Crystallization and characterization of substoichiometric compound (W0.5Al0.5)C0.5 obtained by solid-state reaction

(W_0.5Al_0.5)C_0.5 substoichiometric compound is synthesized by a combination of mechanical milling and high-pressure reactive sintering. X-ray diffraction is used to monitor the phase changes and crystallization of (W_0.5Al_0.5) C_0.5 during the whole reaction process. As a result, (W_0.5Al_0.5) C_0.5 is identified as the hexagonal WC-type belonging to the P-6m2 space group (No. 187), and the lattice parameters of (W_0.5Al_0.5)C_0.5 are calculated to be a=2.907 (1) Å, c=2.838 (1) Å, which are very similar to those of WC even if there are approximately 50 pct carbon vacancies in the cell of (W_0.5Al_0.5)C_0.5 as compared with WC. The substoichiometric (W_0.5Al_0.5)C_0.5 compound has a Vickers microhardness of 2385±70 kg mm^?2, which is as high as that of WC, while its density is far lower than that of WC.     

Magnetic and Transport Properties of La0.5-x Ndx Ba0.5 CoO3 Compounds

Substituting effects of Nd for La in La0.5Ba0.5CoO3 compounds were studied systematically. The results show that Nd doping does not change the itinerant properties of the Co3d electrons. The molecular magnetic moment of the mate-rials decreases monotonically with increasing Nd dopant. When Nd content x ≥0.45, a magnetic phase separation appears in the materials. When x ≤0.45, the Curie temperature decreases monotonically with increasing Nd dopant. This is due to the size effects of the rare earth ions. The electric resistance measurements show that in the studied temperature range, the conduction of the materials belongs to the thermo-diffusion conduction below the Curie temperature, while it belongs to the variable range hopping conduction of polarons over the Curie temperature.     

Characterization and Stability of La0.5Sr0.5CoO2.91 Perovskite-Type Oxide

Compositely doped oxide La0.5Sr0.5CoO2.91 （LSC） was synthesized using solid state reaction and citric acid-nitrate low temperature self-propagating combustion methods. The crystal structure and the particle size micrograph of LSC powders synthesized by different methods were investigated with XRD and SEM. The experimental results show that the single perovskite phase of LSC can be synthesized by solid state reaction method, but LaSrCoO4 phase appears in LSC powder synthesized by citric acid-nitrate low temperature self-propagating combustion method. The LSC particle by citric acid-nitrate low temperature self- propagating combustion method has smaller size. To analyze the character of cathode material based on Ceo.gGdo.101.95（GDC） electrolyte, two types of cathode wafers were fabricated with the two kinds of LSC and GDC powders at the mass rate of 6：4, respectively. The electrical conductivity of the sintered samples was measured by four probe DC method from 300 to 800 ℃. The cathode with LSC particle by citric acid- nitrate low temperature self-propagating combustion method has higher electrical conductivity. In order to investigate the stability, the two samples were put into the muffle furnace to heat up in air at 800℃for 800 h. To analysis the reason for reduced electrical conductivity, the crystal structure and the particle micrograph of the cathode wafers before and after an exposure were investigated with XRD and SEM. The result shows that new crystal structure appears in both the two kinds of cathode wafers and crystal micrographs change a lot.     

Fe-0.5Mn-0.5C预混合钢粉性能及粘结剂作用机制

设计4种不同有机粘结剂,分别对合金元素Mn、石墨进行粘结处理,制备Fe-0.5Mn-0.5C预混合钢粉。研究4种粘结剂对预混合钢粉合金元素与石墨的粘结率、预混合钢粉的流动性、松装密度、压坯密度的影响。并通过对粉末表面基团的表征,研究高分子粘结剂与铁基体间的相互作用方式。结果表明:以丙烯酸类树脂制备的预混合钢粉工艺性能最好,其流动速率为24.3 s/50 g松装密度为24.3 s/50 g,在600 MPa压力下的压坯密度为3.03~3.23 g/cm3粘结剂中的极性基团与铁基粉末通过氢键作用相吸附。     

