Addition Of Pr Research Articles

New Insight into the Doping Effect of Pr2O3 on the Structure–Activity Relationship of Pd/CeO2–ZrO2 Catalysts by Raman and XRD Rietveld Analysis

Pd/CeO2–ZrO2–Pr2O3 (CZP) catalysts were synthesized with different Ce/Zr molar ratios and 8.0 wt % Pr2O3 doping. Their structures were characterized by various techniques, especially using X-ray diffraction (XRD) in combination with Rietveld refinement and Raman analysis. The XRD pattern of CZP with Ce/Zr molar ratios >1 can be indexed satisfactorily to the fluorite structure with a space group Fm-3m. When the Ce/Zr molar ratio reaches 1/2, the XRD patterns only display diffraction peaks of the tetragonal phase (S.G. P42/nmc). The Pr additive in the crystal lattice mainly replaces the position of Ce, which improves the redox reaction activity of catalysts when compared with Pr-free catalysts. Raman results reveal the enrichment of defect sites on the surface. The presence of moderate ZrO2 can increase both oxygen vacancies and the ZrO8-type complex in supports, which is in accord with the change regularity of their oxygen storage capacity (OSC) values. Moreover, the addition of moderate Zr and Pr promotes...

Influence of the Chemical Composition in the Electrochemical Response of Permanent Magnets

The corrosion behavior of permanent magnets with different chemical composition was evaluated. Permanent magnets were tested in 3.5% NaCl solution at room temperature using electrochemical technics such as polarization curves, open-circuit potential, linear polarization resistance, and electrochemical impedance spectroscopy measurements. Results have shown that corrosion rate is affected by Nd, Pr, and Co content. Analysis by scanning electron microscopy has shown that pitting attack is the main mode of degradation of the magnets, while Co addition reduces it and Pr addition increases it.

Influence of Soil Properties on Amounts of Bicarbonate-Extractable P in Soils Incubated With Three Thai Phosphate Rocks of Contrasting Mineralogies

Top- and sub-soil (0–15; 15–100 cm) samples were collected from nine acid soil series of Ultisols and Oxisols from high rainfall areas, Southeast Coastal region of Thailand. Most of them had low soil pH in water (pH Rat-PR > Kan-PR > Roi-PR. Increases in bicarbonate-extractable P (ΔPBC) in soil incubated with PR and MCP were highest at 14 days. Stepwise regression indicated that there was no single soil property that adequately predicted the increases in extractable P (ΔPBC) because of addition of PR and MCP. Soil properties that were most closely and positively related to ΔPBC were the ability of soils to provide hydrogen ions for PR dissolution and the initial amount of available P in the soils.

Effect of Pr Modification Treatment on the Microstructure and Mechanical Properties of Cast Al-Mg<sub>2</sub>Si Metal Matrix Composite

The effect of different concentrations of Pr on the microstructure and tensile properties of cast Al-18 wt.%Mg2Si in situ metal matrix composite was investigated. The results show that the addition of proper amount of Pr has significant modification effect on primary Mg2Si in the Al-18 wt.% Mg2Si composite. With the increase of Pr content from 0.1 to 0.7%, the morphology of primary Mg2Si is changed from irregular or dendritic to polyhedral shape, and its average particle size is significantly decreased from 65 to 17 μm. When the Pr content exceeds 1.0%, the primary Mg2Si become coarse again. Tensile tests reveal that the Pr addition improves the tensile strength and ductility of the material. Comparing with those of unmodified composite, the ultimate tensile strength and percentage elongation with 0.7% Pr are increased by 36.5% and 161.6%, respectively.

Effect of Pr addition on the properties of Ni/Al2O3 catalysts with an application in the autothermal reforming of methane

Ni/xPr-Al2O3 (x = 5, 10, 15, 20 wt%) catalysts with an application in autothermal reforming of methane were prepared by sequential impregnation synthesis; its catalytic performance was evaluated and compared with that of Ni/γ-Al2O3 catalyst; the physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H2-temperature programmed reduction techniques (TPR). The results showed that Pr addition promoted the reduction of nickel particle size on the surface. TPR experiments suggested a heterogeneous distribution of nickel oxide particles over xPr-Al2O3 supports and the promotion of NiO reduction by Pr modification. The CH4 conversion increased with elevating levels of Pr addition from 5% to 10%, then decreased with Pr content from 10% to 20%. For the stability catalytic tests, Ni/xPr-Al2O3 catalysts maintained the high activity after 48 h while Ni/Al2O3 had a significant deactivation.

