homogenous microstructure with acicular colonies was obtained in CP-Ti + La2O3. Due to the increase of nucleation sites in SLM-fabricated CP-Ti + La2O3, the massive phase transformation was suppressed, and the average grain size was refined to 1.47 μm. The spherical La2O3 particles with the size of less than 50 nm were uniformly distributed within the αˊ matrix, containing high-density dislocations and twins. After grain refinement, the yield strength and ultimate tensile strength were enhanced up to 858 MPa and 940 MPa, respectively, with the elongation of 8.6%. The enhancement of mechanical properties was mainly attributed to the combined effects of grain refinement strengthening, dislocation strengthening and La2O3 dispersion strengthening.

Research of both γ‐irradiation and La2O3 addition on structural and magnetoresistivity of Bi‐2223 bulk superconductors

AbstractIn this study, we investigate the effects of both gamma irradiation and the addition of lanthanum oxide (La2O3) on the Bi1.85Pb0.35Sr2Ca2Cu3Oy (Bi‐2223) bulk superconductors. Pure and lanthanum‐added samples prepared by the solid‐state reaction method were analyzed before and after gamma irradiation using various methods such as X‐ray powder diffraction (XRD), the temperature dependence of resistivity under magnetic field (ρ‐T). Bi‐2223 + x La2O3 samples with x = 0.0, 1.0 and 5.0 wt% were fabricated. The synthesized samples were then subjected to gamma irradiation at different intensities, and the effects of radiation on the structural, electrical, and magnetic properties of the materials were examined. For this purpose, Bi‐2223 superconductors in the form of discs were produced and cut into two pieces. One piece was exposed to gamma radiation under high vacuum conditions. The phase analyzes of the materials were carried out by XRD. Then, electrical analysis of the materials was made by measuring resistance under a magnetic field.

Fabrication and characterizations of holmium oxide based magneto-optical ceramics

A significant improvement in the sintering of Ho2O3 powders obtained by self-propagating high-temperature synthesis as a result of the addition of lanthanum oxide was made. It was found that the addition of 5% lanthanum oxide slightly affects the Verdet constant value (which is ~1.3 times higher than the corresponding value for terbium-gallium garnet, and is similar to the value for terbium-aluminum garnet ceramics), but significantly increases the transparency of ceramics. Samples of 5% La:Ho2O3 magneto-optical ceramics with a transmission of up to 76% at a wavelength of 1 μm at a thickness of 1 mm were obtained. Such La:Ho2O3 ceramics have transparency windows in the ranges of 0.93–1.06, 1.3–1.6 and 2.2–7 μm, what distinguishes them from materials containing Tb3+ ions, that are opaque in these ranges. It is shown that La:Ho2O3 ceramics have relatively high mechanical characteristics (HV = 8.4 GPa, E = 182 GPa, KIC = 0.95 MPa m0.5) which vary slightly depending on the lanthanum oxide concentration.

Microstructure and improved mechanical properties of Mo–12Si–8.5B alloys with lanthanum oxide addition

Mo–12Si–8.5B alloys with different La2O3 contents were fabricated by mechanical alloying and then hot pressing. The effects of La2O3 on microstructure, room and elevated temperature mechanical properties of Mo–12Si–8.5B alloys were studied. The microstructure of Mo–12Si–8.5B alloy with La2O3 additions exhibits a continuous α-Mo matrix, where the spherical Mo3Si and Mo5SiB2 intermetallic phases are distributed inside the grains and along the grain boundaries. The detailed microstructure shows that some nanoscale La2O3 particles are dispersed mainly in the α-Mo grains and partially in the intermetallics. These La2O3 particles can refine the grain sizes of α-Mo matrix and intermetallic, but the refining effect is limited with the La2O3 addition further increasing. The mechanical testing results show that the La2O3 addition simultaneously improves the compression strength and fracture toughness of Mo–12Si–8.5B alloy, due to that the α-Mo matrix is strengthened and toughened at ambient temperature and intermetallics are strengthened at elevated temperatures. The enhancing effect is sensitive to the amount of La2O3 additions, and the Mo–12Si–8.5B alloy can obtain a better combination of strength and toughness when the content of La2O3 is 0.9 wt%.

Investigation of the effect of lanthanum oxide on the thermal stability of alumina aerogel

Monolithic alumina aerogels were prepared with inorganic aluminum salts as raw material by epoxide-assisted sol–gel method. The structure and morphology of the monolithic alumina aerogels doped with different lanthanum oxide concentration were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption–desorption method and field emission scanning electron microscope. The results indicate that the pure alumina aerogel is translucent and sky blue in color. Alumina aerogels gradually changes into opaque blocks of ivory with increasing the amount of lanthanum oxide. The addition of lanthanum oxide can increase the specific surface area of alumina aerogels and improve their thermal stability at high calcination temperature. After calcination at 1000 °C for 2 h, alumina aerogel doped with 10 wt% lanthanum oxide is still amorphous phase and its specific surface area can reach 282 m2/g, which is much higher than pure alumina aerogel.

