Vertical section phase diagrams of La−Fe−B ternary system

The vertical sections of the La?Fe?B system were investigated using electron probe microanalysis and differential thermal analysis. Based on the microstructures and phase compositions of the as-cast and equilibrium alloys, together with their heat flow?temperature curves, phase diagrams for three vertical sections were drawn: La_xFe₈₂B_y (x+y=18), La_xFe₇₀B_y (x+y=30) and La_xFe₅₃B_y (x+y=47), where x and y represent mass fraction of La and B, respectively, % . Additionally, according to the phase diagrams, the compound La₂Fe₁₄B was identified as a stable phase at high temperatures. It was found to be stable between 926.2 and 792.6 °C; at low temperatures, however, it decomposed into α-La, α-Fe and LaFe₄B₄, according to the reaction La₂Fe₁₄B→α-Fe+α-La+LaFe₄B₄.     

Nonstoichiometry and diffusivities in iron monosulphide at elevated temperatures

The equilibrium diagram of the iron monosulphide phase has been reviewed in the temperature range 670–1100°C. Thermodynamic properties of the system are derived as a function of composition. Data for the parabolic rate constant for the growth of iron monosulphide on iron are presented as a function of nonstoichiometry for relatively small values of y in Fe_1-yS in the range 750–902°C. From these data the interdiffusion coefficient and the iron self-diffusion coefficient have been derived as a function of the metal deficit in Fe_1-yS.The calculated self-diffusion coefficient seems to be in good agreement with iron tracer diffusion data from the literature. The results indicate that the self-diffusion coefficient is practically independent of composition for values of y less than 0·01 and 0·02 at 750°C and 902°C, respectively. The self-diffusion coefficient is, however, found to be proportional to the square of the metal deficit for 0·015 < y < 0·055 at 750°C and 818°C. Other data show that the iron tracer diffusion coefficient in Fe_1-yO is proportional to the square of the iron deficit within experimental error. The defect structure of Fe_1-yS is discussed in view of the results obtained, but no definite conclusions are given.     

Fabrication of transparent YAG ceramics by traditional solid-state-reaction method

Transparent polycrystalline YAG ceramics were fabricated by solid-state reaction method using commercial ultrafine yttria andα-Al2O3 powders.The starting materials were milled and calcined at 1 400℃,and sintered into transparent YAG ceramics at 1 750℃in the vacuum for 4 h.Neither the starting materials as-milled or those calcined into YAG phase at 1 500℃can be sintered into transparent ceramics.Wide grain boundaries emerge in the YAG ceramics sintered at 1 850℃for 4 h,at the edge of which YAG phases decompose into perovskite YAlO3(YAP)andα-Al2O3.     

Cr doping effect in B-site of La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript> on its phase stability and performance as an SOFC anode

La_0.75Sr_0.25Cr _y Mn_1−y O₃ (LSCM) (y = 0.0–0.6) composite oxides were synthesized by a complexing process of combining ethylene diamine tetraacetic acid (EDTA) and citrate. X-ray diffraction (XRD), temperature-programmed reduction, electrical conductivity, I–V polarization, and impedance spectroscopy were conducted to investigate the Cr doping effect of La_0.75Sr_0.25MnO₃ on its phase stability and electrochemical performance as a solid-oxide fuel cell (SOFC) anode. The chemical and structural stabilities of the oxides increased steadily with increasing Cr doping concentration, while the electrical conductivity decreased on the contrary. At y ≥ 0.4, the basic perovskite structure under the anode operating condition was sustained. a cell with 0.5-mm-thick scandia-stabilized zirconia electrolyte and La_0.75Sr_0.25Cr _y Mn_1−y O₃ anode delivered a power density of ∼15 mW·cm⁻² at 850°C.     