Enhanced hydrogen production by doping Pr into Ce0.9Hf0.1O2 for thermochemical two-step water-splitting cycle

We synthesized (Ce0.9Hf0.1)1−xPrxO2−δ (x=0, 0.05 and 0.1) using the polymerized complex method. The synthesized samples, as well as the samples after thermochemical two-step water-splitting cycles have a fluorite structure and Pr exists in the solid solutions with both trivalent and tetravalent states, as suggested by powder X-ray Diffraction (XRD) Patterns. The reduction fraction of Ce4+ in redox cycles (oxidation step in air) and two-step water-splitting cycles (oxidation step in steam) indicates that the addition of Pr into Ce–Hf oxide solid solution cannot improve the reduction fraction of Ce4+ during the redox cycles but both the reduction fraction of Ce4+ and H2 yield are significantly enhanced during two-step water-splitting cycles. The chemical composition of 10mol% Pr doped Ce0.9Hf0.1O2 exhibits the highest reactivity for hydrogen production in H2-generation step by yielding an average amount of 5.72mlg−1 hydrogen gas, which is much higher than that evolved by Ce0.9Hf0.1O2 (4.50mlg−1). The enhancement effect of doping Pr on the performance during two-step water-splitting cycles is because of the multivalent properties of Pr, which can: (1) reduce the amount of Ce3+ oxidized by contamination air (contamination air eliminated by partial oxidation of Pr3+ to Pr4+) in H2-generation step; (2) enhance the reaction rate in H2-generation step by improving the ionic conductivity (extrinsic oxygen vacancies created by the substitution of Ce4+ by Pr3+).

The effect of Pr co-doping on the densification and electrical properties of Sr-LaAlO3

Perovskite-type materials have been investigated extensively in the attempt to discover new electrolyte materials for solid oxide fuel cells (SOFC) operating at low temperatures. These materials include LaAlO3-based perovskite, which, when adequately doped, presents high ionic conductivity. However, despite the high conductivity of doped LaAlO3, two characteristics limit its application as solid electrolyte: low sinterability and p-type electronic conductivity in oxidizing conditions. The purpose of this work was to investigate the effect of Pr co-doping on the densification and electrical conductivity of Sr-doped LaAlO3. The addition of Pr eliminated the deficiencies mentioned above. Pr in solid solution acts as a perfect sintering aid because promoted densification without forming secondary phase which should be detrimental for electrical conduction. The addition of Pr also increased the bulk electrical conductivity measured in air atmosphere but had no effect at low oxygen partial pressure. However, the addition of Pr had a strong effect on the grain boundary, improving the ionic grain boundary electrical conductivity at air atmosphere which was attributed to the Pr influence on the space charge layer.

Structural and magnetic properties of Pr-alloyed MnBi nanostructures

The structural and magnetic properties of Pr-alloyed MnBi (short MnBi-Pr) nanostructures with a range of Pr concentrations are investigated. The nanostructures include thin films having Pr concentrations 0, 2, 3, 5 and 9 at.% and melt-spun ribbons having Pr concentrations 0%, 2%, 4% and 6%, respectively. Addition of Pr into the MnBi lattice has produced a significant change in the magnetic properties of these nanostructures including an increase in coercivity and structural phase transition temperature, and a decrease in saturation magnetization and anisotropy energy. The highest value of coercivity measured in the films is 23 kOe and in the ribbons is 5.6 kOe. The observed magnetic properties are explained as the consequences of competing ferromagnetic and antiferromagnetic interactions.

Enhancement of thermoelectric performance in strontium titanate by praseodymium substitution

In order to identify the effects of Pr additions on thermoelectric properties of strontium titanate, crystal structure, electrical and thermal conductivity, and Seebeck coefficient of Sr1−xPrxTiO3 (x = 0.02–0.30) materials were studied at 400 < T < 1180 K under highly reducing atmosphere. The mechanism of electronic transport was found to be similar up to 10% of praseodymium content, where generation of the charge carriers upon substitution resulted in significant increase of the electrical conductivity, moderate decrease in Seebeck coefficient, and general improvement of the power factor. Formation of point defects in the course of substitution led to suppression of the lattice thermal conductivity, whilst the contribution from electronic component was increasing with carrier concentration. Possible formation of layered structures and growing distortion of the perovskite lattice resulted in relatively low thermoelectric performance for Sr0.80Pr0.20TiO3 and Sr0.70Pr0.30TiO3. The maximum dimensionless figure of merit was observed for Sr0.90Pr0.10TiO3 and amounted to ∼0.23 at 670 K and ∼0.34 at 1170 K, close to the values, obtained in similar conditions for the best bulk thermoelectrics, based on rare-earth substituted SrTiO3.