Steam and steam-oxygen reforming of methane on NiAl2O3–MxOy (M: La, Ce) based monoliths: effects of catalyst and reaction mixture composition

The effect of rare earth oxides as modifying additives within Ni–MxOy–Al2O3 (M: La, Ce) based catalysts, supported on cordierite monoliths, and the influence of the H2O/CH4 ratio as well as O2 content in the gas reaction mixture on the catalyst activity and selectivity in the steam and steam-oxygen reforming of methane are studied including by means of infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and quasi-equilibrium thermal desorption of ammonia as a probe molecule. The introduction of CeO2 and La2O3 into the catalyst composition as well as oxygen to the reaction mixture of methane steam reforming is shown to enable reducing the water vapor content (up to H2O/CH4 ratios close to stoichiometric) required for stable catalyst operation while maintaining high CH4 conversions and hydrogen yields. The carbon dioxide amount as a by-product in the syngas produced considerably decreases in the presence of Ni–CeO2–Al2O3/cordierite catalysts, which may be explained by slowing the water–gas shift reaction. The introduction of ceria into the catalyst composition leads to a slight decrease in the total number of Lewis acid sites (LAS), whereas the addition of lanthanum oxide causes their increase, which we attribute to formation of two LAS types on the surface of Ni–Al2O3–La2O3/cordierite: lanthanum cations and aluminum ones.

Promoter effect of La2O3 on gold catalyst with different textural structures

Silica supported gold nanoparticles were synthesized and promoted by lanthanum oxide as dopant. The influences of La2O3 and silica textural structure on the gold dispersion, formation of active species, crystalline composition and the reacting role of dopants were studied in detail. The characterization results suggested that the dispersion of gold nanoparticles depended on the textural structure of silica without lanthanum oxide doping where small mesopores are more preferable to disperse gold nanoparticles. The addition of lanthanum oxide largely increased the dispersion of gold nanoparticles and oxygen active sites independent of the textural structure of silica support. The interaction between lanthanum oxide and silica enhanced by the synergy facilitated the release of oxygen vacancies and transition of active oxygen species. In addition, the chemical properties were greatly changed after lanthanum oxide addition which was only inconspicuously impacted by the initial textural structure of silica supports, shedding light on the further design of economic gold catalyst based on simple synthesis method.

Photocatalytic Removal of 2,4-D Herbicide on Lanthanum Oxide-Modified Titanium Dioxide

Titanium dioxide (TiO2) has been recognized as an active photocatalyst for degradation of various organic pollutants. In this study, in order to improve the photocatalytic activity of TiO2, the effect of lanthanum oxide modification was investigated by using commercial P25 as the benchmark. Lanthanum oxide/P25 TiO2 composites with 0.1, 0.5, 1 and 5 mol% of La loadings were prepared via an impregnation method. The resultant composites were characterized by X-ray diffraction (XRD), UV-Vis absorption spectroscopy, transmission electron microscopy (TEM), inductively coupled plasma optical emission spectrometry (ICP-OES) and electrochemical impedance spectroscopy (EIS). It was confirmed that the addition of lanthanum oxide did not much affect the crystallinity, crystal structure and the morphology of P25 TiO2. The catalytic activities of the lanthanum oxide/P25 TiO2 catalysts were tested by using 2,4-dichlorophenoxyacetic acid (2,4-D) as the test pollutant and UV light as the irradiation source. The reaction was caried out for 1 hour at room temperature and the percentage removal was determined using a UV spectrophotometer. The results showed that La loading was an important factor that influenced the photocatalytic activity of the composites. After 1 hour reaction, the best catalyst with 0.1 mol% of La loading showed 24% higher photocatalytic activity than the unmodified P25 TiO2 catalyst. It is shown by EIS that the enhanced photocatalytic activity of the composites was due to the ability of lanthanum oxide in improving the charge separation of the photogenerated electron-hole pairs in TiO2.

Corrosion and wear behavior of laser cladded Ni–WC coatings

A nickel–tungsten carbide (Ni–WC) composite is an ideal protective coating for a harsh environment. In this study, the corrosion and wear behavior of a laser cladded Ni–WC coating fabricated by a high power direct diode laser (HPDDL) with different chemical compositions was investigated. In the modified Ni–60%WC, the chemical compositions were enhanced by the addition of lanthanum oxide (La2O3) and molybdenum and by replacing a portion of micro-sized WC with nano-WC particles. The corrosive resistance of the coatings was investigated utilizing potentiodynamic polarization, long-term immersion tests, and surface analytical techniques. The corresponding wear response was studied by using a dry unidirectional sliding wear test according to the ASTM G99 standard. Modification of the laser-cladded coatings was interpreted on the basis of its microstructure, microhardness, and phases of chemical composition. It has been observed that an optimal addition of nano-WC (5wt.%), La2O3 (1wt.%), and Mo (1wt.%) refines the grain size of the Ni binder and improves hardness, passivation capability of the coating under corrosion, and wear resistance. The pitting corrosive resistance of the modified coatings was enhanced due to a higher chemical stability, a more uniform surface potential, and a higher passivation capability.

Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina.

Catalysis by single isolated atoms of precious metals has attracted much recent interest, as it promises the ultimate in atom efficiency. Most previous reports are on reducible oxide supports. Here we show that isolated palladium atoms can be catalytically active on industrially relevant γ-alumina supports. The addition of lanthanum oxide to the alumina, long known for its ability to improve alumina stability, is found to also help in the stabilization of isolated palladium atoms. Aberration-corrected scanning transmission electron microscopy and operando X-ray absorption spectroscopy confirm the presence of intermingled palladium and lanthanum on the γ-alumina surface. Carbon monoxide oxidation reactivity measurements show onset of catalytic activity at 40 °C. The catalyst activity can be regenerated by oxidation at 700 °C in air. The high-temperature stability and regenerability of these ionic palladium species make this catalyst system of potential interest for low-temperature exhaust treatment catalysts.