Anodic process on Cu−Al alloy in KF−AlF3−Al2O3 melts and suspensions

Anodic processes on Cu−10Al electrode in molten KF−AlF₃−Al₂O₃ (saturated) and suspensions were characterized using chronopotentiometric and cyclic voltammetric techniques. Effects of cryolite ratio (CR= x(KF)/x(AlF₃)), temperature and particle volume fraction (ϕ) on the electrochemical behaviour of the anode were demonstrated. Initially, the anode was polarised in the galvanostatic mode in melt and suspensions (ϕ=0.12, 0.15) at 750 °C with 0.4 A/cm² current density. The anode potential in melt varied between 2.5 and 3.2 V and in suspensions (ϕ= 0.12) between 3.3 and 3.4 V. XRD analysis was conducted to study the oxide phases on the anode surface. Anode limiting current densities and mass transfer coefficients drastically decreased with the increase of ϕ in the suspension. The results suggest that the Cu−10Al electrode works better in suspensions with CR of 1.4 and particle volume fraction of 0.09 at 800 °C.     

Investigation of the corrosion behaviour of a NiCrMo alloy in nuclear process heat helium by means of X-ray diffraction and electron probe microanalysis

Samples of the nickel base alloy Nimonic 86 were exposed to PNP-500 type helium for 1000 h at 650, 750, 850, 900 and 950°C. X-ray diffraction showed 5 additional phases, formed at the sample surfaces during the heat treatment. They were shown to be: (1) a spinel Cr₂MnO₄ (at T ≤ 850°C) containing increasing amounts of Al and Ti with increasing temperature, (2) a sesquioxide Cr₂O₃ (at T ≥ 900°C) containing substantial amounts of Mn for T ≤ 850°C, (3) an ≠₁ oxide Ni₃Mo₃SO (mainly at 750°C) containing some Fe, (4) an ≠₁ carbide (Ni, Cr, Si)₃Mo₃C (at T ≤ 750°C), (5) Cr₂₃C₆ (at T ≤ 850°C) containing some Mo.     

High-temperature superconductor materials for contact layers in solid oxide fuel cells: II. Chemical properties at operating temperatures

The chemical reactivity between superconducting ceramic materials (YBa₂Cu₃O_7−x, Bi₂Sr₂CaCu₂O_8+x and Bi₂Sr₂CuO_6+x) and the cathode material of solid oxide fuel cells (La_0.65Sr_0.3MnO₃) was investigated by long-term annealing experiments of pressed powder mixtures lasting two weeks at 850°C. The chemical properties at the operating temperature of a solid oxide fuel cell revealed that all three superconducting materials reacted with La_0.65Sr_0.3MnO₃ and underwent changes in volume and density after annealing. The chemical compatibility between the superconductors and interconnect material, a ferritic steel (X 10 CrAl 18), was investigated using screen-printed thick layers of Bi₂Sr₂CuO_6+x on steel substrates. The formation of undesirable products, especially SrCrO₄, due to diffusion processes across the interface was confirmed by investigations of metallographic cross-sections. Efforts to stop the interfacial reaction by introducing a thin CuO barrier layer between the superconductor and steel did not solve the problem.     

Preparation and property of spinel LiMn2O4 material by co-doping anti-electricity ions

1 Introduction At present, LiCoO2 is almost the only cathode material of Li-ion batteries, which can be used in large-scale commercialization, because such material possesses high specific capacity, ease of preparation, high discharging flat and favorable…     

Influence of La precursors on structure and properties of CeO2-ZrO2-Al2O3 composite oxides

Three La-doped CeO₂-ZrO₂-Al₂O₃ (CZA) composite oxide samples, namely, CZA-I, CZA-II and CZA-III, were prepared following a co-precipitation method in the presence of La₂O₃, La(NO₃)₃·6H₂O and H[La(EDTA)]·16H₂O precursors, respectively. When the precursor samples are sintered at 1000 °C, the as-prepared composite oxides mainly exhibit the CeO₂-ZrO₂ cubic fluorite phase, while the γ-Al₂O₃ and δ-Al₂O₃ phases appear when the precursor samples are subjected to sintering at 1100 and 1200 °C. CZA-III exhibits improved redox properties after high-temperature treatment compared with CZA-I and CZA-II. CZA-III presents the largest surface area of 97.46 m²/g among the three CZAs when the CZA-III precursor sample is sintered at 1000 °C. Furthermore, the corresponding oxygen storage capacity (OSC) is the largest with value of 400.27 μmol/g when CZA-III precursor sample is sintered at 1000 °C. Additionally, CZA-III exhibits the best thermal stability and the highest reduction temperature. However, by increasing the sintering temperature to 1200 °C, there is a dramatic decline in the properties of surface area and OSC. And a decrease for CZA-III in surface area by 58.94% and a decrease of the OSC value by 74.56% are observed.     