Formation of Fine Multicomponent Precipitates and Enhanced Precipitation-Hardening in an Al–Cr–Pr–Zr Alloy

The microstructure of the Al­1.0Cr­1.4Pr­1.6Zr (mass%) alloy after homogenized at 500°C for 400h has been investigated. Addition of Cr, Pr and Zr in combination into pure aluminum results in the formation of submicron Zr-containing PrCr2Al20 and nanoscale Cr, Pr-containing Al3Zr dispersed phases. Compared with the Al­1.0Cr­1.4Pr and Al­1.6Zr alloys, a denser distribution of new fine multicomponent dispersed phases and their superimposition effect are associated with enhanced precipitation-hardening behavior of Al­1.0Cr­1.4Pr­1.6Zr alloy. (doi:10.2320/matertrans.M2013149) The alloys with the nominal chemical compositions of Al­1.6Zr, Al­1.0Cr­1.4Pr and Al­1.0Cr­1.4Pr­1.6Zr (all in mass%) were prepared by melting high purity Al (99.9mass%) with Al­Zr, Al­Cr and Al­Pr master alloys using a conventional casting method. The cast ingots were homogenized at 500°C for 400h, and then quenched in water at ambient temperature. The microstructure was observed using an optical microscope. The phase composition was measured by X-ray diffractometry (XRD) in reflection with Cu-Ki radiation. The morphologies and compositions of large intermetallic particles were measured using energy dispersive X-ray spectroscopy (EDS) in a JSM-6360LV scanning electron microscopy (SEM). To investigate the fine precipitates, TEM observation was performed by a TECNAI G 2 20 microscopy and a Jeol JEM-2010F field-emission transmission electron microscopy equipped with a scanning unit. Thin foils for standard TEM observation were prepared by the standard electrolytic twin-jet polishing technique in a7 5% methanol and 25% nitric acid solution cooled down to ³253K with an applied potential of 12­15V and current of 70­90mA. The Brinell hardness was measured with a HRBVU-187.5 hardness tester at a load of 980N.

Structural and electrochemical characterization of carbon supported Pt–Pr catalysts for direct ethanol fuel cells prepared using a modified formic acid method in a CO atmosphere

Pt-Pr/C electrocatalysts were prepared using a modified formic acid method, and their activity for carbon monoxide and ethanol oxidation was compared to Pt/C. No appreciable alloy formation was detected by XRD analysis. By TEM measurements it was found that Pt particle size increases with an increasing Pr content in the catalysts and with decreasing metal precursor addition time. XPS measurements indicated Pt segregation on the catalyst surface and the presence of Pr2O3 and PrO2 oxides. The addition of Pr increased the electro-catalytic activity of Pt for both CO and CH3CH2OH oxidation. The enhanced activity of Pt-Pr/C catalysts was ascribed to both an electronic effect, caused by the presence of Pr2O3, and the bi-functional mechanism, caused by the presence of PrO2.

Properties and interfacial microstructure of Sn–Zn–Ga solder joint with rare earth Pr addition

The effects of rare earth (RE) Pr on the wettability, bond strength and interfacial microstructure of Sn–Zn–Ga (SZG)/Cu joints were investigated. The wetting balance results showed that adding a proper amount of Pr greatly improved solder wettability by increasing the wetting force and decreasing the wetting time. Micro-joint strength test results showed that the Pr addition enhanced the shear bond strength of solder joints after both soldering and thermal aging at 100°C. The interfacial microstructure evaluation indicated that the addition of Pr can inhibit the formation of Cu5Zn8 intermetallic (IMC) layer during soldering and the growth of Cu6Sn5 IMC during thermal aging. However, it was discovered that the presence of Pr causes the risk of Sn whisker growth at the joint interfaces due to the oxidation of RE-rich PrSn3 IMCs during aging. Since RE-containing solders have been recommended for future applications because of their superior properties, the findings indicated that further reliability assessments on RE-containing solder joints should be conducted.