Diffusivity of hydrogen and deuterium at low concentration in Fe0.5Ti0.5

The diffusion coefficients of hydrogen and deuterium were measured in the solid solution phase Fe_o.5Ti_o.5Hv/Dv (x < 0.03) in an absorption/desorption experiment with palladium coated bulk samples. The pressure and temperature ranges covered were 1 to 120 bar and 370 to 800 K, respectively. Forx → 0, the diffusion coefficients obey Arrhenius laws. They are (in cm₂ per second withT in K): 10.1 10^?4 exp(-5890/T) and 5.5 10^?4 exp(?5710/T) for hydrogen, 8.2 10^?4 exp(?6080/T) and 5.5 10^?4 exp(?5980/T) for deuterium, as measured during absorption and desorption, respectively. The pick-up and release of hydrogen by uncoated samples was controlled predominantly by surface effects.     

Age Hardening of the Al0.5CoCrNiTi0.5 High-Entropy Alloy

Al_0.5CoCrNiTi_0.5 high-entropy alloy was synthesized by vacuum arc melting in a copper mold. This alloy was aged at 773 K to 1473 K (500 °C to 1200 °C) for 24 hours to investigate the microstructure and hardness. The hardness of the as-cast alloy is HV743, and it exhibits a dendritic structure, in which dendrite is composed of body-centered cubic (bcc), face-centered cubic (fcc), and σ phases, and interdendrite is an eutectic structure consisting of bcc and order bcc phases. Apparent age hardening appears at 873 K to 1173 K (600 °C to 900 °C), and no age softening occurs even after 1473 K (1200 °C) aging. The age hardening of this alloy is attributed to the transformation of the bcc phase to σ phase. Detailed variations of hardness and the microstructure of aged alloys are reported in this article.     

Preparation and Electrical Transport Properties of Perovskite Oxide Ln0.5Sr0.5CoO3

The superfine powders of Ln0.5 Sr0.5 CoO3 （Ln = La, Pr, Nd, Sm, Eu） were obtained by solid state reactions. The crystal structure and electrical transport properties of samples doped with different rare earth elements as well as the forming process of the Perovskite structure were studied. The result shows that when the temperature reaches 1200 ℃, the samples will become a steady and unitary Perovskite phase by solid state reactions. The conductive behavor at low temperature is consistent with small polaron mechanism （i. e., localized electronic carriers having a thermally activated mobility）. However, the maximum of conductivity appears at about 700 ℃, and the conductivity of La0.5Sr0.5CoO3 is the biggest in the intermediate-temperature （600 - 850 ℃ ）, so it is fit for cathode material of intermediate-temperature solid oxide fuel cells.     

Synthesis of Al0.5CoCrCuFeNi and Al0.5CoCrFeMnNi High-Entropy Alloys by Laser Melting

High-entropy alloys (HEAs) are a blend of 5+ metallic elements that can form solid solution disordered structures. Two HEAs were synthesized using laser melting in an argon atmosphere. The relatively well-studied Al_0.5CoCrCuFeNi alloy was first produced to establish the feasibility of laser melting. Manganese was then substituted for copper to potentially lower both cost and density, producing a novel Al_0.5CoCrFeMnNi alloy system. These samples were analyzed with XRD, SEM, EDS, and Vickers microhardness to determine the effects of the manganese substitution, as well as the effects of laser melting in comparison to the more traditional arc melting.     

Substituting Effect of Y in La0.5Ba0.5 CoO3

La0.5-xYxBa0.5CoO3 polycrystals were prepared by solid state reaction. The substituting effects of Y for La on the magnetic and transport properties of the materials were studied systematically. The results indicate that substitution of Y induces two effects. Firstly, the charge transfer from Y to 3d orbital of Co happens. This causes the molecular magnetic moment to decrease. Secondly, the antiferromagnetic exchange interaction of Co ions appears. When the content of Y is less than or equal to 30%, the non-colinear structure of spins in materials is observed. When the content of Y is greater than 30%, the materials transit from predominant ferromagnetic state to predominant antiferromagnetic one. The conductive mechanism for the materials with different content of Y belongs to the variable range hopping conduction of polarons.The resistivity of materials increases sharply with increasing Y content.