Effects of La content on the properties of Ba1−xLaxTiO3 powders prepared by spray pyrolysis

Nano-sized Ba_1?xLa _x TiO₃ (0 ≤ x ≤ 0.03) powders were prepared by ultrasonic spray pyrolysis from the spray solution with citric acid. The mean sizes of the primary particles decreased from 110 nm to 59 nm when the x of the Ba_1?xLa_xTiO₃ powders was changed from 0 to 0.03. The BET surface areas of the powders changed from 9.1 m²/g to 16.9 m²/g. The pure BaTiO₃ and La-doped BaTiO₃ powders had both tetragonal and cubic crystal structures. The average grain size of the sintered BaTiO₃ specimen was 2.8 µm, while those of the La-doped BaTiO₃ pellets ranged from 1.04 µm to 0.68 µm according to the doping concentrations of La. The dielectric constant of Ba_1?xLa_xTiO₃ (0.01 ≤ x ≤ 0.03) pellets ranged from 2500 to 3855 when sintered at 1280 °C.     

Spark plasma sintering of TiC particle-reinforced molybdenum composites

In order to improve the recrystallization resistance and the mechanical properties of molybdenum, TiC particle-reinforcement composites were sintered by SPS. Powders with TiC contents between 6 and 25 vol.% were prepared by high energy ball milling. All powders were sintered both at 1600 and 1800 °C, some of sintered composites were annealed in hydrogen for 10 h at 1100 up to 1500 °C. The powders and the composites were investigated by scanning electron microscopy and XRD. The microhardness and the density of composites were measured, and the densification behavior was investigated. It turns out that SPS produces Mo–TiC composites, with relative densities higher than 97%.The densification behavior and the microhardness of all bulk specimens depend on both the ball milling conditions of powder preparation and the TiC content. The highest microhardness was obtained in composites containing 25 vol.% TiC sintered from the strongest milled powders. The TiC particles prevent recrystallization and grain growth of molybdenum during sintering and also during annealing up to 10 h at 1300 °C. Interdiffusion between molybdenum and carbide particles leads to a solid solution transition zone consisting of (Ti_1 −x Mo_x)C_y carbide. This diffusion zone improves the bonding between molybdenum matrix and TiC particles. A new phase, the hexagonal Mo₂C carbide, was detected by XRD measurements after sintering. Obviously, this phase precipitates during cooling from sintering temperature, if (Ti_1 −x Mo_x)C_y or molybdenum, are supersaturated with carbon.     

Heat capacity measurements and XPS studies on uranium-lanthanum mixed oxides

Heat capacity measurements were carried out on (U_1−yLa_y)O_2±x (y = 0.2, 0.4, 0.6, and 0.8) using differential scanning calorimeter (DSC) in the temperature range 298-800 K. Enthalpy increment measurements were carried out on the above solid solutions using high temperature drop calorimetry in the temperature range 800-1800 K. Chemical states of U and La in the solid solutions of mixed oxides were determined using X-ray photoelectron spectroscopy (XPS). Oxygen to metal ratios of (U_1−yLa_y)O_2±x were estimated from the ratios of different chemical states of U present in the sample. Anomalous increase in the heat capacity is observed for (U_1−yLa_y)O_2±x (y = 0.4, 0.6 and 0.8) with onset temperatures in the range of 1000-1200 K. The anomalous increase in the heat capacity is attributed to certain thermal excitation process, namely, Frenkel pair defect of oxygen. The heat capacity value of (U_1−yLa_y)O_2±x (y = 0.2, 0.4, 0.6, and 0.8) at 298 K are 65.3, 64.1, 57.7, 51.9 J K⁻¹ mol⁻¹, respectively. From the XPS investigations, it was observed that the O/M ratios at the surface are higher than that in the bulk. In uranium rich mixed oxide samples, the surface O/M ratios are greater than 2 whereas that in La rich mixed oxides, they are less than 2, though the bulk O/M in all the samples are less than 2.     