Special features of Nd(Pr) – Dy – Fe – Co – B magnets with high content of Co

The effect of cobalt content in sintered magnets of the Nd(Pr) – Dy – Fe – Co – B system on the sintering temperature, at which the density is equal to 99% of the maximum value and the coercive force H ci is the highest, is determined. The main components forming the liquid phase in sintering of the materials are determined. It is shown that the addition of (Pr, Dy)(Fe, Co)2B2 intermetallic to alloy (Pr, Dy) – (Fe1 – y Co y ) ( y ≈ 0.5) during the operation of fine milling of sintered magnets has a positive effect on the value of H ci .

Effect of Pr on properties and Sn whisker growth of Sn‐9Zn‐xPr solder

PurposeThe purpose of this paper is to improve the properties of Sn−9Zn solder, so as to meet the requirements of industrial applications.Design/methodology/approachThe effects of Praseodymium on property and Sn whisker growth under aging treatment in Sn−9Zn lead‐free solder were investigated.FindingsThe results indicate that with the addition of rare earth Pr, the wettability and mechanical properties of Sn−9Zn solder were improved. The best wettability and comprehensive property of soldered joint is obtained when the content of Pr is 0.08 wt.%. After aging treatment at 150°C for 360 h, the mechanical properties of Sn−9Zn−0.08Pr decreased but are still obviously higher than that of Sn−9Zn. Moreover, when the content of Pr reached 0.1 wt.%, plenty of Sn−Pr compounds were found in the Sn−9Zn solder. The inevitable oxidation of Sn−Pr compounds would cause a high stress accumulated within PrSn3 phases, which would be served as driving force to induce the Sn whisker sprout and growth after aging treatment at 150°C for 120 h to 360 h. Compared with the results in Sn−9Zn−0.5Ga−0.7Pr solder that Sn whisker observed until the addition of Pr reached 0.7 wt.%, it could be inferred that the addition of Ga may react against the sprout of Sn whisker.Originality/valueIt is found that the addition of Pr can improve the properties of solder and avoid Sn whisker growth in the right range and proper conditions. The cost of the solder with added Pr is limited to RMB 2 yuan/kg so it can be widely used in industry.

The effect of praseodymium (Pr) additions on shear strength and microstructure of SnAgCu joints during the ageing process

PurposeThe purpose of this paper is to investigate the influence of praseodymium (Pr) additions (0, 0.05 and 0.5 wt%) on the mechanical properties and microstructure of SnAgCu solder joint during aging process. Moreover, the authors aim to indicate that the decreased soldification undercooling of Sn3.8Ag0.7Cu solder can suppress the formation of Ag3Sn plate to some extent.Design/methodology/approachThe shear strength evolution of SAC, SAC‐0.05Pr and SAC‐0.5Pr solder joint were studied under 150°C aging process with STR‐1000. The effect of Pr additions on the solidification behavior of SnAgCu solder was also studied by differential scanning calorimetry. To study the microstructure evolution, the cross‐sections of all specimens were observed by means of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Meanwhile, the etchant, consisting of 20%HNO3+distilled water was used for deep etching to reveal the interfacial morphology.FindingsThe shear force reduction rate of SAC solder joint during aging was restrained by 0.05%Pr addition but promoted with 0.5% Pr addition. The growth of IMC layer of SnAgCu joint in the aging process was suppressed significantly by different amounts of Pr additions. However, the beneficial effect of Pr addition due to the suppression of IMC layer growth was weakened by the micro‐cracks formed in PrSn3 compounds in SnAgCu‐0.5Pr joint. Pr additions (0.05, 0.5 wt%) decrease the solidification undercooling of SnAgCu solder, which will suppress the formation of Ag3Sn plate to some extent.Research limitations/implicationsFurther studies are necessary for confirmation of the practical application, especially of the manufacturing technology of solder paste containing Pr.Practical implicationsThe appropriate amount of Pr in Sn3.8Ag0.7Cu solder is about 0.05 wt%. It is found that SAC‐0.05Pr solder has an improvement in solder joint reliability in long aging processes. The results suggested the novel solder alloys can meet the requirements of high reliability application.Originality/valueThe paper demonstrates that: Pr additions promote the solidification of SAC solder; shear force reduction rate of SAC solder joint was reduced by 0.05%Pr addition; the IMC layer growth rate of SnAgCu solder joint was suppressed by Pr additions; and micro‐cracks were found in PrSn3 phases after aging.

Evaluation of the microstructure and whisker growth in Sn–Zn–Ga solder with Pr content

Abstract

Preparation, Characterization and Thermal Expansion of Pr Co-Dopant in Samarium Doped Ceria

The compositions Ce0.8-xSm0.2O2-δ(X=0, 0.02, 0.04, 0.06) were prepared through the sol–gel route. The effect of Pr addition on the crystal structure, densification and thermal expansion of Ce0.8Sm0.2O2-δ was studied. The phase identification and morphology was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray diffraction analysis showed that all the samples exhibit a fluorite structure. The lattice parameters were determined by X-ray powder diffraction. Lattice parameters and volume of the unit cell increases with Pr doping. Density of the all samples is more than 90% of theoretical density. The thermal expansion was measured using dilatometric technique in the temperature range 30–1000°C. It was observed that the thermal expansion increased linearly with increasing temperature for all the samples.

Phase transitions and hard magnetic properties for rapidly solidified MnAl alloys doped with C, B, and rare earth elements

MnAl alloys are attractive candidates to potentially replace rare earth hard magnets because of their superior mechanical strength, reasonable magnetic properties, and low cost. In this study, the phase transitions and magnetic properties of melt spun Mn55Al45 based alloys doped with C, B, and rare earth (RE) elements were investigated. As-spun Mn–Al, Mn–Al–C, and Mn–Al–C–RE ribbons possessed a hexagonal e crystal structure. Phase transformations between the e and the L10 (τ) phase are of interest. The e → τ transformation occurred at ~500 °C and the reversed τ → e transformation was observed at ~800 °C. Moderate carbon addition promoted the formation of the desired hard magnetic L10 τ-phase and improved the hard magnetic properties. The Curie temperature T C of the τ phase is very sensitive to the C concentration. Dy or Pr doping in MnAlC alloy had no significant effect on T C. Pr addition can slightly improve the magnetic properties of MnAlC alloy, especially JS. Doping B could not enhance the magnetic properties of MnAl alloy since B is not able to stabilize either the e phase or the L10 hard magnetic τ phase.

Effect of Zr, Cr and Pr additions on microstructures and properties of ultra-high strength Al–Zn–Mg–Cu alloys

Abstract The effect of Zr, Cr and Pr additions on the microstructures, mechanical properties and corrosion resistance of ultra-high strength Al–Zn–Mg–Cu alloy was investigated. By Zr, Cr and Pr adding to Al–Zn–Mg–Cu alloy, 10–20 nm spherical coherent dispersoids were formed in Al matrix and identified as Zn, Mg, Cu, Cr, Pr-containing A1 3 Zr with cubic L1 2 structure. The dispersoids remarkably inhibited the recrystallization of Al matrix, and numerous fine subgrain boundaries were retained. Compared to the partial recrystallized Al–Zn–Mg–Cu–Zr alloy and full recrystallized Al–Zn–Mg–Cu–Cr–Pr alloy, the unrecrystallized Al–Zn–Mg–Cu–Zr–Cr–Pr alloy exhibited higher resistance to intergranular corrosion, exfoliation corrosion and stress corrosion with the improved strength, fracture toughness and ductility.

Chemical expansion of nonstoichiometric Pr 0.1Ce 0.9O 2− δ: Correlation with defect equilibrium model

Undoped and acceptor doped cerium dioxide is known to exhibit non-stoichiometry induced chemical expansion at elevated temperatures and reducing environments with impact on the mechanical integrity of solid oxide fuel cells and permeation membranes. In this paper, the chemical expansion of Pr 0.1Ce 0.9O 2− δ is measured and analyzed with respect to its defect equilibria and the chemical coefficient of expansion, analogous to thermal coefficient of expansion, is extracted. The addition of Pr to CeO 2 leads to major deviations from stoichiometry, and correspondingly to large chemical expansions, under readily accessible experimental conditions (e.g. in air at elevated temperatures). Pr 0.1Ce 0.9O 2− δ , therefore, serves as a model system for studying chemical expansion in ceria-based solid solutions in order to predict the conditions in which they exhibit suppressed chemical expansion.