Effect of sintering temperature and composition on microstructure and properties of PMS-PZT ceramics

The piezoelectric ceramics xPb（Mn1/3Sb2/3）O3-（1-x）Pb（Zr1/2Ti1/2）O3 （abbreviated as PMS-PZT） were synthesized by traditional ceramics process. The effect of sintering temperature and the amount of Pb（Mn1/3Sb2/3）O3 （abbreviated as PMS） on phase structure, microstructure, piezoelectric and dielectric properties of PMS-PZT ceramics was investigated. The results show that the pure perovskite phase is in all ceramics specimens, the phase structure of PMS-PZT ceramics changes from tetragonal phase to single rhombohedral phase with the increasing amount of PMS. The dielectric constant εr, Curie temperature Tc, electromechanical coupling factor kp and piezoelectric constant d33 decrease, whereas the mechanical quality factor Qm and dielectric loss tanδ increase with the increasing amount of PMS in system. The optimum sintering temperature is 1 200-1 250 ℃. It is concluded that the PMS-PZT （x=0.07） ceramics sintered at 1 250 ℃ is suitable for high-power piezoelectric transformer. These properties include εr=674.8, tanδ =0.005 25, kp=0.658, Qm= 1 520, d33=230 pC/N, Tc=275 ℃.     

Tunneling magnetoresistance in sintered Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> samples diluted with Fe and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Electric transport and magnetoresistance characteristics were investigated for Fe₃O₄-x Fe(x=0, 10, 20 wt.%) samples and Fe₃O₄-α-Fe₂O₃ samples sintered at 500°C. For composition dependence of Fe₃O₄-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe₃O₄-10 Fe sample. For the surface heat treatment dependence of Fe₃O₄ powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe₃O₄-α-Fe₂O₃ sample sintered with Fe₃O₄ powders heated at 200°C in air. It was found that these enhanced MR ratios always appear together with the appropriate excess resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe₃O₄-10 Fe and Fe₃O₄-α-Fe₂O₃ samples can be explained by the increased interparticle contact sites and the appropriate thickness of α-Fe₂O₃, respectively.     

Characterization and piezoelectric thermal stability of PIN–PMN–PT ternary ceramics near the morphotropic phase boundary

The phase structure and piezo/dielectric properties of xPb(In_1/2Nb_1/2)O₃–yPb(Mg_1/3Nb_2/3)O₃–zPbTiO₃ (PIN–PMN–PT x/y/z) ternary ceramics with morphotropic phase boundary (MPB) composition were investigated. It was found that Curie temperatures of choosing composition changed from 165 °C to 293 °C and the piezoelectric properties are almost the same at room temperature in PIN–PMN–PT system near MPB. The piezoelectric coefficient d₃₃ and electromechanical coupling factor k_p are higher than 440 pC/N and 60%, respectively. Temperautre and dc bias dependence of piezoelectric response for PIN–PMN–PT ceramics were measured. The usage temperature range was found to be improved, compared with PMN–PT single crystal near MPB.     

Influence of Nd-Co Substitution on Structural,Electrical, and Dielectric Properties of X-Type Hexagonal Nanoferrites

A series of single phase X-type hexagonal ferrites with concentration Sr_2?x Nd _x Ni₂Fe_28?y Co _y O₄₆ (x = 0.02, 0.04, 0.06, 0.08, 0.10 and y = 0.1, 0.2, 0.3, 0.4, 0.5) has been prepared by sol-gel method sintered at 1250 °C for 6 h. The x-ray diffraction analysis reveals the single phase of X-type hexagonal ferrites. The particle size was calculated by using SEM and TEM. The ferrite substituted with Nd³⁺ and Co²⁺ has average particle size in the range of 40-50 nm. The room temperature electrical resistivity experiences the significant enhancement from a value of 1.1 × 10⁷ to 2.03 × 10⁸ Ωcm with the increase in Nd³⁺ and Co²⁺ concentration. The dielectric constant exhibits high value at low frequencies and decreases with the increase of frequency. The tangent dielectric loss shows the abnormal behavior which can be explained on the basis of hopping between the Fe²⁺ and Fe³⁺ ions on octahedral sites. The maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices (MF).     

High-power (Nd,Dy)–(Fe,Co)–B magnets with a low temperature coefficient of induction

High-power (Nd, Dy)–(Fe, Co)–B permanent magnets with a low temperature coefficient of induction (α) were prepared using advantages of strip casting and low-oxygen technologies. The microstructure and temperature dependences of magnetic properties have been studied on sintered (Nd_{1 – x} Dy _x )_13.9(Fe_{1 – y} Co _y )_79.8Cu_0.1Ga_0.1B_6.1 magnets with 0.20 ≤ x ≤ 0.25 and 0 ≤ y ≤ 0.20. The increase in y from 0 to 0.20 is accompanied by an increase in the Curie temperature from 327 to 492°C. This favors a decrease in the value of α from 0.099 to 0.060%/°C, respectively. Magnets with an oxygen content of no more than 2500 ppm which were prepared from the (Nd_0.75Dy_0.25)_13.9(Fe_0.85Co_0.15)_79.8Cu_0.1 Ga_0.1B_6.1 alloy, have the following hysteresis characteristics at 140°C: B _r ≥ 11.3 kG, H _c ≥ 8 kOe, and (BH)_max ≥ 30 MGOe; in this case, α ≤ |–0.07%/°С|.     

x(Mg0.7Zn0.3)0.95Co0.05TiO3-(1−x)(La0.5Na0.5)TiO3 ceramic at microwave frequency with a near zero temperature coefficient of resonant frequency

Dielectric properties of x(Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃-(1?x)(La_0.5Na_0.5)TiO₃ ceramic were investigated at microwave frequencies. A nearly 0 ppm/°C temperature coefficient of resonant frequency was realized at x = 0.9. A two-phase system was confirmed by XRD analysis. A dielectric material applicable to microwave devices with a Q × f of 20,000–87,000 GHz and a dielectric constant of 21.27–26.2 was obtained at 1100 °C after 4 h of sintering. The microwave dielectric material 0.9(Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃-0.1(La_0.5Na_0.5)TiO₃ sintered at 1150 °C for 4 h has a dielectric constant of 24.56, a Q × f of 68,000 GHz, and a τ_f value of 0 ppm/°C. It is proposed as a candidate dielectric for GPS patch antennas.     

Cyclic Oxidation Behavior of the Ti–6Al–4V Alloy

The cyclic oxidation behavior of the Ti–6Al–4V alloy has been studied under heating and cooling conditions within a temperature range from 550 to 850 °C in air for up to 12 cycles. The mass changes, phase, surface morphologies, cross-sectional morphologies and element distribution of the oxide scales after cyclic oxidation were investigated using electronic microbalance, X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy. The results show that the rate of oxidation was close to zero at 550 °C, obeyed parabolic and linear law at 650 and 850 °C, respectively, while at 750 °C, parabolic—linear law dominated. The double oxide scales formed on surface of the Ti–6Al–4V alloy consisted of an inner layer of TiO₂ and an outer layer of Al₂O₃, and the thickness of oxide scales increased with an increasing oxidation temperature. At 750 and 850 °C, the cyclic oxidation resistance deteriorated owing to the formation of voids, cracks and the spallation of the oxide scales.     

Structural and Electrical Analysis of Microwave Processed YSZ Electrolytes for SOFC Prepared by Co-precipitation Method

The aim of the present study is to investigate the effect of microwave energy on the structural and electrical properties of yttria-stabilized zirconia (YSZ) electrolyte for solid oxide fuel cells (SOFC). Five different compositions of Zr_1?x Y _x O_2?x/2 (x = 0.06–0.14) were prepared by a co-precipitation method and were then sintered by microwave as well as conventional heating at 1400°C for 20 min and 240 min, respectively. The structural and electrical properties of the samples sintered by both the methods were compared. The x-ray diffraction (XRD) results revealed that YSZ samples sintered by both methods had either a tetragonal crystal structure or a cubic structure depending on its composition. Almost the same degree of densification as well as conductivity of same order was found from impedance analysis for both microwave- and conventionally sintered YSZ products, which showed that microwave sintering is the better alternative for material processing in terms of saving energy and time without compromising the product quality.